Applications Journal of Biomaterials

Journal of Biomaterials Applications http://jba.sagepub.com/

Water Sorption, Solubility and Dimensional Changes of Denture Base Polymers Reinforced with Short Glass Fibers Tülin N. Polat, Özgül Karacaer, Arzu Tezvergil, Lippo V. J. Lassila and Pekka K. Vallittu J Biomater Appl 2003 17: 321 DOI: 10.1177/0885328203017004006 The online version of this article can be found at: http://jba.sagepub.com/content/17/4/321

Published by: http://www.sagepublications.com

Additional services and information for Journal of Biomaterials Applications can be found at: Email Alerts: http://jba.sagepub.com/cgi/alerts Subscriptions: http://jba.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav Citations: http://jba.sagepub.com/content/17/4/321.refs.html

>> Version of Record - Apr 1, 2003 What is This?

Downloaded from jba.sagepub.com at Ýnönü Üniversitesi on August 28, 2012

Water Sorption, Solubility and Dimensional Changes of Denture Base Polymers Reinforced with Short Glass Fibers ¨ ZGU ¨ LIN N. POLAT,1 O ¨ L KARACAER,2 TU 2,3, ARZU TEZVERGIL, * LIPPO V. J. LASSILA3 AND PEKKA K. VALLITTU3 1

Department of Prosthodontics, Faculty of Dentistry Cumhuriyet University Sivas, Turkey

2

Department of Prosthodontics, Faculty of Dentistry Gazi University, Ankara, Turkey

3

Department of Prosthetic Dentistry and Biomaterial Research Institute of Dentistry, University of Turku, Finland

ABSTRACT: The aim of this study was to determine water sorption, solubility and dimensional stability of injection and compression-molded polymethyl methacrylate based denture base polymer that was reinforced with various concentrations and lengths of E-glass fibers. For water sorption and solubility, 20 test groups with different fiber contents and lengths of fibers were prepared. Test specimens without fibers were used as a control. The water sorption and solubility was measured after 90 days water storage. For dimensional stability, rhombic test specimens were prepared and the dimensional changes were measured after processing, drying and storing in water for 4 days and 30 days and were compared with those on the brass model. The water sorption and solubility of injection-molded denture base polymer was lower compared to compression-molded specimens ( p 0.05).

*Author to whom correspondence should be addressed. E-mail: [email protected]

JOURNAL OF BIOMATERIALS APPLICATIONS Volume 17 — April 2003 0885-3282/03/04 0321–15 $10.00/0 DOI: 10.1177/088532803032823 2003 Sage Publications


321

322

A. TEZVERGIL ET AL.

KEY WORDS: water sorption, fiber reinforcement, solubility, dimensional stability, denture base polymers. INTRODUCTION

D

enture base acrylic resins are usually based on multiphase poly methyl methacrylate (PMMA) and they exhibit dimensional changes during processing. The causes for the dimensional changes are the ratio of polymer powder to monomer liquid, type of denture base resin, polymerization conditions and investment [1,2]. Denture base polymer absorbs water slowly over a period of time. This imbibition is due primarily to the polar properties of the polymer molecules. High equilibrium uptake of water softens denture base polymer because the absorbed water acts as a plasticizer of the polymer [3], and reduce the strength of the polymer. Water sorption also affects other physicochemical and mechanical properties, such as the Young’s modulus [4,5]. In recent years, approaches to strengthen the acrylic resin dentures with different fibers such as carbon/graphite [6–11], aramid [12–16], polyethylene [17–22] and glass [23–30] have been introduced. Glass fibers were shown to be most suitable for dental applications because of good cosmetic qualities and good bonding to the polymer matrix via silane coupling agents [23,31–33]. The most common type of glass fiber is so-called electrical glass (E-glass), which is also in common use for dental applications [34,35]. The use of denture base resins with glass fibers has had difficulties one of them being inadequate impregnation of fibers with the resin [15,36]. This problem was overcome by using an excess of methyl methacrylate (MMA) to impregnate the fibers with the resin mixture [36]. This increases the polymerization shrinkage of the resin, and can result in dimensional changes of the denture. The excess of MMA has also shown to cause voids between the fibers and the polymer matrix. This has been suggested to cause increased water sorption [37]. On the other hand, well-impregnated glass fiber composites had theoretically lower water sorption because glass fibers reduce the quantity of water absorbable polymer of the material [38]. Two mainly used molding techniques for denture base resins are injection molding and compression molding [39,40]. The dimensional accuracy and water sorption and solubility of injection-molded denture base resin denture base material reinforced with E-glass fiber has not been studied. The aim of this study was to investigate and compare the dimensional changes, water sorption and solubility of E-glass fiber


