Mandibular First Molar Relation to Variable Lower Face Skeletal Components

Objective: To evaluate the position of the mandibular first permanent molar in the mandible relative to several factors.

Materials and Methods: A total of 185 untreated Class I and Class II patients were randomly selected from a sample of 350 patients from a single office. The palatal and mandibular planes were related to Frankfort horizontal to create the interjaw or “B” angle. Age and the mesial contact of the mandibular first molars were used. The landmarks were projected at right angles to the Frankfort horizontal for effective mandibular dimension lengths. Actual-length dimensions were projected at right angles to the mandibular plane. Pearson product moment correlation coefficients were computed to evaluate the effect of age, cranial length, and mandibular contribution to the molar's sagittal position in the mandible. Significance was reported only when P < .05 to determine a 95% confidence level.

Results: Statistically significant positive correlations indicated that the mandibular molar is located more forward with increasing age, longer mandibular body length, and increasing posterior facial height. In contrast, significant negative correlations to the interjaw, mandibular plane, ramal inclination angles, and the linear ramal contribution corresponded to a more posterior position of the molar with increasing angles.

Conclusions: The mandibular first permanent molar is located more anteriorly with an older patient, a longer mandibular body, greater posterior facial height, and an acute interjaw angle. In contrast, an increase in the forward tip of the ramus places the molar in a more posterior location.

Class II subdivision malocclusion types and evaluation of their asymmetries

INTRODUCTION

The primary objective of this study was to determine, by means of frontal photographic evaluation, the distribution of the 2 main types of Class II subdivision malocclusions. The secondary objective was to compare the dentoskeletal asymmetries in these 2 types with a group of normal-occlusion subjects by using submentovertex and posteroanterior radiographs.

METHODS

The experimental group included 44 untreated Class II subdivision malocclusion subjects with a mean age of 15.3 years. The control group included 30 subjects with normal occlusions with a mean age of 22.4 years. All had full complements of permanent teeth up to the first molars and had not received orthodontic treatment. Type 1 Class II subdivision malocclusion is coincidence of the maxillary dental midline with the facial midline and deviation of the mandibular midline. Type 2 has the opposite characteristics. The frontal photographs were evaluated subjectively by 2 examiners. In the submentovertex and posteroanterior radiographs, symmetry was assessed by measuring the relative difference in the spatial positions of dentoskeletal landmarks between the right and left sides. Independent t tests were used to compare the dentoskeletal asymmetries of types 1 and 2 with the normal-occlusion group.

RESULTS AND CONCLUSIONS

The results showed that 61.36% had type 1, 18.18% had type 2 Class II subdivision malocclusion, and 20.45% had mixed characteristics. The predominant asymmetric dentoalveolar characteristics of both types of Class II subdivision malocclusions were evident when individually compared with a normal-occlusion control group. There was a tendency for the type 1 subjects to have greater mandibular asymmetry than type 2, as compared with the control group.

Cephalometric facial soft tissue changes with the twin block appliance in Class II division 1 malocclusion patients. A systematic review

OBJECTIVE

To evaluate facial soft tissue changes after the use of the twin block appliance in Class II division 1 malocclusion patients.

MATERIALS AND METHODS

Several electronic databases (PubMed, MEDLINE, MEDLINE In-Process & Other Non-Indexed Citations, Cochrane databases, EMBASE, Web of Science, and LILACS) were searched with the help of a senior health-sciences librarian. Abstracts that appeared to fulfill the initial selection criteria were selected by consensus, and the original articles were retrieved. The article references were hand-searched for possible missing articles. Clinical trials that assessed facial soft tissue changes with the use of the twin block appliance without any surgical intervention or syndromic characteristics were considered. A comparable untreated control group was required to factor out normal growth changes.

RESULTS

Two articles fulfilled the selection criteria and quantified facial soft tissue changes. Although some statistically significant changes in the soft tissue profile were found, the magnitude of the changes may not be perceived as clinically significant. Changes produced in the upper lip seem to be controversial, although the study with sounder methodological quality did not report significant changes. No change in the anteroposterior position of the lower lip and the soft tissue menton or improvement of the facial convexity was found.

