Implant‐Supported Fixed Dental Prostheses with CAD/CAM‐Fabricated Porcelain Crown and Zirconia‐Based Framework

Recently, fixed dental prostheses (FDPs) with a hybrid structure of CAD/CAM porcelain crowns adhered to a CAD/CAM zirconia framework (PAZ) have been developed. The aim of this report was to describe the clinical application of a newly developed implant‐supported FDP fabrication system, which uses PAZ, and to evaluate the outcome after a maximum application period of 36 months. Implants were placed in three patients with edentulous areas in either the maxilla or mandible. After the implant fixtures had successfully integrated with bone, gold‐platinum alloy or zirconia custom abutments were first fabricated. Zirconia framework wax‐up was performed on the custom abutments, and the CAD/CAM zirconia framework was prepared using the CAD/CAM system. Next, wax‐up was performed on working models for porcelain crown fabrication, and CAD/CAM porcelain crowns were fabricated. The CAD/CAM zirconia frameworks and CAD/CAM porcelain crowns were bonded using adhesive resin cement, and the PAZ was cemented. Cementation of the implant superstructure improved the esthetics and masticatory efficiency in all patients. No undesirable outcomes, such as superstructure chipping, stomatognathic dysfunction, or periimplant bone resorption, were observed in any of the patients. PAZ may be a potential solution for ceramic‐related clinical problems such as chipping and fracture and associated complicated repair procedures in implant‐supported FDPs.     

Current status of zirconia-based fixed restorations

Zirconium dioxide (zirconia) ceramics are currently used for fixed restorations as a framework material due to their mechanical and optical properties. This review article describes the current status of zirconia-based fixed restorations, including results of current in vitro studies and the clinical performance of these restorations. Adaptation of zirconia-based restorations fabricated with CAD/CAM technology is within an acceptable range to meet clinical requirements. In terms of fracture resistance, zirconia-based fixed partial dentures (FPDs) have the potential to withstand physiological occlusal forces applied in the posterior region, and therefore provide interesting alternatives to metal-ceramic restorations. Clinical evaluations have indicated an excellent clinical survival of zirconia-based FPDs and crown restorations. However, some clinical studies have revealed a high incidence of chipping of veneered porcelain. Full-coverage zirconia-based restorations with adequate retention do not require resin bonding for definitive cementation. Resin bonding, however, may be advantageous in certain clinical situations and is a necessity for bonded restorations, such as resin-bonded FPDs. Combined surface treatment using airborne particle abrasion and specific adhesives with a hydrophobic phosphate monomer are currently reliable for bonding to zirconia ceramics. Further clinical and in vitro studies are needed to obtain long-term clinical information on zirconia-based restorations.     

牙科硅藻土基底瓷与饰面瓷的结合机制分析

目的 检测硅藻土基纳米复相基底瓷与不同饰面瓷的结合强度,观察结合界面的微观结构并分析元素分布,探讨结合界面的匹配性。方法采用热膨胀仪检测硅藻土纳米复相基底瓷的热膨胀系数,在基底瓷上分别烧结氧化铝饰面瓷（A组）、钛瓷饰面瓷（B组）及E-max饰面瓷（C组）,检测基底瓷与饰面瓷的剪切强度,扫描电镜（SEM）及能谱仪（EDS）观察结合界面的显微结构及元素分布。采用SPSS 17.0软件包对数据进行单因素方差分析。结果硅藻土基纳米复相基底瓷在25~500℃之间的热膨胀系数值为8.85×10^-6 K^-1。硅藻土基底瓷与C组剪切强度最佳,C组与A组间及C组与B组之间相比有显著差异（P<0.05）。SEM及EDS发现,C组结合界面紧密,界线不清晰,无明显间隙,界面两侧元素存在渗透。结论硅藻土基纳米复相基底瓷与E-max饰面瓷具有较好的剪切强度,两者间匹配性较好。     

