[Evaluation of the fracture strength of the post - crowned teeth with and without ferrule]

Various factors affect the distribution of stress and fracture resistance of restored teeth by post and core. One of the major causes is the remaining body of the teeth, [ferrule] which was embraced by crown. The purpose of this study was to asses the effect of developing the ferrule via a crown lengthening procedure, on the fracture strength of endodontically treated teeth. 24 recently extracted second premolar of mandible were selected in this descriptive study and their crowns were cut so far that no more than 15 mm of the root remained. Then they were divided randomly into two groups of 12 and their canals were undergone rootcanal therapy. In the first group, a post-core and full metal crowns were made without ferrule, while in the second group with changing in the optimum ratio of the crown/root height, 2mm ferrule was designed and then the cast post- core and full-metal crowns were made. Finally, in both groups, a compressive load with 1 mm per minute speed and an angle to 150 on the long axis of the tooth was applied. The force was exerted in mesial marginal ridge, in 7 teeth and on the buccal cusp edge in the other 5 teeth to induce fracture. Statistical analysis of the data was performed with student t-test, chi-square and two-way ANOVA analyses 1. There was a significant difference between the mean of fracture load in the ferrule and non-ferrule groups [P<0.001]. 2. No significant difference in the mean fracture load was observed when the load was applied in the buccal-cusp edge instead of mesial marginal ridge. By adding a 2 mm cervical ferrule on top of the finishing line of mandibular premolars restored by cast post-core and crown, we can increase the fracture resistance of these teeth

[Effect of deflasking time on dimenstional stability of two heat-cured acrylic resins]

Dimensional changes of denture base acrylic resins are one of the most frequent phenomena that occur during the production of the dentures in different steps of curing and different times of deflasking. Measurement of the effect of different deflasking times on dimensional stability of acrylic resin can reduce the dimensional changes of these materials. The objective of this study was to compare these dimensional changes in different times of deflasking in two different acrylic resins [Acropars and Meliodent]. In this experimental study, the dimensional changes of two heat-cured poly methyl metacrylate resins [Meliodent and Acropars] were studied in different deflasking times. The initial model included one steel sheet approximately 3 mm thick, cut in the form of a dumbbell and fifty specimens of the same piece were regularly flasked and processed. Acrylic specimens, in different bench cooling times [4 hours, 12, 24, 48, 5 days] were taken out and measured in 4 areas with an accuracy of 0.01 mm using a digital caliper, subsequently, the results were studied using the One Way Anova method. Dimensional changes in two types of acrylic resins [Meliodent and Acropars] showed significant differences after 5 days deflasking [P=0.000], and had the least dimensional changes. No significant differences were observed between the average dimensional changes in reference points. Keeping Meliodent acrylic resin for at least 4 hours and Acropars acrylic resin for at least 12 hours after processing can reduce dimensional changes significantly. Iranian specimens of Acropars acrylic resin even show smaller dimensional changes than German specimens of Meliodent acrylic resin. After 5 days, deflasking time has the least dimensional changes in both acrylic resins

[Assesment of edentulous patients motivation attending to practical denturists for providing a complete denture in mashhad in 2003-2004]

Assessment of edentulous patients' motivation to attend practical denturists office for providing a denture, was important for us. 450 patients were selected by "random sampling" method and each case was analyzed by his or her choices in the questionaire. Results were presented by bar diagrams and pie charts. There was a significant relationship between the number of patients attending denturists office and the patient's level of education. The higher the level of education the less the patients showed up in the partical denturist's office. There was also a relationship between the number of patients attending denturist's office and the patient's economical class, so the higher the economic class of the patients, the less they showed up in the practical denturists office. There were several reasons for referring to the practical denturists but the major reasons were as follow: 1. Rapid construction and delivery of denture. 2. Encouragement of relatives and friends of patients. 3. Practical denturists seemed more experienced to the patients. 4. Lower cost of practical denturist's sevices