The Relation between Matrix Metalloproteinase Activity in Different positions of Dentin in Primary Teeth and its Relation to Root Resorption

Abstract

Aim: The aims of this study were to compare the level of MMP activity in primary teeth in coronal vs. pulpal dentin, teeth with no less than ¾ of the root resorbed (high resorption) vs. teeth with no more than ¼ of the root resorbed (low resorption) and teeth tested immediately vs. teeth tested after 2-month storage. Materials and Methods: 64 exfoliated/extracted human primary posterior teeth were obtained (32 teeth from each category: 1- low resorption, 2- high resorption). Each group was divided into two subgroups of 16 teeth, with each subgroup demonstrating a different storage time. Two pieces of sound dentin 2 mm by 2 mm were cut, one from the coronal dentin and one from pulpal dentin from each tooth. Their weights and volumes were recorded. For all of the teeth in the storage group, 32 coronal slices and 32 pulpal slices were stored in an artificial saliva for 2 months at 37°C, each slice separately. For the other group, the slices were tested for MMP activity immediately. The total MMP activity was determined by measuring the fluorescence intensity at Ex/Em=490 nm/520 nm in a plate reader against blanks. Results: For the immediate testing group, when including observations from both pulpal dentin and coronal dentin, the median (IQR) of the teeth with low resorption was 2081.9 (568.2, 3169.0), while the median (IQR) of the teeth with high resorption was 1105.9 (335.7, 1702.0). Furthermore, when including observations with immediate testing from both the teeth with low resorption and the teeth with high resorption, the median (IQR) of the pulpal dentin was 1285.7 v (555.7, 3880.5), as opposed to 1186.5 (469.7, 2124.1) for the coronal dentin. The generalized linear mixed models (GLMM) for the immediate testing case (including both root resorption group and dentin position in the model) showed no significant difference in the MMP activity between the teeth with low resorption and the teeth with high resorption (p = 0.288) and the coronal and pulpal dentin (p = 0.169). After 2 months of storage, the median (IQR) of the teeth with low resorption was 322.9 (97.9, 1525.7), while the median (IQR) of the teeth with high resorption was 320.7 (51.7, 1308.5). Furthermore, when including observations stored for 2 months from both the teeth with low resorption and the teeth with high resorption, the median (IQR) of the pulpal dentin was 331.1 (93.4, 1470.8), as opposed to 303.0 (62.1, 1401.9) for the coronal dentin. The generalized linear mixed models (GLMM) for the 2 months of storage case (including both root resorption group and dentin position in the model) showed no significant difference in the MMP activity between the teeth with low resorption and the teeth with high resorption (p = 0.687) and the coronal and pulpal dentin (p = 0.987). Conclusion: The overall MMP activity is not significantly different between teeth with no less than ¾ of the root resorbed (high resorption) and teeth with no more than ¼ of the root resorbed (low resorption), and between coronal and pulpal dentin either tested immediately or after storage.