Faculty Bibliography

Recent studies have demonstrated that periodontal ligament-derived (PDL) cells have the potential to regenerate a complete periodontal connective tissue attachment apparatus on both root and artificial substrates. To study the characteristics of endodontic materials conducive to periodontal regeneration, we have established an experimental model using PDL cell cultures that express a 42 kDa protein (CP42) associated with cementum extracellular matrix. In this report, the effect of gutta percha, dental amalgam, composite and calcium hydroxide on PDL cell proliferation, collagen and noncollagen protein synthesis, alkaline phosphatase activity, and CP42 expression are presented. While all substrates supported PDL cell attachment and proliferation, highest levels of alkaline phosphatase activity, collagen and noncollagen protein synthesis were observed in control cultures. Lowest levels of the above parameters were observed with gutta percha while amalgam, composite and calcium hydroxide had intermediate levels. Only control PDL cultures demonstrated CP42 expression. These data suggest that culture substrate can markedly influence periodontal extracellular matrix gene expression in vitro and provide an experimental model to select and develop endodontic materials compatible with periodontal regeneration in vivo.

In the past three years more addition silicones have been supplied as hydrophilic materials and heavier viscosities have been provided in automatic mixing cartridges. Also, a polyether is now supplied in an automatic mixing system. There has been an increase in the number of products available as monophase or single viscosity systems. Both addition silicones and polyethers are available as bite registration materials.

Osteointegration was defined as a "direct structural and functional connection between ordered living bone and the surface of a load-carrying implant." Although osteointegration was meant originally to describe a biologic fixation of the titanium dental implants, it is now used to describe the attachment of other materials used for dental and orthopedic applications as well. Analyses of material-bone interface showed that osteointegrated implants can have an intervening fibrous layer or direct bone apposition characterized by bone-bonding depending on the composition and surface properties of the biomaterial. This article reviews biologic (host tissue properties and response), biomechanical, and biomaterial factors affecting osteointegration. Biologic factors include the quality of bone. Biomaterial factors include the effect of material composition on the bone-material interface. Suggested areas for future research include determining the correlation between oral bone status and osteoporosis, the effect of gender, age, and endocrine status (e.g., osteoporosis) on implant success or failure, the effect of calcium phosphate coating composition and crystallinity on in vivo performance of implants, the factors contributing to accelerated osteointegration, and development of osteoinductive implants.

In this laboratory study six self-threading retention pins were evaluated using the two-dimensional photoelastic technique. The experimental samples consisted of 60 blocks of PSM-1 photoelastic material measuring 1" by 1" by 1/4". The samples were divided into six groups of 10 blocks each, with each group representing one of the pins used in the study. Pins were inserted and cores of amalgam and composite were fabricated over the pins. The samples were observed in the polariscope and photographed after pin insertion and after loading the cores with a constant, compressive force of 20 pounds. Using magnification, fringe orders were counted and rounded to the highest 0.5 fringe order. Each sample was evaluated for apical and shoulder stress. All statistical analyses were done using ANOVA at the P = 0.05 significance level. It was concluded from this study that the insertion of self-threading retention pins results in stress at the apical and shoulder areas of the pin. Pin design features, such as shoulder stops, significantly affect the magnitude and location of stress. There were no significant differences in either the apical or shoulder stresses induced when cores were made of either amalgam or composite resin.

Periodontal disease in the domestic cat may assume debilitating and serious consequences; however, little is known of the biochemical composition or metabolism of feline gingiva in health or disease. In this report the chemical composition and metabolism of gingival lipids from inflamed an non-inflamed sites is presented and compared to other species with naturally occurring periodontitis. The neutral and phospholipid composition of feline gingiva was found to be distinct from that of porcine and human. As a measure of de novo lipid synthesis, the total incorporation of 14C-acetate into fractionated lipid components was determined and revealed an approximate 2 to 3 fold decrease in inflamed versus non-inflamed gingiva. The decrease in 14C-acetate incorporation appeared to result from a 2-fold increase in free acetate pools in inflamed compared to non-inflamed gingival samples, since total lipase and phospholipase activity were comparable in inflamed and non-inflamed gingiva and total lipid composition was not changed between inflamed and non-inflamed sites. These data are similar to those reported for periodontally involved human gingival tissue and suggest a common effect of periodontal inflammation on lipid metabolism in both species.

Modifications in denture plastics, including acrylics containing butadiene-styrenes, block copolymers to increase toughness, and those with added soluble heavy-element salts to increase radiopacity are described. Developments in processing of denture bases by microwave, laser, and injection methods are described. Also reviewed are acrylics and their dimensional stability, including the effect of artificial salivas on properties. In addition, the rheological, glass transition, dynamic, impact, and fatigue properties of denture acrylics are presented. Adhesion of polymers to plastics and metals is reviewed, as well as the biocompatibility and adhesion of organisms to denture plastics. Soft denture materials are reviewed with respect to research on new materials and to clinical evaluations of existing products. Finally, studies on the wear of denture teeth are summarized.

The properties of some recently marketed rubber impression materials were compared with some earlier products. In general, the qualities of addition silicones and polyethers were superior to polysulfides and condensation silicones. However, there were significant differences in the properties of products of the same type and class and thus the selection of a product for a particular application should be based on actual property data rather than on the type and class of rubber impression material.

Insulin at 3-100 nM increased the steady state level of alpha-1(I) procollagen mRNA and stimulated collagen synthesis in the osteoblast-rich segment of central bone from 21-day-old fetal rat calvaria. The increases in the level of procollagen mRNA and the rate of collagen synthesis were observed 18 h after the addition of insulin to the cultures. The removal of insulin from calvaria incubated for 24 h with 3 nM insulin caused collagen synthesis and the level of alpha-1(I) procollagen mRNA to return to control values within 5 h. Adding insulin back to calvaria withdrawn from insulin treatment for 3 h did not rescue the decay in collagen synthesis or the level of alpha-1(I) procollagen mRNA. Insulin increased the steady state levels of alpha-1(I) procollagen mRNA in the presence of the RNA synthesis inhibitor actinomycin-D. Our data suggest that in fetal rat bone, one mechanism by which insulin increases the steady state level of alpha-1(I) procollagen mRNA may be by altering its stability.