Dalkiz, Arslan, Tuncdemir, Bilgin, Aykul DIscuION Polymerization shrinkage and water sorption, in other words, the parameters affecting the di- mensional stability of acrylic resins denture base materials have been the subject of numerous stud- ies.2-7 Thickness of the denture, thermal expan- sion and contraction of the acrylic resin and the gypsum, structural variations between polymer and monomer systems, polymer/monomer ra- tios, packing pressure, polymerization shrinkage, investments, separators, internal stresses, water sorption and desorption and water content of the gypsum were reported as other parameters influ- encing the dimensional stability of an acrylic resin denture.2-10 Two methods were mostly used for the determination of dimensional alterations in acryl- ic resin denture base materials: Determination of the present closeness (adaptation) of acrylic resin base to the definitive stone cast surface,6,7,18 and distance measurement between determined ref- erence points on an acrylic resin denture base.3,5,8 Both methods were used in the present study to provide reliable results. This method provided re- al-time direct dimensional changes of the denture base resin during the fabrication process, as re- ported by Kawara et al.22 Heat polymerized acrylic resin denture base material and conventional flasking technique were used in the present study due to the ease of pro- cessing and to minimize the complications faced during the impregnation of glass fibers into the acrylic resin bulk. Metal wires, grids and various types of metal plates were used previously to strengthen the acrylic resin dentures base materials.6,15,16 How- ever, despite of their satisfactory strenghtening ef- fect, these reinforcing materials were too far from providing even minimal esthetics.6,15,16 The intro- duction of reinforcing fibers of various types and forms in the field of prosthetic dentistry greatly solved this problem.11-14 It was reported in previous studies16,18-21 that glass fibers provided satisfactory impregnation with PMMA, as well as good esthet- ics. Thus, in the present study, wowen and roving type glass fibers were used to provide successful incorporation of fibers with acrylic resin bulk. A second reason for preferring glass fibers was their rare shifting occurrence during flasking of acrylic resin, due to their density.17, 23 The results of the present study demonstrated January 2012 - Vol.6 that palatal vault shape and fiber impregnation into the acrylic resin bases did not affect the magni- tude of interfacial gaps between the bases and the stone cast surfaces, after 30 days of water storage. This finding is in correlation with the statements of Polat et al19 who reported that the dimension- al stability of acrylic resin denture base material used was not affected with fiber reinforcement. In the present study it was shown that water storage of 30 days significantly affected the linear distanc- es between references points marked on acrylic resin bases in all experimental groups. Contrary to these findings, Cal et al18 reported that the un- reinforced group showed the highest dimensional change compared to fiber reinforced groups. The effect of the shape of residual mandibular crest and effects other fiber types on the dimen- sional stability of different acrylic resin denture base materials are to be investigated in future studies. cONcL usION 1. The interfacial distance between the acrylic resin and the relevant stone cast is independent of palatal vault shape and from fiber reinforcement. 2. Water storage of 30 days significantly affect- ed the linear dimensional stability between refer- ences points marked on acrylic resin bases in all experimental groups. rEFErENcEs 1. Brown LR, Flavin C, French H. A new economy for a new century. In: State of the world 1999. New York: W.W. Norton & Company 1999; 5-7. 2. Wolfaardt J, Cleaton-Jones P, Fatti P. The influence of pro- cessing variables on dimensional changes of heat-cured poly(methyl methacrylate). J Prosthet Dent 1986;55:518- 525. 3. Anderson GC, Schulte JK, Arnold TG. Dimensional stabil- ity of injection and conventional processing of denture base resin. J Prosthet Dent 1988;60:394-398. 4. Phillips RW. Skinner’s Science of Dental Materials. 1991; 9th Ed. W.B. Saunders Co, Philadelphia, 177-213. 5. Huggett R, Zissis A, Harrison A, Dennis A. Dimensional ac- curacy and stability of acrylic resin denture bases. J Pros- thet Dent 1992;68:634-640. 6. Dixon DL, Breeding LC, Ekstrand KG. Linear dimensional variability of three denture base resins after processing and in water storage. J Prosthet Dent 1992;68:196-200. 77 European Journal of Dentistry