Spontaneous Early Exposure of Submerged Endosseous Implants Resulting in Crestal Bone Loss: A Clinical Evaluation Between Stage I and Stage II Surgery

Spontaneous Early Exposure of Submerged Endosseous Implants Resulting in Crestal Bone Loss: A Clinical Evaluation Between Stage I and Stage II Surgery
Implant Dentistry: Volume 12(1) March 2003 pp 9-10
Mills, Michael P. DMD, MS
Lippincott Williams & Wilkins, Inc.
The authors present a timely study, which examines the effect of spontaneous early exposure on early crestal bone loss around submerged endosseous dental implants. In a multicenter protocol, two-stage, 3.8-mm diameter threaded implants were placed in patients who were generally healthy and nonsmokers. Sites for implant placement had to be at least 1-year post-extraction and had to show no signs of trauma from conventional removable appliances being worn. During implant placement, the crest of the bone relative to the implant shoulder was measured to the nearest 0.5 mm. Three weeks postsurgery, implant sites were examined by air stream and gentle probing. Sites with cover screw exposure were recorded and examined again at 6 to 8 weeks postsurgery. Mucosa over each implant was classified according to Tal as class 0 (intact mucosa); class 1 (mucosal breach is detected with probe only); class 2 (cover screw is visible but none of its borders can be seen); class 3 (cover screw is visible and in some parts its borders can be seen); and class 4 (cover screw is completely exposed). Classifications were reconfirmed before stage-two surgery at 4 to 5 months. Only those patients who had two or more implants with different exposure classifications were included in the study. Out of 206 implants in 64 patients, 91 were classified as class 0, 35 (class 1), 52 (class 2), 23 (class 3), and 5 (class 4). Of these, 85 groups met the criteria for analysis.
Results demonstrated a statistically significant difference of bone loss between intact mucosa (class 0; 0.12 mm) and class 1 (0.40 mm), class 2 (0.86 mm), and class 3 (0.78 mm). Class 4 exposures were associated with 0.38 mm of bone loss but were too few in number to be entered into statistical analysis. When implants were analyzed individually, bone loss > 1 mm was seen with increasing frequency from class 1 to class 3 exposures. In regard to implant surfaces, the buccal had greater associated loss than mesial, distal, or lingual. These results show that in a two-stage implant system partial exposure of the cover screw after implant placement can lead to bone loss at the implant shoulder before stage-two uncovering. The authors point out that other factors may also have contributed to this early loss such as bone quality and volume.
The data do suggest that it may be prudent to remove the mucosa in cases of partial exposure (class 2 and 3) to reduce bone loss at the implant shoulder. Further study will need to be performed to determine if the bone loss associated with early cover screw exposure is cumulative to that which is usually seen in the first year after uncovering and loading of two-stage implants.