On-line analysis of CAL72 cells on two different titanium surfaces in a perfusion micro-bioreactor.

OBJECTIVES: The aim of the present experiment was to test a prototype microsensoric measuring system (micro-bioreactor) for the investigation of the biocompatibility of different titanium surfaces in a cell culture model. METHODS: Osteosarcoma cells of the cell line CAL72 were seeded onto titanium plates (10mm x 10mm x 1mm) and inserted into the culture chamber of the micro-bioreactor. Titanium plates with two different surface topographies (machined and titanium plasma-sprayed [TPS]) were used for this pilot investigation. Plastic plates served as controls. The online-sensoric device of the micro-bioreactor allowed the continuous monitoring of the metabolism of the cells and the control of the culture conditions. Over a period of 17 h changes in O(2)-consumption in the medium were measured by micro-electrodes and registered by the software of the system. The metabolic activity of the cells was calculated from the difference between the bypass and the chamber values. The cell proliferation and vitality were analyzed before and after the perfusion time in the micro-bioreactor. The cell morphology was studied using scanning electron microscopy. RESULTS: The cells on the machined surfaces showed the highest oxygen consumption after 15 h, after that it decreased. The cells on the TPS plates showed a lower oxygen consumption, which remained stable after 17 h. The highest oxygen consumption was seen with the cells on the control plastic plates. Concerning cell proliferation analysis, it could be shown that more vital CAL72 cells seeded onto TPS and plastic could be detected after the passage through the micro-bioreactor. Hence, the number of vital cells on the machined surface was reduced after the passage. SIGNIFICANCE: Within the limits of this experiment, the presented micro-bioreactor system could offer a valuable method to examine the dynamic interactions of cells and materials under defined in vitro experimental conditions. While the presented system is already successfully used in the ecological/ecotoxicological field, its routine use for investigating dental materials on a cellular level has to be evaluated.     

To splint or not to splint oral implants in the implant‐supported overdenture therapy? A systematic literature review

The objective of this systematic review was to assess the influence of splinted and unsplinted oral implants in the mandibular and maxillary implant-supported overdenture therapy, concerning the implant survival, the peri-implant parameters, the prosthetic complications and the patient satisfaction. An electronic MEDLINE search complemented by manual searching was conducted to identify randomized clinical trials, prospective and retrospective cohort studies on implant-supported overdentures with a mean follow-up of at least 3 years. Twelve studies from an initial yield of 1022 titles were finally selected and data were extracted. After an observation period of more than 3 years, there was no difference in implant survival rates between splinted and unsplinted design. From most of the investigations included in this study, it was mentioned that the unsplinted design needs more prosthetic maintenance. In more of the studies that were dealing with the satisfaction of the patients wearing implant-supported overdentures, no significant difference in the preference of the patients was reported. No significant difference in the peri-implant outcome between splinted and unsplinted design was found. Within the limits of this systematic review, it is concluded that there was no significant difference between the two different designs of implant-supported overdentures with respect to the soft tissue health status or patient satisfaction, although the bar-supported overdentures have been shown to need less prosthetic maintenance.     

In vitro reaction of human osteoblasts on alumina-toughened zirconia

Objectives: Alumina toughening enhances the mechanical properties of zirconia ceramics but the biocompatibility of this material has rarely been addressed. In this study, we examined the osteoblast response to alumina-toughened zirconia (ATZ) with different surface topographies.
Material and methods: Human osteoblasts isolated from maxillary biopsies of four patients were cultured and seeded onto disks of the following substrates: ATZ with a machined surface, airborne-particle abraded ATZ, airborne-particle abraded and acid etched ATZ. Airborne-particle abraded and acid etched titanium (SLA) and polystyrene disks served as a reference control. The surface topography of the various substrates was characterized by profilometry ( R _a, R _p−v) and scanning electron microscopy (SEM). Cell proliferation, cell-covered surface area, alkaline phophatase (ALP) and osteocalcin production were determined. The cell morphology was analyzed on SEM images.
Results: The surface roughness of ATZ was increased by airborne-particle abrasion, but with the R _a and R _p−v values showing significantly lower values compared with SLA titanium (Mann-Whitney U-test P <0.05). The proliferation assay revealed no statistically significant differences between the ATZ substrates, SLA titanium and polystyrene (Kruskal–Wallis test, P >0.05). All substrates were densely covered by osteoblasts. ALP and osteocalcin production was similar on the examined surfaces. Cell morphology analysis revealed flat-spread osteoblasts with cellular extensions on all substrates.
Conclusions: These results indicate that ATZ may be a viable substrate for the growth and differentiation of human osteoblasts. Surface modification of ATZ by airborne-particle abrasion alone or in combination with acid etching seems not to interfere with the growth and differentiation of the osteoblasts.     

