Accuracy of integration of dental cast and cephalograms compared with cone-beam computed tomography: a comparative study.

This study proposes a method that integrates maxillary dental cast and cephalograms and evaluates its accuracy compared with cone-beam computed tomography (CBCT) scans. The study sample comprised 20 adult patients with records of dental casts, cephalograms, and craniofacial CBCT scans. The maxillary dental cast was integrated with lateral and frontal cephalograms based on best-fit registration of palatal and dental outline curves from dental cast with cephalogram tracings. Linear measurement was conducted to assess the intra- and inter-examiner reproducibility of the proposed integration method using intraclass correlation coefficients; linear and angular measurements were conducted to assess its accuracy with CBCT scans as a standard reference. Paired t test, one sample t test, and mean ± standard deviation of the absolute value of difference were used to compare the integrated images and CBCT. The integration method showed good intra- and inter-examiner reproducibility (intraclass correlation coefficients > 0.98). The differences in linear and angular measurements between the integrated images and CBCT were not statistically significant but with a large deviation. When absolute value of difference was computed, the linear distance error was 0.51 ± 0.34 mm, the tooth point coordinate errors in X, Y and Z axes were 0.22 ± 0.22, 0.38 ± 0.32 and 0.21 ± 0.21 mm, respectively; the angular error in pitch, roll and yaw of the dental cast was 0.82 ± 0.51, 0.92 ± 0.59 and 0.80 ± 0.41 degree, respectively. The proposed method for integration of dental cast and cephalograms showed good reproducibility and acceptable accuracy compared with CBCT. It could be helpful for researchers to study three-dimensional tooth growth changes using the existing craniofacial growth data especially cephalograms.

Dynamic Change in Oral Microbiota of Children With Cleft Lip and Palate After Alveolar Bone Grafting.

To investigate the longitudinal influence of alveolar bone grafting on the oral microbiota of children with cleft lip and palate (CLP).Twenty-eight children with nonsyndromic CLP were recruited and underwent secondary alveolar bone grafting at the first time. Unstimulated saliva and plaque samples were collected from the subjects preoperatively and at 2 days, 1 month, and 3 months postoperatively. The v3-v4 hypervariable regions of the 16S rRNA gene from bacterial DNA were sequenced using the Illumina MiSeq sequencing platform.The alpha diversity of the saliva and plaque microbiota was significantly decreased at 2 days postoperatively and then increased at 1 and 3 months postoperatively. The saliva and plaque microbiota compositions at 2 days postoperatively differed from those at the other time points, and the microbiota compositions at 1 and 3 months postoperatively showed a gradual shift toward the preoperative composition. The saliva, but not plaque, microbiota composition 3 months postoperatively was similar to that preoperatively.The effect of secondary alveolar bone grafting on the plaque microbiota in children with CLP lasted longer than the saliva microbiota. Alveolar bone grafting altered the saliva microbiota in children with CLP within 3 months postoperatively.

Apolipoprotein E is an effective biomarker for orthodontic tooth movement in patients treated with transmission straight wire appliances.

INTRODUCTION: Orthodontic tooth movement (OTM) is the core component of orthodontic treatment and is increasingly popular for treating malocclusions. In this study, we aimed to investigate the role of apolipoprotein E (ApoE) in OTM. METHODS: Thirty patients treated with transmission straight wire technology were selected and longitudinally tracked at 2 different stages of orthodontic treatment (initial 2 months and 12 months of orthodontic treatment). Total saliva was collected and analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Western blotting was used to detect the difference in ApoE expression in the saliva samples of the 2 groups. The expression of ApoE was further verified by immunohistochemical staining in a mouse model of tooth movement. RESULTS: The results of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry showed significant differences in the components of the salivary peptides in the 2 groups and peptides with a molecular weight of 2010.7 Da were predicted to be ApoE by database analysis. Western blotting further verified a significant difference in the expression of salivary ApoE in the 2 groups. In addition, an OTM model was successfully constructed in mice. The immunohistochemical staining results showed that ApoE expression significantly increased after force loading in the OTM model. CONCLUSIONS: This study indicated that ApoE participated in and played a role during OTM in patients treated with transmission straight wire technology. This relationship might be related to alveolar bone reconstruction and root resorption. The results provide new ideas for research on the mechanism of tooth movement using precision medicine based on saliva detection.

