Effect of surface conditioning methods on the bond strength of luting cement to ceramics

OBJECTIVES: This study evaluated the effect of three different surface conditioning methods on the bond strength of a Bis-GMA based luting cement to six commercial dental ceramics. METHODS: Six disc shaped ceramic specimens (glass ceramics, glass infiltrated alumina, glass infiltrated zirconium dioxide reinforced alumina) were used for each test group yielding a total number of 216 specimens. The specimens in each group were randomly assigned to one of the each following treatment conditions: (1) hydrofluoric acid etching, (2) airborne particle abrasion, (3) tribochemical silica coating. The resin composite luting cement was bonded to the conditioned and silanized ceramics using polyethylene molds. All specimens were tested at dry and thermocycled (6.000, 5-55 degrees C, 30 s) conditions. The shear bond strength of luting cement to ceramics was measured in a universal testing machine (1 mm/min). RESULTS: In dry conditions, acid etched glass ceramics exhibited significantly higher results (26.4-29.4 MPa) than those of glass infiltrated alumina ceramics (5.3-18.1 MPa) or zirconium dioxide (8.1 MPa) (ANOVA, P<0.001). Silica coating with silanization increased the bond strength significantly for high-alumina ceramics (8.5-21.8 MPa) and glass infiltrated zirconium dioxide ceramic (17.4 MPa) compared to that of airborne particle abrasion (ANOVA, P<0.001). Thermocycling decreased the bond strengths significantly after all of the conditioning methods tested. SIGNIFICANCE: Bond strengths of the luting cement tested on the dental ceramics following surface conditioning methods varied in accordance with the ceramic types. Hydrofluoric acid gel was effective mostly on the ceramics having glassy matrix in their structures. Roughening the ceramic surfaces with air particle abrasion provided higher bond strengths for high-alumina ceramics and the values increased more significantly after silica coating/silanization.     

Comparison of Fracture Toughness of All-Ceramic and Metal–Ceramic Cement Retained Implant Crowns: An In Vitro Study

To evaluate the fracture toughness of cement-retained implant-supported metal–ceramic molar crown with that of all-ceramic crowns, fabricated using IPS Empress 2 and yttria-stabilized zirconia copings. An dental implant and abutment was embedded in a clear polymethyl methacrylate model. A wax pattern reproducing the anatomy and dimension of a mandibular molar was made using inlay wax. Copings were made from the manufacturers guidelines for zirconia, metal ceramic and empress crown, in total of 21 copings, which were built for the crowns with metal layering ceramics specified by the manufacturers. The polymethylmethacrylate block-implant abutment complex was mounted on universal testing machine, and a static continuos vertical compressive load with a crosshead speed of 0.5 mm/min was applied. The breaking load and the peak load (in kilo Newtons) were recorded. The fractures for group I (zirconia–ceramic) and group II (metal–ceramic) occurred on the mesio-buccal aspect of the crowns involving the veneered ceramic layer while the catastrophic/bulk fracture was not observed. The mean value of breaking load for zirconia–ceramic, metal–ceramic and IPS-empress 2 was 3.4335, 3.071 and 1.0673 kN respectively. The mean value of peak load for zirconia–ceramic, metal–ceramic and IPS-empress 2 was 4.7365, 3.2757 and 1.566 kN respectively. It can be concluded that the zirconia–ceramic crown with the fracture toughness of 4.7365 ± 2.2676 kN has sufficient strength to allow clinical testing of these crowns as an alternative for metal–ceramic crowns (3.2757 ± 0.4681 kN).     

Dimensions of hard and soft tissue around adjacent,compared with single-tooth,zirconia implants

Preservation or regeneration of the papilla has always been a challenge around consecutive implants or with implants next to teeth, and many studies have evaluated the papilla’s behaviour and patterns based on surgical technique and prosthetic design, though evidence about its behaviour around zirconia implants is scarce. The aim of this study was to evaluate papilla behaviour between implants and teeth (tooth-implant group) and between consecutive implants (implant–implant group). Ninety patients with 122 zirconia implants (Straumann^® PURE Ceramic Implant) were examined at the one-year follow up. We measured the effect of the distance: first from the base of the contact point of the crowns to the contact with bone at the implant site (D1); secondly, to the contact with the bone at the neighbouring tooth or implant site (D2); and thirdly on the papillary deficit (D3). In both the tooth-implant group and the implant–implant group, D1 and D2 correlated significantly with the papillary deficit (D3), whereas D2 was the major determinant factor (Spearman’s rho = 0.60). In both groups, when D1 and D2 were <6 mm, the papilla was present every time. The papillary deficit was significantly greater in the tooth-implant group than in the implant–implant group (p = 0.048). We conclude that the ideal distance from the base of the contact point to the bone contact at the implant and to the bone contact at the adjacent tooth in both groups is <6 mm. The height of the bone on the teeth adjacent to implants has a significant impact on that of the papilla.     

Three-dimensional finite element modelling of all-ceramic restorations based on micro-CT

ObjectivesTo describe and apply a method of modelling dental crowns and three-unit fixed partial dentures (FPD) for finite element analyses (FEA) from 3D images obtained using a micro-CT scanner.MethodsA crown and a three-unit fixed partial denture (FPD) made of a ceramic framework (Y-TZP) and veneered with porcelain (VM9) were scanned using an X-ray micro-CT scanner with a pixel size of 6.97 μm. Slice images from both structures were generated at each 0.034 mm and processed by an interactive image control system (Mimics). Different masks of abutments, framework and veneer were extracted using thresholding and region growing tools based on X-ray image brightness and contrast. 3D objects of each model were incorporated into non-manifold assembly and meshed simultaneously. Volume meshes were exported to the FEA software (ABAQUS), and the load-generated stress distribution was analyzed.ResultsFEA models showed great shape resemblance with the structures. The use of non-manifold assembly ensured matching surfaces and coinciding nodes between different structural parts. For the crown model, tensile stresses were concentrated in the internal surface of the core, near to the applied load. For the FPD model, the highest tensile stresses were located in the framework, on the cervical area of connectors and pontic.ConclusionsValid 3D models of dental crown and FPD can be generated by combining micro-CT scanning and Mimics software, emphasizing its importance as design tool in dental research.Clinical significanceThe 3D FEA method described in this work is an important tool to predict the stress distribution, assisting on structural design of dental restorations.     

