Effect of coffee thermocycling on the color and translucency of milled and 3D printed definitive restoration materials.

STATEMENT OF PROBLEM: Research on the color and translucency properties of 3-dimensionally (3D) printed definitive resins and the effect of coffee thermocycling on these properties is lacking. PURPOSE: The purpose of this in vitro study was to investigate the effect of coffee thermocycling on the color and translucency parameters of the milled and 3D printed materials used for definitive restorations. MATERIAL AND METHODS: Plate-shaped specimens (12×12×1 mm) of 3 milled (IPS e.max CAD (LDS), Vita Enamic (PICN), Cerasmart (RNC)) and two 3D printed (VarseoSmile Crownplus (VSP), Permanent Crown (PC)) were fabricated (n=12). The brightness (L*), red-green (a*), and yellow-blue (b*) parameters were measured with a spectrophotometer before and after 10 000 coffee thermocycles. The relative translucency parameters (RTP00) and color change were calculated using the CIEDE2000 formula. Stainability (ΔE00) and translucency differences (ΔRTP00) were evaluated. Data were analyzed with the Kruskal-Wallis, Mann-Whitney U, and Wilcoxon tests. The Spearman correlation test was used to analyze the ΔE00 and ΔRTP00 values (α=.05). RESULTS: The type of material and coffee thermocycling significantly affected the evaluated parameters at both measurement periods (P=.001). Coffee thermocycling decreased the L* and RTP00 values while increasing the a* and b* values (P=.001). The highest ΔE00 values were found in VSP and PC, which were statistically similar (P=.291), while the highest | ΔRTP00 | values were observed for VSP (P=.001). The lowest ΔE00 and | ΔRTP00 | values were found in LDS (P=.001). A positive relationship was found between the ΔE00 and | ΔRTP00| values (R=.590, P=.01). CONCLUSIONS: After coffee thermocycling, all tested materials exhibited a darkened, yellowish, and opaque appearance, although the alterations in color and translucency remained within clinically acceptable thresholds (AT00=1.81) for these materials.

The effect of artificial accelerated aging on the color stability, microhardness, and surface roughness of different dental laminate veneer materials.

OBJECTIVE: This study aimed to evaluate the effect of artificial accelerated aging (AAA) on color stability, surface roughness, and microhardness of three laminate veneer (LV) materials. MATERIALS AND METHODS: Specimens of ceramic LV (CLV-IPS E.max Press), hand-layered composite LV (hand-layered laminate veneer [HLV]-Tetric N-Ceram), and prefabricated composite LV (prefabricated laminate veneer [PLV]-Componeer Coltene) were prepared as discs (n = 10). CIE L*, a*, and b* color coordinates, the Vickers microhardness, and surface roughness were measured 24 hours after preparation and reevaluated after aging for 300 hours in an ultraviolet (UV)-AAA system (Ci35 Weather-Ometer). Color difference (CIEDE2000 [ΔE00 ]) was calculated. Data were statistically analyzed with the Shapiro-Wilk test and the Kruskall-Wallis test followed by the Mann-Whitney U tests (α = .05). RESULTS: All of the LV groups showed significant differences in ΔE00 after AAA (P < .001). Comparing the color changes of the HLVs with the PLVs, no significant difference could be found (P = .705). There was a statistically significant difference in the means of changes in microhardness among the LVs materials (P < .001). The changes in surface roughness results showed a significant difference after AAA in all the LVs (P < .001). CONCLUSIONS: Within the limitations of this in vitro study, the color stability, the microhardness, and surface roughness of tested LVs were influenced by AAA. CLINICAL SIGNIFICANCE: The prefabricated composite LV system does not replace the individualized ceramic LV technique, but rather offers an alternative to hand-layered LVs, which is delicate and time-consuming technique.

Comparison of surface roughness and color stainability of 3-dimensionally printed interim prosthodontic material with conventionally fabricated and CAD-CAM milled materials.

