Water sorption by maxillary acrylic resin denture base and consequent changes in vertical dimension.
Many kinds of materials have been tried in the Laboratory and to some extent clinically prior to introduction of acrylic resin. With the introduction of acrylic resin as denture base material, continuous attempts have been made to evaluate its physical properties. To observe the changes in vertical measurements of acrylic resin dentures due to water sorption and to assess variations of vertical movements of individual teeth within dentures due to water sorption; present study was carried out on 25 maxillary acrylic dentures. From results, the maximum water sorption appears to take place within 24 hours and after 28 day of water sorption; there is no change in vertical dimension if the denture is placed for further more time. With the introduction of acrylic resin as denture base material continued attempts have been made to evaluate physical properties so as to determine its suitability as an ideal nonmetalic denture base materials. Several investigations have been carried out on physical properties of this material such as compressive strength, tensile strength, solubility and colour stability. These have proved their superiority over other nonmetalic denture base materials used so far. Also several studies have been carried out to assess dimensional changes that occur in acrylic resin during processing, but very few studies have been carried out about the water sorption changes in the acrylic resin and still few about the vertical dimensional changes in acrylic resin due to water sorption. While fabricating the denture base from the acrylic resin, it comes in contact with water during polishing as well as cleaning, consequently during the use of denture it is constantly wetted by oral fluids. It is the hypothesis that water sorption by denture base acrylic may effect the retention and stability of the denture. It has been shown that water molecules act according to the laws of diffusion. The diffusion presumably occurs between the macromolecules which are forced slightly apart. This separation renders the molecules mobile and the inherent stresses created during heat curing of the acrylic resin can be relieved with consequent intermolecular relaxation and possible changes in the shape of the denture. Exposure time also plays a significant role in water sorption. The present investigation was therefore, carried out by keeping the following objectives: (1) The primary objective was to observe the changes in vertical measurements of acrylic resin dentures due to water sorption. (2) To assess the variations of vertical movement of individual teeth within the dentures due to water sorption.
Available from: Yoshaskam Agnihotri
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ABSTRACT: Aims & Objectives: The aim of this study was to investigate the effect of water sorption on the dimensional stability of acrylic resin denture bases, to quantify the interference to occlusion due to the vertical dimensional change caused by water sorption and to assess the time required for the water sorption related dimensional changes to stabilize. Methods: The sample for this study consisted of tooth bearing specimens of heat cured acrylic resin .The present study was undertaken to determine the dimensional change in heat cure acrylic resin denture bases over a period of 28 days on immersion in water. Micrometer and a comparator were used to record the dimensional change. Measurement for the change in dimension in the vertical direction were recorded on zero, first, second, seventh, fourteenth, twenty first and twenty eighth day of water sorption and the mean dimensional change over this time period was calculated. Results: For statistical analysis the six days of measurement-day 1,2,7,14,21 and 28 were taken as six different treatments. Very little change occurred during the 21-28 day interval and was statistically not significant. The results indicate that the water sorption related dimensional change stabilizes and saturation or equilibrium is attained in 21 days or three weeks. The importance of coinciding centric relation with centric occlusion is an accepted theory in complete dentures but the vertical dimensional change may affect this important relationship. So there may be premature striking of teeth which may cause trauma to the tissues and the patient may experience discomfort which he finds hard to analyse as to location and cause. Therefore, this study has been carried out to determine how an acrylic resin denture behaves when it takes up water. Microwave disinfection decreases the hardness of all acrylic resin denture teeth. Immersion for 7 days in 4% chlorhexidine gluconate or distilled water had significant effect on the hardness of the acrylic resin denture teeth. Disinfection procedures changed the hardness of resin denture teeth.(3). Thus, study of sorption of water by acrylic resin is essential. Materials and Method (Figure-1,2,3,4,5 & 6.Table-1; Fig A) A stainless steel master die was constructed to simulate a unilateral posterior segment of a mandibular arch. (Figure 1) A polyvinyl siloxane impression of the master die was obtained with a self cure acrylic resin special tray (Figure 2 B). A stone cast was obtained by subsequent pouring of the impression with Type-IV die stone (Figure 2 C), The cast was then waxed up on both sides and ends to the level of the lower lip of the long undercut using two layers of base plate wax. A set of four posterior teeth (Premadent mould-32) were set in mesiodistal contact on the crestal surface. A self cure acrylic overcast was fabricated over the master setup so that the occlusal surfaces of the teeth got embedded in the acrylic. The acrylic overcast along with the wax of the master set up was removed from the die stone cast. Each die stone cast was secured from polyvinylsiloxane impression obtained from the master die. The set up was duplicated by obtaining the impression of the cervical portion of the teeth embedded in the acrylic overcast over the waxed up crestal surface of stone cast (Figure 3 B) .The corresponding teeth of same mould (Premadent-mould 32) were positioned into the impression and luted to the waxed up cast (Figure 3 C) .
Available from: Marcelo Ferraz Mesquita
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ABSTRACT: The purpose of this study was to investigate the effect of water storage at 37 degrees C (1 week, 1 month and 3 months) on tooth displacement in maxillary complete dentures. Ten maxillary dentures were constructed with Clássico acrylic resin using the conventional method of packing in metallic flasks. Metallic reference pins were placed in the incisal border of the central incisors (I), labial cusp of the first premolars (PM), and mesiolabial cusp of the second molars (M). Twelve hours after final flask closure, the acrylic resin was cured in water at 74 degrees C for 9 h. The flasks were removed from the thermo-polymerizing unit after water-cooling and the dentures were deflasked, finished and stored in water at a temperature of 37 degrees C for 1 week, 1 month and 3 months. At deflasking and at the water storage intervals, the I-I (incisor to incisor), PM-PM (pre-molar to pre-molar), and M-M (molar to molar) transversal distances, and LI-LM (left incisor to left molar) and RI-RM (right incisor to right molar) anteroposterior distances were measured using an optical microscope with 0.0005 mm accuracy. Data were submitted to ANOVA and Tukey's test (5%). Comparing the evaluation periods for each individual transversal and anteroposterior reference point, no statistically significant differences were observed among deflasking and the water storage intervals for I-I, PM-PM, M-M and RI-RM distances (p>0.05). For LI-LM, however, deflasking values were statistically different from those of 1-week, 1-month and 3-month water storage intervals (p<0.05), which, in turn, did not differ statistically to each other (p>0.05). These results confirm the complexity of tooth displacement in complete dentures. From a clinical standpoint, the difference observed in LI-LM distance after water storage would not be detected by the patients during clinical use.
Available from: Tomislav Badel
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ABSTRACT: Correct occlusal relationships are part of the successful prosthetic treatment of edentulous patients. Occlusal checking should be performed via a remount procedure because denture base materials and fabrication procedures cannot provide dimensionally accurate complete dentures. Occlusal errors caused by the adjustment of denture bases to the denture foundation after a certain period of wearing can also be corrected by means of remounting. The following remount procedures for complete dentures are described: fabrication of transfer casts, transfer of a maxillary denture with a facebow, centric relation record, and mounting of dentures with transfer casts in an articulator with a dental stone. Deflective occlusal contacts of denture teeth in centric occlusion can be eliminated by selective grinding and by tooth-guided excursive movements. In complete denture treatment, priority is given to anterior/canine-guided occlusion.
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