Comparison of tooth widths, arch widths, arch lengths in early mixed and permanent class I normal dentitions to class I and II crowded dentitions

Transcription

1 University of Iowa Iowa Research Online Theses and Dissertations Spring 2016 Comparison of tooth widths, arch widths, arch lengths in early mixed and permanent class I normal dentitions to class I and II crowded dentitions Christopher Paul Wermerson University of Iowa Copyright 2016 Christopher Paul Wermerson This thesis is available at Iowa Research Online: Recommended Citation Wermerson, Christopher Paul. "Comparison of tooth widths, arch widths, arch lengths in early mixed and permanent class I normal dentitions to class I and II crowded dentitions." MS (Master of Science) thesis, University of Iowa, Follow this and additional works at: Part of the Orthodontics and Orthodontology Commons

2 COMPARISON OF TOOTH WIDTHS, ARCH WIDTHS, ARCH LENGTHS IN EARLY MIXED AND PERMANENT CLASS I NORMAL DENTITIONS TO CLASS I AND II CROWDED DENTITIONS by Christopher Paul Wermerson A thesis submitted in partial fulfillment of the requirements for the Master of Science degree in Orthodontics in the Graduate College of The University of Iowa May 2016 Thesis Supervisor: Professor Robert N. Staley

3 Graduate College The University of Iowa Iowa City, Iowa CERTIFICATE OF APPROVAL This is to certify that the Master's thesis of MASTER'S THESIS Christopher Paul Wermerson has been approved by the Examining Committee for the thesis requirement for the Master of Science degree in Orthodontics at the May 2016 graduation. Thesis Committee: Robert N. Staley, Thesis Supervisor Veerasathpurush Allareddy Fang Qian Arwa Owais

4 ABSTRACT This thesis compared tooth widths, arch widths, and arch lengths; their differences between males and females, and changes from early mixed dentitions to adult dentitions. Comparing subjects who were known to have Angle Class I normal occlusion in their permanent dentitions to subjects who were known to be Class I or Class II crowded malocclusions in their permanent dentitions. These comparisons can only be achieved utilizing data from a longitudinal study, such as the Iowa Growth Study. Dental casts in the early mixed dentition (average age of 8.85 years) and in the adult dentition (average age years) taken from subjects who did not receive orthodontic treatment during or in the dates prior to data collection were measured for this study. The casts utilized were from the Iowa Growth Study; all of the subjects were of European descent. The longitudinal sample of casts in the Iowa Growth study were made from white dental stone poured into alginate impressions from 1946 until The objectives of this study were to compare individual tooth widths, mean sum tooth widths, arch widths, arch length segments, and arch perimeters of Class I Normal (CIN) and Class I and II crowded dentitions (CD) in the early mixed (MD) and permanent (PD) dentitions to explore new methods of predicting crowding. The goal was to evaluate the significance of differences between MD and PD for tooth widths, arch lengths, and arch widths in both arches of CIN and CD subjects to determine values that may be useful for MD space analysis. Thirty males and thirty females from the Iowa Growth Study with CIN and CD occlusions were selected from the longitudinal study. Casts of MD and PD subjects were double measured with digital calipers by both the primary and secondary investigators. ii

5 The average of each investigator s two measurements were used to determine measurement error. All other statistical analysis was based on the mean measurements taken by CPW. Descriptive statistics were computed. The normal non-crowded and crowded samples were compared with two-sample t-test, and changes from MD to PD with paired-sample t-test. Examiner measurement errors were tested with intra-class correlation coefficients. When the mean sums of MD and PD tooth widths were compared, using data from all 60 subjects, the CD group had a significantly greater mean sum of tooth widths than the CIN group. In both genders, crowded dentitions had significantly greater mean sum of tooth widths than CIN s for both the maxilla and mandible in MD and PD. When the mean sums of the arch lengths [Perimeters] were compared using data from all 60 subjects, the arch perimeters of the CD and CIN samples did not differ. It was concluded that total arch lengths [Perimeters] were not significant indicators for crowding. Gender comparisons: Within the CIN group, males had numerically larger tooth width sums and arch length sums than females. The sum of maxillary and mandibular tooth widths for CIN s and CD (both males and females) mandibular tooth widths for CIN s and CD (both males and females pooled together and sexes separately. In the MD stage the mean sum of maxillary and mandibular arch lengths in the MD were significantly greater than those in the PD, because arch perimeters decrease during the transition from mixed to permanent dentitions. In summary, the results of this research thesis study showed that the sum of tooth widths in both arches had a significant association with dental crowding. In contrast, the sum of arch lengths [perimeter in both arches] did not differ between the normal and iii

6 crowded samples. Additional analysis of the measurements taken in this thesis research project, the individual arch length segments, especially the canine and posterior arch length segments in the right and left sides of the lower arch in the mixed dentition casts, and their relation to the sum of the widths of the lower permanent canines and premolars in the normal and crowded malocclusions may give us important information about the development of crowded malocclusions. iv

7 PUBLIC ABSTRACT This thesis compared the size of teeth, length of dental arches, and width of dental arches in normal and crowded dentitions. Differences between males and females as well as between mixed dentition subjects and permanent dentition subjects were compared. Subjects who were known to have normal occlusions in their permanent dentition were compared to subjects who were known to have crowding in their permanent dentition. Thirty male and thirty female subjects from the Iowa growth study were measured to make these comparisons utilizing the longitudinal data. Dental casts in the mixed dentition (average age of 8.85 years) and in the permanent dentition (average age years) who did not receive orthodontic treatment during or in the dates prior to data collection were measured for this study with the goal of determining values that may be used in the future as predictors for space analysis in the mixed dentition. Partial analysis of measurements taken in this study showed that the sum of mean tooth widths in the upper and lower arches had a more significant impact on dental crowding than total arch length (perimeter) in both arches. The mean sums of tooth widths in the mixed and permanent dentitions of the crowded sample were significantly greater than the mean sums of the tooth widths of the non-crowded normal occlusion sample. In contrast, no differences were found between the mean sum of the total arch length sums (arch perimeters) in the normal occlusion and crowded samples in the mixed and permanent dentitions. In summary, the upper and lower tooth width sums of the crowded sample were a significant factor for crowding; whereas, the upper and lower arch perimeters were not a v

8 significant factor for crowding. Males in the normal occlusion group had larger tooth widths sums and arch length sums than females in the normal occlusion group. vi

9 TABLE OF CONTENTS LIST OF TABLES... viii LIST OF FIGURES... ix INTRODUCTION... 1 REVIEW OF LITERATURE... 7 ORTHODONTIC CROWDING RESEARCH... 7 ARCH WIDTH ARCH LENGTH [PERIMETER] MIXED DENTITION ANALYSIS SUMMARY OF THE LITERATURE REVIEW WHY THIS THESIS IS IMPORTANT MATERIALS AND METHODS MEASUREMENTS MEASUREMENT OF ARCH LENGTH SEGMENTS MEASUREMENT OF TOOTH WIDTHS MEASUREMENT OF ARCH WIDTHS CALCULATION OF CROWDING AND SPACING MEASUREMENT RELIABILITY STATISTICAL ANALYSIS RESULTS DATA ANALYSIS INTRA-OBSERVER RELIABILITY OF MEASUREMENTS FOR OBSERVER C 43 INTRA-OBSERVER RELIABILITY OF MEASUREMENTS FOR OBSERVER S. 47 INTER-OBSERVER RELIABILITY OF MEASUREMENTS BETWEEN OBSERVERS C AND S STATISTICAL REPORT STATISTICAL RESULTS DISCUSSION CONCLUSION REFERENCES APPENDIX A APPENDIX B vii

10 LIST OF TABLES Table 1 Subjects from Iowa Facial Growth Study, 60subject casts and ages of subject casts measured Table 2 Descriptive Statistics for Observer C, Descriptive Statistics for Sum of Maxillary and Mandibular Tooth Widths and Sum of Maxillary and Mandibular Arch Length Segments (mm) in the Mixed and Permanent Dentitions Measured by Observer C.47 Table 3 Descriptive Statistic for Observer, Descriptive Statistics for Sum of Maxillary and Mandibular Tooth Widths and Sum of Maxillary and Mandibular Arch Length Segments (mm) in the Mixed and Permanent Dentitions Measured by Observer S Table 4 Descriptive Statistics for Observer C and S, Descriptive Statistics for Sum of Maxillary and Mandibular Tooth Widths and Sum of Maxillary and Mandibular Arch Length Segments (mm) in the Mixed and Permanent Dentitions Measured by Observers C and S viii

