Histopathologic study of physiological and pathological resorptions in human primary teeth

Improving radiographic diagnosis of pulpo-periodontal complications in primary molars by training: Application in education and clinical research

INTRODUCTION

The objective of this study was to assess an original learning intervention to train students and paediatric dentistry teachers in radiographic diagnostic accuracy of pulpo-periodontal complications in primary molars.

MATERIALS AND METHODS

The learning intervention was based on 250 different randomly ordered radiographs of primary molars within three quizzes (A, B and C) for 5 sessions (S): quiz A (50 X-rays), B and C (100 X-rays) were, respectively, completed in S1 to assess the extent of agreement with 5 experts' diagnoses, in S2 and S3 (B at days 8 and 23) and in S4 and S5 (C at days 90 and 105). During S1 and at the end of S3 and S5, the participants (48 students and 16 teachers) were informed of correct diagnoses. A satisfaction questionnaire was completed by all the students. Alongside the descriptive analyses, generalised linear mixed model (GLMM) analyses assessed the odds of participants' correct diagnosis over the study duration.

RESULTS

At S1, the odds of diagnostic accuracy among students were significantly lower than those among the teachers. After receiving feedback at S1, GLMM analyses showed that among all the participants, accuracy improved over time with the odds of correct diagnoses higher in S2-5 than in S1; and there were similar increases across sessions between teachers and students, except in S3, where the improvement among teachers tended to be greater than that among the students. All students were satisfied though one-third reported that quizzes with 100 radiographs felt too long.

CONCLUSION

The online case-based learning was a good training format for dental education.

Are electronic apex locators accurate in determining working length in primary teeth pulpectomies? A systematic review and meta-analysis of clinical studies

BACKGROUND

The lack of a well-defined apical constriction in primary teeth raises concerns regarding the accuracy of electronic apex locators (EALs) for measuring working length.

OBJECTIVES

To evaluate the accuracy of EALs in determining working length in primary teeth pulpectomies.

METHODS

Two reviewers searched ten databases up to September 2021. Clinical studies evaluating the accuracy of the electronic measurement of working length in primary teeth pulpectomies were included. Studies without a comparison group, with samples smaller than ten root canals, and that did not use a multiple frequency EAL were excluded. A meta-analysis was conducted to assess the paired differences in mean lengths between measurements obtained by electronic and comparative methods. In addition, a meta-analysis of proportion was applied according to the level of difference between the measures. The risk of bias and applicability of the studies were assessed using the QUADAS-2 tool. The certainty of evidence was assessed with the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach.

RESULTS

Twenty-nine studies were included in the qualitative analysis and twenty-three in the quantitative analysis. The methods of comparison for the electronic measurement were the radiographic method, radiovisiographic, scanning electron microscopy, and direct visualization. The meta-analysis showed that the electronic measurement tends to be shorter than radiographic measurement, while the other methods showed no difference. The proportion analysis showed a higher pooled proportion of difference values between electronic and comparative measurements within -0.5 to +0.5 mm (69.31%). The certainty of the evidence suggested very low confidence in estimating the outcome.

DISCUSSION

The results of this review denote a good performance of the EALs in determining working length in primary teeth pulpectomies. However, these results are based on clinical studies with low methodological quality and high heterogeneity, which require careful interpretation for clinical practice.

CONCLUSIONS

Although the results suggest acceptable accuracy of EALs in determining working length in primary teeth pulpectomies, the low quality of the included studies and the very low certainty of the evidence require clinicians to interpret these results with caution. More robust evidence is required to support that these devices are accurate for primary teeth.

Relationship between Physiological Resorption of Primary Molars with Its Permanent Successors, Dental Age and Chronological Age

The aim of the present study was to analyse root resorption of the primary mandibular molars and their relationship with their permanent successors and the age of the patient.

METHODS

The sample consisted of 408 digital panoramic radiographs. The mesial and distal crown-to-root ratios (CRR) of #74 and #75 were calculated by dividing the measures of the length of each root by its coronal height. The Demirjian formation stage of the premolar was established, and dental age was determined. A descriptive and statistical analysis was performed using SPSS to determine the correlation between the variables (Pearson's correlation coefficient) and to identify the differences between them (Student's t-test), with a confidence level of 95%.

RESULTS

723 molars were measured, and tables of CRR depending on dental and chronological age were obtained. The CRR decreased with increasing dental and chronological age, but not uniformly. The CRR of #74 and #75 decreased slightly when the successor premolar was in the initial stages of formation. Gender differences were obtained with respect to chronological age, mainly in girls, because the root resorption of #74 was always more advanced, and the formation of the #34 more advanced.

CONCLUSIONS

Root resorption of the molar is slight and progressive when the successor premolar begins formation until stage D, and becomes higher starting at stage E. It is possible to determine the state of the child's maturation and the CRR according to dental and chronological age.