Two-body wear of dental porcelain and substructure oxide ceramics

The aim of this in vitro study was to investigate the two-body wear of different ceramics. Two-body wear tests were performed in a chewing simulator with steatite and enamel antagonists, respectively. Specimens were loaded in a pin-on-block design with a vertical load of 50 N for 1.2 × 10(5) cycles; (f = 1.6 Hz; lateral movement, 1 mm; mouth opening: 2 mm). Human enamel was used as a reference. Three zirconia ceramics, three veneering porcelains, two glass-infiltrated and one lithium disilicate ceramic were investigated. Veneering and lithium disilicate ceramics were glazed before testing. Surface roughness Ra (SP6, Perthen-Feinprüf, G) and wear depth were determined using a 3D scanner (Laserscan 3D, Willytec, G). SEM (Quanta FEG 400, FEI, USA) pictures of the worn specimens and antagonists were made for evaluating wear performance. Veneering porcelain provided wear traces between 71.2 and 124.1 μm (enamel antagonist) and 117.4 and 274.1 μm (steatite). Wear of the steatite antagonists varied between 0.618 and 2.85 mm2. No wear was found for zirconia and glass-infiltrated substructure ceramics. Also, no wear was found for the corresponding antagonists. Wear of specimens and antagonists was strongly material dependent. No visible wear was found on zirconia and glass-infiltrated ceramics. Porcelain and lithium disilicate ceramic showed a comparable or lower wear than the enamel reference. Antagonist wear was found to be lower when specimens were made of substructure oxide ceramics instead of veneering porcelain. From the point of wear testing, zirconia may be used for the fabrication of fixed dental prosthesis without veneering.     

Influence of surface treatment on bond strength of veneering ceramics fused to zirconia

In all-ceramic restorations involving a zirconia framework, surface treatment of the zirconia surface is required to enhance bonding strength with the veneering ceramics and thus prevent chipping. The purpose of the present study was to investigate the influence of surface roughness and heat treatment of the zirconia and use of liner porcelain on bond strength between veneering ceramics and a zirconia framework. Debonding/crack-initiation strength (τb) was determined according to ISO 9693. No significant difference was observed among conditions, except with use of a liner under heat treatment, which yielded a τb of 26.0±2.9-28.9±1.7 MPa. Electron probe microanalysis revealed that components of the veneering ceramics remained on the zirconia surface after debonding, suggesting that fractures occur in the veneering ceramics and that improving the strength of the veneering ceramics themselves might increase bond strength.     

SEM observations of porcelain Y-TZP interface

ObjectivesThe metastability of the tetragonal phase of yttria tetragonal zirconia polycrystalline (Y-TZP) ceramics is a cause for concern in dental crown and bridge applications. One specific problematic area is the nature of the interface between the veneering porcelain and the Y-TZP framework and whether the associated preparation procedures and reactions result in a reduction of the stability of the zirconia.MethodsTo investigate this aspect, high-resolution SEM observations were made of polished and etched (HF content gel) cross-sections of the interface area. Dry and moist veneering porcelain powders were built up on the zirconia base.ResultsIn some instances the zirconia grains at the interface appear to show multiplicity of subgrain faceting whereas in other instances they do not. The latter indicate destabilisation of the tetragonal phase occurs and in addition that the porcelain veneering material wets and some dissolution of the Y-TZP occurs.SignificanceThese results and their relevance to the long-term stability of the interface adhesion to the veneering porcelain as well as possible tetragonal to monoclinic crystal transformations at the interface are discussed.     

Influence of porcelain veneering on the marginal fit of Digident and Lava CAD/CAM zirconia ceramic crowns

PURPOSE

Marginal fit is a very important factor considering the restoration''s long-term success. However, adding porcelain to copings can cause distortion and lead to an inadequate fit which exposes more luting material to the oral environment and causes secondary caries. The purpose of this study was to compare the marginal fit of 2 different all-ceramic crown systems before and after porcelain veneering. This study was also intended to verify the marginal fit of crowns originated from green machining of partially sintered blocks of zirconia (Lava CAD/CAM system) and that of crowns obtained through machining of fully sintered blocks of zirconia (Digident CAD/CAM system).

