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Table of Contents   
ORIGINAL RESEARCH  
Year : 2012  |  Volume : 23  |  Issue : 2  |  Page : 140-144
In vitro comparative evaluation of the effect of two different fiber reinforcements on the fracture toughness of provisional restorative resins


1 Department of Prosthodontics, VSPM’s Dental College and Research Center, Nagpur, India
2 Department of Prosthodontics, Government Dental College and Hospital, Nagpur, India

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Date of Submission11-Apr-2011
Date of Decision15-Jul-2011
Date of Acceptance29-Jan-2012
Date of Web Publication3-Sep-2012
 

   Abstract 

Background: Fracture of provisional fixed partial denture (FPD) may jeopardize the success of provisional prosthodontic treatment phase and cause patient discomfort.
Aim: The aim of this study was to compare the fracture toughness of the Polymethyl Methacrylate (PMMA) resin and Bis-Acryl Composite (BAC) resin reinforced with the Polyethylene and Glass fibers.
Materials and Methods: Three groups (N=10) of each of the two materials were prepared for the fracture toughness test. Two groups had the different reinforcements and group without reinforcement served as the control. The mean fracture toughness (MPa.m½ ) was compared by One-way ANOVA, followed by the Scheffe analysis. Fracture toughness between fiber-reinforced PMMA and BAC resin was compared by the independent samples t test.
Results: For the controls, the fracture toughness for PMMA resin (0.91) was significantly lower than for the BAC resin (1.19). Glass fiber reinforcement produced significantly higher fracture toughness for both, PMMA (1.48) and BAC (1.82) resin, but the Polyethylene fibers did not (0.95 for PMMA and 1.23 for BAC resin). Among the reinforced groups, Silane impregnated Glass fibers showed highest fracture toughness for the BAC resin (1.82).
Conclusion: Of two fiber reinforcement methods evaluated, Glass fiber reinforcement for the PMMA and BAC resin produced highest fracture toughness.
Clinical Implications: On the basis of this in--vitro study, the use of Glass and Polyethylene fibers tested may be an effective way to reinforce resins used to fabricate fixed provisional restorations.

Keywords: Compact test specimens, fracture toughness, special tension device

How to cite this article:
Kamble VD, Parkhedkar RD. In vitro comparative evaluation of the effect of two different fiber reinforcements on the fracture toughness of provisional restorative resins. Indian J Dent Res 2012;23:140-4

How to cite this URL:
Kamble VD, Parkhedkar RD. In vitro comparative evaluation of the effect of two different fiber reinforcements on the fracture toughness of provisional restorative resins. Indian J Dent Res [serial online] 2012 [cited 2019 May 27];23:140-4. Available from: http://www.ijdr.in/text.asp?2012/23/2/140/100415

   Introduction Top


The word provisional means established for the time being. During the Prosthetic Rehabilitation procedures, provisional restorations are commonly used to provide both pulpal and periodontal protection till the final restorations are placed. Such temporary restorations should have good marginal integrity, esthetics and sufficient durability to withstand the forces of mastication. Materials commonly used to fabricate provisional restorations are Polymethyl Methacrylate (PMMA), Polyethyl Methacrylate, Bis-Acryl Composite (BAC) resin, and Epimine resins. [1] However, as provisional restorations are used for a short span in the mouth, less attention is paid to their design and the patients also usually tolerate the mild discrepancies, unless the "temporaries" become the "long standing". [2] Provisional FPD materials must be strong enough to withstand the masticatory forces, particularly for long-span FPDs, for long term use, or for patients with parafunctional habits. [3],[4] To meet the requirements of longevity and esthetics necessitated by complex interdisciplinary treatment, the technique of construction, as well as the materials chosen, may have to be altered. [2] Several methods have been used to reinforce the provisional fixed partial dentures (FPD) like metal wires, processed Acrylic resin provisional restoration; lingual cast metal reinforcement, and different types of fibers such as Polyethylene and Glass. [1] Fiber reinforcements have become relatively popular as methods to increase the strength of the provisional restorations.

The aim of this study was to compare the effect of the two different fiber reinforcements i.e., Polyethylene fibers and Glass fibers on the fracture toughness of PMMA and BAC resin.


