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      Timing of loading and effect of micromotion on bone-dental implant interface: Review of experimental literature

      , , ,
      Journal of Biomedical Materials Research
      Wiley

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          Influence of surface characteristics on bone integration of titanium implants. A histomorphometric study in miniature pigs.

          The purpose of the present study was to evaluate the influence of different surface characteristics on bone integration of titanium implants. Hollow-cylinder implants with six different surfaces were placed in the metaphyses of the tibia and femur in six miniature pigs. After 3 and 6 weeks, the implants with surrounding bone were removed and analyzed in undecalcified transverse sections. The histologic examination revealed direct bone-implant contact for all implants. However, the morphometric analyses demonstrated significant differences in the percentage of bone-implant contact, when measured in cancellous bone. Electropolished as well as the sandblasted and acid pickled (medium grit; HF/HNO3) implant surfaces had the lowest percentage of bone contact with mean values ranging between 20 and 25%. Sandblasted implants with a large grit and titanium plasma-sprayed implants demonstrated 30-40% mean bone contact. The highest extent of bone-implant interface was observed in sandblasted and acid attacked surfaces (large grit; HCl/H2SO4) with mean values of 50-60%, and hydroxylapatite (HA)-coated implants with 60-70%. However, the HA coating consistently revealed signs of resorption. It can be concluded that the extent of bone-implant interface is positively correlated with an increasing roughness of the implant surface.
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            Biomechanical considerations in osseointegrated prostheses.

            On the basis of the previous discussions, several conclusions may be drawn. 1. The close apposition of bone to the titanium implant is the essential feature that allows a transmission of stress from the implant to the bone without any appreciable relative motion or abrasion. The absence of any intermediate fibrotic layer allows stress to be transmitted without any progressive change in the bond or contact between the bone and implant. 2. The use of a threaded screw provides a form of interlocking with the bone on a macroscopic scale that allows full development of the strength of the bone in shear or compression. A smooth, cylindrical implant may require an adhesive bond for satisfactory performance, but a screw shape is able to work as long as the apposition of bone and implant is close, whether or not a true adhesive bond is developed. 3. The distribution of a vertical or lateral load applied to a fixed partial denture depends on the number, arrangement, and stiffness of abutment fixtures used, as well as the form and stiffness of the fixed prosthesis itself. In general a stiff fixed partial denture will distribute loads to several fixtures more effectively. A flexible prosthesis may be adequate if the strength developed by each fixture is able to carry the full load that is applied. Cantilevered ends of a fixed partial denture increases the loading on the first screw nearest the cantilevered end. Moderate overhangs may be tolerated if the fixtures are sufficiently strong. 4. A tight connection of the fixed partial denture to fixtures provides a combined structure that can act in concert with the bone to provide a greater strength than that of the fixture or the jaw bone alone. 5. The osseointegrated implant provides a direct contact with bone and therefore will transmit any stress waves or shocks applied to the fixtures. For this reason it is advisable to use a shock-absorbing material such as acrylic resin in the form of acrylic resin artificial teeth in the fixed partial denture. This arrangement allows for the development of a stiff and strong substructure with adequate shock protection on its outer surface.
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              Tissue ingrowth into titanium and hydroxyapatite-coated implants during stable and unstable mechanical conditions.

              Lack of initial mechanical stability of cementless prostheses may be responsible for fibrous tissue fixation of prosthetic components to bone. To study the influence of micromovements on bony ingrowth into titanium alloy (Ti) and hydroxyapatite (HA)-coated implants, a loaded unstable device producing movements of 500 microns during each gait cycle was developed. Mechanically stable implants served as controls. The implants were inserted into the weight-bearing regions of all four femoral condyles in each of seven mature dogs. Histological analysis after 4 weeks of implantation showed a fibrous tissue membrane surrounding both Ti and HA-coated implants subjected to micromovements, whereas variable amounts of bony ingrowth were obtained in mechanically stable implants. The pushout test showed that the shear strength of unstable Ti and HA implants was significantly reduced as compared with the corresponding mechanically stable implants (p less than 0.01). However, shear strength values of unstable HA-coated implants were significantly greater than those of unstable Ti implants (p less than 0.01) and comparable to those of stable Ti implants. The greatest shear strength was obtained with stable HA-coated implants, which was threefold stronger as compared with the stable Ti implants (p less than 0.001). Quantitative determination of bony ingrowth agreed with the mechanical test except for the stronger anchorage of unstable HA implants as compared with unstable Ti implants, where no difference in bony ingrowth was found. Unstable HA-coated implants were surrounded by a fibrous membrane containing islands of fibrocartilage with higher collagen concentration, whereas fibrous connective tissue with lower collagen concentration was predominant around unstable Ti implants. In conclusion, micromovements between bone and implant inhibited bony ingrowth and led to the development of a fibrous membrane. The presence of fibrocartilage and a higher collagen concentration in the fibrous membrane may be responsible for the increased shear strength of unstable HA implants. Mechanically stable implants with HA coating had the strongest anchorage and the greatest amount of bony ingrowth.
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                Author and article information

                Journal
                Journal of Biomedical Materials Research
                J. Biomed. Mater. Res.
                Wiley
                0021-9304
                1097-4636
                22 1998
                22 1998
                : 43
                : 2
                : 192-203
                Article
                10.1002/(SICI)1097-4636(199822)43:2<192::AID-JBM14>3.0.CO;2-K
                9619438
                2533808d-5511-4af5-9139-a9a31653a86f
                © 1998

                http://doi.wiley.com/10.1002/tdm_license_1.1

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