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Purpose: To investigate the effects of recycling lithium disilicate (LD), surface treatment, and thermocycling on the bond strength to resin cement. Materials and Methods: A total of 72 tablets (10 × 10 × 3 mm) of LD were made according to the recycling cycle with 24 tablets for each strategy: control (conventional sintering), 1R (1 recycling cycle), and 3R (3 recycling cycles). For the recycling groups, tablets were waxed, mounted in a silicone ring, and poured with investment material, and residues of sintered LD tablets were pressed by the lost wax technique. The residual LD was reused as described until it reached 3R. Afterward, the tablets were embedded in acrylic resin, sanded, and divided (n = 15) according to the factors of “surface treatment” (hydrofluoric acid [HF] for 20 seconds [HF20s] and silane, HF for 120 seconds [HF120s] and silane, and Monobond Etch & Prime [MEP]) and thermocycling (TC; with 10,000 cycles and without). After surface treatment, cylinders (diameter: 2 mm) of resin cement were made and submitted to SBS test (100 kgf, 1 mm/minute). Data (MPa) were analyzed by three-way ANOVA, Tukey test (5%), and Weibull analysis. Failure analysis was performed with a stereomicroscope. Results: ANOVA revealed that all factors were significant (P = .000*). The group 3RMEP (105.09 ± 19.49) presented the highest SBS among the experimental groups. The 1RHF20s^Tc (7.50 ± 1.97) group had the lowest SBS, similar to CHF20s^Tc (15.69 ± 3.77), 1RHF20s (15.12 ± 3.03), 1RHF120s^Tc (14.60 ± 3.43), and 3RHF20s^Tc (15.65 ± 0.97). The Weibull modulus and characteristic strength varied among the experimental groups (P = .0). Failure analysis revealed adhesive and mixed types. Conclusions: The recycling of DL ceramics increases the SBS to resin cement when the ceramic is treated with HF120s and silane or MEP. Keywords: Shear Strength, lithium disilicate, recycling.

Objective: To evaluate the effect of different adhesives and veneering resins on the shear bond strength (SBS) of polyetheretherketone (PEEK). Methods: A total of 138 PEEK specimens were randomly divided into 6 groups according to adhesive material application: Control (C, no application), Adhese Universal (A) (Ivoclar Vivadent, Schaan, Liechtenstein), Gluma Bond Universal (G) (Heraeus Kulzer, South Bend, IN, USA), G-PremioBOND (P) (GC Corporation, Tokyo, Japan), Single Bond Universal (S) (3M, Saint Paul, MN, USA) and visio.link (V) (Bredent, Senden, Germany). Each adhesive group was divided into two subgroups according to the type of veneering material: Estenia direct composite (D) and Gradia Plus indirect composite (IN) (both GC Corporation). After the veneering process, the specimens were aged by thermal cycling. Kruskal-Wallis and Mann-Whitney U tests were used for SBS analysis (P < 0.05). Results: The highest SBS results were obtained in the VIN group, followed by the VD, PD, GIN, AIN, AD, SIN, SD, PIN, GD, CIN and CD groups, respectively (P = 0.001). There were no significant differences in terms of the type of veneering composite when the same adhesive was applied (P > 0.05), except for Gluma Bond Universal (P = 0.009). All the adhesives tested showed clinically acceptable SBS results. Conclusion: Visio.link offered the highest adhesion to PEEK, whereas the tested universal adhesives may be used as an alternative to visio.link in clinical settings. It was determined that changing the veneer type has no statistical difference when the same adhesive material is used. Keywords: composite resin, polyetheretherketone, shear bond strength, universal adhesives

