Full-mouth rehabilitation with monolithic CAD/CAM-fabricated hybrid and all-ceramic materials: A case report and 3-year follow up.

Esthetic full-mouth rehabilitation represents a great challenge for clinicians and dental technicians. Computer-aided design/ computer-assisted manufacture (CAD/CAM) technology and novel ceramic materials in combination with adhesive cementation provide a reliable, predictable, and economic workflow. Polychromatic feldspathic CAD/CAM ceramics that are specifically designed for anterior indications result in superior esthetics, whereas novel CAD/CAM hybrid ceramics provide sufficient fracture resistance and adsorption of the occlusal load in posterior areas. Screw-retained monolithic CAD/CAM lithium disilicate crowns (ie, hybrid abutment crowns) represent a reliable and time- and cost-efficient prosthetic implant solution. This case report details a CAD/CAM approach to the full-arch rehabilitation of a 65-year-old patient with toothand implant-supported restorations and provides an overview of the applied CAD/CAM materials and the utilized chairside intraoral scanner. The esthetics, functional occlusion, and gingival and peri-implant tissues remained stable over a follow-up period of 3 years. No signs of fractures within the restorations were observed.

Veneered anatomically designed zirconia FDPs resulting from digital intraoral scans: Preliminary results of a prospective clinical study.

OBJECTIVES: The aim of this prospective clinical study was to evaluate the clinical performance of veneered anatomically designed zirconia fixed dental prostheses (FDPs) resulting from intraoral digital impressions. METHODS: 24 patients requiring treatment were provided with all-ceramic FDPs. Intraoral scans (iTero) were performed and veneered anatomically designed CAD/CAM-zirconia FDPs (Zerion/VitaVM9) were fabricated. A feldspar veneering ceramic following a slow cooling firing protocol was applied. A self-curing resin based luting material was used for adhesive cementation. Clinical evaluations were performed at baseline and 6, 12, and 18 months recalls according to the modified USPHS-criteria. Intraoral digital surface scans (iTero) were performed at each recall examination and were digitally superimposed (Geomagic) to evaluate potential veneer cohesive fractures. Kaplan-Meier survival analysis comprised secondary caries, clinically unacceptable fractures, root canal treatment and debonding. Kaplan-Meier success rate included restorations with minimal crevices, tolerable color deviations and clinically acceptable fractures. Data were statistically analyzed. RESULTS: The Kaplan-Meier survival rate and success rate of the FDPs were 100% and 91.7%, respectively. Clinically acceptable veneer cohesive fractures and crevices at the restoration margin were observed in two patients. These shallow veneer fractures were only detected by overlapping baseline and recall scans. Ceramic surface roughness increased significantly over time (p<0.0001). CONCLUSIONS: Veneered zirconia FDPs fabricated from digital intraoral scans showed a favorable clinical performance over an observation period of 18 months. Anatomical zirconia core design and slow cooling firing protocol of the veneering ceramic reduced the incidence of chip fractures to a level that could not be detected clinically. CLINICAL SIGNIFICANCE: The digital workflow on the basis of intraoral digital impressions resulted in clinically satisfying outcomes for veneered zirconia FDPs.

Intermediate rehabilitation with (non)-prep all-ceramic onlays in an adolescent patient with oligodontia--4-year follow-up.

BACKGROUND: Initial rehabilitation in juvenile patients with oligodontia is a major challenge for the dentist. Conventional permanent prosthetic and/or implantological treatment options alongside permanent natural teeth are contraindicated in growing patients, because their skeletal development is still in progress. CASE REPORT: A non-invasive temporary-fixed treatment option for an adolescent patient is presented by the use of adhesively cemented (non-prep) all-ceramic onlays of primary teeth. The outcome of treatment was monitored over a period of 4 years. CONCLUSION: Long-term preservation of persistent primary teeth may be a meaningful alternative to removable dentures in growing patients with oligodontia. Intermediate rehabilitation should cause no more than mild psychological stress for the patient and improve quality of life, especially when extensive orthodontic and/or implantological treatment is planned at the end of the patient's skeletal growth.

An interdisciplinary noninvasive all-ceramic treatment concept for nonsyndromic oligodontia in adolescence.

