Kenji Takada, Sirima Petdachai, and Mamoru Sakuda

Transcription

1 European Journal oforuuxkxuta 15(1993) Europan Onhodonlic Scpcicty Changes in dentofacial morphology in skeletal Class III children treated by a modified maxillary protraction headgear and a chin cup: a longitudinal cephalometric appraisal Kenji Takada, Sirima Petdachai, and Mamoru Sakuda Department of Orthodontics, Faculty of Dentistry, Osaka University, Japan SUMMARY The purpose of the current report was to investigate cephalometrically possible orthopaedic effects of a modified maxillary protraction headgear (MPH) on dentofacial morphology in skeletal Class III female patients before and during the pubertal growth spurt period. Sixtyone patients were divided into three groups, the prepubertal (7-10 years, n=20), the midpubertal (10-12 years, n=22), and the late pubertal (12-15 years, n=19) groups. Longitudinal record sets of subjects with acceptable good occlusion were used as the control. Patients were treated by protracting from the upper canine area. The mean ages at completion of the MPH treatment were 8.9, 11.3, and 13.3 years for the three test groups, respectively. The average treatment time was 1.1, 1.0, and 1.4 years for each of these groups. Lateral cephalograms at the start and completion of use of the MPH were collected. Annual differences were calculated from these paired records for each of 21 dentoskeletal variables in the test groups and compared to those of the control group. The pre- and mid-pubertal groups revealed significant increases in both the SNA (P<0.01 and P<0.001) and the maxillary length (Ptm-A/PP, P<0.01), while the late pubertal group showed a less significant increase in the SNA (P<0.05) alone. The decreased SNB, increased ANB and SNMP of the pre- and mid-pubertal groups was accounted for by the backward and downward rotation of the mandible. The results suggest possible orthopaedic effects of the MPH on dentofacial morphology in young females when it is applied before or during acceleration of the pubertal growth spurt. Introduction There has been a dilemma among orthodontists regarding treatment of skeletal Class III malocclusion in growing children, since it is difficult to provide precise criteria as to whether the treatment could be completed by an orthodontic/orthopaedic approach alone or whether a subsequent surgical approach would be required after growth has ceased. Previous clinical experiences (Susami et al., 1966; Graber, 1977) have suggested that application of an orthopaedic force to the craniofacial complex at an early phase of growth can contribute to treatment of this type of malocclusion. Therefore, if we take into account a risk/benefit factor derived by a surgical approach, a combined approach of an orthopaedic force and a camouflage by dental compensation could be assumed as one of meaningful and realistic options of orthodontic treatment strategies. This strategy may well be accepted in a country like Japan where approximately one-third of orthodontic patients are those with Class III malocclusion because of racial characteristics (Takada et al., 1987). Approximately per cent of the patients with skeletal Class III malocclusion have been reported to show recessive growth of the maxilla or combination of the recessive maxilla and excessive growth of the mandible (Sanborn, 1955; Susami, 1967; Jacobson et al., 1974). To this type of malocclusion, use of a maxillary protraction headgear can provide favourable treatment results (Nanda, 1980; Ishii et al., 1987; Mermigos et al., 1990). Regarding orthopaedic force effects on the maxillary component, numerous animal experiments (Dellinger, 1973; Kambara, 1977; Nanda, 1978) and biomechanical modellings (Itoh et al., 1985; Hata et al., 1987; Canut et al., 1990) have determined rela-

2 212 K. TAKADA ET AL. tionships between the magnitude and direction of forces applied and the nature and/or sites of response in bone tissues. To date, however, there have been no human studies, on a longitudinal basis, which investigated optimum timing for use of the maxillary protraction headgear during pre-adolescent to adolescent periods to stimulate sufficient forward displacement of the maxilla. The purpose of the current report was to investigate cephalometrically possible orthopaedic effects of a modified maxillary protraction headgear, combined with a chin cup (MPH) on dentofacial morphology in skeletal Class III female patients before and during the pubertal period, and to discuss the optimum timing for applying the MPH appliance. Subjects and methods Figure 1 Patient wearing a maxillary protraction headgear (MPH) appliance: a, head cap; b, vertical bow; c, chin cup; d, upper module; e, lower module; f, soldered hooks; g, intra-oral elastic; h, extra-oral