摩擦化学法硅涂层对氧化锆陶瓷粘接强度的影响

目的： 评估摩擦化学法硅涂层对氧化锆陶瓷粘接强度的影响。方法： 将切割烧结后的Lava氧化锆瓷块60件分为6组，每2组分别经喷砂/硅烷偶联剂、喷砂/CoJet Sand/硅烷偶联剂、无处理3种表面处理后，相同表面处理的2组中，每组分别用RelyX Unicem或Panavia F2.0与牙釉质粘接。各组随机抽取5件共30件进行24 h水浴，其余30件进行5000周水热循环，然后进行剪切粘接强度测试。采用SPSS 23.0软件包对数据进行双因素方差分析、Tukey HSD多重比较法及t检验。结果： 喷砂/CoJet/硅烷组的剪切强度均显著高于其他2组（P<0.001）；经老化试验后，喷砂/CoJet/硅烷组使用RelyX Unicem仍保持较高的剪切强度[(21.374±4.433)MPa]，与其他各组相比有显著差异（P<0.001）。结论： 摩擦化学法硅涂层能够有效提高氧化锆的粘接强度及耐久性，表面处理方式与粘接剂之间的相互作用需得到临床关注。     

Mechanical behavior of nano-hybrid composite in comparison to lithium disilicate as posterior cement-retained implant-supported crowns restoring different abutments

ObjectiveResin-based materials are gaining popularity in implant dentistry due to their shock absorption capacity. Therefore, the aim of this study was to evaluate the fracture strength and failure mode of resilient materials for both crowns and abutments and compare them to the most widely used materials in different combinations after subjection to long-term fatigue loading.MethodsForty-eight cement-retained implant-restorations were assembled on titanium implants. Identical custom-made CAD/CAM abutments were milled out of 3 different materials (n = 16); T: titanium, Z: zirconia and P: ceramic-reinforced PEEK. Each group was subdivided, according to the restorative crown material, into two subgroups (n = 8); C: nano-hybrid composite and L: Lithium disilicate. Specimens were subjected to dynamic load of 98 N for 1,200,000 cycles with integrated thermal cycling. The surviving specimens were subjected to quasi-static loading until failure. Shapiro–Wilk test was used to test for normality. One-way ANOVA followed by Tukey’s post-hoc test was used to detect statistically significant differences between groups.ResultsAll specimens withstood 1,200,000 load cycles. The fracture strength values varied from a minimum of 1639 ± 205 N for group PL to a maximum of 2949 ± 478 N for group ZL.SignificanceThe abutment material influenced the fracture strength and failure mode of the restoration. A combination of zirconia abutments and nano-hybrid composite showed the most favorable mode of failure within the test groups. Therefore, this combination might be recommended as an alternative for restoring single implants in the posterior area.     

Structural integrity of extracted teeth restored using three different post-and-core systems: An in vitro comparative study

AimThe objective of the study was to assess the in vitro fracture resistance of endodontically treated teeth restored using different post-and-core materials.Materials and methodsExtracted human mandibular premolars (n = 36) were extracted teeth and equally distributed into four (4) treatment groups: cast metal post-and-core, milled zirconia post-and-core, pre-fabricated post with composite resin core and control group. These samples were then each subjected to the load to fracture test using a universal testing machine. Fracture resistance data were compared among groups by analysis of variance and Fisher’s exact test.ResultsThe highest mean fracture resistance value was observed in the zirconia post-and-core treatment group (1567.26 ± 317.66 N), followed by the cast metal (1355.92 ± 621.56 N) and lastly the pre-fabricated post with composite resin core (725.67 ± 251.05 N) treatment group. Differences among groups were not statistically significantly different (P = 3.77).ConclusionEndodontically treated mandibular premolars with a zirconia post-and-core system exhibited the highest robustness against structural failure based on its mean fracture resistance value. In addition, extracted teeth restored with cast post-and-core resisted a greater stress load than those restored with fiber-reinforced posts. Zirconia showed a more favorable fracture mode than the other restorations.     

磨牙区使用角度螺丝一体冠不同全瓷材料修复种植单冠：1年前瞻性半口自身对照研究

目的 评价种植体支持的角度螺丝一体冠不同全瓷材料修复单冠在随访1年后的临床效果。方法 纳入13例上颌或下颌磨牙区双侧对称缺失的患者,每例患者接受两侧种植治疗。同一患者使用相同尺寸的2颗种植体。3~6个月后采用角度螺丝通道一体全瓷冠修复,每例患者的修复体分为全锆组和传统组。戴牙后即刻和12个月后进行X线检查,记录患者对修复体使用1年后的美学、功能评分及并发症。采用SAS 9.4软件对数据进行统计学分析。结果 13例患者修复后12个月的种植体成功率为100%。美学评价与功能评价在全锆组和传统组无显著差异（P>0.05）。全锆组边缘骨吸收为（-0.117±0.157）mm,传统组边缘骨吸收为（-0.141±0.153）mm,差异无统计学意义（P>0.05）。结论 在本研究范围内,磨牙区使用2种全瓷修复方式的螺丝通道一体冠临床效果良好,全锆冠与传统全瓷冠修复效果无显著差异。