Lithium Disilicate Glass-ceramic Crowns Research Articles

Optimization of lithium disilicate glass-ceramic crowns: finish line, scanning and processing methods.

To investigate the optimal combination of factors (finish line, scanning, and ceramic processing) to achieve the best values of both adaptation and fracture load of lithium disilicate (LD) crowns. Abutment preparations, chamfer (C) and rounded shoulder (S), were produced with a dentin analog material and scanned with extraoral (E) or intraoral (I) scanners. The captured images were processed using CAD software to design a premolar. Blocks of LD were milled using a CAD/CAM system (Cad). For the pressing technique (Pre), crowns were first 3D printed using a polymeric material, and a heat-pressing protocol was performed. The design of experiments was used to plan four experimental groups (n = 10): (1) CadCI; (2) CadSE; (3) PreCE; and (4) PreSI. Two dependent variables were analyzed: (1) adaptation, measured using the replica technique; and (2) fracture load of the cemented crowns. Fractographic analysis was performed. Data were analyzed using ANOVA and regression statistical analyses. There was no significant effect of scanning method or finish line for the gap thickness in the different regions. For the processing method, Cad resulted in larger gap thickness in the occlusal, axial angle, and marginal areas and smaller gap in the axial area (P < .001). There was no effect of the investigated factors on the fracture load. However, PreCE was considered to be the optimal design, as it achieved 100% of the desired fracture load (> 1,000 N) and 40% of the adaptation (< 200 μm). The optimal combination of factors for all-ceramic crowns is chamfer abutment preparation, extraoral scanning, and the press technique (combined with 3D printing).

Clinical outcome of three different types of posterior all-ceramic crowns. A 3-year follow-up of a multicenter, randomized, controlled clinical trial.

To assess and compare the clinical outcomes of three different types of all-ceramic posterior monolithic tooth-supported crowns. A total of 71 patients received 90 all-ceramic crowns randomized to be either high-translucency zirconia (ZC), high-translucency zirconia with a partial buccal veneer (ZC-V), or lithium disilicate glass-ceramic (LDS). All treatments were performed by four general dentists. Choice of material was blinded. Baseline and subsequent annual evaluation were based on modified California Dental Association (CDA) criteria. A questionnaire was used to include patient-reported outcomes and to compare them to the crown quality rating performed by dentists. A total of 66 patients with 84 crowns were examined after 3 years. The survival rate was 98.8%. No crowns fractured during the observation period. One ZC-V crown failed due to loss of retention, and three complications were noted: loss of retention occurred in one ZC crown, and two ZC crowns needed to be endodontically treated. There was no significant difference between the different crowns regarding marginal integrity, surface, or anatomical form. Both patients and examining dentists rated the crowns favorably regarding esthetics, patients more than dentists. Posterior lithium disilicate glass-ceramic crowns and translucent zirconia crowns with or without a partial buccal veneer show excellent and promising clinical outcomes from a short-term perspective. Patients and dentists rate the restorations favorably concerning esthetics and function.

Influence of thermal aging on the marginal integrity of computer aided design/computer aided manufacturing fabricated crowns

Background/purposeThe adaptation and marginal integrity of computer-aided designed and computer-aided manufactured (CAD/CAM) crowns after exposure to thermal aging need to be investigated. The present in-vitro study was designed to investigate the marginal integrity of CAD/CAM fabricated crowns cemented on extracted teeth after thermocycling aging. Materials and methodsTwenty-six newly extracted human premolars were prepared for full-coverage CAD/CAM crowns and were divided into two groups (leucite-reinforced glass-ceramics and lithium disilicate glass-ceramics). Both crowns’ groups were cemented using dual curing resin cement. All specimen margins were measured for marginal integrity using an imaging system 24 h post cementation; then after 1, 3, and 5 estimated clinical years (10,000, 30,000, and 50,000 thermocycles). Two-way ANOVA analysis were used to determine whether the mean value difference is significantly different (ɑ = 0.05). ResultsThe average margin gaps recorded for leucite-reinforced glass-ceramic crowns were: 82.61 μm initial, and 91.02 μm after 5 estimated clinical year). For the lithium disilicate glass-ceramic crowns, the average margin gaps recorded were: 100.01 μm initial, and 120.21 μm after 5 estimated clinical year. During all measuring intervals, the leucite-reinforced glass-ceramic crown group had a lower marginal discrepancy. No statistically significant difference between the two groups was recorded. ConclusionAfter being subjected to thermocycling, both CAD/CAM ceramic crowns, exhibited an increase in their marginal discrepancy; the difference was within the accepted clinical range.