11 LIST OF FIGURES Figure 1 Iowa Growth Study Temporary Room, demonstrating the multiple cast boxes of subjects containing stone casts Figure 2 Crowded mixed dentition casts from the Iowa Figure 3 CIN mixed dentition casts from the Iowa Figure 4 Absolute AOS DIGIMATIC digital caliper made by Mitutoyo Figure 5 Data Gage Input tool and connecting cable, both made by Mitutoyo Figure 6 Complete setup for digitally measuring stone casts, with input directly into an excel spreadsheet Figure 7 Measurements of arch lengths, A, B, and C in arches of permanent dentition...34 Figure 8 Measurements in the mixed dentition: arrows for tooth widths measured on all 10 teeth, mesial to the permanent first molars. Green line is the anterior arch length segment, red canine arch length segment, and blue is the posterior arch length segment...35 Figure 9 Demonstration of measuring the anterior arch length segment Figure 10 Demonstration of measuring the tooth width, #9 (UL1) Figure 11 Demonstration of measuring maxillary inter-canine width Figure 12 Demonstration of measuring mandibular inter-canine width Figure 13 Demonstration of measuring maxillary inter-molar width Figure 14 Demonstration of measuring mandibular inter-molar width ix

12 INTRODUCTION The objective of this thesis was to measure in longitudinal dental casts at the early mixed dentition growth stage (average age of 8.85 years) and in the early permanent dentition growth stage (average age years) subjects who did not receive orthodontic treatment during or in the ages prior to data collection. Class I normal occlusion subjects were compared to a sample of subjects with Class I and Class II crowded malocclusions. The longitudinal stone casts utilized were from the Iowa Facial Growth Study; all of the subjects were of European descent, healthy children, and were not selected with respect to dental or facial characteristics. Our hope was to find differences between the normal non-crowded occlusions and the crowded occlusions in the mixed dentition that will enable clinicians to differentiate crowded dentitions from non-crowded dentitions using measurements taken in the mixed dentition. Crowding results in a frequently observed malocclusion and usually results in a lower esthetic appearance. We were interested in investigating (1) how the early mixed dentition (MD) stage of dental development differs between normal and crowded malocclusions in the mixed dentition, (2) how the early permanent dentition (PD) differs between normal and crowded malocclusions in the early permanent dentition, and (3) how the normal occlusions differ during the transition from the mixed dentition to the early permanent dentition. A sample of 60 subjects from the Iowa Facial Growth Study was selected for this research project. The selection criteria were (1) subjects with CIN occlusion in the permanent dentition, (2) subjects with crowding in the permanent dentition that included Class I crowded malocclusions and Class II malocclusions with crowding. We measured and compared tooth mesio-distal widths, arch widths, arch 1

13 lengths and arch perimeters. We compared males and females, and changes from the early mixed dentition (average age 8.85 years) to early permanent dentition (average age years). The Class I normal occlusion (CIN) sample was known to have Class I normal occlusion in their permanent dentitions and the Class I and Class II crowded (CD) sample was known to have Class I or Class II crowded malocclusions in the permanent dentition. The objectives of this study can only be achieved using subjects from a longitudinal growth study, such as the Iowa Facial Growth Study. The specific purposes of this thesis research project were to compare Class I normal occlusions [CIN] with crowded dentitions [CD] with regard to the following variables in the early mixed dentition [MD], and permanent dentition [PD]: 1. Sum of maxillary tooth widths [SMX] 2. Sum of mandibular tooth widths [SMND] 3. Sum of maxillary arch length segments (6) = Maxillary Arch Perimeter [MxAP] 4. Sum of mandibular arch length segments (6) =Mandibular Arch Perimeter [MdAP] 5. MxAP minus SMX = Spacing +, or Crowding 6. MdAP minus SMND = Spacing +, or Crowding 7. In CIN group compare variables at MD and PD (transition) 8. In Crowded group, compare variables at MD and PD (transition) 9. Gender comparisons within CIN and CD. 2

14 The uniqueness of the present study lies in the fact that the CIN sample was different from that measured by Vermeer, et al (2015); because, CPW removed the minimally crowded Class I subjects from the Vermeer et al CIN sample (2015). The hope was that this refinement of the CIN sample of Vermeer et al (2015) would increase the probability that we could find significant differences between the non-crowded CIN sample and the crowded sample. It was hoped that the findings of this research project will increase our knowledge about the growth of the dentition in the non-crowded CIN and crowded malocclusions (CD). Furthermore, it was hoped that this refinement of the normal occlusion sample would lead to the development of a new, improved method for predicting crowding in mixed dentition patients. Dental crowding in the permanent dentition is defined as a disparity in the relationship between tooth size and dental arch size. The combinations between the three sizes of teeth and three sizes of arch perimeter [very large, normal, and very small] yield 9 combinations, assuming the inheritance of these phenotypes is polygenic. Dental crowding can occur with (1) very large teeth with a normal arch perimeter, (2) very large teeth with a very small arch perimeter, and (3) normal sized teeth with a very small arch perimeter. Two thirds of the crowding subjects according to the above combinations have larger than normal tooth size, and one third have normal size teeth. When the combinations for crowding are examined by arch perimeter, two thirds of the crowded patients have small arch perimeters, and one third have a normal size arch perimeter. These possible combinations are a mixed bag of normal size teeth and large teeth and normal size arch perimeter and smaller than normal size arch perimeter. Another complication is that the upper and lower arches by themselves also are independent with 3

15 regard to arch lengths, arch perimeters, arch widths, and tooth sizes. Normal occlusions occur because the genes properly direct the growth of the upper and lower arches, the relationships between arch dimensions and tooth dimensions, and the growth of the maxilla and mandible. Orthodontists must deal with this complexity in their malocclusion patients. The polygenic inheritance of the growth and development of the face and dentition is complex. In addition, the complexity is a statistical challenge! The past literature about crowding is interesting in that orthodontists have not recognized the complexity of crowding malocclusions. Orthodontists want to simplify the crowding problem, but we must accept and deal with the true complexity of crowding problems in order to best serve our patients that experience crowding. This research entered into the complexity of crowding with the hope that some useful information can be given to orthodontists to better inform them about the crowding problem and its complexity. If the tooth size, arch widths, and arch length measurements of the crowded sample selected in this research project differ significantly from those of the non-crowded Class I normal occlusion sample, the differences may lead to a better understanding of our ability to estimate the crowding potential in the mixed dentition patient. All current methods of estimating crowding or spacing in the permanent dentition using measurements taken in the mixed dentition have only one component: estimation of the mesio-distal widths of non-erupted permanent canines and premolars. The prediction of the widths of the non-erupted permanent canines and premolars using radiographic measurements of the mesio-distal widths of the non-erupted permanent canines is very 4

16 accurate, Staley et al (1984). And the advent of cone beam radiographs will eliminate the small errors of current methods using periapical radiographs. What is missing in all of the currently available mixed dentition analysis methods is the estimate of the change in the arch perimeter, or change in arch length segments in the transition from MD to PD. The change in the arch length and perimeter dimensions are very difficult to predict (Hunter and Smith, 1972). If significant differences can be detected between the lower arch sum of permanent canine and premolar tooth widths and the sum of the canine and posterior arch lengths in the mixed dentition of the CIN normal occlusions (non-crowded) and crowded CD malocclusions, we may be able to measure the arch lengths on the casts of a mixed dentition patient to better estimate whether or not a crowded dentition can be discovered in the mixed dentition. Grossly crowded patients in the mixed dentition (a small group in the population with 6 and more mm of crowding) are readily identified in the mixed dentition; however, the patients with crowding of 3 to 5 mm are difficult to distinguish from the non-crowded patients in the mixed dentition. This is the group of crowded patients that clinicians would like to recognize in the mixed dentition, to improve our diagnosis of crowding. The Iowa Growth Study has the necessary longitudinal data to conduct this study. The small sample size of longitudinal growth studies is a limiting factor. Measurements obtained from the crowded sample were compared to a control sample of normal occlusion data from the Growth Study. Those interested in these findings include orthodontists, pediatric dentists, physical anthropologists, and scientists that study human growth. 5

