A mouse model of inflammatory root resorption induced by pulpal infection

A novel experimental model to investigate fungal involvement shows expression of Dectin-1 in periapical lesion pathogenesis

BACKGROUND

Candida albicans is linked to persistent endodontic lesions. However, the recognition receptor that identifies it is not explored previously.

OBJECTIVES

The aim of this study was to (1) establish a zymosan-induced model of apical periodontitis in mouse, (2) observe the expression of Dectin-1 and its possible relationship with toll-like receptor (TLR) 2 and (3) observe relationship between Osteopontin (OPN) and inflammatory cytokines.

METHODS

A total of 138 Naval Medical Research Institute (NMRI) mice were randomly divided into; Experimental Group n = 69 and Zymosan Group n = 69. Periapical periodontitis was developed in right maxillary molar. The animals were sacrificed at 7, 21 and 42 days. Bone blocks containing the mesial root (n = 15 for qRT-PCR, n = 45 for enzyme-linked immune sorbent assay (ELISA)) were collected for mRNA expression and ELISA. While whole maxilla (n = 3 from each time interval) were used for histology and immunohistochemical analysis. One way analysis of variance (ANOVA) and Tuckey's posthoc was used for statistical analysis at p ≤ .05.

RESULTS

TLR-2, Dectin-1 and TLR4-positive cells was detected at all time intervals in both groups. A strong positive correlation was observed between TLR-2 and Dectin-1 in both lesions (regular r = .680, p = .015, zymosan (r = .861, p < .001)). A significant correlation was found between OPN and tumour necrosis factor-alpha (TNF-α) in zymosan lesion (r = .827, p = .001).

CONCLUSIONS

Immune cells of inflamed periapical tissue expressed Dectin-1 receptor in response to the microbial challenge from infected root canals and showed positive correlation with TLR-2 and OPN suggesting a possible receptor collaboration mediated by OPN. The expression of OPN and TNF-α showed positive correlation in response to fungal antigen, indicating a possible relationship.

Trigeminal neurons control immune-bone cell interaction and metabolism in apical periodontitis

Abstract

Apical periodontitis (AP) is an inflammatory disease occurring following tooth infection with distinct osteolytic activity. Despite increasing evidence that sensory neurons participate in regulation of non-neuronal cells, their role in the development of AP is largely unknown. We hypothesized that trigeminal ganglia (TG) Nav1.8⁺ nociceptors regulate bone metabolism changes in response to AP. A selective ablation of nociceptive neurons in Nav1.8^Cre/Diphtheria toxin A (DTA)^Lox mouse line was used to evaluate the development and progression of AP using murine model of infection-induced AP. Ablation of Nav1.8⁺ nociceptors had earlier progression of AP with larger osteolytic lesions. Immunohistochemical and RNAscope analyses demonstrated greater number of macrophages, T-cells, osteoclast and osteoblast precursors and an increased RANKL:OPG ratio at earlier time points among Nav1.8^Cre/ DTA^Lox mice. There was an increased expression of IL-1α and IL-6 within lesions of nociceptor-ablated mice. Further, co-culture experiments demonstrated that TG neurons promoted osteoblast mineralization and inhibited osteoclastic function. The findings suggest that TG Nav1.8⁺ neurons contribute to modulation of the AP development by delaying the influx of immune cells, promoting osteoblastic differentiation, and decreasing osteoclastic activities. This newly uncovered mechanism could become a therapeutic strategy for the treatment of AP and minimize the persistence of osteolytic lesions in refractory cases.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00018-022-04335-w.

Role(s) of cytokines in pulpitis: Latest evidence and therapeutic approaches

Pulpitis is known as a typical inflammation of dental pulp tissue, and microorganisms of the oral microbiome are involved in this opportunistic infection. Studies indicated that several factors related to host response have a crucial role in pulpitis. Among these factors, inflammatory mediators of the immune system such as cytokines and chemokines contribute to pulpal defense mechanisms. A wide range of cytokines have been observed in dental pulp and these small molecules are able to trigger inflammation and participate in immune cell trafficking, cell proliferation, inflammation, and tissue damage in pulp space. Therefore, the aim of this review was to describe the role of cytokines in the pathogenesis of pulpitis.