Effect of Repeated Heat-Pressing on Marginal and Internal Fit of Lithium Disilicate Glass Ceramic Crowns after Thermo-Mechanical Fatigue

Purpose: To evaluate the effect of repeated heat-pressing on marginal and internal fit of lithium disilicate glass ceramic crowns. Materials and Methods: A freshly extracted caries free human maxillary 1st premolar was prepared according to standardized preparation for all-ceramic crown restoration. The preparation was duplicated to produce thirty epoxy resin dies. The resin dies were divided into three groups (n=10) according to the number of heat-pressings of IPS e.max Press (Shade A2, LT) used for crowns construction. Group 1: Crowns constructed from freshly pressed ingots, Group 2: Crowns constructed from leftover repressed buttons for 1st time, and Group 3: Crowns constructed from leftover repressed buttons for 2nd time. The constructed crowns were cemented to their corresponding resin dies using adhesive resin cement, then samples were subjected to the thermo-mechanical fatigue with a ROBOTA chewing simulator. Each cemented ceramic crown was vertically sectioned bucco-lingually into 2 sections. Marginal, axial, and occlusal gaps were measured at seven defined points on each section using digital microscope. Data were tabulated and statistically analyzed using One-way ANOVA and Pearson’s correlation tests. The significance level was set at P<0.05. Results: The largest marginal and internal gap values were recorded in Group 1, while the lowest marginal and internal gap values were recorded in Group 3. Statistical analysis revealed that there were no significant differences in marginal and internal gaps between the tested groups (P<0.05). Conclusions: Repressing and thermomechanical fatigue have no significant effect on marginal and internal fit of IPS e.max Press crowns.

Effect of Repeated Heat-Pressing on Color and Translucency of Lithium Disilicate Glass Ceramic Crowns

Purpose: To evaluate the effect of repeated heat-pressing and thermomechanical fatigue on color and translucency of lithium disilicate glass ceramic crowns. Materials and Methods: A freshly extracted human maxillary right 1st premolar was prepared according to standardized preparation for all-ceramic crown restoration. The preparation was duplicated to produce thirty epoxy resin dies. The resin dies were divided into three groups (n=10), according to the number of heat-pressings of IPS e.max Press used for crowns construction. Group 1: Control group using freshly pressed ingots, Group 2: Repressed 1 using leftover repressed buttons for 1st time, and Group 3: Repressed 2 using leftover repressed buttons for 2nd time. Thirty IPS e.max Press crowns were fabricated by heat-pressing technique. The constructed crowns were cemented by adhesive resin cement. Color and translucency were measured after cementation by X-Rite Reflective Spectrophotometer. Then samples were subjected to the thermo-mechanical fatigue with a ROBOTA chewing simulator, simulating 6 months chewing conditions. After thermo-mechanical fatigue, color and translucency were measured by X-Rite Reflective spectrophotometer. Results: IPS e.max Press showed no statistically significant color change after repressing and thermomechanical fatigue. Regarding translucency, IPS e.max Press showed no statistically significant difference in translucency after repressing, however, there was a statistically significant decrease in translucency after thermomechanical fatigue. Conclusions: Repressing and thermomechanical fatigue have no significant effect on color of IPS e.max Press crowns. Repressing has no significant effect on translucency, however, thermomechanical fatigue has a significant effect on translucency of freshly pressed and repressed e.max Press crowns.

Six-year clinical performance of lithium disilicate glass-ceramic CAD-CAM versus metal-ceramic crowns.

To assess the clinical performance of monolithic CAD-CAM lithium disilicate glass-ceramic (LDGC) crowns and metal-ceramic (MC) crowns provided by predoctoral students. This study also assessed the effects of patient and provider-related factors on their clinical performance as well as patient preference for these types of crowns. Twenty-five patients who received 50 crowns (25 LDGC CAD-CAM and 25 MC) provided by predoctoral students were retrospectively examined. LDGC CAD-CAM crowns were milled in-house using the CEREC Bluecam system and cemented with either RelyX Unicem or Calibra Esthetic resin cements. MC crowns were cemented with RelyX Unicem cement. Clinical assessment of the crowns and the supporting periodontal structures were performed following the modified California Dental Association (CDA) criteria. Patients' preference was recorded using a visual analog scale (VAS). The results were statistically analyzed using log-rank test, Pearson Chi-squared test and Kaplan-Meier survival analysis. Twelve complications were observed in the MC crown group (9-esthetic, 2-technical and 1-biological). In comparison, 2 complications in the LDGC CAD-CAM crown group were observed (1-technical and 1-esthetic). The 6-year cumulative survival rates for MC crowns and LDGC CAD-CAM were 90.8% and 96%, respectively, whereas the success rates were 83.4% and 96%, respectively. Overall, patients preferred the esthetic outcomes of LDGC CAD-CAM crowns over MC crowns. The high survival and success rates, low number of complications, and the high level of patients' acceptance of monolithic LDGC CAD-CAM crowns lend them well as predictable and viable alternatives to the "gold standard" MC crowns.

