Intisar .doc J Bagh College Dentistry Vol. 27(1), March 2015 The effect of Restorative Dentistry 40 The effect of the addition of silanated poly propylene fiber to polymethylmethacrylate denture base material on some of its mechanical properties Intisar J. Ismaeel, B.D.S., M.Sc., Ph.D. (1) Hasanain K.A. Alalwan, B.D.S., M.Sc. (2)) Mustafa M.J., B.D.S., M.Sc. (2) ABSTRACT Background: Poly propylene fibers with and without silane treatment have been used to reinforce heat cure denture base acrylic but, some mechanical properties like transverse strength, impact strength, tensile strength, hardness, wear resistance and wettability. Which are related to the clinical use of the prosthesis are not evaluated yet. The aim of the study is to identify the influence of incorporation of treated and untreated fibers on these properties Materials and methods: Eighty four heat cure acrylic specimens were constructed by conventional flasking technique. They were divided into six groups according to the tests and each group was subdivided into two subgroups control and experimental groups (seven samples for each subgroup).Transversestrength and Tensile strength test were performed using Instron universal testing machine. The impact strength test was evaluated by the use of Impact testing device. Wear resistance was evaluated by pin on disk wear measurement method while, a digital microscope supplied with high resolution camera was utilized to measure the contact angle reflecting wettability grade. Descriptive statistics and independent t test were used for statistical significance. Results:The results revealed that the addition of Silanated polypropylene fibers produced significant difference in transverse strength and highly significant difference in tensile strength, the impact strength,Wettability value compared with the control group also the results showed that the hardness test was not significant and different control group . Wear resistance was highly significant decreased in experimental groups Conclusion: Incorporation of silanated treated Poly propylene fibers to heat cure Poly methyl methacrylate resin was beneficial regarding the tested properties to improve the mechanical properties of the resin. Key words: Poly propylene fibers, transverse strength, impact strength, tensile strength, hardness, wear resistance, wettability. (J Bagh Coll Dentistry 2015; 27(1):40-47). INTRODUCTION Developments in dentistry have largely been investigated as a result of scientific research. Of particular note, are developments in the field of dental materials and a drive towards the practical dentistry. Many aspects of Prosthodontic treatment; clinical or laboratory based, may impact on overall patient satisfaction and the clinical success of treatment (1). Denture base materials, especially the resin based poly (methymethacrylate) (PMMA) materials are the most widely used non-metallic denture base materials (2). They do, however, have a number of well documented problems. Since its introduction in 1937, poly (methyl methacrylate) (PMMA) has become the most commonly used material for denture bases. It remains most popular of all the polymeric denture base materials. This is largely due to its favourable, although not ideal, characteristics (3). (1)Assistant Professor. Department of Prosthodontics, College of Dentistry, University of Baghdad. (2)Assistant Lecturer. Department of Prosthodontics, College of Dentistry, University of Baghdad. Since PMMA was introduced, most dental material research has been focused upon developing materials with higher strength, lower levels of residual methacrylate monomer after processing, improved dimensional stability, increased radiopacity and improved resistance to candidal infiltration (4). There are three potential avenues for investigation which have been studied in the field of denture base materials. These are: the development of a new alternative to PMMA, the chemical alteration of PMMA; or the reinforcement of PMMA with another material such as fibres of with more favourable fracture resistance properties (5,6) . Acrylic resin dentures are susceptible to fracture during wear or if dropped, Fractures in dentures occur principally due to two different types of forces, flexural fatigue or impact (5). Flexural fatigue results from repeated application of a force. Numerous techniques