ORIGINAL�ARTICLE ABSTRACT Objective: To compare the effects of microwave and light emitting diode disinfection on the dimensional stability of two denture base materials; polymethyl methacrylate and polyamide. Study Design: In-vitro study Place and Duration of Study: Peshawar Dental College and Material Research Laboratories, University of th th Peshawar from 10 June 2021 to 8 December 2021. Materials and Methods: Fifteen specimens each for polymethylmethacrylate and polyamide were divided into three groups, control, microwave & light emitting diode. The specimens for microwave group were irradiated at 1000W for 3 minutes, thrice a week. The specimens for light emitting diode group were disinfected in a device for 30 minutes, thrice a week. The control group specimens were placed in distilled water for 4 weeks. Dimensions were measured before disinfection, and four weeks after the assigned disinfection. The mean and the standard deviation of the differences between three groups were statistically analyzed using one-way ANOVA and after obtaining significant values, through post hoc Tukey HSD. Results: For polymethylmethacrylate highest dimensional difference (-9.02mm) was noted for microwave disinfected group while the control group showed the lowest value (-6.99mm). For polyamide, the highest dimensional changes were recorded for light emitting diode group (8.66mm) and the lowest (-7mm) for the control group. Statistical analysis showed that the differences were significant for both polymethylmethacrylate and polyamide when compared with the control (p<0.05) but insignificant when microwave disinfected group was compared with light emitting diode group (p>0.05) Conclusion: No significant difference in dimensional stability of both the denture base resins was observed after disinfection with microwave and light emitting diode. Key Words: Dimensional stability, Disinfection, Denture base resin, Light emitting diode, Microwave, Polymethyl methacrylate, Polyamide. with the adverse effects due to monomers present in 3 acrylic materials among patients and medical staff. In addition, the aesthetics of PMMA based removable partial denture can be impaired by the appearance of metallic components. A viable or 4 possible alternative to PMMA can be polyamide. Polyamides (PA) are preferred for persons allergic to methyl methacrylate, bone undercuts, in thin mucosa and excessive resorption of bone, in production of temporary dentures after implants 5 placement surgeries. Due to poor oral and denture hygiene, removable 6 prostheses provide a source for microbial growth , 7 and thus causing denture related stomatitis. Denture hygiene is achieved both through chemical and mechanical methods which affect the physicomechanical properties of materials used to 8 make removable prosthesis. To overcome the Introduction Polymethyl methacrylate (PMMA) is widely used for the fabrication of partial and complete dentures. Even though implant treatments are on the rise, but still there is a vast majority of cases that need removable dentures in developed as well as 1 developing countries. Therefore, the use of PMMA in prosthetic dentistry remains substantial as it shows adequate material properties and ease of 2 application. However, concern has been expressed Effects of Microwave and Light Emitting Diode as Disinfection Methods on the Dimensional Stability of Polymethyl Methacrylate and Polyamide Denture Base Resin 1 2 3 4 5 6 7 Hina Rehman , Muhammad Raza , Amjad Hanif , Mehreen Imran , Zia-Ur Rehman Khalil , Salman Khan , Nida Saeed , 8 Zudia Riaz Correspondence: Dr. Hina Rehman Department of Dental Materials Peshawar Dental College, Peshawar E-mail: drhr1979@gmail.com 1,3,4,6,7,8 2 Department of Dental Materials/ Prosthetics / 5 Community Dentistry Peshawar Dental College, Peshawar Received: August 06, 2022; Revised: December 08, 2022 Accepted: December 10, 2022 Effects of Disinfection Methods on Dimensions of Base Resins JIIMC 2022 Vol. 17, No.4 274 DOI: https://doi.org/10.57234/1472 complications, microwave radiation has been advocated as an easy, safe, and effective way for 10 denture disinfection. In a recent review, microwave disinfection has been claimed as an efficient antifungal therapy for the treatment of denture 11 stomatitis. Microwave disinfection is mostly carried 12 out in wet conditions where the denture base is placed in water in the microwave oven, this may 13 cause further polymerization of the resin. Despite the effectiveness of microwave as denture disinfectant, researchers have reached contradictory findings regarding its harmful effects on some properties. These detrimental effects may be due to the heating of material during irradiation, which 14 could affect the structure of polymer. The consequences of microwave disinfection of denture base materials have been vastly studied, but no consensus could be developed regarding the deleterious effects of microwave on prosthodontic 11 materials . Some of these studies showed notable 15 16 dimensional changes of upto -1.12% , & 3% after disinfection with microwave. Blue LED light in the visible spectrum of wavelength (405nm), has been found to have bactericidal/ 18 fungicidal effects. Blue LED light of this wavelength inhibits the candida biofilm production on prosthesis and can also disinfect denture surfaces swiftly than conventional disinfection methods. Therefore, blue LED light can be a promising technique for denture disinfection. However, there is very limited information available for the effects of LED for disinfection of both PMMA and PA denture base resins on their dimensional stability. Similarly, no