elastic. Appliances The MPH assembly consisted of three parts, i.e. a head cap, a vertical bow, and a chin cup (Fig. 1). The total amount of force applied for extra-oral elastics was g on both sides. The vertical bow consisted of upper and lower modules. The lower module had two soldered hooks at its lower third for use of intra-oral elastics. All the patients evaluated in the current study had worn either a lingual arch appliance or an Edgewise archwire with molar bands. The size of the lingual arch was 0.9 mm in diameter. A 0.016x0.022 inch Elgiloy wire was used for Table 1 Summary of the periods of use of modified maxillary protraction headgears for the test groups. Starting age (years) Completion age (years) Duration (years) Test group Range Range Range Sample size Prepubertal Mid-pubertal Late pubertal l.i Subjects A total of 61 Japanese female patients was selected retrospectively as the test group. The subjects had revealed skeletal anterior crossbite and had been diagnosed cephalometrically as having skeletal jaw discrepancy. They were categorized into three subgroups, i.e. the pre-, mid-, and late pubertal groups (Table 1), according to the completion periods of treatment by the MPH (No. 54B,671, Sankin Industrial Co. Ltd., Japan). The prepubertal group consisted of those who had completed the MPH treatment by the age of 10. The mid-pubertal group included those whose MPH treatment had been finished between the ages of 10 and 12, while in the late pubertal group, the treatment had been completed between the ages of 12 and 15. The duration of the MPH treatment was between 4 months and 2 years. The average durations of the use of the appliance were 1.1, 1.0, and 1.4 years for each of the three test groups.

3 PROTRACTION HEADGEAR TREATMENT IN CLASS III 213 the Edgewise archwire. Hooks were soldered at the sites mesial or distal to the upper canines. Elastics were given between these hooks and the aforementioned hooks on the lower module of the vertical bow to protract in a forward and downward direction. The amount of force applied by the intra-oral elastics was between 150 and 250 g per side. The patients were instructed to replace the intra-oral elastics every day and the extra-oral elastics every month. They were also asked to use the MPH for 8 hours a day. At the completion of the MPH treatment, the use of the appliance was stopped after correction of anterior cross-bite or after 2 years treatment in the subjects who did not reveal further improvement. Cephalometry Initial lateral cephalograms had been taken for each patient at the start of treatment by the MPH. The second cephalograms were recorded at the completion of use of the MPH. For comparison, cephalometric control growth data collected at Osaka University were used. Sixtyfour lateral cephalograms of 16 Japanese females with acceptable good occlusion had been recorded as controls at the ages of 6, 8, 11, and 14 years on a longitudinal basis (Table 2). The cephalograms were divided into four record sets A, B, C, and D according to the aforementioned recording stages. Tracings were constructed for each headfilm and 21 landmarks (Takada et al., 1984; Proffit et al., 1986) were identified (Fig. 2). For the bilateral landmarks, the midpoint between the right and the left radiographic images was used. The positions of the landmarks were digitized by a software program (Quick Ceph Image, Ver 2.7, Orthodontic Processing Co., U.S.A.) implemented in a personal computer (Macintosh II, Apple Co., USA). The co-ordinates of each Table 2 Summary of age distributions for the record set of control subjects (n= 16). Record set A B C D age (years) (years) Range (years) Figure 2 Cephalometnc landmarks. 1. S sella; 2. Na nasion; 3. Or orbitale; 4. Po porion; 5. Ba basion; 6. PNS posterior nasal spine; 7. Ptm pterygomaxillary fissure; 8. ANS anterior nasal spine; 9. Point A; 10. Ar articulare; 11. Point B; 12. Pog pogonion; 13. Me menton; 14. Go gonion; 15. Point G; 16. Ul upper central incisor tip; 17. U1A upper central incisor apex; 18. LI lower central incisor tip; 19. LI A lower central incisor apex; 20. U6 upper first molar; 21. L6 lower first molar. point were determined with respect to the standard sella-nasion horizontal axis registered at sella. Twenty-one dentoskeletal variables (Takada et al., 1984; Proffit et al., 1986) were determined and categorized into six subgroups according to their locations relevant to anatomical structures and relationship (Fig. 3). Data analyses The cephalometric data were transferred to spread sheet software (Wingz, JA , Informix Software Inc., USA) for subsequent analyses. To understand morphologic characteristics of dentofacial structures of the test groups before treatment, profilograms with calculated means and s of the X-Y co-ordinates for each cephalometric landmark for the initial records were compared with those of the control group. As for the control, estimated means and s which corresponded to the initial mean ages of each test group were computed for each value by a linear interpolation of two consecut-

