Inter-Arch Tooth Size Discrepancies: Validity of Bolton Analysis

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1 Inter-Arch Tooth Size Discrepancies: Validity of Bolton Analysis Edoardo Sicurezza 1, Giuseppe Palazzo 2 1 Research Assistant, Department of Orthodontics, University of Catania, Italy. 2 Professor, Department of Orthodontics, University of Catania, Italy. Abstract Study background: Bolton Index is one of the most commonly used analysis in order to evaluate tooth-size discrepancy. Even if this measure could represent an important tool in clinical practice, many Authors questioned its widespread applicability. The aim of this study was to compare the anterior and total tooth width ratios of an orthodontic population with the Bolton standards and analyse differences in Bolton Index among genders and three malocclusion groups. Methods: A sample of 647 dental casts form the Department of Orthodontics, University of Catania (312 male and 335 female patients between 12 and 21 years old, mean age 16.9 ± 3.1 years) were considered in this study between January 2012 and June Mesiodistal tooth diameters were evaluated from its mesial contact point to its distal contact point at its greatest interproximal diameter by using a digital calibre and then Bolton indexes were obtained on each model. A one-way ANOVA test was conducted to compare tooth size discrepancies among different malocclusion groups and a Dunn s Multiple Comparison post hoc test was performed to test which means were different. Results: Mean values and standard deviations for maxillary to mandibular anterior tooth-width ratios were 78.8% ± 3.75% and 91.8% ± 2.50%. The discrepancies outside the ± 1 SD and ± 2 SD ranges from the Bolton means were also calculated the results were 16.9% and 61.5% respectively for BA and 21.5% and 33.8%, respectively for BO. Conclusion: No statistically significant differences have been found concerning tooth-size disharmony among the three malocclusion groups. Furthermore our population showed clearly a higher incidence of tooth-size discrepancies. Key Words: Orthodontics, Bolton analysis Introduction Inter-arch tooth-size relationship is an important factor in orthodontic diagnosis and treatment planning [1,2]. In this respect, a primary role is played by the evaluation of mesiodistal tooth size. In fact, it is widely accepted in literature that many malocclusions can occur as a result of abnormalities in tooth size [1] and that a normal condition of occlusion is based on a specific relation among teeth [3-5]. Several authors evaluated different methods of investigation of inter-arch tooth size discrepancies during orthodontic treatment. Seipel [6] studied random 365 patients and concluded that the amount of mesiodistal size of superior and inferior teeth had a specific ratio for each type of tooth. Neff defined a mathematic relation between tooth size and overbite analysing 200 dental cast of orthodontic patients [7]. Nevertheless, Bolton analysis of tooth size discrepancies is the most popular and widely used model in clinical practice [8]. It expresses the ideal centesimal relationship between superior and inferior arch volumes. He developed two ratios between inferior and superior mesiodistal width, an overall ratio (BO, Bolton Overall) of 91.3 ± 0.2 per cent, which involves all permanent teeth except the second and third molars, and the anterior ratio (BA, Bolton Anterior) of 77.2 ± 0.2 per cent, which considers only the sixth anterior maxillary and mandibular teeth. The original analysis was carried out in 1958 on 55 patients with normal occlusion, including 44 orthodontically treated and 11 untreated subjects. Bolton suggested that a discrepancy higher than 1 SD may be responsible of clinical affections even if most authors defined clinically significant ratio as 2 SD outside Bolton s mean [9]. Subsequent researches about Bolton indexes, conducted in different populations, reported that tooth size discrepancies may be influenced by several factors, including ethnical [3,10-13], gender [14,15] and malocclusion group differences [11,16-18]. Since Bolton s ratio represent a useful tool for the orthodontic treatment, clinicians should be conscious of its intrinsic limitation due to different factors as it is based on studies carried out on a unrepresentative sample and therefore could result in a lack of widespread applicability. Accordingly, the aim of this study