Clinical performance and risk factors of all-ceramic screw-retained implant crowns in the posterior region based on a retrospective investigation.

OBJECTIVES: Clinical data on all-ceramic screw-retained implant crowns (SICs) luted on titanium base abutments (TBAs) over more than 3 years are sparse. This study aimed to evaluate the clinical performance and potential risk factors for these restorations. MATERIALS AND METHODS: Analysis took place based on the medical patient-records of three dental offices. Implant survival and prosthetic complications over time were evaluated. The study included SICs in premolar and molar regions made from monolithic lithium disilicate ceramic (M_LiDi) or veneered zirconia (V_ZiO) luted on a TBA documented over an observation time of at least 3 years. Survival and complication rates were calculated and compared by a log-rank test. Cox-Regressions were used to check potential predictors for the survival (p < .05). RESULTS: Six hundred and one crowns out of 371 patients met the inclusion criteria and follow-up period was between 3.0 and 12.9 (mean: 6.4 (SD: 2.1)) years. Over time, six implants had to be removed and 16 restorations had to be refabricated. The estimated survival rates over 10 years were 93.5% for M_LiDi and 95.9% for V_ZiO and did not differ significantly among each other (p = .80). However, V_ZiO showed significantly higher complication rates (p = .003). Material selection, sex, age, and implant diameter did not affect the survival of investigated SICs but crown height influences significantly the survival rate (hazard ratio, HR = 1.26 (95%CI: 1.08, 1.49); p = .043). CONCLUSIONS: Screw-retained SICs luted on TBAs that were fabricated from monolithic lithium disilicate ceramic or veneered zirconia showed reliable and similar survival rates. Increasing crown heights reduced survival over the years.

Assessment of the fit of lithium disilicate crowns at various locations fabricated by three different methods using the triple-scan protocol.

AIM: The present study aimed to evaluate the marginal and internal fit of lithium disilicate crowns at various locations. MATERIALS AND METHODS: A typodont maxillary left first molar was prepared for a lithium disilicate crown, scanned, and a master die fabricated. Three groups were created according to fabrication method (n = 10): conventional impression and press method (group C); scanning of definitive cast and milling method (group D); and intraoral scanning and milling method (group I). Assessment was performed using the triple-scan protocol. At the buccopalatal and mesiodistal sections, the absolute marginal discrepancy (AMD), marginal gap (MG), axial internal gap (AI), and line angle internal gap (LI) were measured. One-way analysis of variance (ANOVA) and post hoc Tukey HSD tests were used for statistical analysis (α = 0.05). RESULTS: AMD values were significantly lower in group C than in groups D and I (P < 0.05). MG values in group C were significantly lower than those in the buccal and distal areas in group D and all areas in group I (P < 0.05). AI values in the buccal and palatal areas in group D were significantly lower than those in the mesial and distal areas in group D and all areas in groups C and I (P < 0.05). LI values were significantly lower in group C than in groups D and I (P < 0.05). CONCLUSION: All three methods were clinically acceptable except for the marginal fit of the intraoral scanning and milling method, which was on the borderline of a clinically acceptable fit. (Int J Comput Dent 2023;26(1): 37-0; doi: 10.3290/j.ijcd.b3818305).

Comparison of marginal adaptation and internal fit of monolithic lithium disilicate crowns produced by 4 different CAD/CAM systems.

OBJECTIVES: To evaluate the marginal adaptation and internal space of crowns produced by 4 CAD/CAM systems using microcomputed tomography (µCT) and replica technique (RT). MATERIALS AND METHODS: Monolithic lithium disilicate crowns were milled (Ceramill, Cerec, EDG, and Zirkonzahn) (n = 10). The cement film obtained with low viscosity silicone was scanned by the µCT system and captured by a stereomicroscope, according to RT. Two-way ANOVA followed by Tukey's test were used for statistical analysis (α = 0.05). A uniformity index (UI) was idealized to describe the distribution of crowns' internal space and submitted to the Kruskal-Wallis and Tukey's test (α = 0.05). The correlation between µCT and RT was performed by Pearson's Correlation Coeficient (α = 0.05). RESULTS: Marginal adaptation and internal space were statistically significant different between the experimental groups for the µCT and RT (p < 0.05). The medians of the 4 systems tested were within clinically acceptable range and the mean (± SD) highest marginal discrepancy was recorded in the Ceramill group at 133.0 ± 71.5 µm (µCT) and 90.6 ± 38.5 µm (RT). For internal fit, the UI disclosed a better distribution of the internal space for the Zirkonzahn group (p < 0.001). There was a strong correlation between the methods (p = 0.01 and r = 0.69). CLINICAL RELEVANCE: Because of the variability of the CAD/CAM systems available, evaluating their accuracy is of clinical interest. The 4 systems are capable to produce restorations adaptated within clinically appropriate levels. The µCT and RT are efficient adaptation methodologies.

