Long-term skeletal effects of high-pull headgear plus fixed appliances: a cephalometric study

Transcription

1 University of Iowa Iowa Research Online Theses and Dissertations Spring 2014 Long-term skeletal effects of high-pull headgear plus fixed appliances: a cephalometric study Eve Erin Bilbo University of Iowa Copyright 2014 Eve Erin Bilbo This thesis is available at Iowa Research Online: Recommended Citation Bilbo, Eve Erin. "Long-term skeletal effects of high-pull headgear plus fixed appliances: a cephalometric study." MS (Master of Science) thesis, University of Iowa, Follow this and additional works at: Part of the Orthodontics and Orthodontology Commons

2 LONG-TERM SKELETAL EFFECTS OF HIGH-PULL HEADGEAR PLUS FIXED APPLIANCES: A CEPHALOMETRIC STUDY by Eve Erin Bilbo 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 2014 Thesis Supervisor: Professor Thomas E. Southard

3 Graduate College The University of Iowa Iowa City, Iowa CERTIFICATE OF APPROVAL MASTER S THESIS This is to certify that the Master s thesis of Eve Erin Bilbo has been approved by the Examining Committee for the thesis requirement for the Master of Science degree in Orthodontics at the May 2014 graduation. Thesis Committee: Thomas E. Southard, Thesis Supervisor Steven Marshall Nathan Holton

4 ACKNOWLEDGMENTS I would like to thank Dr. Southard for being my mentor on this project. Your investment in my education will never be forgotten. Thank you for always having an open door to answer my questions and to provide help. You have an incredible teaching ability, and I owe you a debt of gratitude for admitting me to this orthodontic program where I have learned to love this field. Thank you also to Dr. Marshall, for your willingness to share your vast knowledge and for the kind way with which you do it. I also want to thank Dr. Holton, who was essential to me being able to work through this project. Thank you for your endless patience and kindness toward me. I also want to thank Dr. Karin Southard, Dr. Allyn Thames, and Dr. Marlene Sanabria, who laid the groundwork for this project, long before I became involved. Your hard work was invaluable. Thank you, in addition, for allowing me to use your materials for my thesis. Finally, I want to thank my family, and especially, my wonderful husband, Jonathan. Thank you for always being there for me and for being my #1 fan and my support. ii

5 TABLE OF CONTENTS LIST OF TABLES iv LIST OF FIGURES.v INTRODUCTION...1 LITERATURE REVIEW 4 Class II Malocclusion: What is it?.4 Incidence of Class II Malocclusion..4 Etiology of Class II Malocclusion....5 Class II Growth Compared to Normal Growth 6 Class II Treatment Options Growth Modification...9 Headgear Cervical-Pull Headgear 11 High-Pull Headgear Functional Appliances...17 Removable Functional Appliances 18 Herbst Appliance...19 Summary 21 MATERIALS AND METHODS Sample Cephalometric Landmarks. 27 Construction of X-Y Axis..29 Landmark Assessment...29 Correction for Magnification of Cephalometric Measurements 34 Measurement Reliability 35 Statistical Analysis.35 RESULTS..37 Initial Comparisons Between Control and Headgear Groups...55 Angular Data Findings...55 Horizontal Data Findings...75 Vertical Data Findings...80 DISCUSSION CONCLUSIONS iii

6 REFERENCES.. 89 APPENDIX 94 Overview of Statistical Methods...97 iv

7 LIST OF TABLES Table 1: Total Control Group (n=21).. 24 Table 2: Total Headgear Group (n=21) Table 3: Initial Model Measurements for the Control Group Table 4: Initial Model Measurements for the Headgear Group Table 5: Mean Cephlometric Angular Measures and Changes between Time Points for the Control Group Table 6: Mean Cephalometric Angular Measures and Changes between Time Points for the Headgear Group Table 7: Mean Cephalometric Horizontal Linear Measures and Changes between Time Points for the Control Group 43 Table 8: Mean Cephalometric Horizontal Linear Measures and Changes between Time Points for the Headgear Group. 46 Table 9: Mean Cephalometric Vertical Linear Measures and Changes between Time Points for the Control Group 49 Table 10: Mean Cephalometric Vertical Linear Measures and Changes between Time Points for the Headgear Group Table A1: Control Subjects Ages Table A2: Headgear Subjects Ages Table A3: Time Period Headgear Worn Table A4: Time Period Elastics Worn Table A5: Control Paired T-test Results...99 Table A6: Headgear Paired T-test Results Table A7: Two-Sample T-test Results v

8 LIST OF FIGURES Figure 1: Cephalometric Landmarks Figure 2: X-Y Axis Figure 3: Horizontal Measurements Figure 4: Vertical Measurements vi

9 LIST OF GRAPHS Graph 1: SNA Control Graph 2: SNA Headgear. 56 Graph 3: SNA Control versus Headgear Graph 4: SNA Changes Graph 5: SNB Control Graph 6: SNB Headgear Graph 7: SNB Control versus Headgear Graph 8: SNB Changes 60 Graph 9: ANB Control. 61 Graph 10: ANB Headgear 61 Graph 11: ANB Control versus Headgear Graph 12: ANB Changes. 62 Graph 13: U1 to SN Control 63 Graph 14: U1 to SN Headgear. 64 Graph 15: U1 to SN Control versus Headgear. 64 Graph 16: U1 to SN Changes Graph 17: FMIA Control. 66 Graph 18: FMIA Headgear.. 66 Graph 19: FMIA Control versus Headgear.. 67 Graph 20: FMIA Changes 67 Graph 21: FH to NA Control Graph 22: FH to NA Headgear 69 Graph 23: FH to NA Control versus Headgear 69 Graph 24: FH to NA Changes.. 70 Graph 25: FMA Control vii

10 Graph 26: FMA Headgear Graph 27: FMA Control versus Headgear Graph 28: FMA Changes. 72 Graph 29: SN-MP Control Graph 30: SN-MP Headgear 74 Graph 31: SN-MP Control versus Headgear Graph 32: SN-MP Changes. 75 Graph 33: Y-axis to A-pt Control 76 Graph 34: Y-axis to A-pt Headgear. 76 Graph 35: Y-axis to A-pt Control versus Headgear. 77 Graph 36: Y-axis to A-pt Changes Graph 37: Y-axis to MxH Control Graph 38: Y-axis to MxH Headgear 79 Graph 39: Y-axis to MxH Control versus Headgear Graph 40: Y-axis to MxH Changes. 80 viii

11 1 INTRODUCTION Class II malocclusion is a common malocclusion treated by orthodontists. The incidence of class II malocclusion was studied by Ast et al. (1965), who examined 1413 high school students aged 15 to 18 years old and reported that 23.8% had a Class II malocclusion. Class II malocclusion can result from combinations of both improper skeletal and dental relationships. Mandibular skeletal retrusion is the most common underlying cause (McNamara, 1981). Maxillary protrusion can also result in a Class II relationship, as well as different combinations of mandibular retrusion with maxillary protrusion, mesially-positioned maxillary molars, or distally-positioned mandibular molars (Fisk, 1953). High-pull headgear has been used as a treatment of Class II malocclusion since the 1800 s (Kingsley, 1880). Headgears aid in correction of Class II malocclusions by restraining maxillary growth and by distalizing maxillary teeth (Wieslander, 1963). Headgears can lead to improvement or correction of Class II relationships by restraining maxillary growth, which promotes a differential growth pattern in favor of mandibular growth (Proffitt, 2000). Headgear force is transmitted to the maxillary complex via the molars. The relationship between the headgear s resultant force and the tooth s center of resistance determines the direction of force on the molars. If the resultant force passes below the center of resistance, the maxillary molar crown will tip distally. If the resultant force passes above the center of resistance, the maxillary molar root will tip distally. Finally, if the resultant force passes directly through the tooth s center of resistance, translation of the tooth will occur. An additional benefit of headgear is that it may serve to disarticulate the occlusion, allowing condylar growth to be expressed in the dentition. During normal adolescent growth, the mandible has more growth and grows for a longer period of time

12 2 than does the maxilla (Bjork, 1964; Sinclair et al., 1985). Normal children have a convex profile that tends to become straighter by adulthood, largely due to relatively more mandibular growth than maxillary growth. Class II patients do not have less total mandibular growth, so one may conclude that a Class II relationship, if left untreated, might improve or even correct if enough anterior mandibular growth occurred. However, most clinicians agree that self-correction or improvement of Class II malocclusions is not seen without treatment (Subtelny, 1973). That begs the question of why anterior mandibular growth does not result in the mandibular dentition being positioned anteriorly since the mandible is growing forward. You et al. (2001) reported that the average mandible has 4.36 mm more forward growth than the maxilla. Their research also indicates a strong linear relationship between forward mandibular growth and the positional changes in the dentoalveolar complex. The more the mandible grew forward relative to the maxilla, the more the maxillary teeth moved forward within the maxilla, and the more the mandibular teeth moved backward within the mandible. More forward growth of the mandible only increased the relative movements of the dentition in relation to the jaws. You et. al. stated, the effect of forward growth of the mandible relative to the maxilla, which could potentially bring the lower dentition forward, vanished into the adaptation movements of the dentoalveolar complex. This dentoalveolar adaptation could be why a Class II malocclusion is not self-correcting, even with noticeable mandibular forward growth, without treatment. Moreover, You et. al. concluded that by simply disarticulating the occlusion, these adaptive changes of the occlusion could be greatly minimized or even eliminated (2001). Cervical-pull and high-pull headgears produce different effects and are therefore prescribed based on which resultant force the clinician desires. Firouz et al. (1992) stated that high-pull headgear can cause relative restriction of horizontal and vertical maxillary growth, as well distalization and intrusion of the maxillary molars. Thus, high-pull headgear is commonly indicated for Class II patients with a steep mandibular plane