CONCLUSIONS

Three-dimensional quantification of the soft tissue changes is required to overcome current limitations in our understanding of the soft tissue changes obtained after the use of the twin block appliance in Class II division 1 malocclusion patients.

Dental arch shape and size in Malay schoolchildren with Class II malocclusion

AIM

To quantify and localise differences in Class I and Class II dental arches in Malay schoolchildren.

METHODS

The subjects were 50 Malay schoolchildren (Mean age: 15 + 0.7 years) with either Class I (N = 25) or Class II (N = 25) malocclusions. Fourteen homologous landmarks on the upper and lower study models of the subjects were digitised using MorphoStudio software, and the Procrustes means were computed. The mean Class I and Class II configurations were subjected to ftests and finite element analysis.

RESULTS

Normalised upper arch Class I and Class II configurations were statistically different (p < 0.05), but the lower arches were not. However, normalised Class II linear parameters were statistically smaller in the upper arch and larger in the lower arch. The upper Class II dental arch was narrower by 15 per cent and asymmetric changes in size (11-20 per cent) were localised in the labial and buccal regions of the lower Class II arch.

CONCLUSIONS

Size and shape differences between Class I and Class II dental arches can be identified with finite element analysis.

Lip-to-incisor Relationship and Postorthodontic Long-term Stability of Cover-bite Treatment

Objective: To investigate the impact of a persisting high lip line and other potential relapse-inducing factors on long-term stability of orthodontic correction of retroinclined maxillary central incisors.

Materials and Methods: Thirty-one cover-bite (“Deckbiss”) patients with retroinclined maxillary central incisors and a deep frontal overbite were evaluated. The maxillary central incisor inclination was determined odontometrically with study models made pretreatment, posttreatment, and at a follow-up examination (mean posttherapeutic interval: 9.0 years). The lip-to-incisor relationship, the interincisal angle, and the anteroposterior maxillary central incisor position were measured on lateral cephalograms taken after active treatment.

Results: The relapse tendency of the orthodontic correction of the retroinclined maxillary central incisors displayed great interindividual variability with a range of posttherapeutic inclination change of −6.75° to +8.00°. Multiple regression analysis revealed an increased tendency for relapse in patients with (1) a high posttherapeutic (dorsal) lip line level combined with the maxillary central incisor and lower lip contact only in the incisal crown area (P &lt; .01) and (2) a marked therapeutically induced inclination change of the maxillary central incisors (P &lt; .05). Interrelations between the relapse of the corrected maxillary central incisors and other evaluated parameters were not statistically significant.

Conclusions: For maximum treatment stability, the elimination of an excessive overlap of the upper incisors by the lower lip should be regarded as one of the most important therapeutic objectives when treating this malocclusion.

Lip shape and position in Class II division 2 malocclusion

OBJECTIVE

To determine whether differences exist in the shape and position of the lips between Class II division 2 and Class I malocclusions.

MATERIALS AND METHODS

Lateral cephalometric radiographs of subjects with Class II division 2 (n = 30) and Class I (n = 30) incisor relationships were scanned at 300 dpi to produce digital images. These were subsequently digitized in random order. Twenty-one landmarks characterizing the upper and lower lips and the maxillary and mandibular central incisors were digitized. Procrustes algorithms optimally superimposed the landmark configurations to standardize size, location, and orientation. Discriminant analysis of the principal components of shape determined the differences between the Class II division 2 and Class I groups.

RESULTS

The shape and position of the upper and lower lips differed significantly between the Class II division 2 group and the Class I group (P < .001). Principal component (PC) 1 (46% of the variance) involved an increase in the thickness of the upper and lower lips in the Class II division 2 group. PC2 (11% of the variance) was characterized by a relatively higher lip line in the Class II division 2 group.

CONCLUSIONS

The shape and position of the lips differ between Class II division 2 and Class I malocclusions.

Comparison of Mandibular Rami Width in Patients With Prognathism and Retrognathia

PURPOSE

The purpose of this study was to assess the ramus thickness in skeletal Class III and Class II patients.

METHODS

Forty patients were evaluated using computed tomography scanning.

