Water absorption in artificial composites: Curse or blessing?

OBJECTIVES: This study evaluated the impact of mutable water uptake on the durability of mechanical properties and the long-term reliability of artificial composites. METHODS: Three resin-based CAD/CAM restorative materials (CRMs) were investigated in three-point bending tests to calculate flexural strength (FS), modulus of elasticity (ME), modulus of resilience (MR), modulus of toughness (MT), and elastic recovery (ER). All specimens (n = 180) were stored under the same conditions and tested in four subsets (n = 15 per material) that were respectively withdrawn after repeated thermocycling (5000 cycles; 5-55 °C, H2O) and repetitive drying (7 d; 37 °C, air). For every specimen, weight differences were determined per storage condition. Likewise, loss tangent data were separately recorded via dynamic mechanical analysis to reliably assess damping characteristics. RESULTS: Repeated thermocycling always induced weight increase and a concurrent significant loss in all mechanical properties except for MT and ER of a polymethylmethacrylate-based CRM. Drying consistently provoked weight loss and raised mechanical properties to initial values. Weight increase, however, enhanced loss tangent values and accordingly distinct damping characteristics, whereas weight decrease markedly lowered damping properties. SIGNIFICANCE: Water uptake repeatedly induced a decrease in common mechanical properties but concurrently increased damping behavior. Invertible equilibrium processes were found with no evidence for permanent material degradation.

Damping Behaviour and Mechanical Properties of Restorative Materials for Primary Teeth.

The energy dissipation capacity and damping ability of restorative materials used to restore deciduous teeth were assessed compared to common mechanical properties. Mechanical properties (flexural strength, modulus of elasticity, modulus of toughness) for Compoglass F, Dyract eXtra, SDR flow, Tetric Evo Ceram, Tetric Evo Ceram Bulk Fill, and Venus Diamond were determined using a 4-point bending test. Vickers hardness and Martens hardness, together with its plastic index (ηITdis), were recorded using instrumented indentation testing. Leeb hardness (HLD) and its deduced energy dissipation data (HLDdis) were likewise determined. The reliability of materials was assessed using Weibull analysis. For common mechanical properties, Venus Diamond always exhibited the significantly highest results and SDR flow the lowest, except for flexural strength. Independently determined damping parameters (modulus of toughness, HLDdis, ηITdis) invariably disclosed the highest values for SDR flow. Composite materials, including SDR flow, showed markedly higher reliabilities (Weibull modulus) than Compoglass F and Dyract eXtra. SDR flow showed pronounced energy dissipation and damping characteristics, making it the most promising material for a biomimetic restoration of viscoelastic dentin structures in deciduous teeth. Future developments in composite technology should implement improved resin structures that facilitate damping effects in artificial restorative materials.

Investigation of the Damping Capabilities of Different Resin-Based CAD/CAM Restorative Materials.

The aim of the present study was to evaluate and quantify the damping properties of common resin-based computer-aided design and computer-aided manufacturing (CAD/CAM) restorative materials (CRMs) and assess their energy dissipation abilities. Leeb hardness (HLD), together with its deduced energy dissipation data (HLDdis), and loss tangent values recorded via dynamic mechanical analysis (DMA) were determined for six polymer, four composite, and one ceramic CRM as well as one metal. Data were statistically analyzed. Among resin-based CRMs, the significantly highest HLDdis data were detected for the fiber-reinforced composite FD (p < 0.001) directly followed by the filler-reinforced Ambarino High Class (p < 0.001). The significantly lowest HLDdis values were observed for the polymer-based CRM Telio CAD (p < 0.001). For loss tangent, both PEEK materials showed the significantly lowest data and the polymer-based M-PM the highest results with all composite CRMs in between. HLDdis data, which simultaneously record the energy dissipation mechanism of plastic material deformation, more precisely characterize the damping behavior of resin-based CRMs compared to loss tangent results that merely describe viscoelastic material behavior. Depending on material composition, resin-based CRMs reveal extremely different ratios of viscoelastic damping but frequently show enhanced HLDdis values because of plastic material deformation. Future developments in CAD/CAM restorative technology should focus on developing improved viscoelastic damping effects.

Effect of Cartridge Storage Time and Ambient Laboratory Conditions on the Stability of Mechanical Properties of Bis-Acryl Interim Resin Materials.

