Examination of denture-cleaning methods based on the quantity of microorganisms adhering to a denture

Transcription

1 Original article Examination of denture-cleaning methods based on the quantity of microorganisms adhering to a denture Yasuhiro Nishi 1, Katsura Seto 1, Yuuji Kamashita 2, Chiaki Take 3, Asutsugu Kurono 3 and Eiichi Nagaoka 1 1 Department of Oral and Maxillofacial Prosthodontics, Field of Oral and Maxillofacial Rehabilitation, Advanced Therapeutic Course, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan; 2 Denture Prosthodontic Restoration, Advanced Dentistry Center, Kagoshima University Medical and Dental Hospital, Kagoshima, Japan; 3 Geriatric Health Service Facility Aitoyuinomachi, Kagoshima, Japan doi: /j x Examination of denture-cleaning methods based on the quantity of microorganisms adhering to a denture Objectives: To investigate effective denture-cleaning methods, we examined the relationships between the quantity of microorganisms adhering to dentures and the use of a denture brush and the frequency of use of a denture cleanser. Subjects and Methods: Denture plaque was collected from the mucosal surface of the examined dentures, which were 142 and 80 upper and lower complete dentures, respectively, worn by 96 outpatients (mean age: 71.9 years) of a university hospital and 41 nursing home residents (mean age: 84.8 years). The collected microorganisms were counted in terms of isolated representative colonies that were cultured and identified using standard methods. The use of a denture brush, the frequency of use, and the type and soaking time of denture cleansers as denture-cleaning methods were surveyed. Results: The quantity of microorganisms was significantly lower in dentures of denture brush users than in those of non-users in the outpatients (p < 0.01, Mann Whitney U test). The quantity of microorganisms was significantly lower in the dentures of outpatients who used a denture cleanser daily or 3 4 times a week than in those who used one once or less per month and in the dentures of nursing home residents who used one daily than in those who used one at other frequencies (p < 0.05, Kruskal Wallis test, followed by Dunn s Multiple Comparison test). Conclusion: Within the limitations of this study, it was concluded that the use of a denture brush and daily use of denture cleanser should be recommended to complete dentures wearers as denture-cleaning methods that effectively reduce the quantity of microorganisms adhering to dentures. Keywords: denture-cleaning method, denture brush, denture cleanser, microorganism. Accepted 8 September 2010 Introduction The association of oral microorganisms with various systemic diseases, such as aspiration pneumonia, endocarditis and diabetes, has been reported 1 4. In addition, oral care has been reported to lead to the maintenance of and improvement in the quality of life of elderly persons and those who require nursing care by decreasing fever and preventing aspiration pneumonia and influenza infection Because Japan has already reached the state of a super-ageing society beyond an aged society, with the population ageing rate reaching 22.8% in , it is likely that elderly persons using dentures are increasing in number. The purpose of denture cleaning is to remove plaque adhering to the denture to eliminate the cause of denture stomatitis and reduce microorganisms on dentures 13,14, which have been reported to act as a reservoir of oral microorganisms e259

2 e260 Y. Nishi et al. involved in systemic diseases To prevent systemic diseases in the elderly, denture cleaning is as important as oral cleaning 3. Denture-cleaning methods include mechanical and chemical cleaning. Mechanical cleaning involves the removal of plaque using a toothbrush, various brushes exclusively used for dentures, and ultrasonic cleaning, and chemical cleaning removes and kills microorganisms using drugs, such as a denture cleanser. Although combinations of these methods are reportedly effective 14,15,18,19, it is unclear which cleaning method, such as the brush type and method of using a denture cleanser, is effective. Generally, both denture brushes and toothbrushes are used in mechanical denture cleaning by brushing, but an investigation of which kind of brush is effective is insufficient. In chemical denture cleaning, the most effective frequency of the use of a denture cleanser is unclear. We previously carried out questionnaire surveys concerning denture cleaning in 807 denture users and 807 dental care workers. Among the denture users, cleaning was investigated at the Denture Prosthodontic Restoration Unit of our university hospital, general dental clinics and special nursing care homes for the elderly 20, in which 23.3% of the subjects used a denture brush, which