RESULTS

Compared with the Class II patients, the mandibular ramus of Class III patients was thinner. The ramus thickness in retrognathic patients was 8.84 mm and the ramus thickness in prognathic patients was 7.80 mm.

CONCLUSION

The ramus is thinner in patients with prognathism than in those with retrognathia.

Objective measures as indicators for facial esthetics in white adolescents

The objective of this study was to examine the contribution of objective measures representing anterior-posterior and vertical characteristics, dental esthetics, or their combination that are used in daily orthodontic practice in the assessment of facial esthetics. A panel of 78 laymen evaluated facial esthetics of 32 boys and 32 girls, stratified over the four Angle classes, on a visual analogue scale. The relation between the objective parameters and facial esthetics was evaluated by backward multiple regression analysis. Dental esthetics as expressed by the Aesthetic Component of the Index of Orthodontic Treatment Need (AC/IOTN) appeared to be the most important indicator for facial esthetics. A new parameter, the "horizontal sum" was found to be a reliable variable for the anterior-posterior characteristics of the patient. Addition of this newly defined parameter to the AC/IOTN improved the prognostic value from 25% to 31%.

Sagittal spinal posture in relation to craniofacial morphology

OBJECTIVE

The aim of this study is to determine correlations between the parameters of body posture in the sagittal profile and sagittal jaw position by obtaining objective and valid three-dimensional measurements of the dorsal profile by means of rasterstereography.

MATERIALS AND METHODS

Fifty-three adults with Class II or III malocclusions were examined, and six angular parameters were determined. For the sagittal analysis of body posture, the Fleche Cervicale and Lombaire as well as trunk inclination were evaluated.

RESULTS

Statistically significant correlations (P < .05) were found between Facial Axis and Fleche Cervicale, Mandibular Plane angle and Fleche Cervicale, and Facial Depth and the Fleche Cervicale.

CONCLUSIONS

It can be concluded that the mandible seems to have a greater effect on body posture than other craniofacial parameters. As a clinical result of this study, patients with severe malocclusions should be examined interdisciplinarily before orthognathic surgery is performed to minimize postural influence on the altered jaw relationship after surgery.

Severe anterior open-bite malocclusion

This case report describes the treatment of a severe anterior open bite, Class II malocclusion with a history of dummy sucking. The 9-year-old girl presented with a significant anteroposterior and vertical discrepancy. Her face was convex with procumbent lips. She had an anterior open bite of 9 mm, an overjet of 8 mm, and a transverse maxillary deficiency. In consultation with the parents and patient, a nonsurgical therapy was elected, with the goals of reducing protrusion and closing the anterior open bite.

Changes in the soft tissue profile after extraction orthodontic therapy

PURPOSE

The purpose of this study was to evaluate the effects of extraction therapy and use or nonuse of headgear on the soft tissue profile in subjects with different growth patterns.

METHODS

A total of 41 subjects were included in the study. The patients were treated with standard edgewise mechanics and had 4 first premolars extracted. The type of growth pattern was assessed as mesiodivergent or hyperdivergent. The results were analyzed by 2-way analysis of variance.

RESULTS

When comparing the mean changes between growth pattern types, the vertical changes in Sn and A' were found to be statistically significant (P<.05). The vertical change in A' was also found to be significant between the headgear use and nonuse groups (P<.05). Interaction was found to be significant for Steiner upper and lower lip values and the vertical change in A. The upper and lower lips were retracted significantly more by headgear use in patients with hyperdivergent growth pattern (P<.05).

CONCLUSIONS

The results of this study indicate that the use of headgear should be avoided in hyperdivergent patients. The avoidance of premolar extraction, based on the possibility of a significant detrimental effect on the facial profile, is not justified.

Category 5: Class II Division 1 malocclusion with a high mandibular plane angle

This case report was submitted to the American Board of Orthodontics as part of the board-certification process. The summary of treatment and records are reprinted here much as they were submitted to the board.

