Assessment of the odontoclastic activity in extracted deciduous teeth with and without dental caries

INTRODUCTION

Primary teeth differ from permanent teeth by their nature to undergo physiologic resorption, thereby working toward their own shedding. Exfoliation of deciduous teeth is an essential and indisputable action by nature. The process of resorption may be defined as “a condition associated with either a physiologic or a pathologic process resulting in the loss of dentin, cementum, and/ or bone.”^[1] The cells of resorption, that is, odontoclasts, osteoclasts, and fibroblasts function more actively, as the period of exfoliation/shedding is being approached. Over this phase of time, a substantial amount of changes is seen to occur in these cells and the surrounding environment.

In recent years, several studies have given an in-depth analysis of the pulp, during its resorptive phase and its correlation with the concerned immune cells.^[2] During the episode of physiologic resorption, odontoclasts appear to be originating from the wall of the pulp chamber and hollowing out the tooth from within. Nevertheless, supporting the statement of Harndt and Zerosi, Furseth^[3] in his study stated that in the case of human primary dentition where the normal pulp structure is preserved until its exfoliation, the pulp does not play a part in physiologic resorption. The documentation of time-related histologic changes in the pulp during this resorption process, given by Yildirim et al., has shown that the odontoclastic resorption of coronal dentin takes place just before shedding.^[4] The pattern of resorption by multi-nucleated cells is seen to proceed from predentin to dentin, following the infiltration of inflammatory cells into the pulp and degeneration of odontoblasts.

Sahara et al., in 1994 showed, this internal resorption is always initiated from the predentin surface and proceeds to the dentine. The previous studies indicate that the resorption can occur when the protective unmineralized tissues such as pre-cementum and pre-dentin are breached or mechanically damaged, allowing osteoclasts/odontoclasts to gain access to calcified dental tissues.^[5] At the terminal stages of resorption, odontoclasts gradually disappear, and the resorbed dentine surface is repaired by cementum-like tissue deposition. Although, in the case of internal resorption, this resorption-repair cycle can be witnessed only once, until the teeth are exfoliated.^[6]

The present study aimed to assess the odontoclasts and inflammatory cells in extracted deciduous teeth, with and without dental caries, and thereby evaluate the possibility of decreased rate of resorption/delay in exfoliation due to alteration in cell count of odontoclasts. To the best of our knowledge, there are no other studies that evaluate the histological and numerical changes occurring in the odontoclasts and inflammatory cells in deciduous teeth affected by dental caries. The influence of dental caries over these resorptive functions occurring before shedding and the corresponding sequelae of changes are to be analyzed. Histological and histochemical observations are done to compare and contrast these odontoclastic changes i.e. shape and number. Further, in the retained deciduous tooth, the possibility of decreased rate of resorption/delay in exfoliation, due to alteration in the cell count of odontoclasts is evaluated.

MATERIAL AND METHODS

RESULTS

The present study evaluated the number of odontoclastic cells and inflammatory cells in teeth with and without dental caries. Table 1 shows the number of odontoclasts and inflammatory cells in Group A (without dental caries). The odontoclasts were more commonly observed to have a polygonal, oval shape and the inflammatory cells were scanty. [Table 1 and Figure 1a].

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Figure 1:

(a) Group A specimen under ×400 magnification showing scanty inflammatory cells and odontoclastic activity. (b) – Group B specimen under ×400 magnification showing diffuse and patchy pattern of inflammatory cells and hyperemia.

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Table 2 shows the properties of odontoclasts and inflammatory cells observed in Group B (with dental caries). The odontoclasts were more commonly observed to be polygonal in shape and very few inflammatory cells were observed [Table 2 and Figure 1b].

The number of odontoclasts observed in Group A (without dental caries) had a mean value of 4.5 ± 2.12 which was higher than in Group B (with dental caries), which showed a mean value of 2.70 ± 0.94. The mean value of inflammatory cells observed in Group A (without dental caries) was 1.20 ± 0.42, which was fewer than found in Group B (with dental caries) (2.10 ± 0.56) [Table 3 and Figure 2].

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Figure 2:

Intergroup comparison of number of odontaclasts and inflammatory cells observed.

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The intergroup comparison of odontoclasts observed showed a statistically significant difference between the two groups with p<0.05, and the difference of inflammatory cells observed was highly statistically significant between the groups (p value 0.00) [Table 3].

DISCUSSION

In the sample specimen, various stages of resorption were processed and observed under a light microscope.

Sahara et al.,^[7] reported that odontoclasts are not found inside the pulp until root resorption is near completion. Thus, teeth with more than two-thirds resorption were considered in this study.

In the present study, the odontoclastic cells predominantly appeared polygonal and oval. The rounded appearance of cells was observed only in a single specimen without dental caries. In most samples, the lacunae showcased a thin haematoxyphilic zone. In zones where the odontoclasts were in contact with the tooth surface, the typical brush border appearance could be appreciated.

There was a statistically significant difference in the number of odontoclasts between the two groups with Group A (without caries) having a significantly higher number of cells. The specimens showed scanty inflammatory cells with higher odontoclastic activity [Figure 1a]. The findings of the present study are in accordance with the results of the previous histological studies done on deciduous teeth.^[8-10]

The inflammatory cells in the given sample appeared with varying morphology, scattered across the field of observation.

There seemed to be no uniform pattern of distribution of these cells and a minimal number of cells were noticed in Group A (without caries) specimens. The Group B (with caries) specimens showcased a drastic change in the number of inflammatory cells and the pattern of occurrence was patchy. Hyperemia and necrosis are often witnessed during observation. A zone of internal resorption could be spotted occasionally [Figure 1b].

There was a highly significant difference in the number of inflammatory cells between the two groups with Group B (with caries) having a significantly higher number of cells. Bolan and Rocha^[11] reported similar findings with necrosis, hyperemia, and internal resorption in teeth with dental caries. However, teeth without dental caries were reported to show more inflammatory cells than teeth with dental caries which is contradictory to the findings of the present study. Kronfeld,^[12] Soskolne and Binstein,^[13] and Eronat et al.,^[14] also showed contradictory findings and correlated the findings to secondary infiltration occurring through gingival sulcus at the end stages of resorption.

Di Nicolo et al.,^[15] concluded that the type of dentinal caries is a good indicator of the histological status of the pulp. Murthy et al.^[16] showed irrespective of the nature of teeth in a particular stage of resorption, the ultrastructural pattern of all distinct samples of deciduous teeth presented similar features. On the contrary, the macroscopic pattern varied as the surface of involvement differs amongst the samples.

CONCLUSION

The findings of the present study indicate the clear dominance of inflammatory cells in the carious specimen over the noncarious specimen. Odontoclast number and activity were found to be significantly predominant in non-carious teeth. Regarding the nature of odontoclasts, they appear as multi-nucleated cells embedded in the lacunae and polygonal in shape in both carious and non-carious deciduous teeth. These points of difference establish that dental caries in deciduous teeth influence normal physiologic resorption at the cellular level, thereby reducing the rate of resorption and delaying exfoliation.