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O J Oyen

Publications and source records attributed to O J Oyen.

9 recordsLinked to original sources
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↗
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↗