Evaluating the effect of new denture cleaners on the surface roughness of acrylic resin denture base material ( An in vitro study )

Three newly prepared denture cleaner solutions from materials available in our country [namely; oxalic, citric and tartaric acids dissolved in isopropyl alcohol (5% w/v)] were studied for their effect on 110 specimens of heat cure acrylic resin prepared according to ADA Specification for 7 days, 1 month, 6 months, and 12 months, compared with Steradent denture cleaner by two techniques (immersion and brushing techniques). The concentration (5% w/v) was selected according to the results of pilot study. The results of this study showed that oxalic and tartaric acids have nearly the same effect on surface roughness in relation to Steradent by immersion technique for six months, but this result was increased to show high rough surface of samples treated by citric acid for one year. Treatment with the four solutions led to reduction in weight (0.03 mg) except citric acid (0.49 mg). Statistical analysis was performed using F–test two–sample. The results revealed that there was a significant difference at levels 1% and 5% between the brushing and immersion techniques, roughness of the surfaces, and period of using each solution. ةصلاخلا ا ممت ارممم ا مم نانمم ارممموما نم ممتارممت ةسارمممت ا مممنل ا ا ممميااممملأا ام مممنوة اا ممم ةرل ارن نيمممتوبل ا مة ااموارمي ا م رل ا مياا يم ل ا ميا ا ن يبالنبا با يلآ 5 اىوعا)رجيا/ زاا% 111 ا اجذ رن اا مرل ا ملل ارمن تاررمت با مروبرل اامو ر ا ت مل ان ممم ارمبمممتااسمممرل ا ام ومممشا ممم عا ممم م اا ومممش اريمممتاا ومممشا ام ممممممنرل عا ا مممممم رل اا نس نيممممممتاالمممممم نانمممممم ا مممممموينة ا ا سميمممت ارمم اا ممرسل ارمم ا ممرلأانني مم ا سميممت ي .)رن نن نرل اارن نرنكل ار رل ا ت اا ش و ا ا ممموةرلا ارممم بيمرل ات ممم ةلل ا مممينات ممموظ ا ز م ا نم متا م رل ا مياا منل ا ا مي ا اا ارن م اىموعا نم متاثمنيانم اا نس نيمتاارمبن يلابة ا مممملأانممممكلاا وممممش اريممممتااسممممرلاا ممممرسل ارمممم رياررمممم ل ا مموةرلارمم اا سميممت انمم ار ممتاسمم ياس س مميا نم مميل . ي ل ا ي ا ا سم رباا ز مل ااوا ص ناىلإالنل ةرل ارو اتس 1.13 ا ا يممم ل ا ممميا ممموة ا سمممعا ممم ارمممسو 1.40 ا .)رسو ا ا ج اااة مبي ا سميت ياا صيلإ النوةيل F– test two–sample ا موا م لأا ا مي ل ات موظ اا.) ا يممممممممم اىممممممممملإا ممممممممم م 1 اا% 5 انني مممممممممرل اننمممممممممبا% الممممكلا رمممم ل ارن مممم اارممممن ل ات مممميلل ا نني سميمممم رل . وة ا Evaluating the effect of new denture cleaners on the surface roughness of acrylic resin denture base material (An in vitro study)