Oligodontia has a substantial oral functional and psychosocial impact on the quality of life of children. The treatment of oligodontia in adolescence is an interdisciplinary approach which can include extraction of the primary teeth with orthodontic space closure, or prosthodontic rehabilitation. This case report describes a conservative approach for the rehabilitation of a 12-year-old patient with 19 ageneses (excluding third molars) of permanent teeth, infraocclusion of the persisting primary teeth, deep overbite, and reduced mesiodistal dimension of the maxillary incisors with a central diastema. The treatment plan to restore esthetics and function included an initial noninvasive prosthetic rehabilitation for deep bite correction with additive leucite-reinforced glass-ceramic onlays/veneers until definitive orthodontic and implant therapy are reevaluated and determined in adulthood. Esthetics, functional occlusion, and crown-to-root ratio remained stable over a follow-up period of 3 years. No signs of fractures within the all-ceramic restorations or symptoms of a temporomandibular disorder were evident.

Prospective clinical study of press-ceramic overlap and full veneer restorations: 7-year results.

The aim of this prospective clinical study was to investigate the long-term performance of all-ceramic veneers with overlap (OV) and full veneer (FV) preparation designs. Twenty-five patients were restored using 42 OV restorations (incisal/palatal butt-joint margin) and 24 FV restorations (palatal rounded shoulder margin). All restorations were leucite-reinforced glass-ceramic anterior veneers. The 7-year Kaplan-Meier survival rate was 100% for FV restorations and 97.6% for OV restorations. The all-ceramic veneers revealed significant deterioration over time according to United States Public Health Service criteria, irrespective of the preparation design. Based on the 7-year results of this study, both preparation designs can be considered reliable treatment options for anterior teeth with extended deficits.

Resin bond to indirect composite and new ceramic/polymer materials: a review of the literature.

STATEMENT OF THE PROBLEM: Resin bonding is essential for clinical longevity of indirect restorations. Especially in light of the increasing popularity of computer-aided design/computer-aided manufacturing-fabricated indirect restorations, there is a need to assess optimal bonding protocols for new ceramic/polymer materials and indirect composites. PURPOSE OF THE STUDY: The aim of this article was to review and assess the current scientific evidence on the resin bond to indirect composite and new ceramic/polymer materials. MATERIALS AND METHODS: An electronic PubMed database search was conducted from 1966 to September 2013 for in vitro studies pertaining the resin bond to indirect composite and new ceramic/polymer materials. RESULTS: The search revealed 198 titles. Full-text screening was carried out for 43 studies, yielding 18 relevant articles that complied with inclusion criteria. No relevant studies could be identified regarding new ceramic/polymer materials. Most common surface treatments are aluminum-oxide air-abrasion, silane treatment, and hydrofluoric acid-etching for indirect composite restoration. Self-adhesive cements achieve lower bond strengths in comparison with etch-and-rinse systems. Thermocycling has a greater impact on bonding behavior than water storage. CONCLUSIONS: Air-particle abrasion and additional silane treatment should be applied to enhance the resin bond to laboratory-processed composites. However, there is an urgent need for in vitro studies that evaluate the bond strength to new ceramic/polymer materials. CLINICAL SIGNIFICANCE: This article reviews the available dental literature on resin bond of laboratory composites and gives scientifically based guidance for their successful placement. Furthermore, this review demonstrated that future research for new ceramic/polymer materials is required.

Effect of core ceramic grinding on fracture behaviour of bilayered lithium disilicate glass-ceramic under two loading schemes.

