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.     

F掺杂对纳米Al_2O_3/HA复合陶瓷的结构与性能影响

本研究采用化学沉淀法制备了纳米Al_2O_3/HA复合粉体,采用热压烧结法制备了Al_2O_3/HA复合生物陶瓷,并研究了F掺杂量对复合陶瓷物相组成和力学性能的影响。结果证明复合陶瓷的力学性能随着F掺杂量的提高而逐渐增大,当F掺杂量x=1时,复合陶瓷的力学性能最佳,其弯曲强度和断裂韧性分别为147.2 MPa和2.19 MPa·m~(1/2)。当F掺杂量高于0.5时,可以抑制复合陶瓷中HA的分解,并且在烧结过程中有AlF3相生成,可促进复合陶瓷的致密化。F掺杂可以提高复合陶瓷的生物活性,但是F掺杂量对复合陶瓷的生物活性影响不大。     

Osseointegration of zirconia dental implants in animal investigations: A systematic review and meta-analysis

Objective

To determine the osseointegration rate of zirconium dioxide (ZrO₂) dental implants in preclinical investigations.

临床常用四种全瓷贴面材料光学性能的比较

目的 比较4种临床常用全瓷贴面修复材料的色彩参数和透光率,以期为临床提供参考.方法 制作IPS Empress(R) CAD(高透光率A2色)、IPS e.max(R) Press(高透光率A2色)、IPS e.max(R)CAD(高透光率A2色)及VITABLOCS(R) MarkⅡ(A2色)4种瓷材料的片状试件,分别设为A、B、C、D组,每组10个试件,打磨抛光后控制试件厚度为(1.00±0.01) mm.使用分光测色计和透光率测试仪测量每组试件明度(L*值)、红绿色品(a*值)和黄蓝色品(b*值)及可见光积分透射比(T),计算彩度(C*ab值)以及各组试件与A2色标准比色片的色差(△E).结果 A和D组L*、a*、b*及C*ab值间差异均无统计学意义(P＞0.05),但与B、C组L*、a*、b*及C*ab值间差异均有统计学意义(P＜0.05);B、C组b*及C*ab值间差异均无统计学意义(P＞0.05),但两组L*及a*值间差异均有统计学意义(P＜0.05).A、B、C、D组瓷材料与A2色标准比色片的色差(△E)分别为6.05±0.12、5.11±0.27、3.73±0.27和6.30±0.38;T依次为(29.69±0.31)％、(25.83±0.36)％、(28.92±0.47)％和(26.94±0.33)％.结论 4种瓷贴面材料的色彩参数存在一定差异,均有较高的透光率.瓷材料C与A2色标准比色片的色差最小.     

Biaxial flexural strength of Turkom-Cera core compared to two other all-ceramic systems

Advances in all-ceramic systems have established predictable means of providing metal-free aesthetic and biocompatible materials. These materials must have sufficient strength to be a practical treatment alternative for the fabrication of crowns and fixed partial dentures.

Objectives

The aim of this study was to compare the biaxial flexural strength of three core ceramic materials.

Material and methods

Three groups of 10 disc-shaped specimens (16 mm diameter x 1.2 mm thickness - in accordance with ISO-6872, 1995) were made from the following ceramic materials: Turkom-Cera Fused Alumina [(Turkom-Ceramic (M) Sdn Bhd, Puchong, Selangor, Malaysia)], In-Ceram (Vita Zahnfabrik, Bad Säckingen, Baden-Württemberg, Germany) and Vitadur-N (Vita Zahnfabrik, Bad Säckingen, Baden-Württemberg, Germany), which were sintered according to the manufacturer''s recommendations. The specimens were subjected to biaxial flexural strength test in a universal testing machine at a crosshead speed of 0.5 mm/min. The definitive fracture load was recorded for each specimen and the biaxial flexural strength was calculated from an equation in accordance with ISO-6872.

Results

The mean biaxial flexural strength values were: Turkom-Cera: 506.8±87.01 MPa, In-Ceram: 347.4±28.83 MPa and Vitadur-N: 128.7±12.72 MPa. The results were analyzed by the Levene''s test and Dunnett''s T3 post-hoc test (SPSS software V11.5.0 for Windows, SPSS, Chicago, IL, USA ) at a preset significance level of 5% because of unequal group variances (P<0.001). There was statistically significant difference between the three core ceramics (P<0.05). Turkom-Cera showed the highest biaxial flexural strength, followed by In-Ceram and Vitadur-N.

Conclusions

Turkom-Cera core had significantly higher flexural strength than In-Ceram and Vitadur-N ceramic core materials.     

