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This study aimed to evaluate the fracture resistance of endodontically treated molars restored with ceramic indirect restorations with and without cervical margin relocation. A total of 120 extracted human maxillary molars were used after MOD cavities preparations with the mesial boxes located 2 mm below CEJ. Specimens were randomly assigned to six groups according to the margin location of each indirect restoration type (n = 20); crown without CMR, crown with CMR, endocrown without CMR, endocrown with CMR, onlay without CMR, and onlay with CMR. Mesial proximal boxes of the MOD cavities were elevated with composite resin in cervical margin relocation groups. Each group was further divided according to indirect restoration material (n = 10); CEREC Tessera and Celtra Press. The specimens were subjected to fracture resistance testing in a universal testing machine. Fracture analysis was performed using stereo and scanning electron microscopes. Data were analyzed by using 3-way ANOVA, 1-way ANOVA and the Tukey HSD tests (α = 0.05). The mean fracture resistance values ranged between 2136.57 and 950.47 N. Significantly higher values were detected among Celtra Press than Cerec Tessera in crown restorations. Unrestorable fracture patterns were seen through all study groups. Crown restorations represented the best restorative option in terms of fracture resistance. Cervical margin relocation adversely affected fracture resistance. However, the material of the indirect restorations had no significant impact on fracture resistance. [ABSTRACT FROM AUTHOR]

Objectives: The development of dental adhesives with enhanced bond strength has assisted minimally invasive dentistry. The aim of this study was to evaluate the fracture load and stress distribution pattern of two retainer designs for posterior cantilever resin bonded fixed dental protheses (RBFDPs). Materials and Methods: Forty human mandibular molars were divided into two groups according to the retainer design; lingual coverage (LC) and occlusal coverage (OC) retainers. Each main group was then divided according to the number of inlay boxes (n = 10); one inlay and two inlay boxes. High translucency (3Y) zirconia was used to manufacture all restorations, and a dual‐polymerizing adhesive resin cement was used for bonding. All specimens underwent 10,000 cycles of thermocycling (5–55°C), 240,000 cycles of dynamic loading (50 N, descending speed v = 30 mm/second, frequency = 1.6 Hz), and failure load test. Both one‐way and two‐way ANOVA tests were used to analyze the data. The four models included in the in‐vitro study are part of the finite element analysis (FEA). When the restorations failed, maximal principal stress values on restorations, enamel, dentin, and luting resin were investigated. Results: A statistically significant (p = 0.018) higher failure load was recorded for OC1 (627.00 ± 153.4 N) than the other groups; (548.0 ± 75.6 N, 521.20 ± 11.3 N, and 509.20 ± 14.9 N for LC1, LC2, and OC2, respectively). With regard to failure mode, one inlay box designs showed more favorable failure pattern than those of two inlay boxes. FEA showed higher stress magnitude transmitted to the tooth structure in models LC2 and OC2. Conclusions: Lingual coverage and occlusal coverage retainers are promising designs capable to withstand the normal occlusal force for cantilever RBFDP in premolar area. The use of two inlay boxes decreased the fracture load of the two retainer designs and increased the stress transmitted to the tooth and resulted in high incidence of catastrophic failure. Clinical Significance: Monolithic high translucent zirconia RBFDP could be considered as a viable treatment option to substitute missing posterior tooth, with improved esthetics and biocompatibility. [ABSTRACT FROM AUTHOR]

