Please cite this article in press as: Jafarian M, et al. Assessment of compression and strength of divergent screws mounted on miniplates for fixation of mandibular fractures: an in vitro experimental study. Br J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.bjoms.2015.03.017 ARTICLE IN PRESS YBJOM-4488; No. of Pages 5 British Journal of Oral and Maxillofacial Surgery xxx (2015) xxx–xxx Available online at www.sciencedirect.com Assessment of compression and strength of divergent screws mounted on miniplates for fixation of mandibular fractures: an in vitro experimental study M. Jafarian a , F. Pourdanesh b , M. Esmaeelinejad c , N. Dehghani c , F. Aghdashi c,∗ , R. Tabrizi d a Associate professor, Department of Oral and Maxillofacial Surgery, Dental school, Dental Research Center, Taleghani Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran b Associate professor, Department of Oral and Maxillofacial Surgery, Dental school, Taleghani Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran c Resident, Department of Oral and Maxillofacial Surgery, Dental school, Taleghani Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran d Assistant Professor, Department of Oral and Maxillofacial Surgery, Dental school, Taleghani Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran Accepted 29 March 2015 Abstract An efficient band of tension is critical for the adequate fixation of mandibular fractures, so fixation devices that compress are helpful. We aimed to evaluate the possibility of creating compression using screws inserted divergently into miniplates placed in the tension zone of mandibular fractures and record the effects on the strength of fixation. For this in vitro experimental study we prepared 20 sheep hemimandibles. After angle fractures had been created, the specimens were divided into standard and study groups (n = 10 in each). In the standard group the tension zones were fixed in the standard manner with 4-hole miniplates and 4 parallel screws. Those in the study group were fixed as for the standard group but with 4 × 45 ◦ divergent screws. The differences in the gap in the fracture line before and after fixation were measured as indicators of compression. The strength of fixation was also assessed with a universal testing machine in vitro. The amount of compression was significant only in the study group (p < 0.001), and there was no difference in the strength of fixation between the two groups (p = 0.7). We conclude that divergent drilling and insertion of screws creates more horizontal force when miniplates are used, and results in reduction in the size of the probable gap in the fracture line. Insertion of divergent screws in miniplates may create compression between fractured segments without jeopardising the strength of fixation. © 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Keywords: Mandibular fractures; Fracture fixation; Bone plates Introduction Mandibular fracture is one of the most common fractures of the facial bones. 1 Despite considerable advances in internal fixation during recent decades, we still need to understand ∗ Corresponding author at: Parvaneh Avenue, Velenjak Street, Tehran 1985711151, Iran. Tel.: +98 9126214250; fax: +98 21 88695955. E-mail address: Fal2zad@gmail.com (F. Aghdashi). the behaviour of fixation devices in mandibular tension zones. 2–4 The gap in the fracture line in some parts of the mandible tends to widen as a result of the function of muscles: this is known as tension, 4,5 and different proce- dures have been developed to overcome this. To achieve rapid function, we use maximum rigid fixation to minimise the movement of the bone at the fracture line according to the AO system, and the use of a compression plate is prudent. 6 http://dx.doi.org/10.1016/j.bjoms.2015.03.017 0266-4356/© 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.