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Effect of the microwave irradiation on disinfection of complete denture lined with soft resilient liner
Indian Journal of Dentistry 2012 JulyeSeptember Volume 3, Number 3; pp. 145e149
Original Article
Effect of the microwave irradiation on disinfection of complete denture lined with soft resilient linerq Ahmed Mahmoud Attwaa, Majed Abdulmajid Al-Akhalia,*, Azza Farahat Mtwalyb, Amal Rekaby Tahac
ABSTRACT Background: The fitting surface of denture base promotes accumulation of micro-organisms. The microwave irradiation is used for denture disinfection. It is important therefore to study the effect of different intensities and the exposure time of the microwave irradiation preventing or promoting the accumulation of micro-organisms. The objective of this study aimed to evaluate the effect of microwave irradiation on disinfection of complete denture lined with soft resilient liner. Method: Twenty one edentulous patients were selected from the outpatient clinic of prosthodontics Department, Faculty of Oral and Dental Medicine, Cairo University. Every patient had received upper and lower acrylic complete dentures lined with soft resilient liner which were constructed following the conventional technique. The disinfection of the dentures with microwave for the fitting surfaces of denture bases and mucosa beneath them were swabbed at insertion visit, one week, two weeks & three weeks after denture insertion. Microbial adhesion was determined by counting the colonies forming units (CFU) of the micro-organisms in the collected specimens. Data were tabulated, and statistically analyzed. Results: The number of adhering microorganism on denture lined with soft resilient liner was more than number of adhering microorganism to the mucosa. The three different watts used for denture disinfection were effective in decreasing the number of microorganism in both mucosal swabs and denture swabs. Conclusions: Increasing the watt intensity leads to decreasing the CFU. In mucosal swabs the decrease was non-significant. The adhesion of micro-organisms increases by time on mucosa and the denture base. Keywords: Complete denture, Relining, CFU (colony forming units), Microwave
INTRODUCTION Edentulism is considered a poor health outcome and may compromise the quality of life. The basic objectives of complete denture prosthodontics are the restoration of masticatory function, facial appearance and the maintenance of the patient’s health. The complete denture wearers may complain from masticatory problems, speech and denture hygiene problems.1 However, many epidemiological
studies of the edentulous population have shown that most patients with complete dentures have pathologic tissue changes, that require treatment. These changes have a little relation to a patient’s perception of the denture success, and/or the personal oral health status.2 Because of the friable nature of the supporting mucosa, areas of force concentration or misfit of the denture base may result in tissue trauma and, or sore spots. As a result of these conditions, patients frequently do not wear dentures
q Abstract of Master’s degree dissertation presented at the Prosthodontic Department, Faculty of Oral and Dental Medicine, Cairo University, Egypt. a Post Graduate Student, bAssistant Professor of Removable Prosthodontics, cProfessor of Removable Prosthodontics, Department of Prosthodontics, Faculty of Oral and Dental Medicine, Cairo University, Cairo, Other 002, Egypt. * Corresponding author. Tel.: þ20 1118640847, email: [email protected] Received: 13.12.2011; Accepted: 28.3.2012 Ó 2012 Indian Journal of Dentistry. All rights reserved.
