Contact fracture test of monolithic hybrid ceramics on different substrates for bruxism

ObjectivesTo determine the minimum thickness required for a monolithic hybrid ceramic crown on different substrates (soft vs stiff) used in posterior dentition for bruxism.Methods80 polymer-infiltrated ceramic networks Vita Enamic (PICN VE) disc specimens with four different occlusal thicknesses (0.8, 1.2, 1.6 and 2.0 mm), were produced using a computer-aided design/manufacturing system, and cemented on a stiff (zirconia) or soft (polyamide) substrate of 4-mm thickness. The ten specimens, in soft or stiff groups, were subjected to compressive loading by a MTS machine until fracture or maximum load (4500 N) was reached. The unbroken specimens were examined using optical coherence tomography. Eight axisymmetric finite element models and eight 3D models comprising the four different occlusal thicknesses and two substrates under different vertical loads and sliding movements were constructed. The maximum principal stress was selected to evaluate the stress distribution in this study.ResultsThe fracture resistance of the specimens was significantly different between the two substrates (P < 0.001). Fracture resistance was positively associated with specimen thickness (r = 0.597 and 0.896 for the soft and stiff substrate respectively). Specimens on the soft substrate had lower fracture loads, whilst cone cracks were observed in unbroken samples on different soft/stiff substrate prior to final fracture. The finite element analysis confirmed that samples on the stiff substrate had lower maximum principal stress values than those on the soft substrate. For the maximum principal stress not to exceed the flexural strength of PICN VE, a stiff substrate and minimum thickness of 2.0 mm are required for the prostheses.SignificanceA minimum 2.0 mm thick, stiff substrate was needed for bruxism as shown by the effect of high/large chewing force on the posterior dentition of monolithic PICN VE crowns.     

How oral environment simulation affects ceramic failure behavior

Statement of problem

Investigating the mechanical behavior of ceramics in a clinically simulated scenario contributes to the development of new and tougher materials, improving the clinical performance of restorations. The optimal in vitro environment for testing is unclear.

代型材料力学性能对磨牙氧化锆全瓷冠断裂失效行为的影响

目的研究不同力学性能代型材料对磨牙氧化锆全瓷冠断裂失效行为的影响。 方法制作弹性模量与牙本质（18.6 GPa）近似的复合树脂和多孔钛标准试件（n = 40），测定其维氏硬度、挠曲强度和断裂韧性值。分别用离体牙及上述复合树脂和多孔钛制作代型（n = 10），制作30个单层瓷结构的全锆（M-Zir）冠，采用随机数字表法分为3组，分别粘接于离体牙预备体及多孔钛和复合树脂代型上。所有试件行抗折破坏试验，记录最大断裂载荷（N）及失效模式，并采用扫描电镜行断口形貌学分析。使用SPSS 20.0软件对代型材料的力学性能测定结果进行独立样本t检验，抗折破坏试验进行单因素方差分析和LSD-t检验。 结果多孔钛与P60复合树脂的弹性模量分别为（18.50 ± 1.65）和（17.48 ± 1.70）GPa，两组间差异无统计学意义（t = 1.358，P = 0.191）。多孔钛材料的维氏硬度（165.60 ± 11.17）HV、挠曲强度（522.47 ± 52.46）MPa和断裂韧性（3.67 ± 1.18）MPa·m^1/2显著高于复合树脂（P<0.001）。离体牙组、多孔钛代型组、复合树脂代型组M-Zir冠的平均断裂载荷分别为（5 306 ± 467）、（5 273 ± 447）和（4 695 ± 583）N，3组差异有统计学意义（F = 4.253，P = 0.025）。多孔钛代型组与离体牙组差异无统计学意义（P = 0.890），复合树脂代型组显著低于离体牙组（P = 0.015）及多孔钛代型组（P = 0.021）。全瓷冠断裂模式分析显示，3组的M-Zir冠断裂模式无明显差异，均为瓷全层折裂为颊颚侧2块，裂纹通过中央窝沟向近远中牙尖三角嵴方向扩展。同时，离体牙组试件多伴有预备体的损伤，复合树脂代型组全部试件均伴有代型折裂，多孔钛代型组全部试件均完整。 结论多孔钛的维氏硬度、挠曲强度及断裂韧性优于复合树脂材料。使用复合树脂材料作为代型时M-Zir冠断裂载荷偏低，但对其断裂模式无明显影响。多孔钛代型较复合树脂代型更适用于高强度氧化锆全瓷修复体的体外研究。     

