Flexural strength of novel glass infiltrated monochrome and multilayer high yttrium oxide containing zirconia upon various sintered cooling rates.

PURPOSE: The sintering technique and cooling strategy influence the strength of zirconia. This study examined the impact of altering the cooling rate of glass-infiltrated monolayer and multilayer 5 mol% yttria-partially stabilized zirconia (5Y-PSZ) on their strength. MATERIALS AND METHODS: One-hundred eighty (180) specimens (width × length × thickness = 10 × 20 × 2 mm) were prepared using monolayer (Mo: Cercon-xt) and multilayer (Mu: Cercon-xt ML) 5Y-PSZ. Randomly distributed specimens (n = 15/group) were sintered with traditional (T) versus glass infiltrated (G) technique and cooled down with different cooling rates: slow (S: 5°C/min), normal (N: 35°C/min), and fast (F: 70°C/min). Four-point bending test was used to measure flexural strength (σ). Microstructures were investigated by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Three-way ANOVA and Tamhane comparisons were determined for a significant difference of σ (p < 0.05). Weibull analysis was determined for Weibull modulus (m). RESULTS: The highest σ (MPa) was seen for GMuS (696.8 ± 69.8). Mo-PSZ and Mu-PSZ showed no significant difference in σ. G-sintering presented significantly higher σ (659.9 ± 79.3) than T-sintering (426.0 ± 63.7). S-cooling (560.9 ± 126.1) had the highest σ. The highest m-value was observed in GMuN (12.1 ± 3.8). A significant difference in σ was indicated due to cooling rates and sintering techniques (p < 0.05). CONCLUSIONS: Glass infiltration significantly enhanced strength through elastic gradience. F-cooling reduced grain size, impaired grain boundary integration, and increased the tetragonal to monoclinic phase transition, significantly decreasing flexural strength in traditional sintering. Nevertheless, F-cooling was recommended for glass-infiltrated 5Y-PSZ to enhance strength while reducing processing time.

Flexural Strength of Different Monolithic Computer-Assisted Design and Computer-Assisted Manufacturing Ceramic Materials Upon Accelerated Aging.

OBJECTIVES: The durability of ceramic is crucial, which is probably influenced by aging. This study evaluated the effect of aging on flexural strength of different ceramics. MATERIALS AND METHODS: One-hundred twenty ceramic discs (Ø 12 mm, 1.5 mm thickness) were prepared from zirconia-reinforced lithium silicate (ZLS, C), lithium disilicate (LS2, E), precolored yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP, Ip), and customized color Y-TZP (Ic). Samples were randomly divided into two groups for accelerated aging (A) between 5 and 55°C water baths, 30-second immersing time each, for 10,000 cycles, and nonaged group (N), serving as control. Biaxial flexural strength (σ) was evaluated utilizing the piston-on-three-balls at 0.5 mm/min speed. Analysis of variance and Tukey comparisons were determined for significant differences (α = 0.05). Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristic strength (σo). Microstructures were evaluated with scanning electron microscopy and X-ray diffraction (XRD). RESULTS: The highest σ and σo were seen for IcN, followed by IcA, IpN, IpA, EN, CA, CN, and EA, respectively. CN showed the highest m, while EA showed the lowest m. Significant differences of σ for each ceramic were indicated (p < 0.05). Aging caused a significant difference in σ (p < 0.05). XRD showed t→m phase transformation of Ip and Ic after aging. CONCLUSION: Aging affected strength of ceramics. Comparable strength between LS2 and ZLS was evidenced, but both were less strength than Y-TZP either aging or non-aging. Comparable strength between precolored Y-TZP and customized color Y-TZP was indicated. Better resisting aging deterioration of Y-TZP than LS2 and ZLS is suggested for fabrication restorative reconstruction.

Remineralization potential of apacider mangosteen adhesive pastes on artificial carious lesions.

Background/purpose: Attention to caries administration has altered toward an early finding of lesions and targeted to noninvasive management with a remineralizing agent. This study compared the remineralization potential of apacider mangosteen adhesive pastes (AMAP), 500-ppm fluoride toothpaste (FT500), and 1000-ppm fluoride toothpaste (FT1000) on artificial caries. Materials and methods: Artificial caries were generated to enamel of eighty extracted human premolars. The specimens were allocated to four groups and subjected to pH-cycling with the application of testing agents (2 min each, for 10 days): (1) AMAP, dairy, (2) FT500, twice a day, (3) FT1000, twice a day, and (4) no treatment (NT). The surface microhardness was determined before demineralization, after demineralization, and after application of pH-cycling. The hardness, percent of hardness recovery (%HR), and percent of remineralization potential (%RP) were analyzed with ANOVA and Bonferroni's test (α = 0.05). Polarized light microscopy (PLM) was assessed for lesion depth. Results: Significant differences in remineralization were observed upon various agents compared to NT (P < 0.05). A significant difference in remineralization was found among AMAP, FT1000, and FT500 (P < 0.05). No significant difference in %HR and %RP was observed between AMAP and FT1000 (P > 0.05). PLM signified greater decrease in depth for AMAP, compared to FT1000 and FT500, but no depth reduction for NT. Conclusion: AMAP possesses comparable remineralization ability to FT1000. However, decreasing in depth of carious lesions was evinced with using AMAP more than FT1000 and FT500. AMAP was recommended as a potential remineralization material for handling initial caries.