was lower than the proportion of toothbrush users (70.0%); a denture cleanser was used by 71.3%, a relatively high rate, and the frequency of its use was daily in 44.4%, 2 3 times a week in 26.5% and once a week in 18.0%. Among the dental care workers, the instructions given on the use of a denture cleanser were surveyed among dentists and dental hygienists at our university hospital and general dental clinics, in which the instructed frequency of cleaning with a denture cleanser was 2 3 times a week by 36.7% of the dental care workers, once per week by 24.0%, and daily by 19.1% 21. These surveys indicated a divergence between the use of denture cleansers by the denture users and the instructions given by the dental care workers, and this may have been as a result of a lack of evidence for the effectiveness of the use of a denture brush and the optimal frequency of use of a denture cleanser as denture plaque-removing methods. The purpose of this study was to investigate the relationships between the use of a denture brush, the frequency of use of a denture cleanser and the removal of denture plaque in outpatients at our university hospital and residents of a geriatric health service facility. Our hypothesis was that the quantity of microorganisms adhering to dentures is reduced by the use of a denture brush and higher frequency of use of a denture cleanser. Subjects and methods The denture-cleaning method was surveyed by interviewing denture users. Microorganisms adhering to their dentures were identified and quantified, and the relationship with the cleaning methods was investigated. Subjects The subjects were oral-disease-free users of complete upper and/or lower dentures who were satisfied with and cleaned their dentures by themselves. Forty-nine men and 47 women outpatients (96 in total) at the Denture Prosthodontic Restoration Unit of Kagoshima University Medical and Dental Hospital (outpatients) and 15 men and 26 women residents (41 in total) of a geriatric health service facility (nursing home residents) agreed to participate in this study. The residents of the geriatric health service facility required rehabilitation and care to return home. The mean ages of the outpatients and nursing home residents were 71.9 and 84.8 years, respectively. This study was explained to the subjects using an explanatory document approved by the Clinical Study Ethics Committee of Kagoshima University Hospital (approval number: 18 89) and written consent was obtained. The examined dentures for sampling of microorganisms numbered 83 upper and 59 lower dentures (142 dentures in total) worn by the outpatients and 41 upper and 39 lower dentures (80 dentures in total) worn by the nursing home residents. Survey of cleaning methods In terms of denture-cleaning methods employed by the subjects, the use of a denture brush, the frequency of use, the product type and soaking time of denture cleansers were surveyed by interview, following a questionnaire prepared beforehand. The age and gender of subjects were also surveyed. In the nursing home residents, denture cleansers actually used were checked, and the subjects were interviewed regarding how they cleaned their dentures, which was confirmed by caregivers. Identification and quantification of microorganisms To collect denture plaque, dentures taken out of the mouth were lightly rinsed with running water to remove saliva and lightly air-dried. Denture plaque was collected using a sterile swab (Fukifuki

3 Examination of denture-cleaning methods e261 check II Ò, Eiken Chemical, Tochigi, Japan). A sterile swab was applied twice to the mucosal surface of the right lateral half of the test denture. The microorganisms were identified and quantified by standard culture methods at an independent laboratory. The target microorganisms for culture were causative bacteria of endocarditis, opportunistic infections and aspiration pneumonia 19. General bacteria were cultured on sheep blood and chocolate agar media, intestinal bacteria were cultured on Drigalski lactose agar medium, and fungi were cultured on CHROM agar Candida medium under aerobic conditions at 37 C for 48 h and then identified and quantified. Statistical analysis The chi-square test was used to compare the cleaning methods and detection rates of microorganisms between the facilities. Correlation between the quantity of microorganisms adhering to the Table 1 Use of a denture brush at each facility. The number of dentures Use Non-use Outpatients 89 (62.7%) 53 (37.3%) Nursing home residents 26 (32.5%) 54 (67.5%) (v 2 test: v 2 = , p < ). dentures and each surveyed item was determined with the Spearman rank correlation coefficient. In addition, comparisons between subgroups of the surveyed items were carried out by employing the Mann Whitney