The Effect of Different Chemical Surface Treatments of Denture Teeth on Shear Bond Strength: A Comparative Study
Gauravi Jain1, Umesh Palekar2, Vaibav Awinashe3, Sunil Kumar Mishra4, Abhishek Kawadkar5, Tripti Rahangdale6
ABSTRACT Background: The development of better cross linked acrylic resin teeth has solved the problems related to wearing and discoloration of acrylic teeth. The same cross linking at ridge lap region acts as a double edge sword as it weakens the bond between denture base and tooth. Aim of Study: The purpose of study was to evaluate the effect of surface treatment on the bond strength of resin teeth to denture base resin using monomethyl methacrylate monomer and dichloromethane with no surface treatment acting as control. Settings and Design: Denture base cylinder samples in wax (n=180) were made with maxillary central incisor attached at 450 (JIST 6506). These samples were randomly and equally divided into three groups of 60 each. These specimens were then flasked, dewaxed as per the standard protocol. Materials and Methods: Before acrylization, ridge lap area was treated as follows: Group A- no surface treatment act as control,
Group B treated with monomethyl methacrylate monomer, Group C treated with dichloromethane. Digitally controlled acryliser was used for acrylization as per manufacturer’s instructions and shear bond strength was tested on Universal Testing Machine (Servo Hydraulic, 50kN High Strain, BISS Research). Statistical Analysis used: Result was statistically analyzed with One‑way analysis of variance (ANOVA) and Post‑hoc ANOVA Tukey’s HSD test at 5% level of significance. Results : The application of dichloromethane showed increased bond strength between cross linked acrylic resin teeth and heat cure denture base resin followed by monomethyl methacrylate monomer and control group. Conclusion: The application of dichloromethane on the ridge lap surface of the resin teeth before packing of the dough into the mold significantly increased the bond strength between cross linked acrylic resin teeth and heat cure denture base resin.
Keywords: Acrylic resin, Dichloromethane, Monomethyl methacrylate monomer, Shear bond strength
Introduction Heat-polymerized PMMA resin is used as a denture base material because of its excellent esthetics, low water sorption and solubility, relative lack of toxicity, repair ability, and simple processing technique . Pre‑fabricated acrylic resin teeth for dentures were introduced in 1940. Since then, this material has become the most popular artificial material for denture teeth. Apart from economical advantage, it also bonds chemically to the denture base . Debonding of denture teeth from denture bases is a major problem in the prosthodontic practice . This problem is even more serious in implant-supported over dentures, because the superior chewing capacity increases the risk of displacement of the artificial teeth from the denture base . This detachment may be attributed to the direction of stresses encountered during function; the most probable reason for failure is the crack propagation from areas of high stress concentration . Several studies have been carried to evaluate and study the compatibility of acrylic teeth to denture base resins. The surface modification on the ridge lap surface of acrylic resin teeth by the application of various chemicals before packing has shown variable results on the bond [6,7]. Recently, the application of non-polymerizing solvents like dichloromethane, chloroform and adhesive bonding agent seem to enhance the bond strength between denture base resin and acrylic resin teeth [8-13]. Adeyemi et al.,  stated that the chemical bonding between teeth and the polymer-monomer dough occurs through absorption of monomer by the surface layers of teeth. This monomer subsequently co-polymerizes with the denture teeth to Journal of Clinical and Diagnostic Research. 2014 Jun, Vol-8(6): ZC15-ZC18
form inter-penetrating polymer networks (IPN). Vallittu et al.,  stated that lesser cross linking in polymer structure facilitates better bonding of the polymer tooth to the denture base. Hence, cross-linked polymer matrix is usually non evenly distributed in the tooth structure e.g. the ridge lap area may not be as highly crosslinked as the incisal area of the tooth. Patil SB  reviewed a variety of chemical surface treatments used to increase the bond strength of teeth to denture base resin including application of monomer (methyl methacrylate), an adhesive bonding agents and non polymerizable solvents like dichloromethane. With the above in mind, an in-vitro study was designed and conducted to compare and evaluate the effects of dichloromethane and monomethyl methacrylate monomer treatment on bond strength of acrylic resin teeth with denture base resin.
Materials and methods The investigation was carried out with a single investigator with a sample size of 180 acrylic resin teeth (Maxillary central incisor cross linked, Prestodent) attached to denture base resin (heat cure resin Trevalon; Dentsply, India). Differential surface treatment was done at the ridge lap area with Monomethyl methacrylate monomer (MMM) liquid (Dentsply, India) and Dichloromethane solvent (Qualigens Fine Chemicals). The samples were subjected to shear load in universal testing machine to evaluate the bond strength at the interface. The investigation was completed in one month time period. For the purpose of the study, a two piece metal mold of 35 mm length and 12 mm diameter was fabricated to standardize the attachment of teeth at 450 using wax pattern. Care was taken to 15
Gauravi Jain et al., Surface Treatments of Denture Teeth
[Table/Fig-1]: Wax cylinder with tooth in the metal mold [Table/Fig-2]: Acrylised Samples
[Table/Fig-3]: Digital Vernier Caliper Figure
[Table/Fig-4]: Universal Testing Machine
[Table/Fig-6]: Types of Fracture
Monomethyl methacrylate monomer
[Table/Fig-5]: Shear force applied on incisal 1/3rd