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O J Oyen

Publications and source records attributed to O J Oyen.

14 recordsLinked to original sources
PubMed1996

Strain gauge analysis of the frontozygomatic region of the zygomatic complex.

PURPOSE: This study evaluates the biomechanical consequences of physiologic forces acting on the frontozygomatic suture region, with the ultimate goal of defining appropriate fixation techniques and improving the surgical management of this complex anatomic region. MATERIALS AND METHODS: Single foil strain gauges were bonded to the cortical surface of the frontal process of the zygoma in 13 subadult Cercopithecus africanus. Subdermal electrodes were used to induce tetanic contractions of the jaw elevator muscles, and bite force was measured using a twin-beam bite force transducer placed between the teeth. Microstrain was simultaneously measured and recorded. RESULTS: Tensile strains predominated in the region of the frontal process of the zygoma, with balancing side strains twice as large as working side strains; incisal strains were intermediate. CONCLUSIONS: The tensile strains observed in the frontozygomatic region contradict the concept of this area as a "stress riser" for compressive occlusal forces, and supports the use of compression plate osteosynthesis for improved stabilization of fractures in this region.

Animals↗
PubMed1995

The effects of intra-articular deposition of betamethasone in the goat temporomandibular joint.

PURPOSE: This study evaluated the response of the articular surfaces of the normal goat temporomandibular joint (TMJ) to intra-articular injections of betamethasone suspension. METHODS: Thirty female goats were divided into four experimental groups of seven each and one control group of two animals. The design resulted in 24 joints receiving from one to nine weekly injections of betamethasone suspension, 0.085 mg/kg. The 24 contralateral joints received an identical array of saline injections. In the remaining 12 joints, four were unilaterally injected with saline, four were unilateral uninjected joints, and four were bilateral uninjected joints. All of the joints were inspected grossly and histologically assessed for any intra-articular changes associated with corticosteroid injections. RESULTS: Comparative examination of the gross and histologic features of the injected joints and the eight normal joints showed no significant adverse effects on nondiseased TMJs. CONCLUSION: Intra-articular injection of betamethasone suspension at the dosage and delivery rate used had no harmful effects on the TMJs of nondiseased adult female goats. Because of possible differences between species, these results should not be taken as an indication that betamethasone suspension will not have adverse effects in the human TMJ. These findings support the need for further investigations into the physical and biochemical responses of normal and diseased articular fibrocartilage to different glucocorticosteroids at various concentrations and delivery rates using the goat and other animal models.

Animals↗
PubMed1995

The effect of cobalt-60 irradiation on bone marrow cellularity and alveolar osteoclasts.

The purpose of this study was to investigate the mechanisms of bone resorption in the rat dentoalveolar complex occurring as a result of orthodontic appliance therapy. Utilizing whole body radioactive cobalt 60 (Co60) irradiation in combination with orthodontic tooth movement, the activation, recruitment, and life span of osteoclasts was studied. Thirty-four adult Fischer 344 rats were irradiated with 10 and 20 Gray of Co60. Twelve days after irradiation, each rat was fitted with an orthodontic appliance; the rats were sacrificed 7, 14, or 21 days after appliance placement. To serve as controls, another group of 12 rats was subjected to orthodontic treatment only. Histologic sections were prepared from decalcified maxillary alveolar process, and osteoclasts were counted. In the control group, osteoclasts were presence in the periodontal membrane for four weeks after appliance placement, and the largest number of osteoclasts was observed in the second week. The smaller total irradiation dose (10 Gray, administered in 5 daily fractions) induced a transient reduction in the bone marrow cell count of more than 90%, followed by a complete rebound. The peak osteoclst number also was increased 110%. In contrast, the higher total dose (20 Gray, administered in 10 daily fractions) resulted in a reduction of 60% in bone marrow cellularity and a decrease in the peak osteoclast number by 40%. Fluctuations in bone marrow cellularity generally corresponded to similar variations in the osteoclast number, but there was an apparent lack of correspondence between bone marrow cell and white blood cell values. The total period of osteoclastic presence in the periodontal membrane following orthodontic activation, normally four weeks in duration, was reduced by one week in the irradiated animals. These findings lead us to speculate that the mechanisms of osteoclast activation and recruitment following orthodontic appliance therapy may involve three consecutive waves of osteoclast maturation. The total duration of osteoclastic bone resorption lasts 4 weeks, but the osteoclast lie span is calculated to be 9 to 10 days (9 days x 3 waves = 27 days). If the results of this study are proved to be reproducible, a scientific basis may have been provided to support the common practice in orthodontics wherein the duration between orthodontic appointments is 4-5 weeks.

Alveolar Process↗
PubMed1992

A study of the suitability of two methods used for describing the occlusal plane.

In this study an effort was made to determine which of the two commonly used methods of occlusal plane determination more precisely depicts changes induced by treatment or growth. Longitudinal lateral cephalometric radiographs of 70 individuals, 40 orthodontically treated and 30 with clinically acceptable occlusion, were used. Following an analysis of outcomes obtained through the conventional application of the Downs occlusal plane method and the functional occlusal plane method, there are indications that: 1) the Downs method may provide a better description of what happens to the occlusion following treatment; 2) the notion that the plane reconstructed using the functional method actually represents the location at which the occlusal function takes place is unsubstantiated; and 3) since it is possible that the results of this study could be influenced by the types of malocclusion, skeletal patterns, and methods of orthodontic treatment, further analyses are called for in order to make more conclusive determinations about these methods.

Adolescent↗
PubMed1991

A biomechanical analysis of craniofacial form and bite force.

