Mandibular remodeling measured on cephalograms. 1. Osseous changes relative to superimposition on metallic implants

An open-source, three-dimensional growth model of the mandible

The available reference data for the mandible and mandibular growth consists primarily of two-dimensional linear or angular measurements. The aim of this study was to create the first open-source, three-dimensional statistical shape model of the mandible that spans the complete growth period. Computed tomography scans of 678 mandibles from children and young adults between 0 and 22 years old were included in the model. The mandibles were segmented using a semi-automatic or automatic (artificial intelligence-based) segmentation method. Point correspondence among the samples was achieved by rigid registration, followed by non-rigid registration of a symmetrical template onto each sample. The registration process was validated with adequate results. Principal component analysis was used to gain insight in the variation within the dataset and to investigate age-related changes and sexual dimorphism. The presented growth model is accessible globally and free-of-charge for scientists, physicians and forensic investigators for any kind of purpose deemed suitable. The versatility of the model opens up new possibilities in the fields of oral and maxillofacial surgery, forensic sciences or biological anthropology. In clinical settings, the model may aid diagnostic decision-making, treatment planning and treatment evaluation.

Short- and Long-Term Prediction of the Post-Pubertal Mandibular Length and Y-Axis in Females Utilizing Machine Learning

The aim of this study was to create a novel machine learning (ML) algorithm for predicting the post-pubertal mandibular length and Y-axis in females. Cephalometric data from 176 females with Angle Class I occlusion were used to train and test seven ML algorithms. For all ML methods tested, the mean absolute errors (MAEs) for the 2-year prediction ranged from 2.78 to 5.40 mm and 0.88 to 1.48 degrees, respectively. For the 4-year prediction, MAEs of mandibular length and Y-axis ranged from 3.21 to 4.00 mm and 1.19 to 5.12 degrees, respectively. The most predictive factors for post-pubertal mandibular length were mandibular length at previous timepoints, age, sagittal positions of the maxillary and mandibular skeletal bases, mandibular plane angle, and anterior and posterior face heights. The most predictive factors for post-pubertal Y-axis were Y-axis at previous timepoints, mandibular plane angle, and sagittal positions of the maxillary and mandibular skeletal bases. ML methods were identified as capable of predicting mandibular length within 3 mm and Y-axis within 1 degree. Compared to each other, all of the ML algorithms were similarly accurate, with the exception of multilayer perceptron regressor.

Sagittal and Vertical Growth of the Maxillo-Mandibular Complex in Untreated Children: A Longitudinal Study on Lateral Cephalograms Derived from Cone Beam Computed Tomography

The aim of this longitudinal study was to evaluate the sagittal and vertical growth of the maxillo–mandibular complex in untreated children using orthogonal lateral cephalograms compressed from cone beam computed tomography (CBCT). Two sets of scans, on 12 males (mean 8.75 years at T1, and 11.52 years at T2) and 18 females (mean 9.09 years at T1, and 10.80 years at T2), were analyzed using Dolphin 3D imaging. The displacements of the landmarks and rotations of both jaws relative to the cranial base were measured using the cranial base, and the maxillary and mandibular core lines. From T1 to T2, relative to the cranial base, the nasion, orbitale, A-point, and B-point moved anteriorly and inferiorly. The porion moved posteriorly and inferiorly. The ANB and mandibular plane angle decreased. All but one subject had forward rotation in reference to the cranial base. The maxillary and mandibular superimpositions showed no sagittal change on the A-point and B-point. The U6 and U1 erupted at 0.94 and 1.01 mm/year (males) and 0.82 and 0.95 mm/year (females), respectively. The L6 and L1 erupted at 0.66 and 0.88 mm/year (males), and at 0.41 mm/year for both the L6 and the L1 (females), respectively.

A three-dimensional statistical shape model of the growing mandible

Mandibular growth and morphology are important topics in the field of oral and maxillofacial surgery. For diagnostic and planning purposes, a normative database or statistical shape model of the growing mandible can be of great benefit. A collection of 874 cadaveric children’s mandibles with dental age between 1 and 12 years old were digitized using computed tomography scanning and reconstructed to three-dimensional models. Point correspondence was achieved using iterative closest point and coherent point drift algorithms. Principal component analysis (PCA) was applied to find the main modes of variation in the data set. The average mandible was presented, along with the first ten PCA modes. The first mode explained 78% of the total variance; combining the first ten modes accumulated to 95% of the total variance. The first mode was strongly correlated with age and hence, with natural growth. This is the largest study on three-dimensional mandibular shape and development conducted thus far. The main limitation is that the samples lack information such as gender and cause of death. Clinical application of the model first requires validation with contemporary samples.