for reinforcement of PMMA with inclusion of other materials have been described (7,8). Carbon and Kevlar fibre reinforcement techniques have also been investigated. These were found to be not satisfactory aesthetically. However the complicated etching process required to improve their incorporation into PMMA, and preparation J Bagh College Dentistry Vol. 27(1), March 2015 The effect of Restorative Dentistry 41 and positioning of the fibre layers, was found to be both time consuming and technique sensitive (9). Such factors have thereby, reduced the routine applicability of this method. The use of glass fibres to reinforce PMMA is probably the most common technique described in the literature (9-11), not only have these been found to improve the mechanical properties of PMMA, but they are also highly publishable, aesthetic and easy to manipulate (5,11). The addition of treated and untreated silica to PMMA was investigated by McNally et al.2006 Silica is commonly used as a filler to improve strength and wear characteristics of dental materials. The data collected in the study did not support the hypothesis that silica would improve the material’s impact or transverse strength. Therefore, the authors were unable to recommend the inclusion of silica fillers in PMMA materials (12). Notable efforts have been conducted to solve this problem and to strengthen the dental polymer by incorporating various types of fibers (10, 13, 39–43) and fillers (19,24, 44–46), but it has not been solved (13). Interfacial Phase and Coupling Agents For a composite to have effective clinical performance, a good bond must form between the inorganic filler particles and the organic resin matrix during setting. This phenomenon is achieved through the use of coupling agents, such as silane (14). This interfacial bonding is important to transfer load from the polymer matrix to the reinforcing fillers. The most common types of coupling agents are organ of unctionalsilanes and organotitanates, which are used to improve filler dispersion in matrix, prevent aggregation, and reinforce the interfacial coherence with resin (15). Silane-Coupling Agents Silanes are commonly used in dentistry in different applications to provide the opportunity for chemical bonding. The Silane can function as mediators between dispersed and organic phases. The most common silane, 3-methacryloyloxypropyltrimethoxysilane (MPS, or 3-MPS (15) ,which chemically bond the silica, present in silica-based fillers such as porcelain, quartz, pyrogenic silicon dioxide, and silicate glasses because of the similarity in their ordered structure (16), to the organic matrix of resin by means of siloxane bonds and hydrogen bond (17). Most recent investigations give increasing prominence to transverse strength, impact strength, tensile strength and hardness as these properties give an idea about the resistance of the material during use, in order to develop strong denture base material (17). Wear resulted from removal and relocation of materials via the contact of two or more materials which cause the material to be loss. Wear resistance is deemed as one of the characteristics that be developed by composite (18). Denture base material wettability play an effective role in denture retention, complete wetting of denture surface increase the capillary force therefore, raising denture retention in static and dynamic situations (18). In this study the attempt has been done to incorporate silanated polypropylene fibers to reinforce polymethyl methacrylate denture base material and examine the effect of this addition to some mechanical properties, which are: transverse strength, impact strength, tensile strength, hardness, wear resistance and wettability which are related to the clinical use of the prosthesis. MATERIALS AND METHODS Eighty four acrylic specimens were constructed from heat cure acrylic resin by conventional technique for flasking and curing using heat cure acrylic resin. They were divided into six groups according to the tests and each group was subdivided into two subgroups (control and experimental groups, seven samples for each subgroup). The required amount of the powder of the polymer and polypropylene fibers was used by weighting using digital electronic balance 2.5 %( by weight 6mm length) poly propylene fibers (PP fibers) (Cracecemfiber®) as more