Cyclic fatigue vs static loading for shear bond strength test of lithium disilicate and dentin substrates: A comparison of resin cement viscosities

ObjectiveTo explore the effect of resin cement viscosities on the shear bond strength under static and fatigue load of lithium disilicate and dentin substrates.MethodsBonded tri-layer samples (lithium disilicate ceramic cylinder, resin cement, and substrate – ceramic or dentin) was performed considering 2 factors (n = 15): “resin cement viscosity” (high, HV; or low, LV) and “loading mode” (static, s-SBS; or fatigue shear bond strength, f-SBS). The specimens were subjected to s-SBS (1 mm/min, 1 kN load cell) and f-SBS (cyclic fatigue, initial load: 10 N; step-size: 5 N; 10,000 cycles/step; underwater). Failure mode, topography, and finite element analysis (FEA) were performed.ResultsThe resin cement viscosity did not influence the s-SBS and f-SBS of lithium disilicate substrate; however, it affected the bond strength to dentin, with HV presenting the worst fatigue behavior (f-SBS = 6.89 MPa). Cyclic loading in shear testing induced a notorious detrimental effect with a relevant decrease (16–56 %) in bond strength and survival rates, except for dentin substrate and LV. Most failures were adhesive. A distinct pattern comparing the disilicate and dentin was identified and FEA demonstrated that there was a stress concentration on the top of the cement layer.SignificanceCyclic fatigue loading in shear testing has detrimental effects on the adhesive behavior and survival probabilities of bonded lithium disilicate sets, regardless of resin cement viscosity. In contrast, resin cement viscosity affects the bond strength and the survival rates of dentin substrate submitted to cyclic loading mode, in which a low viscosity results in better performance.     

Effect of temporary cements on the microtensile bond strength of self-etching and self-adhesive resin cement

Objective. The aim of this study was to evaluate the microtensile bond strength (µTBS) of self-etching and self-adhesive resin cement systems to dentin affected by the presence of remnants of either eugenol-containing or eugenol-free temporary cements. Materials and methods. Thirty extracted teeth were obtained and a flat dentin surface was exposed on each tooth. Acrylic blocks were fabricated and cemented either with one of two temporary cements, one zinc oxide eugenol (ZOE) and one eugenol free (ZOE-free), or without cement (control). After cementation, specimens were stored in water at 37°C for 1 week. The restorations and remnants of temporary cements were removed and dentin surfaces were cleaned with pumice. Resin composite blocks were cemented to the bonded dentin surfaces with one of two resin cements, either self-etching (Panavia F 2.0) or self-adhesive (RelyX U-100). After 24 h, the specimens were sectioned to obtain beams for submission to µTBS. The fracture mode was evaluated under a stereoscopic loupe and a scanning electron microscope (SEM). Data from µTBS were submitted to two-way repeated-measure ANOVA and the Tukey test (alpha = 0.05). Results. The cross-product interaction was statistically significant (p < 0.0003). The presence of temporary cements reduced the bond strength to Panavia self-etching resin cements only (p < 0.05). Fracture occurred predominantly at the dentin–adhesive interface. Conclusions. The presence of eugenol-containing temporary cements did not interfere in the bond strength to dentin of self-adhesive resin cements.     

