Evaluation of marginal fit of 2 CAD-CAM anatomic contour zirconia crown systems and lithium disilicate glass-ceramic crown

PURPOSEThis study was to evaluate the marginal fit of two CAD-CAM anatomic contour zirconia crown systems compared to lithium disilicate glass-ceramic crowns.RESULTSThe mean marginal gap of lithium disilicate glass ceramic crowns (IPS e.max®press) was significantly lower than that of the CAD-CAM anatomic contour zirconia crown system (Prettau®Zirconia) (P<.05). Both fabrication systems and finish line configurations significantly influenced the absolute marginal discrepancy (P<.05).CONCLUSIONThe lithium disilicate glass ceramic crown (IPS e.max®press) had significantly smaller marginal gap than the CAD-CAM anatomic contour zirconia crown system (Prettau®Zirconia). In terms of absolute marginal discrepancy, the CAD-CAM anatomic contour zirconia crown system (ZENOSTAR®ZR translucent) had under-extended margin, whereas the CAD-CAM anatomic contour zirconia crown system (Prettau®Zirconia) and lithium disilicate glass ceramic crowns (IPS e.max®press) had overextended margins.     

对磨材料对树脂渗透陶瓷Vita Enamic磨损的实验研究

目的 探究树脂渗透陶瓷(PICN)分别与二氧化锆陶瓷、钴铬合金以及复合树脂材料配副情况下的磨损行为。方法 分别制作尺寸为18 mm×14 mm×3.0 mm PICN试件30片，直径为4 mm的二氧化锆、钴铬合金及复合树脂磨头各10个。相互配副，在干燥环境及人工唾液条件下进行载荷5 N、频率5 HZ，磨程3 mm的线性往复循环磨损试验30 min。实时记录摩擦系数，绘制摩擦系数曲线。利用三维表面形貌仪定量分析磨痕尺寸，计算磨损量。双因素方差分析评估磨头材料及干湿环境对磨痕尺寸及磨损体积的影响。各组抽取试件利用扫描电镜观察磨损区表面微观结构。结果 磨头材料及干湿环境对于PICN磨痕尺寸及磨损体积具有显著影响(P<0.05)，且存在相互作用。在人工唾液中，PICN与树脂磨头的摩擦系数为0.26±0.03，显著低于其他各组(P<0.05)，但树脂磨头反而产生较高的磨损量(P<0.05)。此外二氧化锆磨头对PICN造成的磨损体积为(9.2±5)×10^-2 mm³，显著高于其余各组(P<0.05)。结论 当对颌为二氧化锆修复体时...     

Evaluation of wear behavior of dental restorative materials against zirconia in vitro

ObjectivesTo evaluate two-body wear (2BW) and three-body wear (3BW) of different CAD/CAM and direct restorative materials against zirconia using a dual-axis chewing simulator and an ACTA wear machine.Methods3 CAD-CAM resin-based composite or polymer infiltrated ceramic network blocs, 1 lithium disilicate CAD-CAM ceramic (LS₂), 3 direct resin composites, amalgam and bovine enamel were tested. For 2BW, 8 flat specimens per material were produced, grinded, polished, stored wet (37 °C, 28d) and tested (49 N, 37 °C, 1,200,000 cycles) against zirconia. For 3BW, specimens (n = 10) were stored accordingly, and tested against a zirconia antagonist wheel (3Y-TZP, d = 20 mm, h = 6 mm; 200,000 cycles, F = 15 N, f = 1 Hz, 15% slip) in millet seed suspension. Wear resistance was analysed in a 3D optical non-contact profilometer, measuring vertical wear depth and volume loss for 2BW and mean wear depth and roughness (R_a) for 3BW. Vickers hardness (15 s, HV2) was measured. Statistical analysis was performed using non-parametric tests (Mann-Whitney-U test, p < 0.05).Results2BW and 3BW have a different impact on material surfaces. Similar wear resistance was observed for direct and indirect resin based materials with analogous filler configurations in both methods. Bovine enamel exhibited the best wear resistance in 2BW, but the least wear resistance in 3BW against zirconia. Regarding 2BW, a direct/indirect composite material pair of the same manufacturer showed the significantly highest mean volume losses (2.72/2.85 mm³), followed by LS₂ (1.41 mm³). LS₂ presented the best wear resistance in 3BW (mean wear depth 2.85 µm), combined with the highest mean Vickers hardness (598 MPa). No linear correlation was found between Vickers hardness and both wear testing procedures. The zirconia antagonists showed no recordable signs of wear.SignificanceDental restorative materials behave differently in 2BW and 3BW laboratory testing. Vickers hardness testing alone cannot hold for a correlation with wear behavior of materials. Micromorphological investigation of material composition can reveal insights in wear mechanisms related to variations in filler technologies.     

