Implant-borne suture expansion in rabbits: a histomorphometric study of the supporting bone.

Osseointegrated implants have a large potential for diverse clinical applications, including support for sutural expansion and facial prostheses. The objectives of this study were to evaluate: (1) the histomorphometric response of thin cortical bone to implant placement and (2) whether loading of the bone surrounding these implants affects osseointegration as evaluated by histomorphometry. Eighteen New Zealand White rabbits had two titanium implants placed bilaterally in the anterior surface of their nasal bones. The rabbits were divided into an unloaded control group, one experimental group loaded at 1 Newton (N), and another loaded at 3 N. Fluorescent labels were used to mark areas of active bone formation. All rabbits were euthanized after 12 weeks of loading. Stereological point-hit and line-intercept methods were used to measure bone volume, direct bone-implant contact, new bone volume, and bone turnover rate in the bone surrounding the implants. All the implants remained stable during the loading period. A factorial ANOVA with repeated measures was used to compare the variables. The only significant difference among the three groups was a higher bone volume in the lateral coronal far region in the control group (p < 0. 05). Within all groups, bone volume (p < 0.002), turnover rate (p < 0.001), and percent of new bone (p < 0.05) were higher within 1 mm of the implant compared to 1-3 mm away. This may be due to the increased stress and strain in the bone adjacent to the implant. This study indicates that there are no detrimental effects of loading on osseointegration when implants placed in the thin facial cortices are used as anchors for sutural expansion.

Sutural expansion using rigidly integrated endosseous implants: an experimental study in rabbits.

Rigidly integrated implants offer great promise for orthodontic and orthopedic anchorage in the oral and midfacial regions. Rigid anchorage can be used to control unwanted tooth movement, provide abutments in edentulous arches, and open the vertical dimension of occlusion. To evaluate the use of endosseous implants in the midface region, two flanged titanium implants were placed on either side of the midnasal suture of 18 New Zealand White rabbits. The rabbits were divided into an unloaded control and two experimental groups. One experimental group was loaded at 1 Newton (N) and the other at 3 N. All rabbits were euthanized after 12 weeks of loading. Stereologic point-hit and line-intercept methods were used to analyze microradiographic and multiple fluorochrome histology of the suture. All implants remained stable during the loading period. The distance between the implants increased significantly in the loaded groups compared with the control, and was significantly higher in the 3 N group than in the 1 N group. Percent bone volume was significantly decreased, while the percent suture volume tended to be increased in the loaded groups. Mineral apposition and bone formation rates at the sutural surfaces were increased in the loaded groups (P < 0.05), but did not differ between loaded groups. These results indicate that relatively low loads (1 or 3 N) applied to rigidly integrated endosseous implants across an unfused suture are satisfactory for achieving expansion under the conditions of this study. The 3 N load resulted in slightly more expansion, but did not affect the rate of bone formation at the suture.

Histomorphometrical analysis of the bone-implant interface: comparison of microradiography and brightfield microscopy.

Section thickness has been shown to affect the histomorphometrical measurement of bone-implant contact when analysed under brightfield microscopy. This study investigated whether microradiography of the bone-implant interface eliminated the errors associated with thick section analysis. Seven implant containing sections were utilized. Microadiographs of the thick (approximately 100 microns) sections were taken and the sections were subsequently ground to thicknesses of 50 microns and 25 microns. Photomicrographs were taken of the microradiographs and of the sections at each thickness (100, 50 and 25 microns) under brightfield microscopy. The photomicrographs were analysed for direct bone-implant contact in the cortical passage region and along the total length of the implant. The effect of section thickness on multiple fluorochrome labelling in 10 rabbit femur specimens was also examined. Centre-to-centre interlabel distance was measured for each label pair at a thickness of 100 microns and then again after the sections were ground to 50 microns and 25 microns. The thick (100 microns) sections showed a significantly greater amount of bone-implant contact than either the thin sections or the microradiographs. There was no difference in direct bone-implant contact measured by microradiography or thin sections. However, the microradiographic analysis showed a much lower variability of the bone-implant contact than the sections evaluated under brightfield microscopy. In addition, they have the added benefit of providing information on bone mineral density. Centre-to-centre interlabel distance was not significantly different for any label pair owing to section thickness. Data from this study provides evidence that the use of microradiographs for histomorphometrical analysis of the bone-implant interface is superior to brightfield analysis of thin sections owing to the lower variability of microradiographical data and the ability to obtain bone mineral density measures. Additionally, given that interlabel distance was not significantly affected by section thickness, the use of 100 microns thick sections for analysis of fluorochrome labels in cortical bone is supported.

The influence of surface-blasting on the incorporation of titanium-alloy implants in a rabbit intramedullary model.