   Materials and Methods Top


For fracture toughness, specimens were fabricated according to ASTM E-1820 standards, with the dimensions and shape shown in [Figure 1]. [5] Compact test specimens were fabricated in the form of a double cantilever beam, with a slot that originated from the center of one edge, extending along the specimen's center line to a 60° terminal apex, located slightly beyond the midpoint of the specimen. Two loading holes pierced the specimen. [1] Specimens for each resin type/fiber reinforcement combination, were made using a specially designed metal mold. The design of assembled mold provided triangular ports, which allowed the escape of excess resin during the mold assembly and exposure to pressure during the Polymerization. [6]
Figure 1: Dimensions of compact test specimens for fracture toughness testing.

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Control group

With PMMA (DPI-Heat cure, Dental Product of India, Mumbai, India) resin, manufacturers did not provide accurate proportioning of Polymer and Monomer, therefore trial mixes were made to determine an optimum Polymer/Monomer ratio with adequate working time. The determined ratio for PMMA was in between 1.8- 2.0 gm/ ml. Mix was packed into the mold and the entire assembly was placed in a hand press. Specimens were polymerized at 90 0 C for 2 hours. The specimens were examined for any voids, and defective specimens were discarded. [6] BAC resin specimens (Protemp 4 Garant, 3M ESPE, Seefeld, Germany) were prepared in the same manner, except that material was supplied in an auto mixing syringe. [1]

Reinforcement with polyethylene and glass fibers

Polyethylene fibers (Lotus Polytwist, Daman, India) were soaked in Monomer for ten minutes in a petridish for better bonding with the PMMA resin matrix. [1],[7] The fibers were removed from the Monomer and excess liquid was allowed to dry, then the Polymer and fibers were mixed thoroughly to disperse the fibers. Monomer and Polymer containing fibers was mixed in the ratio of 2:1 gm/ml, allowed to reach dough stage and packed into the prepared mold. For BAC resin, bonding agent (Adper TM , 3M ESPE, Seefeld, Germany) was applied on the Polyethylene fibers and cured for 40 seconds with the Halogen light cure unit (Megalux CS, Megadenta, Radeberg, Germany). With Garant dispenser, both base and catalyst pastes were dispensed on the mixing pad. The mix was hand spatulated after incorporation of fibers for 30 seconds and immediately transferred into the applicator syringe for placement into the mold and mold was assembled. [7] The exposed fibers at the peripheral border of the specimens were trimmed with the diamond bur at slow speed to avoid delamination of the reinforcement. Each specimen was finished and polished. Glass fibers (Saint Gobin Vetrotex International, Chambery, France) were soaked in Silane (Ultradent, Ultradent Products, South Jordon, USA) for five minutes in a petridish for better bonding with the resin matrix. [8] The fibers were removed from the Silane and allowed to air dry completely. The Polymer and fibers were mixed thoroughly to disperse the fibers. The specimens were polymerized and retrieved as in the control group. Specimens were stored in saline at 37 0 C in an incubator for 24 hours, before testing. Specimens were labeled on each end prior to testing so that fractured pieces could be reunited and examined after testing.

60 specimens were tested to measure the fracture toughness of the PMMA and BAC resin.

Group I: - Control group (Unreinforced PMMA)

Group II: - Reinforced with Monomer impregnated Polyethylene fibers.

Group III: - Reinforced with Silane impregnated Glass fibers.

Group IV: - Control group (Unreinforced BAC)

Group V: - Reinforced with Monomer impregnated Polyethylene fibers.

Group VI: - Reinforced with Silane impregnated Glass fibers

Fracture toughness testing

The fracture mechanics approach is considered a reliable indicator of the performance of brittle materials. Brittle fracture failure involves the initiation of crack and its propagation until the restoration is fractured. The characteristic that describes the ability of a material to resist crack propagation is the fracture toughness and may more accurately determine the likelihood of the fracture of a provisional restoration. [6] After preparation of the specimens, a pre-crack was formed to standardize the direction of the force application, with hand pressure on a straight scalpel blade placed at the apex of the slot. [Figure 2] [6] Ten specimens from each group were tested in tension in a universal testing machine (Model 4204, Instron Corp., High Wycombe, UK) with the direction of force perpendicular to the plane of preformed crack with a crosshead speed of 1mm/min. [1] Each specimen was held in a specially designed tension device consisting of steel rods, extending from steel fixtures attached to the loading apparatus, passed through the loading holes of the specimens [Figure 3]. When actuated, the apparatus controlled the gradual separation of the fixtures and transmitted tensile load to the specimens. The peak force (F) in Newtons, which caused fracture of the specimens, was recorded and used to calculate the fracture toughness (K1c) in MPa.m 1/2 from the following equation: [6]
Figure 2: Initiation of pre-crack.