was to compare the anterior and total tooth width ratios of an orthodontic sample with the Bolton standards, evaluating the differences between the different classes of malocclusion and its applicability in our population. Materials and Methods The study was carried out in the Department of Orthodontics, University of Catania, Catania, Italy, between January 2012 and June A sample of 790 dental casts of patients from the Department of Orthodontics, University of Catania was considered in this study but only 647 met the following selection criteria: Good condition of dental casts. No previous orthodontic treatment. No absent permanent teeth (except the second and third molars). No severe tooth abrasion or tooth restorations. No tooth anomalies. Corresponding author: Giuseppe Palazzo, Department of Orthodontics, University of Catania, Italy Via Santa Sofia 78, Policlinico, Catania 95123, Italy; gpalazzo@unict.it 1

2 Coincidence between dental and skeletal classes. The sample comprised 312 male and 335 female between 12 and 21 years old (mean age 16.9 ± 3.1 years). Class I occlusion was diagnosed on a Class I molar and canine relationship and on an ANB angle between 0 and 4 degrees; the diagnosis of Class II occlusion was based on a Class II molar and canine relationship as well as an ANB angle greater than Class I; A Class III molar and canine relationship and an ANB angle less than 0 degrees identified Class III patients. The ethical approval for the study was obtained from the Ethical Committee of the University of Catania. Mesiodistal tooth diameters were evaluated from its mesial contact point to its distal contact point at its greatest interproximal diameter (Figure 1) by using a digital calibre as described in literature [2,19,20]. In order to compare our sample with the Bolton s one, data were classified in Normal for BA and BO values < ± 1 SD, Discrepant for BA and BO values < ± 1 SD and Clinically Significant Discrepant for values < ± 2 SD. All measurements were expressed in millimetres and performed by the same operator (E.S.). Bolton indexes were obtained on each model as following: Bolton overall ratio (%): [summed width of mandibular twelve (6-6)/ [summed width of maxillary twelve (6-6)] x 100% Bolton anterior ratio (%): [summed width of mandibular anterior six (3-3)/ [summed width of maxillary anterior six (3-3) x 100%. Measurement error Measurements were conducted twice by the same operator with a distance of one month. Method error has been calculated by using Dahlberg s equation for repeating measurements. Statistical analysis The subjects were divided by gender and malocclusion Class. Statistical computation was performed by using Prism 4.0 for Macintosh (Graphpad Software Inc, USA, 2007). A Shapiro-Wilk test was performed to test normality. To determine whether there was gender disphormism in tooth size discrepancies, a Student s t-test was performed with a P level of significance of A one-way ANOVA test was conducted to compare tooth size discrepancies among different malocclusion groups and a Dunn s Multiple Comparison Post hoc test was performed to test which means were different. Figure 1. Determination of the mesio-distal widths on models. 2 Furthermore, frequency of discrepancies ± 1 and ± 2 SD in each group were calculated. Results The results are summarized in Table 1. The Shapiro-Wilk test showed a normal distribution for both the anterior and the total tooth widths ratios, so we could use parametric statistical tests. Mean values and standard deviations for maxillary to mandibular anterior tooth-width ratios were 79.5% ± 3.24% and 77.86% ± 4.21% for males and females, respectively, with a P value of 0.12; mean values and standards deviations for the overall tooth-width ratios were ± 2.5% and 92.11% ± 2.49% for females and males, respectively, with a P value= No significant differences were found in anterior and total tooth-width ratios according to sex (P = 0.12 and P = 0.57, respectively), so the groups were combined, and new anterior and total ratios were calculated: 78.8% ± 3.75% and 91.8% ± 2.50%, respectively (Table 1). As reported in Table 2, the anterior and total tooth-size discrepancies outside the ± 1 SD and ± 2 SD ranges from the Bolton means were also calculated for the sample; the results were 16.92% and 61.54% respectively for BA and 21.54% and 33.85%, respectively for BO. Analyzing BA and BO results among the various malocclusion