Biomedical subjects

H R Rawls

Publications and source records attributed to H R Rawls.

30 records · Page 2Linked to original sources

PubMed1989

Biocompatibility testing of an experimental fluoride releasing resin using human gingival epithelial cells in vitro.

Cell culture is a valuable method of evaluating the biocompatibility of new dental materials. The purpose of this study was to compare the in vitro biocompatibility of an experimental fluoride composite resin with fluoride and non-fluoride-releasing materials currently available. The dental materials tested were: MQ Silicate (silicate cement), KETAC-CEM and FUJI (type II glass ionomer cements), VISIO DISPERS (a light-cured, nonfluoridated, microfilled composite resin), and FR-17 (an experimental fluoride-releasing composite resin). The Smulow-Glickman (S-G) human gingival epithelial cell line, which exhibits semidifferentiated characteristics, was used in the study as a test system. Biocompatibility was quantified by counting the viable cells per unit area remaining after 24 and 48 h at two radial distances from cured specimens immersed in the cell culture medium. The test materials were observed to be most toxic to cells nearest the materials. A Time-Distance Cytotoxicity Index (TDCI) was calculated to relate the percentage of dead cells to viable cells at each diffusion distance for each exposure time compared to a nontoxic control. The relative toxicity ranking of the materials tested based on the TDCI was VISIO DISPERS (91%), FUJI (82%), FR-17 (30%), MQ Silicate (23%), and KETAC-CEM (10%), which exhibited the least toxicity. The cytotoxicity of the experimental resin FR-17 was within the range of cytotoxicity of currently accepted restorative materials.

Cell Survival↗

PubMed1989

Clinical evaluation of a fluoride-exchanging resin as an orthodontic adhesive.

The purpose of this study is to examine the clinical durability and caries inhibition potential of a fluoride-exchanging resin (FER) when used as an orthodontic bracket-bonding adhesive. In the clinical durability investigation, orthodontic brackets were bonded to alternate teeth with the FER in 10 patients scheduled for routine orthodontic procedures. The remaining teeth were bonded with Concise orthodontic resin. Number of bonding failures and the site and mode (adhesive or cohesive) of failure were recorded. Also included in the study were 10 patients scheduled for orthodontic care with prescribed extraction of four first premolars. Bracketed teeth were extracted after 60 days and were sectioned and examined with polarized light microscopy using H2O and quinoline as imbibition media. Failure rates for the FER and Concise were 10.8% and 7.3%, respectively. Occurrence of adhesive rather than cohesive, failure indicates that structural integrity was maintained for both adhesives. Microscopic examination of specimens with H2O showed lesion formation to be 2.78% for the FER and 1.73% for Concise. These lesions were large and not seen in positions near the brackets indicating presence before bonding. With quinoline, dark zone formation was 2.3% for the FER and 33.5% for Concise, indicating a 93% reduction in the first stages of enamel alteration. Results demonstrate that the fluoride-exchanging resin holds promise as a practical caries-preventive adhesive.

Acrylic Resins↗

PubMed1989

The measurement of toothbrush wear.

Toothbrushes wear out and progressively lose their ability to clean as the bristles abrade and become curled and matted. To study the factors that influence this process, we developed a quantitative measure of bristle splaying (wear index) and a method for judging and ranking the overall state of brush deterioration (wear rating) and used these to determine the effects of the individual user, brush design, time in use, and bristle material. Wear index is the average increase in brush-head dimensions normalized for maximum bristle length, and is dimensionless. Wear rating is a subjective means of classifying the increasing severity of deterioration on a scale of 0 to 3. The wear characteristics of a variety of commercial and experimental brushes with different design features were determined. Test variables were time in use, brush design (e.g., geometry and size of the brush head), and bristle composition. Time of use, the individual user, and bristle composition were found to have the strongest influences on splaying, and brush design was found to have the least influence. The wear index offers a quantitative means of comparing brushes of different dimensions at various stages of splaying. The wear rating, although qualitative, is a quick means of ranking brushes in various stages of deterioration. The two methods correlate (R2 = 0.87), and both are sensitive to several factors that affect brush durability. Therefore, these methods appear to be suitable not only for research, but also for quality control, the setting of standards, and for substantiation of advertising claims.

Adult↗

PubMed1987

Fluoride-releasing acrylics.

There are numerous examples in dentistry where demineralization, or even frank caries, develops near or in association with restorative or prosthetic materials. Leaking cavity margins and demineralization under bite splints are two examples. A slow-release source of fluoride could help to prevent these problems and provide added protection throughout the mouth. For this purpose a family of fluoride-releasing resins has been developed for use in various adhesive applications, and also for preparing temporary crowns and removable acrylic devices. These materials contain fluoride ions held to covalently bound positive charge sites within the polymer network. Release is by a diffusion/exchange mechanism in which anions from oral fluids diffuse to the charge sites and exchange with fluoride. Fluoride then diffuses to the surface and is released into solution. This method of release allows for the retention of adequate physical properties and is capable of a linear release rate for terms ranging from days to years.

Acrylic Resins↗

PubMed1984

Prevention of in vitro secondary caries with an experimental fluoride-exchanging restorative resin.

We investigated the development of artificial caries lesions adjacent to experimental composite resins which release fluoride by ion exchange. Overall, compared with both a commercial, non-fluoride composite and a restorative silicate cement, the cavity walls and tooth surfaces immediately adjacent to the experimental resins developed fewer and/or smaller lesions. When lesions did develop, they did not penetrate as far along the cavity walls adjacent to the experimental materials. In general, the degree of protection imparted by the fluoride composites increased with increasing fluoride content. These results demonstrate the potential of these adhesive resins for restorative and other dental applications in which an extended fluoride presence would be of benefit.

Composite Resins↗

PubMed1984