Apatite precipitation in gaps between Protooth™ and dentin

Objectives: Gap at the restoration-tooth interface can increase the risk of secondary caries. Although, the optimal use of permanent restorative materials minimizes gap formation, none of the routinely-used restorative materials, like resinous composites, are able to eliminate gaps completely. Novel calcium silicate cement (Protooth™) with calcium hydroxide and fluoride release has been developed with fast-setting at flowable or clay-like consistency. The material is thereby candidate for new applications including: lining, temporary filling, and cementation in the crown. Our previous study demonstrated the formation of apatite layer over Protooth in physiological-like solution (PBS). The aim of this study was to evaluate the ability of Protooth to close the gap entrance between dentin and material by apatite precipitation.
Methods: Calcium silicate-based cement containing 10% radiocontrast (Protooth) and resin-modified glass ionomers (Vitrebond™ and GC Fuji II LC) were tested in this study. Experimental gaps with 300±20 and 50±10µm width and 1 mm length were made between the restorative material and dentin (n = 6). Changes of the entrance area in 300µm gaps immersed in PBS were measured by 2D-nucleator using NEW-CAST software. Micro-tomography (µCT) and SEM/EDX were used to analyze gap precipitation in both gap sizes.
Results: In all Protooth samples precipitation closed the gap entrance area after 96h immersion in PBS. No precipitations were observed in Vitrebond and GC Fuji II LC gap entrance area. Micro-CT scans confirmed the complete closure of gap entrance area in Protooth samples with 50 and 300µm gaps. Voluminous gap precipitation was observed in Protooth samples after 6 months. SEM/EDX analysis revealed the formation of apatite precipitations that closed the entire gap entrance.
Conclusions: Interestingly, gap entrance between Protooth and dentin can be filled with continued apatite deposition. Accordingly, further clinical studies regarding the effect of Protooth on gap closure, microleakage, and secondary caries, seems relevant.