Clinical evidence and Science 31 Bone preservation Factors with an impact on bone remodeling and bone resorption The peri-implant marginal bone level is an important factor for maintaining the soft tissue around the implant and securing the implant health in general. Contrary to an earlier acceptance criteria of 0.2 mm bone loss per year after the first year, modern implants and treatment plans aim to preserve the bone in the long-term after an initial bone loss which is considered as a biologic response to the implant placement (bone remodeling) (Strietzel et al. 2015 (25)). Based on systematic reviews and meta-analyses, a working group Schwarz et al. (2014) (26) pointed out important facts to consider at implant placement to preserve the marginal bone level: 1) positioning of the machined collar (smooth-rough border) has a direct influence on the initial bone response; 2) subcrestal positioning of the microgap may be associated with higher bone loss; 3) the Platform-Switching concept seemed to prevent or minimize bone loss. The controversial discussed topic related to the impact of Platform-Switching was presented within two meta-analyses (Strietzel et al. 2015 (25), Mishra et al. 2019 (27)). Both publications showed a significant effect of platform-switched implants in reducing peri-implant marginal bone level compared to platform matched implants. In the maxilla the effect was even more pronounced (Mishra et al. 2019 (27)). Effect of Platform-Switching versus platform matching The positive effect of Platform-Switching was addressed with multiple studies using both CAMLOG® and CONELOG® implants. Pre-clinical background information: The principle of Platform-Switching in the CAMLOG® Implant System was evaluated in a dog study over six months (Becker et al. 2009 (28)). SCREW-LINE Promote® plus implants (diameter 3.8 mm) were inserted according to the standard surgical protocol. Wide-body matching healing abutments and non- matching abutments were connected in a randomized split-mouth design and served either as control or test implants with a circumferential horizontal platform of 0.3 mm, respectively. The histological evaluation after four weeks demonstrated formation of mature woven bone in the gap between the alveolar bone and the implant surface in both groups. A first tendency for crestal bone changes was noticed in both groups. At 12 weeks, mainly mature lamellar bone was found. Bone loss tended to be slightly increased for the control implants compared to the platform-switched implants. The difference between control and test implants regarding the distance between implant shoulder and bone crest was 0.5 mm at the buccal aspect and 0.4 mm at the lingual aspect (p<0.05), respectively. A similar result could be observed at six months when remodeling at the alveolar crestal bone seemed to decline. The difference of implant shoulder and bone crest between both groups was approximately 0.3 mm. The study demonstrated that the CAMLOG® implant design both in its standard and in its Platform- Switching configuration successfully integrated into hard and soft tissue. Bone remodeling as well as soft-tissue adaption appeared to be minimal at the implant-abutment interface during the first eight weeks of osseointegration and was considerably less pronounced after six months resulting in a stable crestal bone level. The platform-switched implants tended to yield better results regarding maintenance of the bone level. In another dog study, Becker et al. (2007) (29) evaluated the influence of Platform-Switching on crestal bone changes by comparing CONELOG® implants (internal Platform-Switching, referred to as experimental implants) and CAMLOG® implants with matching healing abutments. Bone healing and formation of a junctional epithelium was evaluated histologically up to 28 days. In the implants with standard healing abutments, a significantly increased epithelial downgrowth was noted lingually (1.1 ± 0.6 mm) and buccally (0.9 ± 0.4 mm), which was associated with significant buccal bone loss. In contrast, the Platform-Switching design of the CONELOG® implants prevented apical epithelial downgrowth significantly and reduced bone loss. However, the difference in bone loss between both groups did not reach statistical significance. CLINICAL EVIDENCE FOR CAMLOG® AND CONELOG® IMPLANTS
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