A histological study of the exfoliation of human deciduous teeth

Factors influencing root resorption in retained mandibular second deciduous molars with congenital absence of second premolars: a cross-sectional study

BACKGROUND

There are currently no studies that quantitatively compare the relationship of root resorption to the patient's systemic history or craniofacial and intraoral morphology, especially in relation to possible host factors. Thus, this study aimed to clarify the factors associated with root resorption in retained mandibular second deciduous molars with the congenital absence of second premolars and predict the prognosis of retained mandibular second deciduous molars.

METHODS

A cohort of 5547 patients who visited the orthodontic clinic at Tokyo Medical and Dental University Dental Hospital between 2013 and 2022 was screened. Lateral cephalometric radiographs, panoramic radiographs, upper and lower dental models, and orthodontic treatment questionnaires were used as reference materials to apply the inclusion and exclusion criteria. Ultimately, 111 patients were included in the analyses. The patients were divided into two groups based on the root resorption levels of the retained mandibular second deciduous molars. Those with less root resorption were classified under the good condition (GC) group, whereas those with more root resorption were classified under the poor condition (PC) group. Demographic, clinical, and cephalometric parameters were compared between the groups. A multivariate logistic regression model was used to predict the probability of root resorption.

RESULTS

The prevalence of congenitally missing mandibular second premolars with persistent mandibular second deciduous molars was 2.0%. In a total of 111 patients, eighty-three teeth (53.2%) were classified into the GC group, whereas 73 teeth (46.8%) were classified into the PC group. The Frankfort-mandibular plane angle (FMA) [odds ratio (OR): 0.87], Frankfort-mandibular incisor angle (FMIA) (OR: 0.93), overbite (OR: 1.38), adjacent interdental space (OR: 1.46), distance from occlusal plane (OR: 0.80), and caries treatment (OR: 7.05) were significantly associated with the root resorption of the retained mandibular second deciduous molars.

CONCLUSIONS

Our findings suggest that skeletal morphology, oral morphological patterns, and history contribute to root resorption in retained mandibular second deciduous teeth with congenital absence of subsequent permanent teeth.

Changes in Pulp and Roots of Deciduous Teeth during Different Stages of Physiologic Resorption: A Histologic Study

Background

Resorption of primary teeth and eruption of permanent teeth involves a complex series of changes. The cellular and histological changes occurring during the process of resorption vary stagewise. The knowledge of the changes occurring in the pulp of deciduous teeth would provide information about the resorptive process.

Aim

To evaluate the histologic changes of the pulp of deciduous teeth related to different stages of physiologic root resorption.

Study setting and design

To establish the cause and effect relationship, a contrived histologic study design was planned.

Materials and methods

A total of 60 extracted deciduous incisors, canines, and molars were included in the study. The remaining root length (RRL) was determined based on the standardized photographs. The teeth were then grouped into three based on the percentage of RRL. The teeth were subjected to decalcification with 5% nitric acid, following which histological processing was performed.

Statistical analysis

The present study being a qualitative study design, descriptively explains the histologic findings, and no statistical tests have been applied.

Results

During the initial stages of resorption, there were no histological alterations noted in the pulp, particularly in the cervical 3rd, with the cellular structure relatively maintained. As the resorption progresses, reversal lines were evident, indicating a process of repair occurring simultaneously during the process of resorption. With further advancement, the repair is overtaken by the resorption indicated by the presence of resorptive cells. Neovascularization and an increase in immune cells are also evident in advanced stages.

Conclusion

The pulp exhibits progressive changes as the resorption continues from stage I to stage III. The changes vary from a smaller number of immune cells and odontoclasts in stage I to increasing number of the same as resorption progresses.

How to cite this article

Murthy P, Bhojraj N, Hegde U. Changes in Pulp and Roots of Deciduous Teeth during Different Stages of Physiologic Resorption: A Histologic Study. Int J Clin Pediatr Dent 2023;16(3):437-443.