Weak adhesion between ceramic and resin cement impairs the load-bearing capacity under fatigue of lithium disilicate glass-ceramic crowns

ObjectiveTo evaluate the fatigue behavior of lithium disilicate crowns with a simplified anatomy against progressive cement/ceramic debonding scenarios. Materials and methodsLithium disilicate crowns were fabricated via CAD/CAM and luted onto a dentin analogue material using resin cement following the manufacturer's instructions. Then, the different crown regions were isolated with paraffin oil for the absence of chemical adhesion according to four experimental groups (n = 15): Shoulder; Shoulder + Axial; Fully isolated; and Control (no insulation/fully bonded). Load to failure tests (n = 3) were run to determine cyclic fatigue parameters, and the specimens were subsequently submitted to a cyclic fatigue test (n = 12) (initial load 200 N for 5000 cycles, step 100 N, 15,000 cycles/step, frequency 20 Hz) until cracks were observed, and later fracture. The data were analyzed by Kaplan-Meier + Mantel-Cox post-hoc tests for both outcomes (cracks and fracture). Fractographic, cross-sectional surface, and finite element (FEA) analyzes were performed. ResultsWhen it comes to crack occurrence when the chemical adhesion to the occlusal surface is compromised, there is worsening (p < 0.05) in fatigue behavior compared to groups where the occlusal portion of the crown is still bonded. Considering fracture occurrence, there was no difference (p > 0.05) among the tested groups. All cracks occurred in the occlusal portion, first as a radial crack at the ceramic intaglio surface, and posteriorly unleashing a Hertzian cone crack at the top surface, resulting in fractures on the frontal walls. The interface analysis showed no interference of the insulating agent. FEA showed that as the isolated areas increased, there was also an increase in both tensile and shear stresses concentration in the crown and in the cement layer. ConclusionThe chemical adhesion between cement and ceramic is essential for better fatigue behavior of lithium disilicate crowns with a simplified anatomy, especially in the occlusal portion, but the restoration performance is impaired when such adhesion is compromised. There is an increase in crown and cement stress concentration with the progressive loss of chemical bonding of the crown's walls.

Patient satisfaction and clinical assessment of surface roughness and wear of enamel antagonists for polished versus glazed posterior lithium disilicate glass ceramic crowns

To compare surface roughness of glazed versus polished lithium disilicate crowns as well as wear of enamel antagonists. Methodology: Twenty-two full coverage crowns were fabricated for posterior teeth. Scaling and polishing was performed for all the patients one week prior to preparation. The patients were divided into two groups according to crown finishing. Group 1(control group) fabricated from IPS e.max glazed crowns and Group 2 (intervention group) fabricated from IPS e.max polished crowns. The preparation was standardized with supra-gingival, chamfer finish line for all teeth. Fabrication of the crowns was done using lost wax press technique. The restorations were glazed with e.max ceram glazing liquid; an even layer was applied on the entire surface of the crown using a brush. Polishing was performed using EVE abrasive rubbers. Polishing of each crown was performed with rubbers of three different grains, beginning with the most abrasive one (light crimson) for shaping, then an intermediate one (crimson) for pre polishing, and the last, a less abrasive one (yellow)for high shine polishing. Self-adhesive cement was used for both groups. Roughness of crowns as well as opposing teeth wear were measured using non contact 3D profilometer, patient satisfaction was evaluated in the form of questionnaire.

The Structural Integrity and Fracture Behaviour of Teeth Restored with PEEK and Lithium-Disilicate Glass Ceramic Crowns.

Polyetheretherketone (PEEK) is a unique polymer material which has recently been introduced to dentistry. This study aimed to assess the structural integrity of PEEK as a posterior tooth crown and compared it with ceramic-based material. A total of 31 monolithic CAD-CAM PEEK (JuvoraTM, Strumann, Andover, MA, USA) crowns and 31 lithium disilicate (IPS e.max®CAD, Voclar Vivadent AG, Liechtenstein) crowns were created and cemented on dentin-like teeth (AlphaDie®MF, Schütz Dental GmbH, Rosbach, Germany) in a precise procedure mimicking the physical and mechanical properties of natural teeth and periodontal ligaments. A static compressive strength test using a universal testing machine and a dynamic fatigue test using a chewing simulator machine were used until crown failure to assess the fracture behaviour by mode of fracture (fractographic analysis) and 3D digital subtraction analysis. The results showed that PEEK has a greater fracture resistance than IPS e.max®CAD by 2060 N to 703 N. Additionally, in fatigue limit, IPS e.max®CAD showed a constant failure under 2.0 Kg (=320 N) before 5000 chewing cycles while PEEK survived at a significantly higher load > 11 Kg (930 N). Furthermore, PEEK showed a continued survival at >1,250,000 cycles while the mean fatigue life of IPS e.max®CAD was around 133,470 cycles. PEEK illustrated a significantly less catastrophic failure mode with some plastic deformation at the fractographic stereomicroscope and in the 3D digital subtraction analysis. Using PEEK for crowns looks very promising, however, further clinical studies are required to assure this study’s results.