Bolton tooth size discrepancies in skeletal Class I individuals presenting with different dental angle classifications

The objective of this study was to investigate the frequency and association of Bolton tooth size discrepancies with dental discrepancies. Forty-eight skeletal Class I, 60 Class II, and 44 Class III subjects with similar skeletal characteristics were included in this study. Analysis of variance was performed to compare the mean ratios of Bolton analysis as a function of the Angle classification and sex. To determine the prevalence of tooth size imbalances among the three groups of occlusions and the two sexes, chi-square tests were performed. To determine the correlation of tooth size imbalances with certain dental characteristics, Pearson's correlation coefficients were calculated. No statistically significant differences were determined for the prevalence of tooth size discrepancies and the mean values of Bolton's anterior and overall ratios among the occlusal groups and sexes. Bolton's anterior ratio discrepancies had significant correlations with midline shifts (P < .05) in Angle Class I cases, with U1-SN angle (P < .01) in Angle Class II cases, and with L1-APog distance (P < .05) in Angle Class III cases. Bolton discrepancies related to overall ratio had significant correlations with overjet (P < .05) in Class I cases, with overbite (P < .05) and U1-SN angle (P < .01) in Class II cases, and with IMPA (P < .01) in Class III cases. A high prevalence of tooth size discrepancies in an orthodontic patient population and the statistically significant correlation of some of these with some dental characteristics suggest that the measurement of interarch tooth size ratios might be clinically beneficial for treatment outcomes.

Dental arch dimensions in the mixed dentition: a study of Italian children born in the 1950s and the 1990s

The objective of this study was to compare the dental arch dimensions in the mixed dentition in two modern samples living in the same geographic area and separated by almost 35 years. A group of 83 subjects (39 boys and 44 girls) born between 1953 and 1959 (mean age: eight years and three months +/-15 months for the boys and seven years and 11 months +/-12 months for the girls) were compared with a group of 84 subjects (38 boys and 46 girls) born between 1990 and 1998 (mean age: eight years and eight months +/-12 months for the boys and eight years and four months +/-11 months for the girls). Measurements were taken on dental casts for posterior and anterior arch segments, intermolar and intercanine width, and mesiodistal size of incisors. The available anterior space in both arches and the posterior and anterior transverse dimensions were calculated. Groups were compared using a nonparametric test (Mann-Whitney U-test) for independent samples (P < .05). Results show that both boys and girls of 1990s showed significantly smaller maxillary intermolar width when compared with 1950s. Posterior transverse interarch discrepancy was significantly minor in girls of 1990s. The present population has a greater probability of developing a malocclusion as a consequence of the secular trend toward the reduction of the width of the upper arch.

Occlusal and cephalometric Class II Division 1 malocclusion severity in patients treated with and without extraction of 2 maxillary premolars

INTRODUCTION

The purpose of this study was to compare the initial occlusal and cephalometric severity of Class II Division 1 malocclusion patients treated with and without extraction of 2 maxillary premolars.

METHODS

Dental study models and cephalograms of 62 patients were selected. Those in group 1 (n = 42) were treated without extractions, and those in group 2 (n = 20) were treated with 2 maxillary premolar extractions. Grainger's treatment priority index (TPI) was used to assess the final and the initial occlusal status of each subject. Variables such as overjet and overbite were also evaluated. Independent t tests were used to compare the occlusal variables at the posttreatment stage, the occlusal and cephalometric variables at the pretreatment stage, and the improvement in TPI values between the groups.

RESULTS

Patients treated with 2 maxillary premolar extractions had greater initial occlusal TPI values, overjets, cephalometric apical base anteroposterior discrepancies, maxillary incisor protrusions, and anteroposterior molar discrepancies than those treated without extractions.

CONCLUSIONS

For patients with more severe anteroposterior discrepancies, an extraction plan provides more effective treatment with less need for patient compliance.

Morphology of the temporomandibular joint in subjects with Class II Division 2 malocclusions

INTRODUCTION

Temporomandibular joint (TMJ) morphology has not been studied adequately in subjects with various types of malocclusion, and it is not known if TMJ morphology and facial morphology are related. Such knowledge might assist in the establishment of biological treatment strategies, especially when the TMJ is the target of the treatment plan. The aim of this study was to explore the morphological characteristics of the TMJ in subjects with skeletal Class II Division 2 malocclusions.

METHODS

The material consisted of corrected lateral tomograms of 94 joints in 47 subjects with Class II Division 2 malocclusions (age range, 8.3-42.8 years). The subjects were divided into 5 groups according to age.

