1. Introduction
The prevalence of denture stomatitis is between 15 and 70% [1]. Candida is the most common fungal pathogen that has the ability to adhere to oral tissues [2, 3]. Among the different types of candida, albicans have the highest pathogenicity [5]. Candida infectivity is affected by its attachment to the denture and refers to the physical properties of the denture such as porosity, surface free energy, hydrophobicity and surface roughness [6, 7, 8, 9]. Park reduced the adhesion of candida by altering the acrylic surface [10]. The type of acrylic and the method of making dentures also affect the adhesion of candida [11, 12, 13, 14]. Al-fouzan showed that prosthetics made by CAD/CAM method have less candida adhesion than prosthetics made by conventional method [11]. The present study aims to compare the adhesion of candida to two common types of acrylic resins materials.
2. Materials and Methods
In this experimental study, two types of heat-cured acrylic resins (vertex and ivoclar) were used. Acrylic discs were prepared according to the manufacturer’s instructions. The acrylic discs were first polished with sandpaper and then with pumice impregnated water. The final polishing was done with Tripoli brown paste. Surface roughness was measured by a profilometer in 3 areas of each sample. Two candida albicans strains (clinical and standard) were selected for adhesion evaluation, and yeast cell suspension was prepared.
The discs were disinfected with 70% alcohol. One milliliter of cell suspension was added to each well containing two acrylic disks, and the plates were incubated for 90 minutes at a temperature of 37 ° C and a speed of 75 rpm. The plates were washed three times with sterile phosphate buffer solution to separate loose and non-adherent cells.
To stabilize the remaining candida albicans adherent cells, the samples were immersed in methanol and then in acridine orange staining solution for 5 minutes. All samples were finally examined using a fluorescent microscope. Colony count was performed in 6 fields of each disk. Two-way analysis of variance and t-test was used for statistical analysis of data.
3. Results
The mean surface roughness of vertex and ivoclar was 0.326±0.206 and 0.284±0.103 μm, respectively. The mean surface roughness of ivoclar was lower compared to vertex, but the difference was not statistically significant (P=0.311). The average colony number of standard and clinical strains of candida adhesion to vertex and ivoclar and their comparison are shown in Table 1.


The mean adhesion of standard and clinical strains of candida albicans in ivoclar was significantly lower than in vertex (P=0.000).
4. Discussion
The chemical properties and surface topography of acrylic resins are important in the adhesion ability of fungal cells [4, 14]. The more surface roughness, the greater the adhesion of the candida [15]. Profilometry is a common device for measuring surface roughness [16].
The results of the present study showed that vertex had more surface roughness and, as a result, the adhesion of candida to vertex was higher compared to ivoclar. Ahmad et al. showed that acrylic resin had more surface roughness than nylon base resin, and it caused more adhesion of candida [17]. Xia et al. also found that the rough surfaces of the denture base increased the candida adhesion [18]. Swabi et al. also showed that the adhesion adhesion to unpolished resin surfaces was higher than to polished surfaces [19]. Numerous studies have shown that the higher surface roughness of the base denture material increase the candida adhesion [5, 21, 22].
Ivoclar has less surface roughness compared to vertex. However, the difference in the degree of candida adhesion can be due to the difference in some compounds in different acrylics, which affects the adhesion of microorganisms [14]. The inhibitory effect of compounds such as Vinylsilane, Zinc Dimethyldithiocarbamate, Dibutyltin dilaurate (present in some acrylics and soft liners) on candida has been proven [22, 23]. The different chemical composition of the two acrylics of vertex and ivoclar in the present study may also affected candida adhesion. One of the limitations of the present study was the impossibility of creating conditions that are completely similar to oral conditions.
5. Conclusion
Differences in surface topography and chemical properties of vertex and ivoclar acrylic resins affect the adhesion of candida albicans. 

Ethical Considerations
Compliance with ethical guidelines
This article is approved by the Ethics Committee of Arak University of Medical Sciences (Ethics ID: IR.ARAKMU.REC.1397.283).

Funding
Research Vice-Chancellor of Arak University of Medical Sciences was the financial sponsor of this study.

Authors' contributions
All authors contributed equally in preparing all parts of the research.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgments
The authors are grateful to Arak University of Medical Sciences for the technical support of this research study. We are also grateful to the Vice-Chancellor of Research and the Department of Parasitology and Mycology of Arak University of Medical Sciences for financial support and speeding up the process of conducting the study.



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