A comparison of 2- and 3-dimensional mandibular superimposition techniques against Björk's structural superimposition method

INTRODUCTION

The purpose of this research was to compare mandibular growth rotation relative to the cranial base in different vertical facial patterns on the basis of multiple 2-dimensional (2D) and 3-dimensional (3D) superimposition methods.

METHODS

Cone-beam computed tomography (CBCT) images taken at a mean interval of 54.8 ± 16.8 months were assessed from a sample of 70 growing patients. Three mandibular superimposition methods were compared against Björk's structural method: (1) a 2D landmark method (2D-M1), (2) a voxel-based 3D method based on a previously reported method (3D-M1), and (3) a voxel-based 3D method incorporating symphyseal structures as references (3D-M2). After superimposition, the relative change in cranial base lines as depicted in sagittal views were measured for true mandibular rotation. Agreement between methods was assessed with Lin's concordance correlation coefficient, Bland-Altman's limits of agreement, and the Bradley-Blackwood test.

RESULTS

Lin's concordance correlation coefficients ranged between 0.924 for the 2D-M1 method, 0.695 for the 3D-M1 method, and 0.965 for the 3D-M2 method. Bland-Altman limits of agreement were wide for all but the 3D-M2 method. Finally, the Bradley-Blackwood test of equality of means and variances was significant in all except the 3D-M2 method.

CONCLUSIONS

For time intervals between CBCT volume acquisitions >3 years, the use of the 2D-M1 and 3D-M1 methods is not recommended. There was a high concordance between the 3D-M2 method and Björk's structural method when assessing mandibular growth rotation using relative changes in cranial base lines. The high concordance was displayed across all vertical facial types and for all time differences between first and second CBCT data acquisitions.

Nasomaxillary and mandibular bone growth in primary school girls aged 7 to 12 years

Background/purpose

Facial bone growth manifests in primary school-aged children, especially girls. This study investigated the changes in nasomaxillary and mandibular morphology of primary school girls.

Materials and methods

Cephalograms of 60 primary school girls were divided into 3 groups (group I, aged 7–8 years; group II, aged 9–10 years; and group III, aged 11–12 years). The dimensions of the nasomaxilla (nasal bone length, nasal ridge length, nasal depth, palatal length, and maxillary height) and mandible (condylar length, condylar width, coronoid length, coronoid width, ramus length, body length, symphysis length, and entire mandibular length) were measured. One-way ANOVA and Pearson's correlation coefficient were used for statistical analysis.

Results

Nasal ridge length, nasal depth, and maxillary height were significantly greater in group III than in group I and group II. Condylar width and body length were significantly greater in group III than in group I and group II. Pearson's correlation revealed significant positive correlations between age and nasal ridge length, nasal depth, or maxillary height. There were also significant positive correlations between age and ramus length, body length, or entire length of the mandible.

Conclusion

We found that nasal ridge length, nasal depth, maxillary height, condylar width and body length were significantly greater in group III than in group I or in group II. Moreover, there were significant correlations between age and the nasal ridge length, nasal depth, maxillary height, ramus length, body length, or entire length of the mandible.

Posteroanterior cephalometric analysis of White-American and Chinese adolescents: a cross-sectional study

Objective: To characterize ethnic differences between Chinese and White-Americans between 8.5 and 17.5 years of age, with respect to transverse cephalometric characteristics and to establish transverse craniofacial normative values for Chinese adolescents. Methods: Two-hundred fifty-seven and 547 posteroanterior cephalograms were selected from 35 White-Americans and 157 Chinese with individual normal occlusions. Transverse measurements were obtained and compared between ethnicities to guide determination of normative values for Chinese adolescents. Student's t-test or one-way analysis of variance was used, as appropriate. Results: Chinese girls demonstrated significantly larger measurements than White-American girls at all ages, with the exception of nasal width. Chinese boys exhibited larger measurements than White-American boys at different ages. Chinese boys had larger measurements than girls for most measurements. These data established normative values for Chinese adolescents. Discussion: Ethnic differences existed between Chinese and White-American adolescents with respect to transverse craniofacial measurements. Transverse normative values were established for Chinese adolescents.

Treatment changes of hypo- and hyperdivergent Class II Herbst patients

OBJECTIVES

To determine the relative effects of Herbst appliance therapy in hypo- and hyperdivergent patients.

MATERIALS AND METHODS

The treated group included 45 growing Class II, division 1, patients treated with stainless steel crown Herbst appliances, followed by fixed edgewise appliances. The untreated control group consisted of 45 Class II, division 1, subjects, matched to the treated sample based on Angle classification, age, sex, and pretreatment mandibular plane angle (MPA). Subjects were categorized as hypo- or hyperdivergent based on their MPAs. Pre- and posttreatment cephalograms were traced and superimposed on cranial base and mandibular structures.