不同基底对Sirona CEREC Blocs可切削陶瓷断裂强度的影响

目的：研究不同材料及形状的基底代型对Sirona CEREC Blocs可切削陶瓷断裂强度的影响.方法：选择人第三磨牙12颗,随机分为2组.第1组垂直于牙长轴去除骀面釉质,第2组制成牙本质片.用FiltekZ250光固化复合树脂分别复制第一组和第二组试件各6颗.用Multilink9 Speed树脂粘接剂将瓷片粘接于所有基底代型试件上,粘接1h后储存于37℃蒸馏水中24h,然后测试瓷片断裂强度值,并在光学显微镜下观察粘接破坏情况.结果：树脂牙代型做基底时,瓷片的断裂载荷最高,与离体牙组差异有统计学意义（P＜0.05）,但与树脂片组间差异无统计学意义（P＞0.05）.离体牙组的瓷片断裂载荷高于牙本质片组,差异有统计学意义（P＜0.05）.结论：不同材料及形状的基底代型对全瓷材料的强度均有影响,光固化复合树脂做基底时无论是牙状还是片状,瓷片的断裂载荷都高于对应的离体牙组.     

Effects of dentin surface treatments including Er,Cr:YSGG laser irradiation with different intensities on the push-out bond strength of the glass fiber posts to root dentin

Abstract

Objective. Intra-canal post systems are commonly used to restore root-filled teeth. Bond strengths of the posts can be affected by various surface treatments of the post or the dentin. The aim of this study was to evaluate the effects of dentin surface treatments including erbium-chromium; yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser irradiation with different intensities on the push-out bond strength of the glass fiber posts to root dentin. Materials and methods. Forty single-rooted human maxillary incisors were filled and post spaces were prepared. After these procedures, the specimens were divided randomly into four groups according to the dentin surface treatments, as follows: (i) untreated surface (control), (ii) 1W Er,Cr:YSGG laser application, (iii) 2W Er,Cr:YSGG laser application and (iv) 3W Er,Cr:YSGG laser application. Then the posts were cemented into the root canals using dual-cured resin cement. Bonded specimens were cut into 1-mm-thick slices and push-out tests were performed using a universal testing device. All specimens were loaded until fracture and the failure modes were evaluated with a stereomicroscope at 32× magnification. Representative specimens were analyzed by scanning electron microscopy. Data were analyzed using a one-way ANOVA, Tukey and Wilcoxon tests. Results. The bond strength values ranged from 3.22–4.68 MPa. There were no statistically significant differences among the groups, regardless of the different levels. The coronal and middle levels of the post space had significantly higher bond strength values compared with the apical level (p < 0.05). Conclusion. Er,Cr:YSGG laser irradiation with different intensities did not increase the bond strength of the fiber posts to the root canal dentin walls.     

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...     

Adhesive cementation of zirconia posts to root dentin: evaluation of the mechanical cycling effect

This study evaluated the effect of mechanical cycling on the bond strength of zirconia posts to root dentin. Thirty single-rooted human teeth were transversally sectioned to a length of 16 mm. The canal preparation was performed with zirconia post system drills (CosmoPost, Ivoclar) to a depth of 12 mm. For post cementation, the canals were treated with total-etch, 3-steps All-Bond 2 (Bisco), and the posts were cemented with Duolink dual resin cement (Bisco). Three groups were formed (n = 10): G1 - control, no mechanical cycling; G2 - 20,000 mechanical cycles; G3 - 2,000,000 mechanical cycles. A 1.6-mm-thick punch induced loads of 50 N, at a 45 degrees angle to the long axis of the specimens and at a frequency of 8 Hz directly on the posts. To evaluate the bond strengths, the specimens were sectioned perpendicular to the long axis of the teeth, generating 2-mm-thick slices, approximately (5 sections per teeth), which were subjected to the push-out test in a universal testing machine at a 1 mm/min crosshead speed. The push-out bond strength was affected by the mechanical cycling (1-way ANOVA, p = .0001). The results of the control group (7.7 +/- 1.3 MPa) were statistically higher than those of G2 (3.9 +/- 2.2 MPa) and G3 (3.3 +/- 2.3 MPa). It was concluded that the mechanical cycling damaged the bond strength of zirconia posts to root dentin.     

