Page 15 - Peri-implant health: the effect of implant design and surgical procedure on bone and soft tissue stability

after the surgery. The resulting surface enlargement allowed shorter implants to be used without jeopardizing the prognosis and reduced the necessity for bone grafting procedures.25 Besides the afore-mentioned benefits, related to faster osseointegration and enlarged indication, rough implant systems have been linked to increased bacterial adhesion in vitro.26 However, the applied model in the latter study does not mimic the clinical reality. Nevertheless, two Cochrane systematic reviews suggested, albeit with limited evidence, that smooth surfaces had a 20% reduced risk of being affected by peri-implantitis over a three-year period.27,28
Besides the above-mentioned micro-design factor implant surface roughness the manufactures also adjusted macro- design features of the implant to improve the clinical outcome of implant treatment. An implant macro-design feature, which has been modified over time as well, is the type of abutment connection. Different abutment connections have been used, in order to overcome abutment screw loosening, to enhance long-term bone stability, and to minimize crestal bone loss. In the early years of implant dentistry, the most common abutment connection was the flat-to-flat abutment to implant connection, with an external hexagon to prevent abutment rotation. Nowadays, an internal conical connection or a Morse taper with an internal anti-rotation element is mostly used. A large review of 52 articles by Schmitt and colleagues29 concluded from in-vitro techniques that: (1) no connection yields a 100% perfect seal for bacterial contamination; (2) the implant-abutment interface geometry seems to be an influencing factor for stress and strain transmission around the implant; (3) the conical implant-abutment connection seems to be more resistant to abutment movement and microgap enlargement and has higher torque loss resistance in addition to high resistance to fatigue loading and maximum bending; and (4) the conical implant-abutment connection seems to have lower abutment screw stresses than with the external hexagon connection, but it is comparable to internal hexagon connections. Furthermore, the authors also concluded from in-vivo studies that: (1) conical and non-conical systems are comparable in terms of implant success and survival, and (2) in most cases, conical connection systems seems to produce a lower marginal bone loss. In addition to the implant-abutment connection type, thread design at the coronal part of the implant is claimed to affect crestal bone loss. Several in vitro studies using finite element analysis showed better stress distribution on the surrounding crestal bone for microthreaded compared to non-microthreaded implants.30,31 Multiple in vivo clinical studies showed less crestal bone loss for
GENERAL INTRODUCTION
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