Biomedical subjects

Sias R Grobler

Publications and source records attributed to Sias R Grobler.

6 recordsLinked to original sources

PubMed2003

The effect of different power densities and method of exposure on the marginal adaptation of four light-cured dental restorative materials.

PURPOSE: To determine whether marginal adhesion is sensitive to different irradiation parameters, we investigated the in vitro adhesion values of four dental resins on metal surfaces. METHODS: Four groups of eight specimens each of Z250, Filtek flow, Dyract AP and Dyract flow were placed in pre-treated stainless steel cavities and irradiated using different methods of exposure. The curing lights used were a Spectrum 800 halogen curing light at settings of 800 and 450 mW/cm(2) and an Optilux 501 ramping light. The maximum amount of push-out force required to displace the resin from the metal cavity was equated with adhesive value (shear bond strength). Comparisons (ANOVA, p<0.0001) were made within the same material and between the different materials when using different curing protocols. RESULTS: Significant lower bond strengths were recorded when curing was done by gradually increasing the intensity (ramping method) compared to curing with the fixed intensities (p>0.0001) Comparing the fixed intensities, significant lower bond strength values were obtained at 800 mW/cm(2) compared to 450 mW/cm(2) (p<0.0001). For all exposures, the two flowable materials demonstrated weaker values when compared to the higher filled materials. CLINICAL SIGNIFICANCE: The advantage of initial slow polymerization (more elasticity and less tension) obtained by the so-called "soft start" method, was offset by a rise in total polymerization shrinkage, when final curing was completed at 1130 mW/cm(2). These tests demonstrated that using halogen units, exposure for 40s with an intensity of 450 mW/cm(2) appeared to be the most promising for light-curing dental resin composites.

Dental Marginal Adaptation↗

PubMed2003

The effects of light intensity and method of exposure on the hardness of four light-cured dental restorative materials.

AIM: To determine the microhardness of several light-curing dental restorative materials at the top surface as well as at a depth of 2mm. METHODS: Comparisons were made using different light sources. Four groups of five specimens each (3mm diameter, 2mm thick) of Z250 (composite), Filtek Flow (flowable composite), Dyract AP (compomer) and Dyract Flow (flowable compomer) were cured using different methods of exposure. The curing lights used were a Spectrum 800 halogen curing light at settings of 800 mW/cm2 and 400 mW/cm2 and an Optilux 501 ramping light. Vickers microhardness tests were performed at the top surface and at the bottom surface. RESULTS: Significant differences in microhardness between the top and bottom surfaces were demonstrated for all materials and with all light sources (p<0.05). The different exposures also produced significant differences (p<0.05). The light source used had less of an effect on the hardness of the compomers than the composites. CONCLUSIONS: Effective hardness ratios between the top and bottom surfaces were achieved with all three curing protocols. The effect of total energy application must be taken into account before assumptions can be made as to the effect on hardness using different exposure methods.

Compomers↗

PubMed2003

Compomers: adhesion and setting reactions.

The term compomer is misleading as it suggests a combination of glass-ionomer and composite technology. This has led to confusion as to its clinical uses as well as the way it bonds to tooth structure. However, the properties and adhesion of compomers to tooth structure suggest a closer link to composites than to glass-ionomers. The clinical significance of this is that compomers lack direct chemical adhesion to any tooth structure and therefore needs to be bonded to tooth structure similar to composites via a separate bonding agent. Their closeness to composites however, does not make them composite substitutes or replacements. Dentists should strictly follow instructions by the manufacturers because failure of materials can mostly be blamed on the clinician rather than on the material.

Adhesiveness↗

PubMed2003

The effect of an additional flowable compomer layer on microleakage of Class V compomer restorations.

BACKGROUND: Polymerisation shrinkage and the associated stress on composite resins and surrounding structures have been regarded as a major cause of leakage and clinical failures in modern polymer restorations. The purpose of this study was to investigate the effect of an additional flowable compomer layer on the microleakage of Class V dental cavities, which were further filled with a compomer. METHOD: Cavities (32) were prepared in human premolars, conditioned with a non-rinsing agent (Prime & Bond NRC) and treated with the bonding agent (Prime & Bond NT). Sixteen of these cavities were then lined with a layer of flowable compomer (Dyract Flow, approximately 0.5 mm) and further filled with Dyract AP. The other 16 cavities were filled without the flowable compomer. The specimens were thermo-cycled in a 0.5% basic fuchsin solution, sectioned and evaluated for dye penetration using a scoring system of 0 to 4. RESULTS: Lower microleakage values were found at the enamel as well as at the dentine sides when a layer of Dyract Flow was used as a liner. Furthermore, significantly (p < 0.05) lower microleakage was found in enamel than in dentine for both layered and unlayered restorations. CONCLUSION: It can be concluded that a layer of flowable compomer (i.e. Dyract Flow) in a cavity under a compomer may be recommended to improve the marginal seal of a restoration.

Bicuspid↗

PubMed2002

A 3-year clinical evaluation of a compomer, a composite and a compomer/composite (sandwich) in class II restorations.

PURPOSE: To compare the clinical performance of Dyract, Spectrum-TPH and Dyract layered with Spectrum-TPH (sandwich) in Class II restorations of permanent dentitions. MATERIALS AND METHODS: 23 adult patients aged 25-62 were selected at random in a general dental practice. Each patient had 3 bicuspid teeth restored with Dyract, Spectrum-TPH and a "sandwiched" combination where Dyract was covered by the composite resin TPH. During the entire study, three patients were lost. Restorations were clinically evaluated using a modified Ryge/USPHS system. RESULTS: Over 36 months all three types of restorations performed well clinically. No post-operative sensitivity was reported by any patient indicating proper bonding and sealing. Only one Dyract/TPH sandwich restoration had to be replaced after 2.5 years due to root caries. The Dyract restorations exhibited significantly higher (P = 0.0039) occlusal wear than the TPH and the Dyract/TPH sandwiched restorations. The marginal integrity was also found to be significantly better (P = 0.001) for the TPH and Dyract/TPH restorations compared to Dyract alone, while no significant difference (P > 0.05) could be demonstrated between TPH and Dyract/TPH restorations. The low rate of failure in the three different restorative systems suggests that they are reliable restorative materials in permanent bicuspids over a 3-year period.

Acetone↗

PubMedDate not supplied

Effect of power density on shrinkage of dental resin materials.

This study compares volumetric changes and rates of shrinkage during different stages of polymerization of dental resin composites and compomers exposed to the same total energy by using two different combinations of power density and exposure duration. A hybrid composite and its equivalent flowable and a compomer and its equivalent flowable were exposed using a halogen curing unit set at 400 mW/cm2 for 40 seconds and 800 mW/cm2 for 20 seconds: delivering 16 J/cm2 in both cases. Volumetric changes were recorded every 0.5 seconds using a mercury dilatometer. Ten replications per test condition were performed and the data were subjected to ANOVA. Statistically significant differences in shrinkage values and rates among different power densities were determined by means of paired t-tests at a 95% confidence level. Significantly more shrinkage (p<0.05) was found for the higher filled materials, Z250 and Dyract AP, when higher power density was used. However, no significant differences were found between their flowable counterparts when exposed to various power densities. Of the four materials, only Dyract AP exhibited no significant difference in shrinkage rate when various power densities were used. All the other materials exhibited significantly higher rates (p<0.05) at the higher power density.

Compomers↗