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Biomedical subjects

R J Hinton

Publications and source records attributed to R J Hinton.

At least 37 records · Page 2Linked to original sources
PubMed1990

Myotomy of the lateral pterygoid muscle and condylar cartilage growth.

The influence of lateral pterygoid muscle activity on growth of the condylar cartilage of the mandible remains controversial. As a case in point, two recent studies involving total resection (myectomy) and sectioning (myotomy) of this muscle have come to contradictory conclusions. In the study reported here, it was found that young growing rats in which the lateral pterygoid muscle was bilaterally cut experienced significantly retarded mitotic activity and bone formation relative to their sham-operated counterparts. Changes in the shape and topographical distribution of cartilage over the condylar head, as well as the distribution of labelled cells, were also noted in myotomy animals at 4 days following surgery. Considerable resorption at the insertion of the muscle on the mandibular ramus was apparent at 14 days after surgery. However, the myotomy surgery was accompanied by a significant post-operative loss of body weight and incisal supra-eruption indicative of feeding difficulties, thereby complicating interpretation of the results.

Animals↗
PubMed1989

Effect of condylotomy on matrix synthesis and mineralization in the rat mandibular condylar cartilage.

Little information is available about the influence of biomechanical factors on the rate of matrix synthesis and mineralization in the condylar cartilage. In an attempt to temporarily disrupt articular forces at the temporomandibular joint, bilateral condylotomies were performed on 29 day-old male Sprague-Dawley rats. Animals which underwent a similar surgical procedure except for actual condylotomy comprised a sham-operated control group; a non-operated third group served as further controls. Incorporation of [35S]-sulphate did not differ among the groups at 18 h and 2 days after condylotomy, but was significantly reduced in condylotomy animals at 7 and 14 days. Total alkaline phosphatase activity was reduced at 18 h and increased at 14 days by condylotomy, with no differences at the intermediate time intervals; similarly 45Ca-uptake was increased at the 14-day interval. Thus both matrix synthesis and mineralization of the condylar cartilage were altered in the 2 weeks after condylotomy. The changes are in general similar to those noted in other studies after a lessening or removal of articular forces from the condyle.

Alkaline Phosphatase↗
PubMed1988

Response of the intermaxillary suture cartilage to alterations in masticatory function.

Like the condylar cartilage of the mandible, the cartilage at the intermaxillary suture in the rat is secondary in origin and persists well into adulthood. While the condylar cartilage is generally considered to be responsive to changes in its local biomechanical environment, little is known of the response of the intermaxillary suture cartilage to similar stimuli. In order to study the effect of changes in occlusal loads on intermaxillary suture cartilage metabolism, male weanling Sprague-Dawley rats were divided into four groups: soft diet (to discourage molar mastication), incisor clipped (to discourage incision), incisor clipped/soft diet (both treatments), and control (untreated). At 39 days of age, the intermaxillary suture opposite the first molars was removed and compared to control tissue by using histological, histochemical, and biochemical analyses. Alcian blue-stained coronal sections demonstrated moderate decreases in staining intensity and decreased chondrocyte hypertrophy in the soft diet and incisor-clipped groups. However, sutures in the incisor-clipped/soft diet group showed a considerably reduced extent of cartilage and greatly diminished cartilage hypertrophy. [35S]-sulfate incorporation (dpm/micrograms DNA) into acid-insoluble proteoglycans was significantly reduced (P less than or equal to .01) in all three experimental groups compared to controls. [35S] incorporation was further reduced in the incisor-clipped/soft diet group relative to both of the other experimental groups. Staining for alkaline phosphatase activity showed decreased intensity in the experimental groups and was almost absent in the incisor-clipped/soft diet group. These data demonstrate the plasticity of the intermaxillary suture cartilage and provide circumstantial evidence that the observed changes in cartilage morphology and metabolism may be attributable to alterations in the local biomechanical environment of the suture.