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Figure 3: Specimen loading with special tension device

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K1c = pc/bw 1/2 . F (a/w)

Where, pc is maximum load before crack advance (KN); b is Average specimen thickness (cm); w is the width of the specimen (cm) and



Where (a) = Crack length (cm)

The data was tabulated and analyzed by the Statistical Package for Social Science © 10.0. The mean difference, standard deviation and standard error were calculated for each variable. The data of each resin type were analyzed for difference by use of one-way analysis of the variance (ANOVA) followed by the Scheffe analysis, using a significance level of 0.05 to determine the mean differences. As the intent of this study was to make comparisons between the different materials tested, independent samples t test was used for the analysis.


   Results Top


The results for the mean fracture toughness values (MPa. m 1/2 ) are shown in [Table 1]. Group III showed significantly higher fracture toughness than group I, but no significant difference was found between group I and II. Similarly, group VI showed significantly higher fracture toughness than group IV, but no significant difference found between group IV and V [Table 2].
Table 1: Mean fracture toughness values of PMMA and BAC resin

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Table 2: Multiple comparisons by scheffe analysis between control and fiber-reinforced group

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The results revealed that, the fracture toughness of PMMA and BAC resin reinforced with Silane impregnated Glass fibers was significantly higher than unreinforced PMMA and BAC, whereas, specimens reinforced with the Monomer impregnated Polyethylene fibers were not significantly different from the unreinforced resin. By using independent samples t test, results revealed statistically significant difference between fracture toughness of fiber reinforced PMMA and BAC resin group. Group VI showed highest fracture toughness followed by group III, V and group II in order [Table 3].
Table 3: Independent samples t test: Comparison of fracture toughness between fiber-reinforced PMMA and BAC resin groups

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   Discussion Top


The clinician must be aware of all the attributes of various materials and choose the provisional FPD material, appropriate for each patient. [3] Although laboratory fracture toughness values under static loading may not reflect intraoral conditions; these values are nevertheless helpful in comparing materials under controlled situations and useful predictors of the clinical performance. [1] BAC resins are supplied in cartridge delivery system, presumably providing more consistent mix than the hand mixing of PMMA resin. [9] However, this could not be substantiated by Hasselton et al, who found no lower standard deviations for the bis-acrylate cartridge products compared to the hand mixed PMMA resin products. [3] The present study confirms the higher fracture toughness of the control BAC over the control PMMA resin. Traditional Methyl Methacrylate-type resins are monofunctional. They are low molecular weight linear molecules which exhibit decreased strength and rigidity. In contrast, BAC resins are difunctional and capable of cross-linking with other Monomer chains; resulting into higher toughness and strength. [4] BAC resin has been modified as Protemp 4 Garant, that includes a newly developed Monomer system, not with the rigid intermediate chain characteristic of some bis-Acryl homologues, but with the flexible chain in comparison to other synthetic resins. This attribute allows a balance between high mechanical strength and limited elasticity of the composite materials. [3]

Reinforcement with fibers enhances the mechanical strength characteristics such as transverse strength, ultimate tensile strength and impact strength. [10] In addition, fiber reinforcement has other advantages like improved esthetics, enhanced bonding to the resin matrix, and the ease of repair. [11] The possible reason for the increase in mechanical properties was the transfer of stress from the the weak Polymer matrix to the fibers that have the high tensile strength. [1] When the tensile strength of the Polymer is lower than tensile strength of the fibers, the specimen will gain strength when the fiber is placed in the area of higher tension, away from the load. [12] The stronger the adhesion between the fiber and the matrix, the greater the strengthening effect. [8] One approach to increase the adhesion of fibers in the polymer matrix is, resin impregnation of the fiber before application. [1] In the present study, Polyethylene fibers did not produce higher fracture toughness in either material than unreinforced group, which may be attributed to the poorly bonded fibers. In addition, Polymer to Monomer ratio was changed to create a lower viscosity mixture that would lead to higher polymerization shrinkage of the resin causing a split between the fibers and the Polymer matrix. [7] Improper impregnation also increases the water sorption which might result in a detrimental hydrolytic effect and decreases the mechanical properties of the reinforced resin. [7] To increase the reinforcing effect of the Polyethylene fibers, different surface treatments should be carried out which includes plasma spraying, chemical, flame and radiation treatments. [1] Significant improvement in fracture toughness of the Silane impregnated Glass fiber group can be attributed to the effect of Silane coupling agent which chemically bonds inorganic glass fibers to the organic resin matrix, and makes the mixture more homogenous resulting into the strong PMMA and BAC resin. [8] 2% by weight of each type of fiber was added to each specimen of this study, as fiber incorporation beyond 3% will affect the flow of the dough and represents a large volume of material to be wetted by the Monomer during the mixing and produce dry friable dough. [13] Glass fiber reinforcement provides the best esthetic qualities for the dental applications though more research is necessary to determine whether Glass fibers are carcinogenic in the mouth, attract more plaque, or cause gingival disorders. [14] Fiber reinforcement is a potential technique for strengthening the provisional fixed partial dentures at the connector sites to avoid the fractures. With the most specimens, the fibers were intact, and fracture stopped at the fiber location, suggesting that use of these fibers may be beneficial in reinforcing fixed provisional restorations, which may be used for extended periods.


