|Year : 2021 | Volume
| Issue : 2 | Page : 38-42
Comparative evaluation of shear bond strength of acrylic teeth with heat polymerized acrylic resins using different surface treatments and curing cycles – An in vitro study
KS Amulya1, A Kalyan Chakravarthy2, B Veerendra Prasad3, R Avinash4, Kumbham Kiran Babu1, Kavya Sandhu1
1 Postgraduate Student, Department of Oral and Maxillofacial Prosthodontics and Implantology, Meghna Institute of Dental Sciences, Nizamabad, Telangana, India
2 Professor and HOD, Department of Oral and Maxillofacial Prosthodontics and Implantology, Meghna Institute of Dental Sciences, Nizamabad, Telangana, India
3 Reader, Department of Oral and Maxillofacial Prosthodontics and Implantology, Meghna Institute of Dental Sciences, Nizamabad, Telangana, India
4 Senior Lecturer, Department of Oral and Maxillofacial Prosthodontics and Implantology, Meghna Institute of Dental Sciences, Nizamabad, Telangana, India
|Date of Submission||07-May-2021|
|Date of Acceptance||10-May-2021|
|Date of Web Publication||30-Jun-2021|
Dr. K S Amulya
Postgraduate Student, Department of Prosthodontics, Meghna Institute of Dental Sciences, Nizamabad - 503 001, Telangana
Source of Support: None, Conflict of Interest: None
Purpose: This study evaluated the bond strength of acrylic resin denture teeth to heat cure denture base resin processed under different curing cycles and after various surface treatments on the bonding surface area of acrylic denture teeth.
Materials and Methods: A two-piece metal mold of 35 mm length and 12 mm diameter was fabricated to standardize the attachment of teeth at 45°. Ninety such wax cylinders were obtained and were randomly divided and coded into three groups of 30 samples each: Group “A” – the “Control” group, Group “B” – the “MMM” group, and Group “C” – the “Acetone” group with Subgroup 1 – processing with short curing cycle and Subgroup 2 – processing with long curing cycle in each group. These 90 wax cylinder specimens were then flasked, dewaxed as per the standard protocol and surface treatment of teeth, and curing was done. The samples were tested in a universal testing machine.
Results: ANOVA analysis inferred that there was a statistically significant difference between the mean bond strength values among the groups.
Conclusion: Analysis of mean bond strength values reveals that the mean bond strength values of acetone were significantly higher (P < 0.05) when compared to the other groups.
Keywords: Shear bond strength, surface treatments, universal testing machine
|How to cite this article:|
Amulya K S, Chakravarthy A K, Prasad B V, Avinash R, Babu KK, Sandhu K. Comparative evaluation of shear bond strength of acrylic teeth with heat polymerized acrylic resins using different surface treatments and curing cycles – An in vitro study. Int J Prev Clin Dent Res 2021;8:38-42
|How to cite this URL:|
Amulya K S, Chakravarthy A K, Prasad B V, Avinash R, Babu KK, Sandhu K. Comparative evaluation of shear bond strength of acrylic teeth with heat polymerized acrylic resins using different surface treatments and curing cycles – An in vitro study. Int J Prev Clin Dent Res [serial online] 2021 [cited 2022 Aug 17];8:38-42. Available from: https://www.ijpcdr.org/text.asp?2021/8/2/38/320056
| Introduction|| |
Despite progress in the development of denture base resins and acrylic teeth, debonding of acrylic resin teeth from the denture base remains a major problem in everyday practice. About 26%–33% of denture repairs are the result of debonded teeth, commonly in the anterior region of denture. The principle causes for debonding in the anterior region may be due to the availability of lesser ridge lap surface and direction of stresses encountered during function. Various incentives for the failure at acrylic tooth and denture base resin interface include wax residues on ridge lap surface of denture teeth, type of tooth material used, method of polymerization applied, processing factors such as duration of curing cycle, and available monomer during process.,,,,
Chemical treatment or mechanical modification of the ridge lap surface of the acrylic teeth can be advocated to improve the bond strength. Chemical treatment can be done with various solvents such as chloroform, methyl methacrylate, methylene chloride, acetone, curing agents, acrylic adhesive cyanoacrylate, and ethyl acetate.,,
The aim of this study was to evaluate the bond strength between the acrylic tooth and denture base resin using different types of chemical surface treatment and curing cycles.
| Materials and Methods|| |
Ninety maxillary cross-linked acrylic central incisor denture teeth (cross-dent, solvent-resistant cross-linked acrylic teeth) of the same size and shade were selected [Figure 1]. The 90 teeth were then divided into three groups with 30 central incisor teeth in each group. The study proposal was submitted for approval and clearance was obtained from the ethical committee of our institution.
The three groups were named A, B, and C according to the chemical surface treatments in which Group A served as a control with no surface treatment. The different chemical surface agents used were (i) Heat-curing Methyl methacrylate monomer (DPI, Mumbai, India) – Group B and (ii) Acetone (Merck Specialties Pvt. Ltd., Mumbai, India) – Group C. Further, these groups were divided into two subgroups based on the curing cycles followed during processing [Table 1]. The two subgroups are:
|Table 1: Comparison of bond strengths among short and long curing cycles of Group A, Group B, Group C|
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- Subgroup 1 – processed with short curing cycle and
- Subgroup 2 – processed with a long curing cycle.