Wear of 3D printed and CAD/CAM milled interim resin materials after chewing simulation

PURPOSEThe purpose of this in vitro study was to investigate the wear resistance and surface roughness of three interim resin materials, which were subjected to chewing simulation.MATERIALS AND METHODSThree interim resin materials were evaluated: (1) three-dimensional (3D) printed (digital light processing type), (2) computer-aided design and computer-aided manufacturing (CAD/CAM) milled, and (3) conventional polymethyl methacrylate interim resin materials. A total of 48 substrate specimens were prepared. The specimens were divided into two subgroups and subjected to 30,000 or 60,000 cycles of chewing simulation (n = 8). The wear volume loss and surface roughness of the materials were compared. Statistical analysis was performed using one-way analysis of variance and Tukey''s post-hoc test (α=.05).RESULTSThe mean ± standard deviation values of wear volume loss (in mm³) against the metal abrader after 60,000 cycles were 0.10 ± 0.01 for the 3D printed resin, 0.21 ± 0.02 for the milled resin, and 0.44 ± 0.01 for the conventional resin. Statistically significant differences among volume losses were found in the order of 3D printed, milled, and conventional interim materials (P<.001). After 60,000 cycles of simulated chewing, the mean surface roughness (Ra; μm) values for 3D printed, milled, and conventional materials were 0.59 ± 0.06, 1.27 ± 0.49, and 1.64 ± 0.44, respectively. A significant difference was found in the Ra value between 3D printed and conventional materials (P=.01).CONCLUSIONThe interim restorative materials for additive and subtractive manufacturing digital technologies exhibited less wear volume loss than the conventional interim resin. The 3D printed interim restorative material showed a smoother surface than the conventional interim material after simulated chewing.     

牙科树脂渗透氧化锆陶瓷材料的制备与性能研究

目的 制备一种牙科树脂渗透氧化锆陶瓷（polymer infiltrated zirconia ceramic network,PICN）材料,检测其机械性能。方法 制备纯氧化锆陶瓷、纯树脂以及4种不同孔隙率的陶瓷支架,实验组的陶瓷支架用树脂进行渗透得到陶瓷树脂复合材料（PICN）。通过三点弯曲强度实验检测材料的弯曲强度和弹性模量,采用单边切口梁法检测断裂韧性,通过纳米压痕系统测得材料的硬度以及用扫描电镜观测材料的显微结构。结果 树脂渗透氧化锆陶瓷（PICN）材料的弯曲强度值为135~266 MPa,弹性模量值为41.3~99.3GPa,断裂韧性值为2.20~4.04 MPam1/2,硬度值为1.93~10.83GPa。扫描电镜显示PICN材料中树脂在陶瓷孔隙内渗透完全。结论 这类树脂渗透氧化锆陶瓷材料的机械性能与人类天然牙釉质和牙本质相似,在口腔修复领域具有良好的应用前景。     

Impact of simulated toothbrushing on surface properties of chairside CAD-CAM materials: An in vitro study

