Koutaro Maki

Comparison of airway space with conventional lateral headfilms and 3-dimensional reconstruction from cone-beam computed tomography

INTRODUCTION Changes in the normal pattern of nasal respiration can profoundly affect the development of the craniofacial skeleton in both humans and experimental animals. The orthodontist is often the first clinician to notice that a child is breathing primarily through the mouth, either at the initial examination or later during treatment. The lateral headfilm, part of the patients normal records, might show increased adenoid masses, suggesting that these could be part of the problem. Previous studies have, however, questioned the validity of the information from lateral headfilm. METHODS Our aim was to compare imaging information about nasopharyngeal airway size between a lateral cephalometric headfilm and a 3-dimensional cone-beam computed tomography scan in adolescent subjects. The nasopharyngeal airway area and volume were measured in 35 subjects (8 boys, 27 girls; average age, 14 years). RESULTS Volumetric measurement errors ranged from 0% to 5% compared with known physical airway phantoms used to calibrate. A moderately high (r = 0.75) correlation was found between airway area and volume; the larger the area, the larger the volume. However, there was considerable variability in the airway volumes of patients with relatively similar airways on the lateral headfilms. Nine of the 35 patients had over 25% of the potential nasopharyngeal airway volume occupied by inferior turbinate protuberances, leading to significant airway restriction in some patients. CONCLUSIONS The cone-beam 3-dimensional scan is a simple and effective method to accurately analyze the airway.

A Common Variation in EDAR Is a Genetic Determinant of Shovel-Shaped Incisors

Shovel shape of upper incisors is a common characteristic in Asian and Native American populations but is rare or absent in African and European populations. Like other common dental traits, genetic polymorphisms involved in the tooth shoveling have not yet been clarified. In ectodysplasin A receptor (EDAR), where dysfunctional mutations cause hypohidrotic ectodermal dysplasia, there is a nonsynonymous-derived variant, 1540C (rs3827760), that has a geographic distribution similar to that of the tooth shoveling. This allele has been recently reported to be associated with Asian-specific hair thickness. We aimed to clarify whether EDAR 1540C is also associated with dental morphology. For this purpose, we measured crown diameters and tooth-shoveling grades and analyzed the correlations between the dental traits and EDAR genotypes in two Japanese populations, inhabitants around Tokyo and in Sakishima Islands. The number of EDAR 1540C alleles in an individual was strongly correlated with the tooth-shoveling grade (p = 7.7 x 10(-10)). The effect of the allele was additive and explained 18.9% of the total variance in the shoveling grade, which corresponds to about one-fourth of the heritability of the trait reported previously. For data reduction of individual-level metric data, we applied a principal-component analysis, which yielded PC1-4, corresponding to four patterns of tooth size; this result implies that multiple factors are involved in dental morphology. The 1540C allele also significantly affected PC1 (p = 4.9 x 10(-3)), which denotes overall tooth size, and PC2 (p = 2.6 x 10(-3)), which denotes the ratio of mesiodistal diameter to buccolingual diameter.

Evaluation of the human airway using cone-beam computerized tomography

OBJECTIVE The goal of this project was to define and measure human airway space with radiographic volumetric 3-dimensional imaging and digital reconstruction of the pharynx using cone-beam computerized tomography. STUDY DESIGN This was a randomized retrospective study. Ten patient scans were selected randomly from a pool of 196 subjects seeking dental treatment at the University of California, San Francisco. Digital Imaging and Communications in Medicine-format volume images were captured using a low-radiation rapid-scanning cone-beam computerized tomography system (Hitachi MercuRay). RESULTS Detailed progressive rostrocaudal cross-sectional area histograms indicated that 8 of the 10 subjects demonstrated a region of maximum constriction near the oropharynx level. The most restricted cross-sectional area varied from 90 mm(2) to 360 mm(2). CONCLUSIONS The maximum constriction of the airway in 10 subjects quietly breathing for 10 seconds indicated variation in the level of the pharynx and the extent of the rostrocaudal zone of restriction.

Anthropometric analysis of the human mandibular cortical bone as assessed by cone-beam computed tomography.