groups we found that there was a high prevalence of patients with > 2DS for BA values in each Angle s class group. Considering BO results, Angle I class and Angle II class showed more normal values (45.83% and 55.56% respectively) than Angle III class patients that belonged mainly to the > 1 SD group (Tables 3-5). Discussion Tooth-size discrepancy evaluation has been widely accepted in clinical practice during orthodontic treatment plan by several authors [2,20-23] because it plays a fundamental role for the success of therapy [9,10,18,24,25]. The best-known study of tooth-size disharmony in relation to treatment of malocclusion was done by Bolton in 1958b [8] and his standards have been proposed as a model by many studies in literature [3,15,21,24,26,27]. Comparison with Bolton s sample The descriptive statistics for anterior and overall ratios among various malocclusions groups are shown in Table 3 and 4. In our study the means and the standard deviations of the total and anterior ratios were slightly larger than in Bolton s one. The reason for this finding might be the different population of the sample and the ethnic group. Table 5 compares anterior and overall ratios for various populations (white and Dominican Americans, blacks, Spanish, Peruvians, etc.) as reported by several authors [1,3,11-13, 16,17,21,25,26]. Both the anterior and the overall ratios values were larger than the Bolton standards in all of them, even if total ratios were closer to Bolton s standards. Our results are more similar to those obtained by Paredes [2], Struiić [20], Santoro [25] and Al-Omari [3]. If means of our samples were near Bolton s results, more interesting is the analysis of data when they are divided into three groups according to the standard deviation values from

3 Table 1. Comparison of male and female mean values of tooth size discrepancies. Tooth ratios Male mean ± SD (%) Female mean ± SD (%) P value Total mean ± SD (%) Bolton Index BA ± ± ± BO ± ± ± Table 2. Anterior Bolton ratios and Total (whole arch) Bolton ratios: The distribution of subjects in this study categorized by the standard deviations of Bolton s original study. BA Total BO Total Normal % Normal 44.62% > ± 1 SD 16.92% > ± 1 SD 21.54% > ± 2 SD 61.54% > ± 2 SD 33.85% Table 3. Percentage of subjects with anterior tooth size ratios compared with Bolton s standard. BA Angle I Class Angle II Class Angle III Class Normal % 18.52% 28.57% > ± 1 SD % 11.11% 28.57% > ± 2 SD 66.67% 70.37% 42.86% Table 4. Percentage of subjects with overall tooth size ratios compared with Bolton s standard. BA Angle I Class Angle II Class Angle III Class Normal 45.83% 55.56% 21.43% > ± 1 SD 12.50% 14.81% 42.86% > ± 2 SD 41.67% 29.63% 35.71% Table 5. Dunn s multiple comparison post hoc test for the different malocclusion classes. Tooth ratios Class N Mean ± SD (%) ANOVA Dunn s posthoc test I ± 2.7 I-II= 0.47 BA II ± 4.6 P>0.05 II-III= 0.77 III ± 3.7 I-III= 0.31 I ± 2.2 I-II= 0.86 BO I-II= 0.86 II ± 2.8 II-III= 0.67 P>0.05 III ± 2.4 I-III= 0.76 Table 6. Comparison between previous studies on the Bolton s analysis. Author Population Sample size Occlusion BA BO Bolton Orthodontic 55 Ideal White Americans Crosby and Alexander Orthodontic 109 Class I, II Smith Orthodontic 180 No data Johe Orthodontic 60 Class I, II, III Blacks Smith Orthodontic 180 No data Johe Orthodontic 62 Class I, II, III Hispanics Smith Orthodontic 180 No data Fernandez-Riveiro Europeans Paredes Orthodontic 100 No data Strujić Orthodontic 111 Class I, II, III Present Study Orthodontic 647 Class I, II, III Dominican Americans Santoro Orthodontic 54 No data Peruvians Bernabè School children 200 Different malocclusions Malaysians Othman School children 40 No data Saudi Arabians Sulaimani Orthodontic 98 Class I, II, III Chinese Ta School children 110 Class I, II, III Zhang Orthodontic 110 No data Iranians Fattahi Orthodontic 200 Class I, II, III Jordanians Al-Omari School children 367 No data mean as reported by various authors [11,21,26]. Originally a ratio greater than ± 1 SD from Bolton mean values indicated a need for diagnostic consideration [8]. A significant discrepancy in the anterior ratio was found in 61.5% of the patients (BA > ± 2 SD); on the other hand, a discrepancy > ± 2 3 SD in the total ratio (BO) was found in 33.8% of the subjects. Even if BA and BO mean values of our sample were not so different when compared with Bolton s results, the analysis of our population s SD range putted in evidence a greater difference with the Bolton standard. This evidence might

