Fracture Resistance of CAD/CAM Monolithic Zirconia Crowns Supported by Titanium and Ti-Base Abutments: The Effect of Chewing Simulation and Thermocyclic Aging.

Purpose: To evaluate the effect of chewing simulation and thermocyclic aging on the fracture resistance of CAD/CAM monolithic zirconia crowns supported by titanium and Ti-base abutments. Materials and Methods: Two implant abutment groups-titanium (Ti) and titanium base (Ti-base; Medentika)-were used. A total of 40 mandibular first molar CAD/CAM monolithic zirconia crowns (Vita YZ T) were fabricated, then cemented onto the abutments with Panavia V5. Each abutment group was divided into two subgroups (n = 10). The Ti and Ti-base groups were subjected to a single load until fracture, and the Ti/CT and Ti-base/CT groups (CT: chewing simulation and thermocyclic aging) underwent chewing simulation (1.2 × 106 cycles × 50 N load, 1.4 Hz) and thermocylic aging (3,911 cycles/5°C to 55°C). The fracture resistances of the crowns were tested with a universal testing machine (1 mm/minute). Shapiro-Wilk and one-way ANOVA test were used for statistical analysis (P = .05). Results: The survival rates after chewing simulation and thermocyclic aging were 100% for both CT groups. The fracture resistance values (mean ± SD) of the groups were as follows: Ti = 1,718.18 ± 331.06 N, Ti-base = 1,713.53 ± 233.24 N, Ti/CT = 1,664.82 ± 188.62 N, and Ti-base/CT = 1,551.28 ± 344.79 N. According to one-way ANOVA test results, there was no statistically significant difference between the four groups (P = .526). Conclusion: CAD/CAM monolithic zirconia crowns supported by Ti-base or titanium abutments were found to have sufficient fracture resistance in the treatment of an absent single posterior tooth. However, more in vitro and clinical studies are required to evaluate the long-term performance of Ti-base abutments and CAD/CAM zirconia crowns.

Comparison of Surface Roughness and Color Stability of Different Denture Characterizing Composite Resins: The Effect of Different Surface Treatments.

PURPOSE: This study aimed to investigate the effect of surface treatment and type of composite resin material on the color stability and surface roughness of different denture characterizing composites. MATERIALS AND METHODS: Two nanohybrids [Gradia Plus Gum, (GP) and SR Nexco Paste Gingiva, (SR)] and one microhybrid gingiva-colored composite resin [Amaris Gingiva, (AG)] were investigated. A total of 120 disk-shaped samples were prepared, 40 of each material. Samples were divided into two groups (n = 20) for each material according to the surface treatment applied: conventional polishing (control) and coated with a sealant in addition to the surface polishing. All groups were thermocycled. The surface roughness (Ra) was measured using a profilometer after thermal cycling. The samples were then divided into 2 subgroups (n = 10) and stored for 7 days in distilled water or coffee solution. Color differences (ΔE00 ) were calculated with a spectrophotometer. Results were evaluated with Kruskal-Wallis and Mann-Whitney U statistical analysis. RESULTS: The type of denture characterizing composite material and surface treatment method revealed statistically significant differences for the ΔE00 (after immersion both in coffee and distilled water) and the Ra values of denture characterizing composite (p < 0.001 for both). All sealed groups showed significantly higher Ra than the all polished groups. Both in the polished groups and the sealant applied groups, the GP had the highest mean Ra values (0.29 ±0.05 µm and 0.47 ±0.09 µm, respectively). It was followed by SR (0.23 ±0.06 µm and 0.41 ±0.10 µm, respectively), and AG groups (0.20 ±0.06 µm and 0.39 ±0.09 µm, respectively). According to the mean ΔE00 results, all composite groups showed significantly higher ΔE00 values immersed in coffee solutions compared to distilled water. In coffee solutions, the highest ΔE00 was observed in the polished GP (1.90 ±0.40), and the lowest ΔE00 was observed in the polished SR (0.97 ±0.36). The sealed groups showed higher ΔE00 than the polished groups, except for GP. CONCLUSIONS: The surface roughness value of sealant applied groups were significantly higher than those of the polished groups. The surface sealant application significantly increased the staining of all composite groups compared to conventional polishing, except for GP.

Different Cavity Designs with Additional Wings Increase the Fracture Resistance of Inlay-Retained Monolithic Zirconia Fixed Dental Prostheses.

