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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

Department of Prosthodontics, College of Dentistry, University of Baghdad, Iraq

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

Correspondence Address:
Baraa Hasan Kadhim
Department of Prosthodontics, Collage of Dentistry, University of Baghdad, Baghdad
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/denthyp.denthyp_139_22

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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

How to cite this URL:
Kadhim BH, Mahmood WS. Effect of Gaseous Ozone on Transverse and Impact Strengths of Heat Cure Acrylic Resin: An In Vitro Study. Dent Hypotheses [serial online] 2023 [cited 2023 May 30];14:13-5. Available from:

  Introduction Top

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 Top

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:
  1. Group I (as a control): 20 specimens immersed in distilled water.
  2. Group II (as a positive control): 20 specimens exposed to microwave radiation.
  3. 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 Top

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.

Click here to view

  Discussion Top

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


Conflicts of interest

The authors report no conflicts of interest.

  References Top

Mustafa M. Evaluation of shear bond strength of artificial teeth to heat cure acrylic and high impact heat cure acrylic using autoclave processing method. J Baghdad Coll Dentist 2014;26:71-7.  Back to cited text no. 1
Abdulrazzaq NS, Behroozibakhsh M, Jafarzadeh Kashi TS et al. Effects of incorporation of 2.5 and 5 wt% TiO2 nanotubes on fracture toughness, flexural strength, and microhardness of denture base poly methyl methacrylate (PMMA). J Adv Prosthodont 2018;10:113-21.  Back to cited text no. 2
Kiesow A, Sarembe S, Pizzey RL, Axe AS, Bradshaw DJ. Material compatibility and antimicrobial activity of consumer products commonly used to clean dentures. J Prosthet Dent 2016;115:189-198.e8.  Back to cited text no. 3
Sundus A, Shorouq M. Effect of Alum Disinfectants Solutions on Some Properties of Heat-Cured Acrylic Resin. Thesis. College of Dentistry, University of Baghdad; 2021.  Back to cited text no. 4
Nelson-Filho P, da Silva LA, Ds Silva RA, da Silva LL, Ferreira PD. Efficacy of microwaves and chlorhexidine on the disinfection of pacifiers and toothbrushes: an in vitro study. J Pediatr Dent 2011;33:10-3.  Back to cited text no. 5
Fouad M, Moudhaffer M. Effect of disinfection on some properties of heat-vulcanized maxillofacial silicone elastomer reinforced by nano silicone dioxide. J Bagh Coll Dent 2016;28:16-21.  Back to cited text no. 6
Fortes Carmen BB, Fabrício M, Leitune Vicente CB. Effect of 16 disinfection techniques on physical-mechanical properties of a 17 microwave-activated acrylic resin. Polímeros. 2018; 27:215-219.  Back to cited text no. 7
Ban Z, Leqaa M. Anti-microbial effect of different Time’s exposure of ozonized gas and ozonized water on periodontal pathogens (In Vitro Study). J Baghdad Coll Dent 2017;29:78-82.  Back to cited text no. 8
Tiwari S, Avinash A, Katiyar S, Iyer AA, Jain S. Dental applications of ozone therapy: A review of literature. Saudi J Dent Res 2017;8:105-111.  Back to cited text no. 9
Ban ZA, Liqaa MI. Ozonated gas and ozonated olive oil against anaerobic periodontal pathogens (an in vitro study). Thesis. College of dentistry, University of Baghdad; 2016.  Back to cited text no. 10
Swaney AC, Paffenbarger GC, Caul HJ, Sweeney WT. American Dental Association Specification No. 12 for denture base resin: second revision. J Am Dent Assoc 1953;46:54-66.  Back to cited text no. 11
Campanha NH, Pavarina AC, Vergani CE, Machado AL. Effect of microwave sterilization and water storage on the Vickers hardness of acrylic resin denture teeth. J Prosthet Dent. 2005;93:483-7.  Back to cited text no. 12
Hakan Ç, Uğur T, Recep U. What role does ozone play in preventing dental caries? An evidence-based review, Ozone. Sci Eng J 2015; 37: 563–7.  Back to cited text no. 13
Oizumi M, Suzuki T, Uchida M, Furuya J, Okamoto Y. In vitro testing of a denture cleaning method using ozone. J Med Dent Sci 1998;45: 135-9  Back to cited text no. 14
Powers JM, Wataha JC. Dental Materials: Properties and Manipulation. 36 10th ed. Elsevier Health Sciences; 2013 pp. 17–23.  Back to cited text no. 15
Powers JM, Sakaguchi RL. Craig’s Restorative Dental Materials. 12th. ed. Louis, Mosby Co. 2006: pp. 514–530.  Back to cited text no. 16
Vallittu PK, Miettinen V, Alakuijala P. Residual monomer content and its release into water from denture base materials. Dent Mater 1995;11:338-42.  Back to cited text no. 17
Vergani CE, Seo RS, Pavarina AC, dos Santos Nunes Reis JM. Flexural strength of auto polymerizing denture reline resins with microwave post polymerization treatment. J Prosthet Dent 2005;93:577-83.  Back to cited text no. 18
Nunes de Mello JA, Braun KO, Rached RN, Del Bel Cury AA. Reducing the negative effects of chemical polishing in acrylic resins by use of an additional cycle of polymerization. J Prosthet Dent 2003;89:598-602.  Back to cited text no. 19
Seo RS, Vergani CE, Giampaolo ET, Pavarina AC, Machado AL. Effect of a post-polymerization treatments on the flexural strength and Vickers hardness of reline and acrylic denture base resins. J Appl Oral Sci 2007;15:506-11.  Back to cited text no. 20
Polyzois GL, Tarantili PA, Frangou MJ, Andreopoulos AG. Fracture force, deflection at fracture, and toughness of repaired denture resin subjected to microwave polymerization or reinforced with wire or glass fiber. J Prosthet Dent 2001;86:613-9.  Back to cited text no. 21
Mccabe JF, Walls A. Applied Dental Materials. 9th ed. Blackwell Publishing Ltd; 2008: p. 76.  Back to cited text no. 22
Grumezescu V, Grumezescu A. Materials for Biomedical Engineering. Elsevier Health Sciences; 2019: pp. 297.  Back to cited text no. 23


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