Biomedical subjects

Rolf G Behrents

Publications and source records attributed to Rolf G Behrents.

6 recordsLinked to original sources

PubMed2006

Craniofacial growth in growth hormone-deficient rats after growth hormone supplementation.

INTRODUCTION: Growth hormone (GH) supplementation is an established therapy to increase stature in GH-deficient or short-for-age children, but comparatively little is known of its effects on the craniofacial skeleton. METHODS: Using a mutant strain of Lewis rats (dw/dw) in which GH levels were 6% to 10% of normal, but other trophic hormones were unaffected, we investigated the differential susceptibility of craniofacial measures to GH supplementation, characterized their potential for partial or complete catch-up growth, and compared their growth changes with those in long bones. At 24 days of age and for 3 subsequent weeks, radiographs of the lateral head, upper limb, and lower limb were obtained from 3 groups of growing rats (n = 8-9 in each group): dwarf (experimental) with GH injection, dwarf (sham) with vehicle injection, and wild type (control) with vehicle injection. The x-ray images were scanned, standardized points digitized, and linear distances measured. Absolute growth curves were generated for each group by using multilevel modeling procedures and iterative generalized least-squares curve fitting. RESULTS: For every measure, growth differences were evident between the experimental and the sham groups, but the treatment effect varied inversely with relative maturity of the measure. Although all craniofacial measures showed some catch-up growth, only 31% of craniofacial measures had complete catch-up compared with all limb measures. The percentage of catch-up varied inversely with relative maturity of the measure. Our results suggest that the effects of GH supplementation vary considerably, so that measures with the lowest relative maturity (greatest baseline potential) show the greatest treatment effect and catch-up, whereas more mature measures show less growth response to GH replacement. CONCLUSIONS: These results suggest that, depending on the timing of GH supplementation, there is potential for change in proportions or shape of the craniofacial complex.

Age Factors↗

PubMed2005

Ethnic differences in upper lip response to incisor retraction.

INTRODUCTION: The purpose of this retrospective longitudinal study was to investigate the response of the upper lip to incisor retraction and to ascertain the effect of ethnicity on this response. METHODS: Pretreatment and posttreatment lateral cephalograms of 88 postpubertal female patients (44 black and 44 white; mean age, 18.45 years) were evaluated. The groups were matched by age and the amount of incisor retraction at incisor superius. RESULTS: Although significant pretreatment differences existed between the groups in some cephalometric measurements, analysis of the treatment changes demonstrated significant differences only in incisor inclination. Hard and soft tissue changes of the black group were more downward, whereas changes in the white group were more backward. Multivariate regression analysis showed that the horizontal response of the upper lip to hard tissue changes at subnasale and superior labial sulcus was different in whites than in blacks. At subnasale, stepwise multivariate regression analysis showed that ethnicity contributed to the upper lip response to incisor retraction and was significantly greater in the white group. CONCLUSIONS: The hard and soft tissue treatment changes of the black group were more downward, and those of the white group were more backward. Ethnic differences exist in the soft tissue response to hard tissue changes in the upper lip, and at subnasale and the superior labial sulcus; however, these response differences at superior labial sulcus can be explained by the ethnic differences in initial lip thickness and incisor inclination; they are not due in and of themselves to ethnicity. The change at prosthion was significantly correlated with the response of the upper lip at labrale superius to incisor retraction. Ethnicity added no increase to the predictability of the response. When incisor retraction was performed, the final horizontal upper lip position could be accurately and reliably predicted.

Adolescent↗

PubMed2005

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.

Adolescent↗

PubMed2005

Long-term profile changes in extraction and nonextraction patients.

INTRODUCTION: The purpose of this investigation was to determine the long-term differences in soft tissue profile changes between extraction and nonextraction patients who had been treated to the same incisor position and lip line. METHODS: Twenty extraction and 20 matched nonextraction patients, with posttreatment and long-term follow-up (average 15 years) records, were selected from a single private orthodontic practice. Posttreatment and long-term follow-up profile photos of the patients' nose, lip, and chin areas were evaluated by 105 orthodontists and 225 laypeople, who indicated their preferences and the amount of change they perceived among the 40 profiles. The patients had similar dental protrusion, soft tissue profile measurements, and ages at the posttreatment observation. RESULTS: No significant cephalometric differences between the extraction and nonextraction groups were found at long-term follow-up; both groups showed similar long-term changes. Significant (P < .05) differences were found between males and females at long-term follow-up; male lips became relatively more retrusive, and their profiles became flatter. Significant (P < .05) changes in the profiles were also perceived over time, but there was no relationship between the amount of change perceived and profile changes measured cephalometrically. There were also no significant (P < .05) differences in preferences between orthodontists and laypeople, between extraction and nonextraction patients, or between males and females. CONCLUSIONS: If extraction and nonextraction patients are treated to the same incisor position and lip line, the treatment modality does not affect long-term soft tissue profile changes. Furthermore, the amounts of change perceived by either orthodontists or laypeople were not related to the amount of change measured cephalometrically.

Bicuspid↗

PubMed2005

Tooth shape preferences in an esthetic smile.

INTRODUCTION: The purpose of this study was to evaluate the contributions of tooth shape to the esthetic smile. METHODS: Restorative dentists (120), laypeople (102), and orthodontists (113) evaluated a series of color photographs of men's and women's smiles. The photographs were randomly presented to test the effects of 3 different shapes of maxillary incisors and canines on the same patient. RESULTS: For women, orthodontists preferred round and square-round incisors (P < .01), and restorative dentists preferred round incisors (P < or = .03). Laypeople did not discriminate between incisor shapes. For men, all 3 groups preferred square-round incisors (P < or = .042). There was also a tendency for male judges to rate female images more attractive than did female judges. CONCLUSIONS: Restorative dentists, orthodontists, and laypeople share similarities and display differences when considering esthetic preferences in tooth shape. Although there was no consensus in preference among the laypeople as a group, their preferences differed from those of the dental professionals.

Adult↗

PubMed2004

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.

Adolescent↗