17 We expect, on the basis of past research, that the crowded sample will have both significantly smaller dental arch segments and arch perimeters, arch widths, and significantly larger mesio-distal tooth widths in both males and females compared to those variables in the CIN sample. The following null hypotheses were tested: 1. That the non-crowded and crowded samples do not differ (are statistically similar) in the maxillary and mandibular arch length segments and in the maxillary and mandibular arch perimeters (MxAP) (MdAP) in the mixed and permanent dentitions and in the transition from MD to PD. 2. That the sum of tooth mesio-distal widths (size) are similar in the noncrowded and crowded samples, that the samples do not differ in crowding (TSALD) in the MD and PD, and that the samples do not differ in these variables in the transition from MD to PD. 3. That the sexes do not differ in arch length segments, arch perimeters, arch widths, tooth size, crowding, and in the transition of these variables from MD to PD. 6

18 REVIEW OF LITERATURE ORTHODONTIC CROWDING RESEARCH Speculations were made by Hooten, (1947) that dental crowding may result from an evolutionary trend toward a reduced facial skeleton size without a corresponding reduction in tooth dimension. We skeptics await the evidence. Mills (1964) found little variation to exist between crown diameters of persons with and without malalignment (crowding). Lundstrom (1969) studied 13 year old boys, sample size of 139 and found that tooth size increases as crowding increases. Lundstrom (1969) also found that arch perimeter decreased as crowding increased. This led some researches to believe that people with large teeth are more likely to have crowding than those with small teeth (Lundstrom, 1969). Sex differences have been reported by multiple authors in that they all found more dental crowding in females than in males (La Velle and Foster (1969) Fastlicht (1970) and Foster, et al (1970). The preceding studies reported that males have 4% larger teeth than females. The greatest difference was found in the mandibular canines that were 6% larger in males and the least sex difference was found in the mandibular incisors. These differences were found regardless of race. Therefore, the preceding studies recommended that in a study of tooth sizes, males and females should be analyzed separately. Mean mesio-distal tooth size in crowded arches was uniformly larger than those with non-crowded arches. 7

19 A longitudinal growth study conducted by Hunter and Smith (1972) measured the mandibular arches of 52 essentially Class I untreated subjects at ages of 9 and 16 years. There were 35 males and 17 females in this sample from the Burlington (Ontario) Orthodontic Research Centre, which like the Iowa Growth Study is a longitudinal growth study collection. They found no sex differences. They found the greater the crowding at age nine, the less the arch perimeter decreased by age 16 in the sample of 52 patients. They also found that spacing-crowding at nine years showed a high correlation with spacing-crowding at 16 years. Crowding at nine and 16 years were moderately correlated (r = 0.68). They reported that arches that are crowded at 9 years tend to be crowded at 16 years. They reported that arches that are crowded at 9 years tend to be crowded at 16 years. Arches with spaces at 9 years tended to have spaces at 16 years. Arch perimeter is known to decrease on the average from nine to 12 years of age. Given spacing at age 9 years, arch perimeter reduction from 9 to 16 is on average quite extensive, amounting to 4.4 mm. Very slight average amount of arch perimeter reduction (0.5 mm) from 9 years to 16 years is was observed in the severely crowded sample. The greater the crowding at age 9 years, the less will be the arch perimeter reduction by age 16 years. This apparent reduction in crowding was mostly confined to the posterior segments and hence was due in part to inflation of crowding by substitution of primary molar tooth sizes for missing primary molars at age nine. The moderately crowded and the spaced categories showed an average mesial movement of the mandibular molars of 0.51 and 0.67 mm respectively, relative to the maxillary first molars. Hunter and Smith (1972) reported that it is not the molar relationship that determines how much the arch perimeter will be reduced from the mixed to permanent dentition, but rather the severity of the spacing or crowding that 8

20 determines the reduction of the arch perimeter from the mixed to permanent dentitions. Hunter and Smith (1972) explained that some arches lose more of their arch perimeter than others, therefore, the clinician is wise to believe that any space remaining in an arch at the mixed dentition is space left for molar adjustment. Hunter and Smith (1972) also found that an orthodontist can expect that crowding in the mixed dentition will likely result in crowding in the permanent dentition. This is an important landmark study that described the development and longitudinal growth of crowded malocclusions. Crowding was defined by Van der Linden (1974) as an inherent discrepancy between tooth size and the available arch length, mainly of genetic origin. Secondary crowding is caused by environmental factors influencing the dentition, such as caries and extractions. Tertiary crowding or late crowding occurs in the post-adolescent period. The most frequent orthodontic posttreatment change was re-crowding of anterior teeth (Van der Linden, 1974). Vander Linden (1974) found that the incidence of mandibular incisor crowding increased from 14% at age 6 to 51% at 14 years of age. A number of other articles have also reported a trend toward increased incidence of mandibular incisor crowding with higher ages in untreated persons (Barrow, 1952). Incisor crowding increased during maturation in the normal untreated person, but occurred at a rate that is about one third that of the orthodontic treated persons (Sinclair, 1981). DeKock (1972) found that the average incisor-canine circumference (perimeter) was reduced by 10% from 13 to 18 years of age. Moorrees (1979) claimed that this decrease of incisor-canine circumference (perimeter) was associated with a decrease in arch length rather than a narrowing in arch width. 9

21 According to Moyers (1973) the dental arch is measured through the contact points of the teeth and represents a series of points where the muscle forces acting against the crowns of the teeth are balanced. The basal arch, is the arch formed by the corpus mandibularis or maxillaris. Its dimensions are unaltered by the loss of all permanent teeth and the resorption of the alveolar processes. Moyers (1973) defined the arcal measurement of the apical base. The alveolar arch is the arcal measurement of the alveolar process. The dimensions of the alveolar arch may not coincide with those of the basal arch if the teeth are tipped labially off the basal arch. It should be the goal of orthodontic treatment that all of the combined widths of the teeth once aligned will be identical with the dental arch measurement and the dental arch will be so positioned over the basal bone that gross differences in the dental arch, alveolar arch, and basal arch perimeters will not obscure cosmetics or complicate occlusal function and stability (Moyers, 1973). Arya (1974) reported that male teeth are consistently numerically larger than female teeth. Numerical size does not mean statistically larger. Nordeval (1975) studied subjects with modest mandibular crowding. The crowded sample was found to have larger mesiodistal widths of the four lower incisor teeth than subjects without lower incisor crowding. Doris et al (1981) found that the maxillary lateral incisors and second premolars had the greatest variability in mesio-distal diameters, which was nearly twice as great as that for the other teeth analyzed. These 4 teeth showed the greatest potential for influencing an arch to be crowded. Doris et al (1981) defined crowded arches as those with more than 4 mm of crowding. These crowded arches were compared to patients 10

22 with good tooth alignment. The hypothesis tested was whether the arches with more than 4 mm of crowding consistently had larger teeth than those with lesser or no crowding. The difference in size was found to be significant, P less than Teeth in males were numerically larger than in females, but not to a statistically significant level. Doris et al (1981) recommended that when the cumulative tooth mass of the twenty permanent teeth mesial to the first molars is 140 mm or more, the orthodontist may want to consider extractions. Doris et al (1981) used sliding calipers with a digital scale for measurements. In older studies done prior to the 1980 s, measurements were taken with sliding calipers with a Vernier scale or a pair of engineer s dividers with a millimeter ruler. Holes were then punched on a card and the distances measured with the millimeter ruler to the nearest 0.1 mm. Doris et al (1981) found that poor alignment [crowding] was correlated with larger teeth, that measurement of mesio-distal tooth size was largely a repeatable measure, and there was a weak association between sex and arch status. However, Doris et al (1981) still found males to have larger teeth than females. Doris et al (1981) reported that patients that had extractions had consistently larger teeth and a greater sum of the mesio-distal tooth widths than the group treated by non-extraction. Doris et al (1981) found that measurements of maxillary and mandibular incisors, canines, and premolars were uniformly larger in the group with crowded arches. Doris et al(1981) concluded that an important factor determining whether or not a dental arch will be crowded is the absolute size of teeth in that arch. Doris (1981) found that crowding increased with age until the thirteenth or fourteenth year and then tended to decrease. Howe and McNamara (1983) drew attention to the fact that crowding can result not only from excessive tooth size, but also inadequate apical bases. Howe and 11