doi: 10.1016/j.ijd.2012.03.006
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Indian Journal of Dentistry 2012 JulyeSeptember; Vol. 3, No. 3
because of the discomfort accompanies their use.3 With advancing age the oral mucosa becomes more permeable to noxious agents and more prone to mechanical damage. To alleviate the possibility of discomfort arising from the hard denture base, or the force transfer to oral mucosa, manufacturers have developed soft denture base liners. It has been suggested that the properties of the soft lining materials should be similar to the oral soft tissue that they are covering.4 The viscoelastic properties of the soft liners make them act as shock absorbers and distribute the stresses on the denture-bearing tissues. Moreover, their use gives more patient comfort during the treatment of the atrophic ridge, bone undercuts, bruxism and dentures opposing natural teeth. The adherence of micro-organisms to a surface not exposed to the ‘flushing’ action of fluids is a prerequisite to the colonization and development of pathogenesis and infection.5,6 Some authors have shown that the soft lining materials present a greater retention of candida albicans than the denture acrylic resin and the high values for surface roughness can also enhance adhesion/retention properties.5,7,8 Although some previous studies showed that the soft lining materials are suitable substrates for the microbial colonization, others reported that they inhibit the yeast growth.9,10 The oral deposits and micro-organisms that adhere to a dental appliance bring about several undesirable effects, as unpleasant and unaesthetic.11 Micro-organisms may also serve as reservoirs for disseminated infections with gastrointestinal and pleura-pulmonary involvement.12 The increase in number of patients requiring dentures and the growing awareness of the cross infection, highlights the importance of denture hygiene and denture disinfection. Disinfection of complete dentures has been for many years, and is still and will continue to be a vital subject for many investigators.13 Denture cleaning or disinfection can be carried out by two main approaches: chemical methods and mechanical methods or combination of both. Studies have shown that less than 60% of denture wearers use chemical cleansing products and that 60e90% use mechanical cleansing in association with some product, such as tooth paste, soap or water. Among those who use chemical products there is a preference for homemade products, this being easy to handle, cheap and effective methods that completely satisfy the users’ needs.14,15 Recently, microwave energy has proved to be an effective method to disinfect acrylic dentures as an adjunct to the treatment of oral candidiasis.16 In a preliminary study, acrylic resin specimens previously contaminated with individual suspensions of Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, and Bacillus subtilis showed consistent sterilization of all organisms after 6 min of irradiation at 650 W with the specimens immersed in water during sterilization process.17 Another study had shown that
Attwa et al.
Fig. 1 The finished denture after application of soft resilient liner.
dentures contaminated with a mixture of four aerobic bacteria and one fungus were sterilized after 10 min of microwave irradiation (720 W).18 Webb et al, 1998, indicated that microwaving may be a more effective method of denture sterilization than denture soaking in sodium hypochlorite.19 Neppelenbroek et al, 2003, have evaluated the effectiveness of microwave disinfection (6 min/650 W) of three hard chairside reline resins and showed consistent sterilization of four pathogenic micro-organisms.17
MATERIALS AND METHOD Tested materials: Used in the study namely, Maxillary removable complete denture, constructed from acrylic resin denture base (Acrostone 4008. Heat Cure Denture Base Material, England), which was lined with soft resilient lining material (Mollosil DETAX GmbH Co. KG Ettlingen/Germany).(Fig. 1). Patients: Twenty one edentulous patients were selected from the outpatient clinic of prosthodontics Department, Faculty of Oral and Dental Medicine, Cairo University.
Fig. 2 Palatal mucosal swab.
Effect of the microwave irradiation
Original Article
147
18.0Ò for Windows. Data were presented as mean and standard deviation (SD) values. Tukey’s post-hoc test was used for the pair-wise comparison between the means whenever the results of the ANOVA tests were significant. Repeated measures Analysis of Variance (ANOVA) test was used to study the changes by time within each group. The significance level was set at P 0.05.
RESULTS The results showed that before and after microwaving at 350 W for 5 min and 500 W for 3 min. Also, 650 W for 2 min throughout the study period (Tables 1e3).
Comparison between percentage reduction in CFU in the three studied groups
Fig. 3 Maxillary denture swab.
They were selected to be free from systemic diseases which might lead to increase in the microbial adhesions as diabetes mellitus, AIDS, Anemia. Smoker patients were excluded. Patients with no history of wearing denture. Only co-operative & motivated patients were chosen. Sampling: Swabs were collected as follows: 1. From the mucosa of the denture baring area, before denture insertion (Fig. 2). 2. From the fitting surfaces of denture base, as well as from mucosa beneath each (one, two, & three weeks after denture insertion) (Fig. 3). Sample processing: Samples were serially diluted to 101, 2 10 , and 103. 100 ml of each dilution were spread onto surface of Blood agar plate (Oxoid Ltd., Cambridge, UK). Bacterial counts in different samples were calculated (using plate counting method) by counting the colony forming units (CFUs) on Blood agar plates (Beta Lab., Cairo, Egypt). Statistical analysis: Statistical analysis was performed with (Predictive Analytics Software) PASW Statistics
The percentage reduction was calculated as: CFUðafterÞ CFUðbeforeÞ 100 CFUðbeforeÞ After one week & two and three weeks follow up periods: One-way ANOVA test was used and results are shown: disinfection with 650 Watt showed the highest statistically significant mean percentage reduction in CFU counts. Disinfection with 500 Watt had given lower percentage reduction. However, the least significant mean percentage reduction in CFU counts was recorded with 350 W disinfection.