Analysis of facial features and prediction of lip position in skeletal class III malocclusion adult patients undergoing surgical-orthodontic treatment.

OBJECTIVES: This study presents a retrospective study aimed to analyze the facial features at each stage of surgical-orthodontic treatment for skeletal class III malocclusion, and predict the changes in the lips after treatment. MATERIALS AND METHODS: There were 49 skeletal class III malocclusion patients treated with bimaxillary surgery and orthodontic treatment enrolled in this study. Lateral cephalograms were obtained before treatment (T0), 1 month before surgery (T1), 1 month after surgery (T2), and after debonding (T3) for cephalometric measurements. After the measurement of the required variables, paired t-test, Pearson's correlation analysis, and multiple linear regression were performed using SPSS 19.0. RESULTS: The main factors associated with changes in the upper lip included ΔUIE-V, ΔA-V, ΔU1A-V, and ΔL1A-V, and those associated with changes in the lower lip included ΔLIE-V, ΔL1A-V, ΔB-V, ΔPog-V, and Δfacial angle. The predicted regression equation for the horizontal change in the upper lip was represented as ΔUL-vertical reference line (VRL) = 9.430 + 0.779 (ΔUIE-VRL) - 0.542(VULT) (P < 0.05) with a mean error of 1.04 mm; the corresponding equation for the lower lip was ΔLL-VRL = -1.670 + 0.530 (ΔB-VRL) + 0.360 (Ls-E) + 0.393 (ΔLIE-VRL) (P < 0.05), with a mean error of 1.51 mm. CONCLUSIONS: This study explored the relationship between orthognathic surgery and changes in the lips and obtained the predictive equations of lip position after treatment by using multiple linear regression, which likely offers a reference for prediction of soft tissue changes before surgical-orthodontic treatment in patients with skeletal class III malocclusion. CLINICAL RELEVANCE: The findings can help dentists to rapidly predict the lip changes after surgical-orthodontic treatment in patients with skeletal class III malocclusion. The study has been registered with the Chinese Clinical Trial Registration (No: ChiCTR1800017694).

Exploring the Genomic Diversity and Cariogenic Differences of Streptococcus mutans Strains Through Pan-Genome and Comparative Genome Analysis.

Pan-genome refers to the sum of genes that can be found in a given bacterial species, including the core-genome and the dispensable genome. In this study, the genomes from 183 Streptococcus mutans (S. mutans) isolates were analyzed from the pan-genome perspective. This analysis revealed that S. mutans has an "open" pan-genome, implying that there are plenty of new genes to be found as more genomes are sequenced. Additionally, S. mutans has a limited core-genome, which is composed of genes related to vital activities within the bacterium, such as metabolism and hereditary information storage or processing, occupying 35.6 and 26.6% of the core genes, respectively. We estimate the theoretical core-genome size to be about 1083 genes, which are fewer than other Streptococcus species. In addition, core genes suffer larger selection pressures in comparison to those that are less widely distributed. Not surprisingly, the distribution of putative virulence genes in S. mutans strains does not correlate with caries status, indicating that other factors are also responsible for cariogenesis. These results contribute to a more understanding of the evolutionary characteristics and dynamic changes within the genome components of the species. This also helps to form a new theoretical foundation for preventing dental caries. Furthermore, this study sets an example for analyzing large genomic datasets of pathogens from the pan-genome perspective.

Assessing the Interdental Septal Thickness in Alveolar Bone Grafting Using Cone Beam Computed Tomography.

OBJECTIVE: To assess the interdental septal thickness of grafted bone bridges using cone beam computed tomography (CBCT). PATIENTS: Of 71 patients with cleft lip and/or palate having undergone alveolar bone grafting for the first time at least 6 months previously, 52 patients with 57 grafted sites rated type I or II based on the Bergland scale using occlusal radiographs were selected. INTERVENTIONS: CBCT was performed for each bone-grafted alveolar cleft within 1 week after the occlusal radiographs were taken. MAIN OUTCOME MEASURES: The thickness of the grafted bone bridge was evaluated using CBCT according to the relationship between crest thickness and the root width of cleft-adjacent teeth, and the results were classified into four categories, with scores of 1 to 4 indicating that the thickness of the bony bridge was ≥100%, ≥75%, ≥50%, and <50% of the root width of the cleft-adjacent teeth, respectively. RESULTS: Of the 34 grafted sites rated type I on the Bergland scale, 15 (44.12%), 10 (29.41%), 4 (11.76%), and 5 (14.71%) clefts were scored 1 to 4 on interdental septal thickness using CBCT, respectively. Of the 23 cases of type II, 3 (13.04%), 9 (39.13%), 1 (3.45%), and 10 (43.48%) clefts were scored 1 to 4, respectively. CONCLUSIONS: The interdental septal thickness of grafted bone bridges with clinically successful heights based on the Bergland scale (type I or II) using occlusal radiographs varied significantly in the evaluation using CBCT.