Alkaline Phosphatase↗
PubMed1988

Effect of altered masticatory function on [3H]-thymidine and [35S]-sulfate incorporation in the condylar cartilage of the rat.

The response of the condylar cartilage to alterations in compressive joint reaction forces in vivo has been little studied. In an attempt to reduce or eliminate the occlusal forces resulting from mastication or incision, male weanling rats were fed a soft diet requiring little chewing and/or had their incisors clipped every other day. Incorporation (dpm/micrograms DNA) of [3H]-thymidine and [35S]-sulfate was significantly decreased relative to controls in the incisor-clipped group, but not in the soft-diet group. Animals having both treatments also exhibited significantly lower incorporation values than controls, suggesting the importance of incision for loading at the mandibular joint. These data corroborate in vitro studies which suggest that compressive forces can affect mitotic activity and synthesis of proteoglycans in the condylar cartilage. However, additional factors, both hormonal and biomechanical in nature, may be important in the in vivo environment.

Animals↗
PubMed1987

Effect of condylotomy on DNA synthesis in cells of the mandibular condylar cartilage in the rat.

The role of articular forces and the periosteal envelope in the regulation of condylar cartilage growth is uncertain. Transection of the condylar neck, or condylotomy, influences both by a temporary reduction of articular forces and a transient release of the ramus periosteal envelope. To investigate the effects of this procedure on proliferative activity of the prechondroblast layer of the condylar cartilage, bilateral condylotomies were performed on 29-day-old male Sprague-Dawley rats. A surgical control group underwent identical incision without condylotomy and a non-operated third group also served as controls. Eighteen hours after surgery, there was no difference in [3H]-thymidine incorporation among the different treatment groups. However, by two days after surgery, [3H]-thymidine incorporation was significantly higher in the condylotomy group than in either surgical or untreated controls. Incorporation values remained significantly higher in condylotomy animals at seven days after surgery, but declined to control levels by 14 days after surgery. These findings support other radioautographic and cephalometric evidence of an increased growth rate of the condylar cartilage after condylotomy, but suggest that the increase may be transient and perhaps related to the disruption and restoration of articular function.

Animals↗
PubMed1986

Response of the mandibular joint to loss of incisal function in the rat.

In a study of the rat mandibular joint (MJ), Simon [Acta anat. 97: 351-360 (1977)] suggested that reduction in condylar cartilage thickness noted in animals subjected to removal or trimming of incisors resulted from the lessening of joint reaction forces produced during incision. In order to explore this question further, the microanatomy of the MJ in 47-day-old rats whose incisors had been trimmed every other day was compared to that in control animals and in a third group fed a soft diet as a control for reduced joint reaction forces. Both the incisor-clipped and soft-diet groups exhibited reduced size and density of bony trabeculae underlying the condylar cartilage and diminished staining for alcian blue. The thickness of the prechondroblastic layer of the condylar cartilage was significantly (p less than or equal to 0.01) reduced relative to controls in both experimental groups on the superior aspect of the cartilage, but was reduced in the more posterior parts of the cartilage only in the incisor-clipped group. While not denying that joint reaction forces may affect MJ response, the reduced proliferative response noted in the posterior region of the condylar cartilage in incisor-clipped animals is perhaps best explained by a decrease in the frequency and extent of protrusion of the lower jaw due to a lack of incisal preparation of food items.

Animals↗
PubMed1985

Recovery of jaw muscle function following injection of a myotoxic agent (lidocaine-epinephrine).

Intramuscular injection of 2% lidocaine hydrochloride with epinephrine (1:100,000) bilaterally into the masseter muscles of growing rats resulted in a 30% to 40% decrease in maximal stimulated bite force at 3 days following injection. By 6 days postinjection, bite force had begun to increase, but significant differences from control bite force levels were still present 15 days postinjection. By 25 days postinjection, recovery to control values was complete. These data are consistent with previously documented fiber destruction and subsequent regeneration following exposure to this and other local anesthetic agents. It is suggested that local myotoxic effects produced by the administration of such drugs may result in a transient functional deficit in the injected muscle(s) that may persist for up to 2 weeks.

