Development of functional dentin incisors after a partial resection of the odontogenic organ of rat incisors

Evaluation of tooth eruption rate of incisor teeth in rats with estrogen deficiency

OBJECTIVES

To assess the influence of estrogen deficiency on tooth eruption rate (TER) and gene expression of estrogen receptor alpha and beta (ERα and ERβ) in the odontogenic region of teeth with continuous formation in a rat model.

MATERIALS AND METHODS

Ovariectomies (OVX; n = 25) and sham surgeries (SHAM; n = 25) were performed in female Wistar rats when animals were 25 days old. The TER of the lower incisors, both in impeded (hyperfunction condition) and unimpeded (trimmed incisal edge-hypofunction condition) conditions, was evaluated using standardized digital photographs acquired every 48-72 h for 3 weeks (35th-53rd day of life), using a camera coupled to a stereomicroscope. Quantitative real-time PCR was performed to evaluate the relative gene expression of ERα and ERβ in the odontogenic region.

RESULTS

The OVX group showed a significant reduction in TER when compared to the SHAM group, only in the impeded condition (p = 0.03). There was no statistically significant difference between the groups in ERα gene expression (p = 0.33). ERβ showed a significantly higher gene expression in the OVX group (p ≤ 0.05).

CONCLUSIONS

Estrogen deficiency decreases TER in teeth under impeded condition. Estrogen deficiency also increases ERβ gene expression in the odontogenic region of teeth with continuous formation.

CLINICAL RELEVANCE

Hormonal disturbances affecting estrogen levels can cause alterations in dental formation and teeth eruption.

Ozonated oil effect for prevention of medication-related osteonecrosis of the jaw (MRONJ) in rats undergoing zoledronic acid therapy

OBJECTIVES

The aim of this study was to evaluate the preventive effect of ozonated oil on the development of MRONJ-like lesions at tooth extraction sites in rats submitted to zoledronic acid treatment.

MATERIALS AND METHODS

Twelve rats were divided into two groups. Each rat received an injection of zoledronic acid solution once a week for 5 weeks before having its upper first molar extracted. In group 1, the clotted socket was maintained, while in the group 2, the socket was treated with ozonated oil for 10 min/day during 3 days. After euthanasia, block resection was performed for histological analysis. Necrotic bone was defined as the area of the bone with empty osteocyte lacunae and vital bone as the area with osteocyte-occupied lacunae.

RESULTS

There was no statistically significant difference between the groups in the average area of vital bone (p = 0.2248) and the average area of necrotic bone (p = 0.1208). However, the average area of vital bone in group 1 was smaller (24.1 ± 2.9 cells/cm²) than in group 2 (26.8 ± 4.2 cells/cm²), and the average area of necrotic bone in group 1 was higher (7.0 ± 2.5 cells/cm²) than in group 2 (4.0 ± 1.1 cells/cm²), indicating that ozonated oil may reduce the development of osteonecrosis.

CONCLUSIONS

Our findings suggest that ozonated oil might prevent MRONJ-like lesions at tooth extraction sites in rats submitted to a disease induction protocol. Further research should be conducted to confirm this hypothesis.

CLINICAL RELEVANCE

MRONJ has been reported as a complication of surgical dental procedures, and there are currently no predictable preventive therapies.

Effect of radiotherapy on the eruption rate and morphology of the odontogenic region of rat incisors

OBJECTIVE

The goal in this study was to evaluate the results of doses of 5 and 15 Gy of radiation in odontogenic region of the rats inferior mandibular-incisors by a histological analysis and the rate of eruptions.

DESIGN

Animals were divided into three groups: control, radiotherapy 5 Gy and radiotherapy 15 Gy. In which tooth-eruption-rate was measured every two days.

RESULTS

Animals in Group 5 Gy presented values similar to those of the control group. Animals in Group 15 Gy presented reduction in tooth-eruption-rate as of the sixth day of the experiment, vast disorganization of odontoblasts and ameloblasts, apparent reduction in cell population in the follicle region and alterations in cervical loop formation of the dental organ.

CONCLUSIONS

It was concluded that there was a difference between the researched doses, and histological alteration at 15 Gy lead to statistical reduction in tooth-eruption-rate.