13 3 because avoiding molar extrusion and downward and forward growth of the maxilla is beneficial in these patients (Barton, 1972). On the other hand, cervical-pull headgear inhibits the forward growth of the maxilla, slightly tips the anterior maxilla downward, rotates the mandible backward, increases eruption of the maxillary molars, and distalizes maxillary molars (Derringer, 1990). Cervical-pull headgear is therefore commonly indicated for Class II patients who have a flat mandibular plane and a short lower anterior face height (Barton, 1972). Many studies have been conducted which evaluated the initial, short-term effects of cervical-pull and high-pull headgear. Studies have also evaluated the long-term effects (stability) of cervical-pull headgear. These will be discussed in the literature review. At present, there are nine retrospective post-retention analyses available on the long-term effects of cervical-pull headgear (Southard, 2013). However, the literature currently provides no long-term evaluations of the exclusive use of high-pull or vertical-pull headgear with or without edgewise treatment. The purpose of this research is to investigate the long-term effects of Class II patients treated with high-pull headgear followed by fixed appliances.

14 4 LITERATURE REVIEW Class II Malocclusion: What is it? Angle (1907A) defined Class II malocclusion as the occlusal relationship of the first permanent molars such that, [The] lower molar [is] distally positioned relative to upper molar, line of occlusion not specified. The definition of Class II has broadened since then to include an anteroposterior discrepancy between the maxillary and mandibular dentitions, which may be solely dental, skeletal, or a combination of both. According to Fisk (1953), there is usually both a skeletal and dental contribution to a Class II malocclusion. Forward displacement of the maxilla or the maxillary dentition could, by definition, result in a Class II malocclusion. However, a deficiency in the mandible is more commonly the cause. Such deficiency can include mandibular hypoplasia, mandibular retrusion, or the mandibular teeth being positioned posteriorly within a normal mandible. The most common characteristic present in Class II patients is mandibular skeletal retrusion (McNamara, 1981). Treatment modalities that affect mandibular retrusion are therefore very important in orthodontic practice. Incidence of Class II Malocclusions Class II malocclusions are relatively common in the general population and therefore constitute a significant percentage of the cases treated by practicing orthodontists. When Angle studied the incidence of Class II malocclusion in 1000 Caucasians, he found 69% were class I, 23% were class II, and 3.4% were class III (Angle, 1907A). Massler and Frankel (1951) found similar results for children aged 14 to 18 years, as did Goldstein and Stanton (1936) for white American children between the ages of 2 and 12. However, these percentages vary between races. Horowitz (1970) determined that Caucasians develop the highest percentage of Class II malocclusions when compared to other races (22.5%), while Garner and Butt (1985) showed that Black

15 5 Americans have the lowest prevalence at 16%. Results from Silva and Kang (2001) show that Class II malocclusion is found in 21.5% of Latinos, which falls between whites and blacks. Because the prevalence of Class II malocclusion is high, its causes and treatment approaches are of great interest to orthodontists. Etiology of Class II Malocclusion An understanding of the etiology of Class II malocclusion is essential when determining how to approach its treatment. The ability to differentiate between genetic and environmental factors on an individual s craniofacial growth is important. However, the contribution of genetics versus environmental factors in the development of malocclusions has never been clearly defined and is often different between individuals. The controversy can be traced back to Kingsley and Angle who had opposing views on the subject. Kingsley (1891) felt that inheritance was the key factor in the development of malocclusion, whereas Angle (1907B) believed that local factors had the greatest influence (Mossey 1999). More recent studies have weakened the argument for strong genetic control in the development of Class II malocclusion. In a twin study by Boraas (1988), overjet and overbite were not found to be similar among twins reared apart. Similarly, Harris (1980) found that only about 10 percent of the variation in factors such as overjet, overbite, and molar relationships results from nonenvironmental causes, while other dental variables such as tooth size and morphology had strong genetic correlations. In contrast, environmental factors such as early loss of primary teeth and damaging habits play a clear role in the development of certain malocclusions. In a study examining the environmental factors of breastfeeding and pacifier usage, Peres et. al (2007) found that regular pacifier usage between 12 months and 4 years of age was the greatest risk factor for development of posterior crossbite. In another study, Emmerich (2004) found strong correlations between finger and pacifier sucking and increased overjet.

16 6 It is not uncommon, however, for Class II malocclusions to develop in the absence of any obvious environmental factors. In these cases, genetics must play a stronger role, thereby leading one to conclude that heredity and environment have variable influences on the development of malocclusion in each individual, and such influences must be evaluated and taken into consideration when developing a treatment plan. Class II Growth Compared to Normal Growth Understanding the differences in Class II growth trends when compared to the growth of normal individuals is critical in order to analyze the effects of treatment on a skeletally Class II individual. Bishara and colleagues (1998) evaluated 30 untreated and 91 treated Class II division 1 subjects, and compared them to a normal untreated Class I sample of 35 subjects. They studied cephalometric changes between the following three stages of development: at the completion of the deciduous dentition, once the first permanent molars and most of the incisors had erupted, and after the permanent dentition (excluding third molars) had fully erupted. The only consistent growth difference observed between the untreated Class II division 1 and normal Class I subjects was a significantly shorter mandibular length (Ar-Pog) in the Class II division 1 subjects at earlier stages of development. The pretreatment Class II division I malocclusions also demonstrated increased overjet, overbite, and ANB angle when compared to the normal subjects. However, following treatment plus concomitant growth, an overall normalization of skeletal relationships was noted after a five-year treatment and observation time in the treated Class II division 1 group and no significant difference was noted. The implication is that some catch up mandibular growth occurs later in development in the Class II division 1 subjects. Longitudinal comparisons of growth profiles indicated that the growth trends were essentially similar between the untreated

17 7 Class II patients and normal subjects in the various parameters compared. However, greater skeletal and soft tissue convexities were seen in the untreated Class II group. Reismeijer et al. (2004) found similar results. They compiled a database of longitudinal records of untreated Class I and Class II subjects (ANB of 4 was considered class II) from the Fels Longitudinal Study, the Michigan Growth Study, and the Netherlands Growth Study. They found that Class II subjects had greater SNA and SN-GoMe angles, and, compared with the untreated Class I subjects, the untreated Class II subjects had a shorter mandible in the younger age groups. Interestingly, no differences were found in total mandibular length or mandibular body length in the older age groups. They determined that untreated Class II subjects had a greater increase in mandibular length than Class I subjects. If managed appropriately during treatment, this greater lengthening of the mandible could lead to an improvement or correction of a Class II skeletal discrepancy. However, the authors cautioned that due to great individual biologic variability, average growth patterns cannot be assumed for each individual case. Another important consideration in the treatment planning for Class II patients is the effect of interdigitation on forward mandibular growth. During normal adolescent growth, the mandible typically has more growth and grows for a longer period of time than does the maxilla (Bjork, 1964; Sinclair et al., 1985). Children often have a convex profile that tends to become straighter by adulthood, which can be attributed to greater relative mandibular growth. This would lead one to think that a Class II relationship, if left untreated, could improve or even correct if forward mandibular growth was adequate. On the contrary, Subtelny (1973) showed that Class II malocclusions do not improve nor self-correct without treatment. Though it would seem that anterior mandibular growth would position the mandibular dentition forward relative to the maxillary dentition, You et al. (2001) found that the more the mandible grows forward, the more the maxillary teeth move forward within the maxilla, and the more the mandibular teeth moved backward within the mandibular body. In other words, because of interdigitated

18 8 occlusion, patients do not self-correct into a class I occlusion due to adaptive changes in the dentoalveolar complex that negate any effect of forward mandibular growth. They concluded that disarticulating the occlusion can greatly minimize, if not eliminate, the adaptive changes of the dentition. Fortunately, disarticulation is accomplished with active orthodontic appliances or headgear, supporting Class II correction if adequate forward mandibular growth occurs. With these growth considerations in mind, it is possible to develop appropriate treatment plans for adolescent Class II patients, but variation in patient growth will affect treatment outcomes. Class II Treatment Options There are three basic treatment approaches to correct Class II malocclusions: orthopedics, masking, and surgery. In a young patient who has substantial growth remaining and a mild to moderate discrepancy, growth modification is the ideal treatment option. Ideal treatment timing would be prior to or during the adolescent growth spurt, so that any remaining growth can be utilized to help improve the maxillomandibular relationship, resulting in a Class I occlusion. Alternatively, compensations can be introduced to the dentition to mask the underlying skeletal discrepancy. The existing apical base relationship is unchanged and the teeth are compensated to make up for the skeletal discrepancy. The upper incisors are retracted, frequently by extracting one or two teeth in the maxilla, and the lower incisors are proclined. Overjet is reduced, and a Class I canine relationship is established. The third and final basic treatment option is surgery. Prior to surgery, all dental compensations are removed with orthodontic treatment, and then surgery is performed to correct the skeletal relationship, resulting in Class I canine occlusion. Surgery is normally reserved for severe discrepancies that cannot be fully addressed with growth modification and/or dental compensations, or for patients with profile concerns. Depending on the patient s growth potential, the severity

