Flexural Strength Of Provisional Restorative Materials Upon Aging

Background: Aging may affect strength of provisional restorative materials.Objective: This study evaluated the effect of aging on strength of heat-polymerized polymethyl methacrylate (Hp-PMMA), auto-polymerized (Ap) PMMA, bis-phenyl-glycidyl dimethacrylate (Bis-GMA), and computer-aided design/computer-aided manufacturing (CAD/CAM) containing either PMMA or acrylate resin.Methods: Two hundred-ten bars (2x2x25mm) were fabricated from Hp-PMMA: Major C&B (M); Ap-PMMA: Unifast™ (U); Bis-acryl: Protemp™ (P), Luxatemp® (L); PMMA-CAD/CAM: Telio® CAD (T), artBloc® (R); and acrylate-CAD/CAM: Vita CAD Temp® (V). Each was divided into aging- (A) and non-aging- (N) groups (n=15 each). A-groups were thermo-cycled (5°C v.s 55°C, 30 sec each, 5000 cycles). Flexural strength was determined in universal testing machine at 1 mm/min crosshead speed, 50N/min loading. An analysis of variance (ANOVA) and Bonferroni’s test was determined for significant difference (α=0.05). Weibull statistics were determined for Weibull modulus (m), and characteristics strength (σo). Scanning electron micrographs (SEM) were examined for fracture surfaces.Results: The values (means±sd (MPa), m, σo) were (84.62± 3.73, 25.23, 86.53) and (84.05± 6.39, 13.21, 87.28) for VN and VA, (133.49± 4.32, 34.09, 135.54) and (123.11± 4.55, 28.76, 125.35) for TN and TA, (120.59± 6.94, 19.01, 123.84) and (119.96± 6.90, 19.21, 123.16) for RN and RA, (94.35± 4.07, 25.82, 96.24) and (93.07± 3.22, 32.19, 94.58) for PN and PA, (110.60± 6.20, 19.99, 113.44) and (97.23± 7.77, 13.82, 100.78) for LN and LA, (114.30± 5.21, 23.90, 116.79) and (112.21± 5.70, 19.86, 115.13) for MN and MA, and (89.45± 2.96, 32.77, 90.88) and (84.96± 5.33, 17.66, 87.42) for UN and UA respectively. T revealed the highest, whereas V possessed the lowest strength for both N- and A- condition. Aging significantly affected strength.Conclusions: Flexural strengths were differences among materials. PMMA-CAD/CAM possessed the highest, while acrylate-CAD/CAM possessed the lowest. Hp-PMMA showed better strength than Ap-PMMA. Bis-acryl resin was stronger than Ap-PMMA. Aging reduced strength for all materials tested

Fracture toughness of different monolithic zirconia upon post-sintering processes

Surface treatments are expected to be a reason for alteration in fracture resistance of zirconia. This study evaluated the effect of post-sintering processes on the fracture toughness of different types of monolithic zirconia. Material an

Shear bond strength of ceramic bracket bonded to different surface-treated ceramic materials

This study evaluated the effect of ceramic surface treatments on bond strength of ceramic brackets to machine-able ceramics and ceramic veneering metal. Machined ceramic specimens (10x10x1.5 mm) were prepared from Empress® CAD (EP), and e.max® CAD (EM). Ceramic veneering metal specimens (PF) were fabricated from sintered d.Sign® porcelain (1.27 mm thickness) over d.Sign®10 metal (0.23 mm thickness). Each ceramic was divided into 3-groups and treated surface by Er-YAG laser (LE) or etching with 9.6% HF acid for 5 seconds (A5) or 15 seconds (A15). Resin adhesive (Transbond?-XT) was used for attaching ceramic brackets for each group (n=15) and cured with LED (Bluephase®) for 50 seconds. Specimens were immersed in distilled water for 24 hours before testing for shear bond at crosshead speed of 1.0 mm/min. The data were analyzed for the differences in bond strength with ANOVA and Tukey?s multiple comparisons (? = 0.05). De-bond surfaces were microscopically examined. Bond strength (MPa) were 12.65±1.14 for EMA5, 14.50±2.21 for EMA15, 13.97±1.17 for EMLE, 12.40±1.95 for PFA5, 15.85±3.13 for PFA15, 14.06±2.17 for PFLE, 12.12±1.54 for EPA5, 15.65±1.57 for EPA15, 12.89±1.17 for EPLE. Significant differences in bond strength among groups were found related to surface treatment (p0.05). A15 provided higher bond strength than LE and A5 (P<0.05). No damage of ceramic surface upon de-bonding was indicated except for A15 tends to exhibit ditching. LE showed more uniform treated surface for bonding and no surface destruction upon de-bond compared to others. Bond strength was affected by surface treatment. Both LE and A15 treated surface provided higher bond strength than A5. Considering possibly inducing defect on ceramic surface, LE seems to provide better favorable surface preparation than others. Treated ceramic surface with Er-YAG prior to bracket bonding is recommended