Statement of problemChairside computer-aided design and computer-aided manufacturing (CAD-CAM) materials that do not require any firing steps are a promising option to expedite restoration production; however, little information is available to determine the most suitable material for each clinical situation.PurposeThe purpose of this in vitro study was to evaluate the effect of simulated toothbrushing on surface gloss, roughness, and wear of chairside CAD-CAM materials.Material and methodsDisk-shaped specimens (n=15) were prepared of the following materials: ENA—VITA Enamic; LAV—Lava Ultimate; EMP—IPS Empress CAD; CER—Cerasmart; GRA—Grandio blocs. Gloss (Gloss Unit—GU) and surface roughness (Ra—μm) were evaluated before and after simulated toothbrushing (100 000 strokes). Wear (μm) was assessed by contact profilometry. Additional analyses of microhardness by scanning electron microscopy were also performed. Data were analyzed with 2-way repeated measures ANOVA test for roughness and gloss, and 1-way ANOVA for wear (α=.05). To estimate the correlation between Ra and GU, the Pearson correlation was calculated.ResultsBefore brushing, CER showed the lowest Ra (P<.001), and GRA the lowest GU values. After brushing, the feldspathic ceramic-based materials (ENA and EMP) presented the highest gloss, whereas the ceramic group (EMP) showed the lowest Ra. Before and after brushing, GRA showed the lowest GU values. Higher wear values were found for the composite resin groups (CER>GRA), with the exception of LAVA, which was similar to ENA, and EMP showing improved wear resistance. A strong negative correlation (-0.925) between GU and Ra values was detected (P<.001).ConclusionsThe materials containing a glass phase (ENA and EMP) presented higher wear resistance, higher gloss, and lower roughness after brushing than the other materials tested. The correlation test showed that the higher the surface roughness, the lower the gloss.     

Bond strength of CAD-CAM and conventional veneering materials to different frameworks

Statement of problemNew materials and precise manufacturing processes allow for new processes in the veneering and production of fixed dental prostheses. However, data on the bond strength of computer-aided design and computer-aided manufacturing (CAD-CAM) and conventional veneering materials to substrates bonded with different composite resins are lacking.PurposeThe purpose of this in vitro study was to investigate the shear bond strength (SBS) of 2 CAD-CAM, Lava Ultimate (LVU) and VITABLOCS Mark II (VMII), and 3 conventional veneering materials (VM9, VM13, VTI) to 3 different substrates: zirconia (ZIR), cobalt-chromium (CC), and titanium (TIT).Material and methodsSubstrates and veneering cylinders were manufactured and bonded by using 3 different composite resins, RelyX Unicem (RUL), RelyX Ultimate (RXU), and Sinfony (SIN), after various pretreatments (n=18). Half the specimens underwent artificial aging before SBS testing, and failure types were analyzed. Univariate 1-way ANOVA, Kruskal-Wallis, and Mann-Whitney U were computed (α=.05).ResultsCC substrates bonded with RUL showed the highest SBS (P=.007). ZIR substrates bonded with RXU presented higher SBS than TIT substrates (P=.007). ZIR substrates bonded with SIN showed higher SBS than CC substrates (P<.001). SIN veneered groups showed lower SBS than that observed for VM9/13/VTI (P<.001). SIN veneered LVU and VMII substrates presented lower SBS (P<.001). Thermocycling led to a reduction in SBS for most groups (P=.001-.022). SIN veneered substrates and RXU veneered VMII substrates resulted in lower SBS than that seen for VM9/13/VTI and veneered ZIR substrates bonded with SIN or RXU (P<.001). Adhesive failures were most common.ConclusionsWhile RUL is capable of forming a stable bond to CC without pretreatment, ZIR substrates achieve higher SBS after conditioning with an MDP-containing primer when using RXU or SIN than that seen for RUL. Pretreated CAD-CAM–veneered ZIR substrates bonded with SIN or RXU led to similar SBS results to those observed for conventional veneers, while veneering with SIN resulted in lower SBS.     

Two-body wear of monolithic,veneered and glazed zirconia and their corresponding enamel antagonists

