Surface dissolution and transesterification of thermoset dimethacrylate polymer by dimethacrylate adhesive resin and organic catalyst-alcohol solution.

OBJECTIVES: To evaluate transesterification based dissolution of dimethacrylate and epoxy polymers, the former containing ester groups. Polymer substrates were treated with an adhesive resin (Stick™ Resin) and an organic catalyst-alcohol solution (ethylene glycol and triazabicyclodecene). The surface was chemically and nanomechanically analyzed with Fourier Transform-Infrared (FTIR) spectroscopy, surface profile peak (Rp) and nanohardness and modulus of elasticity. METHODS: A total of 100 specimens each of light-cured dimethacrylate polymer and heat-cured diepoxy polymer were prepared. 20 specimens were randomly selected and used as control group (0s). The remaining specimens were randomly divided into 40 each for treatment with an Stick™ resin and ethylene glycol+triazabicyclodecene. Within each group the 40 specimens were randomly subdivided into 20 each for treatment at 5min and 24h, with 10 specimens for FTIR and nanohardness and modulus of elasticity, and the other 10 for SEM and surface Rp analyses. RESULTS: Dimethacrylate polymer showed a reduction in the nanohardness and modulus of elasticity, Rp values and SEM also showed significant topographical changes after being treated with either Stick™ resin or ethylene glycol+triazabicyclodecene, whereas epoxy resin substrate did not. FTIR analyses affirmed changes in the intensity of ester groups. SIGNIFICANCE: Ester group containing dimethacrylate polymer showed a reduction in NMP within 5min of exposure to the treatment agents with softening by solution ethylene glycol+triazabicyclodecene associated to the reduction of ester groups in the polymer structure by transesterification. Epoxy polymer without ester groups was not affected by surface softening with treatment agents. Adhesive resin caused surface swelling.

Effect of solvent/disinfectant ethanol on the micro-surface structure and properties of multiphase denture base polymers.

AIM OF THE STUDY: The aim of this study was to evaluate the effect of solvent/disinfectant ethanol on the surface of denture base polymers. Changes in surface roughness, topography and some nanomechanical properties were assessed by SEM and nanoindentation plotted against different concentrations of ethanol on heat cured and autopolymerized polymetyl methacrylate based acrylic denture base polymers. MATERIALS AND METHODS: Test specimens (10×10×3mm(3)) of heat-curing (HC) and auto-polymerizing (AP) acrylic resin were prepared and polished to obtain uniform smoothness which were further grouped into 3 sub-groups HC1, HC2, HC3 and AP1, AP2, AP3 respectively 10 specimens (n) in each group. HC1 and AP1, HC2 and AP2, HC3 and AP3 were treated with 99.9%, 70% and 40% respectively for 30, 60 and 120s followed by analysis of surface roughness (Sa), topographical changes and some nanomechanical properties. RESULTS: Both HC and AP resins showed changes in their Sa and nanomechanically measured modulus of elasticity and surface hardness after being treated at different concentrations of ethanol and at different lengths of time. Surface changes were most clearly seen in autopolymerizing denture base polymer, especially at the interface region between the PMMA polymer bead and polymer matrix. There was a correlation (R2=0.83, r=0.91, P<0.001) between the time of treatment by ethanol and thickness of the affected area of denture base polymer. CONCLUSION: The present study demonstrated that denture base polymers, especially autopolymerized denture base polymer is prone for surface crazing and dissolving by solvent/disinfectant ethanol. The interphase region between the PMMA polymer bead and the polymer matrix was most affected by the ethanol.

The effect of mechanical and chemical polishing techniques on the surface roughness of heat-polymerized and visible light-polymerized acrylic denture base resins.

