Biological Evaluation of Materials

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.

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