Use of micro-computed tomography for the assessment of periapical lesions in small rodents: a systematic review

This systematic review aimed to evaluate the literature on the acquisition-, reconstruction- and analysis parameters of micro-computed tomography (micro-CT) for the assessment of periapical lesions in rats and mice, and to illustrate the effect of variation in these parameters. The PubMed database was searched from 2000 to January 2015 (English-language publications) for reports on the use of micro-CT to evaluate periapical lesions in rats and mice. QUADAS criteria were used to rate the quality of the studies. To illustrate the effect of variations in acquisition-, reconstruction-, and analysis parameters on images of periapical lesions, micro-CT examination of two hemi-mandibles of mice, with periapical lesions around the first molar was undertaken. Twenty-one studies were identified, which analysed periapical lesions in rats or mice using micro-CT. According to the QUADAS, no study was classified as high-, seven were classified as moderate-, and 14 as low quality. The effect of variation in parameters was that voxel size may interfere with image sharpness, reconstruction may interfere with image sharpness and contrast, and inadequate plane orientation may alter the size of the periapical lesion. Nonpersonalized ROIs resulted in areas that were not part of the periapical lesion. Changing the limits of the threshold for bone-tissue visualization increased lesion size. There is no defined protocol for acquiring and analysing micro-CT images of periapical lesions in rats and mice. Furthermore, acquisition-, reconstruction- and analysis parameters are not adequately explained, which may compromise the scientific impact of the studies.

Correlation Between Histomorphometric and Micro-computed Tomography Analysis of Periapical Lesions in Mice Model

Periapical lesions are processes mediated from bacterial invasion on the pulp tissue, which results in inflammatory process and bone resorption. Animal models have been used for the study of cell interactions and inflammatory responses involved in periapical lesion. The use of different methods for morphometric evaluation of this lesion has been reported. However, due to the limitation of 2D methods, computerized microtomography (µCT) has been indicated. Therefore, the aim of this study was to evaluate the correlation between the histomorphometric measures of periapical lesions and the µCT analysis obtained in an animal experimental model. Briefly, the periapical lesions were induced by pulp exposal and after the experimental periods (7, 21 and 42 days) the mice were euthanized. The mandibles were evaluated under the µCT scanning and then were subjected to the routine histologic procedures, stained with hematoxilin and eosin. The periapical lesions were measured by the specific softwares of each technique. A weak correlation among the histomorphometric measurement and the 2D µCT analysis (r(2)= .204) and between the histomorphometric measurement and the 3D µCT analysis (r(2)= .237) was observed. A strong correlation between the 2D and 3D µCT analysis (r(2)= .867) was observed. Thereby, it can be concluded that the µCT is a method that allows a precise volumetric scanning and represents an important tool for morphometric evaluation.

RNA interference-mediated silencing of Atp6i prevents both periapical bone erosion and inflammation in the mouse model of endodontic disease

Dental caries is one of the most prevalent infectious diseases in the United States, affecting approximately 80% of children and the majority of adults. Dental caries may lead to endodontic disease, where the bacterial infection progresses to the root canal system of the tooth, leading to periapical inflammation, bone erosion, severe pain, and tooth loss. Periapical inflammation may also exacerbate inflammation in other parts of the body. Although conventional clinical therapies for this disease are successful in approximately 80% of cases, there is still an urgent need for increased efficacy of treatment. In this study, we applied a novel gene-therapeutic approach using recombinant adeno-associated virus (AAV)-mediated Atp6i RNA interference (RNAi) knockdown of Atp6i/TIRC7 gene expression to simultaneously target periapical bone resorption and periapical inflammation. We found that Atp6i inhibition impaired osteoclast function in vitro and in vivo and decreased the number of T cells in the periapical lesion. Notably, AAV-mediated Atp6i/TIRC7 knockdown gene therapy reduced bacterial infection-stimulated bone resorption by 80% in the mouse model of endodontic disease. Importantly, Atp6i(+/-) mice with haploinsufficiency of Atp6i exhibited protection similar to that in mice with bacterial infection-stimulated bone erosion and periapical inflammation, which confirms the potential therapeutic effect of AAV-small hairpin RNA (shRNA)-Atp6i/TIRC7. Our results demonstrate that AAV-mediated Atp6i/TIRC7 knockdown in periapical tissues can inhibit endodontic disease development, bone resorption, and inflammation, indicating for the first time that this potential gene therapy may significantly improve the health of those who suffer from endodontic disease.