19 9 of the skeletal disharmony, the need for tooth extractions, and the patient s desires, any combination of these three treatment options may be included in the treatment plan. Growth Modification Growth modification is an orthopedic approach to treatment, attempting to minimize dental movements while maximizing skeletal correction. The goal of growth modification is to promote the growth of one jaw relative to the other one to correct a discrepancy. In 1907, Edward H. Angle developed the concept that external pressures could readily affect skeletal growth. Angle (1907B) was influenced by Wolff s Law of Bone, which stated that bone responds to the stresses placed on it. Angle deduced that external pressures could be used in orthodontics to affect skeletal relationships. When cephalometric radiography came into widespread use in the 1940 s, it became clear that the majority of Class II malocclusions resulted from improper skeletal relationships. Through growth modification, these improper skeletal relationships can be treated more directly. Growth modification alone can often lead to an improvement, if not a complete correction, of a Class II malocclusion (Kluemper, 2001). Orthopedic appliances alter growth by applying a force to either jaw and include both extraoral and functional appliances. Extraoral appliances include a variety of headgears that transmit force to the maxilla via the teeth. Functional appliances, on the other hand, are intraoral appliances that transmit forces via the teeth and/or soft tissues to distract the mandibular condyles, in order to accelerate mandibular growth (Proffit, 2000). Some functional appliances also have an effect similar to headgear on the maxilla, but their effect is less profound than that of headgear (Derringer, 1990). Both types of appliances have been used effectively to control and modify growth during treatment. Much of the orthodontic literature is focused on determining whether or not any of the orthopedic treatment modalities have significant, long-term effects on facial growth to aid in the correction of Class II malocclusions. Stability of growth

20 10 modification is questioned, with researchers trying to determine if appliances actually enhance mandibular growth or simply accelerate it. Another topic of much study is focused on determining if the jaws revert back to a pre-treatment relationship, with only dental changes persisting long-term. The treatment effects of various growth modification appliances, along with what is known about their long-term stability, will be discussed in the following sections. Headgear American orthodontists like Norman Kingsley commonly used headgear dating back to the late 1800 s. At that time, it was considered an appliance to correct dental relationships (Kingsley, 1880). Later, in the 1950 s, advances in cephalometrics allowed researchers to discover that headgear had skeletal effects in addition to distalization of maxillary teeth (Wieslander, 1963). By restraining forward growth of the maxilla, headgear promotes differential growth in favor of the mandible, leading to an improvement or correction of a Class II relationship (Proffit, 2000). Headgear also serves to break up the occlusion, allowing condylar growth to be fully expressed in the dentition. When headgear is worn, a force is transmitted to the maxillary complex via the molars. Molar movement is determined by the relationship between the headgear s resultant force and the tooth s center of resistance. If the resultant force passes occlusal to center of resistance, the molar crown will tip distally. If the resultant force passes gingival to the center of resistance, the molar root will tip distally. Finally, if the resultant force passes directly through the tooth s center of resistance, the molar will bodily translate. To be effective, headgear should be worn as often and consistently as possible (Jacobson, 1979). Roberts (1994) recommends continuous headgear wear for at least 12 hours per day.

21 11 Cervical-Pull Headgear Orthodontists in the past have claimed that cervical-pull headgear alone can increase the mandibular plane angle and the lower anterior face height in patients by causing maxillary molars to extrude (Wieslander, 1963; Barton, 1972). Cervical-pull headgear is therefore commonly prescribed for Class II patients who have a flat mandibular plane angle and a short lower anterior face height. However, more recent studies have shown that molar extrusion may be minimal with cervical-pull headgear. Kirjavainen et al. (2000) observed only minor extrusion of maxillary first molars with cervical pull headgear alone when compared to normal eruption, and Baumrind et al. (1983) found that molar extrusion associated with cervical traction alone is no more than 1 mm greater than controls. Kirjavainen et al. (2000) also found that cervical-pull headgear caused a relative restraint of forward growth of the maxilla and a downward tipping of the anterior maxilla. Melsen in 1978 and Melson and Dalstra in 2003 evaluated the effects of cervical traction alone on 20 patients in the late mixed dentition. All patients had a one-half to full-step Class II malocclusion without extreme overbite. Each patient had tantalum metal implant markers inserted subperiosteally according to Bjork s technique (Bjork, 1969) to distinguish between orthodontic and orthopedic treatment effects. The patients were instructed to wear their Kloehn headgear for 12 hours per day for eight months. Ten of the patients had the outer bow turned up 20, and ten patients had it turned down 20. The results showed that the patients with the upward outer bow demonstrated a downward and backward translation of the molars, whereas those with the downward bow had a combination of eruption and distal tipping. However, there was no difference in the amount of eruption between the two groups, which the authors attributed to occlusal forces. Similar to previous findings, the growth of the maxilla itself in both groups was altered in a downward and backward direction.

22 12 The stability of distal molar movement with cervical-pull headgear was also evaluated in the 2003 study. Over the 7-year posttreatment period, both the molar displacement and the growth direction reversed. The molars that were initially distalized in the headgear group migrated mesially to a position similar to the control group. When assessing the total intramaxillary displacement of the molars, no significant difference could be found between the groups, suggesting almost complete relapse of the treatment. However, it is interesting to note that, although the maxillary growth direction observed during treatment was reversed to a forward and downward direction and that the maxillary molar migrated mesially, relapse of the Class II occlusion did not occur. Instead, the well-interdigitated dentition ensured the stability of the Class I molar relationship obtained using cervical-pull headgear. The effects of using cervical-pull headgear in conjunction with fixed orthodontic appliances have also been researched thoroughly. Fidler et al. (1995) examined study models and cephalometric films from a group of successfully treated Class II, division 1 patients to evaluate the mechanisms of Class II correction, long-term stability, and posttreatment changes. The treatment sample consisted of 78 patients who had at least an end-on Class II molar relationship and overjet of 5mm or greater; no control group was included. Models and cephalograms were taken before treatment, after treatment, and long-term (mean of 14 years) posttreatment. Cervical-pull headgear was the means used to achieve the Class II correction, and Class II elastics were used only occasionally. They found only minor relapse after Class II correction. Though some statistically significant differences in occlusal relationships could be found, the authors concluded they were not clinically significant. There was no significant change or relapse in SNA, SNB, or ANB from deband to postretention. Backward rotation of the occlusal and mandibular planes was seen, but the vertical position of the maxillary first molar was unchanged. The authors attributed this to late vertical condylar growth counteracting any excess molar extrusion during fixed appliance therapy. However, the authors did state

23 13 that few patients with a hyperdivergent skeletal pattern were included and the majority of patients had favorable growth during and after treatment. As a result, the sample may not be an ideal representation of the entire population of Class II, division 1 malocclusions. The authors, therefore, concluded that growing patients with normal vertical relationships are conducive to successful treatment results and long-term stability. Another study of cervical-pull headgear in conjunction with fixed appliances was done by Filho et al. (2003B). The study evaluated the posttreatment and long-term sagittal and vertical changes in the mandible of Class II, division 1 patients treated with cervical-pull headgear and fixed appliances. The cephalograms of 40 patients were evaluated at the following three time points: pretreatment, posttreatment, and postretention. Treatment began in the late mixed or early permanent dentition, due to the widely held belief that this dentition stage correlates with the facial growth spurt. The patients all had Class II division 1 malocclusion (ANB 5 ) and were treated with cervical-pull headgear with an expanded inner bow (4-8 mm) and a long outer bow bent upwards 10 to 20. The headgear force was 450g, and the patients were instructed to wear the appliance 12 to 14 hours a day. No intermaxillary elastics were used during treatment. No control group was included in this study. The authors observed no significant changes in mandibular plane angle during treatment, although a significant angular decrease was observed at postretention as growth continued. SNB increased significantly during treatment as well as postretention. The cervical-pull headgear efficiently corrected the skeletal Class II relationship, mainly due to anteriorly directed growth of the mandible. The Class II correction was stable during the postretention period. Filho et. al. (2003B) believe that expanding the inner bow of the headgear favors forward positioning of the mandible and consider the expansion to be essential for favorable Class II correction. Filho et al. (2003A) conducted another study using the same materials and methods to look at another parameter. They reported a significant reduction in SNA

24 14 during treatment of 3.18, followed by an average increase of only 0.74 postretention. The small increase in SNA postretention was not significant; therefore, the authors concluded that the maxillary skeletal effects of cervical-pull headgear are stable. Ciger et al. (2005) also documented the treatment effects and long-term stability of cervical traction followed by full fixed orthodontic appliances. Dental casts and lateral cephalograms of 18 Class II division 1 patients were evaluated at pretreatment, posttreatment, and postretention. The patients were all treated to Class I molar relationship with cervical headgear, class II elastics, and edgewise mechanics by the same orthodontist. Cephalometric measurements showed that not only was maxillary growth restrained with treatment, but there was also a decrease in maxillary incisor inclination, overjet and overbite. During treatment, a slight mandibular posterior rotation was seen, but in postretention, the mandible was found to resume its original growth pattern, reversing this rotation. On the other hand, the maxillary skeletal change that occurred in these patients during cervical traction did remain stable. The relapse of backward mandibular rotation and the stability of the maxillary skeletal change is in accordance with the findings of earlier studies of cervical-pull headgear (Fidler, 1995; Filho, 2003). An abridged summary of the orthodontic literature on treatment stability using cervical-pull headgear is as follows: First, regarding the direction of facial growth, the pretreatment tendencies resume once the cervical traction is stopped. As the mandible continues to grow in the postretention period, a reversal of the changes affected with treatment is seen. Secondly, the relative restraint of forward growth of the maxilla is stable, with insignificant changes occurring long-term. Lastly, while dental movements do occur during the posttreatment period, the Class I molar and canine relationship established with treatment will persist with a well-interdigitated occlusion.

