Printer Friendly

Microhardness of heat cure acrylic resin after treatment with disinfectants.

Byline: Faiza Amin, Abdur Rehman and Muhammad Abbas

Abstract

Objective: To evaluate the effect of disinfectants and distilled water on the micro-hardness of heat cure acrylic resins.

Methods: The case-control study was conducted at Dr. Ishrat-ul-Ebad Khan Institute of Oral Health Sciences, Dow University of Health Sciences, and Nadirshaw Edulji Dinshaw University of Engineering and Technology, Karachi, from April to October 2011. Specimens were fabricated from heat cure acrylic resin material and they were divided into four equal groups. Group 1 was evaluated at baseline and was taken as the control group. Group 2 was immersed in distilled water for 20 minutes, Group 3 in1% sodium hypochlorite for 20 minutes, and Group 4 in 2% alkaline gluteraldehyde for 10 minutes. All specimens were polished, stored in distilled water for 24 hours prior to experiment. All the specimens were immersed twice daily for a total of 60 days after which they were tested for Vickers micro-hardness test. Statistical analysis was conducted with one-way analysis of variance and Tukey post hoc test (a=0.05).

Results: There were 72 specimens divided into four groups of 18(25%) each. Statistically significant differences were found among all groups (pless than 0.0001). The storage medium had an effect on the micro-hardness of heat cure acrylic resins. Group 4 showed the most reduction in the hardness value which was followed by Group 3.

Conclusions: The hardness of heat cure acrylic resin was affected by disinfectants.

Keywords: Heat cure acrylic resins, Vickers micro-hardness, Disinfectants.

Introduction

Polymethyl methacrylate is one of the most widely used materials in prosthetic dentistry. Since 1937 this material has been used for denture base manufacturing1,2 because of its low water sorption and solubility, lack of toxicity, simple manipulation technique, excellent aesthetics and reparability. Compression moulding technique is one of the conventional methods for curing resins.3-5 The technique is advantageous because of the lack of a need for any expensive or sophisticated equipment, its familiarity for technicians and dentists, and ease of processing. However, this technique has few disadvantages like it may give rise to inaccuracies in the fitting of the denture base and dimensional changes which result in high- processing stresses during polymerisation induced in the resin.6-8

It has been claimed that there is a statistically significant correlation between denture stomatitis and insufficient cleanliness of the dentures. To maintain the oral health of denture-wearers, the removal of biofilm is clinically necessary. This can be accomplished by decontaminating the prosthesis properly.9 A study indicated that to minimise the adherence and colonisation of micro- organisms on the denture base, denture polishing is essential.10 However, one study11 found that after denture polishing micro-organisms can be easily transmitted to patients.

Literature has shown that for reducing micro-organisms, a 0.5% sodium hypochlorite solution can be used as an effective denture cleanser12 to prevent oral candidiasis.13 Equally, it has been suggested that on maxillary dentures the number of Candida albican (C. albican)colony-forming units and bacterial plaque can be reduced by using alkaline peroxide tablets.14,15 Therefore, it is very important to choose the appropriate methods for cleaning of the denture to prevent microbial adhesion when the objective of the procedures is not to cause damage to the denture base.

The denture base hardness is used to evaluate the changes in the surface characteristics of acrylic resins and that result from denture cleansers,16 thermal cycling17 toothbrush/dentifrice abrasion18 and different systems of denture base polymerisation.19 Literature showed that different acrylic resins present significantly lower hardness after being submitted to 3.78% sodium perborate solutions of 1% sodium hypochlorite and 4% chlorhexidine gluconate solutions.20 Previous studies have shown that the hardness of a denture base is not significantly decreased by decontaminating in 4% chlorhexidine solutions or 1% sodium hypochlorite for 1 minute21 and in sodium perborate for 10 minutes.22

Conversely, the hardness of acrylic resins is reported to be changed by solutions of 4% chlorhexidine, 2% glutaraldehyde or 1% sodium hypochlorite.23 It is possible that due to cleaning and disinfecting treatments, surface hardness of acrylic resins can be decreased which will result in micro-organism adherence and formation of biofilm on the dentures.

Based on these considerations we planned the current study to assess the effect of the chemical disinfection on the surface hardness of acrylic resins.

