ORIGINAL RESEARCH Year : 2023  |  Volume : 14  |  Issue : 1  |  Page : 13-15

Effect of Gaseous Ozone on Transverse and Impact Strengths of Heat Cure Acrylic Resin: An In Vitro Study

Baraa Hasan Kadhim, Wasmaa S Mahmood
Department of Prosthodontics, College of Dentistry, University of Baghdad, Iraq

Date of Submission14-Nov-2022Date of Decision18-Nov-2022Date of Acceptance20-Nov-2022Date of Web Publication20-Mar-2023

Correspondence Address:
Baraa Hasan Kadhim
Department of Prosthodontics, Collage of Dentistry, University of Baghdad, Baghdad
Iraq

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/denthyp.denthyp_139_22

Introduction: This study aimed to find out how exposure to gaseous ozone affected heat-cured acrylic resin’s transverse and impact strengths. Methods: Sixty samples of heat-cured acrylic resin were prepared and divided into three subgroups, control, microwave radiation (positive control), and gaseous ozone. Transverse strength and impact strength were evaluated using testing machines. At a level of significance of 5%, data were assessed using one-way analysis of variance (ANOVA) and Tukey’s post hoc test. Results: Transverse strength analysis showed a significant difference among groups (P < 0.001). Post hoc test revealed significant differences between all multiple groups (P < 0.001). Impact strength analysis results showed a non-significant difference among groups (P = 0.13). Conclusion: Within the limits of this research, it is possible to conclude that gaseous ozone exposure improves the transverse strength of heat-cure acrylic resin.

Keywords: Acrylic resin, denture, disinfection, gaseous ozone, impact strength, microwave, poly methyl methacrylate, transverse strength

How to cite this article:
Kadhim BH, Mahmood WS. Effect of Gaseous Ozone on Transverse and Impact Strengths of Heat Cure Acrylic Resin: An In Vitro Study. Dent Hypotheses 2023;14:13-5
  Introduction 

For denture base applications, poly methyl methacrylate (PMMA) is the most widely used polymer.[1] This is because of its low cost, easy manipulation, and convenience in repair.[2] Denture cleaning is an essential component of dental hygiene because dentures provide a favorable environment for bacterial and fungal pathogens like Streptococci, Candida, and other microorganisms.[3] To minimize cross-contamination and preserve healthy oral mucosa, the decontamination procedure must be carried out in a way that inactivates bacteria without negatively impacting the acrylic resins.[4]

Microwave irradiation has been used for several purposes in dentistry.[5] Including the disinfection of removable dentures.[6] Fortes et al.[7] showed that microwave irradiation exposure at high power for 1 minute on the hardness and flexural strength is safe.

Triatomic oxygen or trioxygen is a naturally occurring compound known as ozone. It can be created by ozone generators or found as a gas in the stratosphere at a concentration of 1 to 10 ppm, the gaseous and aqueous phases of ozone had a potent antibacterial activity that was effective against viruses, bacteria, fungi, and protozoa.[8] One of the effective methods for sterilizing prosthetics is to use ozone as a disinfectant for dentures.[9] Ozone also breaks down quickly into O2 and OH radicals in aqueous solutions.[10] These characteristics make ozone a crucial therapeutic agent for inflammatory and infectious diseases.

However, this study aimed to find out how exposure to gaseous ozone affected the heat-cured acrylic resin’s transverse and impact strengths.

  Materials And Methods 

The study protocol was approved by the ethical committee of University of Baghdad (Approval Number: 669222).

Sixty samples of heat-cured acrylic resin (Spofa dental, Jicin, Czech Republic) were made, the sample size was determined according to the ADA specification, No.12.,[11] and were polymerized by immersing the flask in a water bath (Roya dental lab, ShenZhen, China). The flask was placed in the water bath with cold water, and then gradually the temperature was increased up to 70°C within 30 minutes and was kept at 70°C during the next 30 minutes. After the period of 30 minutes, the temperature was again increased up to 100°C for 30 minutes, and kept as it was for further 30 minutes (total polymerization time is 2 h) according to manufactural instructions.

After the ending of the curing cycle, the flask was allowed to reach room temperature, before being de-flasked and having the acrylic samples removed. All acrylic specimens were polished to eliminate the excess materials.

The specimens were divided into three main groups:

Group I (as a control): 20 specimens immersed in distilled water.Group II (as a positive control): 20 specimens exposed to microwave radiation.Group III: 20 specimens exposed to 3 minutes of gaseous ozone.

