The purpose of this study was to clarify the prevalence and degree of root resorption induced by orthodontic treatment in association with treatment factors. The files of 243 patients (72 males and 171 females) aged 9-51 years were randomly selected from subjects treated with multi-bracket appliances. The severity of root resorption was classified into five categories on radiographs taken before and after treatment. The subjects were divided into extraction (n = 113 patients, 2805 teeth) and non-extraction (n = 130 patients, 3616 teeth) groups and surgical (n = 56 patients, 1503 teeth) and non-surgical treatment (n = 187 patients, 4918 teeth) groups. These subjects were also divided into two or three groups based on the duration of multiloop edgewise archwire (MEAW) treatment, elastic use, and total treatment time: 0 month (T1; n = 184 patients, 4831 teeth), range 1-6 months (T2; n = 37 patients, 994 teeth), more than 6 months (T3; n = 22 patients, 596 teeth); range 0-6 months (n = 114 patients, 3016 teeth) more than 6 months (n = 129 patients, 3405 teeth); range 1-30 months (n = 148 patients, 3913 teeth) and more than 30 months (n = 95 patients, 2508 teeth). The prevalence of overall and severe root resorption evaluated by the number of subjects and teeth was compared with a chi-square test. A Student's t-test for unpaired data was used to determine any statistically significant differences. The prevalence of severe root resorption based on the number of teeth was significantly higher in the group with extractions (P < 0.01). Longer use of a MEAW appliance and elastics also produced a significantly higher prevalence of root resorption (P < 0.05). On the other hand, the prevalence of severe root resorption was not significantly different between the subjects treated with or without surgery, but there was a significant increase when treatment time was prolonged (P < 0.05). A significant difference was found in the amount of root movement of the upper central incisors and the distance from their root apices to the cortical bone surface (P < 0.05). These are regarded as essential factors in the onset of root resorption. These results indicate that orthodontic treatment with extractions, long-term use of a MEAW appliance and elastics, treatment time, and distance of tooth movement are risk factors for severe root resorption.

Amelogenins are the major constituent of developing extracellular enamel matrix proteins and are understood to have an exclusively epithelial origin. Recent studies have demonstrated that amelogenins can be detected in other tissues, including bone marrow mesenchymal stem cells (MSCs), but the role of amelogenins in MSCs remains unclear. The purpose of this study was to examine the effect of recombinant human full-length amelogenin (rh174) on the osteogenic differentiation of cultured human MSCs. MSCs isolated from human bone marrow were cultured in osteoblastic differentiation medium with 0, 10 or 100 ng/ml rh174. The mRNA levels of bone markers were examined by real-time PCR analysis. Alkaline phosphatase (ALP) activity and calcium concentration were determined. Mineralization was evaluated by alizarin red staining. The mRNA levels of ALP, type I collagen, osteopontin and bone sialoprotein in the MSCs treated with rh174 became significantly higher than those in non-treated controls. Treatment of MSCs with rh174 also enhanced ALP activity and calcium concentration, resulting in enhanced mineralization, as denoted by high intensity of alizarin red staining. In conclusion, the present study showed that rh174 enhances the mineralization accompanied by the upregulation of bone markers in human bone marrow MSCs during osteogenic differentiation, suggesting a certain role of amelogenin in the modulation of osteogenic differentiation of MSCs.

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Differentiated embryo chondrocyte 2 (DEC2) is a basic helix-loop-helix-Orange transcription factor that regulates cell differentiation in various mammalian tissues. DEC2 has been shown to suppress the differentiation of mesenchymal stem cells (MSCs) into myocytes and adipocytes. In the present study, we examined the role of DEC2 in the chondrogenic differentiation of human MSCs. The overexpression of DEC2 exerted minimal effects on the proliferation of MSCs in monolayer cultures with the growth medium under undifferentiating conditions, whereas it suppressed increases in DNA content, glycosaminoglycan content, and the expression of several chondrocyte-related genes, including aggrecan and type X collagen alpha 1, in MSC pellets in centrifuge tubes under chondrogenic conditions. In the pellets exposed to chondrogenesis induction medium, DEC2 overexpression downregulated the mRNA expression of fibroblast growth factor 18, which is involved in the proliferation and differentiation of chondrocytes, and upregulated the expression of p16INK4, which is a cell cycle inhibitor. These findings suggest that DEC2 is a negative regulator of the proliferation and differentiation of chondrocyte lineage-committed mesenchymal cells.

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