Lithium Disilicate Ceramic Crowns Research Articles

Evaluating Retention of Onlay Versus Complete Coverage Using E.Max-Restoration

This study compared the retention of different types of indirect restorations (only or full coverage) utilized on endodontically treated molars. Fourteen patients requiring restoration of endodontically treated molars were randomly allocated into two groups (n = 7) according to the type of restoration used. lithium disilicate ceramic crowns were given to the control group. While lithium disilicate ceramic onlays were given to the intervention group. The heat pressing technique was used for the fabrication of both restorations. Following the final cementation with adhesive resin cement, the restoration was assessed at three, six, twelve, and twenty-four months using the modified USPHS criteria. Statistical analysis was performed using the chi-square test. Results: At all intervals, there was no statistically significant difference in retention (P > 0.05) between the two tested groups. Both groups showed comparable results, with full coverage showing somewhat higher retention after 2 years. Regardless of the type of restoration, the emax-press produced high clinical performance in terms of retention. Compared to full coverage, onlay has proven to be a trustworthy substitute.

How does the occlusal contact region influence the mechanical fatigue performance and fracture region of monolithic lithium disilicate ceramic crowns?

ObjectiveTo characterize the effect of the occlusal contact region on the mechanical fatigue performance and on the fracture region of monolithic lithium disilicate ceramic crowns. Materials and methodsMonolithic lithium disilicate ceramic crowns were machined in a CAD/CAM system and adhesively luted onto glass-fiber reinforced epoxy resin preparations with resin cement. The crowns were divided into three groups (n = 16) according to load application region (cusp tip: restricted to cusp tips; cusp plane: restricted to cuspal inclined plane; or mixed: associating tip cusp and cuspal inclined plane). The specimens were submitted to a cyclic fatigue test (initial load: 200 N; step-size: 100 N; cycles/step: 20,000; loading frequency: 20 Hz; load applicator: 6 mm or 40 mm diameter stainless steel) until observing cracks (1st outcome) and fracture (2nd outcome). The data were analyzed by the Kaplan-Meier + Mantel-Cox post-hoc tests for both outcomes (cracks and fracture). Finite element analysis (FEA), occlusal contact region, contact radii measurements, and fractographic analyzes were performed. ResultsThe mixed group presented worse fatigue mechanical behavior (550 N / 85.000 cycles) compared to the cuspal inclined plane group (656 N / 111,250 cycles) (p < 0.05) for the first crack outcome, while the cusp tip group was similar to both groups (588 N / 97,500 cycles) (p > 0.05). The mixed group had the worst fatigue behavior (1413 N / 253,029 cycles) in relation to the other groups (Cusp tip: 1644 N / 293,312 cycles; Cuspal inclined plane: 1631 N / 295,174 cycles) considering the crown fracture outcome (p < 0.05). FEA showed higher tensile stress concentration areas just below the load application region. In addition, loading on the cuspal inclined plane induced a higher tensile stress concentration in the groove region. The most prevalent type of crown fracture was the wall fracture. Groove fracture was observed in 50% of the loading specimens exclusively on the cuspal inclined plane. ConclusionLoad application on distinct occlusal contact regions affects the stress distribution pattern and consequently the mechanical fatigue performance and fracture region of the monolithic lithium disilicate ceramic crowns. A combination of loading at distinct regions is recommended to promote better evaluation of the fatigue behavior of a restored set.

Fracture Resistance of Titanium and Ceramic-Reinforced Poly Ether Ether-Ketone Implant Abutments Supporting Monolithic Lithium Disilicate Ceramic Crowns and Ceramic-Reinforced Poly Ether Ether Ketone (PEEK) Crowns

Fracture Resistance of Titanium and Ceramic-Reinforced Poly Ether Ether-Ketone Implant Abutments Supporting Monolithic Lithium Disilicate Ceramic Crowns and Ceramic-Reinforced Poly Ether Ether Ketone (PEEK) Crowns

Fracture resistance of pressed ZLS crowns versus pressed LD crowns under thermo-mechanical cycling