   Conclusion Top


Within the limitations of this study, the following conclusions were drawn:

  • PMMA resin has significantly lower fracture toughness than the BAC resin.
  • Glass and Polyethylene fibers improved the fracture toughness of the specimens compared to the unreinforced PMMA and BAC resin. This shows that, use of fibers is an effective method to increase the mechanical properties of the provisional restorative resins.
  • Silane impregnated Glass fiber reinforcement produce significantly higher fracture toughness for both, PMMA and BAC resin compared to Monomer impregnated Polyethylene fiber reinforcement. Where space and esthetics are of concern, the Glass fibers seems to be the most appropriate of the methods tested for reinforcing both types of resins.


 
   References Top

1.Hamaza TA, Rosenstiel SF, Mohammed ME, Rabab MI. The effect of fiber reinforcement on the fracture toughness and flexural strength of provisional restorative resins. J Prosthet Dent 2004;91:258-64.   Back to cited text no. 1
    
2.Spear F. An interdisciplinary approach to the use of long-term temporary restorations. J Am Dent Assoc 2009;140:1418-24.  Back to cited text no. 2
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3.Haselton DR, Diaz-Arnold AM, Vargas MA. Flexural strength of provisional crown and fixed partial dentures. J Prosthet Dent. 2002;87:225-28.   Back to cited text no. 3
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4.Koumjian JH, Nimmo A. Evaluation of fracture resistance of resins used for provisional restorations. J Prosthet Dent 1990;64:654-7.  Back to cited text no. 4
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5.Standard test method for measurement of fracture toughness. ASTM E 1820-08. West Conshohocken (PA): ASTM International; 1983.  Back to cited text no. 5
    
6.Gegauff AG, Pryor HG. Fracture toughness of provisional resins for fixed prosthodontics. J Prosthet Dent 1987;58:23-8.  Back to cited text no. 6
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7.Vallittu PK. Flexure properties of acrylic resin polymer reinforced with unidirectional and woven glass fibers. J Prosthet Dent 1999;81:318-26.  Back to cited text no. 7
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8.Solnit GS. The effect of methyl methacrylate reinforcement with silane treated and untreated glass fibers. J Prosthet Dent 1991;66:310-14.  Back to cited text no. 8
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9.Geerts GA, Overturf JH, Oberholzer TG. The effect of different reinforcements on the fracture toughness of materials for interim restorations. J Prosthet Dent 2008;99:461-7.  Back to cited text no. 9
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10.Uzun G, Hersek N, Tincer T. Effect of five woven fiber reinforcements on the impact and transverse strength of a denture base resin. J Prosthet Dent 1999;81:616-20.  Back to cited text no. 10
    
11.Jagger DC, Harrison A, Jandt KD. Review. The reinforcement of dentures. J Oral Rehab 1998;25:100-05.  Back to cited text no. 11
    
12.Vallittu PK. Some aspects of tensile strength of unidirectional glass fiber-polymethyl methacrylate composite used in dentures. J Oral rehab 1998;25:100-5.  Back to cited text no. 12
[PUBMED]    
13.Gutteridge DL. The effect of including ultra-high modulus polyethylene fibers on the impact strength of acrylic resin. Br Dent J 1988;164:177.  Back to cited text no. 13
[PUBMED]    
14.Stipho HD. Effect of glass fiber reinforcement on some mechanical properties of autopolymerizing polymethyl methacrylate. J Prosthet Dent 1998;79:580-4.  Back to cited text no. 14
[PUBMED]    

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Correspondence Address:
Vaibhav D Kamble
Department of Prosthodontics, VSPM’s Dental College and Research Center, Nagpur
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.100415

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    Figures

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    Tables

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