RESULTS

The primary effect of the Herbst in terms of maxillomandibular correction was in the maxilla. It significantly restricted maxillary growth, producing a "headgear effect." Mandibular treatment changes depended on divergence. Hyperdivergent patients experienced a deleterious backward true mandibular rotation with Herbst treatment. Hypodivergent patients, as well as untreated hypo- and hyperdivergent controls, underwent forward true mandibular rotation. However, hypodivergent chins did not advance any more than expected for untreated hypodivergent Class II patients.

CONCLUSIONS

Hypo- and hyperdivergent patients benefit from the Herbst's headgear effect. While the mandibular growth of hypodivergent patients overcomes the negative rotational effects, hyperdivergent patients undergo a deleterious backward mandibular rotation and increases in facial height.

Assessing lower incisor inclination change: a comparison of four cephalometric methods

OBJECTIVE

Cephalometric inclination change of the lower incisors during orthodontics is used to assess treatment outcome. The lower border of the mandible is commonly used for measuring inclination change, despite it being subject to remodelling in growing patients. Superimposition of radiographs using Björk's 'stable structures' is intended to exclude these growth changes. We tested whether there is a significant difference for three commonly used methods to assess inclination change induced by orthodontic treatment (Me-Go, Go-Gn, the tangent to the lower border of the mandible) when comparing it to Björk's 'stable structures'.

METHODS

Björk's superimposition does not allow measuring incisor inclination changes directly; hence, one pre- and mid-treatment cephalogram of 39 growing orthodontic patients were superimposed in this retrospective study. The radiographs were taken at least 1 year apart (120 weeks; SD = 34.4). Patients undergoing growth modification treatment were excluded. Standardized cephalograms were hand traced and changes in lower incisor inclination, using the three mandibular planes, were compared to the changes obtained by anatomical superimposition of Björk's 'stable structures'.

RESULTS

Linear regression showed good intra-class correlation (ICC) between all methods. ICC was 0.96 for Me-Go, 0.94 for Go-Gn, and 0.92 for the lower border tangent. ICC for operator reliability was 0.99.

LIMITATIONS

Measurement errors affect all investigations of both analogue and digital radiographs, but movement artefacts particularly apply to the latter. Cephalometry uses two-dimensional measurements of a three-dimensional subject, which can lead to further inaccuracies. These limitations have to be taken into account when interpreting the results of our investigation.

CONCLUSION

Data obtained from Björk's superimposition did not vary significantly from the other more commonly used techniques (Me-Go, Go-Gn, and the tangent to the lower border of the mandible). Remodelling of the lower border of the mandible was insignificant for the time period investigated.

Mandibular growth comparisons of Class I and Class II division 1 skeletofacial patterns

OBJECTIVE

To determine class and sex differences in mandibular growth and modeling.

MATERIALS AND METHODS

A mixed-longitudinal sample of 130 untreated French-Canadian adolescents, 77 (45 boys and 32 girls) with Class I (normal or abnormal) occlusion and 53 (26 boys and 27 girls) with Class II division 1 malocclusion, was used. Based on eight landmarks, eight traditional measurements were used to compare the anteroposterior position of the maxilla and mandible, relationship between the jaws, and mandibular size. Mandibular superimpositions were used to compare the horizontal and vertical changes of condylion, gonion, and menton.

RESULTS

While there were no differences in maxillary position based on the SNA angle, Class IIs had more retrognathic mandibles than did Class Is. Total mandibular length was greater in Class Is than in Class IIs at 15 years of age. Superior and total growth and modeling changes at condylion and gonion, respectively, were greater for Class Is than Class IIs. Boys were more prognathic than girls; they had larger mandibles and exhibited greater size increases and growth changes than girls did.

CONCLUSIONS

There are both class and sex differences in mandibular growth and modeling.

3D assessment of mandibular growth based on image registration: a feasibility study in a rabbit model

Background. Our knowledge of mandibular growth mostly derives from cephalometric radiography, which has inherent limitations due to the two-dimensional (2D) nature of measurement. Objective. To assess 3D morphological changes occurring during growth in a rabbit mandible. Methods. Serial cone-beam computerised tomographic (CBCT) images were made of two New Zealand white rabbits, at baseline and eight weeks after surgical implantation of 1 mm diameter metallic spheres as fiducial markers. A third animal acted as an unoperated (no implant) control. CBCT images were segmented and registered in 3D (Implant Superimposition and Procrustes Method), and the remodelling pattern described used color maps. Registration accuracy was quantified by the maximal of the mean minimum distances and by the Hausdorff distance. Results. The mean error for image registration was 0.37 mm and never exceeded 1 mm. The implant-based superimposition showed most remodelling occurred at the mandibular ramus, with bone apposition posteriorly and vertical growth at the condyle. Conclusion. We propose a method to quantitatively describe bone remodelling in three dimensions, based on the use of bone implants as fiducial markers and CBCT as imaging modality. The method is feasible and represents a promising approach for experimental studies by comparing baseline growth patterns and testing the effects of growth-modification treatments.