OBJECTIVES: The purpose of this in vitro study was to evaluate the effect of core ceramic grinding on the fracture behaviour of bilayered lithium disilicate glass-ceramic (LDG) under two loading schemes. METHODS: Interfacial surfaces of sandblasted LDG disks (A) were ground with 220 (B), 500 (C) and 1200 (D) grit silicon carbide (SiC) sandpapers, respectively. Surface roughness and topographic analysis were performed using a profilometer and a scanning electron microscopy (SEM), and then underwent retesting after veneer firing. Biaxial fracture strength (σf) and Weibull modulus (m) were calculated either with core in tension (subgroup t) or in compression (subgroup c). Failure modes were observed by SEM, and loading induced stress distribution was simulated and analyzed by finite element analysis. Statistical data analysis was performed using Kruskal-Wallis, one-way ANOVA, and paired test at a significance level of 0.05. RESULTS: As the grits size of SiC increased, LDG surface roughness decreased from group A to D (p<0.001), which remained unchanged after veneer firing. No difference in σf (p=0.41 for subgroups At-Dt; p=0.11 for subgroups Ac-Dc), m values as well as failure modes was found among four subgroups for both loading schemes. Specimens in subgroup t showed higher σf (p<0.001) and m values than subgroup c. Stress distribution between loading schemes did not differ from each other. Cracks, as the dominant failure mode initiated from bottom tensile surface. No sign of interfacial cracking or delamination was observed for all groups. CONCLUSIONS: Technician grinding changed surface topography of LDG ceramic material, but was not detrimental to the bilayered system strength after veneer application. LDG bilayered system was more sensitive to fracture when loaded with veneer porcelain in tension. CLINICAL SIGNIFICANCE: Within the limitations of the simulated grinding applied, it is concluded that veneer porcelain can be applied directly after technician grinding of LDG ceramic as it has no detrimental effect on the strength of bilayered structures. The connector areas of LDG fixed dental prosthesis are more sensitive to fracture compared with single crowns, and should be fabricated with more caution.

Influence of veneer and cyclic loading on failure behavior of lithium disilicate glass-ceramic molar crowns.

OBJECTIVE: This in vitro study was designed to investigate the influence of the veneer and cyclic loading on the failure behavior of lithium disilicate glass-ceramic (LDG) crowns on maxillary first molar. METHODS: Sixty-four LDG crowns were divided into 4 groups (n=16). Thirty-two monolithic crowns were fabricated from IPS e.max Press (M), and the remaining bilayered crowns using cut-back technique and conventional manual layering technique from IPS e.max Press/Ceram (B). Monolithic or bilayered crowns were subjected to single-load-to-fracture (SLF) testing using a universal testing machine, before (M1 and B1) and after exposure to sliding-contact fatigue (SCF) testing (M2 and B2), consisting of 1,200,000 mechanical cycles (Fmax=98 N). Data were statistically analyzed using two-by-two factorial design ANOVA. Fractographic analysis was performed to determine the fracture modes of the failed specimens. RESULTS: The mean fracture load values (N±S.D.) for M1, B1, M2 and B2 were 2686±628 N, 1443±327 N, 2133±578 N and 1464±419 N, respectively. Significant differences were found between the failure loads of all groups (P<0.001), except between groups B1 and B2. Bulk fracture initiating from the occlusal surface is the primary failure mode of monolithic and veneered LDG crowns. Cracking that initiated from core-veneer interfacial defects and ultimately resulted in bulk fracture is another major failure origin of veneered all-ceramic crowns. SIGNIFICANCE: Veneer application resulted in significantly lower fracture load values compared to monolithic LDG crowns. Cyclic loading is an accelerating factor contributing to fracture for monolithic LDG crowns but not for bilayered ones.

Long-term performance of posterior InCeram Alumina crowns cemented with different luting agents: a prospective, randomized clinical split-mouth study over 5 years.