Purpose: To assess the impact of abutment angulation on loosening torque, torque loss, and percentage of torque loss in the prosthesis and abutment screws after aging of the implant-supported prosthesis. Materials and Methods: Fifty epoxy maxillary casts with missing central, lateral, and canine teeth were used, and each cast received two implants. All casts were divided into five groups (n = 10): (1) both implants received straight abutments (0-0); (2) the central implant received a straight abutment and the canine implant received a 17.5-degree angled abutment (0-17.5); (3) the central implant received a straight abutment and the canine implant received a 35-degree angled abutment (0-35); (4) both implants received 17.5-degree angled abutments (17.5-17.5); and (5) both implants received 35-degree angled abutments (35-35). For each cast, a three-unit zirconia restoration was fabricated, and a torque meter was utilized to tighten the abutment screw (25 Ncm) and prosthesis screw (18 Ncm). The reverse torque value was recorded for each screw. All restorations were subjected to 3,500 thermal cycles between 5°C and 55°C and load cycled for 150,000 cycles with 50-N load. After the loosening torque was measured for each screw, the torque loss and percentage of torque loss were calculated. Results: There was a statistically significant difference in the torque loss of the central prosthesis screw (P < .001) and canine prosthesis screw (P < .001) between study groups. The 35-35 group showed the highest percentage of torque loss, while the 0-0 group showed the lowest value. A significant difference was found regarding the torque loss of the central abutment screw (P < .001) and canine abutment screw (P < .001). The abutment screws of the 35-35 group showed the highest percentage of torque loss, while the 0-0 groups showed the lowest percentage of torque loss. Conclusion: Screw loosening of the prosthesis and abutment screws increases with increasing abutment angulation after aging. In the same fixed prosthesis, the torque loss in the prosthesis and abutment screws was higher in canine screws employing different angled abutments. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the influence of retainer design and ceramic materials on the durability of minimally invasive cantilever resin-bonded fixed dental prostheses (RBFDPs) after artificial aging. Methods: One hundred caries-free human mandibular molars were prepared as abutments for all-ceramic cantilevered fixed dental prostheses using the following retainer designs: One wing (OW), Two wings (TW), Inlay ring (IR), Lingual coverage (LC), and Occlusal coverage (OC). Two ceramic materials were used: monolithic high translucent zirconia(z) and zirconia-reinforced lithium disilicate (ZLS2) (n=10). All restorations were adhesively bonded with resin cement. The thermocycling of the specimens were performed between 5°C and 55°C for 10,000 cycles and then exposed to 240.000 cycles of dynamic loading on a chewing simulator. All surviving specimens were loaded onto the pontic until failure using a universal testing machine. Results: The mean failure load ranged from 124.00 to 627.00 N for the zirconia groups and from 133.30 to 230.00 N for the ZLS2 groups. Regarding the materials, a significantly higher failure load was recorded in the zirconia groups than in the ZLS2 groups (P<0.001), except for OW (P=0.748). Regarding the retainer designs, a significant different failure load was recorded between the different designs except for IR and LC in the zirconia groups, IR and OC, OW and TW, and TW and LC in the ZLS2 groups (P<0.001). Conclusions: Zirconia IR, LC, and OC can be used as cantilever RBFDP in the premolar region. The fracture resistance of the ZLS2 design was below the normal bite force and should not be recommended as the first option. [ABSTRACT FROM AUTHOR]

Purpose: To assess the 10-year clinical retention and survival rates of metal-ceramic (MC) and all-ceramic (AC) cantilever resin-bonded fixed dental prostheses (CRBFDPs).Materials and Methods: Forty CRBFDPs constructed from either cobalt-chromium ceramic (MC group; n = 20) or glass-infiltrated alumina ceramic (AC group; n = 20) were placed in 40 patients between August 2007 and December 2009. After baseline recordings, the patients were followed up using modified United States Public Health Services (USPHS) criteria after 6 months and thereafter annually for 10 years. Data were statistically analyzed using Kaplan-Meier estimation with log-rank (Mantel-Cox) test.Results: The 10-year clinical retention rate was 95.0% in the MC group and 70% in the AC group. The difference was statistically significant (P = .02, log-rank test). Three all-ceramic CRBFDPs fractured at 6, 12, and 84 months after insertion. No statistically significant difference in survival rate was observed between the MC and AC groups over the 10 years of clinical observation (MC: 100%; AC: 85%; P = .075) (Kaplan-Meier method, confidence interval = 92.5% to 97.5%).Conclusion: Although glass-infiltrated alumina ceramic anterior CRBFDPs exhibited a lower clinical retention rate compared to metal-ceramic CRBFDPs, the debonded prostheses were recemented and continued in function over the observation period. Additionally, an acceptable 10-year clinical longevity was recorded. [ABSTRACT FROM AUTHOR]

Purpose: To analyze the impact of microthreads on the stresses generated in peri-implant bone surrounding reduced-diameter zirconia and titanium implants under loading. Materials and Methods: Two custommade zirconia implants, microthreaded or smooth neck, and two titanium replicas were made. Strains were recorded in the peri-implant region under 200-N vertical load. Two three-dimensional finite element models were created. Zirconia and titanium implants were tested under 200-N vertical load and 150-N oblique load at 30, 45, and 60 degrees. Results: The lowest peri-implant strain (40 ± 6 με) under vertical load was related to the microthreaded zirconia implant. Oblique load showed higher von Mises stress on bone in comparison with vertical load. The von Mises stress increased by increasing the load angle by approximately 2 MPa per degree. Under oblique load, implants showed more stress in peri-implant bone and the implant itself. On the other hand, total strains were within physiologic limits in all tested cases. Conclusion: Stresses within the peri-implant cortical bone around the reduced-diameter implant with microthreads appeared to be superior compared with the smooth-neck one. Reduced-diameter zirconia implants induced less stress on bone in comparison with the titanium implants, suggesting that zirconia is a feasible alternative for titanium. [ABSTRACT FROM AUTHOR]

