Browsing by Subject "Lithium disilicate"

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    Optical properties Of CAD-CAM lithium disilicate glass-ceramic in different firing temperatures and thicknesses
    (2016) Alqahtani, Nasser; Chu, Tien-Min Gabriel; Phasuk, Kamolphob; Morton, Dean; Levon, John A.
    Background: With the emerging of digital dentistry, IPS e.max® CAD lithium disilicate (LD) glass-ceramic material has become one of the most popular esthetic restorative materials in digital assisted dental esthetic restoration. The mechanical and optical properties of this material have been investigated in several studies. However, there is a lack of information and consensus regarding the optical properties of IPS e.max® LD glass-ceramic materials. Objectives: 1) To investigate the optical properties as translucency parameters (TP), Contrast ratio (CR), light transmissions (Lt) and color changes (CC) between high-translucent (HT) and low-translucent (LT) IPS e.max® CAD LD glass-ceramic materials with different crystalline phases and thickness in different firing stages. 2) To investigate the optical properties as TP, CR, Lt and CC of each translucent (HT and LT) IPS e.max® CAD LD glass-ceramic materials with different crystalline phases and thickness in different firing stages. 3) To determine the mathematical relationships of thicknesses of IPS e.max® CAD LD glass-ceramics materials with TP and Lt. Materials and methods: The total of 120 of shade A2 IPS max CAD samples (HT and LT) were prepared into square shape (15.25 mm X 15.25 mm) and were divided into two main groups according to the material translucency (HT and LT) (n=60). Each main group was further divided into 5 sub-groups according to the thickness (1.00, 1.25, 1.5, 1.75, and 2.00 mm) (n=12). Each thickness group was assigned into three groups based on different crystallization (firing) temperatures (750, 820 °C in single stage heating schedule with 1 second and 10 second holding times, respectively, and 840 °C with two-stage heating schedule (RECOM) (820°C, 840 °C with 10 second and 7 min holding time, respectively) as recommended by manufacturer (n=4). CIEL*a*b*, TP, CR, and Lt were measured and calculated for all samples. Statistical analysis: The effects of the test results were evaluated using 3-way ANOVA with factors for Translucency (HT and LT), Firing Temperature (750, 850, and RECOM) and Thickness (1, 1.25, 1.5, 1.75, and 2), as well as all two-way and three-way interactions among the factors. Pair-wise comparisons were made using Least Significant Differences to control the overall significance level at 5%. Results: The mean irradiance and TP for both HT and LT decrease as the thickness of the samples increases from 1 to 2mm with significant difference between the thickness groups within each material translucency groups (HT and LT) and between both HT and LT. The coefficients of absorption (c) of the two materials were calculated. The effective incidence irradiance when material thickness approaches zero (Ie) was also calculated. There is an unexpected spectral peak shift as the thickness of the samples increases. There is no statistically significant difference in Ie at 750˚C and 820 ˚C between the HT and LT. However, there is a statistically significant higher Ie in HT at the recommended firing temperature as expected. Coefficients of translucency parameter (p) of the materials in various firing temperature were defined and the TP of the material as the thickness approaches zero were calculated (TP0). The TP of the materials is directly correlated to the mean irradiance passing through the samples. There is no statistically significant difference in the TP0 and Ie of the HT and LT groups at the recommended firing temperature. Conclusion: In this project we developed modified Beer-Lambert law to describe the parameters governing the effect of thickness on light transmission in dental ceramic material. We also applied the same equation to describe the translucency parameter. The parameters defined in these equations allow us to compare the optical property of dental ceramic material independent of the thickness of the samples.
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    The science and application of IPS e.Max dental ceramic
    (Elsevier, 2018-04-01) Willard, Alec; Gabriel Chu, Tien-Min; Biomedical and Applied Sciences, School of Dentistry
    The aim of this paper is to report the state of current literature and recommendations for the lithium disilicate glass-ceramic IPS e.Max. The materials science, mechanical and optical properties were reviewed. Additionally an assessment was conducted of current implementation recommendations and clinical outcomes. This paper provides a brief historical overview, summary of the findings the findings of current literature, and clinical recommendation for the use of IPS e.Max CAD in dental applications.
