Influence of implant abutment angulations and two types of fibers on the fracture resistance of ceramage single crowns

Purpose: To assess the effect of three implant abutment angulations and two types of fibers on the fracture resistance of overlaying Ceramage single crowns. Materials and Methods: Three groups, coded A to C, with different implant abutment angulations (group A/0°, group B/15°, and group C/30° angulation) were restored with 45 overlay composite restorations; 15 Ceramage crowns for each angulation. Groups A, B, and C were further subdivided into three subgroups (n = 5) coded: 1, crowns without fiber reinforcement; 2, crowns with Connect polyethylene reinforcement; and 3, crowns with Interlig glass reinforcement. All crowns were constructed by one technician using the Ceramage System. The definitive restorations (before cementation) were stored in distilled water at mouth temperature (37°C) for 24 hours prior to testing. Before testing, the crowns were cemented using Temp Bond. The compressive load required to break each crown and the mode of failure were recorded. The speed of testing was 1 mm/min. The results were statistically analyzed by two‐way ANOVA (p < 0.05). The tested crowns were examined using a stereomicroscope at 40×, and selected crowns (five randomly selected from each group) were further examined by scanning electron microscopy (SEM) to reveal the composite–fiber interface. Results: Fracture resistance of single crowns was not affected (p > 0.05) by the different abutment angulations chosen (0°, 15°, 30°) or fiber reinforcement (Connect and Interlig fibers). Crowns in group A exhibited average loads to fracture (N) of A1 = 843.57 ± 168.20, A2 = 1389.20 ± 193.40, and A3 = 968.00 ± 387.53, which were not significantly different (p > 0.05) from those of groups B (B1 = 993.20 ± 327.19, B2 = 1471.00 ± 311.68, B3 = 1408.40 ± 295.07), or group C (C1 = 1326.80 ± 785.30, C2 = 1322.20 ± 285.33, C3 = 1348.40 ± 527.21). SEM images of the fractured crowns showed that the origin of the fracture appeared to be located at the occlusal surfaces of the crowns, and the crack propagation tended to extend from the occlusal surface towards the gingival margin. Conclusions: Implant abutment angulations of 0°, 15°, and 30° did not significantly (p > 0.05) influence the fracture resistance of overlaying Ceramage single crowns constructed with or without reinforcing fibers. The two types of fibers used for reinforcement (Connect and Interlig) had no effect (p > 0.05) on the fracture resistance of overlaying Ceramage single crowns.     

The effect of preparation taper on the resistance to fracture of monolithic zirconia crowns

ObjectiveMonolithic zirconia crowns have become a viable alternative to conventional layered restorations. The aim of this study was to evaluate whether the taper, and thus wall thickness, of the abutment or pre-defined cement space affect the fracture resistance or fracture mode of monolithic zirconia crowns.MethodsA model tooth was prepared with a taper of 15° and a shallow circumferential chamfer preparation (0.5 mm). Two additional models were made based on the master model with a taper of 10° and 30° using computer-aided design software. Twenty monolithic 3rd generation translucent zirconia crowns were produced for each model with pre-defined cement space set to either 30 μm or 60 μm (n = 60). The estimated cement thickness was assessed by the replica method. The cemented crowns were loaded centrally in the occlusal fossa at 0.5 mm/min until fracture. Fractographic analyses were performed on all fractured crowns.ResultsThe load at fracture was statistically significant different between the groups (p < 0.05). The crowns with 30° taper fractured at lower loads than those with 10° and 15° taper, regardless of the cement space (p < 0.05). The fracture origin for 47/60 crowns (78%) was in the cervical area, close to the top of the curvature in the mesial or distal crown margin. The remaining fractures started at the internal surface of the occlusal area and propagated cervically.SignificanceThe fracture resistance of the monolithic zirconia crowns was lower for crowns with very large taper compared to 10 and 15° taper even though the crown walls were thicker.     