Denture Base Polymers Reinforced with Glass Fibers

323

reinforced injection-molded and compression-molded denture base polymers. MATERIAL AND METHODS

Water sorption and solubility were tested according to ADA Specification No: 12, with the exception of the dimensions of the test specimens [41]. Test specimens were prepared on disk-shaped molds (50 1 mm in diameter and 3 0.05 mm thick). The denture base resin was autopolymerized acrylic resin for injection-molded applications (PalaXpress, Heraeus Kulzer, GmbH, Wehrheim, Germany). The ratio of polymer powder to 1 mL of monomer liquid was 1.5 g for the injectionmolded test specimens without fibers. Additional monomer liquid was used in fiber reinforced test specimens. Based on the fiber quantity additional monomer (0.7 mL liquid per 1 g fiber) was used to improve wettability of the fibers by the resin. The compression-molded specimens were prepared using heat polymerized denture base resin (Meliodent, Bayer UK Ltd Newbury, Berkshire, UK). The resin was mixed using a powder-to-liquid ratio 2.34 g to 1 mL to fabricate unreinforced specimens. Additional monomer liquid was used for fiber reinforced resin groups according to the fiber quantity (0.7 mL liquid per 1 g fiber). Wax patterns of the test specimen were placed in dental stone to form molds for packing the resin dough. Packing of the resin dough and polymerization were carried out according to the manufacturer’s instructions. There were altogether 20 test groups with different fiber content and length, including control groups without fibers (Table 1). E-glass fiber (KCR2 (M), Cam Elyaf San. A.S., Kocaeli, Turkey) was chosen for reinforcement of both acrylic resins. The glass fibers were cleaned in boiling water for 10 min and after air-drying fibers were cut to lengths of 4, 6, 8 mm and were silanated by dipping into a silane ¨ LSsolution, -methacryloxypropyltrimethoxysilane (MPS), (A174, HU Veba GmbH, Germany). The fibers were air-dried for 40 min and then placed in an oven for 1 h at 115 C before adding into the acrylic resin. Fibers were incorporated into the acrylic resin powder at concentrations of 1, 3 and 5 wt.%. The injection-molded test specimens for groups were prepared using an injection system (Heraeus Kulzer). Acrylic resin–fiber mixture was injected into the flask with an air pressure of 600 kPa and remained on the injection unit for 5 min. Then the flask was removed from the injection unit and polymerized at 45 C with a pressure of 300 kPa for 30 min. The flask was cooled at room temperature for 20 min, and then the test specimens removed from the flask.


324

A. TEZVERGIL ET AL.

Table 1. Classification of test groups. Group 1 2 3 4 5 6 7 8 9 10

Injection-molded Resin Fiber Length, Fiber wt.%

Compression-molded Resin Fiber Length, Fiber wt.%

Control (unreinforced) 4 mm,1% fiber 4 mm, 3% fiber 4 mm, 5% fiber 6 mm, 1% fiber 6 mm, 3% fiber 6 mm, 5% fiber 8 mm, 1% fiber 8 mm, 3% fiber 8 mm, 5% fiber

Control (unreinforced) 4 mm, 1% fiber 4 mm, 3% fiber 4 mm, 5% fiber 6 mm, 1% fiber 6 mm, 3% fiber 6 mm, 5% fiber 8 mm, 1% fiber 8 mm, 3% fiber 8 mm, 5% fiber