The inclination of mandibular incisors revisited

OBJECTIVE

To reassess the inclination of lower incisors and evaluate possible associations with gender, age, symphyseal parameters, and skeletal pattern.

MATERIALS AND METHODS

Twelve hundred and seventy-two (605 females, 667 males) cephalograms of untreated subjects of a craniofacial growth study (age: 8-16 years) were evaluated. Correlations between the angulation of the lower incisors and age, symphyseal distances (height, width, and depth), symphyseal ratios (height-width, height-depth), and skeletal angles (divergence of the jaws and gonial angle) were investigated for all ages separately and for both sexes independently.

RESULTS

The inclination of lower incisors increased over age (8 years: girls = 93.9° [95% CI, 92.3°-95.7°], boys = 93.3° [95% CI, 91.8°-94.9°]; 16 years: girls = 96.1° [95% CI, 94.1°-98.2°], boys = 97.1° [95% CI, 95.6°-98.6°]). Inclination of lower incisors correlated with the divergence of the jaws for all ages significantly or highly significantly, except for boys and girls 9 years of age and girls 11 and 12 years of age, for which only a tendency was observed. Similarly, a strong correlation to gonial angle could be observed. No correlation could be found between the inclination of lower incisors and any symphyseal parameters (absolute measurements and ratios), except for symphyseal depth.

CONCLUSION

Lower incisor inclination is linked to the subject's sex, age, and skeletal pattern. It is not associated with symphyseal dimensions, except symphyseal depth. Factors related to natural inclination of lower incisors should be respected when establishing a treatment plan.

Female adolescent craniofacial growth spurts: real or fiction?

The purpose of the study is to determine whether the various aspects of the craniofacial complex exhibit female adolescent growth spurts. Multilevel polynomial models were used to estimate the growth curves of a mixed-longitudinal sample of 111 untreated females 10-15 years of age. To evaluate the horizontal and vertical movements of the individual landmarks relative to stable structures, the tracings were superimposed on the natural reference structures in the anterior cranial base. The horizontal and vertical growth changes of four landmarks and the changes of three traditional linear measurements were evaluated. Posterior nasal spine (PNS) moved posteriorly at a constant rate of approximately 0.12mm/year. Five measures showed changes in growth velocity (i.e. quadratic growth curves) but not adolescent growth spurts, including the anterior movements of anterior nasal spine (ANS) and pogonion (Pg), the inferior movements of gonion (Go), and the increases in ANS-PNS and condylion to pogonion (Co-Pg). Five measurements, including the inferior movements of ANS, PNS and Pg, the posterior movements of Go, and the increases of Go-Pg exhibited adolescent growth spurts. Peak growth velocities were attained between 11.4 and 12.8 years of age, approximately 0.7-1.4 years earlier in the maxilla than mandible. While the vertical aspects of craniofacial growth exhibit distinct female adolescent growth spurts, with peak rates occurring earlier in the maxilla than mandible, most horizontal aspects of craniofacial growth do not exhibit an adolescent spurt.

Evaluation of extraction and non-extraction treatment effects by two different superimposition methods

The aim of this study was to determine whether different evaluation methods may be the cause of the varied outcomes of research that have evaluated the effects of extraction and non-extraction therapy on jaw rotation. This retrospective study consisted of the pre- (T1) and post- (T2) treatment lateral cephalograms of 70 skeletal Class I subjects with an optimal vertical mandibular plane angle, who had undergone fixed orthodontic treatment. Thirty-five of the subjects (20 females and 15 males, mean age: 14.7 years) were treated with four first premolar extractions and 35 (22 females and 13 males, mean age: 15 years) without extractions. T1 and T2 radiographs were superimposed using Björk's structural method and Steiner's method of sella-nasion line registered at sella. A Wilcoxon test was used to evaluate the changes between T1 and T2 and the Mann-Whitney U-test to determine differences between the extraction and non-extraction and Björk and Steiner groups. No significant difference was found between the methods of Steiner and Björk according to the spatial changes of the cephalometric points in the extraction and non-extraction groups. The maxilla showed forward rotation in the extraction group and backward rotation in the non-extraction group with both superimposition methods, but the differences were not significant in either inter- or intraclass comparisons. The mandible showed forward rotation in the extraction group with both superimposition methods but, in the non-extraction group, forward rotation was recorded with Björk's method and backward rotation with Steiner's method. These findings were not significant in either inter- or intraclass evaluations. No significant difference was found between the groups or methods.

Mandibular growth, remodeling, and maturation during infancy and early childhood

OBJECTIVE

To describe the growth, maturation, and remodeling changes of the mandible during infancy and early childhood.