U test or the Kruskal Wallis test with Dunn s Multiple Comparisons test. Statistical analysis was performed using a statistical analysis application (PASW 18; SPSS Inc., Chicago, IL, USA). A p level of 0.05 was considered significant. Results Cleaning methods The numbers of dentures according to the use or non-use of a denture brush in the outpatients and the nursing home residents are shown in Table 1. The rate of usage of a denture brush was lower in the nursing home residents, showing a significant difference between the groups. Table 2 shows the numbers of dentures according to the frequency of use of a denture cleanser in the outpatients and the nursing home residents. There is a significant difference in the frequency of use between the two groups. The numbers of dentures according to the product type of denture cleansers are shown in Table 3. The nursing home residents used only two alkaline peroxide effervescent denture cleansers, Enzymecontaining Polident Ò (GlaxoSmithKline Co. Ltd., Tokyo, Japan) and Toughdent Ò (Kobayashi Pharmaceutical Co. Ltd., Osaka, Japan). Many Table 2 Frequency of use of denture cleanser at each facility. The number of dentures Daily 5 6 times a week 3 4 times a week 1 2 times a week Once or less per month Outpatients 61(42.9%) 3 (2.1%) 21 (14.8%) 34 (23.9%) 23 (16.2%) Nursing home residents 34 (42.5%) 0 (0%) 0 (0%) 17 (21.3%) 29 (36.2%) (v 2 test: v 2 = , p = ). Table 3 Product type of denture cleanser used at each facility. The number of dentures Po To Pi Others Unknown Outpatients 100 (78.7%) 8 (6.3%) 3 (2.4%) 7 (5.5%) 9 (7.1%) Nursing home 33 (64.7%) 18 (35.3%) 0 (0%) 0 (0%) 0 (0%) residents Po, Enzyme-containing PolidentÒ ; To, ToughdentÒ ; Pi, PikaÒ (ROHTO Pharmaceutical Co. Ltd., Osaka, Japan); others, cleansers except for Po, To, and Pi; unknown, cleansers that could not be specified. (v 2 test: v 2 = , p < ).

4 e262 Y. Nishi et al. outpatients used Enzyme-containing Polident Ò, but a small number of denture cleansers containing organic acid, peroxide, titanium dioxide and silver inorganic antibacterial agent were used, as shown in the section of Others of Table 3. Regarding the soaking time of denture cleansers, most of the outpatients and the nursing home residents removed dentures at bedtime and kept them in a cleanser (Table 4). Detection of microorganism species The detection rates of target microorganism species in the outpatients and the nursing home residents are shown in Table 5. Streptococcus spp., Neisseria spp. and Candida spp. were frequently detected in Table 4 Soaking time of denture cleanser at each facility. The number of dentures All night Less than 30 min Outpatients 121 (95.3%) 6 (4.7%) Nursing home 48 (94.1%) 3 (5.9%) residents (v 2 test: v 2 = , p = 0.750) the collected denture plaque. In comparison with the four most frequently detected species between the outpatients and nursing home residents, the detection rates of Streptococcus spp. and Staphylococcus spp. were not significantly different (v 2 = 0.670, p = , v 2 = 2.698, p = , respectively), whereas the detection rate of Neisseria spp. was significantly higher in the outpatients than in the nursing home residents (v 2 = 7.838, p = ) and that of Candida spp. was significantly higher in the nursing home residents than in the outpatients (v 2 = 7.872, p = ). Relationship between the quantity of microorganisms adhering to dentures and cleaning methods Correlation between the quantity of microorganisms and each surveyed item. (Table 6) In terms of denturecleaning methods employed by the subjects, the use or non-use of a denture brush and the frequency of use of a denture cleanser were significantly correlated with the quantity of microorganisms in the outpatients, but only the frequency of use of a denture cleanser was significantly correlated in the nursing home residents. However, these correlation coefficients were not high. No significant correlation was noted between the quantity of microorganisms and the product type and soaking time of denture cleansers in both outpatients and nursing home residents. Table 5 Detection rates of microorganism species adhering to dentures at each facility. Outpatients Nursing home residents Number of detections Detection rate (%) Number of detections Detection rate (%) v 2 test Streptococcus spp ns Neisseria spp * Candida spp * Staphylococcus spp ns Bacillus spp Acinetobacter spp Enterobacter spp Pseudomonas spp Chryseobacterium indologenes spp Enterobactor cloacae spp Serratia spp Citrobacter freundii spp Klebsiella pneumoniae spp Serratia liquefaciens spp Nonfermenting Gram-negative Bacillus spp Pseudomonas aeruginosa spp *Statistically significant difference in the microorganism detection rate between two facilities (p < 0.01). ns: Not statistically significant.

