Novel 3-dimensional analysis to evaluate temporomandibular joint space and shape.

INTRODUCTION: The purpose of this study was to present and validate a novel semiautomated method for 3-dimensional evaluation of the temporomandibular joint (TMJ) space and condylar and articular shapes using cone-beam computed tomographic data. METHODS: The protocol for 3-dimensional analysis with the Checkpoint software (Stratovan, Davis, Calif) was established by analyzing cone-beam computed tomographic images of 14 TMJs representing a range of TMJ shape variations. Upon establishment of the novel method, analysis of 5 TMJs was further repeated by several investigators to assess the reliability of the analysis. RESULTS: Principal components analysis identified 3 key components that characterized how the condylar head shape varied among the 14 TMJs. Principal component analysis allowed determination of the minimum number of landmarks or patch density to define the shape variability in this sample. Average errors of landmark placement ranged from 1.15% to 3.65%, and none of the 121 landmarks showed significant average errors equal to or greater than 5%. Thus, the mean intraobserver difference was small and within the clinically accepted margin of error. Interobserver error was not significantly greater than intraobserver error, indicating that this is a reliable methodology. CONCLUSIONS: This novel semiautomatic method is a reliable tool for the 3-dimensional analysis of the TMJ including both the form and the space between the articular eminence and the condylar head.

Correlation of Airway Volume With Orthognathic Surgical Movement Using Cone-Beam Computed Tomography.

PURPOSE: Orthognathic surgery can induce changes in airway volume. The aim of this study was to determine whether there is a correlation of surgical movement of the maxilla or mandible to airway volume changes. MATERIALS AND METHODS: This was a prospective cohort study and the sample was composed of patients undergoing single-jaw orthognathic procedures from 2004 through 2007. Cone-beam computed tomograms were obtained before surgery (T0), immediately after surgery (T1), and at least 6 months after surgery (T2). The airway was segmented from 3-dimensional images and identified as the whole airway, consisting of the naso-, oro-, and hypopharynx. The volumetric percentage of change of the airway between time points was compared and correlated to the surgical movements using paired t test and cubic regression analysis. The level of statistical significance was set at a P value less than or equal to .05. RESULTS: The sample was composed of 33 patients. Sixteen patients underwent maxillary advancement with mean advancement of 5.4 mm (3 to 8 mm), 13 underwent mandibular advancement with mean advancement of 8.0 mm (5 to 15 mm), and 4 underwent mandibular setback of 4.0 mm. For maxillary advancement at T1, volume percentages of change for the whole airway and the naso-, oro-, and hypopharynx were 18.4 (P ≤ .05), 53.8 (P ≤ .05), 26.3, and 5.5%, respectively, and at T2, the changes were 10.0, 46.7 (P ≤ .05), 6.8, and 1.0%, respectively. For mandibular advancement at T1, volume percentages of change were 34.6 (P ≤ .05), 26.1, 54.1 (P ≤ .05), and 17.4%, respectively, and at T2, the changes were 15.0 (P ≤ .05), -3.7, 23.5 (P ≤ .05), and 12.1%, respectively. There were no meaningful long-term airway changes with mandibular setback. CONCLUSION: The study results suggest that there might be an anatomic limit to pharyngeal airway expansion associated with single-jaw orthognathic surgery.

Cone-beam computed tomographic comparison of surgically assisted rapid palatal expansion and multipiece Le Fort I osteotomy.

PURPOSE: To examine and compare the skeletal and dental effects of surgically assisted rapid palatal expansion (SARPE) and multipiece Le Fort osteotomy using cone-beam computed tomography (CBCT). MATERIALS AND METHODS: This was a prospective cohort study. Patients underwent SARPE or multipiece Le Fort I osteotomy to address maxillary transverse deficiency. CBCT scans were taken preoperatively, immediately postoperatively or after retention, and at least 6 months postoperatively. Four landmark measurements and ratios of dental-to-skeletal change were used to follow skeletal and dental widths in the posterior and anterior maxillary regions. Wilcoxon signed-rank test and Wilcoxon 2-sample rank-sum test were used to compare the landmark measurements and the ratio of dental-to-skeletal change for the 2 surgeries. A P value less than .05 was statistically significant. RESULTS: Thirteen patients (mean, 28.3 yr old; 7 women) were enrolled: 9 were treated by multipiece Le Fort I osteotomy and 4 were treated by SARPE. The ratios of dental-to-skeletal expansion in the posterior maxilla for the Le Fort procedure and SARPE were 0.70 ± 0.41 and 25.20 ± 15.8, respectively, and the dental-to-skeletal relapses were 1.17 ± 0.80 and -3.63 ± 3.70, respectively. The ratios of dental-to-skeletal expansion in the anterior maxilla for the Le Fort procedure and SARPE were 0.58 ± 0.38 and 31.80 ± 59.4, respectively, and the dental-to-skeletal relapses were 2.25 ± 3.41 and 4.86 ± 8.10, respectively. CONCLUSION: There was greater correlation between dental and skeletal changes in the multipiece Le Fort procedure, indicating bodily separation of the segments, whereas the SARPE showed noteworthy dental and skeletal tipping. Dental relapse was greater than skeletal relapse for these 2 procedures.

