Effect of thickness on the translucency of machinable and printable ceramic-glass polymer materials.

OBJECTIVES: To assess the translucency of machinable and printable ceramic-glass polymer materials with different thicknesses. METHODS: Five ceramic-glass polymer materials were tested: one 3D-printable material, Permanent Crown resin (3D), two machinable materials available at low translucency (LT) and high translucency (HT) levels, VITA Enamic (VE) HT/LT, and Cerasmart 270 (CS) HT/LT. A total of 100 specimens were produced across 10 subgroups (n = 10) with thicknesses of 1 mm and 1.5 mm. The colour coordinates of the specimens were measured against black and white backgrounds using a spectrophotometer. Translucency was quantified using the Relative Translucency Parameter (RTP), calculated via the CIEDE2000 formula. A two-way ANOVA followed by post-hoc tests with Bonferroni correction (α = 0.05) was used for statistical analysis. RESULTS: The RTP for both thicknesses were ranked as follows: CSHT > VEHT > CSLT > 3D > VELT. The RTP of the 3D was lower than that of the HT machinable materials (CSHT and VEHT) for both thicknesses (p < 0.05). No significant difference was observed between the RTP of 3D and CSLT at 1.5 mm (p = 1.000); however, at 1 mm, the RTP of the 3D was lower than that of the CSLT (p < 0.05). Notably, the 3D showed the least translucency difference with a 0.5 mm increase in thickness. CONCLUSIONS: Printable ceramic-glass polymer materials demonstrated lower translucency than HT machinable ceramic-glass polymer materials. Both the thickness and type significantly influenced the translucency of the LT machinable counterparts compared to the printable ceramic-glass polymer material. CLINICAL SIGNIFICANCE: Printable ceramic-glass polymer resins may be a suitable option for minimally invasive procedures, especially when attempting to mask undesirable-coloured abutments. When selecting HT machinable ceramic-glass polymers, clinicians should pay greater attention to the abutment colour and thickness of the restorative material.

Effect of internal design changes on the mechanical properties of laser-sintered cobalt-chromium specimens.

STATEMENT OF PROBLEM: Changing the internal design of a metal framework may decrease the manufacturing time, the weight of the restoration, and the amount of alloy powder used, as well as simplify the fabrication process. PURPOSE: The purpose of this in vitro study was to evaluate the effect of framework internal design changes on the mechanical properties of cobalt-chromium (Co-Cr) specimens manufactured by using direct metal laser sintering (DMLS). MATERIAL AND METHODS: Dumbbell-shaped test specimens were designed as per the International Organization for Standardization (ISO) 22674(E) standard by using a 3-dimensional software program. A total of 70 dumbbell-shaped specimens were prepared by using Co-Cr alloy powder and DMLS (n=10). The control group specimens were solid with the internal completely filled. For the test groups, the internal design of the dumbbell-shaped specimens was modified. Leaving the outer shell thickness of the specimens at 0.5 mm for all test groups, 6 different internal designs were created, and the specimens were weighed. The tensile strength test was used to evaluate the mean peak strength, elastic modulus, and percentage elongation of the specimens. One-way ANOVA followed by the Dunnett T3 test was used for statistical analysis (α=.05). RESULTS: A statistically significant difference was found among the groups in terms of bar weight and peak strength (P<.05). The highest values were observed in the control group for all evaluated parameters (mean ±standard deviation bar weight: 1321.3 ±36.6 mg, peak strength: 1045 ±36.7 MPa, elastic modulus: 284.2 ±71.9 GPa, and elongation: 28.7 ±7%). However, no statistically significant difference was observed for elastic modulus or percentage of elongation (P>.05). CONCLUSIONS: Decreasing the weight of the frameworks by changing the internal design of the specimens also decreased the peak strength. However, it did not affect the elastic modulus or the percentage of elongation.

Effect of Internal Design Modification on the Mechanical Properties of Laser Sintered Cobalt-Chromium Multi-Unit Metal-Ceramic Frameworks.

PURPOSE: The purpose of the study was to assess the effect of internal design modifications on the mechanical properties of multi-unit Cobalt-Chromium (Co-Cr) metal-ceramic frameworks manufactured by direct metal laser sintering. MATERIAL AND METHODS: Four-unit fixed partial denture metal-ceramic frameworks were digitally designed on a metal die model using 3D software. A total of 30 specimens were prepared using Co-Cr alloy powder with direct metal laser sintering (n = 10). The control group specimens were solid where the inside of the specimens was completely full. For the test groups, the internal design of the framework was modified. Leaving the outer shell thickness of the framework at 0.5 mm, two different internal designs with hollow geometries were created (1.5 mm and 2 mm inner bar distances) and a cross section area of the connector was calculated. The weights of the specimens were measured and subjected to a 3-point-bending test at 1 mm/min crosshead speed. Data were statistically analyzed using One-way ANOVA followed by Tukey (α = 0.05). RESULTS: There was a statistically significant difference among the groups in terms of weight of the specimens (p ≤ 0.05). However, no significant difference was observed among groups in term of both flexural strength and flexural modulus (p ≤ 0.05). CONCLUSIONS: Within the limitations of the study, it was concluded that changing the internal design of the metal frameworks decreases the weight of the framework, but does not affect the flexural strength and flexural modulus. Therefore, clinical applications of internally modified frameworks seem promising for metal-ceramic restorations.