STATEMENT OF PROBLEM: Studies on the surface roughness and color stainability of interim prostheses produced with 3-dimensional-printing technology are lacking. PURPOSE: The purpose of this in vitro study was to investigate the effect of different surface treatments on the surface roughness and stainability of 3-dimensionally printed, computer-aided design and computer-aided manufacturing (CAD-CAM) milled and conventional interim materials. MATERIAL AND METHODS: A total of 320 specimens were fabricated from autopolymerizing polymethyl methacrylate, bis-acryl composite resin, CAD-CAM polymethyl methacrylate resin (milled), and 3-dimensionally printed composite resin (printed) (n=80). A group of each material was divided into 2 groups (n=40) as per the applied surface treatment procedure: conventional polishing (C) or coated with a surface sealant (B). Surface roughness values were measured with a profilometer. Each group of specimens was then divided into 4 subgroups (n=10) and stored for 1 day, 7 days, and 30 days at 37 °C in different solutions: distilled water, cola, coffee, and red wine. Color parameters were measured with a spectrophotometer before and after each storage period, and color differences (CIEDE2000 [ΔE00]) were calculated. Data were statistically analyzed with the Shapiro-Wilk test, Kruskal-Wallis test, and Mann-Whitney U test followed by the Friedman test (α=.05). RESULTS: The highest surface roughness values were determined for the polymethyl methacrylate -C, and the lowest were observed in the printed-B. After 30 days, the highest mean ΔE00 values were observed in polymethyl methacrylate-C for all staining solutions (P=.001). The highest ΔE00 for all materials was observed in the red wine group. Color change increased significantly with storage duration (P=.001). CONCLUSIONS: All tested materials had a surface roughness higher than the plaque accumulation threshold (0.2 µm). The surface roughness values of coated materials were significantly lower than those of their conventionally polished groups, except for the printed groups. The application of a surface sealant agent significantly decreased the staining of the materials.

Comparative evaluation of the effect of thermocycling on the mechanical properties of conventionally polymerized, CAD-CAM milled, and 3D-printed interim materials.

STATEMENT OF PROBLEM: Studies on the energy absorption characteristics by means of elastic and plastic material deformation of interim materials are lacking. PURPOSE: The purpose of this in vitro study was to compare the effect of different thermocycling periods on the flexural strength (σfs), resilience (Ur), and toughness (UT) of conventionally polymerized, computer-aided design and computer-aided manufacturing (CAD-CAM) milled, and 3-dimensionally (3D) printed interim materials. MATERIAL AND METHODS: Rectangular specimens (n=30 for each material) were fabricated from autopolymerized polymethyl methacrylate (PMMA), bis-acryl resin (Bis-acryl), CAD-CAM polymethyl methacrylate-based polymer (CAD-CAM/Milled), and 3D-printed composite resin (3D-Printed). Each material was divided into 3 groups (n=10) according to the applied thermocycling (5 °C to 55 °C) procedure: control (0 cycles), 2500, and 10 000 cycles. Parameters of the materials such as σfs, Ur, and UT were tested in a 3-point bend test according to International Organization for Standardization (ISO) 10477. Data were statistically analyzed with the Shapiro-Wilk test followed by Kruskal-Wallis test, the Mann-Whitney U test, the Friedman test, and Wilcoxon signed-rank test (α=.05). RESULTS: The tested material and thermocycling had a statistically significant influence on the σfs, Ur, and UT values (P<.05). PMMA showed the lowest mean σfs, Ur, and UT values (P<.05), and CAD-CAM/Milled showed σfs values similar to those of 3D-Printed at all thermocycling periods. CAD-CAM/Milled showed the highest Ur values at 10 000 cycles and the highest UT values at all thermocycles. No significant differences were found in the mean change of σfs and Ur of CAD-CAM/Milled among different thermocycling periods. CONCLUSIONS: The results suggested that digitally fabricated interim materials had better mechanical properties than conventionally polymerized materials and that milled materials had the highest stability in maintaining their initial capacity to absorb energy.