23 McNamara (1983) studied two samples of dental casts from patients in the permanent dentition, one with gross dental crowding and one with no crowding to determine the extent to which tooth size and jaw size contribute to dental crowding. They found that statistically, the crowded and non-crowded groups could not be distinguished from one another on the basis of mesio-distal tooth diameters. However, they found significant differences between the dental arch dimensions of the two samples. The crowded sample was found to have smaller dental arch dimensions than the non-crowded sample. These results suggested that extra consideration should be given to treatment techniques that increase dental arch length rather than reduce tooth mass. Howe and McNamara (1983) introduced a formula to determine whether or not the apical bases of a patient could accommodate the patient s teeth in the permanent dentition. For Howe s Analysis tooth material (TM) equals the sum of the mesio-distal widths of the teeth from the first permanent molars forward. Premolar diameter (PMD) is the arch width measured between the tips of the buccal cusps of the first premolars. The ratio between the premolar diameters and tooth material PMD/TM is obtained by dividing the premolar diameter by the sum of the widths of the 12 teeth. Howe and McNamara (1983) reported that the premolar basal arch width was measured across the apical base on the dental casts at the apices of the first premolars. They reported that the basal arch width should equal approximately 44% of the mesio-distal widths of the 12 teeth in the maxilla, based on measures from the non-crowded sample. A ratio of 44% means that the basal arch width is sufficiently large to accommodate all of the teeth. Howe and McNamara reported that when the ratio is 37% or less, a basal arch deficiency exists that necessitates extraction of premolars. If the premolar basal width is greater than the 12

24 premolar coronal arch width, a non-extraction treatment may be undertaken safely. The Howe and McNamara analysis may be useful for deciding when to extract teeth or treat non-extraction in the permanent dentition. Howe and McNamara (1983) found no clinically significant associations between various mandibular parameters and incisor crowding. They concluded that no predictive equation can accurately forecast the nature and extent of the changes in lower incisor crowding. Howe and McNamara (1983) on the basis of their research asserted that correction of crowding can be accomplished in three ways: (1) reduce the tooth mass by extraction of permanent teeth or inter proximal reduction (IPR), (2) increase dental arch widths with palatal expansion, rapid palatal expansion, quad helix expansion, and functional appliance expansion, or a combination of extraction of teeth and expansion of the arches. They recommended on the basis of their research that it may be more advantageous to correct crowding with arch expansion when possible. [The orthodontic specialty was embarked upon an increase in non-extraction treatment in the 1980s.] Howe and McNamara (1983) found the difference in mean value of maxillary mesiodistal tooth diameters for males between the crowded and non-crowded groups for males was 0.7mm. For the mandibular arch this difference was 0.1 mm. For females the differences were 0.7 mm and 0.5 mm respectively. Due to the dimensional differences between males and females with respect to tooth size and arch size, the data was presented separately for males and females (Howe and McNamara 1983). 13

25 ARCH WIDTH As Howe and McNamara (1983) stated The non-crowded arches were easily identifiable, with broad symmetrical arch forms that were uniform in shape. In contrast, the crowded arches were sometimes asymmetrical, frequently narrow or tapered, and strikingly irregular in arch form. If excessive tooth size alone were responsible for dental crowding, then one might have expected to see crowded arches with broad symmetrical and uniform arch shapes that differed from non-crowded arches only in the amount of overlap and rotation of the teeth. Or, if arch dimension alone were responsible for dental crowding, one might have expected to see dental crowding in symmetrical, uniform arches that were significantly smaller than the non-crowded arches. (Howe, 1983). Inter-canine and inter-molar widths significantly increased between 3 and 13 years of age in both maxillary and mandibular arches. After the complete eruption of the permanent dentition, there was a slight decrease in the dental arch widths, more in the inter-canine than in the inter-molar widths. Mandibular inter-canine width, on the average, was established by 8 years of age, after the eruption of the four incisors. After the eruption of the permanent dentition, the clinician should either expect no changes or a minimal decrease in arch widths (Burdi, 1988). Knott, 1989 also found 97% of subject s inter-canine width in both arches either remained unchanged, increased, or decreased by 1.0 mm from mixed to the permanent dentitions. This was a longitudinal study of subjects that participated in the Iowa Facial Growth Study between deciduous 5.4 years, mixed 9.4 years, early permanent 13.6 years, and early adulthood 25.9 years old (Knott, 1989). 14

26 Sillman (1964) conducted a study of arch widths composed of a mixed longitudinal sample from birth to 25 years of age. From birth to 2 years there was an increase in inter-canine width of 5 mm in the maxilla and 3.5 mm in the mandible. After 2 years of age, inter-canine width continued to increase in the maxilla until 13 years of age and in the mandible until 12 years of age, after this time canine width remained stable. Male subjects, in general, had larger arch widths than female subjects (Sillman, 1964). Lundstrom (1969) by contrast measured arch width changes at the first premolar and permanent first molars. Forty-one pairs of twins were used for the study with an initial age range of 9-19 years and a final age range of years. Lundstrom concluded that arch width changed very little for the older age group. Although the dental arch widths undergo significant changes from birth until midadulthood, the magnitudes as well as the direction of these changes do not provide a scientific basis for expanding the arches, in the average patient, beyond its established dimensions at the time of the complete eruption of the canines and molars (Bishara, 1997). It is for these reasons that some believe the pre-treatment inter-canine width dimension should not be violated and that the mandibular inter-canine width should be used as a guide around which to build the eventual arch form (Herberger, 1981 and Little, 1981). Bishara (1997) reported that for all practical clinical purposes, the arch width dimensions are established in the mixed dentition (8 years of age) with some, but minimal increases until the early permanent dentition (9 to13 years) and progressive but minimal decrease in early and mid-adulthood. Because most orthodontic treatment, whether it is in one or two phases, occurs between 8 and 13 years, it is important for the clinician to 15

27 take into consideration the minimal overall changes that occur in the mandibular anterior dental arch width, with time (Bishara 1997). For example, males increased their maxillary and mandibular inter-molar widths between 3 and 5 years, 5 and 8 years, and 8 and 13 years. Bishara found no significant changes in inter-molar width between 13 and 26 years and 26 and 45 years. Although in general male subjects were significantly larger than female subjects in both maxillary and mandibular arch widths. Females increased up to 13 years of age in both maxillary and mandibular inter-molar widths. Between 13 and 26 and 26 and 45 years there was a slight decrease in both maxillary and mandibular arch widths, but the decrease was not statistically significant. (p= ). Mandibular intercanine width increased between 3 and 13 years of in both male and females. Between 13 and 25 years of age, width decreased in males (avg -0.9 mm) and females (avg -1.6 mm). Maxillary inter-canine increased between 3 and 13 years both male and female. After 13 years maxillary inter-canine widths decreased until 45 years, males -1.4 mm, females - 1.2mm (Bishara, 1997). It should be noted however that Knott (1956) found that between 9 and 15 years of age, maxillary and mandibular arch width means increased over 2.0 mm for males and approximately 1.5 mm for females. In a study conducted at the University of Iowa utilizing the Iowa Facial Growth Study by Kuntz, et al. (2008) found that the Class I crowded (CICR) group had mean maxillary and mandibular inter-molar and alveolar arch widths that were significantly smaller than in the Class I normal (CIN) group. The Class III group also had mean maxillary inter-molar and alveolar arch widths significantly smaller than the CIN group. The growth and etiology of Class I crowded malocclusions involves narrower than normal inter-molar and alveolar arch widths in both arches. The growth and etiology of 16