PURPOSE: To investigate the stability of mechanical properties during the entire shelf life of chemically-activated bis-acryl interim resin materials stored at ambient laboratory conditions. MATERIALS AND METHODS: Four bis-acryl interim resin materials with no explicit recommendation for refrigerator storage were selected (Luxatemp Plus, Visalys Temp, Structur 3, Structur Premium). Following cartridge storage at ambient laboratory conditions in 6-month intervals, 30 specimens (2.0 × 2.0 × 25.0 mm3 ) were prepared in each case and stored in distilled water (37.0 ± 1.0 °C) with 3 different water storage times (2 hours, 24 hours, 7 days). Flexural strength, modulus of elasticity, modulus of toughness, and elastic recovery were determined (3-point bend test). Data were subjected to a three-way multivariate analysis of variance (MANOVA) to determine overall significance, followed by a series of separate one-way ANOVAs after data were split, using Tukey and Games-Howell post hoc tests to identify significant differences between groups (α = 0.05). RESULTS: While Luxatemp Plus showed no significant decrease for all mechanical properties during the investigated shelf life of 21 months (p > 0.05), Visalys Temp exhibited a continuous decline of the corresponding values (p < 0.05), irrespective of the water storage time. Structur 3 and Structur Premium properties remained almost unchanged during the first 6 months of the examination period. Subsequently, a progressive decrease was observed for flexural strength and modulus of elasticity, while most modulus of toughness and elastic recovery results revealed little alteration. CONCLUSION: Depending on the bis-acryl interim resin material, mechanical properties appeared to be susceptible to continuous degradation processes during cartridge storage at ambient conditions, especially towards the end of the material shelf life. For some materials, the chemical stabilization and recommended storage conditions should be revised by the manufacturers to prevent premature aging during shelf life.

Influence of accelerated ageing on the physical properties of CAD/CAM restorative materials.

OBJECTIVES: This study aims to investigate the influence of thermocycling on the physical properties of different CAD/CAM restorative materials and assess their ability to maintain energy dissipation capacities and damping effects. MATERIALS AND METHODS: The results of a 3-point bending test were used to calculate flexural strength (FS), modulus of elasticity (ME), modulus of toughness (MT) and elastic recovery (ER) for three ceramic, twelve composite and five polymer-based materials. Specimens (n = 10, 4.0 × 1.5 × 17.0 mm3) were loaded until rupture after water storage (24 h; 37.0 ± 1.0 °C) or thermocycling (5000 cycles; 5-55 °C). Statistical data analysis was performed using parametric statistics (p = 0.05). RESULTS: Thermocycling had no significant influence on any investigated properties of ceramic materials (p > 0.05). Hybrid composites showed significant differences between water storage and thermocycling (p < 0.05), with the exception of FS of Tetric CAD. Similarly, ME with AMBARINO High-Class, CERASMART, Tetric CAD and Vita Enamic and MT and ER with Paradigm and Tetric CAD were not affected. For polymer-based materials, significant differences were found with the exceptions of FS (PEEK-OPTIMA, Telio CAD), ME (M-PM Disc, PEEK-OPTIMA, Telio CAD, Vita CAD-Temp), MT (Telio CAD) and ER (Telio CAD). CONCLUSIONS: The material properties of composite and polymer-based CAD/CAM materials were susceptible to degradation processes induced by thermocycling. Only Telio CAD and Tetric CAD showed no significant effects like all ceramic materials, thus preserving their inherent ability to elastically and plastically dissipate energy. CLINICAL RELEVANCE: A careful material selection is advisable when planning CAD/CAM restorations as remarkable differences may exist in the durability of physical characteristics through the impact of water.

Microleakage of composite crowns luted on CAD/CAM-milled human molars: a new method for standardized in vitro tests.

