Abstract
There are histological and functional differences between human deciduous and permanent periodontal ligament (PDL) tissues. The aim of this study was to determine the differences between these two types of tissue at the molecular level by comparing their gene expression patterns. PDL samples were obtained from permanent premolars (n = 38) and anterior deciduous teeth (n = 31) extracted from 40 healthy persons. Comparative cDNA microarray analysis revealed several differences in gene expression between the deciduous and permanent PDL tissues. These findings were verified by qRT-PCR (quantitative reverse-transcription–polymerase chain reaction) analysis, and the areas where genes are expressed were revealed by immunohistochemical staining. The expressions of 21 genes were up-regulated in deciduous relative to PDL tissues, and those of 30 genes were up-regulated in permanent relative to deciduous PDL tissues. The genes that were up-regulated in deciduous PDL tissues were those involved in the formation of the extracellular matrix (LAMC2, LAMB3, and COMP), tissue development (IGF2BP, MAB21L2, and PAX3), and inflammatory or immune reactions leading to tissue degradation (IL1A, CCL21, and CCL18). The up-regulated genes in permanent PDL tissues were related to tissue degradation (IL6 and ADAMTS18), myocontraction (PDE3B, CASQ2, and MYH10), and neurological responses (FOS, NCAM2, SYT1, SLC22A3, DOCK3, LRRTM1, LRRTM3, PRSS12, and ARPP21). The analysis of differential gene expressions between deciduous and permanent PDL tissues aids our understanding of histological and functional differences between them at the molecular level.
Highlights
The periodontal ligament (PDL) tissues are components of the dental apparatus that connect the tooth to the alveolar jaw bone in the area surrounding the root surfaces
Collagen type I is a predominant component of PDL tissue, but collagen types III, V, VI, and XII, and proteoglycans, which are known to regulate collagen fibril formation, are found in this tissue [1,2]
PDLs usually tear across their middle during tooth extraction, and they contain PDL fibroblasts, epithelial cell rests of Malassez, cementoblasts, vascular cells, and sensory nerve cells, and osteoblasts, which make and maintain the alveolar bone
Summary
The periodontal ligament (PDL) tissues are components of the dental apparatus that connect the tooth to the alveolar jaw bone in the area surrounding the root surfaces. There are many anatomical, embryological, functional, and structural differences between human deciduous and permanent teeth. Deciduous and permanent teeth exhibit different responses to external stimuli, and the sensory nerve endings are fewer and looser in permanent than in deciduous teeth [3,4]. Because of the different responses of dental pulp tissues, the modalities of pulp therapy should differ between deciduous and permanent teeth [5]. In vitro and in vivo experiments have shown that cells originating from deciduous teeth behave differently to those from permanent teeth [6,7]
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