Surface Morphology Of The Hydroxyapatite Coated Titanium Alloy Implant Material Subjected to Fatique in the Presence of a Periodontal Pathogen
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INTRODUCTION: The analysis of retrieved dental implants indicates that bacteria influence the stability of the hydroxyapatite (HA) coating in the dental implants ( I ) . Dissolution and cyclic fatigue loading occurring i n vivo could lead to failure of the HA coating. Improperly applied coatings dissolve when significant amorphous or unstable crystalline phases exist (2). The objective of this study is to report the surface morphology and compositions of HA coated (different crystallinity) dental implants subjected to fatigue when exposed to a periodontal pathogen Actinobacillus actinomycetemcomitans (Aa). MATERIALS and METHODS: Titanium alloy (ASTM F-136) rods of 4.0 mm dia x 19.7 mm and coupons of 25.4 x 25.4 x 3.2 mm as controls were HA coated (Biocoat) at three levels of crystallinity, which was determined by Xray Diffraction (XRD). The organism Aa (ATCC33384) was grown in a brain heart infusion medium (BHI) at 37'C under 5% CO2 . Aa in log phase of growth (10 hours) was added to inoculate the tube containing a sterile rod or coupon suspended in the BHI broth. Tubes were then incubated under CO2 at 37'C for 48 hours. After the removal of adherent Aa by sonication and washing, they were transferred in a sample holder for fatigue testing. Eight specimens per group immersed in a Lactated Ringer's solution were then fatigue tested at 10 Hz for 5 million cycles, which took 14 days. The fatigue tested samples along with non fatigue controls were characterized by scanning electron microscopy (SEM) (Joel 733). Also the surface calcium (Ca) and phosphorous 0') contents were measured with the Wave Length Disperse (WDS) probe attached to the SEM. Two locations in the rod (top and mid sections) were examined. RESULTS and DISCUSSION: Crystallinity levels of the three samples were 61, 53 and 48% (XRD) which were significantly different, p<0.05. Both Ca and P concentrations of the rods fatigued in the presence of bacteria were lower than those fatigued in the absence of bacteria (Table 1). The SEM pictures of the rods and coupons in Figure 1 showed the presence of more granular morphology when fatigued in the presence of Aa. CONCLUSIONS: Ca and P levels on the surface of HA coated rods fatigued after exposure to Aa were lower than those fatigued without bacterial exposure. The morphology of the fatigued samples in Aa appeared to show more granular morphology than that seen in fatigued samples without the presence of bacteria. REFERENCES: 1. Krauser J et al: J Dent Res, 70:224 abstr. 65,1991. 2. Kay E: Dental Clinics of North America 36: 1-18, 1992.