Influence of the preparation design on the survival probability of occlusal veneers

ObjectivesThe fracture resistance of ultrathin computer-aided design and computer-aided manufacturing (CAD/CAM) occlusal veneers with different preparation designs was investigated under cycling mechanical loading and via finite element analysis (FEA).MethodsEighty molars were prepared with a circular enamel ring until complete exposure of the occlusal dentin occurred. Forty were prepared via additional circular chamfer preparation. The teeth were restored with 0.5 mm-thick occlusal veneers. Each group received a CAD/CAM fabricated occlusal veneer with a low modulus of elasticity (composite, CeraSmart) and a high modulus of elasticity material (ceramic, Celtra Duo). The restorations were adhesively luted and underwent 2000 thermocycling cycles. The samples were loaded at 50 N under 1,000,000 cycles in a chewing simulator and were checked for failure after various cycles. A visible crack was defined as failure, and the Kaplan-Meier survival rate was used for data analysis.One sample per group was digitized using microcomputed tomography, and FEA was performed using open-source software. The comparative stresses were analyzed for specimens with and without chamfer preparation.ResultsThe survival probabilities were 60% for occlusal ceramic veneers without preparation and 40% for veneers with chamfer preparation, with no statistically significant differences. Composite veneers achieved 95% survival probability regardless of the preparation method.The main principal stress in ceramic restoration was visualized via FEA. In composite veneers, stress was also visible in the luting composite and dentin.SignificanceThe preparation method had no influence on mechanical fatigue. Minimally invasive preparation can be recommended. The restoration material is crucial for survival.     

The effect of preparation designs on the marginal and internal gaps in Cerec3 partial ceramic crowns

Objectives

The purpose of this study was to evaluate the marginal and internal gaps in Cerec3 partial ceramic crowns (PCCs) of three different preparation designs in vitro using microcomputed tomography (μCT).

Methods

Cerec3 PCCs of three different preparation designs (n = 20) were fabricated according to the following: Group I-conventional functional cusp capping/shoulder preparation, Group II-horizontal reduction of cusps and Group III-complete reduction of cusps/shoulder preparation. After fixation of PCCs, the μCT scanning was performed. For obtaining the average internal gap (AIG), the μCT sections were reconstructed 3-dimensionally, and then the total volume of the internal gap was divided by the contact surface area. The 2-dimensional (2D) μCT views were used to investigate the gaps at predetermined key positions in seven bucco-lingual sections and three mesio-distal cross sections. The gaps were measured using the μCT at each reference point. Statistical analysis was performed using one-way ANOVA and Tukey's test.

Results

For the 3D reconstruction technique, the AIGs were as followed: Group I 197.3 ± 48.2 μm, Group II 171.2 ± 45.1 μm, and Group III 152.7 ± 27.1 μm. For the 2D μCT views, the gaps of each group were the smallest on the margins ranging from 35.4 ± 32.2 to 128.4 ± 69.5 μm, and the largest on the horizontal or angle walls ranging from 184.5 ± 41.2 to 406.5 ± 176.1 μm. According to the results, Group I showed larger marginal and internal gaps compared with the other groups.

Conclusions

For the PCCs, the simplified designs (Groups II and III) demonstrated superior results compared to the traditional cusp capping design (Group I). The marginal gaps were smaller than the internal gaps in all groups.     

烧结次数对椅旁计算机辅助设计与制作二硅酸锂玻璃陶瓷贴面不同部位颜色的影响

目的 评价烧结次数和渐变厚度及其交互性对椅旁计算机辅助设计与制作（CAD/CAM）二硅酸锂玻璃陶瓷贴面不同部位颜色的影响。方法 在标准中切牙模型上制备贴面修复模型,用椅旁扫描仪采集光学印模,椅旁CAD/CAM系统制作24个二硅酸锂玻璃陶瓷贴面样本共4组（n=6）,初次结晶组为对照组S0,其余按上釉烧结次数依次为S1、S2、S3组。使用Vita easyshade电子比色仪测定每个贴面的色彩参数L、C、H、a、b,用SAS 9.1.3统计软件采用重复测量多因素方差方法分析不同烧结次数以及不同部位厚度间各颜色指标的差异性。最后扫描电镜（SEM）观察每组贴面的晶体排列和致密度。结果 随着烧结次数增加,试件的L值总体呈减小趋势（P<0.05）。C和b的烧结次数有统计学意义（P<0.05）,其中,除S2组与S3组之间差异无统计学意义外（P>0.05）,其余各组之间的两两比较差异均有统计学意义（P<0.05）。SEM观察发现二硅酸锂晶体随着烧结次数增加,晶体变大,晶体间的孔隙变小,晶体间的锁结变得更为紧密。结论 上釉次数和厚度及其交互性对二硅酸锂玻璃陶瓷的色相、明度、彩度均存在影响。     