28 Class III malocclusions involves narrower than normal maxillary inter-molar and alveolar arch widths. Mean difference between maxillary and mandibular inter-molar widths in CICR adults was -0.1 mm. Negative differences discovered in this sample without posterior cross-bites imply that some CICR patients without a posterior cross-bite could benefit from widening of the maxillary arch (Kuntz, 2008). Heikinheimo et al (2011) conducted a Finish longitudinal growth study with untreated normal Angle Class I occlusions. The subjects were examined at ages 7, 10, 12, 15, and 32. Longitudinal findings showed that in both arches of young adults the arch widths narrowed slightly from adolescence to 32 years of age. All increases in arch width took place before 15 years of age. The means of the changes were small, in the order of 0.5 mm to a few millimeters. Variability in arch width changes was considerable. ARCH LENGTH [PERIMETER] Bishara (1998) studied arch perimeter or circumference measurements that included the sum of the right and left anterior and posterior segmental arch lengths for the maxillary and mandibular arches. Bishara reported that arch perimeter continued to increase until 13 years in the maxillary arch and until 8 years in the mandibular arch. He also reported that significant and consistent decreases occurred in both arches mesial to the first molars. Changes in the dental arch dimensions that occur as a result of growth and treatment are of interest to the orthodontist and must be carefully considered when planning treatment. Bishara found from 6 weeks to 2 years maxillary arch length increased significantly averaging 15.1 mm in males and 16.4 mm in females. From 3 to 17

29 13 years, maxillary arch length increased significantly, by 4.0 mm in males and 2.4 mm in females. However, the increase in mandibular arch length was completed by 8 years of age. Average increase in arch length from 3 to 8 years was 1.9 mm in males and 2.0 mm in females. Between 8 and 13 years, mandibular arch length started to decrease significantly, by 2.4 mm in males and 3.2 mm in females. Between 13 and 45 years, maxillary arch length decreased significantly in both males (5.7mm) and females (4.6 mm). Mandibular arch length also decreased between 8 and 45 years, by an average of 7.4 mm in males and 8.3 mm in females. Bishara (1998) concluded that males had significantly greater (p less than or equal to 0.05) total arch perimeter in both arches than females. Bishara (1998) reported that the greatest incremental increases in both the maxillary and mandibular arch perimeters occurred during the first two years of life. Teeth do not change significantly in crown size [width] except through interproximal attrition. As a result, the decrease in arch length is translated as an increase in the tooth size-arch length discrepancy, unless interproximal attrition keeps pace with the decrease in arch lengths. Arch perimeter continued to increase until 13 years in the maxillary arch and 8 years in the mandibular arch. Following these ages, significant decreases in arch perimeter occurred until 45 years of age (Bishara, 1998). Vermeer et al. AADR poster (2015) reported that arch perimeter and tooth width sums in Class I normal occlusions (CIN) underwent significant reductions in the transition from mixed to early permanent dentitions. Vermeer et al (2015) reported that tooth width sums [primary canines and molars] transitioned from MD to PD in the maxilla of Class I normal occlusions from 73.3 mm to (-1.9 mm); and in the 18

30 mandible from mm to 62.0 mm (-5.5 mm). They reported that arch perimeters transitioned from MD to PD in the maxilla from mm to (-2.39 mm); and in the mandible from to (-5.12). These findings were from a study utilizing a sample of mildly crowded and non-crowded Class I normal occlusions. A study conducted by Hunter and Smith in 1972 measured the mandibular arches of 52 essentially Class I untreated subjects at ages of 9 and 16 years. There were 35 males and 17 females in this sample from the Burlington (Ontario) Orthodontic Research Centre, which like the Iowa Growth Study is a longitudinal growth study collection. They found no sex differences. They found the greater the crowding at age nine the less the arch perimeter decreased by age 16 in the sample of 52 patients. They also found that spacing-crowding at nine years showed a high correlation with spacing-crowding at 16 years. Crowding at nine and 16 years were significantly moderately correlated (r = 0.68). Arches which are spaced at 9 years tended to be spaced at 16 years. They reported that arches which are crowded at 9 years tend to be crowded at 16 years. Arch perimeter decreased on the average from nine to 12 years of age. Given spacing at age 9 years, arch perimeter reduction from 9 to 16 is on average quite extensive, amounting to 4.4 mm. Very slight average amount of arch perimeter reduction (0.5 mm) from 9 years to 16 years was seen for the severely crowded sample. The greater the crowding at age 9 years the less will be the arch perimeter reduction by age 16 years. This apparent reduction in crowding was mostly confined to the posterior segments and hence was due in part to inflation of crowding by substitution of primary molar tooth sizes for missing primary molars at age nine. The moderately crowded and the spaced categories showed an average mesial movement of the mandibular molars of 0.51 and 0.67 mm respectively, 19

31 relative to the maxillary first molars. Thus this study indicated that it is not, as it has been implied, the molar relationship which determines how much the arch perimeter will be reduced from the mixed to permanent dentition, but rather the severity of the spacing or crowding. With some arches diminishing more than others, thus the clinician is wise to believe that any space remaining at the time of the mixed dentition estimate is space left for molar adjustment. (Hunter and Smith, 1972). All this allows the orthodontist to know is that crowding in the mixed dentition will likely result in crowding in the permanent dentition as well. MIXED DENTITION ANALYSIS All mixed dentition analysis methods use measurement variables in the mixed dentition that predict the combined mesio-distal widths of the non-erupted canines and premolars in each of the 4 quadrants of the dentition. The complexity of the crowded malocclusions makes any attempt to develop a mixed dentition prediction method. Mixed dentition analyses were created to predict the amount of space available in the arch for succeeding permanent teeth and necessary occlusal adjustments. To complete these analyses the size of the permanent teeth anterior to the first permanent molar, and the change in arch perimeter, are studied. There is one major way of developing a mixed dentition prediction. All methods try to predict the size of the non-erupted canines and premolars that are estimated from measurements of their radiographic images and from measuring the size of permanent teeth already erupted in the mouth. The correlation between the widths of erupted lower incisors and the widths of the non-erupted canines and premolars are about r = The correlation between radiographic images of the 20

32 non-erupted canines and premolars is r = 0.9 a much improved and accurate method. The difficulty of the prediction methods lies in their inability to predict the loss of arch length or perimeter that occurs during the transition from the mixed to permanent dentitions. SUMMARY OF THE LITERATURE REVIEW The literature review is full of contradictory claims about the nature and description of crowding malocclusions in humans. It reminds us of the blind persons that are asked to describe an elephant. Human crowding malocclusions are variable and very complex. The hope of this research project is to shed more light and information about the extent of the complexity of human dental crowding. WHY THIS THESIS IS IMPORTANT The most frequent orthodontic malocclusion is crowding and it is a result of the discrepancy between the volume of alveolar bone, arch length (perimeter) and tooth size (Rose, 2009). Several past studies explored the relationships of tooth size, arch length, arch perimeter, and dental crowding. There have been contradictory reports from previous studies regarding which variable most influences dental crowding. One group claims that tooth size has a greater role in developing dental crowding [Poosti et al (2007), Doris et al (1981), Begg (1965)]. Another group claims that dental arch dimensions play a greater role in crowding [Howe et al (1983), Lavelle (1969)]. This study examined these relationships in order to determine which parameters had a more 21

33 significant impact on dental crowding. This study also hoped to examine which of the six arch length segments or individual teeth affected crowding the most. Dr. Moyers (Moyers, 1973) stated in his book malocclusion is not a disease process and hence cannot be approached with a dependence on Koch s postulates. The use of group averages alone is not suitable enough for a practical clinical analysis. Research is done by the hundreds treatment is done one by one (Moyers, 1973). More can often be learned by comparing a child with himself or herself than by comparing the same child with a table of norms for the group in which he or she belongs. It is for this reason that the Iowa Growth study was used for this thesis research. We wanted a longitudinal sample so we could compare individual subjects longitudinally rather than comparing one group to another group. In this present study, the objectives were to study the growth of CIN and Class I and II crowded subjects using longitudinal data. In this way we could also compare for the first time, Class I normal and Class I and II crowded malocclusions to find how the normal and crowded samples differ in their tooth size, arch perimeters, arch widths and growth of these dimensions from the late mixed dentitions to their early permanent dentitions. 22