Do resin cement viscosity and ceramic surface etching influence the fatigue performance of bonded lithium disilicate glass-ceramic crowns?

ObjectiveTo assess the effects of a resin cement in high and low viscosity and distinct conditioning of the intaglio surface of lithium disilicate glass-ceramic crowns on fatigue performance of the crowns. MethodsProsthetic preparations (full-crown) in resin epoxy and crowns in lithium disilicate glass-ceramic were machined and allocated considering 2 factors (n = 10): “surface treatment” (HF – 5% hydrofluoric acid etching, followed by silane application; or E&P–self-etching ceramic primer) and “resin cement” (high or low viscosity). The preparations were etched with 10% hydrofluoric acid and an adhesive was applied. The intaglio surfaces of the ceramic crowns were treated as aforementioned (HF or E&P) and luted with high or low viscosity. The bonded sets were subjected to fatigue testing (step-stress approach: initial load of 200 N, step-size of 50 N, 10,000 cycles/step, 20 Hz) and complementary analyses (fractographic, topographic, and cross-sectional bonded interfacial zone analyses) were performed. ResultsTreatment with HF and silane with high viscosity resin cement (955 N/156,000 cycles) and E&P with low viscosity resin cement (1090 N/183,000 cycles) showed the best fatigue performance (statistical similarity between them). The failures originated from defects of the cement-ceramic interface, and the HF treatment induced a more pronounced topographical alteration. SignificanceDistinct topographical patterns from the HF and E&P treatments induced better fatigue results for the specific viscosity of the resin cement. Therefore, the fatigue performance depended on the existing topography, type of intaglio surface’s defects/irregularities after surface treatment, and how the luting agent filled the irregularities.

EFFECT OF A NOVEL CERAMIC SURFACE TREATMENT ON THE RETENTION OF LITHIUM DISILICATE CROWNS BONDED WITH TWO DIFFERENT LUTING APPROACHES AN INVITRO STUDY

Aim: to evaluate the effect of the novel one step ceramic surface treatment on the retention of lithium disilicate crowns cemented with two different luting approaches (self-etch and self- adhesive resin cements) compared to the conventional surface treatment technique. Materials and methods: 28 extracted molar teeth were prepared to receive full coverage lithium disilicate glass ceramic crowns with lateral projections for pull out test. The crowns were divided into 2 main groups according to the surface treatment applied, Group 1: conventional surface treatment by hydrofluoric acid followed by silane coupling agent(HF+silane), Group 2: the new self-etching ceramic primer Monobond etch and prime(MEP). Each group was subdivided into 2 subgroups according to cementation protocol: In Subgroup A crowns were bonded using self- etch resin cement (Rely X Ultimate) while in subgroup B, crowns were bonded using self- adhesive resin cements (Rely X U200). Crowns were tested for retention using pull out test until failure occurred. Results: Group 2 showed statistically insignificant higher retention mean value (204.63±35.30 N) than Group 1(196.21±39.76 N), while subgroup A (265.75±49.35 N) showed statistically significant higher retention mean value than subgroup B (135.09±25.71 N). Subgroup 2A (MEP and Rely X Ultimate) had the highest bond strength (267.42 ±40.92 N) followed by 1A (HF+ silane and Rely X Ultimate), 2B (MEP and Rely X U200), 1B(HF+ silane and Rely X U200). Conclusion: Self-etching ceramic primer MEP is strongly recommended to replace conventional surface treatment. Self-etching ceramic primer(MEP) with self-etch resin cement provided the highest bond strength.

Effect of Thermo-Mechanical Aging and Repressing on Fracture Resistance of Lithium Disilicate Crowns

Objective: The recycling of heat pressed lithium disilicate glass-ceramic leftover material has been reported to be done by dental laboratories. The effect of this procedure on the fracture resistance of single crowns is unknown, especially when it is functioning inside the oral cavity with subsequent exposure to temperature changes and cycles of mastication. Material and Methods: A total of 28 lithium disilicate glass-ceramic crowns (IPS emax Press) were constructed and randomly assigned into two groups (n = 14); Group (P): Included crowns fabricated from new e.max ingots. Group (R): Included crowns fabricated from repressed e.max buttons. Specimens of each group were divided into two equal subgroups (n = 7) according to whether the aging of specimens will be performed or not before fracture resistance testing. Subgroup (N), samples were subjected to fracture resistance without thermo-mechanical aging, while subgroup (A), samples were subjected to thermo-cycling and cyclic loading before being subjected to fracture strength testing. Different methods; SEM, XRD, EDAX were used to characterize the properties of lithium disilicate glass-ceramics before and after repressing. Results: The highest statistically significant fracture resistance value was recorded for the subgroup (RN) repressed/non-aged, followed by the subgroup repressed/aged (RA), while the lowest statistically significant mean value was recorded for the subgroup pressed/aged (PA). There was no significant difference between pressed/non-aged (PN) and repressed/aged (RA) subgroups. Conclusion: Repressing of leftover buttons may increase the fracture resistance of IPS emax Press crowns. Thermo-mechanical aging may negatively affect the fracture resistance of IPS emax Press crowns, yet Repressing may decrease this effect. Clinical implications: This is a novel approach that targets a point of research that has not been investigated before. It elaborates how repressing may decrease the effect of aging and increase the fracture resistance of lithium disilicate crowns. Thus, recycling of lithium disilicate glass ceramics might decrease its failure and prolong their serviceability. Keywords Fracture resistance; Heat pressed; Lithium disilicate; Recycling; Repressing; Thermo-mechanical aging.

Clinical performance of CAD-CAM crowns provided by predoctoral students at the University of Toronto

Statement of problemThe clinical success of monolithic lithium disilicate glass-ceramic (LDGC) crowns manufactured with computer-aided design and computer-aided manufacturing (CAD-CAM) technology provided by predoctoral students has not been fully investigated. PurposeThe purpose of this retrospective clinical study was to evaluate the performance of laboratory-fabricated monolithic posterior LDGC CAD-CAM crowns provided by predoctoral students at the University of Toronto. Specific patient- and provider-related factors were also investigated. Material and methodsA sample of posterior LDGC CAD-CAM crowns (IPS e.max) provided by predoctoral students was evaluated. Crown preparations were made according to specific criteria, and crowns were milled in an in-house laboratory by using the CEREC Bluecam system. The crowns were cemented with Rely-X Unicem (3M ESPE) and Calibra Universal (Dentsply Sirona) resin cements. Clinical assessments of the crowns and supporting periodontal structures were performed following the modified California Dental Association (CDA) criteria. Intraoral photographs and periapical and bitewing radiographs were obtained for further assessment by 2 evaluators. Descriptive statistics, McNemar, t test, log rank (Mantel-Cox) tests, Pearson chi-squared tests, simple logistic regression, odds ratios, and Kaplan Meier survival analyses were performed (α=.05). ResultsA total of 189 patients receiving 210 crowns (108 premolar and 102 molar) were examined with a follow-up period of up to 6 years. Altogether, 28 complications were observed (12 technical, 11 biological, and 5 esthetic). No significant association was found between patient age, sex, periodontal condition, tooth type, tooth vitality, cement type, and crown longevity. However, significantly lower survival and success rates were found for mandibular crowns than for maxillary crowns (P=.029). The provider’s experience had no significant effect on the clinical performance of LDGC CAD-CAM crowns. The 6-year cumulative survival rate was 93.0%, and the success rate was 86.4%. ConclusionsThe ease of use of the CAD-CAM system and clinical performance of LDGC suggest that this technology should be used in the dental school setting by predoctoral students.

Marginal and Internal Fit of Ceramic Restorations Fabricated Using Digital Scanning and Conventional Impressions: A Clinical Study.

This clinical study was designed with the aim of fabricating four ceramic crowns using the conventional method and digital methods with three different intraoral scanners and evaluate the marginal and internal fit as well as clinician satisfaction. We enrolled 20 subjects who required ceramic crowns in the upper or lower molar or the premolar. Impressions were obtained using digital scans, with conventional impressions (polyvinyl siloxane and desktop scanner) and three different intraoral scanners (EZIS PO, i500, and CS3600). Four lithium disilicate glass-ceramic crowns were fabricated for each patient. In the oral cavity, the proximal and occlusal adjustments were performed, and the marginal fit and internal fit were evaluated using the silicone replica technique. The clinician satisfaction score of the four crowns was evaluated as per the evaluations of the proximal and occlusal contacts made during the adjustment process and the marginal and internal fit. For statistical analysis, the differences among the groups were analyzed with one-way analysis of variance and Tukey HSD test as a post-test; Pearson correlation analysis was used for analyzing the correlations (α = 0.05). There was a significant difference in the marginal and internal fit of the ceramic crowns fabricated using three intraoral scanner types and one desktop scanner type (p < 0.001); there was a significant difference in the clinician satisfaction scores (p = 0.04). The clinician satisfaction score and marginal fit were significantly correlated (absolute marginal discrepancy and marginal gap) (p < 0.05). An impression technique should be considered for fabricating a ceramic crown with excellent goodness-of-fit. Further, higher clinician satisfaction could be obtained by reproducing the excellent goodness-of-fit using the intraoral scanning method as compared to the conventional method.

Convergence Angle of Preparations for Lithium Disilicate Glass-Ceramic Crowns by Dental Students and Its Effect on Crown Retention.

The aims of this study were to determine the convergence angles of posterior teeth prepared by dental students at the University of Toronto for lithium disilicate glass-ceramic (LDGC) CAD/CAM crowns and to investigate their effect on loss of retention rate. A total of 280 preparations for posterior monolithic LDGC CAD/CAM crowns were performed on 270 patients (169 women and 101 men). Crowns were cemented with RelyX Unicem and Calibra Universal resin cements. Mesial, distal, and angle of convergence were measured on the bitewing radiographs. Cemented crowns were followed for up to six years. Data were analyzed for tooth type and location and for operator experience. The results showed the majority of convergence angles were greater than the recommended guidelines but fell within a clinically acceptable range (20 to 24 degrees). However, angles of convergence for mandibular molar preparations were highest (28.06±5.50 degrees), while maxillary premolars exhibited the lowest values (24.72±6.59 degrees). No significant difference was found between the results of dental students and foreign-trained dentists. Over a six-year observation period, only two crowns lost retention. The findings of this study indicated that ideal taper angles were impractical and difficult to achieve in clinical education settings.

Scanning electron microscope evaluation of the marginal gap and internal fit of additive versus subtractive fabrication techniques for posterior lithium disilicate crowns

Statement of the problem: The wide use of digital dentistry in fixed prosthodontics using 3D printers and CAD/CAM in fabricating crowns and partial fixed dental prosthesis created a need for more information about their marginal gap and internal fit.Purpose: This study aimed to evaluate the effect of fabrication technique using CAD/CAM manufactured and heat pressed lithium dislicate crowns made from milled wax and 3D printed resin patterns on their marginal gap and internal fit.Material & Methods: A total of 50 prepared mandibular first molar resin models were used and divided into two main groups according to their fabrication phase: Patterns group and fully fabricated crowns group. Patterns group was subdivided into milled wax patterns (W) (n=10) and 3D printed resin patterns (P) (n=10). Fully fabricated crowns group was subdivided according to fabrication technique of lithium disilicate crowns into: Machinable ceramics (M), using IPS e-max CAD blocks (n=10), Pressable ceramics (Pw), using IPS e-max press ingots following wax milling (n=10) and Pressable ceramics (Pp), using IPS e-max press ingots following 3D resin printing (n=10). All patterns and ceramic crowns were cemented with Rely-X self-adhesive resin cement. Marginal and internal adaptations were measured using SEM at 300 × magnification. Kruskal-Wallis and Wilcoxon signed-rank tests were applied to compare between the groups. Data were presented as median and range values. The significance level was set at P ≤ 0.05.Results: P group showed a significant higher median total marginal gap of 111.4 μm (80.8-139.7) than W group of 51.3 μm (45.1-57.8) before heat pressing. While M group showed the significant highest median marginal gap of 138.4 μm (83.4-191.8) and no significant difference between heat pressed groups (Pw and Pp) (P ≤ .05). Regarding changes after heat pressing, Pw group showed no significant decrease, while Pp group showed a significant decrease in median total marginal gap. For internal fit, there was no significant difference between the pattern groups (W and P) before heat pressing (P ≤ .05). After heat pressing, Pp group showed the significantly highest median gap of 195 μm (138.9-441.5) with no significant difference between M and Pw groups (P ≤ .05). Pw group showed a significant decrease in median gap, and Pp group showed no significant decrease after pressing (P ≤ .05). Conclusions: Heat pressed lithium disilicate glass ceramic crowns produced from CAD/CAM waxing or resin 3D printing techniques resulted in better marginal and fit accuracy than CAD/CAM. 3D printed resin patterns yielded internal fit values higher than other groups, but with promising clinical acceptability.Clinical implications: Both the additive and subtractive production for patterning phase before heat pressing allow clinical acceptability in terms of marginal and internal adaptation when a single unit posterior ceramic lithium disilicate crown is fabricated.

