J Bagh College Dentistry Vol. 26(1), March 2014 Evaluation the effect Restorative Dentistry 37 Evaluation the effect of nano-fillers (TiO2, AL2O3, SiO2) addition on glass transition temperature, E-Moudulus and coefficient of thermal expansion of acrylic denture base material Ihab N. Safi, B.D.S., M.Sc. (1) ABSTRACT Background: The PMMA polymer denture base materials are low in thermal and strength properties. The aim of the study was to investigate the change in glass transition temperature, E-Moudulus and coefficient of thermal expansion of acrylic denture base material by addition of Al2O3, TiO2 and SiO2nano-fillers in 5% by weight. Materials and methods: The type of polymerization is free radical bulk polymerization. one hundred twenty (120) specimens were prepared , the specimens were divided into four groups according to the material had been added (one control and three for Al2O3, TiO2 and SiO2nanocomposite) each group was subdivided in to three groups according to the test had been done on it, the degree of transition (Tg) was measured by The differential scanning calorimeter (DSC), E-Modulus and coefficient of thermal expansion and contraction was measured by Thermo Mechanical Analyzer (TMA) .Each sample was tested at different temperatures (30,40,50,60,70C°). Results: Highly significant decrease in coefficient thermal expansion and contraction and in E-Modulus occurred in acrylic incorporated with Al2O3, TiO2 and SiO2 nano-fillers in 5% by weight when compared to control group. For glass transition temperature a significant increase had occurred with the addition of nanofillers at 5% when compared to control group. Conclusion: The results showed that the polymer nanocomposites possess material properties different from that of unmodified PMMA, nanocomposite has thermal and mechanical stability more than heat neat PMMA. Keyword: Acrylic denture base, nano fillers, thermal properties. (J Bagh Coll Dentistry 2014; 26(1):37-41). الخالصة -Eمنخفضة في الخصائص الحرارية والقوة .. وكان الهدف من الدراسة للتحقيق التغيير في درجة حرارة التحول الزجاجي ، PMMAخلفية : البوليمر بدلة المواد األساسية ال Moudulus و معامل التمدد الحراري لل مادة االكريليك قاعدة أسنان بإضافةAL2O3 ،TIO2 وSIO2 من وزنها . ٪ 5الحشو في نانو ( العينات ، تم تقسيم العينات إلى أربع مجموعات وفقا للمادة ) عنصر تحكم 021المواد و األساليب: نوع البلمرة مجانية البلمرة الراديكالية األكبر . قد أضيفت أعدت مائة وعشرين ) سيم كل مجموعة إلى ثالث مجموعات وفقا الختبار زيارتها تم القيام به على ذلك، تم قياس درجة التحول بمركب متناهي في الصغر ( تم تق SIO2و AL2O3 ،TIO2واحد وثالثة ل ( . تم اختبار كل عينة في TMAمعامل و معامل التمدد الحراري واالنكماش و تقاس الحرارية محلل الميكانيكية ) -E، ( DSC) تيراغرام ( بواسطة المسعر المسح التفاضلي ) ° ( . C 01،01،51،01،01ت حرارة مختلفة ) درجا من الوزن مقارنة ٪ 5نانو الحشو في SIO2و AL2O3 ،TIO2معامل وقعت في االكريليك تدمج مع -Eالنتائج : انخفاض كبير للغاية في معامل التمدد الحراري واالنكماش و مقارنة بالمجموعة الضابطة . ٪ 5ثت مع إضافة المالئة النانومترية في بالمجموعة الضابطة . ل درجة حرارة التحول الزجاجي زيادة كبيرة حد معدلة ، بمركب متناهي في الصغر لديه االستقرار الحراري و PMMAو البوليمر تمتلك خصائص مواد مختلفة عن تلك التي nanocompositesاالستنتاج : أظهرت النتائج أن أنيق. PMMAالميكانيكي أكثر من الحرارة لكلمة الرئيسية: أكريليك قاعدة أسنان ، والحشو نانو، الخواص الحرارية .