COMPARISION OF IMPACT STRENGTH IN THREE DIFFERENT TYPES OF DENTURE BASE RESINS AN IN-VITRO STUDY

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1 Original Article COMPARISION OF IMPACT STRENGTH IN THREE DIFFERENT TYPES OF DENTURE BASE RESINS AN IN-VITRO STUDY ABSTRACT 1 R ARUN JAIKUMAR, MDS 2 N MADHULIKA, MDS 3 R PRADEEP KUMAR, MDS 4 K VIJAYALAKSHMI, MDS The aim of this study was to evaluate whether the impact strength of a commercially available, heat polymerized acrylic denture base material could be improved using reinforcements. A total of 30 specimens (65 mm x 10 mm x 3 mm) were fabricated, the specimens were divided into 3 groups with 10 specimens each. They were Group 1 conventional denture base resins, Group 2 high impact denture base resins and group 3 glass reinforced denture base resins. The impact strength of specimens was measured using charpy s test. One-way analysis of variance (ANOVA) was used to determine statistical differences among the impact strength of three groups. Data were analyzed by SPSS software and the results were obtained. The flexural strength values showed statistically significant differences among experimental groups (P<0.005). Within the limitations of the study PMMA reinforced with glass fibers showed the highest impact strength values, and this was followed by PMMA reinforced with butadiene styrene and the least strength was observed in the conventional denture base resins. Key Words: Comparison of impact strength, denture base resins. INTRODUCTION 1 Senior lecturer Prosthodontics, Rajah Mutiah Dental College 2 Pg student, Dept of oral medicine & radiology, Indira Gandhi Institute of Dental science 3 Pg student, Department of oral & maxillofacial surgery, Rajah Mutiah Dental college 4 Professor & Head of the Department of Orthodontics, Adhiparasakthi Dental college For Correspondence: Dr. R. Arun jaikumar M.D.S Senior Lecturer, Rajah Mutiah Dental College, Annamalai University, Chidambaram , jaikumar.arun@gmail.com Received for Publication: March 13, 2014 Accepted: May 28, 2014 Poly methyl methacrylate (PMMA) was first introduced in 1937 by Walter Wright and is currently the material of choice for fabrication of removable partial denture and complete denture. 1 PMMA is continued to be used, because of its favorable working characteristics, processing ease, accurate fit, stability in the oral environment and superior esthetics. Despite these excellent properties, there is a need for improvement especially in-terms of strength properties. 2 The denture base resin is subjected to various stresses during function, these includes, compressive, tensile, shear and impact stresses. A frequent problem that occurs with removable dentures is fracture, which may be due to accidental dropping, repeated masticatory forces, and areas of stress concentrations around frenal notches. 3 For this reason, the impact strength (IS) of polymers used for the production of denture bases has been investigated 4,5,6,7, with focus on the incorporation of different types of reinforcements. 3,8 So the aim of this study was to evaluate whether the impact strength of a commercially available, heat polymerized acrylic denture base material could be improved using reinforcements. METHODOLOGY In this study, 60 acrylic specimens were prepared. Based on the type of acrylic resin used, the specimens were divided into 3 groups with 20 specimens each. They were Group 1 conventional denture base resins, Group 2 high impact denture base resins and group 3 glass reinforced denture base resins. Each group 373