MATERIALS AND METHODS

20 crowns were made per each system and the marginal fit was evaluated through a light microscope with image processing (Accura 2000) at 50 points that were randomly selected. Each crown was measured twice: the first measurement was done after obtaining a 0.5 mm coping and the second measurement was done after porcelain veneering. The means and standard deviations were calculated and statistical inferences among the 2 groups were made using independent t-test and within the same group through paired t-test.

RESULTS

The means and standard deviations of the marginal fit were 61.52 ± 2.88 µm for the Digident CAD/CAM zirconia ceramic crowns before porcelain veneering and 83.15 ± 3.51 µm after porcelain veneering. Lava CAD/CAM zirconia ceramic crowns showed means and standard deviations of 62.22 ± 1.78 µm before porcelain veneering and 82.03 ± 1.85 µm after porcelain veneering. Both groups showed significant differences when analyzing the marginal gaps before and after porcelain veneering within each group. However, no significant differences were found when comparing the marginal gaps of each group before porcelain veneering and after porcelain veneering as well.

CONCLUSION

The 2 all-ceramic crown systems showed marginal gaps that were within a reported clinically acceptable range of marginal discrepancy.     

Effect of veneering technique on the fracture resistance of zirconia fixed dental prostheses

Summary To compare the fracture resistance of zirconia 3‐unit posterior fixed dental prostheses (FDPs) frameworks veneered with different veneering materials and techniques before and after artificial ageing. Forty‐eight zirconia 3‐unit FDPs, representing a missing first molar, were adhesively cemented on human teeth. The zirconia frameworks were randomly distributed according to the veneering materials and techniques into three groups, each containing 16 samples: group LV (layering technique/Vintage ZR), group LZ (layering technique/ZIROX) and group PP (CAD/CAM and press‐over techniques/PressXZr). Half of each group was artificially aged through dynamic loading and thermocycling to simulate 5 years of clinical service. Afterwards, all specimens were tested for fracture resistance using compressive load. An analysis of variance (anova ) was used to assess the effect of veneering ceramic and artificial ageing on fracture resistance (P < 0·05). Except for one minor cohesive chipping in group LV1, all specimens survived artificial ageing. The mean fracture resistance values (in Newton) of different non‐aged (± s.d.)/aged (± s.d.) groups were as follows: LV0 2034 (± 401)/LV1 1625 (± 291); LZ0 2373 (± 718)/LZ1 1769 (± 136); and PP0 1959 (± 453)/PP1 1897 (± 329). Artificial ageing significantly reduced the fracture resistance in groups veneered with the layering technique (P < 0·05), whereas no significant effect was found in specimens veneered with the CAD/CAM and press‐over techniques. All tested systems have the potential to withstand occlusal forces applied in the posterior region. The combination of the CAD/CAM and press‐over techniques for the veneering process improved the overall stability after artificial ageing, relative to the layering technique.     

Evaluation of zirconium-oxide-based ceramic single-unit posterior fixed dental prostheses (FDPs) generated with two CAD/CAM systems compared to porcelain-fused-to-metal single-unit posterior FDPs: a 5-year clinical prospective study

Purpose: The purpose of this prospective clinical study was to determine the success rate of single‐unit posterior fixed dental prostheses (FDPs) with zirconia copings generated with two CAD/CAM systems, compared to porcelain‐fused‐to‐metal (PFM) single‐unit posterior FDPs after 5 years of function. Materials and Methods: From 2005 to 2006, 60 patients who needed a single‐unit FDP on a first molar in the mandibular jaw (left or right) in a private office setting were included in this study. The 60 first mandibular molars were randomly divided into three groups (n = 20): in the control group (group C), 20 PFM FDPs were included. In the other two groups CAD/CAM technology was used for the fabrication of the zirconium‐oxide copings: 20 single‐unit posterior FDPs with zirconia copings were generated with the Procera system (group P, Nobel Biocare); 20 single‐unit posterior FDPs with zirconia copings were generated with the Lava system (group L, 3M ESPE). For the ANOVA follow‐up data, the clinical life table method was applied. The statistical analysis was performed using two nonparametric tests, the log‐rank test for k‐groups and the Fisher exact test. Results: No statistically significant difference in the clinical outcome of zirconia–ceramic FDPs of both groups (P and L) evaluated together and metal–ceramic posterior single FDPs was found at 5 years of function; however, clinical data showed that technical problems, such as extended fracture of the veneering ceramic, tended to occur more frequently in the zirconia–ceramic FDP groups. The difference in the frequency of failure was statistically significant only in the comparison of groups C and P. Conclusions: Even if no statistically significant difference in the clinical outcome of zirconia–ceramic FDPs of both groups (P and L) considered together and metal–ceramic posterior single FDPs was found at 5 years of function, clinical data showed that the two zirconia–ceramic FDP groups tended to have more frequent clinical problems: for this reason all the clinical and technical variables related to the use of zirconia–ceramic FDPs generated with CAD/CAM systems should be carefully considered prior to all treatment procedures.     

