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 Table of Contents  
Year : 2017  |  Volume : 4  |  Issue : 1  |  Page : 9-12

Comparative evaluation of flexural strength of conventional and reinforced heat cure acrylic resins: An In vitro study

1 Department of Prosthodontics, Sibar Institute of Dental Sciences, Guntur, Andhra Pradesh, India
2 Department of Prosthodontics, Drs. Sudha and Nageswararao Institute of Dental Sciences, Krishna, Andhra Pradesh, India

Date of Web Publication3-Jul-2017

Correspondence Address:
Ravikanth Anne
SF-3, AGS Towers, Srinivasa Nagar Bank Colony, Vijayawada - 520 008, Andhra Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jdrr.jdrr_7_17

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Aim: The aim is to comparatively evaluate flexural strengths (FSs) of conventional and various types of reinforced heat cure acrylic resins. Objectives: To determine the FS of conventional (polymethylmethacrylate [PMMA]) denture base material and reinforced resins by the addition of 2% by weight glass fibers and metal mesh reinforcement, respectively. Materials and Methods: A total of 30 specimens of similar dimensions were prepared for each of the three experimental groups: conventional acrylic resin and the same resin reinforced with glass fibers and with metal mesh. FS was evaluated with a three-point bending test. The results were analyzed with a one-way analysis of variance. Results: All reinforced specimens showed better FS than the conventional acrylic resin. Specimens reinforced with metal mesh showed the highest FS, followed by glass fibers. Conclusion: Within the limitations of this study, the FS of heat-polymerized PMMA denture resin was improved after reinforcement with glass fibers and metal mesh.

Keywords: Flexural strength, glass fibers, metal mesh, resin reinforcement

How to cite this article:
Anne G, Mukarla NP, Manne P, Anne R, Muvva SB, Krishna G P. Comparative evaluation of flexural strength of conventional and reinforced heat cure acrylic resins: An In vitro study. J Dent Res Rev 2017;4:9-12

How to cite this URL:
Anne G, Mukarla NP, Manne P, Anne R, Muvva SB, Krishna G P. Comparative evaluation of flexural strength of conventional and reinforced heat cure acrylic resins: An In vitro study. J Dent Res Rev [serial online] 2017 [cited 2023 Mar 27];4:9-12. Available from: https://www.jdrr.org/text.asp?2017/4/1/9/209365

  Introduction Top

Polymethylmethacrylate (PMMA) is the most commonly used denture base material. Its biocompatibility, ease of handling, dimensional stability in oral conditions, low density, ability to stain, and low cost of production made it popular in the field of prosthodontics and orthodontics.[1] However, due to its low flexural strength (FS), repeated flexing of the material occurs when subjected to loads. This leads the areas of stress concentration to develop microcracks. Further, stress intensification beyond the mechanical capacity of the material leads to midline fracture of the denture. This is well pronounced when opposed by natural dentition.[2]

The FS is a combination of tensile, compressive, and shear strengths.[2],[3] Hence, it is desirable to have a denture base material with greater FS. Various trails have been done to increase the FS of PMMA such as chemical reinforcement by graft copolymerization which induces stronger cross-linkage;[4],[5] mechanical reinforcement in the form of metal mesh or addition of various fibers such as glass, carbon, Kevlar, sapphire, polyester, nylon, rigid polyethylene, and stainless steel. Although the results seem to be encouraging, there are various disadvantages. For example, addition of metal wire leaves a weak bond between mesh and resin leading to an insignificant change in mechanical properties. Furthermore, they are susceptible to corrosion in oral environment. Addition of fibers is known to cause problems including tissue irritation, increased production time, difficulties in handling, need for precise orientation and placement, and bonding of the fibers within the resin.[4],[6]

The present study was conducted to evaluate and compare the FSs of conventional heat cure resins, fiber reinforced, and metal mesh reinforced resins.

  Materials and Methods Top

An In vitro study was conducted in the Department of Prosthodontics, Sibar Institute of Dental Sciences, Guntur, India. Aluminum die [Figure 1] was fabricated by computerized milling (Indo-German Institute of Advanced Technology, Visakhapatnam) to fabricate a standard mold with dimensions of 65 mm × 10 mm × 3 mm (according to the American Dental Association specification no. 12 for the measurement of FS of denture resins). This mold is used to produce a wax pattern by melting modeling wax [Figure 2]. The wax patterns were used for flasking. Conventional compression molding technique was followed to fabricate all the samples.
Figure 1: Aluminum die (American Dental Association specification no. 12)

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Figure 2: Wax patterns

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The test specimens were divided into three different groups each containing thirty samples. Group A includes samples fabricated by conventional heat cure acrylic (Trevalon, Dentsply, Mumbai) [Figure 3]. Group B contains acrylic samples reinforced with glass fibers (Voltas Pvt. Ltd., Pune) [Figure 4]. Group C included samples reinforced with metal mesh (Dentarum, Germany) [Figure 5]. All the samples were preserved in water at room temperate for 1 week and are later tested for their FSs.
Figure 3: Group A specimens

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Figure 4: Group B specimens

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Figure 5: Group C specimens

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Testing of flexural strength

Each specimen was subjected to the three-point bending test at a crosshead speed of 2 mm/min at a 55 mm distance with a universal testing machine test apparatus (model 3366, Instron) [Figure 6] with a load of 250 kg applied at the center of the specimen. The specimens were supported on the jigs with a diameter of 3 mm and the span length was 55 mm. The load applied to the center of the specimens was measured by a load cell, attached to the crosshead of the machine through a data acquisition system connected to a computer [Figure 7]. Stress–strain curves were recorded on a chart with the help of the analysis software (Qmat 3.63 HTE S-Series-10K, Surrey, UK) of the testing machine throughout the test. FS values were automatically calculated by the software and the results were recorded. The breaking load was converted to FS by the formula:[5]
Figure 6: Universal testing machine (Instron 3366)

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Figure 7: Application of load for testing flexural strength using universal testing machine

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  • FS = 3PL/2bd 2
  • Where FS is flexural strength
  • P is the load at fracture
  • L is the length between the jig tips (55 mm)
  • b is the width, and d is the thickness of the specimen.