25 15 High-Pull Headgear The applied force vector is distinct when high-pull headgear is used instead of cervical-pull headgear, so differences in terms of treatment effects are expected. Firouz et al. (1992) studied the dental and skeletal effects of high-pull headgear alone in 12 Class II, Division 1 adolescent patients who wore the headgear for a minimum of 12 hours a day for 6 months. Cephalometric evaluation revealed that with high-pull headgear, the maxillary molars were simultaneously translated distally and intruded with a force directed through the trifurcation (which approximates the center of resistance). The distal molar movement was substantial (2.6 ± 0.6 mm), resulting in significant dental improvement in a Class II molar relationship. No vertical eruption of the maxillary molars was seen in any patient. Further, the applied force of 500g was sufficient to initiate maxillary orthopedic changes, including relative restriction of horizontal and vertical maxillary growth and distal movement of the maxillary anterior border relative to the control group. These findings showed that orthopedic effects are possible with highpull headgear, even without fixed appliances. This study did not evaluate the long-term stability of these changes. Baumrind et al. (1983) studied the differences between high-pull headgear, cervical-pull headgear, modified-activator, and untreated Class II controls. These patients were treated in mixed dentition, none of the treated patients were fully banded, and orthodontic and orthopedic effects of the appliances were considered separately. Orthopedic distal displacement of ANS was found to be significantly greater in both the headgear groups than in the activator group. The mean orthopedic effect was similar between the headgear groups, but the high-pull headgear group showed significantly greater orthodontic distalization of the maxillary molar compared to the cervical-pull headgear group. Significant intrusion of the maxillary molar was seen in the high-pull headgear group, while extrusion was seen in the cervical-pull headgear group, but the

26 16 average extrusion was no greater than 1 mm. Again, posttreatment changes were not discussed. In fact, a study looking at the treatment and long-term effects of high-pull headgear alone followed by fixed appliances cannot be found in the orthodontic literature. On the other hand, multiple investigators have looked at the effects and stability of high-pull headgear treatment in combination with various functional appliances. If the restraint on maxillary growth of a headgear could be combined with a stimulation of mandibular growth of a functional appliance, effective anteroposterior skeletal correction of a Class II discrepancy could be achieved. In theory, the headgear-activator combination therapy restricts the forward growth of the maxilla, inhibits the mesial displacement of the maxillary teeth, inhibits maxillary tooth eruption and alveolar height increase, increases horizontal growth of the mandible, remodels the condyle and glenoid fossa, and by mesially moves the mandibular teeth (Wieslander et al., 1979; Vargervik et al., 1985). In 2002, Bendeus et al. looked at growth changes in patients treated with a headgear-activator appliance. Seventeen Class II, division 1 male patients with increased overjet wore the headgear-activator for 10 to 12 hours per day for 12 months. Records were made pretreatment, after 6 and 12 months of treatment, and 2 years posttreatment. The results revealed that the treatment changes in overjet, overbite, and molar relationship were both dental and skeletal changes. The skeletal effect of the headgearactivator appliance was mainly limited to the maxilla, where it restrained forward growth. A minimal enhancement of mandibular growth was seen, but only during the early phase of treatment; in fact, the mandibular contribution to correction of the anteroposterior relationship was similar to that of normal growth. During the posttreatment period, no catch-up growth of the maxilla was observed, indicating a relative stability of maxillary growth inhibition with treatment.

27 17 Janson et al (2004) studied the stability of dentoskeletal changes in 23 Class II division 1 patients after edgewise-orthodontic treatment using a high-pull headgearactivator combination. The treated patients were compared with two control groups, one group class I and the other Class II, division 1. The class II control group was used to assess the dentoskeletal changes that occurred in the treatment group. The Class I control group was used to compare the posttreatment changes to normal growth. The results of the investigation showed that there was long-term stability in the anteroposterior dentoalveolar changes and in the maxillary and mandibular positions. Posttreatment, SNA increased 0.56 mm. While this amount of growth is statistically insignificant, the authors state that it shows that the maxilla resumes its normal growth pattern after treatment, resulting in a slight increase in ANB and A-Nperp. The overbite showed significant relapse. The initial overjet showed a significant correlation with molar relationship relapse and overjet relapse. However, it is interesting to note that active treatment time, length of the posttreatment period, initial Class II severity, and initial molar relationship did not correlate with relapse of molar relationships and overjet. High-pull headgear is commonly indicated for Class II patients who have a steep mandibular plane, because it is important in these patients to slow down or prevent molar extrusion and downward and forward growth of the maxilla (Barton, 1972). However, even though it is important to understand the prognosis and stability of a particular treatment modality when making treatment decisions in orthodontics, there is a lack of information in the literature regarding the long-term stability of using high-pull headgear followed by fixed appliances. Functional Appliances The desire for clinicians to stimulate mandibular growth led to the development of functional appliances in the early 1900s. These appliances hold a patient s hypoplastic mandible forward, exerting pressures on the teeth and jaws by stretching the facial

28 18 musculature and soft tissues, which results in tooth movement and growth modification. In theory, if the condyle is maintained out of its fossa anteriorly and inferiorly during appliance wear, growth of the condyle is stimulated. Multiple functional appliances were developed throughout the years, including various activator designs, the bionator, the twin block, the Fränkel regulator, and the Herbst appliance. By the later part of the 20th century, clinical success of these appliances was demonstrated thru correction of distocclusion. It was not clear, however, whether or not mandibular growth was actually stimulated or simply accelerated, and this has continued to be a topic of considerable interest in the orthodontic literature. Removable Functional Appliances The twin-block functional appliance consists of two separate acrylic plates that interlock to posture the mandible forward. Sidlauskas (2005A, 2005B) has done many studies on the treatment effects of the twin-block functional appliance. In his studies, he compared the changes in Class II division 1 malocclusion patients treated with a twinblock appliance with growth of untreated controls. He found that mandibular length increased 2.4 mm more after 12 months of treatment and overjet decreased 4.7 mm more than in the control group. Also noted were uprighting of the maxillary incisors, proclination of the mandibular incisors, distal movement of the upper molars, and forward movement of the mandibular molars. Trenouth (2000, 2006) reported similar results for the twin-block, and Pancherz (1984) found very similar results for the activator appliance, but the long-term stability of these treatments was not discussed by any of these authors. Jena et al. (2006) evaluated the dentoalveolar and skeletal treatment effects of the twin-block and bionator appliances. Fifty-five girls with Class II division 1 malocclusion were involved in the study and were divided into 3 groups: a twin-block group (n = 25), a bionator group (n = 20), and a control group (n = 10). The results showed that neither

29 19 the twin-block nor the bionator significantly restricted forward maxillary growth. The twin-block group showed significantly more mandibular growth than the controls, but the bionator group did not. All treated subjects exhibited molar correction, overjet reduction, and proclination of the mandibular incisors compared to controls. Therefore, both appliances were considered effective in correcting molar relationships and overjet in the two treatment groups, but the authors concluded that the twin-block was more efficient in the treatment of Class II division 1 malocclusion than the bionator. The long-term stability of these effects was not discussed. Animal studies have shown a significant long-term increase in mandibular length associated with the use of functional appliances, but human studies have been less conclusive. In 1991, DeVincenzo designed a new functional appliance that closely resembled the ones used in the animal studies to attempt to resolve this disparity. In his study, he included 47 girls with Class II malocclusion whose rate of mandibular growth during treatment at least doubled a previously-established pretreatment growth rate. Only patients who wore the appliance full-time and had substantial orthopedic effect were selected. He then evaluated the long-term stability of this response to treatment and compared it to controls. Following the functional appliance treatment phase, the mandibular growth rate was greatly reduced compared to controls. At 2 years posttreatment the mandibular length was still highly significant, and at 3 years it was significant, by the end of 4 years, there was no difference between the treated patients and controls. Herbst Appliance Unlike the removable functional appliances, the Herbst is a fixed appliance, but it postures the mandible forward to correct of Class II malocclusions similarly to the removable appliances. Since it is not a removable appliance, the clinician does not have to rely on patient compliance, thereby enhancing treatment efficiency. Pancherz et al

