Cavity Preparation Design - The life span of dental restorations has been difficult to predict. Current life-span predictions are based on clinical evaluation that in general does not account for the amount of tooth structure removed during the operative process. The effect that preparation dimensions have on the survivability of the restoration is only qualitatively known. Present research efforts are aimed toward determining the volumetric changes that occur when tooth structure is removed during various tooth preparation procedures. Future research will focus on determining the fatigue resistance of prepared teeth with various cavity preparation sizes. This will ultimately permit the development of a failure prediction model for teeth that are candidates for given cavity/crown preparation procedures. Restoration life-span information could allow the dentist and patient to make more accurate treatment planning decisions.
Tooth Wear - Occlusal and incisal wear can account for significant losses of tooth structure from the human dentition. Currently very little is known about the etiology and mechanisms that govern wear. The extent of tooth wear is currently evaluated by means of qualitative or ordinal scales that are insensitive to small changes in loss of tooth structure. The rate of wear cannot be ascertained using these methods. These problems are being addressed by the development of a quantitative measuring method that uses a computer-aided-design (CAD) software program to record and model the incisal and occlusal wear facets of the human dentition. When fully developed, this system will allow the location, size and distribution of wear facets to be recorded, as well as determining the rate of wear. The effect of dental treatment and disorders like bruxism and bulimia on the loss of tooth structure are some of the areas that could apply this technique.
Temporomandibular Joint - In synovial joints such as the temporomandibular joint (TMJ), mechanical stress and its resulting deformation of lining tissues are important factors in the generation of fluid transport and nutrition for the articular tissues. If stresses are too high, or too frequent, fatigue damage to the tissues is likely. The final clinical manifestation of this process is osteoarthritis of the joint. Therefore, for the long-term health of the tissues lining the synovial joints, it is important that there should be mechanisms controlling the magnitudes of stresses in the articular tissues. The work that is progressing in this area uses various techniques to explore the mechanisms controlling stresses in the TMJ. Such techniques include computer generated numerical modelling of muscle and joint forces and in vivo testing, in human subjects, of computer modelling predictions. Moreover, given the utility of computer modelling to predict in vivo conditions, in vitro simulation of these conditions has been used to test the effects of static and dynamic loads on the TMJ disc and how these factors influence the ability of the disc to control intracapsular stresses.
Mechanical physical properties
Maxillofacial Elastomers - Maxillofacial prosthetic devices are those that replace missing facial structures lost to head and neck cancer, such as replacement eyes, ears and noses. These materials are time consuming to fabricate, costly to the patient and deteriorate rapidly during usage. A long-term research goal is to isolate and study the role of several environmental factors responsible for this degradation and to eventually identify mechanisms that are responsible. Present research is focusing on why the color and mechanical properties of these biomaterials can change in response to exposure to ultraviolet light. This research is important in the development of more durable maxillofacial prosthetic materials, which is particularly relevant since the long-term survival rate for most head and neck cancers has dramatically increased in the past twenty years.
Marginal Adaptation of Dental Restorations - Since the resin-based indirect inlay systems exhibit polymerization shrinkage, it is likely that marginal gaps may occur in various locations of the cavity preparation. The size of the marginal gap interface may be significant due to the fact that the resin luting agents will disintegrate and wear much more rapidly than tooth structure or the restorative material. This disintegration may result in marginal staining and voids that cause restoration fracture or recurrent caries. The location and size of marginal gaps may be dependent on cavity preparation width and depth, and may also be dependent on the material type. The goal of this research is to compare the marginal adaptation of composite and ceramic inlay systems versus gold castings. Interface thickness measurements will be made at various locations of the cavity preparation. Correlation with clinical performance data will be the ultimate goal of this laboratory research.
Microleakage - Research has identified microleakage as a significant problem associated with restorative materials. Microleakage can result in secondary caries, tooth discoloration and pulpal irritation. Several studies have investigated the use of dentin bond agents as a liner with dental amalgam and have produced varying results with regard to minimizing microleakage. Adhesive resin liners may be used as dentin bond agents alone or in combination with viscous resin liners. The goal of this research is to discover whether using dentin bond agents alone as an amalgam alloy liner is sufficient to inhibit microleakage, or whether the use the viscous liner component as recommended by manufacturers is necessary.