The disk-shaped test specimens were dried in a desiccator containing thoroughly dry anhydrous silica gel (freshly dried at 130 C) at 37 2 C for 24 h, removed to a similar desiccator at room temperature for one hour, and then weighed with a precision of 0.2 mg (Sartorius AG, Gottingen, Germany). This drying cycle was repeated until the weight loss of each disk was not more than 0.5 mg in any 24-h period (W1). The disks were stored in distilled water for 1 week at 37 C then they were weighed again (W2). The disks were dried and weighed again (W3). Water sorption was calculated by the following formula: W2ðgÞ W3ðgÞ Disk volume (cm3 Þ Solubility was calculated by the following formula: W1ðgÞ W3ðgÞ Disk volume (cm3 Þ

Dimensional Stability Five rhombic brass plates with dimensions of (20 12 3) mm were used. Signs were marked with their centers 2.0 mm away from the corners of the brass plates and they were designated by the letters A, B, C and D. Distances AB, BC, CD, and DA were measured, and numeric



325

vector calculations of these values were made. The distances between the points were measured with a Measuring Microscope (Scherr Tumico, St. James, Minnesota, U.S.A.) that had a tolerance of 0.0002 mm. The brass plates were used to fabricate the 20 rhombic denture base polymer specimens (5 unreinforced specimens and 5 reinforced specimens for each method with 8 mm 5 wt.% (fiber content) in molds of dental stone. Polymerization of the resin was carried out as mentioned before. A microscope was used for the measurement of dimensional changes of the specimens. Four distances, AB, BA, CD, and DA, were measured, and then numeric vector calculations of these values were made. The numeric vector was defined as: ~k ¼ kV

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi AB2 þ BC2 þ CD2 þ DA2

where AB ¼ distance between A and B, and so on; and V ¼ distance vector of the specimen. Four points in each specimen (A, B, C, and D) and 4 dimensional vector calculations were made. The dimensions were measured in 5 different stages, and vector values were calculated: ~ 1) . Initial measurements on brass models (V ~ 2) . Immediately after deflasking of the acrylic resin specimens (V ~ 3) . After drying the specimens for 4 days at 37 C under vacuum (V ~ . After storing the specimens in 37 C water for 15 days (V4 ) ~ 5) . After storing the specimens in 37 C water for 30 days (V Additionally the fracture surface of the test specimens was gold sputtered and examined with a scanning electron microscope (5500, Jeol Ltd, Tokyo, Japan). Following data collection, the mean values and standard deviations of the water sorption, solubility and dimensional changes values were calculated using the SPSS statistical software program, SPSS software (version 10.0) (Statistical Package for Social Science, SPSS, Inc., Chicago, Illinois, USA) with a 95% confidence level to examine the effects of variables. Differences between the water sorption and solubility values were compared by one-way ANOVA. Tukey post hoc test was used for further comparisons. Differences between the dimensional changes of test specimens that were reinforced with 5 wt.% fiber content and the control group were compared by 2-way analysis of variance (ANOVA) at 5 different stages. To compare the differences of mean values of test specimens after 5 different stages, one-way ANOVA was applied for groups with vector values of kV1 V2 k, kV1 V3 k, kV1 V4 k, and kV1 V5 k.


326

A. TEZVERGIL ET AL.

RESULTS

The water sorption results of compression-molded and injectionmolded specimens in mg/mm3 were shown in Figure 1. The results indicated that the water sorption decreased with increased fiber content in both groups (Figure 1). But the decrease in injection-molded specimens was more clear compared to compression-molded specimens. The lowest water sorption value of injection acrylic resin was seen in groups 9 and 10. The lowest water sorption value for compression molded was seen in group 10. The solubility decreased with increased fiber content having the lowest value at 5 wt.% fiber matrix fraction for injection-molded specimens (Figure 2). Injection-molded specimens showed lower water sorption and solubility values compared to compression-molded specimens and p 0.05). The SEM micrographs from the fracture surface confirmed relatively good impregnation of the fibers in the injection-molded denture base

Figure 1. Water sorption of denture base polymer made of either injection or compression molded resin reinforced with various length and content of fibers.