4 find answer in the sample chosen by Bolton who selected 55 subjects with an ideal occlusion, while our sample was made by pre-orthodontic treatment patients. So the Bolton standards may underestimate the incidence of tooth-size discrepancies in a treated population [21]. Furthermore it seems to be interesting to evaluate the great variability of our sample with respect to the interact relationship, as confirmed by most other authors in different populations [11,21,26]. This could require a deeper understanding of its possible clinical therapeutic evaluation in a large portion of the population. Bolton s analysis remains the key point in the orthodontic treatment plan, nevertheless several authors [1,2,12,16,20] found some limitation in his studies. Bolton s sample was obtained from 55 models with excellent occlusion - 44 orthodontically treated and 11 untreated. Furthermore Bolton didn t explain in detail the population s ethnicity and the gender composition. Unlike the initial Bolton s sample, our study was conducted on all young patients (12 to 21 years) from Southern Italy. This aspect could be very interesting considering that, as clearly reported in Table 6, BA and BO values seemed to vary consistently among different populations in relation to their ethnicity. Comparison of tooth size discrepancies between different malocclusion classes Different results have been proposed in literature concerning the relationship between the malocclusion classes and the tooth size ratios. Strujić [20] and Qiong [28] found statistically significant differences among the malocclusion classes, especially regarding the overall ratio. Sperry, Lavelle, Nie [10,14,29] showed in their studies that Class III subjects presented an higher mandibular tooth size and smaller maxillary teeth. Also Araujo and Souki [24] reported that individuals with Angle Class I and III malocclusion had more tooth size discrepancies when compared with Class II subjects. On the contrary, in our research, the statistical analysis of Bolton anterior and overall ratios calculated in the three classes of malocclusion studied showed no significant difference (P = 0.88 and P= 0.69 respectively for BA and BO, Table 5). Our results was in agreement with other authors findings: in fact Laino [27] studied 94 dental cast and reported no relationship between the three malocclusion group and the Bolton index; Crosby [11] found a large number of inter-arch tooth size discrepancies in the three malocclusion samples but none of these was statistical significant; finally Johe [21] reported that Bolton Index was not influenced by the Angle s skeletal classification and confirmed no statistical differences among malocclusion groups. Tooth size discrepancy between genders The results of the present study showed no significant differences for overall and anterior ratios between male and female (Table 1). This findings supports a diffuse conclusion in literature as recently reported by O Mahony [22], Johe [21], Al Sulaimani [26], Araujo [24] and Othman [23]. On the contrary, other authors founded differences in tooth width ratio between male and female samples [13-16] but it is important to note that in studies where differences have been found, they have been small, with male having slightly larger ratios [20]. Conclusions - No statistically significant differences have been found concerning tooth-size disharmony among the three malocclusion groups. - Analogously no gender difference has been discovered between male and female subjects. - Even if the mean values of BA and BO of our Italian sample were similar to Bolton standards, our population showed clearly a higher incidence of toothsize discrepancies and tooth-size variations based on the evaluation of the obtained standard deviation considering the potential diagnostic and therapeutic implications. References 1. Tadesse P, Zhang H, Long X, Chen L. A clinical analysis of tooth size discrepancy (Bolton index) among orthodontic patients in Wuhan of Central China. Journal of Huazhong University of Science and Technology [Medical Sciences]. 2008; 28: Paredes V, Gandia JL, Cibrian R. Determination of Bolton tooth-size ratios by digitization, and comparison with the traditional method. European Journal of Orthodontics. 