Influence of the Microgap in the Peri-Implant Hard and Soft Tissues: A Histomorphometric Study in Dogs

Influence of the Microgap in the Peri-Implant Hard and Soft Tissues: A Histomorphometric Study in Dogs
Implant Dentistry: Volume 12(1) March 2003 p 10
Oates, Thomas W. Jr. DDS, PhD¨?
Lippincott Williams & Wilkins, Inc.
We have made tremendous progress in our ability to use dental implants. This is no more evident than by the increasing emphasis placed on esthetics in implant therapy, and implant esthetics is becoming increasingly dependent upon soft tissue contours. This leads to the question of implant design and soft tissue stability. Several articles have supported the concept of biologic width in the peri-implant tissues. It has been proposed that the connection between the implant and abutment, or microgap, significantly influences the tissue position and that, at least in part, this influence is related to chronic soft tissue inflammation associated with bacterial contamination along the microgap. These seemingly subtle differences become very important when magnified in the dental implant market because it suggests potentially important differences between one-piece and two-piece implant designs. Therefore, the purpose of this study was to identify soft tissue dimension of two-stage dental implants.
Four dogs, with six implants per animal were studied. Implants were placed (1)1 mm coronal to the osseous tissue (not countersunk); (2) level with the bone crest (as recommended by the manufacturer); or (3) countersunk an added 1 mm below the osseous crest. Implants were allowed to integrate for 3 months before abutment placement at phase two surgery. Tissues were then allowed to heal for 3 months before histologic assessment of the soft tissue dimensions.
The results of this study show that groups I and II had a biologic width of 2.8 to 2.9 mm, whereas group III had a biologic width of 4.4 mm. Looking at the epithelial attachment level, group III (2.8 mm) had about 1 mm more of attachment than group I, with group II being intermediate. A similar pattern was found for connective tissues with group III (1.6 mm) greater than groups I and II (1.1 and 0.9 mm, respectfully). However, looking at the distance from abutment margin to bone crest, group III (1.7 mm) had less distance than group I (2.5 mm) and group II (2.3 mm). The authors report no significant inflammation around any of the implants.
The authors seem to focus on the fact that there was slightly less than 2 mm of distance from abutment margin to osseous crest and that submerging the implant deeper into the bone caused no additional bone loss. I think that these differences are too fine to make a strong statement of difference with previous studies. Clearly, the distance from bone crest to abutment has increased from 1 mm (at placement) to 1.7 mm, and this distance is not too far from the 2 mm distance under debate. This study, as with the previous studies looking at this situation, did not have adequate controls so as to know exactly what the tissue dimensions were at the time of placement, so the debate over 0.3 mm distance seems trite.
However, the greater truth, as I see it, is that this study supports previous knowledge of the basic biology of tissue healing and that there is some distance that must be established between the epithelium and the bone after the surgical intervention. The more interesting questions remain: what determines exactly how far along the implant or abutment interface will the epithelium be established?; where will it end up relative to the microgap?; and what is the role of marginal tissue inflammation in altering these dimensions?