30 20 (1993) studied the immediate and long-term effects of the Herbst appliance in 45 patients with a Class II malocclusion. The patients were followed for an average of 6.4 years after treatment. Pretreatment and long-term posttreatment cephalograms were analyzed. The results showed that during treatment, 96% of the subjects had distalized maxillary molars and 69% of the subjects had intruded maxillary molars. In addition, the maxillary occlusal plane opened in 82% of the subjects. The sagittal maxillary jaw base position did not change with treatment. After only 6 months, most of these treatment effects reverted back to pretreatment values. Subsequently, after an average of 6.4 years, normal growth and developmental changes prevailed. The maxillary molars moved mesially, the teeth extruded, the occlusal plane closed, and the maxilla grew forward. Pancherz concluded the Herbst appliance demonstrated a significant high-pull headgear effect on the maxillary complex, but that without proper retention, this effect is unstable. On a long-term basis, the Herbst appliance only has a temporary effect on the skeletofacial growth pattern. In spite of Pancherz s conclusions, the stability of growth changes due to the Herbst appliance is still a matter of controversy. Recently, VanLaecken et al. (2006) reported greater skeletal stability associated with edgewise Herbst treatment than has been previously reported. In their study, 32 Class II patients treated with a crown Herbst and fixed appliances were included. Mean treatment time with the Herbst appliance was 8.0 ± 1.8 months, and stability was evaluated 16 months after Herbst removal. The treatment results were compared with 32 untreated Class II subjects from the Bolton- Brush study. Skeletal and dental contributions to Class II correction included a backward movement of A point, forward movement of the mandible, retroclining of the maxillary incisors, proclining of the mandibular incisors, and molar movement that resulted in a Class III molar relationship. Of the 8.4 mm of overjet change, 37% was attributed to dental changes and 63% to skeletal changes. Of 7.2 mm of molar correction, 43% was contributed by skeletal changes and 56% by dental changes. During the 16-month

31 21 posttreatment period, the following changes were seen: molars relapsed into a Class I relationship, maxillary incisors had no net movement, the mandibular incisors had a net forward movement of only 0.3 mm, a net restraint of maxillary growth of 1.3 mm, and a net forward mandibular movement of 1.0 mm. The authors concluded that skeletal changes contributed 85% of the overall treatment correction and that these changes were stable. They ventured that the glenoid fossa remodels to adapt to the changes in condylar position, resulting in a stable result as seen on tomographic evaluation. However, the treatment results should be interpreted cautiously, since the 16 month posttreatment evaluation period is relatively short and cannot be considered long-term, especially considering the patients, at ages roughly between 11.5 and 12.5, still had a considerable amount of growth remaining. Huang et al. (2005) reported that the literature offers no evidence that functional appliances significantly increase horizontal mandibular growth when evaluated longterm. Functional appliances do affect the maxilla, the glenoid fossa, and the dentoalveolar structures during treatment and may produce postural changes of the mandible. However, any effect functional appliances may have on increasing total mandibular growth is so small that it does not reach statistical significance. In the longterm, there is no greater total mandibular growth in functional appliance patients than in untreated controls (Pancherz 1990). Summary Clearly, correcting Class II malocclusions is paramount to successful orthodontic practice, since a good percentage of orthodontic patients are Class II. As a result, the ability of various appliances to correct Class II malocclusions has been studied extensively. The clinical significance involves both whether the appliances cause beneficial changes during treatment and whether or not those changes are stable in the long-term. The treatment effects and stability of various Class II appliances have been

32 22 measured, but there is a currently a lack of evidence in the orthodontic literature regarding the long-term stability of treatment with high-pull headgear followed by fixed appliances. The treatment effects of high-pull headgear have been thoroughly studied, resulting in a general understanding of the associated dental and skeletal changes. The controversy surrounding treatment using high-pull headgear is not whether favorable profile and dental changes occur, but rather if these changes remain stable in the long term after growth is complete. The purpose of this research is to investigate the long term effects of Class II patients treated with high-pull headgear.

33 23 MATERIALS AND METHODS Sample For this research project, the control sample consisted of twenty-one untreated Class II subjects selected from two large-scale longitudinal growth studies. Eleven subjects came from The University of Iowa Facial Growth Study. The subjects in this study were from northern European descent and above socioeconomic status living near Iowa City, Iowa. They were enrolled by professors L. Bodine Higley and Howard V. Meredith in a long-term research program at the University of Iowa, which started in These patients had records taken semi-annually from age 3 to age 12, then annually through adolescence, and finally once during early adulthood. Ten subjects came from the Bolton-Brush Growth Study conducted at Case Western Reserve University. Dr. T. Wingate Todd initiated this study in 1928, which became a long-term endeavor with funding from the Brush Foundation and the Charles Bingham Bolton fund. The subjects for the Bolton-Brush study were recruited from the Cleveland, Ohio area. They were recalled every 3 months in infancy (0-1 year of age), biannually until age 5, and yearly through adolescence for radiographs, as well as physical, mental, and psychological exams. The Bolton-Brush Study began as two closely aligned studies of the same subjects. Originally, The Bolton Study focused on normal development of the facial skeleton and dentition, while the Brush Inquiry charted the physical and mental progression of the normal, healthy child. The two projects merged in Both growth studies were screened in search of subjects with a Class II relationship along with lateral cephalograms and orthodontic study models taken at the appropriate age and time intervals. No control subject had any orthodontic treatment. The ages and time intervals were matched as closely as possible to the ages and time intervals of the treatment sample. Based on this inclusion criteria, 7 males and 4 females

34 24 were selected from the Iowa growth study to serve as control subjects, and 5 males and 5 females were selected from the Bolton-Brush study. Tables 1 and 2 summarize the descriptive statistics for the collective control group and Tables 3 and 4 summarize the model measurements. Table 1: Total Control Group (n=21) Time Point Mean Age (range) Mean ANB Mean SN-MP T (10-12) 4.09 ( ) ( ) T ( ) 4.06 ( ) ( ) T ( ) 3.98 ( ) ( ) T ( ) 3.52 ( ) ( ) The treatment sample was taken from patients treated at the University of Iowa, Department of Orthodontics. The records of patients who were treated or directly supervised by Dr. Karin Southard and Dr. Tom Southard were initially screened to determine if they met the inclusion criteria for this research. The inclusion criteria consisted of patients with a skeletal and a dental Class II relationship that was corrected to Class I relationship using a high-pull headgear and who had cephalograms and models taken at the appropriate time points. The required cephalograms taken during treatment included the following four time points: T1, initially before any treatment; T2, after Class II correction with only high-pull headgear; and T3, after treatment with high-pull headgear and fixed appliances. Dental models were also required at timepoints T1 and T2. Forty patients were identified who met this criterion. Next, these forty patients were recalled to obtain long term records (T4) in order to evaluate stability. Twenty-one

35 25 patients (10 males and 11 females) were successfully recalled for use in this research. Tables 4-6 summarize the descriptive statistics for the headgear group. Patients were instructed to wear high-pull headgear continuously for 12 to 14 hours per day with an average force of 400 grams. In all these patients headgear was used as the primary means of anteroposterior skeletal and dental correction; however, 12 of the 20 patients also wore Class II elastics for an average time period of 3.48 months. Table 2: Total Headgear Group (n=21) Time Point Mean Age (range) Mean ANB Mean SN-MP T ( ) 5.02 ( ) ( ) T ( ) 4.08 ( ) ( ) T ( ) 3.37 ( ) ( ) T ( ) 2.70 ( ) ( ) Table 3: Initial Model Measurements for the Control Group Patient Overbite Overjet Right Magnitude Left Magnitude Div. % (mm) Molar (mm) Molar (mm) B II 1.5 II 1.5 I B II 2.5 II 5 II B II 2.5 II 1 II B II 2.5 II 2 I B II 4.5 II 3.75 II B II 3 I 0 I B II 1.5 II 1.5 II

36 26 Table 3 continued B II 5.0 II 3.5 I B II 2.0 I 0.0 I M II 1.75 II 2.0 I M II 4.0 II 3.0 II M II 2.5 II 2.5 II F II 1.5 I 0.0 I M II 3.0 II 5.5 I F II 4.5 II 4.5 I F II 2.0 II 2.0 I M II 3.5 II 3.5 I M II 0.5 II 1.5 I F II 3.5 II 4.5 I M II 3.5 II 3.0 I Table 4: Initial Model Measurements for the Headgear Group Patient Overbite Overjet Right Magnitude Left Magnitude Div. % (mm) Molar (mm) Molar (mm) K.A II 5.0 II 4.0 II N.C II 4.5 I 0.0 I S.C II 2.75 II 3.0 I L.C II 6.0 II 5.0 II M.D I 0.0 II 1.5 I A.D II 5.0 II 3.0 I E.D II 4.0 II 3.5 I C.D II 3.5 I 0.0 I P.G II 4.0 II 3.5 II J.K II 4.0 II 2.5 I A.K II 3.0 II 1.0 I M.L II 3.0 II 2.5 II N.L II 3.0 II 4.5 I C.L II 3.5 II 2.0 I N.M II 2.0 II 2.0 I W.P II 2.5 II 2.0 II A.R II 5.0 II 5.0 I A.S II 6.0 II 6.5 I N.W II 5.0 II 4.0 I M.W II 2.0 II 1.0 I J.W II 3.5 II 3.0 I