Materials and Methods

The in vitro case-control study was conducted at Dr. Ishrat-ul-Ebad Khan Institute of Oral Health Sciences, Dow University of Health Sciences, and Nadirshaw Edulji Dinshaw (NED) University of Engineering and Technology,Karachi, from April to October 2011.Conventional (Vertex Rapid Simplified Holland) (Table-1) heat-polymerised acrylic resins were used to manufacture rectangular samples 13.0mm in length and 4.0mm in thickness. These dimensions were according to the American Society for Testing and Material standard D 256-O6a.24,25

A vertex rapid simplified resin with ratio of 1ml of liquid (monomer) and 2.3gm of powder (polymer) was manipulated according to manufacturer's recommendation. When it reached the dough stage, the resulting mass was inserted in stainless steel mould (Figure-1) and polymerised at 100C for 20 minutes according to manufacturer's instructions, using curing tank. After curing the mould, it was bench-cooled at room temperature for 30 minutes. Specimens were then taken out from mould and the excess margins were trimmed with tungsten carbide bur. Subsequently, the specimens were submitted to finishing and polishing with 320-, 400- and 600-silicon carbide paper. Finishing and polishing procedures were carried out for 8 seconds under a load of 20g. The specimens were then stored in water at room temperature for 24 hours.

They were divided into four equal groups. Group 1 was

Table-1: Material used.

Material###Type###Processing method###Manufacturer

Heat cure acrylic resins###PMMA###Heat cure polymerization 100C for###VertexTM Rapid Simplified

###20 min in the curing tank

Disinfectants###Hospital Based Disinfectants###1% Sodium Hypochlorite for 20 minutes 2%###UniversalTraders Chemical Supplies Pakistan.

###Alkaline Gluteraldehyde for 10 minutes

Table-2: Mean of micro-hardness at baseline (0 day) and 60 days of immersion in various groups.

Groups###Mean and Standard Deviation

Baseline (0 day) (Control)###19.950.20c

Distilled water###19.770.30c

1% Sodium Hypochlorite###12.3110.18b

2% Alkaline Gluteraldehyde###10.080.07a

evaluated at baseline and was taken as the control group. Group 2 was immersed in distilled water for 20 minutes, Group 3 in1% sodium hypochlorite for 20 minutes, and Group 4 in 2% alkaline gluteraldehyde for 10 minutes. This was done according to American Dental Association (ADA) specifications.

The specimens in the control group were measured at day 0. All the other specimens were placed in their respective containers filled with distilled water. After 24 hours the distilled water was discarded and the container was filled with their respective denture cleansers. The specimens were washed with distilled water and stored in distilled water. This was repeated twice a day for 60 days after which micro-hardness test was carried out by Vickers micro-hardness tester (Wolpert W Group micro Vickers hardness tester digital auto-turret model number 402MVD) (Figure-2). Specimens were placed in distilled water during storage.

Data analysis was performed using SPSS16. One-way analysis of variance (ANOVA) was used for a quantitative dependent variable by a single factor (independent) variable. To identify which of the mean differed significantly, Tuckey's Honestly significant difference (HSD) was used at 0.05 significance level.

Results

There were 72 specimens divided into four groups of 18(25%) each. Statistically significant differences were found among all groups (pless than 0.0001). The storage medium had an effect on the micro-hardness of heat cure acrylic resins. Group 4 showed the most reduction in the hardness value which was followed by Group 3 (Table-2).

Post Hoc analysis showed that when specimens were immersed in distilled water for 60 days and compared with the specimens at 0 day, the difference was not statistically significant (p=0.067). In Group 3, the difference was significant (pless than 0.0001), and the same was the case with Group 4 (pless than 0.0001).

Discussion

The study evaluated the hardness of denture base acrylic resin after an infection control protocol. The hypothesis that both disinfectants could not cause any adverse effects on the hardness of the denture base was rejected. The study investigated the effect of disinfectant solutions on the hardness of denture base resins after long-term storage in disinfectants and distilled water. The results demonstrated that specimens that were stored in 1% of sodium hypochlorite exhibited statistically significant differences in the surface hardness when compared with the specimens that were stored in the distilled water. No significant differences were found between the specimens at baseline (control) (0 day) and at 60 days of storage in distilled water. The results oppose those of a study26 in which disinfection with hypochlorite solution did not influence the hardness of the denture base material.