Influence of the supporting die structures on the fracture strength of all-ceramic materials

This study investigated the influence of the elastic modulus of supporting dies on the fracture strengths of all-ceramic materials used in dental crowns. Four different types of supporting die materials (dentin, epoxy resin, brass, and stainless steel) (24 per group) were prepared using a milling machine to simulate a mandibular molar all-ceramic core preparation. A total number of 96 zirconia cores were fabricated using a CAD/CAM system. The specimens were divided into two groups. In the first group, cores were cemented to substructures using a dual-cure resin cement. In the second group, cores were not cemented to the supporting dies. The specimens were loaded using a universal testing machine at a crosshead speed of 0.5 mm/min until fracture occurred. Data were statistically analyzed using two-way analysis of variance and Tukey HSD tests (α = 0.05). The geometric models of cores and supporting die materials were developed using finite element method to obtain the stress distribution of the forces. Cemented groups showed statistically higher fracture strength values than non-cemented groups. While ceramic cores on stainless steel dies showed the highest fracture strength values, ceramic cores on dentin dies showed the lowest fracture strength values among the groups. The elastic modulus of the supporting die structure is a significant factor in determining the fracture resistance of all-ceramic crowns. Using supporting die structures that have a low elastic modulus may be suitable for fracture strength tests, in order to accurately reflect clinical conditions.     

A comparison of fatigue crack growth in resin composite, dentin and the interface.

OBJECTIVES: The objective of this in vitro study was to evaluate the fatigue crack growth properties of the dentin/resin adhesive interface. METHODS: Compact tension (CT) specimens were prepared from coronal dentin, resin composite, and dentin bonded to resin composite using Optibond Solo Plus adhesive. All specimens were then subjected to cyclic Mode I loading while fully hydrated at a stress ratio of R=0.1 and frequency of 5 Hz. Steady state fatigue crack growth was modeled using the Paris Law in terms of the exponent (m) and coefficient (C). RESULTS: The average fatigue crack growth rates in the resin composite ranged from 1.6E-06 to 3.8E-05 mm/cycle with growth occurring over a stress intensity range from 0.40 to 0.77 MPa m(1/2); the average growth exponent was 6.9+/-3.1. Average fatigue crack growth rates for the dentin/resin interface specimens ranged from 5.5E-07 to 6.4E-03 mm/cycle with growth occurring over a stress intensity range from 0.37 to 0.64 MPa m(1/2). The Paris Law exponent for these specimens ranged from 16相似文献   

Effect of immediate dentin sealing on load-bearing capacity under accelerated fatigue of thin occlusal veneers made of CAD-CAM glass-ceramic and resin composite material

ObjectiveThe objective of this study was to assess the influence of immediate dentin sealing (IDS) on the fatigue behavior of laminate occlusal veneers fabricated with CAD/CAM lithium disilicate ceramic and resin composite.MethodsForty sound human molars were prepared and randomly divided into 4 groups (n = 10): RC–IDS+ (IDS and resin composite occlusal laminate veneer); RC–IDS- (resin composite occlusal laminate veneer without IDS); LD–IDS+ (IDS and lithium disilicate laminate veneer); LD–IDS- (lithium disilicate occlusal laminate veneer without IDS). The restorations were obtained using a digital workflow. After surface conditioning and bonding, thermocycling and accelerated fatigue tests (20 Hz, 5000 cycles with an initial load of 300 N, step-size of 100 N for 10,000 cycles, up to 1000 N, and then a step-size of 50 N until failure) were conducted. Fatigue data were recorded for both outcomes (crack or fracture) and statistically analyzed. Fractographic and adhesive interface analysis were conducted.ResultsThe indirect resin composite groups showed better fatigue behavior compared to lithium disilicate. IDS only had a positive effect for the survival of resin composite restorations for the ‘fracture’ outcome. Evident presence of micro-gaps at the adhesive interface in the LD–IDS- group could be noted.SignificanceImmediate dentin sealing improved fatigue resistance behavior of resin composite occlusal veneers. However, this effect was not observed in lithium disilicate veneers.     