CAD/CAM ZIRCONIA VS. SLIP-CAST GLASS-INFILTRATED ALUMINA/ZIRCONIA ALL-CERAMIC CROWNS: 2-YEAR RESULTS OF A RANDOMIZED CONTROLLED CLINICAL TRIAL

The aim of this randomized controlled clinical trial was to compare the early clinical outcome of slip-cast glass-infiltrated Alumina/Zirconia and CAD/CAM Zirconia all-ceramic crowns. A total of 30 InCeram^® Zirconia and Cercon^® Zirconia crowns were fabricated and cemented with a glass ionomer cement in 20 patients. At baseline, 6-month, 1-year, and 2-year recall appointments, Californian Dental Association (CDA) quality evaluation system was used to evaluate the prosthetic replacements, and plaque and gingival index scores were used to explore the periodontal outcome of the treatments. No clinical sign of marginal discoloration, persistent pain and secondary caries was detected in any of the restorations. All InCeram^® Zirconia crowns survived during the 2-year period, although one nonvital tooth experienced root fracture coupled with the fracture of the veneering porcelain of the restoration. One Cercon^® Zirconia restoration fractured and was replaced. According to the CDA criteria, marginal integrity was rated excellent for InCeram^® Zirconia (73%) and Cercon^® Zirconia (80%) restorations, respectively. Slight color mismatch rate was higher for InCeram^® Zirconia restorations (66%) than Cercon^® Zirconia (26%) restorations. Plaque and gingival index scores were mostly zero and almost constant over time. Time-dependent changes in plaque and gingival index scores within and between groups were statistically similar (p>0.05). This clinical study demonstrates that single-tooth InCeram^® Zirconia and Cercon^® Zirconia crowns have comparable early clinical outcome, both seem as acceptable treatment modalities, and most importantly, all-ceramic alumina crowns strengthened by 25% zirconia can sufficiently withstand functional load in the posterior zone.     

Fracture load and chewing simulation of zirconia and stainless‐steel crowns for primary molars

Aesthetic alternatives to stainless‐steel crowns for restoring primary molars attain growing interest. We studied the mechanical properties of prefabricated zirconia crowns and conventional crowns. Three brands of prefabricated zirconia crowns were compared with computer‐aided design/computer‐aided manufacturing (CAD/CAM) zirconia crowns, preveneered stainless‐steel crowns, and conventional stainless‐steel crowns regarding: (i) fracture load under each of three conditions [no pretreatment, artificial aging in saliva for 12 wk, and after chewing simulation/thermocycling (1.68 × 10⁶ cycles/5–55°C)]; and (ii) survival rate during chewing simulation, considering decementation, fracture, chipping, fatigue cracks, and occlusal holes. Without pretreatment, the prefabricated zirconia crowns showed mean fracture load values between 893 N and 1,582 N, while the corresponding values for CAD/CAM zirconia crowns and preveneered stainless‐steel crowns were 2,444 N and 6,251 N. Preveneered stainless‐steel crowns showed significantly lower fracture loads after artificial aging (5,348 N after saliva aging; 3,778 N after chewing simulation) than without artificial aging, whereas the fracture load of zirconia crowns was not influenced negatively. The survival rate of the different groups of zirconia crowns and preveneered stainless‐steel crowns during chewing simulation was 100%, but only 41.7% for the stainless‐steel crowns. These in‐vitro data suggest that prefabricated zirconia crowns are aesthetically and durable alternatives to stainless‐steel crowns for primary molars.     

Fracture resistance of zirconia‐based all‐ceramic crowns after bur adjustment

Intra‐oral grinding is often required to optimize occlusion of all‐ceramic restorations. The effect of burs of different grit size on the fracture resistance of veneered zirconia crowns was investigated in this study. Forty‐eight standardized zirconia copings were produced. The ceramic veneer was designed with a positive ellipsoidal defect on the palatal aspect of the crowns. To simulate adjustment of dental restorations by burs, this palatal defect was removed by use of three different diamond‐coated burs with grit sizes 46, 107, or 151 μm (fine, medium, or coarse, respectively). Each different grit size of bur was used to grind 16 crowns. All crowns were then polished and surface roughness was measured. Half of the specimens underwent thermomechanical aging (10,000 thermocycles between 6.5°C and 60°C) and 1.2 million cycles of chewing simulation (F = 108 N). A linear regression model was computed to test the effect of aging and grinding grit size at a level of significance of α = 0.05. Fracture loads increased with decreasing grit size. Grit size and aging had a significant effect on the fracture resistance of the crowns. Use of fine and coarse burs for intra‐oral adjustments resulted in different fracture resistance of veneered zirconia crowns. Coarse burs should be avoided in the final stage of grinding before polishing.     