EFFECT OF CYCLIC LOADING ON FRACTURE STRENGTH OF ENDODONTICALLY TREATED TEETH RESTORED WITH CONVENTIONAL AND ESTHETIC POSTS

Introduction:

Esthetic post and core systems were recently introduced. There are few reports regarding their behavior under cyclic loading.

Objectives:

This study compared the effect of cyclic loading on survival rate, residual strength and mode of fracture of endodontically treated teeth restored with esthetic and direct metallic post systems subjected to mechanical cyclic loading.

Materials and Methods:

Thirty canines were endodontically treated, decoronated and prepared for metal free ceramic crowns, leaving 1.5 mm of dentin for ferrule effect. They were distributed in 3 groups and restored as follows: group 1 with zirconia posts (Cosmopost) and glass-ceramic cores (IPS Empress Cosmopost); group 2 with fiber reinforced composite posts (FibreKor) and group 3 with titanium posts (AZthec Anchor). Direct resin composite (Build It FR Resin Composite) was used as core in groups 2 and 3. All specimens were restored with all ceramic crowns (IPS Empress 2). A resin cement/adhesive system (Cement It/Bond It Primer A+B) was used to lute the posts to root canals and metal free porcelain crowns to the teeth preparation. Specimens were subjected to mechanical load of 250 N for 500,000x at a frequency of 1.7 Hz and then to static load until failure in a universal testing machine. Data were analyzed using One-way ANOVA and Fischer Exact tests α=0.05.

Results:

All groups had 100% survival rate after cyclic loading; fracture strength values (SD) in N were: group 1 = 886.5(170.6), group 2 = 762.2(113.6) and group 3 = 768.9(72.9); there was no difference among groups (p=0.08); the percentage of mode of favorable fracture found was: group 1 = 60%, group 2 = 90% and group 3 = 50%; there was no correlation between the mode of failure and post and core system used (P=0.142).

Conclusions:

Esthetic post and core systems showed statistically equivalent fracture strength values, mode of failure and survival rate compared to conventional direct metallic post and resin composite core system after cyclic loading.     

Void filling of tibia compression fracture zones using a novel resorbable nanocrystalline hydroxyapatite paste in combination with a hydroxyapatite ceramic core: first clinical results

Introduction

It is a generally accepted standard surgical practice to fill-in the metaphyseal defect zones resulting from the reduction of tibia compression fractures. The development of various innovative bone substitutes is also currently on the increase.

Materials and methods

In our prospective study, we used Ostim^®, a novel resorbable nanocrystalline hydroxyapatite paste, together with Cerabone^®, a solid hydroxyapatite ceramic, in combination with angularly stable osteosynthesis to treat 24 tibia compression fractures. Types B2 and B3, as well as types C2 and C3 fractures, according to the AO classification, were included in the study.

Results

The mean total range of joint motion in terms of flexion and extension was improved from the immediate postoperative value of 79 ± 14° to 97 ± 13° at 6 weeks after surgery, to 109 ± 16° at 3 months, and finally to 118 ± 17° at 1 year. In three patients, a delayed wound healing was observed as a local complication.

Conclusion

The use of the Ostim^® and Cerabone^® combination is an effective method in treating tibia compression fractures with large defect zones left after reduction.     

骨组织工程材料的研究进展

细胞外基质(ECM)的构建是骨组织工程研究中一项主要的工作。本文阐述了理想骨组织工程基质材料的要求,介绍了几种可降解材料在骨组织工程中的应用现状。作者认为,新型基质材料必将在未来骨组织工程研究中展示出可喜的应用前景。     

Color stability of fully- and pre-crystalized chair-side CAD-CAM lithium disilicate restorations after required and additional sintering processes

PURPOSEThe aim of this study was to investigate shade changes in fully- and pre-crystalized CAD-CAM lithium disilicate crowns after the required and additional firing processes.MATERIALS AND METHODSOne hundred and five crowns of shade A1 with high translucency were milled out of CAD-CAM lithium disilicate blocks and categorized as follows (n = 15): (1) restorations fabricated from Straumann n!ce with no additional sintering process; (2) restorations fabricated from Straumann n!ce with one additional sintering process; (3) restorations fabricated from Straumann n!ce with two additional sintering processes; (4) restorations fabricated from Amber Mill with one sintering process; (5) restorations fabricated from Amber Mill with two sintering processes; (6) restorations fabricated from IPS e.max CAD with one sintering process; (7) restorations fabricated from IPS e.max CAD with two sintering processes. All restorations were evaluated with a color imaging spectrophotometer.RESULTSAll restorations presented some color alteration from the original shade both after a single and after two firing processes.CONCLUSIONThe required and additional sintering processes for restorations fabricated with chairside CAD-CAM lithium disilicate blocks cause an alteration of the original shade selected. Shade A1 high translucency restorations tend to change to a more yellowish B1 shade after a sintering process.