The results, however, are similar to a study27 which evaluated the hardness of denture teeth by immersing them into the disinfectant solution. In both the studies, surface hardness was higher at baseline (0 day) and decreased after immersion in water and solution. This might have been possible because of the presence of cross-linking agents in the materials. According to a study,28 the denture base resins acquire two valuable properties because of cross-linking agent. Solubility of the denture base to organic solvents is reduced. During stress, these cross-linking agents prevent the denture from crazing. In the present study, vertex rapid simplified heat cure acrylic resin was used and it also contained cross- linking agent so it can be assumed that because of the cross-linking of the acrylic resin, the surface hardness remained unaffected after immersing into the disinfectant solutions in both the studies.

The reason of similar results in both the studies might be due to the fact that the specimens were placed in water throughout the study period. This caused leaching of residual methyl methacrylate (MMA) content from the resins resulting in increased or unaffected hardness of the material.28

In the present study, when the specimens were treated with 1% sodium hypochlorite and 2% alkaline gluteraldehyde, there was significant decrease in the micro-hardness of the material when compared with the baseline and distilled water. However, contrasting results were obtained in a study27,28 which reported increased hardness after 7 days of immersion in 1% sodium hypochlorite and 4% chlorhexidine gluconate for 10 minutes. There might be slow leaching of residual monomer into the storage solutions, causing an increase in the hardness of acrylic resins. It should be emphasised that the increase in hardness values which were obtained in the present study were not significant and the increase was extremely small (less than 1 Vickers hardness number [VHN]) and not of any practical importance. In our study, the hardness values were higher at baseline compared to the hardness values after 60 days of immersion.21

Our results are similar to those of a study20 which showed that after immersion in 1% sodium hypochlorite, there was significant decrease in hardness value of heat cure acrylic resin. The slight difference in the results may be due to the fact that the studies used different brands of material which possesses different curing cycle and properties.

Immersion in disinfectants solution used in this study did not turn out to be a safe disinfection process for surface hardness of dentures. However, our study has limitations and it is not possible to extrapolate these results to other types of denture base resins having different compositions or different processing techniques. The effect of disinfectants and cleansers on other physical and chemical properties after long immersion period is also unknown in this study.

Conclusion

Immersion in sodium hypochlorite and alkaline gluteraldehyde produced significant changes on surface hardness of heat cure acrylic resins, while immersion in distilled water did not produce significant changes.

References

1. Kuhar M, Funduk N. Effects of polishing techniques on the surface roughness of acrylic denture base resins. J Prosthet Dent 2005; 93: 76-85.

2. Mese A. Effect of denture cleansers on the hardness of heat- or auto-cured acrylic- or silicone-based soft denture liners. Am J Dent 2007; 20: 411-5.

3. Oliveira LV, Mesquita MF, Henriques GE, Consani RL, Fragoso WS. Effect of polishing technique and brushing on surface roughness of acrylic resins. J Prosthodont 2008; 17: 308-11

4. Braun KO, Mello JA, Rached RN, Del BelCury AA. Surface texture and some properties of acrylic resins submitted to chemical polishing. J Oral Rehabil 2003; 30: 91-8

5. Rahal JS, Mesquita MF, Henriques GE, Nobilo MA. Surface roughness of acrylic resins submitted to mechanical and chemical polishing. J Oral Rehabil 2004; 31: 1075-9.

6. Lee SY, Lai YL, Hsu TS. Influence of polymerization conditions on monomer elution and microhardness of autopolymerized polymethyl methacrylate resin. Eur J Oral Sci 2002; 110: 179-83.

7. Kahn RC, Lancaster MV, Kate Jr W. The Microbiologic Cross- Contamination of Dental Prostheses. J Prosthet Den 1982; 47: 556-9.

8. Sousa-Porta, S. R., Lucena-Ferreira, S. C.,Silva, W. J. and Del BelCury, A. A." Evaluation Sodium Hypochlorite as a Denture Cleanser: A Clinical Study," Gerodontology 201; doi: 10.1111/ger.12104. [Epub ahead of print]

9. Haselden CA, Hobkirk JA, Pearson GJ, Davies EH. A Comparison between the Wear Resistances of Three Types of Denture Resin to Three Different Dentifrices. J Oral Rehabil 1998; 25: 335-9.

10. He XY, Neurman JH, Kari K, Rautemaa R, Samaranayake LP. In Vitro Adhesion of Candida Species to Denture Base Materials. Mycoses 2006; 49: 80-4.

11. Skupien JA, Valentini F, Boscato N, Pereira-Cenci T. Prevention and Treatment of Candida Colonization on Denture Liners: A Systematic Review. J Prosthet Den 2013; 110: 356-62.