Exosome analysis: a promising biomarker system with special attention to saliva.

Today, exosome-related studies have become a focus in science and technology. Recently, three scientists won the Nobel Prize for determining the mechanisms of exosomal transport, making exosomes a promising biomarker system for disease diagnosis and treatment. This review provides a general introduction of exosomes and explores the recent progress on the function, application, isolation, and identification of exosomes as biomarkers in blood and other body fluids, especially in saliva. Detailed information of exosomal proteins and RNAs is discussed in the paper because of their ability to determine the function of exosomes. Due to their noninvasive assessment for quick and convenient diagnosis of diseases, salivary exosomes may well be promising biomarkers.

Tooth lengths of the permanent upper incisors in patients with cleft lip and palate determined with cone beam computed tomography.

Objective : To measure the tooth lengths of fully developed permanent upper incisors and to qualitatively evaluate the root shapes of the incisors in patients with cleft lip and palate (CLP). Design : Cross-sectional, noninterventional, case-control imaging study. Setting : Hospital and Stomatology Unit of Peking University, Beijing, China (institutional tertiary care). Participants : Sixty consecutive nonsyndromic CLP patients (including 40 unilateral [UCLP] and 20 bilateral [BCLP]), and 53 age- and sex-matched controls were selected for this study. Main Outcome Measure : Crown heights and root lengths of permanent upper incisors were measured from cone beam computed tomography scans, and the root shapes of upper incisors were evaluated. Results : Compared with controls, the crown heights of upper incisors in CLP patients were reduced by 9.7% to 22.5% (p < .05), and the root lengths were reduced by 15.8% to 31.7% (p < .05). BCLP patients had greater reductions than the UCLP cases (p < .05). There were no significant differences between incisors and their antimeres in controls and BCLP patients. However, measurements on the cleft side in UCLP patients were lower than those of the noncleft side (p < .05). The prevalence of atypical root shape was higher in CLP than in the control group (p  =  .002); of these, 83.3% (30/36) occurred in central incisors near the cleft. Conclusion : The permanent upper incisors in nonsyndromic CLP patients are underdeveloped. Incisor developmental deficiency was greater in teeth adjacent to the cleft.

Inclination of mandibular incisors and symphysis in severe skeletal class III malocclusion.

OBJECTIVE: The aim of this study was to systematically explore the inclination of the lower central incisor and symphysis in alveolar bone in severe skeletal class III patients. MATERIALS AND METHODS: A total of 198 severe skeletal class III patients (ANB ≤ -4°) who underwent combined orthodontic and orthognathic treatment were divided into three groups based on the mandibular plane angle (MP-SN). Pretreatment lateral cephalograms were analysed and compared among the three groups. We also assessed cone-beam computed tomography (CBCT) images of 11 samples to investigate the reliability of the cephalometric analysis. RESULTS: ANOVA showed no statistically significant differences in the angle between the long axis of the mandibular symphysis and the long axis of the lower central incisor (MIA) among the low-angle, normal-angle and high-angle groups (P > 0.05), while significant differences were found in the angle between the axis of the lower incisor and the mandibular plane (IMPA) among the three groups (P < 0.001). The mean IMPA decreased with increasing MP-SN in the 198 patients. The mean MIA in the low-angle and normal-angle groups was 3.70° and 3.52°, respectively, while the value (2.33°) was smaller in the high-angle group. Paired-samples t test showed no statistically significant differences between the cephalometric and CBCT measurements of the MP-SN, the angle between the mandibular plane and the Frankfort plane (FH-MP) and the MIA (P > 0.05). CONCLUSIONS: In severe skeletal class III patients, the long axis of the lower central incisor was highly consistent with the long axis of the mandibular symphysis, which was more obvious in the high-angle subjects. The MIA reflects the physiological inclination of the lower central incisor better than the IMPA.