Fracture load of tooth-implant-retained zirconia ceramic fixed dental prostheses: effect of span length and preparation design

Objectives: Evaluation of the effect of different span length and preparation designs on the fracture load of tooth–implant‐supported fixed dental prostheses (TIFDPs) manufactured from yttrium‐stabilized zirconia frameworks. Material and methods: Forty‐eight TIFDPs were manufactured using a CAD/CAM system and veneered with a press ceramic. Rigidly mounted implants (SLA, diameter 4.1 mm, length 10 mm) in the molar region with a titanium abutment were embedded in PMMA bases pairwise with premolars. All premolars were covered with heat‐shrink tubing to simulate physiological tooth mobility. Six different test groups were prepared (a) differing in the preparation design of the premolar (inlay [i]; crown [c]), (b) the material of the premolar (metal [m]; natural human [h]) and (c) the length of the TIFDPs (3‐unit [3]; 4‐unit [4]). All TIFDPs underwent thermomechanical loading (TCML) (10,000 × 6.5°/60°; 6 × 10⁵× 50 N). The load to fracture (N) was measured and fracture sites were evaluated macroscopically. Results: None of the restorations failed during TCML. The mean fracture loads (standard deviations) were 1,522 N (249) for the 3‐unit, inlay‐retained TIFDPs on a metal abutment tooth (3‐im), 1,910 N (165) for the 3‐cm group, 1,049 N (183) for group 4‐im, 1,274 N (282) for group 4‐cm, 1,229 N (174) for group 4‐ih and 911 N (205) for group 4‐ch. Initial damages within the veneering ceramic occurred before the final failure of the restoration. The corresponding loads were 24–52% lower than the fracture load values. Conclusions: All restorations tested could withstand the mastication forces expected. Fracture‐load values for 3‐ and 4‐unit inlay–crown and crown–crown‐retained TIFDPs should spur further clinical investigation.     

Comparison of Fracture Resistance and Fit Accuracy of Customized Zirconia Abutments with Prefabricated Zirconia Abutments in Internal Hexagonal Implants

Background: Customized zirconia abutments are increasingly applied for the fabrication of esthetic implant restorations aimed at imitating the natural situation. These abutments are individually shaped according to the anatomical needs of the respective implant site. Purpose: This study sought to compare the fracture resistance and fit accuracy of prefabricated and customized zirconia abutments using an internal hexagonal implant system (TSV®, Zimmer, Carlsbad, CA, USA). Materials and Methods: Two zirconia abutment groups were tested: prefabricated zirconia abutments (ZirAce, Acucera, Seoul, Korea) and customized zirconia abutments milled by the Zirkonzahn milling system. Twenty zirconia abutments per group were connected to implants on an acrylic resin base with 30‐Ncm torque. The fracture resistance of zirconia abutments was measured with an angle of 30° at a crosshead speed of 1 mm/min using the universal testing machine (Z020, Zwick, Ulm, Germany). Marginal and internal gaps between implants and zirconia abutments were measured after sectioning the embedded specimens using a digital microhardness tester (MXT70, Matsuzawa, Tokyo, Japan). Results: The customized abutments were significantly stronger (1,430.2 N) than the prefabricated abutments (1,064.1 N). The mean marginal adaptation of customized abutments revealed a microgap that was increased (11.5 µm) over that in prefabricated abutments (4.3 µm). Conclusion: Within the limitations of this study, the customized abutments are significantly stronger than prefabricated abutments, but the fit is less accurate. The strength and fit of both abutments are within clinically acceptable limit.     

Mechanical stability of angulated zirconia abutments supporting maxillary anterior single crowns on narrow-diameter implants

Objectives

To investigate the fracture strength of angulated hybrid abutments supporting anterior single crowns on narrow-diameter implants (NDIs).

Material and methods

Zirconia abutment with angulations of labial inclination 0° (TZ0Z), 15° (TZ15Z), 30° (TZ30Z) and palatal inclination 15° (TZ???15Z) was designed on 3.3-mm titanium-zirconium (Ti–Zr) NDIs. Titanium abutment connected with Ti–Zr implant (TZ0T) and 0° zirconia abutment connected with pure titanium (Ti) implant (T0Z) were control groups. Thirty-six un-restored abutments and 36 abutments restored with highly translucent zirconia (HTZ) crowns were tested. Failure loads were compared among 6 groups, and bending moments were calculated for comparison between un-restored and restored abutments.

