DENTURE BASE RESINS(Dr.ANJU SREE DURGA)
- 2. DENTURE BASE RESINS Dr.Anju Sree Durga.B Department of Prosthodontics
- 4. Introduction • Denture prosthesis is composed of artificial teeth attached to a denture base • Although individual denture bases may be formed from metals or metal alloys, the majority of denture bases are fabricated using common polymers • Such polymers are choosen based on availability, dimensional stability, handling characteristic, color and compatability with oral tissues.
- 5. Contents • Definition • Classification • Dental polymers • Ideal requirements of denture base resin • Ingredients • Types • Properties • Cytotoxicity • Conclusion • References
- 6. Definition • Denture base- the part of a denture that rest on the foundation tissues and to which the teeth are attached (GPT- 9) • Denture base material – any substance of which a denture base may be made.(GPT-9)
- 7. History
- 8. • Polimers :- chemical compound of huge organic or inorganic molecules formed by large number of repeating smaller structural units • Monomer :- simple chemical compounds or repeating units reacting to form a polymer.
- 9. Classification • According to ISO 1567 • Type 1 – Heat processed denture base material • Type 2 – Autopolimerised denture base material • Type 3 Thermoplastic blank • Type 4 Light activated materials • Type 5 Microwaved cured materials.
- 10. • Based on usage:- • Temporary denture base resin • Self cure acrylic • Shellac base plate • Permanent denture base resin • Heat cure denture bases • Light cure resins
- 11. Polymerisation
- 12. • Powder Prepolymerised spheres of polymethyl methacrylate Ethyl or butyl methacrylate(5%) Benzoyl peroxide Dibutyl phthalate Compounds of mercuric sulphide or cadmium sulphide Zinc or titanium oxide Dyed synthetic nylon or acrylic fibres Liquid Nonpolymerised methylmethacrylate Dibutyl phalate Glycol dimethacrylate Hydroquinone
- 14. Copolymerization • Macromolecules may be formed by polymerization of single type of structural units. • To change the inherent properties of the homopolymer, two or more chemically different monomer are used • Act as internal plasticizer.
- 15. Types of copolymer • Random type • Monomers are randomly distributed • Graft type • Sequence of one of the monomer are grafted onto the backbone of second monomer. • Block type • Identical monomer units occur in relatively long sequence along the main polymer chain
- 16. Types of polymers Linear polymers
- 17. Cross linked polymers The backbone chains are cross linked by covalent bonding , by adding a cross linkng agent. This improves the physical properties of the polymer Eg :- Ethyleneglycol dimethacrylate
- 18. Polymerisation Condensation polymerization Chemical reaction between bifunctional or trifunctional molecules resulting in stepwise growth to form polymers. Some byproducts of small molecules are formed Polymerization is not fast Low degree of polymerization Low molecular weight
- 19. Addition Polymerization Ionic addition • Hydrogen ion transfer from one to another Ring opening addition • Monomer containing terminal rings are opened by amines Free radical addition • Polymerisation begins from an active centre like a free radical
- 20. Stages of polymerization Induction • Free radicals are produced by dissociation of certain chemicals by different activation energy system. • Free radicals may later combine with monomer and initiates polymerization. • This interval is known as induction period.
- 21. Propagation • Radical monomer complex act as free radical and combines with another monomer and forms dimer radical • This process repeats one after other to form a polymer chain • This takes place instantaneously until all monomers are exhausted • Reaction is exothermic.
- 22. Chain transfer • Active free radical energy of the growing chain, can get transferred to another monomer or already terminated polymer . • The first polymer chain gets terminated and next one starts growing by this hydrogen ion transfer .
- 23. Termination • Chain reaction can be terminated either by direct coupling or by exchange of hydrogen atoms from one growing chain to the other.