327

Figure 2. Solubility of denture base polymers made of either injection or compression molded resin and reinforced with various length and content of fibers.

unreinforced injectionmolded

21.80 21.60 Dimensional change (mm)

21.40

8 mm %5 fiber reinforced compression molded

21.20 21.00 20.80

unreinforced compression molded

20.60 20.40 20.20 20.00 19.80 v1

v2

v3

v4

v5

8 mm %5 fiber reinforced compression molded

Figure 3. The dimensional stability of reinforced and unreinforced test specimens. V1 ¼ initial measurements on brass models, V2 ¼ immediately deflasking of the specimens, V3 ¼ after drying of the specimens, V4 ¼ after 15 days water storage, V5 ¼ after 30 days water storage.

resins. The short fibers seemed to be evenly distributed in the polymer matrix and no voids around the fibers were observed (Figure 4a). But the compression-molded specimens showed grouping of fibers and voids (Figure 4b).


328

A. TEZVERGIL ET AL.

DISCUSSION

This study demonstrated the effect of fiber content and length of fibers on water sorption, solubility and dimensional accuracy of injection and compression-molded denture base polymer reinforced with short E-glass fiber. From clinical perspective, water sorption of fiber-reinforced composites plays an important role in durability of fiber-reinforced dental a)

b)

Figure 4. SEM micrographs from fracture surfaces of: (a) Injection-molded specimens, Original magnification 250, bar ¼ 100 mm; (b) Compression-molded specimens, Original magnification 150, bar ¼ 100 mm.



329

appliances in an aqueous environment such as in the oral cavity [42]. It has been shown that hydrophilic polymer matrix of fiber-reinforced composite looses its strength up to 45% when stored in water due to high water sorption [43]. The uptake of water by resin materials is a diffusion-controlled process. Water molecules diffuse through polymer during the immersion in water or saliva and reach the interface of polymer matrix and reinforcing fiber. Water molecules can diffuse through polymer matrix because of the small size of the water molecule, i.e. the diameter of water molecule is less than 0.28 nm, which is smaller than the polymer chain distance in the polymer matrix [44]. Water is absorbed into polymer by unsaturated bonds of the molecules or unbalanced intermolecular forces in the polymers [1]. Adhesion between polymer matrix and glass fiber can be weakened as a result of leaching of glass forming oxides from the fiber surface and by reversible hydrolytic degradation of polysiloxane network obtained by polycondensation of silane coupling agents [45]. Thus, this may influence the strength of the appliance and long-term stability in the oral environment. One method for measuring water sorption is to determine the increase in weight of the resin per unit of surface area exposed to the water. This method is recommended by the American Dental Association [41], which was used in this study. According to the ADA the increase in weight of the polymer shall not be more than 0.8 mg/cm2 of surface after immersion in water for seven days at (37 1) C. For denture-base polymers, the value of water sorption should be less or equal to 32 mg/mm3. According to earlier studies the water sorption of different types of acrylates was found as 10–25 mg/mm3 [5,46]. The volume percentage of fillers should be taken into account during comparison of water sorption values of previously reported results [45]. Chow et al. [47] suggested that the decrease of water sorption is broadly directed proportional to fiber content of the reinforced polymer, Ladizesky et al. [48] studied the water sorption and dimensional changes of denture base acrylic resin reinforced with woven high molecular weight polyethylene fiber. Increasing the fiber volume up to 30% reduced the water sorption of the resin by about 25%. Braden and Clarke [49] suggested that materials with lower filler content, i.e., higher resin content, had higher water sorption. At the present study relatively high water sorption of compressionmolded specimens compared to injection-molded ones could be attributed to the homogenous distribution of fibers and less void formation in the injection-molded specimens. The SEM micrographs from the fracture surface confirmed relatively good impregnation of the fibers


