Wear, roughness and microhardness analyses of single increment restorative materials submitted to different challenges in vitro

Effect of various surface coating methods on surface roughness, micromorphological analysis and fluoride release from contemporary glass ionomer restorations

OBJECTIVE

To evaluate the effect of various surface coating methods on surface roughness, micromorphological analysis and fluoride release from contemporary resin-modified and conventional glass ionomer restorations.

MATERIALS & METHODS

A total of 72 permanent human molars were used in this study. The teeth were randomly assigned into 2 groups according to type of restorative materials used; resin modified glass ionomer cement and conventional glass ionomer (SDI Limited. Bayswater Victoria, Australia). Each group was subdivided into 3 subgroups according to the application of coat material; Sub-group1: without application of coat; Sub-group2: manufacturer recommended coat was applied and sub-group3: customized (vaseline) coat was applied. Each group was then subdivided into two divisions according to the time of testing; immediate (after 24 h) and delayed (after 6 months of storage). Three specimens from each sub-group were selected for surface roughness test (AFM) and another 3 specimens for the micromorphological analysis using scanning electron microscope (SEM). For the fluoride release test, a total of 60 cylindrical discs were used (n = 60). The discs were randomly split into 2 groups according to type of restorative materials used (n = 30); resin modified glass ionomer cement and conventional glass ionomer. Each group was subdivided into 3 subgroups (n = 10) according to the application of the coat material; Sub-group1: without application of coat; Sub-group2: with the manufacturer recommended coat and sub-group3: with application of customized (vaseline) coat. Data for each test was then collected, tabulated, were collected, tabulated, and tested for the normality with Shapiro-Wilk test. Based on the outcome of normality test, the significant effects of variables were assessed using appropriate statistical analysis testing methods.

RESULTS

Regarding the data obtained from surface roughness test, Shapiro-Wilk test showed normal distribution pattern of all values (p > 0.05). Accordingly, Two-way ANOVA outcome showed that the 'type of restoration' or 'test time' had statistically significant effect on the AFM test (p < 0.05). Regarding Fluoride specific ion electrode test 2-way ANOVA followed by Least Significant Difference (LSD) Post-hoc test revealed significant difference among the groups (p < 0.05). It showed that SDI GIC group after 14 days of measurement had the highest mean of fluoride release (36.38 ± 3.16 PPM) and SDI RMGIC after 30 days of measurement had the second highest mean of fluoride release (43.28 ± 1.89 PPM). Finally, regarding the micromorphological analysis using SEM, a slight difference was observed between the studied groups.

CONCLUSIONS

Based on the results of this study, various coatings enhance surface roughness in the initial 24 h of restoration insertion. Different coat types seems that have no influence on fluoride release and the micromorphological features of the restoration/dentin interface.

Efficacy of bioactive materials in preventing Streptococcus mutans-induced caries on enamel and dentine

The study investigated the ability of bioactive materials used to restore enamel and dentine specimens to prevent caries. Enamel (n = 50) and dentine (n = 50) specimens were obtained from bovine incisors, prepared, and randomly allocated to one of five groups according to the restorative treatment: alkasite without adhesive system; alkasite with adhesive system; high viscosity glass ionomer cement; resin composite; no restoration; negative control group. Specimens were restored, exposed to a thermal cycling aging protocol, sterilized, and exposed to a cariogenic challenge induced by Streptococcus mutans and then submitted to surface and subsurface microhardness tests and polarized light microscopy to verify the caries lesion development in enamel or dentine surrounding the restorative materials. Data were analyzed using one-way ANOVA. In enamel and dentine, glass ionomer cement, alkasite without and with adhesive system presented a lower percentage surface microhardness loss than resin composite and negative control. Enamel subsurface microhardness presented no statistically significant differences between glass ionomer cement, alkasite without and with adhesive system. Glass ionomer cement also did not present statistically significant differences from resin composite and the negative control. In dentine, glass ionomer cement showed the highest subsurface microhardness values. In conclusion, bioactive restorative materials provide greater protection to enamel and dentine against surface caries development than resin composite.

Diatomaceous earth as a drug-loaded carrier in a glass-ionomer cement

The effect of a natural filler (diatomaceous earth [DE], a promising drug-delivery agent) and its content was investigated on the performance of a model glass-ionomer cement (GIC). Three sample series, differing in DE content (0, 2.5 and 5 wt%), were prepared using a commercial GIC as a matrix (3M Ketac Molar Easymix). The resultant surface microhardness and roughness, wear performance, and compressive strength of the samples were measured after the samples had been stored in deionized water at 37°C for a fixed time. Moreover, the film thickness was tested for the freshly mixed samples. The numerical data was subjected to statistical analysis, in order to test the null hypotheses of the equality of the measured properties between the reference and the DE-modified samples. According to the results, diatomaceous earth particles are uniformly distributed in the GIC matrix, and the cavities of frustules tend to be filled with the GIC. This translates into the observed performance of the DE-loaded GIC. Compared with the reference material (0 wt% DE), the surface microhardness (2.5 wt% DE, p = 0.014; 5 wt% DE, p = 0.005) and roughness (e.g. Ra; 2.5 wt% DE, p = 0.003; 5 wt% DE, p < 0.001) are increased. No effect on the wear performance (p = 0.530 and 0.256, respectively) or compressive strength (p = 0.514) was noticed in the case of DE partially substituting the glass phase. Based on the study results, it is evidenced that diatom frustules are a suitable filler for application in conventional glass-ionomer cements as the glass-substituting drug-loaded carrier. Notably, however, the surface finish method of the DE-filled materials needs development.

In vitro wear of (resin-coated) high-viscosity glass ionomer cements and glass hybrid restorative systems

OBJECTIVES

The aim of the present study was to investigate the volumetric abrasive wear of a high-viscosity glass ionomer cement (hvGIC; Equia Fil) and a glass hybrid restorative system (ghRS; Equia Forte), each being recommended as amalgam alternatives. Both materials were applied with or without their respective resinous coating, and were compared with a conventional GIC (Ketac Fil) and a hybrid composite resin (CR; G-ænial Posterior).

METHODS

78 standardized occlusal Class I cavities were restored with the various materials (n = 13 per group). Before and after chewing simulation (30,000 cycles at 40 N), each sample underwent optical scanning procedures (Omnicam). A comparison of the total wear using a fluorescence-aided identification technique (OraCheck) followed, and differences (α = 5%) between groups were compared by means of MANOVA.

RESULTS

Regarding the wear rates of hvGIC and ghRS, no differences could be observed (p > .050), and this was not affected by the resinous coating. All hvGIC and ghRS restorations showed significantly higher abrasive wear than CR (p < .001), while the conventional GIC displayed a significant underperformance compared with any other material (p < .001).

CONCLUSIONS

Resinous coating of hvGIC or ghRS does not appear to exert an effective long-term protection against advanced abrasive wear. Compared to the conventional GIC showing a considerable substance loss, both hvGIC and ghRS materials revealed an improved abrasion resistance, but clearly failed to meet the excellent values of the CR.

CLINICAL SIGNIFICANCE

Occlusal loading should be carefully considered when using hvGIC or ghRS as amalgam (or composite resin) alternatives for the restoration of posterior teeth.