Biomedical subjects

L Gionso

Publications and source records attributed to L Gionso.

4 recordsLinked to original sources

PubMed2000

Experimental and computational approach for the evaluation of the biomechanical effects of dental bridge misfit.

Dental bridges supported by osseointegrated implants are commonly used to treat the partially or completely edentulous jaw. The bridges are manufactured in metal alloy using a sequence of technological steps which well match the requirement to get custom overstructures but does not guarantee geometrical and dimensional tolerances. Dentists often experience that a perfect fit of the bridge with the abutments is almost impossible to achieve. When a misfitting bridge is forced on the abutments, deformations may occur inducing a permanent preload at the fixture-bone interface and the greater the misfit the greater is the preload and the risk of implant failure. This work gives an evaluation of the biomechanical effects induced by a misfitting bridge when forced on two supporting dental implants. The strains induced in the bridge have been measured using two purposely designed and fabricated experimental devices allowing different types of misfit. FEM 3D models of the bridge and of the bridge anchored to the bone by implants have been developed. The former has been validated by simulating the same loading conditions as in the experimental tests and comparing the bridge strains. Both models have been used for the evaluation of the stress induced in the bridge and at the fixture-bone interface by bridge length errors. The results show that the method may help to estimate the stress distribution in the bridge and bone as a consequence of different dental bridge misfits.

Biomechanical Phenomena↗

PubMed2000

An in vitro study on compensation of mismatch of screw versus cement-retained implant supported fixed prostheses.

In common practice a perfect fit of the prosthetic framework with the implant abutments is almost impossible to achieve. The mismatch, which is principally induced by the technological process adopted to manufacture the fixed prostheses, strains the framework thus generating constraint reactions. These are static forces that load the implant components and the bone at the implant-bone interface and may cause the bone remodelling. Depending on the magnitude of such forces, i.e. depending on the magnitude of the mismatch, the bone remodelling may lead to the loosening of the screws and of the implant-bone interface and hence cause implant failure. The present study shows an in vitro comparison of 3 different connecting abutments (standard, EsthetiCone and CerAdapt, Nobel Biocare AB, Göteborg, Sweden) with relation to the mechanical stresses induced by geometrical mismatches (technology induced errors). Two experimental devices were purposely realized and used to assess the ability of the different abutments to compensate errors. One was designed for translation errors and the other for rotation errors. The experimental apparatus set-up includes 2 freestanding implants supporting a prosthetic structure and the connecting abutments. The implants and the abutments were used as delivered by the manufacturer, while the prostheses were purposely realized and instrumented with strain gauges. The data obtained with the error devices do not give quantitative information on what happens in clinical applications where the implants are connected to living bone, which is a tissue much more deformable than the steel used for the error devices. Results allow direct comparisons of the behaviour of the different investigated abutments with respect to position errors. The CerAdapt system (cement retained ceramic abutments) showed the least strain in presence of translation errors. The standard system (screw retained abutments) showed the least strain in presence of rotation errors.

Biomechanical Phenomena↗

PubMedDate not supplied

Guided bone regeneration using resorbable and nonresorbable membranes: a comparative histologic study in humans.

Resorbable membranes of poly(lactic acid) and poly(glycolic acid) (PLA/PGA) were compared to nonresorbable expanded polytetrafluoroethylene (e-PTFE) membranes in the treatment of defects around titanium dental implants placed in postextraction sockets. Two partially edentulous and three completely edentulous patients requiring implant-supported restorations participated. Sixteen Brånemark implants were placed into extraction sockets and covered with modified titanium cover screws, called harvest cover screws, which allow tissue biopsy at second-stage implant surgery. Seven defects were treated with PLA/PGA membranes, five were treated with e-PTFE membranes, and four were left untreated (control sites). After 6 months of healing, the harvest cover screws were retrieved and processed for light microscopy examination together with the regenerated tissues. Very little or no bone formation was detected in control specimens. The e-PTFE membranes were found to be the most effective barrier material, in that denser and a greater amount of regenerated bone was found. The PLA/PGA membranes produced some bone regeneration when compared to control sites, but to a lesser extent compared to e-PTFE sites.

Adult↗

PubMedDate not supplied

Treatment of dehiscences and fenestrations around dental implants using resorbable and nonresorbable membranes associated with bone autografts: a comparative clinical study.

This study was carried out to evaluate the efficacy of poly(lactic acid) and poly(glycolic acid) (PLA/PGA) resorbable membranes in conjunction with autogenous bone grafts when used for the treatment of implant dehiscences and/or fenestrations. Nine patients with a total of 18 implants participated. Nine implants were associated with dehiscences, and 9 with fenestrations; 16 implants were in the maxilla, and 2 in the mandible. Nine defects were treated with PLA/PGA membranes (test group), and the nine were treated with expanded polytetrafluoroethylene (e-PTFE) membranes (control group). Second-stage surgery was performed after 6 to 7 months of healing. Overall results of the regenerative therapy of the 18 defects showed a highly significant (P < .001) defect reduction, with a 93.38% (SD = 15.88) bone fill. A slightly higher percentage of bone fill was found in the e-PTFE group (98.20%) than in the PLA/PGA group (88.56%), but the difference was not statistically significant (P = .207). This study demonstrated that resorbable PLA/PGA membranes can be equally effective as e-PTFE in the treatment of implant dehiscences and fenestrations when associated with autogenous bone chips.

Adult↗