MATERIALS AND METHODS

Seven Bolton-Brush Growth Study longitudinal cephalograms (N = 336) of each of 24 females and 24 males, taken between birth and 5 years of age, as well as early adulthood, were traced and digitized. Five measurements and nine landmarks were used to characterize mandibular growth, remodeling, and degree of adult maturity.

RESULTS

Overall, mandibular length showed the greatest growth changes, followed by ramus height and corpus length. Corpus length was the most mature of the three linear measures; ramus height was less mature than overall mandibular length. The greatest growth rates occurred between 0.4-1 year; yearly velocities decelerated thereafter. The ramus remodeled superiorly only slightly more than it remodeled posteriorly. Male mandibles were significantly (P < or = .05) larger, displayed greater growth rates, and were significantly less mature than female mandibles. There were no significant differences in mandibular growth or maturation between Class I and Class II patients.

CONCLUSIONS

The mandible displays decelerating rates of growth and a maturity gradient during infancy and early childhood, with males showing more growth and being more mature than females.

Age-dependant cephalometric standards as determined by multilevel modeling

INTRODUCTION

The purpose of this study was to evaluate the feasibility of constructing age-dependant cephalometric standards for white subjects by using 3 data sets.

METHODS

The data sets were the samples from the Fels Longitudinal Study (United States), the Michigan Growth Study (United States), and the Nijmegen Growth Study (The Netherlands). The 3 mixed-longitudinal samples provided data for 218 girls and 231 boys between 9 and 14 years of age and were compared based on 4 cephalometric angles: SNA, SNB, ANB, and SN/GoMe. Curve-fitting and statistical comparisons were performed with multilevel modeling procedures.

RESULTS

All 4 angles showed linear changes over time. SNA and SNB increased, whereas ANB and SN/GoMe decreased. Based on paired-sample comparisons, the samples displayed statistically significant (P <0.05) differences for 50% of the growth velocities and 8% to 17% of the intercepts (size of the angle at 11 years). The SNA and SNB angles showed small and inconsistent differences across the samples. The ANB angle for the Fels boys decreased less than in the other 2 samples. The Nijmegen and Fels girls had the greatest and the least decreases, respectively, in the SN/GoMe angle. Most sample differences decreased over time.

CONCLUSIONS

Based on the growth differences identified, we concluded that sagittal and vertical jaw relationships have different patterns of growth in different samples of white subjects; indiscriminate pooling of data, to create age-dependant cephalometric standards for white subjects is not recommended.

Mandibular Growth Changes and Cervical Vertebral Maturation

Objective: To evaluate mandibular dimensional changes and regional remodeling occurring during five intervals of circumpubertal growth.

Materials and Methods: This investigation evaluated a unique sample of subjects in whom tantalum implants were placed into the craniofacial complex during childhood. The sample was obtained from the Mathews and Ware implant study originally conducted at the University of California San Francisco in the 1970s, with longitudinal cephalometric records of 20 subjects (13 female, 7 male) available for evaluation. Cephalograms at six consecutive stages of cervical vertebral maturation (CS1 through CS6) were analyzed.

Results: Peak mandibular growth was noted during the interval from CS3 to CS4. Forward rotation of the mandible was due to greater mandibular growth posteriorly than anteriorly. Progressive closure of the condylar-ramus-occlusal (CRO) angle resulted in a forward and upward orientation of the ramus relative to the corpus of the mandible due to increased vertical growth of the condyle.

Conclusions: A peak in mandibular growth at puberty was substantiated. Mandibular remodeling and condylar rotation continue to occur after the growth spurt.

Nasomaxillary remodeling and facial form in robust Australopithecus: a reassessment

In a previous study of the patterns of facial growth remodeling characteristic of early hominid taxa, Bromage (1989) demonstrated that the nasoalveolar clivus of A. robustus was resorptive throughout ontogeny. Based upon the remodeling information provided by small samples (n=6 each) of chimpanzees and modern humans, he concluded that the clival resorption pattern characteristic of robust Australopithecus differed significantly from that of chimpanzees and was instead somewhat convergent upon that of modern humans, in that it served to emphasize a downward facial growth vector. The present study used the SEM/replica technique to assess nasomaxillary remodeling in larger, more age-varied samples of chimpanzee (n=33) and modern human crania (n=22). Results indicate far more intraspecific variability in nasomaxillary remodeling than suggested by Bromage's earlier study. In particular, results from an expanded sample demonstrate that the nasoalveolar clivus of chimpanzees is frequently resorptive, especially at later stages of ontogeny. However, the pattern of clival remodeling observed in chimpanzees is unlike that typical of robust Australopithecus, in which clival resorption occurs throughout ontogeny and in expansive fields that cover the entire clival surface. Although Bromage (1989) considered the pattern of nasomaxillary remodeling observed in robust Australopithecus to have been a byproduct of an extreme maxillary growth rotation, the failure of A. africanus to display a similar pattern suggests that some other factor(s) may have been involved. Regardless, it is unlikely that clival resorption in robust Australopithecus would have significantly impacted the overall vector of facial growth. Instead, the primary morphogenetic effect of this pattern of clival resorption would have been one of local surface sculpting.

