Adaptation of a rat dentoalveolar complex was illustrated using various imaging modalities. Micro-X-ray computed tomography for 3D modeling, combined with complementary techniques, including image processing, scanning electron microscopy, fluorochrome labeling, conventional histology (H&E, TRAP), and immunohistochemistry (RANKL, OPN) elucidated the dynamic nature of bone, the periodontal ligament-space, and cementum in the rat periodontium. Tomography and electron microscopy illustrated structural adaptation of calcified tissues at a higher resolution. Ongoing biomineralization was analyzed using fluorochrome labeling, and by evaluating attenuation profiles using virtual sections from 3D tomographies. Osteoclastic distribution as a function of anatomical location was illustrated by combining histology, immunohistochemistry, and tomography. While tomography and SEM provided past resorption-related events, future adaptive changes were deduced by identifying matrix biomolecules using immunohistochemistry. Thus, a dynamic picture of the dentoalveolar complex in rats was illustrated. 1. Introduction The load-bearing bone is a dynamic tissue and continuously adapts to changes in loads [1]. In the periodontium, the cementum of a tooth is attached to the alveolar bone by the periodontal ligament (PDL), and the root is contained within the alveolar bone socket. Cementum and bone are calcified tissues of similar chemical composition, but cementum is far less dynamic [2]. The vascularized and innervated PDL consists of basic constituents that resist and dampen mechanical loads. Different types of collagen and noncollagenous proteins including polyanionic water attracting molecules, the proteoglycans (PGs), all of which accommodate cyclic occlusal loads of varying magnitudes and directions. Unlike other ligaments within the musculoskeletal system, the blood vessels in the PDL are continuous with blood vessels in the endosteal spaces of bone [3]. Although PDL and bone are two dissimilar tissues in physical and chemical properties, the continuity formed by blood vessels enables a flow of nutrients and maintains cellular activity responsible for PDL turnover and bone remodeling and modeling. Development and growth superimposed with functional loads [4] may cause posterior lengthening of the rat jaw [5], and can contribute to PDL turnover, bone remodeling, and load-related modeling during the lifespan of a rat. As a result, rat molars are thought to exhibit an inherent distal drift [6], but this theory continues to be controversial [7, 8]. Regardless, the drift of the
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