Histological and Radiographical Evaluation of Deciduous Teeth during Shedding (Human and Experimental Study)

AIM: The aim of this study was to evaluate the process of deciduous teeth shedding histologically and radiographically. METHODS: The design of the present study included both human and experimental animals. A total number of twenty human primary teeth, aged 8–10 years, were collected for light microscope and scanning electron microscopy (SEM). Furthermore, ten nameless copies of dental/occlusal X-rays of children aged 9–10 years were used to measure the radicular dentin radiodensity. For the experimental part, 4-month-old beagles were used for histological examination of the process of shedding in situ. RESULTS: Histologically, the decalcified beagles deciduous teeth specimens showed deep resorption fossae occupied with many odontoclasts together with periodontal ligaments disorganization. Furthermore, SEM examination of human exfoliated teeth revealed variable-sized plentiful resorption lacunae with irregular edges. Interestingly, radiographic examination of the human deciduous teeth at late resorption stage revealed significant decrease in radicular dentin radiodensity. CONCLUSION: Shedding is a complex physiological process that involves intermittent resorption of deciduous teeth supporting tissues together with significant decrease in root dentin radiodensity at late root resorption stage in comparison to other various stages of root resorption.

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.

Oral cancer in a 5-year-old boy: a rare case report and review of literature

Oral cancer in children is rare. Diagnosis may be delayed as a result of confusion with reactive lesions. Furthermore, cancer staging, with or without bony invasion, can be complicated during tooth eruption. Literature on pediatric oral cancers is lacking, making determination of the possible etiopathology difficult. We describe an exceptional case of a 5-year-old male child who presented with anterior maxillary gingival pseudoepitheliomatous hyperplasia that progressed to carcinoma cuniculatum with invasive oral squamous cell carcinoma (OSCC). Because of the interesting timing of events, we hypothesize that human papillomavirus (HPV) inoculation through cutaneous squamous papilloma played a contributory role. A review of similar case reports in the literature is included. Biopsy of suspicious oral lesions should not be delayed because of the young age of the patient. Atypical hyperplasia should include squamous cell carcinoma (SCC) in the differential diagnoses. For surgical management of aggressive lesions during the mixed dentition, permanent successors should be included in the surgical margins to prevent recurrence.

Pulpal status of human primary molars with coexisting caries and physiological root resorption

AIM

This study sought to investigate the effect of caries, in association with physiological root resorption, on the pulpal status of human primary molars.

DESIGN

Fifty-three mandibular primary molars were obtained from children requiring extractions under general anaesthesia. Following extraction, teeth were split longitudinally and placed in Zamboni's fixative. Teeth were categorised according to i) the depth of caries (less than or greater than halfway through dentine thickness) and ii) the degree of physiological root resorption (<33%, 34-66% or >67% of the root length). Ten-micrometre pulp sections were subject to indirect immunofluorescence using a combination of PGP 9.5 (a general neuronal marker), CD45 (a general neuronal marker), and Ulex europaeus agglutinin I (a marker of vascular endothelium). Image analysis was used to determine the percentage area of staining (PAS) for innervation and immune cells.

RESULTS

Marked differences were seen between different samples, but there were no significant differences in mean PAS for PGP 9.5 or CD45 according to the degree of caries or extent of physiological root resorption (two-way anova, P > 0.05).

CONCLUSION

Findings suggest that even if primary molars are undergoing exfoliation, they show comparable caries-induced changes to teeth without physiological root resorption, thus retaining potential for healing and repair.

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.

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.

Physiologic root resorption in primary teeth: molecular and histological events

Root resorption is a physiologic event for the primary teeth. It is still unclear whether odontoclasts, the cells which resorb the dental hard tissue, are different from the osteoclasts, the cells that resorb bone. Root resorption seems to be initiated and regulated by the stellate reticulum and the dental follicle of the underlying permanent tooth via the secretion of stimulatory molecules, i.e. cytokines and transcription factors. The primary root resorption process is regulated in a manner similar to bone remodeling, involving the same receptor ligand system known as RANK/RANKL (receptor activator of nuclear factor-kappa B/ RANK Ligand). Primary teeth without a permanent successor eventually exfoliate as well, but our current understanding on the underlying mechanism is slim. The literature is also vague on how resorption of the pulp and periodontal ligament of the primary teeth occurs. Knowledge on the mechanisms involved in the physiologic root resorption process may enable us to delay or even inhibit exfoliation of primary teeth in those cases that the permanent successor teeth are not present and thus preservation of the primary teeth is desirable.