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    Silica infiltration on translucent zirconia restorations: effects on the antagonist wear and survivability
    (Elsevier, 2022) Martins Alves, Larissa Marcia; da Silva Rodrigues, Camila; de Carvalho Ramos, Nathalia; Buizastrow, Jeff; Bastos Campos, Tiago Moreira; Bottino, Marco Antonio; Zhang, Yu; de Melo, Renata Marques; Biomedical and Applied Sciences, School of Dentistry
    Objective: To assess potential antagonist wear and survival probability of silica-infiltrated zirconia compared to glass-graded, glazed, and polished zirconia. Methods: Table top restorations made of 3Y-TZP (3Y), 5Y-PSZ (5Y), and lithium disilicate (LD) were bonded onto epoxy resin preparations. Each zirconia was divided into five groups according to the surface treatment: polishing; glaze; polishing-glaze; glass infiltration; and silica infiltration. The LD restorations received a glaze layer. Specimens were subjected to sliding fatigue wear using a steatite antagonist (1.25 ×106 cycles, 200 N). The presence of cracks, fractures, and/or debonding was checked every one/third of the total number of cycles was completed. Roughness, microstructural, Scanning electron microscopy, wear and residual stress analyses were conducted. Kaplan-Meier, Mantel-Cox (log-rank) and ANOVA tests were performed for statistical analyses. Results: The survival probability was different among the groups. Silica infiltration and polishing-glaze led to lower volume loss than glaze and glass-infiltration. Difference was observed for roughness among the zirconia and surface treatment, while lithium disilicate presented similar roughness compared to both glazed zirconia. Scanning electron microscopy revealed the removal of the surface treatment after sliding fatigue wear in all groups. Compressive stress was detected on 3Y surfaces, while tensile stress was observed on 5Y. Significance: 3Y and 5Y zirconia behaved similarly regarding antagonist wear, presenting higher antagonist wear than the glass ceramic. Silica-infiltrated and polished-glazed zirconia produced lower antagonist volume loss than glazed and glass-infiltrated zirconia. Silica-infiltrated 3Y and lithium disilicate restorations were the only groups to show survival probabilities lower than 85%.
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    Stepwise stress testing of different CAD/CAM lithium disilicate veneer application methods to lithium disilicate substructure
    (2019) May, Jaren Thomas; Feitosa Sochacki, Sabrina; Diefenderfer, Kim; Cook, N. Blaine
    Objective: CAD/CAM technology allows fabrication of thin lithium disilicate (LD) veneers to a LD crown substructure in place of using traditional feldspathic porcelain (FP) which has inferior mechanical properties. This project investigated the effect of different LD veneer applications to LD substructure on the biaxial flexural fatigue of LD veneer/substructure restorations. Materials/Methods: Forty-five LD discs (Ø = 120.7 mm) were fabricated that, when combined with the veneering discs, achieve final dimensions of (Ø = 121.2mm). Experimental groups were (n = 15) as follows: (1) Resin Bonded LD Veneer (RBLDV), LD veneer (Ø = 120.5 mm) adhesively cemented to LD (0.7 mm); (2) Sintered LD Veneer (SLDV), LD veneer (Ø=120.5 mm) sintered to LD (0.7 mm); (3) Sintered Feldspathic Veneer (SFV), feldspathic porcelain (FP) applied to LD discs to achieve a final dimension of (Ø = 121.2 mm). A fourth group of (1.2 mm) monolithic LD served as the control. Weibull-distribution survival analysis was used to compare the differences of the resistance to fracture after fatigue between groups. Total number of cycles were analyzed using one-way Anova (p < 0.05). Hypothesis: Adhering or sintering a thin laminate layer of LD on another LD surface would result in increased fracture resistance in comparison to sintered FP on LD. Results: The SFV group had significantly lower fatigue resistance than SLDV and RBLDV groups (p < 0.05). The RBLDV group fractures resulted in significantly more fractured fragments in comparison to the other groups. No statistical difference was observed in the number of cycles. The results also showed that the LD veneered groups presented similar resistance to fatigue as monolithic discs of the same overall dimensions. Conclusion: The hypothesis was accepted suggesting that veneering a LD substructure with a LD veneer, bonded or sintered, has increased resistance to fatigue as FP veneering material on a LD substructure. In addition, it was observed to have similar resistance to fatigue in comparison to the monolithic LD group.