data is available to compare the effect of microwave and LED disinfection of two denture base materials on their dimensional stability. The aim of this study was to compare the effects of microwave and LED disinfection on the dimensional stability of polymethyl methacrylate and polyamide denture base resins. Materials and Methods th This was an in-vitro, study conducted from 10 June th 2021 to 8 December 2021, in Peshawar Dental College and Material Research Laboratories, University of Peshawar. A total of thirty specimens were made, fifteen each for the two materials used; Polymethyl methacrylate (Engropolymer, Meadway, UK) and Polyamide (Vertex Dental B.V, Netherland). The specimens for each material were further subdivided into three groups: Group (A) Control (without treating either with MW or LED), group B microwave (MW) and group C light emitting diode (LED) disinfected 19 containing five specimens each (n=5) (Table I). Each specimen measuring 25×25×5mm was made in a stainless-steel split mold. Four holes, measuring 0.5mm in depth, were engraved in the metal mold as index marks. After fabrication of specimens, wax patterns were invested in curing flask with dental stone type III. The flasks were put in boiling water for about 10 minutes. After removal of wax, sodium alginate was applied to the mold. Heat cure acrylic powder was mixed with 20 its monomer in a ratio of 2.5:1 w/v and was packed into the molds. The flasks were gradually heated to ° 100 C in a period of one and a half hour. This temperature was maintained for 30 minutes. The flasks were bench cooled overnight. The specimens were taken out and immersed in water for 48 hours. The specimens were then trimmed, using belt emery paper (400-800 grit). Further refined with grade 1200 and finished with grade 2400 emery paper. Final polishing was done with a motor driven revolving disc, with a velvet polishing cloth. Wax patterns for PA specimens were made in stainless steel molds and invested in the flasks with dental stone (type III), following the procedure adopted for PMMA specimens. Wax sprues were then attached to the wax patterns. The investment was coated with petroleum jelly. The flasks were then filled with dental stone and placed in boiling water. After dewaxing, the flasks were placed in the hydraulic injector for flexible denture base resin. Molten polyamide was forced into the flask by using polyamide injection system at a pressure of 5 bars for 3 minutes. The flasks were bench cooled before 15 deflasking . Following deflasking, finishing was performed with 600 and 800 grit silicon carbide paper, and then polished with white cotton yam wheel polishing brush. Measurements were recorded with a digital caliper (Mitutoyo, Mfg Co., Japan), using elevated indentations labeled by letters A, B, C & D. Six dimensions (distances AB, BC, CD, AD, AC and BD) were documented for each specimen. Five measurements were recorded for each of the six Effects of Disinfection Methods on Dimensions of Base Resins JIIMC 2022 Vol. 17, No.4 275 DOI: https://doi.org/10.57234/1472 dimensions before calculating the mean. The algebraic norm was calculated by taking the square 21 root of sum of squares of individual dimensions. 22 2 2 2 2 2 2 1/2 Norm = [AB +BC +CD +AC +AD +BD ] For control group (A) specimens, after initial measurement were kept in distilled water at room te m p e rat u re a n d t h e wate r wa s c h a n ge d corresponding to the water change for the interventional groups (B & C). For group B, after taking the initial measurements, individual specimens were placed in 200ml of distilled water at room temperature in a microwave oven (Dawlance, model: DW-162H, Korea) and then subjected to disinfection at 1000W for 3 minutes, thrice a week for 4 weeks. For group C (LED disinfection), after the initial measurements, the specimens were subjected to irradiation for 30 min, 3 times a week for 4 weeks. Water for sample immersion was changed after conducting 2 disinfection protocols for groups B & C th and after every 4 day for group A. After completing 12 disinfection cycles, specimens were measured for final measurement. The percent difference was 21 determined as follow : Percent Difference = final measurement - initial measurement / initial measurement × 100 Mean and standard deviation values for the linear dimensions were determined. Data collected before and after disinfection with microwave and LED, were statistically analysed by one-way ANOVA and post hoc Tukey's test using SPSS version 26. P value less than 0.05 was considered as significant. Results The mean values of the initial, final measurements and their differences for all the groups of PMMA are given in Table I. Group B1 (disinfected using microwave) exhibited the highest change in dimensions (-9.02mm) while the control group (A1) displayed the lowest change in dimensions (- 6.99mm) (Table I). One way ANOVA showed highly significant difference (p=0.002) among the groups after disinfection protocol (Table I). Post hoc Tukey's test for multiple comparison showed significant difference for both the groups B1&C1 when compared to control (A1) (p=0.004) &(p=0.006) respectively while the difference between group B1 & group C1 was insignificant (p=0.964) (Table II). The mean values of the initial, final measurements and their differences in mm with standard deviations for each group of PA are given in Table III. It can be seen from the Table III that group C2 exhibited the highest (-8.66mm) while the control group, displayed the lowest change in dimensions (- 7.0mm). One way ANOVA showed statistically significant difference among the three