Influence of bonding surface and bonding methods on the fracture resistance and survival rate of full-coverage occlusal veneers made from lithium disilicate ceramic after cyclic loading

ObjectivesThe purpose of this laboratory study was to evaluate the influence of bonding method and type of dental bonding surface on fracture resistance and survival rate of resin bonded occlusal veneers made from lithium disilicate ceramic after cyclic loading.MethodsFourty-eight extracted molars were divided into three groups (N = 16) depending on the preparation: within enamel, within dentin/enamel or within enamel/composite resin filling. Lithium disilicate occlussal veneers were fabricated with a fissure-cusp thickness of 0.3–0.6 mm. Restorations were etched (5% HF), silanated and adhesively luted using a dual-curing luting composite resin. Test groups were divided into two subgroups, one using a only a self-etching primer, the other additionally etching the enamel with phosphoric acid. After water storage (37 °C; 21 d) and thermocycling (7500 cycles; 5–55 °C), specimens were subjected to dynamic loading in a chewing simulator (600,000 cycles; 10 kg/2 Hz). Surviving specimens were loaded until fracture using a universal testing machine.ResultsAll specimens survived artificial aging, several specimens showed some damage. ANOVA revealed that enamel etching provided statistically significantly (p ≤ 0.05) higher fracture resistance than self-etching when bonding to enamel and dentin. Self-etching provided statistically significant (p ≤ 0.05) higher fracture resistance for the enamel-composite group than for the enamel group. Enamel etching provided statistically significant (p ≤ 0.05) higher fracture resistance for the enamel and dentin group than for groups enamel and enamel-composite.SignificanceEtching enamel improved the fracture resistance of occlusal veneers when bonding to dentin and enamel and increased the survival rate when bonding to enamel.     

Influence of the preparation design and artificial aging on the fracture resistance of monolithic zirconia crowns

PURPOSE

The aim of this study was to evaluate the fracture resistance and fracture behavior of monolithic zirconia crowns in accordance with the preparation design and aging simulation method.

MATERIALS AND METHODS

An upper first molar was prepared sequentially with three different preparation designs: shoulderless preparation, 0.4 mm chamfer and 0.8 mm chamfer preparation. For each preparation design, 30 monolithic zirconia crowns were fabricated. After cementation on Cr-Co alloy dies, the following artificial aging procedures were performed: (1) thermal cycling and mechanical loading (TCML): 5000 cycles of thermal cycling 5℃–55℃ and chewing simulation (1,200,000 cycles, 50 N); (2) Low Temperature Degradation simulation (LTD): autoclave treatment at 137℃, 2 bar for 3 hours and chewing simulation; and (3) no pre-treatment (control group). After artificial aging, the crowns were loaded until fracture.

RESULTS

The mean values of fracture resistance varied between 3414 N (LTD; 0.8 mm chamfer preparation) and 5712 N (control group; shoulderless preparation). Two-way ANOVA analysis showed a significantly higher fracture loads for the shoulderless preparation, whereas no difference was found between the chamfer preparations. In contrast to TCML, after LTD simulation the fracture strength of monolithic zirconia crowns decreased significantly.

CONCLUSION

The monolithic crowns tested in this study showed generally high fracture load values. Preparation design and LTD simulation had a significant influence on the fracture strength of monolithic zirconia crowns.     

Effect of three different preparation designs on the marginal adaptation of indirect overlay restoration fabricated from lithium disilicate ceramic material: An in-vitro comparative study

ObjectivesMarginal adaptation is considered one of the key factors influencing the success of indirect restorations. This study aimed to estimate the marginal fit of lithium disilicate overlays with three distinct preparation designs before and after cementation.MethodsThirty maxillary first premolars were divided into the hollow chamfer design (HCD¹) group, butt-joint design (BJD²) group, and conventional occlusal box design (COD³) group (n = 10 each). The samples were scanned using an intra-oral scanner, and overlays were fabricated using computer-assisted design and milled on a computer-assisted machine. The finished restorations were luted using a self-adhesive resin RelyX Ultimate. The marginal gap was assessed using a digital microscope with 230X magnification power. Statistical analysis was conducted using analysis of variance and post hoc (Bonferroni correction) tests, assuming a significance level of 5%.ResultsThe HCD and BJD groups recorded significantly lower marginal gap, (11.39 ± 0.72, 16.29 ± 0.75) and (11.59 ± 0.75, 16.93 ± 0.65) respectively, than the COD group (24.57 ± 1.18, 34.45 ± 1.09) both pre- and post-cementation.ConclusionThis study demonstrated that modification of tooth preparation plays a significant role in the marginal adaptation of the lithium disilicate overlays. The gap was smaller with the HCD and BJD than with the COD, with a statistically significant difference.     