RESULTS

Intragroup comparisons showed statistically significant differences for condylar angle, condylar position, eminence height, eminence inclination, ramus height, and condylar-neck height. These differences were found mainly between the youngest and oldest groups. The Pearson correlation coefficient was greater than 0.60 for eminence height and eminence inclination, eminence height and ramus inclination, eminence inclination and ramus inclination, fossa posterior-eminence midpoint and fossa posterior-eminence top, and fossa posterior-eminence midpoint and fossa posterior-fossa roof. Condylar shape was most often round, followed by oval, flattened, and triangular; fossa shape was most often oval, followed by triangular, trapezoidal, and round.

CONCLUSIONS

The results suggest that (1) fossa morphology and condylar length attain their final sizes early; (2) articular eminence and ramus morphology (height, inclination) have great variability; (3) some joint components such as eminence height with eminence inclination, eminence height with ramus inclination, eminence inclination with ramus inclination, and fossa anteroposterior dimensions are highly correlated with each other; and (4) the most prevalent condylar and fossa anteroposterior shape is oval.

Clinical Application and Histological Examination of the FAMI Screw for Skeletal Anchorage—a Pilot Study*

Maximum anchorage often presents a problem that is difficult to solve during orthodontic tooth movement. Stationary, skeletal anchorage can be achieved in a simple, minimally-invasive manner, and unwanted tooth movements in opposite directions can be prevented by using transmucosally-inserted bone screws. Our initial experience using the FAMI screw as an orthodontic micro-implant proved to be clinically and histologically successful.

Tooth size discrepancies and arch parameters among different malocclusions in a Jordanian sample

The objectives of this study were to determine the mean mesiodistal tooth width of the dentition, Bolton anterior and overall ratios, arch length, and arch width in the different malocclusions in a Jordanian sample. The mesiodistal tooth width, arch width, and length were measured on a total of 140 orthodontic models of school students aged 13-15 years of different occlusal relationships (Class I, Class II division 1, Class II division 2, and Class III malocclusions). Anterior and overall Bolton ratios were calculated. The mean and standard deviation were calculated. Student's t-test and analysis of variance were used for the statistical analysis. The results show that (1) females have smaller teeth than males; (2) Class III malocclusion showed larger teeth than the rest of the other occlusal categories; (3) no statistically significant differences were found in Bolton ratios between the different malocclusions; (4) Class II division 1 showed the narrowest maxillary arch compared with the other types of malocclusion; (5) the mandibular intercanine width was significantly larger in Class III group than in Class II division 1 and Class II division 2 groups; (6) the maxillary arch was significantly longer in Class II division 1 than in Class II division 2; and (7) the mandibular arch of both Class II categories was significantly shorter than Class III malocclusion group. In conclusion, tooth size differences were found between right and left sides, between females and males, and between the different malocclusions. Arch width and length also showed differences among the different malocclusions.

A comparison of dental arch forms between Class II Division 1 and normal occlusion assessed by euclidean distance matrix analysis

INTRODUCTION

The purpose of the study was to use euclidean distance matrix analysis to compare dental arch forms between subjects with Class II Division 1 malocclusions and normal occlusions.

METHODS

The sample consisted of 60 subjects with Class II Division 1 malocclusions and 60 subjects with normal occlusions, all between 13 and 17 years of age. Fourteen landmarks, corresponding to cusp tips and incisor edges, were identified on the dental casts with a 3-dimensional measuring machine. All possible linear distances between pairs of landmarks in an arch were computed, and arch-form differences between Class II Division 1 and normal-occlusion subjects were tested by euclidean distance matrix analysis.

RESULTS

In both sexes, the maxillary arches of the Class II Division 1 subjects were larger than the arches of the normal-occlusion subjects (1.8% and 2.7% larger for girls and boys, respectively), and arch shape was also significantly different (P < .001). The posterior teeth contributed to the shape difference between 2 groups more than the anterior teeth, moreover the main factor was narrow maxillary posterior arch width in the Class II Division 1 subjects. The mandibular arches of the Class II Division 1 subjects were also slightly larger, and arch shape was not significantly different regardless of sex.