330

A. TEZVERGIL ET AL.

in the injection-molded denture base resins. It should be noted that the fiber concentration used for reinforcement was low in the present study. Solubility represents the mass of the soluble materials from polymers. The only soluble materials present in denture base resins are initiators, activators, plasticizers and residual monomers [50]. According to the ADA, the loss of weight of the polymer shall not be more than 0.04 mg/cm2 of surface. Many studies suggested that water sorption and solubility of fiber-reinforced composites vary according to the brand ¨ rtengren et al. [53] and homogeneity of the polymer matrix [51,52]. O suggested that the sensitivity of the sorption and solubility behavior to time and pH of the materials tested seems to be related to the hydrophilicity of the matrix and the chemical composition of the filler. The higher water sorption and solubility values for the compressionmolded specimens in the present study can be attributed to the voids seen in the fracture surfaces of the specimens. On the other hand, as the reactivity of oxygen with free radicals is higher than that of radical contained monomers to each other, the polymerization reaction is inhibited by oxygen. This may result in higher residual monomer content in polymer with air voids than with dense polymer structures [36]. The internal oxygen inhibition might be one reason for the high solubility values of the compression-molded specimens. The dimensional accuracy of the test specimens was determined by measuring the distances between measurement points on specimens and the differences between these points on specimens and the differences between these points and the original brass plates. Many factors can influence the dimensional changes of denture base polymers, and these changes have been evaluated by making specimens of various shapes (U-shaped, rhombic, simulating an edentulous maxillary cast). Also, many factors, such as the size and shape, thickness of the denture and the presence of teeth, can contribute dimensional changes during processing. It is convenient and practical to use a rhombic shape rather than dentures or denture shape specimens to examine the dimensional changes of acrylic resin itself. Thus, the results of the dimensional changes could be directly attributed to the acrylic resin, fillers, and filler content as well as the processing method [38]. It should be emphasized that the short fiber reinforced composite used in this study is isotropic. With regard to the dimensional changes this means that main dimensional changes were due to polymerization shrinkage and water sorption. The net effect could be seen as a change between the two measuring points. In principal, the fiber inclusion should diminish the polymerization shrinkage. Previously made investigations have used for example U-shaped specimen with continuous unidirectional fibres [54]. In that case, the dimensional



331

changes and distortion were more complex because of the anisotropy of the material. Therefore the values of the present study could not directly be compared to those of previous studies. The use of excess of monomer liquid to ensure better wetting of fibers with the resin increases the polymerization shrinkage and could cause dimensional changes within the denture [54]. Vallittu [54] suggested that the polymerization shrinkage of MMA caused lower dimensional accuracy of test specimens reinforced with glass fiber. Cheng [55] et al. were concerned with water uptake of polyethylene fiber reinforced denture base polymer and the dimensional changes during water immersion. They showed that a significant reduction in water sorption and in dimensional change occurred when fibers were included to the polymer. On the other hand some studies [56,57] reported less polymerization shrinkage and other studies reported better dimensional accuracy [39,40] with the use of injection-molded denture base resins compared to the compression-molded resins. In the present study no statistically significant difference was obtained between the brass control and experimental groups having fibers manufactured with both the methods. The results of the present study suggested that addition of short E-glass fibers showed more clear decrease in the water sorption and solubility values of injection-molded denture base polymer compared to compression-molded specimens. The addition of fibers or the manufacturing method did not show any difference on the dimensional accuracy of the specimens. CONCLUSIONS

Within the limitations of the study, the following conclusions were made: 1. Randomly oriented short glass fibers decreased water sorption and solubility of the injection-molded denture base polymers. 2. Randomly oriented short glass fiber did not affect dimensional accuracy of the acrylic denture base polymers. REFERENCES 1. Phillips, R.W. (1991). Skinner’s Science of Dental Materials, 9th Edn., pp. 193–195, WB Saunders Co., Philadelphia. 2. Wolfaardt, J., Cleaton-Jones, P. and Fatti, P. (1986). The Influence of Processing Variables on Dimensional Changes of Heat-cured Poly(methyl methacrylate), J. Prosthet. Dent., 55: 518–525.