Proportional Analysis of Longitudinal Craniofacial Growth Using Modified Mesh Diagrams

Objective: To study the craniofacial changes of adolescents followed longitudinally with their heads oriented in natural head position.

Materials and Methods: Longitudinal cephalograms of adolescents (n = 28) with normal occlusion, selected from among 900 candidates, were taken at 13 and again at 18 years of age. Modified elaborate mesh diagrams were developed defined by 90 anatomic landmarks and an additional 172 interpolated points for each cephalogram using a preset computer program. Detailed proportional and disproportional craniofacial changes were showed by both statistical and graphical methods.

Results: In females, most craniofacial regions exhibited growth that was proportionate to the mesh core rectangle reference on extracranial true vertical. In males, there was an upward, disproportional enhanced shift of the anterior cranial base and a downward enhanced shift of the mandibular symphysis and inferior border of the corpus.

Conclusions: This elaborate mesh analysis, based on mesh core rectangle and referenced on estimated natural head position, provides a novel graphical as well as quantitative method of assessing craniofacial growth. From 13 to 18 years of age, two sexes with normal occlusion displayed different growth patterns referenced on estimated natural head position. In females, most craniofacial regions exhibited growth proportional to the mesh core rectangle. In males, there was an upward, enhanced shift of the anterior cranial base and a downward enhanced shift of the mandibular symphysis and inferior border of the corpus.

Orthodontic treatment changes of chin position in Class II Division 1 patients

INTRODUCTION

Because most patients with skeletal Class II malocclusions also have mandibular deficiencies, treatment plans should include improvement in chin projection. On that basis, the purposes of this study were to (1) determine how Class II treatment affects anteroposterior (AP) chin position in growing subjects and (2) ascertain the most important determinants of AP chin position.

METHODS

Pretreatment and posttreatment lateral cephalograms of 67 treated patients (25 extraction headgear and Class II elastics, 23 nonextraction headgear, and 19 Herbst) were collected, traced, and digitized. The average pretreatment age was 12.2 years (range, 9-14 years), and the average treatment duration was 30.2 months (range, 17-65 months). Cephalometric changes were compared with 29 matched untreated Class II controls. Mandibular superimpositions were used to evaluate condylar growth and true mandibular rotation.

RESULTS

All 3 treatment methods produced normal dental relationships and restricted or inhibited AP maxillary growth, with no significant improvement of AP chin position. Differences between changes in vertical position of the maxilla, maxillary and mandibular molars, and condylar growth could not reliably predict changes in chin position. Analyses demonstrated that true mandibular rotation was the primary determinant of AP chin position. Stepwise multiple regression showed that, combined with true mandibular rotation, condylar growth and movements of the glenoid fossa accounted for 81% of the variation in AP changes of pogonion.

CONCLUSIONS

Contemporary treatments do not adequately address mandibular deficiencies. Future treatments must incorporate true mandibular rotation into Class II skeletal correction.

Mandibular Remodeling After Bilateral Sagittal Split Osteotomy for Prognathism of the Mandible

PURPOSE

To describe the postoperative remodeling changes in the mandible after bilateral sagittal split osteotomy to correct mandibular prognathism.

PATIENTS AND METHODS

Twenty patients who underwent bilateral sagittal split osteotomy for the correction of mandibular prognathism were studied for postoperative remodeling changes within the mandible. The 6-week, 1-year, and long-term postoperative cephalometric mandibular tracings of 12 patients were superimposed using the fixation wires as the stable reference points to demonstrate the specific locations of the intrabony remodeling.

RESULTS

There was a general direction of remodeling at the condylion and gonion anteriorly and superiorly, while the B point and pogonion did not show much change in remodeling. At the condylion, 60% and 40% of the cases showed significant horizontal and vertical remodeling, respectively. At the gonion, 50% and 55% of the cases showed significant horizontal and vertical remodeling, respectively. No correlation was found between the remodeling changes at condylion and gonion and the surgical movement or relapse at B point and pogonion. There was a significant correlation between the observed horizontal relapse at gonion and the horizontal remodeling changes at this point showing that the postoperative displacement of this point is a result of both positional translocation and remodeling changes.

CONCLUSION

The results of this study show that there are intrabony remodeling changes that occur in the mandible after sagittal split osteotomy and that these continue for a long period of time in some patients. This remodeling occurred more in the condylar and gonial areas, while the chin remained relatively stable.

Identification of temporal pattern of mandibular condylar growth: a molecular and biochemical experiment

OBJECTIVES

Based on the phenomenon that expression of type X collagen and capillary endothelium correlates with endochondral ossification, the prime aim of this study was to establish the temporal pattern of condylar growth in Sprague-Dawley rats by biochemically identifying the expression of these two factors.

