Hello everyone and welcome back to easy dentistry hope you all are doing really good and enjoying studying with us friends if you like our videos please comment and do tell us because your comments are really really our motivation to upload more videos also friends please subscribe to our channel and please don't forget to hit on the bell icon so that whenever we upload a new video you get notified. Today we are here with an important and vast topic from dental materials which is the denture base materials. We will be studying this vast topic in four parts.
Today we are studying the part one in which we will be studying the introduction, the classification, what are synthetic resins, what are the classification of synthetic resins what are the ideal requirements of the resins and what are the uses then we will be studying about the polymers what is the basic nature of the polymer what are the various structures of the polymer then we will be studying about the polymerization process what are the chemical stages of polymerization what causes inhibition of polymerization then we will be studying about the copolymers copolymerization and finally we will be studying about what are the plasticizers which are used in the denture based materials so coming to the introduction in the earlier days for making dentures certain materials were used these were the vulcanite nitrocellulose phenol formaldehyde and porcelain But each of these anciently used denture based materials had some disadvantages. So in this picture we can see a denture which is made up of vulcanite. This vulcanite contains 32% sulfur and certain metallic oxides.
So the advantages of this vulcanite denture based resin was that it was non-toxic. and non-irritant to the oral tissues and had excellent mechanical properties and sufficiently hard. But the limitations of the vulcanite denture material is that it absorbs saliva. And because of the absorption of saliva, you can see here there is bacterial proliferation. And this bacterial proliferation gives an unpleasant taste an unpleasant odor from the denture.
And because of this bacterial colony formation, there is poor aesthetic appearance to this denture. And also dimensional changes may occur during processing of the vulcanite denture. So, these are all the disadvantages of vulcanite denture material.
Now, the other denture-based material which was used initially was the nitrocellulose. This is a denture which is made up of nitrocellulose. You can see the denture base made up of nitrocellulose. This nitrocellulose was dimensionally unstable. It had an unpleasant taste.
There was an increased tendency of warpage of this denture based material. So, the fit of the denture was not proper. Also, water absorption took place in this denature-based material and there is poor color stability in nitrocellulose. Another denature-based material which was used in ancient times is phenol formaldehyde. This phenol formaldehyde was under easy discoloration.
And it was un-aesthetic in appearance and it was very difficult to repair if the denture was broken. Then porcelain was used. This is a picture of a porcelain denture based material. But using porcelain as a denture based material, it is difficult to fabricate and also the material is easy to break. Now, the classification of denture based materials.
An important question which is asked in exams frequently as MCQs in your viva. So, get thorough with it. The denture-based materials are classified in two types.
The first basis of classification is whether the denture-based material is metallic or non-metallic. The metallic denture-based materials include the cobalt chromium, gold, aluminium and stainless steel. while the non-metallic include the acrylic resins and the vinyl resins. Other method of classification is whether the denture-based material is temporary or permanent.
The temporary denture-based materials include the self-cure or the cold-cure resins, then the shellac base plate and the base plate wax, while the permanent denture-based materials include the heat cure and the metallic denture-based materials. So, these are the two methods of classification of denture based materials. Now, what are synthetic resins?
Modern living is greatly influenced by synthetic plastics. These synthetic plastics are non-metallic compound and they may be Of two types, they may be fibrous and rubber-like or they may be hard, resinous type. These synthetic plastics are high molecular weight polymers and they were earlier considered as a lab waste.
These are waxy, sticky residues left after certain organic reactions and are lab waste. After 40 years, this lab waste, it attracted attention of the chemist and this lab waste gave rise to the wide field of plastics. So, if we classify the resin, the resins are classified on the basis of their thermal behavior, their response to temperature, They are classified as thermoplastic and thermoset. So the thermoplastic resins they are softened under heat and pressure. If the heat increases or if the material is heated it undergoes softening.
It undergoes softening under heat and pressure and it is cooled after molding. In thermoplastic resins, no chemical changes occur. Only the change occur in response to temperature.
