Influence on early osseointegration of dental implants installed with two different drilling protocols: a histomorphometric study in rabbit Juan Blanco Elena Alvarez Fernando Mun ˜oz Antonio Lin ˜ares Antonio Cantalapiedra Authors’ affiliations: Juan Blanco, Elena Alvarez, Antonio Lin ˜ares, Department of Stomatology – Periodontology, School of Dentistry, University of Santiago de Compostela, Santiago de Compostela, Spain Fernando Mun ˜oz, Antonio Cantalapiedra, School of Veterinary of Lugo, University of Santiago de Compostela, Santiago de Compostela, Spain. Corresponding author: Juan Blanco Department of Stomatology – Periodontology School of Dentistry University of Santiago de Compostela c/Entrerrı ´os s/n 15702 Santiago de Compostela Spain Tel.: þ 34 981 571 826 Fax: þ 34 981 571 620 e-mail: jblanco@blancoramos.net Key words: bone implant contact, early healing, primary stability, resonance frequency analysis Abstract Objective: To evaluate early osseointegration of dental implants installed with two different drilling protocols. Material and methods: Thirty-six cylindrical shape Mozo Grau implants, with a diameter of 3.75 and 11 mm long, were placed into the distal condyle (submerged) of each femur of 18 New Zealand rabbits. In the control group, a 3.3 mm diameter drill was used as the last one prior implant installation (standard protocol). In the test group, the same procedure was carried out but an additional 3.5 mm drill was used as the final one (oversized protocol) Thus, we could obtain different primary stability at day 0 between groups. Sacrifice of the animals was after 2, 4 and 8 weeks. Histomorphometric analysis (bone-to-implant contact ratio [BIC%]) and implant stability quotient (ISQ) values (Ostell s ) were registered at each sacrifice time. Results: The ISQ values were statistically significant different between groups at day 0 (control: 69.65; test: 64.81); and after 2 weeks (control: 77.93; test: 74). However, after 4 and 8 weeks the results were similar. BIC% showed a similar tendency, with 58.69% for the control group and 40.94% for the test group after 2 weeks, this difference being statistically significant. At 4- and 8-week interval, BIC% was similar. Conclusion: At 2-week interval (early healing), osseointegration had been influenced by different primary stability at implant installation, being slower in the oversized protocol (lower primary stability), which could be especially risky in challenging clinical situations, such as soft bone (class 3 and 4) and early/ immediate loading. However, from 4 week on, these differences disappeared. Nevertheless, we have to consider that a direct transfer of the results of this animal study (time bone repair mechanisms) into clinic has to be done with caution. The term ‘‘osseointegration’’ refers to the process whereby alloplastic materials (dental implants) and bone are joined in a rigid, clinically asympto- matic union that withstands functional loading (Zarb & Albrektsson 1991). This is a definition based on the mechanical stability of the implant. In order to understand the healing process, it is necessary to know the biological mechanisms that play a role in the integration of the implant with the surrounding bone. Dental implant primary stability has been demonstrated to be a key factor for implant survival rates. Primary mechanical stability is directly related to the quality and quantity of bone at the recipient site, the type of implant used and the surgical technique used to place the implant (Meredith 1998). Biologically, this pri- mary stability is obtained if the marginal and/or apical areas of the implant site hold a large enough quantity of compact bone and if the spongy bone contains a sufficient number of trabeculae (Albrektsson Berglundh & Lindhe 2003). Clini- cally, at the time of implant placement, this kind of primary stability is achieved by ‘‘tight fitting’’ between the implant surface and the avascular cortical bone in the marginal area of the implant bed. This intimate bone-to-implant contact (BIC) is also the effect of the minute lateral displace- ment exerted in the bone tissue during implant adaptation, where the trabeculae of the marginal portion shift towards the medullar space and the sectioned blood vessels bleed. As a consequence, a blood clot forms and is trapped between the implant surface and the bone. This blood clot will mature over the next few days and eventually be replaced by granulation tissue (Albrektsson et al. 1983), woven bone and lamellar bone, producing secondary stability. Therefore, secondary stability is the consequence of the formation of new bone and the remodelling process in both the area of most direct contact (the bone–implant interface itself) and a more distant area (Meredith 1998). Date: Accepted 12 June 2010 To cite this article: Blanco J, Alvarez E, Mun ˜oz F, Lin ˜ ares A, Cantalapiedra A. Influence on early osseointegration of dental implants installed with two different drilling protocols: a histomorphometric study in rabbit Clin. Oral Impl. Res. 22, 2011; 92–99. doi: 10.1111/j.1600-0501.2010.02009.x 92 c  2010 John Wiley & Sons A/S