Effects of pilot holes on longitudinal miniscrew stability and bony adaptation.

INTRODUCTION: The purposes of this study were to longitudinally evaluate the effects of pilot holes on miniscrew implant (MSI) stability and to determine whether the effects can be attributed to the quality or the quantity of bone surrounding the MSI. METHODS: Using a randomized split-mouth design in 6 skeletally mature female foxhound-mix dogs, 17 MSIs (1.6 mm outer diameter) placed with pilot holes (1.1 mm) were compared with 17 identical MSIs placed without pilot holes. Implant stability quotient measurements of MSI stability were taken weekly for 7 weeks. Using microcomputed tomography with an isotropic resolution of 6 µm, bone volume fractions were measured for 3 layers of bone (6-24, 24-42, and 42-60 µm) surrounding the MSIs. RESULTS: At placement, the MSIs with pilot holes showed significantly (P <0.05) higher implant stability quotient values than did the MSIs placed without pilot holes (48.3 vs 47.5). Over time, the implant stability quotient values decreased significantly more for the MSIs placed with pilot holes than for those placed without pilot holes. After 7 weeks, the most coronal aspect of the 6- to 24-µm layer of cortical bone and the most coronal aspects of all 3 layers of trabecular bone showed significantly larger bone volume fractions for the MSIs placed without pilot holes than for those placed with pilot holes. CONCLUSIONS: MSIs placed with pilot holes show greater primary stability, but greater decreases in stability over time, due primarily to having less trabecular bone surrounding them.

Cortical bone thickness at common miniscrew implant placement sites.

INTRODUCTION: The purpose of this study was to assess age, sex, and regional differences in the cortical bone thickness of commonly used maxillary and mandibular miniscrew implant placement sites. METHODS: Cone-beam computed tomography images, taken at 0.39-mm voxel size, of 52 patients, including 26 adolescents (13 girls, ages 11-13; 13 boys, ages 14-16) and 26 adults (13 men and 13 women, ages 20-45), were evaluated. The cone-beam computed tomography data were imported into 3-dimensional software (version 10.5, Dolphin Imaging Systems, Chatsworth, Calif); standardized orientations were used to measure cortical bone thickness at 16 sites representing the following regions: 3 paramedian palate sites, 1 infrazygomatic crest site, 4 buccal interradicular sites of the mandible, and 4 buccal and 4 lingual interradicular sites in the maxilla. RESULTS: Multivariate analysis of variance (MANOVA) showed no significant differences in cortical bone thickness between the sexes. There were significant (P <0.05) differences between adolescents and adults, with adult cortices significantly thicker in all areas except the infrazygomatic crest, the mandibular buccal first molar-second molar site, and the posterior palate site. Cortical bone was thicker in the posterior than in the anterior mandibular sites. In the adults, interradicular bone in the maxillary first premolar-second premolar, and second premolar-first molar sites was thicker than bone at the lateral incisor-canine and first molar-second molar sites. Anterior paramedian palatal bone was significantly thicker than bone located more posteriorly. The mandibular buccal and infrazygomatic crest regions had the thickest cortical bone; differences between the maxillary buccal, the maxillary lingual, and the palatal regions were small. CONCLUSIONS: Maxillary and mandibular cortical bones at commonly used miniscrew implant placement sites are thicker in adults than in adolescents. There are also differences in cortical bone thickness between and within regions of the jaws that must be considered when placing miniscrew implants.

Relative contributions of occlusion, maximum bite force, and chewing cycle kinematics to masticatory performance.

INTRODUCTION: The purpose of this study was to explore the contributions of occlusion, maximum bite force, and chewing cycle kinematics to masticatory performance. METHODS: A prospective cross-sectional study was performed on 30 subjects with Class I occlusion. Masticatory performance was measured with the test food Cuttersil (Heraeus Kulzer, South Bend, Ind) and the fractional-sieve technique. Blu-Mousse (Parkell Biomaterials, Farmingdale, NY) bite registrations were used to measure occlusal contact areas. The American Board of Orthodontics occlusal discrepancies were measured on the subjects' dental models. Maximum bite forces were recorded with a custom transducer, and 3-dimensional chewing cycle kinematics were tracked with an opto-electric computer system and Optotrak software (Northern Digital, Waterloo, Ontario, Canada). RESULTS: Masticatory performance was most closely correlated with occlusal contact area, indicating larger contact areas in subjects with better performance. Occlusal contact area and occlusal discrepancies were also related to bite force and chewing cycle kinematics. Maximum bite force was positively related with masticatory performance. CONCLUSIONS: Although masticatory performance is related, both directly and indirectly, to a number of morphologic and functional factors, it is most closely related to occlusal factors.

Transverse dentoalveolar changes after slow maxillary expansion.