Evaluation of bond strength of resin cement to Er:YAG laser-etched enamel and dentin after cementation of ceramic discs.

The purpose of this study was to investigate the shear bond strength (SBS) of ceramic discs luted to differently etched enamel and dentin surfaces. Occlusal surfaces of 64 carious-free human molars and vestibule surfaces of 64 first maxillary incisors were ground to get flat superficial dentin and flattened enamel respectively. After generating 4 groups according to the surface etching method (37% orthophosphoric acid, Er:YAG laser-contact handpiece/scanning handpiece (1 or 2 times of scanning)), ceramic discs were luted to the surfaces with adhesive resin cement (Variolink N, Vivadent Ets., Schaan/Liechtenstein). After etching and cementation, thermocycling of 5000 cycles (Sd Mechatronik Gmbh, Feldkirchen-Westerham, Germany) and SBS test (Servopulser EHFFD1; Shimadzu, Kyoto, Japan) were performed respectively. The surface morphologies of 2 specimens, etched enamel and dentin, prepared for each group were examined with SEM analysis. Failure modes were determined under a USB digital microscope. Data were analyzed with one-way analysis of variance (ANOVA) and Tukey HSD test (α = 0.05). SBS values in dentin surfaces showed statistically significant differences (p < 0.05) among tested groups. The highest SBS among dentin groups was determined in the group which had 2 times etching by Er:YAG laser (11.42 MPa) by a scanning handpiece. No statistical differences were observed in the other dentin or enamel groups. Laser etching seems to be a viable alternative to acid etching on both enamel and dentin surfaces while double etching of dentin with a scanning handpiece can improve the adhesion.

Evaluation of strain distribution on an edentulous mandible generated by cobalt-chromium metal alloy fixed complete dentures fabricated with different techniques: An in vitro study.

STATEMENT OF PROBLEM: Fixed complete dentures (FCDs) have been used in the treatment of completely edentulous patients for over 40 years. However, few reports have investigated misfit values and strain distribution in the context of FCDs fabricated with new technologies. PURPOSE: The purpose of this in vitro study was to evaluate misfit values and strain distribution in FCDs and their relation to the fabrication technique of the cobalt-chromium (Co-Cr) metal framework. MATERIAL AND METHODS: Four implants were placed in the interforaminal region of a mandibular cast at the bone level. The Co-Cr metal alloy frameworks were fabricated using the following techniques: computer-aided design and computer-aided manufacturing (CAD-CAM), milling from hard blocks, CAD-CAM milling from soft blocks, and direct metal laser sintering (DMLS). The superstructures of equal sizes with acrylic resin bases and acrylic resin denture teeth were fabricated on the Co-Cr metal alloy framework, and a digital microscope was then used to measure the misfit between the abutments and the implants. The stress formed after the application of torque was measured with a strain-gauge stress analysis technique. Data were statistically analyzed using 1-way ANOVA and the Tukey Honestly Significant Difference test (α=.05). The correlation between the misfit and the strain values was evaluated with the Pearson Correlation test (α=.001). RESULTS: The lowest mean misfit values (99 ±17 µm) were observed in the hard block group (P<.05) and the highest in the DMLS group (139 ±29 µm). A statistically significant positive relationship was found between the misfit and the stress distribution after torque application (P<.05). Moreover, the lowest misfit group, hard blocks, had the lowest mean strain values (81.1 ±54 MPa) after torque application. CONCLUSIONS: Within the limitations of this in vitro study, the fabrication technique used for Co-Cr metal alloy frameworks appears to influence the passive fit significantly (P<.05). The hard-block technique was found to be the most precise fabrication technique for Co-Cr metal alloy frameworks. A significant relationship was observed between the amount/distribution of misfit and the strain on the FCD (P<.05).