STATEMENT OF PROBLEM: Digital impression systems have undergone significant development in recent years, but few studies have investigated the accuracy of the technique in vivo, particularly compared with conventional impression techniques. PURPOSE: The purpose of this in vivo study was to investigate the precision of conventional and digital methods for complete-arch impressions. MA-TERIAL AND METHODS: Complete-arch impressions were obtained using 5 conventional (polyether, POE; vinylsiloxanether, VSE; direct scannable vinylsiloxanether, VSES; digitized scannable vinylsiloxanether, VSES-D; and irreversible hydrocolloid, ALG) and 7 digital (CEREC Bluecam, CER; CEREC Omnicam, OC; Cadent iTero, ITE; Lava COS, LAV; Lava True Definition Scanner, T-Def; 3Shape Trios, TRI; and 3Shape Trios Color, TRC) techniques. Impressions were made 3 times each in 5 participants (n=15). The impressions were then compared within and between the test groups. The cast surfaces were measured point-to-point using the signed nearest neighbor method. Precision was calculated from the (90%-10%)/2 percentile value. RESULTS: The precision ranged from 12.3 m (VSE) to 167.2 m (ALG), with the highest precision in the VSE and VSES groups. The deviation pattern varied distinctly according to the impression method. Conventional impressions showed the highest accuracy across the complete dental arch in all groups, except for the ALG group. CONCLUSIONS: Conventional and digital impression methods differ significantly in the complete-arch accuracy. Digital impression systems had higher local deviations within the complete arch cast; however, they achieve equal and higher precision than some conventional impression materials. techniques. Impressions were made 3 times each in 5 participants (n = 15). The impressions were then compared within and between the test groups. The cast surfaces were measured point-to-point using the signed nearest neighbor method. Precision was calculated from the (90%-10%)/2 percentile value.Results. The precision ranged from 12.3 µm (VSE) to 167.2 µm (ALG), with the highest precision in the VSE and VSES groups. The deviation pattern varied distinctly according to the impression method. Conventional impressions showed the highest accuracy across the complete dental arch in all groups, except for the ALG group.Conclusions. Conventional and digital impression methods differ significantly in the complete-arch accuracy. Digital impression systems had higher local deviations within the 2 complete arch cast; however, they achieve equal and higher precision than some conventional impression materials. CLINICAL IMPLICATIONSThe accuracy of complete-arch impression casts differs significantly between conventional techniques and digital impression systems. Local deviations are greater in casts generated using digital impression systems; however, digital systems show adequate accuracy across the complete arch. As digital impression systems continue to improve, they may prove to be an equivalent or better alternative to convent...

STATEMENT OF PROBLEM: A new approach to both 3-dimensional (3D) trueness and precision is necessary to assess the accuracy of intraoral digital impressions and compare them to conventionally acquired impressions. PURPOSE: The purpose of this in vitro study was to evaluate whether a new reference scanner is capable of measuring conventional and digital intraoral complete-arch impressions for 3D accuracy. MATERIAL AND METHODS: A steel reference dentate model was fabricated and measured with a reference scanner (digital reference model). Conventional impressions were made from the reference model, poured with Type IV dental stone, scanned with the reference scanner, and exported as digital models. Additionally, digital impressions of the reference model were made and the digital models were exported. Precision was measured by superimposing the digital models within each group. Superimposing the digital models on the digital reference model assessed the trueness of each impression method. Statistical significance was assessed with an independent sample t test (=.05). RE-SULTS: The reference scanner delivered high accuracy over the entire dental arch with a precision of 1.6 ±0.6 µm and a trueness of 5.3 ±1.1 µm. Conventional impressions showed significantly higher precision (12.5 ±2.5 µm) and trueness values (20.4 ±2.2 µm) with small deviations in the second molar region (P<.001). Digital impressions were significantly less accurate with a precision of 32.4 ±9.6 µm and a trueness of 58.6 ±15.8µm (P<.001). More systematic deviations of the digital models were visible across the entire dental arch. CONCLUSIONS: The new reference scanner is capable of measuring the precision and trueness of both digital and conventional complete-arch impressions. The digital impression is less accurate and shows a different pattern of deviation than the conventional impression. Methods: A steel reference model was scanned with the reference scanner to evaluate precision and trueness. The reference model then was used to perform five conventional impressions with a polyvinylsiloxanether material (Identium, Kettenbach) in a putty and wash technique with standard stock trays (ASA Permalock, ASA Dental). The conventional impressions were poured with Type IV stone (CamBase, Dentona) and scanned with the reference scanner. Five digital impressions with a optical intraoral scanning system (CEREC AC, Sirona) were made. In each group, the models were superimposed and the differences computed with a signed nearest neighbour method. The 90-10%/2 percentile of the differences from each comparison was taken to compute the mean value for precision. The trueness of each impression method was assessed through superimposition of the impressions with the refefence scan of the steel reference model. Results:The reference scanner delivers an accuracy with 1.6±0.6 µm for precision and 5.3±1.1 µm for trueness over a full dental arch scan. The conventional impression method shows significant higher (p<0.001) precision (12.5±2.5 µm) and trueness (20....

