In Vitro Investigations in a Biomimetic Approach to Restore One-Piece Zirconia Implants

The objective of this study was to evaluate the fracture load and retention force of different bonding systems while restoring one-piece zirconia implants with a novel cementation approach using a mesostructure. Polymer-infiltrated ceramic mesostructures (n = 112) were therefore designed as caps on the implant abutment, and a molar feldspathic ceramic crown was constructed on top of it as a suprastructure. For cementation, different bonding systems were used. Fracture load and retention force were measured immediately after storage in water at 37 °C for 24 h (n = 8) as well as after artificial aging in a chewing simulator and subsequent thermal cycling (n = 8). Combined restorations showed higher fracture load compared to monolithic restorations of polymer-infiltrated ceramic (n = 8) or feldspathic ceramic (n = 8) identical in shape. However, the fracture load of the combined restorations was significantly affected by aging, independent of the primers and cements used. Restorations cemented with primers containing methyl methacrylate and 10-methacryloyloxydecyl dihydrogen phosphate exhibited the highest retention force values. Aging did not affect the retention force significantly. Similar fracture load values can be expected from combination restorations when compared with monolithic crowns.

Surface Integrity of Dimethacrylate Composite Resins with Low Shrinkage Comonomers

The goal of current research was to investigate the influence of adding low shrinkage “Phene” like comonomers hexaethylene glycol bis(carbamate-isoproply-α-methylstyrene) (HE-Phene) and triethylene glycol bis(carbamate-isoproply-α-methylstyrene) (TE-Phene) on the surface and color characteristics of composite resin. A range of weight fractions (0, 10, 20, 30, 40 wt.%) of HE/TE-Phene monomers were mixed with bisphenol A glycidyl methacrylate (GMA)/triethylene glycol dimethacrylate (TEGDMA) monomer. Experimental composite resins were made by mixing 71 wt.% of silica fillers to 29 wt.% of the resin matrix. A Vickers indenter and glossmeter were used for testing surface hardness (SH) and gloss (SG) at 60°. A chewing-simulator was used to evaluate the surface wear after 15,000 cycles. Color change (∆E) and translucency parameter (TP) were measured using a spectrophotometer. Data showed that HE/TE-Phene monomer had no negative impact (p > 0.05) on surface gloss, wear, color change and translucency of experimental composite resins. Surface hardness was in a reducing direction with the increas in HE/TE-Phene weight fraction (p < 0.05). The study results suggested that incorporating HE/TE-Phene monomers up to 30 wt.% with Bis-GMA/TEGDMA resin did not negatively influence the surface integrity of composite resins except for SH.

Impact of Fast High-Intensity versus Conventional Light-Curing Protocol on Selected Properties of Dental Composites

To study the influence of fast high-intensity (3-s) and conventional (20-s) light curing protocols on certain physical properties including light-transmission and surface wear of two nano-hybrid composite resins (Tetric PowerFill and Essentia U) specifically designed for both curing protocols. According to ISO standards, the following properties were investigated: flexural properties, fracture toughness and water sorption/solubility. FTIR-spectrometry was used to calculate the double bond conversion (DC%). A wear test using a chewing simulator was performed with 15,000 chewing cycles. A tensilometer was used to measure the shrinkage stress. Light transmission through various thicknesses (1, 2, 3 and 4 mm) of composite resins was quantified. The Vickers indenter was utilized for evaluating surface microhardness (VH) at the top and the bottom sides. Scanning electron microscopy was utilized to investigate the microstructure of each composite resin. The light curing protocol did not show a significant (p > 0.05) effect on the mechanical properties of tested composite resins and differences were material-dependent. Shrinkage stress, DC% and VH of both composite resins significantly increased with the conventional 20 s light curing protocol (p < 0.05). Light curing conventional composite resin with the fast high-intensity (3-s) curing protocol resulted in inferior results for some important material properties.

Importance of Chewing Simulators in the Difference of Test Results of Dental Materials. Systematic Review

Objectives: With new dental materials constantly being launched on the market, the number of researches on the properties of dental materials have increased substantially in the past few years. However different results about physical properties of the same material are frequently found in the literature. In an endeavor to elucidate the cause(s) of these disparate results, a review of the literature published in the last five years was conducted, to investigate whether these differences are due to the testing machines - also called chewing simulators – used in the studies. Data: We searched for data of indicators of test accuracy, maintenance of test parameters during all experiments, reproducibility of test and standards in the articles, or in the manufacturers’ sites. Sources: The database searched was CAPES PORTAL (http://www-periodicos-capes-gov-br.ez27.periodicos.capes.gov.br) Study Selection: In the search, the following keywords were used: “bite force” AND “simulator”, “chewing simulator” and “mastication simulator”, and the publication filter date of “January 1, 2016”. As a result, 100 articles were selected and recovered in order of appearance by using the filter “relevance”. Conclusion: based on the data obtained in this review, the disparate results of experiments with dental materials appeared to be more related to the test conditions rather than with the testing machines.

Wear of Ceramics Systems with Different Surface Applications in a Chewing Simulator

Objective: This study was aimed to compare the wear of four types of the ceramic dental materials with different surface treatments. Material and Methods: Porcelain (low-fusing feldspathic, monolithic zirconia, lithium disilicate glass, and leucite glass-ceramic) samples (9 x 3 mm) were prepared with different surface treatments (glazed and mechanical polished). Samples were mechanically loaded in a chewing simulator (600.000 cyles of 50N) and 64 teeth were used to simulate as the antagonist. To evaluate the wear of the samples before and after the test, samples were scanned by 3D scanner, Dental Wings 7 Series. Then they were transformed into the digital platform. Surface analysis was performed by using an optical profilometer and scanning electron microscope. A sensitive digital scale was used for weight measurements of antagonist's teeth. Results: It was a significant difference between the volume values of the groups with mechanical polish and the groups with glaze, except for zirconia samples (p<0.05). While the least change in volume and surface roughness was observed in the zirconia mechanic polished group (ZP), this change was not statistically significant (p>0.05). In terms of the weight measurement results of the antagonist teeth, while leucite reinforced overglazed group (PRG) has the highest weight loss as a result of wear, ZP group has the least weight loss. Conclusion: It was concluded that glazed groups of ceramics lose more substances than polished groups, and that causes more wear on antagonist teeth. Zirconia ceramics showed less substance loss, and that causes less wear on antagonist teeth.

Impact of Coping Veneering Techniques on the Survival of Implant-Supported Zirconia-Based-Crowns Cemented to Hybrid-Abutments: An-In-Vitro Study

The objective of this study is to investigate the influence of veneering technique (hand-layering vs. milling) on the fracture resistance of bi-layer implant-supported zirconia-based hybrid-abutment crowns. Mandibular molar copings were anatomically designed and milled. Copings were then veneered by hand-layering (HL) (n = 20) and milling using the Cad-On technique (LD) (n = 20). Crowns were cemented to zirconia hybrid-abutments. Ten samples of each group acted as a control while the remaining ten samples were subjected to fatigue in a chewing simulator. Crowns were loaded between 50 and 100 N for 1.2 million cycles under simultaneous temperature fluctuation between 5 and 55 °C. Crowns were then subjected to static load a to fracture test. Data were statistically analysed using the one-way ANOVA. Randomly selected crowns from each group were observed under scanning electron microscopy to view fractured surfaces. Study results indicate that during fatigue, LD crowns had a 100% survival rate; while HL crowns had a 50% failure rate. Fracture resistance of LD crowns was statistically significantly higher than that of HL crowns at the baseline and after fatigue (p ≤ 0.05). However, fatigue did not cause a statistically significant reduction in fracture resistance in both LD and HL groups (p > 0.05). Copings fractured in the LD crowns only and the fracture path was different in both LD and HL groups. According to the results, it was concluded that milled veneer implant-supported hybrid-abutment crowns exhibit significantly higher fracture resistance, and better withstand clinical masticatory loads in the posterior region compared to the hand-layered technique. Also, fatigue application and artificial aging caused no significant strength reduction in both techniques. Clinical significance: Different veneering techniques and materials (hand-layering or milling) act differently to clinical forces and environment and may be prone to early chipping during service. Therefore, practitioners are urged to consider the appropriate veneering protocol for posterior implant-supported hybrid-abutment restorations.

Evaluation of wear and fracture strength of zirconia-based ceramics and metal-supported ceramics after treatment with the chewing simulator

Background: The aim of this study was to evaluate the fracture resistance and wear amounts of different zirconia and metal-supported ceramics. Methods: Katana, Prettau, Zenostar, InCoris TZI, BruxZir and porcelain fused to metal (PFM) were used (n=10). All samples were aged via thermal-cycling. Wear test was performed in chewing simulator. Occlusal wear was measured via a 3D laser-scanner. Fracture resistance of samples was determined via a universal testing machine. For statistics, One-Way ANOVA and Tukey were used. Results: PFM had the highest wear area, and differences among groups were significant. BruxZir, Zenostar, and InCoris TZI had lower wear than Prettau and Katana, but the differences were not significant. All groups had similar wear volume. Fracture resistance was significantly lower in Katana and PFM than Zenostar, InCoris TZI, and Prettau. The difference between Katana and PFM was significant. BruxZir samples were not broken even with the highest force applied. Conclusions: Monolithic zirconia ceramics showed superior wear behavior compared to PFM in terms of wear area; however 3D wear measurements were similar. Fracture resistance was also higher in zirconia except for Katana, which had the lowest value. BruxZir was the hardest material with the lowest wear and highest fracture resistance.