Evaluating the Bond Strength of a Polymer Infiltrated Ceramic Network to Zirconia Using the Crossbeam Push-Off Method.

Porcelains and glass-ceramics have been used to produce CAD-milled veneers and crowns for zirconia copings and implant-abutments. This study evaluated the bondstrength of a polymer-infiltrated-ceramic-network to zirconia using two adhesive cement systems: Panavia 21 and Multilink Automix. Lithium disilicate and feldspathic porcelain were also tested as reference CAD-On materials. Long beams (3x6x40 mm³) of zirconia and short beams (3x6x15 mm³) of the CAD-On materials were prepared. Zirconia and each CAD-On material were bonded in a crossbeam arrangement and subjected to a modified tensile bond-strength test. Half of the samples in each group (n=10) were tested 5 days after bonding (baseline) and the remaining (n=10) underwent aging (50,000 thermocycles at 5°C and 55°C) prior to bond-strength testing. The effects of material, cement, and aging on the tensile bond-strength were tested using a three-way ANOVA. The reference lithium disilicate/Multilink system showed no significant differences in bond strength compared to polymer-infiltrated-ceramic-network and porcelain. The long-term retention of polymer-infiltrated-ceramic-network was not statistically different compared to the baseline values and the two reference materials. With comparable bond strength between all materials, polymer-infiltrated-ceramic-network is the favorable choice for CAD-On to zirconia copings and implant-abutments due to its superior resistance to fatigue fracture relative to porcelain.

Failure probability and stress distribution of milled porcelain-zirconia crowns with bioinspired/traditional design and graded interface.

OBJECTIVE: To evaluate the failure probability and stress distribution of traditional and bioinspired porcelain-zirconia milled crowns, with and without silica infiltration (graded zirconia). METHODS: Traditional crown design had a zirconia infrastructure veneered with porcelain; Bioinspired, had a porcelain infrastructure with translucent-zirconia veneer; Graded and Graded Bioinspired crowns had their zirconia layer infiltrated by silica (n = 25). The cameo surface of each crown (porcelain or zirconia) was glazed. The restoration layers were fused by a vitreous connector and the crowns were adhesively cemented to dies. The specimens were then mechanically cycled in a sliding machine using 100 N load at 4 Hz. The specimens were tested until 2 × 106 cycles, and every 0.5 × 106 cycles the crowns were evaluated under stereomicroscopy for the presence of failures. The stress distribution was inspected with Finite Element Analyses. RESULTS: The predominant failure modes for the Traditional and Graded crowns were delamination and cracking, respectively. The Weibull parameters beta and eta were, respectively: Traditional 1.30 and 2.3 × 106 cycles, and Graded 1.95 and 2.3 × 106 cycles. Thus, the Traditional and Graded crowns presented greater susceptibility to failure due to fatigue, while the Bioinspired and Graded Bioinspired crowns showed no fatigue effect using 100N load, showing beta = 1 and eta of approximately 17 × 106 cycles. Also, through finite element analyses, it was verified that the Bioinspired and Graded Bioinspired crowns presented the best stress distribution on both crowns and dental structures. SIGNIFICANCE: Bioinspired and Graded Bioinspired crowns had the lowest failure probability and better stress distribution and may be considered robust long lasting restorations.

Sliding contact wear and subsurface damage of CAD/CAM materials against zirconia.

OBJECTIVE: Most previous work conducted on the wear behavior of dental materials has focused on wear rates and surface damage. There is, however, scarce information regarding the subsurface damage arising from sliding contact fatigue. The aim of this study was to elucidate the wear mechanisms and the subsurface damage generated during sliding contact fatigue in 5 contemporary CAD/CAM materials against a zirconia indenter. METHODS: Forty discs (Ø12mm, 1.55mm thick) were cut out of IPS e.max CAD (e.CAD), Suprinity PC (SUP), Enamic (ENA), Vitablocs Mark II (VMII) and Lava Ultimate (LU) blocks and mirror polished. After cementation onto a dentin-like composite, off-axis mouth-motion cycling was conducted with a spherical zirconia indenter (r=3.18mm) in water (200N load, 2Hz frequency) for 5 different cycling periods (102, 103, 104, 105, 106 cycles, n=8). Analysis of the wear scars was conducted using light-microscopy, scanning-electron-microscopy and optical profilometry. Subsurface damage was assessed using sagittal and transverse sections of the samples. RESULTS: Fatigue wear mechanisms predominated in glassy materials (e.CAD, SUP, VMII), accompanied by extensive subsurface damage, whereas abrasive wear mechanisms were responsible for the large wear craters in the resin composite (LU) with an absolute absence of subsurface fracture. A combination of both mechanisms was observed in the polymer-infiltrated reinforced-glass (ENA), displaying large wear craters and severe subsurface damage. SIGNIFICANCE: Well-controlled laboratory simulation can identify wear and subsurface damage susceptibility of various classes of restorative materials. Both wear and subsurface fracture are determining factors for the long-term success of restorations.

Silica-Based Infiltrations for Enhanced Zirconia-Resin Interface Toughness.