34 MATERIALS AND METHODS The Iowa Growth Study began in 1946 and lasted until It followed 183 children (91 males and 92 females) from their sixth until their sixteenth birthday. Enrollment in the study was based on the likelihood of continuing residence in the Iowa City community and willingness to participate. The subjects were physically normal children unselected in respect to cephalic or facio-dental characteristics (Meredith and Chadha 1962). In addition to casts, height, weight, dietary information, and medical history data are included among materials gathered at each appointment. Semi-annual dental casts, anterior and profile photographs, full intraoral radiographs, posterior-anterior and lateral cephalometric radiographs were taken for each respective individual from 5 to 12 years of age, and yearly from 12 to 16 years. The Iowa Facial Growth Study is a unique longitudinal study, meaning the same individuals were followed throughout their growth. In general they had good dental health meaning they had a low number of decayed, missing, and filled teeth; also called a low DMF score. Data was derived from casts of this study population. The Iowa Facial Growth Study was started in March of 1946 by Dr. V. Meredith and Dr. L. Higley. Eighty-nine boys and 86 girls not younger than 3 years were originally enrolled. All records were taken semiannually until age 12, annually during adolescence, and once during early adulthood. The subjects were predominately of northern European descent, and, at the beginning of the study, were living in or near Iowa City, Iowa. Most were from families of above average socioeconomic status. All had clinically acceptable facial skeletal features and occlusion---that is, class I molar and canine relationship, anterior crowding of less than 2 mm at the time of eruption of the permanent second molars, and no apparent facial 23

35 disharmony. None of these subjects had congenitally missing teeth and none had undergone orthodontic therapy. In addition each subject had a complete set of records at 3, 5, 8, 13, 25, and 45 years of age (quoted from Bishara, 1994 and Knott, 1989). The Iowa Growth study is one of twelve known collections of longitudinal craniofacial growth records in the United States and Canada. These can be found online at These collections include cephalograms, intraoral radiographs, hand wrist films, study casts, and written records charting the physical development through time of children of different ethnicities and growth patterns (Baumrind, 2015). The sample for this study was taken from the Iowa Growth Study longitudinal casts collected from 1946 to A total of 60 subjects were used for this study. Fifteen males and fifteen females with CIN occlusions from the Iowa Facial Growth Study and fifteen males and fifteen females with Class I or II crowded occlusions were selected from the longitudinal study. The casts in the Iowa Growth study were derived from white dental stone poured into alginate impressions. In order to select the necessary subjects and casts from the Iowa Growth Study all of the cast boxes were opened and the casts visually inspected. Casts were inspected for completeness of their dentition as well as being of the proper age, mixed dentition and early permanent dentition. The following selection criteria were used to create the samples: [1] subjects that had multiple fillings or extractions were excluded; [2] When a filling in a tooth at the mixed and permanent dentition stages accurately reproduced the crown anatomy and crown mesio-distal width, the width of the tooth was measured on a cast at a younger age for the same subject before the tooth was restored with amalgam; [3] Subjects that had no casts with full compliments of teeth at the proper age were 24

36 omitted from the study; [4]Visual inspection was used to select casts with CIN and crowding; [5] The casts were evaluated for crowding and if crowding of 3 mm or more existed, the cast was included in the Class I or II crowded sample, if all the previous criteria were satisfied; [5] If a cast had 1 mm or less crowding it was included in the CIN normal group, if the articulated upper and lower permanent first molars occluded in a Class I relationship in the permanent dentition and all the previous criteria were satisfied. Figure 1 Iowa Growth Study Temporary Room, demonstrating the multiple cast boxes of subjects containing stone casts. 25

37 Figure 2 Crowded mixed dentition casts from the Iowa Facial Growth Study. 26

38 Figure 3 CIN mixed dentition casts from the Iowa Facial Growth Study. 27

39 Normal mixed Males Subject M1 M2 M3 M6 M16 M24 M28 M33 M38 M41 M68 M73 M76 M80 M82 Age , 10-6 fo , 7 for L8-5, 8 L for Normal Adult Males Subject M1 M2 M3 M6 M16 M24 M28 M33 M38 M41 M68 M73 M76 M80 M82 Age , 12 for L1' Normal mixed Females Subject F3 F7 F18 F19 F20 F21 F32 F33 F39 F43 F46 F52 F59 F62 F68 Age 7, 12 for U 8, 9 U for U6 U, 6-6 L, U, , 10 L fo10, 7 U for 9, 8-6 for a9 8, 4-6 L for , No LLE8 U, 7-6 L, 5 Normal Adult Females Subject F3 F7 F18 F19 F20 F21 F32 F33 F39 F43 F46 F52 F59 F62 F68 Age Crowded Mixed Males Subject M7 M9 M13 M19 M21 M35 M37 M40 M47 M50 M60 M65 M66 M67 M77 Age 8, 10U, U left s9 10-6, 6 U fo8 L, 8-6 U , 5-6 L f 10 U, 8 U fo , 6-6 fo 8-6, 6-6 U f Crowded Adult Males Subject M7 M9 M13 M19 M21 M35 M37 M40 M47 M50 M60 M65 M66 M67 M77 Age , 12 for U Crowded Mixed Females Subject F8 F10 F13 F23 F30 F38 F41 F44 F45 F47 F49 F50 F66 F72 F77 Age , 7 L for in9-6, 8 L for9 9 U, 8-6 L, 8-6 U, 8 L U, 7 U fo10 8, 6 U for U8, 6-6 U fo 9, 5-2 L for9 Crowded Adult Females Subject F8 F10 F13 F23 F30 F38 F41 F44 F45 F47 F49 F50 F66 F72 F77 Age , 11-7 U Table 1 Subjects from Iowa Facial Growth Study, 60 subject casts and ages of subject casts measured. 28

40 In the past orthodontic researchers analyzed the mixed dentition as anterior (incisor liability) and posterior segments (Leeway Space) and emphasized the differences between the sizes of the primary and permanent incisors (incisor liability) and differences between the widths of primary canines and molars and the permanent canines and premolars (leeway space). This study takes a different view of the transitions that occur from the mixed to permanent dentitions. By measuring the arch perimeters, tooth widths, and arch widths in the mixed and permanent dentitions in Class I normal subjects and in Class I and II crowded subjects, we hoped to learn how the arches grow to accommodate the erupting permanent teeth. Comparisons of CIN s with the development of malocclusions may give us a better understanding of the abnormal development in crowded malocclusions. Measurements were made directly on non-soaped dental casts. The accuracy of plaster casts fabricated from alginate impressions as a representation of actual tooth sizes was investigated by Hunter and Priest (1960). They concluded that measurements made on dental casts were more reliable than those made directly in the mouth. Cast measurements were found to be slightly larger than direct measurements made in the mouth. A study by Hunter and Priest (1960) compared soaped versus non-soaped models and found the soaped models slightly larger in over-all dimension. However, they conceded that measurements made from dental casts are more consistent and therefore more accurate than direct measurements taken from the mouth, particularly in the posterior segments where measures made in the oral cavity becomes more difficult Hunter and Priest (1960). 29

41 The Class I normal occlusions had a Class I molar relationship, with no apparent skeletal discrepancies, no congenital craniofacial anomalies, and no history of orthodontic treatment. The early permanent dentitions had fully erupted permanent incisors, canines, premolars, and first molars on both sides of the maxillary and mandibular dental arches. Figure 4 Absolute AOS DIGIMATIC digital caliper made by Mitutoyo. 30

42 Figure 5 Data Gage Input tool and connecting cable, both made by Mitutoyo. Figure 6 Complete setup for digitally measuring stone casts, with input directly into an excel spreadsheet. 31

43 MEASUREMENTS Double measurements were obtained for each parameter using an Absolute AOS DIGIMATIC digital caliper made by Mitutoyo, which is accurate to the 1/100 mm. Therefore measurements were recorded to the nearest hundredth of a millimeter. The digital caliper was connected to the computer utilizing a data gage input tool made by Mitutoyo (item number ). The data gage was connected to the computers USB port utilizing a connecting cable that was also made by Mitutoyo (item number ). The data was then directly inputted into a custom made excel spreadsheet (Charts 1-16 in the Appendix). To ensure measurement accuracy, all measurements were taken twice at two different times by two individual measurers. MEASUREMENT OF ARCH LENGTH SEGMENTS In order to measure arch length, study casts were measured with calipers from the height of the interdental papilla between teeth in the six segments. These were measured at the height of the interdental papilla of the central incisors to the interdental papilla between the lateral incisor and the canine (A), the interdental papilla between the lateral incisor and mesial of the canine to the papilla between the distal of the canine and the mesial of the first premolar (B), and the papilla between the distal aspect of the canine and the mesial aspect of the permanent first molar (C). These measurements were made for both the maxillary and mandibular arches (figure 8). The measurements are similar in the mixed dentition, except the primary canines and molars are present instead of the permanent canine and premolars, as demonstrated by the mixed dentition cast in figures 9 32