Aim: The present study aimed to evaluate the retention strength of nonretentive zirconia occlusal veneers bonded to different bonding surfaces (enamel, enamel and dentin, and enamel with composite filling) using two adhesive resin cement systems that use either organophosphate carboxylic acid or organophosphate monomers as a ceramic primer. Materials and methods: Sixty extracted mandibular molars were prepared to receive occlusal veneers as follows (n = 20): 1-mm reduction within enamel; 2-mm reduction within enamel and dentin; 1-mm reduction within enamel with composite filling. Each occlusal veneer was designed with an occlusal bar to aid in the retention test, then milled from a zirconia block, and sintered. Within each group, the zirconia occlusal veneers were bonded using either Duo-Link Universal or Panavia V5 (10 specimens each). All specimens were thermocycled for 5000 cycles. After the pull-off test, the retention strength was calculated for each specimen. Each specimen was examined under magnification to determine its mode of failure. Representative specimens were examined using a scanning electron microscope. Data were analyzed using the two-way analysis of variance (ANOVA) and Tukey HSD tests (P = 0.05). Results: Both bonding substrate and cement type had a significant influence on retention strength values (P < 0.05). The two-way ANOVA showed a significant interaction between bonding substrate and cement type (P = 0.003). There were significant differences in the retention strength between the cements in both the enamel and enamel and dentin substrates (P < 0.05), but no significant difference between the cements in the enamel with composite filling substrate (P > 0.05). The predominant mode of failure was cement remaining principally in the restoration surface (adhesive failure), followed by cement adhesion to both the tooth and the restoration surface (mixed failure). Conclusions: Among the studied substrates, enamel was the optimal dental bonding surface. However, bonding to dentin was not a limiting factor for the retention of zirconia occlusal veneers. The resin cement using an organophosphate (Panavia V5) provided superior retention strength compared with the cement using organophosphate carboxylic acid monomer (Duo-Link Universal). (Int J Esthet Dent 2023;18:292-308) [ABSTRACT FROM AUTHOR]

Background: It is more cost-effective to press many restorations from a single ingot of lithium dislilicate glassceramics during the heat-pressing process. However, in many cases this is impossible and can lead to a substantial amount of waste (The sprues and button). Some dental labs reportedly recycle (repress) the remaining materials after heat pressing. Objective: The aim of the current study was to evaluate the effect of repressed lithium silicate ceramics on translucency (TP). Materials and methods: A total 60 discs were divided in 2 groups. The first group was pressed, and the second group was repressed ceramics. Each group included 30 discs (10 IPS e.max Press, 10 Celtra, 10 Ambria). The changes in translucency difference between the compared groups were evaluated. Results: Translucency parameter in IPS e.max Press translucency parameter in press (19.5±1.4) decreased in repress (17.3±1.4) with Δ TP (2.2±0.08), while Celtra translucency parameter in press (16.2±1.4) decreased in repress (14.2±1.4) with Δ TP (1.9±0.07), and Ambria translucency parameter in press (11.4±1.4) decreased in repress (10.11±1.4) with Δ TP (1.3±0.09). Contrast ratio of both press and repress were equal (0.7± 0.13). Conclusions: The translucency of repressed ceramics decreased after repress. We advise pressing glass ceramics for a single injection. [ABSTRACT FROM AUTHOR]