DISCUSSION Generally speaking, the results of the preset study had emphasized the importance of disinfecting dental prosthesis and the upper complete denture in particular. The
Table 1 The effect of time on the bacterial counts (log10 values of CFU) in mucosal swabs after disinfection in each group. Period
Group I (350 W) Mean
Before insertion After insertion One week (Before disinfection) One week (After disinfection) Two weeks (Before disinfection) Two weeks (After disinfection) Three weeks (Before disinfection) Three weeks (After disinfection) P-value Standard deviation (SD) values. *: Significant at P 0.05.
5.91 5.93 5.94 5.92 5.94 5.91 5.93 5.91 0.674*
SD 0.40 0.22 0.23 0.22 0.23 0.24 0.22 0.22
Group II (500 W) Mean 5.93 5.94 5.96 5.90 5.92 5.88 5.93 5.90 0.575*
SD 0.37 0.23 0.25 0.23 0.24 0.25 0.22 0.24
Group III (650 W) Mean 5.92 5.95 5.96 5.90 5.92 5.86 5.93 5.85 0.575*
SD 0.39 0.21 0.25 0.24 0.25 0.27 0.25 0.27
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Attwa et al.
Table 2 The effect of time on the bacterial counts (log10 values of CFU) in denture swabs after disinfection in each group. Period
Group I (350 Watt) Mean
After insertion One week (Before disinfection) One week (After disinfection) Two weeks (Before disinfection) Two weeks (After disinfection) Three weeks (Before disinfection) Three weeks (After disinfection) P-value
d
6.00 6.25c 5.99d 6.39b 6.07d 6.58a 6.18c <0.001*
SD 0.18 0.15 0.20 0.13 0.11 0.10 0.14
Group II (500 Watt) Mean d
6.05 6.22c 5.86e 6.42b 6.04d 6.60a 6.11d 0.575
SD 0.15 0.12 0.16 0.16 0.15 0.11 0.18
Group III (650 Watt) Mean d
6.03 6.30c 5.85e 6.40b 5.88e 6.60a 5.80e 0.575
SD 0.13 0.17 0.15 0.18 0.14 0.12 0.17
Standard deviation (SD) values. *: Significant at P 0.05, Different letters are statistically significantly different.
emphasize the importance of disinfection. Moreover, microwave irradiation may be a potential treatment preventing cross contamination between the dental personnel and patients. The risk of re-infection of the palatal oral mucosa and denture surface seems to be reduced or delayed, but not completely eliminated. The efficacy of microwave seems to be associated with the time of exposure, the intensity of the microwave oven, and the type of microorganism colonizing the dentures.20 The lethal effect of microwave irradiation on the oral micro-organisms such as candida albicans suspensions may be due to the heat generated by the microwaves.21 Moreover, microwave irradiation may produce alterations on cell structural integrity, cell membrane permeability and cell metabolism, which resulted in cell death.22 The non-thermal effects of microwave could be considered as an interaction between the electromagnetic field created by the microwaves and the cell molecules, resulting in molecular, mechanical or selective heating mechanisms.23 The combination of lethal mechanisms described in the literature could explain the high susceptibility of micro-organisms present in the denture biofilms observed in the present study. In the present study, Table 3 The means, standard deviation (SD) values and results of paired t-test results for the comparison between bacterial counts (log10 values of CFU). Period One week Two weeks Three weeks
Site
Mean
SD
P-value
Mucosa Denture Mucosa Denture Mucosa Denture
6.46 6.57 6.49 6.60 6.58 6.66
0.17 0.01 0.15 0.01 0.14 0.01
0.012* <0.001* 0.007* 0.001* 0.001* 0.002*
*: Significant at P 0.05.