Animals↗
PubMed1983

Histological changes in the articular eminence and mandibular fossa during growth of the rhesus monkey (Macaca mulatta).

Unlike the mandibular condyle, the temporal component of the temporomandibular joint (TMJ) has been the object of relatively few investigations concerning its growth and remodeling. This report provides qualitative and quantitative documentation of microanatomical changes in the mandibular fossa and articular eminence during growth of the rhesus monkey (Macaca mulatta). The thickness of the fibrous articular tissue and the presence of cartilage cells in its deeper layers were examined histologically in 43 rhesus monkeys at five maturational levels (neonate, infant, juvenile, adolescent, and young adult). Absolute thickness of the articular tissue increased with maturational level in all areas studied, with the increase somewhat more pronounced on the posterior slope and crest of the articular eminence than in the roof of the mandibular fossa. Relative to condylar size, an increase in articular-layer thickness characterized the first three maturational levels, and was followed by a decrease during adolescent and young-adult stages. Articular tissue in the fossa roof constituted a steadily decreasing fraction of the total articular-tissue thickness with age, while relative thickness of the tissue on the posterior slope and crest of the eminence increased with age. These results parallel those obtained for the mandibular condyle, and they are best interpreted to indicate that forces delivered to the joint become directed more anteriorly with age. The overall pattern of topographical variation in articular-tissue thickness and cartilage-cell distribution suggests that greater loading of the lateral aspect of the TMJ, postulated in the human TMJ by various workers, may not be as pronounced in the monkey.

Animals↗
PubMed1983

Relationships between mandibular joint size and craniofacial size in human groups.

Substantial evidence attests to the capability of the joint to undergo morphological alteration in response to biomechanical forces transmitted to it during function. Measurements expressing the size of mandibular condyles and fossae were obtained from skulls representative of a broad spectrum of subsistence practices and tooth use. Craniofacial dimensions were measured for some groups. Considerable differences in joint size were noted between groups roughly consistent with known or presumed intensity of masticatory stress. Size was largest in the hunter-gatherers, intermediate in aboriginal horticulturalists and smallest in 20th century American caucasoids and 17th century British. In each group, male joint size was absolutely larger than females. With the exception of condylar breadth, male joint dimensions were not relatively larger than female when corrected for differences in craniofacial size. In contrast, same-sex comparisons of Eskimo and American caucasoid means adjusted for differences in craniofacial size showed joint size in Eskimos to be significantly larger, both absolutely and relatively. Eskimo females had relatively larger joints than American caucasoid males. Thus, intergroup differences in joint size persist even when differences in craniofacial size are taken into account. Although the influence of genetic factors cannot be excluded, differences in the nature or intensity of tooth use during growth may account, at least in part, for the observed differences in joint size.

Adult↗
PubMed1982

Differences in interproximal and occlusal tooth wear among prehistoric Tennessee Indians: implications for masticatory function.

Breadth of the interproximal wear facet between lower P2 and M1 and between lower M1 and M2 was measured in human skeletal samples representing the Archaic, Woodland, and Mississippian periods of Tennessee River Valley prehistory, with the aim of assessing relative magnitudes of applied masticatory forces. When stratified by level of occlusal wear, mean interproximal facet breadth was consistently larger in the Archaic sample than in the Mississippi sample, with the Woodland sample intermediate. An analysis of covariance demonstrated that there was significant (p less than or equal to 0.01) differences in facet size among the three groups even when differencs in crown breadth were taken into account. Similar results were obtained in regressions of facet size on chronological age (Archaic larger than Mississippian at P less than or equal to 0.01). Since rate of occlusal wear appears to be somewhat greater in the Archaic sample than in the later samples, the differences in interproximal wear are probably underestimated. It is suggested that the high levels of interproximal wear in the Archaic are indicative of the large occlusal forces and repetitive chewing required to masticate a diet of seeds, wild plant foods, and small animals, for which prior preparation (e.g., grinding, cooking) was minimal or nonexistent (as indicated by paleofecal samples). The lower amounts of interproximal wear observed in the Woodland and Mississippian samples imply considerable reductions in strenous mastication, perhaps due to the widespread adoption during these period of pottery and the earth oven, together with ethnographically-documented techniques of food preparation that transformed most foods to a soft consistency.