And these thermoplastic resins are soluble in organic solvents. Examples of the thermoplastic resins include polymethyl methacrylate, polyvinyl acrylics and polystyrene. While the thermoset resins, in the setting of the thermoset resins, there is occurrence of a chemical reaction. So, because of this chemical reaction, the final product which is formed is chemically totally different from the original substance.
These thermoset resins are insoluble in any organic solvent. Examples of the thermoset resins include cross-linked polymethyl methacrylate and the silicones. So, we will now see the ideal requirements of dental resins.
This is a question which is asked as a short answer question in exam. So, ideally any denture based resin should be tasteless, odorless, it should be non-toxic. and non-irritant.
Also, it should be aesthetically very good. It should be dimensionally stable so that the fit of the denture is maintained. And it should have adequate strength, resilience, abrasion and resistance to fracture.
It should be insoluble and impermeable to the liquids. It should be light in weight. It should, it should, the softening temperature of the denture-based material should be more than the temperature of the food which is taken into the mouth. So, in short, it should, this denture-based material should not be softened by the usual food which is taken into the mouth.
Also, this denture based material should be easy to fabricate and repair. It should have high thermal conductivity and it should be radio opaque. Why it should be radio opaque? The reason is that if a denture fragment is accidentally swallowed by the patient, if it is radio opaque, it can be easily detected with the help of the X-rays. Ideally, no resin meet all these requirements.
But all these are the important ideal requirements of the denture base resins. So, what are the uses of these resins? First, it is used to make dentures in dentistry.
Then, these resins are also used to make the artificial teeth to be used in dentures. Then the resins are also used as a restorative material. We will be studying in detail the restorative resins or the composites in detail in the further lectures which will be uploaded soon after this lecture. After we complete the entire denture based material, we will upload a lecture on restorative resin. So here keep it in mind.
the resins are also used as a denture based material as you can see here a tooth colored filling is made on this tooth then these resins are also used as cements as for fabrication of space maintainers this is a maxillary transpalatal space maintainer so to maintain a space between these teeth A space maintainer is constructed. This is entire the space maintainer which is made up of resins. Then another important use of resins is to make the crown and bridge facings.
So you can see here this is a bridge of four units. So the buckle facing or the facing the side of the tooth which is visible to other people is made up of a facing which is made up of the resins also it is used for making the maxillofacial prosthesis so you can see here the this is the maxillofacial prosthesis which will cover this defect on the face so this prosthesis is made up of resins Also, it is used for making temporary crowns. Raisins may also be used as a root canal filling material. So, you can see here the root canal filling material may be of the raisins.
Also, the dental raisins are used for making the athletic mouth protector. During the sports to avoid injury to the teeth. The athletic mouth protector is used which is made up of the resins. Also impression trays are made up of resins. So these are all the uses of the resins.
Hope you will all remember this based upon the pictorial representation. So now let us study what are the polymers. What is the basic nature of the polymers? The word mer is the simplest repeating chemical structural unit.
So polymer is a structure which is made up of numerous number or poly or numerous mer units. So the word poly means many and mer is the simplest structural unit. So the polymer is made up of many mers or the monomers. So this is a chain of polymer which is made up of numerous monomers. So the polymer is made up of numerous monomers.
So monomer is from which the polymer is constructed. And the polymer is made up of numerous monomers. I think this concept of polymers and monomer is very much clear in your mind.
So for a easy understanding this these are individual monomer units and when these units they join with each other they form a polymer. So polymethylmethacrylate is a polymer having chemical structure derived from the methyl methacrylate. So, polymethyl methacrylate is a polymer which is made up of methyl methacrylate monomer.
Various numerous molecules of methyl methacrylate, they join to form the polymethyl methacrylate. Now, Those molecules having molecular weight more than 5000 are considered as polymers. The what are copolymers? Copolymers are mixture of different types of monomers. For example, if there is one type of monomer which link with another type of monomer which link with the third type of monomer.
