Analysis of enamel microhardness at various hard tissue states and depth of the microfissures

Abstract

In clinical practice are often diagnosed precervical lesions: wedge-shaped defects and cracks. Long phases of the confrontation of the body as a damaging influence in the formation of thicker tissue sections of higher salinity, density and sustainability occur prior to the integrity of the enamel. Micro-hardness is one of the important characteristics of the micro-mechanical strength of the tooth-related physical and chemical changes that occur in the enamel as a result of external and internal influences. The purpose of the study was to identify possible differences in the micro-hardness of enamel, depending on the depth of fissures and pathology of hard tissues of the teeth.

We investigated the longitudinal sections of 27 teeth (18 - intact, 5 - with wedge-shaped defect, 4 - with cervical caries) of both jaws removed for clinical indications in patients aged 25-54 years, who were diagnosed three types of fractures (SB Ivanov, 1984). Hardness was determined in the outer, middle, inner layers of enamel in three topographical locations: in the cusp tip (cutting edge) of the tooth equator and neck as in previously described technique (S. Remizov, 1965).

The obtained results showed decrease in strength with micro-cracks enamel, compared with apparently intact ones, on the average 10% more in the incisal areas (tuber), less - in the equatorial zone. In intact teeth with micro-cracks and having a wedge-shaped defect the indices differed significantly depending on the depth of the defects of the cutting edge (tuber) and the equator: they were the smallest in the deep type III micro-cracks (p <0.05). The opposite picture was observed in samples with cervical caries. Thus, the statistically significant difference in terms of the micro-hardness of the enamel, depending on the depth of defects has been identified only in the area of cutting edge (tuber): in samples with deep micro-cracks of enamel type III they were the highest (P = 0.017). The greatest values of micro-hardness of enamel have been identified in the cervical area: the presence of defects of type I - in intact teeth, defects of II and III types - in the teeth with wedge-shaped defect. The least indices, regardless of the depth of micro-cracks in teeth, were diagnosed in cervical caries. In samples with carious and non-carious pathology the largest micro-hardness of enamel in the cervical area were recorded in deep micro-cracks type III, and the lowest - in the teeth with defects type I. In intact samples, conversely, the strength of enamel was higher in minor defects type I, lower - in the presence of micro-cracks type II.

Changes in the mechanical properties of the enamel were due to its chemical composition, which was confirmed by microroentgen-spectral analysis. Thus, the content of calcium and phosphorus in the cervical region was significantly different depending on the pathology of hard tissues (p <0,05). The higher content of macro-elements was determined in the wedge-shaped defects. Some discrepancy of the obtained indices with the depth of micro-cracks indicates that complex of adaptive processes occurs not only in the enamel but in the strength of the enamel, depending on the depth of cracks and pathology of hard tissues and demand further investigation. The revealed features should be used for a substantiation of principles of treatment and prophylaxis  of   the dental hard tissues defects.