Adolescent↗
PubMed1982

Histologic analysis of temporomandibular joint adaptation to protrusive function in young adult rhesus monkeys (Macaca mulatta).

It is generally believed that the adult temporomandibular joint is incapable of a significant adaptive response to forces produced by functional jaw orthopedics. To evaluate this view, twelve young adult female rhesus monkeys were fitted with functional protrusive appliances for periods ranging from 2 to 24 weeks. Histologic analysis of the temporomandibular joint demonstrated that six of the experimental animals exhibited a tissue response that was qualitatively similar to that noted in juvenile animals. However, the response in young adults was greatly reduced in magnitude from that seen in juveniles and was not related to duration of treatment. It must also be noted that three adult animals developed cross-bites in response to appliance placement, and three animals who functioned anteriorly exhibited little or no detectable condylar response. This study indicates that while some adaptive capability may still be present in the temporomandibular joints of young adults, the potential magnitude of the joint response is limited and highly variable in occurrence.

Activator Appliances↗
PubMed1981

Changes in articular eminence morphology with dental function.

Measurements of mandibular fossa depth and slope of the articular eminence were obtained for human skeletal samples chosen to represent a wide spectrum of subsistence strategies and oral function: hunter-gatherers (Eskimos, Australians), American Indians dependent to a variable extent on maize agriculture, and early twentieth century American whites and blacks. In the Eskimo and Australian samples, a generalized and steady increase in fossa depth and slope was observed with increasing functional age (tooth wear) through wear level 5 (of 8), followed by a levelling off or slight decrease in fossa depth in later wear levels on the anterior teeth and sharp decrease in fossa depth in later wear levels on the molars. Although much less consistent due in part to extensive and early molar loss, patterns of variation in the remaining samples were characterized overall by a decrease in fossa depth and slope with increasing wear, especially on the molars. Further, in those samples with high incidences of posterior tooth loss, fossa depth was routinely less and the eminence more gently sloped in subsamples having experienced molar loss than in subsamples retaining all their molars. These data provide evidence that the temporomandibular joint (TMJ) undergoes continuous morphological alteration throughout adult life, and that these alterations are probably mediated by dental function. Moreover, they suggest that differences in patterning of such alterations may exist among human groups with contrasting patterns of tooth use.

Biomechanical Phenomena↗
PubMed1981

Form and patterning of anterior tooth wear among aboriginal human groups.

Form and severity of dental attrition was assessed in aboriginal human groups including hunter-gatherers (Eskimos, Australians) and those with dependence to a varying degree on food production (Southwest U.S. and Ohio American Indians). Wear on anterior teeth was both relatively and absolutely greater in the hunter-gatherers, as indicated by comparisons of wear on anterior and posterior teeth which come into occlusion at roughly the same time. Distinct differences in form of anterior wear were also apparent: The hunter-gatherers exhibited steadily increasing incidences of labially rounded wear with greater functional age, while the food-producing groups showed little or no rounding but instead high frequencies of heavily cupped wear (especially in those with premature loss of posterior teeth). These differences were attributed to nonmasticatory utilization of the front teeth in hunter-gatherers and to employment of the anterior teeth in masticatory (grinding) activities necessitated by large-scale molar loss in food producers.

Age Factors↗