The aim of this study was conducted to assess the fracture resistance of zirconia reinforced lithium silicate all ceramic material "Celtra Press" compared to lithium disilicate one "IPS e-max Press" under simulated oral conditions. Fourteen ceramic crowns were fabricated on epoxy dies which were duplicated from stainless steel master die and divided into two equal groups (n=7) according to the material of construction; Group A: Crowns fabricated with IPS e-max Press material and Group B: Crowns fabricated with Celtra Press material. The crowns were then cemented onto their corresponding dies with a self-adhesive resin cement and subjected to thermocycling and cyclic loading. Then they were loaded to fractur in a universal testing machine. The results were tabulated and statistically analyzed using Kolmogorov-Smirnov and Shapiro-Wilk tests. Student t-test used to compare mean values. The significance level was set at P ≤ 0.05 and 95% Confidence interval. Statistical analysis was performed using Graph Pad Instat (Graph Pad, Inc.) software for windows. The mean ± SD values of fracture resistance were recorded for lithium Disilicate group (1706.01 ±154.32 N) meanwhile the mean ± SD value recorded with celtra group were (1550.67±196.71 N). Zirconia reinforced lithium silicate ceramic crowns produced comparable fracture resistance values to lithium disilicate ceramic crowns and both tested materials are within the clinically acceptable values in the posterior area.

Vertical Marginal Discrepancy Performance of a CAD-CAM System with Multiple Users.

The purpose of this evaluation was to evaluate the vertical marginal discrepancies of a computer-aided design-computer-aided manufacture (CAD-CAM) system used by different providers at separate time intervals. Lithium disilicate monolithic crowns on mandibular third molars were fabricated by three different providers inexperienced in digital dentistry. Using a precision rotary stage mounted on a digital recording microscope, the crown vertical marginal discrepancy was assessed using 160× magnification at 5-degree intervals around the crown marginal circumference for a total of 72 measurements per specimen. In addition to mean vertical marginal discrepancy, the maximum vertical marginal discrepancy, and its location as well as the percent of closed marginal assessments, were assessed. Mean data was analyzed using Kruskal-Wallis and Dunn post hoc testing at a 95% level of confidence (α=0.05). The mean marginal vertical discrepancy for all specimens was 21.1 ± 5.5 μm and a significant difference (p=0.0016) existed between groups but with noted wide similarity overlap. No difference (p=0.65) was observed with the mean closed margin percentage, but a significant difference (p=0.0012) existed in the observed maximum marginal discrepancy between groups. The 2-mm axial wall height (AWH), 20-degree total occlusal convergence (TOC) had significantly less (p<0.017) mean vertical marginal discrepancies than the 4-mm AWH, 20-degree TOC, and the 3-mm AWH, 16-degree TOC groups with the remaining groups similar (p>0.147). The plotted location of the specimen's maximum vertical discrepancy suggests a potential pattern amid the 360-degree margin circumference. Under the conditions of this study, CAD-CAM-derived monolithic lithium disilicate ceramic crowns fabricated by different clinicians demonstrated mean vertical marginal discrepancy results that were less than the suggested maximum clinically acceptable values. A potential for patterns of marginal discrepancy results was identified and deserves further evaluation. Results should be interpreted with caution as in vitro methodologies vary and do not directly correlate with clinical conditions.

CAD/CAM lithium disilicate ceramic crowns: Effect of occlusal thickness on fracture resistance and fractographic analysis.

This study uses fracture tests and fractographical analysis to compare computer-aided design and computer-aided manufacturing (CAD/CAM) lithium disilicate molar crowns with the previous occlusal thickness recommendation of 1.5-mm, the new recommendation of 1.0-mm, and a less invasive thickness of 0.8-mm. After fatigue application, fracture tests and fractographic analysis were conducted. The fracture resistance of CAD/CAM lithium disilicate molar crowns was different depending on the occlusal thickness of the restoration, and decreased with lower the thickness. However, the fracture resistance of crowns of all three thicknesses exceeded the reported maximum bite force in the first molar region after the fatigue process, and can be considered acceptable for use in the clinic.

Fatigue and failure analysis of restored endodontically treated maxillary incisors without a dowel or ferrule

