Oral submucous fibrosis: Review on aetiology and pathogenesis. Tilakaratne WM, Klinikowski MF, Saku T, Peters TJ, Warnakulasuriya S. The Centre for Research in Clinical and Diagnostic Oral Sciences, School of Medicine and Dentistry, Barts and The London, London, UK; Department of Oral Pathology, Faculty of Dental Sciences, University of Peradeniya, Sri Lanka; Division of Oral Pathology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan. Data from recent epidemiological studies provide overwhelming evidence that areca nut is the main aetiological factor for OSF. A clear dose-dependent relationship was observed for both frequency and duration of chewing areca nut (without tobacco) in the development of OSF. Commercially freeze dried products such as pan masala, Guthka and mawa (areca and lime) have high concentrates of areca nut per chew and appear to cause OSF more rapidly than by self prepared conventional betel quid that contain smaller amounts of areca nut. It is logical to hypothesise that the increased collagen synthesis or reduced collagen degradation as possible mechanisms in the development of the disease. There are numerous biological pathways involved in the above processes and, it is likely that the normal regulatory mechanisms are either down regulated or up regulated at different stages of the disease. Among the chemical constituents, alkaloids from areca nut are the most important biologically whilst tannin may have a synergistic role. These chemicals appear to interfere with the molecular processes of deposition and/or degradation of extracellular matrix molecules such as collagen. In vitro studies on human fibroblasts using areca extracts or chemically purified arecoline support the theory of fibroblastic proliferation and increased collagen formation that is also demonstrable histologically in human OSF tissues. The copper content of areca nut is high and the possible role of copper as a mediator of fibrosis is supported by the demonstration of up regulation of lysyl oxidase in OSF biopsies. It has been postulated that areca nut may also induce the development of the disease by increased levels of cytokines in the lamina propria. Increased and continuous deposition of extracellular matrix may take place as a result of disruption of the equilibrium between matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMP). Current evidence implicates collagen-related genes in the susceptibility and pathogenesis of OSF. The individual mechanisms operating at various stages of the disease-initial, intermediate and advanced-need further study in order to propose appropriate therapeutic interventions.

  Expression of type X collagen and capillary endothelium in condylar cartilage during osteogenic transition--a comparison between adaptive remodelling and natural growth. Shen G, Zhao Z, Kaluarachchi K, Rabie AB. Department of Orthodontics, Shanghai Ninth People's Hospital, Shanghai JiaoTong University, China. Adaptive remodelling of the condylar cartilage in response to mandibular protrusion constitutes the rationale for bite-jumping appliances to solicit growth modification. By investigating the expression of type X collagen and capillary endothelium, this study was designed to evaluate the osteogenic transition of chondrogenesis during adaptive remodelling of condylar cartilage and compare it with that under natural condylar growth. One hundred female Sprague-Dawley rats, 35 days of age, were divided into five experimental groups (n = 15, fitted with bite-jumping appliances) where condylar adaptation was created by forward repositioning of the mandible, and five control groups (n = 5) where the condyles underwent natural growth. The animals were sacrificed at 3, 7, 14, 21 and 30 days and 7 microm serial sections of the condyles were processed for in situ hybridization and immunohistochemical analyses. The expression of type X collagen in the hypertrophic zone and capillary endothelium in the erosive zone of condylar cartilage were examined to evaluate osteogenic transition, a critical programme leading to endochondral ossification. The results showed that (1) The temporal pattern of the expression of type X collagen and capillary endothelium during condylar adaptation coincided with that during natural condylar growth. (2) The amount of the expression of these two factors during condylar adaptation was significantly higher than that during natural growth (P < 0.001). It is suggested that condylar adaptation in growing rats triggered by mandibular forward positioning enhances osteogenic transition which eventually results in increased bone formation.

A quantitative assessment of the healing of intramembranous and endochondral autogenous bone grafts

RWK Wong and ABM Rabie

Orthodontics, University of Hong Kong, Hong Kong Special Administrative Region, PRC

The aim of the study was to assess quantitatively the amount of new bone formed in the early stages of healing of intramembranous and endochondral autogenous bone grafts so as to gain further insight into their integration with host bone. Eighteen critical size defects were created in the parietal bone of nine New Zealand White rabbits. In the experimental group (five rabbits), each rabbit was grafted with intramembranous bone in one defect and with endochondral bone in the other. In the control group (four rabbits), one defect was left empty (passive control) and the other was grafted with rabbit skin collagen (active control). After 14 days, the rabbits were killed and the defects were prepared for histological analysis. Serial sections were made across the whole defect. Each defect was divided into five regions spaced 1500 µm apart. Two sections were randomly drawn from each region. Quantitative analysis was performed on 100 sections using an image analyser computer software system to assess the amount of new bone formed in each defect. No bone was detected across the defect in either the active or passive controls. One-hundred-and-sixty-six per cent more new bone was formed in defects grafted with intramembranous bone than those grafted with endochondral bone. This represented an extremely significant difference (P<0.0001, unpaired t-test) between the two groups. The results show that intramembranous autogenous bone produced more bone than the endochondral bone when grafted in the skull. Clinically, it is recommended that intramembranous bone is used to replace lost membranous bone in the oral cavity, as well as in skull defects, whenever possible

Compensatory bone formation in young and old rats during tooth movement

Satoshi Shimpo¹, Yuji Horiguchi¹, Yoshiki Nakamura¹, Minyeon Lee², Takashi Oikawa¹, Koji Noda¹, Yosuke Kuwahara¹ and Kenzo Kawasaki³

1 Departments of Orthodontics, Tsurumi University, Yokohama, Japan 2 Department of Orthodontics, Hallym University, Seoul, Korea 3 Departments of Anatomy, Tsurumi University, Yokohama, Japan

The aim of this study was to investigate compensatory lingual alveolar bone formation during tooth movement in young and old rats, using the vital bone marker tetracycline. Wistar male rats were separated into the following groups: 13-week-old rats without appliances (13C: control, n = 5), 60-week-old rats without appliances (60C: control, n = 5), 13-week-old rats with appliances (13E: experimental, n = 10), and 60-week-old rats with appliances (60E: experimental, n = 10). The upper first molars of the 13E and 60E groups were moved lingually using fixed appliances. On the third day of tooth movement, tetracycline (TC) was intra-peritoneally injected in all animals including the controls. On the 21st day of tooth movement, the animals were killed and unfixed, and undecalcified, 5-µm frozen frontal sections of the rat first molar areas in both control and experimental groups were examined under light and fluorescent microscopes.

In the 13C group without tooth movement, tetracycline labelling lines were obvious in the alveolar crest, apical areas, and interradicular septum, indicating vertical alveolar bone growth. However, in the 60C control group, tetracycline labelling was almost undetectable throughout the alveolar bone.

Although the lingual alveolar crest was resorbed from the periodontal side after lingual tooth movement, the sharp, bright labelling lines were still present from the crest to the lingual periosteal alveolar bone in the 13E group. In the 60E group the lines appeared in the lingual periosteal alveolar bone containing the crest, indicating considerable new bone formation. The results indicate that compensatory bone formation occurs in the alveolar crest area and, consequently, alveolar bone height is maintained, even in aged rats.