CONCLUSIONS

Expanding the maxillary posterior arch width in Class II Division 1 subjects might be an important method to harmonize maxillary and mandibular arch forms.

Dental and alveolar arch widths in normal occlusion, class II division 1 and class II division 2

The aim of this study was to compare the transverse dimensions of the dental arches and alveolar arches in the canine, premolar, and molar regions of Class II division 1 and Class II division 2 malocclusion groups with normal occlusion subjects. This study was performed using measurements on dental casts of 150 normal occlusion (mean age: 21.6 +/- 2.6 years), 106 Class II division 1 (mean age: 17.2 +/- 2.4 years), and 108 Class II division 2 (mean age: 18.5 +/- 2.9 years) malocclusion subjects. Independent-samples t-test was applied for comparisons of the groups. These findings indicate that the maxillary interpremolar width, maxillary canine, premolar and molar alveolar widths, and mandibular premolar and molar alveolar widths were significantly narrower in subjects with Class II division 1 malocclusion than in the normal occlusion sample. The maxillary interpremolar width, canine and premolar alveolar widths, and all mandibular alveolar widths were significantly narrower in the Class II division 2 group than in the normal occlusion sample. The mandibular intercanine and interpremolar widths were narrower and the maxillary intermolar width measurement was larger in the Class II division 2 subjects when compared with the Class II division 1 subjects. Maxillary molar teeth in subjects with Class II division 1 malocclusions tend to incline to the buccal to compensate the insufficient alveolar base. For that reason, rapid maxillary expansion rather than slow expansion may be considered before or during the treatment of Class II division 1 patients.

Uvulo-glosso-pharyngeal dimensions in different anteroposterior skeletal patterns

The aim of this study was to investigate the uvulo-glosso-pharyngeal dimensions in subjects with different anteroposterior jaw relationship. Cephalometric radiograph of 90 subjects (45 females and 45 males, aged 14-17 years) were divided into three groups according to the ANB angle, ie, group 1, skeletal Class I (ANB angle 1-5); group 2, skeletal Class II (ANB angle >5); and group 3, skeletal Class III (ANB angle <1). In addition, each group was divided into two subgroups according to sex. Statistical analysis was undertaken using analysis of variance and least significant difference test. Pearson's Correlation test was also performed. Sex differences were found in Class I and III subjects. No sex differences were detected in Class II subjects. On average, tongue length was significantly shorter in Class III subjects (P < .05), tongue height was reduced in Class II female subjects, the soft palate was thicker in Class III females and the vertical airway length (VAL) was reduced in Class II male subjects (P < .01). In Class II subjects, the hyoid bone was closer to the mandible vertically and to C3 horizontally compared with Class I (P < .01) and Class III (P < .001) male subjects. Anteroposterior skeletal pattern showed a weak, but significant correlation with inferior pharyngeal airway space (R = -0.24, P = .024), vertical position of hyoid bone in relation to mandibular plane (R = -0.26, P = .014), and anteroposterior position of hyoid bone in relation to C3 (R = -0.561, P = .000). In conclusion, uvulo-glosso-pharyngeal dimensions are affected by anteroposterior skeletal pattern.

Class II malocclusion with maxillary protrusion from the deciduous through the mixed dentition: a longitudinal study

The aim of this study was to analyze the skeletal characteristics of Class II malocclusion with maxillary protrusion in the deciduous dentition and to describe the growth features of this type of skeletal imbalance during the transition from the deciduous through the mixed dentition. A group of 17 subjects having skeletal Class II malocclusions in the deciduous dentition due to maxillary protrusion was compared with a control group of 30 untreated subjects with ideal occlusion at the same stage of development. Both groups were observed for the first time in the deciduous dentition (T(1)) and followed during the transition from the deciduous to the mixed dentition (T(2)). During this time no orthodontic treatment was provided. Lateral cephalograms were taken for all subjects at T(1) and T(2). A cephalometric analysis was performed based on a reference system that consisted of two perpendicular lines traced through stable basicranical structures. The results indicate that a Class II skeletal pattern due to a maxillary protrusion is established early in the deciduous dentition and remains unmodified in the transition to the mixed dentition. The maxilla appeared to be displaced forward in Class II subjects, whereas the mandibles of the Class I and Class II subjects did not show any significant differences at this stage of growth. In the passage from the deciduous through the mixed dentition, Class I and Class II subjects showed growth increments that were not significantly different from each other. Sucking habits appeared to be correlated with the skeletal maxillary protrusion.

