Identifying early osteoclastic resorptive lesions in feline teeth: a model for understanding the origin of multiple idiopathic root resorption.

BACKGROUND AND OBJECTIVE: Domestic cats commonly suffer from external osteoclastic tooth resorption, a disease with many similarities to human multiple idiopathic root resorption. In both diseases, it is unclear whether anatomical features of the tooth surface are associated with a predisposition for resorptive lesions. The aim of the present study was to investigate the origin and progression of early feline osteoclastic resorptive lesions in teeth exhibiting no clinical signs of disease. MATERIAL AND METHODS: The entire surfaces of 138 teeth from 13 adult cats were analysed using back-scattered electron microscopy. The distribution of lesions was assessed by tooth type, location and between individuals. RESULTS: Seventy-three (53%) teeth showed at least one resorptive lesion. Eleven (85%) cats had lesions, and there was a significant association between increasing age and incidence of resorptive lesions. The highest frequency occurred in mandibular molars (82%). On average, there were 3.5 lesions per tooth. Fifty-two (38%) teeth featured resorptive lesions at the cemento-enamel junction. Twenty-three per cent of teeth with resorptive lesions showed evidence of repair of lesions that was limited to the root surface. There was no evidence of repair of resorptive lesions at the cemento-enamel junction. CONCLUSION: Resorption is prevalent without evidence of clinical disease, and occurred at younger ages than previously reported. It can initiate anywhere on the root surface, but lack of repair of lesions at the cemento-enamel junction indicates that mechanisms of replacement are absent or compromised in this region. Whereas resorption of the root may undergo repair, resorption at the cervix may progress to clinically evident lesions.

Analysis of the surface characteristics and mineralization status of feline teeth using scanning electron microscopy.

External resorption of teeth by odontoclasts is a common condition of unknown origin affecting domestic cats. Odontoclastic resorptive lesions involve the enamel cementum junction (ECJ, cervix) and root surface, leading to extensive loss of enamel, dentine and cementum. This study was undertaken in order to determine whether features of the surface anatomy and mineralization of feline teeth could explain why odontoclastic resorptive lesions are so prevalent in this species. Backscattered electron scanning electron microscopy was used to study enamel, cementum and dentine in non-resorbed, undemineralized teeth from adult cats. Analysis of the ECJ revealed thin enamel and cementum and exposed dentine at this site. Furthermore, enamel mineralization decreased from the crown tip to the ECJ, and dentine mineralization was lowest at the ECJ and cervical root. Analysis of cementum revealed variations in the organization and composition of fibres between the cervical, mid- and apical root although no significant differences in mineralization of cementum were detected between different regions of the root. Reparative patches associated with resorption of cementum by odontoclasts and repair by cementoblasts were present on the root surface. In conclusion, results suggest that the ECJ and cervical dentine could be at a greater risk of destruction by odontoclasts compared with other regions of the tooth. The relationship of these features to the development and progression of resorption now requires further examination.

A comparison of methods for measuring serum and urinary markers of bone metabolism in cats.

Biochemical markers of bone cell activity have recently been shown to be useful for monitoring skeletal health in domestic animals, including dogs and horses. The aim of this study was to evaluate a number of biochemical assays, originally developed for use in humans, for their ability to measure indicators of bone cell activity in serum and urine of normal cats over a range of ages. Bone alkaline phosphatase (BAP), a marker of bone formation, was measured in serum using wheatgerm lectin precipitation (WGL) and by ELISA. The curve derived from serial dilution of feline serum was parallel with the ELISA standard curve, indicating species cross-reactivity, and there was a significant relationship between assays (rs = 0.97, P < 0.001). Deoxypyridinoline (DPD), a marker of bone resorption, was measured in its total form in urine by HPLC and ELISA, and in its free form in serum and urine by ELISA. The dilution curve for free DPD in urine showed parallelism with the assay standard curve; however, the curves for total DPD in urine and serum did not. A significant relationship was established between total urinary DPD (HPLC) with total serum DPD (rs = 0.69, P < 0.001), and with free urinary DPD (rs = 0.95, P < 0.001) concentrations. Carboxy-terminal telopeptide of type I collagen (CTX) concentration, another marker of bone resorption, was measured in serum and urine by ELISA, and there was a significant relationship between assays (rs = 0.82, P < 0.001). CTX could not be measured reliably using an auto-analysis method. A significant relationship was established between total urinary DPD (HPLC) with serum CTX (rs = 0.59, P < 0.05), and urinary CTX (rs = 0.65, P < 0.001) concentrations. BAP (ELISA and WGL), total urinary DPD (HPLC), urinary CTX (ELISA), and serum CTX (ELISA) concentrations were significantly inversely correlated with age (rs = -0.66, -0.88, -0.61, -0.70, and -0.51, P < 0.05 respectively). Cats under two years of age had significantly higher BAP, total urinary DPD (HPLC), and urinary CTX concentrations compared to older cats. In conclusion, this study has shown that a number of commercially available assays provide reliable methods for non-invasively monitoring bone cell activity in cats and has shown that bone turnover decreases within the first two years of life, until complete skeletal maturity is attained. Future studies can now be directed at evaluating the potential clinical application of these methods.

Cytokine expression in feline osteoclastic resorptive lesions.

Feline osteoclastic resorptive lesions (FORL) of the teeth are common in cats, and lead to pain, destruction of the periodontal ligament, and tooth loss. The expression of interleukin (IL)-1 beta and IL-6 mRNA was higher in teeth with FORL than in normal teeth (P<0.01 and P<0.001, respectively), but no such differences were found between pathological and normal gingival tissue samples. There were no differences between teeth affected with FORL and normal teeth in respect of the expression of receptor activator of NF kappa B ligand (RANKL) mRNA or osteoprotegerin (OPG) mRNA. However, OPG mRNA expression was higher in gingival tissue associated with teeth affected with FORL than in normal gingival tissue (P<0.05), whereas the reverse was true of RANKL mRNA expression (P<0.05). OPG mRNA expression was significantly higher in teeth than in femoral and alveolar bone (P<0.001). RANKL and OPG mRNAs were detected in all tissues examined. The data suggest that the elevated expression of IL-l beta and IL-6 mRNA plays a role in the mediation of osteoclast activity in advanced FORL. In contrast, OPG and RANKL do not appear to regulate osteoclasts in advanced disease. The results also suggest that OPG and RANKL mRNA play a role in mediating inflammatory responses in gingival cells, and that OPG has an inhibiting effect on tooth resorption.