Three-dimensional longitudinal changes in craniofacial growth in untreated hemifacial microsomia patients with cone-beam computed tomography.

INTRODUCTION: The purpose of this study was to evaluate the concept that the affected and contralateral sides do not grow at the same rate in patients with hemifacial microsomia. Changes in the cranial base, maxilla, mandible, and occlusal plane were evaluated on 3-dimensional images from cone-beam computed tomography data in untreated patients. METHODS: Six patients were classified as having mandibular Pruzansky/Kaban type I, IIA, or IIB hemifacial microsomia. Cone-beam computed tomography (MercuRay; Hitachi, Tokyo, Japan) scans were taken before orthodontic treatment during both growth and postpuberty periods. RESULTS: The cranial base as defined by the position of the mastoid process was in a different position between the affected and contralateral control sides. The nasomaxillary length or height was shorter on the affected side for all 6 patients with hemifacial microsomia regardless of its severity, and it grew less than on the contralateral control side in 5 of the 6 patients. The occlusal plane angle became more inclined in 4 of the 6 patients. The mandibular ramus was shorter on the affected side in all patients and grew less on the affected side in 5 of the 6 patients. The mandibular body grew slower, the same, or faster than on the control side. CONCLUSIONS: The cranial base, position of the condyle, lengths of the condyle and ramus, and positions of the gonial angle and condyle can vary between the affected and contralateral control sides of patients with hemifacial microsomia, with the ramus and nasomaxillary length usually growing slower than they grow on the control side. These results suggest that many factors affect the growth rate of the craniofacial region and, specifically, the mandible in patients with hemifacial microsomia.

Predicting tooth-size discrepancy: A new formula utilizing revised landmarks and 3-dimensional laser scanning technology.

INTRODUCTION: The goal of this study was to develop a more accurate formula to forecast tooth-size discrepancies in patients based on not only the size of the whole teeth but also functional arch components derived from normal cusp-fossa interdigitation that should be obtained as the final treatment goal. METHODS: A total of 141 dental casts from Dr Larry Andrews' collection of "normal occlusions" that never received orthodontic treatment were scanned with an Ortho Insight 3D Laser Scanner (Motion View Software, Chattanooga, Tenn). Individual tooth sizes and portions of tooth sizes were measured with the Motion View Software. For each set of models, potential tooth-size discrepancies were calculated by using both the original Bolton analysis and the new Johnson/Bailey analysis developed by this team at the University of California at San Francisco (UCSF). Six tooth-size discrepancy ratios were computed and included the Bolton (2) and the new (4) Johnson/Bailey analysis ratios for the anterior arch component, posterior arch component, and overall ratio of the maxillary and mandibular arches. The Johnson/Bailey analysis utilized different landmarks and groups of teeth. It consequently divided the maxillary segment by the mandibular segment, in contrast to the Bolton ratios, which divided the mandibular sums by the maxillary totals. RESULTS: The Bolton anterior segment ratio ranged from 70.68 to 84.81, with a mean of 77.91 (SD, 2.43) (3.1%). The Bolton overall ratio ranged from 86.19 to 96.62, with a mean of 91.64 (SD, ±1.74) (1.8%). The Johnson/Bailey posterior discrepancy ratio ranged from 0.98 to 1.23, with a mean of 1.10 (SD, ±0.04) (3.6%). Its anterior discrepancy ratio ranged from 0.91 to 1.14, with a mean of 1.03 (SD, ±0.04) (3.9%). The Johnson/Bailey overall discrepancy ratio ranged from 0.98 to 1.15, with a mean of 1.06 (SD, ±0.03) (2.8%). CONCLUSIONS: Two methods were used to forecast tooth-size discrepancies between opposing arches in a sample with clinically acceptable occlusions. The new approach provided more specific ratios utilizing more clinically relevant functional arch components derived from dental cusp-fossa interdigitation.