recent study showed an incorporation of 2.5% percentage had the best effect regarding impact and transverse strengths as that considered to be important in measuring the strength of materials (19). Polypropelene fibers were treated with 3- (methacryloyloxy)propyltrimethoxysilane (MPS) to improve the bonding between pp fibers and PMMA matrix to get PMMA/pp fibers composite with improved properties over pure PMMA . One hundred milliliter of ethanol aqueous solution (70 vol%) was prepared using 99.8 vol% ethanol and deionized water, and adjusted to pH of 4.5 by titrating with 99.9% acetic acid using a pH meter. Then, 5wt%, g of MPS was added respectively into ethanol aqueous solution, and stirred. This MPS solution was stored in a 100 mL polyethylene cup with a cover, and allowed 5 min for hydrolysis and silanol formation. Then, 100 g pp fibers were added into MPS solution. The mixture was stirred with magnetic stirrer for 30 J Bagh College Dentistry Vol. 27(1), March 2015 The effect of Restorative Dentistry 42 minutes, then the mixture was sonicated with probsonication apparatus for 30 minutes, then the solution left dried at room temperature for 14 days (20). The (FTIR) spectrophotometer where done to determine whether or not functional group of the MPS have been attached to pp fibres by analyzing characteristic vibrations of functional groups (21) . When there was change in the vibration or absorption of functional group indicated to be used to complete the study,change which has been occurred indicated by the FTIR spectra as shown in figure 1and 2. After silanization of pp fibers, the selection of the percentage of the fiber has been done. 2.5% were used as percentages of fiber to be added to the PMMA according to previous study (19), mixing of polymer powder and fibers was done by using mortar and Pestle to attained homogenous mixture for about 3.0 minutes, All the specimens for all the six tests were finished and polished. the addition of silanated pp fiber to the PMMA was done only to the experimental groups Fig. 1: FTIR of polypropylene fiber without silanation Fig. 2: FTIR of silanated polypropylene fiber The tests used in this study were: A- Transverse strength test Specimens were prepared with dimensions (65mm x 10mm x 2.5 + 0.1mm). All the specimens were stored in distilled water at 37 0oC for 48 hours before performing the test (22). The test was performed using Instron universal testing machine (WDW-200 E), each specimen was positioned on the bending fixture which consist of two parallel supports (50 mm apart), the full scale was 50 Kilo and the load was applied with across head speed of1mm/min until fracture occurs. B- Impact strength test Specimens have dimension of (80mm x 10mm x 4mm) (ISO 179, 2000) for unnotched specimens. Specimens were stored in distilled water at 370C for 48 hours before being tested (22). The impact strength test was evaluated following the procedure recommended by the ISO 179 with Impact testing device. By supporting the specimen horizontally at each end and struck by free swinging pendulum of 2 Joules. The scale readings give the impact energy in Joules. The charpy impact strength of unnotched specimens was calculated in Kilo joules per square meter by the following equation: Impact strength =E/bd X103 (ISO, 2000) E: The impact energy in Joules b: Is the width of the specimens in millimeters d: Is the depth of the specimens in millimeters C- Tensile strength test Dumbbell shaped specimens were fabricated according to ASTM specification D- 638M(1986).Conditioning of the specimen was done by storing them in distilled water for two days at room temperature25ºC±2before testing according to ADA specifications. The testing procedure was accomplished using Instron universal testing machine (LARYEE, make test easy, china) with crosshead speed 1 mm/min and maximum loading of 20 Kg. Tensile strength calculations was performed are automatically done by the program of the testing machine software. D-Surface hardness test Specimens were prepared with a dimension of (65mm x 10mm x 2.5 + 0.1mm). All specimens were stored in distilled water at 370C for 48 hours before being tested (22). (Shore D) durometer hardness tester Surface hardness were used for measuring the hardness which is suitable for acrylic resin material. It consists of spring – loaded indenter (0.8mm in