Optical Characteristics of Monochrome and Multilayer Fully Stabilized Zirconia Upon Sintered Cooling Speed.

OBJECTIVES: Firing protocols influence optical properties of dental ceramics. Effects of varying cooling rates of monochrome and multilayer 5 mol% yttria-stabilized tetragonal polycrystalline (5YTZP) on optical properties are subjected for investigation. MATERIALS AND METHODS: Ninety specimens (width, length, thickness = 10 × 20 × 2 mm) were prepared from monochrome (Mo: Cercon xt) and multilayer (Mu: Cercon xt ML with cervical (C) and incisal (I) zoning) 5YTZP. Specimens were sintered and randomly treated with three cooling rates (n = 15/group): slow (S: 5°C/min), normal (N: 35°C/min), and fast (F: 70°C/min). Color appearance (∆EW), color appearance difference (∆E diff), translucency parameter (TP), contrast ratio (CR), and opalescence parameter (OP) were evaluated in CIEL*a*b* (Commission International de I'Eclairage) system. ∆E diff was achieved from the coordinate difference of specimen to VITA classic shade A2. Microstructures and compositions were evaluated by scanning electron microscope and energy dispersive spectroscopy. Monoclinic (m), tetragonal (t), and cubic (c) phases were investigated with X-ray diffraction. STATISTICAL ANALYSIS: An analysis of variance and Bonferroni multiple comparisons were determined for significant differences (p < 0.05). RESULTS: ΔEW of MoF was highest (66.04 ± 1.86), while MuN-I was lowest (62.60 ± 0.86). TP and OP of MoS were highest at 2.85 ± 0.11, and 2.25 ± 0.10, while MuF-I was lowest at 2.16 ± 0.10 and 1.60 ± 0.12. CR of MuF-I was highest (0.948 ± 0.005), while MoS was lowest (0.936 ± 0.005). ΔEdiff of MoF was highest (3.83), while MuN-I was lowest (0.93). Limited grain growth and m-phase composition were indicated upon fast cooling. There were significant differences for all color parameters due to varied materials, cooling rates, and their interactions (p < 0.05) except for interaction in ∆EW and OP. CONCLUSIONS: Translucency of monochrome and multilayer 5YTZP were different, possibly due to colorant additives. Incisal layer of multilayer 5YTZP was perfectly matched with VITA shade. Increasing cooling speed resulted in smaller grain size, t-m transformation, and finally lower translucency and opalescence. Therefore, to achieve most favorable optical properties, slow cooling rate is recommended.

Microleakage and penetration capability of various pit and fissure sealants upon different sealant application techniques.

Background: Sealant application that yields superior marginal adaptation and deeper fissure penetration potentially improves success in preventive and restorative dentistry. This study evaluated the amount of in-vitro microleakage and penetration capabilities of different pit-fissure sealants as the effect of different application techniques. Material and Methods: 160 freshly extracted human sound premolars, assigned as suitable for sealant application, selected and allocated randomly into 8 groups (n=20 teeth/group) and applied with different sealants including Embrace-Wetbond® (E), UltraSeal XT® (U), Clinpro™ (CL), Helioseal® (H), using either conventional (C) or induced application (I). The sealed teeth were thermocycling for 500 cycles between 5°C and 55°C with 30 seconds dwelling time. The tooth was coated with 2 layers of nail varnish, leaving 1 mm around the sealant margin, then immersed in 5% methylene blue solution for 24 hours. Subsequently, 2 pieces were segmented vertically in a buccolingual direction, yielding 4 surfaces/tooth for determination of microleakage and penetration proportion of sealant with polarized light microscopy (PLM) and image-J software. ANOVA and Bonferroni multiple comparisons were determined for significant differences (α=0.05). Sealant adaptability was detected using a scanning electron microscope (SEM). Results: The highest microleakage was observed for EC, followed by CLC, HC, UC, CLI, HI, EI, and UI. The highest penetration was seen in UI, followed by HI, CLI, CLC, UC, HC, EI, and EC. ANOVA indicated significant differences in microleakage and penetration on the type of sealant and application method (p<0.05). SEM revealed that the I-application method significantly promoted less microleakage and better penetration than the C-application (p<0.05). Conclusions: Microleakage and penetration capabilities of sealant are greatly affected by the types of sealant and the method by which the sealant is applied. U-sealant exhibited less microleakage and better penetration capability than others. I-application reduced microleakage, promoting enhanced penetration and adaptation, is the recommended sealant application. Key words:Microleakage, penetration, dental sealant.

