Effects of cleaning agents on flexural modulus and light transmittance of polypropylene dental material / Liew Liang Huey

Liew , Liang Huey (2024) Effects of cleaning agents on flexural modulus and light transmittance of polypropylene dental material / Liew Liang Huey. Masters thesis, Universiti Malaya.

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Abstract

Introduction: Polypropylene is commonly used as a clear plastic retainer in orthodontics. Clear plastic retainers are popular due to aesthetic, good patient acceptability and cost-effectiveness. To date, no ideal cleaning methods for retainers are found in the current literature. Previous studies have primarily focused on the effect of commercial chemical cleaning agents on the flexibility and translucency of polypropylene. However, the effects of baking soda, different concentrations of vinegar and Polident® Pro Retainer & Guard remain unexplored. Aims: The aim of this study was to evaluate the effects of baking soda, vinegar, and Polident® Pro Retainer & Guard on the flexibility and translucency of polypropylene dental materials. The objectives were to compare the flexural modulus and light transmittance of polypropylene dental material at baseline and after 30 days of exposure to these cleaning agents and analyse the mean difference in flexural modulus and light transmittance among the cleaning agents after the 30-day period. Methodology: Eighty-five polypropylene thermoforming foil (Erkolign, Erkodent) of 1-mm thickness were thermoformed onto a stainless-steel block of 65 mm x 60 mm x 6 mm using thermoforming machine (Erkopress ES-200E, Erkodent). These foils were cut into two dimensions: (A) 50.8 mm x 12.7 mm and (B) 50.0 mm x 35.0 mm. Specimens sized (A) and (B) were assigned randomly to five groups with 17 samples per group namely 10% baking soda solution, 2.5% vinegar, 5.0% vinegar, Polident® Pro Retainer & Guard, and distilled water. Specimens sized (A) were tested for baseline flexural modulus and specimens sized (B) were tested for baseline light transmittance. These specimens were placed into their respective beaker separated by glass beads. They were immersed in their respective cleaning agents for 15 minutes except Polident® Pro Retainer & Guard for three minutes as per manufacturer instructions. Subsequently, the specimens were rinsed thoroughly with distilled water and stored in artificial saliva maintained at 37 °C. The specimens underwent this process for 30 days. After 30 days of exposure to cleaning agents, the specimens were tested for flexural modulus and light transmittance respectively. Data was collected and analysed using SPSS version 22.0. Results: Significant statistical differences were observed in the flexural modulus (p < 0.001) and light transmittance (p < 0.05) of polypropylene dental material between baseline and after 30 days of exposure to cleaning agents. The mean difference in flexural modulus (p = 0.02, < 0.05) and light transmittance (p < 0.001) after 30 days varied significantly among the cleaning agents. Baking soda significantly reduced (p = 0.019) the flexural modulus of the polypropylene compared to 5.0% vinegar. Regarding light transmittance, 2.5% vinegar differed significantly from other cleaning agents except for 5.0% vinegar. Conclusion: Baking soda, vinegar, and Polident® Pro Retainer & Guard affected the flexural modulus and light transmittance of polypropylene dental materials after 30 days of exposure by reducing its flexural modulus, signifying increased flexibility and increasing its light transmittance, indicating increased translucency while mean difference in flexibility and translucency varied between cleaning agents.

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