AICRG, Part V: Factors Influencing Implant Stability at Placement and Their Influence on Survival of Ankylos Implants
Problem: Several factors influence primary stabilization of dental implants at placement surgery. These include implant design, bone quality, implant jaw location, and the use of a bone tap. Purpose: This report evaluates clinical data gathered by the Ankylos Implant Clinical Research Group (AICRG) to assess (1) the influence of several variables on primary stability and (2) the potential for an Ankylos implant (Friadent GmbH, Mannheim, Germany) that is mobile at placement to integrate and survive for at least 3 years of clinical function. Methods: The Ankylos implant is a roughened grade-2 titanium screw. A total of 1554 implants were placed in 478 patients. At both the time of placement and abutment connection, the implants were tested for evidence of clinical mobility by attempting to rotate or move the implant with an application of force. Survival was recorded from placement and up to 36 months following placement. Results: At placement, 2.8% were found to be mobile. In the maxillary posterior quadrant, 6.3% were clinically mobile. Implant mobility was frequent (12.2%) in jaw regions with poor-quality bone (BQ-4) or with short implants (8 mm = 8.3% mobile). Of the implants mobile at placement, 97.7% were stable at uncovering. The 3-year postplacement survival of initially mobile implants was 84.1% compared with 96.8% for implants not mobile at placement (χ2 test, P = .001). Conclusions: The Ankylos implant predictably promoted primary stability during surgical placement. Poor bone quality, short implants, and maxillary posterior jaw locations were all associated with a slightly higher rate of mobility at placement. Primary implant stability, while highly desirable, is not absolutely necessary for achieving osseointegration of Ankylos implants.Abstract
(A) Percentage of implants found to be mobile at the time of placement vs those that were stable. A small percentage (2.8%) of the total number of Ankylos implants were found to be mobile at placement. (B) Percentage of implants that were documented as either mobile or stable at placement that appeared to be clinically stable at the time of uncovering (stage II, abutment connection). Most implants mobile at placement appeared to be clinically stable at the time of uncovering
(A) Influence of jaw regions on implant mobility at placement. UPPE exhibited the greatest percentage of mobile implants, whereas the UCE, LPPE, and the LCE jaw regions were very similar. (B) Influence of anterior vs posterior jaw regions. The posterior jaw regions exhibited a greater percentage of implants that were mobile at placement. This difference was not clinically significant. UPPE indicates maxillary posterior partially edentulous regions; UCE, maxillary completely edentulous; LPPE, mandibular posterior partially edentulous; LCE, mandibular completely edentulous jaw regions
(A) Influence of bone density on mobility at placement; BQ-4 had the highest percent of implants that were mobile at the time of placement, which may be clinically significant. (B) Influence of crestal bone reduction at the time of placement on mobility at placement; crestal bone reduction did not have a major influence on the percent of implants mobile at placement. BQ-1 indicates bone density-1; BQ-2, bone density-2; BQ-3, bone density-3; BQ-4, bone density-4
(A) Influence of implant diameter on mobility at placement. In general, as the diameter increases, the number of implants that exhibit mobility at placement tends to decrease. (B) Influence of implant length on mobility at placement. There is a decrease in mobility at placement as the implant length increases
(A) The use of the bone tap did not have a major influence on mobility at placement. (B) The implants that were mobile at the time of placement and were functional for a period of 36 months exhibited a more positive Periotest value (PTV). The positive PTVs indicate that the bone-implant interface is not as rigid as for implants that were stable at placement. Although not statistically significant, this would be of considerable clinical interest, since it may suggest that the bone-implant interface for integrated implants that were mobile at placement is more fragile and may be prone to failure during long-term clinical performance
(A) Influence of mobility at placement on survival to at least 36 months. Implants that exhibited mobility at placement tended to fail more frequently than those not mobile at placement. This difference was statistically significant (χ2 test, P = .001). (B) Influence of mobility at placement on survival to at least 36 months for each stage of treatment. Stage I (healing): few implants from either group failed. Stage II (uncovering/abutment connection) implants that were mobile at placement were more likely to fail than those not mobile. Stage III (following uncovering but before prosthesis placement): there was a larger number of implants that were mobile at placement that failed when exposed to their oral environment. Stage IV (prosthesis loading): of those implants that reached this stage of treatment, few implants failed. Total (from the time of placement to 36 months): mobile implants failed more frequently than those not mobile at placement
Contributor Notes
Harold F. Morris, DDS, MS, is codirector of the Dental Clinical Research Center (DCRC) and project codirector of the Ankylos Implant Clinical Research Group (AICRG), Department of Veterans Affairs Medical Center (VAMC), Ann Arbor, Mich. Correspondence should be addressed to Dr Morris at the DCRC (154), VA Medical Center, 2215 Fuller Road, Ann Arbor, MI 48105.
Shigeru Ochi, PhD, is codirector of the DCRC and project codirector of the AICRG, VAMC, Ann Arbor, Mich.
Ira H. Orenstein, DDS, is staff dentist at the VAMC, Bronx, NY, and at the Columbia University School of Dental and Oral Surgery, New York, NY.
Vincent Petrazzuolo, DDS, is staff dentist at the VAMC, Bronx, NY.