Context: The use of denture cleansers significantly reduce the number of microorganisms on dentures but their effect on the physical properties of denture base are debatable.
Aim: The study was designed to compare and evaluate the hardness, flexural strength and surface roughness after treating heat activated acrylic resin specimens with different denture cleansers and ozone.
Material and Methods: 45 heat activated acrylic resin specimens were treated with three different denture cleansers Ozone (liquid dilution 1000ch SBL private limited), Distilled water, Clinsodent (ICPA health products ltd) and immersed in the respective solution for seven days. The immersed heat activated acrylic resin specimens were evaluated for flexural strength, hardness and surface roughness.
Statistical Analysis: The statistical analysis was done using the non-parametric Kruskal Wallis test to compare means of the three different denture cleansers.
Results: The flexural strength of group C (Ozone) was significantly higher than that of the control group A (Distilled water) and group B (Clinsodent). The surface roughness of group C (Ozone) was lower compared to control group A (Distilled Water) and group B (Clinsodent). The Hardness of Group C (Ozone) was higher followed by control Group A (Distilled Water), and then by Group B (Clinsodent) but the values were not statistically significant.
Conclusion: The heat activated acrylic resin displayed increased flexural strength and least surface roughness when ozone was used as denture cleanser; the values were statistically significant. Ozone did not show any significant effect on the hardness property of heat activated acrylic resin.
Keywords: Ozone in dentistry, Flexural strength, Hardness, Surface roughness
Denture care is an important factor for general health, especially in aged patients who cannot effectively brush their dentures because of disease, dementia and reduced dexterity1. The increase in the number of dentures in service has stimulated interest in measures to control the deposits and stains that normally collect on them. The use of teeth with more natural contours and the trend toward stippled surfaces tend to provide more recessed areas for the accumulation of plaque, stain, and debris and consequently increase the patient’s cleaning problems. Denture cleanliness is essential to prevent malodor, poor esthetics, and accumulation of plaque/calculus and consequent deleterious effects on the mucosa.
Mechanical methods are the most common and effective procedures for biofilm removal on prosthesis surfaces 2,[^3]. Ozone, discovered in 1839, is a tri atomic molecule that is widely used in industry because of its strong oxidizing ability. Ozone is used in both aqueous and gaseous form in medicine and dentistry as it inhibits bacterial proliferation, obtain wound healing by enhancing oxygen supply. Ozone in an aqueous solution decomposes rapidly to reproduce oxygen and leads no harmful residues 5^,^ 6. It has a strong antibacterial action against fungi, bacteria, protozoa and viruses. Additionally it also has several effects such as anti-hypoxic, anti-haemostatic and analgesic effect7. It is highly biocompatible with fibroblast, cementoblast and epithelial cells. In clinical field it is used to sanitize soft tissues as it increases the amount of oxygen in blood8,9.The necessity of removing plaque from dentures is very important for denture maintenance, thus ozone was considered for the study due to its high biocompatibility, strong disinfecting and deodorizing power.[^10^]In addition, it rapidly decomposes and leaves no residues; thus a promising material for denture cleansing.
This study is aimed to compare the hardness, flexural strength and surface roughness after immersing the heat activated acrylic resin specimens in three different denture cleansers. The study was begun with the null hypothesis that is there is no difference in hardness, flexural strength and surface roughness when heat polymerized acrylic is immersed in three different denture cleansers like Distilled Water, Clinsodent (ICPA Health Products Ltd) and Ozone-liquid dilution (1000ch SBL private limited).
A total of 45 heat activated acrylic resin specimens (Trevlon, Dentsply G- 7, Saket, New Delhi) were made in the following manner. The samples were prepared in a conventional method by flasking, packing and curing (Fig 1)
Fig :1. Fabrication of heat activated acrylic resin specimens
The flasks were allowed to cool to room temperature before opening. Flash and excess were removed by using acrylic burs. The blanks were then cut into strips by a band saw and were polished according to the measurements of 65102.5mm respectively. In each group 15 heat activated acrylic resin specimens were immersed for a period of seven days prior to testing (fig.2a,b,c).
The denture cleansing solutions used corresponded to the following groups- Group A (Distilled Water), Group B (Clinsodent, ICPA Health Products Ltd) and Group C (Ozone-liquid dilution l000ch SBL private limited) (fig.3). These specimens after immersion were then subjected to three different tests- flexural strength, hardness and surface roughness.
A Universal testing machine (fig.4) was used to measure the flexural strength of heat activated acrylic resin specimens after immersion in various denture cleansers. The measurements were made by placing the length of the material across a span supported on either ends of the material and bringing down a point source to the center of the span and bending until failure. The value is displayed digitally and calculated for each of the sample.
