Dental technology-Effect of surface treatment on bonding of reline poly (methyl methacrylate) to denture base resin.

OTAGO UNIVERSITY
Effect of surface treatment on bonding of reline poly(methyl methacrylate) to denture base resin: literature review
ID: 2842238

Introduction
Because of alveolar bone resorption and/or change of oral mucosal underlying, all complete dentures will suffer from losing retention after a period of use. In the clinical area, a successful reline denture is depending on the ability of reline resin to bond to the denture base resin.11The purpose of this literature review was to identify the effect of surface treatment on bonding of reline poly (PMMA) to denture resin.
With the aging of complete or partial dentures after years, the gradual changes of oral tissues need the denture to be relined to improve the fitness to the supporting tissue. There are several significant problems for the denture wearing patient, such as chronic soreness patients with diabetes, heavy bruxing or clenching habits patients.4 However, it is very important to have a close evaluate of the character and quality of the denture before examining it intraorally. Some conditions of the denture may not be suitable for the reline treatment. 1. Poor color or appearance of the base resin, 2. Excessive thinness of the denture borders(less than 2mm), 3. Small circumference and physical size of the denture, 4. Low height of the vestibular borders and 5. Palatal vault at or near the same horizontal level to the ridges. 8There are two main lining materials being used in the denture reline procedure which are hard lining and soft lining materials. For the hard lining materials, different subgroups are divided, such as cured-in-mouth, light-cured and heat-cured. For the over-sensitive mucosal patients soft or resilient liners are especially preferred. To achieve the best results for relining process, the same type of cured lining materials are suggest to be used since the similar tensile strength and bonding properties.4Futhermore, the proper functioning of relining PMMA to denture base resin depends to a great extent on their characteristics and mechanical properties. Previous studies of reline materials are evaluated their chemical compositions and residual monomer content. Physical and mechanical properties are such as hardness, flexural strength, solubility and water sorption also being observed. However, surface treatments by using different burs during denture reline procedure are another field need to discover.

Reviews
1. Silicone based denture liners were better than those acrylic based denture liners, but the adhesion with denture base was the problem of failure. Soft denture liners are usually used for management of pain or atrophic mucosa, bone cutting or ulcer and denture related area. Denture liner provide the patient with comfortable, may through the bearing area in the function is reduced in the process of residual alveolar ridge and also provides the function of uniform load distribution to reduce the impact force. Soft lining materials as polyethylene resin plasticizing first developed in 1945, followed by silicones in 1958. The soft lining materials can be divided into two main groups: acrylic and silicone based. Silicone based liner was found compliance and fracture resistance, better and plasticizing acrylic denture liner based on in the saliva of low adsorption, dissolution. However, silicon resin as the main problem based denture liners is the strength of denture base resin adhesive with interface damage. Silicone adhesion failure with acrylic denture base material is an important clinical problem. Between the liner and denture base resin adhesion failure will create a potential interface for micro leakage which has the potential for bacterial growth and accelerate the decomposition of the deteriorating, prosthetic. In order to achieve a better bonding of denture lining material and denture base resin, several experimental process such as mechanical surface preparation have been conducted. i.e., roughening of denture base resin which including both chemical and mechanical surface treatment. The present study shows that chemical surface treatment of denture base resin increased the tensile bond strength of silicone based liner whereas decreased the flexural strength of denture base resin.1

2. Although the resilient lining materials have been used in dentistry for many years, they are not widely used, because they do not have the optimal properties. Heat-polymerized silicone-based resilient lining material has better adhesion strength compare to autopolymerized silicon-based resilient. Therefore, it is commonly used in the clinical dentistry . There were also some studies on the postpolymerization treatments of autopolymerization reline resins shows increasing of the flexural strength by using microwave and water bath post-polymerization treatments7.
3. Many hard denture re-lining materials available on the market today, but displayed with some problems in the polymerization process, high polymerization temperature, microstructure, porosity, filling the mouth color and denture plaque. In recent years, less tissue irrigation during polymerization has been improved by various chemical accelerated and lightactivited polymers. And there was a study on the effects of thermal stress on the flexural strength of denture base polymers, hard relines polymers, and combination polymers. The study shows that the flexural strength of polymer composite samples after thermal cycling was significate greater than that of all hard reline polymer only specimens .

4. Direct relining of dentures made with “chairside reline systems ” are better than those in the lab processing, because of the direct method is faster, does not cause significant changes dimensionally. In some clinical situations, the thickness of the denture base resin is much greater than reline resins. Therefore, dynamic mechanical properties of these materials may affect the difference of the interface stress5. The method of using autopolynerizing acrylic resins direct relining of denture bases is inexpensive and not time sonsuming. However, there are also some disadvantages appears in the clinical such as unpleasant odour, taste and soft mouth tissue irritation. Therefore, the hard chairside resins for relining the denture bases would eliminate the disadvantages.

5. The application of bonding agents, methacrylate monomer, or other organic solvents on the denture base resin surface can improve the adhesion of reline materials. These treatments lead to the polymer surface expansion, polymerization and formation of interpenetrating polymer network structure which have been observed increasing depth of the swollen layer on the denture base surface and high bond strength for reline bonding agents6. In the process of the relining procedure, treating with monomer, solvent, or bonding agent are recommended to achieve proper adhesion between reline materials and denture base materials.