Aim: To evaluate the influence of resin cement on the color stability of lithium disilicate and zirconia restorations immersed in coffee after aging. Materials and methods: Eighty maxillary premolars were classified into eight groups (n = 10) based on restorative material type (lithium disilicate or zirconia), resin cement type (G-CEM LinkForce; GC Corporation or Panavia SA Cement Plus Automix; Kuraray Noritake Dental), and preheating temperature (25°C or 54°Q. Following tooth preparation, each restoration was bonded to its corresponding substrate. Using a reflectance spectrophotometer, Commission Internationale de I'Eclairage (CIE) tristimulus values were detected and calculated Spy standard illumination, 10-degree observer angle). All specimens were aged (240,000 load cycles followed by 10,000 thermal cycles), then immersed in coffee (18 h). Following that, the second measurements of the color coordinates were determined. The total color differences were measured, and the data Were statistically analyzed (a = 0.05). Results: The temperature had a significant effect on, ▲ AL' (P < 0.001), ▲C (P < 0.001), and ▲h (P < 0.0011 The lithium disilicate restorations were more color stable than the zirconia restorations. Also, there was a significant difference (P = 0.047) between the LinkForce (2.28 ± 0.48) and Panavia SA (2.15 ± 0.46) cement. The restorations cemented at a temperature of 54°C (1.76 + 0.11) showed significant color differences (P < 0.001) compared with those cemented at a temperature of 25°C (2.67 + 0.15), A three-way analysis of variance (ANOVA) test revealed that the interaction between the ceramic material, cement type, and temperature had no statistically significant effect (P = 0.611) on the color stability of the ceramic restorations. Conclusions: Cement type has a significant effect on the color stability of lithium disilicate and zirconia restorations. Cement at a temperature of up to 54°C enhances the color stability of lithium disilicate and zirconia restorations. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the fracture load and stress magnitude of different retainer designs of minimally invasive cantilever resin‐bonded fixed dental prostheses (RBFDPs) after artificial aging. Materials and methods: Fifty caries‐free human mandibular molars were prepared as abutments for cantilever fixed dental prostheses using different retainer designs: one wing (OW), two wings (TW), inlay ring (IR), lingual coverage (LC), and occlusal coverage (OC). Computer‐aided design and computer‐aided manufacturing were used for milling the RBFDPs using fiber‐reinforced composite (FRC), and the restorations were adhesively bonded. The specimens were then subjected to thermomechanical aging and loaded until failure. The 3D finite element analysis (FEA) was performed with five models of retainer designs similar to the in vitro test. Modified von Mises stress values on enamel, dentine, luting resin, and restorations were examined. Data were analyzed with Kruskal–Wallis and Mann–Whitney U tests (p < 0.001). Results: A statistically significant difference (p < 0.001) was found between all groups except between IR and LC and between OW and TW designs, with the highest mean failure load detected for OC (534.70 N) and the lowest detected for OW (129.80 N). With regard to failure mode, OW, TW, and LC showed more incidences of favorable failure patterns than IR and OC designs. FEA showed that FRC transmitted low stresses in tooth structure and high stresses to the luting resin. Conclusions: LC and OC designs can be used to design cantilever RBFDPs in premolar area. IR design transmitted more stresses to the tooth structure and resulted in 30% catastrophic failure. OW and TW were below the normal occlusal force and should be carefully used. [ABSTRACT FROM AUTHOR]

Purpose: To test the effect of surface conditioning protocols on the reparability of CAD/CAM zirconia-reinforced lithium silicate ceramic compared to lithium-disilicate glass ceramic. Materials and Methods: Zirconia-reinforced lithium silicate ceramic (Vita Suprinity) and lithium disilicate glass-ceramic blocks (IPS e.max CAD) were categorized into four groups based on the surface conditioning protocol used. Group C: no treatment (control); group HF: 5% hydrofluoric acid etching for 60 s, silane (Monobond-S) application for 60 s, air drying; group HF-H: 5% HF acid etching for 60 s, application of silane for 60 s, air drying, application of Heliobond, light curing for 20 s; group CO: sandblasting with CoJet sand followed by silanization. Composite resin (Tetric Evo Ceram) was built up into 4 x 6 x 3 mm blocks using teflon molds. All specimens were subjected to thermocycling (5000x, 5°C to 55°C). The microtensile bond strength test was employed at a crosshead speed of 1 mm/min. SEM was employed for evaluation of all the debonded microbars, the failure type was categorized as either adhesive (failure at adhesive layer), cohesive (failure at ceramic or composite resin), or mixed (failure between adhesive layer and substrate). Two-way ANOVA and the Tukey's HSD post-hoc test were applied to test for significant differences in bond strength values in relation to different materials and surface pretreatment (p < 0.05). Results: The highest microtensile repair bond strength for Vita Suprinity was reported in group CO (33.1 ± 2.4 MPa) and the lowest in group HF (27.4 ± 4.4 MPa). Regarding IPS e.max CAD, group CO showed the highest (30.5 ± 4.9 MPa) and HF the lowest microtensile bond strength (22.4 ± 5.7 MPa). Groups HF, HF-H, and CO showed statistically significant differences in terms of all ceramic types used (p < 0.05). The control group showed exclusively adhesive failures, while in HF, HF-H, and CO groups, mixed failures were predominant. Conclusions: Repair bond strength to zirconia-reinforced lithium silicate ceramics and lithium-disilicate glass ceramic could be improved when ceramic surfaces are sandblasted with CoJet sand followed by silanization. [ABSTRACT FROM AUTHOR]