2 was further subdivided into two subgroups with 10 specimen in each and was subjected to either flexural or impact strength evaluation. MAKING OF ACRYLIC SPECIMEN To make the mould space for the specimens, three stainless steel cuboidal dies were milled measuring 65.5 mm x 10.5 mm x 3.5 mm in length, breadth and thickness respectively. Sixty acrylic specimens were fabricated using these three stainless steel dies. The metal dies were flasked using type II dental plaster to complete the flasking procedure. The plaster was allowed to set for an hour and parts of the flask were separated. The stainless steel dies were retrieved to create the mould space for the acrylic specimen. The separating medium (cold mould seal) was applied to the mould space created and is allowed to set for 20 minutes. Three different PMMA were evaluated, namely Group 1 conventional denture base resins (DPI heat cure resins) Group 2 high impact denture base resins (Trevalon Hi) Group 3 glass reinforced denture base resins (Acrylic composite). The polymer and monomer were proportioned as suggested by the manufacturer in a ratio of 3;1 by volume. All the manipulation was done at the same room temperature. The acrylic resin was packed into the mould, after trial closure the flasks were tightened to their final position. The specimens were subjected to curing cycle starting from room temperature to reach 74 degree centigrade in 30 minutes and held at this temperature for approximately 2 hours and then terminal boiling point was done at 100 degree centigrade for 1 hour. After bench cooling, the acrylic specimens were retrieved, trimmed, finished and polished to the required dimension measuring 65 mm x 10 mm x 3 mm in length, breadth and thickness respectively. (According to ISO standardization 1567). The polished specimens were measured using a digital vernier caliper. The exclusion criteria for the samples were specimens with smaller dimensions, internal porosity, external porosity, worn out edges and surface defects. All the sixty specimens were immersed in distilled water for 28 days at room temperature to simulate the oral conditions. EVALUATION OF THE IMPACT STRENGTH The impact strength of specimens was measured using charpy s test. The specimens were prepared by marking three lines D, E and F. The first line D was drawn at a distance of 10 mm from the border of the specimens. The second line E was marked at 45 mm away from line D these two lines D and E correspond the location of supporting arm in the testing machine. A midline between these lines D and E was marked as line F. At the midpoint F, a V shaped notch along the side of the specimen, and on the other side of the specimen, the pendulum of the testing machine would come and contact the specimen. As the pendulum plunges into the specimen, the specimen would fracture and this maximum load before fracture (F) is displayed in the machine. This value is the impact strength of the given specimens in joules. The mean value of the flexural strength and impact strength of all the groups were computed and then statistically analyzed using One way analysis of variance of ANOVA, using SPSS software. RESULTS One way analysis of variance (ANOVA) was used to determine statistical differences among the flexural and impact strength of three groups. Data were analyzed by SPSS software and the results were obtained (Table 1, 2 & 3). The mean impact strength of conventional Conventional PMMA (group 1) was 2 J, for High impact PMMA (group 2) it was 2.6 J and for E Glass reinforced PMMA (group 3) it was 3.1 J. All reinforced specimens showed higher impact strength than the conventional unreinforced acrylic resin. Specimens reinforced with glass fibers showed the highest impact strength values, followed by a specimen reinforced with butadiene styrene and followed by conventional unreinforced acrylic resin. The results of statistical analysis for impact strength were shown in the bar diagram below (statistics Fig 1). The mean transverse strengths of all test groups have statistically significant differences (P<0.005). The analysis of data revealed significant difference between group I and group II, and III. (P<0.005). Scheffe S Post Hoc test was done to substantiate this (Table 4). 374

3 TABLE 1: RESULTS OF IMPACT STRENGTH BETWEEN THREE DENTURE BASE RESINS MEASURED IN TERMS OF MEGAPASCALS S. No. Conventional PMMA (in joules) High impact MMA (in joules) E-Glass Reinforced PMMA (in joules) 1 2 J 3 J 3 J 2 2 J 3 J 3 J 3 2 J 2 J 3 J 4 2 J 3 J 3 J 5 2 J 3 J 3 J 6 2 J 3 J 4 J 7 2 J 2 J 3 J 8 2 J 2 J 3 J 9 2 J 3 J 3 J 10 2 J 2 J 3 J Mean 2 J 2.6 J 3.1 J Impact Strength TABLE 2: DESCRIPTIVE ANALYSIS OF DATA ON IMPACT STRENGTH Conventional PMMA High Impact PMMA E-Glass Reinforced PMMA DISCUSSION TABLE 3: ANALYSIS OF VARIANCE ON IMPACT STRENGTH Sum of Squares df Mean Square F Sig. Between Groups Within Groups TABLE 4: SCHEFFÉ S POST HOC TEST ON IMPACT STRENGTH Conventional PMMA High Impact PMMA E-Glass Reinforced PMMA Mean Difference * * * Significant at 0.05 level of confidence The confidence interval value required for significance is The prime and most frequent site of fracture in the upper denture is in the medial line. During chewing, denture base material is subjected to flexural deformation. Flexural strength is a measure to know the resistance of the polymer to flexural deformation. The other reason for fracture is dropping the dentures. The patients wearing complete denture are usually old aged people, with poor neuro-muscular coordination and are more prone for accidental dropping of dentures. 9 Impact strength is a measure of capacity of the material to absorb energy when it suffers sudden impact. Therefore in this study, impact strength was evaluated for the above three denture base resins. The Charpy s type test selected * for the present study has been used by investigators to evaluate the impact strength of denture base acrylic resins. 10,11,12,13 Over the years, there have been various modifications attempted to improve the mechanical properties of poly methyl methacrylate (PMMA). The modifications include, chemical modification of PMMA, through the incorporation of butadiene styrene to produce graft copolymer (HIGH IMPACT DENTURE BASE RESINS) and mechanical reinforcement through the inclusion of various fibers (FIBER REINFORCED DENTUREBASE RESINS). 14,15,16 Therefore all the three denture base resins (conventional resins, high impact and glass reinforced) were included in this study. Artificial aging, such as, underwater storage in thermally controlled condition was simulated in this study. Dif- 375