PURPOSE The purpose of this study is to assess cortical thickness, height, and width with cone-beam computed tomography (CBCT), and determine the relationship of these parameters with age. PATIENTS AND METHODS A total of 113 subjects from the University of California at San Francisco Orthodontic Clinic with a CBCT scan were enrolled. Subjects were stratified by age in decades. Thickness of buccal and lingual cortices and mandibular height and width were evaluated in 5 regions (13 sites). A single factorial ANOVA was used to compare the parameters among age groups. P less than or equal to .05 was statistically significant. RESULTS There were 44 (38.9%) males; 69 females. For all groups, the thickest to the least thick cortical plates were: base of the mandible, lower buccal one third, upper lingual one third, upper buccal one third, and lower lingual one third. In all groups, the mandible increased in height as the midline was approached, and the width of the upper third of the mandible decreased from the second molar to the symphysis whereas the reverse occurred in the lower third. Comparison of the age groups showed that subjects 10 to 19 years old had thinner cortical plates than other age groups (P <or= .05) with peak thickness in subjects 40 to 49 years old. The subjects 10 to 19 years old also had lower posterior mandibular height (P <or= .05). There was no statistical difference in width among the groups. CONCLUSIONS The mandibular cortical bone is thickest at the base, on the buccal side. Subjects who are 10 to 19 years old have thinner cortical bone and decreased mandibular height compared with all other age groups. The mandible continues to mature through 40 to 49 years of age and then decreases in thickness after this period.

Consistency and precision of landmark identification in three-dimensional cone beam computed tomography scans

The purpose of this study was to quantify the consistency and precision of locating three-dimensional (3D) anatomic landmarks. The hypotheses tested are that these landmarks have characteristic and variable error patterns associated with their type and location. The consistency and precision of nine orthodontists identifying 32 landmarks of 19 patients were quantified. The cone beam computed tomography (CBCT) data were acquired using a Hitachi CB MercuRay system. Prior to the study, all examiners were calibrated with respect to the definitions of the landmarks and on the use of the software program (Dolphin) for identifying the landmarks. In addition, a reference guide was provided that had the definitions and sample images of the landmarks. Data were collected in spreadsheets as x, y, and z co-ordinates and statistically analysed to determine the mean and standard deviation (SD). The mean location for a given landmark on a given patient served as the reference point. The mean of the distances from the reference point was used as the consistency, while the SD of this mean was used as a measure of precision. The error in the x, y, and z planes was calculated in order to determine the specific characteristics of each landmark. The consistency in landmark location and precision did not differ significantly among the nine examiners. Sella turcica was the most consistently (0.50 mm) and most precisely (0.23 mm) identified anatomic landmark. The most inconsistent landmark was porion-right (2.72 mm) and the most imprecise landmark was orbitale-right (1.81 mm). Due to the lack of even distribution of the errors, careful use of these landmarks for analysis purposes is needed.

Success rate of gingivoperiosteoplasty with and without secondary bone grafts compared with secondary alveolar bone grafts alone.

Background: Gingivoperiosteoplasty has been shown to eliminate the need for secondary alveolar bone grafting in 60 percent of patients. The purpose of this study was to compare radiographic alveolar anatomy following infant gingivoperiosteoplasty, secondary alveolar bone grafting, and secondary alveolar bone grafting in patients who had prior infant gingivoperiosteoplasty with inadequate bone formation. Methods: Seventy-four consecutive nonsyndromic patients (complete bilateral cleft lip–cleft palate, n = 12; complete unilateral cleft lip–cleft palate, n = 46; complete unilateral cleft lip and alveolus, n = 14) treated at New York University Medical Center were available for evaluation. Eighty-two complete alveolar cleft sites were assigned to three groups: gingivoperiosteoplasty (n = 30), secondary alveolar bone grafting (n = 41), and secondary alveolar bone grafting following gingivoperiosteoplasty (n = 11). All gingivoperiosteoplasties were performed at the time of primary lip surgery, and secondary alveolar bone grafting (cancellous iliac crest at 7 to 12.5 years of age) was performed before eruption of the permanent canine. Radiographs were measured according to the modified method of Long. Results: Seventy-three percent of gingivoperiosteoplasty cases did not require secondary alveolar bone grafting and none had fistulas. The rate of missing teeth in the total sample, adjacent to the cleft, was within normal limits for the population. Group 1 alone and groups 1 and 3 combined had superior alveolar anatomy compared with group 2 (p < 0.01). No significant differences existed between groups 1 and 3 (p > 0.05). Crest height was best in group 1 (p < 0.01), followed by group 3 and then group 2, with no difference between the latter two groups. Conclusion: Gingivoperiosteoplasty alone or combined with secondary alveolar bone grafting results in superior bone levels when compared with conventional secondary alveolar bone grafting alone.

Effects of an Asian-specific nonsynonymous EDAR variant on multiple dental traits.