Microwave exposure in which specimens were individually placed in a 200 mL beaker of distilled water at room temperature (21°C ± 1), after that in a microwave oven (Hisense, Qingdao, China) with an output of 650 W (2450 MHz) for 6 minutes, and then again immersed in distilled water. [12]

Gaseous ozone exposure in which the specimens were exposed to gaseous ozone with the use of an ozone generator machine (Okay energy equipment Co., Changsha, China) with an output of 3 g/h. The ozone generator was operated following the manufacturer’s specifications. Specimens were placed in a plastic jar with a plastic cover with one ozone gas injection port and distributed evenly throughout the jar, and one gas outlet for the release of the ozone gas. The ozone generator feeds dry compressed air as a feed gas. Ozonized air bypassed the specimens to supply a total airflow of ozone. The ozone gas/dry air mixture flowed into the jar for a certain 3 minutes, as determined by a pilot study. The ozone level inside the plastic jar was kept consistent during the time period by adjusting the outlet port.

Transverse strength testing machine (Guangdong Jian Qiao Co., Ltd., Dongguan, China) was used for the evaluation of transverse strength of acrylic specimens with dimensions of 65 × 10 × 2.5 mm in length, width, and thickness respectively. Also, impact strength testing machine (TMI. Inc., Pointe-Claire, Canada) was used for the evaluation of impact strength. The acrylic samples of the impact strength test were made with dimensions of 80 × 10 × 4 mm in length, width, and thickness respectively.

Statistical analysis was performed using a one-way analysis of variance (ANOVA) F test and the Tukey’s post hoc test using R software (R Foundation for Statistical Computing, Vienna, Austria).

  Results 

Transverse strength analysis showed a significant difference among groups (P < 0.001). Post hoc test revealed significant differences between all multiple groups (P < 0.001). Impact strength analysis results showed a non-significant difference among groups (P = 0.13) [Figure 1].

Figure 1 Violin plot depicted summary statistics and the density of data related to impact strength (kJ/m2) and transverse strength (MPa) test results.

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  Discussion 

Ozone is a form of oxygen, which has an effective role as an antibacterial and antioxidant agent. It is widely used in many areas of dentistry and has been established as an efficient, reliable, and consistent disinfection.[13]

The impact of ozonated water on dental plaque and oral bacteria was evaluated.[3] After 1 minute of exposure to flowing ozonated water (2 or 4 mg/L), few oral microorganisms and no viable Candida albicans were detected, indicating that the use of ozonated water may help lower the amount of C. albicans on denture bases. Gaseous ozone has a greater effect than ozonated water, as reported by Oizumi et al. in 1998.[14]

This research was designed to study the influence of gaseous ozone on transverse and impact strengths of heat-cure acrylic resin.

Transverse strength is the ability of a material to resist fracture when subjected to load from above. Transverse strength is influenced by compressive and tensile strengths, but it is used instead of these two strengths as it predicates the clinical situation.[15] Three-point bending is used to measure acrylic specimens’ transverse strength. This test measures the transverse strength of the material tested and determines the expected amount of distortion.[16]

In this study, transverse strength was significantly increased after gaseous ozone exposure, as compared with control group and microwave exposure group. These results agree with that of Vallittu et al.[17] who stated that PMMA might form complexes with ozonated water that might increase the degree of cross-linking with the corresponding increase in transverse strength. There was a significant increase after microwave radiation exposure, as compared with the control group, which can be explained by the fact that microwave disinfection results in residual monomer conversion into the polymer. Conversion of the residual monomer into polymer will improve the physical properties.[18] Other explanations may be the heat that occurs during microwave disinfection has promoted the diffusion of unreacted monomer molecules to the surface and their subsequent volatilization.[19] The increase in transverse strength after exposure to microwave irradiation agrees with Seo et al.,[20] and Polyzois et al.[21]

Acrylic dentures may become broken when suddenly dropped on a hard surface, which is related to the amount of energy adsorption that tends to break a material when subjected to sudden blow and this indicated the impact strength of the material.[22] A Charpy impact tester was used in this study.The result of this study revealed a non-significant decrease after gaseous ozone exposure as compared with the control group. This decrease may be the result of increasing surface roughness which causes very small surface defects, which under load will cause a fracture.[23] The impact strength test showed a non-significant decrease after microwave radiation exposure as compared with the control group, this decrease in impact strength may be a result of increasing monomer content, by the additional heat generated through microwave irradiation. Residual monomer acts as empty space, or a micro void, which, under load may cause a fracture.[19]

Reader must note to the fact that in vitro tests cannot predict exactly the clinical situation and more clinical studies is necessary to reach a definitive conclusion. Also, we must bear in mind that statistically non-significant results may be related to the low sample size.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors report no conflicts of interest.

 

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  [Figure 1]