Original Full Length Article Microstructural properties of the mid-facial bones in relation to the distribution of occlusal loading Aleksa Janovic a,b , Petar Milovanovic b , Igor Saveljic c , Dalibor Nikolic c , Michael Hahn d , Zoran Rakocevic a , Nenad Filipovic c , Michael Amling d , Bjoern Busse d , Marija Djuric b, ⁎ a Department of Radiology, School of Dentistry, University of Belgrade, 6 Rankeova, 11 000 Belgrade, Serbia b Laboratory for Anthropology, Institute of Anatomy, Faculty of Medicine, University of Belgrade, 4/2 Dr Subotica, 11 000 Belgrade, Serbia c Bioengineering Research and Development Center (BioIRC), Faculty of Engineering, University of Kragujevac, 6 Prvoslava Stojanovica, 34 000 Kragujevac, Serbia d Department of Osteology & Biomechanics, University Medical Center Hamburg-Eppendorf, 59 Lottestr., D-22529 Hamburg, Germany abstract article info Article history: Received 31 March 2014 Revised 22 July 2014 Accepted 25 July 2014 Available online 2 August 2014 Edited by: David Fyhrie Keywords: Micro-architecture Bone Mid-facial skeleton Micro-CT Finite element analysis Although the concept of the occlusal load transfer through the facial skeleton along the buttresses has been extensively studied, there has been no study to link microarchitecture of the mid-facial bones to the occlusal load distribution. The aim of this study was to analyze micro-structural properties of the mid-facial bones in relation to occlusal stress. The study was performed by combining the three-dimensional finite element analysis (3D FEA) and micro-computed tomography analysis (micro-CT). Clenching was simulated on the computer model of the adult male human skull which was also used as a source of bone specimens. After the FEA was run, stress was measured at the specific sites in cortical shell and trabecular bone of the model along and between the buttresses. From the corresponding sites on the skull, twenty-five cortical and thirteen cancellous bone specimens were harvested. The specimens were classified into high stress or low stress group based on the stress levels measured via the FEA. Micro-architecture of each specimen was assessed by micro-CT. In the high stress group, cortical bone showed a tendency toward greater thickness and density, lower porosity, and greater pore separation. Stress-related differences in microstructure between the groups were more pronounced in trabecular bone, which showed significantly greater bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) in the high stress group. Our results suggest that the mid-facial bones in the adult dentate male skull exhibit regional variations in cortical and trabecular bone micro-architecture that could be a consequence of different occlusal stress. © 2014 Elsevier Inc. All rights reserved. Introduction Early descriptions of the maxillofacial architecture were made at the beginning of the 20th century, when a few researchers observed pillar- like areas within the mid-facial skeleton composed of a thick cortical bone [1–3]. These areas were assumed to act as “buttresses” that ensure structural integrity of the mid-facial skeleton during mastication by transferring occlusal loads from the teeth to the skull [3]. Seven vertical buttresses had been suggested to transfer most of the occlusal loads [3, 4], while three horizontal buttresses were proposed to be indirectly in- volved in performing this task by interconnecting the vertical buttresses at different levels [4,5]. The remaining bony regions between the but- tresses were assumed fragile and not involved in the occlusal load trans- fer due to their thin cortical bone structure [2,3]. However, recent investigations of the buttresses via finite element analysis (FEA) brought new findings related to the pattern of occlusal load distribution to light. Stress along buttresses was frequently regis- tered only in the anterior maxilla, whereas it was distributed uniformly over the posterior maxilla having no form of buttresses [6,7]. It was also demonstrated that cortical bone in the anterior maxilla bears most of the load, while in the posterior maxilla the load distributes evenly through the cortical bone [7]. Moreover, recent finite element analysis revealed that the areas of the mid-facial bones that were initially considered irrelevant for the dissipation of occlusal forces actually experience very high stress during biting [6–8]. Along with the analyses of the mid-facial biomechanics, recent investigations of the facial bone structure revealed tremendous regional variations in cortical and trabecular bone architecture in dentulous indi- viduals [9–11]. Thin cortical bone placed between the buttresses was found to be generally denser in comparison to areas containing thick cortical bone [9,10]. Regional variations in density of both cortical and trabecular bone were also detected on CT images in dentulous patients [11]. Beside structural differences, the elastic modulus of the cortical bone varied significantly across the dentulous maxilla [10]. These Bone 68 (2014) 108–114 ⁎ Corresponding author at: Laboratory for Anthropology, Institute of Anatomy, School of Medicine, University of Belgrade, 4/2 Dr Subotica, 11000 Belgrade, Serbia. Fax: +381 11 2686 172. E-mail address: marijadjuric5@gmail.com (M. Djuric). http://dx.doi.org/10.1016/j.bone.2014.07.032 8756-3282/© 2014 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Bone journal homepage: www.elsevier.com/locate/bone