Improvement of Biological Effects of Root-Filling Materials for Primary Teeth by Incorporating Sodium Iodide

Therapeutic iodoform (CHI₃) is commonly used as a root-filling material for primary teeth; however, the side effects of iodoform-containing materials, including early root resorption, have been reported. To overcome this problem, a water-soluble iodide (NaI)-incorporated root-filling material was developed. Calcium hydroxide, silicone oil, and NaI were incorporated in different weight proportions (30:30:X), and the resulting material was denoted DX (D5~D30), indicating the NaI content. As a control, iodoform instead of NaI was incorporated at a ratio of 30:30:30, and the material was denoted I30. The physicochemical (flow, film thickness, radiopacity, viscosity, water absorption, solubility, and ion releases) and biological (cytotoxicity, TRAP, ARS, and analysis of osteoclastic markers) properties were determined. The amount of iodine, sodium, and calcium ion releases and the pH were higher in D30 than I30, and the highest level of unknown extracted molecules was detected in I30. In the cell viability test, all groups except 100% D30 showed no cytotoxicity. In the 50% nontoxic extract, D30 showed decreased osteoclast formation compared with I30. In summary, NaI-incorporated materials showed adequate physicochemical properties and low osteoclast formation compared to their iodoform-counterpart. Thus, NaI-incorporated materials may be used as a substitute for iodoform-counterparts in root-filling materials after further (pre)clinical investigation.

Advances in the Study of the Mechanisms of Physiological Root Resorption in Deciduous Teeth

Physiological root resorption of deciduous teeth is a complex physiological process that is essential for the normal replacement of deciduous teeth and permanent teeth in clinical practice, but its importance is often overlooked due to the presence of permanent teeth. This physiological process includes not only the resorption of hard tissues of deciduous teeth, such as dentin and cementum, but also the elimination of soft tissues, such as pulp and periodontal ligament (PDL). However, the mechanisms of physiological root resorption are not yet clear. In this article, the advances of research on the mechanisms related to physiological root resorption will be reviewed in two main aspects: hard tissues and soft tissues of deciduous teeth, specifically in relation to the effects of inflammatory microenvironment and mechanical stress on the resorption of hard tissues, the repair of hard tissues, and the elimination and the histological events of soft tissues.

The variability of electric pulp response thresholds in primary molars: a clinical study

PURPOSE

The variability of the EPT response threshold is the most important part of accurate diagnosis of pulp status of caries-affected resorbing primary teeth. This study evaluated the mean EPT threshold values and appropriate electrode placement sites for primary molar teeth based on their physiological root resorption levels.

METHODS

This study was conducted with 100 primary second molars in 100 children ages 3-12 (mean age: 7.88 years). Teeth were divided into 2 groups according to physiological root resorption levels. EPT response thresholds were recorded at the mesiobuccal cusp, occlusal third, middle third and cervical third of the crown. Data were analyzed according to resorption level using one-way analysis of variance and Duncan tests, with the level of significance set at 0.05.

RESULTS

Mean threshold values at all placement sites were higher in the group with the higher level of physiological root resorption. In terms of placement, the lowest mean EPT threshold values were obtained at the mesiobuccal cusp regardless of resorption level.

CONCLUSIONS

According to the study results, higher resorption levels were associated with higher physiologocial threshold values for EPT of primary second molars, with the mesiobuccal site identified as the most appropriate electrode placement site, regardless of resorption level.

Axonal Degeneration in Dental Pulp Precedes Human Primary Teeth Exfoliation

The dental pulp in human primary teeth is densely innervated by a plethora of nerve endings at the coronal pulp-dentin interface. This study analyzed how the physiological root resorption (PRR) process affects dental pulp innervation before exfoliation of primary teeth. Forty-four primary canine teeth, classified into 3 defined PRR stages (early, middle, and advanced) were fixed and demineralized. Longitudinal cryosections of each tooth were stained for immunohistochemical and quantitative analysis of dental pulp nerve fibers and associated components with confocal and electron microscopy. During PRR, axonal degeneration was prominent and progressive in a Wallerian-like scheme, comprising nerve fiber bundles and nerve endings within the coronal and root pulp. Neurofilament fragmentation increased significantly during PRR progression and was accompanied by myelin degradation and a progressive loss of myelinated axons. Myelin sheath degradation involved activation of autophagic activity by Schwann cells to remove myelin debris. These cells expressed a sequence of responses comprising dedifferentiation, proliferative activity, GAP-43 overexpression, and Büngner band formation. During the advanced PRR stage, increased immune cell recruitment within the dental pulp and major histocompatibility complex (MHC) class II upregulation by Schwann cells characterized an inflammatory condition associated with the denervation process in preexfoliative primary teeth. The ensuing loss of dental pulp axons is likely to be responsible for the progressive reduction of sensory function of the dental pulp during preexfoliative stages.

Radicular maturity level of primary teeth and its association with trauma sequelae

AIM

This study aimed to investigate the influence of the radicular maturity level of primary teeth on the sequelae of traumatic dental injury (TDI).

MATERIALS AND METHODS

A longitudinal retrospective study that collected data from dental records and radiographs of patients with TDI in one or both maxillary primary central incisors was conducted. Sequelae such as crown discoloration, pulp canal obliteration (PCO) and inflammatory root resorption (IRR) were evaluated during a 12- to 18-month follow-up period after the trauma.