5 Examination of denture-cleaning methods e263 Table 6 Correlation between the quantity of microorganisms adhering to dentures and each surveyed item at each facility group. Outpatients Nursing home residents Items Correlation coefficient p-value Correlation coefficient p-value Age * Gender ) ) * Use or non-use of a denture brush ** Product type of denture cleanser ) Soaking time of denture cleanser Frequency of denture cleanser use ** ** *Statistically significant difference (p < 0.05). **Statistically significant difference (p < 0.01). Figure 1 Quantity of microorganisms by denture brush use **p < 0.01 (Mann Whitney U test). In the nursing home residents, increase in age significantly and weakly correlated with increase in the quantity of microorganisms. Moreover, gender significantly correlated with the quantity of microorganisms, and the quantity of microorganisms in dentures worn by women was significantly lower than in those worn by men (p = 0.014, Mann Whitney U test). Relationship with the use or non-use of a denture brush. Regarding the quantity of microorganisms according to the use of a denture brush, the quantity was significantly lower in dentures cleaned with denture brush than in those cleaned without a denture brush in the outpatients (p < 0.01, Fig. 1), but no significant difference was noted in the quantity of microorganisms between nursing home residents who used a denture brush and those who did not use a denture brush. The quantity of microorganisms in dentures cleaned with a denture brush was significantly lower in the outpatients than in the nursing home residents (p < 0.01, Fig. 1), but no significant difference was noted when no denture brush was used. Relationship with the use of a denture cleanser. A significant difference in the quantity of microorganisms associated with the frequency of use of a denture cleanser was noted in both outpatients and nursing home residents (p = , p = 0.006, respectively, Kruskal Wallis test). The quantity of microorganisms on dentures cleaned Figure 2 Quantity of microorganisms by the frequency of denture cleanser use **p < 0.01 (Dunn s multiple comparison test) *p < 0.05 (Dunn s multiple comparison test).

6 e264 Y. Nishi et al. daily or 3 4 times a week with a denture cleanser in outpatients was significantly lower than that in dentures cleaned using a cleanser once or less per week (p < 0.01, Fig. 2). The quantity of microorganisms on dentures cleaned daily with a denture cleanser in nursing home residents was significantly lower than that in dentures cleaned using a cleanser 1 2 times or less per week (p < 0.05, Fig. 2). The quantity of microorganisms on dentures cleaned with a denture cleanser 5 6 or 3 4 times a week was as low as that on dentures cleaned daily with a denture cleanser in the outpatients, but no nursing home resident cleaned dentures with a denture cleanser 5 6 times or 3 4 times a week. There was no significant difference as determined by the Mann Whitney U test or the Kruskal Wallis test in the quantity of microorganisms associated with the product type and soaking time of denture cleansers in both outpatients and nursing home residents (type: outpatients, p = 0.127; nursing home residents, p = 0.055; soaking time: outpatients, p = 0.968; nursing home residents, p = 0.240). Discussion In vitro 22,23 and in vivo 19 studies on the effects of denture cleansers, the relationship between the surface roughness and cleaning effect 24, effect of combination with ultrasonic cleaning 25 and cleaning effect of a novel cleanser 26,27 have so far been performed, but no study has investigated the frequency of use of denture cleansers. Regarding mechanical cleaning, the cleaning effect of a combination of mechanical cleaning using a brush and chemical cleaning with paste has been investigated in vivo in numerous studies 28 31, but no study has described differences in cleaning using a denture brush and a conventional toothbrush without the use of a chemical cleanser, such as denture-cleaning paste. Regarding the study method, although a