Hydroxyapatite (HA)-coated implants were developed to promote osseointegration of titanium implants and to overcome the mechanical drawbacks of solid HA implants. Although many clinical reports on the prognosis of HA-coated implants have reported high success rates, the risks of dissolution and weakening of the coating have been noted. We hypothesized that the chemical and mechanical stability of HA coating are affected by its microstructural characteristics. The present study investigates differences in the microstructures of available HA-coated implants, before and after implantation into the coxal bones of dogs for periods ranging from 3 weeks to 10 months and under the coxal periosteum of dogs for 10 months. The results of transmission electron microscopy and energy-dispersive x-ray analysis revealed that crystallization of super-fine HA crystals occurred in the amorphous phase of the HA coating and progressed over time. This crystallization weakens HA-coated implants by making the amorphous phase brittle, causing stress accumulation within the coating, and causing a decrease in the binding strength between the coating and the substrate. Furthermore, the HA coating dissolved in soft tissue. Dissolution started with the super-fine HA crystals in the crystallized portion that was originally part of the amorphous phase.
Adell R., Lekholm U., Rockler B., Branemark P-I. (1981). A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg10:387-416.
2.
Block MS, Kent JN, Kay JF (1987). Evaluation of hydroxylapatite-coated titanium dental implants in dogs. J Oral Maxillofac Surg45:601-607.
3.
Chen J., Tong W., Cao Y., Feng J., Zhang X. (1997). Effect of atmosphere on phase transformation in plasma-sprayed hydroxyapatite coatings during heat treatment. J Biomed Mater Res34:15-20.
4.
Cook SD, Kay JF, Thomas KA, Jarcho M. (1987). Interface mechanics and histology of titanium and hydroxylapatite-coated titanium for dental implant applications. Int J Oral Maxillofac Implants2:15-22.
5.
Cook SD, Thomas KA, Dalton JE, Volkman TK, Whitecloud TS, Kay JF (1992). Hydroxylapatite coating of porous implants improves bone ingrowth and interface attachment strength. J Biomed Mater Res26:989-1001.
6.
De Groot K., Geesink R., Klein CP, Serekian P. (1987). Plasma sprayed coatings of hydroxylapatite. J Biomed Mater Res21:1375-1381.
7.
Denissen HW, Kalk W., Veldhuis Aah, Van Den Hooff A. (1989). Eleven-year study of hydroxyapatite implant. J Prosthet Dent61:706-712.
8.
Denissen HW, De Nieuport HM, Kalk W., Schaeken HG, Van De Hooff A. (1991). Fluorapatite and hydroxyapatite heat-treated coatings for dental implants. In: Bioceramic and human body. Ravaglia A, Krajewski A, editors. Amsterdam: Elsevier, pp. 130-140.
9.
Ducheyne P., Raemdonck WV, Heughebaert JC, Heughebaert M. (1986). Structural analysis of hydroxyapatite coatings on titanium. Biomaterials7:97-103.
10.
Ducheyne P., Radin S., King L. ( 1993). The effect of calcium phosphate ceramic composition and structure on in vivo behavior. 1. Dissolution. J Biomed Mater Res27:25-34.
11.
Golec TS, Krauser JT (1992). Long-term retrospective studies on hydroxyapatite coated endosteal and subperiosteal implants. Dent Clin North Am36:39-65.
12.
Gottlander M., Albrektsson T. (1991). Histomorphometric studies of hydroxylapatite-coated and uncoated CP titanium threaded implants in bone. Int J Oral Maxillofac Implants6:399-404.
13.
Henry PJ, Bower RC, Wall CD ( 1995). Rehabilitation of the edentulous mandible with osseointegrated dental implant: 10-year follow-up. Aust Dent J40:1-9.
14.
Huaxia JI, Ponton CB, Marquis PM (1992). Microstructural characterization of hydroxyapatite coating on titanium. J Mater Sci Mater Med3:283-287.
15.
Jaffin RA, Berman CL (1991). The excessive loss of Branemark fixtures in Type IV bone: A 5-year analysis. J Periodontol62:2-4.
16.
Jarcho M. (1992). Retrospective analysis of hydroxyapatite development for oral implant applications. Dent Clin North Am36:19-26.
17.
Johns RB, Jemt T., Heath MR, Hutton JE, McKenna S., McNamara DC, et al. (1992). A multicenter study of overdentures supported by Branemark implants. Int Oral Maxillofac Implants7:513-522.
18.
