Objectives: This study aimed to assess the effect of three commonly consumed beverages on surface roughness of polished and glazed zirconia-reinforced lithium silicate (ZLS) glass ceramics. Materials and Methods: In this experimental study, 104 rectangular specimens were cut from Vita Suprinity blocks with 2 mm thickness. After ultrasonic cleaning and firing of the specimens, they were finished and polished in two groups. Specimens in the first group were polished using a 2-step polishing kit while the second group specimens were glazed and heated in a porcelain firing oven according to the manufacturer’s instructions. Baseline surface roughness was measured using a profilometer. Specimens in each group were then randomly divided into 4 subgroups (n=13) for immersion in artificial saliva (control group), cola, orange juice and black tea. Surface roughness was measured again and data were analyzed using two-way ANOVA. Results: The highest and the lowest mean Ra were found in orange juice and saliva subgroups, respectively in both glazed and polished groups. The Ra values of both polished and glazed groups significantly increased after immersion in orange juice and cola (P<0.05). The polished surfaces showed insignificantly higher surface roughness compared with glazed surfaces (P>0.05). Conclusion: Orange juice and cola significantly increased the surface roughness of both polished and glazed ZLS ceramics. Type of surface finishing (polishing versus glazing) had no significant effect on the surface roughness of specimens following immersion in different beverages.

Objectives: This study aimed to compare the marginal fit of temporary restorations fabricated by the conventional chairside method, 3D printing, and milling. Materials and Methods: In this in vitro, experimental study, 14 temporary restorations were conventionally fabricated over an implant abutment and analog that had been mounted in a phantom model at the site of canine tooth, using auto-polymerizing acrylic resin and putty index. In digital manufacturing, the original model was scanned, and the final restoration was designed. Fourteen temporary restorations were milled out of polymethyl methacrylate (PMMA) blocks, and 14 others were printed by a 3D printer. Temporary crowns were placed on the abutment, and images were obtained from specific areas under a stereomicroscope at x100 magnification to measure the amount of marginal gap. Data were analyzed using one-way ANOVA and Tukey’s test (α=0.05). Results: The mean marginal gap values for the temporary crowns in the 3D printing, milling, and chairside groups were 91.40, 75.28 and 51.23 µm, respectively. The crowns that were conventionally fabricated chairside exhibited the lowest marginal gap, and the difference in this respect was significant among the three groups (P<0.05). Conclusion: Temporary crowns fabricated by the chairside method showed significantly smaller marginal gap; however, the marginal gap of all three groups was within the clinically acceptable range.

Objectives: This study aimed to assess the effect of three commonly consumed beverages on surface roughness of polished and glazed zirconia-reinforced lithium silicate (ZLS) glass ceramics. Materials and Methods: In this experimental study, 104 rectangular specimens were cut from Vita Suprinity blocks with 2 mm thickness. After ultrasonic cleaning and firing of the specimens, they were finished and polished in two groups. Specimens in the first group were polished using a 2-step polishing kit while the second group specimens were glazed and heated in a porcelain firing oven according to the manufacturer’s instructions. Baseline surface roughness was measured using a profilometer. Specimens in each group were then randomly divided into 4 subgroups (n=13) for immersion in artificial saliva (control group), cola, orange juice and black tea. Surface roughness was measured again and data were analyzed using two-way ANOVA. Results: The highest and the lowest mean Ra were found in orange juice and saliva subgroups, respectively in both glazed and polished groups. The Ra values of both polished and glazed groups significantly increased after immersion in orange juice and cola (P<0.05). The polished surfaces showed insignificantly higher surface roughness compared with glazed surfaces (P>0.05). Conclusion: Orange juice and cola significantly increased the surface roughness of both polished and glazed ZLS ceramics. Type of surface finishing (polishing versus glazing) had no significant effect on the surface roughness of specimens following immersion in different beverages.

This study aimed to compare the bond strength of porcelain to cobalt-chromium dental alloy fabricatedby selective laser melting (SLM) and casting methods.Twelve rectangular barsmeasuring 25x3x0.5 mmwere fabricated of cobaltchromium alloy for each of the SLM and casting groupsaccording to ISO9693:1999. Porcelain was appliedat the center of each bar measuring 3  8 mm with 1 mm thickness. Three-point fl exural bond strength test was performed to assess the bond strength of porcelain to alloy. Data were analyzed and compared between the SLM and casting groups via Independent sample t-test (alpha=0.05). Mode of failure was also determined by visual inspection of samples. The mean bond strength of porcelain to SLM alloy (35.26±1.22 MPa) was signifi cantly higher than that to casting alloy (33.21±3.02 MPa) (P<0.05). Most failures in both groups were mixed and no sample showed adhesive failure. The SLM metal-ceramic system showed higher bond strength than the required threshold by ISO9693:1999. Compared to alloys fabricated by the casting method, the SLM method showed higher bond strength to porcelain. This relatively new technology is promising for dental application and can serve as a suitable alternative to the conventional casting method for the fabrication of metal-ceramic restorations.

No abstract

The aim of this study was to assess the effect of dynamic loading and abutment type on removal torque value. Thirty-two analogs of fi xtures with internal taper connections were divided into two groups of 16. The one-piece (OP) group received solid (one-piece) abutments and the two-piece (TP) group received two-piece abutments. Each group was further subdivided into subgroups C (control) without mechanical loading and T (test) with mechanical loading. The screw of abutments in OPC and TPC groups, were tighten and then removed to record the removal torque value (RTV). In OPT and TPT groups, abutments were tighten, mechanically loaded (300,000 cycles), removed, and the RTV were recorded. Two-way ANOVA and Tukey's HSD post-hoc testwere used for data analysis.The signifi cance threshold was set at 0.05. The mean torque loss of OPC group was signifi cantly lower than both TPC and OPT groups (P < 0.05). But there was not signifi cant different in torque lossvalues between abutments in TPC and TPT groups.Under mechanical loading, theremoval torque of both one-piece and two-piece groups decreased and this reduction was only signifi cant for one-piece group. Also, the abutment type has signifi cant effect on removal torque value.

Background: Screw loosening is one of the most common problems associated with implant-supported prostheses. The type and material of the abutment play an important role in the esthetic appearance of implant-supported restorations. Metal abutments create an unaesthetic grayish halo in the gingival margin of the implant due to the reflection of light from the surface of titanium abutment. Zirconia is highly popular for the fabrication of abutments due to its optimal color, along with the quality of light transmission and its resistance. The present study aimed to evaluate the torque loss in titanium and one- and two-piece zirconia abutments under cyclic loading. Methods: In general, 24 abutments in three groups (n=8) of one- and two-piece zirconia abutments, and titanium abutments were evaluated in this experimental study. The abutments were attached to the analog of fixtures with 30 N/cm torque and the samples were subjected to loads applied to the center of abutments at 30° angle. After cyclic loading, the removal torque value was measured for each abutment and its numerical mean was calculated as well. Finally, the groups were compared using SPSS16 via ANOVA and Games-Howell tests at a 0.05 level of significance. Results: The mean removal torque value was 23.925, 23.913, and 22.538 N/cm in titanium and two- and one-piece zirconia abutments, respectively, with no statistically significant difference in between (P>0.05). Conclusions: The highest mean removal torque value belonged to prefabricated titanium abutments while the lowest value was related to one-piece zirconia abutments.

No abstract