Magnetic bead-based salivary peptidome profiling analysis during orthodontic treatment durations.

Orthodontic treatment induces various biological responses, including tooth movement and remodeling of alveolar bone. Although some studies have investigated the contribution of orthodontic procedures to changes in saliva conditions, little is known about the effects of different treatment durations on the saliva proteome. To identify the discriminating protein profiles in unstimulated whole saliva of orthodontic patients with different treatment durations, we used matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) combined with magnetic bead, and peptide mass fingerprints were created by scanning MS signals. Saliva samples from 40 patients (10 in each of four groups: the group without an appliance and groups under treatment for 2, 7, and 12 months) were analyzed. The results showed eight mass peaks with significant differences. Furthermore, mass peak intensities at proteins 1817.7, 2010.7, 2744 and 2710.2 Da represented a steady time-dependent increasing trend, whereas protein 4134 Da exhibited a decreasing tendency. Differential expression of the peptidome profile also occurred in the multiple comparisons, and we established a fitting model. Thus, the potential discriminating biomarkers investigated in this study reflected the complicated changes in periodontal tissues during orthodontic treatment and indicated dynamic interactions between orthodontic treatment and the saliva proteome. The results provide novel insights into alterations in salivary proteins due to different orthodontic treatment durations and may lead to the development of a therapeutic monitoring strategy for orthodontics.

Magnetic bead-based salivary peptidome profiling for periodontal-orthodontic treatment.

BACKGROUND: Patients with periodontitis seek periodontal-orthodontic treatment to address certain functional and aesthetic problems. However, little is known of the effect of periodontitis on orthodontic treatment. Thus, we compared the differences in peptide mass fingerprints of orthodontic patients with and without periodontitis by MALDI-TOF MS using a magnetic bead-based peptidome analysis of saliva samples. In this way, we aimed to identify and explore a panel of differentially-expressed specific peptides. RESULTS: Saliva samples from 24 patients (eight orthodontic patients without periodontitis, eight with periodontitis and another eight with periodontitis but no orthodontic treatment) were analyzed, and peptide mass fingerprints were created by scanning MS signals using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) combined with magnetic beads. Nine mass peaks showed significant differences. Orthodontic patients in the group without periodontal disease showed higher mass peaks for seven peptides of the nine, whereas the mass peaks for the other two peptides were higher in the periodontal-orthodontic patients. Besides, these differentially-expressed peptides were sequenced. CONCLUSIONS: The elucidated candidate biomarkers indicated interactions between periodontal condition and orthodontic treatment and their contributions to the changes of saliva protein profiles. Our results provide novel insight into the altered salivary protein profile during periodontal-orthodontic treatment, and may lead to the development of a therapeutic monitoring strategy for periodontics and orthodontics.

Local osteoprotegerin gene transfer inhibits relapse of orthodontic tooth movement.

INTRODUCTION: In orthodontic treatment, teeth can relapse after tooth movement without retention. The aim of this study was to evaluate the inhibition effects of local osteoprotegerin (OPG) gene transfer on orthodontic relapse. METHODS: Eighteen male Wistar rats were divided into 3 groups. The maxillary right first molars of all animals were subjected to orthodontic force and moved mesially. Three weeks later, the force was removed, and the teeth relapsed. During the 2-week relapse period, the 3 groups of rats received local OPG gene transfer (experimental group), mock vector transfer (mock group), and no injections (control group). Tooth movement and relapse were measured by using palatal superimpositions of 3-dimensional digital models. Histomorphometric analysis was used to quantify osteoclasts, and microcomputed tomography analysis was done to quantify the alveolar bone and the tibia. RESULTS: Relapse was significantly inhibited and the number of osteoclasts was reduced in the experimental group. On the other hand, bone mineral density and bone volume fraction of alveolar bone were significantly increased. Bone mineral density and bone volume fraction of the tibia showed no significant difference between the groups. CONCLUSIONS: Local OPG gene transfer to periodontal tissues could inhibit relapse after orthodontic tooth movement, through the inhibition of osteoclastogenesis.

Accuracy and repeatability of computer aided cervical vertebra landmarking in cephalogram.