Novel silica-based infiltrations on the surface of zirconia have the potential to improve their bondability, allowing for the etching/silane adhesive bonding technique. Nonetheless, adhesively bonded joints are subject to mixed tensile and shear stresses when the restoration is in occlusal service. Thus, we aimed to investigate the effect of 2 novel silica-based infiltrations on the interfacial toughness of adhesively bonded zirconia using the Brazil nut method, which allows for controlled types of stresses to be applied at the interfaces. In total, 150 3Y-TZP (In-Ceram YZ; Vita) Brazil nuts were machined and randomly assigned to 3 groups: C, control (air abraded); SG, sol-gel silica infiltration; and GI, glass infiltration. SG specimens were immersed twice in silicic acid for 20 min and dried (100°C, 1 h). GI specimens were presintered (1,400°C, 1 h) before a glass powder slurry was applied to the intaglio surface. All specimens were then sintered (1,530°C, 2 h). Following adhesive bonding (Panavia F 2.0, Kuraray) and water storage (37°C) for 10 d, the Brazil nuts were subdivided into groups baseline and aged (40,000 thermal cycles between 5°C and 55°C, with a dwell time of 30 s). The Brazil nuts were subjected to axial-loading tests using various inclinations (precrack angle with load direction): Θ = 0°, 5°, 10°, 15°, or 25°, which define the stress type at the interface, from pure tension (0°) to increasing levels of shear. Under pure tension (0°), GI yielded superior interfacial fracture energy, SG and C were similar, and aging had no effect. Under predominantly shear stresses (25°), aging significantly decreased interfacial fracture energy of C and SG, while GI remained stable and was superior. The glass infiltration of the zirconia intaglio surface increases its adhesive bonding interfacial toughness. The sol-gel silica infiltration method requires improvement to obtain a homogeneous surface infiltration and an enhanced bond strength.

Wear Behavior of Graded Glass/Zirconia Crowns and Their Antagonists.

Monolithic zirconia crowns have become very popular; their surface finish is considered a key factor for restoration longevity. While polishing has shown excellent results in vivo, the surface glass infiltration of zirconia may offer superior damage resistance and aesthetic advantages by using tooth-colored glasses. Thus, the purpose of this study is to evaluate the efficacy of polishing and glass infiltration on the wear behavior of monolithic zirconia crowns. The wear behavior of intact natural molar teeth was investigated as a reference. Zirconia crowns were divided into 3 groups: PolZ-sintered then polished; PolGZ-polished in the presintered state and then glass infiltrated and sintered; NoPolGZ-as machined, glass infiltrated and sintered. Crowns were adhesively bonded to a dentin-like abutment. Zirconia crowns and molar teeth ( n = 15) were subjected to contact-slide-liftoff cyclic loading (200 N, 1.25 million cycles) with a steatite sphere ( r = 3 mm) as an antagonist in water. Surface and subsurface damages were investigated with optical and scanning electron microscopies. Wear depth and volume loss were determined with micro-computed tomography. PolGZ and NoPolGZ crowns exhibited shallow wear scars, where material loss remained within the glass/zirconia layer with no visible cracks. Meanwhile, PolZ crowns presented no visible wear damage. Volume loss (mm3) in the steatite antagonist was as follows (mean ± SD): PolZ = 0.022 ± 0.007, PolGZ = 0.011 ± 0.004, and NoPolGZ = 0.014 ± 0.006. Molar teeth yielded no measurable wear on the antagonist, while the wear scar on the teeth was greater than that on zirconia crowns, ranging from 0.07 to 0.35 mm3. The combination of polishing and glass infiltration on the occlusal surface of monolithic zirconia crowns yielded reduced wear on both crown and antagonist.

Graded Ultra-Translucent Zirconia (5Y-PSZ) for Strength and Functionalities.

Ultra-translucent zirconias are drawing immense attention due to their fascinating esthetic appearance. However, the high translucency came at the expense of diminishing strength along with the reduced ability of transformation toughening due to the increased cubic zirconia content. We aim to address these issues by infiltrating glass on the surface of an ultra-translucent zirconia (5Y-PSZ). Glasses of different shades can be used and the resulting graded glass/zirconia layer is expected to improve the material's flexural strength without compromising its esthetics. We also aim to elucidate how clinically relevant surface treatments-namely, air abrasion, glazing, or polishing-affect the fracture resistance of these zirconias with a high cubic content. All surface treatments were performed on bar-shaped (2 × 3 × 25 mm3) and plate-shaped (12 × 12 × 1 mm3) specimens, which were then subjected to a 4-point bending test and translucency measurements, respectively. 5Y-PSZ proved to be significantly more translucent than 3Y-TZP but also much weaker. Our hypothesis was accepted, as the strength of the glass-infiltrated ultra-translucent 5Y-PSZ (582 ± 20 MPa) is over 70% higher than its uninfiltrated counterpart (324 ± 57 MPa). Its strength is also over 25% higher than the highly polished 5Y-PSZ (467 ± 38 MPa). In addition, the translucency of 5Y-PSZ (translucency parameter [ TP] = 34, contrast ratio [ CR] = 0.31) is not affected by glass infiltration ( TP = 34, CR = 0.32) when the residual surface glass is removed by gentle polishing using 6- and then 3-µm diamond grits. Finally, both air abrasion and the presence of a glaze layer on the tensile surface decreased flexural strength significantly, being 274 ± 55 and 211 ± 21 MPa, respectively. With a combined high strength and translucency, the newly developed glass-infiltrated 5Y-PSZ may be considered a suitable material for next-generation, damage-resistant, and esthetic dental restorations.

Masking Colored Substrates Using Monolithic and Bilayer CAD-CAM Ceramic Structures.

OBJECTIVE: To evaluate the masking ability and translucency of monolithic and bilayer CAD-CAM ceramic structures. METHODS: Discs of high translucency (HT) and low translucency (LT) lithium disilicate-based ceramic (IPS e.max CAD) with different thicknesses (0.7, 1, 1.5, and 2 mm) were evaluated as a monolithic structure or combined (bilayer) with a 0.5-mm-thick zirconia framework (IPS e.max ZirCAD). The masking ability and translucency were calculated based on CIE L*a*b* color coordinates measured with a spectrophotometer (SP60, X-Rite). The translucency parameter (TP) was calculated using color coordinates measured over standard white-and-black backgrounds. The masking ability was calculated by CIEDE2000 color difference metric (ΔE00) for each specimen measured over a tooth-colored substrate (shade A2) compared to three darker backgrounds (shade C4 and two metal substrates). Confidence intervals (CI) for the means (95% CI) were calculated for TP and ΔE00. The Pearson correlation between ΔE00 and TP was investigated for monolithic and bilayer structures over all backgrounds. RESULTS: The thinner the lithium disilicate layer, the greater the translucency and the higher the ΔE00 values. The effect of ceramic thickness on both translucency and masking ability was more pronounced for the monolithic structures. In addition, monolayers always presented a greater color variation than their bilayer counterparts. The metallic background produced greater ΔE00 than the C4-shaded substrate. CONCLUSION: Monolithic veneers were able to mask C4-shaded background but did not mask metallic backgrounds. Bilayer structures showed greater shade masking ability than monolithic structures.

Silica Coating of Nonsilicate Nanoparticles for Resin-Based Composite Materials.

This study was designed to develop and characterize a silica-coating method for crystalline nonsilicate ceramic nanoparticles (Al2O3, TiO2, and ZrO2). The hypothesis was that the coated nonsilicate nanoparticles would stably reinforce a polymeric matrix due to effective silanation. Silica coating was applied via a sol-gel method, with tetraethyl orthosilicate as a silica precursor, followed by heat treatment. The chemical and microstructural characteristics of the nanopowders were evaluated before and after silica coating through x-ray diffraction, BET (Brunauer-Emmett-Teller), energy-dispersive x-ray spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy analyses. Coated and noncoated nanoparticles were silanated before preparation of hybrid composites, which contained glass microparticles in addition to the nanoparticles. The composites were mechanically tested in 4-point bending mode after aging (10,000 thermal cycles). Results of all chemical and microstructural analyses confirmed the successful obtaining of silica-coated nanoparticles. Two distinct aspects were observed depending on the type of nanoparticle tested: 1) formation of a silica shell on the surface of the particles and 2) nanoparticle clusters embedded into a silica matrix. The aged hybrid composites formulated with the coated nanoparticles showed improved flexural strength (10% to 30% higher) and work of fracture (35% to 40% higher) as compared with composites formulated with noncoated nanoparticles. The tested hypothesis was confirmed: silanated silica-coated nonsilicate nanoparticles yielded stable reinforcement of dimethacrylate polymeric matrix due to effective silanation. The silica-coating method presented here is a versatile and promising novel strategy for the use of crystalline nonsilicate ceramics as a reinforcing phase of polymeric composite biomaterials.

Do educational methods affect students' ability to remove artificial carious dentine? A randomised controlled trial.

This trial aimed to evaluate the influence of two educational methods on students' ability to remove artificial carious dentine. Traditional lecture and lecture plus a live demonstration of artificial carious tissue removal were compared in a blind two-parallel-group design. Twenty-six students were randomly divided into two groups, and their skills were evaluated according to the following criteria: time spent on the dentine excavation procedure (in min), students' perceived confidence in conducting the procedure (graded assessed on a scale from 0 to 10), and the outcome of artificial carious tissue removal, evaluated by measuring the residual dyed artificial carious dentine layer (in µm). Statistical analyses were carried out using a t-test to compare the students' confidence and time spent on the procedure, and a two-way ANOVA was used to compare residual artificial decayed dentine with educational methods and tooth region (incisal, medium, and cervical thirds) as factors. There were no differences between the methods regarding excavation time (P = 0.898) and students' confidence (P = 0.382). The residual artificial carious dentine results showed that the educational method (P < 0.001) and cavity region (P < 0.001) were statistically significant, as was their interaction (P = 0.040). The lecture plus live demonstration group presented the best results for artificial caries removal. Although there were no differences between the two groups for the cervical region, the best results for the lecture plus live demonstration group was in the other two-thirds of the tooth.