- 24. Inhibition of polymerization • Certain impurity atoms can react with free radicals or neutralize the growing chain. • Eg:- hydroquinone
- 25. Physical stages of polimerisation
- 26. Polymer – monomer interaction Sandy stage • Little or no interaction occur on a molecular level • Consistency of mixture is coarse or grainy Stringy stage • Monomer attacks surfaces of individual polymer beads • These polymer chains uncoils, therby increasing the viscosity of the mix • This stage is characterized by stringiness or stickiness Doughlike stage • Increased number of polymer chains enter the solution • Mass behaves as a pliable dough. • Ideal for compression molding
- 27. Rubbery stage • Monomer is dissipated by evaporation and penetration into remaining polymer beads • Mass rebounds when compressed or streched Stiff stage • Evaporation of free monomer • Mixture appears very dry and resistant to mechanical deformation
- 28. Ideal requirements of denture base resins
- 34. Types of denture resins • Heat activared denture resins • Chemically activated denture resins • Light activated denture resins • Microwave activated resin
- 35. Heat activated denture base resins • Heat activated materials are used in the fabrication of nearly all denture bases. Powder Prepolymerised polymethyl methacrylate Ethyl or butyl methacrylate(5%) Benzoyl peroxide Dibutyl phthalate Compounds of mercuric sulphide or cadmium sulphide Zinc or titanium oxide Dyed synthetic nylon or acrylic fibres Liquid Nonpolymerised methylmethacrylate Dibutyl phalate Glycol dimethacrylate Hydroquinone
- 36. Compression molding technique Heat activated denture base resins are shaped via compression molding. Steps:- • Preparation of split mold • Application of separating medium • Packing • Curing • Finishing and polishing
- 38. Polymer to Monomer ratio • Polymerisation of methylmethacrylate to form polymethylmethacrylate yields 21% decrease in volume of material • Using 3:1 ratio , volumetric shrinkage may be limited to approximately 7% and 0.5% linear shrinkage
- 39. Injection molding technique • Wax sprues are attached to wax denture base. • Flask is placed into a carrier that maintain pressure during resin introduction and processing. • Resin mixture is introduced into room temperature mold • Flask is then placed on the water bath for polymerization • As the material polymnerises , additional material is introduced into mold cavity. • Upon completion denture is recovered, finished and polished.
- 41. • Advantages • Dimensional accuracy • Homogenous denture bases • No increase in vertical dimension • Low free monomer content • Good impact strength • Disadvantages • Higher cost of equipment • Less craze resistance
- 42. Polymerisation procedure Polymerisation of denture base resin is exothermic process Above 70°c benzoyl peroxide decompose and gives of free radicals for the reaction As the reaction proceeds , temperature of resin will rises. Temperature of resin should not be allowed to rise above 100.8°c as this may leads to internal porosity.
- 43. Polymerisation cycles • A constant temperature waterbath at 74°c for 8hrs or longer, with no terminal boiling treatment. • Processing in a 74°c waterbath for 8hrs and then increasing the temperature to 100°c for 1hr. • Processing the resin at 74°c for approximately 2hrs and increasing the temperature of waterbath to 100°c and processing for 1hr. • Following completion of polymerization cycle , denture flask should be cooled slowly to room temperature.
- 44. Polymerization via microwave energy This technique employs a specially formulated resins and a nonmetallic flask. Polymerization heat is dispersed more efficiently and polymerization is rapid with minimal porosity. Microwave acts only on the monomer, which decreases in the same proportion as the polymerization decreases.
- 45. Advantage:- • Greatly reduced curing time • Shortened dough forming time • Minimal color changes • Less fracture • Lower residual monomer ratio • Most stable
- 46. Disadvantages • Less bond strength of resin to denture teeth • Plastic flask and policarbon bolts are very expensive
- 47. Chemically activated resin Heat activated resin Heat Benzoyl peroxise Production of free radical Polymerisation Chemically activated resin Dimethyl-para-toluidine (tertiary amine) Benzoyl peroxide Production of free radical Polymerisation
- 48. Techniques Sprinkle on technique Fluid resin technique Compression mold technique
- 50. • There is greater amount of monomer which creates 2 difficulties:- • A) It act as a plasticizer which decrease the transverse strength of denture base . • B) Residual monomer act as a tissue irritant, therby compromising the biocompatibility of the denture base.
- 51. Light activated denture base resin • This material has been described as a composite having a matrix of urethane dimethacrylate and microfine silica • Visible light is activator. • Camphoroquinones act as initiator for polymerization. • Single component denture base resin is available in sheet and rope form in light proof pouches.
- 52. Technique • After teeth arrangement, denturebase is molded on accurate cast • Then the denture base is exposed to high intensity visible light source for an appropriate period. • Following polymerization denture is removed from the cast, finished and polished in a conventional manner.
- 53. Advantages • Less porosity than chemically activated resin • Facilitates final fabrication in mouth • Lighter • Decreased polymerization shrinkage • Non toxic
- 54. Disadvantage Cannot be flasked in conventional manner. Factors such as light intensity, angle of illumination, distance of resin from light source can affect number of free radicals formed making this system technique sensitive.