Flexural Strength of Two Multilayered and Monochromatic High Yttria Containing Zirconia Materials Following Different Sintering Parameters.

OBJECTIVES: Sintering parameters influence the properties of zirconia. This study examined the effect of altering sintering temperature and time of monochrome and multilayer 5 mol% yttria-partially stabilized zirconia (5Y-PSZ) on flexural strength. MATERIALS AND METHODS: Three hundred specimens (width × length × thickness = 10 × 20 × 2 mm) were prepared from monolayer (ZX) and multilayer (ZM) 5Y-PSZ and randomly sintered at decreasing (TD: 1,450°C), regular (TR: 1,500°C), and increasing (TI: 1,550°C) sintering temperature, with extremely short (HE: 10 minutes), ultrashort (HU: 15 minutes), short (HS: 30 minutes), and regular (HR: 135 minutes) sintering time (n = 15/group). The precrack was induced on the tension side before testing for flexural strength (σ). STATISTICAL ANALYSIS: Analysis of variance and Tukey's test were used for significant differences of σ at p < 0.05. The microstructure and crystalline (monoclinic; m, tetragonal; t, cubic; c) phase were evaluated by scanning electron microscope (SEM) and X-ray diffractometer (XRD). RESULTS: ZXTIHS indicated the highest σ for ZX (315.81 ± 18.91 MPa), whereas ZMTIHS indicated the highest σ for ZM (335.21 ± 36.18 MPa). There was no significant difference for σ between ZX and ZM (p > 0.05). Sintering zirconia at TI or HR indicated significantly higher σ than sintering at TD or TR or with HS, HE, or HU for both ZX and ZM (p < 0.05). There was no significant difference for σ between TRHR and TIHS, TIHU, and TIHE (p > 0.05). SEM indicated intergranular and transgranular fractures. XRD revealed predominately c- and t-phases and minor amounts of m-phase. CONCLUSION: Increasing sintered temperature with decreasing time offers acceptable strength to regular sintering. Raising sintering temperature with decreasing time is suggested to facilitate chairside restorative reconstruction.

Bond strength of ceramic veneered CAD-milled alloy upon prolonged sintering.

OBJECTIVES: Ceramic-sintering affects bond strength and longevity of metal-ceramic. This study investigated the effect of sintering temperatures and times on metal-ceramic bond strength vis-a-vis interfacial fracture toughness. MATERIALS AND METHODS: One hundred eighty rectangular-shaped (25 × 8 × 1 mm) casting (Auriloy® (CA)) and CAD-milling (Ceramill Sintron® (MA)) alloys were prepared and randomly veneered with ceramic at normal (930 °C; (TN)), increased (940 °C; (TI)), and extremely increased (950 °C; (TE)) sintering temperatures and normal (1 min; (HN)), increased (2 min; (HI)), and extremely increased (3 min; (HE)) sintering time (n = 10/group). Pre-cracked was subjected to four loading-unloading cycles at 0.05 mm/min speed to determine interfacial fracture toughness from strain energy release rate (G). Microstructures were examined with a scanning electron microscope (SEM), energy-dispersive X-ray (EDX), and atomic force microscopy (AFM). ANOVA and Tukey comparisons were determined for significant differences (α = 0.05). RESULTS: Significant differences in G due to the effect of alloy, sintering temperature, and time (p < 0.05) were indicated. MA revealed higher G than CA. Raising temperatures enabled increasing G for CA, not for MA. Extended sintering permitted increasing G for both alloys. Rougher surface of MA than CA was observed. Interfacial ion exchange was differently indicated between CA and MA. CONCLUSIONS: Bond strength was influenced by alloy, sintering temperature, and time. Ceramic has better adhesion to MA than CA. Enhancing bond for CA was succeeded through increasing sintering temperature and time, whereas through extended sintering for MA. CLINICAL RELEVANCE: MA offers stronger bond than CA. Enhancing bond is suggested by extended sintering. Raising temperature can enhance bond for CA, not for MA.

Flexural strength of high yttrium oxide-doped monochrome and multilayered fully stabilized zirconia upon various sintered cooling rates.

