Porous ceramic materials as immediate root implants

Experimental reconstruction of the mandible using polylactic acid tubes and basic fibroblast growth factor in alloplastic scaffolds

PURPOSE

This study evaluated the use of a mitogenic growth factor in combination with barrier membranes and porous alloplastic scaffolds for the repair of segmental defects of the mandible.

MATERIALS AND METHODS

Fifteen Göttingen minipigs were used for the study. In five animals, mandibular defects of 2 cm were created on both sides of the mandible and bridged by a system of polylactic acid (PLA) tubes and pyrolized bovine bone. On one side of the mandible, the alloplastic scaffolds were loaded with 115 microg recombinant human basic fibroblast growth factor (rhbFGF). In five other animals, defects 4 cm in length were created bilaterally, similarly bridged, and loaded with 230 microg of rhFGF. In five control animals, bilateral 2-cm defects were created that were left empty on one side and bridged with an empty PLA tube on the other. Mitogenic efficacy of the growth factor was assessed on fibroblast cultures by di-methyl-thiazol-2-tetrazolium-bromide assay before implantation.

RESULTS

After 5 months, there was negligible bone regeneration in the control defects, regardless of whether they had been left completely empty or bridged by empty PLA tubes. The 2-cm defects showed bridging in 8 of 10 tubes, with complete consolidation by bone ingrowth in four defects. The 4-cm defects showed bony union in six cases, with complete bone fill in two tubes, and four defects incompletely filled. The bFGF had no appreciable effect with regard to velocity, quantity, and three-dimensional structure of bone formation, neither in the short nor in the long defects despite clear in vitro efficacy.

CONCLUSION

Repair of segmental defects using bioresorbable membranes appears to be possible. However, a single-dose application of bFGF is apparently ineffective, possibly because of rapid dilution.

Influence of pore dimensions on bone ingrowth into porous hydroxylapatite blocks used as bone graft substitutes. A histometric study

The aim of the present study was to determine the influence of pore dimensions of porous hydroxylapatite (HA) blocks on bone ingrowth when used as interposed grafts in alveolar ridge bone defects. HA blocks with pore diameters of 150 microns and 260 microns were used. Ten animals received one implant each with small pore sizes, whilst in 10 other animals blocks with larger pore sizes were used. The blocks were examined histometrically and spatially reconstructed for determination of 3-dimensional distribution of bone ingrowth. In the group of implants with 150 microns pore diameter a high rate of implant loss occurred. The blocks with 260 microns pore diameter had 3 times more bone ingrowth compared with the 150 microns group with uniform distribution.

Designing to counteract the effects of initial device instability: materials and engineering

Implants for hard tissue replacement have evolved over the last few decades, but a critical assessment of their design reveals that most dental implants and most orthopedic appliances for any given indication are basically similar in design to their commercial competitors. Some unique features are contained in the outer 0.7 mm, but shadow pictures of the devices could almost be superimposed upon one another. Near-optimal designs have evolved for the materials systems commonly in use. The fight to minimize initial instability of implants, which leads to failure, has caused certain attachment mechanisms to emerge as acceptable, based upon research that indicates firm fixation in bone has resulted in longer average implant lifetime. The problem of initial stabilization is one of materials and design, both of which are necessary for a successful implant system. The nonmetallic calcium phosphate glass and ceramics technology available today provides materials that may counteract the effects of initial device instability by not relying on mechanical means of retention, alone, but chemical as well.

Effect of the surface geometry of smooth and porous-coated titanium alloy on the orientation of fibroblasts in vitro

The migration and orientation of human gingival fibroblasts in relation to the rim of smooth-surfaced and porous-coated titanium discs placed on multilayers in vitro was investigated. Samples were examined after 6 h, 24 h, 3 days, and 7 days of culture using phase-contrast and scanning electron microscopy. The cells migrated from the multilayer onto the smooth-surfaced discs forming bridges between them, and orientated along parallel circumferential grooves in the rim of the discs. This resulted in the cellular bridges orientating at an acute angle to the rim of the disc, and adjacent cells in the multilayer orientating parallel to the rim. Cellular bridges were also formed between the porous-coated discs and the multilayer but, because the cells that migrated onto, and between, the spheres of the porous-coat showed no preferred orientation, the bridges retained their orientation at right angles to the surface of the rim. This in turn resulted in the cells of the adjacent multilayer becoming similarly orientated. These observations suggest that the geometrical configuration of the surface of implants could influence whether a capsule or an orientated fibrous attachment is developed in relation to implants in vivo.