44 and 10. Arch length was measured papilla to papilla, from the side of the casts. Tooth widths were measured between anatomic contact point to anatomic contact point not the contact of 2 teeth, because this may be different. For this study the early mixed dentition was defined as having permanent incisors and first molars fully erupted without any permanent premolars or canines erupted (early mixed dentition). Arch length measurements: Anterior segments, between the gingival papilla at the mesial contact point of the permanent central incisors and the papilla between the permanent lateral incisor and primary canine. Primary canine segments, were measured between the papilla near mesial contact point of the canine and lateral incisor and the papilla near the distal contact point of the primary canine and primary first molars. Posterior segments were measured from the papilla between the primary canine and first primary molar and the papilla between the second primary molar and the mesial of the first permanent molar. 33

45 Figure 7 Measurements of arch lengths, A, B, and C in arches of permanent dentition. 34

46 Figure 8 Measurements in the mixed dentition: arrows for tooth widths measured on all 10 teeth, mesial to the permanent first molars. Green line is the anterior arch length segment, red canine arch length segment, and blue is the posterior arch length segment. 35

47 Figure 9 Demonstration of measuring the anterior arch length segment. MEASUREMENT OF TOOTH WIDTHS Tooth widths were measured from the mesial anatomical contact point to the distal anatomical contact point on each respective fully erupted tooth without restorations. If a tooth was found with a restoration involving the mesial or distal contact area, a cast having a measurable tooth before its restoration was substituted for the measurement. Any subject who had multiple restorations of the first molars, primary molars, premolars, canines, or incisors involving the mesial and distal surfaces was eliminated from the study. 36

48 Figure 10 Demonstration of measuring the tooth width, #9 (UL1). MEASUREMENT OF ARCH WIDTHS Arch widths were measured at the inter-canine width and 1 st molar widths for both arches for all subjects. Both primary and permanent Inter-canine widths were measured from canine cusp tip to canine cusp tip of primary or permanent canines, respectively. First permanent molars were used for the molar widths in both early mixed and permanent dentition casts. Maxillary inter-molar widths were measured between the mesio-buccal cusp tips of the maxillary permanent first molars. Mandibular inter-molar width was measured between the middle of the main buccal grooves at the middle of the permanent first molars. If one of the canines or first molars was not present in the study cast, the inter-molar width on a cast 6 months older or younger was used in its place for that measurement in the mixed dentition. 37

49 Figure 11 Demonstration of measuring maxillary inter-canine width. Figure 12 Demonstration of measuring mandibular inter-canine width. 38

50 Figure 13 Demonstration of measuring maxillary inter-molar width. Figure 14 Demonstration of measuring mandibular inter-molar width. 39

51 CALCULATION OF CROWDING AND SPACING Crowding or spacing in the upper and lower arches was calculated by subtracting the sum of the tooth widths in each arch from the sum of the arch lengths (the arch perimeter) in each arch. Crowding was recorded as a negative number. Spacing was recorded as a positive number. MEASUREMENT RELIABILITY The principal observer CJW and the second observer SC measured tooth widths, arch widths, and arch lengths on the casts and entered the measurements into an excel data sheet utilizing digital calipers. The principal observer and the second observer both utilized the same measurement guidelines when measuring casts for this study. These measurement guidelines can be found in the below section, titled measurements. Neither observer was able to view the others measurements until the analysis for the reliability of measurements was completed by the statistician. To ensure the correct points were being measured both observers carefully familiarized themselves with the measurement guidelines and to make sure both were making measurement in a similar fashion in accordance to the measurement guidelines the principal observer trained the second observer prior to the second observer making measurements. Double measurements were made by each observer to evaluate the intra-observer agreement and the average of each observer s measurements was used to evaluate the inter-observer agreement. If the two observer s measurements had significantly low intra- or inter-observer agreement, a third measurement was going to be made. However, 40

52 the data showed that there was strong intra- and inter agreement between the two measurements made by the same observer or by the two observers therefore, no third measurements were needed for either principal or secondary observers. Repeated measurements allowed for a more definitive evaluation of each patient. The repeated measures can increase statistical power for detecting differences as well as allow the analyses of intra- and inter-observer reproducibility. STATISTICAL ANALYSIS The statistical analysis of the data collected in this thesis were completed by Dr. Fang Qian of Biostatistics Unit at the University Of Iowa College Of Dentistry. Intraclass correlations were used to analyze measurement error. T-tests were used to compare the Class I normal and the crowded sample. 41

53 RESULTS Measurement Error: The analysis of intra-observer reproducibility showed almost perfect agreement for all the measurements made by each of the two observers (Intraclass Correlation Coefficient (ICC) =0.99 in each instance). For the inter-observer reproducibility, the ICCs were between 0.90 and 0.99 and indicated strong agreement between the two repeated measurements made by the two observers. Moreover, for intrareliability of measurements, the results showed that there was no significant difference between first and second measurements made by the primary measurer (CPW) (p>0.05 for all selected variables) For the second measurer (SC) the results for measurement error revealed that there was strong agreement between his first and second measurements using the ICC, and no significant difference was found between his two duplicate measurements, except for one case in Table 2 highlighted in yellow. The mean difference was 0.12mm, which was in the acceptable range previously proposed. A paired-sample t-test or nonparametric Wilcoxon signed-rank test, as appropriate, were used to determine the significance of a difference between two duplicated measurements made by either a single observer or by two observers. Significant differences were found between the two observers CPW and SC for five out of eight variables (highlighted in yellow in Table 4). The mean difference for those five variables were: 0.18, 0.19, 0.36, 0.46 and 0.56mm. The ICC showed strong agreement, the inter-observer reliability of measurements were determined to be acceptable since the mean difference values are in an acceptable range. For this study measurement errors were all acceptable. The acceptable errors were smaller for individual tooth dimension and were larger for arch length and arch width measurements 42

54 The average of the primary observer s measurements (CPW) were used for the analysis of the data and to test the hypotheses. All tests utilized a significance level of SAS for Windows (v9.4, SAS Institute Inc., Cary, NC, USA) was used for the data analysis. DATA ANALYSIS Sixty subjects form the Iowa Facial Growth Study were included in the study, comprising 15 females and 15 males with Class I Normal (CIN) along with 15 females and 15 males with Class I and II crowed (CD) in their permanent occlusion. Eight variables were selected to measure and assess tooth widths and arch perimeters in the mixed dentition (MD) and permanent dentition (PD) stages of development in the CIN and CD occlusions. Intra- and inter-observer reliability of measurements were conducted for each variable. INTRA-OBSERVER RELIABILITY OF MEASUREMENTS FOR OBSERVER C Intra-observer reliability of measurements on tooth widths and arch perimeters was evaluated to assess the agreement between the first and second measurements made by Observer C. The following summarizes the results on each variable. 43

55 (1)MD_Max_TWS (sum of maxillary tooth widths in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of maxillary tooth widths in the MD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer C. Additionally, no significant difference was found between the two duplicate measurements made by Observer C (p=0.0807) using a paired-sample t-test (Table 2). (2)MD_Mand_TWS (sum of mandibular tooth widths in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of mandibular tooth widths in the MD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer C. Additionally, no significant difference was found between the two duplicate measurements made by Observer C (p=0.5701) using the nonparametric Wilcoxon singed-rank test (Table 2). (3)MD_Max_ArchP (maxillary arch perimeter in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the maxillary arch perimeter in the MD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer C. 44