OBJECTIVES: This prospective, randomized clinical split-mouth study investigated the 5-year performance of InCeram Alumina posterior crowns cemented with three different luting cements. 4-META- and MDP-based cements were used for adhesive luting. Glass ionomer cement served as control. MATERIALS AND METHODS: Sixty patients were treated with 149 (n = 62 Panavia F/MDP; n = 59 SuperBond-C&B/4-META; n = 28 Ketac Cem/glass ionomer) InCeram Alumina crowns on vital molars and premolars in a comparable position. Follow-up examinations were performed annually up to 5 years after crown placement using the modified United States Public Health Service (USPHS) criteria. Kaplan-Meier survival analysis comprised secondary caries, clinically unacceptable fractures, root canal treatment and debonding. Kaplan-Meier success rate included restorations with minimal crevices, tolerable color deviations (<1 Vitashade), and clinically acceptable fractures. Logistic regression models with a random intercept were fitted. RESULTS: The 5-year Kaplan-Meier survival probabilities were: SuperBond-C&B 88.7 %, Panavia F 82.8 %, Ketac Cem 80.1 % with no significant difference (p = .813). Endodontical treatment was carried out on 7.4 % of all abutment teeth, and 5.4 % revealed secondary caries. Unacceptable ceramic fractures were observed in 7.4 %. Debonding was a rare complication (1.3 %). The 5 year Kaplan-Meier success rate was 91.6 % for SuperBond-C&B-, 87.4 % for Ketac Cem- and 86.3 % for Panavia F-bonded restorations with no significant difference (p = .624). All cement types showed significant marginal deterioration over time (p < .0001). CONCLUSIONS: Posterior InCeram Alumina crowns showed acceptable long-term survival and success rates independent of luting agent used. Ceramic fractures, endodontical treatments and secondary caries were the most frequent failures. CLINICAL RELEVANCE: Glass-infiltrated Alumina crowns in combination with adhesive as well as conventional cementation can be considered as a reliable treatment option in posterior teeth.

Marginal and internal fit of heat pressed versus CAD/CAM fabricated all-ceramic onlays after exposure to thermo-mechanical fatigue.

OBJECTIVES: The aim of the study was to evaluate the marginal and internal fit of heat-pressed and CAD/CAM fabricated all-ceramic onlays before and after luting as well as after thermo-mechanical fatigue. MATERIALS AND METHODS: Seventy-two caries-free, extracted human mandibular molars were randomly divided into three groups (n=24/group). All teeth received an onlay preparation with a mesio-occlusal-distal inlay cavity and an occlusal reduction of all cusps. Teeth were restored with heat-pressed IPS-e.max-Press* (IP, *Ivoclar-Vivadent) and Vita-PM9 (VP, Vita-Zahnfabrik) as well as CAD/CAM fabricated IPS-e.max-CAD* (IC, Cerec 3D/InLab/Sirona) all-ceramic materials. After cementation with a dual-polymerising resin cement (VariolinkII*), all restorations were subjected to mouth-motion fatigue (98 N, 1.2 million cycles; 5°C/55°C). Marginal fit discrepancies were examined on epoxy replicas before and after luting as well as after fatigue at 200× magnification. Internal fit was evaluated by multiple sectioning technique. For the statistical analysis, a linear model was fitted with accounting for repeated measurements. RESULTS: Adhesive cementation of onlays resulted in significantly increased marginal gap values in all groups, whereas thermo-mechanical fatigue had no effect. Marginal gap values of all test groups were equal after fatigue exposure. Internal discrepancies of CAD/CAM fabricated restorations were significantly higher than both press manufactured onlays. CONCLUSIONS: Mean marginal gap values of the investigated onlays before and after luting as well as after fatigue were within the clinically acceptable range. Marginal fit was not affected by the investigated heat-press versus CAD/CAM fabrication technique. Press fabrication resulted in a superior internal fit of onlays as compared to the CAD/CAM technique. CLINICAL RELEVANCE: Clinical requirements of 100 µm for marginal fit were fulfilled by the heat-press as well as by the CAD/CAM fabricated all-ceramic onlays. Superior internal fit was observed with the heat-press manufacturing method. The impact of present findings on the clinical long-term behaviour of differently fabricated all-ceramic onlays warrants further investigation.

Influence of preparation design and ceramic thicknesses on fracture resistance and failure modes of premolar partial coverage restorations.