prospective cohort study or a randomised controlled trial is more favourable, we selected a method that is less stressful for the subjects and applicable for nursing home residents considering the burden of a long study and strict experimental conditions. This study did not strictly specify the denture-cleaning conditions, such as the type of denture cleanser or duration of immersion in a denture cleanser, but this was compensated for by increasing the number of samples, and significant differences were noted on statistical analysis, suggesting the validity of this study method. De Visschere et al. 32 reported that the rate of denture brush use in long-term health care institutions for the elderly was 19.3%. The cause of the higher rate (32.5%) in the nursing home residents of this study is unclear, but a difference in the degree of dependence of residents between these facilities may have influenced the use rate. The high rate of denture brush use in outpatients of this study could reflect the recommendations and instructions given at our clinic. In this study, the rate of daily use of a denture cleanser showed that nearly half of the subjects used a denture cleanser daily at both facilities. However, outpatients using a denture cleanser at other frequencies were also present, but nursing home residents were divided into those who used one daily and those who hardly used a cleanser. The cost-effectiveness of using denture cleansers may have influenced the outpatients, while support for purchasing a denture cleanser by facility staff and families may have influenced nursing home residents. Streptococcus spp., Neisseria spp. and Candida spp. were frequently detected in denture plaque in this study, as previously reported 16. The Candida spp. detection rate was higher in the nursing home residents than in the outpatients, and this was consistent with reports in which the prevalence of fungi was higher in elderly persons requiring nursing care than in independent elderly persons 33. The prevalence of Candida was high in nursing home residents using dentures, and fungi were also frequently observed on the tongue 34,35. These findings indicate that special consideration for the elimination of Candida is necessary for denture cleaning in nursing home residents. The quantity of microorganisms was significantly lower in dentures worn by women than by men among nursing home residents. It is considered that this finding is related to the usage rate of the denture cleanser by women having been significantly higher than that by men among nursing home residents (v 2 = , p < 0.001). The quantity of microorganisms was significantly lower in denture brush users than in non-users among the outpatients. In a study that compared the effectiveness of a denture brush and a toothbrush by staining denture plaque 28, a denture brush was found to be more effective than a toothbrush, although denture-cleaning paste was concomitantly used, and the effectiveness of denture brushes was consistent with the results of the outpatients in this study. However, no significant difference because of the use of a denture brush was noted in the quantity of microorganisms in the

7 Examination of denture-cleaning methods e265 nursing home residents. The fact that we selected persons who cleaned dentures by themselves and seventeen nursing home residents with hemiplegia-associated disability of the fingers who could not sufficiently brush dentures were included may have influenced the results. Moreover, the quantity of microorganisms was higher in the nursing home residents than in the outpatients, as previously reported 33,34. Considering these findings, assistance is necessary to effectively use denture brushes, and the development of an oral care system to establish an oral environment to prevent an increase in the quantity of microorganisms is desirable 36. Regarding the frequency of denture cleanser use, a large quantity of microorganisms was present in both outpatients and nursing home residents who used a denture cleanser 1 2 or fewer times a