Comparison of pharyngeal airway changes on plain radiography and cone-beam computed tomography after orthognathic surgery.

PURPOSE: The purpose of the present prospective study was to develop a 3-dimensional analysis of the airway using cone-beam computed tomography (CBCT) and to determine whether changes in the airway before and after orthognathic surgery correlate on 2-dimensional lateral cephalogram and 3-dimensional CBCT images. MATERIALS AND METHODS: Patients requiring orthognathic surgery during 2004 to 2005 were recruited for the present study. Lateral cephalograms and CBCT scans were obtained at 3 points: preoperatively, within 1 month postoperatively, and after 6 months postoperatively. The nasopharynx, oropharynx, and hypopharynx were segmented on both the radiograph and the CBCT scan for each patient in a repeatable manner at each point. For the lateral cephalogram, linear measurements in the middle of each of the 3 segments were obtained. For the CBCT, volumetric measurements of each of the 3 segments were obtained. The intrarater variability was assessed, and Pearson's correlation was used to compare the 2 imaging modalities. RESULTS: A total of 20 patients scheduled for orthognathic surgery were recruited for the present study. Of the 20 patients, 13 were female and 7 were male. The mean age at surgery was 23.85 years (range 14 to 43). Of the 20 patients, 6 underwent maxillary advancement only, 8 underwent mandibular advancement with or without genioplasty, and 6 underwent 2-jaw surgery or mandibular setback. We examined the entire cohort without separation into procedure or examination point and found a weak, but statistically significant, correlation between the linear and volume measurements in the nasopharyngeal and oropharyngeal regions but not in the hypopharyngeal region (r = 0.43, P < .002; r = 0.49, P < .0002; r = 0.16, P = .26, respectively). The maxillary advancement group (n = 6) demonstrated a correlation between the linear and volume measurements in the nasopharyngeal region (r = 0.53, P = .03). The mandibular advancement with or without genioplasty group (n = 8) showed a correlation in the nasopharyngeal and oropharyngeal regions (r = 0.55, P < .02, and r = 0.46, P = .05, respectively). For the combination/setback procedures (n = 6), a correlation was found in the oropharyngeal region (r = 0.64, P < .01). All other comparisons between the linear and volume measurements did not correlate. Additionally, no correlations were found between the linear and volumetric change in airway size between 6 months postoperatively and preoperatively, except for the oropharyngeal region (r = 0.67, P < .01). CONCLUSION: We present a method of measuring the airway that could be used for both 2-dimensional and 3-dimensional images. It includes segmentation of the pharyngeal airway into its nasopharyngeal, oropharyngeal, and hypopharyngeal components. Correlations were found between the linear and volumetric measurements of the segmented airway in patients who had undergone orthognathic surgery; however, the correlations were generally weak.

Cross-sectional human mandibular morphology as assessed in vivo by cone-beam computed tomography in patients with different vertical facial dimensions.

INTRODUCTION: The goal of this study was to look at mandibular cortical bone in live patients using cone-beam computed tomography (CBCT) to determine differences in cortical plate thicknesses and mandibular cross-sectional height and width in patients with different vertical facial dimensions. METHODS: A total of 111 scanned patients were used. Of these subjects, 43 were included in the average vertical facial dimension group (average face), 34 in the high vertical facial group (long face), and 34 in the low vertical facial group (square short face). Cross-sectional slices of the mandible were developed with the cone-beam scans to evaluate the cortical bone between the dentition at 13 locations. Each section was then measured at 8 sites, which included 1 height and 2 width measures of the cross-sectional area and 5 cortical plate thicknesses. An analysis of variance (ANOVA) with a posthoc Bonferroni statistical analysis was used with a significance level of P  ≤0.0167. RESULTS: The long-face group had slightly more narrow cortical bone than the other 2 facial groups at a few selected sites of the mandible. The height of the cross-sectional area of the mandible in the long-face group was shorter posteriorly than in the other 2 groups and became greater toward the symphysis. CONCLUSIONS: Mandibular height and width differed more than cortical bone thickness among the 3 types of subjects with different vertical facial dimensions, but statistically significant differences were evident is some sites for cortical bone thickness.

A comparison of simulated jaw dynamics in models of segmental mandibular resection versus resection with alloplastic reconstruction.