Abstract

Objective. This study tested whether the two-body wear of monolithic zirconia and their corresponding enamel antagonists was higher compared to monolithic alloy and veneered zirconia. Materials and methods. Cylindrical specimens (N = 36, n = 6) were prepared out of (A) veneered zirconia (VZ), (B) glazed zirconia using a glaze ceramic (GZC), (C) glazed zirconia using a glaze spray (GZS), (D) manually polished monolithic zirconia (MAZ), (E) mechanically polished monolithic zirconia (MEZ) and (F) monolithic base alloy (control group, MA). Wear tests were performed in a chewing simulator (49 N, 1.7 Hz, 5°C/50°C) with enamel antagonists. The wear analysis was performed using a 3D profilometer before and after 120,000, 240,000, 640,000 and 1,200,000 masticatory cycles. SEM images were used for evaluating wear qualitatively. The longitudinal results were analysed using linear mixed models (α = 0.05). Results. Materials (p < 0.001) and number of masticatory cycles (p < 0.001) had a significant effect on the wear level. The least enamel antagonist wear was observed for MAZ and MEZ (27.3 ± 15.2, 28 ± 11.1 μm, respectively). GZC (118 ± 30.9 μm) showed the highest wear of enamel antagonists. The highest wear rate in the material was observed in GZS (91.3 ± 38.6 μm). While in the groups of MA, VZ, GZC and GZS 50% of the specimens developed cracks in enamel, it was 100% in MAZ and MEZ groups. Conclusion. Polished monolithic zirconia showed lower wear rate on enamel antagonists as well as within the material itself but developed higher rates of enamel cracks.     

Wear resistance of crowns made from different CAM/CAD materials

ObjectivesThe aim of this laboratory study was to evaluate the wear resistance of crowns made from current computer-aided design and computer-aided manufacture (CAD/CAM) materials. In addition, the abrasion of the steatite antagonist against these materials was compared.MethodsIdentically shaped crowns of lithium disilicate, zirconia-reinforced lithium disilicate and a polymer-infiltrated ceramic network (PICN) were fabricated with an occlusal thickness of 1.5 mm and a lateral wall thickness of 1.2 mm (n = 8). The crowns were cemented with a dual-polymerizing luting resin on composite resin dies. Using spherical steatite antagonists, all specimens were loaded with 49 N for 1,200,000 cycles in a mastication simulator with additional thermocycling. After 120,000, 240,000, 480,000, 960,000, and 1,200,000 cycles, precision impressions were made and investigated with a laser scanning microscope. The vertical and volume substance loss was measured. Additionally, the substance loss of the antagonists was evaluated after 1,200,000 loading cycles.ResultsNo significant difference (p > 0.05) was found in the median volume loss of the test materials after 1,200,000 cycles (lithium disilicate: 0.405 mm³, PICN: 0.362 mm³, zirconia-reinforced lithium disilicate: 0.340 mm³). The vertical substance loss of PICN (157 μm) was significantly lower (p ≤ 0.05) than that of lithium disilicate (201 μm) and zirconia reinforced lithium disilicate (191 μm). However, the substance loss of steatite against zirconia-reinforced lithium disilicate (0.191 mm³) was significantly lower (p ≤ 0.05) than against lithium disilicate (0.296 mm³) and PICN (0.531 mm³).SignificanceAll three CAD/CAM materials showed wear resistance that seems appropriate for clinical application. Also, the abrasion of the antagonist looks promising.     

Microcomputed tomography evaluation of cement shrinkage under zirconia versus lithium disilicate veneers

