MODELLING OF STRESS STATE OF DENTAL HARD TISSUES WHILE CARIOUS CAVITIES OF I CLASS RESTORATION

A number of problems, worsening restorative material retention in carious cavities and resulting in reduction of restorations working lifespan, occur while dental preparing and restoration. It concerns technical errors during treatment, methods of forming carious cavities. Internal stress arises in the enamel and dentine of both intact and restored teeth, which may cause secondary decay. Purpose of research is to study stress in dental hard tissues in computer modeling of restored I class carious cavities, which were prepared with classic method. Methods. Three-dimensional model «enamel-dentine-restoration» was created in SolidWorks program and based on mandibular molar radiograph, it was exported in software complex ANSYS Workbench, and finite element model was formed. Von-Mises equivalent stress was calculated on the condition that dental root was rigidly fixed, all the model components were isotropic, vertical uniaxial load on tooth centre was 500 Н. Results. A masticator surface stresses in enamel corresponds topographically to projection of molars fissures in an intact tooth. Several stress fields, spreading concentrically from maximum values in the point of load action to minimum values to fissures perimeter, occur there. The first field appears in the point of vertical load action, maximum stress is 74.2 MPa. The second field is located around the first one, its values are lesser up to 50 MPa. Indices of the third field reduce to 25-30 MPa. In the area of medial and distal edge isolated stress zones are noticed up to 35 MPa. The fourth stress field has the lowest indices 10-20 MPa. Enamel stress nature in a restored tooth is equal to the nature in an intact tooth. But the first field starts around the dental filling, maximum stress value in an enamel is 119 MPa, which is 60% higher than in an intact tooth. The second stress field is about 100 MPa (100% higher than then intact tooth). Stress in full enamel thickness, in a sagittal section of an intact tooth in a load point, is equal to 52-55 MPa, and in the area of dentine-enamel junction reaches a maximum (74 MPa). Indices in a dentine decrease to 10 MPa. The same stress force is noticed in precervical area of enamel and dentine. The same stress arises in the top filling layers of restored tooth, as in an enamel of an intact tooth (52-55 MPa). However, a stress is increased to about 120 MPa in the area of direct contact of a filling and enamel. In the thickness of mantle dentine, and in precervical area stress force of hard tissues decreases to 10-15 MPa. Conclusions. Stress in hard tissues of intact and restored tooth has different value. In unidirectional vertical stress on restored tooth in molar of lower teeth caries of I class maximum stress arises in enamel on the boundary of direct contact with restoration