PURPOSE: Firing protocols influence the mechanical properties of dental ceramics. This study examined the impact of altering the cooling rate of mono- and multilayered 5 mol% yttria-partially stabilized zirconia (5Y-PSZ) on their strength. MATERIALS AND METHODS: Ninety specimens (width × length × thickness = 10 × 20 × 2 mm) were prepared using 5Y-PSZ monolayer (Mo: Cercon-xt) and 5Y-PSZ multilayered (Mu: Cercon-xt ML) blocks. Randomly distributed specimens were sintered at the recommended firing schedule for three different categories of cooling rates (n = 15/group): slow (S: 5°C/min), normal (N: 35°C/min), and fast (F: 70°C/min). A universal testing machine with four-point bending test was used to measure the flexural strength (σ). The microstructure, fracture characteristics, and chemical composition were evaluated by scanning electron microscope and energy-dispersive spectroscopy. The monoclinic, tetragonal, and cubic phases were investigated using X-ray diffraction. Two-way ANOVA and post hoc Bonferroni comparisons were applied to determine the σ, ( p < 0.05 $p<0.05 $ ), and Weibull analysis was performed to determine the Weibull modulus (m) and characteristic strength (σ0 ). RESULTS: The highest σ and σ0 (MPa) were seen for MuN (454.2 ± 62.0, 480.8 ± 62.9) followed by MuS (453.5 ± 52.6, 476.4 ± 54.3) and MoS (451.5 ± 44.5, 471.2 ± 46.6), whereas MuF had the lowest σ and σ0 (379.8 ± 50.2, 401.6 ± 51.3). The σ value of S-cooling (452.5 ± 47.9) was higher than those for N-cooling (443.4 ± 61.3) and F-cooling (382.3 ± 58.0). The m-value for MoS was the highest (11.4 ± 3.6), whereas that for MoF was the lowest (6.1 ± 1.6). Different cooling rates resulted in a significant difference in σ values (p < 0.05). CONCLUSIONS: S- and N-cooling resulted in significantly higher flexural strength than that obtained by F-cooling. Increasing the cooling rate of 5Y-PSZ resulted in smaller grain size, less grain boundary integration, and higher t- to m-transformation, leading to lower strength. Therefore, a slow and normal cooling rate was recommended to achieve the optimum strength for 5Y-PSZ.

Color Appearance of Various Provisional Restorative Materials for Rehabilitation Upon Aging.

OBJECTIVES: Color stability of provisional restoration is crucial for full mouth reconstruction, which is probably influenced by aging. Therefore, this study evaluated the effect of aging on the color appearance of different provisional materials. MATERIALS AND METHODS: Rectangular specimens (10 × 10 × 2 mm) were fabricated from computer-aided design-computer-aided manufacturing (CAD-CAM) (Vita CAD-Temp [VC], TelioCAD [TC], artBloc [RC]), autopolymerized (ProtempIV [PA], Luxatemp [LA], UnifastTrad [UA]), and heat-polymerized polymer (Major C&B [MH]). Each was divided into aging (AG, 5,000 thermocycles of 5°/55°C) and non-aging group (n = 21/group). Color parameters were determined using a spectrophotometer through the CIELAB system. The L*, a*, and b* data were calculated for color appearance (∆E), translucency parameter (TP), contrast ratio (CR), and opalescence parameter (OP) for each. STATISTICAL ANALYSIS: An analysis of variance and multiple comparisons were determined for a significant difference in color appearance alteration of materials upon aging (α = 0.05). RESULTS: Statistically significant differences of L*, a*, b*, ∆E, TP, CR, and OP due to the effect of types of material (p < 0.05), aging effect (p < 0.05), and their interactions (p < 0.05) were indicated. Aging affects the color appearance, lightness, chromaticity, translucency, contrast, and opalescence of various types of provisional materials. Color appearance alteration of provisional materials was significantly indicated upon aging (p < 0.05) but within the perceivable limit of clinical acceptance (∆E diff < 3.0), except for PA and MH. Color stability of CAD-CAM-based poly-methyl methacrylate (PMMA) and autopolymerized PMMA upon aging were better than bis-acryl resin and heat-polymerized PMMA. The TP, CR, and OP alterations of tested materials upon aging were within the perceivable limit. CONCLUSION: Color appearance of provisional restorative materials was influenced by aging. The CAD-CAM-based PMMA and autopolymerized PMMA materials showed better color stability than bis-acryl provisional resin and heat-polymerized PMMA upon aging. Therefore, they were suggested as provisional materials for oral rehabilitation.

Flexural Strength of Various Provisional Restorative Materials for Rehabilitation After Aging.