Dental morphology is highly diverse among individuals and between human populations. Although it is thought that genetic factors mainly determine common dental variations, only a few such genetic factors have been identified. One study demonstrated that a nonsynonymous single-nucleotide polymorphism (370V/A, rs3827760) in the ectodysplasin A receptor gene (EDAR) is associated with shoveling and double-shoveling grades of upper first incisors and tooth crown size. Here, we examined the association of EDAR 370V/A with several dental characters in Korean and Japanese subjects. A meta-analysis that combined analyses of Korean and Japanese subjects revealed that the Asian-specific 370A allele is associated with an increase in the grades of shoveling and double shoveling, as previously found. We also showed a highly significant association between EDAR 370V/A genotype and crown size, especially mesiodistal diameters of anterior teeth. Moreover, we found that the 370A allele was associated with the presence of hypoconulids of lower second molars. These results indicated that the EDAR polymorphism is responsible, in part, for the Sinodonty and Sundadonty dichotomy in Asian populations, and clearly demonstrated that the EDAR polymorphism has pleiotropic effects on tooth morphology. As the 370A allele is known to be a most likely target of positive selection in Asian populations, some phenotypes associated with the variant may be ‘hitchhiking phenotypes’, while others may be actual targets of selection.

Exome resequencing combined with linkage analysis identifies novel PTH1R variants in primary failure of tooth eruption in Japanese

Massively parallel sequencing of target regions, exomes, and complete genomes has begun to increase the opportunities for identifying genetic variants underlying rare and common diseases dramatically. Here we applied exome resequencing to primary failure of tooth eruption (PFE) to identify the genetic causality of the disease. Two Japanese families having PFE were recruited and examined by genome‐wide linkage study and subsequently exome analyses. Linkage analyses of these two families comprising eight affected individuals and two unaffected individuals revealed linkage signals at 10 loci with a maximum LOD score of 1.5. Four affected individuals in one family were pooled and further processed for exome analysis, followed by massive parallel sequencing. After three‐step filtering including annotation and functional expectation, three variants were found to be candidates for PFE. Among the three variants, only a novel variant of parathyroid hormone 1 receptor gene (PTH1R), R383Q, was cosegregated in the first PFE family. Accordingly, we screened the gene for variants at all coding exons and the respective intron‐exon boundaries in the second family and two sporadic individuals with PFE. We also identified a novel missense variant, P119L, cosegregating in the second family and missense variants P132L and R147C in the sporadic cases. These variants all were in the highly conserved region across zebrafish to chimpanzee and not observed in 192 unrelated controls, supporting the pathogenicity of the variants. The combination of linkage and exome analyses employed in this study provides a powerful strategy for identifying genes responsible for Mendelian disorders.

The mechanical properties of dental thermoplastic materials in a simulated intraoral environment

Abstract The present study assessed the mechanical properties of dental thermoplastic materials in a simulated intraoral environment. Eight dental thermoplastic products – EVA (Bioplast), PE (Copyplast), PETG (Duran), PP (Hardcast), PC (Imprelon“S”), A+ (Essix A+), C+ (Essix C+), and PUR (Invisalign) – were examined using the following tests: (1) 2-week water absorption test, (2) thickness-change tests with thermoforming and water absorption, (3) tensile tests under room temperature (23 °C) and in a simulated intraoral environment (37 °C). The results were as follows: (1) water absorption increased with time and ranking was (from highest to lowest): PUR, PETG, A+, PC, EVA, PP, C+, and PE. (2) The changes in thickness ranged from 74.9 to 92.6% in comparison with the specimens before thermoforming. Linear expansion with water absorption ranged from 100.3 to 119.9%. (3) The elastic moduli of PC, PETG, and A+ in the simulated intraoral environment showed significant increases in original sheets; in contrast PP, C+, PE, and EVA were significantly reduced. No significant changes were observed in PUR. Tensile yield stress of the specimens in the simulated intraoral environment decreased in comparison with original sheets. The present result suggests that the mechanical properties of dental thermoplastic materials varied due to environmental factors. Moreover, behavior change is influenced by molecular structure and orientation. The application of thermoplastic materials for orthodontic tooth movement requires a sufficient understanding of the material characteristics, optimal material selection, and design.

Effects of mastication on mandibular growth evaluated by microcomputed tomography.

It is well known that mastication has a significant influence on mandibular growth and development, but the mechanism behind this effect has not yet been clarified. Furthermore, no studies have examined the effects of changes in mastication on the three-dimensional (3D) morphometry of the mandible. The aim of the present study was to investigate the influences of changes in mastication on mandibular growth and morphology. Twenty-five 3-week-old (at the time of weaning) imprinting control region mice were randomly divided into three groups: mice fed a hard diet (HD), mice fed a soft diet (SD), and mice alternately fed hard and soft diets (HSDs) every week for 4 weeks. The morphometry of the mandible was analysed using 3D microcomputed tomography (muCT). Statistical analysis was undertaken using a t-test. muCT analysis showed that the condylar width was significantly greater in the HD group than in the SD group after 1 week. After 4 weeks, mandibular length was significantly longer and ramus height was greater in the HSD group than in the other two groups. Bone volume was significantly less in the SD group than in the other two groups after 4 weeks. These findings suggest that changes in mastication markedly affect mandibular condylar cartilage growth and mandibular morphology. It is considered that dietary education at an early age is important in order to prevent disruption of the development of the mandible.