Importance of the Roughness and Residual Stresses of Dental Implants on Fatigue and Osseointegration Behavior. In Vivo Study in Rabbits
This study focuses on the fatigue behavior and bone-implant attachment for the more usual surfaces of the different CP-titanium dental implants. The implants studied were: as-received (CTR), acid etching (AE), spark-anodization (SA), and with a grit-blasted surface (GB). Residual stresses were determined by means of X-ray diffraction. The fatigue tests were carried out at 37°C on 160 dental implants, and the stress-failure (S-N) curve was determined. The fatigue tests showed that the grit-blasting process improved fatigue life. This is a consequence of the layer of compressive residual stresses that the treatment generates in titanium surfaces. Further, our aim was to assess and compare the short- and midterm bone regenerative potential and mechanical retention of the implants in bone of New Zealand rabbits. The mechanical retention after 4 and 10 weeks of implantation was evaluated with histometric and pull-out tests, respectively, as a measure of the osseointegration of the implants. The results demonstrated that the GB treatment produced microrough that accelerated bone tissue regeneration and increased mechanical retention in the bone bed at short periods of implantation in comparison with all other implants tested. The GB surface produced an improvement in mechanical long-time behavior and improved bone growth. These types of treated implants can have great potential in clinical applications, as evidenced by the outcomes of the current study.
Representative scheme of the experimental titanium dental implant used.
Scanning electron microscopy images of (a) as-received (CTR), (b) acid-etched, (c) spark-anodization, and (d) grit-blasted surface. As can be noted in the images, the different treatments provided significant differences in topography, presenting a slightly rough surface for the CTR, with similar morphology to AE although with slightly higher roughness. Further, the SA implants presented a considerable difference, a porous structure due to the electrochemical reaction and the hydrogen scape. Finally, the GB surfaces presented the highest roughness with similar morphological features to AE and CTR.
Figure 3 . Surface residual stresses calculated at the 4 different types of Ti dental implant surfaces, showing that the grit-blasted surface (GB) treatment provided the higher residual stress, whereas the other treatments provided similar residual stresses to that of as-received (CTR) samples. Figure 4. Fatigue test results, showing the number of cycles needed for failure (Nf) (left axis) and the cumulative plastic strain (ɛcum) (right axis) for the different treated surfaces. AE indicates acid-etched; SA, spark-anodization.
Representative histological images of as-received (CTR), acid-etched (AE), spark-anodization (SA), and grit-blasted surface (GB) implants after different times of implantation (4 weeks and 10 weeks). Bone remodeling is present in all cases, presenting as light color in the new bone formation and as dark color in the old bone. Especially for AE and GB, new bone is in close contact with the implant.
Figure 6. In vivo animal study quantification of bone index contact (BIC) of the different types of surfaces, showing significant increased values for the GB samples. Columns with the same letter indicate no significant differences among the different groups and studied time points (P < .05). Figure 7. Retention force of the implants implanted in the rabbit condyle, showing the strength needed to pull the implants from the bone for the different surface treatments at the two different time points. Columns with the same letter indicate no significant differences among the different groups and studied time points (P < .05). CTR indicates as-received; AE, acid-etched; SA, spark-anodization; GB, grit-blasted surface.
Pull-out tests. Cylinder-shaped implants after pull-out tests: (a) acid-etched implant and (b) grit-blasted surface implant with an attached piece of the surrounding bone tissues.
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