Effect of cement color and tooth-shaded background on the final color of lithium disilicate and zirconia-reinforced lithium silicate ceramics: An in vitro study.

OBJECTIVE: To evaluate the translucency and effects of different cement colors on the final shade of lithium disilicate ceramics (LDS) and zirconia-reinforced lithium silicate ceramics (ZLS) over an A1 and A3 tooth-shaded background. MATERIALS AND METHODS: Eighty-eight rectangular-shaped specimens were sliced from LDS and ZLS blocks. The final thickness of the specimens was set at 0.8 ± 0.01 mm. Spectrophotometric measurements for the translucency were taken against black and white backgrounds. Composite resin tooth-shaded background disks were fabricated in two shades (A1 and A3), as were resin cement disks (opaque and translucent) (n = 11). Next, the ceramic specimens and tooth-shaded backgrounds were connected with glycerin, and baseline measurements were taken. These measurements were used as a reference. Then, the ceramic specimens, cement specimens, and tooth-shaded backgrounds were connected together with glycerin, and a second set of measurements was taken. The CIEDE2000 (ΔE00 ) color formula was used to calculate the translucency and color differences. A Mann-Whitney U test was also performed for the translucency, and a three-way ANOVA (analysis of variance) test was performed for the ΔE00 values (α = .05). RESULTS: The LDS and ZLS groups had similar translucency (P = .055). The ΔE00 values of the specimens were significantly affected by the cement color and tooth-shaded backgrounds in the LDS and ZLS groups (P < .05). Using the opaque cement color resulted in statistically significant differences against the light and dark (A1 and A3) tooth-shaded backgrounds in both the LDS and ZLS groups (P = .022 and P = .006). CONCLUSIONS: The material type did not affect the translucency or final color. However, the cement color did affect the final shade when thin ceramic restorations were used. CLINICAL SIGNIFICANCE: It should be noted that the cement color and tooth-shaded background used may change the final color of thin high translucency ceramic restorations that contain lithium disilicate and zirconia-reinforced lithium silicate.

Effects of the Cervical Marginal Relocation Technique on the Marginal Adaptation of Lithium Disilicate CAD/CAM Ceramic Crowns on Premolars.

AIM AND OBJECTIVE: To evaluate the effect of cervical margin relocation (CMR) for crowns designed using CAD/CAM technology and fabricated from lithium disilicate (e.max, CAD) before and after aging; and to compare the fracture forces and failure type of the tested crowns. MATERIALS AND METHODS: Mesio-occluso-distal(MOD) cavities 1 mm above the cementoenamel junction(CEJ) were prepared on 40 maxillary first premolars. The teeth were divided into four groups. In group A, all cervical margins (CM) were located 1 mm above the CEJ. However, in both mesial and distal proximal boxes of groups B, C, and D, in addition to the MOD cavities, the CMs were extended 2 mm on both sides below the CEJ apically to simulate the CMR technique. In group B, the mesial and distal proximal boxes were filled with flowable composite, while for group C and group D, specimens were filled with composite resin fillings. To simulate the CMR technique, the cavities were filled with composite layers of 3 mm in two increments. Using the CAD/CAM system, 40 standard crowns were prepared on premolars, then cemented using a dual-curing adhesive cement. Assessments of the marginal integrity of interfaces of the proximal boxes of the cemented crowned teeth were recorded. Statistical differences between groups were analyzed using the ANOVA and Bonferroni's posthoc test. RESULTS: The first null hypothesis was accepted since no statistically significant differences were found in marginal integrity before and after aging (p>0.05), while the second was partially rejected since different fractured force values were recorded and a significant difference was detected between group D and group B. The third hypothesis was rejected because the catastrophic fracture rate was the highest among the four groups. CONCLUSION: The implementation of CMR before and after aging had a good effect on the marginal integrity of CM relocation. The CMR technique with resin luting cement of lithium disilicate crowns is effective and recommended for the restoration in deep proximal boxes of premolars or posterior teeth. CLINICAL SIGNIFICANCE: CAD/CAM-generated e. max all-ceramic crowns with composite as the CMR enable the reconstruction of severely destroyed teeth irrespective of the position of the cavity margins.

