Liliana Gressler May

Effect of silica coating combined to a MDP-based primer on the resin bond to Y-TZP ceramic

The aim of this study was to evaluate the influence of silica coating and 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based primer applications upon the bonding durability of a MDP-based resin cement to a yttrium stabilized tetragonal zirconia (Y-TZP) ceramic. Ninety-six Y-TZP tabs were embedded in an acrylic resin (free surface for adhesion: 5 × 5 mm(2)), ground finished and randomly divided into four groups (N = 24) according to the ceramic surface conditioning: (1) cleaning with isopropanol (ALC); (2) ALC + phosphoric acid etching + MDP-based primer application (MDP-primer); (3) silica coating + 3-methacryloyloxypropyl trimethoxysilane (MPS)-based coupling agent application (SiO2 + MPS-Sil); and (4) SiO2 + MDP-primer. The MDP-based resin cement was applied on the treated surface using a cylindrical mold (diameter= 3 mm). Half of the specimens from each surface conditioning were stored in distilled water (37 °C, 24 h) before testing. Another half of the specimens were stored (90 days) and thermo-cycled (12,000 x) during this period (90 d/TC) before testing. A shear bond strength (SBS) test was performed at a crosshead speed of 0.5 mm/min. Two factors composed the experimental design: ceramic conditioning strategy (in four levels) and storage condition (in two levels), totaling eight groups. After 90 d/TC (Tukey; p < 0.05), SiO2 + MDP-primer (24.40 MPa) promoted the highest SBS. The ALC and MDP-primer groups debonded spontaneously during 90 d/TC. Bonding values were higher and more stable in the SiO2 groups. The use of MDP-primer after silica coating increased the bond strength.

Adhesive Quality of Self-adhesive and Conventional Adhesive Resin Cement to Y-TZP Ceramic Before and After Aging Conditions

PURPOSE This study evaluated the adhesive quality of simplified self-adhesive and conventional resin cements to Y-TZP in dry and aged conditions. METHODS Y-TZP ceramic blocks (N = 192) (5 x 5 x 2 mm) were embedded in acrylic resin and randomly divided into two groups, based on surface conditioning: 96% isopropanol or chairside tribochemical silica coating and silanization. Conditioned ceramics were divided into four groups to receive the resin cements (Panavia F 2.0, Variolink II, RelyX U100 and Maxcem). After 24 hours, half of the specimens (n = 12) from each group were submitted to shear bond strength testing (0.5 mm/minute). The remaining specimens were tested after 90 days of water storage at 37 degrees C and thermocycling (12,000x, 5 degrees C-55 degrees C). Failure types were then assessed. The data were analyzed using three-way ANOVA and the Tukeys test (alpha = 0.05). RESULTS Significant effects of ceramic conditioning, cement type and storage conditions were observed (p < 0.0001). The groups cleaned using alcohol only showed low bond strength values in dry conditions and the bond strength was reduced dramatically after aging. Groups conditioned using silica coating and silanization showed higher bond strengths both in dry and aged conditions. A high number of specimens failed prematurely prior to testing when they were cleaned using 96% isopropanol. CONCLUSION Overall, silica coating and silanization showed higher, stable bond strengths with and without aging. The durability of resin-ceramic adhesion varied, depending on the adhesive cement type.

Influence of the resin cement thickness on the fatigue failure loads of CAD/CAM feldspathic crowns

OBJECTIVES to evaluate the influence of the occlusal resin cement thickness on the cyclic loads-to-failure of feldspathic crowns and to compare the results to data from monotonic tests. A large range of cement thickness (50μm and 500μm) was tested, in order to better measure the influence of this variable. METHODS Feldspathic ceramic crowns (Vita Mark II blocks, Vita Zahnfabrik) were bonded to dentin analog dies (G10 (NEMA grade G10, International Paper), with occlusal resin cement thicknesses of 50μm and 500μm (Multilink Automix, Ivoclar). The dies were prepared with microchannels for water transport to the cement layer. After 96-h water storage, the specimens (n=20) were submitted to cyclic loads (500,000 cycles at 20Hz; initial maximum load=40% of monotonic load, from previous data) following a staircase sensitivity design (step size=25N). Failure loads at 500,000 cycles were compared to monotonic failure loads (from a previous study with specimens produced by the same author, using the same materials, specimen configuration and cementation protocol). RESULTS Crowns with an occlusal cement layer of 50μm were more resistant than those cemented with 500μm (246.4±22.9N vs. 158.9±22.9N), under wet cyclic testing conditions (p<0.001). The fatigue failure loads were reduced compared to monotonic loads: to 37% of monotonic for 50μm; to 53% of monotonic for 500μm. SIGNIFICANCE An occlusal cement thickness of 50μm was more favorable for the structural performance of feldspathic crowns than was 500μm. Cyclic fatigue reduced failure loads well below those found under monotonic loading.

