AICRG, Part II: Crestal Bone Loss Associated with the Ankylos Implant: Loading to 36 Months
Problem: The Ankylos endosseous dental implant is a new implant design that will be available in the United States in early 2004. It features an internal tapered abutment connection, a smooth polished collar without threads at the coronal part of the implant body, and a roughened surface with variable threads on the body of the implant fixture. A precise, tapered, conical abutment connection eliminates the microgap often found in 2-stage implant systems. This microgap may allow the accumulation of food debris and bacteria, as well as micromovement between the parts during clinical function, both of which can lead to a localized inflammation and crestal bone loss. Purpose: The purpose of this section of the study was to assess any crestal bone loss associated with this new implant. Method: The clinical performance of this new implant design was studied under well-controlled clinical conditions. Over 1500 implants were placed and restored. The vertical crestal bone loss was measured “directly” between the time of implant placement and uncovering, using a periodontal probe. Serial dental radiographs were taken between loading, and the 12-, 24-, and 36-month follow-up visits to determine “indirect” crestal bone loss within a specific period. Results: Bone loss varied among the participating centers from less than 0.5 mm to 2.0 mm. The largest amount of bone loss occurred between the time of placement and uncovering. Following loading, the mean bone loss for all implants for a period of 3 years was about 0.2 mm/y. Conclusions: The extent of the crestal bone loss after loading was minimal for patients regardless of age, gender, prosthetic applications, bone density, and remote or crestal incisions, as well as for smokers or nonsmokers. Bone loss per year is well within the guidelines of 0.2 mm/y proposed by others.Abstract
(A) Method used to determine crestal bone loss from radiographs. The actual bone loss (a) is calculated from the proportion of measurements in millimeters; A = actual length of implant from records; r = length of implant on radiograph; a = actual (calculated) bone loss; r = measured bone loss on radiograph. (B) Crestal bone loss at each time period from loading to 12, 24, and 36 months. Average bone loss is about 0.2 mm each year for the 36-month period that was well within the loss suggested for determining implant success. CBL indicates crestal bone loss on mesial or distal of implant; LI, length of implant
Clinical case photographs (courtesy of Dr Cherng-Tezh Chou, Taiwan, China). (A) Abutment connection; (B) clinical case, 4 years postloading (note health of soft tissue surrounding the implant restoration). (C) Radiograph of postloading to 24 months (no apparent clinically significant crestal bone loss). (D) Radiograph of postloading to 48 months (no apparent clinically significant crestal bone loss)
(A) Crestal bone loss for each jaw region ranged from 0.6 to 0.8 mm for the period from loading to 36 months. This represented an annual loss of between 0.20 and 0.26 mm. (B) The crestal bone loss for patients under the age of 60 and those over the age of 60 was not found to be significantly different. The mean crestal bone loss from loading to 36 months was 0.59 mm (around 0.2 mm annually). UPPE indicates maxillary posterior partially edentulous; UCE, maxillary completely edentulous; LPPE, mandibular posterior partially edentulous; LCE, mandibular completely edentulous
(A) Crestal bone loss associated with the health status of the patient (ASA-I indicates healthy; ASA-2, mild systemic disease; ASA-3, severe systemic disease). There was no major difference in the crestal bone loss for ASA-1 and ASA-2 groups, whereas ASA-3 patients experienced somewhat higher amounts of bone loss. (B) Crestal bone loss associated with patients with a history of smoking and those who did not smoke. There was no significant difference between the 2 groups
(A) Crestal bone loss associated with each bone density: bone loss was greater for dense BQ-1, which is more resistant to the preparation of the implant site and can result in an increase in surgical trauma. (B) Crestal bone loss associated with the type of incision used for implant placement: there was no significant difference between the remote and the crestal incisions. (C) Crestal bone loss associated with the type of incision used for the connection of the abutment: the crestal bone loss was almost identical to that found during the placement of the implant
Contributor Notes
Cherng-Tzeh Chou, DDS, is a clinical instructor in the School of Dentistry, Taipei Medical University, Taipei, Taiwan.
Deborah DesRosiers, DDS, MS, is a staff dentist at the VAMC, Ann Arbor, Mich.
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.
Lori Walker, DDS, is a staff dentist at the VAMC, Sepulveda, Calif.