Statement of problemComputer-aided design and computer-aided manufacturing (CAD-CAM) technology and the improved translucency of recently developed high-strength monolithic zirconia could make them clinically acceptable for veneers if bonding to zirconia was as predictable as to glass-ceramics. Few studies have compared how resin cements behave between glass-ceramic and zirconia veneers before and after polymerization.PurposeThe purpose of this in vitro study was to evaluate the volumetric polymerization shrinkage of resin cement, marginal discrepancy, and cement thickness before and after polymerization for glass-ceramic and zirconia veneers with light-polymerizing resin cement.Material and methodsTen lithium disilicate veneers and 10 zirconia veneers were fabricated with a CAD-CAM workflow on extracted human maxillary anterior teeth with intact enamel surfaces. Zirconia veneers were treated with airborne-particle abrasion, and lithium disilicate veneers were etched with 5% hydrofluoric acid. All specimens were treated with ceramic primer and cemented with a light-polymerized resin cement. All specimens were scanned before and after resin cement polymerization by microcomputed tomography. The data were processed by the Amira software program to compare polymerization volumetric shrinkage, cement thickness, and marginal discrepancy. The data were compared by using a t test and analysis of variance (α=.05). Two bonded veneers were loaded in a mastication simulator for 400 000 cycles to investigate the effect of cyclic fatigue loading.ResultsMean volumetric polymerization shrinkage was 4.2 ±0.8% for the lithium disilicate group and 6.4 ±3.5% for the zirconia group. No significant difference was found for volumetric shrinkage between materials (P=.132). The mean ±standard deviations of the marginal discrepancies before and after polymerization were 178 ±41 μm and 158 ±37 μm for lithium disilicate and 115 ±33 μm and 107 ±32 μm for zirconia. A smaller marginal discrepancy was found for both materials after polymerization (P=.011) and for zirconia compared with lithium disilicate (P=.004). The mean ±standard deviation cement thickness values before and after polymerization were 157 ±27 μm and 147 ±27 μm for lithium disilicate and 162 ±53 μm and 147 ±52 μm for zirconia. Smaller cement thickness was found after polymerization (P<.001), whereas no significant difference was found in cement thickness between materials (P=.144). No changes were noted in marginal discrepancy and cement thickness as a result of the fatigue loading.ConclusionsThe difference in the volumetric polymerization shrinkage of cement between lithium disilicate and zirconia veneers was not statistically significant. Polymerization shrinkage resulted in smaller marginal discrepancy and cement thickness for both veneer materials.     

Wear evaluation of the human enamel opposing different Y-TZP dental ceramics and other porcelains

PurposeThis study examined the wear resistance of human enamel and feldspathic porcelain after simulated mastication against 3 zirconia ceramics, heat-pressed ceramic and conventional feldspathic porcelain.Materials and methodsHuman teeth and feldspathic porcelain cusp were tested against ceramic discs. 5 brands were tested – 3 monolithic zirconia, Prettau, Lava, and Rainbow, one lithium disilicate, IPS e.max Press, and one feldspathic porcelain, Vita-Omega 900. The surface was polished using a 600 grit and 1200 grit SiC paper. Each group was loaded for 300,000 cycles in a chewing simulator. The wear resistance was analyzed by measuring the volume of substance lost. The wear surfaces were observed by scanning electron microscopy to determine the wear characteristics.ResultsVita-Omega 900 led to the greatest amount of enamel wears followed by IPS e.max Press, Prettau, Lava and Rainbow. There was a significant difference between Vita-Omega 900 and IPS e.max Press (p < 0.05). The wear values for human enamel were significantly greater than those for feldspathic porcelain, regardless of the surface roughness of the ceramic specimens (p < 0.05).ConclusionThe wear behaviour of human enamel and feldspathic porcelain varies according to the type of substrate materials. On the other hand, 3 zirconia ceramics caused less wear in the abrader than the conventional ceramic.Clinical significanceDental professionals should be aware of the wear effect of dental restorations on the opposing teeth or restorations. The amount of enamel wear was highest in feldspathic porcelains whereas zirconia ceramics caused less wear on the opposing teeth.     

PERFORMANCE OF BRAZILIAN AND IMPORTED GLASS IONOMER CEMENTS USED IN ATRAUMATIC RESTORATIVE TREATMENT (ART) REGARDING MICROLEAKAGE IN PRIMARY MOLARS

With the aim of assessing the performance of Brazilian and imported glass ionomer cements (GIC) with regard to microleakage, 40 primary molars received two standard class II cavity preparations with margins in enamel. Twenty cavities were filled with Brazilian materials (Vidrion® R and Vidrion® R_Caps) and the other 20 cavities were filled with imported materials (Fuji® IX and Fuji® IX_GPFast capsule). All fillings were performed by a single operator according to the manufacturer''s instructions. Teeth were immersed in 0.5% methylene blue and half-sectioned. Three independent calibrated examiners assessed microleakage using scores (0-3). Data were submitted to the Kruskal-Wallis statistical test and Wilcoxon analysis. High microleakage indexes were verified for all ionomer cements: 59.5% of the samples restored with Vidrion® R or Vidrion® R_Caps and 83.4% of the samples restored with Fuji® IX or Fuji® IX_GpFast capsule obtained the maximum score (3). The Brazilian ionomer cements presented less microleakage than imported cements, although this difference was only significant (p=0.003) among the encapsulated materials.     