ا INTRODUCTION Polymer nanocomposite gained attention of researches because of their novel properties that are derived from the two components (1).The addition of very small amount less than 5%fillers to apolymeric matrix has significant impact on the thermal and mechanical properties of the polymer (2).The PMMA polymer denture base materials are low in thermal and strength properties (3,4). when The temperature increases polymers show a large variation of mechanical and physical properties .The acrylic resin is hard and glass like at room temperature and with increase in the temperature to a critical temperature a transition occur to flexible and soft material, this transition occurs over a critical temperature termed glass transition temperature (Tg)(5). At (Tg) temperature a sharp increase in the thermal expansion coefficient occurs, indicating increased molecular mobility (6). (1) Assistant Lecturer. Department of Prosthodontics, College of Dentistry, University of Baghdad. The dimensional stability of acrylic denture base resin was related to this temperature, as the polymers goes from a hard state to a soft state. The coefficient of thermal expansion of the polymer changes, this change corresponds to Tg (7) .The denture should be above the Tg while it is in service during finishing and polishing by dentist and technician and during cleaning in hot water by the patient. Now attention is directed toward addition of inorganic nanoparticles to PMMA to improve its thermal stability and thermal mechanical behavior (8-10). The nanofillers particles are expected to disperse more homogeneously than large microfillers within a polymer host, this interaction between nanofiller and polymer lead to the properties of the composite materials. Nanocomposites display glass transition temperature and thermal degradation that are higher 15 °C and 60 °C than PMMA respectively (11). Nanocomposites had higher storage modulus and higher glass transition temperature (Tg) than J Bagh College Dentistry Vol. 26(1), March 2014 Evaluation the effect Restorative Dentistry 38 pure PMMA which were measured by dynamic mechanical properties (12). There is improvement in glass transitiontemperature and in heat resistance of nanocomposite reached to 16 °C and 14 °C respectively (13). Young modulus decreased by 20% after addition of nanofillers to PMMA nanocomposite. The best result in physical and mechanical properties was observed in denture base reinforced with 5wt% of nano-ZrO2 (14). In this study three types of inorganic nanofillers were used that were added to heat cure PMMA at 5wt% and evaluate the effect ofthis addition on physical (Tg, coefficient of thermal expansion and contraction) and mechanical property (E-Modulus) of heat cured acrylic denture base material. MATERIALS AND METHODS Table 1: List of the materials that were used Material TiO2nanofiller Al2O3nano filler SiO2 nanofiller Heat-curing resin for denture Manufacturer Sigma-Aldrich Germ. Sigma-Aldrich Germany. Sigma-Aldrich Germ. Superacr-yl plus Czechoslovakia Test specimens preparation Two different metal patterns were constructed according to the required test. The pattern that was constructed for coefficient of thermal expansion and contraction test and E-Modulus test was a cylindrical shaped specimen (15mm x 6mm) length, diameter respectively (5) .For glass transition temperature test: a bar shaped specimen was constructed (65mm X 10mm X 2.5mm) length, width, thickness respectively (15-17). Mould preparation Addition of fillers An electronic balance was used with accuracy of (0.0001g) (Sartorius BP 30155, Germany) for addition of nanofillers powder at weight 5% to monomer. After the addition of nano filler to monomer, the powder of fillersseparated into individual nano crystals which were dispersed in the monomer byusing sonication apparatus (Soniprep-150, England) at 120 W, 60 KHz for 3 minutes (14).To reduce the possibility of particle aggregation Proportioning and mixing of the acrylic The suspension of the monomer with nano filler was immediately mixed with acrylic powder. All materials were mixed and manipulated according to manufacture’s instructions for acrylic resin at ratio of (2.5g:1g) P/L .The mixing was carried outby a clean wax knife in a clean and dry mixing vessel and mixed for 30 second. The