STATEMENT OF PROBLEM: Composite mandibular resection resulting in mandibular discontinuity can alter jaw motion, occlusal forces, and mastication, whether or not the jaw is reconstructed. The biomechanical events associated with these changes are difficult to assess clinically and, therefore, are not well documented or researched. PURPOSE: The purpose of this study was to model movements of a mandible with a discontinuity defect, and to compare them to movements of a mandible with its continuity restored by alloplastic reconstruction. MATERIAL AND METHODS: Computational models were created with a novel simulation platform. The variables designed into the models included gravity, external forces, and jaw muscle activity. Each jaw was observed at rest, when opened by external force or by muscle drive, and during the generation of unilateral occlusal force on the nonoperated side. Scarring was simulated with springlike forces. Outputs included individual muscle forces and torques, as well as mandibular incisor and condylar motions. RESULTS: Both models displayed plausible resting postures, and jaw opening with deviation toward the defect side when scarring was simulated. Opening caused by downward force on the incisors differed from that due to muscle activation. Jaw rotations during unilateral molar contact on the unaffected side were muscle specific and influenced by mandibular discontinuity. CONCLUSIONS: Plausible jaw movements after hemimandibulectomy and/or alloplastic reconstruction could be predicted by dynamic modeling. The effect of soft tissue forces on jaw posture and movements varied with the condylar support available. In both models, different opening trajectories were produced by external force on the jaw and by jaw muscle activation. Mandibular rotation during unilateral molar contact depended on which muscles were activated, and the availability of bilateral condylar support.

Evaluating the mandible with cone-beam computed tomography.

INTRODUCTION: The purpose of this research was to examine methods for assessing the shape and growth of the mandible 3 dimensionally. Furthermore, 1 method was defined and applied. METHODS: Thirty mandibles were assessed. An average or mean shape was determined, and the mandibles were ranked quantitatively, by using the root mean square (RMS), according to their variation from the mean. The rankings ranged from mandibles that were small, short, and narrow at the minus-RMS end, to large, tall, and broad at the plus-RMS end. A second analysis provided a method to superimpose a mandible over the average mandible and determine the differences from the average-derived mandible by using a spectrum of colors to indicate changes in a region. RESULTS: Variations in the mandible were greatest in the condylar heads, coronoid tips, canine-incisor dentoalveolar segment, and chin point. CONCLUSIONS: The visual images of the 30 segmented mandibles suggest that a new method of classification needs to be developed that extends the original 2-dimensional lateral evaluation to a total 3-dimensional view that provides new relationships, such as the direction of the condylar heads to the ramus and the ratio of the intergonial angle length to the intercondylar head length to define the narrowness of a mandible.

Comparative analysis of traditional radiographs and cone-beam computed tomography volumetric images in the diagnosis and treatment planning of maxillary impacted canines.

INTRODUCTION: In this prospective study, we compared differences in the diagnosis and treatment planning of impacted maxillary canines between 2 imaging modalities. METHODS: Twenty-five consecutive impacted maxillary canines were identified from the pool of patients seeking orthodontic treatment. The first set of radiographs consisted of traditional 2-dimensional (2D) images including panoramic, occlusal, and 2 periapical radiographs. The second set comprised prints of 3-dimensional (3D) volumetric dentition images obtained from a cone-beam computed tomography (CBCT) scan. Seven faculty member completed a questionnaire for every impacted canine and diagnostic radiographic modality (2D and 3D). RESULTS: The data show that the judges produced different decisions regarding localization depending on the x-ray method. There were 21% disagreement (or discordance) in the perceived mesiodistal cusp tip position and 16% difference in the perceived labiopalatal position. In the perception of root resorption of adjacent teeth, there was 36% lack of congruence. Twenty-seven percent of the teeth that were planned to be left, recovered, or extracted with the 2D radiographs had different treatment plans when the judges viewed the 3D CBCT images (McNemar test, chi-square, 4.45; P = 0.035). The clinicians' confidence of the accuracy of diagnosis and treatment plan was statistically higher for CBCT images (P <0.001). CONCLUSIONS: These results showed that 2D and 3D images of impacted maxillary canines can produce different diagnoses and treatment plans.

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

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 patient's 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.

Tobacco control in pediatric dental practices: a survey of practitioners.