three different microwave watts and exposure times were used, 350 W for 5 min, 500 W for 3 min and 650 W for 2 min. The effectiveness of the previously mentioned methods was evaluated. The microbial counts on the complete dentures (CFU/ml) had decreased in comparison to the initial collection. However, when 500 W, 650 W was used there was a statistically significant decrease in the mean counts of micro-organisms. Those results indicated that the increase in microwave watt is associated with a more decrease in the number of micro-organisms. Although, when 350 W for 5 min and 500 W for 3 min were used to disinfect the denture, the decrease in bacterial count was lower in reduction than that occurred with 650 W disinfection. However, the efficacy of microwave disinfection seems to be associated with the time of exposure, the level of power of the microwave oven, and the type of microorganism colonizing the dentures. In addition, due to the high resistance of the biofilm micro-organisms, five and 3 min microwaving cycles were not sufficient to cause their inactivation and microbiological growth was observed in both selective and non-selective media. In the present study after one week, two and three weeks at 650 W showed the highest statistically significant mean percentage reduction in the CFU counts. Therefore, the findings of the present study for 2 min exposure to the microwave irradiation are consistent with authors demonstrated that disinfection of specimens contaminated with three bacterial species after 2 min exposure to microwave irradiation at 650 W.20 Goodson et al, 2003 evaluated clinically the effectiveness of 2 min microwave irradiation associated with a denture cleansing agent; they found that although the acrylic complete dentures were not sterilized, they were effectively decontaminated.24 On the other hand, Mima et al, 2008 verified that 2 min of microwaving at 650 W had promoted the sterilization of specimens contaminated with candida albicans.20
Effect of the microwave irradiation
CONCLUSION Increasing the Microwave watt intensity leads to decreasing the CFU in the relining denture fitting surface. The adhesion of micro-organisms increases by time on mucosa and the denture base. ACKNOWLEDGMENT I would like to thank all staff members of Microbiology department who participated in this work.
REFERENCES 1. Roessler DM. Complete denture success for patients and dentists. Int Dent J. 2003;53:340. 2. Bloem TJ, Razzog ME. An index for assessment of oral health in the edentulous population. Spec Care Dentist Assoc J. 1982;2(3):121e124. 3. Parr GR, Rueggeberg FA. In vitro hardness, water sorption and resin solubility of laboratory processed and autopolymerized long-term resilient denture liners over one year of water storage. J Prosthet Dent. 2002;88:139e144. 4. Hayakawa I, Hirano S, Kabayashi S, Nagao M, Masuhara E. The creep behavior of denture-supporting tissues and soft lining materials. Int J Prosthodont. 1994;7:339e347. 5. Verran J, Maryan C. Retention of Candida albicans on acrylic resin and silicone different surface topography. J Prosthet Dent. 1997;77:535e539. 6. Glass RT, Bullard JW, Hadley CS. Partial spectrum of microorganisms found in dentures and possible disease implications. J Am Osteopath Assoc. 2001;101:92e94. 7. Radford DR, Sweet SP, Challacombe SJ. Adherence of Candida albicans to denture-base materials with different surface finishes. J Prosthet Dent. 1998;26:577e583. 8. Zissis AJ, Polyzois GL, Yannikakis SA. Roughness of denture materials: a comparative study. Int J Prosthodont. 2000;13: 136e140. 9. Burns DR, Burns DA, DiPietro G, Gregory RL. Response of processed resilient liner to Candida albicans. J Prosthet Dent. 1987;57:507e512. 10. Nikawa H, Jin C, Hamada T. Interactions between thermal cycled resilient denture lining materials, salivary and serum pellicles and Candida albicans in vitro. Part I. Effects on fungal growth. J Oral Rehabil. 2000;27: 41e51.
