Six-month Performance of Implants with Oxidized and Machined Surfaces Restored at 2, 4, and 6 Weeks Postimplantation in Adult Beagle Dogs

Purpose: The purpose of this study was to compare machined-surface implants (control) and oxidizedsurface titanium screw-type implants (test) loaded with fixed partial dentures at 2, 4, and 6 weeks postplacement in terms of implant survival and stability. Materials and Methods: The beagle model was chosen for the study. Four mandibular premolars were extracted bilaterally from each dog. After 2 months of healing, 4 implants were placed in each dog. HaIf of the dogs (n = 6), the test group, received oxidized-surface implants; the other half (n = 6), the control group, received machined-surface implants. In each group, 2 dogs were randomly assigned to a 2-week preloading healing period, 2 to a 4-week period, and 2 to a 6-week period. Three implants were loaded in each dog; 1 was left unloaded as a control. Clinical stability and survival were monitored every 2 weeks for 6 months. Results: Failures were noted only among the implants assigned to the 2- and 4-week groups. Failures accounted for 9.4% (9/96) of the implants-12.5% (6/48) of the control implants and 6.3% (3/48) of the test implants. One hundred percent prosthesis stability was noted for the test-surface implant group. Stability of the test implants was significantly better than stability of the control implants (-2.6 vs -1.7, P .05). Mean Periotest values at loading were 3.7 for the group loaded at 2 weeks, 1.6 for the group loaded at 4 weeks, and 0.6 for the group loaded at 6 weeks. Fifty percent of the 6-week group, 25% of the 4-week group, and 12.5% of the 2-week group had a Periotest value 0 at loading. Discussion: The results reveal a qualitative difference in performance between the implant groups. Twice as many failures occurred in the control group, few failures occurred following loading, and no failures occurred after 4 weeks postplacement. The survival curves for both implants were flat after 4 weeks; however, the duration of follow-up may hide effects of time-dependent factors on survival and poses a concern for clinical inference. Conclusions: Early loading of both implant types was well tolerated, as only 2 failures occurred following loading. A subsequent report will review these outcomes along with histomorphometric data collected at 6 months to better understand the significance of tissue- level implant-surface interaction for survival and stability.