Shade reproduction and the ability of lithium disilicate ceramics to mask dark substrates

Objectives@#This study aimed to evaluate the ability of lithium disilicate ceramics to reproduce the A2 shade and to mask A4 substrates. @*Materials and Methods@#Twenty-four discs (8 mm in diameter, shade A2) of high translucency (groups 1–3) and low translucency (groups 4–6) of IPS e.max ceramic with different thicknesses (0.5, 0.75, and 1 mm) were fabricated as monolithic structures. In addition, discs of medium opacity (group 7–8) with different core/veneer combinations (0.3 mm/0.7 mm and 0.5 mm/0.5 mm) were fabricated as bilayer structures. Specimens were superimposed on an A4 substrate (complex). The color changes of the complex were measured using a spectrophotometer on a black background, and the ΔE values of the complex were compared with either the A4 substrate or the A2 shade tab. One-way analysis of variance, the Tukey honest significant difference test, and the Fisher test were used to analyze the data (p < 0.05). @*Results@#Significant between-group differences were found for comparisons to both the A4 substrate and the A2 shade (p < 0.05). When compared with the A4 substrate, the ΔE values in all groups were in the non-acceptable range. When compared with the A2 shade, the ΔE values in all groups, except groups 2 and 3, were in the clinically acceptable range. @*Conclusions@#All translucencies and thicknesses masked the underlying dark substrate.However, the low-translucency IPS e.max Press better reproduced the A2 shade.

Shade reproduction and the ability of lithium disilicate ceramics to mask dark substrates

Objectives@#This study aimed to evaluate the ability of lithium disilicate ceramics to reproduce the A2 shade and to mask A4 substrates. @*Materials and Methods@#Twenty-four discs (8 mm in diameter, shade A2) of high translucency (groups 1–3) and low translucency (groups 4–6) of IPS e.max ceramic with different thicknesses (0.5, 0.75, and 1 mm) were fabricated as monolithic structures. In addition, discs of medium opacity (group 7–8) with different core/veneer combinations (0.3 mm/0.7 mm and 0.5 mm/0.5 mm) were fabricated as bilayer structures. Specimens were superimposed on an A4 substrate (complex). The color changes of the complex were measured using a spectrophotometer on a black background, and the ΔE values of the complex were compared with either the A4 substrate or the A2 shade tab. One-way analysis of variance, the Tukey honest significant difference test, and the Fisher test were used to analyze the data (p < 0.05). @*Results@#Significant between-group differences were found for comparisons to both the A4 substrate and the A2 shade (p < 0.05). When compared with the A4 substrate, the ΔE values in all groups were in the non-acceptable range. When compared with the A2 shade, the ΔE values in all groups, except groups 2 and 3, were in the clinically acceptable range. @*Conclusions@#All translucencies and thicknesses masked the underlying dark substrate.However, the low-translucency IPS e.max Press better reproduced the A2 shade.

Effect of water storage on flexural strength of silorane and methacrylate-based composite resins

OBJECTIVES: This study assessed the effect of water storage on the flexural strength (FS) of low shrinkage composites. MATERIALS AND METHODS: A total of 165 bar-shaped specimens (2 × 2 × 25 mm) were fabricated of 2 low shrinkage composites (Filtek P90 [3M ESPE], GC Kalore [GC International]) and a conventional methacrylate-based composite (Filtek Z250 [3M ESPE]). The specimens were subjected to 3-point bending test at 6 time intervals, namely: immediately after curing, at 24 hours, 1 week, 1 month, 6 months, and 1 year following storage in wet and dry conditions. The FS of the specimens were measured by applying compressive load at a crosshead speed of 1.0 mm/min. Data was analyzed using 3-way analysis of variance (ANOVA) and Tukey's test. RESULTS: Three-way ANOVA revealed significant interactions between time, type of composite, and storage condition (p = 0.001). Tukey's multiple comparison test revealed significant reductions in FS of all composites after 6 months and 1 year of storage in distilled water compared to dry condition. CONCLUSIONS: Filtek P90 showed the highest and GC Kalore showed the lowest FS after 1 year storage in distilled water. The immediate high strength of Filtek Z250 significantly decreased at 1 year and its final value was lower than that of Filtek P90.

Comparison of compressive strength of five hydraulic cements

Objectives: maintaining pulp vitality is a main goal in restorative dentistry. Introduction of pulp capping agents paved the way to eliminate the shortcomings of these materials and obtain successful restorations. On the other hand, nanotechnology is an emerging field of science with increasing use in dental materials. This study sought to assess the effect of addition of nano-TiO[2], nano-SiO[2] and nano-Al[2]O[3] on compressive strength of five hydraulic cements

Methods: in this in vitro, experimental study, three experimental formulations of nano hybrid MTA, MTA Angelus and MTA Angelus+ nano-oxide particles cements were placed in molds measuring 4+/-0.1mm in internal diameter and 6+/-0.1mm in height made of stainless steel [ISO9917-1]. Ten samples were fabricated for each of the five groups of materials. Sound samples were stored at 37degreeC and 95+/-5% humidity and were subjected to compressive strength testing in a universal testing machine at a crosshead speed of 0.5mm/minute after 24 hours and one month. Two-way ANOVA, one-way ANOVA and independent samples t-test were used for comparison of compressive strength of groups at different time points

Results: the highest compressive strength belonged to MTA Angelus+ nanohydroxyapatite and nano-hybrid MTA C at 24 hours and 30 days, respectively. The lowest compressive strength belonged to nano-hybrid MTA B and MTA Angelus at 24 hours and 30 days, respectively [P<0.05]

Conclusion: addition of nanoparticles affected the compressive strength of cements. Compressive strength significantly increased over time in all groups