4 214 K. TAKADA ET AL. was determined where S, and Sj were s at the stages /" and j, respectively (Walpole, 1974). For comparison with the test groups, the values obtained for the record sets B and A were used for the prepubertal group, and those for C and B, and for D and C were used for the mid- and the late pubertal groups, respectively. The significance of differences between the mean annual differences of the test and control groups was determined by a Student /-test (Blalock, 1972; Walpole, 1974) by means of a statistical analysis software (StatView II, A , Abacus Concepts, Inc., USA). Statistical significance was arbitrarily determined at the P=0.05, 0.01, and levels. Above 5 per cent level was interpreted as non-significant. Figure 3 Dentoskeletal variables. 1. S-N; 2. SNA; 3. SNPP; 4. Ptm-A/PP; 5. SNB; 6. SNP; 7. SNMP; 8. GoA; 9. SNRP; 10. Go-Me; II. Ar-Me; 12. ANB; 13. PPMP; 14. U1PP; 15. U6/PP; 16. IMPA; 17. Ll/MP; 18. N-Me; 19. N/PP; 20. Me/PP; 21. L6/MP. ive records. For example, given that an estimated mean value of the control which corresponded to the mean age of the prepubertal test group, i.e. 7.8 years, was_expressed as c^m.7.8- The estimated value cv c V mls was determined by calculating the equation, = ^,7. 8 = c V m (c ^m.8.5 " c K m ) X [( )/ ( )]. The values cv mi8.s and cv m6i were means of the record sets B and A (mean ages 8.5 and 6.5 years, respectively). To evaluate possible treatment effects by the MPH appliance, annual differences between paired records taken at the initial and the completion of use of the MPH were computed for all the variables in the test groups. That is, provided that values for a given variable at the initial and the second cephalometric records were V, and V 2, respectively, for a given patient, an annual difference of (V 2 V,)/T was calculated to normalize differences in treatment periods among individuals. T was the interval between the two records in years. For the control data, the annual difference (c v m.) ~ c v m.i)l(j-i) wa s calculated for all the variables, where cv mi and cv mj were mean values for the variables determined at two consecutive recorded ages, i and j, respectively. For the s, the value e5. = Results Figures 4, 5, and 6 provide comparison of mean profilograms at the start of the MPH treatment in each test group and the corresponding control group. All three test groups revealed a smaller maxilla, a larger mandible with retroclined lower anteriors while proclined upper incisors were determined except in the prepubertal group -3 6 cm cm Figure 4 Comparison of mean profilograms between the prepubertal group (dotted lines) at the start (mean age 7.8 years) of treatment by the MPH and the corresponding control group (solid lines). The control data are the estimates at the age of 7.8 years calculated by a linear interpolation of two consecutive records A and B as a function of age.

5 PROTRACTION HEADGEAR TREATMENT IN CLASS HI cm Figure 5 Comparison of mean profilograms between the mid-pubertal group (dotted lines) at the start (mean age 10.3 years) of treatment by the MPH and the corresponding control group (solid lines). The control data are the estimates at the age of 10.3 years calculated by a linear interpolation of two consecutive records B and C as a function of age. 6 cm Figure 6 Comparison of mean profilograms between the late pubertal group (dotted lines) at the start (mean age 12.0 years) of treatment by the MPH and the corresponding control group (solid lines). The control data are the estimates at the age of 12.0 years calculated by a linear interpolation of two consecutive records C and D as a function of age. whose data were not available because teeth were not fully erupted in some patients. Table 3 provides comparison of mean annual differences determined for the dentoskeletal variables between the prepubertal test group and the corresponding normal data. The mean annual differences for the maxillary variables, i.e. the SNA and the maxillary length (Ptm-A/ PP), in the test group were significantly larger (P<0.0\) than those determined for the control group. In other words, the test group revealed forward displacement of the maxilla whose magnitude surpassed that of the control. As for the mandible, the test group showed significant decreases in the SNB and SNP angles (P< 0.001) and increases in the SNMP, SNRP (P<0.01), and ANB (P< 0.001) angles. The overall changes reflect the backward rotation of the