STATEMENT OF PROBLEM: Preparation designs and ceramic thicknesses are key factors for the long-term success of minimally invasive premolar partial coverage restorations. However, only limited information is presently available on this topic. PURPOSE: The purpose of this in vitro study was to evaluate the fracture resistance and failure modes of ceramic premolar partial coverage restorations with different preparation designs and ceramic thicknesses. MATERIAL AND METHODS: Caries-free human premolars (n=144) were divided into 9 groups. Palatal onlay preparation comprised reduction of the palatal cusp by 2 mm (Palatal Onlay Standard), 1 mm (Palatal-Onlay-Thin), or 0.5 mm (Palatal Onlay Ultrathin). Complete-coverage onlay preparation additionally included the buccal cusp (Occlusal Onlay Standard; Occlusal Onlay Thin; Occlusal Onlay Ultrathin). Labial surface preparations with chamfer reductions of 0.8 mm (Complete-Veneer-Standard), 0.6 mm (Complete-Veneer-Thin), and 0.4 mm (Complete Veneer Ultrathin) were implemented for complete veneer restorations. Restorations were fabricated from a pressable lithium disilicate ceramic (IPS-e.max-Press) and cemented adhesively (Syntac-Classic/Variolink-II). All specimens were subjected to cyclic mechanical loading (F=49 N, 1.2 million cycles) and simultaneous thermocycling (5°C to 55°C) in a mouth-motion simulator. After fatigue, restorations were exposed to single-load-to-failure. Two-way ANOVA was used to identify statistical differences. Pair-wise differences were calculated and P-values were adjusted by the Tukey-Kramer method (α=.05). RESULTS: All specimens survived fatigue. Mean (SD) load to failure values (N) were as follows: 837 (320/Palatal-Onlay-Standard), 1055 (369/Palatal-Onlay-Thin), 1192 (342/Palatal-Onlay-Ultrathin), 963 (405/Occlusal-Onlay-Standard), 1108 (340/Occlusal-Onlay-Thin), 997 (331/Occlusal-Onlay-Ultrathin), 1361 (333/Complete-Veneer-Standard), 1087 (251/Complete-Veneer-Thin), 883 (311/Complete-Veneer-Ultrathin). Palatal-onlay restorations revealed a significantly higher fracture resistance with ultrathin thicknesses than with standard thicknesses (P=.015). Onlay restorations were not affected by thickness variations. Fracture loads of standard complete veneers were significantly higher than thin (P=.03) and ultrathin (P<.001) restorations. CONCLUSIONS: In this in vitro study, the reduction of preparation depth to 1.00 and 0.5 mm did not impair fracture resistance of pressable lithium-disilicate ceramic onlay restorations but resulted in lower failure loads in complete veneer restorations on premolars.

Load-bearing properties of minimal-invasive monolithic lithium disilicate and zirconia occlusal onlays: finite element and theoretical analyses.

OBJECTIVE: The aim of this study was to test the hypothesis that monolithic lithium disilicate glass-ceramic occlusal onlay can exhibit a load-bearing capacity that approaches monolithic zirconia, due to a smaller elastic modulus mismatch between the lithium disilicate and its supporting tooth structure relative to zirconia. METHODS: Ceramic occlusal onlays of various thicknesses cemented to either enamel or dentin were considered. Occlusal load was applied through an enamel-like deformable indenter or a control rigid indenter. Flexural tensile stress at the ceramic intaglio (cementation) surface-a cause for bulk fracture of occlusal onlays-was rigorously analyzed using finite element analysis and classical plate-on-foundation theory. RESULTS: When bonded to enamel (supported by dentin), the load-bearing capacity of lithium disilicate can approach 75% of that of zirconia, despite the flexural strength of lithium disilicate (400MPa) being merely 40% of zirconia (1000MPa). When bonded to dentin (with the enamel completely removed), the load-bearing capacity of lithium disilicate is about 57% of zirconia, still significantly higher than the anticipated value based on its strength. Both ceramics show slightly higher load-bearing capacity when loaded with a deformable indenter (enamel, glass-ceramic, or porcelain) rather than a rigid indenter. SIGNIFICANCE: When supported by enamel, the load-bearing property of minimally invasive lithium disilicate occlusal onlays (0.6-1.4mm thick) can exceed 70% of that of zirconia. Additionally, a relatively weak dependence of fracture load on restoration thickness indicates that a 1.2mm thin lithium disilicate onlay can be as fracture resistant as its 1.6mm counterpart.

Prospective clinical split-mouth study of pressed and CAD/CAM all-ceramic partial-coverage restorations: 7-year results.

