Üst tam protezlerin kaide plağında oluşan gerilimler (Stress) üzerinde incelemeler

Abstract

- 71 - ÖZET Üst tam protezlerin kaide plağında oluşan gerilimler 3-Boyutlu fotoelastik analiz yöntemi ile incelendi. Bunun için öncelikle normal, derin ve sığ olmak üzere 3 değişik damak şekli alındı. Bu damakların modelleri hacım- sal olarak üç misli büyütüldü. Üzerlerine optik açıdan aktif bir madde olan Araldit-D maddesinden birer kaide plağı hazır landı. Bu kaide plakları ile modeller arasına mukozayı taklit edebilmek amacıyla silikon RTV M 400*den bir ara tabaka yer leştirildi. Yük uygulanacak bölgeler olarak A, B ve C noktaları saptandı. A (Kret içine konulduğu varsayılan üst birinci bü yük azının santral fossasınm tam ortası), B(Kret üzeri kesici orta nokta), C(Kret üzerine konulduğu varsayılan üst birinci büyük azının santral fossasınm tam orta noktası). Sonra Özel olarak hazırlanan bir yükleme apareyi ile bu noktalardan yükleme yapıldı. Gerilim çizgilerini dondurmak için modeller üzerlerindeki kaide plakları ile birlikte yük leme fırınında toplam 13 saat bırakıldı. Daha sonra yükleme bölgelerinden kesitler alındı. Alınan kesitler polariskop' ta incelendi, gerilim çiz gileri sayıldı ve resimleri çekildi.

72 - SUMMARY AND CONCLUSION The three-dimensional photoelastic stress analysis was used to evaluate the stress distribution in complete upper denture bases. Three different forms of palatal casts such as normal, flat and deep palates have been magnified three times by volume. An epoxy resin Araldit-D was used to prepare base plates on each magnified models. Between the magnified models and the epoxy base plates there were silicone layers (RTV M 400). Silicone layers whose thickness were approximately 2 mm., placed on magnified models on which epoxy base plates were seated to simulate the oral mucosa. The A, B and C points were determined as the areas to apply loads on models. A was the point assumed as the first upper molar positioned inside the ridge and C was the point assumed as the first upper molar positioned over the ridge. B was the mid point of incisors assumed as positioned over the ridge.- 73 - Then the loading device which was constructed for this purpose was used to apply loads to these determined points. The loading device and the base plates on magnified models were placed in a large oven and left there for raising the temperature and cooling the base plates totally 13 hours. This cycle `froze` the stresses in the denture bases. After then slices were made and each slice was examin ed in a circular polariscope and the fringe orders for speci fic areas were recorded. The Findings Were as Follows: 1- Generally it seemed that highest stresses had been found in the deep and the lowest stresses in the normal shaped palates. The fait shaped palate took place between them. 2- It seemed that the geometrical shape of the palates had affected the stress distribution. 3- In three types of palates, stress was decreased when the posterior teeth were positioned inside the ridge and increased when the posterior teeth were positioned just over the ridge. In other words, the fringe orders increased progressively in the area of molars from palatinal to buccal. 4- In flat, normal and deep shaped palates when the load was applied inside the ridge in the area of molars and over the ridge in the area of incisors at the same time, the fringe orders were found in the anterior region. In deep shaped palates when the denture bases were loaded over the ridge from the area of molars and incisors, again the higher stresses were observed in the anterior region.- 74 - 5- If there was an undercut at the labial aspect of the deep shaped palate then whereever the load was applied, the highest stresses had been observed in the anterior region of the denture base. 6- In fait and normal shaped palates when the denture bases were loaded over the ridge from the area of molars and incisors, the higher stresses were recorded in the region of molars. 7- It seemed that the stress distribution was more homogenous in the normal shaped palate than the others. In other words, the applied load was distributed to a large carrying area instead of concentrating at a certain point..;` But in flat shaped palates the stress distribution was not homogenous and generally the fringe orders concen trated at the point of load applied. In deep shaped palates, although the higher fringe orders are recorded at the point of load applied, there also appeared a few amount of stress distribution around that point. While constructing a prosthesis on flat and deep shaped palates, we may propose to make denture bases thicker at the regions where loads are directly applied. In these regions modelling must be done thicker both from the outside (buccal) and the inside (palatinal) regions. Also we may propose the setting of teeth over the ridge as in the conventional manner in normal shaped palates and a little inside the ridge in deep and flat shaped palates. But this lingualized position must never limit the- 75 - freedom of tongue movements and push the prosthesis by con fining the Space of Donders. 8- The above ideas are just proposed from the view point of stresses on different palatal forms and must never oppose with the factors such as the statics and the esthetics of the denture and the confinement of tongue room.