A two-piece metal mold of 35 mm length and 12 mm diameter was fabricated to standardize the attachment of teeth at 45° [Figure 2]. Care was taken to embed the tooth only up to the neck of the central incisor into the wax cylinder. Silicone mold of the metal die was fabricated. Silicone mold was sectioned longitudinally in two halves to facilitate retrieval of wax patterns from the silicone mold. Modeling wax was poured into this silicone mold to get identical samples. Wax patterns were measured with digital Vernier calipers. Wax models were made from the mold such that the tooth was placed with a 45° inclination [Figure 3]. The wax models were invested, dewaxed, and application of chemical surface agents on the bonding surface was done according to grouping. Strict protocols were maintained in the dewaxing step as literature warrants incomplete wax elimination as one of the most important causes of tooth debonding. Boiling water was used once to dewax any wax residues. It was ensured that wax was eliminated fully. After removal of the wax, Cold Mold Seal (Dental Products of India, Mumbai, India) was applied as a separating medium over the entire plaster area.
Application of various chemicals on the ridge lap area of acrylic teeth
The dewaxed and grouped samples were then subjected to surface treatments. The entire application time and packing time were monitored [Figure 4].
|Figure 4: Application of chemical on the ridge lap surface area of tooth|
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After dewaxing and application of separating medium on plaster area, the DPI heat-curing acrylic resin was placed in the mold space and packed without any application of chemicals on the bonding surface and this group served as a control.
On the dewaxed ridge lap areas of the acrylic teeth, heat-polymerizing MMA monomer universal liquid was applied. The monomer was applied with a brush continuously on the ridge lap area of the teeth for 180 s. This application time of 180 s was found to result in better bond strengths as compared to shorter duration application times of 30 s and 60 s from literature. Packing was done immediately after the particular duration.
Acetone was applied with a brush continuously for 30 s on the ridge lap area of the teeth. Thirty-second application time made the surfaces completely clean and this is supported by previous studies. After 30 s, packing with denture base resin was done.
After the packing procedure was completed, the curing procedure was done as per the manufacturer's instruction as follows. The flasks were immersed in water at room temperature in the Acrylizer (Unident Dental Equipments). The samples are processed under two curing cycles which include short curing cycle involving processing the resin at 74°C for approximately 2 h and increasing the temperature of the water bath to 100°C and processing for 1 h and long curing cycle involving processing in a 74°C water bath for 8 h and then increasing the temperature to 100°C for 1 h [Figure 5]. Polishing of the acrylized samples was done and samples were tested in a universal testing machine such that the shear load was applied to the incisal one-third of the tooth to best simulate clinical forces on the maxillary central incisor at a crosshead speed of 0.6 mm/min and a load cell range of 1000 N until a fracture occurs [Figure 6]. Upon fracture, each sample was removed and the shear load applied (Newton, N) was recorded.
| Results|| |
Within the limitations of the study, all the specimens were tested for tensile and shear bond strength in a universal testing machine. One-way ANOVA was used to compare the means of three or more groups to determine whether they differ significantly from one another and to estimate the differences between specific groups [Table 1]. The mean bond strength values of Acetone were significantly higher when compared to other groups [Graph 1].
| Discussion|| |
Debonding, the most common problem encountered clinically in denture patients, is attributed to multifactorial reasons which include: (1) improper wetting of ridge lap surface of denture teeth with monomer, (2) contamination of ridge lap surface area with wax residues or cold mold seal, (3) inadequate powder to liquid ratio and curing cycle as recommended by the manufacturer, (4) inadequate mutual solubility or compatibility of two polymers for the establishment of the interwoven polymer, and thus for the strength of the bond, and (5) immersion with Fittydent cleansing tablets, 4% chlorhexidine gluconate, and 1% sodium hypochlorite also significantly reduced the bond strength of acrylic teeth to denture bases.,
Different types of denture base resins also affect the bond between acrylic teeth and denture base resins. Several studies have compared the bonding of acrylic teeth to microwave-polymerized, light-polymerized, heat-polymerized, and autopolymerizing denture base resins and observed that heat-polymerized resins revealed the highest bonding values.
Monomer application dissolves part of poly (methyl methacrylate (PMMA) of the tooth and provides free double bonds that may copolymerize with the PMMA of the denture base resin.
Wetting the repair surface with MMA dissolved the surface structure of PMMA and that a duration of 180 s of wetting with MMA improved adhesion, compared with shorter durations of wetting. In addition, the authors reported that a duration of 180 s of wetting with MMA created smoother surface texture than a shorter duration.
Acetone is an organic compound with the formula (CH3)2CO. It is a colorless, mobile, flammable liquid, being the simplest of the ketones. Acetone is miscible with water and is a good solvent for most plastics and synthetic fibers including those used in laboratory bottles made of polystyrene, polycarbonate, and some types of polypropylene and it is used by the pharmaceutical industry and as a denaturation agent in denatured alcohol.
Acetone application created a smoother surface but with more superficial pits. Similar to this study, Rached and Del Bel Cury found that acetone application demonstrated a smoother and cleaner surface than monomer on PMMA surface texture.
Dalal et al. reported that a short curing cycle produced specimens with low bond strengths irrespective of the type of heat-cured acrylic resin used. Long curing cycles produced specimens with acceptable bond strengths.
Clinically, the most important stress factors leading to bond failure are the shear stresses. For this reason, the shear test was chosen as the more appropriate one to determine the bond strength under masticatory stresses.
The results of the present study revealed that acrylic resin teeth treated with acetone surface treatment processed under a long curing cycle (Group C subgroup II) recorded the highest mean shear bond strength value, whereas the control group samples which were left untreated processed with short curing cycle recorded the least mean shear bond strength value. Although the most likely mechanism for the increase in bond strength of acrylic tooth to denture base is the result of tooth surface treatment, the effects of the inherent strengths of acrylic tooth and denture base material cannot be eliminated.
| Conclusion|| |
From the results obtained, it was clear that the surface treatment on the bonding surface of acrylic teeth before packing definitely improved bond strength. Acetone surface-treated group processed with long curing cycle had good bond strength values and control group with short curing cycle had the least bond strength values.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]