week. In the outpatients, the quantity of microorganisms was reduced in those who used one 5 6 and 3 4 times per week to a level similar to that with daily use, suggesting that the usage frequency of 3 4 times or more per week effectively removes microorganisms. However, fewer outpatients used a cleanser 5 6 times per week and no nursing home resident used a denture cleanser 5 6 or 3 4 times a week. Thus, it is considered necessary to investigate whether the microorganism-eliminating effect differs between frequencies of use of a cleanser 3 4 times a week and daily because it is desirable to establish an efficient frequency of denture cleanser use from the viewpoint of costeffectiveness. However, from the viewpoint of instruction of denture cleaning for nursing home residents, it seems that instruction of using a denture cleanser 3 4 times per week will be difficult, and instruction of daily use of a cleanser will be more easily understood. Moreover, although it has been reported that there are few clinical problems associated with a deterioration of the mechanical properties of the resin by soaking in chemical solutions, such as denture cleansers 27,37 39, denture cleaning is preferable because it should not change the physical properties of the acrylic resin. Furthermore, as a large quantity of microorganisms were present on the dentures of nursing home residents and a weak effect of commercial denture cleansers on viruses has been reported 40,itisnecessary to develop a safe and effective denture cleanser. Conclusion It can be concluded that the quantity of microorganisms adhering to dentures reflects the denturecleaning method used. The use of a denture brush and the daily use of a denture cleanser should be recommended to complete denture wearers to effectively reduce the quantity of microorganisms adhering to dentures. References 1. Bentley DW. Bacterial pneumonia in the elderly: clinical features, diagnosis, etiology, and treatment. Gerontology 1984; 30: Yoneyama T, Yoshida M, Matsui T et al. Oral care and Pneumonia. Lancet 1999; 354: Coulthwaite L, Verran J. Potential pathogenic aspects of denture plaque. Br J Biomed Sci 2007; 64: Van Dyke TE, Sheilesh D. Risk factors for periodontitis. J Int Acad Periodontol 2005; 7: Awano S, Ansai T, Takata Y et al. Oral health and mortality risk from pneumonia in the elderly. J Dent Res 2008; 87: Scannapieco FA. Pneumonia in nonambulatory patients. The role of oral bacteria and oral hygiene. J Am Dent Assoc 2006; 137: 21S 25S. 7. Sjögren P, Nilsson E, Forsell M et al. A systematic review of the preventive effect of oral hygiene on pneumonia and respiratory tract infection in elderly people in hospitals and nursing homes: effect estimates and methodological quality of randomized controlled trials. J Am Geriatr Soc 2008; 56: Abe S, Ishihara K, Adachi M et al. Oral hygiene evaluation for effective oral care in preventing pneumonia in dentate elderly. Arch Gerontol Geriatr 2006; 43: Adachi M, Ishihara K, Abe S et al. Effect of professional oral health care on the elderly living in nursing homes. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002; 94: Abe S, Ishihara K, Adachi M et al. Professional oral care reduces influenza infection in elderly. Arch Gerontol Geriatr 2006; 43: Yoneyama T, Yoshida M, Ohrui T et al. Oral care reduces pneumonia in older patients in nursing homes. J Am Geriatr Soc 2002; 50: National Institute of Population and Social Security Research: Population Projections for Japan (December 2006). Retrieved from go.jp/site-ad/index_japanese/suikei.html on 3 June Sadamori S, Kotani H, Nikawa H et al. Clinical survey on denture stomatitis. 2. The relation between the maintenance of denture and denture stomatitis. Nihon Hotetsu Shika Gakkai Zasshi 1990; 34: Budtz-Jørgensen E, Kelstrup J, Poulsen S. Reduction of formation of denture plaque by a protease (Alcalase Ò ). Acta Odontol Scand 1983; 41: Kokubu K, Senpuku H, Tada A et al. Impact of routine oral care on opportunistic pathogens in the institutionalized elderly. J Med Dent Sci 2008; 55: 7 13.