groups ((p=0.013). Post hoc Tukey's test showed statistically significant difference between group B2 and the group A2, similarly the difference between group C2 and group A2 was significant (p=0.042). The difference between the group B2 and group C2 was also statistically insignificant (p=0.835). Table I: Comparison of Dimensional Changes In PMMA* Using One Way ANOVA * PMMA: Polymethylmethacrylate, ** M/W: Microwave, *** LED: Light Emitting Diode. Table II: Post Hoc Analysis (Tukey's HSD) of Dimensional Changes In PMMA Table III: Comparison of Dimensional Changes in PA Using One Way ANOVA Effects of Disinfection Methods on Dimensions of Base Resins JIIMC 2022 Vol. 17, No.4 276 DOI: https://doi.org/10.57234/1472 Discussion Dimensional stability of denture bases during service is of great importance as it helps in retention of the 23 dentures and cuspal interdigitation. Therefore, any effects of the adopted disinfection techniques on the dimensions of denture bases may pose problems. There are no standard specifications for measuring 24 linear dimensions of denture bases. Wolfaardt et al stated, that many factors affect the dimensional changes of denture bases such as size and shape etc. It has been recommended to test specimens of 21 simple shapes for dimensional measurements. Therefore, square shaped specimens were used in the present study. Statistically significant difference was observed, when the interventional groups were compared with the control group whereas comparison of the MW with LED showed insignificant results. Therefore, the null hypothesis of this study was partially rejected as significant differences were observed for both the resins after disinfection with MW and LED when compared with control. The contraction of resin for the control groups of this study could be attributed to the thermal contraction during storage and due to release of stresses that 25 were induced during polymerization. The storage of resin in water helps in residual monomer dispersion 26 in PMMA. This elution of monomer continues for a 27 few days of storage in water. Such loss of monomer from the polymerized specimens can be accredited for the shrinkage or decreased dimensions of specimens of control groups of PMMA, after storage 25 in water for four weeks. The shrinkage in PA control group was recorded to be around 7mm. Dimensional accuracy of PA is technique sensitive and require more precise and careful processing. It has been reported in literature that storage of nylon (PA) in water has shown 28 decrease in dimensions after about 24 hours. However, an increase in dimensions of the same PA used in the present study after storage in water has 29 also been reported by Chuchulska & Zlatev , which contrasts with the results of this study. This might be due to aging of the specimens for 5000 thermocycles. The change in dimensions of both denture base resins can be explained by the fact that microwave irradiation causes increase in temperature of the 17 specimens. Despite all the precautions taken and careful processing of PMMA, some monomer 30 content is left unreacted in the final product. This increase in temperature can cause reaction of the unreacted monomer at reactive sites of the polymer and thus cause further shrinkage due to 1 5 thiolymerization. Resins can experience a plasticizing effect after their Tg is exceeded, which 31 causes rearrangement of the polymer chains and thus this change in dimensions could be due to the plasticizing effect of resins above their Tg. The highly significant result for MW disinfected PMMA group in comparison with the control group of this study is in accordance with results reported 17 15 by Wemken et al. Polychronakis et al reported shrinkage of 0.35mm for heat cure PMMA and 0.09mm for Valplast after wet microwaving at 450 W for 3 minutes. This can be considered in accordance with the present investigation, as they had measured only the length of the specimens, while in this study, means were calculated for the six measurements of each specimen and the algebraic norm was calculated. 32 Polyzois et al contradicts the results of the present study as disinfection of acrylic base resin specimens with a 500W MW for 3 minutes and 15 minutes manifested linear shrinkage of - 0.005%. Although the changes were significant statistically but were of no clinical importance. It can be noted in the arguments presented so far that the microwaves Table IV: Post Hoc Analysis (Tukey HSD) of Dimensional Changes in PA *PA: Polyamide Effects of Disinfection Methods on Dimensions of Base Resins JIIMC 2022 Vol. 17, No.4 277 DOI: https://doi.org/10.57234/1472 used for disinfection of denture base resins specimens were of low powers. The power levels of MW ranged between 450W and 700W, with most studies conducted with 650W. 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A critical review of protocols for conventional microwave oven use for denture disinfection. Community Dental Health; 35:228-234. https://doi.org/10.1922/cdh_4372brondani07 CONFLICT OF INTEREST Authors declared no conflicts of Interest. GRANT SUPPORT AND FINANCIAL DISCLOSURE Authors have declared no specific grant for this research from any funding agency in public, commercial or nonprofit sector. DATA SHARING STATMENT The data that support the findings of this study are available from the corresponding author upon request. This is an Open Access article distributed under the terms of the Creative Commons Attribution- Non- Commercial 2.0 Generic License. Effects of Disinfection Methods on Dimensions of Base Resins JIIMC 2022 Vol. 17, No.4 279 DOI: https://doi.org/10.57234/1472