PURPOSE: Durability of provisional restoration is crucial for full-mouth reconstruction, which may be influenced by aging. This study evaluated the effect of aging on the flexural strength of provisional materials for oral rehabilitation. MATERIALS AND METHODS: Bar specimens (2×2×25 mm) were fabricated from CAD-CAM [Vita CAD-Temp® (VC), Telio® CAD (TC), artBloc® (RC)], autopolymerized [Protemp™IV (PA), Luxatemp® (LA), Unifast™Trad (UA)], and heat-polymerized polymer [Major® C & B; (MH)]. Each was divided into aging (AG, 5000 thermocycles of 5°/55°C) and nonaging groups (NG, n = 15/group). Flexural strength (σ, MPa) was determined in a universal testing machine at 1 mm/min crosshead speed. An analysis of variance and multiple comparisons were determined for significant difference (α = 0.05). RESULTS: TCNG indicated the highest mean of σ (133.49 ±4.32), whereas VCNG indicated the lowest mean of σ (84.62 ±3.73) for nonaging. Upon aging process, TCAG revealed the highest mean of σ (123.11 ±4.55), while VCAG possessed the lowest mean of σ (84.05 ±6.39). Significant differences among various provisional materials were indicated (p = 0.001). Aging significantly affected flexural strength (p = 0.001). CONCLUSIONS: The CAD-CAM provisional material possessed higher flexural strength than heat-polymerized PMMA and autopolymerized PMMA, which was suggested as a provisional material for rehabilitation. Aging reduced strength for all materials tested.

Masking ability of different ceramics upon various underlying structures.

OBJECTIVE: To evaluate masking ability of different types and thicknesses of ceramics upon various substructures. MATERIALS AND METHODS: Discs (Ø 12 mm, thickness 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0 mm) were prepared from Bruxzir-Anterior® (Bc), Celtra-DUO® (Cc), and Vita-Suprinity® (Vc) (n = 15/group). Substructures (2 mm thickness) were prepared from natural dentine (Ds), tetracycline-stained dentine (Ts), zirconia (Zs), resin composite (Rs), and cast metal (Ms). A spectrophotometer was used to measure the CIE L*a*b* color coordinates of a specimen. Masking ability was determined from the color difference (∆E00 ) of ceramics between before- and after combining with substructure using ANOVA and Bonferroni test (α = 0.05). ∆E00 value was compared with acceptable clinical threshold (∆E00  = 1.8) and an ideal threshold (∆E00  = 0.8). RESULTS: Type-thickness of ceramics and substructures were significantly affected ∆E00 . Ts significantly influenced ∆E00 more than Rs, Ms, Zs, and Ds. No significant ∆E00 upon Ms and Zs was indicated. Bc completely masked Ts and Rs if thickness was ≥0.6 mm, and Zs, Ms, and Ds if ≥0.4 mm. Cc completely masked Ts and Rs if thickness was >1.6 mm, and Zs, Ms, and Ds if >1.4 mm. Vc completely masked Ts if thickness was >1.4 mm, Rs and Ms if >1.2 mm, and Zs and Ds if >1 mm. CONCLUSION: Ts is the most influential substructure impact on color appearance, requiring a minimum thickness of 0.6 mm Bc, 1.2 mm Vc, or 1.6 mm Cc to be perfectly masked. CLINICAL SIGNIFICANCE: Masking ability was significantly influenced by the type and thickness of ceramic material and underlying structure. Monolithic zirconia had a significantly higher masking ability than lithium silicate/phosphate glass ceramic. Ts indicated the most influencial substructure impacting the color appearance of ceramic restoration, which require a minimum thickness of 0.6 mm Bc, 1.2 mm Vc, or 1.6 mm Cc to achieve ideal masking capability.

Biaxial Flexural Strength of Different Monolithic Zirconia upon Post-Sintering Processes.

OBJECTIVE: Different post-sintering processes are expected to be a reason for alteration in the strength of zirconia. This study evaluated the effect of post-sintering processes on the flexural strength of different types of monolithic zirconia. MATERIALS AND METHODS: A total of 120 classical- (Cz) and high-translucent (Hz) monolithic zirconia discs (1.2 mm thickness and 14 mm in Ø) were prepared, sintered, and randomly divided into four groups to be surface-treated with (1) as-glazed (AG); (2) finished and polished (FP); (3) finished, polished, and overglazed (FPOG); and (4) finished, polished, and heat-treated (FPHT) technique (n = 15). Biaxial flexural strength (σ) was determined on a piston-on-three ball in a universal testing machine at a speed of 0.5 mm/min. STATISTICAL ANALYSIS: Analysis of variance, and post hoc Bonferroni multiple comparisons were determined for significant differences (α = 0.05). Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristic strength (σ0). The microstructures were examined with a scanning electron microscope and X-ray diffraction. RESULTS: The mean ± standard deviation value of σ (MPa), m, and σ0 were 1,626.43 ± 184.38, 9.51, and 1,709.79 for CzAG; 1,734.98 ± 136.15, 12.83, and 1,799.17 for CzFP; 1,636.92 ± 130.11, 14.66, and 1,697.63 for CzFPOG; and 1,590.78 ± 161.74, 10.13, and 1,663.82 for CzFPHT; 643.30 ± 118.59, 5.59, and 695.55 for HzAG; 671.52 ± 96.77, 3.28, and 782.61 for HzFP; 556.33 ± 122.85, 4.76, and 607.01 for HzFPOG; and 598.36 ± 57.96, 11.22, and 624.89 for HzFPHT. The σ was significantly affected by the post-sintering process and type of zirconia (p < 0.05), but not by their interactions (p > 0.05). The Cz indicated a significantly higher σ than Hz. The FP process significantly enhanced σ more than other treatment procedures. CONCLUSION: Post-sintering processes enabled an alteration in σ of zirconia. FP enhanced σ, while FPOG and FPHT resulted in a reduction of σ. Glazing tends to induce defects at the glazing interface, while heat treatment induces a phase change to tetragonal, both resulted in reducing σ. Finishing and polishing for both Cz and Hz monolithic zirconia is recommended, while overglazed or heat-treated is not suggested.