Results

Failure loads of un-restored abutments were affected by the abutment angle. Sixty-seven percent samples in TZ30Z and 83% samples in TZ???15Z group fractured at the thinnest part of the zirconia abutment and exhibited lower failure load (p?<?.05). Failure loads of restored abutments were close to or exceeded the maximum bite force of anterior teeth, and no differences were found among six groups (p?>?.05). Except TZ15Z and TZ0T group, the bending moment increased with the crown construction, especially for TZ30Z and TZ???15Z groups (p?<?.001).

Conclusions

The fracture strength of hybrid abutments restored with HTZ crown on Ti–Zr NDIs exceeded the bite forces of anterior teeth for all the groups and were not affected by the abutment angle.

Clinical relevance

In terms of fracture strength, Ti–Zr NDIs combined with angulated hybrid abutments and HTZ crowns can be used in the anterior region.

     

CAD/CAM氧化锆全瓷单冠抗折裂随访4年临床分析

目的 回顾分析评价CAD/CAM氧化锆全瓷单冠抗折裂性能。 方法 为189例患者制作CAD/CAM氧化锆全瓷冠284颗,随访到156例患者的226颗全瓷冠,随访2.5~5.5年,对修复体的位置、崩瓷、基底冠折断、修复体松动脱落等情况进行观察。 结果 CAD/CAM全瓷冠1年的折裂率0.9%,2年的折裂率为2.1%,3年的折裂率为3.3%,4年的折裂率为7.1%,观察期间全瓷冠的总折裂率为9.7%。其中2例患者发生基底冠折裂。当对颌分别为天然牙或瓷修复体时,全瓷冠的折裂率有显著性差异（P=0.034）。全瓷冠的折裂后牙明显高于前牙区（P<0.01）。 结论 CAD/CAM氧化锆全瓷冠整体抗折裂性能临床可接受,可作为临床首选的美学修复体。     

Conical crowns with electroplated gold copings: retention force changes caused by wear and combined off‐axial load

Objectives: The aim of this study was to examine the wear behavior of conical crowns of gold alloy and zirconium dioxide ceramics facing electroplated gold copings. Methods: The conical crowns were milled in Group A of a cast gold alloy (Degunorm^®, DeguDent^®) and B zirconium dioxide (Cercon^®, DeguDent^®). Fifteen specimens were milled per group with a conicity of 2°. The electroplated coping was established by direct electroforming with the Solaris system (DeguDent^®) and glued into a framework. An apparatus accomplishing 5000 wear cycles performed the wear test. After each of the cycles, extra axial forces (80 N) were loaded 1 million times on an extension of the framework. The retentive forces and the correlating distance during insertion and separation were measured. The wear test was separated in a start phase, an initial wear phase and the long‐term wear period. The retention force value and the force–distance integral of the first 0.3 mm of each cycle were calculated. Results: The changes of retention force (ΔF) and integral (ΔF_d) differed significantly between both groups in the start phase (ΔF: A ?1.85 N, B +1.39 N, P=0.0028; ΔF_d: A ?0.155 N mm, B +0.2685 N mm, P=0.0378) and the initial wear phase. The long‐term wear period showed no differences in force and integral development. As a statistical test for the comparison of the median values of the two groups, the Mann–Whitney test was used. The median force never fell below 4 N or exceeded 12 N. Conclusions: Within the limitations of this study, the conical crowns tested showed clinically acceptable retentive properties. The values of about 4–6 N mentioned as sufficient in the recent literature were always attained. As the most retentive elements for dentures, both groups showed the main changes in retentive forces during the first 2000 cycles. The retention force development of the zirconia group appears to be less excursive over the whole wear test. To cite this article:
Bayer S, Zuziak W, Kraus D, Keilig L, Stark H, Enkling N. Conical crowns with electroplated gold copings: retention force changes caused by wear and combined off‐axial load.
Clin. Oral Impl. Res. 22 , 2011; 323–329.
doi: 10.1111/j.1600‐0501.2010.02003.x     