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

ObjectiveMost 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.MethodsForty discs (Ø12 mm, 1.55 mm 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 = 3.18 mm) in water (200 N load, 2 Hz 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.ResultsFatigue 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.SignificanceWell-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.     

Wear behavior and microstructural characterization of translucent multilayer zirconia

ObjectiveTo characterize the composition, microstructure and wear properties of a multilayer translucent zirconia relative to the conventional 3Y-TZP.MethodsTwo types of ceramics were evaluated: a multilayer zirconia (MULTI, IPS e.max ZirCAD Multi, Ivoclar Vivadent) and a control 3Y-TZP (IPS e.max ZirCAD LT, Ivoclar Vivadent). Pre-sintered CAD-CAM blocks were cut, ground, sintered and polished to 1 μm finish. The phase fraction and grain size were measured using XRD and FE-SEM. For wear testing (n = 12), square-shaped specimens (16 × 16 × 1 mm) were adhesively bonded to a dentin analog. Sliding wear tests were performed using a spherical zirconia antagonist (r = 3.15 mm), with 30 N load at 1.5 Hz for 500,000 cycles in water. Optical and scanning electron microscopes and 3D laser scanner were used for quantitative wear analyses. Data were analyzed using Student’s t-test (α = 0.05).ResultsFor MULTI, the enamel layer had the highest cubic content and the largest grain size, followed by the two transition layers, and the dentin layer. 3Y-TZP showed the smallest grain size and cubic content. A significant amount of wear was observed in both materials up to 50,000 cycles until it reached a plateau. MULTI showed higher volume loss and greater wear depth than 3Y-TZP (p < 0.01). The higher volume loss was associated with extensive lateral fracture, leading to material spalling from the surface of cubic-containing zirconias.SignificanceThe wear pattern in multi-layered zirconia was more severe than 3Y-TZP. Additionally, the different layers of the multi-layered zirconia had similar wear behavior.     

Comparative study on the impact-sliding wear behaviour of CAD/CAM resin-ceramic materials and tooth enamel

ObjectivesTo compare the impact-sliding wear of different CAD/CAM resin-ceramic materials and tooth enamel, and explore the corresponding wear damage mechanism.MethodsHuman tooth enamel (EN), Vita ENAMIC (Vita, VE), Lava Ultimate (3 M, LU), and GC CERASMART (GC, CS) were used in this study. The hardness, elastic modulus, and roughness values of the samples were measured. Further, impact-sliding wear tests were performed in a ball-on-flat configuration with spherical zirconia antagonists and the coefficients of friction (CoF) were recorded simultaneously. Additionally, a white light interferometer was used to determine the volume losses and scanning electron microscopy was used to observe the wear morphology of the wear scars and the damage feature in the vertical sections to clarify the damage mechanism during the impact-sliding wear test.ResultsEN exhibited the highest elastic modulus and CoF, followed by VE, LU, and CS. The hardness and roughness of EN and VE were similar and were higher than those of LU and CS. Throughout the wear tests, VE exhibited the highest volume loss, whereas CS exhibited the lowest. The wear damage characteristics of VE were similar to those of EN, displaying brittle fractures of inorganic substances and plastic deformation of organic substances in the impact part, exhibiting plough marks in the sliding parts. In the case of LU and CS, the entire wear areas displayed plastic deformation of the resin matrix, exfoliation of the filler particles, and plough marks.SignificanceEnamel and polymer-infiltrated ceramic network materials exhibit similar wear damage modes. Additionally, the high-density nanocomposite resin material is the most resistant to impact-sliding wear from a tribological perspective.     