The effect of core material, veneering porcelain, and fabrication technique on the biaxial flexural strength and weibull analysis of selected dental ceramics

Purpose: The objective of this study was to compare the effect of veneering porcelain (monolithic or bilayer specimens) and core fabrication technique (heat‐pressed or CAD/CAM) on the biaxial flexural strength and Weibull modulus of leucite‐reinforced and lithium‐disilicate glass ceramics. In addition, the effect of veneering technique (heat‐pressed or powder/liquid layering) for zirconia ceramics on the biaxial flexural strength and Weibull modulus was studied. Materials and Methods: Five ceramic core materials (IPS Empress Esthetic, IPS Empress CAD, IPS e.max Press, IPS e.max CAD, IPS e.max ZirCAD) and three corresponding veneering porcelains (IPS Empress Esthetic Veneer, IPS e.max Ceram, IPS e.max ZirPress) were selected for this study. Each core material group contained three subgroups based on the core material thickness and the presence of corresponding veneering porcelain as follows: 1.5 mm core material only (subgroup 1.5C), 0.8 mm core material only (subgroup 0.8C), and 1.5 mm core/veneer group: 0.8 mm core with 0.7 mm corresponding veneering porcelain with a powder/liquid layering technique (subgroup 0.8C‐0.7VL). The ZirCAD group had one additional 1.5 mm core/veneer subgroup with 0.7 mm heat‐pressed veneering porcelain (subgroup 0.8C‐0.7VP). The biaxial flexural strengths were compared for each subgroup (n = 10) according to ISO standard 6872:2008 with ANOVA and Tukey's post hoc multiple comparison test (p≤ 0.05). The reliability of strength was analyzed with the Weibull distribution. Results: For all core materials, the 1.5 mm core/veneer subgroups (0.8C‐0.7VL, 0.8C‐0.7VP) had significantly lower mean biaxial flexural strengths (p < 0.0001) than the other two subgroups (subgroups 1.5C and 0.8C). For the ZirCAD group, the 0.8C‐0.7VL subgroup had significantly lower flexural strength (p= 0.004) than subgroup 0.8C‐0.7VP. Nonetheless, both veneered ZirCAD groups showed greater flexural strength than the monolithic Empress and e.max groups, regardless of core thickness and fabrication techniques. Comparing fabrication techniques, Empress Esthetic/CAD, e.max Press/CAD had similar biaxial flexural strength (p= 0.28 for Empress pair; p= 0.87 for e.max pair); however, e.max CAD/Press groups had significantly higher flexural strength (p < 0.0001) than Empress Esthetic/CAD groups. Monolithic core specimens presented with higher Weibull modulus with all selected core materials. For the ZirCAD group, although the bilayer 0.8C‐0.7VL subgroup exhibited significantly lower flexural strength, it had highest Weibull modulus than the 0.8C‐0.7VP subgroup. Conclusions: The present study suggests that veneering porcelain onto a ceramic core material diminishes the flexural strength and the reliability of the bilayer specimens. Leucite‐reinforced glass‐ceramic cores have lower flexural strength than lithium‐disilicate ones, while fabrication techniques (heat‐pressed or CAD/CAM) and specimen thicknesses do not affect the flexural strength of all glass ceramics. Compared with the heat‐pressed veneering technique, the powder/liquid veneering technique exhibited lower flexural strength but increased reliability with a higher Weibull modulus for zirconia bilayer specimens. Zirconia‐veneered ceramics exhibited greater flexural strength than monolithic leucite‐reinforced and lithium‐disilicate ceramics regardless of zirconia veneering techniques (heat‐pressed or powder/liquid technique).     