Effectiveness of Nanohydroxyapatite on Demineralization of Enamel and Cementum Surrounding Margin of Yttria-Stabilized Zirconia Polycrystalline Ceramic Restoration

Introduction. Prosthetic dentistry has shifted toward prevention of caries occurrence surrounding restorative margin through the anti-demineralization process. This study examines the ability of nanohydroxyapatite (NHA) gel and Clinpro (CP) on enhancing resistance to demineralization of enamel and cementum at margin of restoration. Materials and Methods. Thirty extracted mandibular third molars were segregated at 1 mm above and below cementoenamel junction (CEJ) to separate CEJ portions and substituted with zirconia disks by bonding to crown and root portions with resin adhesive. The enamel and cementum area of 4 × 4 mm2 neighboring zirconia was applied with either NHA or CP, while one group was left no treatment (NT) before demineralized with carbopal. Vickers hardness (VHN) of enamel and cementum was evaluated before material application (BM), after material application (AM), and after demineralization (AD). Analysis of variance (ANOVA) and post hoc multiple comparisons were used to justify for the significant difference (α = 0.05). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were determined for surface evaluations. Results. The mean ± SD of VHN for BM, AM, and AD for enamel and cementum was 393.24 ± 26.27, 392.89 ± 17.22, 155.00 ± 5.68 and 69.89 ± 4.59, 66.28 ± 3.61, 18.13 ± 0.54 for NT groups, respectively, 390.10 ± 17.69, 406.77 ± 12.86, 181.55 ± 7.99 and 56.01 ± 9.26, 62.71 ± 6.15, 19.09 ± 1.16 for NHA groups, respectively, and 387.90 ± 18.07, 405.91 ± 9.83, 188.95 ± 7.43 and 54.68 ± 7.30, 61.81 ± 4.30, 19.22 ± 1.25 for CP groups, respectively. ANOVA indicated a significant increase in anti-demineralization of enamel and cementum upon application of NHA or CP (p0.05) as evidenced by SEM and XRD data indicating NHA and CP deposition and crystallinity accumulation. Conclusion. NHA and CP were capable of enhancing anti-demineralization for enamel and cementum. The capability in resisting the demineralization process of NHA was comparable with CP. NHA was highly recommended for anti-demineralization for enamel and cementum surrounding restorative margin

Remineralization Potential of Nanohydroxyapatite Toothpaste Compared with Tricalcium Phosphate and Fluoride Toothpaste on Artificial Carious Lesions

Introduction. Nanohydroxyapatite (nano-HA) has been utilized as an alternative agent for dental enamel remineralization. This study compared remineralization potential of nano-HA toothpaste (NHT), functionalized tricalcium phosphate toothpaste (TCPT), and fluoride toothpaste (FT) on carious lesions. Materials and Methods. Sixty extracted human premolars were prepared for artificial carious lesions with synthetic polymer gel. Samples were divided into four groups according to testing agents: NHT, TCPT, FT, and one group with no treatment (NT). Each group was subjected to pH-cycling with the application of toothpaste in slurry form twice a day (2-min each) for 10 days. Surface microhardness was measured before demineralization, after demineralization, and after pH-cycling. Hardness at different periods, percentage of hardness recovery (% HR), and percentage of remineralization potential (%RP) were determined and statistically analyzed with ANOVA and Tukey comparisons (α = 0.05). Polarized light microscopy (PLM) was utilized to assess lesion depth. Results. Significant remineralization of carious lesions was observed among different toothpastes compared to NT (p0.05). No significant difference in % HR and % RP was seen among NHT, TCPT, and FT (p>0.05). PLM indicated a greater decrease in carious depth upon using NHT compared to TCPT and FT, with minimal increase in depth for NT. Conclusions. NHT has comparable capability to TCPT and FT in hardness recovery. However, decrease in carious depth was evidenced with PLM for NHT more than TCPT and FT. Thus, NHT was suggested as a potential remineralization product for treating initial carious lesions. Clinical Significance. The study showed that NHT had the potential to remineralize artificial carious lesion. It was confirmed in potential in the lesion depth reduction and forming a new enamel layer. NHT showed its capability as an alternative for dental caries therapeutic