Clinical trials in zirconia: a systematic review

Summary Zirconia is unique in its polymorphic crystalline makeup, reported to be sensitive to manufacturing and handling processes, and there is debate about which processing method is least harmful to the final product. Currently, zirconia restorations are manufactured by either soft or hard‐milling processes, with the manufacturer of each claiming advantages over the other. Chipping of the veneering porcelain is reported as a common problem and has been labelled as its main clinical setback. The objective of this systematic review is to report on the clinical success of zirconia‐based restorations fabricated by both milling processes, in regard to framework fractures and veneering porcelain chipping. A comprehensive review of the literature was completed for in vivo trials on zirconia restorations in MEDLINE and PubMed between 1950 and 2009. A manual hand search of relevant dental journals was also completed. Seventeen clinical trials involving zirconia‐based restorations were found, 13 were conducted on fixed partial dentures, two on single crowns and two on zirconia implant abutments, of which 11 were based on soft‐milled zirconia and six on hard‐milled zirconia. Chipping of the veneering porcelain was a common occurrence, and framework fracture was only observed in soft‐milled zirconia. Based on the limited number of short‐term in vivo studies, zirconia appears to be suitable for the fabrication of single crowns, and fixed partial dentures and implant abutments providing strict protocols during the manufacturing and delivery process are adhered to. Further long‐term prospective studies are necessary to establish the best manufacturing process for zirconia‐based restorations.     

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目的    分析计算机辅助设计与计算机辅助制作（CAD／CAM）后牙氧化锆全瓷冠桥崩瓷原因并探讨预防方法。方法    对2007年12月至2009年7月在大连市口腔医院修复科行CAD／CAM后牙氧化锆全瓷冠桥修复后崩瓷的16例患者的崩瓷原因进行分析。结果    16例后牙氧化锆全瓷冠桥崩瓷中,后牙单冠10例、后牙固定桥6例;15例为瓷折裂,1例为瓷剥脱。结论    正确选择适应证,严格遵循边缘和基牙形态设计原则,细致地进行临床操作及技工制作,可防止崩瓷的发生。     

A 3-year retrospective and clinical follow-up study of zirconia single crowns performed in a private practice

Objectives

All-ceramic crowns have become increasingly used also in the posterior regions, but there are only few studies documenting the clinical outcome of these restorations. The aim was therefore to present the 3-year outcome of zirconia (NobelProcera™) single crowns.

Methods

All patients treated with porcelain-veneered zirconia single crowns in a private practice during the period October 2004 to November 2005 were included. The patient records were scrutinized for data on the restorations and the supporting teeth. Information was available for 161 patients and 204 crowns. At the 3-year recall appointments, a sample of 18 patients with 25 crowns was clinically examined and interviewed regarding patient satisfaction.

Results

Most crowns (78%) were placed on premolars and molars. The clinical outcome of the crowns was favourable. No zirconia core fractured and no caries was observed on the abutment teeth. Some types of complication were recorded for 32 (16%) crowns or abutment teeth. The most severe complications, in total 12 restorations (6%), were recorded as failures: abutment tooth was extracted (5), remake of crown due to lost retention (4), veneer fracture (2) and persistent pain (1). The CDA criteria for 25 crowns were rated favourably, and patient satisfaction with the zirconia crowns was in general high.

Conclusions

The porcelain-veneered zirconia crowns (NobelProcera™) showed good clinical results, were well accepted by the patients, and only few complications were reported over the 3-year follow-up period.     

Occlusal geometrical considerations in all-ceramic pre-molar crown failure testing

Objectives

To evaluate the influence of occlusal geometry of all-ceramic pre-molars, namely cusp angle and associated notch radius, on the scatter of load to failure tests.

Methods

Forty-five all-ceramic upper pre-molar crowns with three zirconia core thicknesses (0.4, 0.6 and 0.8 mm) were broken on dental implant abutments oriented in three angulations (0°, 15°, and 30°). The crowns were loaded using a 4 mm diameter steel cylindrical bar placed along the midline fissure at a crosshead speed of 1 mm min⁻¹. The scatter of the failure load was evaluated using Weibull analysis. The cusp angle of each crown was critically evaluated to determine the cusp angle and effective radius of the fissure notch root. The relationship between failure load and cusp angle was compared with that between failure load and effective radius as well as notch induced stress concentration by considering R² values of fitted trend lines with these relationships.