DESIGN

Sprague-Dawley rats were divided into five groups representing five different stages during somatic pubertal growth. In situ hybridization and immunoperoxidase were performed to examine expression of type X collagen in hypertrophic zone and capillary endothelium in erosive zone of condylar cartilage. Computer-assisted imaging analyses were conducted to allow for a quantitative assessment of the expression of these two factors, from which the temporal pattern of condylar growth was inferred.

RESULTS

(1) Synthesis of type X collagen and emergence of capillary endothelium were critical factors during the transition of condylar cartilage from chondrogenesis into osteogenesis, a biological pathway that leads to endochondral bone formation, the mode through which the condyle grows. (2) Quantitative analyses revealed the temporal pattern of the expression of these two factors, indicating that the thrust of natural growth of the condyle in the rats occurred in concomitance with somatic pubertal growth, featured by an acceleration starting from day 38, a maximum growth rate on day 56, followed by a decrease afterwards.

CONCLUSION

It is suggested that the biochemical examination of growth markers, such as type X collagen, might be a new approach to accurately depict temporal pattern of condylar growth which is too delicate to be reflected by gross measurement not only in Sprague-Dawley rats but potentially also in other species.

The validity of superimposing oblique cephalometric radiographs to assess tooth movement: an implant study

Assessment of the exact position of the posterior teeth on lateral headfilms is of limited validity because of the superimposition of the 2 sides. Lateral headfilms are also of limited use for evaluating orthodontic tooth movement, especially in cases of asymmetric mechanics. To solve this problem, the oblique cephalometric radiograph, which brings only 1 side of the image into focus, was introduced. We evaluated whether the projection of the cranial base could be used for evaluating facial growth and whether structures that were stable relative to the implants could be identified and thus replace the implants in future evaluations. Thirty sets of headfilms from growing patients with metallic implants were analyzed. Three types of superimpositions were performed. Displacement of the metallic implants in the maxillary complex and the mandible with respect to the superimposed structures of the cranial base was evaluated. When the development of the lateral parts of the facial skeleton was evaluated in relation to the cranial base, the reproducibility of the superimpositioning was significantly better in the vertical-S(e) = 0.41-than in the horizontal plane of space-S(e) = 1.35). The error of the method when superimposed on the stable structures in the maxillary complex varied between 0.31 and 0.72 and did not differ in the vertical and sagittal directions. In the mandible, the stable structures suggested for superimposition of the lateral headfilms were applicable on the oblique cephalometric radiograph-S(e) = 0.33-0.57. Oblique projection is recommended when individual analysis of the 2 sides is needed.

Postsurgical growth changes in the mandible of adolescents with vertical maxillary excess growth pattern

This case-control study investigates the effects of superior maxillary repositioning by LeFort I osteotomy on adolescent mandibular growth. A total of 15 growing patients (average age, 12.8 years) with vertical maxillary excess who had undergone maxillary surgery were compared with matched untreated control subjects. Lateral cephalograms were evaluated and superimposed to describe the presurgical (1.6 years), surgical, and postsurgical (4.0 years) changes. During the presurgical period, comparisons of traditional measures and mandibular modeling changes showed no significant differences between the 2 groups. During surgery, the maxilla was impacted approximately 3 mm anteriorly and 1 mm posteriorly, which caused a 3.2 degrees autorotation of the mandible. During the postsurgical period, there was no change in the vertical growth pattern of the surgical patients, with the vertical facial heights increasing the same as the control subjects and the mandible rotating backwards. Although there was no inhibition of mandibular growth in the patients postsurgically, there was a decrease in horizontal maxillary growth compared with control subjects. There were clear postsurgical changes in the mandibular modeling and condylar growth, which were indicative of adaptive compensations for surgical mandibular repositioning and autorotation. It is concluded that early maxillary impaction does not normalize or inhibit the vertical maxillary excess growth pattern; mandibular modeling and condylar growth undergo adaptive changes in response to repositioning.