mixture was then covered and left to stand until a dough stage was reached.Using a conventional denture flasking technique. Thermal analysis and mechanical tests 1-Measuring of Tg . a-Specimen form: The specimen should be in powder form 10 mg powder is prepared so the acrylic specimens were shaved with a sharp knife (figure 1) . Figure 1: Prepared powder form b-The procedure: The differential scanning calorimeter (DSC-60 from Shimadzu, Japan) (figure 2) is an instrument that is used to determine the thermal transition (Tg). The DSC device is connected to a control and program unit that show the data ,Tg value is determined by computer .The acrylic powder of the specimen was put in an aluminum pan of DSC device, with an empty aluminum pan as a reference, Tg value was determined on DSC thermogram. Before starting measurement the heating rate used was (10 C/min) and chart speed of (20mm/min) was selected for all the heating operations. Using a predefined temperature range from 20 C to 190 C in dynamic air atmosphere (flow rate 25 cm3/min). Figure 2: DSC device 2-Measuring of the coefficient of the thermal expansion and contraction ( ) . a-specimen form :The acrylic specimen should be in cylindrical form of dimension 15mm in length and 6 mm diameter to coincide the probe of J Bagh College Dentistry Vol. 26(1), March 2014 Evaluation the effect Restorative Dentistry 39 thermo-mechanical analyzer(TMA) which is 5 -6 mm in diameter (figure 3). Figure 3: Cylindrical form. b-The procedure: Thermo Mechanical Analyzer (TMA, PT1000 from Linseis, UN) (figure4) is an instrument that is used to determine thecoefficient of thermal expansion and contraction ( ).The probe of TMA device has 5-6 mm in diameter which rests on cylindrical specimen of 6mm in diameter and 15 mm in length .TMA device was connected with programs units that show the data on computer . Before measurement a heating rate of 10 C/min was selected (15). Figure 4: TMA device Coefficient of thermal expansion and contraction ( ) was determined by measuring the change in length (L) per unit length for each C temperature change (t)or measuring the change in volume by increase the temperature at constant pressure per unit volume. In this study the following equation was used: ( )= 3- Measuring of Modulus of Elasticity (E- Modulus). a- Specimen form: The acrylic specimen should be in cylindrical form of dimension 15mm in length and 6 mm diameter. b-The procedure: The same method as in TMA was used,a heating rate of 10 C/min and load of 50 gm was selected (15). E-Modulus was determined by computer by measuring the ratio of elastic stress to elastic strain. E=stress/strain RESULTS Mean values, standard deviation, standard error, t-test and p-value forglass transiaion temperatureare presented in Table (2). Table 2: Descriptive of glass transition temperature Control TiO2 SiO2 AL2O3 ANOVA Mean 85.6 118.6 102.4 113.2 F- test=60.852 P<0.01 HS SD 6.693 2.607 3.361 2.588 t-test - 8.578 4.221 7.819 P-value - 0.001 0.013 0.001 Sig - HS S HS Coefficient of thermal expansion and contraction tests result are presented in Table (3,4,5,6,7),one way ANOVA test betweengroups at different temperatures (30,40,50,60,70C°) is presented in Table(8) . Table 3: Descriptive data of coefficient of thermal expansion and contraction at 30 C° Temp. 30 C° Control TiO2 SiO2 AL2O3 Mean 72 57 68 63 SD 1.58113 1.5811 1.58113 1.58113 t-test - 17.928 4.781 10.757 P-value - P<0.01 P<0.01 P<0.01 Sig - HS HS HS Table 4: Descriptive data of coefficient of thermal at 40 C°. Temp. 40 C° Control TiO2 SiO2 AL2O3 Mean 85 75 81 77 SD 1.5811 1.5811 1.5811 1.5811 t-test - 7.906 2.902 9.562 P-value - 0.001 0.044 0.001 Sig - HS S HS Table 5: Descriptive data of coefficient of thermal at 50 C° Temp. 50 C° Control TiO2 SiO2 AL2O3 Mean 93 86 90 86 