The enamel hardness is defined by enamel ability to resist against the action of mechanical forces and to suffer surface distortion through scretching. The enamel hardness is comparable with the hardness of the medium steel, with values situated within 200-500 KHN (Knoop hardness number- defined by raport between loading and indendation area). The factors that influence the hardness degree are as follows: mineralisation degree, enamel prisms orientation, hydroxiapatite cristals orientation, the presence and distribution inside the cristals of some metal ions.
There are many method to measure the human enamel hardness. Because of the numerous variables for enamel and dentin, the techniques based on microabrasion and microindendation are preferable.
Our study was made on freshly extracted teeth for orthodontic and periodontal reasons. We selected 10 teeth (bicuspids and molars), divided in two groups: study group (1) – 5 teeth with incipient carious lesions on smooth surfaces and in occlusal fisural system; control group (2)- 5 unaffected (healthy) teeth. The teeth were sectioned with discs and the sections were processed according to the standard procedures. The Vikers hardness indendations were measured and analysed with optic microscope Metalografic Neophot 21. The aim of the research was to establish if the medium values of the microhardness for the two groups are significantly different. According to the dates of the study and to statistical analysis, the medium values of the microhardness (VHN) are lower for the study group (teeth with incipient carious lesions), compared with the control group 2 (unaffected teeth).