PURPOSE: The study purpose was to determine tobacco-related knowledge, attitudes, and practice behaviors of American Academy of Pediatric Dentistry (AAPD) members. METHODS: A 26-item survey was distributed to a national, random sample of 1,700 AAPD members. Frequencies, odds ratios and 95% confidence intervals assessed factors related to tobacco control behaviors. RESULTS: Of 1,700 questionnaires, 1,292 (82%) were returned and usable. Over 75% of respondents agreed that it is a pediatric dentist's responsibility to help patients who wish to stop using tobacco; only 142 (11%) had prior tobacco prevention/cessation training. Of those untrained, 905 (70%) were willing to be trained. Not knowing where to send patients for counseling and feeling ineffective with helping patients to stop their tobacco use were significant barriers reported by nearly half the respondents. Two hundred forty-five (19%) reported always/often asking their adolescent patients about tobacco use; 491 (38%) reported always/often advising known tobacco users to quit; and 284 (22%) reported always/often assisting with stopping tobacco use. Feeling well prepared to ask about tobacco was significantly associated with assisting tobacco users (odds ratio=8.9; 95% confidence interval=6.6-12). CONCLUSION: Continuing education programs are needed to enhance the knowledge and skills of pediatric dentists to promote tobacco control behaviors.

Patterns and correlates of tobacco control behavior among american association of pediatric dentistry members: a cross-sectional national study.

BACKGROUND: To determine the tobacco-related knowledge, attitudes, and practice behaviors among US pediatric dentists. METHODS: A survey was conducted in 1998 among a national, random sample of 1500 American Academy of Pediatric Dentistry members. Chi-square tests and logistic regression with odds ratios (ORs) and 95% confidence intervals assessed factors related to pediatric dentists' tobacco control behaviors. RESULTS: Response was 65% for the survey. Only 12% of respondents had prior tobacco prevention/cessation training. Of those untrained, 70% were willing to be trained. Less than two-thirds correctly answered any of four tobacco-related knowledge items. Over one-half agreed pediatric dentists should engage in tobacco control behaviors, but identified patient resistance as a barrier. About 24% of respondents reported always/often asking their adolescent patients about tobacco use; 73% reported always/often advising known tobacco users to quit; and 37% of respondents always/often assisting with stopping tobacco use. Feeling prepared to perform tobacco control behaviors (ORs = 1.9-2.8), a more positive attitude score (4 points) from 11 tobacco-related items (ORs = 1.5-1.8), and a higher statewide tobacco use prevalence significantly predicted performance of tobacco control behaviors. CONCLUSION: Findings suggest thatraining programs on tobacco use and dependence treatment in the pediatric dental setting may be needed to promote tobacco control behaviors for adolescent patients.

Reliability and validity of a manual dexterity test to predict preclinical grades.

The University of California, San Francisco School of Dentistry wanted to determine if a predental school manual dexterity test predicts: 1) subsequent grades in preclinical restorative courses, and 2) faculty perceptions of satisfactory performance in these skills that would indicate the student is ready to advance to the clinic. The study population was comprised of all 244 applicants admitted to UCSF School of Dentistry's D.D.S. program from Classes of 2000 to 2002 and who matriculated into the program. The manual dexterity test (MDT) consisted of a two-hour block-carving test. Three preclinical faculty, three clinical faculty, and two basic science faculty graded the blocks. Even after instruction and calibration, faculty varied greatly in their grading (intra-rater reliability kappa statistics ranging from 0.34 to 1.00). Two of three preclinical raters gave No Passes for the MDT in 9.8 percent of the incoming, first-year dental students. Of these twenty-three students, only four (17 percent) were in the lower 10 percent of their classes according to their five preclinical restorative laboratory courses after two years, and four (33 percent) were among the twelve students the three preclinical laboratory directors identified as laboratory cautions. The MDT did not significantly (p=0.342) predict students in the bottom 10 percent after five restorative preclinical laboratory courses, above and beyond current admissions criteria. Among current admissions criteria, PAT score was the only item at least moderately correlated with preclinical average percentile class rank (Spearman correlation = 0.34). In conclusion, the MDT did not appear to add information to the current admissions criteria.

Student-led courses to teach cone beam CT in the predoctoral dental curriculum.

Cone beam computed tomography (CBCT) provides a new method to evaluate the craniofacial region. The goal of our project was to introduce into the predoctoral dental curriculum a student-initiated, student-led introduction to CBCT and how to use it, with minimal expenditure of financial resources. A third-year student worked with two faculty members to design a course in which a small number of third-year students would lead a small group of second-year students. The first approach involved each small group of second-year dental students discussing one clinical case in which the patient's CBCT record was included. Representatives of each of the ten small groups presented the patient and that patient's clinical problem (e.g., an impacted tooth) to the entire class as well as demonstrating the superiority and limitations of using CBCT in clinical dentistry. The second approach also used small-group meetings led by third-year dental students, but paired two second-year dental students as a team to present the patient's CBCT data in the small-group setting. There were five teams each presenting a different type of patient as assessed only from the CBCT data. The first model focused on the problem (e.g., an impacted tooth), while the second model focused on how to evaluate and use CBCT scans to determine the patient's primary problem. Based on surveys conducted at the end of each course, the majority of students felt they had gained a better understanding of CBCT.