A morphological study of the relationship between arch dimensions and craniofacial structures in adolescents with Class II Division 1 malocclusions and various facial types

INTRODUCTION

The objective of this study was to evaluate dental arch forms associated with various facial types in adolescents with Class II Division 1 malocclusions by using mathematical functions to describe the arch form at clinical bracket points.

METHODS

Pretreatment lateral cephalograms and dental study casts of 73 white Brazilians were divided into 3 groups according to facial type: 17 brachyfacial, 24 mesofacial, and 32 dolichofacial. Fifteen landmarks on each dental cast were digitized. Computer-generated mathematical arch forms (fourth-degree polynomial equation and beta function) were used to evaluate arch form differences by superimposition.

RESULTS

The constant term related to dental arch depth of the brachyfacial subjects was significantly greater than that of the mesofacial subjects in the maxillary arch (P = .004). Superimposition of maxillary arch analysis showed that the posterior segment width of the mathematically computed arch form tended to increase from dolichofacial type to brachyfacial type. The arch forms drawn by the 2 equations coincided at the incisal and molar regions.

CONCLUSIONS

The beta function is appropriate for predicting the finishing arch form, and the polynomial equation is appropriate for the analysis (diagnosis) of various Class II malocclusions, including ovoid, tapered, and square arch forms and dental arch asymmetry.

Short- and long-term skeletal relapse after mandibular advancement surgery

This study analyzes short- and long-term skeletal relapse after mandibular advancement surgery and determines its contributing factors. Thirty-two consecutive patients were treated for skeletal Class II malocclusion during the period between 1986 and 1989. They all had combined orthodontic and surgical treatment with BSSO and rigid fixation excluding other surgery. Of these, 15 patients (47%) were available for a long-term cephalography in 2000. The measurement was performed based on the serial cephalograms taken preoperatively; 1 week, 6 months and 14 months postoperatively; and at the final evaluation after an average of 12 years. Mean mandibular advancement was 4.1 mm at B-point and 4.9 mm at pogonion. Representing surgical mandibular ramus displacement, gonion moved downwards 2 mm immediately after surgery. During the short-term postoperative period, mandibular corpus length decreased only 0.5 mm, indicating that there was no osteotomy slippage. After the first year of observation, skeletal relapse was 1.3 mm at B-point and pogonion. The relapse continued, reaching a total of 2.3 mm after 12 years, corresponding to 50% of the mandibular advancement. Mandibular ramus length continuously decreased 1 mm during the same observation period, indicating progressive condylar resorption. No significant relationship between the amount of initial surgical advancement and skeletal relapse was found. Preoperative high mandibulo-nasal plane (ML-NL) angle appears to be associated with long-term skeletal relapse.

Midfacial and mandibular morphometry of children with Class II and Class III malocclusions

There is insufficient evidence in conventional cephalometric analysis of the actual sites of putative maxillofacial change in Class II and Class III malocclusions. The purpose of this study was to provide more information about the morphological characteristics of the midfacial complex and mandible in children with Class II or III malocclusions. Seventy children with Class II, division 1 malocclusion and 70 children with Class III malocclusion were compared with 70 children with normal occlusion. This study was conducted to carry out geometric morphometric assessments to localize alterations using Procrustes analysis and thin-plate spline analysis. Procrustes analysis indicated the midfacial and mandibular morphologies differed between normal occlusion subjects and subjects with Class II or Class III malocclusion (P<0.0001). The deformations in subjects with Class II malocclusion may represent a developmental elongation of the palatomaxillary complex and a shortening of the mandible anteroposteriorly, which leads to the appearance of a protruding midface and retruding mandibular profile. In contrast, the deformations in subjects with Class III malocclusion may represent a developmental shortening of the palatomaxillary complex and elongation of the mandible anteroposteriorly, which leads to the appearance of a retrognathic midface and prognathic mandibular profile.