The efficiency of laser application for debonding laminate restorations manufactured of current CAD-CAM materials with different thicknesses.

BACKGROUND: Using lasers for adhesive restoration removal can be practical and atraumatic. AIMS: The purpose of this study was to investigate Er: YAG laser exposure on debonding the adhesive cementation between enamel and feldspar ceramic, lithium disilicate-reinforced and resin nano ceramic composite laminate restorations. MATERIALS AND METHODS: Vita Cerec Blocs, IPS e.max Computer-aided design (CAD). Computer-aided design and manufacturing (CAD-CAM) in full and Lava Ultimate restorative materials were chosen. The 3 × 3 mm2 standardized, 0.5-mm and 1 mm thick specimens were cemented on an enamel surface. After thermocycling, each material group was randomly divided into laser treated and control (non-laser treated) groups. Shear bond strength test was done with a universal testing machine with crosshead speed 0.5 mm/min. Factorial ANOVA Technique and TUKEY HSD multiple comparison test were used for statistical analyses. Moreover, the surface morphology of the debonded samples and the enamel was observed using a scanning electron microscope. RESULTS: The laser application was found to weaken the SBS values significantly (P < 0.05) for all groups; however, the most dramatic SBS decrease was observed for laser treated IPS e.max at both thicknesses. CONCLUSIONS: Laser treatment can serve as a practical and effective method that eliminates the risk the enamel damage and restoration fracture.

Influence of cleaning methods on the bond strength of resin cement to saliva-contaminated lithium disilicate ceramic.

OBJECTIVES: The aim of the present study was to examine the influence of different cleaning methods on the bond strength of resin cement to saliva-contaminated lithium disilicate ceramic. MATERIALS AND METHODS: Lithium disilicate ceramic specimens (n = 8/group) were etched with 5% hydrofluoric acid (HF) to comprise the control group. After or before saliva contamination, specimens were cleaned with one of five methods: rinsing with water-spray (WS), K etchant GEL (PA), Ivoclean (IC), AD Gel (ADG), or application of a silane coupling agent before immersion in saliva (SCA). Stainless steel rods were bonded to the ceramic with resin cement. The tensile bond strength was measured after 24 h (TC0) and after thermal cycling at 4-60 °C (TC20000). Specimen surfaces were also evaluated using X-ray photoelectron spectroscopy. Data were statistically analyzed using two-way ANOVA and Tukey tests (α = 0.05). RESULTS: Both the cleaning method (p = 0.0001) and storage condition (p = 0.0001) significantly affected the bond strength results. Before or after TCs, no significant differences in bond strength were observed between the control group and the other cleaning groups except for the WS group, which had a significantly lower bond strength than did the PA, IC, ADG, or SCA groups (p < 0.05). The level of nitrogen in the ADG group was almost equal to that in the control group. CONCLUSIONS: WS cleaning did not restore the bond strength of resin cement to saliva-contaminated lithium disilicate ceramic etched with HF, while PA, IC, ADG, and SCA all benefited. CLINICAL RELEVANCE: Lithium disilicate ceramic restorations etched with HF should to be cleaned with ADG after saliva contamination.

Comparison of Fracture Load and Surface Wear of Microhybrid Composite and Ceramic Occlusal Veneers.

PURPOSE: To compare in vitro fracture load, surface wear, and roughness after thermal cycling and cyclic mechanical fatigue loading among cemented microhybrid resin-based composite and ceramic occlusal veneers fabricated at two thicknesses (1.5 and 2.5 mm). MATERIALS AND METHODS: Sixty-four extracted premolars without root canal treatment were prepared and restored with occlusal veneers of two thicknesses (1.5 and 2.5 mm), using four different materials: microhybrid composite (MC), fiber-reinforced microhybrid composite (FMC), heat-pressed lithium disilicate ceramic (HPC), and computer-aided design/computer-aided manufactured lithium disilicate ceramic (CCC). The specimens underwent thermal cycling and cyclic mechanical fatigue loading, and were then subjected to fracture testing, with loads at failure recorded as fracture load. Wear and surface roughness were recorded before and after fatigue loading. Results were analyzed using one-way ANOVA, two-way ANOVA (α = 0.05). RESULTS: All specimens survived thermal cycling and cyclic mechanical fatigue loading. At 1.5-mm thickness, the mean fracture load of FMC was highest (3926.48 ± 556.54 N), while that of CCC was highest (3066.45 ± 559.94 N) at 2.5 mm. Regardless of thickness, the fracture load of CCC was higher than that of HPC (p = 0.004 and p = 0.023). The wear of MC and FMC was significantly higher than those of HPC and CCC (p ≤ 0.001), but was similar in terms of the wear rate of tooth enamel. HPC exhibited the lowest surface roughness after fatigue loading (p ≤ 0.001). CONCLUSION: All tested occlusal veneers exhibited a fracture load considerably exceeding the maximum occlusal force in the posterior dentition. When the attainable space for restoration varies, different occlusal veneer materials should be considered. The surface wear and roughness also need to be considered when selecting materials.