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11. Hyde RJ, Feller RP, Sharon IM. Tongue brushing, dentifrice, and age effects on taste and smell. J Dent Res. 1981;60:1730e1734. 12. Gornitsky M, Paradis II, Landaverde G, Malo AM, Velly AM. A clinical and microbiological evaluation of denture cleansers for geriatric patients in long-term care institutions. J Can Dent Assoc. 2002;68:39e45. 13. Buergers R, Rosentritt M, Schneider Brachert W, Behr M, Handel G, Hahnel S. Efficacy of denture disinfection methods in controlling Candida albicans colonization in vitro. J Acta Odontol Scadin. 2008;66:174e180. 14. Veres EM, Wolfaardt JF, Hnizdo E. Denture cleansers: part Ia survey of material and methods employed by denture wearers. J Dent Assoc South Africa. 1985;40:591. 15. Arita M, Nagayoshi M, Fukuizumi T, et al. Microbicidal efficacy of ozonated water against Candida albicans adhering to acrylic denture plates. J Oral Microbiol Immunol. 2005;20:206e210. 16. Banting DW, Hill SA. Microwave disinfection of dentures for the treatment of oral candidiasis. Spec Care Dentist Assoc J. 2001;21(1):4e8. 17. Neppelenbroek KH, Pavarina AC, Spolidorio DM, Vergani CE, Mima EG, Machado AL. Effectiveness of microwave sterilization on three hard chair side relining resins. Int J Prosthodont. 2003;16:616e620. 18. Rohler DM, Bulard RA. Microwave sterilization. J Am Dent Assoc. 1985;110:194e198. 19. Webb BC, Thomas CJ, Harty DW. Effectiveness of two methods of denture sterilization. J Oral Rehabil. 1998;25:416e423. 20. Oliveira MEG, Pavarina AC, Neppelenbroek KH. Effect of different exposure times of microwave irradiation on the disinfection of a hard chair side reline resin. J Prosthodont. 2008;17(4):312e317. 21. Jeng DK, Kaczmarek KA, Woodworth AG, Balasky G. Mechanism of microwave sterilization in the dry state. Appl Environ Microbiol J. 1987;53:213e217. 22. Campanha NH, Pavarina AC, Brunetti IL, Vergani CE, Machado AL, Spolidorio DM. Candida albicans inactivation and cell membrane integrity damage by microwave irradiation. Mycoses, Diagn Ther Prophylaxis Fungal Dis. 2007;50(1):140e147. 23. Hiti K, Walochnik J, Faschinger C, Haller-Schober EM, Aspöck H. Microwave treatment of contact lens cases contaminated with acanthamoeba. Cornea J Cornea Extern Dis. 2001;20:467e470. 24. Goodson LB, Glass RT, Bullard JW, Conrad RS. A statistical comparison of denture sanitation using a commercially available denture cleaner with and without microwaving. Gen Dent J. 2003;51:148e151.
Original Article
Effect of the microwave irradiation on disinfection of complete denture lined with soft resilient linerq Ahmed Mahmoud Attwaa, Majed Abdulmajid Al-Akhalia,*, Azza Farahat Mtwalyb, Amal Rekaby Tahac
ABSTRACT Background: The fitting surface of denture base promotes accumulation of micro-organisms. The microwave irradiation is used for denture disinfection. It is important therefore to study the effect of different intensities and the exposure time of the microwave irradiation preventing or promoting the accumulation of micro-organisms. The objective of this study aimed to evaluate the effect of microwave irradiation on disinfection of complete denture lined with soft resilient liner. Method: Twenty one edentulous patients were selected from the outpatient clinic of prosthodontics Department, Faculty of Oral and Dental Medicine, Cairo University. Every patient had received upper and lower acrylic complete dentures lined with soft resilient liner which were constructed following the conventional technique. The disinfection of the dentures with microwave for the fitting surfaces of denture bases and mucosa beneath them were swabbed at insertion visit, one week, two weeks & three weeks after denture insertion. Microbial adhesion was determined by counting the colonies forming units (CFU) of the micro-organisms in the collected specimens. Data were tabulated, and statistically analyzed. Results: The number of adhering microorganism on denture lined with soft resilient liner was more than number of adhering microorganism to the mucosa. The three different watts used for denture disinfection were effective in decreasing the number of microorganism in both mucosal swabs and denture swabs. Conclusions: Increasing the watt intensity leads to decreasing the CFU. In mucosal swabs the decrease was non-significant. The adhesion of micro-organisms increases by time on mucosa and the denture base. Keywords: Complete denture, Relining, CFU (colony forming units), Microwave
