Abstract
In our study, deformation properties of maxillar major connectors which are commonly used in our country for Kennedy Class I removable partial dentures were investigated by photogrammetry and microcrack measures. In this study, complete palatal plate, U-shaped palatal connector, palatal strap and the combination of anteriorpalatal strap - posteriorpalatal bar were used as four different maxillar major connectors. For each major connector type 2 test prothesis and totally 8 test prothesis were prepared. The occlusal surfaces in the opposing jaws were made of acrylic resin. During the loading stage, a computerized hydraulic testing machine was programmed for a frequency of 4 Hertz per second, load 100 kg. and a maximum of 300.000 cycle. In the first part of this study, the photogrammetric method was applied for the first time in the field of partial dentures. The test prothesis including control group were analyzed by a special analytical instrument at the end of 3.000, 30.000 and 300.000 cycling periods. As a result of statistical evaluation of photogrammetric findings, it was determined for the whole area, in respect to gradually decreasing deformation amounts, that the major connectors were taken place in the sequence of complete palatal plate, palatal strap, U-shaped palatal connector and the combination of anteriorpalatal strap - posterior palatal bar. When a comparison is made in terms of anterior and posterior points on middle line, junctional points of posterior margins with saddles, right and left half points of posterior margin and M.O.R.S that have some special properties, different sequences were obtained in some points with respect to the whole area, whereas in some other points no significant differences were found among the major connector groups. When evaluated in respect to deformation amounts formed between the posterior middle point and the junctional points of posterior margin with saddles, no difference was observed in the U-shaped palatal connector type major connector group.-121- In the second part of this study, at the end of 300.000 cycling period; the microcrack measures which were carried out by liquid fluorescense penetration system, microcracks were observed in complete palatal plate and palatal strap types major connectors. Although in our study major connectors as complete palatal plate and palatal strap type were taken the first places in the sequences of deformation for the whole area, when the results were considered as a whole, sudden changes in sectional thickness and subsequent microcracks were proven effective in getting these results; proving the necessity of stress concentrating factors elimination, it was clear that especially the complete palatal plate type major connector was of the prior importance due to its supporting and rigidity quality for maxillar Kennedy Class I removable partial dentures. As a consequence of this study, making a decision for the planning of partial dentures, it was found out that special consideration had to be given to the rigidity properties in the selection of major connectors and waxing phase should be completed in such a manner that sudden changes in sectional thickness wouldn't result in the preparation of metal substructure. The results also revealed that the combination of anteriorpalatal strap - posteriorpalatal bar which showed the least deformation among the test prothesis by distributing the masticatory forces to a large area can be used safely because of its rigidity. Key words: Deformation, load transmission, major connectors, maxillar Kennedy Class I dentures, stereophotogrammetry.