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OBJECTIVE: This study investigated the effect of sintering temperatures on flexural strength, contrast ratio, and grain size of zirconia. MATERIALS AND METHODS: Zirconia specimens (Ceramill ZI, Amann Girrbach) were prepared in partially sintered state. Subsequently, the specimens were randomly divided into nine groups and sintered with different final sintering temperatures: 1,300°C, 1,350°C, 1,400°C, 1,450°C, 1,500°C, 1,550°C, 1,600°C, 1,650°C, or 1,700°C with 120 min holding time. Three-point flexural strength (N = 198; n = 22 per group) was measured according to ISO 6872: 2008. The contrast ratio (N = 90; n = 10 per group) was measured according to ISO 2471ISO : 2008. Grain sizes and microstructure of different groups were investigated (N = 9, n = 1 per group) with scanning electron microscope. Data were analyzed using one-way ANOVA with Scheffé test and Weibull statistics (p < 0.05). Pearson correlation coefficient was calculated between either flexural strength or contrast ratio and sintering temperatures. RESULTS: The highest flexural strength was observed in groups sintered between 1,400°C and 1,550°C. The highest Weibull moduli were obtained for zirconia sintered at 1,400°C and the lowest at 1,700°C. The contrast ratio and the grain size were higher with the higher sintering temperature. The microstructure of the specimens sintered above 1,650°C exhibited defects. Sintering temperatures showed a significant negative correlation with both the flexural strength (r = -0.313, p < 0.001) and the contrast ratio values (r = -0.96, p < 0.001). CONCLUSIONS: The results of this study showed that the increase in sintering temperature increased the contrast ratio, but led to a negative impact on the flexural strength. CLINICAL RELEVANCE: Considering the flexural strength values and Weibull moduli, the sintering temperature for the zirconia tested in this study should not exceed 1,550°C. 20]. In fact, the stability of the complete system consisting both the zirconia framework and the veneering ceramic is of clinical importance.In order to decrease the costs and at the same time overcome the chipping problem, it is possible today to produce zirconia FDPs without veneering ceramic.Such monolithic zirconia FDPs require higher translucency with superior mechanical properties especially when they are to be used in the anterior region. Framework translucency is therefore one of the primary factors with respect to aesthetic properties in the selection of dental materials [21,22]. The translucency of dental ceramic is highly dependent on light scattering [23]. When the majority of light passing through a ceramic is intensely scattered and diffusely reflected, the material would appear opaque. However, if only part of the light is scattered and most of it is diffusely transmitted, the material would appear translucent where Y B was the value with a black background, and Y w was the value with a white background. In all calculations, 0 was considered as totally transparent and 1 as

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