INTRODUCTION Edentulism is considered a poor health outcome and may compromise the quality of life. The basic objectives of complete denture prosthodontics are the restoration of masticatory function, facial appearance and the maintenance of the patient’s health. The complete denture wearers may complain from masticatory problems, speech and denture hygiene problems.1 However, many epidemiological
studies of the edentulous population have shown that most patients with complete dentures have pathologic tissue changes, that require treatment. These changes have a little relation to a patient’s perception of the denture success, and/or the personal oral health status.2 Because of the friable nature of the supporting mucosa, areas of force concentration or misfit of the denture base may result in tissue trauma and, or sore spots. As a result of these conditions, patients frequently do not wear dentures
q Abstract of Master’s degree dissertation presented at the Prosthodontic Department, Faculty of Oral and Dental Medicine, Cairo University, Egypt. a Post Graduate Student, bAssistant Professor of Removable Prosthodontics, cProfessor of Removable Prosthodontics, Department of Prosthodontics, Faculty of Oral and Dental Medicine, Cairo University, Cairo, Other 002, Egypt. * Corresponding author. Tel.: þ20 1118640847, email: [email protected] Received: 13.12.2011; Accepted: 28.3.2012 Ó 2012 Indian Journal of Dentistry. All rights reserved.
doi: 10.1016/j.ijd.2012.03.006
146
Indian Journal of Dentistry 2012 JulyeSeptember; Vol. 3, No. 3
because of the discomfort accompanies their use.3 With advancing age the oral mucosa becomes more permeable to noxious agents and more prone to mechanical damage. To alleviate the possibility of discomfort arising from the hard denture base, or the force transfer to oral mucosa, manufacturers have developed soft denture base liners. It has been suggested that the properties of the soft lining materials should be similar to the oral soft tissue that they are covering.4 The viscoelastic properties of the soft liners make them act as shock absorbers and distribute the stresses on the denture-bearing tissues. Moreover, their use gives more patient comfort during the treatment of the atrophic ridge, bone undercuts, bruxism and dentures opposing natural teeth. The adherence of micro-organisms to a surface not exposed to the ‘flushing’ action of fluids is a prerequisite to the colonization and development of pathogenesis and infection.5,6 Some authors have shown that the soft lining materials present a greater retention of candida albicans than the denture acrylic resin and the high values for surface roughness can also enhance adhesion/retention properties.5,7,8 Although some previous studies showed that the soft lining materials are suitable substrates for the microbial colonization, others reported that they inhibit the yeast growth.9,10 The oral deposits and micro-organisms that adhere to a dental appliance bring about several undesirable effects, as unpleasant and unaesthetic.11 Micro-organisms may also serve as reservoirs for disseminated infections with gastrointestinal and pleura-pulmonary involvement.12 The increase in number of patients requiring dentures and the growing awareness of the cross infection, highlights the importance of denture hygiene and denture disinfection. Disinfection of complete dentures has been for many years, and is still and will continue to be a vital subject for many investigators.13 Denture cleaning or disinfection can be carried out by two main approaches: chemical methods and mechanical methods or combination of both. Studies have shown that less than 60% of denture wearers use chemical cleansing products and that 60e90% use mechanical cleansing in association with some product, such as tooth paste, soap or water. Among those who use chemical products there is a preference for homemade products, this being easy to handle, cheap and effective methods that completely satisfy the users’ needs.14,15 Recently, microwave energy has proved to be an effective method to disinfect acrylic dentures as an adjunct to the treatment of oral candidiasis.16 In a preliminary study, acrylic resin specimens previously contaminated with individual suspensions of Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, and Bacillus subtilis showed consistent sterilization of all organisms after 6 min of irradiation at 650 W with the specimens immersed in water during sterilization process.17 Another study had shown that
Attwa et al.