Load-bearing capacities of ultra-thin occlusal veneers bonded to dentin

ObjectivesTo test whether the load-bearing capacity of occlusal veneers made of ceramic or hybrid materials bonded to dentin does differ from those of porcelain-fused-to metal or lithium disilicate glass ceramic crowns. Material and methodsIn 80 human molars, occlusal tooth substance was removed so that the defects extended into dentin, simulating defects caused by attrition/erosion. Restorations at a standardized thickness of either 0.5 mm or 1.0 mm were digitally designed. For both thicknesses, 4 test groups (n = 10 per group) were defined, each including a different restorative material: “0.5-ZIR”: 0.5 mm thick zirconia (Vita YZ HT); “1.0-ZIR”: 1.0 mm thick zirconia (Vita YZ HT); “0.5-LDC”: 0.5 mm thick lithium disilicate ceramic (IPS e.max Press); “1.0-LDC”: 1.0 mm thick lithium disilicate ceramic (IPS e.max Press); “0.5-HYC”: 0.5 mm thick PICN (Vita Enamic); “1.0-HYC”: 1.0 mm thick PICN (Vita Enamic); “0.5-COC”: 0.5 mm thick tooth shaded resin composite (Lava Ultimate) and “1.0-COC”: 1.0 mm thick tooth shaded resin composite (Lava Ultimate). Consecutively, the specimens were thermo-mechanically aged and then loaded until fracture. The load-bearing capacities (Fmax) between the groups were statistically compared using the Kruskal-Wallis test (p < 0.05) and pairwise group comparison applying the Dunn's method. In addition, the results were compared to those of conventional lithium-disilicate ceramic crowns (“CLD”) and to porcelain-fused to metal crowns (“PFM”). ResultsThe median Finitial values for the 0.5 mm thin restorations were 1′350 N for 0.5-ZIR, 850 N for 0.5-LDC, 1′100 N for 0.5-HYC and 1′950 N for 0.5-COC. With CLD as the control, a significant difference was found between the groups 0.5-COC and 0.5-LDC (KW: p = 0.0124). With PFM as the control, the comparisons between PFM and 0.5-LDC as well as between 0.5-COC and 0.5-LDC were significant (KW: p = 0.0026). Median Fmax values of 2′493 N in the group 0.5-ZIR, 1′165 in the group 0.5-LDC, 2′275 N in the group 0.5-HYC and 2′265 N in the group 0.5-COC were found. The medians of the Finitial values for the 1.0 thick restorations amounted of 2′100 N in 1.0-ZIR, 1′750 N in 1.0-LDC, 2′000 N in 1.0-HYC and 2′300 N in 1.0-COC. Testing the multiple comparisons with Dunn's method no significant differences were found (p > 0.05). The median Fmax values of the 1.0 mm thick restorations were: 2′489 N in the group 1.0-ZIR, 1′864 N in the group 1.0-LDC, 2′485 N in the group 1.0-HYC and 2′479 N in the group 1.0-COC. With CLD as the control group, a significant difference between zirconia and lithium-disilicate was found for the 0.5 (p = 0.0017) and 1.0 mm (p = 0.0320) thick specimens. Comparing the 0.5 mm thick specimens with CLD as the control, a significant difference was found between 0.5-HYC and 0.5-LDC (p = 0.0017). With PFM as the control, the comparison of lithium disilicate and zirconia was statistically significant for both thicknesses (p = 0.0009 for the 0.5 mm thick specimens; p = 0.0074 for the 1.0 mm thick specimens). In addition, with PFM as control group, significant differences were seen between 0.5-LDC and all other groups with restorations in 0.5 mm thickness (p = 0.0017). ConclusionsRegarding their maximum load-bearing capacity, minimally invasive occlusal veneers made of ceramic, hybrid materials or polymeric materials can be applied to correct occlusal tooth wear with exposed dentin and thus replace conventional crown restorations in cases of normally expected intraoral bite forces.

Influence of veneer pore defects on fracture behavior of bilayered lithium disilicate glass-ceramic crowns

ObjectiveTo identify the conditions under which fabrication pore defects within veneering porcelain in bilayered lithium disilicate glass-ceramic (LDG) crowns will influence and jeopardize the mechanical integrity of the structure. MethodsThirty standardized molar crowns (IPS e.max Press) were fabricated and microCT scanned to 3D-analyze the size, morphology and distribution of pores in veneering porcelain, followed by in vitro fracture test and SEM fractographic observation. Finite element analysis (FEA) of the microCT reconstructed models was used to evaluate the stress state. ResultsThe volumes of pores in samples ranged from 3241μm3 to 1.29×109μm3 with the equivalent radius between 10μm to 680μm. Deviation of sphericity of pores ranged from 0.10 to 0.81 and the average of 99.97% pores was near 0.63. For the smaller pores their distribution tended to be uniform, while the larger pores were irregular with elongated ellipsoidal form and located at or near the veneer–core interface. During wedge loading blunt contact fracture testing 21 crowns failed from the fissure on the occlusal surface, of which 16 failed from surface or near surface pores, 2 from the midpoint of the oblique ridge, and 7 from larger interfacial pores. FEA analysis indicated that defects were detrimental to veneer integrity only in regions of tensile stress and where the pore radius associated with crack initiation ranged from 30 to 50μm. Pore morphology appeared to have only a minor effect on fracture. SignificanceWithin the limitation of the microCT resolution and FEA, it suggests that pores radius large than 30–50μm and located in the tensile stress area like grooves and fissures on the occlusal surface or near surface as well as cervical margins of veneering porcelain will jeopardize the bilayered structure and mechanical integrity of LDG.

Effect of Molar Preparation Axial Height on Retention of Adhesively-luted CAD-CAM Ceramic Crowns.