Results

The fracture load differences either between abutment angulations or zirconia thicknesses were not clearly revealed in this study. Except for the group of 30° abutment angulation, the crowns present high scatter of failure loads with low Weibull modulus. However, a simple dependence between fracture load and effective cusp angle was observed.

Significance

Occlusal geometry is an important issue that affects the degree of stress concentration and should be understood by both technician and clinician for appropriate design and material selection of all-ceramic crowns.     

CAD/CAM氧化锆及Empress全瓷冠修复三年临床效果比较

目的:比较CAD/CAM氧化锆及Empress全瓷冠修复3年的临床效果。方法:选择350例患者共838个全冠修复体(其中CAD/CAM氧化锆全冠428颗、Empress铸瓷全冠410颗),平均观察期36.2±5月,随访检查基牙和修复体情况,分别对两组全瓷冠的存留率和修复成功率进行统计学分析。结果:观察期内共有41颗全瓷冠(19颗为氧化锆,22颗为Empress铸瓷)完全失败,需重新制作。氧化锆全瓷冠和Empress铸瓷全冠的存留率分别为95.1%和95.8%,成功率分别为90.7%和91.2%,其差异均无统计学意义。结论:CAD/CAM氧化锆和Empres铸瓷全冠均能满足临床需要,有较好的修复效果。     

Computer-aided evaluation of preparations for CAD/CAM-fabricated all-ceramic crowns

Objective

The aim of this study was the evaluation of preparations from general dental practitioners for zirconia crowns and their correlation with clinical recommendations using a digital approach.

Material and method

Seventy-five datasets of left first upper molars (FDI 16) prepared for single zirconia crowns by general dental practitioners were analyzed using a computer-aided design software (LAVA^TM Design; 3M ESPE, Seefeld, Germany) and a 3D-inspection software (COMETinspect®plus version 4.5; Steinbichler Optotechnik, Neubeuern, Germany). Evaluated parameters were convergence angle, undercuts, interocclusal reduction, abutment height, and design of preparation margin.

Results

The mean convergence angle was determined to be 26.7°. The convergence angle in the mesiobuccal to distopalatal dimension was significantly the highest (31.7°), and the abutment height showed a mean value of 4.1 mm. Convergence angle and abutment height showed a negative correlation. Seventy-three percent of the evaluated locations revealed a margin design conforming to ceramic restorations. In over 30 % of the cases, the interocclusal reduction was insufficient. Generally, no preparation fulfilled all recommendations. Five (6.66 %) of the preparations fulfilled four criteria, 16 (21.33 %) preparations fulfilled three criteria, 31 (41.33 %) fulfilled two criteria, 17 (22.66 %) preparations fulfilled one criterion, and 6 (8 %) fulfilled no criterion.

Conclusions

Within the limitations of this study, most general dental practitioners seem to have difficulties fulfilling all clinical recommendations given for the preparation of zirconia crowns. The presented digital approach seems to be a useful method to evaluate the preparation geometry.

Clinical relevance

The correct preparation geometry represents an important prerequisite for the success of all-ceramic full crowns. As preparations clearly need to be improved, the approach presented could be the basis of a future tool to increase preparation quality in practice and education by direct objective feedback.     

Fracture behavior of straight or angulated zirconia implant abutments supporting anterior single crowns

The aim of the study was to evaluate the influence of artificial aging on the fracture behavior of straight and angulated zirconia implant abutments (ZirDesign?; Astra Tech, Mölndal, Sweden) supporting anterior single crowns (SCs). Four different test groups (n?=?8) representing anterior SCs were prepared. Groups 1 and 2 simulated a clinical situation with an ideal implant position (left central incisor) from a prosthetic point of view, which allows for the use of a straight, prefabricated zirconia abutment. Groups 3 and 4 simulated a situation with a compromised implant position, requiring an angulated (20°) abutment. OsseoSpeed? implants (Astra Tech) 4.5 mm in diameter and 13 mm in length were used to support the abutments. The SCs (chromium cobalt alloy) were cemented with glass ionomer cement. Groups 2 and 4 were thermomechanically loaded (TCML?=?1.2?×?10⁶; 10,000?×?5°/55°) and subjected to static loading until failure. Statistical analysis of force data at the fracture site was performed using nonparametric tests. All samples tested survived TCML. Artificial aging did not lead to a significant decrease in load-bearing capacity in either the groups with straight abutments or the groups with angulated abutments. The restorations that utilized angulated abutments exhibited higher fracture loads than the restorations with straight abutments (group 1, 280.25?±?30.45 N; group 2, 268.88?±?38.00 N; group 3, 355.00?±?24.71 N; group 4, 320.71?±?78.08 N). This difference in load-bearing performance between straight and angulated abutments was statistically significant (p?=?0.000) only when no artificial aging was employed. The vast majority of the abutments fractured below the implant shoulder.     