INTRODUCTION
Prosthesis has been identified as a source of cross contamination because of the increased risk of infection through constant exposure to debris, plaque and saliva, which harbor pathogenic organisms that adhere to prosthesis. (1) Adequate plaque control is essential for the maintenance of a healthy oral mucosa. (2,3) Denture cleaners are used as a popular method by denture wearers for cleaning. To clean their dentures, patients may use proprietary cleaners, or household cleaning materials. This is in order to keep the denture free of plaque, staining and calculus. (3) The denture cleaner's constituents, efficiency, adverse effects and safety are very important because such denture cleaner may affect the denture surface and rough surface produced make it difficult to maintain clean surface. (4) A smooth acrylic denture base surface is more desirable in terms of cleaning ability, and infection control due to the effectiveness of denture cleaning agents against microorganisms, since roughened surface will facilitate the retention of yeast. (4)(5)(6) The most commonly used diluted acidic cleaner is household vinegar. Other chemical cleaners which are classified under this heading include weak solutions of hydrochloric, phosphoric and sulfuric acids. (7) Oxalic acid, citric and tartaric acids (weak organic acids) found in many plants and vegetables. Oxalic acid found parti-cularly in buckwheat (family Polygoniaceae), rhubarb and oxalis (family Oxalidaceae); used as a hemostatic in vete-rinary medicine, and it is used in removal of stains. (8,9) All three organic acids used in this study are naturally occurring carboxylic acids present in citrus foods with a moderate solubility in water and alcohol besides its bleaching effect. Oxalic acid is present in small amounts in many plants such as oxalis and spinach, and used as rust remover. (8)(9)(10) The aims of this study were to evaluate the effect of newly prepared denture cleaners on hot cure acrylic resin denture surface regarding roughness, weight in relation to surface area and staining removal; and to compare them with other commercially available cleaners.

MATERIALS AND METHODS
Materials used in this study were: 1) Chemical materials used (tartaric acid, citric acid, oxalic acid and isopropyl alcohol), were purchased from Fluka chemicals and were of high purity. Isopropyl alcohol was chosen as solvent due to its antiseptic effect moderate boi-ling point (97 ºC). (8,9) 2) Denture base: Acrylic denture base material (Quayle Dental, Ltd) heat cured acrylic powder Cl I and liquid pink colour Batch No. BS2487. 3) Steradent denture (Alkaline Peroxide) cleaning tablets (Reckitt GmbH for Reckitt and Colman products Ltd. Hull/England).
Five different concentrations (1-5%) w/v of each oxalic, citric and tartaric acids were dissolved in isopropyl alcohol. Each solution was diluted with distilled water (50:50) prior to use. Steradent tablet was dissolved in distilled water according to manufacturer's instructions.
Dry tea (4 g) was boiled in 500 ml of distilled water for four minutes, and then allowed to cool at room temperature, then decanted from its leaves. Fresh tea solution was prepared daily. (11) A total of 110 heat cured acrylic resin specimens were prepared from wax plated (65 × 10 × 2.5 + 0.3 mm) dimensions according to ADA specifications. Curing was done in the conventional method using long cycle water bath technique, then the acrylic specimens were finished and polished according to Hatim and Kazanji. (12) The specimens were placed in a thermostatically controlled incubator at 37 ºC + 1 ºC to simulate mouth temperature for 7 days before treatment for conditioning of the samples. (13) A pilot study was done to determine the significant concentration of acid to be used. Thirty specimens of heat cured acrylic resin were divided into six groups, each group of 3. The specimens were immersed in tea solution for twenty-four hours. Then each specimen was immersed in one of the solutions prepared with different concentrations. The sixth group of specimens was immersed in distilled water only as a control group.
Timer was used to determine the significant time to clean the specimens (complete removal of the staining) from 5 minutes to 8 hours daily.
The results of this study showed that the favorable time for complete cleaning of the specimens was 8-10 minutes daily by using 5% concentration of oxalic acid, while the other solutions need more time to remove the stain.
The results of surface roughness of heat cured acrylic denture base showed slight effect of 5% concentration of the prepared acid solution in relation to control group of distilled water.
Two techniques were followed for all specimens to measure surface roughness, weight loss and linear dimensional changes using a computerized surface texture measuring and recording machine (perthometer) M3P Perthen-West (Germany) with accuracy up to 0.001 μm, electronic balance (Mettler, West Germany), and optical measuring micrometer microscope (Leitz, Wetzlar, GmbH, West Germany) with accuracy up to 0.001 mm at magnification power (×10). The two techniques were: 1) Immersion Technique: Forty speci-mens were divided into four groups randomly. Each group consists of 10 specimens. The specimens were im-mersed in tea solution overnight, then washed with distilled water and immersed in the tested solutions; i.e., oxalic acid, citric acid, tartaric acid and Steradent solution (prepared by diss-olving a Steradent tablet in distilled water according to the manufacturer's instructions). Daily immersion of spec-imens in solutions for 10 minutes was done for 1 year. After each immersion, the specimens were washed with dis-tilled water and stored in an incubator. The samples were examined after 1 month, 6 months and 12 months. 2) Brushing Technique: Another 40 specimens were divided in the same way as in immersion technique. For each specimen a special brush was used for 1 week only. The brush head was fixed to the bur of a handpiece of micromotor engine in order to obtain a constant pressure, speed and time. The surface of the specimens was brushed with test solution for 10 minutes, and then the specimens were washed with distilled water and measured. Visual examination of staining removal was assessed by visual inspection in a daylight by five observers (complete or incomplete cleaning). Measurements of the samples were done after treatment with solutions (immersion and brushing techniques) at 1 month, 6 months and 12 months, in addition to the measurement of the samples before treatment at 7 days.