The aim of this prospective clinical split-mouth study was to investigate the longterm performance of pressed and computer-aided design/computer-assisted manufacture (CAD/CAM) all-ceramic partial-coverage restorations (PCRs). Twentyfive patients were restored with 40 lithium disilicate pressed PCRs (IPS e.max-Press, Ivoclar Vivadent) and 40 leucite-reinforced glass-ceramic CAD/CAM PCRs (ProCAD, Ivoclar Vivadent). All restorations were placed in vital first or second molars. The 7-year Kaplan-Meier survival rate was 100% for pressed PCRs and 97% for CAD/ CAM PCRs. Both systems showed significant deterioration over time in all modified United States Public Health Service criteria. Increased surface roughness and impaired color match were significantly more prevalent with pressed PCRs. Based on the 7-year data, both all-ceramic systems can be considered reliable treatment options for posterior PCRs.

Monolithic and bi-layer CAD/CAM lithium-disilicate versus metal-ceramic fixed dental prostheses: comparison of fracture loads and failure modes after fatigue.

OBJECTIVES: The authors analyzed the effect of fatigue on the survival rate and fracture load of monolithic and bi-layer CAD/CAM lithium-disilicate posterior three-unit fixed dental prostheses (FDPs) in comparison to the metal-ceramic gold standard. MATERIALS AND METHODS: The authors divided 96 human premolars and molars into three equal groups. Lithium-disilicate ceramic (IPS-e.max-CAD) was milled with the CEREC-3-system in full-anatomic FDP dimensions (monolithic: M-LiCAD) or as framework (Bi-layer: BL-LiCAD) with subsequent hand-layer veneering. Metal-ceramic FDPs (MC) served as control. Single-load-to-failure tests were performed before and after mouth-motion fatigue. RESULTS: No fracture failures occurred during fatigue. Median fracture loads in [N], before and after fatigue were, respectively, as follows: M-LiCAD, 1,298/1,900; BL-LiCAD, 817/699; MC, 1,966/1,818. M-LiCAD and MC FPDs revealed comparable fracture loads and were both significantly higher than BL-LiCAD. M-LiCAD and BL-LiCAD both failed from core/veneer bulk fracture within the connector area. MC failures were limited to ceramic veneer fractures exposing the metal core. Fatigue had no significant effect on any group. CONCLUSIONS: Posterior monolithic CAD/CAM fabricated lithium-disilicate FPDs were shown to be fracture resistant with failure load results comparable to the metal-ceramic gold standard. Clinical investigations are needed to confirm these promising laboratory results. CLINICAL RELEVANCE: Monolithic CAD/CAM fabricated lithium-disilicate FDPs appeared to be a reliable treatment alternative for the posterior load-bearing area, whereas FDPs in bi-layer configuration were susceptible to low load fracture failure.

Effect of core design and veneering technique on damage and reliability of Y-TZP-supported crowns.

OBJECTIVES: To evaluate the effect of framework design modification and veneering techniques in fatigue reliability and failure modes of veneered Yttria-Stabilized Tetragonal Zirconia Polycrystals (Y-TZP) crowns. METHODS: A CAD-based mandibular molar crown preparation served as a master die. Y-TZP crown cores (VITA-In-Ceram-YZ, Vita-Zahnfabrik, Bad Säckingen, Germany) in conventional (0.5mm uniform thickness) or anatomically designed fashion (cusp support) were porcelain veneered with either hand-layer (VM9) or pressed (PM9) techniques. Crowns (n=84) were cemented on 30 days aged dentin-like composite dies with resin cement. Crowns were subjected to single load to fracture (n=3 each group) and mouth-motion step-stress fatigue (n=18) by sliding a WC indenter (r=3.18 mm) 0.7 mm buccally on the inner incline surface of the mesio-lingual cusp. Stress-level curves (use level probability lognormal) and reliability (with 2-sided 90% confidence bounds, CB) for completion of a mission of 50.000 cycles at 200 N load were calculated. Fractographic analyses were performed under light-polarized and scanning electron microscopes. RESULTS: Higher reliability for hand-layer veneered conventional core (0.99, CB 0.98-1) was found compared to its counterpart press-veneered (0.50 CB 0.33-65). Framework design modification significantly increased reliability for both veneering techniques (PM9 [0.98 CB 0.87-0.99], VM9 [1.00 CB 0.99-1]) and resulted in reduced veneer porcelain fracture sizes. Main fracture mode observed was veneer porcelain chipping, regardless of framework design and veneering technique. SIGNIFICANCE: Hand-layer porcelain veneered on conventional core designs presented higher reliability than press-veneered with similar core designs. Anatomic core design modification significantly increased the reliability and resulted in reduced chip size of either veneering techniques.