Early treatment of vertical skeletal dysplasia: the hyperdivergent phenotype

This cephalometric study evaluated an early nonextraction treatment approach for patients with severe vertical skeletal dysplasia and maxillary transverse constriction. Thirty-eight patients, 8.2 years (+/- 1.2 years) of age, were treated for 1.3 years (+/- 0.3 years) with lip seal exercises, a bonded palatal expander appliance, and a banded lower Crozat/lip bumper. The bonded palatal expander functioned as a posterior bite-block and was fixed in place throughout treatment. Patients with poor masticatory muscle force (79%) wore a high-pull chincup 12 to 14 hours per day. A control group was matched for age, sex, and mandibular plane angle. Treatment changes for chincup and other patients were not significantly different. Overall, treatment significantly enhanced condylar growth, altered it to a more anterosuperior direction, and produced "true" forward mandibular rotation 2.7 times greater than control values. Posterior facial height increased significantly more in patients than in controls, and the maxillary molars showed relative intrusion. In treated patients, articular angle increased, gonial angle decreased, and the chin moved anteriorly twice as much as in controls. Treatment also led to increased overbite and decreased overjet. Maxillary and mandibular expansion did not cause the mandibular plane angle to increase. The 16 patients with openbite malocclusions exhibited a 2.7 mm increase in overbite and inhibition of growth in anterior lower facial height. The aggregate of individual changes demonstrates a net improvement, indicating this treatment approach may be suited for hyperdivergent patients with skeletal discrepancies in all 3 planes of space.

Proposed cephalometric diagnosis for osteogenic obstructive sleep apnea (OSA): the mandibular/pharyngeal ratio

The purpose of this laboratory study is to devise a simple, diagnostic test to assess possible osteological deficiency as a probable cause of OSA. Modern day skulls of fifty males and forty eight females of Tuscan origin and an additional seventy-five skulls, from India, with their cephalograms were used for this study. Mandibular length and antero-posterior dimension of the nasopharynx--pharyngeal tubercle (PhT) to posterior nasal spine (PNS)--were measured on the Tuscan skulls. The nasopharynx was similarly measured on the Indian skulls and readings multiplied by 1.14, the magnification factor of the cephalometric apparatus used. The PhT-PNS distance was then plotted on the cephalogram of Indian skulls with point PhT at the basiocciput. The possible presence of an osteogenic etiology of OSA can be determined by comparison of the mandibular/pharyngeal ratio obtained from the skull cephalograms to that of the individual patient.

Interrelationships of brain, cranial base and mandible

The purpose of this study is to evaluate the neural and masticatory growth factors that contribute to the development of the cranial base. Cephalometric and submentovertex (SMV) radiographs of 66 adult human skulls, of Caucasian (India) origin and unknown gender were used in this study. Results indicate that the cranial base, posterior to the foramen caecum, develops in response to brain growth. The part anterior to the foramen caecum develops in response to the mandible. Our findings indicate that: 1. the glabella instead of the nasion should be considered as the most anterior point of the cranial base. Mandibular dimensions (the height and the length) have a better correlation with CG than CN. 2. Instead of a single parameter, sella-nasion (SN), two parameters, the foramen caecum-glabella (CG) and the foramen caecum-sella (CS) should be considered. In cephalometry the more stable line CS, rather than SN, can be used for registration of successive radiographs; 3. The typical mandibular retrognathia, and/or the decrease in the posterior height (ascending ramus) of a Class II malocclusion could be explained by their positive correlation with SB (sella-basion) and the negative correlation with angle GSB.

Condylar growth and glenoid fossa displacement during childhood and adolescence

This study evaluated age and gender differences in the growth of the mandibular condyle and displacement of the glenoid fossa. The results pertain to longitudinal samples of untreated French Canadians, including 118 children and 155 adolescents. Childhood and adolescent growth were described for girls aged between 6 and 10 years and 9 and 13 years, respectively, and for boys aged between 8 and 12 years and 11 and 15 years, respectively. Four-year growth changes of the cephalometric landmarks condylion and articulare were evaluated. Mandibular and cranial/cranial base structural superimpositions were used to assess condylar growth and fossa displacement, respectively. The results showed that the condyle grew between 0.8 and 1.3 mm posteriorly and between 9.0 and 10.7 mm superiorly over the 4-year periods; the articulare landmark showed significantly more posterior and less superior growth than the condylion landmark. Relative to the cranial base reference structures, the fossa was displaced between 1.8 and 2.1 mm posteriorly and between 1.0 and 1.8 mm inferiorly. The articulare showed significantly more inferior movement than the condylion. Boys showed significantly greater superior condylar growth during adolescence than during childhood. The glenoid fossa demonstrated greater posterior and inferior displacement during adolescence than during childhood.

Superimposition and structural analysis

Superimposition on the lower border of the mandible has been severely criticized. It has allegedly been responsible for causing chaos and confusion in the literature. This report indicates that this is not true and that superimposition on the lower border of the mandible is valid. We have shown that changes resulting from superimposing on implants are a part of the sella-nasion superimposition. The implant changes are contained within the sella-nasion superimposition and are a part of it. The gonion angle grows approximately parallel to the mandibular plane. The lower border of the mandible is a part of the big picture all through the growing period, always containing the implant changes. The mandibular plane changes its inclination as the relation of vertical to horizontal growth changes. Examples are shown to illustrate the "give and take" between vertical and horizontal growth, and its effect on the facial complex. Objective evidence is shown that seems to indicate that the implant changes may have been counted and then counted again. This new analysis places a different interpretation on the implant studies.