Mineral features of connective dental hard tissues in hypoplastic amelogenesis imperfecta.

OBJECTIVE: To explore the mineral features of dentin and cementum in hypoplastic Amelogenesis imperfecta AI teeth. MATERIALS AND METHODS: Forty-four (44) teeth cleaned and free of caries were used: 20 control and 24 affected by hypoplastic amelogenesis imperfecta. Thirty-two teeth were studied by pQCT, cut in sections, and analyzed under microradiography, polarized light microscopy, and confocal Raman spectroscopy. Eight teeth were observed under scanning electron microscope. Four teeth were used for an X-ray diffraction. The mineral density data were analyzed statistically with the Mann-Whitney U test, using GraphPad InStat software. RESULTS: Both coronal dentin and radicular dentin were less mineralized in AI teeth when compared to control (respectively 6.2% and 6.8%; p < .001). Root dentinal walls were thin and irregular, while the cellular cementum layers were thick, reaching sometimes the cervical region of the tooth. Regular dentinal tubules and sclerotic dentin areas were noticed. Partially tubular or cellular dysplastic dentin and hyper-, normo-, or hypomineralized areas were noticed in the inter-radicular areas of hypoplastic AI teeth. The main mineral component was carbonate hydroxyapatite as explored by Raman spectroscopy and X-ray diffraction. CONCLUSIONS: Dentin and cementum in hypoplastic AI teeth are (i) hypomineralized, (ii) constituted of carbonate hydroxyapatite, and (iii) of non-homogenous structure.

Souakine mouth rinse solution protects deciduous enamel from simulated erosion in vitro.

AIM: To determine whether a souakine mouth rinse solution can provide protection of deciduous teeth against simulated erosion in vitro. MATERIALS AND METHODS: Thirty deciduous anterior teeth were used. Half of each tooth was covered with a varnish and teeth were randomly divided into a treated (S) and a control group (C). Each group was immersed in cola drink for 5 minutes and treated with an aqueous solution of Souakine (S) or water (C) for 2 minutes. The treatment was renewed 5 times a day for 8 days. Teeth were then embedded, sectioned and observed under polarised light microscope. Observed data were quantitatively analysed by SPSS software. RESULTS: In group (C), the unvarnished part of the enamel showed a deep green layer of erosion, compared to the varnished part. The difference in depth of this layer was significant (p<0.05). In group (S), the green layer of erosion was highly located in the unvarnished part as compared to the unvarnished part of the control group (C) (p<0.05). This layer of erosion was comparable to that in the varnished part, either in control or treated groups. CONCLUSION: The beneficial results of Souakine against erosion are validated either by a protective or a remineralisation effect.

Mandibular bone alterations of ovariectomized rats under vitamin D insufficiency.

UNLABELLED: Experimental osteoporosis was studied in mandible bone by means of ovariectomy and vitamin D insufficiency. METHODS: 42 female Wistar rats were divided into the following four groups: (1) ovariectomized rats maintained in 12h day-night light conditions (ov-l), (2) ovariectomized rats maintained in 24h dark light conditions (ov-ob), (3) sham-operated rats maintained in 12h day-night light conditions (ch-l) and (4) sham-operated rats maintained in 24 h dark conditions (ch-ob). 12 weeks later the animals were sacrificed, the mandibles were excised, cleaned and weighed, the right side of the mandibles were histologically examined and the left side of the mandibles were prepared for mineral phase analysis by X-ray diffraction. Immunohistochemical analysis was performed to detect apoptotic cells by anti-PARP p85 antibody. RESULTS: In group 2, the weight of mandibles significantly decreased. Chondroid areas were observed in ovariectomized groups and polarized light observation validated the collagen distribution disturbance in these groups (groups 1 and 2). Apoptotic osteoblasts were localized in groups 1, 2 and 4. They were numerous in group 2. The mineral phase analysis did not find differences between the groups. CONCLUSION: This study validates a new model of osteoporotic animal associating estrogens deficiency and vitamin D insufficiency where matrix synthesis and osteoblast biology are altered, but not biomineralization.