The effect of the menstrual cycle on the sense of touch, grip strength and manual dexterity of dental students.

Objectives. This study aimed to evaluate through comparative tests the effect of the menstrual cycle on levels of depression, sleep quality and grip strength, fingertip touch and manual dexterity of students in the Dental Faculty. Methods. The study sample was formed from female students of the Dental Faculty. The total 70 participants comprised 31 from the first year and 39 from the final year. Evaluations were made in two different consecutive phases of the menstrual cycle. Data were collected using the Beck depression inventory (BDI), the Pittsburgh sleep quality index (PSQI), handgrip and lateral grip strength measurements, fingertip two-point discrimination sensory measurement, the Semmes-Weinstein monofilament test, the O'Connor tweezers skill test and the Purdue pegboard test. Results. A statistically significant difference was determined between the menstrual and ovulation phase measurements of the BDI, PSQI, Semmes-Weinstein monofilament test (right), the O'Connor tweezers skill test and Purdue pegboard test (right + left), and the Purdue Pegboard test (total and assembly) (p < 0.05). Conclusions. The menstrual cycle does not affect the sense of touch, grip strength and simple hand skills. However, task-focused skills requiring care and the manual dexterity needed for the use of instruments are affected.

Analysis of color differences in stained contemporary esthetic dental materials.

STATEMENT OF PROBLEM: Although contemporary analytical methods are available for application to data which exhibit a lack of equality of variances or a lack of normality in the error distribution, little guidance is provided for selecting the methods of data handling and analysis which best fit color difference data for stained esthetic materials. PURPOSE: The purposes of this in vitro study were to apply information criteria of analysis of variance (ANOVA) methods of differing error distributions and covariance structures when analyzing color differences to determine the degree of alienation among 3 Commission Internationale de l'Eclairage (CIE) color difference formulae to assess the linearity of relationships among these formulae and to independently assess differences among various computer-aided design and computer-aided manufacture (CAD-CAM) materials in any color change after common forms of staining over time. MATERIAL AND METHODS: Hybrid ceramic, resin nanoceramic, feldspathic-ceramic, and lithium-disilicate ceramic specimens (N=128) were subjected to staining from water, tea, coffee, and red wine over 1, 7, and 30 days, with color differences calculated from baseline. Akaike information criteria (AIC) and Bayesian information criteria (BIC) values were determined for Gaussian and lognormal error distributions at covariance structures of standard variance components and compound-symmetry. The analysis of variance used to analyze any significant effects on these color differences was the one with the lowest AIC and BIC values. Then, for each solution, day, and CIE color difference formula, any significant difference in the color differences between all pairs of materials was found by Bonferroni-corrected Student t tests. Those statistically significant pairwise comparisons where the larger of the color differences met or exceeded the acceptability threshold were labeled as statistically and visually noteworthy. RESULTS: For this color difference data set, the lognormal error distribution and the covariance structure of compound symmetry provided the best AIC and BIC. Because the interaction between material, solution, and day was statistically significant (P<.001), pairwise comparisons were made between all pairs of materials for each level of solution and day studied. Noteworthy differences were identified, where hybrid ceramic and resin nanoceramic each had color changes after staining in coffee and red wine that were greater than each of feldspathic-ceramic and lithium-disilicate ceramic. CONCLUSIONS: AIC and BIC values evaluate distinctively the Gaussian and lognormal error distributions when analyzing highly varying color differences. Although there is a high linear correlation between the 3 color difference formulae studied, each formula is unique, and each represents a different assessment of the perceived color difference. CAD-CAM materials, staining liquids, and time points affected the notable color changes.

Color and translucency of zirconia infrastructures and porcelain-layered systems.

STATEMENT OF PROBLEM: A good color match combined with a proper translucency match results in excellent esthetics for a metal-free restoration, yet basic color and translucency comparisons between available zirconia systems are not well described. PURPOSE: The purpose of this in vitro study was to compare the color and translucency of commercially available zirconia materials. MATERIAL AND METHODS: Eight specimen disks were formed in each of the single-layer (0.5-mm thick) groups and double-layer (0.5-mm zirconia with 1.0-mm porcelain) groups for each of 5 zirconia-based substructure systems. Colors on black, gray, and white backings were used to obtain CIEDE2000 color differences between the zirconia systems in the layering groups and to obtain relative translucency parameter (RTP) values. Color differences were compared with perceptibility and acceptability thresholds, and comparisons in RTP were made using analyses of variance and the Bonferroni corrected Student t tests (α=.05). RESULTS: The Shrout-Fleiss random set reliability for the duplicate L* determinations was 0.9992, 0.9756 for a*, and 0.9959 for b*. Although some mean color differences were below or at the perceptibility threshold, most differences were at or above the acceptability threshold. For the single-layer configuration, 1 material system had higher RTP values than every other material (P<.001), and another material had lower RTP values than every other material (P<.001). CONCLUSIONS: The results of this study present significant differences in both color and translucency among 5 ceramic substrate systems when studied in single layers. Perceivable and often unacceptable differences in color were also found among these materials when layered with porcelain. It is concluded that the esthetics of restorations which use a ceramic substrate is notably affected by the ceramic system used.