Fracture load of CAD/CAM-fabricated and 3D-printed composite crowns as a function of material thickness.

OBJECTIVES: Indirect CAD/CAM restorations can be fabricated using both subtractive and additive CAD/CAM technology. This study investigated the fracture load of crowns fabricated from three particle-filled composite CAD/CAM materials and one 3D-printed composite material. MATERIALS AND METHODS: Lava Ultimate, Cerasmart and Brilliant Crios were used as particle-filled composite CAD/CAM material and els-3D Harz as 3D-printed composite material. For each group, crowns with three different material thicknesses (0.5/1.0/1.5 mm) were fabricated. Control group was composed of ceramic-based CAD/CAM materials e.max CAD and Enamic. Totally, n = 180 crowns were fabricated and adhesively seated on SLA fabricated dies. Thermomechanical loading and fracture testing were performed. The data for fracture loading force were statistically analyzed by two-way ANOVA followed with multiple comparisons by post hoc Tukey's test (α = 0.05). RESULTS: In contrast to ceramics, all particle-filled composite crowns with 0.5-mm thickness survived fatigue testing. Forces varied statistically significantly. Brilliant Crios showed highest maximum loading force with 1580.4 ± 521.0 N (1.5 mm). Two-way ANOVA indicated that both the material and the thickness affected the fracture load (p < 0.05). CONCLUSIONS: Particle-filled composite resin CAD/CAM materials may have advantageous material characteristics compared to ceramic CAD/CAM materials for minimal restoration thicknesses. CLINICAL RELEVANCE: Composite-based CAD/CAM materials may offer new possibilities in minimally invasive restorative treatment concepts.

Fully digital workflow, integrating dental scan, smile design and CAD-CAM: case report.

BACKGROUND: This report is a presentation of a clinical case that follows a full digital workflow. CASE PRESENTATION: A 47-year old man presented with pain in the TMJ (temporomandibular joint) and whose aesthetic concern was having a chipped maxillary central incisor veneer. The concern was solved following a fully digital workflow: it was applied the digital smile design protocol, as well as CAD-CAM monolithic lithium disilicate ceramic veneers and crowns (following a minimal invasive preparation approach). The aim of this rehabilitation was to solve a loss of vertical dimension, subsequent aesthetics and temporomandibular joint disorders. CONCLUSION: Thanks to the evolution of technology in dentistry, it is possible to do a full digital case and solve problems such as loss of vertical dimension successfully. Nevertheless, more clinical studies are needed to obtain consistent results about the digital work flow compared to the conventional technique in loss of vertical dimension cases.

Microtensile Bond Strength of a Resin Cement to Silica-Based and Y-TZP Ceramics Using Different Surface Treatments.

