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Biomedical subjects

D H Retief

Publications and source records attributed to D H Retief.

At least 109 records · Page 6Linked to original sources
PubMed1982

Microleakage of conventional and microfilled composite restorative resins.

Microfilled composite resins have been introduced in clinical dentistry because of the difficulty in finishing conventional composite resins satisfactorily. Owing to the difference in coefficients of thermal expansion of the two resin systems, the objective of this in vitro study was to evaluate microleakage of a conventional and a microfilled composite resin. Class V cavities with butt cavosurface margins were prepared in the middle third of the facial surfaces of the crowns of 80 noncarious human premolar teeth; they were acid etched within the preparations only. Forty preparations were restored with Concise composite and forty with Silar microfilled resin. Ten teeth from each group were subjected to cyclic temperature changes between 5 and 55 degrees C for 1000, 2500, or 5000 cycles, respectively, and ten teeth from each group were not cycled (controls). After suitable preparation, the teeth were immersed in 45Ca solution for 18 h and contact radiographs were prepared. Microleakage was scored 0-3 at both the cervical and occlusal margins of the restorations. Microleakage was significantly greater at the cervical margins than at the occlusal margins. Differences within occlusal and cervical microleakages among the two resins were not significant.

Composite Resins↗
PubMed1982

The effect of contact time of acidulated phosphate fluoride on fluoride concentration in human enamel.

Polished enamel blocks with known surface areas were obtained from human mandibular incisors. Acidulated phosphate fluoride was applied for 4 min and washed off after additional contact times of 0, 2, 6 and 24 h, respectively. The enamel fluoride concentrations were determined in three successive etch depths before and after extraction in 1 M KOH for 24 h. The predominant reaction product was CaF2. The concentration of the fluoride bound as fluorapatite or fluorhydroxyapatite reached an optimal level after a 6-h contact time.

Acidulated Phosphate Fluoride↗
PubMed1982

Effect of cavosurface treatment on marginal leakage in class V composite resin restorations.

Under the experimental conditions used in this in vitro study, the following conclusions may be drawn: 1. Etching of the enamel walls in butt and beveled preparations significantly reduces incisal marginal leakage. 2. The application of a low-viscosity bonding resin to the etched enamel walls of preparations prior to the insertion of the composite resin is not necessary to obtain minimal incisal leakage at the composite resin/etched enamel interface. 3. Cavosurface configuration has no significant effect on incisal marginal leakage. 4. Cavosurface configuration and the restorative techniques used in this study affect the degree of gingival microleakage to some extent but do not eliminate it.

Acid Etching, Dental↗
PubMed1982

The apical seal via the retrosurgical approach. II. An evaluation of retrofilling materials.

In this investigation heat-sealed gutta-percha (A) reinforced with Adaptic (B), ASPA (C), Cupralloy without (D) and with (E) varnish, Spheraloy without (F) and with (G) varnish were used as retrofilling materials. Seventy maxillary central incisors with Class I canal anatomy were selected. Marginal leakage at the apical filling/root canal interface was evaluated quantitatively by means of a fluorescent dye technique. All statistical tests were computed at the 5 percent level of significance. Analysis of variance revealed that differences in microleakage among retrofillings were significant. Tukey's test of multiple contrasts was used to isolate statistically significant differences between all pairs of means. The following results were obtained: D F A G E C B Retrofillings are ranked in descending order of microleakage. Means that are linked were not significantly different.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1982

The apical seal via the retrosurgical approach. I.A. preliminary study.

The results of this study indicated that heat-sealed gutta-percha alone and when reinforced with Adaptic or a glass ionomer cement provided the most effective apical seal. It is therefore proposed to expand this study to include these materials and zinc-free Spheraloy and Cupralloy amalgams as retrofilling materials. The amalgams will be used with and without cavity varnish.

Apicoectomy↗
PubMed1981

Tensile and shear strengths of bonded and rebonded orthodontic attachments.

The objective of this study was to investigate the effect of a low-viscosity sealing resin and temperature cycling on the tensile and shear strengths of bonded and rebonded attachments. Eighty extracted noncarious human maxillary central incisors were used. The tensile bond strengths of a chemically activated bonding paste to etched enamel, with and without a low-viscosity sealing resin and with and without 500 temperature cycles between 5 degrees C. and 55 degrees C., were determined. The tensile bond strengths on rebonding were determined on the same teeth in such a way that the rebonded specimens were subjected to the same two variables as the originally bonded teeth. The shear bond and rebond strengths were determined on the remaining forty teeth. The specimens were tested to failure in an Instron machine. The bond strengths were expressed in MN.m-2. Analysis of variance was used to analyze the data. Temperature cycling adversely affected tensile bond and rebond strengths, while the sealing resin had no additional effect on tensile and shear bond and rebond strengths. Tensile versus shear and bond versus rebond strengths for similarly prepared specimens were not significantly different.

Acid Etching, Dental↗
PubMed1981

Enamel fluoride uptake from orthodontic cements and its effect on demineralization.

This study was undertaken to determine the in vitro enamel fluoride uptake and distribution from fluoride-containing orthodontic cements after 21 days' exposure and the effect on acid demineralization. Three successive acid-etch biopsy specimens were taken from tne facial middle third of thirty maxillary central incisors. Orthodontic bands were cemented to these teeth, ten each with (A) zinc phosphate, (B) zinc phosphate containing 5 percent SnF2, and (C) silicophosphate cement, respectively. The teeth were suspended individually in synthetic saliva at 37 degrees C. in a shaking incubator for 21 days. The bands were removed, the cement was cleaned off, and three successive biopsies were carried out electrometrically and for calcium by atomic absorption spectroscopy. Fluoride concentrations were adjusted to depths of 10.0, 20.0, and 30.0 micron for the three biopsies, respectively. The acquired fluoride was calculated and the data were analyzed statistically. In addition, six teeth each with bands cemented with cements A, B, and C, respectively, were incubated in synthetic saliva for 21 days, after which the bands were loosened and the teeth were suspended for a further 3 months in a caries-producing medium. After careful cleaning, the enamel surfaces were examined by microradiography and scanning electron microscopy for demineralization. Results showed that acquired fluoride at the first depth was highest with cement C, followed by cement B, with cement A producing a net loss of fluoride. Further, the greater the fluoride uptake, the more resistant the enamel was to demineralization.

Dental Caries↗
PubMed1981

In vivo enamel fluoride uptake from and caries inhibition by topical fluoride agents.

Acidulated phosphate fluoride (APF), Duraphat or Fluor Protector, was applied to the molar teeth of rats fed a cariogenic diet. The first maxillary molar teeth were subjected to a microbiopsy procedure for fluoride analysis and the mandibular molars scored for caries. All three topical fluoride agents produced a significant increase in the fluoride content of the outermost 5.0 micron of enamel. Only APF produced a significant reduction in caries incidence at all sites.

Acidulated Phosphate Fluoride↗