Dr. Pranav R Tulle, Dr. Banashree S. Sankeshwari, Dr. Raghavendra V. Adaki, Dr. Dayanand A. Huddar
Professor and Head of Department,
Department of Prosthodontics, Crown & Bridge.,
Bharati Vidyapeeth Dental College and Hospital, Sangli, Maharashtra, India.
Introduction: Soft denture liners are commonly used in removable prostheses to prevent damage to the underlying mucosa, but they have the ability to absorb water which may lead to fungal infections in the oral cavity. Several denture cleansers including natural essential oils have been previously used as denture cleansers but there is minimal literature regarding the use of Cymbopogon nardus essential oil and its effect on the properties of soft liners. Cymbopogon nardus has been used as an antifungal agent but its use in dentistry is not noted so there is a need to evaluate its effect on soft liners.
Aim: To evaluate the effect of distilled water, denture cleanser and Cymbopogon nardus on water sorption and solubility of acrylic based soft liner at different time intervals.
Materials and methodology: A stainless steel mold of 50 mm x 0.5 mm was used to create specimens of standard dimensions. A total of 45 specimens of acrylic based soft liner were prepared and divided into 3 groups of 15 specimens each. All specimens of group A were immersed in distilled water, whereas those in group B and C were immersed in denture cleansing solution and citronella oil, respectively. Five samples from each group were checked for water sorption and solubility at 1, 4 and 6 weeks, respectively.
Results: The water sorption for all the groups was more at 1 week. The amount of solubility at 1 week was less as compared to the water sorption, so the weight remained more than the initial weight. The water sorption for all the groups was more which caused an increase from the initial weight at 4 weeks whereas the solubility was also more, so the weight reduced from the initial weight. The water sorption was more which caused an increase from the initial weight at 6 weeks for Groups A and B whereas the sorption was less for Group C when compared to 4 weeks. The solubility was also more, so the weight reduced than the initial weight for groups A and B, but for Group C the solubility was much lesser when compared to 4 weeks.
Conclusion: Water sorption was highest in Group C at 1 and 4 weeks whereas it was highest in Group B at 6 weeks. The solubility was highest in Group B at 1 and 6 weeks whereas it was highest in Group C at 4 weeks.
Keywords: Soft liner, Citronella oil, Essential oil, Water sorption, Solubility
Citations: Tulle P, Sankeshwari B, Adaki R, Huddar D. Evaluation of Effect of Distilled Water, Denture Cleanser and Cymbopogon Nardus on Water Sorption and Solubility of Acrylic Based Soft Liner At Different Time Intervals. J Prosthodont Dent Mater 2021;2(1): 49-57.
Removable complete denture prosthodontics includes replacing patient’s missing teeth and soft tissue with hard acrylic dentures.1 In cases of extremely resorbed and knife edge ridges, there is decrease in thickness of overlying mucosa due to which its shock-absorbing effect is diminished and masticatory impact forces are directly transmitted to the underlying tissue. As a result, the mucosa is traumatized. Hence, it is necessary to reline the intaglio surface of the denture base with a soft material similar to the mucosa in order to compensate for the lost thickness and viscoelastic behavior of mucosa.
Soft denture lining materials provide a cushioning effect for maintaining the health of abused, traumatized, swollen and deformed mucosa through absorption and equal redistribution of stresses over the entire area covered by denture, thus eliminating the distortion of oral mucosa.1 Acrylic-based soft liners are available in a powder/liquid form– the powder consisting of a higher methacrylate polymer and liquid consisting of higher methacrylate monomer along with phthalate plasticizer.
The soft denture liners are immersed in saliva inside the oral cavity or they may be stored and/or exposed to water/aqueous cleansing solutions when not in use. During immersion, water and saliva are absorbed and plasticizer and other water-soluble components are leached out. Due to this, water sorption and solubility problems are most often encountered.1,3-8
Candida albicans biofilms on denture acrylic are directly associated with the oral infection denture-induced stomatitis (DS). The key factor in the treatment of this chronic infection is efficient denture cleansing. Many studies have shown that commercially available denture cleansers are not completely effective in removing denture biofilms. Daily use of denture cleansers has detrimental effects on the physical properties of acrylic resin as it affects the color, surface roughness, flexural strength and the hardness of resins.
Natural antimicrobials derived from plants have been recognized as having therapeutic benefits in denture cleansing. Examples of such oils include those present in thyme oil, origanum oil, cinnamon oil, tea tree oil, etc. One of such oils that has recently been used in dentistry is Cymbopogon nardus (Citronella).9 Citronella oil, though used as an antifungal agent in dentistry, there is minimal literature regarding its use and effect on soft liners.
Ideal requirement of the material includes that the denture cleanser used should not alter the properties of the soft liner. As Cymbopogon nardus is a new essential oil used in dentistry there is a need to evaluate its effect on the properties of soft liners. Hence, this study was done to evaluate the effect of distilled water, denture cleanser and Cymbopogon nardus on water sorption and solubility of acrylic based soft liner.