2006; 28: Al-Omari IK, Al-Bitar ZB, Hamdan AM. Tooth size discrepancies among Jordanian schoolchildren. Europeon Journal of Orthodontics. 2008; 30: Andrews LF. The six keys to normal occlusion. American Journal of Orthodontics and Dentofacial Orthopedics. 1972; 62: Redahan S, Lagerstrom L. Orthodontic treatment outcome: The relationship between anterior dental relations and anterior interarch tooth size discrepancy. Journal of Orthodontics. 2003; 30: Seipel C. Variation in tooth position. A metric study of variation and adaptation in the deciduous and permanent dentitions. 4 Swedish Dental Journal. 1946; 39: Neff CW. Tailored occlusion with the anterior coefficient. 1949; 35: Bolton WA. Disharmonies in tooth size and its relation to the analysis and treatment of malocclusions. Angle Orthodontist. 1958; 28: Szulc BW, Olszowska JJ, Stepien P. Overall and anterior Bolton ratio in Class I, II, and III orthodontic patients. Europeon Journal of Orthodontics. 2010; 32: Sperry TP, Worms FW, Isaacson RJ, Speidel TM. Toothsize discrepancy in mandibular prognathism. American Journal of Orthodontics. 1977; 72: Crosby DR, Alexander CG. The occurrence of tooth size discrepancies among different malocclusion groups. American Journal of Orthodontics and Dentofacial Orthopeadics. 1989; 95: Paredes V, Gandia JL, Cibrian R. Do Bolton's ratios apply to a Spanish population? American Journal of Orthodontics and Dentofacial Orthopeadics. 2006; 129: Smith SS, Buschang PH, Watanabe E. 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5 relationships of 3 populations: "does Bolton's analysis apply?". 2000; 117: Lavelle CL. Maxillary and mandibular tooth size in different racial groups and in different occlusal categories. American Journal of Orthodontics. 1972; 61: Bishara SE, Jakobsen JR, Treder JE, Stasi MJ. Changes in the maxillary and mandibular tooth size-arch length relationship from early adolescence to early adulthood. A longitudinal study. 1989; 95: Fattahi HR, Pakshir HR, Hedayati Z. Comparison of tooth size discrepancies among different malocclusion groups. Europeon Journal of Orthodontics. 2006; 28: Ta TA, Ling JY, Hagg U. Tooth-size discrepancies among different occlusion groups of southern Chinese children. American Journal of Orthodontics and Dentofacial Orthopeadics. 2001; 120: Xia Z, Wu XY. The application of dentocclusal measurement in malocclusion. Stomatology. 1983; 3: Moorrees CF, Jensen E, Kai-Jen Yen P, Thomsen SO. Mesiodistal crown diameters of the deciduous and permanent teeth in individuals. Journal of Dental Research. 1957; 36: Strujic M, Anic-Milosevic S, Mestrovic S, Slaj M. Tooth size discrepancy in orthodontic patients among different malocclusion groups. Europeon Journal of Orthodontics. 2009; 31: Johe RS, Steinhart T, Sado N, Greenberg B, Jing S. Intermaxillary tooth-size discrepancies in different sexes, malocclusion groups, and ethnicities. American Journal of Orthodontics and Dentofacial Orthopeadics. 2010; 138: O'Mahony G, Millett DT, Barry MK, McIntyre GT, Cronin MS. Tooth size discrepancies in Irish orthodontic patients among different malocclusion groups. Angle Orthodontist. 2011; 81: Othman S, Harradine N. Tooth size discrepancies in an orthodontic population. Angle Orthodontist. 2007; 77: Araujo E, Souki M. Bolton anterior tooth size discrepancies among different malocclusion groups. Angle Orthodontist. 2003; 73: Santoro M, Ayoub ME, Pardi VA, Cangialosi TJ. Mesiodistal crown dimensions and tooth size discrepancy of the permanent dentition of Dominican Americans. Angle Orthodontist. 2000; 70: Al Sulaimani F, Afify AR. Bolton analysis in different classes of malocclusion in a Saudi Arabian sample. Egyptian Dental Journal. 2006; 52: Laino A, Quaremba G, Paduano S, Stanzione S. Prevalence of tooth-size discrepancy among different malocclusion groups. Progress in Orthodontics. 2003; 4: Qiong N, Jiuxiang L. Comparison of intermaxillary tooth size discrepancies among different malocclusion groups. American Journal of Orthodontics and Dentofacial Orthopedics. 1999; 73: Nie Q, Lin J. Comparison of intermaxillary tooth size discrepancies among different malocclusion groups. American Journal of Orthodontics and Dentofacial Orthopedics. 1999; 116:

Determining Tooth Size Ratio in an Iranian-Azari Population

Determining Tooth Size Ratio in an Iranian-Azari Population Abstract Aim: The aim of this investigation was to determine the tooth size ratio in an Iranian-Azari population. Method and Materials: The Bolton