The measurement of surface roughness of the heat activated acrylic resin specimens was done before and after immersion by a surface roughness analyzer (fig.5).The surface roughness analyzer measures the microscopic valleys and peaks present on the heat activated acrylic resin specimens and thus gives a digital value of average mean roughness. Shore D hardness test (fig.6) was used to determine hardness of the heat activated acrylic resin specimens. The Principle used to measure hardness is based on resistance force of a pin into the test material under a known spring load. The hardness was measured by the penetration (max.2.5mm) depth of the indenter under load on a scale with 100 units.
The results obtained were subjected to statistical analysis using the non-parametric Kruskal Wallis test to compare means of the three different denture cleansers and to find whether the independent variables were statistically significant. The mean flexural strength in distilled water was 0.22, Clinsodent was 0.21 and Ozone was 0.28 (Table I, Chart 1).
|Group||Mean||SEM||Kruskal Wallis test||P value|
The flexural strength of group C (Ozone) was significantly higher (p= 0.005) than that of the control group A (Distilled water) and group B (Clinsodent).The mean surface roughness for specimen immersed in distilled water was 2.62, Clinsodent was 2.65 and Ozone was 2.61 (Table II, Chart 2). The surface roughness of group C (Ozone)was lower compared to control group A (Distilled Water) and group B (Clinsodent) where p=0.002. The mean hardness for specimen in distilled water was 75, Clinsodent was 74 and Ozone was 76 (Table III, Chart 3). The Hardness of Group C (Ozone) was higher followed by control Group A (Distilled Water), and then by Group B (Clinsodent) but the values were not statistically significant where p=0.201.
Immersion of heat activated acrylic specimens in cleansing solutions should ideally not bring about any change in physical, chemical or mechanical properties.11,12The changes in the flexural strength, modification of the surface morphology are direct impacts from the decontamination process.13 Effective removal of biofilms and stains is achieved by using effervescent tablets and there are chances of alkaline peroxide solution changing the resin properties when it is not correctly used. Several studies have been aimed to understand the influence on the physical and mechanical properties of dentures due to the use of denture cleaners. A report by Bollen et al14concluded that surface roughness of acrylic resin depends on the polishing grit. A comparative study on the retention of Candida albicans on smooth and rough acrylic resin was undertaken by Verranand Maryan15; in this study it was noticed a greater number of cells were seen on the roughened surface. To overcome bias due to rough surfaces on the specimen, the following technique was utilized in the current study, where a series of sandpaper finishing and a wet rag wheel with a slurry of pumice was used. Studies and the evidence given above provides proof that the dental cleanser causes the alteration16,17.The dimensional instability and fatigue causes a major problem and can eventually lead to the formation of cracks. This is mainly due to water absorption by the acrylic resin subsequently leading to fracture of the denture.18The endurance of the dentures relies on a part of flexural strength of acrylic resin after immersion in denture cleansers.19,20
However there are many studies to justify the color stability and antimicrobial effect of ozone on acrylic resin but the mechanical properties have not been tested. In the present study, 45 heat activated acrylic resin specimens (Trevlon,Trevlon, Dentsply G- 7, Saket, New Delhi)of dimensions 65x10x2.5 mm were fabricated for testing flexural strength, hardness and surface roughness. The specimens were immersed in three different denture cleansers for a period of seven days. The values thus obtained were subjected to statistical analysis using Kruskal Wallis test. The results reveal that the flexural strength of heat activated acrylic resin immersed in ozone was higher in comparison to clinsodent and distilled water. 21The results of the current study could be hypothesized based on the porosity and water absorption ability observed in the heat activated acrylic resin sample which reduce their flexural strength and weaken the resin. The heat activated acrylic resin specimen immersed in clinsodent had the maximum amount of surface roughness in comparison to other two groups. The oxygen released by sodium perborate denture cleanser has a high dissolving effect on plasticizers and loosens debris through mechanical means. Therefore, the use of this denture cleanser causes hydrolysis and decomposition of polymerized acrylic resin itself. Studies have shown that when the surface roughness increases by a value of 0.2 µm the amount of microbial adhesion also increases.21The hardness of heat activated acrylic resin specimen after immersion in the different denture cleanser was maximum in ozone followed by water and clinsodent but however, the values were not statistically significant. Decrease in hardness of conventional heat cure acrylic resin specimens can be attributed to the continuous polymerization reaction, monomer release, and the combination of monomers with free active radicals by bonding with liberated oxygen. The PMMA denture base resins are hydrophilic that attract more water soluble materials on the surface that absorption is undoubtedly due to the polar properties of resin molecules. However, it has been proven that the mechanism is due to the diffusion of water molecules that penetrate according to diffusion law. The limitation of the study could be smaller sample size and duration of immersion time being restricted to seven days. More studies could be conducted with a larger sample size and increasing the immersion time to get different results.
Within the limitations of the present study, the heat activated acrylic resin displayed increased flexural strength and least surface roughness when ozone was used as denture cleanser; the values were statistically significant. Ozone did not show any significant effect on the hardness property of heat activated acrylic resin.