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.

Three-dimensional changes in the condyle during development of an asymmetrical mandible in a rat: a microcomputed tomography study.

A rapidly growing postnatal animal model was used to study changes in the calcified tissue of the mandibular condyle during altered muscle function. A maxillary occlusal splint was designed to shift the mandible laterally (left) during closure. Groups of 5 Wistar rats were killed at 5, 9, 15, 21, 30, and 40 weeks (n = 30), with an equal number of controls. The experimental animals developed shorter, asymmetrical mandibles compared with the control animals. The left condyle became larger and thicker than the right condyle. Microcomputed tomography assessment of the left and right condylar trabecular bone indicated that both had less bone volume than the control condyle. The right masseter muscle significantly lost fiber size and type IIA oxidative fibers, suggesting that the right masseter muscle was used with less tension development. In contrast, the left masseter maintained its fiber size and was similar to the control masseter fiber diameters. Comparison in the sequence of changes indicated that the morphologic changes occurred first in the ramus (age, 5 weeks), before the corpus (age, 15 weeks), and before changes in masseter fiber size and composition (age, 9 weeks). This study showed that both the mandible and the condyle modified their shape and size, as well as the trabecular bone of the condyle, during shifting of the mandible to one side as it closed.

Comparison between traditional 2-dimensional cephalometry and a 3-dimensional approach on human dry skulls.

The cephalogram is the standard used by orthodontists to assess skeletal, dental, and soft tissue relationships. This approach, however, is based on 2-dimensional (2D) views used to analyze 3-dimensional (3D) objects. The purpose of this project was to evaluate and compare a 3D imaging system and traditional 2D cephalometry for accuracy in recording the anatomical truth as defined by physical measurements with a calibrated caliper. Thirteen skeletal landmarks were located by both radiographic methods on 9 dry human skulls. Intraclass correlation (0.995), variance (0.054 mm(2)), and standard deviation (SD) (0.237 mm) were averaged over 76 measurements and derived from precision calipers to establish these physical measurements as a reliable gold standard to make comparisons of the 2D and 3D radiographic methods. The results showed great variability of the 2D from the gold standard, with the range varying from -17.68 mm (underestimation of Gn-Zyg R) to +15.52 mm (overestimation of Zyg L-Zyg R). In contrast, the 3D method (Sculptor, Glendora, Calif) indicated a range of the SD from -3.99 (underestimation) mm to +2.96 mm (overestimation). The 3D evaluation was much more precise, within approximately 1 mm of the gold standard. These results indicate that, when the actual distance is measured on a human skull in its true dimensions of 3D space, the Sculptor program, by using a 3D method, is more precise and 4 to 5 times more accurate than the 2D approach. Evaluating distances in 3D space with a 2D image grossly exaggerates the true measure and offers a distorted view of craniofacial growth. There is an inherent problem of representing a linear measure occupying a 3D space with a 2D image.

Mechanical strain on the human skull in a humanoid robotic model.

Patterns of strain were analyzed in a dry human skull at 15 different regions on the lateral and medial surfaces of the mandible. The strains were induced with a human robotic system that represented each of 8 bilateral muscles by a DC servomotor connected to a wire and pulley. The tractions of the simulated muscles (masseter, medial pterygoid, anterior temporalis, and posterior temporalis) were increased from 1x to 4x with each representing different levels of traction or force (5, 3, 4, and 4 N, respectively). The study was done with the teeth in maximum intercuspal occlusion. Bite forces were also measured with a transducer and reached a maximum of 40 N on the posterior teeth with less force on the anterior dentition. The smallest traction level (1x) developed some small strains. At 2x, compressive strains developed more on the medial (lingual) side beneath the molars through the corpus and radiated into the anterior ramus. Strains at 3x to 4x significantly increased both the tensile and compressive strains throughout the mandible with more strains developing in the ramus. The increased bilateral traction and loading developed significant compressive forces on both sides of the mandible. Evaluation of disparities between compressive and tensile strains at one site, and comparison between the medial and lateral sides of strain, suggested some visible distortion of portions of the mandible under the higher loads.