A 5-year retrospective study of survival of zirconia single crowns fitted in a private clinical setting

ObjectivesThe aim of this report was to evaluate the 5-year clinical performance and survival of zirconia (NobelProcera?) single crowns.MethodsAll patients treated with porcelain-veneered zirconia single crowns in a private practice during the period October 2004 to November 2005 were included. The records were scrutinized for clinical data. Information was available for 162 patients and 205 crowns.ResultsMost crowns (78%) were placed on premolars and molars. Out of the 143 crowns that were followed for 5 years, 126 (88%) did not have any complications. Of those with complications, the most common were: extraction of abutment tooth (7; 3%), loss of retention (15; 7%), need of endodontic treatment (9; 4%) and porcelain veneer fracture (6; 3%). No zirconia cores fractured. In total 19 restorations (9%) were recorded as failures: abutment tooth extraction (7), remake of crown due to lost retention (6), veneer fracture (4), persistent pain (1) and caries (1). The 5-year cumulative survival rate (CSR) was 88.8%.ConclusionsAccording to the present 5-year results zirconia crowns (NobelProcera?) are a promising prosthodontic alternative also in the premolar and molar regions. Out of the 143 crowns followed for 5 years, 126 (88%) did not have any complications. However, 9% of the restorations were judged as failures. Further studies are necessary to evaluate the long-term success.     

Fatigue analysis of computer‐aided design/computer‐aided manufacturing resin‐based composite vs. lithium disilicate glass‐ceramic

Resin‐based composite molar crowns made by computer‐aided design/computer‐aided manufacturing (CAD/CAM) systems have been proposed as an inexpensive alternative to metal‐ceramic or all‐ceramic crowns. However, there is a lack of scientific information regarding fatigue resistance. This study aimed to analyze the fatigue behavior of CAD/CAM resin‐based composite compared with lithium disilicate glass‐ceramic. One‐hundred and sixty bar‐shaped specimens were fabricated using resin‐based composite blocks [Lava Ultimate (LU); 3M/ESPE] and lithium disilicate glass‐ceramic [IPS e.max press (EMP); Ivoclar/Vivadent]. The specimens were divided into four groups: no treatment (NT); thermal cycling (TC); mechanical cycling (MC); and thermal cycling followed by mechanical cycling (TCMC). Thermal cycling was performed by alternate immersion in water baths of 5°C and 55°C for 5 × 10⁴ cycles. Mechanical cycling was performed in a three‐point bending test, with a maximum load of 40 N, for 1.2 × 10⁶ cycles. In addition, LU and EMP molar crowns were fabricated and subjected to fatigue treatments followed by load‐to‐failure testing. The flexural strength of LU was not severely reduced by the fatigue treatments. The fatigue treatments did not significantly affect the fracture resistance of LU molar crowns. The results demonstrate the potential of clinical application of CAD/CAM‐generated resin‐based composite molar crowns in terms of fatigue resistance.     

计算机辅助设计和制作全解剖形态氧化锆冠修复后牙牙体缺损的临床效果

目的探讨计算机辅助设计和制作系统制作全解剖形态氧化锆冠（全锆冠）修复后牙牙体缺损的即刻修复质量和短期疗效。方法选取36例后牙牙体缺损患者,使用计算机辅助设计和制作系统,制作40颗全锆冠,修复后即刻及1年采用改良的美国牙科协会评价标准对修复体进行评价,对患者进行满意度调查。结果 40例修复体1次戴牙成功率达100%,戴牙后1年患者满意率为100%。结论全解剖形态氧化锆冠短期疗效确切,可以作为后牙牙体缺损的有效修复方案。