Immunohistochemical expression of hard tissue related factors in the mouse dental pulp after immediate teeth separation

Abstract

We examined change of Runx2 and ALP expression in mouse tooth pulp which exposed to teeth separation experiment by immunohistochemistry as a model for conservative dentistry treatment. 8-week-old 36 male ddY mice were used and wedge was inserted between upper 1st and 2nd molars. The wedge was removed 30 minutes as well as 3 hours after the insertion and the samples were prepared extending up to 1 week of time period for regular histopathological and immunohistochemical examinations for ALP and Runx2 expression. The opposite sides without wedge insertion were taken as controls. In the control group pulp, weak expressions of Runx2 and ALP in the vessel endothelial cells as well as the pulp cells were revealed, suggesting the appearance of these genes upon mechanical stress induced by mastication and tongue pressure etc. On the other hand in the experiment group, Runx2 expression increased both in 30-minute and 3-hour teeth separation group. The expression became maximum at 24 hours. Then it gradually decreased and became similar level with the control group at 1-week after the wedge insertion. Similarly ALP expression increased after the wedge insertion and was maximum at 24 hours and then gradually decreased to the levels similar with the control group. These results suggest that when immunohistochemical expression of Runx2 as well as ALP was used as an index, no severe damage occur upon clinical application of wedge insertion.

Regeneration of Dentin Using Stem Cells Present in the Pulp

“…In our previous studies, we induced the differentiation of dental pulp cells by adding injurious stimulation to the periodontium and pulp [10,11]. Nabeyama et al have shown that there is a weak positive reaction for Runx2 in the pulp tissue that has not been artificially stimulated [10]. This is similar to the results of the study conducted by Nakano et al [35,36], and it is presumed that it is a reaction to physiological stimuli, such as mastication and occlusion.…”

“…Additionally, ALP expressed in the early stage of calcification associated with odontoblast differentiation is an index of odonoblastic activity [33]. In our previous studies, we induced the differentiation of dental pulp cells by adding injurious stimulation to the periodontium and pulp [10,11]. Nabeyama et al have shown that there is a weak positive reaction for Runx2 in the pulp tissue that has not been artificially stimulated [10].…”

“…This is similar to the results of the study conducted by Nakano et al [35,36], and it is presumed that it is a reaction to physiological stimuli, such as mastication and occlusion. Furthermore, Nabeyama et al observed tissue changes in the pulp by stimulating the pulp with the immediate teeth separation method used for dental treatment for 30 min and observed the expression of Runx2 in odontoblasts, vascular endothelial cells of the pulp, and pulp-specific cells [10]. Additionally, its expression reached the maximum levels after 24 h, then gradually disappeared, and decreased to the same level as that of the control group at 1 week.…”

“…We have shown previously that orthodontic mechanical stress and artificial inflammation stimulate the cells of the periodontium and dental pulp to express various cell differentiation factors. The osteoblast marker alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2), which induces osteoblast differentiation, and heat shock proteins (HSPs), which are involved in homeostasis and cell differentiation, may be strongly expressed in cells exposed to injurious stimuli [7][8][9][10][11][12]. Moreover, periodontal tissue and dental pulp respond to mechanical stresses and inflammation, causing periodontal tissue remodeling and expression of cell differentiation-related factors [13].…”

“…Moreover, periodontal tissue and dental pulp respond to mechanical stresses and inflammation, causing periodontal tissue remodeling and expression of cell differentiation-related factors [13]. Furthermore, orthodontic mechanical stress on the periodontium causes activation of hard tissue-forming cells in the pulp tissue [10,11]. This indicates the potential of dental pulp stem cells to differentiate into hard tissue-forming cells upon stimulation.…”