MATERIALS AND METHODOLOGY :
A standardized stainless-steel mold of dimension 50 mm x 0.5 mm was fabricated as per ADA specification no. 12 (fig 1).10 The mold was used to create specimens of standardized dimension which were made according to the manufacturer’s instructions (2.2 gm/1.8 gm) (fig 2). A total of 45 specimens were divided into 3 groups of 15 specimens each based on the media used for immersion (fig 3).
Group A- Immersion in distilled water at 37+/-1°C in incubator for 10 mins
Group B- Immersion in denture cleansing solution according to manufacturer’s instructions for 30 mins
Group C- Immersion in 10% Cymbopogon nardus (Citronella) for 10 mins
Prior to immersion, all the disks were dried in a desiccator containing silica gel at 37+/-2˚C for 24 hours, transferred to a similar desiccator at room temperature for 1 hour then weighed with precision of 0.2 mg (fig 4). This cycle was repeated until weight loss of each disk was not more than 0.5 mg in any 24-hour period. This was the initial weight of the disks (W1) (fig 5).
After immersion, the samples were stored in artificial saliva to simulate intraoral conditions in an incubator at 37°C. Five samples from each group were checked for water sorption and solubility at 1, 4 and 6 weeks respectively. After 1, 4 and 6 weeks, the disks were removed from artificial saliva with tweezers, cleaned in distilled water and excess water was removed by blotting with filter paper and the disks were weighed in electronic precision balance (fig 6). This was the weight of the disks after sorption (W2).
The amount of soluble material lost was measured by placing the specimens back in the desiccator after each sorption cycle and then weighed them at regular intervals until a constant weight was reached. This weight was the final weight after desiccation (W3). Sorption and solubility was determined by ADA Specification No.12 for denture base polymers measuring water sorption and solubility in mg/cm2 where:
Sorption (mg/cm2) = (W2 – W1)/Surface area
Solubility (mg/cm2) = (W1 – W3)/Surface area
Surface area = 2πr(h+r) where,
h- Thickness of the acrylic based soft liner disk
r- Radius of the acrylic based soft liner disk
STATISTICAL ANALYSIS :
Data obtained was compiled on a MS Office Excel Sheet (v 2010, Microsoft Redmond Campus, Redmond, Washington, United States).
Data was subjected to statistical analysis using Statistical package for social sciences (SPSS v 21.0, IBM).
Inter group comparison (>2 groups) was done using one way ANOVA followed by pairwise comparison using post hoc test.
Intra group comparison was done using repeated measures ANOVA (for >2 observations) followed by post Hoc test.
For all the statistical tests, p<0.05 was considered to be statistically significant, keeping α error at 5% and β error at 20%, thus giving a power to the study as 80%.
Table 1 shows descriptive analysis for water sorption and solubility between different groups at different time intervals using one way ANOVA test
- It suggests that the water sorption for all the groups was more which caused an increase in the initial weight at 1 week. The amount of solubility at 1 week was less as compared to the water sorption, so the weight remained more than the initial weight (giving negative mean value).
- At 4 weeks, the water sorption for all the groups was more which caused an increase from the initial weight whereas the solubility was also more, so the weight reduced from the initial weight (giving positive mean value).
- At 6 weeks, the water sorption was more for Groups A and B which caused an increase from the initial weight whereas the sorption was less for Group C when compared to 4 weeks. The solubility was also more, so the weight reduced than the initial weight for groups A and B, but for Group C the solubility was much lesser when compared to 4 weeks.
Table 2 shows comparative analysis for water sorption and solubility between different groups at different time intervals using Scheffe Post Hoc test
- The intragroup comparison between different time intervals for water sorption shows that the difference was statistically non-significant for group A.
- Similar result was observed with group B where the difference was statistically non-significant.
- The intragroup comparison for solubility between 1 & 4 weeks and 1 & 6 weeks, shows that the difference was statistically highly significant for both groups A and B. However, for both groups A and B, the difference was statistically non-significant between 4 & 6 weeks.
- The values suggest that for groups A and B there was increased water sorption at all time intervals but it was non-significant whereas there was increased solubility upto 4 weeks after which it decreased between 4 & 6 weeks.
- The intragroup comparison for group C between different time intervals for water sorption shows that the difference was statistically non-significant whereas for solubility it was statistically highly significant.
- On comparison of values for group C at different time intervals, the water sorption was maximum at 4 weeks whereas it reduced between 4 & 6 weeks (giving positive mean difference). The solubility values were highly significant between 1 & 4 weeks and 1 & 6 weeks suggesting that the solubility was maximum upto 4 weeks. The values were also statistically highly significant between 4 & 6 weeks because the solubility drastically reduced between 4 and 6 weeks (giving positive mean difference).
Table 3 shows intergroup comparison for sorption and solubility at different time intervals done using post hoc test.
- At 1 week, there was no significant difference seen for water sorption. The values were significant for water solubility between groups B and C.
- At 4 weeks, there was no significant difference seen for water sorption but there was a statistical significant difference seen for water solubility between groups (A and C) and (B and C).
- At 6 weeks, there was no significant difference seen for sorption as well as solubility.
