Stress Distribution on Edentulous Mandible and Maxilla Rehabilitated by Full-Arch Techniques: A Comparative 3D Finite-Element Approach

Many surgical protocols and guidelines are actually available in clinical practice for rehabilitating edentulous patients (Bocklage, 2002; Ganeles et al., 2001). They generally differ for number, type, and positioning of implants that support the full-arch prostheses. Moreover, each technique is characterized by a specific healing period and exhibits a success rate strongly affected by individual morphological and biological conditions (Drago, 1992). The actual clinical trend is to reduce both the number of implants and the healing period by employing threaded devices based on novel design concepts, advanced materials, and enhanced surgical procedures. In this context, the immediate-loading techniques, firstly introduced in Seventies, have been recently rediscovered. They usually allow a functional rehabilitation of edentulous arches in a single surgical session, resulting in promising aesthetic and functional results. Clinical practice confirms that rehabilitation systems based on osseointegrated implants mainly fail because of bone weakening or loss at the peri-implant region rather than as a result of the mechanical failure of the load-bearing prosthetic structure (e.g., Eckert & Wollan, 1998; Lekholm et al., 1999; Piattelli et al., 1996; Romeo et al., 2002; Roos-Jansåker et al., 2006; Tonetti, 1999; Weyant, 2003). Furthermore, the failure rate is generally higher for implants in posterior region than in the anterior (Drago, 1992; Romeo et al., 2002; Roos-Jansåker et al., 2006; Tonetti, 1999; Weyant, 2003), and in maxilla rather than in mandible (Eckert & Wollan, 1998; Lekholm et al., 1999; Piattelli et al., 1996). These evidences, especially in edentulous patients, are strictly related to the poor bone quality and quantity in molar regions, as well as to the different bone density between upper and lower jaws (Devlin et al., 1998). Possible reconstructive alternatives in atrophic cases could be considered (e.g., Keller et al., 1987; Tatum, 1986), but these practices are often characterized by postoperative discomfort, questionable predictability, and surgical complexity (Al-Nawas et al., 2004; Chung et al., 2007). In light of previous considerations and since the presence of sinuses (in maxilla) and mental foramina (in mandible), nowadays full-arch restorations are mainly obtained by placing implants in the anterior region, generally resulting in the use of long cantilevered prostheses. 8