PURPOSE: To evaluate the effects of different surface treatments on the microtensile bond strength (µTBS) of bonding between resin cement and lithia or zirconia-based ceramics using an in vitro study. MATERIALS AND METHODS: Three zirconia ceramic blocks (IPS e.max ZirCAD) and three lithium disilicate ceramic blocks (IPS e.max CAD) were sintered and duplicated in resin composite. The zirconia specimens underwent various treatments (n = 1): (i) Sandblast + primer (ZiSa); (ii) sandblast + laser irradiation + primer (ZiSaLa); or (iii) laser irradiation + primer (ZiLa). The lithium disilicate specimens also underwent various treatments: (i) sandblast + HF + silane (LiSaE); (ii) sandblast + silane (LiSa); or (iii) sandblast + laser irradiation + silane (LiSaLa). The ceramic-composite blocks were cemented with resin cement and cut to produce bars with approx. 1 mm2 bonding areas. The specimens were thermocycled, and bond strength tests were performed in a universal testing machine. The fracture type was determined by observing the fractured surface under a stereomicroscope. The mean bond strengths of the specimens were statistically analyzed using one-way ANOVA and Duncan's tests (α = 0.05). RESULTS: Mean comparison of the µTBS showed no significant difference between LiSaE and LiSa (p > 0.05), but significant differences between LiSaE and other groups (p ≤ 0.01). No significant differences were found between the ZiSaLa and ZiSa groups (p > 0.05). The modes of failure in all groups were mostly adhesive (57% to 80%). The mean bond strengths in laser-irradiated ceramics were significantly lower than those from other surface treatments. All ZiLa specimens debonded before testing (pretest failure). CONCLUSIONS: Lithium disilicate ceramic surface treated with a combination of sandblasting and silane application provided a bond strength comparable to that provided by sandblasting in combination with acid etching and applying silane. Groups treated with laser irradiation had significantly lower bond strengths than other groups.

Comparative Evaluation of Flexural Strength of Nano-zirconia-integrated Pressable Feldspathic and Lithium Disilicate Ceramics.

AIM: The purpose of the study was to evaluate and compare the flexural strength of nano-reinforced zirconia feldspathic porcelain, lithium disilicate ceramics, and zirconia. MATERIALS AND METHODS: Ten bar-shaped specimens of computer-aided design (CAD)/computer-aided manufacturing (CAM) zirconia, reinforced feldspathic porcelain, and reinforced lithium disilicate were fabricated in accordance to International Organization for Standardization (ISO 6872; n = 10). Feldspathic porcelain and lithium disilicate ceramic specimens were reinforced with 5, 10, 15, and 20% of zirconia nanoparticles through a customized technique. The specimens were subjected to three-point flexural strength test using universal testing machine (UTM) and examined for crack propagation using a scanning electron microscope (SEM). Oneway analysis of variance (ANOVA) and Tukey test were used to analyze the data (p < 0.05). RESULTS: The flexural strength of feldsphatic porcelain increased with the increase in the concentration of zirconia particles. The mean flexural strength of 5, 10, 15, and 20% nano-zirconia-incorporated lithium disilicate was 93.8, 97.1, 100.6, and 100.8 MPa respectively, and was lower than the control group (221.7 MPa). A significant difference in the flexural strength was found with the incorporation of nano-zirconia particles. CONCLUSION: The flexural strength of zirconia-integrated feld-spathic porcelain increased and lithium disilicate ceramics decreased with the nano-zirconia reinforcement. CLINICAL SIGNIFICANCE: The simplified approach of reinforcing feldspathic porcelain with zirconia nanoparticles can be adapted in clinical situations of higher masticatory forces.

Effect of Erbium-yttrium, scandium, gallium and garnet (Er-YSGG) laser on the bond strength of lithium disilicate ceramics.

OBJECTIVES: To assess the bond strength of LD ceramics with resin composite material and surface conditioning using Er: YSGG laser and HF acid. METHODS: Thirty LD ceramic (Emax, Ivoclar vivadent) discs were prepared using hot pressing technique and treated with hydroflouric acid (Group-1-HF acid) (9%) (n=10) and Er- yttrium, scandium, gallium and garnet laser (Group-2-ER-YSGG laser) (Waterlase iPlus, 10 Hz and power of 0.5 W, pulse duration of 230 µs) (n=10). Ten specimens were left untreated to be included as controls (Group-3-Control). All the specimens were treated with Adper Single Bond adhesive (3MESPE, St. Paul, MN, USA). Multicore buildups (3mmx3mm) were performed using a rubber mold on the ceramic surfaces and cured using LED light-curing unit for 140 sec. All specimens were tested using shear bond test and failure modes were assessed with a stereomicroscope and scanning electron microscope. Data was analysed using ANOVA and Tukey Kramer multiple comparisons test. RESULTS: The maximum and minimum shear bond strength values were achieved in HF Acid specimens (Group-1) (28.15±4.72 MPa) and control specimens (13.47± 3.14 MPa) respectively. Specimens treated with HF acid showed significantly higher bond strength in comparison to laser treated and control specimens (p<0.01). Laser treated specimens had significantly higher bond strength as compared to controls (p<0.01). CONCLUSIONS: Hydrofluoric (HF) acid treatment showed significantly better outcomes than YSGG laser surface treatment.