J Bagh College Dentistry Vol. 27(1), March 2015 The effect of Restorative Dentistry 43 diameter), that attached to digital scale scored from 0 to 100 units. Three readings were done on each specimen (one in the center and other at each end) then the mean of three readings was calculated. E- Wear rate test Special device was used to test the wear that was designed at University of Technology Material, engineering department, resistance laboratory-Iraq. called Pin on disk wear testing device ,it was recognized with high accuracy of results (23,24), The specimens were cylindrical in shape with dimensions of 20mm length and 10mm diameter according to the device requirement(figure 3). It consisted of pin which was the held specimen and disk made from stainless steel wheel which revolve 950 r/min, the specimen was weighed before and after the testing procedure, after that the specimen was secured to the holder and was put 10N load on the horizontal arm, the device switched on for 10 minutes (wear testing time)(25). The distance between the center of the disk and center of the specimen was 65mm. the following equation to was used determine the wear resistance: wear resistance (grm/mm) =change in weight/slide distance (slide distance=2π×radius distance between centers of disk and specimen×number of cycles ×time of test)(25). Cleaning of the disk must be done after each test All specimens were immersed in distilled water for 48 hours before testing.as shown in figure 3. F- Wettability Measurement of the contact angle was necessary to determine the wettability; the angle was between the base of the sessile drop and the tangent line contacting the solid, liquid and air simultaneously. Dispersing of distilled water 10µL at the center of the fabricated sample using pipette. The sample dimensions was 8×30×2mm width, length and thickness respectively (26).Static sessile drop method was utilized in this study. As the water dispersed, wait for 5 minutes to allow the drop to be in status of equilibrium. Measurement of the contact angle was accomplished employing a digital microscope (Dino-lite digital microscope pro -Taiwan) at magnification 45× supplied with camera (high resolution 1024×768 pixel) and software (Dino capture2.0 Version 1.3.3.) granted a complete and precision analysis to the contact angle(27) (Figure 4). Statistical analysis The data collected of the tested specimens were translated to computerized statistical analysis system by using (SPSS) statistical package for social sciences version 20. Descriptive statistics and independent t test where used for statistical significance. RESULTS Characterization of silanized pp fiber The absorption bands of MPS can be assigned to the presence of the functional groups, which are two prominent peaks at 2945cm-1 and 2841cm-1 which can be attributed to the (C-H) stretching, and the characteristic (C=O) stretching occurs at 1720cm-1, and the characteristic for (C=C) stretching occurs at 1637cm-1 for (CHR2R- andCHR3R) occurs at 1413cm-1,and groups of peaks between 1296cm-1 and 1166cm-1can be attributed (C-O-C) stretching, the characteristic (Si-O-CHR3R) stretching occurs between (400 - 470)cm-1figure (1,2) . The descriptive statistics which include Means, Standard deviations, standard error of mean value, of the tests which are conducted to evaluate the effect of silanizedpp fibers addition on some properties of PMMA are shown in table 1. By using independent samples t-test, the results revealed statistically significant difference between flexural strength of fiber reinforced PMMA and the control resin group. Fig. 3: Pin on disk with the specimen Fig. 4: Digital microscope with specimen. J Bagh College Dentistry Vol. 27(1), March 2015 The effect of Restorative Dentistry 44 Table 1: statistical analysis between control and experimental groups for all the tests Tests performed Studied groups Descriptive statistics Comparison N Mean S.D. S.E. t-test df P-value Transverse strength Control 7 86.9187 7.2264 2.7313 2.632 12 .022 Silanated pp fiber 2.5% 7 76.5621 7.4945 2.8327 Impact strength Control 7 12.2601 1.0234 .3868 -6.352 12 .000 Silanatedpp fiber 2.5% 7 23.1549 4.4210 1.6710 Tensile strength Control 7 54.2143 1.5126 .5717 -3.421 12 .005 Silanatedpp fiber 2.5% 7 57.1286 1.6710 .6316 Hardness Control 7 83.0000 .9018 .3409 .499 12 .627 silanated pp fiber 2.5% 