Fig 1: Milled stainless steel die Fig 2: Three Stainless Steel Die were placed in a Single Flask Fig 3: Ten acrylic specimens taken from each group for testing flexural strength Fig 4: Acrylic

periods of underwater storage, but the important influence of water on the flexural strength occurs during the first four weeks of immersion causing decrease of the flexural strength values.

Regarding the fiber reinforcement in denture base resins, it has long been hypothesized that the addition of synthetic fibers to the monomer-polymer mixture may strengthen the resultant acrylic resin.

17,18 The result of present study showed that silianized (E)-glass fibers could considerably enhance the impact strength of dental polymers, which could be due to proper impregnation of fibers with

The other factors that are related to the strength of the fiber composite are the type of fibers, percentage of fibers in polymer matrix, the orientation of the fibers, fiber form (chopped,

4 Fig 1: Milled stainless steel die Fig 2: Three Stainless Steel Die were placed in a Single Flask Fig 3: Ten acrylic specimens taken from each group for testing flexural strength Fig 4: Acrylic Specimens Placed In Position For Testing Impact Strength Statistics Fig 1: Graphical representation of impact strength for the three types of Denture Base Resins ferent authors use different time periods of underwater storage, but the important influence of water on the flexural strength occurs during the first four weeks of immersion causing decrease of the flexural strength values. Hence a 28 days immersion in distilled water at 37 degree C was used in this study. Regarding the fiber reinforcement in denture base resins, it has long been hypothesized that the addition of synthetic fibers to the monomer-polymer mixture may strengthen the resultant acrylic resin. Different authors used various types of fibers such as carbon, aramid, glass, polyethylene fibers. 17,18 The result of present study showed that silianized (E)-glass fibers could considerably enhance the impact strength of dental polymers, which could be due to proper impregnation of fibers with resin polymer. The other factors that are related to the strength of the fiber composite are the type of fibers, percentage of fibers in polymer matrix, the orientation of the fibers, fiber form (chopped, continuous, unidirectional, bidirectional) and the adhesion of the fibers to polymer. 18,19,20,21 The use of carbon and aramid fibers produced important clinical problem, namely poor esthetics and difficulties in polishing. Polyethylene (HDLPE) fibers appear to be a promising choice. It is biocompatible and possesses high stiffness and strength. Other advantages include its white translucent appearance, negligible water sorption and excellent polishing characteristics. Glass fiber reinforcement has been the most clinically successful; glass fibers are also esthetically suitable and are reported to have improved flexural strength, flexural modulus, fatigue strength and impact strength of resin. Therefore out of all the fibers, self reinforced glass fibers were selected for this study. In the present study, the flexural strength of unreinforced and reinforced acrylic resin specimens were tested according to ISO /DIS All reinforced specimens showed higher flexural strength than the conventional unreinforced acrylic resin. Specimens reinforced with glass fibers showed the highest flexural strength values, followed by specimens reinforced with butadiene styrene and followed by conventional unreinforced acrylic resin. The reason behind this would be the presence of glass fibers, which may prevent the propagation of crack, when the stresses are applied. Hence, glass fibers are strongly recommended in patients with heavy occlusal load or when fracture strength of denture base resin is of great concern. This finding is in agreement with results of previous studies. For better understanding the fracture and deformation mechanisms future researches about the effects of the residual monomer content and the viscoelastic properties on the fracture process and microstructure of acrylic resins could be performed. 376