RESULTS

Of the 132 patients included in the study, 103 (78%) had luxations and 29 (22%) had dental fractures. At the initial postinjury examination, 12 teeth (9.1%) were found to have immature roots, 107 (81.1%) had closed apexes and 13 (9.8%) had visible root resorption. Inflammatory root resorption occurred mostly in traumatized teeth that presented with physiological root resorption at the moment of trauma (P = 0.004). The frequency of PCO was higher in teeth with a closed apex at the moment of the injury (P = 0.026). There was also an association between the type of injury and the occurrence of crown discoloration (P = 0.008) as well as between the type of injury and the development of PCO (P = 0.001).

CONCLUSIONS

The occurrence of TDI sequelae can be determined by the type of injury as well as by the radicular maturity level of the primary teeth at the moment of injury.

Deciduous dental pulp stem cells are involved in osteoclastogenesis during physiologic root resorption

Multipotent mesenchymal stem cells are derived from the dental pulps of permanent teeth and exfoliated deciduous teeth, and are known to induce bone and dentin generation. However, the role of deciduous dental pulp stem cells (DDPSCs) in physiologic root resorption remains unclear. In this study, dental pulp stem cells (DPSCs) in permanent teeth (P) were retrieved and compared to DDPSCs from deciduous incisors at different root resorption stages: stable (S), middle (M), and final (F). Decalcified teeth sections showed that osteoclasts and resorption lacunae were most prevalent in the M resorption stage. DDPSC proliferation rate was also highest in the M stage. DDPSCs in the F stage produced more calcified nodules than those in the S or M stages. Alkaline phosphatase (ALP) expression was highest in the F stage, indicating that DDPSCs promote mineralization. In addition, the ratio of receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) expression was significantly higher in the M stage, indicating that DDPSCs promote resorption. Dickkopf 1 (Dkk1) expression was remarkably higher in the F and P groups, suggesting that the Wnt pathway is inhibited during the resorption process. Interestingly, despite the fact that Wnt3a down-regulated OPG in osteogenic induction medium and up-regulated RANKL in medium with 1,25-dihydroxy vitamin D3 (VD(3) ), the RANKL/OPG ratio was reduced only with VD(3) . Collectively, our data indicate that DDPSCs influence osteoclastogenesis during the physiologic root resorption process, and that the canonical Wnt pathway can change the RANKL/OPG expression ratio in DDPSCs.

Pulpal status of human primary teeth with physiological root resorption

OBJECTIVE

The overall aim of this study was to determine whether any changes occur in the pulpal structure of human primary teeth in association with physiological root resorption.

METHODS

The experimental material comprised 64 sound primary molars, obtained from children requiring routine dental extractions under general anaesthesia. Pulp sections were processed for indirect immunofluorescence using combinations of: (i) protein gene product 9.5 (a general neuronal marker); (ii) leucocyte common antigen CD45 (a general immune cell marker); and (iii) Ulex europaeus I lectin (a marker of vascular endothelium). Image analysis was then used to determine the percentage area of staining for each label within both the pulp horn and mid-coronal region. Following measurement of the greatest degree of root resorption in each sample, teeth were subdivided into three groups: those with physiological resorption involving less than one-third, one-third to two-thirds, and more than two-thirds of their root length.

RESULTS

Wide variation was evident between different tooth samples with some resorbed teeth showing marked changes in pulpal histology. Decreased innervation density, increased immune cell accumulation, and increased vascularity were evident in some teeth with advanced root resorption. Analysis of pooled data, however, did not reveal any significant differences in mean percentage area of staining for any of these variables according to the three root resorption subgroups (P > 0.05, analysis of variance on transformed data).

CONCLUSIONS

This investigation has revealed some changes in pulpal status of human primary teeth with physiological root resorption. These were not, however, as profound as one may have anticipated. It is therefore speculated that teeth could retain the potential for sensation, healing, and repair until advanced stages of root resorption.

Ex vivo study of manual and rotary instrumentation techniques in human primary teeth

OBJECTIVE

This study aimed to evaluate, ex vivo, time and dentin removal by manual and rotary instrumentation in human primary teeth.

STUDY DESIGN

Eighty primary teeth were divided into 2 groups, embedded in resin, and sectioned for evaluation before and after instrumentation. For manual technique, teeth were prepared using K-type files and rotary preparation was performed with Hero 642. All root canals were prepared up to size 40, and the instrumentation time was recorded. Dentin removal was calculated using digital image software. Data was statistically analyzed using chi-squared, Mann-Whitney, and t tests.

RESULTS

Manual instrumentation removed more dentin in all groups compared with rotary instrumentation (P < .05). In some specimens, root perforations were observed in areas coinciding with largest root resorption. Rotary technique showed the shortest instrumentation time (P < .05).

CONCLUSIONS

Deciduous teeth, without significant root resorption, have enough root structure for instrumentation up to size 40. Rotary technique required less time and generated less dentin removal.