6. Lased and sandblasted surface preparations also affect the bonding strength.
Sandblasting by using aluminum oxide particles on the denture base is conflicted to increase bond strength of acrylic resin denture base and soft lining material. Laser has become widely used in dentistry since the ruby laser was developed by Maiman in 1960.13It has not been used to roughen PMMA surfaces yet in clinical, but it has been commonly used in ceramic process to etch the metals before application of porcelain. Theoretically, increased surface and mechanical locks by sandblasting and laser should all benefit from the stronger bond. From the previous research shows that if polymethyl methacrylate surface was treated by sandblasting or lasing before applying resilient liner relining agents, it would reduce peel strength compare to the untreated polymethyl methacrylate surface. It may because of stresses which happened during the interface of the PMMA and soft liner junction.12

Discussion
To achieve a more equal distribution of the load on regaining the optimal adaptation of the denture base to residual ridges, lining materials are being used. 4
In the process of the relining, interpenetrating polymer networks are formed by diffusion and polymerization of monomer across the reline resins-denture base interface. 9From the previous studies, an autopolymerising reline resin shows lower flexural strength than heat –polymerised denture base resins. And the flexural strength of denture base resins can be significantly decreased after relining. Also to prevent fracture of the denture, impact strength is essential. During the research test, the strength of the interfacial adhesion will cause failure occur differently when the cracks reach the interface. To avoid creating conditions for staining and bacterial adhesion in denture, surface treatments such as the application of surface primers before relining will improve the bonding strength.
Summary

Ideally, the bond strength between the denture base resin and the reline material should be as strong as the original denture base before the relining procedure. In order to achieve better bonding results, denture base surface treatment before relining seems necessary and several methods have been suggested.9
References

1. Saloni G. Indian Prosthodontic Society: Effect of Surface Treatment on the Flexural Strength of Denture Base Resin and Tensile Strength of Autopolymerizing Silicone Based Denture Liner Bonded to Denture Base Resin: An In Vitro Study: J Indian Prosthodont Soc (Oct-Dec 2010) 10(4):208–212.

2. Mustafa G, Zeynep YD, Murat A. Effect of surface treatments on the bond strength of soft denture lining materials to an acrylic resin denture base. The Journal of Prosthetic Dentistry.
3. N. Archadian, F. Kawano, T. Ohguri, T. Ichikawa, N. Matsunoto. Flexural strength of rebased denture polymers. Journal of Oral Rehabilitation 2000 27; 690–696.
4. A.K. Aydın, H. Terziog˘lu, A.E. Akınay, K. Ulubayram, N. Hasırcı. Bond strength and failure analysis of lining materials to denture resin. Dental Materials 15 (1999) 211–218.
5. Hiroshi M., Rosangela S S., Taizo H., Gregory L. Mary J F. Dynamic mechanical properties of hard, direct denture reline resins. The Journal of Prosthetic Dentistry.
6. Alessandro R G., Ana L M., Carlos E V., Eunice T G., Ana C P. The Journal of Adhesion: Effect of Disinfection on Adhesion of Reline Polymers. The Journal of Adhesion, 83:139–150, 2007.
7. Rosangela S S., Carlos E V., Eunice T G., Ana C P., Ana L M. EFFECT OF POST-POLYMERIZATION TREATMENTS ON THE FLEXURAL STRENGTH AND VICKERS HARDNESS OF RELINE AND ACRYLIC DENTURE BASE RESINS. J Appl Oral Sci. 2007; 15(6):506-11.
8. Russell J., Joseph N. General considerations prior to relining of complete dentures. THE JOURNAL OF PROSTHETIC DENTISTRY, FEBRUARY 1984, VOLUM51, NUMBER 2.
9. C. R. LELES, A. L. MACHADO, C. E. VERGANI, E. T. GIAMPAOLO & A. C. PAVARINA. Bonding strength between a hard chairside reline resin and a denture base material as influenced by surface treatment. Journal of Oral Rehabilitation 2001 28; 1153±1157.
10. Luciano Elias da Cruz Perez, Ana L M., Sebastia˜o V C., Carlos E V., Eunice T G. and Ana Cla´ udia Pavarina. Effect of reline material and denture base surface treatment on the impact strength of a denture base acrylic resin. Journal compilation 2009 The Gerodontology Association and Blackwell Munksgaard Ltd, Gerodontology 2010; 27: 62–69.
11. Fazrina A., Mirza B. and Norsiah Y. The effect of bur preparation on the surface roughness and reline bond strength of urethane dimethacrylate denture base resin. Indian Journal of Dental Research. 22.2 (March-April 2011): p210.
12. Nancy L. J.,Donald L. M.,Dean L. J.,Raleigh A. H. Lased and sandblasted denture base surface preparations affecting resilient liner bonding. The Journal of Prosthetic Dentistry: Volume 78, Issue 2, August 1997, Pages 153–158.
13. Hakan A., Faik T., Burcu M., Gulsah A., A. Kemal Ozdemir. Effect of different surface treatments on tensile bond strength of silicone-based soft denture liner. Lasers Med Sci (2011) 26:783–788.