Fracture resistance of endodontically treated roots after restoration

This study evaluated the shear strength resistance of endodontically treated roots that were restored by two different techniques. Twenty-seven recently extracted single-rooted teeth with similar anatomic characteristics were sectioned to obtain the same length for all specimens. Group I (GI) consisted of 14 roots restored with cast post-core (nickel–chromium alloy) and cemented using zinc phosphate cement; group II (GII) consisted of 13 roots restored with steel prefabricated posts (FKG^®) cemented with zinc phosphate cement and rotated with caution for anchorage. The crown portion of this group was made using a hybrid composite resin (Prisma APH^®). Results showed that on all specimens of GI the fracture occurred in the cervical root structure while in GII the composite resin fractured in all specimens. Statistical analysis showed a significantly higher resistance to fracture for GI than GII. The specimens were sectioned longitudinally for stereoscopic microscope analysis (63×) and did not show fracture lines in the dentin anchorage post area for any of the specimens.     

Effect of screw-access hole and mechanical cycling on fracture load of 3-unit implant-supported fixed dental prostheses

Statement of problem

The effect of screw-access holes and mechanical cycling on fracture resistance of 3-unit screw-retained zirconia-based implant-supported fixed dental prostheses (ISFDPs) is unknown.

Bond Strength of Fiber Posts to Weakened Roots After Resin Restoration With Different Light-Curing Times

IntroductionThis study evaluated the bond strength of translucent fiber posts to experimentally weakened radicular dentin restored with composite resin and polymerized with different light-exposure time.MethodsRoots of 60 maxillary incisors were used. Twenty-four hours after obturation, the filling materials of root canals were removed to a depth of 12 mm, and 4 groups were randomly formed. In 3 groups, root dentin was flared to produce a space between fiber post and canal walls. In the control group, the roots were not experimentally weakened. The flared roots were bulk restored with composite resin, which was light-activated through the translucent post for 40, 80, or 120 seconds. Posts were cemented, and after 24 hours, all roots were sectioned transversely in the coronal, middle, and apical regions, producing 1-mm-thick slices. Push-out test was performed, and failure modes were observed.ResultsThe quantitative analysis showed significant statistical difference only among groups (P < .001). Comparing the weakened/restored groups, composite light-exposure time did not influence the results. Overall, adhesive failures occurred more frequently than other types of failures. Cohesive failures occurred only in the weakened/restored roots.ConclusionsIntracanal root restoration with composite resin and translucent fiber posts provided similar or higher bond strength to dentin than the control group, regardless of the light-exposure time used for polymerization.     

Effect of Resin Luting Film Thickness on Fracture Resistance of a Ceramic Cemented to Dentin

PURPOSE: The aim of this study was to evaluate the fracture resistance of ceramic plates cemented to dentin as a function of the resin cement film thickness. MATERIALS AND METHODS: Ceramic plates (1 and 2 mm thicknesses) were cemented to bovine dentin using resin composite cement. The film thicknesses used were approximately 100, 200, and 300 microm. Noncemented ceramic plates were used as control. Fracture loads (N) were obtained by compressing a steel indenter in the center of the ceramic plates. ANOVA and Tukey tests (alpha= 0.05) were used for each ceramic thickness to compare fracture loads among resin cement films used. RESULTS: Mean fracture load (N) for 1-mm ceramic plates were: control-26 (7); 100 microm-743 (150); 200 microm-865 (105); 300 microm-982 (226). Test groups were significantly different from the control group; there was a statistical difference in fracture load between groups with 100 and 300 microm film thicknesses ( p < 0.01). Mean fracture load for 2-mm ceramic plates were: control-214 (111); 100 microm-1096 (341); 200 microm-1067 (226); 300 microm-1351 (269). Tested groups were also significantly different from the control group ( p < 0.01). No statistical difference was shown among different film thicknesses. CONCLUSIONS: Unluted specimens presented significantly lower fracture resistance than luted specimens. Higher cement film thickness resulted in increased fracture resistance for the 1-mm ceramic plates. Film thickness did not influence the fracture resistance of 2-mm porcelain plates.     