The accuracy and repeatability of computer aided cervical vertebra landmarking (CACVL) were investigated in cephalogram. 120 adolescents (60 boys, 60 girls) aged from 9.1 to 17.2 years old were randomly selected. Twenty-seven landmarks from the second to fifth cervical vertebrae on the lateral cephalogram were identified. In this study, the system of CACVL was developed and used to identify and calculate the landmarks by fast marching method and parabolic curve fitting. The accuracy and repeatability in CACVL group were compared with those in two manual landmarking groups [orthodontic experts (OE) group and orthodontic novices (ON) group]. The results showed that, as for the accuracy, there was no significant difference between CACVL group and OE group no matter in x-axis or y-axis (P>0.05), but there was significant difference between CACVL group and ON group, as well as OE group and ON group in both axes (P<0.05). As for the repeatability, CACVL group was more reliable than OE group and ON group in both axes. It is concluded that CACVL has the same or higher accuracy, better repeatability and less workload than manual landmarking methods. It's reliable for cervical parameters identification on the lateral cephalogram and cervical vertebral maturation prediction in orthodontic practice and research.

[Indication of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) in gingival crevicular fluid to remodeling of alveolar bone during retention].

OBJECTIVE: To investigate the level of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) in gingival crevicular fluid (GCF) during orthodontic retention and corresponding expression of OPG and RANKL in periodontal tissues. METHODS: Fifteen male Wistar rats (age, 6 weeks) were divided into three groups with 5 rats for each. GCF samples were collected at the baseline, 14 days after orthodontic force application, and 14 days after orthodontic force removal. enzyme linked immunosorbent assay (ELISA) was used to quantify the concentration of OPG and sRANKL (soluble receptor activator of nuclear factor kappa B ligand) in GCF. Immunohistochemical staining was performed to identify the OPG and RANKL expression in periodontal tissues. RESULTS: The concentration of sRANKL in GCF increased statistically significant from baseline to T2 (P<0.05) while decreased significantly from T2 to T3 (P<0.05). The concentration of OPG had minimum fluctuation from baseline to T3 without any statistical significance (P>0.05). The sRANKL/OPG ratio in GCF and that in periodontal tissues during the three time points were similar which showed a prominent increase in T2 (P<0.05 and P<0.01, respectively) and sharp decrease in T3 (P<0.05). CONCLUSION: sRANKL/OPG ratio may be one of the predictors reflecting the remodeling of periodontal tissues in orthodontic retention.

A Novel PAX3 Variant in a Chinese Pedigree with Nonsyndromic Cleft Lip With or Without Palate.

Objectives: Nonsyndromic cleft lip with or without palate (NSCL/P) is a common congenital orofacial defect, which is associated with severe disruption of orofacial development. The present study was designed to identify potential underlying gene variants in a Chinese pedigree with NSCL/P, in which the proband and the proband's father were affected. Methods: DNA was extracted from the participants' peripheral venous blood, and whole-exome sequencing was performed on the proband and the proband's parents. Results: After filtering, a paired box gene 3 (PAX3) missense variant (c.92C>G_p.Thr31Ser) was identified, which was verified by Sanger sequencing. This variant, which was not present in 113 unrelated healthy individuals or in a Chinese public database, may affect the transcription inhibition domain of the PAX3 protein. Conservation analysis and in silico predictions suggested that this variant may be evolutionarily conserved and potentially deleterious. In addition, it was reported that mice with PAX3 variants show cleft palates. Thus, the PAX3 missense variant (c.92C>G_p.Thr31Ser) is a candidate causative variant in this family. Conclusions: To the best of our knowledge, the present study is the first to report on a PAX3 variant in a pedigree with NSCL/P. The present study further suggests that PAX3 may be associated with CL/P etiology.

Functional identification of a rare vascular endothelial growth factor a (VEGFA) variant associating with the nonsyndromic cleft lip with/without cleft palate.

Vascular endothelial growth factor A (VEGFA) is a crucial growth factor, which participates in multiple processes of human growth and development, such as angiogenesis and osteogenesis and is also necessary for development of palate. The purpose of this study was to investigate the effect of a rare VEGFA mutation (NM_001025366.2 773 T > C p.Val258Ala) on the cell functions and osteogenesis. Here, we found that the VEGFA mutation has adverse effects on the function of human embryonic palatal plate mesenchymal (HEPM) cells, and may affect the development of palate. The VEGFA mutation has adverse effects on promoting cell proliferation and migration and inhibiting apoptosis in HEPM and HEK-293 cells. In addition, the mutant VEGFA allele has a negative influence on osteogenesis. Taken together, the rare variant of the VEGFA gene had an adverse effect on cell functions and osteogenesis, which may impact the development of the palate. And these findings suggested that VEGFA mutation (c.773 T > C) may lead to nonsyndromic cleft lip with or without cleft palate and also provide a new insight into the mechanism of VEGFA gene in osteogenesis and palatogenesis.