Nano-Hydroxyapatite Gel and Its Effects on Remineralization of Artificial Carious Lesions.

INTRODUCTION: Nano-hydroxyapatite gel (NHG) has never been investigated for enamel remineralization. This study evaluated the effects of two concentrations of NHG on remineralization of an artificial carious lesion in comparison with nano-HA toothpaste (NHT) and fluoride varnish (FV). MATERIALS AND METHODS: Carious lesions were prepared on 100 enamel samples and divided into 5 groups: FV, NHT, 20% NHG, and 30% NHG. One untreated (NT) group was left as control. The hardness of the surface was evaluated before, during, and after remineralization. Microhardness at various phases and the percent recovery of hardness (%HR) were determined and analyzed with ANOVA. Polarized-light micrographs (PLM) were evaluated for depth of the carious lesion. RESULTS: Significantly different remineralization capability was indicated for tested agents (p < 0.05). NHT was significantly capable of remineralization greater than NHG, FV, and NT (p < 0.05). No noticeable difference in %HR between 20% NHG and 30% NHG (p > 0.05) was found. Decreasing in the depth of caries lesion was notified by PLM as applying either NHT or NHG as greater than FV, with no reduction in the depth for NT. CONCLUSIONS: Nano-HA both in toothpaste and gel form was capable of remineralization better than fluoride varnish. Comparable remineralization of 20% versus 30% NHG was evidenced. NHG for both concentrations was recommended as a capable remineralizing agent for caries remineralization. Clinical Significance: This study indicated that an application of nano-HA gel is an attractive route to deliver the material and can be more effective and less toxic than conventional formulations and provide its effectiveness directly at the site of action, especially for a noncooperative young child and medicinally intimidated patients who may face with inconvenience in using toothbrush and toothpaste for hygiene control.

Fracture toughness of different monolithic zirconia upon post-sintering processes.

BACKGROUND: 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 AND METHODS: Classical- (Cz) and high-translucent (Hz) monolithic zirconia discs (1.2 mm thickness, 14 mm in Ø) were prepared, and randomly divided for surface treatments with 1) as-glazed (AG); 2) finished and polished (FP); 3) finished, polished, and overglazed (FPOG); and 4) finished, polished, and heat-treated (FPHT) technique (n=15/group). Fracture toughness (KIC) was determined with indentation fracture toughness method at load 1 kg for AG, FPOG and 10 kg for FP, FPHT with 15 sec dwelling time. Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristic toughness (K0). Microstructures were examined with SEM and XRD. ANOVA and multiple comparisons were determined for significant differences (α=0.05). RESULTS: The mean±sd value of KIC (MPa.m1/2), m, and K0 were 1.60±0.19, 7.27, 1.71 for CzAG; 9.57±0.89, 9.97, 10.96 for CzFP; 1.61±0.15, 10.56, 1.68 for CzFPOG; 6.45±0.31, 20.31, 6.60 for CzFPHT; 1.45±0.13, 10.91, 1.51 for HzAG; 6.58±0.24, 27.00, 6.70 for HzFP; 1.24±0.05, 23.90, 1.27 for HzFPOG; and 5.07±0.16, 30.51, 5.15 for HzFPHT. The KIC was significantly affected by the post-sintering process, type of zirconia (p<0.05). The Cz indicated a significantly higher KIC than Hz. The FP significantly enhanced KIC, while OG was unable to raise KIC. HT reduced KIC due to reverse phase transformation. CONCLUSIONS: Post-sintering processes caused alteration in fracture resistance of zirconia. Fracture toughness was enhanced with FP, but not with either OG or HT process for both Cz and Hz. Surface treatment of zirconia through a finished-polished process is recommended, while glazing and heat-treated are not suggested. Key words:Fracture toughness, glazing, heat treatment, polishing, post-sintering process, zirconia.