332

A. TEZVERGIL ET AL.

3. Gilbert, A.S., Pethrik, R.A. and Phillips, R.W. (1977). Acoustic Relaxation and Infrared Spectroscopic Measurements of Plasticization of Poly(methyl methacrylate) by Water, J. Appl. Polymer Sci., 21: 319–330. 4. Barsby, M.J. and Braden, M.J. (1979). A Hydrophilic Denture Base Resin, J. Dent. Res., 6: 1581–1584. 5. Barsby, M.J. (1992). A Denture Base Resin with Low Water Absorption, J. Dent., 20: 240–244. 6. Schreiber, C.K. (1971). Polymethyl Methacrylate Reinforced with Carbon Fibres, Br. Dent. J., 130: 29–30. 7. Schreiber, C.K. (1974). The Clinical Application of Carbon Fibre/Polymer Denture Bases, Br. Dent. J., 137: 21–22. 8. Manley, T.R., Bowman, A.J. and Cook, M. (1979). Denture Bases Reinforced with Carbon Fibres, Br. Dent. J., 146: 25. 9. Larson, R., Dixon, L., Aquilion, A. and Clansy, S. (1991). The Effect of Carbon Graphite Fiber Reinforcement on the Strength of Provisional Crown and Fixed Partial Denture Resins, J. Prosthet. Dent., 66: 816–820. 10. Bowman, J. and Manley, R. (1994). The Elimination of Breakages in Upper Dentures by Reinforcement with Carbon Fibre, Br. Dent. J., 156: 87–89. 11. Viguie, G., Malwuarty, G., Vincent, B. and Bourgerous, D. (1994). Epoxy/ Carbon Composite Resins in Dentistry. Mechanical Properties Related to Fiber Reinforcement, J. Prosthet. Dent., 72: 245–249. 12. Berrong, J.M., Weed, R. and Young, J.M. (1990). Fracture Resistance of Kevlar Reinforced Poly(methyl-methacrylate) Resin: A Preliminary Study, Int. J. Prosthodont., 3: 391–395. 13. Powell, B., Nicholls, I., Youdelis, A. and Strygler, A. (1994). A Comparison of Wire and Kevlar Reinforced Provisional Restorations, Int. J. Prosthodont., 7: 81–89. 14. Amin, A.E. (1997). The Effect of Poly-aramide Fiber Reinforcement on the Transverse Strength of a Provisional Crown and Bridge Resin, Egypt Dent. J., 41: 1299–1304. 15. Vallittu, P.K., Lassila, V.P. and Lappalainen, R. (1994). Acrylic Resin-fiber Composite-Part 1: The Effect of Fiber Concentration on Fracture Resistance, J. Prosthet. Dent., 71: 607–612. 16. Uzun, G., Hersek, N. and Tinçer, T. (1999). Effect of Five Woven Fiber Reinforcement on the Impact and Transverse Strength of a Denture Base Resin, J. Prosthet. Dent., 81: 616–620. 17. Ladizesky, H. and Ward, M. (1983). A Study of the Adhesion of Drawn Polyethylene Fibre/Polymeric Resin Systems, J. Mater. Sci., 18: 533–544. 18. Braden, M., Davy, M., Pakers, S., Ladizesky, H. and Ward, M. (1988). Denture Base Poly(methyl methacrylate) Reinforced with Ultra High Modulus Polyethylene Fibres, Br. Dent. J., 164: 109–113. 19. Andreopoulus, A.G., Papaspyrides, C.D. and Tsilibonvidis, S. (1991). Surface Treated Polyethylene Fibers as Reinforcement for Acrylic Resins Biomaterials, 12: 83–87. 20. Chow, W., Ladizesky, H. and Clarke, A. (1992). Acrylic Resins Reinforced with Woven Highly Drawn Linear Polyethylene Fibres 2. Water Sorption and Clinical Trials, Aust. Dent. J., 37: 433–438.