Purpose: The study evaluated the clinical performance of partial indirect resin composite (PIRC) restorations with “proximal box elevation” (PBE) placed in molars.Materials and Methods: Sixty-three patients received 80 posterior PIRC (SR Nexco, Ivoclar Vivadent) restorations. Large posterior defects with cuspal loss and deep cervical margins were included in the study. PBE was performed prior to preparation and impression making. Two independent observers evaluated the restorations using the FDI criteria (scores 1-5) for esthetic, functional, and biological properties. Patients were recalled at 6 months and 1, 2, and 3 years. Overall success rates were calculated (Kaplan-Meier analysis) and compared (log-rank tests) according to baseline variables. The impact of the baseline variables on the failure of the restorations was analyzed (multiple proportional Cox regression).Results: Seventy-nine (98.7%), 69 (88.4%), 66 (92.9%), 44 (86.2%) and 45 (91.8%) PIRCs completed their follow up at baseline, 6 months, and 1, 2 and 3 years, respectively. In total, 10 failures were observed: 5 with partial loss, 4 with material chipping, and one with secondary caries, yielding an overall success rate of 87.5% and a survival rate of 93.8%, with a mean observation time of 26.5 ± 13.6 months.Conclusions: PIRCs with PBE demonstrated a high survival rate and satisfactory esthetic properties. Failure was less likely for PIRC restorations with partial cuspal coverage (onlay) compared to full cuspal coverage (overlay). Keywords: adhesive dentistry, clinical trial, dental materials, indirect resin composite, survival, proximal box elevation

Purpose: To investigate the effect of adhesive type and long-term aging on the shear bond strength (SBS) between silica-based ceramics and composite cement (CC).Materials and Methods: Lithium-silicate (LS), feldspathic (FD) and polymer-infiltrated ceramic (PIC) blocks were sectioned (10 x 12 x 2 mm) and divided into 24 groups considering the factors: “ceramics” (LS, FD, and PIC), “adhesive” (Ctrl: without adhesive; 2SC: 2-step conventional; 3SC: 3-step conventional; 1SU: 1-step universal), and “aging” (non-aged or aged [A]). After the surface treatments, CC cylinders (n = 15, Ø = 2 mm; height = 2 mm) were made and half of the samples were subjected to thermocycling (10,000) and stored in water at 37°C for 18 months. The samples were submitted to SBS testing (100 kgf, 1 mm/min) and failure analysis. Extra samples were prepared for microscopic analysis of the adhesive interface. SBS (MPa) data was analyzed by 3-way ANOVA and Tukey’s test (5%). Weibull analysis was performed on the SBS data.Results: All factors and interactions were significant for SBS (p<0.05). Before aging, there was no significant difference between the tested groups and the respective control groups. After aging, the LS_1SU (22.18 ± 7.74) and LS_2SC (17.32 ± 5.86) groups exhibited significantly lower SBS than did the LS_Ctrl (30.30 ± 6.11). Only the LS_1SU group showed a significant decrease in SBS after aging vs without aging. The LS_1SU (12.20) group showed the highest Weibull modulus, which was significantly higher than LS_2SC_A (2.82) and LS_1SU_A (3.15) groups.Conclusion: No type of adhesive applied after silane benefitted the long-term adhesion of silica-based ceramics to CC in comparison to the groups without adhesive. Keywords: adhesive, ceramics, dentin-bonding agents, dental materials, surface treatment

Aim: The aim of the present study was to compare the load bearing capacity of monolithic or bilayered single crowns with zirconia or polyetherketoneketone frameworks designed and fabricated using CAD/CAM systems. Materials and methods: Cr-Co–based metal dies (n = 60) were duplicated from an extracted and prepared premolar and then restored with different CAD/CAM materials. The specimens were divided into five groups (n = 12) according to the type of materials: group S: monolithic zirconia-reinforced lithium disilicate; group ZI: bilayered zirconia framework with lithium disilicate; group ZE: bilayered zirconia framework with resin-infiltrated hybrid ceramic; group PI: bilayered polyetherketoneketone (PEKK) framework with lithium disilicate; group PE: bilayered PEKK framework with resin-infiltrated hybrid ceramic. The crown specimens were cemented on Cr-Co metal dies with a resin cement (Multilink N). The specimens were subjected to cyclic mechanical loading followed by load bearing testing. Data were analyzed using the Kruskal-Wallis and Mann-Whitney U tests (α = 0.05). Results: The monolithic crowns in group S (1930 ± 452.18 N) presented significantly higher load bearing capacity than those of the other groups (P < 0.05). This was followed by group ZI (1165.41 ± 264.04 N). The remaining groups demonstrated comparable results. Failure types were more frequent in all zirconia specimens that included veneering ceramic. Conclusions: Monolithic zirconia-reinforced lithium disilicate CAD/CAM ceramics showed superior load bearing capacity compared with all other bilayered counterparts. All CAD/CAM materials tested remarkably exceeded the average occlusal force in the posterior region. Keywords: bilayered all-ceramics, CAD/CAM, dental materials, load bearing capacity, monolithic, PEKK, zirconia, prosthodontics