Biaxial Flexural Strength of High-Translucence Monolithic Ceramics upon Various Thicknesses.

INTRODUCTION: High-translucence ceramics have been used increasingly. This study evaluated the biaxial flexural strength of different ceramics as a result of varying thicknesses. MATERIALS AND METHODS: Circular discs with varied thickness of 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0 mm were prepared from high-translucence yttria-partially stabilized zirconia (HTY-PSZ); Bruxzir® Anterior (Bc), and zirconia-reinforced lithium silicate (ZLS) including Celtra® DUO (Cc) and VITA Suprinity® (Vc) (n = 15 discs/group). Biaxial flexural strength (σ) was evaluated utilizing piston-on-three-balls in a testing machine at a speed of 0.5 mm/min. A scanning electron microscope (SEM) was used to determine the microscopic structure. ANOVA and multiple comparisons were analyzed for significant differences (a = 0.05). RESULTS: The mean ± sd value of σ (MPa) for thickness 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0 mm was 672.66 ± 107.54, 655.93 ± 93.98, 589.01 ± 63.63, 624.89 ± 87.08, 618.82 ± 83.36, 672.64 ± 84.61, 659.81 ± 122.89, 632.79 ± 92.54, and 657.86 ± 73.17, for Bc; 477.64 ± 88.23, 496.39 ± 86.36, 461.56 ± 57.00, 450.26 ± 86.60, 468.28 ± 83.65, 472.45 ± 53.63, 453.05 ± 72.50, 462.67 ± 47.57, and 535.28 ± 84.33, for Cc; and 500.97 ± 76.36, 506.70 ± 87.76, 557.82 ± 62.78, 543.76 ± 87.29, 507.53 ± 86.09, 502.46 ± 64.75, 557.70 ± 80.91, 527.04 ± 80.78, and 499.88 ± 57.35, for Vc. A significant difference in flexural strength was indicated among groups (p < 0.05). Bc was significantly stronger than Cc and Vc (p < 0.05). Varying thickness did not have a significant influence on strength (p > 0.05). SEM revealed a tight arrangement of crystals for Bc and needle-like crystals diffusing in glass for Vc and Cc. CONCLUSION: Flexural strength of ceramics varied among types, but each retained strength equitably with varying thickness. HTY-PSZ was stronger than ZLS, but each was equally strong for thickness in the range of 0.4-2.0 mm.

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 (B M), after material application (A M), and after demineralization (A D). 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 B M, A M, and A D 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 (p < 0.05). Multiple comparisons indicated the capability in inducing surface strengthening to resist demineralization for enamel and cementum of NHA which was comparable to CP (p > 0.05) 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 (p < 0.05). No significant difference in remineralization potential was found among NHT, TCPT, and FT (p > 0.05). 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.

Influence of Margin Designs on Crack Initiation of High Translucency Monolithic Zirconia Crowns.

PURPOSE: Zirconia crowns often crack at the margin. This study determined the loads and the times at which cracks are initiated in high-translucency monolithic zirconia crowns with different margin designs. MATERIALS AND METHODS: A total of 90 crowns were fabricated from Zirconia blanks. The fabricated crowns had different margin thicknesses (light-chamfer, CL and heavy-chamfer, CH ) and collar heights (no-collar, NC ; low-collar, LC ; high-collar, HC ). They were grouped as CL NC , CL LC , CL HC , CH NC , CH LC , and CH HC (15 crowns/group). The crowns were seated on a metal model and loaded vertically through round end punch (Φ = 10 mm) at 0.2 mm/min crosshead speed until cracks began to be seen. Videos of the crack initiation were recorded at the rate of 50 frames/second. Load-initiated cracks and durability time were compared for significant differences using analysis of variance. RESULTS: The mean ± standard deviation values of load (N) and time (s) taken to initiate cracks were 3190 ±775, 212 ±47 for CL NC ; 2754 ±1109, 180 ±42 for CL LC ; 2887±832, 191±27 for CL HC ; 4082 ±896, 241 ±36 for CH NC ; 4180 ±1029, 220 ±28 for CH LC ; 4119 ±1124, 222 ±39 for CH HC . This indicates that the thickness of the margin has a significant influence on load-withstanding crack initiation capacity and durability time (p < 0.05). No significant impact of collar height was observed on either load-withstanding capacity or durability time (p > 0.05). No interaction was observed among these factors. CONCLUSION: Heavy chamfer margin provided a stronger zirconia crown than the light chamfer margin, but both of them were capable of withstanding crack-initiated load higher than the theoretical maximum masticatory force. The presence or absence of a collar did not have any impact on the crack initiation. Fabrication of zirconia crowns with either a heavy or light chamfer margin and with or without the presence of a collar should be generated by considering the relevant emergence profile.

