Journal of Dental Medicine

Statement of Problem: Different temperature and moisture around Iran and wide usage of stone type IV in dental laboratories in our country were the reasons for us for doing this study.

Purpose: In this survey the effect of temperature, moisture and time on dimensional change of dental stone type IV (Velmix) were investigated.

Materials and Methods: In this experimental study cube shape Metal models (10×10×10mm) was made for Taking impression. We used special tray, which has ten holes (15×20×25mm) and made impression with condensational silicone in two-step procedure, and poured it with stone type IV. stone cubes were divided to different groups. 3 groups holed in fix moisture and variable tempraure and 5 groups in fix temperature and variable moisture. After 2 hours, 24 hours and one-week dimension of stone cubes were measured. Then analysis was done with ANOVA and dauncan.

Results: The following conclusions were achieved: 1-Time has no effect on dimensional changes. 2-Tempreture and moisture has some effect on dimensional changes in stone IV. Increasing of temperature result in stone contraction and increasing in moisture result in stone expansion.

Conclusion: The best temperature for least dimensional change is 20C and the best moisture for a least dimensional change is 30 %.

Statement of Problem: In the treatment of edentulous patients with implant supported fixed partial dentures several factors such as implant numbers, implant position, superstructure pattern and cantilever length must be considered. Mandibular flexture in function exerts forces in peri-implant bone, however this phenomenon has received little attention.

Purpose: The goal of this finite element analysis (FEA) study was to evaluate the effect of mandibular dimensional changes on peri-implant bone stress in different prosthesis and implant treatment plans.

Materials and Methods: In this experimental study, three dimensional finite element computer model of mandible was simulated according to data from CT-Scan in 0.5 mm sections. The model of 4.110 mm ITI implant, measured by profile projector, was simulated in solid works 2003 software. Implant models were inserted, in two different patterns, on mandible and three different superstructures were placed on implants. Two clenching tasks were modeled (incisal clench and right molar clench).

Results: Analysis of Von Misses stress for peri-implant bone revealed the lowest stress values in three-piece superstructure.

Conclusion: According to this study, additional placement of implants in order to fabricate independent prostheses and to achieve the freedom of mandibular flexture are recommended.