Accuracy of Root ZX II in locating foramen in teeth with apical periodontitis: an in vivo study

INTRODUCTION

This study was conducted in vivo to investigate the accuracy of Root ZX II in locating the apical foramen in teeth with apical periodontitis (AP).

METHODS

Twenty-seven single-root teeth scheduled for extractions were selected; in AP group, there were 12 teeth with pulp necrosis and radiographic evidence of apical lesions, and VT group consisted of 15 vital teeth. After endodontic access, the coronal portion of the canal was flared, and electronic measurement was performed by using a 15 K-file until the device level reading "APEX" was reached. The file was fixed in place, and the tooth was extracted. The apical third of the root was shaved until exposure of the file. The distance from the file tip to the most coronal border of the apical foramen was obtained.

RESULTS

The mean distance in AP group was +0.117 (standard deviation, 0.373) and in VT group was -0.105 (standard deviation, 0.218). The unpaired t test showed no difference between the groups when comparing the mean distances (P > .05). The apical foramen was accurately located within ±0.5 mm in 83% of the teeth in AP group and in 100% of VT group. Statistical analysis showed no difference between the groups (P = .1092).

CONCLUSIONS

The Root ZX II device was accurate in locating the apical foramen regardless of the presence of AP.

Root and periodontal tissue development after allogenic tooth transplantation between rat littermates

OBJECTIVE

The study was designed to investigate the development of roots and periodontal tissues after allogenic tooth transplantation between rat littermates by micro-computed tomography (micro-CT) and histology.

MATERIALS AND METHODS

The upper right second molars in 2-week-old rats were extracted and immediately transplanted into the upper right first molar socket of rat littermates under anesthesia. The upper left second molars in 2-week-old recipient rats were used as a control. The rats were fixed and tissues analyzed at 0, 4, 8, or 12 weeks after transplantation. Root development of seven rats in each group was analyzed quantitatively using micro-CT. Periodontal tissue formation was examined qualitatively by histologic methods.

RESULTS

Roots developed after allogenic transplantation, but they were significantly shorter than control roots. The number of roots varied from one to four in transplanted teeth, while it was consistently four in control teeth. Periodontal tissue formation in transplanted teeth was equivalent to that of the control teeth.

CONCLUSION

Allogenic transplantation between rat littermates permits root development and periodontal tissue formation.

Quantitative measurements obtained by micro-computed tomography and confocal laser scanning microscopy

OBJECTIVES

To compare measurements obtained by micro-CT with those obtained by confocal laser scanning microscope in simulative internal resorption cavities.

METHODS

An extracted human maxillary central incisor tooth was divided into two in the coronal plane. Four artificial internal resorption cavities were prepared with standardized burs on each section, and diameters and volumes were measured using a laser scanning electron confocal microscope and a desktop cone beam micro-CT-40. Differences between means of quantitative measurements for both methods were tested using the paired t-test; the correlation between quantitative measurements was tested by regression analysis.

RESULTS

Mean diameter and volume differences between the two methods were 0.061 mm and 0.004 mm(3), respectively. Average diameter and volume calculations obtained by micro-CT were significantly lower (P < 0.001 for diameter and P < 0.01 for volume). A significantly strong relationship was found in the average diameters (R(2) = 92.9%) and calculated volumes (R(2) = 91%), (P < 0.001).

CONCLUSIONS

Although a strong correlation between both methods was found, micro-CT significantly underestimated the diameters and volumes.

Histopathologic study of physiological and pathological resorptions in human primary teeth

This study presents a histological analysis through optical microscopy of primary teeth with physiological and pathological resorptions to outline the histological profile of resorptions. Sixty teeth were examined: 19 primary teeth with physiological resorption and 41 primary teeth with pathological resorption. To analyze the histological conditions of the pulp, periradicular tissue, and the resorption areas, and to investigate the presence, intensity, and location of bacteria, slides were prepared using the hematoxylin-eosin and the Brown-Brenn techniques. For the teeth with physiological resorption, normal pulps and no evidence of bacteria were found. For the teeth with pathological resorption, pulpal alterations, atypical resorption, and bacteria were observed.