mandible. Also, remarkable increases in the total face height (P<0.0\) and the lower face height (P< 0.05) were shown. As for the denture pattern, retroclination of the lower incisor (P<0.05) and overeruption of the lower first molar (P<0.0\) were determined. Table 4 gives comparison of mean annual differences determined for the cephalometric variables between the test group and the control group at the mid-pubertal stage. The test group revealed significant annual increases in the SNA angle (P< 0.001) and Ptm-A/PP (/><0.01). The observed forward displacement of the maxilla in the test group reflects possible orthopaedic effects of the MPH appliance. There was a tendency for the palatal plane to show posteriorly-downward rotation (SNPP, P<0.05). As for the mandible, decreases in the SNB and the SNP angles (P<0.0\), and increases in the SNMP (/><0.01), SNRP (P<0.05), and ANB (P<0.00\) angles were determined. The test group also revealed significant increases in the total and lower face heights (P< 0.001). The overall changes are explained by the backward rotation of the mandible. In regard to the dentition, there was significant over-eruption of the upper first molar (P< 0.001), the lower central incisor (/><0.01), and the lower first molar (/><0.05). A typical case at the start and completion of use of the MPH in a patient in this group is illustrated by cephalometric tracings and dental relationships (Fig. 7). Table 5 provides comparison of mean annual differences for the cephalometric variables between the test and the corresponding control

6 216 K. TAKADA ET AL. Table 3 Comparison of mean annual differences for dentoskeletal variables between the test group (n = 20) and the control group (/J= 16) during the prepubertal stage. Test group Control group Variable i Value Cranial base SN (mm) Maxilla SNA (degrees) SNPP (degrees) Ptm-A/PP (mm)t Mandible SNB (degrees) SNP (degrees) - SNMP (degrees) Go Angle (degrees) SNRP (degrees) :,, Go-Me (mm) Ar Me (mm) Maxillo-mandible ANB (degrees) Denture pattern U1PP (degrees) U6/PP (mm) IMPA (degrees) Ll/MP (mm) L6/MP (mm) Vertical proportion N-Me (mm) N/PP (mm) Me/PP (mm) s : : 2.94 o.3o : io : : ll.a. il.a. ) : i.2o : 2.15 Statistically significant at */><0.05; **/><0.01; ***P<0.00\. : Data not available. fthe projected length from the pterygomaxillary fissure and the point A to the palatal plane (maxillary length) ** " "* "* 2.688" ** "* * " 3.110" * groups during the late-pubertal period. There was a weak tendency for the maxilla to reveal forward positioning by an increase in the SNA angle (P<0.05). The ANB angle of the test group increased significantly (P< 0.001) when compared with the control group. Discussion Success and failure of orthopaedic treatment of children with skeletal Class III malocclusion is partly, but substantially dependent on growth potential. Accordingly, the treatment requires a long-term period. This makes patients' motivation to the Edgewise or surgical orthodontic therapy which may become necessary at a later stage somewhat difficult. Therefore, it would be beneficial if we could obtain precise knowledge on optimum timing for wearing the MPH appliance to obtain better orthopaedic treatment effects with a shorter period of use of the appliance. Previous studies (Ishii et al., 1987; Wisth et al., 1987; Mermigos et al., 1990) have investigated the effects of the MPH in mixed samples of both sexes with a broader age range of between 4 and 14 years. Also, their treatment periods varied between 3 months and 34 months (Irie and Nakamura, 1975; Ishii et al, 1987; Wisth et al., 1987; Mermigos et al., 1990). These conditions are not suitable for obtaining a clinical rationale to specify the optimum timing for wearing the MPH appliance. We therefore focused on female subjects alone with a narrower age range, limited treatment periods, and different age groups according to the completion periods of treatment. Also, longitudinal records were used as the control data for comparison. In addition, we randomly included not only the subjects who were successfully treated by the appliance, but also those who did not reveal