Flexural Strength of Different Monolithic Computer-Assisted Design and Computer-Assisted Manufacturing Ceramic Materials upon Different Thermal Tempering Processes.

OBJECTIVE: Strength of ceramics related with sintering procedure. This study investigated the influence of different tempering processes on flexural strength of three monolithic ceramic materials. MATERIALS AND METHODS: Specimens were prepared in bar-shape (width × length × thickness = 4 × 14 × 1.2 mm) from yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP, inCoris TZI [I]), zirconia-reinforced lithium silicate (ZLS, Vita Suprinity [V]), and lithium disilicate (LS2, IPS e.max CAD [E]), and sintered with different tempering processes: slow (S), normal (N), and fast (F) cooling procedure (n = 15/group). Flexural strength (σ) was determined using three-point bending test apparatus at 1 mm/min crosshead speed. STATISTICAL ANALYSIS: The analysis of variance and Bonferroni's multiple comparisons were determined for significant difference (α = 0.05). Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristics strength (σo). Microstructures were evaluated with scanning electron microscope and X-ray diffraction. RESULTS: The mean ± standard deviation (MPa) of σ, m, and σo were: 1,183.98 ± 204.26, 6.23, 1,271.80 for IS; 1,084.43 ± 204.79, 5.76, 1,170.08 for IN; 777.19 ± 99.77, 8.78, 819.96 for IF; 267.15 ± 32.71, 9.11, 281.48 for VS; 218.43 ± 38.46, 6.40, 234.23 for VN; 252.67 ± 37.58, 7.20, 269.23 for VF; 392.09 ± 37.91, 11.37, 409.23 for ES; 378.88 ± 55.38, 7.45, 403.11 for EN, and 390.94 ± 25.34, 16.00, 403.51 for EF. Thermal tempering significantly affected flexural strength of Y-TZP (p < 0.05), but not either ZLS or LS2 (p > 0.05). Y-TZP indicated significantly higher flexural strength upon slow tempering than others. CONCLUSION: Enhancing flexural strength of Y-TZP can be achieved through slow tempering process and was suggested as a process for monolithic zirconia. Strengthening of ZLS and LS2 cannot be accomplished through tempering; thus, either S-, N-, or F- tempering procedure can be performed. Nevertheless, to minimize sintering time, rapid thermal tempering is more preferable for both ZLS and LS2.

Effect of Marginal Designs on Fracture Strength of High Translucency Monolithic Zirconia Crowns.

INTRODUCTION: Monolithic zirconia is able to achieve certain aesthetic, but its durability in resisting fracture has been questioned, as fractures often originate from margins of restoration. This study determined fracture resistance of highly translucent monolithic zirconia crowns with different margin designs in terms of marginal thickness and collar height. MATERIALS AND METHODS: Zirconia blanks (Ceramill® Zolid HT+) were selected for the fabrication of zirconia crowns according to different designs, including varying margin thicknesses (light chamfer, CL; heavy chamfer, CH) and collar heights (no collar, NC; low collar, LC; high collar, HC), which resulted in CLNC, CLLC, CLHC, CHNC, CHLC, and CHHC groups (15 crowns each). The crowns were seated on a metal die and loaded vertically through round end punch (θ = 10 mm), contacting with inclined planes of cusp in a testing machine with crosshead speed of 0.2 mm/min until fracture. Videos with a rate of 50 frames/second were used to record fracture. Fracture load (N) and durable period (s) were compared for significant differences using ANOVA and Bonferroni test (α = 0.05). RESULTS: The mean ± sd of fracture load (N) and durable time (s) were 3211 ± 778 and 212 ± 47 for CLNC; 3041 ± 1370 and 188 ± 53 for CLLC; 2913 ± 828 and 192 ± 27 for CLHC; 4226 ± 905 and 245 ± 35 for CHNC; 4486 ± 807 and 228 ± 29 for CHLC; and 4376 ± 1043 and 227 ± 37 for CHHC. This indicated that marginal thickness had a significant influence on load-bearing capacity and durable time (p < 0.05). No significant impact of collar height was shown, either on load-bearing capacity or durable time (p > 0.05). No interaction between two factors was presented (p > 0.05). CONCLUSIONS: Heavy chamfer margin provided stronger zirconia crown than light chamfer, but both were capable of withstanding fracture load higher than maximum masticatory force. Neither presence nor absence of collar indicated any impact on strength. Fabrication of zirconia crowns with either heavy or light chamfer margin and either presence or absence of collar, with the consideration of emergence profile, should be considered.