A device for determination of a plane ensuring parallel preparation.

PURPOSE: Parallel preparation of a greater number of teeth with a different tilt is a difficult clinical task. For precise guidance of the preparation instruments with a fixed individual tilt it is necessary to determine the "working preparation plane". A device for orientation and fixation of an individual direction for parallel preparation is created. METHODOLOGY: We have prepared 47 bridge abutments using our methodology. The working models are subjected to control and comparative analysis with a precise laboratory parallelometer. The reported results do not show differences requiring statistical analysis. DISCUSSION: The device serves to determine the working preparation plane. It promotes the fixing of an intraoral parallelometer that controls the achieved parallelism between the homonymous surfaces of dental stumps.

Finite element tension analysis of the supporting tissues of a maxillary canine.

INTRODUCTION: The distribution of masticatory load on the teeth and the arising force tensions in them are factors that determine the origine of destructive processes in their periodontium. The development of mathematical models and application of new computer technologies make possible their precise study. They are still not thoroughly studied. PURPOSE: To study the tensions, originating in the periodontium of a canine tooth during occlusal load by the modern method of finite elements (MFE). MATERIALS AND METHODS: A three-dimensional model of a maxillary canine is built by MFE containing 304 finite elements with six varieties of geometrical form, linked in 1409 nodes. It is supposed that the tooth is fixed firmly to the outer surface of the periodontal membrane to the alveolar bone and is loaded in the lingual wall by a force perpendicular to its longitudinal axis and directed from the lingual to the vestibular wall. RESULTS: As a result of the calculations according to MFE the tension state of dental tissues is calculated for diferent degrees of destruction of the alveolar bone. It was established that with the increase of destruction of the alveolar bone for one and the same masticatory load, the tensions in the periodontal membrane also increase. The maximal tensions act in the apex of the root and around the clinical neck of the teeth. CONCLUSION: The results obtained provide precise information of distribution of force tensions in the periodontium of maxillary canines during occlusal load. They serve as a serious theoretical base for future investigations.

[Line of cutting edges of the upper teeth and its conformity with the contours of nose and lower lip while smiling]. / Liniia na rezheshtete rubove na gornite zube i suotvetstvieto y s konturite na nosa i ha dolnata ustna pri usmivka.

Observations were carried out--visual and via photos--of 180 subjects (83 males and 97 females) in order to establish the incidence of coincidence between the line of the cutting edges of the upper front teeth with the contours of the base of the nose and the lower lip while smiling. It has been established that the total configuration of the cutting edges is perceived visually as a curved wave-like line, whose arch, in the majority of the cases, does not correspond to the form of the nose but, most often, coincides with the contuour of the lower lip. Attaining of the mentioned harmonious conformity between those two linesis recommended in the working out of aesthetic prosthetic constructions.

[Horizontal measurements of buccal vestibules]. / Khorezontalni razmeri na bukalnite koridori.

In order to establish the horizontal measurements of the buccal vestibules- an important index for the aesthetic quality of prostheses, a total of 250 subjects, 119 males and 131 females, were measured. The size of the buccal vestibule is calculated as the half of the difference between the size of a smiling mouth and the width of the visible dentition. It has been established that the mean linear measure of the buccal vestibule is 6.5 mm and varies from 5 and 8.5 mm. Its value is directly proportional to the size of the smile and inversely proportional--to the width of the visible dentition; no discrepanciens have established depending on sex and age of the subject.