Randomized,Controlled Clinical Trial of Bilayer Ceramic and Metal‐Ceramic Crown Performance

Purpose : Analyzing the clinical performance of restorative materials is important, as there is an expectation that these materials and procedures will restore teeth and do no harm. The objective of this research study was to characterize the clinical performance of metal‐ceramic crowns, core ceramic crowns, and core ceramic/veneer ceramic crowns based on 11 clinical criteria. Materials and Methods : An IRB‐approved, randomized, controlled clinical trial was conducted as a single‐blind pilot study. The following three types of full crowns were fabricated: (1) metal‐ceramic crown (MC) made from a Pd‐Au‐Ag‐Sn‐In alloy (Argedent 62) and a glass‐ceramic veneer (IPS d.SIGN veneer); (2) non‐veneered (glazed) lithium disilicate glass‐ceramic crown (LDC) (IPS e.max Press core and e.max Ceram Glaze); and (3) veneered lithia disilicate glass‐ceramic crown (LDC/V) with glass‐ceramic veneer (IPS Empress 2 core and IPS Eris). Single‐unit crowns were randomly assigned. Patients were recalled for each of 3 years and were evaluated by two calibrated clinicians. Thirty‐six crowns were placed in 31 patients. A total of 12 crowns of each of the three crown types were studied. Eleven criteria were evaluated: tissue health, marginal integrity, secondary caries, proximal contact, anatomic contour, occlusion, surface texture, cracks/chips (fractures), color match, tooth sensitivity, and wear (of crowns and opposing enamel). Numerical rankings ranged from 1 to 4, with 4 being excellent, and 1 indicating a need for immediate replacement. Statistical analysis of the numerical rankings was performed using a Fisher's exact test. Results : There was no statistically significant difference between performance of the core ceramic crowns and the two veneered crowns at year 1 and year 2 (p > 0.05). All crowns were rated either as excellent or good for each of the clinical criteria; however, between years 2 and 3, gradual roughening of the occlusal surface occurred in some of the ceramic‐ceramic crowns, possibly caused by dissolution and wear of the glaze. Statistically significant differences in surface texture (p= 0.0013) and crown wear (p= 0.0078) were found at year 3 between the metal‐ceramic crowns and the lithium‐disilicate‐based crowns. Conclusion : Based on the 11 criteria, the clinical performance of ceramic‐ceramic crowns was comparable to that of the metal‐ceramic crowns after 2 years; however, gradual roughening occurred between years 2 and 3, which resulted in differences in surface texture and wear.     

Porcelain Fracture Resistance of Screw‐Retained,Cement‐Retained,and Screw‐Cement‐Retained Implant‐Supported Metal Ceramic Posterior Crowns

Purpose: The purpose of this in vitro study was to compare the porcelain fracture resistance between screw‐retained, cement‐retained, and combined screw‐ and cement‐retained metal–ceramic (MC) implant‐supported posterior single crowns; and to investigate the effect of offsetting the occlusal screw‐access opening on porcelain fracture resistance of screw‐retained and cement‐retained MC implant‐supported posterior single crowns. Materials and Methods: Forty standardized MC molar‐shaped restorations were fabricated. The 40 restorations were divided into four groups (SRC, SRO, CRP, and CSC) of 10 specimens each. Group SRC: screw‐retained, screw‐access hole placed in the center of the occlusal surface; Group SRO: screw‐retained, screw access hole placed 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group CRP: cement‐retained, zinc phosphate cement was used; Group CSC: cement‐retained with a screw‐access hole in the center of the occlusal surface. The screw‐retained restorations and abutments were directly attached to 3i implant fixtures embedded in acrylic resin blocks. Subsequently, all test specimens were thermocycled and vertically loaded in a universal testing machine at a crosshead speed of 2 mm/min until fracture. Mean values of load at fracture (in N) were calculated in each group and compared with a one‐way ANOVA and Tukey's Studentized test (α= 0.05). Results: Mean values of loads required to fracture the restorations were as follows (N): Group SRC: 1721 ± 593; Group SRO: 1885 ± 491; Group CRP: 3707 ± 1086; Group CSC: 1700 ± 526. Groups SRC, SRO, and CSC required a significantly lower force to fracture the porcelain than did the CRP group (p < 0.05). Conclusion: The cement‐retained restorations showed significantly higher mean fracture loads than the restorations having screw‐access openings in their occlusal surface. The position of the screw‐access hole within the occlusal surface did not significantly affect the porcelain fracture resistance.     

