Journal of Dr. NTR University of Health Sciences

: 2015  |  Volume : 4  |  Issue : 1  |  Page : 21--23

The effect of aluminum oxide addition on the flexural strength of heat activated acrylic resin: An in vitro study

Gopinadh Anne, Swetha Hima Bindu Oliganti, Jyothi Atla, Sreedevi Budati, Prakash Manne, Sandeep Chiramana 
 Department of Prosthodontics, Sibar Institute of Dental Sciences, Guntur, Andhra Pradesh, India

Correspondence Address:
Dr. Jyothi Atla
Department of Prosthodontics, Sibar Institute of Dental Sciences, Takkellapadu, Guntur - 522 509, Andhra Pradesh


Aim: This study was done to investigate the effect of adding 5-20% aluminum oxide (Al 2 O 3 ) powder by weight on the flexural strength of heat-polymerized acrylic resin. Materials and Methods: A total of 50 specimens of heat-polymerized acrylic resin were fabricated and were divided into five groups (n = 10). Group A was the control group (unmodified acrylic resin specimens). The specimens of the remaining four groups i.e., Groups B, C, D and E were reinforced with Al 2 O 3 powder to achieve loadings of 5%, 10%, 15% and 20% by weight. Specimens were stored in distilled water for 1 week and the flexural strength of the specimens was tested in a universal testing machine (5 mm/min crosshead speed). Results were analyzed by one-way analysis of variance. Weibull analysis was used to calculate the Weibull modulus, characteristic strength and the required stress for 1% and 5% probabilities of failure. Results: The mean flexural strength values of the heat-polymerized acrylic resin were (in MPa) 92.01, 114.46, 116.77, 123.11 and 129.72, for Groups A, B, C, D and E, respectively. The flexural strength increased significantly with the incorporation of Al 2 O 3 . Conclusion: Al 2 O 3 fillers are potential components to be added in denture bases to provide increased flexural strength. Adequate flexural strength of denture base is quite essential for the longevity of the prosthesis.

How to cite this article:
Anne G, Bindu Oliganti SH, Atla J, Budati S, Manne P, Chiramana S. The effect of aluminum oxide addition on the flexural strength of heat activated acrylic resin: An in vitro study.J NTR Univ Health Sci 2015;4:21-23

How to cite this URL:
Anne G, Bindu Oliganti SH, Atla J, Budati S, Manne P, Chiramana S. The effect of aluminum oxide addition on the flexural strength of heat activated acrylic resin: An in vitro study. J NTR Univ Health Sci [serial online] 2015 [cited 2022 Jul 2 ];4:21-23
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Full Text


Polymethyl methacrylate (PMMA) introduced in 1937 by Dr. Walter Wright, was considered to be the near ideal denture base material due to its various advantages. [1] However low impact strength of an acrylic resin is a potential disadvantage. Besides its high hardness and good thermal properties, aluminum oxide (Al 2 O 3 ) was proved to be biocompatible material which makes it the material of choice to reinforce acrylic resins in order to improve its strength properties. [2] The present in vitro study was done to evaluate the flexural strength of heat cure acrylic resin reinforced with Al 2 O 3 in various proportions.

 Materials and Methods

As per the ISO 1567 standards a Teflon die measuring 65 mm 3 × 10 mm 3 × 3 mm 3 [Figure 1] was prepared and flasked to obtain mould space for acrylic specimens preparation. [3],[4] Heat cure acrylic resin was then proportioned with aluminum oxide at various concentrations. Packing, curing and acrylization of the specimens were done in a conventional way. A total of fifty specimens were prepared and the specimens were divided into five groups namely A, B C, D and E, each` group consisted of 10 samples. Group A was the control group whereas the B, C, D and E groups consisted of specimens reinforced with Al 2 O 3 at 5, 10, 15 and 20 weight % respectively.{Figure 1}

Flexural strength of the specimen was determined by using a 3-point bending testing device in universal testing machine Instron (Model™ 5565, Canton) [Figure 2]. The specimens were centered on the device in such a way that the loading wedge was set to travel at a cross head speed of 5 mm/min, engaged at the centre of the upper surface of the specimens [Figure 3]. Specimens were loaded until fracture occurred completely.{Figure 2}{Figure 3}

The results were analyzed using one-way analysis of variance (ANOVA) which was used to determine whether significant differences existed between the means of the experimental groups. Weibull analysis was used to calculate the weibull modulus, characteristic strength and the required stress for 5% and 95% probabilities of failure.


Mean value and standard deviation values of A, B, C, D and E groups are presented [Table 1].{Table 1}

One-way ANOVA analysis showed the F value of 20.54667. Since P < 0.05 there is a significant difference in the flexural strength between the different groups [Table 2].{Table 2}

Weibull analysis depicted the strength of 5% and 95% probability of failure of all the Groups A, B, C, D and E [Table 3].{Table 3}


Despite of the fact that we have landed up in a very modern era of dentistry, the continuous search for an ideal denture base material ever remained as a challenge. [5] In the 1850's vulcanite, a hardened rubber became the most widely used denture base material. [6] Acrylic resins represent approximately 95% of the denture base materials that are now being used in the field of prosthodontics. [3] It is considered to be the popular denture base material because of its advantages such as esthetics, dimensional stability, ease in manipulation and processing. [1],[7] However, its properties like low strength and thermal conductivity, polymerization shrinkage differs it from being an ideal denture base material. Several efforts are being made to improve its properties.

Fracture of the dentures made from acrylic resin is an unresolved problem and fracture occurs in spite of metal reinforcement. [8],[9] According to Kelly fatigue failure was a real problem in well-fitting maxillary dentures occluding against natural mandibular teeth. [10] A study by John et al., showed that 68% of the acrylic resin dentures fracture within a few years after fabrication, which may be primarily because of impact or fatigue failure. [1] Impact fatigue may occur outside the mouth when the denture is dropped accidentally whereas flexural fatigue may occur in the mouth due to repeated flexing from chewing. [1] This ultimately fractures the dentures in the mouth and causes inconvenience to both the dentist and the patients. So in order to overcome these failures many authors tried reinforcing PMMA with various materials likely glass, aramid and nylon fibers.

The present study was done by reinforcing PMMA with Al 2 O 3 powder which was widely recommended by many of the authors due to its positive properties like its abundancy, inexpensiveness, good thermal properties, high hardness and refractoriness. [11],[12] However, few limitations of the use of this material includes a decrease in tensile strength, toughness, decreased esthetic appearance when used in higher proportions (>25%). [11],[13]


Within the limitations of the study the following conclusions can be drawn. Incorporating Al 2 O 3 powder from 5% to 20% by weight into conventional heat polymerized denture base resin resulted in an increase in the flexural strength. Significant enhancement in the flexural strength values were seen with an increase in the weight proportions of Al 2 O 3 .


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