Influence of veneer application on fracture behavior of lithium-disilicate-based ceramic crowns.

OBJECTIVES: To assess the influence of veneer application on fracture behavior, namely failure load and failure mode, of standardized lithium-disilicate-based crowns. METHODS: Forty molar crowns (IPS e.max Press, IvoclarVivadent) were fabricated in full anatomic (without veneer, 1.5-2.0mm at occlusal surface) and bi-layer (the occlusal surface is 0.7 mm of veneer and 0.8-1.3mm core) contour representing two groups. Crown specimens were seated and adhered on composite resin dies. All specimens were loaded with a 6mm diameter steatite sphere over the central fissure to failure. Failure modes and fractographic patterns were analyzed by optical stereo and scanning electron microscopy (SEM). Fracture loads of the two groups were compared by the t-test, while the failure modes were analyzed by Pearson Chi-square test. RESULTS: There was a statistically significant difference in mean fracture load values (N±S.D.) between full anatomic [(2665.4±759.2)N] and veneered crowns [(1431.1±404.3)N] (p<0.001) and also in failure modes (χ(2)=6.465, p=0.011). Full anatomic crowns mainly showed bulk fracture, whereas veneered specimens predominately showed cohesive veneer and ceramic interface failure (75%); solely cohesive veneer failure (20%); and bulk fracture (5%). SIGNIFICANCE: Within the limitations of this study, veneer application resulted in significant lower fracture load values compared to full anatomic crowns. Fracture initiated from occlusal fissures near the load application site. A combination of cohesive veneer and ceramic interface failure represents the main failure mode of lithium-disilicate-based bi-layered crowns, whereas full anatomic crowns failed mainly from ceramic bulk fracture at the occlusal fissures.

All-ceramic systems: laboratory and clinical performance.

Several all-ceramic systems have been developed in dentistry to meet the increased expectations of patients and dentists for highly aesthetic, biocompatible, and long-lasting restorations. However, early bulk fractures or chippings have led the research community to investigate the mechanical performance of the all-ceramic systems. This overview explores the current knowledge of monolithic and bilayer dental all-ceramic systems, addressing composition and processing mechanisms, laboratory and clinical performance, and possible future trends for all-ceramic materials.

Monolithic CAD/CAM lithium disilicate versus veneered Y-TZP crowns: comparison of failure modes and reliability after fatigue.

PURPOSE: The aim of this research was to evaluate the fatigue behavior and reliability of monolithic computer-aided design/computer-assisted manufacture (CAD/CAM) lithium disilicate and hand-layer-veneered zirconia all-ceramic crowns. MATERIALS AND METHODS: A CAD-based mandibular molar crown preparation, fabricated using rapid prototyping, served as the master die. Fully anatomically shaped monolithic lithium disilicate crowns (IPS e.max CAD, n = 19) and hand-layer-veneered zirconia-based crowns (IPS e.max ZirCAD/Ceram, n = 21) were designed and milled using a CAD/CAM system. Crowns were cemented on aged dentinlike composite dies with resin cement. Crowns were exposed to mouth-motion fatigue by sliding a WC-indenter (r = 3.18 mm) 0.7 mm lingually down the distobuccal cusp using three different step-stress profiles until failure occurred. Failure was designated as a large chip or fracture through the crown. If no failures occurred at high loads (> 900 N), the test method was changed to staircase r ratio fatigue. Stress level probability curves and reliability were calculated. RESULTS: Hand-layer-veneered zirconia crowns revealed veneer chipping and had a reliability of < 0.01 (0.03 to 0.00, two-sided 90% confidence bounds) for a mission of 100,000 cycles and a 200-N load. None of the fully anatomically shaped CAD/CAM-fabricated monolithic lithium disilicate crowns failed during step-stress mouth-motion fatigue (180,000 cycles, 900 N). CAD/CAM lithium disilicate crowns also survived r ratio fatigue (1,000,000 cycles, 100 to 1,000 N). There appears to be a threshold for damage/bulk fracture for the lithium disilicate ceramic in the range of 1,100 to 1,200 N. CONCLUSION: Based on present fatigue findings, the application of CAD/CAM lithium disilicate ceramic in a monolithic/fully anatomical configuration resulted in fatigue-resistant crowns, whereas hand-layer-veneered zirconia crowns revealed a high susceptibility to mouth-motion cyclic loading with early veneer failures.

Fatigue life and failure modes of crowns systems with a modified framework design.

OBJECTIVES: To evaluate the effect of framework design on the fatigue life and failure modes of metal ceramic (MC, Ni-Cr alloy core, VMK 95 porcelain veneer), glass-infiltrated alumina (ICA, In-Ceram Alumina/VM7), and veneered yttria-stabilized tetragonal zirconia polycrystals (Y-TZP, IPSe.max ZirCAD/IPS e.max,) crowns. METHODS: Sixty composite resin tooth replicas of a prepared maxillary first molar were produced to receive crowns systems of a standard (MCs, ICAs, and Y-TZPs, n=10 each) or a modified framework design (MCm, ICAm, and Y-TZPm, n=10 each). Fatigue loading was delivered with a spherical steel indenter (3.18mm radius) on the center of the occlusal surface using r-ratio fatigue (30-300N) until completion of 10(6) cycles or failure. Fatigue was interrupted every 125,000 cycles for damage evaluation. Weibull distribution fits and contour plots were used for examining differences between groups. Failure mode was evaluated by light polarized and SEM microscopy. RESULTS: Weibull analysis showed the highest fatigue life for MC crowns regardless of framework design. No significant difference (confidence bound overlaps) was observed between ICA and Y-TZP with or without framework design modification. Y-TZPm crowns presented fatigue life in the range of MC crowns. No porcelain veneer fracture was observed in the MC groups, whereas ICAs presented bulk fracture and ICAm failed mainly through the veneer. Y-TZP crowns failed through chipping within the veneer, without core fractures. CONCLUSIONS: Framework design modification did not improve the fatigue life of the crown systems investigated. Y-TZPm crowns showed comparable fatigue life to MC groups. Failure mode varied according to crown system.

Fatigue and damage accumulation of veneer porcelain pressed on Y-TZP.

OBJECTIVES: This study compared the reliability and fracture patterns of zirconia cores veneered with pressable porcelain submitted to either axial or off-axis sliding contact fatigue. METHODS: Forty-two Y-TZP plates (12mm x 12mm x 0.5mm) veneered with pressable porcelain (12mm x 12mm x 1.2mm) and adhesively luted to water aged composite resin blocks (12mm x 12mm x 4mm) were stored in water at least 7 days prior to testing. Profiles for step-stress fatigue (ratio 3:2:1) were determined from single load to fracture tests (n=3). Fatigue loading was delivered on specimen either on axial (n=18) or off-axis 30 degrees angulation (n=18) to simulate posterior tooth cusp inclination creating a 0.7mm slide. Single load and fatigue tests utilized a 6.25mm diameter WC indenter. Specimens were inspected by means of polarized-light microscope and SEM. Use level probability Weibull curves were plotted with 2-sided 90% confidence bounds (CB) and reliability for missions of 50,000 cycles at 200N (90% CB) were calculated. RESULTS: The calculated Weibull Beta was 3.34 and 2.47 for axial and off-axis groups, respectively, indicating that fatigue accelerated failure in both loading modes. The reliability data for a mission of 50,000 cycles at 200N load with 90% CB indicates no difference between loading groups. Deep penetrating cone cracks reaching the core-veneer interface were observed in both groups. Partial cones due to the sliding component were observed along with the cone cracking for the off-axis group. No Y-TZP core fractures were observed. CONCLUSIONS: Reliability was not significantly different between axial and off-axis mouth-motion fatigued pressed over Y-TZP cores, but incorporation of sliding resulted in more aggressive damage on the veneer.