Stability of prototype two-piece zirconia and titanium implants after artificial aging: an in vitro pilot study

Background: Zirconia oral implants are a new topic in implant dentistry. So far, no data are available on the biomechanical behavior of two‐piece zirconia implants. Therefore, the purpose of this pilot investigation was to test in vitro the fracture strength of two‐piece cylindrical zirconia implants after aging in a chewing simulator. Materials and Methods: This laboratory in vitro investigation comprised three different treatment groups. Each group consisted of 16 specimens. In group 1, two‐piece zirconia implants were restored with zirconia crowns (zirconia copings veneered with Triceram®; Esprident, Ispringen, Germany), and in group 2 zirconia implants received Empress® 2 single crowns (Ivoclar Vivadent AG, Schaan, Liechtenstein). The implants, including the abutments, in the two zirconia groups were identical. In group 3, similar titanium implants were reconstructed with porcelain‐fused‐to‐metal crowns. Eight samples of each group were submitted to artificial aging with a long‐term load test in the artificial mouth (chewing simulator). Subsequently, all not artificially aged samples and all artificially aged samples that survived the long‐term loading of each group were submitted to a fracture strength test in a universal testing machine. For the pairwise comparisons in the different test groups with or without artificial loading and between the different groups at a given artificial loading condition, the Wilcoxon rank‐sum test for independent samples was used. The significance level was set at 5%. Results: One sample of group 1 (veneer fracture), none of group 2, and six samples of group 3 (implant abutment screw fractures) failed while exposed to the artificial mouth. The values for the fracture strength after artificial loading with 1.2 million cycles for group 1 were between 45 and 377 N (mean: 275.7 N), in group 2 between 240 and 314 N (mean: 280.7 N), and in the titanium group between 45 and 582 N (mean: 165.7 N). The fracture strength results without artificial load for group 1 amounted to between 270 and 393 N (mean: 325.1 N), for group 2 between 235 and 321 N (mean: 281.8 N), and between 474 and 765 N (mean: 595.2 N) for the titanium group. The failure mode during the fracture testing in the zirconia implant groups was a fracture of the implant head and a bending/fracture of the abutment screw in the titanium group. Conclusions: Within the limits of this pilot investigation, the biomechanical stability of all tested prototype implant groups seems to be – compared with the possibly exerted occlusal forces – borderline for clinical use. A high number of failures occurred already during the artificial loading in the titanium group at the abutment screw level. The zirconia implant groups showed irreparable implant head fractures at relatively low fracture loads. Therefore, the clinical use of the presented prototype implants has to be questioned.     

Comparison of bioabsorbable and bioinert membranes for guided bone regeneration around non‐submerged implants. An experimental study in the mongrel dog.

The aim of this clinical investigation was to evaluate the effect of guided bone regeneration around non-submerged implants using different barrier membranes. Five adult mongrel dogs were used in this investigation. After having all premolars extracted and implant osteotomies performed in the regions of the former premolars, buccal bone defects were created. Subsequently, 3 implants were placed and the defects treated with 1 of the following 3 modalities: a) guided bone regeneration using an expanded polytetrafluoroethylene membrane, b) guided bone regeneration using a bioabsorbable membrane made from a synthetic copolymer of glycolide and lactide and c) no membrane application. Following implant and membrane placement, the mucoperiosteal flaps were repositioned and tightly sutured around the neck of the implants allowing for a non-submerged healing. After a healing period of 6 months, the animals were sacrificed and the specimens processed for histologic evaluation. The clinical pre-treatment defects between the different treatment groups were not statistically different (bioinert membrane group: 4.9 mm; control group: 4.8 mm; bioabsorbable membrane group: 4.5 mm). The remaining histological defects after 6 months of healing amounted to approximately 2.5 mm in the bioinert membrane group, 5.7 mm in the control group and 6.0 mm in the bioabsorbable membrane group. A significant difference was observed between the bioinert membrane group and the other 2 groups. The mineralized bone-to-implant contact in the bioinert membrane group was 51.5%, in the control group 46.3% and in the bioabsorbable membrane group 37.5%. The values between the bioinert membrane group and the bioabsorbable membrane group were statistically different. The results of this study indicate that bone regeneration with bioinert e-PTFE membranes around non-submerged implants is possible. The utilized absorbable polyglycolic/polylactid membrane did not show any bone regenerative effect and the results did not differ from the control group without membrane application.