Evaluation of thermal cycling and mechanical loading on bond strength of a self-etching primer system to dentin.

OBJECTIVE: The aim of this study was to evaluate the in vitro durability and fracture modes of the tooth-resin interface following thermal cycling, fatigue load cycling (FLC) and micro-tensile bond strength testing (MTBS). METHODS: Twenty-four human molars were divided into two groups. In group A, coronal dentin was ground flat with #600-grit SiC paper, Clearfil Linerbond.2V (LB.2V) adhesive was applied and a crown fabricated with Clearfil AP-X resin composite. Samples were loaded in the FLC simulator and thermal cycle device. In group B, Class I cavities were prepared with a diamond bur and the cavity restored with LB.2V/AP-X. Samples were simultaneously subjected to FLC and thermal cycling. After storage of the specimens in water for 1 week, MTBS tests were performed, and fracture modes examined by SEM. RESULTS: For group A, MTBS were approximately 40 MPa with cohesive failures in the bonding resin of all specimens. Neither thermal nor mechanical stressing altered bond strengths on flat dentin surfaces. In group B, MTBS in the unstressed control group was 21 MPa with cohesive failures in the resin. As both thermal and mechanical stresses increased, there was a significant decrease in bond strength (16 MPa, P<0.05) and the fractures were seen in the resin-dentin interface and hybrid layer. SIGNIFICANCE: Surface preparation, C-factor, cavity depth, the dentin substrate and character of the smear layer strongly influence the bond strength values after thermal and fatigue loading. The FLC simulator in combination with MTBS testing provides meaningful in vitro evaluation of dentin bonding durability.     

Substrate masking ability of bilayer and monolithic ceramics used for complete crowns and the effect of association with an opaque resin-based luting agent

PurposeTo evaluate the substrate masking ability of different ceramic systems used for complete crowns and assess the influence of their association with an opaque resin-based luting agent (OLA).MethodsEleven ceramic groups were tested (n = 10). Bilayer groups were: ZrPc — zirconia + porcelain; CAD-onHT — zirconia + high translucent lithium disilitace; CAD-onLT — zirconia + low translucent lithium disilicate; LDPc — high opaque lithium disilicate + porcelain. Monolithic groups were: TZ — high translucent zirconia; TLS — translucent, zirconia-reinforced lithium silicate; HTLS — high translucent, zirconia-reinforced lithium silicate; LTLD — low translucent lithium disilicate; HTLD — high translucent lithium disilitace; LGC — leucite-reinforced glass ceramic; FC — feldsphatic ceramic. The substrates adopted were resin composites shaded A1 (control), A3.5 and C4; coppery and silvery metals. Color differences (ΔE₀₀) and translucency parameter (TP₀₀) were assessed with the CIEDE2000 formula. ΔE₀₀ was obtained assessing the ceramic influence only and in association with OLA.ResultsZirconia groups presented lower ΔE₀₀ and TP₀₀. CAD-on structures associated to OLA led to the lower ΔE₀₀ when tested over metals. ΔE₀₀ for LDPc were similar to zirconia when associated to OLA. Monolithic groups presented significant higher ΔE₀₀ and TP₀₀ compared to bilayers, with ΔE₀₀ below the acceptability threshold only when associated to OLA over substrate shade A3.5.ConclusionsCeramic type and the white-opaque resin-based luting agent presented a significant effect on the substrate masking ability. All the discolored substrates tested are adequately masked with veneered zirconia or with LDPc (preferably associated to OLA). The CAD-on technique associated with OLA improved the masking ability over metallic substrates.     