7 82.7143 1.2158 .4595 Wear rate Control 7 .000012.000001.000000 3.795 12 .003 silanated pp fiber 2.5% 7 .000010.000001.000000 Wettability Control 7 45.8739 1.6865 .6374 21.015 12 .000 silanated pp fiber 2.5% 7 28.2646 1.4391 .5439 The addition of 2.5% silanized pp fiber lead to decrease in the mean value of transverse strength from (86.9187 MPa)to (76.5621 MPa) and when applying t. test the results revealed a significance difference P= 0.022 as shown in table 1 and the mean in figure 5. The impact strength test results showed a highly significant difference, between the control which has been found (12.2601 Kj/m2) mean value, with the silanated pp fiber group which had (23.1549 Kj/m2) mean value,p 0.000.as seen in table 1.fig 6,7. The tensile test revealed highly significant difference between the control (54.2143 Mpa) and the silanated pp fiber group (57.1286 Mpa), p= .005,as shown in (table 1. and figure 7.) No significant difference was found in the hardness test, decreased wear rate from (.000012 to 0.000010 gm/mm) and decreased wettability after addition of ppfiber 2.5 %, as shown in Table 1 and figure 8. Fig. 5: Bar chart for the mean value of transverse strength of the control and ppf groups reinforced PMMA Fig.6: Graph showing mean impact strength of control and ppfiber- reinforced polymethyl methacrylate J Bagh College Dentistry Vol. 27(1), March 2015 The effect of Restorative Dentistry 45 DISCUSSION The use of fibers to reinforce denture base material has an acceptable success rate mainly because of the advancements in the fiber- reinforcing materials. Reinforcement with fibers enhances the mechanical strength characteristics such as transverse strength, ultimate tensile strength, and impact strength (9). In this study, using a type of olefin fibers named polypropylene (pp) as reinforcing filler to PMMA denture base resin has many properties like high strength, good surface finish and polish, low cost and excellent biocompatibility (28). However, these fibers break- up the homogenous matrix of acrylic resin due to poor interface between fiber and resin affecting the mechanical properties. In order to avoid this, the polypropylene fiber surface energy increased by chemical or plasma treatment (29), surface chemistry and topography may be influenced to result in improved adhesion between the polymer matrix and fibers used. plasma treated polypropylene fiber had been used (19) , which results in improvement in the mechanical properties, but in this study the attempt has been done to use chemical surface treatment for the fibers, by treated with 3-(methacryloyloxy) propyltrimethoxysilane (MPS) to improve bonding between pp and PMMA matrix. The results revealed that the addition of Silanated polypropylene fibers produced significant difference decrease in transverse strength mean value compared with the control group, this may be related to the fact that the random orientation of fibers allows only small portion of the reinforcement to be directed perpendicular to the applied stress. Also this may be due to the internal voids formed in the resin- fiber composite caused by poor wetting of fibers with resin (perhaps the using fibers not undergo changes from silane treatment), these voids were oxygen reserves that allowed oxygen to inhibit radical polymerization of the acrylic resin inside composite, this can lead to higher residual monomer content and affect strength, these results were with no agreement with result of Waffae(19) who found increase in transverse strength after addition of plasma treated pp fiber but was not significant. Highly significant increase in impact strength mean value (23.1549 Kj/m2)compared with control group, this increase which could be related to the presence of silanated pp fibers which prevent the crack propagation and change in direction of cracks resulting in smaller flows between the fibers, These results are in agreement with results obtained by Waffae,2013 and Mowade et al 2012., this increase could be attributed to the fact that silane introduce functional groups on the surface of fibers there by making the surface polar, which improve the surface energy of the fiber and its compatibility with other materials therefore, enhance the impact strength. The results also revealed highly significant difference in tensile test, for the 2.5 wt% silanated pp