Comparison of the Fracture Resistance of Six Denture Base Acrylic Resins

Abstract

Fracture strength of denture base resins is of great concern, and many approaches have been used to strengthen acrylic resin dentures. Fracture resistance of six commercially available acrylic resin denture base materials were compared, through impact and transverse strength tests. Three rapid heat-polymerised resins (QC 20, Meliodent and Trevalon), two high-impact strength resins (Trevalon Hi and Lucitone 199) and a strengthened injection-moulded acrylic resin (SR Ivocap plus) were included in the study. Twenty acrylic resin test specimens were fabricated from each resin. For impact strength test, ten notched specimens were tested in a Charpy-type impact tester. The other ten specimens were used for transverse strength tests, deflection and modulus of elasticity values were also determined, which were assessed with three-point bending tests using an Universal Testing Machine. Impact test values showed significant differences among acrylic resins (F= 4.817 p = 0.0). SR Ivocap resin showed the highest impact strength values, followed by Trevalon Hi and Lucitone 199. The transverse strength test values were not significant when six acrylic resins were compared (F= 1.705 p = 0.151). High-impact resins can be recommended to increase the impact strength of denture base. If the cause of fracture is mechanical or anatomical, strengthened acrylic resins and conventional acrylic resins have similar fracture resistance.

Correlation in the mechanical properties of acrylic denture base resins

“…Since flexural strength of polymers is very sensitive to the testing procedure, such as amount of deflection or specimen dimensions, direct comparison between the results of this study and those of previous reports should be cautious 10) . However, in general the flexural strength and modulus results of the present study are similar with those of previous reports that tested in water bath 10,[33][34][35] , whereas, particularly for IVO and LUC, they are slightly lower than those of other previous reports tested in air or unknown condition 13,20,36,37) . Our results support findings from the earlier report showing that the breaking load and deflection of acrylic resins tested in 37°C water medium were lower than those tested in air 8) .…”

“…These results were supported by the same link in literature data 14,33,34,40) . However, this should be interpreted with caution, because other previous studies showed poor correlation in mean FM-FS data of denture base materials 11,13) . However, for PL-FS association, a previous study reported higher positive correlation coefficient (r=0.94) in one denture base resin with relining materials 14) .…”

“…The corrected flexural strength (FSc) of IVO and LUC showing large deflection (>5 mm) was significantly higher than their uncorrected values. Specimen deflection during the flexural test is depending on the thickness and type of materials 10,13) . Thus, this factor should be considered when comparing the actual flexure strength of various materials.…”

“…Results of impact test have been frequently compared with flexural properties and fracture toughness in many previous reports. However, it was found that there are poor correlations between impact test and flexural strength or flexure modulus result 9,11,13,33) . Zappini et al demonstrated that results of impact tests showed only moderate correlation with fracture toughness 19) .…”

“…The most common method of measuring flexural properties of denture base is the three-point flexural (transverse) test, adopted by international standards for polymer materials, including ISO 1567:1999, Dentistry-Denture base polymers 7) . This specification for flexural test has been used in many studies to compare flexural strength, proportional limit, flexural modulus, and fracture energy of various denture base materials [8][9][10][11][12][13][14][15][16] . Other frequently used methods for comparing mechanical performance of denture base resins are fracture toughness and the impact test [17][18][19][20][21] .…”