Aim: To evaluate the fracture load and type of failure of two different monolithic restorative materials bonded to standardized titanium bases and fabricated by two different procedures regarding the bonding interface. Materials and methods: All screw-retained implant crown specimens (n = 40), subjected to fatigue by thermomechanical loading, differed in the restorative material (lithium disilicate [LDS] or polymer-infiltrated ceramic network [PICN], referred to as ‘hybrid ceramic’ [HYC]) and the interface type between the restorative material and the titanium base abutment (prefabricated ex-factory or produced during a CAM-milling procedure). This resulted in the following groups (n = 10/group): 1) LDS-M: lithium disilicate crown with a CAM-milled interface; 2) LDS-P: lithium disilicate crown with a prefabricated interface; 3) HYC-M: PICN crown with a CAM-milled interface; and 4) HYC-P: PICN crown with a prefabricated interface. Aged specimens underwent static fracture load testing. The load (N) at which the initial crack occurred was denoted as Finitial, and the maximal load (N) at which the restorations fractured as Fmax. All specimens were examined under a stereomicroscope to determine the failure mode. Results: The median Finitial values were 180 N for LDS-M, 343 N for LDS-P, 340 N for HYC-M, and 190 N for HYC-P. The median Fmax values were 1822 N for LDS-M, 2039 N for LDS-P, 1454 N for HYC-M, and 1581 N for HYC-P. The intergroup differences were significant for Finitial (KW: P = 0.0042) and for Fmax (KW: P = 0.0010). The failure types also showed differences between the restorative groups. Conclusions: The choice of restorative material had a stronger influence on the fracture load than the abutment interface workflow. Lithium disilicate showed the highest load for initial crack appearance (Finitial) and for complete fracture of the restoration (Fmax). Keywords: lithium disilicate, dental materials, polymer-infiltrated ceramic network, thermomechanical aging, fracture load, failure mode, prosthetic dentistry, restorative material, abutment interface

Ziel: Ziel dieser Studie war es, den Einfluss des Typs und der Vorwärmtemperatur des Befestigungskomposits auf die Farbstabilität von Lithiumdisilikat- und Zirkonoxidrestaurationen nach künstlicher Alterung und Lagerung in Kaffeelösung zu untersuchen. Material und Methoden: Insgesamt 80 obere Prämolaren wurden anhand des für die Restauration verwendeten Materials (Lithiumdisilikat- oder Zirkonoxidkeramik) und Befestigungskomposits (GCEM LinkForce, Fa. GC, oder Panavia Sa Cement Plus Automix, Fa. Kuraray Noritake Dental) sowie dessen Vorwärmtemperatur (25 °C oder 54 °C) acht Gruppen (n = 10) zugeordnet. Nach der Präparation wurden alle Restaurationen mit ihren Stümpfen verklebt. Mit einem Reflexionsspektralfotometer wurden CIE-XYZ-Werte bestimmt (D65-Normlich, Betrachterwinkel 10°). Alle Proben wurden künstlich gealtert (240.000 Lastzyklen gefolgt von 10.000 Temperaturzyklen) und anschließend in Kaffee getaucht (18 Stunden). Anschließend wurden die Farbkoordinaten erneut bestimmt. Die Gesamtfarbdifferenzen zwischen beiden Messungen wurden berechnet und die gewonnenen Daten statistisch analysiert (α = 0,05). Ergebnisse: Die Temperatur des Befestigungskomposits hatte signifikanten Einfluss auf ΔL΄ (p < 0,001), ΔC΄ (p < 0,001) und ΔC΄ (p < 0,001). Die Lithiumdisilikat-Restaurationen zeigten sich farbstabiler als diejenigen aus Zirkonoxid. Ferner fand sich ein signifikanter Unterschied (p = 0,047) zwischen LinkForce (2,28 ± 0,48) und Panavia Sa (2,15 ± 0,46). Die mit einer Vorwärmtemperatur von 54 °C (1,76 ± 0,11) befestigten Restaurationen wiesen gegenüber den mit 25 °C (2,67 ± 0,15) befestigten signifikant geringere Farbdifferenzen auf (p < 0,001). Eine dreifaktorielle Varianzanalyse ergab, dass zwischen Keramik, Befestigungskomposit und Vorwärmtemperatur keine Interaktion mit statistisch signifikantem Einfluss (p = 0,611) auf die Stabilität der Restaurationsfarbe bestand. Schlussfolgerungen: Das Befestigungskomposit hat signifikanten Einfluss auf die Stabilität der Farbe von Lithiumdisilikat- und Zirkonoxidrestaurationen. Vorwärmen des Befestigungskomposits auf 54 °C verbessert die Farbstabilität von Lithiumdisilikat- und Zirkonoxidrestaurationen.