Effect of supporting substrate on the failure behavior of a polymer-infiltrated ceramic network material

Statement of problemRestorative materials are cemented on different types of substrates, such as dentin, metal, and glass-fiber posts with composite resin cores.PurposeThe purpose of this in vitro study was to evaluate the failure behavior after cycling fatigue of a polymer-infiltrated ceramic network material (PICN; VITA ENAMIC) cemented on different supporting substrates.Material and methodsPICN plates (N=80) were obtained from computer-assisted design and computer-assisted manufacturing (CAD-CAM) blocks and cemented with a resin cement to 4 different supporting substrates (n=20): (1) human dentin (PICNDen); (2) dentin analog (PICNDenAn); (3) nickel-chromium alloy (PICNNiCr); and (4) composite resin plus fiberglass post (PICNRc). For comparison, the fracture behavior of a feldspathic ceramic (FelDenAn; VITABLOCS Mark II) and an indirect composite resin (ResDenAn; Opallis LAB Resin) cemented to the DenAn substrate was investigated (n=20). Thus, specimens were composed of the restorative material layer (1-mm thick) resin cemented (0.1-mm-thick layer) to a 2-mm-thick supporting substrate. All specimens were subjected to mechanical cycling (MC) using a pneumatic cycling machine (500 000 cycles, 2 Hz, 50 N). Specimens that did not fracture during cycling were tested under compression using a universal testing machine at a cross-head speed of 0.5 mm/min until the sound of the first crack was detected using an acoustic system. Failure data were statistically evaluated using Weibull distribution. Failures were classified as radial crack, cone crack, combined, and catastrophic fracture.ResultsAll FelDenAn specimens were fractured during MC. Only 4 PICNRc specimens survived MC, so their fracture load data were not statistically analyzed. PICNNiCr showed the greatest characteristic load (L₀) value, followed by ResDenAn. Groups PICNDenAn and PICNDen showed lower and similar L₀ but statistically different Weibull modulus (m). There was a significant relationship between experimental group and failure mode (P<.001). FelDenAn and PICNRc had a higher frequency of radial cracks, whereas PICNNiCr failed from cone cracking.ConclusionsThe supporting substrate influenced the failure behavior of PICN. When the substrate had a higher elastic modulus than the restorative material, better mechanical behavior was observed.     

Microshear bond strength of dual-cure resin cement in zirconia after different cleaning techniques: an in vitro study

PURPOSEThis study aimed to compare the microshear bond strength (µSBS) of dual-cure resin cement in CAD-CAM zirconia after different cleaning techniques.MATERIALS AND METHODSFifty discs of zirconia-based ceramic from Ivoclar Vivadent were embedded in acrylic resin. The discs were divided into five groups according to the cleaning methods used: Group 1: drying with spraying + sandblasting with Al₂O₃; Group 2: washed with water and dried with spraying + sandblasting with Al₂O₃; Group 3: washed with distilled water and dried with spraying + sandblasting with Al₂O₃ + zirconium oxide (Ivoclean); Group 4: washed with distilled water and dried with spraying + sandblasting with Al₂O₃ + potassium hydroxide (Zirclean); and Group 5: washed with distilled water and dried with spraying + sandblasting with Al₂O₃ + 1% NaClO. All of the groups were contaminated with artificial saliva for 1 minute and then cleaned. Statistical analyses were performed using ANOVA and Tukey''s tests. RESULTSThere were statistically significant differences among all groups for µSBS (P < .05). The group treated with zirconium oxide (Group 3) showed the highest µSBS (18.75 ± 0.23 MPa).CONCLUSIONWhen applied to zirconia, the cleaning methods affected the bonding with resin cement differently.     

Wear of primary teeth caused by opposed all-ceramic or stainless steel crowns

PURPOSE

This study was conducted to evaluate the effects of full-coverage all-ceramic zirconia, lithium disilicate glass-ceramic, leucite glass-ceramic, or stainless steel crowns on antagonistic primary tooth wear.

MATERIALS AND METHODS

There were four study groups: the stainless steel (Steel) group, the leucite glass-ceramic (Leucite) group, the lithium disilicate glass-ceramic (Lithium) group, and the monolithic zirconia (Zirconia) group. Ten flat crown specimens were prepared per group; opposing teeth were prepared using primary canines. A wear test was conducted over 100,000 chewing cycles using a dual-axis chewing simulator and a 50 N masticating force, and wear losses of antagonistic teeth and restorative materials were calculated using a three-dimensional profiling system and an electronic scale, respectively. Statistical significance was determined using One-way ANOVA and Tukey''s test (P<.05).

