The effect of thermal cycling on metal–ceramic bond strength

Objectives

The aim was to evaluate the effect of thermal cycling on the metal–ceramic bond strength.

Methods

Four different noble metal alloys were used. Specimens for the crack initiation test according to ISO 9693 were prepared to assess metal–ceramic bond strength (n = 10). The metal substrates were either air-borne particle abraded or polished prior to veneering. Bond strength was measured after veneering or after 6000 thermal cycles. With one alloy in addition long-term thermal cycling with 15,000 and 50,000 cycles was carried out. Statistical analysis was performed with one-way ANOVA followed by a post hoc Bonferroni test.

Results

Polished metal substrates showed a significantly lower bond strength compared to the air-borne particle abraded substrates. Treatment with 6000 thermal cycles did not significantly reduce the bond strength. Long-term thermal cycling resulted in an exponential decrease of bond strength for both polished and air-borne particle abraded specimens.

Conclusions

Air-borne particle abrasion significantly increases metal–ceramic bond strength. Thermal cycling of metal–ceramic composites results in an exponential decrease of bond strength. The crack initiation test is a sensitive method for assessing the metal–ceramic bond strength.     

烧结次数对3种金属基底烤瓷冠颜色的影响

目的研究烧结次数对不同的金瓷修复体颜色的影响。方法利用同一副带有1活动代型的标准模型,分别制作A2色镍铬合金烤瓷冠、金合金烤瓷冠、金沉积烤瓷冠,每组各6件,反复烧结,应用CIE1976 L*a*b*颜色系统,采用高像素数码摄影及计算机处理技术,在标准光源及相同条件下,每次烧结后对其颜色进行测定。结果3种金瓷修复体随着烧结次数增加,明度、彩度均不断增大,烧结8次时明度最高,但继续烧结至10次后,明度逐渐下降;在色差上,3种金瓷修复体烧结6次时变色,金沉积烤瓷冠颜色稳定性优于其它两种。结论多次烧结对金瓷修复体颜色有一定的影响,技工制作金瓷修复体时烧结次数适宜控制在6次内;3种金瓷修复体颜色稳定性,金沉积烤瓷冠和金合金烤瓷冠优于镍铬合金烤瓷冠。     

The impact of cement mixing and storage errors on the risk of failure of glass–ceramic crowns

This study evaluated the impact of different mixing ratios and wrongly stored blends of dual-curing composite cements on Empress2 glass–ceramic crowns by means of a flexural strength test and a fracture resistance test. Thermally damaged blends and fresh blends were mixed using different mixing ratios of dual-curing Panavia F and Variolink II composite cement (2:1; 1:1; 1:1.5; 1:1.75; base/catalyst). Sixteen groups of rectangular beams of both cements (two blends, four ratios, chemical-curing, light-curing) were constructed. Their flexural strength was determined in a three-point bending test. Furthermore, 64 Empress2 all-ceramic crowns were luted onto human molars, again using fresh and thermally damaged blends as well as different mixing ratios of the luting agents. After aging, fracture resistance was investigated. The flexural strength of dual-curing composite cements was influenced to a statistically significant extent by mixing ratios and storage conditions. In particular, the chemical curing mode of these cements was affected by the thermal damage of the blends. However, this study could not demonstrate a significant impact on the fracture resistance of Empress2 glass-ceramic crowns when different mixing ratios or wrongly stored cements were used. Dual-curing composite luting agents seem to tolerate a wide range of mixing errors, but their chemical curing mode may be affected by storage errors.     

5种牙体修复材料对L929细胞凋亡及相关基因的影响

目的研究新型硅藻土可切削陶瓷及临床常用口腔修复材料对L929细胞致凋亡作用。方法提取新型硅藻土可切削陶瓷及其他4种口腔材料的浸提液作用于细胞,流式细胞仪检测细胞周期进程及诱导细胞凋亡作用;Annexin V-FITC/PI双染细胞凋亡检测试剂盒对细胞死亡类型进行检测;逆转录聚合酶链反应检测Bcl-2和Bax基因的表达。结果各实验组对细胞周期均无特殊影响,新型陶瓷组凋亡率与阴性组接近（P>0.05）。树脂组凋亡率最高,细胞坏死水平也显著提高,与新型陶瓷组间差异有统计学意义（P<0.05）。新型陶瓷组Bcl-2和Bax mRNA表达水平与阴性组间差异无统计学意义（P>0.05）。结论新型硅藻土可切削陶瓷无明显细胞毒性,符合临床应用要求。     