12. Uludamar A, Ozkan YK, Kadir T, Ceyhan I. In Vivo Efficacy of Alkaline Peroxide Tablets and Mouthwashes on Candida Albicans in Patients with Denture Stomatitis, J Appl Oral Sci 2010; 18: 291-6.

13. Rossato MB, Unfer B, May LG, Braun KO. Analysis of the Effectiveness of Different Hygiene Procedures Used in Dental Prostheses. Oral Health Prev Dent 2011; 9: 221-7.

14. Kulak-Ozkan Y, Kazazoglu E, Arikan A. Oral Hygiene Habits, Denture Cleanliness, Presence of Yeasts and Stomatitis in Elderly People. J Oral Rehabil 2002; 29: 300-4.

15. Radford DR, Sweet SP, Challacombe SJ, Walter JD. Adherence of Candida Albicans to Denture-Base Materials with Different Surface Finishes. J Dent 1998; 26: 577-83.

16. Durkan R, Ayaz EA, Bagis B, Gurbuz A, Ozturk N, Korkmaz FM. Comparative effects of denture cleansers on physical properties of polyamide and polymethyl methacrylate base polymers. Dent Mater J 2013; 32: 367-75.

17. Goiato MC, Dos-Santos DM, Baptista GT, Moreno A, Andreotti AM, Dekon SF. Effect of Thermal Cycling and Disinfection on Microhardness of Acrylic Resin Denture Base. J Med Eng Technol 2013; 37: 203-7.

18. Richmond R, Macfarlane TV, Mccord JF. An Evaluation of the Surface Changes in PMMA Biomaterial Formulations as a Result of Toothbrush/Dentifrice Abrasion. Dent Mater 2004; 20: 124-32

19. Ali IL, Yunus N, Abu-Assan MI. Hardness, Flexural Strength, and Flexural Modulus Comparisons of Three Differently Cured Denture Base Systems. J Prosthodont 2008; 17: 545-9.

20. Neppelenbroek KH, Pavarina AC, Vergani CE, Giampaolo ET. Hardness of Heat-Polymerized Acrylic Resins after Disinfection and Long-Term Water Immersion. J Prosthet Dent 2005; 93: 171-6.

21. Azevedo A, Machado AL, Vergani CE, Giampaolo ET, Pavarina AC, Magnani R. Effect of Disinfectants on the Hardness and Roughness of Reline Acrylic Resins. J Prosthodont 2006; 15: 235-42.

22. Machado AL, Breeding LC, Vergani CE, Perez LE C. Hardness and Surface Roughness of Reline and Denture Base Acrylic Resins after Repeated Disinfection Procedures. J Prosthet Dent 2009; 102: 115-22.

23. Carvalho CF, Vanderlei AD, Marocho SM, Pereira SM, Nogueira L, Paes-Junior TJ. Effect of Disinfectant Solutions on a Denture Base Acrylic Resin. Acta Odontol Latinoam 2012; 25: 255-60.

24. Mohammed SH, Al-Jadi Alb M, Ajaal T. Using of HPLC analysis for evaluation of residual monomer content in denture base material and their effect on mechanical properties. J Phys Sci 2008; 19: 127-35.

25. American Society For Testing and Machine. ASTM D256 Test method for determining the Pendulum impact resistance.

26. Sartori EA, Schmidt CB, Mota EG, Hirakata LM, Shinkai RS. Cumulative effect of disinfection procedures on microhardness and tridimensional stability of a poly (methyl methacrylate) denture base resin. J Biomed Mater Res B Appl Biomater 2008; 86: 360-4.

27. Pavarina AC, Vergani CE, Machado AL, Giampaolo ET, Teraoka MT. The effect of disinfectant solutions on the hardness of acrylic resin denture teeth. J Oral Rehab 2003; 30:749-52.

28. O'brien WJ. Dental Materials and their Selection.2nd ed. Chicago, IL, USA: Quintessence Publishing, 1997; pp 79.
COPYRIGHT 2015 Asianet-Pakistan
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2015 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Publication:Journal of Pakistan Medical Association
Date:Aug 31, 2015
Words:2752
Previous Article:Asymmetric dimethylarginine in experimental breast cancer; action of Vitamin C and E.
Next Article:Status of oxidant, antioxidantand serum enzymes in thalassaemic children receiving multiple blood transfusions.
Topics:

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters