Thermoanalytical Investigations on the Influence of Storage Time in Water of Resin-Based CAD/CAM Materials

New resin-based composites and resin-infiltrated ceramics are used to fabricate computer-aided design (CAD) and computer-aided manufacturing (CAM)-based restorations, although little information is available on the long-term performance of these materials. The aim of this investigation was to determine the effects of storage time (24 h, 90 days, 180 days) on the thermophysical properties of resin-based CAD/CAM materials. Thermogravimetric Analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used in the study. TGA provided insight into the composition of the resin-based materials and the influence of internal plasticization and water sorption. Resin-based composites showed different decomposition, heat energy and mechanical behavior, which was influenced by storage time in water. Individual materials such as Grandio bloc showed lower influence of water storage while maintaining good mechanical properties

Surface properties of monolithic zirconia after dental adjustment treats and in vitro wear simulation

Objectives To investigate the surface properties (roughness, composition, phase transformation) of monolithic zirconia specimens after dental adjustment procedures (grinding, polishing) and wear simulation. Methods Zirconia specimens (Cercon base, Cercon ht, DeguDent, G; n = 10/material) were successively sintered, ground, and polished with an intraoral polishing kit in a three-step procedure. Sintered zirconia specimens with high surface roughness served as a reference. For each treatment step, wear simulations with steatite plates (d = 10 mm) as antagonists were conducted as well as surface roughness tests (Ra), EDX analysis, and X-ray diffraction (XRD) measurements. SEM pictures were taken, and data were statistically analyzed (one-way ANOVA, post hoc Bonferroni, α = 0.05). Results Grinding significantly (p = 0.000) increased the roughness of sintered zirconia up to values of 1.36 ± 0.11 μm (Ra). Polishing significantly (p = 0.000) reduced Ra. The lowest roughness value after the final polishing step was 0.20 ± 0.03 μm. Wear testing resulted in a further slight decrease of Ra. After the grinding procedure, SEM pictures showed deep grooves that were progressively smoothed by polishing. The EDX spectra showed that magnesium was transferred from steatite antagonists to zirconia by wear. In the XRD-patterns, monoclinic (m) peaks were observed after grinding and polishing. The maximum intensity ratio between the m (1 1 −1) peak and the tetragonal t (1 1 1) peak decreased after the completion of all polishing steps. Wear did not induce phase transformation. Conclusions Adequate polishing reduced the roughness of ground zirconia. Wear had little influence on roughness and no influence on phase transformation. Clinical significance Careful polishing is recommended to keep surface roughness and phase transformation low

Martens Hardness of CAD/CAM Resin-Based Composites

Background: The properties of CAD/CAM resin-based composites differ due to differences in their composition. Instrumented indentation testing can help to analyze these differences with respect to hardness, as well as energy-converting capabilities due to viscoelastic behavior. (2) Methods: Eleven materials were investigated using instrumented indentation testing. Indentation depth (hr), Martens hardness (HM), indentation hardness (HIT), indentation modulus (EIT), the elastic part of indentation work (ηIT), and indentation creep (CIT) were investigated, and statistical analysis was performed using one-way ANOVA, Bonferroni post-hoc test, and Pearson correlation (α = 0.05). (3) Results: All of the investigated parameters revealed differences between the analyzed materials. Besides the differences in hardness-associated parameters (hr, HM, and HIT), instrumented indentation testing demonstrated differences in energy-converting properties. The subsequent one-way ANOVA revealed significant differences (p 0.576) correlation between the materials and HM, HIT, or EIT was identified. (4) Conclusions: Due to the differences found in the energy-converting properties of the investigated materials, certain CAD/CAM resin-based composites could show superior stress-breaking capabilities than others. The consequential reduction in stress build-up may prove to beneficial, especially for implant-retained restorations or patients suffering from parafunction

Characterisation of the Filler Fraction in CAD/CAM Resin-Based Composites

The performance of dental resin-based composites (RBCs) heavily depends on the characteristic properties of the individual filler fraction. As specific information regarding the properties of the filler fraction is often missing, the current study aims to characterize the filler fractions of several contemporary computer-aided design/computer-aided manufacturing (CAD/CAM) RBCs from a material science point of view. The filler fractions of seven commercially available CAD/CAM RBCs featuring different translucency variants were analysed using Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS), Micro-X-ray Computed Tomography (µXCT), Thermogravimetric Analysis (TG) and X-ray Diffractometry (XRD). All CAD/CAM RBCs investigated included midifill hybrid type filler fractions, and the size of the individual particles was clearly larger than the individual specifications of the manufacturer. The fillers in Shofu Block HC featured a sphericity of ≈0.8, while it was <0.7 in all other RBCs. All RBCs featured only X-ray amorphous phases. However, in Lava Ultimate, zircon crystals with low crystallinity were detected. In some CAD/CAM RBCs, inhomogeneities (X-ray opaque fillers or pores) with a size <80 µm were identified, but the effects were minor in relation to the total volume (<0.01 vol.%). The characteristic parameters of the filler fraction in RBCs are essential for the interpretation of the individual material’s mechanical and optical properties

Biofilm formation on denture base resin including ZnO, CaO, and TiO2 nanoparticles

PURPOSE. This laboratory study aimed to investigate the effect of doping an acrylic denture base resin material with nanoparticles of ZnO, CaO, and TiO2 on biofilm formation. MATERIALS AND METHODS. Standardized specimens of a commercially available cold-curing acrylic denture base resin material were doped with 0.1, 0.2, 0.4, or 0.8 wt% commercially available ZnO, CaO, and TiO2 nanopowder. Energy dispersive X-ray spectroscopy (EDX) was used to identify the availability of the nanoparticles on the surface of the modified specimens. Surface roughness was determined by employing a profilometric approach; biofilm formation was simulated using a monospecies Candida albicans biofilm model and a multispecies biofilm model including C. albicans, Actinomyces naeslundii, and Streptococcus gordonii. Relative viable biomass was determined after 20 hours and 44 hours using a MTT-based approach. RESULTS. No statistically significant disparities were identified among the various materials regarding surface roughness and relative viable biomass. CONCLUSION. The results indicate that doping denture base resin materials with commercially available ZnO, CaO, or TiO2 nanopowders do not inhibit biofilm formation on their surface. Further studies might address the impact of varying particle sizes as well as increasing the fraction of nanoparticles mixed into the acrylic resin matrix

In Vitro Shock Absorption Tests on Implant-Supported Crowns: Influence of Crown Materials and Luting Agents

Purpose: To investigate the force absorption capacity of implant-supported crowns made of different restorative materials and connected to abutments with different luting agents. Materials and Methods: Molar crowns were milled of different computer-aided design/computer-aided manufacture materials (n = 8 crowns per material): polymethyl methacrylate, polyether ether ketone, composite, lithium disilicate, titanium, and zirconia. Crowns were mounted on titanium implant replicas using different luting agents: uncemented, temporarily cemented (zinc oxide-eugenol cement), conventionally cemented (zinc oxide phosphate cement), and adhesively bonded. As a reference, one implant replica was tested without a crown. Force absorptions of the different combinations of crown materials and luting agents were determined by applying an increasing force (0 to 250 N) on the occlusal crown surface and measuring the resulting force below the implant. Mean curves of applied and resulting forces up to 200 N were determined (six measurements per group), and slopes were calculated. Statistical analysis was performed (one-way analysis of variance, Bonferroni post hoc test, alpha = .05). Results: Significant (P < .001) differences in the applied and resulting forces were found between the crown materials that were uncemented, temporarily cemented, cemented, and adhesively bonded. Materials with higher moduli of elasticity (ceramics, titanium) showed steeper slopes of the force curves and lower shock-absorbing capacity than resin-based materials, but were influenced more by the luting agents. The damping effects of resin-based materials were higher in combination with all cementation and luting modes. Conclusion: Shock absorption tests exhibited a strong material-dependent damping behavior of implant-supported crowns. The shock-absorbing capacity of crown materials with high moduli of elasticity may benefit from conventional cementation

In vitro performance of one- and two-piece zirconia implant systems for anterior application

Objectives: To investigate the long-term in vitro performance and fracture resistance of one-piece and bonded two-piece zirconia implant systems for anterior application. Methods: Two groups of bonded two-piece zirconia (ZZB), four groups of one-piece zirconia (Z), and two groups of two-piece titanium (ITS, reference) implant systems were restored with identical monolithic zirconia crowns (n = 10/group). Eight specimens per group were mounted at an angle of 135 degrees in the chewing simulator and subjected to thermal cycling (TC:18,000 cycles; 5 degrees/55 degrees) and mechanical loading (ML:3.6 x 10(6) cycles; 100N) simulating an anterior situation. Fracture resistance and maximum bending stress were determined for specimens that survived aging and for two references per group after 24 h water storage. SEM pictures were used for failure analysis. Data were statistically analysed (one-way-ANOVA, post-hoc Bonferroni, Kaplan-Meier-Log-Rank, alpha = 0.05). Results: A one-piece zirconia and a two-piece titanium implant system survived TCML without failures. Both bonded two-piece zirconia implant systems and a one-piece zirconia implant system totally failed (fractures of abutment or implant). Failure numbers of the other systems varied between 1 x (1 group) and 5 x (2 groups). Significantly different survival rates were found (Log-Rank-test: p = 0.000). Maximum fracture forces/bending stresses varied significantly (ANOVA: p = 0.000) between 188.00 +/- 44.80 NI 381.02 +/- 80.15 N/mm(2) and 508.67 107.00 N/751.45 +/- 36.73 N/mm(2). Mean fracture values after 24 h water storage and TCML were not significantly different. Conclusion: Zirconia implant systems partly showed material defects or connection insufficiencies. Bonded two-piece systems had higher failure rates and lower fracture resistance than one-piece implants. Clinical significance: Individual zirconia implant systems may be applied in anterior regions with limitations. (C) 2016 Elsevier Ltd. All rights reserved

Investigation of Clinical and Laboratory Wear in Locator-Supported, Implant-Retained Overdentures

Purpose: To investigate the mechanical properties and wear of nylon inserts and abutments in Locator-retained, implant-supported overdentures (L-IODs). Materials and Methods: Clinical wear of inserts and abutments was qualitatively rated in a group of 16 patients with L-IODs. The inserts were also subjected to microscopic analysis, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Results: Wear was identified in almost all inserts and abutments. These results were corroborated by DSC and TGA analyses, which showed significant mechanical deterioration of the inserts. Conclusion: Nylon inserts and Locator abutments show relevant signs of deterioration in clinical use, indicating that regular maintenance is an issue that should be addressed with the patients prior to treatment

Cycle-dependent in vitro wear performance of dental ceramics after clinical surface treatments

AIM: To investigate the two-body wear performance of dental ceramics after different clinical surface treatments as a function of number of wear cycles. MATERIAL AND METHODS: Standardized specimens (n=72/material) were prepared from two different zirconia ceramics, a veneering porcelain, and a lithiumdisilicate glass ceramic. Specimens were progressively glazed, ground, and polished. After each treatment step 24 specimens per material were kept at the obtained surface state. Steatite and human enamel specimens served as reference materials. Two-body wear tests were performed with steatite spheres as antagonists in a pin-on-block design (50N, 1.6Hz, lateral movement: 1mm, mouth opening: 2mm) under simultaneous thermal cycling (5/55 degrees C, 2min/cycle). For investigating the dynamic evolution of the wear process, 9 groups per material (n=8/group) were defined, differing in surface state (glazed, ground, and polished) and number of chewing cycles (40T, 80T, and 120T; T: X1000): glazed 40T, glazed 80T, glazed 120T, ground 40T, ground 80T, ground 120T, polished 40T, polished 80T, polished 120T. Surface roughness, wear depth of the specimens and relative wear area of the steatite antagonists were determined using an optical 3D laser scanning microscope. SEM evaluation was done. Mean values and standard deviations were calculated and statistically analyzed (one-way ANOVA, post-hoc Bonferroni, alpha=0.05). RESULTS: Veneering and lithiumdisilicate ceramics showed higher wear depths than zirconia ceramics (p<0.05). Wear of veneering and lithiumdisilicate ceramics and their antagonists increased with wear cycles but was only marginally influenced by the initial surface state. Wear of zirconia was not influenced by wear cycles but antagonists of zirconia showed a cycle-dependent wear increase. Polished zirconia surfaces showed lowest wear for material and antagonist. Wear mechanism of common ceramics was characterized by abrasive wear. Zirconia in contrast showed a superficial cyclic shifting of worn material of the antagonist. CONCLUSIONS: Wear of zirconia and standard ceramics showed different wear performances, strongly influenced by surface treatments as well as number of wear cycles. Copyright (C) 2015 Elsevier Ltd. All rights reserved