In vitro analysis of durability of S-PRG filler-containing composite crowns for primary molar restoration

ObjectiveTo evaluate the reliability, maximum principal stress, shear stress, and crack initiation of a computer-aided design/computer-aided manufacturing (CAD/CAM) resin composite (RC) incorporating surface pre-reacted glass (S-PRG) filler for primary molar teeth.MethodsMandibular primary molar crowns fabricated by experimental (EB) or commercially available CAD/CAM RCs (HC) were prepared and cemented to a resinous abutment tooth using an adhesive resin cement (Cem) or a conventional glass-ionomer cement (CX). These specimens were subjected to a single compressive test (n = 5/each) and the step-stress accelerated life testing (SSALT) (n = 12/each). Data was evaluated using Weibull analyses and reliability was calculated. Afterwards, the maximum principal stress and crack initiation point of each crown was analyzed by finite element analysis. To evaluate bonding of EB and HC to dentin, microtensile bond strength (μTBS) testing was conducted using primary molar teeth (n = 10/each).ResultsThere was no significant difference between the fracture loads of EB and HC for either cement (p > 0.05). The fracture loads of EB-CX and HC-CX were significantly lower than EB-Cem and HC-Cem (p < 0.05). The reliability at 600 N for EB-Cem was greater than that for EB-CX, HC-Cem, and HC-CX. The maximum principal stress concentrated on EB was lower than that on HC. The shear stress concentrated in the cement layer for EB-CX was higher than that for HC-CX. There was no significant difference among the μTBSs of EB-Cem, EB-CX, HC-Cem, and HC-CX (p > 0.05).SignificanceThe crowns fabricated with the experimental CAD/CAM RC incorporating S-PRG filler yielded greater fracture loads and reliability than the crowns manufactured with commercially available CAD/CAM RC regardless of the luting materials. These findings suggest that the experimental CAD/CAM RC crown may be clinically useful for the restoration of primary molars.     

Effect of thickness,translucency, and substrates on the masking ability of a polymer-infiltrated ceramic-network material

Objective

The aim of this in vitro study is to evaluate the masking ability of polymer-infiltrated ceramic-network materials (PICN) with different translucencies and thicknesses on multiple types of substrates.

Materials and Methods

Ceramic samples were prepared of VITA ENAMIC blocks in two different translucencies (2M2-T, 2M2-HT) in a thickness range of 0.5–2.5 mm (±0.05 mm). Layered specimens were obtained using composite substrates in nine shades and transparent try-in paste. Spectral reflectance of specimens was measured using a Konica Minolta CM-3720d spectrophotometer and D65 standard illumination. CIEDE2000 color difference (ΔE₀₀) between two samples was evaluated using 50%:50% perceptibility and acceptability thresholds. Specular component of the reflection was examined with Specular Component Excluded (SCE) and Included (SCI) settings. Statistical evaluation was performed by linear regression analysis, Kruskal–Wallis test, and multiplicative effect analysis.

Results

An increase in thickness of 0.5 mm reduces ΔE₀₀ of HT samples to 73.5%, of T samples to 60.5% (p < 0.0001). Five substrates with HT specimens, and three substrates with T specimens had significantly different results from average (p < 0.05). There is a significant difference between SCE and SCI data depending on the wavelength (p < 0.0001).

Conclusions

Masking ability of PICN materials is influenced by the thickness and translucency of the ceramic, and by the substrate. Reflection of the examined PICN material is characterized by both diffuse and specular reflection.

Clinical Significance

Although PICN materials have been available on the market for 10 years now, there is a lack of information regarding their masking ability. Acquiring in-depth data and thereby practical experience of the factors affecting the esthetics of PICN materials is essential for creating perfectly lifelike restorations.