Statement of problemInformation on the survival and mode of failure of endodontically treated incisors without a ferrule and restored without dowels is lacking. PurposeThe purpose of this in vitro study was to compare the survival and failure mode of endodontically treated incisors without a ferrule and restored with bonded ceramic crowns and various composite resin foundation restorations without dowels with a control group with fiber dowels. Material and methodsForty-five decoronated endodontically treated bovine incisors without ferrule were divided into 3 experimental groups and restored with different adhesive foundation restorations without dowel: nanohybrid composite resin (Nd), bulk-fill composite resin foundation restoration (NdB), and fiber-reinforced bulk-fill composite resin (NdFR). A control group with conventional foundation restorations (glass-fiber dowel with nanohybrid composite resin foundation restoration without ferrule) (D) was included for comparison. All teeth were prepared to receive bonded lithium disilicate ceramic crowns luted with dual-polymerizing composite resin cement and were subjected to accelerated fatigue testing. Cyclic isometric loading was applied to the incisal edge at an angle of 30 degrees and a frequency of 5 Hz, beginning with a load of 100 N (5000 cycles). A 100-N load increase was applied each 15 000 cycles. Specimens were loaded until failure or to a maximum for cycles endured of 1000 N (140 000 cycles). Groups were compared by using the Kaplan-Meier survival analysis (log rank test at α=.05 and pairwise post hoc comparisons) and life table analysis for load-at-failure (followed by Wilcoxon pairwise comparison α=.05). ResultsAll the specimens failed before 140 000 load cycles. Even though no statistically significant differences were found between the experimental groups without dowel (P>.127), the fiber-reinforced foundation restoration yielded the highest mean ±standard deviation cycles to failure (46 023 ±4326) compared with Nd (38 899 ±2975) and NdB (39 751 ±2998). NdFR, however, outperformed the foundation restoration with glass-fiber dowel (35 026 ±2687) (P<.05). Most failure in groups without dowel were restorable, while 100% of catastrophic failure (unrestorable) were found in the group with dowels. ConclusionsBased on the present in vitro study, dowels did not improve the performance of the adhesive restoration of endodontically treated incisors without a ferrule. The use of a short fiber-reinforced composite resin foundation restoration without a dowel was able to not only improve the resistance of the restorations compared with adhesive foundation restorations with dowels but also minimize catastrophic failures.

Clinical Evaluation of Reduced-Thickness Monolithic Lithium-Disilicate Crowns: One-Year Follow-Up Results

Purpose: The purpose of this in vivo study was to investigate whether the less invasive approach (reduced thickness of the restoration) will result in a comparable risk of failure and similar aesthetic results, compared to conventional layered full porcelain crowns, and can, therefore, be used as a good alternative. Material and Methods: The tested ceramic was lithium-disilicate ceramic (IPS e.max). Forty-four patients with endodontically treated premolars or molars were randomized into two groups and provided with single crowns. One group received conventional all-ceramic crowns made from a lithium-disilicate core and hand-veneered aesthetic ceramic, while another group received full-contoured lithium-disilicate ceramic crowns with reduced wall thickness than manufactures recommendations. The teeth for conventional crowns were prepared with 1 mm rounded shoulder and 2 mm occlusal reduction, while teeth for monolithic crowns were prepared with 0.6 mm wide rounded shoulder and 1 mm occlusal reduction. All crowns were prepared by the same clinician and manufactured in the same laboratory by the same technician. The survival and aesthetics of the crowns were assessed by the independent clinician. Apart from this, patients’ aesthetic satisfaction was evaluated. The assessment was double blind as both the examiner and the patients did not know which type of crown was provided. The observation period was 36 months. Survival of the crowns was assessed using the modified United States Public Health Service (USPHS) criteria and aesthetics and participants’ aesthetic satisfaction with the crowns was evaluated using a visual analogue scale. Results: The one-year survival rate for layered crowns was 100% and for monolithic crowns 95.5%. The median patients’ aesthetic satisfaction with both crowns was 100%. Conclusions: The results indicate similar one-year survival rate of reduced-thickness monolithic lithium-disilicate crowns and conventional veneered crowns. Differences with patients’ satisfaction with the aesthetics of both crowns were not statistically significant and it can be said that the patients’ aesthetic satisfaction was the same for both crowns.

Randomized clinical trial of zirconia and polyetheretherketone implant abutments for single-tooth implant restorations: A 5-year evaluation