RESULTS AND DISCUSSION
Mean and standard deviation of the surface roughness of the acrylic resin samples before and after treatment with four solutions for 1 month, 6 months and 12 months were listed in Table (1). Oxalic and tartaric acids have almost nearly the same effect on surface roughness in relation to Steradent by immersion technique for six months (Figures 1, 2 and 3). But this result was increased to show high rough surface of samples treated by citric acid (immersion and brushing techniques) for one year (0.421-0.583 μm).
The results also showed that all denture cleaners have the ability to attack the surface of acrylic resin depending on the length of treating time, type of solution and the technique in agreement with other studies. (2,(14)(15)(16)(17)    The results of this study showed a loss in weight of the samples treated by solutions (0.03 mg) except citric acid (0.49 mg) ( Table 2). Change in weight in relation to surface area were ranged between 0.01-0.03 mg/cm 2 for Steradent and oxalic acid in immersion technique which is near to the ADA Specification No. 12 (0.04 mg/cm 2 ), while the result was 0.05-0.23 mg/cm 2 for brushing technique of the other solutions except citric acid (Figures 4 and 5). These results were attributed to the fact that oxalic acid is the weaker acid. (6)(7)(8)18,19) The results revealed that there was a significant difference at level 1% and 5% by using F-test two-sample between the two techniques, roughness of the surface and period of using each solution (Table 3).   Chemical denture cleansing methods have several advantages over the mechanical method. Chemical denture cleansing solutions can easily reach all areas of the denture and result in complete cleaning; damage from mishandling of the denture is minimized; abrasion is not possible and since the procedure is simple, it is easily carried out by handicapped persons or by individuals lacking the physical coordi-nation to adequately clean their dentures by brushing. (2,(15)(16)(17)20) Oxalic acid showed complete removing of the stain within 8-10 minutes daily, Steradent and tartaric acid need 6-8 hours daily.

CONCLUSIONS
Preparation of new Iraqi denture cleansers (oxalic, citric and tartaric acids 5%); oxalic and tartaric acids have almost nearly the same effect on surface roughness in relation to Steradent by immersion technique for six months.
Treatment with the four solutions lead to reduction in weight (0.03 mg) except citric acid (0.49 mg).
The results revealed that there was a significant difference at level 1% and 5% between the brushing and immersion techniques, roughness of the surfaces and period of using each solution.
Changes in weight in relation to surface area were ranged between 0.01-0.03 mg/cm 2 for Steradent and oxalic acid in immersion technique, while the result was 0.05-0.23 mg/cm 2 for brushing technique of the other solutions except citric acid.
Oxalic acid showed complete removing of the stain within 8-10 minutes, Steradent and tartaric acid need 6-8 hours, while citric acid needed more time to give the same result.