Regional variations in mineralization and strain distributions in the cortex of the human mandibular condyle I. Cioffi a, ⁎ , L.J. van Ruijven b , G.A.P. Renders b , M. Farella a , A. Michelotti a , T.M.G.J. van Eijden b a Department of Oral and Maxillo-Facial Sciences, Section of Orthodontics and Clinical Gnathology, University of Naples “Federico II”, via Pansini 5, I-80131 Naples, Italy b Department of Functional Anatomy, Academic Centre for Dentistry Amsterdam (ACTA), Universiteit van Amsterdam and Vrije Universiteit, Netherlands Received 6 April 2007; revised 15 May 2007; accepted 17 August 2007 Available online 5 September 2007 Abstract The strain (i.e. deformation) history influences the degree of mineralization of cortical bone (DMB) as well as its osteonal microstructure. This study aimed to examine the relationships of stress and strain distributions with the variations in DMB and the osteonal orientations in the cortical bone of the human mandibular condyle. It was hypothesized that strains are inversely proportional to local DMB and that the principal strains are oriented parallel to the osteons. To test this, ten human mandibular condyles were scanned in a microCT system. Finite element models were created in order to simulate static clenching. Within each condyle, 18 volumes of interest were selected to analyze regional differences in DMB, stress and strains. Subchondral bone showed a lower equivalent strain (2652 ± 612 με) as compared to the anterior (p = 0.030) and posterior cortex (p = 0.007) and was less mineralized. Contrary to our hypothesis, the results show that strains correlated positively with regional variations in DMB (r = 0.750, p b 0.001). In the anterior and the posterior cortex, the first principal strain was parallel to the cortical surface and oriented supero-inferiorly with a fan-like shape. In subchondral bone, the first and the second principal strain were parallel to the surface and oriented antero-posteriorly and medio- laterally, respectively. It was concluded that the strain distributions, by themselves, cannot explain the regional differences found in DMB. In agreement with our second hypothesis, the orientation of the osteonal network of the mandibular condyle was closely related to the strain orientations. The results of this study suggest that the subchondral and the cortical bone are structured to ensure an optimal load distribution within the mandibular condyle and have a different mechanical behaviour. Subchondral bone plays a major role in the transmission of the strains to the anterior and posterior cortex, while these ensure an optimal transmission of the strains within the condylar neck and, eventually, to the mandibular ramus. © 2007 Elsevier Inc. All rights reserved. Keywords: Mineralization; Strain; Cortical bone; Mandibular condyle; Finite element model Introduction Bone is a dynamic tissue capable of adapting its structure to local mechanical stimuli by continuous bone renewal [1–3]. It has been noted that strains occurring within bone affect this turnover and hence bone macrostructure (i.e. shape and size of bones) and microstructure (i.e. osteons, plates, rods etc.) by initiating cell-mediated remodelling [4,5]. Consequently, bone morphology and internal architecture strongly depend on the deformation history [6–8]. Except for the bone structure, the deformation history also influences the mineralization of bone since the average age of bone tissue is inversely proportional to the remodelling rate, and the mineralization is proportional to the bone age. Therefore, bone mineral content is commonly believed to be inversely proportional to the rate of remodelling [9]. For cortical bone, the relationship between mechanical loading and mineralization has been investigated in several bones. Regional variations in cortical bone mineralization have been related to the amount or to the mode (i.e. tensile/com- pressive) of locally occurring strains [10–12]. A significant Bone 41 (2007) 1051 – 1058 www.elsevier.com/locate/bone ⁎ Corresponding author. Fax: +39 08119722885. E-mail address: iacopo.cioffi@unina.it (I. Cioffi). 8756-3282/$ - see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.bone.2007.08.033