5 CONCLUSION Within the limitation of the current study, the following conclusions were drawn The impact strength values of heat polymerized PMMA were considerably enhanced by reinforcements. PMMA reinforced with glass fibers showed the highest impact strength values this was followed by PMMA reinforced with butadiene styrene and the least strength was observed in the conventional denture base resins. REFERENCES 1 Eick JD. Biological properties of denture base resins. Dent Clin North Am: 1977; 21: Smith DC. The acrylic denture. Mechanical evaluation, mid-line fracture. Journal of Prosthetic Dentistry 1961; 110: Doğan OM, Bolayir G, Keskin S, Doğan A, Bek B, Boztuğ A. The effect of esthetic fibers on impact resistance of a conventional heat-cured denture base resin. Dent Mat J 2007; 26: Oku J. Impact properties of acrylic denture base resin. Part 2. Effect of temperature and residual monomer on impact characteristics. Dent Mat J 1989; 8: Memon MS, Yunus N, Razak AA. Some mechanical properties of a highly cross-linked, microwave-polymerized, injectionmoldeddenture base polymer. Int J Prosthodont 2001; 14: Straioto FG, Ricomini Filho AP, Fernandes Neto AJ, Del Bel Cury AA. Polytetrafluorethylene added to acrylic resins: mechanical properties. Braz Dent J 2010; 21: Consani RL, Azevedo DD, Mesquita MF, Mendes WB, Saquy PC. Effect of repeated disinfections by microwave energy on the physical and mechanical properties of denture base acrylic resins. Braz Dent J 2009; 20: Jagger DC, Harrison A, al-marzoug K. Effect of the addition of poly (methyl methacrylate) beads on some properties of acrylic resin. Int J Prosthodont 2000; 13: Beyli MS, von Fraunhofer JA. An analysis of causes of fracture of acrylic resin dentures. Journal of Prosthetic Dentistry 1981; 46: Doğan OM, Bolayir G, Keskin S, Doğan A, Bek B, Boztuğ A. The effect of esthetic fibers on impact resistance of a conventional heat-cured denture base resin. Dent Mat J 2007; 26: Memon MS, Yunus N, Razak AA. Some mechanical properties of a highly cross-linked, microwave-polymerized, injection-molded denture base polymer. Int J Prosthodont 2001; 14: Straioto FG, Ricomini Filho AP, Fernandes Neto AJ, Del Bel Cury AA. Polytetrafluorethylene added to acrylic resins: mechanical properties. Braz Dent J 2010; 21: da Cruz Perez LE, Machado AL, Canevarolo SV, Vergani CE, Giampaolo ET, Pavarina AC. Effect of reline material and denture base surface treatment on the impact strength of a denture base acrylic resin. Gerodontology 2010; 27: Saygili G, Sahmali SM, Demirel F. The Effect of placement of glass fibers and aramid fibers on the fracture resistance of provisional restorative materials. Journal of Operative Dentistry 2003; 28: Aydin C, Yilmaz H, Caglar A. Effect of glass fiber reinforcement on the flexural strength of different denture base resin. Quintessence Journal 2002; 33: Kim SH, Watts DC. The effect of reinforcement with woven E-glass fibers on the impact strength of complete denture fabricated with high-impact acrylic resin. Journal of Prosthetic Dentistry 2004; 91: Kim SH, Watts DC. The effect of reinforcement with woven E-glass fibers on the impact strength of complete denture fabricated with high-impact acrylic resin. Journal of Prosthetic Dentistry 2004; 91: Vallittu PK. Flexural properties of acrylic resin polymers reinforced with unidirectional and woven glass fibers. Journal of Prosthetic Dentistry 1999; 81: Vallitu PK. Impregnation of glass fiber with polymethyl methacrylate by using a powder coating method. Journal of Dental Materials 1995; 2: Vallittu PK, Ruyter IE, Ekstrand K. Effect of water storage on the flexural properties of E-glass and silica fibers acrylic resin composite. International Journal of Prosthodontics 1998; 11: Kanie T, Arikawa H, Fujii K, Ban S. Mechanical properties of woven glass fiberreinforced composites. Journal of Dental Materials 2006; 25: Iso/DIS Dentistry: Denture base polymers. Geneva: International Organization for Standardization. 1998:

Transverse Strength of Reinforced Denture Base Resin with Metal Wire and E-Glass Fibers

Original Article Transverse Strength of Reinforced Denture Base Resin with Metal Wire and E-Glass Fibers M. Vojdani 1, AAR. Khaledi 2 1 Assistant Professor, Department of Prosthodontics, Faculty of Dentistry,