PURPOSE: To evaluate the effect of different cavity designs and cement types on the fracture resistance of monolithic zirconia inlay-retained fixed dental prostheses (IRFDPs). MATERIALS AND METHODS: Four study models consisting of a second premolar, a missing first molar, and a second molar were used for the different cavity designs. Four different inlay cavity designs were prepared: DO-MO (disto-occlusal-mesio-occlusal cavity), MOD-MOD (mesio-occlusodistal-mesio-occlusodistal cavity), WDO-WMO (DO-MO with additional wings), and WMOD-WMOD (MOD-MOD with additional wings). A total of 64 epoxy resin models were produced and scanned individually. IRFDPs were then fabricated from monolithic zirconia using CAD/ CAM software. The bonding surface of the IRFDPs was airborne particle abraded (50-µm alumina/2 MPa), then cemented onto the epoxy resin models using two cementation protocols (n = 8 per group): (1) P = cemented with Panavia SA Cement Plus Automix; and (2) Z/C = cemented with MDP-containing primer (Z-Prime Plus) combined with Calibra Universal resin cement. All IRFDPs were fatigued through thermal aging (6,000 cycles/5°C to 55°C) and chewing simulations (600,000 cycles × 50-N load, 2.1 Hz). All IRFDPs were then subjected to a fracture resistance test using a universal testing machine with a crosshead speed of 0.2 mm/minute. Data were statistically analyzed using one- and two-way ANOVA and Bonferroni multiple comparisons test (P = .001). RESULTS: The mean fracture load (N) of the designs were as follows: WMODWMOD = 1,111.1; WDO-WMO = 1,057.4; MOD-MOD = 725.6; DO-MO = 682.7. According to two-way ANOVA, the differences among the cavity designs were statistically significant (P < .05). CONCLUSION: The cavity design of IRFDPs affected the fracture resistance. However, the fracture resistance of monolithic zirconia IRFDPs with any cavity design was enough to withstand expected posterior chewing forces.

Finite Element Analysis of Stress Distribution in Mandibles with Different Bone Types Loaded by Implant-Supported Overdentures with Different Localizations of Locator Attachments.

PURPOSE: Prosthetic rehabilitation of completely edentulous patients has been traditionally performed with complete dentures for many years. However, patient complaints are reported due to insufficient retention and high mobility of mandibular dentures. Therefore, in these patients, overdenture prostheses, which are usually made by placing at least two implants in the interforaminal region of the mandible, have become widespread. In these prostheses, bar, stud, magnetic, or ball and locator attachments are used. This study aimed to evaluate the stress on mandibles by an overdenture with locator attachments supported by two implants placed on three different bone types in three different regions. MATERIALS AND METHODS: Finite element analysis (3D) was used to design a mandible and overdenture. Two implants and locator attachment systems were placed into the lateral incisor, canine, and premolar regions. In computer-generated mandible and overdenture models, a force of 100 N was loaded obliquely and vertically from the mandibular first molar teeth region; then, the values obtained from the forces were compared. Eighteen analyses were performed with two different loading options in nine different models. Von Mises, compressive, and tensile stress values were analyzed. RESULTS: As the bone type changed from D1 to D3, the stresses on the bone increased in direct proportion. However, with all three bone types, lower tensile values were found in cortical bone in an above-implant removable prosthesis supported by an implant in the lateral incisor region. CONCLUSION: Biomechanically, the lateral incisor and canine regions were more advantageous than the first premolar tooth region in prosthesis designs where two implants were used in all bone types.

Disinfection of polyvinyl siloxane impression material by gaseous ozone.

STATEMENT OF PROBLEM: Impression materials must be disinfected to avoid cross-contamination before they are sent to the dental laboratory. However, whether aqueous state disinfectants affect material wettability is unclear. PURPOSE: The purpose of this in vitro study was to compare the efficacy of gaseous ozone and sodium hypochlorite (NaOCl) in disinfecting light-body consistency hydrophilized polyvinyl siloxane (PVS) impression specimens inoculated with a cocktail of Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis. The effect of both disinfectants on the wettability of the material was also evaluated on uninoculated specimens. MATERIAL AND METHODS: Disk-shaped specimens (N=140) were subjected to the either gaseous ozone or NaOCl for up to 30 minutes at room temperature. In the ozone group, the specimens were ozonated under a continuous stream of gaseous ozone at a concentration of 12.8 mg/L, while the specimens in the NaOCl group were immersed into 0.5% NaOCl solution. Reductions in the size of the bacterial population at the end of the exposure times were determined by the plate count technique. The contact angle measurements on the impression surface were used to determine the wettability of the specimens. Results were analyzed with 1-way ANOVA followed by the Tukey post hoc test (α=.05). RESULTS: The material exposed to both disinfectants for 30 minutes demonstrated a reduction in the number of bacteria of up to more than 3 log. The contact angle of water on the material increased significantly (P<.001) after only 5 minutes of contact with the NaOCl solution. However, the treatment with gaseous ozone for 30 minutes resulted in a reduced contact angle (P<.001). CONCLUSIONS: Gaseous ozone treatment was identified as a promising method of disinfecting polymerized PVS impression materials because of its positive effect on the wettability of the material.