Bovine deciduous dentine is more susceptible to osteoclastic resorption than permanent dentine: results of quantitative analyses

Many clinical reports suggest that deciduous teeth exhibit a greater susceptibility to resorption than permanent ones. To examine the difference between deciduous and permanent dentine in their susceptibility to osteoclastic resorption, osteoclast-like cells (OCLs) were cultured on deciduous and permanent dentine slices. The number, area, depth, and volume of resorption pits were then measured, using image-analyzing systems. We measured the level of degraded collagen (cross-linked N-telopeptide of type I collagen; NTx) in culture medium using an enzyme-linked immunosorbent assay (ELISA). The levels of cathepsin K, matrix metallo proteinase (MMP)-9, and MMP-13 mRNAs in the cells attached to dentine were also analyzed by real-time reverse transcription polymerase chain reaction (RT-PCR). Deciduous dentine slices exhibited a significant (twofold) increase in resorbed area compared with the permanent slices. Three-dimensional analysis revealed that the volume of pits in deciduous dentine differed significantly (fourfold) compared to that in the permanent dentine. The depth of pits also followed the same trend. However, there was no significant difference in the number of pits or osteoclasts on the dentine slices. The NTx level in deciduous media was significantly more than that in permanent media. The mRNA levels also followed the same trend. These results suggest that deciduous dentine is more susceptible to resorption than permanent dentine and signals from the substrate play an important role in physiological resorption.

Root resorption in deciduous teeth after applying orthodontic forces

The relation between orthodontic forces applied to deciduous teeth and the occurrence of root resorption, as a possible outcome of these forces, has not been studied to date. The aim of this work was to study root resorption in deciduous teeth of patients receiving orthodontic treatment. Twenty-four deciduous molars extracted for therapeutic purposes were studied: nineteen molars treated with light orthodontic forces and five untreated molars that served as control. Histological and histomorphome tric studies were performed to determine the magnitude of root resorption. Location of root resorption in treated deciduous teeth was different from that of physiological root resorption. Extent and volume of root resorption were more extensive and deeper in treated than in untreated teeth. These results suggest that radiographic follow-up of deciduous teeth subjected to orthodontic forces would be useful to prevent root fractures.

Immunocompetent cells in the pulp of human deciduous teeth

This immunohistological study sought to determine how the distribution and density of various immunocompetent cells change in the pulp of human deciduous teeth during the process of physiological root resorption. Forty-three extracted deciduous teeth at various stages of resorption were subjected to immunoperoxidase staining with the use of antibodies directed to HLA-DR, CD68, factor XIIIa and lymphocyte subsets. In intact deciduous teeth (group 0), all types of cells examined, except for CD20+ B lymphocytes, were detected. In teeth in which resorption was less than 1/3 of the root length (group 1), all types of cells showed a statistically significant increase compared with group 0 (P<0.05; Mann-Whitney's U-test). HLA-DR+, CD68+, and factor XIIIa+ cells with a dendritic profile kept their distribution in the periphery of the pulp, and oval and round, newly recruited macrophages accumulated in the central portion of the pulp and near the resorption sites. In teeth where resorption was 1/2 to 2/3 (group 2), all the cell types increased further. Aggregations of HLA-DR+, CD68+, and factor XIIIa+ cells were frequently seen in the central portion of the pulp, and T and B lymphocytes occasionally formed some clusters. Comparisons with group 1 revealed that the density of these cells, except for CD20+ cells, showed significant increases (P<0.05; Mann-Whitney's U-test). These results provided evidence showing that immunocompetent cells of deciduous tooth pulp increase with the progress of physiological root resorption, suggesting that immunocompetency of deciduous teeth is altered by this process.

Histological investigation of physiologically resorbing primary teeth using Ag-NOR staining method

OBJECTIVE

The aim of this study was to investigate pulpal tissue of primary teeth in early and late stages of physiological resorption by means of silver-binding nucleolar organizer region (Ag-NOR) staining.

STUDY DESIGN

Ten primary teeth in early, ten in the late stage of resorption and five sound premolar teeth pulps as the control group were investigated by means of silver-binding nucleolar organizer region (Ag-NOR) staining.

RESULTS

The mean number of Ag-NOR's per nucleus increased with the continuing of the resorption process. The difference in the mean number of Ag-NORs was statistically significant both in the early and late stage of resorption compared with controls (P > 0.001). In the early stage of resorption calcific plates in the apical part of the pulps were observed. Odontoclasts, as well as inflammatory cells, were observed in the late stages of resorption.