Fig. 1 The finished denture after application of soft resilient liner.
dentures contaminated with a mixture of four aerobic bacteria and one fungus were sterilized after 10 min of microwave irradiation (720 W).18 Webb et al, 1998, indicated that microwaving may be a more effective method of denture sterilization than denture soaking in sodium hypochlorite.19 Neppelenbroek et al, 2003, have evaluated the effectiveness of microwave disinfection (6 min/650 W) of three hard chairside reline resins and showed consistent sterilization of four pathogenic micro-organisms.17
MATERIALS AND METHOD Tested materials: Used in the study namely, Maxillary removable complete denture, constructed from acrylic resin denture base (Acrostone 4008. Heat Cure Denture Base Material, England), which was lined with soft resilient lining material (Mollosil DETAX GmbH Co. KG Ettlingen/Germany).(Fig. 1). Patients: Twenty one edentulous patients were selected from the outpatient clinic of prosthodontics Department, Faculty of Oral and Dental Medicine, Cairo University.
Fig. 2 Palatal mucosal swab.
Effect of the microwave irradiation
Original Article
147
18.0Ò for Windows. Data were presented as mean and standard deviation (SD) values. Tukey’s post-hoc test was used for the pair-wise comparison between the means whenever the results of the ANOVA tests were significant. Repeated measures Analysis of Variance (ANOVA) test was used to study the changes by time within each group. The significance level was set at P 0.05.
RESULTS The results showed that before and after microwaving at 350 W for 5 min and 500 W for 3 min. Also, 650 W for 2 min throughout the study period (Tables 1e3).
Comparison between percentage reduction in CFU in the three studied groups
Fig. 3 Maxillary denture swab.
They were selected to be free from systemic diseases which might lead to increase in the microbial adhesions as diabetes mellitus, AIDS, Anemia. Smoker patients were excluded. Patients with no history of wearing denture. Only co-operative & motivated patients were chosen. Sampling: Swabs were collected as follows: 1. From the mucosa of the denture baring area, before denture insertion (Fig. 2). 2. From the fitting surfaces of denture base, as well as from mucosa beneath each (one, two, & three weeks after denture insertion) (Fig. 3). Sample processing: Samples were serially diluted to 101, 2 10 , and 103. 100 ml of each dilution were spread onto surface of Blood agar plate (Oxoid Ltd., Cambridge, UK). Bacterial counts in different samples were calculated (using plate counting method) by counting the colony forming units (CFUs) on Blood agar plates (Beta Lab., Cairo, Egypt). Statistical analysis: Statistical analysis was performed with (Predictive Analytics Software) PASW Statistics
The percentage reduction was calculated as: CFUðafterÞ CFUðbeforeÞ 100 CFUðbeforeÞ After one week & two and three weeks follow up periods: One-way ANOVA test was used and results are shown: disinfection with 650 Watt showed the highest statistically significant mean percentage reduction in CFU counts. Disinfection with 500 Watt had given lower percentage reduction. However, the least significant mean percentage reduction in CFU counts was recorded with 350 W disinfection.
DISCUSSION Generally speaking, the results of the preset study had emphasized the importance of disinfecting dental prosthesis and the upper complete denture in particular. The
Table 1 The effect of time on the bacterial counts (log10 values of CFU) in mucosal swabs after disinfection in each group. Period
Group I (350 W) Mean
Before insertion After insertion One week (Before disinfection) One week (After disinfection) Two weeks (Before disinfection) Two weeks (After disinfection) Three weeks (Before disinfection) Three weeks (After disinfection) P-value Standard deviation (SD) values. *: Significant at P 0.05.
5.91 5.93 5.94 5.92 5.94 5.91 5.93 5.91 0.674*
SD 0.40 0.22 0.23 0.22 0.23 0.24 0.22 0.22
Group II (500 W) Mean 5.93 5.94 5.96 5.90 5.92 5.88 5.93 5.90 0.575*
SD 0.37 0.23 0.25 0.23 0.24 0.25 0.22 0.24
Group III (650 W) Mean 5.92 5.95 5.96 5.90 5.92 5.86 5.93 5.85 0.575*
SD 0.39 0.21 0.25 0.24 0.25 0.27 0.25 0.27
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Table 2 The effect of time on the bacterial counts (log10 values of CFU) in denture swabs after disinfection in each group. Period
Group I (350 Watt) Mean
After insertion One week (Before disinfection) One week (After disinfection) Two weeks (Before disinfection) Two weeks (After disinfection) Three weeks (Before disinfection) Three weeks (After disinfection) P-value
d
6.00 6.25c 5.99d 6.39b 6.07d 6.58a 6.18c <0.001*
SD 0.18 0.15 0.20 0.13 0.11 0.10 0.14
Group II (500 Watt) Mean d
6.05 6.22c 5.86e 6.42b 6.04d 6.60a 6.11d 0.575
SD 0.15 0.12 0.16 0.16 0.15 0.11 0.18
Group III (650 Watt) Mean d
6.03 6.30c 5.85e 6.40b 5.88e 6.60a 5.80e 0.575
SD 0.13 0.17 0.15 0.18 0.14 0.12 0.17
Standard deviation (SD) values. *: Significant at P 0.05, Different letters are statistically significantly different.