So more than one types of monomers they are present in this molecule. So this is called as a copolymer. The molecular weight of this polymer may be from thousands to millions and this molecular weight they determine the physical properties of this polymer.
So the molecular weight of polymer can be explained as the molecular weight of various monomers. multiplied by the number of the monomers. I'll repeat the molecular weight of the polymer can be calculated as the molecular weight of various monomers multiplied by the number of monomers. So what is the degree of polymerization? The degree of polymerization is defined as the total number of mers in a polymer so the increased molecular weight causes increased degree of polymerization if the molecular weight of the polymer is high it means it has a high degree of polymerization this increased degree of polymerization it increases the strength of the polymer now Let us see the molecular weight distribution.
If the molecular weight distribution is narrow, it is the most useful polymer. So, ideally the molecular weight distribution should be narrow. If the molecular weight distribution is more, then the material becomes more stiff and the melting point it increases. Let us now study the structure of polymers.
The structure of polymers, the polymers are of three types, the linear polymer, branched polymer and the cross-linked polymer. In the linear polymer, the mer units are connected to each other in a linear sequence. So, this linear type of polymers are again of three types. The linear homopolymer, the random copolymer of linear type and the block type copolymer.
So, in the linear homopolymer, The monomer units are of same type. You can see here the monomer units are of same type. In random copolymer of linear type, the monomer units are randomly distributed along the chain. You can see here the monomer units are of different types. One is this M, one is this Y and they are randomly distributed in a linear chain.
So this is called as random copolymer in which more than one type of monomer is present and it is of linear type. Then again it is block copolymer. In this type, two types of monomers are distributed in block. So, you can see here, this is one block of monomers, this is another block of monomers and this is the third type, third block of monomers.
So, the monomers are distributed in blocks. Now, the second type of polymers are the branch type. This branch type of polymers are again of three types the branched homo polymer, the random copolymer of branch type and the So the branched type of polymer is again of three types the branched homo polymer, the random copolymer of branch type and the graft copolymer. The branched homopolymer is made of mer units or the monomer units of the same type. So you can see here the monomers are of the same type and they are just arranged in branched fashion.
Then the random copolymer of branch type. These in this type two types of monomers. So you can see here two types of monomers are distributed randomly in a branched fashion.
Now what is graft copolymer? In graft copolymer, One type of monomer unit form the main chain. So you can see here one type of monomer unit it forms the main chain.
And on this main chain another type of monomers are present as branch. So this is called as graft copolymer. Now the third type of polymer are the cross-linked ones.
In this cross-linked polymer two types of monomers are present. You can see here two types of monomers are present on the main chain and these two main chains are then connected by a single type of monomer. So you can see here in the main chain two types of monomers are present the Y and the M and these two main chains are connected by a single type of monomers which is Y.
So this is called as cross linked polymer. So what is the polymerization chemistry? So polymerization is defined as a series of chain reaction by which polymer is formed from the monomer. In simple diagram if two monomers are connected to each other it forms a polymer. So, polymerization is a repetitive intermolecular reaction capable of proceeding indefinitely.
There are two types of polymerization reaction, the condensation polymerization and the addition polymerization. Now, let us study the condensation polymerization in detail. Condensation polymerization is always associated with the elimination of small molecules. And in another type, the functional groups are repeated to form the polymer chain. The small molecules which are eliminated are also called as the byproducts, which are water, halogen acids and ammonia.
By condensation polymerization, high molecular weight molecules are very difficult to form. So, as high molecular weight molecules are not formed, these are not routinely used in dentistry. Another type of polymerization is the addition polymerization.
In addition polymerization, there is no change in the chemical composition. So, no byproducts are formed in addition polymerization. So just the structure of the monomers is repeated many times in the polymer. So the reaction it just starts at an active center and one molecule is added at a time and the chain it grows rapidly.
