Assessing Fracture Toughness and Impact Strength of PMMA Reinforced with Nano-Particles and Fibre as Advanced Denture Base Materials

Abstract

Statement of Problem: Polymethyl methacrylate (PMMA) denture resins commonly fracture as a result of the denture being dropped or when in use due to heavy occlusal forces. Purpose: To investigate the effects of E-glass fibre, ZrO2 and TiO2 nanoparticles at different concentrations on the fracture toughness and impact strength of PMMA denture base. Materials and Methods: To evaluate fracture toughness (dimensions: 40 × 8 × 4 mm3; n = 10/group) and impact strength (dimensions: 80 × 10 × 4 mm3; n = 12/group), 286 rectangular tested specimens were prepared and divided into four groups. Group C consisted of the PMMA specimens without any filler (control group), while the specimens in the remaining three groups varied according to the concentration of three filler materials by weight of PMMA resin: 1.5%, 3%, 5%, and 7%. Three-point bending and Charpy impact tests were conducted to measure the fracture toughness and impact strength respectively. Scanning Electron Microscope (SEM) was utilised to examine the fractured surfaces of the specimens after the fracture toughness test. One-way analysis of variance (ANOVA) followed by Tukey post-hoc tests were employed to analyse the results at a p ≤ 0.05 significance level. Results: Fracture toughness of groups with 1.5 and 3 wt.% ZrO2, 1.5 wt.% TiO2, and all E-glass fibre concentrations were significantly higher (p < 0.05) than the control group. The samples reinforced with 3 wt.% ZrO2 exhibited the highest fracture toughness. Those reinforced with a 3 wt.%, 5 wt.%, and 7 wt.% of E-glass fibres had a significantly (p < 0.05) higher impact strength than the specimens in the control group. The heat-cured PMMA modified with either ZrO2 or TiO2 nanoparticles did not exhibit a statistically significant difference in impact strength (p > 0.05) in comparison to the control group. Conclusions: 1.5 wt.%, 3 wt.% of ZrO2; 1.5 wt.% ratios of TiO2; and 1.5 wt.%, 3 wt.%, 5 wt.%, and 7 wt.% of E-glass fibre can effectively enhance the fracture toughness of PMMA. The inclusion of E-glass fibres does significantly improve impact strength, while ZrO2 or TiO2 nanoparticles did not.

Behaviour of PMMA Resin Composites Incorporated with Nanoparticles or Fibre following Prolonged Water Storage

“…An additional explanation could be that the use of a silane coupling agent promoted better bonds between the glass fibre/ZrO 2 nanoparticles and the polymer matrix [6,38]. This was supported by the SEM images in the previous work, which confirmed that little or no gap had formed around the fibres on the fracture surface of the E-glass fibres specimens [28,29].…”

“…Furthermore, 1.5 and 3.0 wt.% ZrO 2 and 1.5 wt.% TiO 2 , and all E-glass fibre concentrations significantly increased the fracture toughness of the PMMA. Incorporating ZrO 2 or TiO 2 nanoparticles at any concentration did not enhance the impact strength of the PMMA, but adding 3.0, 5.0, and 7.0 wt.% of E-glass fibres did significantly increased the impact strength [29].…”

“…The relatively low enhancement in solubility might be attributed to the incorporated ZrO 2 nanoparticles that fill any potential spaces within the PMMA resin [16] and thereby decreasing the water sorption and mass change within the samples. Our previous SEM images displayed the fracture surfaces of 7.0 wt.% ZrO 2 nanoparticle specimens and revealed that this material was less brittle compared to the control group specimens [28,29].…”

“…In our previous studies, the effects of incorporating ZrO 2 and TiO 2 nanoparticles or E-glass fibre at various concentrations (1.5, 3.0, 5.0 and 7.0 wt.%) on the flexural strength, hardness, fracture toughness, and impact strength of PMMA denture base were examined [28,29]. The findings revealed that the optimal filler concentrations for significantly increasing the flexural strength of PMMA denture base were 3.0 wt.% ZrO 2 , and 5.0 wt.% and 7.0 wt.% E-glass fibre.…”

“…Several researchers have aimed to enhance the mechanical properties of PMMA denture bases by incorporating fillers into such constructs [26][27][28][29] as opposed to enhancing the physical properties of the PMMA itself [30]. Nanoparticles have been increasingly used as fillers for polymer reinforcement due to their high flexural strength, corrosion and abrasion resistance, excellent toughness, and biocompatibility [31,32].…”