OBJECTIVES: To investigate debonding of full crowns made of CAD/CAM composites, CAD/CAM technology was applied to manufacture standardized test abutments to increase the reproducibility of human teeth used in in vitro studies. MATERIALS AND METHODS: A virtual test abutment and the corresponding virtual crown were designed and two STL data sets were generated. Sixty-four human third molars and CAD/CAM blocks were milled using a CNC machine. Crowns of four different composite blocks (Lava Ultimate (LU), Brilliant Crios (BC), Cerasmart (CS), Experimental (EX)) were adhesively bonded with their corresponding luting system (LU: Scotchbond Universal/RelyX Ultimate; BC: One Coat 7 Universal/DuoCem; CS: G-PremioBond/G-Cem LinkForce; EX: Experimental-Bond/Experimental-Luting-Cement). Half of the specimens were chemical-cured (CC) and the others were light-cured (LC). Afterwards, specimens were artificially aged in a chewing simulator (WL-tec, 1 million cycles, 50-500 N, 2 Hz, 37 °C). Finally, a dye penetration test was used to detect debonding. For inspection, the specimens were sliced, and penetration depth was measured with a digital microscope. Data were analyzed with the Mann-Whitney U test. RESULTS: No cases of total debonding were observed after cyclic loading. However, the LC specimens showed a significantly lower amount of leakage than the CC ones (p < 0.05). Furthermore, the CC specimens exhibited broad scattering. Only the LC-EX blocks showed no debonding. The CC-CS blocks showed the highest leakage and scattering of all tested specimens. CONCLUSIONS: Natural human teeth can be manufactured by CAD/CAM technology in highly standardized test abutments for in vitro testing. For CAD/CAM composites, light curing should be performed. CLINICAL RELEVANCE: The success of a restoration depends on the long-term sealing ability of the luting materials, which avoids debonding along with microleakage. For CAD/CAM composites, separate light curing of the adhesive and luting composite is highly recommended.

Energy dissipation capacities of CAD-CAM restorative materials: A comparative evaluation of resilience and toughness.

STATEMENT OF PROBLEM: Well-balanced physical properties of computer-aided design and computer-aided manufacturing (CAD-CAM) materials are important to ensure the clinical success and longevity of restorations. Therefore, the capacity of a material to dissipate destructive fracture energy by means of elastic and plastic material deformation is of interest. However, little information is available on how to quantify the resilience and toughness of CAD-CAM materials. PURPOSE: The purpose of this in vitro study was to investigate and compare the resilience and toughness of CAD-CAM restorative materials and assess their capability to dissipate destructive fracture energy in comparison with a high-gold-content alloy. MATERIAL AND METHODS: Restorative materials for 3-unit fixed partial dentures (Alphador No. 1, IPS e.max CAD, Lava Plus, PEEK Optima), crowns and onlays (CERASMART, CEREC Blocs, Lava Ultimate, VITA ENAMIC), and interim prostheses (M-PM Disc, Telio CAD) were investigated. The strain energy density was determined with a 3-point bend test to calculate the modulus of toughness, the modulus of resilience, and the elastic recovery and thus characterize the material properties of resilience and toughness. Data were statistically analyzed with a generalized linear mixed model by using the Huber-White sandwich estimator (α=.05). RESULTS: Significant differences were found among the materials concerning the modulus of toughness, the modulus of resilience, the elastic recovery, and the difference between the elastic recovery and the modulus of resilience (P<.001). Alphador produced the highest mean regarding the modulus of toughness followed by Telio CAD, Lava Plus, M-PM Disc, CERASMART, and Lava Ultimate; all showed significantly higher capacities to dissipate energy by elastic and plastic deformation when compared with the ceramic materials (IPS e.max CAD, VITA ENAMIC, CEREC Blocs). For the modulus of resilience and elastic recovery, Lava Plus and Alphador showed the highest mean values and therefore better able to only elastically absorb destructive fracture energy; the least able materials were VITA ENAMIC and CEREC Blocs. As PEEK Optima, M-PM Disc, and Lava Ultimate showed higher mean values for the modulus of resilience than IPS e.max CAD, they were better able to elastically dissipate energy. CONCLUSIONS: Alphador had the highest values for the modulus of toughness, the elastic recovery, and the difference between the elastic recovery and the modulus of resilience; this was equivalent to pronounced energy dissipation capacities. In comparison, Lava Plus showed the highest modulus of resilience but significantly lower results for all other parameters and therefore fewer energy-consuming capabilities. The new polymer-based CAD-CAM restorative materials in general had a higher modulus of toughness and elastic recovery than ceramics and thereby partially resemble Lava Plus, all with similar capacities to dissipate destructive energy.

The effect of phosphoric and phosphonic acid primers on bone cement bond strength to total hip stem alloys.