The apposition of new bone to polished solid implants and to implants with surfaces that had been blasted with one of three methods of grit-blasting was studied in a rabbit intramedullary model to test the hypothesis that blasted implant surfaces support osseous integration. Intramedullary titanium-alloy (Ti-6Al-4V) plugs, press-fit into the distal aspect of the femoral canal, were implanted bilaterally in fifty-six rabbits. Four surface treatments were studied: polished (a surface roughness of 0.4 to 0.6 micrometer) and blasted with stainless-steel shot (a surface roughness of five to seven micrometers), with thirty-six-grit aluminum oxide (a surface roughness of five to seven micrometers), or with sixty-grit aluminum oxide (a surface roughness of three to five micrometers). Localized attachment of new bone to the surfaces of the blasted implants was present radiographically at twelve weeks. The total bone area was significantly affected by the level of the section (the diaphysis had a greater bone area than the proximal part of the metaphysis and the proximal part of the metaphysis had a greater bone area than the distal part of the metaphysis; p < 0.001) and the quadrant within each section (the posterior and anterior quadrants had greater bone area than the medial and lateral quadrants; p < 0.00001). The length of the bone-implant interface was significantly affected by the surface treatment (the length of the bone-implant interface for the implants that had been blasted with sixty-grit aluminum oxide was greater than the length for the polished implants; p = 0.02), the time after implantation (the interface was longer at six and twelve weeks than at three weeks; p < 0.00001), and the level of the section (the interface was longer at the diaphysis than at the proximal part of the metaphysis and longer at the proximal part of the metaphysis than at the distal part of the metaphysis; p = 0.004). Blasting of the surface of titanium-alloy implants did not have an effect on the area of bone formation around the implants, but it did significantly affect the area of bone formation on the implant and the shear strength at the bone-implant interface. The two effects were not necessarily parallel, as significantly less (p < 0.05) bone formed on implants that had been blasted with stainless-steel shot than on those blasted with aluminum grit, whereas their interface shear strengths were similar.

Remodeling dynamics of bone supporting rigidly fixed titanium implants: a histomorphometric comparison in four species including humans.

The long-term maintenance of a rigid bone-implant interface (osseointegration) is the clinical goal of most dental implant systems, although the biological mechanism for retaining a foreign object in living bone is unclear. Little data are available on the physiological turnover (remodeling) of the supporting osseous tissue. The objective of this study was to histomorphometrically assess bone remodeling surrounding rigidly integrated titanium implants in multiple species. Implants, in place from 6 months to 5 years, were recovered from human, monkey, dog, and rabbit subjects. With the use of stereological point-hit and linear-intercept methods, indices of bone formation and resorption were determined. Remarkably similar patterns emerged among all investigated species. Repeated-measures ANOVA showed a 3 to 9 fold increase in remodeling within 1 mm of the bone-implant interface (P<0.001; data expressed as percent turnover / month, mean +/- SEM for n = 3-11). All morphometric indices (percent new bone, percent fluorochrome-labeled bone, percent resorption space) showed similar trends. These data suggest that the physiological mechanism for maintaining rigid osseous integration (osseointegration) is a sustained elevation of remodeling adjacent to the bone-implant interface.

The influence of a hydroxyapatite and tricalcium-phosphate coating on bone growth into titanium fiber-metal implants.

A study was done in rabbits to determine the effect of a hydroxyapatite and tricalcium-phosphate coating on bone growth into titanium fiber-metal implants. Titanium fiber rods with a solid titanium core were implanted bilaterally into the distal aspect of the femora of fifty-five New Zealand White rabbits. One rod was uncoated and the other rod was surface-coated with hydroxyapatite and tricalcium phosphate by the plasma-spray technique. Thirty-five rabbits were labeled sequentially with fluorochromes; killed at one, two, three, four, six, twelve, or twenty-four weeks after the operation; and studied histologically and histomorphometrically. The implants in the remaining twenty rabbits were subjected to pull-out testing to determine the shear strength at the implant-bone interface at three, six, twelve, and twenty-four weeks after the operation. Histomorphometry revealed significant effects of the hydroxyapatite and tricalcium-phosphate coating. When whole-group means (which included all time-points) were compared, it was found that 44 per cent of the perimeter of the hydroxyapatite and tricalcium-phosphate-coated implants was covered with bone compared with 12 per cent of the perimeter of the uncoated implants. The percentage of the internal surface of the implant that was covered with bone was also significantly higher in the hydroxyapatite and tricalcium-phosphate-coated implants: 27 per cent of the internal surface of the coated implants was covered compared with 8 per cent in the uncoated implants. The amount of bone in the pores of the implants was also higher in the hydroxyapatite and tricalcium-phosphate-coated implants: 12 per cent of the available pore space in the hydroxyapatite and tricalcium-phosphate-coated implants was filled with bone compared with 4 per cent in the uncoated implants. Scanning electron microscopy of the implants, done in backscatter mode, demonstrated apposition of new bone directly on the hydroxyapatite and tricalcium-phosphate coating, with variable degrees (amounts) of hydroxyapatite and tricalcium-phosphate resorption and new-bone replacement over time. Bone was never directly apposed to uncoated titanium fiber-metal. The pull-out strength of the hydroxyapatite and tricalcium-phosphate-coated implants was consistently greater than that of the uncoated implants, at all time-periods.

Biochemical differentiation in large colonies of Enterobacter cloacae.

Large colonies of Enterobacter cloacae which were about 700 micrometer thick were frozen in liquid nitrogen and sectioned horizontally. The sections were disrupted and several oxidative enzymes were assayed in the crude unfractionated homogenates. In the top 120 micrometer of the colonies the specific activities of the enzymes were high and characteristic of aerobically adapted cells. Cells nearer the base of colonies had very low enzyme activities.