CONCLUSIONS

The increase in the mean number of Ag-NORs per nucleus with the progression of the resorption process in primary teeth suggests that metabolic cell activity in the early stages of resorption is enhanced and increased with the continuing of the process, thus showing the importance of the pulp tissue in the resorption process.

Ultrastructural features of odontoclasts that resorb enamel in human deciduous teeth prior to shedding

Three dental hard tissues, i.e., cementum, dentin, and enamel, are resorbed by multinucleated cells referred to as "odontoclasts." These cells have morphological and functional characteristics similar to those of bone-resorbing osteoclasts. However, concerning enamel resorption, which is a process that may occur during tooth eruption, satisfactory ultrastructural data on odontoclastic resorption are still lacking. Ultrastructural and histochemical characteristics of odontoclasts resorbing enamel of human deciduous teeth prior to shedding were examined by means of light microscopy and transmission and scanning electron microscopy. Odontoclasts that that resorbed enamel were tartrate-resistant acid phosphatase (TRAP)-positive multinucleated giant cells that were essentially the same as those that resorbed dentin and cementum. Ultrastructurally, they had numerous mitochondria, lysosomes, and free polysomes in their cytoplasm. In addition, they were characteristically rich in large cytoplasmic vacuoles containing enamel crystals in the cytoplasm opposite the ruffled border. Although they extended a well-developed, ruffled border against enamel surface, a clear zone--an area typically devoid of organelles--was rarely seen in these cells. In many cases, the cells were in very close contact with the enamel surface by the peripheral part of their cytoplasm. The enamel prisms at the resorption surface contained more loosely packed and electron-lucent enamel crystals compared with those of unresorbed, intact enamel. Furthermore, numerous thin needle- or plate-like enamel crystals that were liberated from the enamel matrix were found in the extracellular channels of the ruffled border and in various-sized cytoplasmic vacuoles in their cytoplasm. The superficial layer of the enamel matrix undergoing odontoclastic resorption stained positively with toluidine blue and for TRAP activity. The results of the present study suggest that odontoclasts resorbing enamel secrete acids as well as organic components, including hydrolytic enzymes, into the resorption zone underlying their ruffled border and that they phagocytose crystals that have been liberated from the partially demineralized enamel matrix by acids, subsequently dissolving them intracellularly.

Cytodifferentiation of the odontoclast prior to the shedding of human deciduous teeth: an ultrastructural and cytochemical study

BACKGROUND

In human deciduous teeth, odontoclastic resorption takes place at the pulpal surface of the coronal dentine prior to shedding, and this resorption shows clear time-related histological changes (Sahara et al., 1992).

METHODS

Using this phenomenon as an observation system, we examined the cytodifferentiation of human odontoclasts by light and electron microscopy. For a histochemical marker of odontoclast differentiation and function, tartrate-resistant acid phosphatase (TRAP) activity was determined by light and electron microscopic enzyme histochemistry.

RESULTS

As root resorption neared completion, TRAP-positive mononuclear cells were initially detected in the pulp chamber. They had abundant mitochondria, small lysosomes, and moderately developed rough endoplasmic reticulum throughout their cytoplasm. In these mononuclear cells, TRAP activity was localized in compartments of the biosynthetic pathway, i.e., in cisternae of the endoplasmic reticulum and Golgi lamellae, as well as small lysosomes. The TRAP-positive mononuclear cells first made contact with the predentine surface by their elongated cellular processes. After attachment, they spread out along the predentine surface and developed specialized membrane structures, clear zones, and ruffled borders. Next, they fused with each other on the predentine surface and formed typical multinucleate odontoclasts. After termination of their resorption function, the odontoclasts lost their ruffled borders and became detached from the resorbed surface. Most of the detached odontoclasts had numerous large pale vacuoles and secondary lysosomes and appeared to be in the process of degeneration.

CONCLUSIONS

The present study demonstrates that: (1) odontoclasts differentiated from TRAP-positive mononuclear cells, which presumably originate from circulating progenitor cells, (2) membrane specialization of odontoclasts, i.e., development of a clear zone and ruffled border, is induced following their contact with the resorption surface, (3) multinucleation of odontoclasts takes place only after their attachment to the resorption surface, (4) mature multinucleate odontoclasts can resorb predentine as well as dentine in the same way as osteoclasts resorb bone, and (5) at the end of the resorption, odontoclasts gradually lose their ruffled borders and become detached from the resorbed surface.