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.

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.

Effect of splinting scan bodies on trueness of complete-arch implant impression using different intraoral scanners: an in vitro study.

AIM: To evaluate the trueness of seven different intraoral scanners (IOSs) in making a complete-arch digital scan with and without splinting the scan bodies. MATERIALS AND METHODS: A polyurethane cast of an edentulous mandible with four dental implant analogs was prepared. A reference scan was made using a laboratory scanner. The reference model was scanned with each of the seven investigated IOSs (control groups, n = 10 per scanner), and scanned again after splinting the scan bodies (study groups, n = 10 per scanner). Each scan was exported as a standard tessellation language (STL) file and transferred to a comprehensive metrology software program (Geomagic Control X). In order to measure the trueness, four points (A, B, C, and D) were determined on the scan bodies, and the distance between point A and the other points (DAB, DAC, and DAD) was measured. The measurements were tested for normality using the Kolmogorov-Smirnov test and probability plots. Trueness was compared using three-way analysis of variance (ANOVA), and pairwise comparisons were performed using the post hoc Tukey and paired sample t tests. Statistical analyses were two-sided, and the significance level was set at 5%. RESULTS: Splinting the scan bodies improved the trueness values of the digital scans, while increasing the interimplant distance decreased them. A significant association was found between the trueness values and all three tested variables, including splinting the scan bodies, type of IOS, and interimplant distance (P < 0.001). CONCLUSION: Based on the present findings, splinting the scan bodies can improve the trueness of complete-arch digital implant scans due to the improvement in morphologic landmarks by the stitching process, regardless of the type of IOS or the interimplant distance. (Int J Comput Dent 2023;26(1): 19-0; doi: 10.3290/j.ijcd.b2599297).

Fully Digital Workflow for Fabrication of A 3D Printed Ear Stent for Auricular Keloids: A Technique Article.

Keloids are skin lesions which result from an aberration in the physiological healing process marked with overgrowth of collagen fibers. Keloid of the ear is cosmetically challenging and has an increased chance of re-growth. To minimize recurrence, pressure therapy in combination with other treatment forms has been used. Various techniques have been used to fabricate a passive or active stent. This report presents a fully digital workflow to fabricate an ear stent after intralesional excision and skin autografting of an extensive recurrence of a keloid lesion of the left ear involving the helix, antihelix, scapha, and conchal bowl.

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.

Retention of CAD/CAM resin composite crowns following different bonding protocols.

PURPOSE: To evaluate the effect of different surface treatments and primers with a CAD/CAM resin composite block on its crown retention. METHODS: 120 human molars were prepared with a 24° total convergence angle, 1.5 mm height, and axial walls in dentin. Surface area was measured by digital microscopy. Crowns were machined from CAD/CAM resin composite blocks. Teeth were randomly allocated to 12 groups (n= 10) based on possible combinations of three surface treatments: [Control, Alumina air abrasion (50-µm Al2O3 at 0.28 MPa) ]; 5% hydrofluoric acid etch (20-second scrub); silane application (with or without Kerr Silane primer); and adhesive application (with or without Optibond XTR Adhesive). Optibond XTR Adhesive was applied to the tooth preparations and crowns were bonded with MaxCem Elite cement. Crowns were fatigued for 100,000 cycles at 100 N in water and debonded in tension (1 mm/minute). Crown retention strength (maximum load/surface area) values were analyzed using a three-way ANOVA with Tukey's post-hoc tests (α= 0.05). RESULTS: Surface treatment, silane and adhesive applications independently affect retention force (P< 0.05). All interactions were not significant (P> 0.05). Alumina airborne abrasion surface treatment, silane and adhesive applications all improve retention strength. Therefore, CAD/CAM resin composite crowns can withstand debonding while undergoing mechanical fatigue. Although all forms of surface treatment and primer application improve bond strength, the highest mean retention strength values were recorded when the crowns were alumina particle abraded and coated with adhesive (with or without silane). CLINICAL SIGNIFICANCE: In order to improve the bonding of resin composite crowns, application of alumina airborne particle abrasion and a coat of adhesive (proceeded by an optional coat of silane) is recommended. If hydrofluoric acid is utilized, the crowns should be treated with a coat of silane followed by adhesive application.

Comparison of the mechanical properties of translucent zirconia and lithium disilicate.

STATEMENT OF PROBLEM: Three mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) possesses excellent mechanical properties but is relatively opaque. Five mol% yttria-stabilized zirconia polycrystal (5Y-ZP) offers improved translucency, but many of its clinical properties have not been compared with those of 3Y-TZP and lithium disilicate. PURPOSE: The purpose of this in vitro study was to compare the flexural strength, translucency parameter, bond strength, and enamel and material wear of 5Y-ZP (Katana UTML) with 3Y-TZP (Katana HT) and lithium disilicate (e.max CAD). MATERIAL AND METHODS: Flexural strength bars were sectioned (n=10, 25×4×2 mm), sintered or crystallized, polished, and fractured at 1 mm/min. Translucency specimens (1 mm thick) were fabricated (n=10). Their L*a*b* values were measured against a black-and-white background with a spectrophotometer, and ΔE00 was calculated. Zirconia bond strength specimens were airborne-particle abraded with 50 µm alumina followed by the application of a 10-methacryloxydecyl dihydrogen phosphate-containing primer (Clearfil Ceramic Primer). Lithium disilicate bond strength specimens were etched with 5% hydrofluoric acid followed by application of a silane-containing primer (Clearfil Ceramic Primer). A Tygon tube filled with resin cement (Panavia SA) was fixed to the surface of the ceramics and light-polymerized. After 1 day or 150 days of water storage, the resin cement was debonded in a macroshear test (n=10). The cusps of extracted human molars were isolated and mounted into the University of Alabama at Birmingham wear-testing device. Wear testing was performed with a 20-N load for 300000 cycles in 33% glycerin. The volumetric wear of polished zirconia, lithium disilicate, and enamel were measured along with the wear of the opposing enamel cusps using a noncontact profilometer (n=8). The data were compared by ANOVA and Tukey-Kramer analysis (α=.05). RESULTS: No statistical difference was seen between the bond strengths (P=.155) or the opposing enamel wear (P=.533) of different ceramics. A statistically significant difference was seen between the flexural strength (P<.001), translucency parameter (P<.001), and wear (P<.001) of the materials. The flexural strength values (MPa) were 1194 ±111 (Katana HT), 688 ±159 (Katana UTML), and 450 ±53 (e.max LT). The translucency parameter values were 6.96 ±0.53 (Katana HT), 8.30 ±0.24 (Katana UTML), 9.28 ±0.36 (e.max LT), and 12.64 ±0.48 (e.max HT). Bond strength values (MPa) at 1 and 150 days were 34.22 ±5.14 and 28.37 ±6.03 (Katana HT), 35.04 ±5.69 and 25.03 ±6.44 (Katana UTML), and 35.50 ±3.45 and 22.32 ±3.45 (e.max LT). Material and enamel wear (mm3) were 0 and 0.24 ±0.19 (Katana HT), 0 and 0.23 ±0.09 (Katana UTML), 0.28 ±0.13 and 0.31 ±0.10 (e.max CAD), and 0.09 ±0.03 and 0.31 ±0.14 (enamel). CONCLUSIONS: 5Y-TZP has a flexural strength and translucency parameter between those of 3Y-TZP and lithium disilicate. Both the short-term and long-term bond strength of 5Y-ZP and 3Y-TZP was shown to be similar to lithium disilicate. 5Y-ZP demonstrated no measurable material wear and opposing enamel wear similar to that of all the other materials tested.

Machinability of CAD-CAM materials.

STATEMENT OF PROBLEM: Although new materials are available for computer-aided design and computer-aided manufacturing (CAD-CAM) fabrication, limited information is available regarding their machinability. The depth of penetration of a milling tool into a material during a timed milling cycle may indicate its machinability. PURPOSE: The purpose of this in vitro study was to compare the tool penetration rate for 2 polymer-containing CAD-CAM materials (Lava Ultimate and Enamic) and 2 ceramic-based CAD-CAM materials (e.max CAD and Celtra Duo). MATERIAL AND METHODS: The materials were sectioned into 4-mm-thick specimens (n=5/material) and polished with 320-grit SiC paper. Each specimen was loaded into a custom milling apparatus. The apparatus pushed the specimens against a milling tool (E4D Tapered 2016000) rotating at 40 000 RPM with a constant force of 0.98 N. After a 6-minute timed milling cycle, the length of each milling cut was measured with image analysis software under a digital light microscope. Representative specimens and milling tools were examined with scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy. RESULTS: The penetration rate of Lava Ultimate (3.21 ±0.46 mm/min) and Enamic (2.53 ±0.57 mm/min) was significantly greater than that of e.max CAD (1.12 ±0.32 mm/min) or Celtra Duo (0.80 ±0.21 mm/min) materials. SEM observations showed little tool damage, regardless of material type. Residual material was found on the tools used with polymer-containing materials, and wear of the embedding medium was seen on the tools used with the ceramic-based materials. Edge chipping was noted on cuts made in the ceramic-based materials. CONCLUSIONS: Lava Ultimate and Enamic have greater machinability and less edge chipping than e.max CAD and Celtra Duo.