Longitudinal study of relative growth rates of the maxilla and the mandible according to quantitative cervical vertebral maturation.

INTRODUCTION: The purpose of this study was to investigate the relative growth rates (RGR) of the maxilla and the mandible according to quantitative cervical vertebral maturation (QCVM) of adolescents with normal occlusion. METHODS: Mixed longitudinal data were used. The sample included 87 adolescents (32 boys, 55 girls) from 8 to 18 years of age with normal occlusion, selected from 901 candidates. Sequential lateral cephalograms and hand-wrist films were taken once a year for 6 consecutive years. The growth magnitude (GM) and RGR of the maxilla and the mandible were measured and analyzed. RESULTS: GM and RGR were not always consistent, because subjects had different periods of time between the QCVM stages. GM was not as reliable as RGR. RGR had no significant sex differences in the maxilla and the mandible, in spite of different decelerating curves. However, statistically significant sex differences were found in the GM of mandibular measurements. The greatest growth potentials were not synchronized between the maxilla and the mandible. For both sexes, the greatest RGR of maxillary length and height was in QCVM stage I; then, deceleration occurred. The greatest RGR of mandibular length and height was in QCVM stage II, and the next largest was in QCVM stage I. CONCLUSIONS: Understanding the RGR can provide references for orthodontic treatment and orthognathic surgery.

Clinical study of frontal chewing patterns in various crossbite malocclusions.

INTRODUCTION: The purpose of this study was to clarify the frontal chewing patterns of various crossbite malocclusions. METHODS: A mandibular kinesiograph was used to record the masticatory movements of 106 subjects (ages, 12-35 years) with crossbite malocclusion and 22 subjects (ages, 16-30 years) with normal occlusion. The chewing patterns were classified into 8 chewing types according to the cycle shape of the frontal incisor point movement. The crossbite subjects were divided into 5 groups by the anteroposterior position of the crossbite, and then the subjects with posterior crossbite were divided into 3 groups by the transverse position of the crossbite. The Mann-Whitney U test was used to compare the frequency of each chewing type between any crossbite group and the control group; and between the various crossbite groups. RESULTS: In the crossbite groups, normal chewing occurred much less often than in subjects with normal occlusion. In the posterior crossbite group, reverse chewing was greater (P = 0.002), and normal chewing was less frequent (P = 0.001) compared with the anterior crossbite group. When accompanied by mandibular shift, mandibular prognathism, arch crossbite, in the crossbite or shift side, reverse type, and reverse-crossing type occurred more often than in contralateral side. CONCLUSIONS: In the frontal plane, patients with posterior crossbite might have more abnormal chewing types than those with anterior crossbite, and posterior crossbite could contribute to the high frequency of reverse and reverse-crossing chewing types, especially when accompanied by mandibular shift, mandibular prognathism, or arch crossbite.

Longitudinal changes in mandibular arch posterior space in adolescents with normal occlusion.

INTRODUCTION: The purpose of this study was to investigate the changes of available mandibular space in the posterior dental arch of teenagers from 13 to 18 years old. METHODS: Longitudinal cephalograms of 28 adolescents (13 boys, 15 girls) with normal occlusion, selected from among 901 candidates, were taken annually from 13 to 18 years of age inclusively. Modified analyses with occlusal plane and occlusal plane perpendicular as reference planes were used to evaluate the changes of available space of the posterior mandibular arch. RESULTS: From 13 to 18 years of age, significant differences of mandibular posterior space were found among ages and sexes. The total increases of available space were 5.12 mm in the girls and 5.79 mm in the boys. For girls before age 16 and boys before age 17, the increased available space was contributed mainly by resorption of bone on the anterior border of the ramus. Mesial drift of the dental arch did not occur until the eruption of the third molars. The average available spaces increased 1.22 mm in girls less than age 16 and 1.45 mm in boys less than age 17 per side per year. CONCLUSIONS: The prediction of available space in the posterior mandibular arch should be based on age and sex.

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.