Statement of problemTitanium-supported polyetheretherketone (PEEK) abutments provide an economic alternative to zirconia abutments in esthetically important areas. Research comparing the performance regarding esthetics, longevity, and biologic parameters of PEEK abutments is lacking. PurposeThe purpose of this clinical study was to determine whether PEEK implant abutments provide similar esthetic and biologic parameters and survival rates as zirconia implant abutments. Material and methodsForty participants (age 20 to 50 years) receiving maxillary anterior and premolar implants were enrolled in the study and randomly assigned into 1 of 2 groups: Group PEEK (20 titanium-supported PEEK abutments) and group ZIR (20 zirconia abutments). Both groups were restored with pressed lithium disilicate ceramic crowns. Technical, biologic, and esthetic evaluation was performed at baseline and at 1, 3, and 5 years. The probing pocket depth, plaque control record, and bleeding on probing were recorded at the abutments (test) and compared with those at the corresponding contralateral teeth (control) and also between the 2 test groups. Standardized digital radiographs of the implants were made, and the bone level was recorded with the implant shoulder as the reference on the mesial and distal sides. The color difference between the peri-implant mucosa and control teeth gingiva and the discoloration of the implant crowns were determined with a spectrophotometer. The Student unpaired t test and repeated-measure ANOVA were used to statistically analyze the data (α=.05). ResultsFrom the 5-year evaluation, both PEEK and zirconia abutments with ceramic crowns showed 100% survival rate without any fracture or restoration loss. Differences in the biologic parameters of zirconia and PEEK abutments were statistically similar: mean probing pocket depth (group ZIR: 2.32 ±0.50 mm, group PEEK: 2.13 ±0.60 mm); mean plaque control record (group ZIR: 0.19 ±0.19, group PEEK: 0.15 ±0.17); and mean bleeding on probing (group ZIR: 0.12 ±0.11, group PEEK: 0.08 ±0.12). The mean marginal bone loss at 5 years was similar for implants supporting zirconia and PEEK abutments: mean mesial bone level (group ZIR: 1.8 ±0.5 mm; group PEEK: 1.9 ±0.6 mm), and mean distal bone level (group ZIR: 1.7 ±0.6 mm, group PEEK: 1.8 ±0.3 mm). The initial color difference (ΔE) between the peri-implant mucosa and gingiva of the analogous contralateral teeth diminished over time. No discoloration of the definitive restoration supported by PEEK or zirconia was detected over 5 years. ConclusionsAt the 5-year evaluation, zirconia and PEEK abutments exhibited the same survival rate with similar biologic and esthetic outcomes.

Influence of the Application and Light-Curing of Bonding Adhesives Inside Lithium Disilicate Ceramic Crowns.

This in vitro study evaluated the effect of the application and previous photoactivation of bonding adhesives in lithium disilicate ceramics. This was achieved by analyzing the bond strength of the cement-ceramic interface, nanohardness and elastic modulus of bonding adhesives and resin cements. The bonding adhesives used were Scotchbond Multi-Purpose (SBMP); Scotchbond Multi-Purpose light-cured (SBMP+LC); Single Bond 2 (SB2); Single Bond 2 light-cured (SB2+LC); Single Bond Universal (SBU) and Single Bond Universal light-cured (SBU+LC). After luting the ceramic in composite resin blocks, all specimens were subjected to 10,000 thermocycles. Sticks were obtained for the microtensile bonding strength test and the nanohardness and elastic modulus of the bonding adhesive and resin cements. Data were submitted to one-way ANOVA and Fishers tests (α =0.05). The results indicated that the bonding strength and mechanical properties were influenced by the interaction of the bonding adhesive and resin cement. For the mechanical properties analyzed, no statistically significant differences were observed between the groups. Single Bond Universal was the only system that was effective with or without previous light activation. For the other adhesive systems, Scotchbond Multi- Purpose and Single Bond 2, the previous light activation was necessary to optimize the bonding strength of the adhesive interface.

Maxillary Implant-supported Hybrid Prosthesis Fabricated using a Polyetherketoneketone Framework: A Case Report

This clinical report describes a case involving a 74-year-old woman with maxillary edentulism who was successf ully treated using an implant-supported hybrid prosthesis. The f ramework of the prosthesis was fabricated using polyetherketoneketone (PEKK), which is a high-performance polymer, and individual lithium disilicate ceramic crowns were cemented for optimal esthetics. No mechanical or biological complications were observed during a 3-year follow-up period. Further clinical studies and long-term clinical data regarding the usef ulness of PEKK as a f ramework material for dental prostheses are necessary.

Influence of Bioactive, Resin and Glass Ionomer luting cements on the fracture loads of dentin bonded ceramic crowns.