Aseptic loosening at alloy-cement interfaces constitutes a main failure mechanism of cemented total hip replacements (THR). As a potential solution we investigated the effect of metal primers containing phosphoric and phosphonic acid on shear bond strength (SBS) of bone cement to THR alloys (CoCrMo, TiAlNb) and pure tin (Sn) substrates (20×8×3 mm). Metal surfaces were modified by polishing or Al2O3 blasting and primer application. Substrates without primer treatment served as references. Cylindrical cement pins (Ø 5mm) were polymerised onto substrate surfaces and aging (1, 5, 14 and 150 days) was simulated in aqueous NaCl solution (0.9%) before SBS determination and failure mode evaluation. Regardless of surface roughness and aging time, SBS for THR alloys and Sn was always significantly higher with primer treatment. Compared to untreated reference specimens (≤0.2MPa) SBS values increased even up to 350 fold (TiAlNb, 14 days) or 400 fold (CoCrMo, 5 days). In general, the phosphoric acid containing primer revealed significant higher SBS values on THR alloys compared to the phosphonic acid containing one. Al2O3 blasted specimens showed generally higher SBS values than polished ones with the exception of Sn which showed high SBS values in general. With primer treatment on polished Sn a significant reduction of SBS could not be detected even up to 150 days, whereas THR alloys showed only an SBS improvement in the short term (≤14 days). A NaCl-pitting corrosion probably led to an increasing and durable SBS on polished Sn surfaces over time. Compared to modern THR in clinical practice that shows survival rates of 10, 15, 20 or more years, the receivable bond strength enhancements described in this study appeared to be very short. The improved SBS on THR alloys lasted only a few days before it was lost again. In contrast, the phosphoric acid primer treatment of polished Sn appeared to be very promising and may play a key role in further investigations dealing with the prevention of the stem-cement debonding in THR.

Bonding resin thixotropy and viscosity influence on dentine bond strength.

OBJECTIVES: To investigate the influence of bonding resin thixotropy and viscosity on dentine tubule penetration, blister formation and consequently on dentine bond strength as a function of air-blowing pressure (air-bp) intensity. METHODS: Two HEMA-free, acetone-based, one-bottle self-etch adhesives with similar composition except disparate silica filler contents and different bonding resin viscosities were investigated. The high-filler-containing adhesive (G-Bond) featured a lower viscous bonding resin with inherent thixotropic resin (TR) properties compared to the low-filler-containing adhesive (iBond) exhibiting a higher viscous bonding resin with non-thixotropic resin (NTR) properties. Shear bond strength tests for each adhesive with low (1.5bar; 0.15MPa; n=16) and high (3.0bar; 0.30MPa; n=16) air-bp application were performed after specimen storage in distilled water (24h; 37.0±1.0°C). Results were analysed using a Student's t-test to identify statistically significant differences (p<0.05). Fracture surfaces of TR adhesive specimens were morphologically characterised by SEM. RESULTS: Statistically significant bond strength differences were obtained for the thixotropic resin adhesive (high-pressure: 24.6MPa, low-pressure: 9.6MPa). While high air-bp specimens provided SEM images revealing resin-plugged dentine tubules, resin tags and only marginally blister structures, low air-bp left copious droplets and open dentine tubules. In contrast, the non-thixotropic resin adhesive showed no significant bond strength differences (high-pressure: 9.3MPa, low-pressure: 7.6MPa). CONCLUSIONS: A pressure-dependent distinct influence of bonding resin thixotropy and viscosity on dentine bond strength has been demonstrated. Stronger adhesion with high air-bp application is explained by improved resin fluidity and facilitated resin penetration into dentine tubules. CLINICAL SIGNIFICANCE: Filler particles used in adhesive systems may induce thixotropic effects in bonding resin layers, accounting for improved free-flowing resin properties. In combination with high air-bp this effect allows an easy plugging of dentine tubules and elimination of blister structures, both resulting in superior dentine bond strength.

Osteogenic potential of a biosilica-coated P(UDMA-co-MPS) copolymer.

A P(UDMA-co-MPS) copolymer was surface-functionalized through the polycondensation activity of the enzyme silicatein. The resulting biosilica coating significantly enhanced mineralization of osteoblastic cells, thereby revealing its osteogenic potential. Consequently, the functionalized copolymer may be explored as an alternative to conventionally used acrylics in applications where stable bone-material interfaces are required.