锆瓷基底表面形貌对锆瓷饰瓷间结合强度影响的研究

目的：探讨锆瓷基底表面形貌对其与饰瓷结合强度的影响.方法：切削制备1 1mm×10mm×5mm锆瓷烧结瓷块40块,随机均分至4组即对照组（烤瓷面烤瓷前经过常规打磨、喷砂及抛光处理）,垂直组（与对照组不同处在于剪切加载方向与切削瓷面的刀路方向垂直）,平行组（与对照组不同处在于剪切加载方向与切削瓷面的刀路方向一致）,突起组（与对照组不同处在于烤瓷面制备有2个直径2mm,高0.3mm的圆柱状突起）.各组试件烤瓷面涂布粘接瓷,堆积4mm厚饰瓷后烧结.以万能试验机测试饰瓷与锆瓷基底间的剪切强度.结果：对照组、垂直组、平行组、突起组锆瓷与饰瓷间的剪切强度均数与标准差分别为24.1±2.64 MPa、27.9±4.53MPa、27.5±4.79MPa和37.2±7.03MPa,单因素方差分析显示差异有统计学意义,突起组强度显著高于垂直组、平行组（P＜0.05）及对照组（P＜0.01）.结论：锆瓷烤瓷面切削刀路方向对锆瓷与饰瓷间的烧结剪切强度无显著影响;锆瓷烤瓷面制备出适当的突起可显著增强饰瓷抗剥脱的能力.     

Comparative fracture strength analysis of Lava and Digident CAD/CAM zirconia ceramic crowns

PURPOSE

All-ceramic crowns are subject to fracture during function. To minimize this common clinical complication, zirconium oxide has been used as the framework for all-ceramic crowns. The aim of this study was to compare the fracture strengths of two computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia crown systems: Lava and Digident.

MATERIALS AND METHODS

Twenty Lava CAD/CAM zirconia crowns and twenty Digident CAD/CAM zirconia crowns were fabricated. A metal die was also duplicated from the original prepared tooth for fracture testing. A universal testing machine was used to determine the fracture strength of the crowns.

RESULTS

The mean fracture strengths were as follows: 54.9 ± 15.6 N for the Lava CAD/CAM zirconia crowns and 87.0 ± 16.0 N for the Digident CAD/CAM zirconia crowns. The difference between the mean fracture strengths of the Lava and Digident crowns was statistically significant (P<.001). Lava CAD/CAM zirconia crowns showed a complete fracture of both the veneering porcelain and the core whereas the Digident CAD/CAM zirconia crowns showed fracture only of the veneering porcelain.

CONCLUSION

The fracture strengths of CAD/CAM zirconia crowns differ depending on the compatibility of the core material and the veneering porcelain.     

钇稳定氧化锆基底材料与饰面瓷结合性能的实验研究

目的考察国产氧化钇稳定四方晶体氧化锆（3Y-TZP）与4种氧化锆专用饰面瓷界面的结合性能。方法粉浆涂塑方法分别将VITA VM9、SHOFU VINTAGE ZR、IPS e.max Ceram、Cercon ceram kiss 4种氧化锆专用饰面瓷烧结在15 mm×5 mm×5 mm的3Y-TZP核瓷试件上,另外制作相同尺寸镍铬合金烤瓷试件作为对照,测试界面剪切强度。制作氧化锆基底与饰面瓷双层瓷试件,扫描电镜（SEM）观察结合界面微观形貌;能谱分析（EDS）检测界面元素分布。结果氧化锆与VITA VM9、SHOFU VINTAGE ZR、IPS e.max Ceram、Cercon ceram kiss 4种氧化锆专用饰面瓷的剪切强度分别为（18.83±1.77）MPa、（23.83±7.05）MPa、（17.87±2.30）MPa、（22.26±7.45）MPa,各组与金属烤瓷对照组比较,差异均无统计学意义（P＞0.05）。各3Y-TZP烤瓷组试件破坏模式以界面破坏为主。扫描电镜观察氧化锆和饰面瓷结合界面结合紧密;能谱分析结果显示二者存在化学元素渗透。结论国产3Y-TZP与饰面瓷材料界面结合良好,可以满足临床需要。     