In vivo measurements of bite force and bone strain obtained in growing African green monkeys were used to study skull biology and geometry. Strain values and distributional patterns seen in association with forceful jaw elevation were inconsistent with most conventional explanations that link upper facial morphology with masticatory function and use beam models of craniofacial architecture. The results mandate careful use of concepts about skeletal geometry based on static analysis that have not been experimentally verified with in vivo procedures. In particular, a reevaluation of conventional ideas about the generation and dissipation of forces during contraction of the jaw elevator muscles seems called for.

Animals↗
PubMed1989

Live primates and dental replication: new problems and new techniques.

Dental microwear analyses are beginning to provide new insights into the intricacies of jaw movement and tooth use in modern and extinct mammals. However, these analyses are also raising new questions that are best answered through studies of live animals with known diets. The process of taking dental impressions from live animals is a difficult one that presents problems different from those encountered in working with museum material. This report presents a review of some of those problems together with solutions that have been developed in the course of laboratory work with nonhuman primates. It also summarizes recent developments in dental casting.

Anesthesia↗
PubMed1989

In vivo and in vitro turnover in dental microwear.

Given the potential usefulness of dental microwear analyses in interpretations of archaeological and paleontological material, it is surprising how little we know about changes in individual microwear features through time. The purpose of this study was to document the turnover in primate dental microwear through in vivo dental studies of monkeys raised on different diets, and through in vitro studies of the abrasive effects of monkey chow biscuits on isolated monkey teeth. As in previous studies, epoxy replicas were prepared from dental impressions and examined under a scanning electron microscope. Results indicate that, under certain conditions, the turnover in primate dental microwear can be on the order of days, hours, or even minutes. Individual microscopic wear features can be obliterated within 24 hours on the molars of laboratory monkeys, and monkey chow biscuits can easily scratch the enamel of isolated monkey teeth. Monkeys raised on a hard diet showed more rapid turnover in dental microwear than monkeys raised on a soft diet. However, paired-sample tests revealed that, for all animals, the molar shearing facets were being abraded at a significantly slower rate than molar crushing/grinding facets. In light of these results, investigators should make every effort to use large samples in interspecific comparisons of dental microwear involving species with variable diets. Another implication of these results is that changes in dental microwear might be useful indicators of changes in oral behavior over relatively short periods of time.

Animals↗
PubMed1989

Differences in the rate of molar wear between monkeys raised on different diets.

The purpose of this study was to make detailed comparisons of rates and patterns of tooth wear in 15 growing vervet monkeys raised on hard vs. soft diets. Dental impressions were taken every six to eight weeks over a four-year period. Cusp heights and areas of dentin exposure on the buccal cusps of the left mandibular first molar were measured from high-resolution epoxy casts, by use of a Reflex Measuring Microscope. Areas of dentin exposure were regressed against time (by use of least-squares regression) so that the course of tooth wear in animals from both diet groups could be charted. By use of a two-sample t test and the Mann-Whitney test, slopes of the regressions and changes in cusp height were compared between diet groups. In both comparisons, animals raised on the hard diet showed more rapid tooth wear than did animals raised on the soft diet. Analyses of other parameters indicate that this was probably because of differences in dietary consistency between the two groups.

Animals↗
PubMed1982

Masticatory function and histogenesis of the middle and upper face in chimpanzees (Pan troglodytes).

Evidence has been offered suggesting that masticatory function is an important factor governing development of the supraorbital region. Data have also been provided showing that a mechanism which enables rapid skeletal growth to occur is present in the supraorbital region in the form of fine cancellous woven bone tissue. That Browridge morphogenesis is linked with masticatory function is not a novel interpretation. On the contrary, numerous investigators have offered a variety of evidence in support or refutation of this notion [Toldt, 1914; Weidenreich, 1941, 1946; Endo, 1966, 1970; Moss and Young, 1960]. This study differs from most previous efforts, however, in that it specifically identifies some of the factors and mechanisms; i.e., bite forces and bone tissues involved in growth and development of the upper facial skeleton and the masticatory system. The nature of the relationships among these developmental and functional phenomena remains to be experimentally demonstrated.

Aging↗
PubMed1980

Supraorbital development in chimpanzees, macaques and baboons.

Macroscopic and histological parameters are considered in an analysis of bone formation in the supraorbital region of macaques (Macaca mulatta), baboons (Papio cynocephalus anubis), and chimpanzees (Pan troglodytes verus). Results indicate that post-natal osteogenesis of the supraorbital segment of the frontal bone in these primates occurs as a cyclic phenomenon that coincides wth dental eruption patterns.

Animals↗
PubMed1979

Craniofacial growth in olive baboons (Papio cynocephalus anubis): browridge formation.

The examination of a developmental series of skulls of olive baboons has led to the generation of a model for browridge formation. Evidence in support of the model comes from surface configuration of browridge bone as studied by scanning electron microscopy, histology of the bone by the analysis of thin sections and by measurements that reflect both depositional cycles in browridge bone and the biomechanics of mastication. The model relates sudden changes in the biomechanical system caused by the tooth eruption cycle to cyclical changes in the formation of browridge bone. We suggest that browridge bone is added during periods of peak stress caused by the positive response of the masticatory muscles to relatively sudden reduction of their biomechanical efficiency.

Animals↗
PubMed1977

Stereometric craniometry.

A method is described whereby three-dimensional co-ordinates of points on a cranium can be recorded in terms of azimuth, elevation and radial distance from a selected point. These co-ordinates can be used to create two-dimensional representations of single crania, the differences between many crania or growth stages of individuals or series of individuals. The co-ordinates can be used in more conventional analytic ways in the same way as cartesian co-ordinates.

Animals↗