INTRODUCTION: In this study, we evaluated the transverse dentoalveolar changes in the maxillary first molar region after early treatment with the quad-helix appliance. METHODS: Seventy-three consecutive patients (39 boys, 34 girls) who had phase 1 quad-helix treatment were evaluated with cone-beam computed tomography scans taken before phase 1 (mean age, 9.2 years) and phase 2 (mean age, 11.9 years) treatments. Buccal bone thickness, buccal cortical plate thickness, lingual bone thickness, alveolar width, palatal width, and intermolar width were measured by using standardized orientations. RESULTS: Slow palatal expansion with the quad-helix decreased buccal bone thickness (1.6 mm ± 0.8), and increased lingual bone thickness (1.6 mm ± 1.3) and alveolar width (0.5 mm ± 1.0). Intermolar widths and palatal widths increased 6.5 mm ± 2.9 and 3.9 mm ± 1.8, respectively. At the beginning of phase 2, approximately one third of the patients showed little or no buccal cortical plate on at least 1 side. Patients retained with the Hawley demonstrated some relapse tendencies; patients without retention had the greatest relapse tendencies. CONCLUSIONS: Early treatment with the quad-helix appliance proved to be highly effective in increasing intermolar, palatal, and alveolar widths. The teeth moved through the alveolus, leading to substantial decreases in buccal bone thickness and increases in lingual bone thickness.

Demographic characteristics of orthodontic practice sites in the United States.

Few studies have addressed the demographic characteristics of dental-practice sites, including orthodontic practice sites. In this study, we investigated the demographic characteristics of orthodontic practice sites in the United States. Demographic data and orthodontic practices were organized by zip codes and analyzed with discriminant analysis. The demographic characteristics associated with zip codes that contained an orthodontic practice were determined vs those without an orthodontic practice. The resulting model correctly classified 90.3% of the 30,134 zip code areas, based on the presence or absence of an orthodontic practice. The variables most closely associated with a zip code containing an orthodontic practice included number of dental practices (general practice) and population size. Several variables related to the socioeconomic status of the area were also positively related to zip codes with an orthodontic practice. Further analysis indicated a positive relationship between the model's output and its ability to predict single vs several orthodontic practices in a zip code area. A practical method for assessing the relative merits of alternate site locations is also provided.

Development and testing of multilevel models for longitudinal craniofacial growth prediction.

INTRODUCTION: The aims of this study were to (1) develop longitudinal growth curves that would allow individual variations to be accurately modeled and (2) use these models to predict craniofacial growth changes in children with varying amounts of longitudinal data available. METHODS: Based on a sample of 159 girls (994 cephalograms) and 128 boys (947 cephalograms), multilevel population models were derived. Polynomial models of the population's growth curve were derived for the measurements MPA, Me-X, Me-theta, Me-Y, and Me-R. Angular and horizontal measures (MPA, Me-X, and Me-theta) were described by simpler, second-order models, and vertical measures (Me-Y and Me-R) were described by more complex, fifth-order models. RESULTS: Decreases in MPA during childhood and increases in Me-theta during adolescence could be explained by the relative contributions of the horizontal (Me-X) and vertical (Me-Y) movements of menton. There was greater anterior movement of menton during childhood and greater inferior movement during the adolescent growth spurt. By using varying numbers of longitudinal cephalograms between 6 and 10 years of age, the models were used to predict subjects' craniofacial growth changes from ages 10 to 15. Based on correlations, root mean squared error, and percent accuracy, individual growth predictions for the various measures were found to be highly accurate on an independent subsample drawn from the larger sample and on an independent validation sample. Correlations between predicted and actual values on the sample used to develop the models ranged from 0.81 to 0.95. Accuracy was best for the measurements that changed the most during the prediction period (Me-Y and Me-R), with accuracies between 83% and 90%. More longitudinal data did not increase the predictive accuracy for all measurements. The models that were least accurate (Me-X, MPA, and Me-theta) showed the greatest improvement in prediction accuracy with more longitudinal data. These improvements ranged from 1.6% to 15%. CONCLUSIONS: Longitudinal growth curves based on multilevel procedures can accurately describe population and individual growth curves, and 5-year predictions with this method are highly accurate and externally valid.

Variation in Class II malocclusion: comparison of Mexican mestizos and American whites.

This study compared the skeletal and dental characteristics of Class II Division 1 white Americans and Mexicans. It was designed specifically to the evaluate ethnic, age, and sex differences of 101 whites and 107 Mexican mestizos, with approximately equal numbers in each subgroup. Three-way analyses of variance were used to simultaneously evaluate the effects of age, sex, ethnicity, and their interactions. Although Mexicans and whites in the United States had similar maxillomandibular relationships, Mexicans showed greater protrusion of the jaws and teeth. Mexican subjects with Class II malocclusions also showed less divergence of the cranial base (SN-FH angle) and greater vertical tendencies (MPA, Y-axis, and palatal plane angle) than their white counterparts. In comparison with children (mean age 9.0 years), young adults (mean age 20.1 years) had significantly larger craniofacial dimensions, jaws that were positioned more forward, and teeth that were more protruded. Sex differences pertained only to size (men were larger) and maxillary incisor angulation (men were more protrusive). The findings pertaining to the ethnic differences have important clinical implications regarding treatment decisions for Mexican and white patients. In addition, this study provides a foundation for future studies pertaining to Class II malocclusion in Mexicans.