- 55. Physical properties of denture base resin
- 56. Physical properties Methyl methacrylate • It is a clear transparent, volatile liquid at room temperarure • Melting point : -48°c • Boiling point : 100.8°c • Density : 0.94g/cm3 • Heat of polymerization : 12.9Kcal/mol • Volume shrinkage : 21% Polymethyl methacrylate • It is an amorphous structure which is tasteless and odourless. • Density is 1.19
- 57. Polymerisation shrinkage • Volumetric shrinkage : 21% • When prepolymerised polymer is used, volumetric shrinkage becomes 7%. • Shrinkage exhibited by this material is distributed uniformly to all surfaces. • Based on projected volumetric shrinkage of 7%, linear shrinkage should exhibit approximately 2% • Thermal shrinkage is responsible for linear shrinkage phenomenon • Processing shrinkage for • Heat activated resin : 0.53% • Chemically activated resin :0.26%
- 58. Porosity • Causes • Vapourisation of unreacted monomer and low molecular weight polymer • Inadequate mixing of powder and liquid components • Inadequate pressure or insufficient material in the mold cavity • Air inclusion
- 59. Water absorption • Cause of water absorption : diffusion, polarity of molecules • Effect of water absorption : act as plasticizer Expansion of polymerized mass. • Water sorption value : 0.69mg/cm3 • It has been estimated that for each 1% increase in wt produced by water absorption, acrylic resin expands by 0.23% linearly • ANSI/ADA Specification No : wt gain should not be more than 0.8mg/cm2
- 60. Crazing • It is suface flaws or microcracks on denture base resin • Causes : stress application Solvent action(ethyl alcohol) • Transparent resin : hazy or foggy appearance • Tinted resin : whitish appearance • Surface cracks predispose a denture resin to fracture.
- 61. Strength • Factors affecting strength a) Composition of resin b) Processing technique c) Degree of polymerization d) water sorption e) condition presented by oral environment • Compressive strength : 76MPa • Tensile strength : 48 – 62 MPa
- 62. • Impact strength • It is a measure of the energy absorbed by a material when it is broken by a sudden blow • Heat cure acrylic> Autopolymerising acrylic
- 63. Denture warpage • It is the deformity or change of shape of the denture which can affect the fit of the denture. • Causes :- • Stress caused by curing shrinkage or uneven cooling • Rise in temperature during polishing • Immersion of denture in hot water • Packing of resin in rubbery stage
- 64. Resistance to acids, bases, and organic solvents • Resistant to weak acids or bases and organic solvents • Soluble in aromatic hydrocarbons, ketones and esters. • Solution containing alcohols should not be used for cleaning or storing the dentures • Incorporating ethylene glycol dimethacrylate as a crosslinking agent improves solvent resistance.
- 65. Solutions for microbial control • Microorganisms like Candida albicans, Streptococcus oralis, Bacteroids gingivalis, S. sanguis can adhere to denture base acrylic • Chlorhexidine can bind to acrylic surfaces for atleast 2 weeks • Treating acrylic with nystatin, followed by drying, produces similar results. • Using phenol disinfectant can cause surface damage to denture base resin • Several studies have identified that metal oxide nanoparticles (MgO, TiO2, ZnO) reinforced dentures has antimicrobial property.
- 66. Denture cleansers • Dentures are cleansed by either immersion in an agent or brushing with cleanser. • Immersion agents contains alkaline compounds, detergents, sodium perborate and flavouring agents • Perborate alkaline peroxide oxygen • Vinegar is effective in dissolving calculus.
- 67. Cytotoxicity • Residual monomer has the potential to cause • Irritation • Inflammation • Allergic response to oral mucosa • Clinical signs and symptoms includes • Erythema • Erosion • Burning sensation of mucosa and tongue.
- 68. • They are most commonly manifested as type I hypersensitivity reactions (anaphylaxis) or type IV (contact stomatitis, dermatitis and, upon repeated contact with the allergen). • According to the standard (ISO 1567: • 1999) the maximum allowed amount of residual • MMA for hot polymerized acrylate is 2.2%, and • for the cold polymerized is 4.5%.
- 69. Conclusion • There are wide variety of denture base materials and the ever growing urge to find the best and the most feasible material will always bring an evolution in denture base material science. • As clinicians, we must understand the basic nature of each of these, to provide the best possible treatment to our patients.
- 71. Reference • Kenneth J Anusavice; Philips science of dental materials 11th edition • Robert C Craig , John M Powers, John C Wataha; Dental materials properties and manipulation; 11th edition • V K Subbarao; notes on Dental materials 4th edition • Basic dental materials – John J Manapallil 3rd edition
- 72. Evaluation of Cellular Toxicity of Three Denture Base Acrylic Resins M. Ebrahimi Saravi, M. Vojdani, F. Bahrani Residual monomer content and its release into water from denture base materials Pekka K. Vallittd, Varpu Miettinen’, Pekka Alakuijala2 Adverse reactions to denture resin materials m Kostic, A Pejcic, Gligorigevic