Method: Twenty-four dentin beams (1x1x4 mm) were obtained from sound third molars and deciduous molars (n=12). The beams were completely demineralized in 10% phosphoric acid for 18h at 3-4oC and rinsed in deionized water for 2h. The total MMP activity was analyzed by a colorimetric assay (SensoLyte®). Collagen degradation was assessed by dry mass loss, elastic modulus (E) change and ICTP and CTX release after 1 week, 1 month and 2 months in artificial saliva at 37oC. Data from each response variable were submitted to ANOVA and Tukey tests at 5% level of significance.
Result: Total MMP activity was not statistically different between deciduous and permanent dentin. Loss of dry mass was higher for deciduous dentin after 1 week of storage compared to permanent dentin. However, no difference was seen after 1 and 2 months. Although the initial elastic modulus was lower for deciduous dentin (1.28±0.40 MPa) compared to permanent dentin (1.84±0.53 MPa), there was a similar reduction in that property for both substrates. After only 7 days of storage, primary dentin had the elastic modulus reduced by 54.3%, while the reduction was 51.8% for permanent dentin. No further reduction was seen after 1 or 2 months of storage. Both ICTP and CTX fragments were higher for deciduous dentin than for permanent dentin reaching a significant difference at the 1-week storage.
Conclusion: Both deciduous and permanent dentin presented comparable proteolytic activity. However, the rate of collagen degradation seems to be faster for primary dentin.