Influence of thickness and cooling rate on development of spontaneous cracks in porcelain/zirconia structures

Background: Clinical studies reporting the outcome of zirconia‐based restorations indicate that the strength of the zirconia frameworks is sufficient to withstand masticatory forces. However, a significant incidence of cohesive fracture of the veneering porcelain has been reported. The aim of this study was to investigate spontaneous crack development (chipping, rupture) in a range of porcelains veneered to a zirconia core as a result of thermal stresses induced by changes in thickness and cooling rate. The hypothesis tested was that crack incidence would increase with increased veneer thickness and faster cooling rates. Methods: Zirconia spheres (diameter 7.8 mm) were veneered with 1.5 gm (thickness ratio 1:2) and 2.5 gm (thickness ratio 1:1) of five nominally compatible commercially available porcelains. The manufacturers’ firing cycles and a rapid cooling firing cycle were followed. Results: Multiple regression analysis showed positive associations between the occurrence of cracks and the three covariates (materials, thickness and cooling rate). The incidence of cracks and rupture of the veneering porcelain increased with a faster cooling rate and increased thickness of the specimens in three porcelain–zirconia combinations. Conclusions: Crack incidence increased with increased porcelain veneer thickness and faster cooling rates in nominally compatible porcelain/zirconia systems in the geometrically configured specimens tested.     

高度抛光无釉瓷氧化锆全瓷冠的临床效果研究

目的评估高度抛光无釉瓷氧化锆全瓷冠的临床效果。方法牙体缺损磨牙80颗,分为2组,40例40颗患牙进行高度抛光无釉瓷的氧化锆全瓷冠修复（试验组）,40例40颗患牙常规制作钯金烤瓷牙单冠修复（对照组）。戴固后即刻、3个月、6个月、12个月、24个月、36个月临床观察和评价修复体破损和对袷牙磨耗情况,比较2组修复体的存留率和成功率。结果试验组中有1件修复体出现小面积瓷裂,修复后12个月2件全瓷冠对冶天然牙牙出现I级磨耗。对照组中有3件修复体出现小面积瓷裂,但对殆天然牙均无明显磨耗。试验组和对照组修复体3年存留率分别为100％和97．5％,成功率分别为97．5％和90％,差异均无统计学意义（P〉0．05）。结论高度抛光无釉瓷氧化锆全瓷冠修复磨牙牙体缺损不易破损,对猞天然牙磨耗轻微,成功率高.     

Influence of the fabrication process on the in vitro performance of fixed dental prostheses with zirconia substructures

Chipping of the applied veneering ceramic is reported to be a main clinical failure type of computer-aided design/computer-aided manufacturing- or manually copy-milled zirconia restorations. The aim of this in vitro study was to investigate whether different substructure designs and veneering processes done by different dental technicians do significantly influence chipping in zirconia-based all-ceramic fixed dental prostheses during simulated oral service. Five groups (n = 8 per group) of three-unit zirconia substructures were fabricated in three different laboratories using copy-milling technique. Three series were veneered with identical porcelain (groups 1–3) and one with a second different porcelain (group 4). The fifth group was milled to final contour design without veneering. Dimensions of the connector areas were determined. All fixed partial dentures (FPDs) were adhesively boned on human teeth and thermally cycled and mechanically loaded (1.2 × 10⁶ × 50 N; 6,000 × 5°C/55°C) using human antagonists. Restorations were monitored during thermal cycling and mechanical loading (TCML). FPDs which survived were loaded to fracture. FPDs which failed during TCML were investigated with fractographic means. During TCML, chipping took place in groups 1 (two times), 2 (four times) and 3 (five times) (Table 1). Chipping areas varied between 2.3 mm² (group 3) and 58.7 mm² (group 2). Groups 4 and 5 provided no failures during TCML. Failure in all cases started from contact points, where superficial wear and disruption of the porcelain were found. No significant correlation could be determined between connector thickness and number of failures. Median fracture results varied between 1,011 N (group 3) and 2,126 N (group 2). The results show the necessity of considering individual design and manufacturing of restorations as well as contact situation. Advanced technical training on zirconia-based restorations is recommended.     