A Quick Esthetic Remount Cast for All‐Ceramic Restorations

A technique is presented for the expedited fabrication of a remount cast for the alteration of all‐ceramic crowns and fixed partial dentures. The remount cast allows the laboratory technician to know the precise location of the gingival tissues and allows modification of all‐ceramic restorations.     

Impact Fracture Resistance of Two Titanium‐Abutment Systems Versus a Single‐Piece Ceramic Implant

Background: The number of patients with oral implants has increased significantly. However, the literature addressing the effect of impact force on titanium and/or ceramic implants is inconclusive. This study sought to determine the fracture resistance to impact load of titanium and ceramic endosseous oral implants. Materials and Methods: Endosseous oral implants were vertically positioned in two different mounting media: brass and a bone‐simulation material. The implant configurations tested included an experimental one‐piece Y‐TZP implant and a commercially available titanium implant (external hex) with both titanium and zirconia abutments. The specimens were subjected to an impact load using a pendulum impact tester with tup weights varying from 0.9 to 4.5 kg delivered at a radius of 40.64 mm. Loads were delivered to the abutment at a point 4.27 mm above the implant fixture and block junction. Statistical differences (p < .05) were established using the F‐test for variances and, when different, t‐test assuming unequal variances. Results: For implants clamped in brass, the titanium implant with titanium abutment required the greatest energy to fracture the implant‐abutment system (only the abutment screw failed). The ceramic implant and ceramic abutment on titanium implant presented the lowest fracture energy (p < .01). No significant differences were observed when different systems were inserted into the foam blocks of the bone substitute (p > .25). Conclusion: This investigation showed that the fracture energy of two titanium‐abutment systems versus a single‐piece Y‐TZP implant in foam blocks simulating bone elastic modulus was not different, and that differences occurred when the embedding material elastic modulus was increased an order of magnitude.     

The all‐ceramic,inlay supported fixed partial denture. Part 1. Ceramic inlay preparation design: a literature review

The effect of cavity design is a controversial and underrated factor in the clinical success of ceramic inlays and inlay supported prosthesis. Many articles and studies have been conducted into the advantages and disadvantages of isolated aspects of preparation design, but lacking is a review of the most relevant papers which bring together a consensus on all the critical features. Hence, a review and analysis of cavity depth, width, preparation taper and internal line angles is warranted in our attempts to formulate preparation guidelines that will lead to clinically successful, all‐ceramic inlay restorations and ceramic inlay supported prosthesis.     

Marginal Gap,Internal Fit,and Fracture Load of Leucite‐Reinforced Ceramic Inlays Fabricated by CEREC inLab and Hot‐Pressed Techniques

Purpose: This in vitro study was designed to evaluate and compare the marginal gap, internal fit, and fracture load of resin‐bonded, leucite‐reinforced glass ceramic mesio‐occlusal‐distal (MOD) inlays fabricated by computer‐aided design/manufacturing (CAD/CAM) or hot pressing. Materials and Methods: Fifty caries‐free extracted human molars were prepared for standardized MOD inlays. Impressions of each specimen were made and poured using type IV dental stone. Dies were randomly divided into two equal groups. Twenty‐five ceramic inlays were fabricated by the hot‐pressed technique using IPS Empress leucite‐reinforced glass ceramics, and the other 25 ceramic inlays were produced by CAD/CAM technology using ProCAD leucite‐reinforced ceramic blocks and CEREC inLab facilities. Inlays were bonded to the teeth using a dual‐cured resin cement. The specimens were stored in distilled water at 37°C for 24 hours and then thermocycled for 5000 cycles. The marginal gap measurements were taken with a stereomicroscope. Specimens in each group of inlay systems were randomly divided into two subgroups of 10 and 15 specimens each. Ten specimens in each subgroup were sectioned mesiodistally for evaluation of the internal fit. The fracture load of specimens in the second subgroup (n = 15) of the two inlay systems was determined under compressive load in a universal testing machine. Data were analyzed using Student's t‐test at a significance level of p < 0.05. Results: The mean marginal and internal gap size in both IPS Empress and ProCAD inlays were less than 100 μm; however, the marginal gap for the IPS Empress restorations was significantly higher than that of ProCAD restorations (p < 0.05). There was no significant difference in the mean internal fit or the fracture load between the two glass ceramic inlays (p > 0.05). Conclusions: The leucite‐reinforced glass ceramic inlay restorations fabricated by CEREC inLab (CAD/CAM) and the hot‐pressed technique provided clinically acceptable marginal and internal fit with comparable fracture loads after luting.     

Knoop Hardness and Effectiveness of Dual‐Cured Luting Systems and Flowable Resin to Bond Leucite‐Reinforced Ceramic to Enamel

Purpose: The aim of this study was to evaluate the Knoop microhardness and microshear bond strength (MSBS) of dual‐cured luting systems and flowable resin bonded to leucite‐reinforced ceramics and enamel. Materials and Methods: Eighty bovine incisors were randomly divided into four groups per test (microhardness and microshear; n = 10) according to the bonding procedure: Excite DSC/Variolink, Clearfil SE Bond/Panavia F, Adper Scotchbond Multi‐Purpose Plus/RelyX ARC, and Adper Single Bond 2/Filtek Z350 Flow. For the KHN measurement, the cement was applied on the enamel surface and light‐cured through a ceramic disk (5 mm diameter × 1.2 mm thick). Five indentations were performed in each specimen and measured at HMV‐2. For the microshear test, two cylinders of a leucite‐reinforced ceramic (1 mm diameter × 2 mm height) were bonded to the enamel substrate in accordance with the bonding procedures previously established. One cylinder was tested 24 hours after cementation, and the other was subjected to thermocycling (2000 cycles) and then submitted to an MSBS test. The data from the hardness and bond strength tests were subjected to one‐ and two‐way repeated‐measures analysis of variance (ANOVA), respectively, and to Tukey's test (α= 0.05). Results: Scotchbond/RelyX ARC presented higher values of bond strength, while Single Bond/Z350 Flow showed lower values. The thermocycling promoted a reduction in the bond strength values for all groups. Panavia F presented higher values of KHN, and the flowable resin presented the lowest. RelyX ARC and Variolink presented intermediate values on hardness evaluation. Conclusions: For ceramic cementation, dual‐cured resin luting systems promoted more reliable bonding and microhardness values than the flowable resin.     

Fracture Loads of All‐Ceramic Crowns under Wet and Dry Fatigue Conditions

Purpose: The aim of this study was to test the hypothesis that fracture loads of fatigued dental ceramic crowns are affected by testing environment and luting cement. Materials and Methods: One hundred and eighty crowns were prepared from bovine teeth using a lathe. Ceramic crowns were prepared from three types of ceramic systems: an alumina‐infiltrated ceramic, a lithia‐disilicate‐based glass ceramic, and a leucite‐reinforced ceramic. For each ceramic system, 30 crowns were cemented with a composite resin cement, and the remaining 30 with a resin‐modified glass ionomer cement. For each ceramic system and cement, ten specimens were loaded to fracture without fatiguing. A second group (n = 10) was subjected to cyclic fatigue and fracture tested in a dry environment, and a third group (n = 10) was fatigued and fractured in distilled water. The results were statistically analyzed using one‐way ANOVA and Tukey HSD test. Results: The fracture loads of ceramic crowns decreased significantly after cyclic fatigue loading (p≤ 0.05); furthermore, fracture loads of crowns fatigued in a wet environment were statistically lower than those in a dry environment (p < 0.05). Crowns luted with a composite resin cement showed statistically greater fracture loads than those luted with a resin‐modified glass ionomer cement (p≤ 0.05). Conclusions: Fracture load of the three ceramic systems was found to be influenced by ceramic composition. Moreover, cement and fatigue condition influenced the fracture loads of the crown specimens evaluated in this study.     

The Effects of Adhesive Type and Thickness on Stress Distribution in Molars Restored with All‐Ceramic Crowns

Purpose: This study investigated the effects of luting cement type and thickness on the stress distribution within all‐ceramic crowns using finite element analysis. Materials and Methods: An all‐ceramic crown restoration of the mandibular right first molar was prepared according to standard dental processes and scanned using micro‐computed tomography. Eight 3D FE models were then developed that accounted for two adhesive systems, each with cement thickness of 60 μm, 90 μm, 120 μm, and 150 μm. The models were subjected to four loading conditions, and stresses in the veneer and core layers were evaluated. Results: The stress distribution and maximum stresses in the veneer, core, and cement are presented in corresponding loading conditions. The cement with higher elastic modulus resulted in lower tensile stresses in the veneer and core layers, and the shear strength of the cement was critical to the intactness of the all‐ceramic crown. Conclusion: The cement thickness acts as a cushion between the crown and dentin substrate. Although there is an optimal thickness (approximately 90 μm) that can reduce the stress level in ceramic crowns, cement thickness is not very important to stresses in the core or veneer in most cases when compared to the influence of loading conditions or cement moduli.     

The Effect of Multiple Firings on Microtensile Bond Strength of Core‐Veneer Zirconia‐Based All‐Ceramic Restorations

Purpose: Differences in core and veneer coefficients of thermal expansion, firing shrinkage, and speed of increasing and decreasing the temperature may generate stress in veneered all‐ceramic restorations. Given the necessity of performing multiple firing cycles to achieve improved contour, color, and esthetics, the purpose of this study was to determine the effect of multiple firing cycles on the microtensile bond strength (MTBS) of zirconia core to the porcelain veneer in zirconia‐based all‐ceramic restorations. Materials and Methods: Thirty blocks (12 × 12 × 4 mm³) of semi‐sintered zirconia were machined and sintered according to manufacturer's instruction. Specimens were placed in three groups based on the number of firing cycles (4, 6, 8) for the veneering process. After veneering, the specimens were sectioned into microbars with 8 mm length and 1 mm cross‐section. Twenty sound microbars in each group were stressed to failure in a microtensile tester machine at 1 mm/min. Fractured specimens were surveyed under a scanning electron microscope and classified as cohesive in core, cohesive in veneer, and mixed. MTBS data were analyzed using one‐way ANOVA and Tukey test (p < 0.05). Results: The mean MTBS (MPa) after 4, 6, and 8 firing cycles were 30.33 ± 2.13, 27.43 ± 1.79, and 25.06 ± 1.76, respectively. There was a statistically significant difference between the bond strengths of each of the three groups (p < 0.001). Conclusion: Increase in firing cycles decreased MTBS. Most of the failures (90–95%) in all three groups were cohesive in the veneering porcelain and did not change as the number of firing cycles increased.     

Fracture Resistance of Three Ceramic Inlay‐Retained Fixed Partial Denture Designs. An In Vitro Comparative Study

Purpose: The fracture resistance of ceramic inlay‐retained fixed partial dentures (CIRFPDs) was studied. Materials and Methods: Thirty CIRFPDs were constructed using ice zircon milled ceramic material. Specimens were divided into three groups, 10 specimens each, according to the abutment preparation: inlay‐shaped (occluso‐proximal inlay + proximal box), tub‐shaped (occluso‐proximal inlay), and proximal box‐shaped preparations. Each group was then subdivided into two subgroups of five specimens each, according to the span of the edentulous area representing a missing premolar or molar. All specimens were subjected to a fracture resistance test. Results: CIRFPDs with inlay‐shaped retainers showed the highest fracture resistance values for missing premolars and molars. CIRFPDs with box‐shaped retainers showed lower fracture resistance values. Statistical analysis revealed a significant difference between the three tested CIRFPD designs. There was a statistically significant difference between CIRFPDs constructed for the replacement of molars and those constructed for the replacement of premolars. The CIRFPD constructed for the replacement of molars gave lower fracture resistance values with the three tested designs. All the fracture resistance values obtained in this study were superior to the assumed maximum mastication forces. Failure mode was delamination and chipping of the veneering material. Conclusions: There was a statistically significant difference between the three designs of CIRPFDs tested. There was a statistically significant difference between CIRFPDs constructed for the replacement of molars than those constructed for the replacement of premolars. The CIRFPDs constructed for the replacement of molars gave lower fracture resistance values with the three tested designs. All fracture resistance values obtained in this study were superior to the assumed maximum mastication forces.