Fracture resistance and failure modes of lithium disilicate or composite endocrowns.

PURPOSE: The aim of this study was to determine the fracture strength of endocrowns made of lithium disilicate ceramic and two different indirect resin composites. MATERIALS AND METHODS: Forty human mandibular molars were randomly separated into four groups (n = 10 in each group) - Group IN: control group, Group IPS: endocrowns made of lithium disilicate ceramic (IPS e.max CAD, IvoclarVivadent, Schaan, Liechtenstein); Group SL: Endocrowns made of Solidex microhybrid composite (Shofu, Ratingen, Germany); and Group GR: Endocrowns made of Grandia microhybrid composite (GC Europa, Leuven, Belgium). In all of the groups, dual-cure resin cement (Relyx Ultimate Clicker, 3M ESPE, St. Paul, MN, USA) was used to cement the endocrowns. All of the teeth were subjected to fracture by means of a universal testing machine (Instron), and compressive force was applied. The failure type and location after fracture were classified. The data were analyzed using one-way ANOVA, Tukey's post hoc test, and Chi-square test (P < 0.05). RESULTS: Group IPS showed significantly higher fracture strength than Groups SL and GR (P < 0.05). There was no significant difference between the SL and GR groups (P > 0.05). In Group SL, 80% of the specimens exhibited favorable fractures; also, 60% of the specimens exhibited favorable fracture in group GR, and only 10% of the specimens exhibited favorable fracture in group IPS. CONCLUSIONS: The lithium disilicate ceramic endocrowns exhibited higher fracture resistance than indirect composite groups. Both of the composite endocrowns showed more favorable failure than the lithium disilicate ceramic endocrowns.

Chair-side generated posterior monolithic lithium disilicate crowns: clinical survival after 6 years.

OBJECTIVES: The objective of this prospective clinical study was to evaluate the clinical performance of chair-side generated monolithic lithium disilicate crowns after 72 months. MATERIALS AND METHODS: Forty-one posterior full contour crowns made of lithium disilicate ceramic were inserted in 34 patients with a chair-side CAD/CAM technique. One crown per patient was randomly selected for evaluation at baseline, 6, 12, 24, 36, 48, 60 and 72 months according to the modified US Public Health Service criteria. RESULTS: After a mean examination time of 73.2 months (SD ± 1.7 months), 25 crowns were available for re-examination. Within the observation period, three failures occurred due to one crown fracture after 2.9 years, an abutment fracture after 6.0 years, and one severe endodontic problem after 6.1 years. One lithium disilicate crown showed a loss of retention after 2 years but could be reinserted. There were two events of caries below the crown margin, one after 24 and another one after 48 months. Both teeth received cervical adhesive composite fillings. Two abutment teeth changed their sensibility perception from positive to negative within the first 13 months. The failure-free rate was 87.6%, and the complication-free rate was 70.1% after 6 years according to the Kaplan-Meier analysis. CONCLUSIONS: Due to the fact that there was only one severe technical complication and the severe biological complications were in a normal range, the clinical performance of monolithic lithium disilicate crowns in the posterior region was completely satisfying. CLINICAL RELEVANCE: The chair-side application of monolithic lithium disilicate crowns can be recommended.

Fracture Resistance of Molar Crowns Fabricated with Monolithic All-Ceramic CAD/CAM Materials Cemented on Titanium Abutments: An In Vitro Study.

PURPOSE: To assess the fracture resistance of single-tooth implant-supported crown restorations made with different CAD/CAM blocks. MATERIALS AND METHODS: Thirty-six titanium abutments were put on dental implant analogs (Mis Implant). For each of three test groups (n = 12/group), implant-supported, cement-retained mandibular molar single crowns were produced. Crowns were made of lithium disilicate glass (LD) IPS e.max CAD, feldspathic glass ceramic (FEL) Vita Mark II, and resin nano-ceramic (RNC) Lava Ultimate. The crowns were cemented with self-adhesive resin cement RelyX Unicem 2. After chewing cycling, crowns were tested to failure in a universal testing machine. Fracture values were calculated as initial (F-initial) and maximum fracture (F-max). RESULTS: The study groups were ranked, in order of having highest value, (LD > FEL) > RNC for F-initial load value and (LD > RNC) > FEL for F-max load value. This demonstrated that there was no parallel change in the F-initial and F-max values presenting the fracture resistance of specimens. CONCLUSIONS: There was no accordance between the F-initial and F-max values of the LD, RNC, and FEL after chewing simulation with thermocycling resembling 5 years of clinical functional use. LD had the highest fracture resistance during the fracture test. RNC had low fracture resistance; however, it had considerably high fracture resistance during the fracture test. FEL had considerably low fracture resistance values.