Johnson BW (1992). HA-coated dental implants: long-term consequences . J CA Dent Assoc20:33-41.
19.
Kay JF, Golec TS, Riley RL (1987). Hydroxyapatite-coated subperiosteal dental implants: Design rationale and clinical experience. J Prosthet Dent58:339-343.
20.
Kent JN, Block MS, Finger IM, Guerra L., Larsen H., Misiek DJ (1990). Biointegrated hydroxylapatite-coated dental implants: five-year clinical observations. J Am Dent Assoc121:138-144.
21.
Klein CP, Wolke JG, De Bleich-Hogervorst JM, De Groot K. (1994). Calcium phosphate plasma-sprayed coatings and their stability: An in vivo study. J Biomed Mater Res28 :909-917.
22.
Koch B., Wolke JG, De Groot K. (1990). X-ray diffraction studies on plasma sprayed calcium phosphate-coated implant. J Biomed Mater Res24:655-667.
23.
Lewandowski JA, Johnson CM (1989). Structural failure of osseointegrated implants at the time of restoration. A clinical report. J Prosthet Dent62:127-129.
24.
Ogiso M., Tabata T., Ichijo T., Borgese D. (1992a). Bone calcification on the hydroxyapatite dental implant and the bone-hydroxyapatite interface. J Long-Term Effects Med Implants2:137-148.
25.
Ogiso M., Tabata T., Ichijo T., Borgese D. (1992b). Examination of human bone surrounded by a dense hydroxyapatite dental implant after long-term use. J Long-Term Effects Med Implants2:235-247.
26.
Ogiso M., Tabata T., Kuo PT, Borgese D. (1994). A histologic comparison of the functional loading capacity of an occluded dense apatite implant and the natural dentition. J Prosthet Dent71:581-588.
27.
Ogiso M., Nakabayashi N., Matsumoto T., Yamamura M. , Lee RR (1996). Adhesive improvement of the mechanical properties of a dense HA-cemented Ti dental implant. J Biomed Mater Res30:109-116.
28.
Ogiso M., Yamamura M., Kuo PT, Borgese D., Matsumoto T. (1998). A comparative push-out test of dense HA implants and HA-coated implants: Findings in a canine study. J Biomed Mater Res39:364-372.
29.
Oonishi H., Yamamoto M., Ishimaru H., Tsuji E., Kushitani S., Aono M., et al. (1989). The effect of hydroxyapatite coating on bone growth into porous titanium alloy implants. J Bone Joint Surg71[Br]:213-216.
30.
Pilliar RM, Deporter DA, Watson PA, Pharoah M., Chipman M., Valiquette N., et al. (1991). The effect of partial coating with hydroxyapatite on bone remodelling in relation to porous-coated titanium-alloy dental implants in the dog. J Dent Res70:1338-1345.
31.
Radin SR, Ducheyne P. (1992). Plasma spraying induced changes of calcium phosphate ceramic characteristics and the effect on in vitro stability. J Mater Sci Mater Med3:33-42.
32.
Saadoun AP, LeGall ML (1992). Clinical results and guidelines in Steri-Oss endosseous implants. Int J Periodont Rest Dent12:486-495.
33.
Thomas KA, Cook SD ( 1992). Letters to the editor. J Biomed Mater Res26:831-833.
34.
Thomas KA, Kay JF, Cook SD, Jarcho M. (1987). The effect of surface macrotexture and hydroxylapatite coating on the mechanical strengths and histologic profiles of titanium implant materials. J Biomed Mater Res21:1395-1414.
35.
Tracy BM, Doremus RH (1984). Direct electron microscopy studies of bone hydroxylapatite interface. J Biomed Mater Res18:719-726.
36.
Van Raemdonck W., Ducheyne P., De Meester P. (1984). Auger electron spectroscopic analysis of hydroxyapatite coating on titanium. J Am Ceram Soc67:381-384.
37.
Weng J., Liu XG, Li XP, Zhang XD (1995). Intrinsic factors of apatite influencing its amorphization during plasma-spray coating. Biomaterials16:39-44.
38.
Weng J., Liu X., Zhang X., De Groot K. (1996). Integrity and thermal decomposition of apatite in coatings influenced by underlying titanium during plasma spraying and post-heat-treatment . J Biomed Mater Res30:5-11.
39.
Wheeler SL (1996). Eight-year clinical retrospective study of titanium plasma-sprayed and hydroxyapatite-coated cylinder implants. Int J Oral Maxillofac Implants11:340-350.