RESULTS

The Leucite group (2.670±1.471 mm³) showed the greatest amount of antagonist tooth wear, followed by in decreasing order by the Lithium (2.042±0.696 mm³), Zirconia (1.426±0.477 mm³), and Steel groups (0.397±0.192 mm³). Mean volume losses in the Leucite and Lithium groups were significantly greater than in the Steel group (P<.05). No significant difference was observed between mean volume losses in the Zirconia and Steel groups (P>.05).

CONCLUSION

Leucite glass-ceramic and lithium disilicate glass-ceramic cause more primary tooth wear than stainless steel or zirconia.     

Wear performance of substructure ceramics and veneering porcelains

Aim

The aim of this in vitro study was to compare the two-body wear resistance of substructure zirconia and veneering porcelain versus steatite and human enamel antagonists, respectively.

Materials and methods

Two-body wear tests were performed in a chewing simulator with steatite and enamel antagonists (enamel cusps). A pin-on-block design with a vertical load of 50 N for 1.2 × 10⁵ cycles; (f = 1.6 Hz; lateral movement: 1 mm, mouth opening: 2 mm) was used for the wear test. For quantification of the wear resistance, wear tests were performed with standardized steatite spheres. Human enamel was used as a reference. Five zirconia ceramics and four veneering porcelains were investigated. One zirconia ceramic was tested with superficial glaze, which was applied after polishing or sandblasting, respectively. Surface roughness R_a (SP6, Perthen-Feinprüf, G) and wear depth were determined using a 3D-Profilometer (Laserscan 3D, Willytec, G). SEM (Quanta FEG 400, FEI, USA) pictures were used for evaluating wear performance of both, ceramics and antagonists.

Results

No wear was found for zirconia substructures. Veneering porcelain provided wear traces between 186.1 ± 33.2 μm and 232.9 ± 66.9 μm (steatite antagonist) and 90.6 ± 3.5 μm and 123.9 ± 50.7 μm (enamel). Wear of the steatite antagonists varied between 0.812 ± 0.256 mm² and 1.360 ± 0.321 mm² for zirconia and 1.708 ± 0.275 mm² and 2.568 ± 0.827 mm² for porcelain. Enamel generally showed wear, cracks or even fractures at the ridge, regardless whether opposed by zirconia or porcelain/glaze. Enamel was polished, when opposed to zirconia, or plowed, provoked and grinded, when opposed to porcelain/glaze.

Conclusion

The results of the wear test with steatite or enamel antagonists indicated no measurable wear on zirconia surfaces. Porcelain showed higher wear than zirconia, but comparable or lower wear than an enamel reference. Antagonistic wear against zirconia was found to be lower than wear against porcelain.     

A novel method for volumetric assessment of tooth wear using three-dimensional reverse-engineering technology: A preliminary report

Objective:To describe a newly developed three-dimensional (3D) digital superimposition method for quantitative evaluation of tooth wear that occurs during orthodontic treatment.Materials and Methods:The sample consisted of dental casts obtained from 56 patients (23 male patients and 33 female patients; mean ± standard deviation age  =  21.8 ± 5.1 years) who received orthodontic treatment with extraction of four premolars. The maxillary and mandibular dental casts taken before (T1) and after (T2) orthodontic treatments were scanned, and 3D images of the canines were constructed. The canines at T1 were superimposed with those at T2 with the best-fit method using the middle third of the labial and lingual surface as the reference area. To measure the volume of the canines, four boundary planes were constructed, and the differences in volume before and after orthodontic treatment were calculated.Results:The mean volume of tooth wear of the 224 canines was 2.0 mm³ after 35.5 months of orthodontic treatment. The volume of canine tooth wear was 2.3 ± 1.5 mm³ in male subjects and 1.9 ± 1.2 mm³ in female subjects. The mean wear of the upper right canines (2.4 ± 2.0 mm³) was significantly greater than that of the lower right canines (1.9 ± 2.6 mm³).Conclusions:Regional registration of teeth in 3D digital models is useful for quantitative evaluation of tooth wear in orthodontic patients. This method may also be used to assess treatment results in restorative dentistry.