37 27 Cephalometric Landmarks On each of the cephalograms, as seen in Figure 1, the following landmarks were identified: 1. Sella (S): the midpoint of the cavity of sella turcica. 2. Nasion (Na): the frontonasal suture at its most superior point on the curve at the bridge of the nose. 3. Mandibular Plane: a line from menton tangent to the posterior inferior border of the mandible. 4. Pogonion (Pg): the most anterior point on the contour of the bony chin. 5. Menton (Me): the most inferior point on the mandibular symphysis. 6. Gonion (Go): the most posterior inferior point at the angle of the mandible; identified by bisecting the angle formed by tangents to the posterior border of the ramus and the inferior border of the mandible. 7. A-point (A): the innermost point on the bony curvature of the maxilla between ANS and the maxillary incisor. 8. B-point (B): the innermost point on the bony curvature of the mandible between the incisor tooth and the bony chin. 9. Antegonion (Ag): the highest point of the notch of concavity of the lower border of the ramus where it joins the body of the mandible. 10. Maxillary First Molar (Horizontal) (MxH): the contact point between the maxillary first molar and the maxillary second premolar. 11. Maxillary Molar (Vertical) (MxV): the mesiobuccal cusp tip of the maxillary first molar. 12. Mandibular Molar (Horizontal) (MdH): the contact point between the mandibular first molar and the mandibular second premolar. 13. Mandibular Molar (Vertical) (MdV): the mesiobuccal cusp tip of the mandibular first molar.

38 Maxillary Incisor (Is): the anterior most portion of the maxillary incisal edge. 15. Mandibular Incisor (Ii): the anterior most portion of the mandibular incisal edge. Figure 1: Cephalometric Landmarks

39 29 Construction of X-Y Axis An x-y axis was constructed in the same manner on each lateral cephalogram so that linear measurements could be made and compared between lateral cephalograms. The origin of the x-y axis was sella. The x-axis was represented by a line through sella that was 7 degrees below the sella-nasion line (Figure 2). This line is parallel to the average Frankfort horizontal line connecting porion to orbitale. The y-axis was perpendicular to the x-axis, passing through sella. This coordinate system is similar to the one described Hack et al. (1993). Landmark Assessment The decision to use certain landmarks for vertical and anteroposterior assessments was based on the envelope of error described in the reliability of landmark identification study by Baumrind and Frantz (1971). The following cephalometric landmarks were used for assessment of linear horizontal changes in the facial skeleton: A-point, B-point, nasion, pogonion, maxillary molar, maxillary incisor, mandibular molar, and mandibular incisor (Figure 3). The following cephalometric landmarks were used for assessment of vertical changes in the facial skeleton: antegonion, anterior nasal spine, posterior nasal spine, menton, maxillary molar, maxillary incisor, mandibular molar, and mandibular incisor (Figure 4). All landmarks were identified on each cephalogram for the control and the treated subjects. All the cephalograms were digitized, uploaded, and traced using Dolphin Imaging software Version 11.5 (Dolphin Imaging & Management Solutions; Chatsworth, CA). Linear measurements were calibrated by defining the known distance between fiduciary points for each radiograph on Dolphin. For any landmark that did not lie in the midsagittal plane, the average distance between the right and left points was used. Angular measurements included SNA, SNB, ANB, Upper 1 to SN, FMIA, FH to NA,

40 30 FMA, and SN:MP. All linear measurements were made to the established x-y axis on each film. The dental models were measured using the ABO measuring gauge. Molar relationship was measured from the maxillary molar mesiobuccal cusp to the buccal groove of the mandibular molar. Overjet was measured from the facial surface of the most lingual incisor to the midpoint of the incisal edge of the most facial incisor. Overbite was measured as the vertical overlap of the central incisor with the greatest amount of overbite. A statistical analysis was done to confirm there were no significant differences in the model measurements at timepoint T1 between the control and headgear groups. Both models and cephalograms were used to assess whether each patient was Class 2, Division 1 or 2. Patients with upright maxillary incisors and minimal overjet were classified as Division 2, as described by Angle (1907). From this study, 14 of the controls were Division 1, while 7 were Division 2. The treated group contained 17 Division 1 patients and 4 Division 2 patients.

41 Figure 2: X-Y axis 31

42 Figure 3: Horizontal Measurements 32

43 Figure 4: Vertical Measurements 33

44 34 Correction for Magnification of Cephalometric Measurements Measurements located in the midsagittal plane of lateral cephalograms must be corrected for enlargement due to magnification. The amount of enlargement is a function of (a) the distance between the x-ray source and the midsagittal plane, (b) the distance from the x-ray source and the roentgenogram, and (c) the actual measured dimension. Most of the linear measurements in this study were to points in the midsagittal plane. However, if a point was used that did not lie in the midsagittal plane, the average distance between left and right points was used. Thus, all measures were adjusted to be considered in the midsagittal plane. All linear measures were corrected for magnification prior to statistical analysis. The radiographs for the control samples and treatment group were taken at varying magnification factors. The x-ray source to median plane and x-ray source to roentgenogram distances varied between patients and by age of the subjects in the both control samples. The values used for conversion can be located in the Iowa Facial Growth Study files and on each Bolton-Brush radiograph. Calculations were performed to convert the radiographic linear measures to true measures in both control samples. The treatment group radiographs had a ruler of known dimensions, so no correction for magnification was needed, as this ruler distance was entered into Dolphin. The following formula was used to correct for enlargement of the control samples (Telle 1956): True Linear Value = x-ray source to median plane X roentgenographic linear measure x-ray source to roentgenogram The following is an example using subject M60 at age 11-0 to correct for radiographic enlargement for the horizontal measurement of A point to the constructed y-axis on the lateral cephalogram: Measured horizontal dimension = mm Distance of x-ray source to median plane = mm

45 35 Distance from x-ray source to roentgenogram = mm Corrected distance = (150.48) (73.60 mm) = mm (165.0 mm) Measurement Reliability To evaluate measurement reliability, twenty cephalograms representing five patients at each time interval (i.e., 10% of the total sample) were randomly selected and remeasured. Three patients were from the control group and two were from the headgear group. The investigator was blind to any previous measurements. The paired-sample t- test was used to determine if the mean measurement difference between the two measurements was equal to zero. Of the angular and linear measurements, only four measures were found to have significant differences, but the average intraclass correlation coefficient across all measures was (range: ) and the average percent difference between the measurements was 1.5% (range:0.42%-5.67%). These results indicate strong agreement between the duplicate measurements with a single-rater. The highest percent difference was for ANB, but the correlation coefficient for ANB was The high percent difference for ANB appears inflated because of the small angular values for this measure. Statistical Analysis Descriptive statistics including the mean, standard deviation, and minimum and maximum value for each angular and linear measurement were calculated. Comparisons were made within the control group and within the headgear group at each time point. Next, comparisons were made between the control and headgear groups. Finally, comparisons were made for mean changes of measurements over two time points. When the assumption of normality was valid, the paired-sample t-test was used to determine whether significant differences existed in the changes of measurements between the two

46 36 time points within each group. The two-sample t-test was conducted to assess significance between the two groups (control versus headgear) at each time point. When the data was not normally distributed, the nonparametric Wilcoxon signed-rank test (analog of the paired-sample t-test) and Wilcoxon rank-sum test (analog of the twosample t-test) were performed.