emphasize the importance of disinfection. Moreover, microwave irradiation may be a potential treatment preventing cross contamination between the dental personnel and patients. The risk of re-infection of the palatal oral mucosa and denture surface seems to be reduced or delayed, but not completely eliminated. The efficacy of microwave seems to be associated with the time of exposure, the intensity of the microwave oven, and the type of microorganism colonizing the dentures.20 The lethal effect of microwave irradiation on the oral micro-organisms such as candida albicans suspensions may be due to the heat generated by the microwaves.21 Moreover, microwave irradiation may produce alterations on cell structural integrity, cell membrane permeability and cell metabolism, which resulted in cell death.22 The non-thermal effects of microwave could be considered as an interaction between the electromagnetic field created by the microwaves and the cell molecules, resulting in molecular, mechanical or selective heating mechanisms.23 The combination of lethal mechanisms described in the literature could explain the high susceptibility of micro-organisms present in the denture biofilms observed in the present study. In the present study, Table 3 The means, standard deviation (SD) values and results of paired t-test results for the comparison between bacterial counts (log10 values of CFU). Period One week Two weeks Three weeks
Site
Mean
SD
P-value
Mucosa Denture Mucosa Denture Mucosa Denture
6.46 6.57 6.49 6.60 6.58 6.66
0.17 0.01 0.15 0.01 0.14 0.01
0.012* <0.001* 0.007* 0.001* 0.001* 0.002*
*: Significant at P 0.05.
three different microwave watts and exposure times were used, 350 W for 5 min, 500 W for 3 min and 650 W for 2 min. The effectiveness of the previously mentioned methods was evaluated. The microbial counts on the complete dentures (CFU/ml) had decreased in comparison to the initial collection. However, when 500 W, 650 W was used there was a statistically significant decrease in the mean counts of micro-organisms. Those results indicated that the increase in microwave watt is associated with a more decrease in the number of micro-organisms. Although, when 350 W for 5 min and 500 W for 3 min were used to disinfect the denture, the decrease in bacterial count was lower in reduction than that occurred with 650 W disinfection. However, the efficacy of microwave disinfection seems to be associated with the time of exposure, the level of power of the microwave oven, and the type of microorganism colonizing the dentures. In addition, due to the high resistance of the biofilm micro-organisms, five and 3 min microwaving cycles were not sufficient to cause their inactivation and microbiological growth was observed in both selective and non-selective media. In the present study after one week, two and three weeks at 650 W showed the highest statistically significant mean percentage reduction in the CFU counts. Therefore, the findings of the present study for 2 min exposure to the microwave irradiation are consistent with authors demonstrated that disinfection of specimens contaminated with three bacterial species after 2 min exposure to microwave irradiation at 650 W.20 Goodson et al, 2003 evaluated clinically the effectiveness of 2 min microwave irradiation associated with a denture cleansing agent; they found that although the acrylic complete dentures were not sterilized, they were effectively decontaminated.24 On the other hand, Mima et al, 2008 verified that 2 min of microwaving at 650 W had promoted the sterilization of specimens contaminated with candida albicans.20
Effect of the microwave irradiation
CONCLUSION Increasing the Microwave watt intensity leads to decreasing the CFU in the relining denture fitting surface. The adhesion of micro-organisms increases by time on mucosa and the denture base. ACKNOWLEDGMENT I would like to thank all staff members of Microbiology department who participated in this work.
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