Objective:To investigate the failure loads of dentin bonded all-ceramic crowns when luted with Bioactive, resin and glass ionomer cements (GIC) in an in-vitro setting.Methods:This study was conducted at King Saud University, Saudi Arabia, from Nov.2018 to March 2019. In this study, 60 premolar teeth were prepared for dentin-bonded ceramic crowns. Lithium disilicate ceramic crowns fabricated using CAD-CAM technique were cemented to teeth using Bioactive (ACITVA), Resin (Nexus 3 Gen) and GIC (Ketac Cem- Maxicap). Half of the bonded specimens in each group were thermocycled (50000 cycles), however the remaining half were not aged (n=10). Fracture loads of bonded crowns were assessed by exposing them to static axial occlusal loads (1mm/min) using a round ended metal probe in a Universal testing machine. Means and standard deviations among the study groups were compared with ANOVA and Tukey-Kramer multiple comparisons test.Results:Highest failure loads were observed in resin group without ageing (thermocycling) (689.13±89.41 N), however, the lowest loads were observed in GIC specimens with ageing (243.16±49.03 N). Among non-aged samples, failure loads for Bioactive (480.30±47.26 N) group were less than Resin (689.13±89.41 N) samples but higher than GIC (307.51±45.29 N) specimens respectively. Among the aged specimens, Bioactive (404.42±60.43 N) showed significantly higher failure loads than GIC (243.16±49.03 N), however lower failure loads than Resin (582.33±95.95 N) samples.Conclusions:Dentin boned crowns with resin cementation showed higher failure loads than Bioactive and GIC luted crowns. Crowns luted with Bioactive cement showed acceptable failure loads for use as restoration on anterior teeth.

Influence of Computer-aided Design/Computer-aided Manufacturing Diamond Bur Wear on Marginal Misfit of Two Lithium Disilicate Ceramic Systems.

Marginal misfit of monolithic lithium disilicate ceramic crowns obtained from a chairside computer-aided design/computer-aided manufacturing system is affected after successive millings using a single diamond bur set. This fact can be critical for the longevity of indirect restorations.

The effect of crown fabrication process on the fatigue life of the tooth-crown structure.

To compare the fatigue strength of lithium disilicate ceramic crowns when cemented as a compound structure, as a function of the manufacturing process and the type of ceramic variation. A typodont maxillary first premolar was prepared for an all-ceramic crown in accordance with the manufacturer's guidelines for monolithic ceramic crowns (IPS e. max®; Ivoclar-Vivadent, Liechtenstein). 60 dies were duplicated in a polymer with a Young's Modulus closely matched to dentine (Alpha die, Schütz GmbH). Three different crown fabrication techniques were used (n = 20): (i) Manually applied wax spacer and pressed-crown; (ii) digitally scanned preparation, CAD-printed wax-pattern (D76PLUS, Solidscape Inc.) and pressed-crown; (iii) digitally scanned preparation and machined-crown (CEREC-inLab® v3.6 Sirona GmbH). Resin-based cement (Variolink-II®, Ivoclar-Vivadent, Liechtenstein) was employed with a standardised mechanised cementation technique to apply a controlled axial cementation pressure [Universal testing machine (Lloyd LRX®, Lloyd Materials Testing Inc)]. The samples were subjected to fatigue life testing with a cyclic impact load of 453 N for 1.25 × 106cycles at 37C⁰ and 1 Hz frequency until the point of fracture. There was a significant difference in the resistance to fatigue loading between the three groups. Weibull probability analysis and the α and β Weibull parameters indicate that the teeth restored with a 'Manually-applied wax spacer and pressed-crown' are best able to resist cyclic fatigue loading. They also have the most uniform interface geometry. Teeth restored with IPS e. max® crowns constructed by manually applied wax spacer and pressing, have a more uniform interface and a greater structural integrity than wax CAD-printed patterns or CAD-CAM crowns.

Marginal Gap Distance and Fracture Resistance of Lithium Disilicate and Zirconia-Reinforced Lithium Disilicate All-Ceramic Crowns Constructed With Two Different Processing TechniquesWith Two Different Processing Techniques