8 e266 Y. Nishi et al. 16. Marsh PD, Percival RS, Challacombe SJ. The influence of denture-wearing and age on the oral microflora. J Dent Res 1992; 71: Sumi Y, Kagami H, Ohtsuka Y et al. High correlation between the bacterial species in denture plaque and pharyngeal microflora. Gerodontology 2003; 20: Odman PA. The effectiveness of an enzyme-containing denture cleanser. Quintessence Int 1992; 23: Augsburger RH, Elahi JM. Evaluation of seven proprietary denture cleansers. J Prosthet Dent 1982; 47: Nishi Y, Mizuguthi K, Nakamura Y et al. Survey studies on denture cleaning and maintenance report 1: present status and awareness of cleaning executants for instruction. Jpn J Gerodontol 2006; 21: [in Japanese] 21. Mizuguthi K, Nishi Y, Hashiguti M et al. Survey on denture cleaning instruction report 1: status of enforcement. Jpn J Gerodontol 2006; 21: 250. [in Japanese] 22. Nikawa H, Yamamoto T, Hamada T et al. Cleansing efficacy of commercial denture cleansers: ability to reduce Candida albicans biofilm activity. Int J Prosthodont 1995; 8: Nikawa H, Hamada T, Yamashiro H et al. A review of in vitro and in vivo methods to evaluate the efficacy of denture cleansers. Int J Prosthodont 1999; 12: Harrison Z, Johnson A, Douglas CW. An in vitro study into the effect of a limited range of denture cleaners on surface roughness and removal of Candida albicans from conventional heat-cured acrylic resin denture base material. J Oral Rehabil 2004; 31: Goodson LB, Glass RT, Bullard JW et al. A statistical comparison of denture sanitation using a commercially available denture cleaner with and without microwaving. Gen Dent 2003; 51: Murakami H, Mizuguchi M, Hattori M et al. Effect of denture cleaner using ozone against methicillin-resistant Staphylococcus aureus and E. coli T1 phage. Dent Mater J 2002; 21: Hashiguchi M, Nishi Y, Kanie T et al. Bactericidal efficacy of glycine-type amphoteric surfactant as a denture cleaner and its influence on properties of denture base resins. Dent Mater J 2009; 28: Silva-Lovato CH, Paranhos HFO. Efficacy of biofilm disclosing agent and of three brushes in the control of complete denture cleansing. J Appl Oral Sci 2006; 14: Paranhos HFO, Silva-Lovato CH, Souza RF et al. Effects of mechanical and chemical methods on denture biofilm accumulation. J Oral Rehabil 2007; 34: Salles AE, Macedo LD, Fernandes RA et al. Comparative analysis of biofilm levels in complete upper and lower dentures after brushing associated with specific denture paste and neutral soap. Gerodontology 2007; 24: Coulthwaite L, Verran J Evaluation of in vivo denture plaque assessment methods. Br Dent J 2009; 207: E12; discussion De Visschere LM, Grooten L, Theuniers G et al. Oral hygiene of elderly people in long-term care institutions a cross-sectional study. Gerodontology 2006; 23: Loesche WJ, Schork A, Terpenning MS et al. Factors which influence levels of selected organisms in saliva of older individuals. J Clin Microbiol 1995; 33: Honda E. Oral microbial flora and oral malodour of the institutionalized elderly in Japan. Gerodontology 2001; 18: Sumi Y, Miura H, Nagaya M et al. Colonisation on the tongue surface by respiratory pathogens in residents of a nursing home-a pilot study. Gerodontology 2006; 23: Samson H, Berven L, Strand GV. Long-term effect of an oral healthcare programme on oral hygiene in a nursing home. Eur J Oral Sci 2009; 117: Pavarina AC, Machado AL, Giampaolo ET et al. Effects of chemical disinfectants on the transverse strength of denture base acrylic resins. J Oral Rehabil 2003; 30: Sato S, Cavalcante MR, Orsi IA et al. Assessment of flexural strength and color alteration of heatpolymerized acrylic resins after simulated use of denture cleansers. Braz Dent J 2005; 16: Peracini A, Davi LR, Queiroz Ribeiro N et al. Effect of denture cleansers on physical properties of heat-polymerized acrylic resin. J Prosthodont Res 2010; 54: Glass RT, Bullard JW, Conrad RS et al. Evaluation of the sanitization effectiveness of a denture-cleaning product on dentures contaminated with known microbial flora. An in vitro study. Quintessence Int 2004; 35: Correspondence to: Yasuhiro Nishi, , Sakuragaoka, Kagoshima City, Kagoshima , Japan. Tel.: Fax: shar@dent.kagoshima-u.ac.jp