Rolf G. Behrents

Components of Class III Malocclusion in Juveniles and Adolescents

A statistical comparison of cross-sectional cephalometric records of Class III malocclusion subjects from ages 5-15 with serial Class I controls, finding strong tendencies for early appearance of distinctive characteristics.

Sexual dimorphism in normal craniofacial growth.

The purpose of this investigation is to re-evaluate an existing sample of Caucasian individuals, of mostly Northern European ancestry and undefined ethnic origins, who have been characterized as having excellent occlusions and balanced facial proportions (from a subjective assessment). The focus is the emergence of sexual dimorphism in the skeletal and dental relationships. Serial lateral cephalograms of 51 subjects were obtained from the Bolton-Brush Study at ages 6, 9, 12, 14, 16 and 18 yrs. At each age, the records of 16 males and 16 females were selected. Cephalometric evaluation indicated that the length of the anterior cranial base was larger in males but the cranial base angle was similar for both sexes at all age intervals studied. The effective lengths of the maxilla and mandible were similar in both sexes up to 14 years; thereafter in females this length remained relatively constant while in males it increased. The direction of facial growth was similar for both sexes, with a tendency towards a more horizontal growth pattern in females.

The pattern of facial skeletal growth and its relationship to various common indexes of maturation

INTRODUCTIONnSequential stages in the development of the hand, wrist, and cervical vertebrae commonly are used to assess maturation and predict the timing of the adolescent growth spurt. This approach is predicated on the idea that forecasts based on skeletal age must, of necessity, be superior to those based on chronologic age. This study was undertaken to test this reasonable, albeit largely unproved, assumption in a large, longitudinal sample.nnnMETHODSnSerial records of 100 children (50 girls, 50 boys) were chosen from the files of the Bolton-Brush Growth Study Center in Cleveland, Ohio. The 100 series were 6 to 11 years in length, a span that was designed to encompass the onset and the peak of the adolescent facial growth spurt in each subject. Five linear cephalometric measurements (S-Na, Na-Me, PNS-A, S-Go, Go-Pog) were summed to characterize general facial size; a sixth (Co-Gn) was used to assess mandibular length. In all, 864 cephalograms were traced and analyzed. For most years, chronologic age, height, and hand-wrist films were available, thereby permitting various alternative methods of maturational assessment and prediction to be tested. The hand-wrist and the cervical vertebrae films for each time point were staged. Yearly increments of growth for stature, face, and mandible were calculated and plotted against chronologic age. For each subject, the actual age at onset and peak for stature and facial and mandibular size served as the gold standards against which key ages inferred from other methods could be compared.nnnRESULTSnOn average, the onset of the pubertal growth spurts in height, facial size, and mandibular length occurred in girls at 9.3, 9.8, and 9.5 years, respectively. The difference in timing between height and facial size growth spurts was statistically significant. In boys, the onset for height, facial size, and mandibular length occurred more or less simultaneously at 11.9, 12.0, and 11.9 years, respectively. In girls, the peak of the growth spurt in height, facial size, and mandibular length occurred at 10.9, 11.5, and 11.5 years. Height peaked significantly earlier than both facial size and mandibular length. In boys, the peak in height occurred slightly (but statistically significantly) earlier than did the peaks in the face and mandible: 14.0, 14.4, and 14.3 years. Based on rankings, the hand-wrist stages provided the best indication (lowest root mean squared error) that maturation had advanced to the peak velocity stage. Chronologic age, however, was nearly as good, whereas the vertebral stages were consistently the worst. Errors from the use of statural onset to predict the peak of the pubertal growth spurt in height, facial size, and mandibular length were uniformly lower than for predictions based on the cervical vertebrae. Chronologic age, especially in boys, was a close second.nnnCONCLUSIONSnThe common assumption that onset and peak occur at ages 12 and 14 years in boys and 10 and 12 years in girls seems correct for boys, but it is 6 months to 1 year late for girls. As an index of maturation, hand-wrist skeletal ages appear to offer the best indication that peak growth velocity has been reached. Of the methods tested here for the prediction of the timing of peak velocity, statural onset had the lowest errors. Although mean chronologic ages were nearly as good, stature can be measured repeatedly and thus might lead to improved prediction of the timing of the adolescent growth spurt.

