Biomechanical Evaluation of Undersized Drilling on Implant Biomechanical Stability at Early Implantation Times Paulo G. Coelho, DDS, PhD, * Charles Marin, DDS, PhD,y Hellen S. Teixeira, DDS, MS,z Felipe E. Campos, DDS, MS,x Julio B. Gomes, DDS, MS,k Fernando Guastaldi, DDS, MS,{ Rodolfo B. Anchieta, DDS, MS,# Lucas Silveira, DDS, MS, ** and Estevam A. Bonfante, DDS, PhDyy Purpose: The present study evaluated the effect of different drilling dimensions (undersized, regular, and oversized) in the insertion and removal torques of dental implants in a beagle dog model. Methods: Six beagle dogs were acquired and subjected to bilateral surgeries in the radii 1 and 3 weeks before euthanasia. During surgery, 3 implants, 4 mm in diameter by 10 mm in length, were placed in bone sites drilled to 3.2 mm, 3.5 mm, and 3.8 mm in final diameter. The insertion and removal torque was recorded for all samples. Statistical analysis was performed by paired t tests for repeated measures and by t tests assuming unequal variances (all at the 95% level of significance). Results: Overall, the insertion torque and removal torque levels obtained were inversely proportional to the drilling dimension, with a significant difference detected between the 3.2 mm and 3.5 mm relative to the 3.8 mm groups (P < 0.03). Although insertion torque–removal torque paired observations was statis- tically maintained for the 3.5 mm and 3.8 mm groups, a significant decrease in removal torque values relative to insertion torque levels was observed for the 3.2 mm group. A different pattern of healing and interfacial remodeling was observed for the different groups. Conclusions: Different drilling dimensions resulted in variations in insertion torque values (primary stability) and stability maintenance over the first weeks of bone healing. Ó 2013 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 71:e69-e75, 2013 Long-term implant success is dependent on both the biologic tissue response and mechanical factors. 1-4 For achieving successful osseointegration, implant stability is one of the fundamental prerequisites and must be maintained for the entire healing period to avoid micromovements, which could lead to fibrous tissue formation around the fixture. 5-7 The implant stability over time can be considered a variable combination of primary and secondary stability. Primary implant stability is a mechanical *Assistant Professor, Department of Biomaerials and Biomi- metics, New York University, New York, NY, USA / Director for Research, Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, NY. yAssistant Professor, Postgraduate Program in Dentistry, UNIGRANRIO University, School of Health Sciences, Duque de Caxias, RJ, Brazil. zPhD Candidate, Department of Biomaterials and Biomimetics, New York University, New York, NY. xPhD Candidate, Department of Oral and Maxillofacial Surgery, Universidade Federal de Uberlandia, MG, Brazil. kPhD Candidate, Department of Oral and Maxillofacial Surgery, Universidade Federal de Uberlandia, MG, Brazil. {PhD Candidate, Department of Biomaterials and Biomimetics, New York University, New York, NY. #PhD Candidate, Department of Biomaterials and Biomimetics, New York University, New York, NY. **PhD Candidate, Department of Biomaterials and Biomimetics, New York University, New York, NY. yyAssistant Professor, Postgraduate Program in Dentistry, UNIGRANRIO University, School of Health Sciences, Duque de Caxias, RJ, Brazil. Address correspondence and reprint requests to Dr Bonfante: UNIGRANRIO University, School of Health Sciences, Postgraduate Program in Dentistry. Rua Prof. Jose de Souza Herdy, 1.160 - 25 de Agosto, Duque de Caxias, RJ, Brazil, 25071-202; e-mail: estevamab@gmail.com Ó 2013 American Association of Oral and Maxillofacial Surgeons 0278-2391/12/7008-0/$36.00/0 http://dx.doi.org/10.1016/j.joms.2012.10.008 e69