An ultrasound investigation of the lip levator musculature.

The aims of this study were to determine if there were any differences in the thickness of the lip levator musculature in men and women, and whether the height of the smile line in adults was related to the thickness of the lip levator musculature. Thirty Caucasian (13 males, 17 females), and 24 Asian (11 males, 13 females) undergraduate dental students participated in this study. The subjects were placed in high, medium, and low smile-line groups, according to the height of their upper lip while smiling. The thickness of the levator labii superioris and zygomaticus major muscles was measured on ultrasound scans of the relaxed muscles. Gender, right-left side, and ethnic differences in muscle thickness were determined, and the thicknesses of the lip levator musculature in subjects in the high, medium, and low smile-line groups were compared. There were significantly more women than men with high smile-lines and the zygomaticus major muscle was significantly thicker in the women, as compared with the men. There were, however, no statistically significant differences in muscle thickness in the three smile-line groups. While it appears that women have higher smile-lines and significantly thicker zygomaticus major muscles than men, the height of the smile line is not due to the thickness of either the levator labii superioris or zygomaticus major muscles.

Alterations to mandibular form following motor denervation of the masseter muscle. An experimental study in the rat.

The form of the mandible in young rats was studied following denervation of the masseter muscle. Wistar-derived male rats aged 27 d were randomly assigned either to experimental, sham-operated or control groups. The main trunk and initial branches of the masseteric nerve were resected on one side in each experimental animal. The nerve was exposed, but not resected, in the sham-operated group. No surgery was performed on the control group. All animals were killed at 69 d of age, examined and standardised contact radiographs taken of the cleaned and dried mandibles. Radiographic measurements describing the form and size of the mandibles were compared. On the operated side in the experimental animals the masseter muscle was smaller and the temporalis muscle larger as compared with the unoperated side. The angular process and the subcondylar incisure were also smaller and the coronoid process was positioned more rostrally. The most striking feature was that relatively little change accompanied denervation of masseter in the growing experimental rats. It is concluded that some of the changes previously attributed to muscle denervation may be due to other causes.

Linkage of an autosomal dominant clefting syndrome (Van der Woude) to loci on chromosome Iq.

Van der Woude syndrome (VWS) is an autosomal dominant disorder in which affected individuals have one or more of the following manifestations: cleft lip, cleft palate, hypodontia, or paramedian lower-lip pits. VWS is a well-characterized example of a single-gene abnormality that disturbs normal craniofacial morphogenesis. As a first step in identifying genes involved in human development, we used a candidate-gene-and-region approach to look for a linkage to VWS. Six families with 3 or more generations of affected individuals were studied. Evidence for linkage (theta = 0.02, lod score = 9.09) was found between the renin (REN) gene on 1q and VWS. Other linked loci included CR1, D1S58, and D1S53. The genes for laminin B2 (LAMB2), a basement-membrane protein, and for decay-accelerating factor (DAF) were studied as possible candidate genes on 1q. Recombinants between VWS and both LAMB2 and DAF excluded these genes from a causal role in the etiology of VWS for the families studied in this report. Multipoint linkage analysis indicated that the VWS locus was flanked by REN and D1S65 at a lod score of 10.83. This tight linkage with renin and other nearby loci provides a first step in identifying the molecular abnormality underlying this disturbance of human development.

Growth of the humerus after denervation. An experimental study in the rat.

The purpose of the study was, firstly, to determine if muscle activity in the rat has any effect on the growth in length of the humerus and on the migration of the deltoid tuberosity and, secondly, to evaluate the effect of muscle activity on the size and shape of the deltoid tuberosity. Three groups of 25 days old male rats were used. In the first group the brachial plexus innervating one forelimb was resected (the treatment side) and the opposite side was unoperated (the non-treatment side). The second group was sham-operated on one side and the third group, the control group, was unoperated. All animals were killed at 53 days of age and the dried humeri measured and compared. For all dimensions the experimental group varied significantly from the remaining two groups in the magnitude of the differences between the treatment and non-treatment sides. In the experimental group the deltoid tuberosities were smaller, less curved, and closer to the proximal end of the bone in humeri from the treatment sides compared to humeri from the non-treatment sides. Humeri from the treatment sides were significantly shorter and were narrower opposite the deltoid tuberosity. A prominent nutrient artery canal was significantly closer to the proximal end of the bone in humeri from the treatment side. These results indicate that after denervation more growth occurred distally and less growth occurred proximally. The differences were, however, small. The present study provides evidence of the contribution made by muscle activity to the form and growth in length of a long bone, and provides indirect evidence of the interaction between the activity of the growth plates and periosteal tension. It is postulated that muscle pull affects periosteal tension and consequently bone form and growth in length.

Growth spurts in transplanted rat humeri in adult hosts.

The growth of young rat humeri, some with small metallic implants, when transplanted to older sex-matched isohistogenic hosts has been studied longitudinally using radiography. Similarities between the pattern of growth at the proximal growth plate of transplanted humeri and that in intact humeri were found. The distal ends of the transplanted bones underwent resorption. Resorption did not occur at the distal end of the intact bones. Significant negative correlations were found between the age of the host and the bone marker to distal end length in the male humerus transplants at 47 and 54 days; and between the bone marker to proximal end length in the female transplants at 61 and 75 days. Significant negative correlations were also found between the age of the host and the velocity of growth of the bone marker to proximal end length in the female humerus between 19 and 26, 33 and 47 and, 54 and 61 days. These findings support the view that intrinsic, presumably genetic factors regulate the pattern of timing of growth velocity changes in the humerus.

Growth spurt in rat cranial bases transplanted into adult hosts.

The growth of young rat cranial bases, consisting of the basioccipital, basisphenoid and a fragment of presphenoid bones, transplanted to older sex-matched isohistogenic hosts has been studied longitudinally. Detailed figures are given for absolute growth and velocity of growth both in transplants and in situ. Similarities between the pattern of growth of basisphenoid and in particular the timing of the so-called adolescent growth spurt in the transplanted bones and in situ were found. There was less similarity in the pattern of velocity changes in basiocciput. This was attributed to resorption of basion in the transplants. Significant negative correlations were found between host age and basioccipital length in the females and the velocity of growth of the basisphenoid in the males between 47 and 54 days. There was also a trend for host age to be negatively correlated with basisphenoid length in the males. These findings support the view that intrinsic, presumably genetic, factors regulate the pattern of timing of growth velocity changes in the cranial base.

Growth of transplants of rat humerus following circumferential division of the periosteum.

The growth of transplants of young rat humeri has been studied following circumferential division of the periosteum at either the proximal or the distal end of the shaft. Periosteal division resulted in bones that were longer than those in which the periosteum was not cut. Following proximal division the experimental bones grew 30% more at both ends than the control bones and 16% more at the proximal end following distal division. There was, however, no difference between the growth of the experimental and control bones at the distal end following distal division of the periosteum. The experimental humeri had less new subperiosteal bone deposited over their diaphyses than the control humeri. These findings support the view that the periosteum is under tension as a result of the activity of the growth plates, and that changes in periosteal tension affect both the growth in length and the deposition of subperiosteal bone.

Treatment planning from study models: an examiner variability study.

Four orthodontists of comparable but differing experience examined fifty sets of study models obtained from a random sample of 12 year-old schoolgirls. On the basis of these study models only, assessments were made of need for treatment, for timing, length and complexity of treatment. The degrees of agreement have been analysed and discussed.