3种临床常用烤瓷合金对小鼠成纤维细胞L929的毒性评价

目的:评价3种临床常用牙科烤瓷合金材料的细胞毒性.方法:采用一种能快速评定细胞增殖率和细胞毒性的CCK-8比色法,检测镍铬合金(Ni,77.36%)、钴铬合金(Co,61.0%)、金合金(Au,58.0%)等3种烤瓷合金材料对小鼠成纤维细胞L929相对增殖率的影响;应用单细胞凝胶电泳(彗星电泳),检测3种烤瓷合金材料对小鼠成纤维细胞L929 DNA的损伤情况.采用SAS9.0软件包对数据进行统计学分析.结果:镍铬合金组、钴铬合金组和金合金组细胞的相对增殖率分别为(75.9510±7.6244)%、(84.8920±8.2660)%和(88.5420±12.3611)%.镍铬合金组的细胞毒性显著高于钴铬合金组(P＜0.05)和金合金组(P＜0.05),而钴铬合金组与金合金组之间无显著差异(P＞0.05),但3种材料的细胞毒性分级均为1级,表现为轻微毒性;镍铬合金组DNA损伤程度的彗星数目显著高于钴铬合金组(P＜0.05)和金合金组(P＜0.05).而钴铬合金组与金合金组无显著差异(P＞0.05).结论:钴铬烤瓷合金材料的细胞毒性显著低于镍铬烤瓷合金材料,而与58%金烤瓷合金材料的细胞毒性接近.临床上应尽可能选择钴铬烤瓷合金或58%金烤瓷合金等细胞毒性较低的烤瓷合金材料.     

Assessment of an Indirect Metal Ceramic Repair System

Purpose: This study was designed to compare an alternative indirect treatment to repair fractured or chipped veneering metal ceramic using recently developed ultra‐low‐fusing ceramics. Materials and Methods: One conventional feldspathic ceramic, Vita Omega, and three ultra‐low‐fusing ceramics (ULFC), Finesse, Duceram LFC, and Vision‐low, were used. Forty ceramic specimens were prepared and divided into two groups. Group I (n = 20) was designed for bond strength testing. It comprised four subgroups (A, B, C, D): one Ceramic‐resin (A) and three Ceramic‐ULFC disc specimens of different diameters (B, C, D). Group II was composed of repaired ceramic discs using direct and indirect repair methods for biaxial testing. It was comprised of five subgroups: the fractured discs from subgroup A; Omega discs (n = 20) formed the repaired specimens of the four remaining subgroups: B, C, D, E. Data were presented as means and standard deviation (SD) values. One‐way analysis of variance (ANOVA) was used for comparison between means. Tukey's post hoc test was used for pairwise comparison between the means when ANOVA test was significant. The significance level was set at p≤ 0.05. Results: Within group I, Omega‐Ducera LFC showed the statistically highest mean bond strength (25.8 MPa) values, followed by Omega‐Finesse (15.8 MPa). No statistically significant difference was apparent between Omega‐Vision (9.3 MPa) and the control Omega‐Composite group (7.5 MPa). Regarding group II, the Control Omega subgroup showed statistically the highest mean biaxial strength values (168.8 MPa). No statistically significant difference was evident between the values of Omega‐Finesse (78.7 MPa), Omega‐Vision (78.4 MPa), and Omega‐Composite (82.5 MPa). Omega‐Ducera LFC subgroup, showed statistically the lowest mean values (53 MPa). Conclusions: Omega‐Ducera LFC yielded the statistically highest mean bond strength values, and the lowest biaxial strength values. All values were within the reported bond strength values for resin repair. All the tested groups showed significantly lower values compared to the initial biaxial strength mean values of the Omega ceramic; however, two of the tested ULFC (Vision, Finesse), recorded means that were statistically equal to the resin‐ceramic direct subgroup. Duceram LFC showed the lowest values, probably due to its totally glass composition, which showed low strength values of the repaired specimens. The recorded bond and biaxial values suggest that indirect repair of fractured LFC using some ULFC ceramics may offer an alternative solution to the traditional direct resin repair method; however, the choice of the used ceramic should be one containing some leucite crystals. Further studies are needed to investigate the long‐term performance of the proposed repair treatment.     

