الفهرس 
REVIEW OF LITRATUREOnly 14 pages are availabe for public view
 |  | from | 185 |  |  |
| | | from | 185 | | |
Abstract
The aim of this study was to investigate 2 relatively economic fabrication methods to produce simple-design zirconia implant specimens. The two implant designs attempted were: a cylindrical implant with a 4 mm diameter and 8 mm length having either a plain or vertically grooved surfaces as an incorporated macrofeatures. The second design was a screw from implant specimen having a 3.7 diameter and 8 mm length with either a square thread or a buttress thread variations.
The first fabrication technique relied on scanning metal analogues of different implant specimens in the CAD/CAM system, then machining at least 5 implants out of a single zirconia presintered block. The second technique was accomplished by carefully compressing fine zirconia powder inside a destructible investment mold having internally all the design features previously described but magnified up to 30% to compensate for shrinkage during the sintering cycle.
The CAD/CAM fabrication method produced four groups of zirconia specimens:
group I: CAD-CAM plain cylinders.
group II: CAD-CAM grooved cylinders.
group III: CAD-CAM screw stepped implants”square thread”
group IV: CAD-CAM screw thread implants”buttress thread”
The compression method only produced 2 groups
group V: Compression molding plain cylinders.
group VI: Compression molding grooved cylinders
Specimens fabricated by both techniques were examined at specific parameters to assess fabrication methods, and both techniques showed some shortcomings necessitating further refinements.
Regarding evaluation of physical properties, all specimens were tested for bulk density and total porosity using mercury intrusion porosimeter, and for surface roughness using portable profilometer. For the purpose of mechanical evaluation, all specimens were loaded whether statically to failure or dynamically for 2 million cycles in wet condition and their surfaces tested using microhardness indenter. Sample size (n) was 5 specimens per group for each previously mentioned tests.
For evaluation of osseointegration, 7 groups of Spain V line rabbits were used, each containing 5 animals. Each animal group received a total of 10 zirconia specimens representing one of the 6 groups of zirconia used in this study, one implant in each hind limb. The seventh animal group received 10 commercially available titanium implants. At sacrifice time, half of the specimens were used for histological and histomorphometric examination and the other half was removed in block to perform reverse torque testing.
Results for physical properties revealed that compression cylinders (2 groups) had statistically higher porosity percentage and surface roughness values than other groups while CAD/CAM groups had statistically higher bulk densities. Results of mechanical properties showed that any CAD/ CAM fabricated group had a statistically higher Vickers hardness value than any other compression molded group. Also CAD/CAM groups were virtually unbreakable under the static and dynamic test conditions performed in this study. Whereas the compression cylinders withstood static loading of values higher than those recorded in anterior region of the mouth, they suffered various cracking patterns under dynamic fatigue.
All specimens and control groups showed similar osseointegration and biocompatibility behavior evidenced by well formed mature bone around them. Titanium control group demonstrated significantly higher bone implant contact and reverse torque values followed closely by zirconia screws with buttress threads. Bone density around implants was significantly higher around zirconia screws with buttress threads than any other tested groups. Machined cylinders generally showed inferior morphometric and removal torque values than same designs fabricated by compression molding. Vertical grooves as a macrofeature to zirconia cylinders did not elicit any significant favorable biological effects.