Influence of tooth preparation design on the stress distribution in maxillary central incisors restored by means of alumina porcelain veneers: A 3D-finite element analysis

AIM: The present study aimed at providing 3D-FEA engineering tools for the understanding of the influence of tooth preparation design on the stress distribution and localization of critical sites in maxillary central incisors restored by means of alumina porcelain veneers under functional loading. METHODS: A 3D-FEM model of a maxillary central incisor is presented. An arbitrary chewing static force of 10 N was applied with an angulation of 60 and 125 degrees to the tooth longitudinal axis at the palatal surface of the crown. The model was considered to be restored by means of alumina porcelain veneers with different tooth preparation designs. The differences in occlusal load transfer ability of the two restorative systems are discussed. RESULTS: The maximum Von Mises equivalent stress values were observed in the window restorative system for both 125 and 60 degrees load angulations. When the chamfer with palatal overlap preparation was simulated, the stress distributed uniformly in the cement layer, whereas in the window preparation the stress mainly occurred in the incisal area of the cement layer. SIGNIFICANCE: When restoring a tooth by means of porcelain veneers, the chamfer with palatal overlap preparation better restores the natural stress distribution under load than the window technique.     

隙料厚度和覆盖面积对CerconCAD/CAM底层冠适合性的影响

目的通过研究隙料厚度和覆盖面积对Cercon CAD/CAM底层冠边缘和内部适合性的影响,评价CerconCAD/CAM系统的加工精度。方法通过模拟下颌第一磨牙,加工1个不锈钢主模型。扫描后,根据不同隙料厚度和覆盖面积,分为6组,分别为S10C70、S10C90、S30C70、S30C90、S60C70、S60C90,每组6个试件。采用硅橡胶印模复制技术和图像分析系统测量底层冠内部适合性和边缘适合性。结果方差分析显示底层冠内部适合性的差异与测量位置、隙料厚度和覆盖面积有关。覆盖面积不同组间差异有统计学意义。隙料厚度10 μm和30 μm组间、10 μm和60 μm组间差异有统计学意义。内部适合性不均匀,远中与近中相对位置间、颊侧与舌侧相对位置间有显著差异。隙料厚度30 μm和60 μm组间差异无统计学意义。平均边缘适合性为（27.7±7.6）μm,近远中和颊舌侧间边缘适合性差异有统计学意义;近中与远中边缘适合性、颊侧与舌侧边缘适合性间差异无统计学意义。结论CerconCAD/CAM新系统制作的氧化锆底层冠有良好的边缘和内部适合性,达到临床可接受范围。隙料厚度和覆盖面积对底层冠内部适合性有显著影响。     

Effect of occlusal thickness design on the fracture resistance of endocrowns restored with lithium disilicate ceramic and zirconia

目的 探讨二硅酸锂陶瓷和氧化锆制作的下颌第一磨牙髓腔固位冠的面厚度设计对抗折性能的影响。方法 根据修复设计（冠部材料及厚度）的不同,将24个下颌第一磨牙树脂仿真牙随机分成4组,每组6个。二硅酸锂2 mm组：采用二硅酸锂陶瓷制作修复体,面厚度2 mm,固位体长4 mm;二硅酸锂4 mm组：采用二硅酸锂陶瓷制作修复体,面厚度4 mm,固位体长2 mm;氧化锆2 mm组：采用氧化锆制作修复体,面厚度2 mm,固位体长4 mm;氧化锆4 mm组：采用氧化锆制作修复体,面厚度4 mm,固位体长2 mm。使用树脂水门汀粘接系统（RelyX Ultimate Clicker）粘接后,冷热循环10 000次。将万能试验机与牙长轴呈135°,位移速度0.5 mm·min^-1,在颊尖加载,测定抗折力及折裂方式,并用SPSS 15.0软件进行方差分析和多重比较。结果 二硅酸锂2 mm组、二硅酸锂4 mm组、氧化锆2 mm组、氧化锆4 mm组的抗折力分别为（890.54±83.41）、（2 320.87±728.57）、（2 258.05±557.66）和（3 847.70±495.99）N。氧化锆4 mm组的抗折力最高,二硅酸锂2 mm组的抗折力最低。结论 磨牙髓腔固位冠使用氧化锆较二硅酸锂陶瓷有更高的抗折力,增加修复体面厚度可提高抗折力,但基牙折裂风险也增加。