Statement of problem: The microstructure and processing methods used to produce any dental restoration might affect the final mechanical outcomes as well as the clinical success. Objectives: The purpose of this study was to evaluate the fracture resistance of lithium disilicate and zirconia reinforced lithium disilicate ceramic crowns constructed using two processing techniques after fatigue loading namely, CAD/CAM technique and pressing technique. The marginal integrity of the crowns was examined before and after fatigue loading. Methods: A total number of thirty-two freshly extracted maxillary first molars were collected. The teeth were chosen to be of similar bucco-lingual and mesiodistal dimensions. The teeth were mounted vertically into epoxy resin templates. Full coverage all-ceramic preparation was performed for all samples using a standardized technique. The prepared teeth were randomly divided into four equal groups (n=8) according to the all-ceramic materials and technique used for crown fabrication as follows: Group I: IPS e-max CAD(EC): eight prepared teeth were restored with machinable lithium disilicate glass ceramics. Group II: Celtra Duo(CD): eight prepared teeth were restored with machinable zirconia-reinforced lithium disilicate glass ceramics. Group III: IPS e-max Press (EP): eight prepared teeth were restored with pressable lithium disilicate glass ceramics. Group IV: Celtra Press (CP): eight prepared teeth were restored with pressable zirconia-reinforced lithium disilicate glass ceramics. The crowns were cemented using self-adhesive resin cement (Rely X Unicem). Vertical margin gap distance of all the crowns was measured using a stereomicroscope. Following vertical marginal gap distance measurements, the samples were subjected to fatigue cyclic loading for 60000 cycles which is equivalent to six months clinical service. The vertical marginal gap distance for all samples were subsequently remeasured after the fatigue loading testing. Fracture resistance test was done using universal testing machine. The fracture load was recorded in Newton. Data was collected, tabulated and statistically analyzed. Results: One-way ANOVA test for comparison between the fracture resistance of the four types of all-ceramic crowns revealed that there was a statistically significant difference between mean fracture resistance of different all ceramic materials and techniques used in this study (P-value <0.001). For the marginal gap distance either before or after fatigue cyclic loading; there was a statistically significant difference between the four all ceramic crowns used in this study.Conclusions: CAD/CAM techniques showed better fracture resistance values than pressable techniques, even if the same material was used. The addition of zirconia to lithium disilicate ceramics did not improve the fracture resistance of all ceramic crowns. Pressable processing techniques showed better vertical marginal gap distance than CAD/CAM techniques for both ceramic materials used. Cyclic loading resulted in significant increase in the vertical marginal gap distance for all ceramic crowns using different processing techniques.

Fracture Resistance of CAD/CAM Lithium Disilicate of Endodontically Treated Mandibular Damaged Molars Based on Different Preparation Designs.

The aim of this study was to evaluate the fracture resistance of 2 different types of all-ceramic crown using immediate dentin sealing (IDS), obtained using a CAD/CAM system on molars with different preparations. Forty extracted lower molars were endodontically treated and divided into four groups (n = 10) according to the dental preparation. Group 1 (SP0) was prepared without filling the pulp chamber and crown-root junction was located at the cementoenamel junction (CEJ). Group 2 (SP1) was prepared without filling the pulp chamber and crown-root junction was located 1-mm above the CEJ. Groups 3 and 4 contained a flat preparation surface with no axial wall height. Group 3 (CP0) was made IDS with complete filling of the pulp chamber with composite resin and crown-root junction was located at the CEJ. Group 4 (CP1) was prepared with complete filling of the pulp chamber and crown-root junction was located 1-mm above the CEJ. All groups were restored with CAD/CAM lithium disilicate ceramic crowns. Specimens were subjected to the fracture test and statistically analyzed using analysis of variance (ANOVA). Fracture mode was determined using a stereoscopic microscope, classified as repairable or nonrepairable, and analyzed using Fischer's exact test. Results indicated that there were no significant differences between the groups in terms of fracture resistance or fracture pattern (p >0.05). Fracture resistance was the lowest in the SP0 group, followed by the SP1 group (1634.38 N) of CP0 (1821.50 N), and it was the highest in the CP1 group. There was a predominance of nonrepairable fractures and there were no significant differences in the fracture resistance and fracture mode of CAD/CAM lithium disilicate molar all-ceramic crowns. Endodontically treated molars teeth might be restored with endocrowns or all-ceramic crowns on flat preparation; however tooth fracture failures that affect reliability of these types of restorations should be considered.

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.

Effects of substrate, ceramic thickness, translucency, and cement shade on the color of CAD/CAM lithium-disilicate crowns.

