Calcium hydroxide induces dentine formation in permanent teeth, while it causes resorption of tooth in deciduous teeth. How is this dual role explained?
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For more than 70 years calcium hydroxide has played a major role in endodontic therapy, although many of its functions are now being taken over by the recently introduced material MTA. Calcium hydroxide may be used to preserve the vital pulp if infection and bleeding are controlled; to repair root fractures, perforations, open apices and root resorptions [1].
Calcium ions released from calcium hydroxide stimulates fibronectin synthesis in dental pulp cells. Fibronectin might induce the differentiation of dental pulp cells to mineralized tissue forming cells that are the main cells to form dentine bridges, via contact with cells [2].
Calcium hydroxide ($Ca(OH)_2$) is known to cause internal resorption in the deciduous dentition. Though this has been attributed to chronic inflammation and odontoclasts, the exact mechanism has not been elucidated. $Ca(OH)_2$-induced odontoclastogenesis could be multifactorial. Odontoclasts may result from fusion of cells of monocyte/macrophage series either due to inflammatory mediators or through stimulation by stromal odontoblasts / fibroblasts. Pre-existing progenitor cells of primary tooth pulp because of their inherent propensity may transform into odontoclasts [3].
References:
Carrotte P. Endodontics: Part 9. Calcium hydroxide, root resorption, endo-perio lesions. Br Dent J. 2004 Dec 25;197(12):735-43. doi: 10.1038/sj.bdj.4811897. PubMed PMID: 15608732.
Mizuno M, Banzai Y. Calcium ion release from calcium hydroxide stimulated fibronectin gene expression in dental pulp cells and the differentiation of dental pulp cells to mineralized tissue forming cells by fibronectin. Int Endod J. 2008 Nov;41(11):933-8. doi: 10.1111/j.1365-2591.2008.01420.x. PubMed PMID: 19133082.
Ravi G R, Subramanyam R V. Calcium hydroxide-induced resorption of deciduous teeth: A possible explanation. Dent Hypotheses [serial online] 2012 [cited 2014 Jun 7];3:90-4.
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2$\begingroup$ Teeth are made of calcium hydroxyl apatite: $(Ca_5(PO_4)_3 OH)$, which can be transformed by fluoride ions into the much harder calcium fluor apatite $(Ca_5(PO_4)_3 F)$. $\endgroup$– Chris ♦Commented Jun 7, 2014 at 18:24