47 37 RESULTS Table 5: Mean Cephalometric Angular Measures and Changes between Time Points for Control Group Variable N Minimum Maximum Mean Std. Dev. SNA SNA SNA SNA SNB SNB SNB SNB ANB ANB ANB ANB U1_SN U1_SN U1_SN U1_SN FMIA FMIA FMIA FMIA FMA FMA FMA FMA MP_SN MP_SN MP_SN MP_SN FH to NA FH to NA FH to NA FH to NA FH_NPg FH_NPg FH_NPg FH_NPg SNAT2_T

48 38 Table 5 continued SNAT3_T SNAT4_T SNAT3_T SNAT4_T SNAT4_T SNBT2_T SNBT3_T SNBT4_T SNBT3_T SNBT4_T SNBT4_T ANBT2_T ANBT3_T ANBT4_T ANBT3_T ANBT4_T ANBT4_T U1_SNT2_T U1_SNT3_T U1_SNT4_T U1_SNT3_T U1_SNT4_T U1_SNT4_T FMIAT2_T FMIAT3_T FMIAT4_T FMIAT3_T FMIAT4_T FMIAT4_T FMAT2_T FMAT3_T FMAT4_T FMAT3_T FMAT4_T FMAT4_T MP_SNT2_T MP_SNT3_T MP_SNT4_T MP_SNT3_T MP_SNT4_T MP_SNT4_T

49 39 Table 5 continued MxDepthT2_T MxDepthT3_T MxDepthT4_T MxDepthT3_T MxDepthT4_T MxDepthT4_T FH_NPgT2_T FH_NPgT3_T FH_NPgT4_T FH_NPgT3_T FH_NPgT4_T FH_NPgT4_T

50 40 Table 6: Mean Cephalometric Angular Measures and Changes between Time Points for the Headgear Group Variable N Minimum Maximum Mean Std. Dev. SNA SNA SNA SNA SNB SNB SNB SNB ANB ANB ANB ANB U1_SN U1_SN U1_SN U1_SN FMIA FMIA FMIA FMIA FMA FMA FMA FMA MP_SN MP_SN MP_SN MP_SN FH to NA FH to NA FH to NA FH to NA FH_NPg FH_NPg FH_NPg FH_NPg SNAT2_T

51 41 Table 6 continued SNAT3_T SNAT4_T SNAT3_T SNAT4_T SNAT4_T SNBT2_T SNBT3_T SNBT4_T SNBT3_T SNBT4_T SNBT4_T ANBT2_T ANBT3_T ANBT4_T ANBT3_T ANBT4_T ANBT4_T U1_SNT2_T U1_SNT3_T U1_SNT4_T U1_SNT3_T U1_SNT4_T U1_SNT4_T FMIAT2_T FMIAT3_T FMIAT4_T FMIAT3_T FMIAT4_T FMIAT4_T FMAT2_T FMAT3_T FMAT4_T FMAT3_T FMAT4_T FMAT4_T MP_SNT2_T MP_SNT3_T MP_SNT4_T MP_SNT3_T MP_SNT4_T MP_SNT4_T

52 42 Table 6 continued FH to NA T2_T FH to NA T3_T FH to NA T4_T FH to NA T3_T FH to NA T4_T FH to NA T4_T FH_NPgT2_T FH_NPgT3_T FH_NPgT4_T FH_NPgT3_T FH_NPgT4_T FH_NPgT4_T

53 43 Table 7: Mean Cephalometric Horizontal Linear Measures and Changes between Time Points for Control Group Variable N Minimum Maximum Mean Std. Dev. ACB ACB ACB ACB IiHorz IiHorz IiHorz IiHorz IsHorz IsHorz IsHorz IsHorz MxhHorz MxhHorz MxhHorz MxhHorz MdhHorz MdhHorz MdhHorz MdhHorz A_ptHorz A_ptHorz A_ptHorz A_ptHorz B_ptHorz B_ptHorz B_ptHorz B_ptHorz PgHorz PgHorz PgHorz PgHorz ACBT2_T ACBT3_T ACBT4_T ACBT3_T ACBT4_T ACBT4_T

54 44 Table 7 continued IiHorzT2_T IiHorzT3_T IiHorzT4_T IiHorzT3_T IiHorzT4_T IiHorzT4_T IsHorzT2_T IsHorzT3_T IsHorzT4_T IsHorzT3_T IsHorzT4_T IsHorzT4_T MxhHorzT2_T MxhHorzT3_T MxhHorzT4_T MxhHorzT3_T MxhHorzT4_T MxhHorzT4_T MdhHorzT2_T MdhHorzT3_T MdhHorzT4_T MdhHorzT3_T MdhHorzT4_T MdhHorzT4_T A_ptHorzT2_T A_ptHorzT3_T A_ptHorzT4_T A_ptHorzT3_T A_ptHorzT4_T A_ptHorzT4_T B_ptHorzT2_T B_ptHorzT3_T B_ptHorzT4_T B_ptHorzT3_T B_ptHorzT4_T B_ptHorzT4_T PgHorzT2_T PgHorzT3_T PgHorzT4_T PgHorzT3_T PgHorzT4_T

55 45 Table 7 continued PgHorzT4_T

56 46 Table 8: Mean Cephalometric Horizontal Linear Measures and Changes between Time Points for the Headgear Group Variable N Minimum Maximum Mean Std. Dev. ACB ACB ACB ACB IiHorz IiHorz IiHorz IiHorz IsHorz IsHorz IsHorz IsHorz MxhHorz MxhHorz MxhHorz MxhHorz MdhHorz MdhHorz MdhHorz MdhHorz A_ptHorz A_ptHorz A_ptHorz A_ptHorz B_ptHorz B_ptHorz B_ptHorz B_ptHorz PgHorz PgHorz PgHorz PgHorz ACBT2_T ACBT3_T ACBT4_T ACBT3_T ACBT4_T ACBT4_T

57 47 Table 8 continued IiHorzT2_T IiHorzT3_T IiHorzT4_T IiHorzT3_T IiHorzT4_T IiHorzT4_T IsHorzT2_T IsHorzT3_T IsHorzT4_T IsHorzT3_T IsHorzT4_T IsHorzT4_T MxhHorzT2_T MxhHorzT3_T MxhHorzT4_T MxhHorzT3_T MxhHorzT4_T MxhHorzT4_T MdhHorzT2_T MdhHorzT3_T MdhHorzT4_T MdhHorzT3_T MdhHorzT4_T MdhHorzT4_T A_ptHorzT2_T A_ptHorzT3_T A_ptHorzT4_T A_ptHorzT3_T A_ptHorzT4_T A_ptHorzT4_T B_ptHorzT2_T B_ptHorzT3_T B_ptHorzT4_T B_ptHorzT3_T B_ptHorzT4_T B_ptHorzT4_T PgHorzT2_T PgHorzT3_T PgHorzT4_T PgHorzT3_T PgHorzT4_T

58 48 Table 8 continued PgHorzT4_T

59 49 Table 9: Mean Cephalometric Vertical Linear Measures and Changes between Time Points for Control Group Variable N Minimum Maximum Mean Std. Dev. IiVert IiVert IiVert IiVert IsVert IsVert IsVert IsVert IsHorz IsHorz IsHorz IsHorz PNSVert PNSVert PNSVert PNSVert ProsVert ProsVert ProsVert ProsVert MdvVert MdvVert MdvVert MdvVert MxvVert MxvVert MxvVert MxvVert ANSVert ANSVert ANSVert ANSVert MentVert MentVert MentVert MentVert IiVertT2_T IiVertT3_T

60 50 Table 9 continued IiVertT4_T IiVertT3_T IiVertT4_T IiVertT4_T IsVertT2_T IsVertT3_T IsVertT4_T IsVertT3_T IsVertT4_T IsVertT4_T PNSVertT2_T PNSVertT3_T PNSVertT4_T PNSVertT3_T PNSVertT4_T PNSVertT4_T ProsVertT2_T ProsVertT3_T ProsVertT4_T ProsVertT3_T ProsVertT4_T ProsVertT4_T MdvVertT2_T MdvVertT3_T MdvVertT4_T MdvVertT3_T MdvVertT4_T MdvVertT4_T MxvVertT2_T MxvVertT3_T MxvVertT4_T MxvVertT3_T MxvVertT4_T MxvVertT4_T ANSVertT2_T ANSVertT3_T ANSVertT4_T ANSVertT3_T ANSVertT4_T ANSVertT4_T MentVertT2_T

61 51 Table 9 continued MentVertT3_T MentVertT4_T MentVertT3_T MentVertT4_T

62 52 Table 10: Mean Cephalometric Vertical Linear Measures and Changes between Time Points for Headgear Group Variable N Minimum Maximum Mean Std. Dev. IiVert IiVert IiVert IiVert IsVert IsVert IsVert IsVert IsHorz IsHorz IsHorz IsHorz PNSVert PNSVert PNSVert PNSVert ProsVert ProsVert ProsVert ProsVert MdvVert MdvVert MdvVert MdvVert MxvVert MxvVert MxvVert MxvVert ANSVert ANSVert ANSVert ANSVert MentVert MentVert MentVert MentVert IiVertT2_T IiVertT3_T

63 53 Table 10 continued IiVertT4_T IiVertT3_T IiVertT4_T IiVertT4_T IsVertT2_T IsVertT3_T IsVertT4_T IsVertT3_T IsVertT4_T IsVertT4_T PNSVertT2_T PNSVertT3_T PNSVertT4_T PNSVertT3_T PNSVertT4_T PNSVertT4_T ProsVertT2_T ProsVertT3_T ProsVertT4_T ProsVertT3_T ProsVertT4_T ProsVertT4_T MdvVertT2_T MdvVertT3_T MdvVertT4_T MdvVertT3_T MdvVertT4_T MdvVertT4_T MxvVertT2_T MxvVertT3_T MxvVertT4_T MxvVertT3_T MxvVertT4_T MxvVertT4_T ANSVertT2_T ANSVertT3_T ANSVertT4_T ANSVertT3_T ANSVertT4_T ANSVertT4_T MentVertT2_T

64 54 Table 10 continued MentVertT3_T MentVertT4_T MentVertT3_T MentVertT4_T MentVertT4_T

65 55 Initial Comparisons Between Control and Headgear Groups At time point T1, there was no difference between the headgear and control groups for all angular measures. There were no differences between the two groups at T1 for horizontal measures. Finally, there were no differences at T1 between the two groups for vertical measures. Angular Data Findings The results for SNA within the control group demonstrated no significant differences in the mean changes of measurements between any two time points (Graph 1). On the other hand, the results for SNA within the headgear group demonstrated significant differences in the mean changes of measurements between time points T1 and T2, T1 and T3, T1 and T4, and T3 and T4 (Graph 2). When the SNA measurements were compared between the control and headgear group at each time point, no significant differences were found (Graph 3). The mean changes in SNA demonstrated significant differences between T1 and T2, T1 and T3, T1 and T4, and T2 and T3 (Graph 4). The headgear group demonstrates a decrease in SNA throughout treatment with a slight relapse posttreatment.

