The present study comprised 36 patients with 93 dental implants under conditions of an SIT program in a private practice setting from the 10th to 20th year of intraoral service. We assessed the peri-implant bone-level changes during the 2nd decade of function and found a median change in PBL of 0.7 mm and a mean change in peri-implant bone level of 0.8 mm. In the first investigation, three subgroups were built according to the implant–abutment connection concepts (BLC, BLB, and TLC; Figs. 1, 2, 3, 4). In the statistical analysis, no significant differences in peri-implant bone level were found. In a second investigation, two subgroups were built according to the different implant surfaces (machined vs. roughened), which also showed no significant differences after 10 and 20 years.
The criteria for acceptable values of peri-implant bone loss introduced by Albrektsson et al. were < 1.5 mm during the first year and < 0.2 mm during each following year based on the knowledge of Branemark implants . Transferred to a 20-year observational period, this would result in an ‘acceptable’ change in peri-implant bone level of up to 5.3 mm in total, which seems to be quite extensive. Since then, a variety of studies on peri-implant bone-level changes have been published.
After implant placement and after installation of the implant-supported prostheses, peri-implant bone remodeling processes are inevitable. This remodeling starts from the moment when the implant is installed (one-part/tissue-level implant types) or from the moment of implant uncovering surgery (two-stage BL implant types) when the implant/abutment connection is exposed to the intraoral microbial biofilm . From this moment on, the peri-implant soft tissues (epithelium and subepithelial connective tissue) are in contact with the implant and/or abutment surface, and the biologic width is established [22,23,24].
To date, two different types of dental implants have been used. Two-piece implants are placed at BL height. Usually, they have to be uncovered in a second surgery, and then, the abutment is installed. In contrast, one-piece implants are placed at or above the soft-tissue level and, therefore, contain a part that contacts the soft tissue. They do not require second-stage surgery. In a comparison of the two types of implants, no significant differences in the vertical dimension of the biologic width were detected . Another study compared three different implant systems: hex connection/BL, morse-taper connection/BL and conical connection/tissue level. No significant differences were found; the junctional epithelium had a height of 1.5–2 mm, and the connective tissue had a height of 1–2 mm .
However, the installation of the implant abutment at the BL implicates a microgap or microleakage between the two components that is accessible for the sulcus fluid and, therefore, for the intraoral microbia as well [26, 27]. Consequently, a biological reaction of the human host leads to the establishment of an inflammatory cell infiltrate . In a review, Linkevicius and Apse found that there is ‘enough evidence … to state that the function of the biologic width around implants is to protect underlying bone’ . Therefore, it seems likely that in cases of microgap-induced inflammation, the biologic width is established apically to the ‘infection’, which has to be realized via peri-implant bone resorption (1.5–2 mm circular) during the first period after loading. Implant types without microleakage (one-part implants, implant types with abutment connections at the soft tissue level and not at the BL) do not show this initial circular peri-implant bone loss (Figs. 1, 2, 3, 4). A recent review indicated that microleakage seems to be ‘very reduced in morse taper implants in comparison to other implant connections’ .
Ravald et al. compared the change in PBL between turned implants and roughened implants after 12–15 years in a retrospective study . At 12 years after bridge installation, the authors found an annual change in the PBL value of 0.04 mm for the turned implants and that of 0.07 mm for the roughened implants. In the present study, the patients displayed an annual change in PBL of 0.08 mm during years 10 to 20, which seems to be within the same range.
In a prospective study design, Vervaeke et al. assessed 39 patients with 243 implants after 9 years of function, and they found a mean change in PBL of 1.7 mm using implant installation as baseline . This represents exactly the same 10-year baseline PBL value of the present study.
In a 20-year life table analysis of a longitudinal study of > 12,500 implants with a roughened surface and a morse-taper connection, Krebs et al. found relatively low rates of bone loss . After 204 months, 135 implants were assessed. Overall PBL values were not indicated, but 115 implants (85.2%) displayed a vertical bone loss of ≤ 1 mm, and 11 (8.1%) showed a change in PBL ≥ 2 mm. Our findings referring to the same implant system were different. We found a mean bone loss of 1.87 mm after 10 years and a mean change in PBL of 3.0 mm after 20 years.
Radiographic bone gain: In long-term studies, not all implants followed display peri-implant bone loss. In our investigation, 10.8% of the implants showed radiographic bone gain (RBG). This is in accordance with the findings of Roos-Jansaker et al., who analyzed 999 implants after 9 to 14 years . Discounting the change in PBL during the first year, they found RBG in 10.7% of the implants.
Unfortunately, comparable studies with similar designs and observational periods were scarce. Due to the long observational period and to the retrospective character of the present study, it was not possible to create a control group. Moreover, no information concerning dropouts were available. Finally, only 36 patients could be comprised. Therefore, the validity of the presented results is obviously limited. Consequently, these findings will have to be verified by other researchers, greater patient samples, in different settings and including control groups. The fact that only one experienced periodontal surgeon performed all treatment steps may represent another limitation. It should be stated that the present results were assessed under professional SIT conditions and, therefore, must not be transferred readily to other patient conditions.
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