The aim of this in vitro study was to evaluate the effects of substrate colors, different levels of ceramic thickness and translucency, and cement shades on the color difference from a reference color of lithium-disilicate crowns. A premolar tooth preparation was made on a study model for 1.0 and 1.5 mm thick full-ceramic crowns. Digital impressions were taken (3Shape TRIOS) and crowns designed in a CAD program (DentalDesigner). Shade A1 crowns were milled (Everest, Kavo) from high-translucency (HT) and low-translucency IPS e.max (Ivoclar Vivadent) blocks. Twelve substrates were made of different colors and materials (Natural Die Material, Co-Cr, zirconia, and gold-colored alloy). Three different shades of try-in pastes were used to simulate the effect of cements (Variolink Esthetic try-in paste; Ivoclar). Shade measurement was done three times for each crown by a spectrophotometer (VITA Easyshade Advance); averages were compared to a reference crown (A1, HT, 1.5 mm, ND2 abutment, neutral try-in paste) with ΔE00 (CIEDE2000, according to the CIE latest standard) calculated. All the examined parameters influenced the ΔE00 of the crowns. The weakest effect was exerted by the try-in paste. All examined parameters influenced the final color of e.max CAD lithium-disilicate ceramic crowns. Matching the shade of ceramic crowns to the natural tooth color is a great challenge in dentistry. To meet patients' increasing esthetical expectations, CAD/CAM methods are very popular for full-ceramic crowns. However, several factors such as the shade of the abutment, luting cement color, ceramic thickness, and translucency may influence the final color. Our objective was to measure the optical effect of these factors on the final shade of CAD/CAM lithium-disilicate ceramic crowns.

Evaluation of patient satisfaction and shade matching of Vita Suprinity versus lithium disilicate (E-max) ceramic crowns in the esthetic zone: a randomized controlled clinical trial

Background: Optical impairments of teeth in the esthetic zone constitute a problem for many dentists and patients as several studies concluded that patients were dissatisfied of their dental appearance because of their restorations' color. The purpose of this study was to assess patient satisfaction combined with shade matching of VITA SUPRINITY versus lithium disilicate (IPS e-max CAD) all-ceramic crowns in esthetic zone. Methods: 26 patients with teeth problems indicated for full coverage restoration on one tooth in the esthetic zone (from upper central incisor to 1st premolar) were randomized into 2 equal groups (n=13) for which different CAD-CAM ceramic materials were used; (VITA SUPRINITY) a zirconia reinforced lithium silicate ceramic and (IPS e.max CAD) lithium disilicate glass ceramic. The crowns were fabricated to match the shade of the contra-lateral/ adjacent tooth and assessed using the modified USPHS criteria. Also patient satisfaction was assessed. The data obtained by evaluating each assessment criteria were statistically analyzed using the Chi-square test that was performed in categorical data. Results: According to the modified USPHS criteria, 100% of the patients were Alpha score with 0% for Bravo, Charlie and Delta scores in both groups. While according to the visual analogue scale (VAS), 100% of the patients were satisfied while 0% were dissatisfied by the restoration in both groups. Conclusions: The results for both materials in terms of patient satisfaction and shade matching were Alpha. This indicated that both materials are clinically accepted to be used as full coverage restorations for excellent esthetic outcome. Registration: NCT0284611.

Effect of Different Wall Thicknesses on Fracture Strength, Marginal Accuracy and Translucency of Monolithic Ceramic Restorations

The present study was conducted to evaluate the effect of different crown wall thicknesses (0.5mm, 1mm and 1.5mm) on the fracture load, marginal accuracy, and translucency of monolithic CAD-CAM manufactured lithium disilicate and Zirconia crowns. Materials and Methods: 60 monolithic single were constructed using CAD/CAM machine divided into two groups according to the material of construction Group (E): Monolithic IPS e.max CAD lithium disilicate crowns and Group (B): Monolithic BruxZir Solid zirconia based crowns. Each group was divided into three subgroups according to the axial wall thickness of the crown into Subgroup (0.5): 0.5 mm margin thickness, Subgroup (1): 1mm margin thickness and Subgroup (1.5): 1.5mm margin thickness. The Vertical Marginal gap was determined using Digital microscope, while translucency parameter was determined using a Spectrophotometer, then the fracture load was determined using universal testing machine and finally fracture pattern was detected by scanning electron microscope. The collected data were statistically analyzed. Results: Vertical marginal gap values for both groups (E and B) were within the acceptable clinical range. The translucency parameters (TP) values in group E revealed a higher mean value than in group B for all subgroups. The fracture load in group B revealed a higher mean value than in group E for all subgroups.Conclusion: Increasing the wall thickness can effectively increase the fracture strength while decrease the marginal gap and translucency of the monolithic lithium disilicate ceramic crowns and zirconia crowns.