SD 1.58113 2.2360 2.549 2.549 t-test - 7.376 5.447 12.780 P-value - 0.002 0.005 P<0.01 Sig - HS HS HS J Bagh College Dentistry Vol. 26(1), March 2014 Evaluation the effect Restorative Dentistry 40 Table 6: Descriptive data of coefficient of thermal expansion and contraction at 60 C° Temp. 60 C° Control TiO2 SiO2 AL2O3 Mean 100 95 96 93 SD 1.58113 1.5811 1.58113 1.5811 t-test - 9.129 2.981 5.916 P-value - 0.001 0.041 0.004 Sig - HS S HS Table 7: Descriptive data of coefficient of thermal expansion and contraction at 70 C° Temp. 70 C° Control TiO2 SiO2 AL2O3 Mean 105 100 97 98 SD 2.5495 2.5495 3.3911 3.1622 t-test - 0.00 7.628 2.746 P-value - 1.000 0.002 0.049 Sig - NS HS S Table 8: ANOVA of coefficient of thermal expansion and contraction ANOVA Control TiO2 SiO2 AL2O3 F-test 265.8 388.56 143.43 200.31 P-value P<0.01 P<0.01 P<0.01 P<0.01 Sig HS HS HS HS Mean values, standard deviation, standard error, t-test and p-value for E-Modulus tests result are presented in Table (9,10,11,12,13), one way ANOVA test between groups at different temperatures (30,40,50,60,70C°) is presented in Table (13) . Table 9: Descriptive data of E-Modulus (N/mm2) at 30 C° Temp. 30 C° Control TiO2 SiO2 AL2O3 Mean 2119 451 1233 1738 SD 17.117 4.1231 26.580 24.738 t-test - 286.06 63.627 105.657 P-value - P<0.01 P<0.01 P<0.01 Sig - HS HS HS Table 10: Descriptive data of E-Modulus (N/mm2) at 40 C° Temp. 40 C° Control TiO2 SiO2 AL2O3 Mean 2522 531.2 1405 2305.4 SD 11.510 22.653 21.908 25.880 t-test - 215.502 112.54 14.554 P-value - P<0.01 P<0.01 P<0.01 Sig - HS HS HS Table 11: Descriptive data of E-Modulus (N/mm2) at 50 C° Temp. 50 C° Control TiO2 SiO2 AL2O3 Mean 2748.8 602.8 1772.6 2684.2 SD 74.30141 23.40299 25.48137 27.09613 t-test - 48.786 42.05 2.932 P-value - P<0.01 P<0.01 0.043 Sig - HS HS S Table 12: Descriptive data of E-Modulus (N/mm2) at 60 C° Temp. 60 C° Control TiO2 SiO2 AL2O3 Mean 2785 682.2 2068.4 2023.4 SD 24.217 25.655 27.790 49.952 t-test - 131.26 82.167 36.05 P-value - P<0.01 P<0.01 P<0.01 Sig - HS HS HS Table 13: Descriptive data of E-Modulus (N/mm2) at 70 C° Temp. 70 C° Control TiO2 SiO2 AL2O3 Mean 2824 772.6 2217 2201.8 SD 97.203 14.518 78.185 129.438 t-test - 41.27 13.001 6.146 P-value - P<0.01 P<0.01 0.004 Sig - HS HS HS Table 14: ANOVA of E-Moudulus (N/mm2) ANOVA Control TiO2 SiO2 AL2O3 F-test 134.52 202.8 505.7 143.9 P-value P<0.01 P<0.01 P<0.01 P<0.01 Sig HS HS HS HS Figure: 5 DSC curve DISCUSSION The present study was conducted to evaluate and compare the effect of addition (Al2O3, TiO2 and SiO2nano-fillers) to PMMA on thermal and mechanical properties of acrylic denture base. These types of nanofillers were used because of their thermal properties and also because of being white are less likely to alter esthetic. The thermal stability of the samples was examined by TMA J Bagh College Dentistry Vol. 26(1), March 2014 Evaluation the effect Restorative Dentistry 41 and DSC (16). Thermal properties and E-modulus are tested over a physiologic temperature range (30-70C°). The introduction of nanofillers into PMMA caused decrease in the value of coefficient of expansion and contraction, statistically highly significant decrease in low temperature at 30 and became significant decrease at high temperatures (60,70C°). The decrease in the thermal expansion coefficient was due to the greater interfacial interaction between nanofillers and matrix which limited the molecular mobility of polymer (12,13). Homogenous distribution of very fine size and high surface area of nanofiller enable them to restrict the motion of macromolecule chains and enhance thermal properties (6,18), that means the PMMA nanocomposite has thermal stability more than neat PMMA ,in addition to decrease in volume of PMMA with present of nanofillerat 5%. In this study Tg measured from the