Histologic evaluation and immunohistochemical localization of STRO-1 and BMP-4 in rat immature teeth: A comparison between vital and induced pulp necrosis

Cytotoxicity of intracanal dressings on apical papilla cells differ upon activation with E. faecalis LTA

Objective

The aim of this study was to investigate the cytotoxic effects of modified triple antibiotic paste and an experimental composition using calcium hydroxide on lipoteichoic acid (LTA)-primed apical papilla cells (APC).

Material and Methods

Human APC were tested for in vitro cytotoxicity of modified Triple Antibiotic Paste (mTAP – Ciprofloxacin, Metronidazole and Cefaclor at 1:1:1) and of a paste of Ciprofloxacin, Metronidazole and Calcium hydroxide (CMC – 1:1:2) and modified CMC (mCMC – 2:2:1) by using MTT assay. The substances were reconstituted in DMEM at 1,000 µg/mL and ¼ serially diluted before being kept in contact with cells for 1, 3, 5 and 7 days. Further, cells were primed with 1 µg/mL of Enterococcus faecalis LTA for 7 days prior to the viability test with 1,000 µg/mL of each substance. Statistical analysis was performed using one-way analysis of variance (ANOVA) and two-way ANOVA respectively followed by Tukey’s post-test. Significance levels were set at p<0.05.

Results

In the first assay, the higher cytotoxic rates were reached by mTAP for all experimental periods. CMC was found toxic for APC at 5 and 7 days, whereas mCMC did not affect the cell viability. Only CMC and mCMC were able to induce some cellular proliferation. In the second assay, when considering the condition with medium only, LTA-primed cells significantly proliferated in comparison to LTA-untreated ones. At this context, mTAP and CMC showed similar cytotoxicity than the observed for LTA-untreated cells, while mCMC was shown cytotoxic at 7 days only for LTA-primed APC. Comparing the medications, mTAP was more cytotoxic than CMC and mCMC.

Conclusion

mTAP showed higher cytotoxicity than CMC and mCMC and the effect of topic antimicrobials might differ when tested against apical papilla cells under physiological or activated conditions.

The role of Osterix protein in the pathogenesis of peripheral ossifying fibroma

Peripheral ossifying fibroma (POF) is a reactive lesion of oral tissues, associated with local factors such as trauma or presence of dental biofilm. POF treatment consists of curettage of the lesion combined with root scaling of adjacent teeth and/or removal of other sources of irritants. This study aimed to analyze the clinical and pathological features of POF and to investigate the immunoexpression of Osterix and STRO-1 proteins. Data such as age, gender, and size were obtained from 30 cases of POF. Microscopic features were assessed by conventional light microscopy using hematoxylin-eosin staining and immunohistochemical markers, and by polarized light microscopy using Picrosirius red staining. The age range was 11-70 years and 70% of the patients were female. Moreover, the size of POF varied from 0.2 to 5.0 cm; in 43.33% of the cases, the mineralized content consisted exclusively of bony trabeculae. The immunohistochemical analysis showed nuclear staining for Osterix in 63% and for STRO-1 in 20% of the cases. Mature collagen fibers were observed in mineralized tissue in 76.67% of the cases. The clinical and microscopic features observed were in agreement with those described in the literature. Osterix was overexpressed, while STRO-1 was poorly expressed. Osterix was expressed particularly in cells entrapped in and around mineralized tissue, indicating the presence of a stimulus that triggers the differentiation of these cells into osteoblasts or cementoblasts, i.e., cells that produce mineralized tissue. Based on our results, Osterix may play a role in the pathogenesis of POF.

Differential expression between "DSP-only" and DSP-PP523 transcripts in rat molar teeth

OBJECTIVE

To compare the expression patterns of two multiple transcripts derived from DSP-PP gene during tooth development. One is DSP-only transcript (i.e. does not encode PP) and the other is DSP-PP₅₂₃ transcript, a main DSP-PP transcript.

DESIGN

Unique antisense and sense riboprobes were generated from DSP-only and DSPPP₅₂₃ cDNAs for in situ studies to examine DSP-only and DSP-PP₅₂₃ transcript expression in developing molars. Paraffin-embedded sections (5-7μ m) from embryonic 20day, postnatal 2, 3 and 6days were deparaffined and hydrated. Tissues were prehybridized, then hybridized with DSP-only and DSP-PP₅₂₃ anti-sense (AS) or sense (S) Digoxigenin labeled-riboprobes overnight, and washed. Anti-Digoxigenin antibodies conjugated to alkaline phosphatase were used to detect the presence of bound riboprobes by color reaction with NBT/BCIP. Stro-1 antibody was used for immunohistochemical analysis of Stro-1 protein expression in rat molars.

RESULTS

We found that unlike the DSP-PP₅₂₃ transcript, the DSP-only transcript does not express in the entire polarized mature odontoblasts but is expressed in the areas subjacent to the mature odontoblast layer. In addition, DSP-only transcript is expressed in the dental pulp. Interestingly, Stro-1 protein, a stem cell marker, was also identified in the areas subjacentto odontoblasts and in dental pulp.

CONCLUSION

Differential expression of DSP-only and DSP-PP₅₂₃ transcripts suggest that these two kinds of transcripts may play different roles during dentinogenesis. DSP-PP₅₂₃ transcript is expressed in mature odontoblasts, which actively participates in dentin formation. DSP-only transcript might have a different function.