Alumina‐reinforced zirconia implants: survival rate and fracture strength in a masticatory simulation trial

Background: Alumina‐toughened zirconia (ATZ) is a possible alternative material to titanium for oral implants. No data are available on the fracture strength of ATZ oral implants. Purpose: The purpose of this study was to examine one‐piece implants made of ATZ ceramic under artificial loading conditions and to compare the fracture strength of these implants with implants fabricated from tetragonal zirconium dioxide poylcrystal (TZP)‐A. Materials and methods: A total of 72 implants, 48 ATZ implants (groups A and B) and 24 TZP‐A implants (group C), were investigated. A chamfer preparation at the implant heads was performed on all implants of groups B and C. Eight implants of each group underwent 1.2 or five million thermomechanical loading cycles in the chewing simulator (load value: 98 N). Further eight implants of each group were not cyclic loaded. Finally, the fracture strength of all implants was determined using a universal testing machine. Results: No implant fractured during loading in the chewing simulator. All implants were placed in the universal testing machine to evaluate fracture strength. The mean fracture strength values±standard deviations for the implants without artificial loading were 1734±165 N (ATZ, no preparation), 1220±85 N (ATZ, with preparation), and 578±49 N (TZP‐A, with preparation); 1489±190 N (ATZ, no preparation), 1064±121 N (ATZ, with preparation), and 607±57 N (TZP‐A, with preparation) with 1.2 million loading cycles; and 1358±187 N (ATZ, no preparation), 1098±97 N (ATZ, with preparation), and 516±45 N (TZP‐A, with preparation) with five million cycles. The ATZ implants showed significantly higher mean fracture strengths compared with the TZP‐A implants. Modification of the implant head using diamond burs and increased loading time also led to a significant decrease in fracture strength. Conclusions: The ATZ implants showed an increased mechanical stability compared with the TZP‐A. Modification of the implant head resulted in a decrease in fracture strength. However, within the limits of this in vitro investigation it can be concluded that ATZ implants will withstand functional loading over an estimated period of 20 years. To cite this article:
Kohal R‐J, Wolkewitz M, Mueller C. Alumina‐reinforced zirconia implants: survival rate and fracture strength in a masticatory simulation trial.
Clin. Oral Impl. Res. 21 , 2010; 1345–1352.
doi: 10.1111/j.1600‐0501.2010.01954.x     

Promotion of osteoblast differentiation in 3D biomaterial micro-chip arrays comprising fibronectin-coated poly(methyl methacrylate) polycarbonate

Due to the architecture of solid body tissues including bone, three-dimensional (3D) in vitro microenvironments appear favorable, since herein cell growth proceeds under more physiological conditions compared to conventional 2D systems. In the present study we show that a 3D microenvironment comprising a fibronectin-coated PMMA/PC-based micro-chip promotes differentiation of primary human osteoblasts as reflected by the densely-packed 3D bone cell aggregates and expression of biomarkers indicating osteoblast differentiation. Morphogenesis and fluorescence dye-based live/dead staining revealed homogenous cell coverage of the microcavities of the chip array, whereat cells showed high viability up to 14 days. Moreover, Azur II staining proved formation of uniform sized multilayered aggregates, exhibiting progressive intracellular deposition of extracellular bone matrix constituents comprising fibronectin, osteocalcin and osteonectin from day 7 on. Compared to 2D monolayers, osteoblasts grown in the 3D chip environment displayed differential mostly higher gene expression for osteocalcin, osteonectin, and alkaline phosphatase, while collagen type I remained fairly constant in both culture environments. Our results indicate that the 3D microenvironment, based on the PMMA biomaterial chip array promotes osteoblast differentiation, and hereby renders a promising tool for tissue-specific in vitro preconditioning of osteoblasts designated for clinically-oriented bone augmentation or regeneration.     

The effects of cyclic loading and preparation on the fracture strength of zirconium-dioxide implants: an in vitro investigation

Objectives: Zirconia is a potential material for the fabrication of oral implants. The aim of this study was to evaluate the effects of cyclic loading and preparation on the fracture strength of a zirconia implant system. Materials and methods: Forty‐eight one‐piece implants were divided into two groups of 24 implants: group A (without modification) and group B (1 mm chamfer preparation). Groups A and B were divided into three subgroups of eight implants each (1=no artificial load, 2=artificial load [98 N; 1.2 million loading cycles], and 3=artificial load [98 N; 5 million loading cycles]). After completion of the loading, the fracture strength of each implant was determined in a universal testing machine. A two‐way analysis of variance was used, the continuous response variable (fracture strength in Newtons) is modeled as a function of preparation, cycles, and the corresponding interaction as explanatory variables. Results: The mean fracture strength values obtained for the groups were: A1 (no preparation, no load)=1928.73 N, A2 (no preparation, 1.2 million cycles)=2044.84 N, A3 (no preparation, 5 million cycles)=1364.50 N, B1 (preparation, no load)=1221.66 N, B2 (preparation, 1.2 million cycles)=967.11 N, and B3 (preparation, 5 million cycles)=884.89 N. Fracture values were significantly different between subgroups A1 vs. A3 and B1 vs. B3. There was no significant difference between subgroups A1 vs. A2 and B1 vs. B2. Conclusions: Preparation as well as cyclic loading can decrease the fracture strength resistance of zirconia implants. Nevertheless, even the lowest values of mean fracture strength of the implants used in our study seem to withstand average occlusal forces even after an extended interval of artificial loading. To cite this article:
Kohal RJ, Wolkewitz M, Tsakona A. The effects of cyclic loading and preparation on the fracture strength of zirconium‐dioxide implants: an in vitro investigation.
Clin. Oral Impl. Res. 22 , 2011; 808–814.
doi: 10.1111/j.1600‐0501.2010.02067.x     

Does an association between increased homocystein levels and cognitive dysfunction also exist in multimorbid geriatric patients

Background

Total blood homocysteine (Hcys) and folate have been investigated in association with cognitive dysfunction (CD) in healthy but not in multimorbid elderly patients. We hypothesized that total Hcys and folate are adequate markers to identify multimorbid elderly patients with CD.

Methods

According to the Short Performance Cognitive Test (SKT) CD was determined in a cross-sectional study with 189 (131 f/58 m) multimorbid elderly patients with a mean age of 78.6 ± 7.3 yrs. Besides the analyses of biochemical parameters (Hcys, folate, vitamin B₁₂, hemogram) nutritional status (BMI, Mini Nutritional Assessment) as well as activities of daily living were assessed. Daily nutritional intake was measured with a 3-day nutrition diary. For analysis, we used the nutritional software program DGE-PC professional.

Results

According to SKT 25.4% showed no cerebral cognitive dysfunction, 21.2% had a suspicion about incipient cognitive dysfunction, 12.7% showed mild, 9.0% moderate, 31.7% of patients severe cognitive deficits. Median plasma Hcys was about 20% elevated in multimorbid elderly patients independent of CD. Serum folate and vitamin B₁₂ levels were within range, though dietary folate intake (97 [80–128] µg/d) was reduced about 75% (recommendation 400 µg/d). Significant correlations between vitamin intake and plasma/serum levels of Hcys, folate and vitamin B₁₂ were not present. We did not find significant differences between SKT groups of nutritional status, activities of daily living, index of diseases, medications, or selected biochemical parameters.

Conclusion

We analysed elevated serum Hcys levels in multimorbid elderly patients with normal plasma folate and vitamin B₁₂ concentration and CD. Plasma Hcys or serum folate did not appear as an important biological risk factor on CD in multimorbid elderly patients.