Zirconia in fixed implant prosthodontics

Background: CAD/CAM technology in combination with zirconia ceramic has increasingly gained popularity in implant dentistry. Purpose: This narrative review presents the current knowledge on zirconia utilized as framework material for implant‐borne restorations and implant abutments, laboratory tests and developments, clinical performance, and possible future trends for implant dentistry are addressed. Material and Methods: A review of available literature from 1990 through 2010 was conducted with search terms zirconia,”“implants,”“abutment,”“crown,” and “fixed dental prosthesis” using electronic databases (PubMed) and manual searching. Results: Latest applications of zirconia in implant dentistry include implant abutments, multiple unit and full‐arch frameworks as well as custom‐made bars to support fixed and removable prostheses. High biocompatibility, low bacterial surface adhesion as well as favorable chemical properties of zirconia ceramics are reported. Zirconia stabilized with yttrium oxide exhibits high flexural strength and fracture toughness due to a transformation toughening mechanism. Preliminary clinical data confirmed the high stability of zirconia for abutments and as a framework material for implant borne crowns and fixed dental prostheses. Zirconia abutment or framework damage has rarely been encountered. However, veneering porcelain fractures are the most common technical complication in implant‐supported zirconia restorations. These porcelain veneer failures have led to concerns regarding differences in coefficient of thermal expansions between core and veneering porcelain and their respective processing techniques. Conclusion: As presently evidence of clinical long‐term data is missing, caution with regard to especially extensive implant‐borne zirconia frameworks is recommended.     

Implant-supported full-arch zirconia-based mandibular fixed dental prostheses. Eight-year results from a clinical pilot study

Abstract

Objective. The purpose of this pilot study was to evaluate the long-term clinical performance of implant-supported full-arch zirconia-based fixed dental prostheses (FDPs). Materials and methods. Ten patients received full-arch zirconia-based (Cercon) mandibular FDPs supported by four implants (Astra Tech). Nine patients received 10-unit FDPs and one patient received a 9-unit FDP. The FDPs were cemented onto individually prepared titanium abutments and were evaluated at baseline and after 12, 24, 36 and 96 months. Results. Nine patients attended the 8-year follow-up. None of the restorations showed bulk fracture, all FDPs were in use. Fractures of the veneering porcelain were, however, observed in eight patients. A total of 36 out of 89 units (40%) showed such fractures. Patient satisfaction was excellent despite the veneering material fractures. Conclusion. Results from this 8-year pilot study suggest that implant-supported full-arch zirconia-based FDPs can be an acceptable treatment alternative.     

Y-TZP口腔修复材料的低温老化及抗低温老化的相关研究

综合国内外相关研究,了解氧化钇稳定的四方氧化锆多晶陶瓷(Y-TZP)口腔修复材料的低温老化现象,探讨抗Y-TZP修复陶瓷低温老化的方法,展望抗低温老化Y-TZP陶瓷在口腔临床中的应用.抗Y-TZP低温老化的方法包括:稳定剂类型和含量的选择、加工工艺的改善、适宜的表面处理、合成复合陶瓷等,其中Y-TZP/Al2O3复合陶瓷对Y-TZP的低温老化有较大程度的缓解作用,且能明显改善Y-TZP的机械性能,是一种在口腔临床应用中具有发展前景的氧化锆基陶瓷材料.