Pulp capping materials protect the vital pulp tissue after exposure due to deep dental caries or trauma. Most of the available pulp capping materials has several advantages and disadvantages [15, 16]. Therefore the research on new pulp capping materials is still continuing.
Recently, a new calcium silicate-based material called Tech Biosealer Capping is introduced to the market. To our knowledge, there are no in vivo studies on Biosealer as a pulp capping agent. Therefore this study compared the efficacy of TBC and Biodentine as direct pulp capping materials. We selected Biodentine for comparison due to its excellent results as pulp capping agent. Moreover, there are several in vivo studies on MTA [6,7,9].
Both animal and human teeth are suitable to demonstrate the effects of pulp capping materials on vital pulp tissue . Therefore, dogs were enrolled in this study as an animal model because the mechanism of reparative dentinogenesis is similar to that of human in a short time. Additionally, the dog has a suitable pulp size for the histopathological evaluation and good number of teeth that allow the comparison of several pulp capping cements in the same dog . The used teeth were disinfected with antiseptic solution and isolation with sterile cotton rolls. Application of a rubber dam was difficult due to anatomical consideration of dog’s teeth.
Like several previous studies [19,20], direct pulp capping technique was used in our study to induce the formation of reparative dentin at the injury site. The formation of dentine bridge was considered as a sign of success of pulp capping material.
Although both Biodentine and TBC are calcium silicate based products, there are several differences. For example, the dental amalgamator is essential for preparation of Biodentine while no additional tools are needed for TBC preparation. The powder of Biodentine has tricalcium and dicalcium silicate, calcium carbonate and oxide filler, iron oxide shade, and zirconium oxide. The liquid consists of calcium chloride and a hydrosoluble polymer . According to the manufacturer, the powder of TBC consists of a mixture of white Calcium Enriched Mixture (CEM), calcium sulphate, calcium chloride, montmorillonite and the liquid has DPBS.
Mechanical perforation of the cavity floor with a probe was used to expose the pulps in this study. This technique was recommended previously because it protects the pulp from extensive damage and creates a uniform pulp exposure . Although this technique may lead to pushing of dentin fragments into the pulp, these fragments do not induce an inflammatory pulpal response . In addition, the auto-induction of reparative dentinogenesis could be observed on the surfaces of these fragments .
In the present study, the evaluation depended upon histopathological changes elicited with the pulp capping procedure and detection of dentine bridge formation, which are essential criteria for monitoring of the healing process.
Our results showed better therapeutic effects of Biodentine than TBC as direct pulp capping materials regarding dentine bridge formation and pulp integrity preservation.
Formation of the dentinal bridge at the interface between the pulp and pulp-capping cement is a controversial issue because it can be a reaction to irritation or a sign of healing . In the present study, formation of dentine bridge was interpreted as a positive reaction to stimulation and a sign of healing according to the histological findings.
In the present study, both Biodentine and TBC cements induced an early reparative dentinogenesis because the physicochemical properties of these materials enhanced the mineralization process. Moreover, stimulation of cell proliferation and differentiation might be attributed to tricalcium silicate present in the tested materials and presence of both calcium and silicon ions. Similar explanation was mentioned in previous studies [26, 27].
After one month, dentine bridge was completed in BD group while it was incomplete with tunnel defect in BS group. This tunnel defect was regarded as undesirable site facilitating the migration of the microorganisms towards the pulp. This favorable therapeutic action of Biodentine cement might be attributed to a significant release of TGF-β1 in pulp cells that stimulated odontoblasts to increase their activity and enhance the reparative dentinogenesis. Similar findings were reported before .
In BS group, vacuole-like spaces, complete degeneration of the pulp tissue, multiple edematous spaces, hyperemic blood vessels, extravasated RBCs and vacuolated odontoblastic layer were observed after one month. These findings might be due to the difference in cytotoxicity between Biodentine and TBC. Biodentine had significantly less cytotoxic effect compared to TBC . This difference may be due to the specific chemical compositions of these cements and this difference requires more research in the future.
In BD group, dentine bridge was observed in all teeth after 2 months with normal pulp. In most teeth of BD group, odontoblasts were arranged just below the dentine bridge with some structural changes. These cells were not true odontoblasts, but odontoblast-like cells having elongated shape and palisade orientation. These findings are consistent with other previous studies [30–32]. Odontoblast-like cells produce extracellular matrix that becomes complete dentine bridge after mineralization. The thickness of dentine bridge and pulp preservation depends upon the amount of odontoblast-like cells. With increased layers of these cells, the thickness of dentine bridge is increasing and the pulp remains vital .
After 3 months, normal pulp tissues, layers of odontoblasts with normal architecture and arrangement, predentin, secondary reparative dentin were detected in BD group. These findings are in agreement with several studies [31,33]. While in BS group, predentin layer, reparative dentin and new odontoblasts were recorded. These findings were considered as an improvement in pulp healing process after our findings at 2 months where the odontoblasts had ill-defined boundaries. This improvement might be due to decreasing of cytotoxic effects of Biosealer with time. Therefore further investigations are recommended to evaluate the biocompatibility of TBC.