temperature of the peak maxima of DSC curves obtained for the pure PMMA and PMMA nanocomposite. The value of glass transition temperature increased for Al2O3 and SiO2nanocomposite at 5wt%, the DSC peak shifted toward higher temperature when compared to control group, it was found that the addition of TiO2 nanofillers to PMMA caused highly increased in Tg , it is shows in figure (5),this may be due to the melting temperature of nanofillers are higher, the magnitude of the shift being dependant onthe type and amount of nanofillers. The addition of nanofillers at 5% to PMMA led to decrease E-Modulus beyond that of pure PMMA, these changes are due to excessive interactions between PMMA and the large surface area of nanofillers REFERENCES 1. Jorge JH, Giampolo ET, Machado Al, Vergani CE. Cytotoxicity of denture base acrylic resin. Literature review. J Prosthet Dent 2003; 90(2): 190-230. 2. Costache MC, Wang D, Heidecker MJ, Wilkie CA.The thermal degradation of poly methyl methacrylate nanocomposite with montmorillonite, layered double hydroxides and carbon nanotubes. Polym Adv Technol 2006; 17: 272-80. 3. Craig RG. Restorative dental materials.11th ed. St. Louis: Mosby Co.; 2002. 4. Koroglu A, Ozdemir T, Sanmaz A.Comparative study of the mechanical properties of fiber reinforced denture base resin. J App Polym Sci 2009; 113(2): 716-20. 5. Jerolimor V, Jagger RG, Millward PL, CarekV. Effect of heating rate on glass transition of cross-linked denture base resin. Acta Stomatol Croat 1996; 30(4): 249-54. 6. Anusavice KJ. Phillips science of dental materials .11th. St. Louis: 2008. 7. Craig RG, Powers JM, Wataha JC. Dental material properties and manipulation. 8th ed. St. Louis: Mosby Co.; 2004. 8. Arrighi V, Kraft A, Khlifa MA. Thermal and dynamic mechanical properties of solution dispertion nanopartical filler-PMMA composites ACC national meeting, United States, 2010. 9. Ahmed ZA, Alhareb AO. Effect of AL2O3/ZrO2 reinforcement on the mechanical properties of PMMA denture base. J Reinforced Plastics and Composite. 2011; 30(1): 86-93. 10. Escobar CA, Zaragoza EA, Lucero A.Thermal and mechanical Analysis of silver/carbon nanopartical– PMMA obtained by mini-emulsion polymerization. Polym J 2009; 41(10): 816-21. 11. Zhang Weian, Shen X, Li Yu, Fang Y. Synthesis and characterization of poly methyl methacrylate OMMT nanocomposite by gamma-irradiation polymerization. Radiation physics and Chemistry 2003; 67: 651-6. 12. Yan D, Ling Xu, Chen C, Tang J, Xu Ji. Enhanced mechanical and thermal properties of rigid polyurethane foam composites containing graphenenanosheets and carbon nanotubes, 2012. 13. Benjamin JM, Jason S, Diana FR, Linda SS. Investigation into thermal and mechanical behavior of PMMA/Alumina nanocomposites .Materials Research Society, proceedings library. 661,http:/dxdoi org/2000.10-557. 14. Safi IN. Evalution the effect of modified nanofillers addition on some properties of heat cured acrylic resin denture base material. M.Sc. thesis. College of Dentistry /University of Baghdad, 2011. 15. Al-Taie GA. The effect of different curing methods and water absorption on glass transition temperature and coefficient of thermal expansion and contraction of acrylic denture base material. MSc. thesis. College of Dentistry /University of Baghdad, 2002. 16. Morsy MA, Aldaous MA. Mechanical properties evaluation of new AuNP-PMMA composite. International review of chemical engineering. 5:1. special section on 4 th CEAM. 2012. 17. McCabe JF, Wilson HJ. The used of differential scanning calorimetry for evaluation of dental materials. J Oral Rehabil 1980; 1(7): 235-43. 18. Katsikis N, Franz Z, Anne H, Vital A.Thermal stability of PMMA/Silica nano and microcomposite as investigated by dynamic –mechanical experiments. Polymer Degradation and Stability 2007; 92:1966-76.