333

21. Ladizesky, H. and Chow, W. (1992). The Effect of Interface Adhesion, Water Immersion and Anatomical Notches on the Mechanical Properties of Denture Base Resins Reinforced with Continuous Performance Polyethylene Fibres, Aust. Dent. J., 37: 277–289. 22. Gutteridge, L. (1998). The Effect of Including Ultra High Modulus Polyethylene Fibre on the Impact Strength of Acrylic Resin, Br. Dent. J., 164: 177–180. ¨der, P.O. (1979). Fiber Glass Splints, 23. Friskopp, J., Blomlo¨f, L. and So J. Peridontol., 50: 193–196. 24. Solnit, G.S. (1991). The Effect of Methyl Methacrylate Reinforcement with Silane-treated and Untreated Glass Fibers, J. Prosthet. Dent., 66: 310–314. 25. Vallittu, P.K. and Lassila, V.P. (1992). Reinforcement of Acrylic Resin Denture Base Material with Metal or Fibre Strengtheners, J. Oral. Rehabil., 19: 225–230. 26. Vallittu, P.K. (1999). Flexural Properties of Acrylic Resin Polymers Reinforced with Unidirectional and Woven Glass Fibers, J. Prosthet. Dent., 81: 318–326. 27. Marei, M.K. (1999). Reinforcement of Denture Base Resin with Glass Fillers, J. Prosthod., 8: 18–26. 28. Vallittu, P.K. (2000) Effect of 180 Week Water Storage on the Flexural Properties of E-glass and Silica Fiber Acrylic Resin Composite, Int. J. Prosthodont., 13: 334–339. 29. Narva, K.K., Vallittu, P.K., Helenius, H. and Yli-Urpo, A. (2001). Clinical Survey of Acrylic Resin Removable Denture Repairs with Glass-fiber Reinforcement, Int. J. Prosthodont., 14: 219–224. 30. Chen, S.Y., Liang, W.M. and Yen, P.S. (2001). Reinforcement of Acrylic Denture Base Resin by Incorporation of Various Fibers, J. Biomed. Mater. Res., 58: 203–208. 31. Vallittu, P.K. (1998). The Effect of Glass Fibre Reinforcement on the Fracture Resistance of a Provisional Fixed Partial Denture, J. Prosthet. Dent., 79: 125–130. 32. Rosen, M.R. (1978). From Treating Solution to Filler Surface and Beyond, The Life History of a Silane Coupling Agent, J. Composite Technol., 50: 70–82. 33. Vallittu, P.K. (1997). Curing of a Silane Coupling Agent and its Effect on the Transverse Strength of Autopolymerizing Polymethyl Methacrylate-glass Fiber Composite, J. Oral Rehabil., 24: 124–130. 34. Vallittu, P.K. (1998). Compositional and Weave Pattern Analyses of Glass Fibers in Dental Polymer Fiber Composites, J. Prosthod., 7: 170–176. 35. Vallittu, P.K., Ruyter, I.E. and Ekstrand, K. (1998). Effect of Water Storage on the Flexural Properties of E-glass and Silica Fiber Acrylic Resin Composite, Int. J. Prosthodont., 11: 340–350. 36. Vallittu, P.K. (1995). The Effect of Void Space and Polymerization Time on Transverse Strength of Acrylic-glass Fibre Composite, J. Oral Rehabil., 22: 257–261. 37. Vallittu, P.K., Lassila, V.P. and Lappalainen, R. (1994). Transverse Strength and Fatigue of Denture Acrylic-glass Fiber Composite, Dent. Mater., 10: 116–121.