7 PROTRACTION HEADGEAR TREATMENT IN CLASS III 217 Table 4 Comparison of mean annual differences for dentoskeletal variables between the test group (n = 22) and the control group («= 16) during the mid-pubertal stage. Test group Control group Variable l Value Cranial base SN (mm) Maxilla SNA (degrees) SNPP (degrees) Ptm-A/PP (mm)t Mandible SNB (degrees) SNP (degrees) SNMP (degrees) Go Angle (degrees) SNRP (degrees) Go-Me (mm) Ar-Me (mm) Maxillo-mandible ANB (degrees) Denture pattern U1PP (degrees) U6/PP (mm) IMPA (degrees) Ll/MP (mm) L6/MP (mm) Vertical proportion N-Me (mm) N/PP (mm) Me/PP (mm) Statistically significant at *P<0.05; **P<0.0\; ***/ > < fthe projected length from the pterygomaxiuary fissure and the point A to the palatal plane (maxillary length) *" * 2.672** ** ** 3.148** * *** *** ** 2.404* 4.233*** *** apparent improvement. The reason was that it was preferable to obtain the results from all the subjects who might or might not be sensitive to the applied orthopaedic force. Takaishi et al. (1968) reported that the average period of menarche among Japanese girls was 12.7 years. Hence, it would be reasonable to assume that the peak time for general growth spurt could be around 11.5 years since menarche occurs years after the occurrence of the peak height velocity (Marshall and Tanner, 1969). According to Asai (1973), maxillary growth spurt revealed almost no change after 12 years of age on average. In addition, Mitani (1977) reported that girls revealed occurrence of the maximum peak growth of the craniomaxillary component at years old. Based on this information, we made an assumption that the average age when the acceleration of the pubertal growth spurt in the current subjects occurred was between the ages of 10 and 12 years. Accordingly, the effect of the MPH appliance was evaluated for each of the three growth stages, where the prepubertal stage included patients who had completed treatment before commencement of the pubertal growth spurt, the mid-pubertal stage with those whose completion age of treatment was during acceleration of the growth spurt, and the late-pubertal stage with those who had completed the MPH treatment during declining of the growth spurt. In the current study, hand-wrist radiographs were not used for evaluation of growth maturity, since they were not taken in younger children for ethical reasons. In cephalometric assessment, orthopaedic effects derived by the appliance are determined by subtracting the change due to growth which occurs during use of the appliance from the overall apparent morphological change. In this

8 218 study, annual changes of cephalometric variables (Thilander, 1963; Harvold and Vargervik, 1977; Mills, 1991) in the control group were determined from the longitudinal records during periods which corresponded to those when the MPH appliance was used in the test group. These annual changes were assumed as the 'component due to growth'. The apparent changes in the test group were assumed as the sum of the growth and the orthopaedic force effect. As for the dentoskeletal patterns of the patients at the initial stage, all three test groups revealed a recessive maxilla in combination with an excessive mandible. Furthermore, the test subjects showed the upper incisor proclination and the lower incisor retroclination which are known as the characteristic dental compensation in skeletal Class III malocclusion (Sanborn, 1955; Jacobson et ai, 1974). Previous experimental studies have shown anterior displacement of the maxilla in response to anteriorly-directed orthopaedic force by sutural modification of the circum-maxillary sutures (Dellinger, 1973; Kambara, 1977; Nanda, 1978) and the maxillary tuberosity area (Kambara, 1977). Also, the zygomaticomaxillary suture was found to be the most critical (Nanda, 1978). In the present study, both the pre- and mid-pubertal groups revealed more anterior displacement of the maxilla than was expected by natural growth. The changes reflected the effect of the protracting device (Irie and Nakamura, 1975; Nanda, 1980; Ishii et ai, 1987). From the results of the current study, and the findings of Asai (1973) and Mitani (1977), it would be reasonable to assume that growth of the maxillary bones around the sutures is stimulated by the orthopaedic force applied by the MPH before and during acceleration of the pubertal growth spurt. For the mandible, the chin cup had the effect of backward and downward rotation (Thilander, 1963; Susami et ai, 1966; Graber, 1977; Sugawara et al., 1990) in both groups and such rotation may produce more extrusion of the lower first molar (Susami et ai, 1966). In addition, extrusion of the upper molar occurred in the midpubertal group which may be ascribed to the effect of the protracting device (Canut et ai, 1990; Itoh et ai, 1985), while in the prepubertal group, the data for height of the upper permanent first molar to the palatal plane were not available because of incomplete eruption. In the late pubertal group, it seems less possible for the MPH to have an effect on the maxilla and the mandible since the dentoskeletal variables did not reveal any significant changes. Figure 7 Cephalometric tracings (top) and dental relationships of a patient in the test group showing typical changes at the start (a) and the completion (b) of use of the MPH. Solid lines, pretreatment; dotted lines, post-treatment. K. TAKADA ET AL.