Biological evaluation of materials
Mercury Toxicity - Potential adverse effects arising from mercury exposure are important issues of increasing concern to the dental profession and the public. At present, there is a paucity of information regarding mercury concentrations in patients with neurological disorders. In previous studies, we reported that the blood and urine concentrations of mercury and selenium from patients with probable Alzheimer's disease (AD) are not statistically different from controls. However, blood and urine mercury concentrations are not reliable indicators to predict body burden of mercury. Recently, we determined brain tissue concentrations of mercury and selenium from deceased subjects with AD or multiple sclerosis (MS), and compared these to normal controls without known central nervous system disorders. Since brain mercury concentrations from deceased subjects with either AD or MS were not significantly higher than controls, the present study provides no scientific support for the hypothesis that mercury plays a significant role in the pathogenesis of these neurodegenerative disorders.
Dental Sealants - For about 30 years, plastic resins have been used in dentistry as restorative materials to repair/seal teeth. Recently, a study indicated that a significant amount of bisphenol A, a chemical building block of these resins, leached into the saliva of patients one hour after placement of a bisphenol A diglycidyl ether methacrylate (Bis-GMA)-based sealant. Bisphenol A, the precursor of many monomers including Bis-GMA, and bisphenol A dimethacrylate have been shown to exert estrogenic activity in tissue cultures of breast tumor cells. This finding generated considerable public concern regarding the potential adverse effects of dental sealants. We are designing studies to determine the quantities and time-course of leachable bisphenol A, bisphenol A dimethacrylate and bis-GMA from composite resin after placement in fields containing human saliva and blood.
Nicotine - Nicotine is the most pharmacologically active ingredient in tobacco products. A tobacco-related deficit in bone mass has been reported among both pre- and post-menopausal women, implicating tobacco use as a risk factor in osteoporosis. Although nicotine has been shown to depress osteoblast activity in a number of in vitro and animal studies, limited information is available regarding the effects of nicotine on bone development and remodeling. Furthermore, fundamental questions about the effects of nicotine on serum levels of several important endocrine hormones, which include 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, parathyroid hormone and calcitonin, remain unanswered. With the dramatic increase in smokeless tobacco use among children and youths, studies will be conducted to determine the effects of nicotine in old and young female rats to provide information on the role of nicotine in mature and rapidly developing skeletal systems. Together, the results of these studies will clarify the role of nicotine on bone. Furthermore, they will provide a basis for understanding the potential health implications associated with the use of tobacco products.
Cytotoxicity of Dental Materials - The biocompatibility of dental materials must be assured to prevent adverse biological reactions. We have focused on the effects of two restorative dental materials, namely, denture base resins and root canal sealing materials, in an effort to determine their cytotoxicity. Recent studies have shown that, in vitro, eluate from microwave-activated resin decreases gingival fibroblast cell viability more than heat-activated resin eluate, but less than eluate from the chemically-activated resin. The proposal for use of glass ionomer cements as a root perforation material has drawn attention to its biocompatibility with tissues of the periodontium. We determined that eluate from two glass ionomer cements, one chemically-activated and one both chemically and light-activated, were slightly less harmful to periodontal ligament cells than eluate from dental amalgam. These research projects exemplify our efforts to test the cytotoxicity of new dental materials and materials intended for novel applications.
Caries Control Treatment - Rampant caries presents a challenging technical and socio-economic problem to the dental profession. While full restoration of the dentition is the ideal treatment, economic considerations and/or the lack of modern dental operatories in under-served geographic areas can make this goal unrealistic. Caries control involving the minimal use of dental instrumentation is the first and primary treatment goal. The recent introduction of resin modified glass ionomer dental cements (RGIC) may make this first rehabilitation step possible.
A clinical trial of a caries control treatment (CCT) that involves the placement of RGIC in teeth prepared without the use of rotary instrumentation is being conducted at the UNMC College of Dentistry. The longitudinal study of CCT restorations with an average age of 10.2 months has found that all restorations are satisfactory in performance and no restorations have required replacement. This treatment allows patients with complicated treatment needs to receive care over an extended period of time, minimize the patient's financial burden and facilitate treatment scheduling.
Orthodontic Bracket Cements - An increase in dental caries occurrence is common during orthodontic treatment. The application of fluoride-releasing glass ionomer cements for the attachment of orthodontic brackets is seen as a possible solution to this problem. A clinical trial is being conducted to evaluate the use of these cements. Patients receiving comprehensive orthodontic care at the UNMC College of Dentistry are receiving brackets bonded either with a conventional resin adhesive or with a new light-cured glass ionomer cement adhesive. The incidence of bracket de-bonding and dental caries formation is being evaluated.