66 56 Graph 1: SNA Control Control Timepoints Graph 2: SNA Headgear

67 57 Graph 3: SNA Control versus Headgear Graph 4: SNA Changes

68 58 The SNB values within the control group demonstrated significant differences in the mean changes of measurements between time points T1 and T4, T2 and T4, and T3 and T4 (Graph 5). The results showed that the mean measurements at T4 were significantly greater than at time points T1, T2, and T3. Similar significant differences were found for the headgear group (Graph 6). The results indicated that the mean SNB value at T4 was significantly greater than the SNB values at T1, T2, and T3. When the SNB measurements were compared between the control and headgear group at each time point, no significant differences were found (Graph 7). The comparison of the mean changes in SNB between the control and headgear groups demonstrated no significant differences at any time point (Graph 8). Graph 5: SNB Control

69 59 Graph 6: SNB Headgear Graph 7: SNB Control versus Headgear

70 60 Graph 8: SNB Changes The mean ANB measurements within the control group showed significant differences between timepoints T1 and T4, T2 and T4, and T3 and T4 (Graph 9). However, the greatest difference was between timepoints T1 and T4, and the difference in the mean values was 0.57 degrees, which may be statistically significant but is unlikely clinically significant. Within the headgear group, significant differences in the mean changes of ANB measurements were found between all timepoints: T1 and T2; T1 and T3; T1 and T4; T2 and T3; T2 and T4; and T3 and T4 (Graph 10). When the ANB measurements were compared between the control and headgear groups at each time point, no significant differences were found at any time points (Graph 11). The comparison of the mean changes in ANB between the control and headgear groups demonstrated significant differences for the time points T1 to T2, T1 to T3, T1 to T4, T2 to T3, and T2 to T4 (Graph 12).

71 61 Graph 9: ANB Control Graph 10: ANB Headgear

72 62 Graph 11: ANB Control versus Headgear Graph 12: ANB Changes

73 63 The results for U1 to SN within the control group demonstrated no significant differences in the mean changes of measurements between any timepoints (Graph 13). Similarly, the data showed no significant differences between any two time points for U1 to SN measurements within the headgear group (Graph 14). When the U1 to SN measurements were compared between the control and headgear group at each time point, significant differences were found at time points T3 and T4 (Graph 15). The results indicated that the headgear measurements for those two time points were significantly greater in the headgear group than in the control group. The comparison of the mean changes of U1 to SN between the control and headgear groups demonstrated no significant differences for any two time points (Graph 16). Graph 13: U1 to SN Control

74 64 Graph 14: U1 to SN Headgear Graph 15: U1 to SN Control versus Headgear

75 65 Graph 16: U1 to SN Changes The FMIA values within the control group showed no significant differences in the mean changes of measurements between any timepoints (Graph 17). On the other hand, for the headgear group, significant differences were found between time points T1 and T3, and T3 and T4 (Graph 18). The results indicated that the mean FMIA measurement in the headgear group at T3 was significantly smaller than at T1, and the mean measurement at T4 was significantly greater than at T3. When the FMIA measurements were compared between the control and headgear groups at each time point, a significant difference was found at T3 (Graph 19). The comparison of the mean changes of FMIA between the control and headgear groups demonstrated significant differences for the time points from T1 to T3 and T1 to T4 (Graph 20).

76 66 Graph 17: FMIA Control Graph 18: FMIA Headgear

77 67 Graph 19: FMIA Control versus Headgear Graph 20: FMIA Changes

78 68 The mean measurements for FH-NA within the control group demonstrated a significant difference between timepoints T1 and T3 and T1 and T4 (Graph 21). On the other hand, the results for FH-NA within the headgear group demonstrated significant differences in the mean changes of measurement values between time points T1 and T2, T1 to T4, and T3 and T4 (Graph 22). The results indicated that the mean FH-NA value at T1 was significantly greater than those observed at T2, T3, and T4. When the FH-NA measurements were compared between the control and headgear groups at each time point, a significant difference was found at T3 and T4 (Graph 23). The comparison of the mean changes of FH-NA between the control and headgear groups demonstrated significant differences for the time points from T1 to T2, T1 and T3, and T1 to T4 (Graph 24). Graph 21: FH-NA Control

79 69 Graph 22: FH-NA Headgear Graph 23: FH-NA Control versus Headgear

80 70 Graph 24: FH-NA Changes The results for FMA within the control group demonstrated significant differences in the mean changes of measurement values between time points T1 and T2, T1 and T3, T1 and T4, and T2 and T4 (Graph 25). The results for FMA within the headgear group showed no significant differences in the mean changes of measurements at any timepoints (Graph 26). When the FMA measurements were compared between the control and headgear groups at each time point, significant differences were found at T3 and at T4 (Graph 27). There was a consistent tendency for the headgear group to have a higher FMA than the control group. The comparison of the mean changes of FMA between the control and headgear groups demonstrated no significant differences between any two time points (Graph 28). A general decreasing trend for FMA is present for both control and headgear groups throughout treatment and long-term.

81 71 Graph 25: FMA Control Graph 26: FMA Headgear

82 72 Graph 27: FMA Control versus Headgear Graph 28: FMA Changes

83 73 The mean measurements for SN-MP within the control group demonstrated significant differences in the mean changes between time points T1 and T2, T1 and T3, T1 and T4, T2 and T4, and between T3 and T4 (Graph 29). The results for SN-MP within the headgear group demonstrated significant differences in the mean changes of measurements between time points T1 and T4, T2 and T4, and between T3 and T4 (Graph 30). When the SN-MP measurements were compared between the control and headgear groups at each time point, no significant differences were found (Graph 31). Like FMA, there was a consistent tendency for the headgear group to have a higher SN- MP angle. The comparison of the mean changes of SN-MP between the control and headgear groups demonstrated no significant differences at any time point (Graph 32). A general decreasing trend for SN-MP is present for both control and headgear groups throughout treatment and long-term. Graph 29: SN-MP Control

84 74 Graph 30: SN-MP Headgear Graph 31: SN-MP Control versus Headgear

85 75 Graph 32: SN-MP Changes Horizontal Data Findings The results for the horizontal linear measurement Y-axis to A-point within the control group demonstrated significant differences in the mean changes of measurement values between all time points (Graph 33). In the headgear group, the Y-axis to A-point horizontal measurement was found to have significant differences in the mean changes only between T2 and T4 (Graph 34). When the Y-axis to A-point linear measurements were compared between the control and headgear groups at each time point, no significant differences were found (Graph 35). The comparison of the mean changes of Y-axis to A-point between the control and headgear groups demonstrated that there were significant differences in the measurement change values at all timepoints except from T1 to T2 and from T3 to T4 (Graph 36).

86 76 Graph 33: Y-axis to A-point Control Graph 34: Y-axis to A-point Headgear

87 77 Graph 35: Y-axis to A-point Control versus Headgear Graph 36: Y-axis to A-point Changes

88 78 The results for the horizontal linear measurement Y-axis to Maxillary Molar (MxH) within the control group demonstrated significant differences in the mean changes of measurement values between all timepoints (Graph 37). In the headgear group, the Y- axis to MxH horizontal measurement was also found to have significant differences in the mean changes between all time points except for between timepoints T1 and T2 and T1 and T3 (Graph 38). This represents restraint of forward molar movement during growth from the initial time point to the time of molar correction, and through the period of fixed appliances. When the Y-axis to MxH linear measurements were compared between the control and headgear groups at each time point, no significant differences were found (Graph 39). The comparison of the mean changes of Y-axis to MxH between the control and headgear groups demonstrated that there were significant differences in the measurement change values from time points T1 to T2, T1 to T3, and from T1 to T4 (Graph 40). Graph 37: Y-axis to MxH Control

89 79 Graph 38: Y-axis to MxH Headgear Graph 39: Y-axis to MxH Control versus Headgear

90 80 Graph 40: Y-axis to MxH Changes Vertical Data Findings Vertical measurements within each group increased significantly at each time point as a result of normal growth, with the exception of five measurements, of which two increased but not enough to achieve statistical significance. The remaining three measures were between timepoints T3 and T4, where growth is beginning to plateau for a majority of patients (see Tables A5 and A6). There were significant differences between the two groups in the amount of change between time points for six vertical measurements. The measurement from the constructed x-axis to the mandibular incisor was greater in the headgear group at T2 and T3. The difference at T3 is likely due to the leveling of the curve of spee that occurs during fixed treatment, resulting in intrusion of the mandibular incisor. Similarly, the headgear group had a greater vertical measurement at T3 for the maxillary incisor and