Durability and Weibull Characteristics of Lithium Disilicate Crowns Bonded on Abutments with Knife-Edge and Large Chamfer Finish Lines after Cyclic Loading.

PURPOSE: The aim of this study was to evaluate the durability of lithium disilicate crowns bonded on abutments prepared with two types of finish lines after long-term cyclic loading. MATERIALS AND METHODS: Pressed lithium disilicate all-ceramic molar crowns were bonded (Variolink II) to epoxy abutments (height: 5.5 mm, Ø: 7.5 mm, conicity: 6°) (N = 20) with either knife-edge (KE) or large chamfer (LC) finish lines. Each assembly was submitted to cyclic loading (1,200,000×; 200 N; 1 Hz) in water and then tested until fracture in a universal testing machine (1 mm/min). Failure types were classified and further evaluated under stereomicroscope and SEM. The data (N) were analyzed using one-way ANOVA. Weibull distribution values including the Weibull modulus (m), characteristic strength (0), probability of failure at 5% (0.05), 1% (0.01), and correlation coefficient were calculated. RESULTS: Type of finish line did not significantly influence the mean fracture strength of pressed ceramic crowns (KE: 1655 ± 353 N; LC: 1618 ± 263 N) (p = 0.7898). Weibull distribution presented lower shape value (m) of KE (m = 5.48; CI: 3.5 to 8.6) compared to LC (m = 7.68; CI: 5.2 to 11.3). Characteristic strengths (0) (KE: 1784.9 N; LC: 1712.1 N) were higher than probability of failure at 5% (0.05) (KE: 1038.1 N; LC: 1163.4 N) followed by 1% (0.01) (KE: 771 N; LC: 941.1 N), with a correlation coefficient of 0.966 for KE and 0.924 for LC. Type V failures (severe fracture of the crown and/or tooth) were more common in both groups. SEM findings showed that fractures occurred mainly from the cement/ceramic interface at the occlusal side of the crowns. CONCLUSION: Lithium disilicate ceramic crowns bonded onto abutment teeth with KE preparation resulted in similar fracture strength to those bonded on abutments with LC finish line. CLINICAL SIGNIFICANCE: Pressed lithium disilicate ceramic crowns may not require invasive finish line preparations since finish line type did not impair the strength after aging conditions.

Effects of ceramic thickness, ceramic translucency, and light transmission on light-cured bulk-fill resin composites as luting cement of lithium disilicate based-ceramics.

PURPOSE: To assess the effects of ceramic thickness, ceramic translucency, and light transmission on restorative composites used as luting cement for lithium disilicate-based ceramics. METHODS: Four luting types of cement were tested (n=8); a dual-cured resin cement (Multilink N), a light-cured conventional flowable composite (Tetric N-Flow), and two light-cured bulk-fill flowable composites (Tetric N-Flow Bulk Fill and X-tra base). The 20 s- or 40 s-light (1000 mW/cm2) was transmitted through 1- or 2-mm-thick high- or low-translucency (HT- or LT-) ceramic discs (IPS e.Max press) to reach the 1-mm-thick luting cement. Light transmitted to cement without ceramic served as a control. Vickers hardness number (VHN), flexural strength (FS), fractography, and degree of conversion (DC) were evaluated. One-way and multi-way analysis of variance was conducted to determine the effects of factors on VHN and FS. RESULTS: Ceramic thickness, light transmission time, and cement type significantly affected the VHN of the luting cement (P < .000). Only Multilink N (LT- and HT-1mm) and Tetric N-Flow (HT-1mm) reached 90% VHN of corresponding control by 20 s-light transmissions, but Tetric N-Flow exhibited lowest VHN and approximately 1/3-1/2 VHN of Multilink N (P < 0.05). X-tra base expressed superior physicochemical properties to Tetric N-Flow Bulk Fill (P < 0.05) and reached >90% VHN of control in all conditions with 40 s-light transmissions except for LT-2 mm. DC, FS, and fractography supported these findings. CONCLUSIONS: The light-cured bulk-fill composite served as a luting cement for lithium-disilicate-based ceramics in a product-dependent manner. Light transmission time is crucial to ensure sufficient luting cement polymerization.