OBJECTIVE: The purpose of this study was to compare the effects of mechanical polishing (MP) and chemical polishing (CP) on the average surface roughness (Ra) of heat-cured (HC) and light-cured (LC) denture base acrylic resins. METHODS: A total of 120 specimens (30 × 15 × 3 mm) were prepared from one HC and one LC acrylic resin. To remove nodules and gross surface irregularities, all specimens were finished with a lathe-mounted small acrylic bur and 360-grit sandpaper. Ten finished specimens of each acrylic resin were randomly assigned to each of six polishing techniques: Resilit High-luster Polishing Liquid (RHPL), Universal Polishing Paste, Abraso-star K50, pumice, Jet Seal Liquid, or Acrypoint. MP was performed with an automatic polishing machine for 2 min, under 50 rpm and 500 g of load. CP was performed by immersing the HC and LC specimens in preheated methyl methacrylate at 75 ± 1 °C for 10 s. The surface roughness of the acrylic resin specimens was measured with a contact profilometer. The Ra values were analyzed by two-way analysis of variance, post hoc Scheffe's test, and paired t-test (p â©½ 0.05). Polished and tested acrylic resin surfaces were evaluated by scanning electron microscopy. RESULTS: MP was more effective than CP. The smoothest surface was obtained with the use of the RHPL on the LC (0.05 ± 0.01 µm) or HC (0.07 ± 0.01 µm) acrylic resin. Two-way ANOVA showed a statistically significant difference between MP and CP. CONCLUSIONS: MP produced the smoothest surface of denture base acrylic resin. The mean surface roughness values after MP and CP were not influenced by the type of acrylic resin.

The prevalence of malocclusion and its association with dental caries among 12-18-year-old disabled adolescents.

BACKGROUND: To assess the prevalence of malocclusion among 12-18-year-old disabled adolescents in Chennai, Tamil Nadu, India, by using the Dental Aesthetic Index (DAI) and to determine the association of malocclusion with dental caries. METHODS: This cross-sectional study included 243 children with various mental disabilities with or without physical infirmities. The Dental Aesthetic Index (DAI) and the dentition status were recorded using the World Health Organization Oral Health Surveys - Basic Methods (1997) Pro-forma. The Decayed (D), Missing (M) and Filled (F) components of the DMF index were calculated using the Dentition Status and Treatment Need (DSTN). A Chi-square test, ANOVA, and t-test were used to derive inferential statistics. RESULTS: The mean DAI score ± standard deviation was 39.0 ± 12.3. A total of 123 (50.6%) participants (74 males and 49 females) had DAI scores of 36 and above, which indicated a handicapping malocclusion requiring mandatory orthodontic treatment. Sixty-nine (28.4%) adolescents (36 males and 33 females) had DAI scores between 31 and 35, which indicated severe malocclusion, for which orthodontic intervention was desirable. Incisal segment crowding (84.8%) was the most common aspect of the malocclusion. The mean DMFT score was 4.36 ± 3.81, and 82.8% of the participants had a DMFT score > 0. There was no statistically significant correlation between the mean DAI and DMFT scores (r = 0.090, p = 0.15). Only 16 (6.6%) of the adolescents had minor or no anomaly not needing orthodontic treatment. CONCLUSIONS: The prevalence of malocclusion and dental caries was found to be high. However, there was no positive correlation between the severity of malocclusion and dental caries among the surveyed disabled adolescents.

Effect of different beverages on the color stability and degree of conversion of nano and microhybrid composites.

This study sought to evaluate the effects of different staining solutions on the colour stability of nanocomposites compared with microhybrid resin and to evaluate the degree of conversion of these two materials. Two different shades of two different composites were cured in polytetraflouroethylene disk rings. Coffee, tea and cola drinks were used as staining solutions, and distilled water was used as a control. Data were statistically analysed using a paired T-test with a significance level of 5%. Nano composite showed the highest degree of conversion (DC) values based on calculation of the bonded and free carbonyl peak intensities in the spectrum. The colour analysis showed that nanohybrid had the highest ΔE values when exposed to coffee solutions; they showed less color stability despite having a higher degree of conversion. Nano resin composite showed significantly higher discoloration than microhybrid composite.

A comparison of the mechanical properties of a modified silorane based dental composite with those of commercially available composite material.

OBJECTIVES: The aim of this study was to compare the mechanical properties of the nano-hydroxyapatite incorporated silorane composite material with the commercially available dental composites. METHODS: Filtek Silorane resin composite was incorporated with 5% and 10% nano-hydroxyapatite crystals and then mechanically tested in comparison along with the commercially available Filtek Silorane and Filtek Supreme XT after 1, 14, 30 and 90 days period. RESULTS: The mechanical tests revealed that the modified silorane based dental composite had a significant increase in the mechanical properties than the commercially available Filtek Silorane and Filtek Supreme XT. SIGNIFICANCE: The collected data suggests that nano-hydroxyapatite crystals modified silorane may provide the clinicians with a better composite materials having a longer life especially in the posterior restorations where the masticatory forces are very much high.