9 PROTRACTION HEADGEAR TREATMENT IN CLASS III 219 Table 5 Comparison of mean annual differences for dentoskeletal variables-between the test group (n= 19) and the control group {n= 16) during the late pubertal stage. Test group Control group Variable / Value Cranial base SN(mm) Maxilla SNA (degrees) SNPP (degrees) Ptm-A/PP (mm)t Mandible SNB (degrees) SNP (degrees) SNMP (degrees) Go Angle (degrees) SNRP (degrees) Go Me (mm) Ar-Me (mm) Maxillo-mandible ANB (degrees) Denture pattern U1PP (degrees) U6/PP (mm) IMPA (degrees) LI/MP (mm) L6/MP (mm) Vertical proportion N-Me (mm) N/PP (mm) Me/PP (mm) * "* Statistically significant at / > <0.05; *"/ > < fthe projected length from the pterygomaxillary fissure and the point A to the palatal plane (maxillary length). Protraction from the upper first molar area has been shown to produce posteriorlydownward rotation of the palatal plane (Itoh et al., 1985; Hata et al., 1987; Ishii et al., 1987; Canut et al., 1990). To reduce such rotation, protraction was made from the upper canine area (Rygh and Tindlund, 1982) in the current study. The observed changes for the three test groups were clinically negligible. There have been conflicting opinions (Greene, 1982; Reynders, 1990; Sadowsky, 1992) as to the possible occurrence of temporomandibular joint dysfunction (TMD) during and/or after orthodontic treatment. Dibbets and van der Weele (1991, 1992) concluded that treatment with a chin cup with 500 g force each side and 14-hour minimal wearing time per day, did not have a causal relationship with TMD over 10-, 15-, and 20-year observation periods. Also, in the current study where lighter forces ( # per side) and shorter wearing time (8 hours per day, 1 year on average) were applied to the patients, none of them revealed clinical symptoms of TMD, particularly pain or limitation of jaw movement, after the MPH treatment. Therefore, it would be reasonable to assume that if the MPH appliance were used with the aforementioned magnitude of force and duration, the change to TMD would be, if any, minimal. Although the interpretation of the current two-dimensional cephalometric data should be accepted with caution, the results suggest that the MPH appliance can provide orthopaedic effects on dentofacial morphology in skeletal Class III female patients when it is applied

10 220 K. TAKADA ET AL. before or during the period of acceleration of the pubertal growth spurt. Address for correspondence Dr Kenji Takada, Department of Orthodontics Faculty of Dentistry Osaka University 1-8 Yamadaoka, Suita, Osaka 565, Japan Acknowledgements The authors are indebted to Dr R. Susami of the Takimoto Institute of Orthodontics and Dr K. Wada for their advice in data collection. This work was supported by a grant from the Mother and Child Health Foundation. References Asai Y 1973 Growth changes of maxillofacial skeleton of Japanese from 12 to 20 years of age: A longitudinal study by means of cephalometric roentgenograms. Journal of Japan Orthodontic Society 32: (in Japanese) Blalock H M 1972 Social statistics. McGraw Hill, Kogakusha, Tokyo Canut J A, Dalmases F, Gandia J L, Salvador R 1990 Effects of maxillary protraction determined by laser metrology. European Journal of Orthodontics 12: Dellinger E L 1973 A preliminary study of anterior maxillary displacement. American Journal of Orthodontics 63: Dibbets J M H, van der Weele L Th 1991 Extraction, orthodontic treatment, and craniomandibular dysfunction. American Journal of Orthodontics and Dentofacial Orthopedics 99: Dibbets J M H, van der Weele L Th 1992 Long-term effects of orthodontic treatment, including extraction, on signs and symptoms attributed to CMD. European Journal of Orthodontics 14: Graber L W 1977 Chin cup therapy for mandibular prcgnathism. American Journal of Orthodontics 72: Greene C S 1982 Orthodontics and the temporomandibular joint. Angle Orthodontist 52: Harvold E P, Vargervik K 1977 Morphogenetic response to activator treatment. American Journal of Orthodontics 60: Hata S, Ito T, Nakagawa M, Kamogashira K, Ichikawa