Study of the effect of aqueous extract of Grewia tenax fruit on iron absorption by everted gut sac.

Grewia tenax roots, leaves, juice and fruit decoctions have been used in Africa and Southeast Asiatic countries for a variety of medical purposes. In this investigation, we report the effect of aqueous extract of Grewia tenax fruit (AEGTF) on the variation in vitro of iron absorption. The incubation of freshly prepared rat everted gut sac (EGS) in Ringer medium containing FeSO(4) in the absence of AEGTF showed that in stomach there is iron absorption only at 15 min of incubation time, whereas, at duodenum and jejunum, iron uptake occurs just after 1 min of incubation time and the maximum of iron absorption is registered at 15 min of incubation time. Addition of AEGTF at different concentrations favors significantly this iron transfer from the mucous side toward the serous one. The maximum of iron absorption was carried out in the presence of AEGTF at 10 mg/ml and 5 min of incubation time in stomach, duodenum and jejunum. AEGTF used at high doses (20 and 30 mg/ml) reduced significantly iron uptake suggesting a probable toxic effect of this extract. Histological studies confirmed the presence of cytotoxic signs as multinucleated giant cells and the disappearance of enterocyte border brush. With the aim of elucidating the mechanism of action of AEGTF, we are attempting to isolate the active principles present in this extract.

Msx1 homeogene antisense mRNA in mouse dental and bone cells.

Msx1 plays a key role in early dental and cranio-facial patterning. A systematic screening of Msx1 transcripts during late postnatal stages of development evidenced not only sense mRNA but also antisense mRNA in the skeleton. Natural antisenses are able to bind their corresponding sense RNAs and block protein expression. Specific reverse-transcription polymerase chain reaction (RT-PCR) Northern-blotting using riboprobes and primer extension analysis allowed to identify and sequence a mouse 2184-base Msx1 antisense transcript. The transcription start site was located in a region including a consensus TATA box. In situ hybridization evidenced an increase in antisense mRNA expression during dental and bone cell differentiation in prenatal (Theiler stages E15.5-18.5) and newborn mice. This upregulation was related to Msx1 protein downregulation in cells expressing Msx1 sense mRNA. In vitro, transient Msx1 sense and antisense mRNA overexpression was performed in MO6-G3 cells, which pertain to the odontoblast lineage (polarization and dentin sialoprotein and phosphoprotein synthesis). The balance between antisense and sense Msx1 mRNAs appeared to control Msx1 protein levels. These data suggest that a bidirectional transcription of Msx1 homeogene may control Msx1 protein levels, and therefore may be critical in cell communication and differentiation during dental and cranio-facial development and mineralization.

Endogenous Msx1 antisense transcript: in vivo and in vitro evidences, structure, and potential involvement in skeleton development in mammals.

Msx1 is a key factor for the development of tooth and craniofacial skeleton and has been proposed to play a pivotal role in terminal cell differentiation. In this paper, we demonstrated the presence of an endogenous Msx1 antisense RNA (Msx1-AS RNA) in mice, rats, and humans. In situ analysis revealed that this RNA is expressed only in differentiated dental and bone cells with an inverse correlation with Msx1 protein. These in vivo data and overexpression of Msx1 sense and AS RNA in an odontoblastic cell line (MO6-G3) showed that the balance between the levels of the two Msx1 RNAs is related to the expression of Msx1 protein. To analyze the impact of this balance in the Msx-Dlx homeoprotein pathway, we analyzed the effect of Msx1, Msx2, and Dlx5 overexpression on proteins involved in skeletal differentiation. We showed that the Msx1-AS RNA is involved in crosstalk between the Msx-Dlx pathways because its expression was abolished by Dlx5. Msx1 was shown to down-regulate a master gene of skeletal cells differentiation, Cbfa1. All these data strongly suggest that the ratio between Msx1 sense and antisense RNAs is a very important factor in the control of skeletal terminal differentiation. Finally, the initiation site for Msx1-AS RNA transcription was located by primer extension in both mouse and human in an identical region, including a consensus TATA box, suggesting an evolutionary conservation of the AS RNA-mediated regulation of Msx1 gene expression.