Pitch and Longitudinal Fluting Effects on the Primary Stability of Miniscrew Implants

OBJECTIVEnTo test the hypotheses that pitch and fluting have no effect on the primary stability of miniscrew implants (MSIs).nnnMATERIALS AND METHODSnMaximum placement torque and pullout strength of experimental MSIs were compared with those of control MSIs with the use of synthetic and cadaver bone. MSIs with 1.00 mm pitch were compared with those with 1.25 mm and 0.75 mm pitch; MSIs with three longitudinal flutes were compared with the same MSIs without flutes. A total of 60 MSIs (15 of each design) were evaluated with synthetic bone; a split-mouth cadaver model was used to compare the three experimental designs against the 1 mm control MSIs (total of 90 MSIs).nnnRESULTSnThe synthetic bone model showed higher placement torque and pullout strength for the 0.75 pitch than for the 1.0 mm and 1.25 mm pitch MSIs, but differences were significant (P < .05) only for pullout strength. The cadaver model showed no significant differences in placement torque or pullout strength associated with pitch. Both synthetic and cadaver bone models showed that MSIs with flutes had significantly (P < .05) higher placement torque and pullout strength. Spearman correlations between placement torque and pullout strength were statistically significant for both synthetic (r = .504) and cadaver (r = .502) bone.nnnCONCLUSIONnWithin limits, decreasing MSI pitch increases pullout strength, and fluting increases both placement torque and pullout strength.

Cortical bone and ridge thickness of hyperdivergent and hypodivergent adults.

INTRODUCTIONnThe purpose of this study was to assess differences in dentoalvolar cortical bone thickness between hyperdivergent and hypodivergent young adults.nnnMETHODSnPretreatment cone-beam computed tomography images of 57 patients, including 30 hypodivergent subjects (22 women, 8 men) and 27 hyperdivergent subjects (20 women, 7 men), were analyzed. The data were imported into imaging software (version 10.5; Dolphin Imaging Systems, Chatsworth, Calif); standardized orientations were used to measure buccal and lingual cortical bone thicknesses at 16 interradicular sites of the maxilla and the mandible. Total alveolar ridge thickness and medullary space thickness were measured at the same sites.nnnRESULTSnT tests showed significant (Pxa0<0.05) group differences, with hypodivergent subjects having significantly thicker buccal cortices. The lingual cortex of the maxilla was also significantly thicker in the hypodivergent than in the hyperdivergent subjects. Alveolar ridge thickness was significantly greater at all sites of the hypodivergent mandible and at the anterior 2 sites of the hypodivergent maxilla. Medullary thickness was significantly greater only in the hypodivergent mandibles between the first molars and the second premolars, and between the first and second premolars. Buccal cortical bone was significantly thicker than lingual cortical bone in the mandible; lingual bone was significantly thicker in the maxilla.nnnCONCLUSIONSnCortical bone tends to be thicker in hypodivergent than in hyperdivergent subjects. This explains the concomitant differences in alveolar ridge thickness. Medullary space thickness is largely unaffected by facial divergence.

Evaluation of skeletal and dental asymmetries in Angle Class II subdivision malocclusions with cone-beam computed tomography

INTRODUCTIONnThe purpose of this study was to determine whether Angle Class II subdivision malocclusions have skeletal or dental asymmetries between the Class II and Class I sides.nnnMETHODSnA sample of 54 untreated Angle Class II subdivision patients with pretreatment photos and cone-beam computed tomography (CBCT) scans was used. The photos were used to identify the Class II subdivision malocclusion and to record the amount of crowding per quadrant. Landmarks were plotted on each CBCT volume so that direct 3-dimensional measurements could be made to compare the positions and dimensions of the skeletal and dental structures on the Class II side vs the Class I side.nnnRESULTSnSignificant differences were found for 2 skeletal measurements: the position of the maxilla relative to the cranial base, and the mandibular dimension from the mandibular foramen to the mental foramen. Statistically significant dental differences were found for the position of the mandibular first molars and canines in relation to the maxilla and the mandible. Statistically significant differences were found for the maxillary first molars and canines in relation to the mandible.nnnCONCLUSIONSnThere were significant skeletal and dental differences between the Class I and Class II sides. The dental asymmetries accounted for about two thirds of the total asymmetry.

Effects of screw and host factors on insertion torque and pullout strength

OBJECTIVEnTo experimentally study the effects of altering implant length, outer diameter, cortical bone thickness, and cortical bone density on the primary stability of orthodontic miniscrew implants (MSIs).nnnMATERIALS AND METHODSnMaximum insertion torque (IT) and pullout strength (POS) of 216 MSIs were measured in synthetic bone with different cortical densities (0.64 g/cc or 0.55 g/cc) and cortical thicknesses (1 mm or 2 mm). Three MSIs were evaluated: 6-mm long/1.75-mm outer diameter, 3-mm long/1.75-mm outer diameter, and 3-mm long/2.0-mm outer diameter. To test POS, a vertical force was applied at the rate of 5 mm/min until failure occurred.nnnRESULTSnThe 6-mm MSIs displayed significantly (P < .001) higher IT and POS than the 3-mm MSIs did. The 3-mm MSIs with 2.0-mm outer diameters showed significantly higher (P < .001) IT and POS than the 3-mm MSIs with 1.75-mm outer diameters. The IT and POS were significantly (P < .001) greater for the MSIs placed in thicker and denser cortical bone.nnnCONCLUSIONnBoth outer diameter and length affect the stability of MSIs. Increases in cortical bone thickness and cortical bone density increase the primary stability of the MSIs.