56 Additionally, no significant difference was found between the two duplicate measurements made by Observer C (p=0.0791) using the nonparametric Wilcoxon signed-rank test (Table 2). (4)MD_Mand_ArchP (mandibular arch perimeter in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the mandibular arch perimeter in the MD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer C. Additionally, no significant difference was found between the two duplicate measurements made by Observer C (p=0.9603) using a paired-sample t-test (Table 2). (5)PD_Max_TWS (sum of maxillary tooth widths in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of maxillary tooth widths in the PD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer C. Additionally, no significant difference was found between the two duplicate measurements made by Observer C (p=0.1074) using the nonparametric Wilcoxon signed-rank test (Table 2). 45

57 (6)PD_Mand_TWS (sum of mandibular tooth widths in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of mandibular tooth widths in the PD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer C. Additionally, no significant difference was found between the two duplicate measurements made by Observer C (p=0.4721) using the nonparametric Wilcoxon signed-rank test (Table 2). (7)PD_Max_ArchP (maxillary arch perimeter in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the maxillary arch perimeter in the PD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer C. Additionally, no significant difference was found between the two duplicate measurements made by Observer C (p=0.4551) using a paired-sample t-test (Table 2). (8)PD_Mand_ArchP (mandibular arch perimeter in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the mandibular arch perimeter in the PD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer C. 46

58 Additionally, no significant difference was found between the two duplicate measurements made by Observer C (p=0.6982) using a paired-sample t-test (Table 2). Table 2 Descriptive Statistics for Observer C, Descriptive Statistics for Sum of Maxillary and Mandibular Tooth Widths and Sum of Maxillary and Mandibular Arch Length Segments (mm) in the Mixed and Permanent Dentitions Measured by Observer C. INTRA-OBSERVER RELIABILITY OF MEASUREMENTS FOR OBSERVER S Intra-observer reliability of measurements on tooth widths and arch perimeters was evaluated to assess the agreement between the first and second measurements made by Observer S. The following summarizes the results on each variable. 47

59 (1)MD_Max_TWS (sum of maxillary tooth widths in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of maxillary tooth widths in the MD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer S. Additionally, no significant difference was found between the two duplicate measurements made by Observer S (p=0.6584) using a paired-sample t-test (Table 3). (2)MD_Mand_TWS (sum of mandibular tooth widths in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of mandibular tooth widths in the MD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer S. Additionally, no significant difference was found between the two duplicate measurements made by Observer S (p=0.4434) using a paired-sample t-test (Table 3). (3)MD_Max_ArchP (maxillary arch perimeter in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the maxillary arch perimeter in the MD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer S. Additionally, no significant difference was found between the two duplicate measurements made by Observer S (p=0.7066) using a paired-sample t-test (Table 3). 48

60 (4)MD_Mand_ArchP (mandibular arch perimeter in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the mandibular arch perimeter in the MD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer S. Additionally, no significant difference was found between the two duplicate measurements made by Observer S (p=0.1041) using a paired-sample t-test (Table 3). (5)PD_Max_TWS (sum of maxillary tooth widths in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of maxillary tooth widths in the PD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer S. Additionally, no significant difference was found between the two duplicate measurements made by Observer S (p=0.9594) using the nonparametric Wilcoxon signed-rank test (Table 3) (6)PD_Mand_TWS (sum of mandibular tooth widths in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of mandibular tooth widths in the PD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer S. 49

61 Additionally, there was a significant difference between the two duplicate measurements made by Observer S (p=0.0396) using a paired-sample t-test. The mean (SD) difference between first and second measurements made by Observer S was 0.12 (0.44) mm (Table 3). (7)PD_Max_ArchP (maxillary arch perimeter in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the maxillary arch perimeter in the PD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by Observer S. Additionally, no significant difference was found between the two duplicate measurements made by Observer S (p=0.3943) using a paired-sample t-test (Table 3). (8)PD_Mand_ArchP (mandibular arch perimeter in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the mandibular arch perimeter in the PD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made Observer S. Additionally, no significant difference was found between the two duplicate measurements made by Observer S (p=0.3879) using the nonparametric Wilcoxon signed-rank test (Table 3). 50

62 Table 3 Descriptive Statistic for Observer, Descriptive Statistics for Sum of Maxillary and Mandibular Tooth Widths and Sum of Maxillary and Mandibular Arch Length Segments (mm) in the Mixed and Permanent Dentitions Measured by Observer S. INTER-OBSERVER RELIABILITY OF MEASUREMENTS BETWEEN OBSERVERS C AND S Inter-observer agreement was evaluated to assess an agreement on the two duplicate measurements made by the two observers C and S. Note that an average of the first and second measurements made by each observer was used to evaluate the interreliability of measurements between the two observers in the study. 51

63 (1)MD_Max_TWS (sum of maxillary tooth widths in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of maxillary tooth widths in the MD (p<0.0001), and the intraclass correlation coefficient of 0.97 indicated strong agreement between the two duplicate measurements made by the two observers C and S. Additionally, a significant difference was found between the two duplicate measurements made by Observers C and S (p=0.0004) using a paired-sample t-test. The mean (SD)/median difference between the two measurements was 0.36 (0.74)/0.51mm (Table 4). (2)MD_Mand_TWS (sum of mandibular tooth widths in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of mandibular tooth widths in the MD (p<0.0001), and the intraclass correlation coefficient of 0.97 indicated strong agreement between the two duplicate measurements made by the two Observers C and S. Additionally, a significant difference was found between the two duplicate measurements made by Observers C and S (p=0.0310) using the nonparametric Wilcoxon signed-rank test. The median/mean (SD) difference between the two measurements was 0.30/0.19 (0.73) mm (Table 4). (3)MD_Max_ArchP (maxillary arch perimeter in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the maxillary arch perimeter in the MD (p<0.0001), and the 52

64 intraclass correlation coefficient of 0.95 indicated strong agreement between the two duplicate measurements made by the two Observers C and S. Additionally, a significant difference was found between the two duplicate measurements made by Observers C and S (p=0.0005) using the nonparametric Wilcoxon signed-rank test. The median/mean (SD) difference between the two measurements was 0.30/0.46 (1.01) mm (Table 4). (4)MD_Mand_ArchP (mandibular arch perimeter in the MD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the mandibular arch perimeter in the MD (p<0.0001), and the intraclass correlation coefficient of 0.90 indicated strong agreement between the two duplicate measurements made by the two Observers C and S. Additionally, a significant difference was found between the two duplicate measurements made by Observers C and S (p=0.0006) using the nonparametric Wilcoxon signed-rank test. The median/mean (SD) difference between the two measurements was 0.33/0.56 (1.18) mm (Table 4). (5)PD_Max_TWS (sum of maxillary tooth widths in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of maxillary tooth widths in the PD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by the two Observers C and S. 53

65 Additionally, no significant difference was found between the two duplicate measurements made by Observers C and S (p=0.8230) using a paired-sample t-test (Table 4). (6)PD_Mand_TWS (sum of mandibular tooth widths in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the sum of mandibular tooth widths in the PD (p<0.0001), and the intraclass correlation coefficient of 0.99 indicated strong agreement between the two duplicate measurements made by the two Observers C and S. Additionally, no significant difference was found between the two duplicate measurements made by Observers C and S (p=0.7321) using a paired-sample t-test (Table 4). (7)PD_Max_ArchP (maxillary arch perimeter in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the maxillary arch perimeter in the PD (p<0.0001), and the intraclass correlation coefficient of 0.98 indicated strong agreement between the two duplicate measurements made by the two Observers C and S. Additionally, a significant difference was found between the two duplicate measurements made by Observers C and S (p=0.0299) using a paired-sample t-test. The mean (SD) /median difference between the two measurements was 0.18 (0.63)/0.22mm (Table 4). 54

66 (8)PD_Mand_ArchP (mandibular arch perimeter in the PD) There was very strong evidence that intraclass correlation differed from zero for the measurements on the mandibular arch perimeter in the PD (p<0.0001), and the intraclass correlation coefficient of 0.98 indicated strong agreement between the two measurements made by the two Observers C and S. Additionally, no significant difference was found between the two duplicate measurements made by Observers C and S (p=0.2817) using a paired-sample t-test (Table 4). Table 4 Descriptive Statistics for Observer C and S, Descriptive Statistics for Sum of Maxillary and Mandibular Tooth Widths and Sum of Maxillary and Mandibular Arch Length Segments (mm) in the Mixed and Permanent Dentitions Measured by Observers C and S. 55