Journal of Oral Rehabilitation 1995 22; 105-111 The influence of a flexible coating on the bone stress around dental implants G.J. MEIJER,* F.J.M. STARMANS,* C. DE PUTTER* & C A . VAN BLITTERSWIJK+ ^Department of Oral-Maxillofacial Surgery, Prosthodontics and Special Denta! Care, Facu!ty of Medicine, University of Utrecht, Utrecht and ^Laboratorium for Otobidogy and Biocompatability. Biomaterials Research Group, Faculty of Medicine. University of Leiden, Leiden, the Netherlands SUMMARY The influence of a three-layered flexible coating of Polyactive® on bone stress distribution was investigated by three-dimensional finite element models of mandibular hone, in which a titanium implant (coated or uncoated) v\'as located. Poly- active® is a system of poly(ethylene oxide) poly(buty- lene terephthalate) segmented co-polymers with bone-honding capacity. In the case of sagittal and transversal loading, the use of a Polyactive* coating reduced both the minimum principal stress in the bone and the compressive radial stress at the bone- implant interface. However, it raised the maximum principal and the tensile radial stress. In the case of vertical loading, the application of a flexible coat- ing reduced the compressive radial stress at the bone-implant interface around the neck of the im- plant by a factor of 6-6 and the tensile radial stress by a factor of 5*6. Variations in composition and thick- ness of the coating did not affect the results significantly. Introduction Although much research in oral implaniology has focused on the biological performance oi implants, the imporiance ol a good biofunctionaliiy has recently gained more alleniion. Biofunciionality is defined as all mechanical and physical properties of an implant that enable it to perform its function (Williams, 1981). One important funaional parameter concerns the correct transfer of chewing forces applied on the supra- structurc of the implant to the surrounding bone. In the concept offibro-osseointegration(Weiss, 1989), there is a layer of fibrous connective tissue between the bone and the implant which reduces critical stress peaks effectively (Borchers & Reichart, 1983). However, in the concept of osseointegration, introduced by Branemark el al (1977), forces on the implant will be directly transferred to the bone. Many investigators have suggested the use of devices with a low Young's modulus that can be placed between the implant and suprastructure in order to reduce chewing stresses (James, 1975; Koch, 1976; Buser e! al, 1990). These devices were given various names: shock resorber (Skalak, 1983; Chapman &• Kirsch, 1990); stress- distributor (van Rossen ei al, 1990); stress-breaker (Lill etal, 1988; Sctzetal, 1989); intramobile element (Koch, 1976); flexible inserts (Siegele, Soltesz & Scheicher, 1985); or flexible element (van Rossen, 1991). In contrast to the above approach, it would be closer to the clinical situation to simulate a periodontal ligament by coating implants with a flexible layer. Tberefore, in tbis study, we investigated the influence of a flexible coating on the bone stress around implants. Within the concept of osseointegration (Branemark ei al, 1977) we aimed for a flexible coating of Polyactive®* between the implant and bone. Polyaaive®, a poly(etbyleneoxide) poly(butylene terephthalate) segmented co-poiymer is a bone-bonding material (Bakker et al, 1989, Van Blitterswijk fM/.. 1989, 1991, 1992; Radder ^r a/., 1990) witb a relatively low modulus of elasticity (Young's modulus). The finite element method (FEM) was chosen to evaluate the mecbanical behaviour as it offers several advantages, including accurate representation of com- plex geometries, easy model modification, calculation - HC Implants B.V.. Zernikedreef 6, 2333 CK Leiden, the Netherlands. 105