To evaluate the effect of axial wall height (AWH) on failure resistance of CAD-CAM adhesively-bonded, all-ceramic crowns on molar preparations with a conservative total occlusal convergence (TOC). 60 newly extracted maxillary third molars were divided into 5 groups (n = 12) and prepared for all-ceramic crowns with occlusal cervical AWH of 0, 1, 2, 3, and 4 mm, all containing a conservative 10-degree TOC. Scanned preparations were fitted with lithium-disilicate glass-ceramic crowns using a self-adhesive resin-composite luting agent after intaglio surface preparation with hydrofluoric acid and silane. Specimens were stored at 37°C/98% humidity for 24 h and tested to failure at a 45-degree angle applied to the palatal cusp on a universal testing machine. Mean results were analyzed using ANOVA and Tukey's test (p = 0.05). Preparations containing 2, 3, and 4 mm AWH demonstrated similar and higher failure resistance than the 0- and 1-mm axial wall height groups. Under the conditions of this study, evidence is presented that under certain conditions CAD-CAM adhesive technology may compensate for less than optimal AWH. Based on both failure load results and failure mode analysis, adhesively-luted maxillary molar CAD-CAM crowns based on a preparation containing 10-degree TOC require at least 2 mm AWH for adequate resistance and retention. However, adoption of these findings is cautioned until both fatigue analysis and appropriate clinical evidence has been provided.

Ultra-thin occlusal veneers bonded to enamel and made of ceramic or hybrid materials exhibit load-bearing capacities not different from conventional restorations

ObjectivesThe objective of this study was to test whether or not the load-bearing capacity of occlusal veneers bonded to enamel and made of ceramic or hybrid materials does differ from those of porcelain-fused-to-metal or lithium disilicate glass ceramic crowns. Material and methodsIn 80 human molars occlusal enamel was removed without extending into the dentin in order to mimic substance defects caused by attrition. The restorations were digitally designed at a standardized thickness of either 0.5 mm or 1.0 mm. For each thickness, 4 test groups were formed each including a different restorative material: “0.5-ZIR”: 0.5 mm thick zirconia (Vita YZ HT); “1.0-ZIR”: 1.0 mm thick zirconia (Vita YZ HT); “0.5-LDC”: 0.5 mm thick lithium disilicate ceramic (IPS e.max Press); “1.0-LDC”: 1.0 mm thick lithium disilicate ceramic (IPS e.max Press); “0.5-HYC”: 0.5 mm thick PICN (Vita Enamic); “1.0-HYC”: 1.0 mm thick PICN (Vita Enamic); “0.5-COC”: 0.5 mm thick tooth shaded resin composite (Lava Ultimate) and “1.0-COC”: 1.0 mm thick tooth shaded resin composite (Lava ultimate). Each group consists of 10 specimens. Two additional groups of 10 specimens each were used as controls and exhibited conventional crown preparations. In one group the crowns were made of lithium-disilicate ceramic (“CLD”: IPS e.max CAD) and the other group consisted of porcelain-fused to metal crowns (“PFM”). All restorations were cemented onto the prepared teeth following the manufacturer's instruction of the corresponding luting cement. Subsequently, they were thermo-mechanically aged and then loaded until fracture. Load-bearing capacities (Fmax) between the groups were compared applying the Kruskal-Wallis test (p < 0.05) and pairwise group comparisons using the Dunn's method. ResultsMedian values (and quartiles) for the load-bearing capacity amounted to (Fmax) 2′407 (1′670; 2′490) N for the CLD group and to 2′033 (1′869; 2′445) N for the PFM group. For the 0.5 mm thick restorations Fmax reached the highest median value in group 0.5-HYC 2′390 (1′355; 2′490) N, followed by 0.5-COC 2′200 (1′217; 2′492) N and 0.5-LDC 1′692 (1′324; 2′355) N. No results were obtained for group 0.5-ZIR due to the impracticability to fabricate ultra-thin specimens. The distribution of the values for the 1.0 mm thick restorations was 2′489 (2′426; 2′491) N for 1.0-COC, 2′299 (2′156; 2′490) N for 1.0-ZIR, 2′124 (1′245; 2′491) N for 1.0-HYC, and 1′537 (1′245; 1′783) N for 1.0-LDC. The differences of the medians between the test and the control groups did not reach statistical significance for the 0.5 mm thick specimens (KW: p = 0.6952 and p = 0.6986). Within the groups exhibiting 1.0 mm thickness, however, significant different medians were found: 1.0-LDC < 1.0-ZIR and 1.0-LDC < 1.0-COC (KW: p < 0.0209). ConclusionsRegarding their maximum load-bearing capacity, minimally invasive occlusal veneers made of ceramic and hybrid materials can be applied to correct occlusal tooth wear and thus replace conventional crown restorations.