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°C). Following tooth preparation, each restoration was bonded to its corresponding substrate. Using a reflectance spectrophotometer, Commission Internationale de l’Éclairage (CIE) tristimulus values were detected and calculated (D65 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 (α = 0.05). Results: The temperature had a significant effect on ΔL΄ (P < 0.001), ΔC΄ (P < 0.001), and ΔH΄ (P < 0.001). 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.

Purpose: To evaluate the minimum ceramic thickness needed to increase the lightness by one value by means of glass-ceramic restorations, as perceived by dental technicians, dentists, and laypersons. Materials and Methods: A total of 15 assessment pairs (= reference and test sample) were formed using glass-ceramic blocks in four different colors. Each assessment pair was comprised of two underground blocks differing by one value of lightness. On top of the underground blocks, glass-ceramic platelets were cemented in 5 different thicknesses (0.1 to 0.5 mm) in the same color as the reference. Dental technicians, dentists, and laypersons (n = 41/group) were asked to determine the presence of a color difference between the two samples under standardized light conditions. The threshold ceramic thickness was defined as the thickness at which ≥ 50% of the evaluators were not able to perceive a difference within an assessment pair. The thresholds were analyzed, and groups were compared by applying chi-square test (P < .05). Results: The majority of dentists and dental technicians (> 50%) detected a lightness difference between test and reference samples up to a ceramic thickness of 0.5 mm. The majority of laypersons (≥ 50%) did not perceive lightness differences with ceramic thicknesses of 0.5 mm. If separated by the different color changes, the threshold ceramic thickness started at 0.4 mm and varied within the groups of evaluators and the lightness of the assessed color. Conclusions: A considerable number of evaluators perceived a lightness difference when minimally invasive ceramic restorations of 0.5-mm thickness were applied. The threshold ceramic thickness, however, was reduced when the lightness of the substrate was lower.

Purpose: To identify the most effective cleaning method for saliva-contaminated zirconia surface before adhesive cementation through a systematic review and meta-analysis. Materials and Methods: PubMed, Scopus, and Web of Science databases were searched to select in vitro studies published through October 2021. Studies that did not perform aging methods, had a sample size less than 5 per group, or did not present a group with zirconia contaminated only with saliva were excluded. Data were extracted and risk of bias was assessed. Statistical analysis comparing the cleaning methods was conducted, and the standardized mean difference was assessed using the R software program. Results: Among 804 potentially eligible studies, 36 were selected for full-text reading, of which 13 were included in qualitative analysis, and 11 of these were subsequently included in the quantitative analysis. A meta-analysis revealed a significant difference in the bond strength between the cleaning methods. Sandblasting with Al2O3 showed a higher bond strength than cleaning solution (Ivoclean, Ivoclar Vivadent) (p < 0.01, I2 = 65%), and both methods promoted higher resin-bond strength to zirconia than water cleaning. In addition, there was no significant difference in the bond strength between alcohol (p = 0.35, I2 = 79%), phosphoric acid (p < 0.23, I2 = 90%), and water cleaning. Conclusion: Sandblasting with Al2O3 seems to be the best method for zirconia surface cleaning before adhesive luting, promoting better resin-bond strength to zirconia. Keywords: adhesion, bond strength, decontamination, dental materials, saliva contamination, surface cleaning, zirconia