Milk basic protein increases alveolar bone formation in rat experimental periodontitis

BACKGROUND AND OBJECTIVE

It is conceivable that the active components extracted from milk whey protein (i.e. milk basic protein, MBP) stimulate bone formation and suppress bone resorption. Periodontitis is characterized by excessive alveolar bone resorption. We examined whether milk basic protein could recover alveolar bone loss in rat experimental periodontitis.

MATERIAL AND METHODS

A nylon ligature was placed around the cervix of molars in 8-wk-old male Fischer rats for 20 d. Then, the ligature was removed and a powder diet containing 0.2 or 1.0% milk basic protein was provided daily for another 45-90 d. On days 45 and 90, the maxillae were extracted and analyzed using microcomputerized tomography (micro-CT), followed by histological analysis.

RESULTS

Micro-CT images showed that alveolar bone resorption was severely induced around the molar by the 20-d ligature procedure. Treatment with high-dose milk basic protein (1.0%) clearly recovered ligature-induced alveolar bone resorption on days 45 and 90, whereas low-dose milk basic protein (0.2%) did not show such a clear effect. Histological examination clarified that the osteoid thickness of alveolar bone was dose dependently increased by milk basic protein treatment for 90 d.

CONCLUSION

These findings suggest that a systemic administration of milk basic protein may be effective for the recovery of alveolar bone loss in periodontitis.

The effect of chemical inhibition of matrix metalloproteinases on the size of experimentally induced apical periodontitis

AIM

To determine the effect of matrix metalloproteinase (MMP) inhibition on periapical lesion formation in a rat model.

METHODOLOGY

The pulp chambers of mandibular fist molars of adult SD rats were exposed to be infected by oral microbes. The experimental group was fed 20 mg kg(-1) MMP-inhibitor chemically modified tetracycline-3 (CMT-3) daily in an oral gavage and the controls were fed the vehicle. After 2 and 4 weeks, the mandibles (n = 10 in both groups at both times) were radiographed, decalcified and subjected to histological analysis. Extension of necrosis in first molar distal root canals was measured from the histological sections, and periapical lesion sizes in the same roots were determined from radiographs and histological sections. Mann-Whitney U-test was used for the statistical analysis.

RESULTS

There was a statistically significant difference in the extension of necrosis in root canals between 2 and 4 weeks in the control group (P < 0.05), but not with MMP inhibition. Radiographically, MMP inhibition increased the periapical lesion size by 70% and 34% after 2 and 4 weeks respectively (P < 0.05 in after 2 weeks). In histological measurements, lesion size increased with MMP inhibition by 26% and 8% after 2 and 4 weeks respectively.

CONCLUSIONS

MMP inhibition affects pulpal and periapical inflammation, increasing the rate of spreading of necrosis in root canals and the rate of periapical lesion formation.

Dentin sialophosphoprotein knockout mouse teeth display widened predentin zone and develop defective dentin mineralization similar to human dentinogenesis imperfecta type III

Dentin sialophosphoprotein (Dspp) is mainly expressed in teeth by the odontoblasts and preameloblasts. The Dspp mRNA is translated into a single protein, Dspp, and cleaved into two peptides, dentin sialoprotein and dentin phosphoprotein, that are localized within the dentin matrix. Recently, mutations in this gene were identified in human dentinogenesis imperfecta II (Online Mendelian Inheritance in Man (OMIM) accession number 125490) and in dentin dysplasia II (OMIM accession number 125420) syndromes. Herein, we report the generation of Dspp-null mice that develop tooth defects similar to human dentinogenesis imperfecta III with enlarged pulp chambers, increased width of predentin zone, hypomineralization, and pulp exposure. Electron microscopy revealed an irregular mineralization front and a lack of calcospherites coalescence in the dentin. Interestingly, the levels of biglycan and decorin, small leucine-rich proteoglycans, were increased in the widened predentin zone and in void spaces among the calcospherites in the dentin of null teeth. These enhanced levels correlate well with the defective regions in mineralization and further indicate that these molecules may adversely affect the dentin mineralization process by interfering with coalescence of calcospherites. Overall, our results identify a crucial role for Dspp in orchestrating the events essential during dentin mineralization, including potential regulation of proteoglycan levels.