fibers group, these are unlike the study done by Alalwan (27) who used 2.5 wt% pp fibers plasma treated and found negative effect of plasma treatment to PP on the tensile strength, it could be inferred to the water absorption of PP fibers which was improved by plasma treatment, while silanated pp fiber may show reduced water absorption. Because the functional group which Fig. 7: Graph showing means tensile strength of control and fiber-reinforced PMMA Fig. 8: Graph showing mean wear rate test of control and pp fiber-reinforced polymethyl methacrylate J Bagh College Dentistry Vol. 27(1), March 2015 The effect of Restorative Dentistry 46 cause stretching not include polar group-OH, many, studies reported that incorporation of oxygen plasma treated poly propylene fibers to PMMA had increased the water absorption significantly (19) and PMMA tensile strength is negatively affected by water absorption and ambient moisture, this is in agreement with Ishiyama et al (30), in addition to the acrylic used in this study was of cross linked type that might exaggerate the water absorption (31), in addition to that the orientation of the fibers and the bonding with the matrix of PMMA affect the mechanical properties. Plasma treatment for fibers can lessen the tensile strength of the fibers themselves due to their loss of weight and diameter reduction (32), this is not present with silanation,in contrast , there is addition of layer to the fibers. In this study there was slight decrease in the hardness number which statistically not significant, this decrease could be related to no presence of these fibers near or at the surface of the composite which extremely hard and stiff (33,34) . Highly significant (p=0.003) decrease in the wear rate could be attributed to that high abrasion resistance of PP fiber(35) ;however, after silane treatment it significantly improved in comparison to control group and this may be attributed to formation of functional groups on the pendant methyl group of the isotactic PP fiber leading to increased cross linking that decreased plastic flow which in turn increased the wear resistance and that was consistent with Kyomoto et al2007 and Drobny2013(36,37). Wettability of acrylic reinforced with silanated treated PP fiber was highly significant, regarding the treated PP, it might be pp fibers used are insoluble in water and could reduce the overall volume of the absorbing polymer (38). The second factor could be the silane coupling agent which was used to silanization of pp fibers The silane coupling agent had similar chemical nature to polymer matrix (methacrylate at one side). Thus, the pp fibers-resin interface provided by silane coupling agent could lead to a reduction in the amount of water that reached to the inner layers of the polymer matrix.This is in agreement with several researchers (39,40), that overwhelmed on PMMA-PP fiber composite wettability and occurrence of new functional groups as noticed guiding the change in a surface layer structure. REFERENCES 1. Beth GY, Allen SM, Harrison A. An investigation into the transverse and impact strength of "high strength" denture base acrylic resin. J Oral Rehabil 2002; 29: 263-7. 2. 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(IVSL). الخالصة لكن لحد االن لم یختبر تاثیرھا على لقاعدة الطقم قد استخدمت في تقویة الراتنج االكریلي الحراري بالسیالنحدیثا الیاف البولي بروبیلین مع و بدون معالجة :الخلفیة .طب ومقاومة البلىرقوة الشد وقابلیة الت ئیسة تحوي مجموعتان ریة ومقسمة على ستة مجامیع ولكل مجموعة رارة الحریقة البلمرت بطرمبع وثمانونعینھ استخدمت في البحث بلرا:المواد و االسالیب عن طریق استخدام جھاز اختبار البلى ، تم تقییم مقاومةونرباستخدام شھاز االنستضةرالمستعقوة االختبار الشد واقوة اختباز أجریتعیة سبع عینات لكل منھا رف مع السطح عالیة الدقة لقیاس زاویة االتصال قمیةراریكامواستخدمت لقیاس قوة الصالدة رامیتراستخدم جھاز الدییوقیاس الوقت، ورصبطریقة المسمار على الق . صفة الترطیبلقیاس قابلیة المعالجة البولي بروبیلینلیاف لصالح اضافة اصفة الترطیبقابلیة قوة الصالدةوضةورالمستعقوة االختبار وااظھرت النتائج تباینا واضحا عند فحص قوة الشد:النتائج .صالبة السطح یخص ق فیمارفي ما یخص صفة مقاومة البلى وال یوجد فلاللیاف المعالجة ایجابيبینما بینت تاثیر بالسیالن . وسةالیاف البولي بروبیلین المعالجة اثر ایجابیا بالصفات المدرث یستنتج بأن اضافة مع محدودیة البح:االستنتاج http://journals.cambridge.org/action/displayA http://textilelearner.blogspot.com/2013/01/polyp