K, Matsumoto M, Chaconas S J 1987 Biomechanical effects of maxillary protraction on the craniofacial complex. American Journal of Orthodontics and Dentofacial Orthopedics 91: Irie M, Nakamura S 1975 Orthopedic approach to severe skeletal Class III malocclusion. American Journal of Orthodontics 67: Ishii H, Morita S, Takeuchi Y, Nakamura S 1987 Treatment effect of combined maxillary protraction and chin cap appliance in severe skeletal Class III cases. American Journal of Orthodontics and Dentofacial Orthopedics 92: Itoh T, Chaconas J J, Caputo A A, Matyas J 1985 Photoelectric effects of maxillary protraction on the craniofacial complex. American Journal of Orthodontics 88: Jacobson A, Evans W G, Preston C B, Sadowsky P L 1974 Mandibular prognathism. American Journal of Orthodontics 66: Kambara T 1977 Dentofacial changes produced by extraoral forward force in Macaca irus. American Journal of Orthodontics 71: Marshall W A, Tanner J M 1969 Variation in pattern of pubertal changes in girls. Archives of Disease in Childhood 44: Mermigos J, Full C A, Andresen G 1990 Protraction of the maxillofacial complex. American Journal of Orthodontics and Dentofacial Orthopedics 98: Mills J R E 1991 The effect of functional appliances on the skeletal pattern. British Journal of Orthodontics 18: Mitani H 1977 Occlusal and craniofacial growth changes during puberty: American Journal of Orthodontics 72: Nanda R 1978 Protraction of maxilla in rhesus monkeys by controlled extraoral force. American Journal of Orthodontics 74: Nanda R 1980 Biomechanical and clinical considerations of a modified protraction headgear. American Journal of Orthodontics 78: Proffit W R, Fields H W, Ackerman J L, Thomas P M, Tullock J F C 1986 Contemporary orthodontics. CV Mosby, St Louis Reynders R M 1990 Orthodontics and temporomandibular disorders: A review of the literature ( ). American Journal of Orthodontics and Dentofacial Orthopedics 97: Rygh P, Tindlund R 1982 Orthopedic expansion and protraction of the maxilla in the cleft palate patients A new treatment rationale. Cleft Palate Journal 19: Sadowsky C 1992 The risk of orthodontic treatment for producing temporomandibular mandibular disorders: A literature overview. American Journal of Orthodontics and Dentofacial Orthopedics 101: Sanborn R T 1955 Differences between the facial skeletal pattern of Class III malocclusion and normal occlusion. Angle Orthodontist 25: Sugawara J, Asano T, Endo N, Mitani H 1990 Long-term effects of chincap therapy on skeletal profile in mandibular prognathism. American Journal of Orthodontics and Dentofacial Orthopedics 98: Susami R 1967 A cephalometric study of dentofacial growth in mandibular prognathism. Journal of Japan Orthodontic Society 26: 1-34 (in Japanese) Susami R, Akiyama K, Ohnishi K, Yamano C, Deguchi T 1966 Cephalometric survey of reaction to orthodontic treatment in anterior crossbite cases: Part III Cases treated with chin cap. Journal of Japan Orthodontic Society 25: (in Japanese)

11 PROTRACTION HEADGEAR TREATMENT IN CLASS III 221 Takada K, Lowe A A, Freund V V 1984 Canonical correlations between masticatory muscle orientation and dentoskeletal morphology in children. American Journal of Orthodontics 86: Takada K, Yasuda Y, Masuda T, Kunisu S, Sakuda M 1987 Dynamic statistics of new patients in the Department of Orthodontics before and after moving of Osaka University Dental Hospital. Journal of Osaka University Dental Society 32: (in Japanese) Takaishi M, Ohmori S, Miyabe R, Iwamoto S 1968 Studies on patterns of physical growth at adolescence: Part 2, Height velocity and weight velocity in girls and their relation to menarcheaj age. Research on Pediatric Insurance 26: (in Japanese) Thilander B 1963 Treatment of Angle Class III malocclusion with chin cup. Transactions of the European Orthodontic Society 39: Walpole R E 1974 Introduction to statistics. Macmillan Publishing, New York Wisth P J, Tritrapunt A, Rygh P, Bee O E, Nordeval K The effect of maxillary protraction on front occlusion and facial morphology. Acta Odontologjca Scandinavica 45: