The Effect of Die Material on the Crown Fracture Strength of Zirconia Crowns.

BACKGROUND: Determination of the eligibility of several tooth analog materials for use in crown fracture testing. METHODS: A standardized premolar crown preparation was replicated into three types of resin dies (C&B, low modulus 3D printed resin; OnX, high modulus 3D printed resin composite; and highest modulus milled resin composite). 0.8 mm zirconia crowns were bonded to the dies and the maximum fracture load of the crowns was tested. Twelve extracted human premolars were prepared to a standardized crown preparation, and duplicate dies of the prepared teeth were 3D printed out of C&B. Zirconia crowns were bonded to both the dies and natural teeth, and their fracture load was tested. RESULTS: There was no statistical difference between the fracture load of zirconia crowns bonded to standardized dies of C&B (1084.5 ± 134.2 N), OnX (1112.7 ± 109.8 N) or Lava Ultimate (1137.5 ± 88.7 N) (p = 0.580). There was no statistical difference between the fracture load of crowns bonded to dentin dies (1313 ± 240 N) and a 3D-printed resin die (C&B, 1156 ± 163 N) (p = 0.618). CONCLUSIONS: There was no difference in the static fracture load of zirconia crowns bonded to standardized resin dies with different moduli or between a low modulus resin die and natural dentin die.

Shear bond strength of orthodontic brackets bonded to high-translucent dental zirconia with different surface treatments: An in vitro study.

PURPOSE: The objective of this study was to compare the shear bond strengths of orthodontic brackets bonded to translucent dental zirconia samples which are anatomically accurate and treated with various surface treatments. METHODS: This in vitro study included 156 samples from 3 brands of high-translucent zirconia split into a control group and 4 surface treatment groups: 9.6% hydrofluoric acid etching, 50-micron aluminium oxide particle air abrasion, and 30-micron tribochemical silica coating (TBS) particle air abrasion with and without silane application. After surface treatment, all groups were primed with a 10-MDP primer and bonded to metal orthodontic brackets. Shear bond strength (SBS) was tested and results were compared between all groups. Data analysis consisted of a balanced two-factor factorial ANOVA, a Shapiro-Wilks test, and a non-parametric permutation test. The significance level was set at 0.05. RESULTS: Among all surface treatments, aluminium oxide particle abrasion produced significantly higher SBS (P≤0.002). Lava™ Plus zirconia samples had significantly higher SBS than Cercon® samples (P<0.0001). TBS surface treatment produced significantly higher SBS on Lava™ Plus samples than it did on the other zirconia brands (P=0.032). CONCLUSIONS: This study indicated that mechanical abrasion using aluminium oxide in combination with a 10-MDP primer creates a higher SBS to high-translucent zirconia than the bond created by tribochemical silica coating. Also, there was no significant difference in ARI regardless of zirconia brand or surface preparation.

Wear of lithium disilicate opposed by various ceramic materials.

OBJECTIVES: To compare volumetric wear of lithium disilicate against different ceramic (3 mol% yttria-stabilized (3Y) zirconia, 5 mol% yttria-stabilized (5Y) zirconia, lithium disilicate, porcelain and enamel antagonists). MATERIALS AND METHODS: Forty lithium disilicate (e.max CAD) specimens (n = 8/antagonist) were wet sanded to 1200grit SiC and mounted into a UAB wear device. Antagonist spheres (diameter = 4.75 mm) were made from polished 3Y zirconia, 5Y zirconia, lithium disilicate, porcelain and human enamel. A two-body wear test was performed with 20 N load and 1.5 mm slide for 400,000 cycles at 1 Hz. 33% glycerin was used as a lubricant. Wear facets were measured with optical profilometry. Wear scar areas of antagonists were measured with digital microscopy. Scanning electron microscopy was performed on wear facets and scars. Vicker's microhardness was measured of all antagonist materials. All data were compared with 1-way ANOVA and Tukey post-hoc analysis. RESULTS: Significant differences in lithium disilicate volumetric wear (mm3 ) occurred with various antagonist materials: 0.38 ± 0.01a (3Y zirconia), 0.33 ± 0.01b, (5Y zirconia), 0.16 ± 0.01c (lithium disilicate), 0.11 ± 0.03d, (enamel), and 0.07 ± 0.01e (porcelain). The lithium disilicate antagonist demonstrated a larger wear scar than other materials. Zirconia was the hardest material and enamel the least hard. CONCLUSIONS: Zirconia causes significant wear on lithium disilicate and lithium disilicate causes significant wear against itself. CLINICAL SIGNIFICANCE: When selecting a material to oppose an existing lithium disilicate crown, a porcelain or lithium disilicate surface would cause significantly less wear to the existing crown. If an existing zirconia crown exists opposed to a prepared tooth, lithium disilicate may not be an ideal material selection to restore the tooth.

Methods to Clean Residual Resin Cement from Lithium-Disilicate Glass-Ceramic.

PURPOSE: To compare the effect of different methods of cleaning residual composite cement from the surface of lithium-disilicate glass-ceramic on its bond strength. MATERIALS AND METHODS: Blocks of lithium-silicate glass-ceramic (e.max CAD) were coated with composite cement. Blocks in a positive control (CO+) group received no cement; negative controls (CO-) received composite cement. After water storage (24 h), specimens were cleaned as follows (n = 20/group): BUR: grinding with a fine-grit diamond bur (20 s); ALUM: air abrasion with 50-µm alumina (10 s); GLASS: air abrasion with 50-µm glass beads (10 s); FURN: firing in ceramic furnace and cleaning with ethanol; SULF: immersion in sulfonic acid solution (1 h); HYFL: no additional treatment. All specimens were etched with hydrofluoric acid, aside from the CO- group, and treated with silane. A 1.5-mm diameter cement-filled tube was affixed to the specimens and light polymerized. Specimens were stored in 37°C water for 24 h (n = 10) or 90 days (n = 10). Shear bond strength was tested. Two-way ANOVA and post-hoc Tukey tests were performed. Specimens from each group were examined with SEM. RESULTS: Bond strength significantly differed according to surface cleaning method (p < 0.01) and storage time (p < 0.01), but their interaction was not significant (p = 0.264). Longer storage time decreased the bond strength. BUR, ALUM, GLASS, and FURN did not differ statistically significantly from CO+, but were significantly greater than CO-. SULF and HYFL did not differ statistically significantly from CO- and were significantly lower than CO+. CONCLUSIONS: Cleaning composite cement with BUR, ALUM, GLASS, and FURN restored bond strengths to that of the positive control. However, only GLASS and FURN did not roughen the surface of the underlying lithium-silicate glass-ceramic.

Effect of Endodontic Access Preparation on Fracture Load of Translucent versus Conventional Zirconia Crowns with Varying Occlusal Thicknesses.

PURPOSE: To evaluate the effect of endodontic access hole preparation on fracture resistance of translucent zirconia (5Y) and conventional zirconia crowns (3Y) with varying occlusal thicknesses. MATERIALS AND METHODS: Polymethylmethacrylate (PMMA) dies, representing a prepared tooth, were milled. Zirconia crowns with 1 mm thick axial walls and varying occlusal thicknesses were milled from 3Y (Cercon HT) or 5Y (Cercon XT) zirconia discs and sintered. 160 crowns were divided into 16 groups (n = 10 per group) based on the zirconia type (3Y, 5Y), occlusal thickness (0.5, 1.0, 1.5, 2.0 mm), and access hole preparation (with access hole, control). Crowns were cemented on the PMMA dies with resin-modified glass ionomer cement (Rely X Luting Plus) under constant weight (500 g) and thermocycled for 10,000 cycles. In half of the samples, following 5000 cycles of thermocycling, a uniform endodontic access hole was created using a diamond bur and restored immediately with resin composite (Filtek Supreme Ultra, 3M ESPE). The fracture resistance of the specimens was tested on an Instron 5566 universal testing machine with a stainless steel ball indenter (9.0 mm dia.) and the maximum load before failure was recorded as fracture load (N). Three-way ANOVA testing examined the effect of zirconia type, occlusal thickness, and access hole preparation on fracture loads of the crowns. Statistical tests were two-sided and significance level was set at 95% (α = 0.05). RESULTS: Fracture load was significantly affected by the type of zirconia, occlusal thickness, and access hole preparation (p < 0.001). Pairwise comparisons revealed that access hole preparation significantly reduced the fracture load of 3Y crowns with 0.5 or 1.0 mm of occlusal thickness and 5Y zirconia crowns with 0.5, 1.0, or 1.5 mm of occlusal thickness (p < 0.05). Increasing occlusal thickness reduced the effect of access hole preparation on fracture load. CONCLUSION: Type of zirconia, occlusal thickness, and access hole preparation had significant effects on the fracture load of zirconia crowns. The effect of endodontic access was significant on the 3Y and 5Y zirconia crowns with ≤1.0 and ≤1.5 mm occlusal thicknesses, respectively.

The utilization of snap-on provisionals for dental veneers: From an analog to a digital approach.

OBJECTIVE: There are multiple treatment options to enhance a patient's smile, from conservative bleaching procedures to composite resins, porcelain veneers, or full-coverage crowns. Treating patients with porcelain veneers is a commonly used approach in esthetic dentistry. Provisional restorations for veneers can be time-consuming to make and difficult to retain. This article illustrates a technique for fabricating indirect snap-on provisional restorations for veneer cases, describing both analog and digital approaches. CLINICAL CONSIDERATIONS: The present article presents an alternative provisionalization technique using snap-on restorations for dental veneers. Application of these techniques will allow for ease of cleansability by the patient leading to healthier soft tissues before the final cementation. Delivery of veneers is more predictable with healthy soft tissue, as bleeding and inflammation may affect the bonding process. CONCLUSIONS: This technique is an effective provisionalization option in most veneer cases. This approach seems to be well accepted by patients and a good alternative in helping to maintain optimal gingival health with interim restorations before delivery. CLINICAL SIGNIFICANCE: The use of snap-on provisionals for veneer restorations will allow the clinician to have an efficient technique with better tissue response before cementation. This prevents inflammation and facilitates a controlled delivery process.

Wear of resin teeth opposing zirconia.

STATEMENT OF PROBLEM: The use of dissimilar materials for opposing complete-mouth implant-supported prosthesis has become popular, especially when one arch is made from anatomical contour zirconia. However, the amount of wear zirconia causes on resin and other denture tooth materials is largely unknown. PURPOSE: The purpose of this in vitro study was to determine the volumetric wear of 4 commercially available resin materials used for denture teeth in complete-arch implant-supported prostheses opposed by zirconia. MATERIAL AND METHODS: A total of 32 maxillary central incisor denture teeth were evaluated (n=8): double crosslinked polymethyl methacrylate (PMMA) (DCL), nanohybrid composite resin (PHO), and computer-aided design and computer-aided manufacturing (CAD-CAM)-fabricated teeth made from crosslinked PMMA (TEL) and acrylate polymer (ZCAD). Antagonist cone-shaped specimens were milled from zirconia. Specimens were mounted in acrylic resin, polished to a flat surface by using 1200-grit SiC paper, and stored in water (37 °C for 24 hours) before exposure in a custom dual-axis wear simulator for 200 000 cycles with a vertical load of 20 N, a horizontal slide of 2 mm, and a frequency of 1 Hz. Volumetric wear was measured by using a noncontact profilometer and a superimposition software program. Data were analyzed with a 1-way analysis of variance (ANOVA) and the Tukey Honestly Significant Difference (HSD) post hoc test (α=.05). RESULTS: A statistically significant difference in volumetric wear was found between groups (P<.001), with PHO (4.3 ±1.0 mm3)

In vitro comparison of shear bond strengths of ceramic orthodontic brackets with ceramic crowns using an aluminium oxide air abrasion etchant.

OBJECTIVE: The aim of this study was to determine if there are differences between the shear bond strengths of 3 types of ceramic brackets when bonded to different ceramic substrates using an aluminium oxide air abrasion etchant protocol. MATERIALS AND METHODS: Substrate groups consisting of thirty-six lithium disilicate (e.max® CAD) samples and thirty-six lithium silicate infused with zirconia (CELTRA® DUO) samples were fabricated to replicate the facial surface of a left maxillary central incisor. The surface of all samples was prepared with an aluminium oxide air abrasion etchant protocol. Each substrate group was split into three test groups (n=12). Each test group was bonded using a different brand of ceramic orthodontic bracket. Shear bond strength (SBS) testing was conducted and the mean SBS values for each group were calculated and recorded in MPa. An Adhesive Resin Index (ARI) score was also assigned to each sample to assess the location of bond failure. RESULTS: Mean SBS of the e.max® CAD groups were significantly less than the CELTRA® DUO groups. Symetri brackets showed significantly higher shear bond strengths to both substrates than both of the other brackets tested. ARI scores of the e.max® CAD groups were significantly less than the CELTRA® DUO groups. CONCLUSION: The Symetri bracket was the only bracket that was effective for both substrates (mean SBS>6mPa). The Etch Master protocol does not appear effective for e.max® CAD.

Shear bond strength of orthodontic brackets bonded to a new all-ceramic crown composed of lithium silicate infused with zirconia: An in vitro comparative study.

AIM: This study sought to determine whether a clinically acceptable shear bond strength (SBS) of metal orthodontic brackets is achievable to CAD/CAM (Computer-Aided Design/Manufacturing) lithium silicate infused with zirconia and whether a chemical pre-treatment bonding protocol produced a higher shear bond strength. MATERIALS AND METHODS: Twenty lithium silicate infused with zirconia (CELTRA® DUO) samples, twenty zirconia samples, and twenty lithium disilicate samples were fabricated to replicate the facial surface of a mandibular left first molar. The samples were split into two test groups, one of which received a chemical pre-treatment protocol (hydrofluoric acid etch). Shear bond strength testing was conducted and the mean, maximum, minimal, and standard deviation SBS values for each were calculated and recorded in MPa. An Adhesive Resin Index (ARI) score was also assigned to each sample to assess the mode of bond failure. RESULTS: SBS of the lithium silicate infused with zirconia groups were significantly less than the chemically pre-treated lithium disilicate group, however both materials, when chemical pre-treatment protocol was used, were not statistically different than the enamel control. CONCLUSIONS: Orthodontic bonding to lithium silicate infused with zirconia yielded a weaker shear bond strength than bonding to traditional lithium disilicate, however, when the surface was pre-treated with hydrofluoric acid etch it provides a bond strength that is within an acceptable clinical range.

Shear bond strength of zirconia-based ceramics veneered with 2 different techniques.

STATEMENT OF PROBLEM: Delamination of veneering ceramic is reported as one of the most frequent problems associated with veneered zirconia restorations. PURPOSE: The purpose of this in vitro study was to compare the shear bond strength of sintered lithium disilicate to that of pressed fluorapatite glass-ceramic on a zirconia substrate. MATERIAL AND METHODS: Thirty zirconia blocks (20×15×2.5-mm thick) were cut, sintered, and divided into 2 groups. A pressed group, a zirconia liner, was applied and sintered, and the lost-wax technique was used to fabricate fluorapatite glass-ceramic blocks (3×3×3 mm), which were pressed onto the sintered zirconia blocks. A sintered group, lithium disilicate blocks, were cut (3×3×3 mm) and sintered to the sintered zirconia blocks by using a low-fusing glass-ceramic. The thickness of the low-fusing glass-ceramic was standardized to approximately 80 µm prior to sintering. The shear bond strength levels of the specimens were tested using a universal testing machine at a crosshead speed of 1 mm/min until failure. Representative separated specimen surfaces were examined for fracture characteristics, using scanning electron microscopy at ×50 magnification. Debonding data were compared using a 2-tailed, unpaired Student t test (α=.05). RESULTS: The sintered group demonstrated mean shear bond strength values (41.2 ±6.3 MPa), which were significantly higher (P<.001) than those of the pressed group (21.3 ±4.3 MPa). CONCLUSIONS: Sintering of computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate ceramic achieved higher shear bond strength values than pressing fluorapatite glass-ceramic to zirconia substructure material.

Porcelain surface conditioning protocols and shear bond strength of orthodontic brackets.

AIM: The objective of the present study was to determine which of six bonding protocols yielded a clinically acceptable shear bond strength (SBS) of metal orthodontic brackets to CAD/CAM lithium disilicate porcelain restorations. A secondary aim was to determine which bonding protocol produced the least surface damage at debond. METHODS: Sixty lithium disilicate samples were fabricated to replicate the facial surface of a mandibular first molar using a CEREC CAD/CAM machine. The samples were split into six test groups, each of which received different mechanical/chemical pretreatment protocols to roughen the porcelain surface prior to bonding a molar orthodontic attachment. Shear bond strength testing was conducted using an Instron machine. The mean, maximum, minimal, and standard deviation SBS values for each sample group including an enamel control were calculated. A t-test was used to evaluate the statistical significance between the groups. RESULTS: No significant differences were found in SBS values, with the exception of surface roughening with a green stone prior to HFA and silane treatment. This protocol yielded slightly higher bond strength which was statistically significant. CONCLUSION: Chemical treatment alone with HFA/silane yielded SBS values within an acceptable clinical range to withstand forces applied by orthodontic treatment and potentially eliminates the need to mechanically roughen the ceramic surface.

Reliability of implant surgical guides based on soft-tissue models.

The purpose of this study was to determine the accuracy of implant surgical guides fabricated on diagnostic casts. Guides were fabricated with radiopaque rods representing implant positions. Cone beam computerized tomograms were taken with guides in place. Accuracy was evaluated using software to simulate implant placement. Twenty-two sites (47%) were considered accurate (13 of 24 maxillary and 9 of 23 mandibular sites). Soft-tissue models do not always provide sufficient accuracy for fabricating implant surgical guides.

Comparison of marginal fit between all-porcelain margin versus alumina-supported margin on Procera Alumina crowns.

PURPOSE: Procera Alumina crowns are widely used; however, the effect of crown margin design on marginal fit is unknown. This study measured and compared the precision of fit of Procera Alumina crowns with two crown margin designs: all-porcelain versus alumina-supported margins. MATERIALS AND METHODS: Sixteen noncarious extracted human premolars were prepared for Procera((R)) Alumina crowns with an internally rounded shoulder preparation. Impressions were made from all teeth, and master dies were poured with type IV dental stone. The specimens were randomly divided into two groups. Procera Alumina crowns were fabricated: eight crowns with circumferential porcelain-butt (all-porcelain) margins and eight crowns with coping (alumina-supported) margins (control). Precision of fit was measured at six points on each crown with a profilometer (profile projector). The data were statistically analyzed with an independent-samples t-test (alpha < 0.05). RESULTS: The mean marginal gap size (microm) of coping margins was 68.07 +/- 16.08 and of porcelain-butt margins was 101.29 +/- 43.71. There was no statistically significant difference (p= 0.065) of the marginal gap size between coping margins and porcelain-butt margins. CONCLUSION: The results of this study demonstrate that there was no statistically significant difference in the marginal fit of coping and porcelain-butt margins. Both margin designs are within clinically acceptable ranges. Therefore, clinicians may choose to use a coping margin, as it is less labor intensive and requires less time for fabrication, unless there is a specific high esthetic need for a porcelain-butt margin.