Denture stomatitis is caused due to colonization of pathological microorganisms especially due to the porous nature of denture lining materials.1 Candida spp. an ubiquitous fungi, belonging to the phylum Ascomycota are one of the most common causes of opportunistic mycoses. Clinically important Candida species in humans include C.albicans, C.glabrata, C.tropicalis, C.krusei, C.parapsilosis and C.dubliniens. Amongst these, C.albicans is the most prevalent pathogenic species responsible for majority of oral and systemic infections.
Recommended method of cleaning soft denture liners is by using soft brush under cold running water. Along with this, various modalities like denture cleansers are also used.13 In this study, Clinsodent, a sodium perborate monohydrate-based denture cleanser has been used as it is most commonly used amongst denture wearers.
A new trend in treatment of Candida-associated denture stomatitis is using natural compounds from essential oils like eugenol, farnesol, geraniol, linalool, menthol, menthone, terpinen- 4-ol, α-terpineol, tyrosol and carvacrol.13 In this study we have used essential oil from one such plant species i.e. Citronella oil (Cymbopogon nardus).
Citronella is a grass cultivated in subtropical and tropical regions of Asia, Africa and America, including Brazil. Its major chemical constituents are citronellal (37.75%), geraniol (18.84%), citronellol (14.27%) and citral. It has disinfectant properties but it has also been shown to have antifungal activity against C.albicans.14 Trindade et al15 (2015) in their study on biological activity of the essential oil from Cymbopogon nardus on inhibition of adherence of C.albicans to dental implants and cover screws concluded that the oil showed antifungal activity similar to nystatin and chlorhexidine and was able to inhibit the adherence of C.albicans to the surfaces of dental implants and cover screws. It acts by disrupting cell membranes and degrading other organic structures that may compromise the extracellular polymeric substances of biofilms.
In this study, the specimens were tested at 1, 4 and 6 weeks as the commercially available acrylic based soft liners are short term liners which can be used for 4-8 weeks.
Water sorption at 1 week was highest in Group C with a mean value of 0.999133 followed by Group B and least in Group A. The highest water sorption after 4 weeks was seen in Group C with a mean value of 3.30867 followed by Group B and least in Group A. After 6 weeks, the highest water sorption was seen in Group B with a mean value of 3.611396 followed by Group A and least in Group C. Water sorption at 1, 4 and 6 weeks was found to be statistically non-significant for all three groups.
Poly (methyl methacrylate) absorbs relatively small amounts of water when placed in the aqueous environment. Although absorption is facilitated by the polarity of poly (methyl methacrylate) molecules, the mechanism primarily responsible for the ingress of water is diffusion. Following diffusion, water molecules penetrate the poly (methyl methacrylate) mass and occupy a position between polymer chains. The values of our in-vitro study were in correlation with the studies done by El-Hadary and Drummond4 who found that acrylic resin soft liner has higher sorption at 1, 4 and 6 weeks in distilled water.
The solubility for Groups A, B and C was found to be statistically highly significant only at 1 and 4 weeks. This may be because:
- Denture cleansers have higher ionic concentrations as compared to water which might have led to a higher release of soluble components.
- The specimens were stored in artificial saliva throughout the day apart from the time immersed in the respective solutions, as saliva is more ionic than water.
- It may also be due to loss of ethyl alcohol and leaching out of low molecular weight plasticizers, as plasticizers are not bound within the resin mass.
The values of our in-vitro study were in correlation with the studies done by Kazanji MNM and WatkinonAC where the mean percentage solubility of different soft liners in sodium hypochlorite denture disinfectant solution (5.25%) and artificial saliva was found to be highly significant at 1 and 4 weeks. El-Hadary and Drummond found that acrylic resin soft liner has higher solubility at 1, 4 and 6 weeks in distilled water.
The contrast values were observed at 6 weeks for Group C where sorption as well as solubility values significantly reduced as compared to the values at 4 weeks. This may be due to the fact that lower water uptake will lead to less swelling of the matrix thus restricting leaching of the material from the matrix. These results are in agreement with the studies done by Parker and Braden.
Based on the statistical analysis, the results of the present study led to a conclusion that distilled water, denture cleanser and Cymbopogon nardus have non-significant effect on water sorption, whereas they have significant effect on solubility upto 4 weeks on acrylic based soft liner.
Within the limitations of this in-vitro study, the following conclusions could be drawn:
a) Water sorption was highest in Group C at 1 and 4 weeks whereas it was highest in Group B at 6 weeks. However, the water sorption was found to be statistically non-significant at all time intervals.
b) The solubility was highest in Group B at 1 and 6 weeks whereas it was highest in Group C at 4 weeks. However, the solubility was found to be statistically highly significant for Groups A and B between 1 & 4 weeks and 1 & 6 weeks but it was statistically non-significant between 4 & 6 weeks. For group C, it was statistically highly significant at all time intervals.
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Fig 1: Standardized stainless steel mold
Fig 2: Armamentarium for specimen preparation
Fig 3: Media used for immersion
Fig 4: Desiccator
Fig 5: Weighing of specimen
Fig 6: Blotting with filter paper