Nano-structural and compositional basis of devitalized tooth fragility.

OBJECTIVE: Increased tooth fragility after devitalization is commonly observed but there is no definite mechanistic explanation for such phenomenon. Therefore, it is important to analyze more profoundly structural and compositional properties of this altered form of dentin. The present study investigates the differences between normal and devitalized dentin using advanced techniques. METHODS: Atomic force microscopic imaging (AFM), energy dispersive X-ray analysis (EDX) and micro-Raman spectroscopy were performed on 16 dentin specimens, eight vital and eight that underwent root-canal treatment at least two years before extraction and had no infection in root canals before or after devitalization. RESULTS: The mean size of mineral crystals showed by AFM was larger in devitalized than in healthy dentin in the same age category. AFM phase shifts in devitalized cases revealed altered mechanical characteristics and suggested differences in composition of material between devitalized teeth and healthy controls. No significant difference in Ca/P ratio between vital and devitalized teeth was found using EDX. However, micro-Raman analyses showed that in devitalized teeth, apart from hydroxyapatite, dentin contained significant amounts of apatite phases with lower calcium content: octacalcium phosphate, dicalcium phosphate dihydrate and tricalcium phosphate. SIGNIFICANCE: Differences between vital and devitalized dentin bring new insights into the basis of devitalized tooth fragility. Larger mineral crystals could account for decreased mechanical strength in devitalized teeth. Moreover, calcium-phosphate phases with lower Ca content have lower material strength, and the presence of these phases in devitalized teeth may explain their increased fragility.