334

A. TEZVERGIL ET AL.

38. C ¸ al. N.E., Hersek, N. and Sahin, E. (2000). Water Sorption and Dimensional Changes of Denture Base Polymer Reinforced with Glass Fibers in Continuous Unidirectional and Woven Form, Int. J. Prosthodont., 13: 487–493. 39. Nogueira, S.S., Ogle, R.E. and Davis, E.L. (1999). Comparison of Accuracy Between Compression- and Injection-molded Complete Dentures, J. Prosthet. Dent., 82(3): 291–300. 40. Huggett, R., Zissis, A., Harrison, A. et al. (1992). Dimensional Accuracy and Stability of Acrylic Resin Denture Bases, J. Prosthet. Dent., 68(4): 634–640. 41. Denture Base Polymers (1999). American National Standard/American Dental Association Specification No. 12, Council on Scientific Affairs, Chicago. 42. Miettinen, V.M. and Vallittu, P.K. (1997). Release of Residual Methyl Methacrylate into Water from Glass Fibre-poly(methylmethacrylate) Composite used in Dentures, Biomaterials, 18: 181–185. 43. Lassila, L.V., Nohrstrom, T. and Vallittu, P.K. (2002). The Influence of Short-term Water Storage on the Flexural Properties of Unidirectional Glass Fiber-reinforced Composites, Biomaterials, 23: 2221–2229. 44. Ohno, H., Endo, K., Araki, Y. and Asakura, S. (1992). Destruction of Metalresin Adhesion due to Water Penetrating Through the Resin, J. Mater. Sci., 27: 5149–5153. 45. Miettinen, V.M., Narva, K.K. and Vallittu, P.K. (1999). Water Sorption, Solubility and Effect of Post-curing of Glass Fibre Reinforced Polymers, Biomaterials, 20: 1187–1194. 46. Arima, T., Murata, H. and Hamata, T. (1996). The Effects of Cross-linking Agents on the Water Sorption and Solubility Characteristics of Denture Base Resin, J. Oral Rehabil., 23: 476–480. 47. Chow, T.W., Cheng, Y.Y. and Ladizesky, N.H. (1993). Polyethylene Fiber Reinforced Poly(methyl methacrylate)—Water Sorption and Dimensional Changes During Immersion, J. Dent., 21: 367–372. 48. Ladizesky, N.H., Chow, T.W. and Cheng, Y.Y. (1994). Denture Base Reinforcement Using Woven Polyethylene Fiber, Int. J. Prosthodont., 7: 307–314. 49. Braden, M. and Clarke, R.L. (1984). Water Absorption Characteristics of Dental Microfine Composite Filling Materials, Biomaterials, 5: 369–372. 50. Knott, N., Randall, D., Bell, G., Satgurunathan, R., Bates, J.F. and Huggett, R. (1988). Are Present Denture Base Materials and Standards Satisfactory?, Br. Dent. J., 165: 198–200. 51. Miettinen, V.M. and Vallittu, P.K. (1997). Water Sorption and Solubility of Glass Fiber-reinforced Denture Polymethyl Methacrylate Resin, J. Prosthet. Dent., 77: 531–534. 52. Gutteridge, D.C. (1992). Reinforcement of Poly(methyl methacrylate) with Ultra High-modulus Polyethylene Fibre, J. Dent., 20: 50–54. 53. Ortengren, U., Anderson, F., Elgh, U., Verselius, B. and Karlsson, S. (2001). Influence of pH and Storage Time on the Sorption and Solubility Behaviour of Three Composite Resin Materials, J. Dent., 29: 35–41. 54. Vallittu, P.K. (1996). Dimensional Accuracy and Stability of Polymethylmethacrylate Reinforced with Metal Wire or with Continuous Glass Fiber, J. Prosthet. Dent., 75: 617–621.



335

55. Cheng, Y.Y., Chow, T.W. and Ladizesky, N.H. (1993). Denture Base Resin Reinforced with High-performance Polyethylene Fiber: Water Sorption and Dimensional Changes During Immersion, J. Macromol. Sci. Phy., B32: 433–481. 56. Anderseon, J., Schulte, J. and Arnold, T. (1988). Dimensional Stability of Injection and Convensional Processing of Denture Base Acrylic Resin, J. Prosthet. Dent., 60: 394–398. 57. Murphy, W.M., Bates, J.F., Huggett, R. and Bright, R. (1982). A Comparative Study of Three Denture Base Materials, Br. Dent. J., 152: 263–273.