Effects of the bisphosphonate alendronate on molars of young rats after lateral luxation

BACKGROUND AND AIM

The bisphosphonate alendronate (ALN) was employed with the aim of investigating its effects on dental and periodontal tissues after lateral luxation of developing molars.

MATERIAL AND METHODS

Twenty-one-day-old Wistar rats had their second upper molars laterally luxated. Daily 2.5 mg kg(-1) ALN injections started at the day of the luxation; controls received sterile saline solution. The teeth were analyzed 7, 14, and 21 days after the procedure. On the days cited, the maxillae were fixed, decalcified, and embedded in paraffin or Spurr resin. The paraffin sections were stained with H&E, incubated for TRAP histochemistry or immunolabeled for osteopontin (OPN). Spurr ultrathin sections were examined in a transmission electron microscope.

RESULTS

After 21 days, the root apex of luxated molars without ALN was wide open and disorganized and also covered by an irregular layer of cellular cementum, which was not observed in ALN-treated animals. Ankylosis sites were observed in ALN rats in both luxated and non-luxated teeth. The TRAP-positive osteoclasts were more numerous in ALN group, despite their latent ultrastructural appearance without the presence of resorption apparatus compared to controls. OPN immunolabeling revealed a thick immunopositive line in the dentin that must be resultant from the moment of the luxation, while ALN-treated specimens did not present alterations in dentin.

CONCLUSION

The present findings indicate that alendronate inhibits some alterations in dentin and cementum formation induced by dental trauma.

The relationship between the cusp pattern and plural stem cell compartments in Guinea pig cheek teeth by chasing BrdU-labeling

Continuously growing rodent incisors have a special epithelial structure for maintaining adult stem cells that shows a bulbous epithelial protrusion at the apical end and is referred to as an "apical bud". Guinea pig cheek teeth (premolars and molars), also continuously growing teeth, have a complex crown shape consisting of plural cusps. The present study clarifies the existence of apical buds in guinea pig premolars/molars as it examines the relationship between the crown shape and the orientation of the apical buds by micro-computed tomography (micro-CT) and immunohistochemistry for 5-bromo-2'-deoxyuridine (BrdU). One premolar and three molar teeth in each side of the maxillae and mandibles assumed characteristic features: each horizontally-sectioned tooth showing a complex zigzag shape was composed of a core of dentin covered by a layer of enamel on all axial surfaces except the buccal of the uppers and the lingual of the lowers. Furthermore, four bulbous epithelial protrusions--including the stellate reticulum--were recognized in the apical end of each tooth, where slow-cycling long-term label-retaining cells resided 20 days after a peritoneal injection of BrdU. These data indicate that guinea pig premolars/molars have four apical buds where the epithelial adult stem cells reside. In contrast, rodent incisors, which show a single cone appearance, are covered by enamel on the labial side and possess only one apical bud. The results of this study suggest that plural apical buds, being arranged bucco-lingually and mesio-distally, produce the crown mold in a zigzag fashion.

Enamel-free teeth: Tbx1 deletion affects amelogenesis in rodent incisors

TBX1 is a principal candidate gene for DiGeorge syndrome, a developmental anomaly that affects the heart, thymus, parathyroid, face, and teeth. A mouse model carrying a deletion in a functional region of the Tbx1 gene has been extensively used to study anomalies related to this syndrome. We have used the Tbx1 null mouse to understand the tooth phenotype reported in patients afflicted by DiGeorge syndrome. Because of the early lethality of the Tbx1-/- mice, we used long-term culture techniques that allow the unharmed growth of incisors until their full maturity. All cultured incisors of Tbx1-/- mice were hypoplastic and lacked enamel, while thorough histological examinations demonstrated the complete absence of ameloblasts. The absence of enamel is preceded by a decrease in proliferation of the ameloblast precursor cells and a reduction in amelogenin gene expression. The cervical loop area of the incisor, which contains the niche for the epithelial stem cells, was either severely reduced or completely missing in mutant incisors. In contrast, ectopic expression of Tbx1 was observed in incisors from mice with upregulated Fibroblast Growth Factor signalling and was closely linked to ectopic enamel formation and deposition in these incisors. These results demonstrate that Tbx1 is essential for the maintenance of ameloblast progenitor cells in rodent incisors and that its deletion results in the absence of enamel formation.