Load-bearing capacity, internal accuracy and time-efficiency of heat-pressed, milled and 3D-printed lithium disilicate ultra-thin occlusal veneers.

OBJECTIVES: The primary aim of this in vitro study was to compare the load-bearing capacity of lithium disilicate occlusal veneers, fabricated via different manufacturing processes. Secondary objectives included assessing internal accuracy and production time-efficiency. METHODS: Four fabrication methods for ultra-thin lithium disilicate occlusal veneers on extracted human molars with simulated erosive defects were compared (n = 20/group): CAM: milled lithium disilicate (IPS e.max CAD); HPR: heat-pressed lithium disilicate (IPS e.max Press) out of a milled PMMA template (Ddpmma CAST); 3DP: 3D-printed lithium disilicate (experimental lithium disilicate); PTE: heat-pressed lithium disilicate (IPS e.max Press) out of a 3D-printed template (SilaPrint cast). Internal accuracy was measured prior to thermo-mechanical aging, followed by static loading to measure the load-bearing capacity (Fmax). Fabrication time (time-efficiency) was also recorded. Statistical analysis was performed using the Kruskal-Wallis (KW) test. RESULTS: No statistically significant differences were found in median load-bearing capacities (Fmax) between the groups (KW p = 0.5902): CAM 1821 N, HPR 1896 N, 3DP 2003 N, PTE 1687 N. Significant differences were found in internal accuracy between the groups that employed printing processes (3DP, PTE) and all other groups in margins (p < 0.001), cusps (p < 0.0018), and fossae (p < 0.0346). The time-efficiency measurements indicated an increase in fabrication time, starting from CAM 67.2 ± 5.8 min, followed by HPR 200.8 ± 33.0 min, PTE 289.2 ± 38.7 min, and peaking with the highest duration observed for 3DP 701.6 ± 8.1 min. SIGNIFICANCE: The fabrication method of ultra-thin lithium disilicate occlusal veneers does not significantly impact their load-bearing capacity, but affects the clinical fit and adaptation of the veneers.

A Study to Evaluate the Effect of Cleaning Solutions on Shear Bond Strength of Resin Cement to Saliva-Contaminated Lithium Disilicate (LDS) Ceramic.

BACKGROUND: One of the greatest benefits of contemporary restorative dentistry is the creation of fixed partial dentures. The retention and durability of the fixed partial dentures may be improved by using a variety of tooth preparation methods, surface treatments, and luting resins. AIM: To measure the shear binding strength of resin cement to saliva-contaminated lithium disilicate (LDS) ceramic after being exposed to various cleaning treatments. METHODOLOGY: Over 30 LDS samples were examined. In Group 1, a cleansing solution comprising 15% zirconium oxide (Ivoclean) was employed for a duration of 20 s. This was succeeded by a rinsing phase lasting 15 s utilizing deionized water, followed by a 15-s period for drying. Subsequently, a final stage of air drying was conducted over a span of 15 s. In contrast, Group 2 underwent a washing procedure of 20 s involving a cleansing solution containing 30% sodium silicate. This was then ensued by a rinsing interval of 15 s with deionized water, succeeded by an air-drying process spanning 15 s. After applying cleaning solutions to the surface and adhering the specimens to the composite blocks using resin cement Multilink Automix (Ivoclar Vivadent, Schaan, Liechtenstein), the shear bond strength was assessed. RESULTS: Using a 30% sodium silicate solution (Group 2), we were able to get the highest mean shear bond strength value after saliva-contaminated LDS. Group 1, 15% zirconium oxide (Ivoclean) had the weakest decontamination agents as measured by mean shear bond strengths. The shear bond strength values of the two groups were found to vary significantly between individuals using the independent sample t-test. LDs ceramic cleaned with a 30% sodium silicate solution had a higher shear bond strength than ceramic cleaned with Ivoclean (p<0.05). CONCLUSION: The application of a 30% sodium silicate solution rendered the highest shear bond strength for saliva-contaminated LDS ceramic. In comparison, ceramic cleaned with Ivoclean exhibited notably lower shear bond strength values. The outcome of this investigation highlights the potential of diverse cleaning agents in influencing the adhesive qualities of resin cement, thereby contributing to the enhancement of fixed partial denture durability and efficacy.