Implant-abutment gap versus microbial colonization: Clinical significance based on a literature review

Microorganisms from the oral cavity may settle at the implant-abutment interface (IAI). As a result, tissue inflammation could occur around these structures. The databases MEDLINE/PubMed and PubMed Central were used to identify articles published from 1981 through 2012 related to the microbial colonization in the implant-abutment gap and its consequence in terms of crest bone loss and osseointegration. The following considerations could be put forward, with respect to the clinical importance of IAI: (a) the space present at the IAI seems to allow bacterial leakage to occur, in spite of the size of this space; (b) bacterial leakage seems to occur at the IAI, irrespective of the type of connection. More studies are necessary to clarify the relationship between leakage at IAI and abutment connection designs; (c) losses at the peri-implant bone crests cannot be related to the IAI size, since few studies have shown no relationship. Also, the microbial leakage at the IAI cannot be related to the bone crest loss, since there are no articles reporting this relationship; remains controversial the influence of the IAI position on the bone crest losses.

CAD/CAM machining Vs pre-sintering in-lab fabrication techniques of Y-TZP ceramic specimens: Effects on their mechanical fatigue behavior

This study evaluated the effects of different pre-sintering fabrication processing techniques of Y-TZP ceramic (CAD/CAM Vs. in-lab), considering surface characteristics and mechanical performance outcomes. Pre-sintered discs of Y-TZP ceramic (IPS e.max ZirCAD, Ivoclar Vivadent) were produced using different pre-sintering fabrication processing techniques: Machined- milling with a CAD/CAM system; Polished- fabrication using a cutting device followed by polishing (600 and 1200 SiC papers); Xfine- fabrication using a cutting machine followed by grinding with extra-fine diamond bur (grit size 30 μm); Fine- fabrication using a cutting machine followed by grinding with fine diamond bur (grit size 46 μm); SiC- fabrication using a cutting machine followed by grinding with 220 SiC paper. Afterwards, the discs were sintered and submitted to roughness (n=35), surface topography (n=2), phase transformation (n=2), biaxial flexural strength (n=20), and biaxial flexural fatigue strength (fatigue limit) (n=15) analyses. No monoclinic-phase content was observed in all processing techniques. It can be observed that obtaining a surface with similar characteristics to CAD/CAM milling is essential for the observation of similar mechanical performance. On this sense, grinding with fine diamond bur before sintering (Fine group) was the best mimic protocol in comparison to the CAD/CAM milling.

Color stability of ceramic laminate veneers cemented with light-polymerizing and dual-polymerizing luting agent: A split-mouth randomized clinical trial

Statement of problem The color stability of luting agents influences the esthetics of ceramic laminate veneers. Clinical studies that have evaluated the color changes of veneers cemented to enamel with light‐ and dual‐polymerizing resin cement are lacking. Purpose The purpose of this split‐mouth randomized clinical trial was to evaluate the color change and marginal discoloration of dual‐ and light‐polymerizing cement used for cementation of ceramic laminate veneers. Material and methods In 10 participants, 0.3‐mm‐thick ceramic laminate veneers were cemented on the buccal surface of the second premolars without tooth preparation. A randomized application of light‐polymerized cement was used on one side and a dual‐polymerized cement on the contralateral side. The operator and participants were blinded to the activation mode. Color was evaluated by a blinded evaluator with a spectrophotometer at 24 hours and at 2, 6, 12, and 24 months after cementation. The CIELab (&Dgr;E*ab) and CIEDE2000 (&Dgr;E*00) formulas were used to quantify color alteration, and &Dgr;a*, &Dgr;b*, and &Dgr;L* were calculated between the first and subsequent measurements. US Public Health Service guidelines were used to evaluate the marginal discoloration. Results Wilcoxon tests did not show a statistical difference in &Dgr;E*ab and &Dgr;E*00 between the groups (P>.05). At 24 months, the median &Dgr;E*ab was 2.31 (interquartile ranges [IQR]: 3.34) for the light‐polymerizing mode and 1.57 (IQR: 0.41) for the dual‐polymerizing mode, while the median &Dgr;E*00 was 1.65 for the light‐polymerizing mode (IQR: 2.34) and 1.18 for the dual‐polymerizing mode (IQR: 0.25). The thresholds for clinically acceptable color changes &Dgr;E*ab>3.46 and &Dgr;E*00>2.25 were found for both curing modes. Marginal discoloration was observed from the 2‐year assessment. Conclusions The color stability of ceramic laminate veneers was similar for both of the polymerizing modes for all evaluated periods. Marginal discoloration increased over a 2‐year period for both the light‐ and the dual‐polymerizing modes.

Impact of machining on the flexural fatigue strength of glass and polycrystalline CAD/CAM ceramics

OBJECTIVES To assess the effect of machining on the flexural fatigue strength and on the surface roughness of different computer-aided design, computer-aided manufacturing (CAD/CAM) ceramics by comparing machined and polished after machining specimens. METHODS Disc-shaped specimens of yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP), leucite-, and lithium disilicate-based glass ceramics were prepared by CAD/CAM machining, and divided into two groups: machining (M) and machining followed by polishing (MP). The surface roughness was measured and the flexural fatigue strength was evaluated by the step-test method (n=20). The initial load and the load increment for each ceramic material were based on a monotonic test (n=5). A maximum of 10,000 cycles was applied in each load step, at 1.4Hz. Weibull probability statistics was used for the analysis of the flexural fatigue strength, and Mann-Whitney test (α=5%) to compare roughness between the M and MP conditions. RESULTS Machining resulted in lower values of characteristic flexural fatigue strength than machining followed by polishing. The greatest reduction in flexural fatigue strength from MP to M was observed for Y-TZP (40%; M=536.48MPa; MP=894.50MPa), followed by lithium disilicate (33%; M=187.71MPa; MP=278.93MPa) and leucite (29%; M=72.61MPa; MP=102.55MPa). Significantly higher values of roughness (Ra) were observed for M compared to MP (leucite: M=1.59μm and MP=0.08μm; lithium disilicate: M=1.84μm and MP=0.13μm; Y-TZP: M=1.79μm and MP=0.18μm). SIGNIFICANCE Machining negatively affected the flexural fatigue strength of CAD/CAM ceramics, indicating that machining of partially or fully sintered ceramics is deleterious to fatigue strength.

Effect of the bur grit size on the flexural strength of a glass-ceramic

The purpose of the present study was to determine the biaxial flexural strength (BFS) of a CAD/CAM leucite reinforced glass-ceramic ground by diamond burs of different grit sizes and the influence of surface roughness on the BFS. For this, 104 plates were obtained from CAD/CAM ceramic blocks and divided into 4 groups (n = 26), according to bur grit size: extra-fine, fine, medium and coarse. Roughness parameters (Ra, RyMax) were measured, and plates were kept dry for 7 days. The flexural test was carried out and BFS was calculated. Ra, RyMax and BFS data were subjected to analysis of variance and post-hoc test. Weibull analysis was used to compare characteristic strength and Weibull modulus. Regression analysis was performed for BFS vs. Ra and RyMax. When burs with coarse grit were used, higher surface roughness values were found, causing a negative effect on the ceramic BFS (117 MPa for extra-fine, and 83 MPa for coarse). Correlation (r) between surface roughness and BFS was 0.78 for RyMax and 0.73 for Ra. Increases in diamond grit size have a significant negative effect on the BFS of leucite-reinforced glass-ceramics, suggesting that grinding of sintered glass-ceramic should be performed using burs with the finest grit possible in order to minimize internal surface flaws and maximize flexural strength.

The effect of extended glaze firing on the flexural fatigue strength of hard-machined ceramics

Statement of problem. It is unclear whether an extended glaze firing could improve the long‐term mechanical performance of densely sintered CAD‐CAM ceramics. Purpose. The purpose of this in vitro study was to analyze the effect of an extended glaze firing on the flexural fatigue strength (FFS) of densely sintered milled (hard‐machined) leucite‐based (LEU) and lithium disilicate‐based (DIS) ceramics. Material and methods. Disks were machined from ceramic blocks and divided into 6 groups (n=20) according to the material, LEU or DIS, and to the applied glaze firing: manufacturer‐recommended glaze (G group), extended glaze (EG group), and control/no firing (C group). The surface roughness of the disks was measured before and after firing by using a contact profilometer, and data were compared by paired sample tests. Specimens were submitted to fatigue by using the staircase test design in water (piston‐on‐3 balls; 500 000 cycles, 20 Hz, and sinusoidal loading). Mean (±SD) FFS values were then calculated and analyzed by using 1‐way analysis of variance and post hoc Tukey test (&agr;=.05). Results. Surface roughness did not change after the firing (P>.05). The highest FFS value in both ceramics was obtained after EG firing (LEU‐EG=80.52 ±6.3 MPa; DIS‐EG=147.25 ±10.5 MPa), which was statistically superior to G firing (LEU‐G=73 ±6.8 MPa, P=.003; DIS‐G=134.34 ±15.6 MPa; P=.023) and C group (LEU‐C=61.94 ±6.3 MPa; P<.001; DIS‐C=134.13 ±17.3 MPa; P=.023). Conclusions. EG firing optimized the biaxial flexural fatigue strength of hard‐machined leucite and lithium disilicate ceramics compared with conventional glaze firing.

Does veneering technique affect the flexural strength or load-to-failure of bilayer Y-TZP? A systematic review and meta-analysis

Statement of problem. Causes of failures of bilayer yttria‐stabilized tetragonal zirconia polycrystal (Y‐TZP) restorations include the processing technique and the properties of the veneer ceramic. The effect of the veneering method on the mechanical behavior of veneered Y‐TZP remains unclear. Purpose. The purpose of this systematic review was to assess the effect of the veneering method on the flexural strength and failure load of bilayer Y‐TZP. Material and methods. This study followed the Preferred Reporting Items for the Systematic Reviews and Meta‐Analyses (PRISMA) statement. Searches were performed through August 2017 in PubMed/MEDLINE, Web of Science (Core Collection), Scopus, and Embase, with no year or language limit, targeting in vitro studies evaluating the effect of the veneering technique on the flexural strength and load‐to‐failure of bilayer Y‐TZP immediately or after aging. Statistical analyses were conducted using an appropriate software. Comparisons were drawn with random effect models (&agr;=.05). Results. From 3242 identified studies, 241 were selected for full‐text analysis; from these, 33 studies were included. Manual searching yielded no additional papers. The meta‐analysis consisted of 32 studies. Meta‐analysis was performed separately for flexural strength and failure load data to compare the hand‐layered method (control) with pressed, fused, and cemented veneering techniques. The cemented and fused methods were analyzed using subgroups depending on the veneering material being examined (predominantly glass–ceramics and particle‐filled glass–ceramics), and the results were compared with those of the hand‐layered method. The pressed group presented flexural strength (7 studies) (P=.150) and failure load (19 studies) (P=.140) values that were similar to those of the hand‐layered group. Subgroup analysis revealed that the fused group with particle‐filled glass–ceramics (7 studies) produced higher load‐to‐failure (P=.006) values than the hand‐layered group. Subgroup analyses showed a statistical difference that favored the hand‐layered over the cemented method, with predominantly glass–ceramic materials (5 studies) (P=.002). Conclusions. The fused technique with particle‐filled glass–ceramics seems more appropriate for the veneering of Y‐TZP, with improved failure load, than the hand‐layered method with predominantly glass–ceramic materials. The use of predominantly glass–ceramics for the cemented method is not recommended as failure load was lower than for the hand‐layered group. Pressed veneers showed failure load and flexural strength values similar to those of the the hand‐layered technique.