The results of the study were statistically analyzed by one-way ANOVA test to determine whether a significant difference existed between the means of the experimental groups.

  Results Top

When comparison was made among the groups, mean FS of Group C (187.45 MPa) is more than Group A (105.02 MPa) and Group B (120.47 MPa) [Table 1] and [Graph 1].
Table 1: Mean, standard deviation and coefficient of variation, minimum and maximum of flexural bend strength in MPa of three groups (Groups A, B, and C)

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A statistically significant difference was found between the FS of all the groups (P < 0.05) which indicates that the increase in the FS is due to the addition of the glass fibers and metal mesh [Table 2].
Table 2: Mean comparison among groups

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When a mean comparison was made between groups, there is a difference of 15.45 ± 7.65 MPa in flexural bend strength between control group resin (Group A) and glass fiber reinforced resin (Group B), and a difference of 82.43 ± 1.89 MPa between control group resin (Group A) and metal mesh reinforced resin (Group C), and a difference of 66.98 ± 5.76 MPa between Group B and C groups [Table 3] and [Graph 2].
Table 3: Mean comparison between groups

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  Discussion Top

PMMA has a favorable combination of properties that accounts for its popularity of use; however, it is not without limitations. Fracture of the denture base is the major problem. The denture base is subjected to various stresses during function, these include compressive, tensile, and shear stresses.[7] Some of the factors responsible for denture fracture include stress intensification, increased ridge resorption leading to an unsupported denture base, deep incisal notching at the labial frenum, sharp changes at the contours of the denture base, deep scratches, and induced processing stresses. The present study was conducted to compare the methods for enhancing FS of PMMA with that of conventional method.

Addition of glass fibers offers an esthetic advantage as the fibers are invisible and provide a metal-free solution with no additional bulk of the prosthesis. It enhances the FS of conventional acrylic due to increased filler content in the matrix that allows wider force dissipation.[2],[3] In group B, the conventional heat cure acrylic is reinforced with glass fibers. The samples showed improved FSs as compared to that of Group A. The results are in accordance with the studies conducted by John et al. and Diaz-Arnold et al.[6],[8]

The FS values can be further improved by metal mesh reinforcement of conventional acrylics. As the metal matrix is more rigid than glass fibers,[9],[10] it offers highest FS. Furthermore, metal mesh provides resistance to flexure as it is arranged at right angles to load application unlike the glass fibers that are irregularly scattered in the matrix. Furthermore, as the metal mesh does not show water sorption, it is dimensionally stable as compared to Group A and B samples. In Group C, the conventional heat cure acrylic is reinforced with metal mesh. This improved FS over Group B samples. The findings are similar to the observation by Vallittu and Lassila. However, clinically it is difficult to reline or repair the denture. Acceptance by patient is low due to unesthetic metal display.[1],[7]

  Conclusion Top

Within the limitations of the study, it can be concluded that addition of metal mesh greatly enhances FS over fiber reinforced and conventional dentures. Fiber reinforcement exhibited significant increase of FS over conventional PMMA resin.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

McCracken WM. An evaluation of activated methyl methacrylate denture base materials. J Prosthet Dent 1952;2:68-83.  Back to cited text no. 1
Vallittu PK, Lassila VP. Reinforcement of acrylic resin denture base material with metal or fibre strengtheners. J Oral Rehabil 1992;19:225-30.  Back to cited text no. 2
Craig RG, Powers JM, Sakaguchi RL. Craig's Restorative Dental Materials. St. Louis, MO: Mosby Elsevier; 2006.  Back to cited text no. 3
Jagger DC, Harrison A, Jandt KD. The reinforcement of dentures. J Oral Rehabil 1999;26:185-94.  Back to cited text no. 4
Jagger D, Harrison A, Jagger R, Milward P. The effect of the addition of poly (methyl methacrylate) fi bres on some properties of high strength heat-cured acrylic resin denture base material. J Oral Rehabil 2003;30:231-5.  Back to cited text no. 5
John J, Gangadhar SA, Shah I. Flexural strength of heat-polymerized polymethyl methacrylate denture resin reinforced with glass, aramid, or nylon fi bers. J Prosthet Dent 2001;86:424-7.  Back to cited text no. 6
Ajaj-Alkordy NM, Alsaadi MH. Elastic modulus and flexural strength comparisons of high-impact and traditional denture base acrylic resins. Saudi Dent J 2014;26:15-8.  Back to cited text no. 7
Diaz-Arnold AM, Vargas MA, Shaull KL, Laffoon JE, Qian F. Flexural and fatigue strengths of denture base resin. J Prosthet Dent 2008;100:47-51.  Back to cited text no. 8
Dagar SR, Pakhan AJ, Thombase RU, Motwani BK. The evaluation of flexural strength and impact strength of heat polymerized poly methyl methacrylate denture base resin reinforced with glass and nylon fi bers. J Inf Process Syst 2008;8:98-104.  Back to cited text no. 9
Anusavice KJ, Phillips RW, Shen C, Rawls HR. Phillips' Science of Dental Materials. St. Louis, MO: Elsevier, Saunders; 2013.  Back to cited text no. 10


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]

  [Table 1], [Table 2], [Table 3]


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