Fracture Resistance of Three Ceramic Inlay‐Retained Fixed Partial Denture Designs. An In Vitro Comparative Study

Purpose: The fracture resistance of ceramic inlay‐retained fixed partial dentures (CIRFPDs) was studied. Materials and Methods: Thirty CIRFPDs were constructed using ice zircon milled ceramic material. Specimens were divided into three groups, 10 specimens each, according to the abutment preparation: inlay‐shaped (occluso‐proximal inlay + proximal box), tub‐shaped (occluso‐proximal inlay), and proximal box‐shaped preparations. Each group was then subdivided into two subgroups of five specimens each, according to the span of the edentulous area representing a missing premolar or molar. All specimens were subjected to a fracture resistance test. Results: CIRFPDs with inlay‐shaped retainers showed the highest fracture resistance values for missing premolars and molars. CIRFPDs with box‐shaped retainers showed lower fracture resistance values. Statistical analysis revealed a significant difference between the three tested CIRFPD designs. There was a statistically significant difference between CIRFPDs constructed for the replacement of molars and those constructed for the replacement of premolars. The CIRFPD constructed for the replacement of molars gave lower fracture resistance values with the three tested designs. All the fracture resistance values obtained in this study were superior to the assumed maximum mastication forces. Failure mode was delamination and chipping of the veneering material. Conclusions: There was a statistically significant difference between the three designs of CIRPFDs tested. There was a statistically significant difference between CIRFPDs constructed for the replacement of molars than those constructed for the replacement of premolars. The CIRFPDs constructed for the replacement of molars gave lower fracture resistance values with the three tested designs. All fracture resistance values obtained in this study were superior to the assumed maximum mastication forces.     

Effect of Aging on Coronal Microleakage in Access Cavities through Metal Ceramic Crowns Restored with Resin Composites

Purpose: The purpose of this in vitro study was to determine if packable resin composite with/without flowable resin composite has the ability to prevent coronal leakage in restored endodontic access openings following aging. Materials and Methods: Eighty simulated standardized access cavities of metal‐ceramic crowns were fabricated and fixed on Vitrebond cavities filled with an epoxy resin. The specimens were randomly divided into two main groups: (1) Group A—Access cavities filled with only packable composite (Filtek P60); (2) Group B—Access cavities filled with Filtek P60 and a flowable composite (Filtek Z350) as liner. Each main group was further subdivided randomly into four subgroups according to water storage and thermocycling periods. All specimens were immersed in blue ink solution for 24 hours and then sectioned into quadrants. The extension of blue ink along the metal‐ceramic crown/composite resin interface was measured linearly using image analyzer and then analyzed by three‐way ANOVA and independent t‐test with a Mann‐Whitney test. The level of significance was set at p < 0.05. Results: All tested subgroups demonstrated different levels of microleakage. There was no significant difference related to restorative technique; however, there was a significant difference related to water storage and thermocycling. Conclusions: All tested techniques and materials in this study showed microleakage. Packable composite while a flowable liner showed a marginally better result than packable composite alone. Excessive thermocycling resulted in significant differences among the test groups.     

A Quick Esthetic Remount Cast for All‐Ceramic Restorations

A technique is presented for the expedited fabrication of a remount cast for the alteration of all‐ceramic crowns and fixed partial dentures. The remount cast allows the laboratory technician to know the precise location of the gingival tissues and allows modification of all‐ceramic restorations.     

Influence of Preliminary Damage on the Load‐Bearing Capacity of Zirconia Fixed Dental Prostheses

Purpose: The objective of this investigation was to evaluate the influence of differently shaped preliminary cuts in combination with artificial aging on the load‐bearing capacity of four‐unit zirconia fixed dental prostheses (FDPs). Materials and Methods: Forty frameworks were fabricated from white‐stage zirconia blanks (InCeram YZ, Vita) by means of a computer‐aided design/computer‐aided manufacturing system (Cerec inLab, Sirona). Frameworks were divided into four homogeneous groups with ten specimens each. Prior to veneering, frameworks of two groups were “damaged” by defined saw cuts of different dimensions, to simulate accidental flaws generated during shape cutting. After the veneering process, FDPs, with the exception of a control group without preliminary damage, were subjected to thermal and mechanical cycling (TMC) during 200 days storage in distilled water at 36°C. Following the aging procedure, all specimens were loaded until fracture, and forces at fracture were recorded. The statistical analysis of force at fracture data was performed using two‐way ANOVA, with the level of significance chosen at 0.05. Results: Neither type of preliminary mechanical damage significantly affected the load‐bearing capacity of FDPs. In contrast, artificial aging by TMC proved to have a significant influence on the load‐bearing capacity of both the undamaged and the predamaged zirconia restorations (p < 0.001); however, even though load‐bearing capacity decreased by about 20% due to simulated aging, the FDPs still showed mean load‐bearing capacities of about 1600 N. Conclusions: The results of this study reveal that zirconia restorations have a high tolerance regarding mechanical damages. Irrespective of these findings, damage to zirconia ceramics during production or finishing should be avoided, as this may nevertheless lead to subcritical crack growth and, eventually, catastrophic failure. Furthermore, to ensure long‐term clinical success, the design of zirconia restorations has to accommodate the decrease in load‐bearing capacity due to TMC in the oral environment.