Stability of immediately loaded 3- and 6-mm miniscrew implants in beagle dogs―a pilot study

INTRODUCTIONnWe compared the stability of 3- and 6-mm long miniscrew implants (MSIs) loaded with orthopedic force levels.nnnMETHODSnUsing a split-mouth experimental design, we placed MSIs into the jaws of 5 mature beagle dogs and immediately loaded them for 6 weeks. Continuous forces were applied by reciprocally loading pairs of MSIs with nickel-titanium coil springs. The mandibles had the 3-mm MSIs randomly loaded with forces of 600 or 900 g. In the maxilla, the 3- and 6-mm MSIs were randomly assigned and loaded with 600 g of force. An unloaded, control MSI was placed in each quadrant. Overall success was defined as MSIs that remained intact; net success rates excluded MSIs that had sheared off and all implants placed in a dog that frequently chewed his run bars and food bowl.nnnRESULTSnThe overall success rates of the loaded and the control 6-mm MSIs were 100%. Overall and net success rates for the 3-mm experimental MSIs were 66.7% and 95.2%, respectively. Similarly, the overall and net success rates of the 3-mm control MSIs were 66.7% and 81.8%, respectively. The overall success rates of the 3-mm mandibular MSIs loaded with 900 and 600 g of force were both 60%; their net success rates were 100% with 900 g and 85.7% with 600 g. Overall success rates of the 3-mm experimental MSIs in the maxilla and the mandible were 80% and 60%, repectively. The net success rates were 100% (maxilla) and 85.7% (mandible). There were no significant (P > 0.05) differences in stability associated with force or location. The loaded 3- and 6-mm MSI pairs demonstrated significant decreases in interimplant distance, averaging 2.2 and 1.8 mm, respectively; the 3-mm MSIs loaded with 900 g showed significantly more displacement than those loaded with 600 g.nnnCONCLUSIONSnSuccess rates of immediately loaded 3-mm MSIs were significantly lower than those of immediately loaded 6-mm MSIs. Neither force nor location explained differences in the success rates. The linear displacements of the MSIs were associated with load amount rather than implant length.

Mandibular dimensions of subjects with asymmetric skeletal Class III malocclusion and normal occlusion compared with cone-beam computed tomography

INTRODUCTIONnThe purpose of this study was to use cone-beam computed tomography to compare mandibular dimensions in subjects with asymmetric skeletal Class III malocclusion and those with normal occlusion.nnnMETHODSnCone-beam computed tomography scans of 38 subjects with normal occlusion and 28 patients with facial asymmetry were evaluated and digitized with Invivo software (Anatomage, San Jose, Calif). Three midsagittal and 13 right and left measurements were taken. The paired t test was used to compare the right and left sides in each group. The Mann-Whitney U test was used to compare the midsagittal variables and the differences between the 2 sides of the group with normal occlusion with those of asymmetry patients.nnnRESULTSnThe posterior part of the mandibular body showed significant differences between the deviated and nondeviated sides in asymmetric Class III patients. The difference of the asymmetry group was significantly greater than that of the normal occlusion group for the mediolateral ramal and the anteroposterior condylar inclinations (P = 0.007 and P = 0.019, respectively).nnnCONCLUSIONSnThe asymmetric skeletal Class III group showed significant differences in condylar height, ramus height, and posterior part of the mandibular body compared with the subjects with normal occlusion. These results might be useful for diagnosis and treatment planning of asymmetric Class III patients.

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

OBJECTIVEnTo describe the growth, maturation, and remodeling changes of the mandible during infancy and early childhood.nnnMATERIALS AND METHODSnSeven Bolton-Brush Growth Study longitudinal cephalograms (N = 336) of each of 24 females and 24 males, taken between birth and 5 years of age, as well as early adulthood, were traced and digitized. Five measurements and nine landmarks were used to characterize mandibular growth, remodeling, and degree of adult maturity.nnnRESULTSnOverall, mandibular length showed the greatest growth changes, followed by ramus height and corpus length. Corpus length was the most mature of the three linear measures; ramus height was less mature than overall mandibular length. The greatest growth rates occurred between 0.4-1 year; yearly velocities decelerated thereafter. The ramus remodeled superiorly only slightly more than it remodeled posteriorly. Male mandibles were significantly (P < or = .05) larger, displayed greater growth rates, and were significantly less mature than female mandibles. There were no significant differences in mandibular growth or maturation between Class I and Class II patients.nnnCONCLUSIONSnThe mandible displays decelerating rates of growth and a maturity gradient during infancy and early childhood, with males showing more growth and being more mature than females.