As the molecules are added, the chain grows very rapidly. And indefinitely and the process is very simple but not easy to control. What are the chemical stages of polymerization? There are four chemical stages of polymerization. The induction, propagation, termination and finally the chain transfer.
So let us study each of this chemical stage in detail. This is an important question. What are the chemical stages of polymerization? Asked frequently in exams, so get thorough with it.
Stage 1 is the induction. So, what happens in the induction? In the induction phase or the initiation phase, the molecules of this initiator is energized. As a result of which, this energy is transferred to the monomer molecules.
This energy is transferred to the monomer molecules and the initiation of polymerization occurs due to transfer of this energy from the initiator to the monomer. Now, if any impurities are present, they increase the length of initiation, increase in temperature. If the material is heated, then the initiation period is reduced. The initiation energy for activation of each monomer molecule is 16000 to 29000 calories per mole. There are three types of induction systems, the heat activation, chemical activation and the light activation.
By heat activation, most of the polymerization reaction occurs. When heat is applied to the benzoyl peroxide molecule, this benzoyl peroxide release the free radicals which initiate and then it increases the polymerization. Then what is chemical activation?
Two reactants, at least two reactants. For example, this is reactant 1 and this is reactant 2. When they undergo chemical reaction, free radicals are produced and these free radicals causes the polymerization. Then what is light activation? Photons of light energy. Photons, they activate the initiator and this initiator, it releases the free radicals which causes polymerization.
For example, if visible light it falls on camphor, quinone and amine, they release the free radicals for polymerization. The stage 2 of polymerization is the propagation. Once initiation is done, propagation of polymerization occurs.
5000 to 8000 calories per mole energy is required to continue with the chain reaction. And the polymerization is never complete. The chain reaction should continue until all the monomer is converted into polymer. The stage 3 of polymerization is the termination. The termination may occur by direct coupling or exchange of hydrogen atom.
And the final stage is the chain transfer. Chain termination occurs from chain transfer. So, these are the four stages of polymerization.
What causes inhibition or reduces the polymerization? First, the impurities. These impurities, they directly react with the activated initiator or activated nucleus or growing chain and prevent it from growing further.
Hydroquinone, it inhibits this polymerization. So, hydroquinone is intentionally added to prevent polymerization of the monomer during storage. Also, the oxygen present in the air, it reduces polymerization.
Now, let us also study what is copolymerization in detail. So, in copolymer, two or more monomers, they join to each other to form a polymer and the polymer which is formed by different types of monomers is called as a copolymer. These copolymer has improved physical properties.
So, the copolymers are made up of different monomer units. The copolymers can be of three types. The random copolymer in which the monomer units are randomly distributed along the chain.
The graft copolymer in which the backbone of or the main chain of one type of monomer is present and on which other types of monomers are grafted as you can see here. and the block type in which monomer units are distributed in the form of blocks in the main chain. Applications of copolymerization When small amount of ethyl ethyl acrylate may be copolymerized with methyl methaacrylate, it increases the flexibility of the material. Also, when block polymer and copolymer are used together, there is increased impact strength and increased adhesive properties and surface features of the material. What is crosslinking?
Formation of chemical bonds or bridges between linear polymers is referred to as crosslinking. So these are the linear polymers. And formation of bridges in between these linear polymers is called as a cross-linking.
This form a 3D network. Applications of cross-linking, it increases the strength, it increases the solubility, it decreases the water absorption of the material and it increases the resistance to crazing. What is crazing?
We will be studying in the subsequent lectures. Now, what are the plasticizers which are added to the resins? The plasticizers are added to reduce the brittleness, to increase the solubility of the polymer and to reduce the strength. There are two types of plasticizers, external and the internal.
The external plasticizers penetrate between the macromolecules while the internal plasticizers are an integral part of the polymer. So, here we complete with the part 1 in which we have studied the basics of the denture based materials. In part 2, we will be studying the heat activated, chemical activated and the light activated denture based reasons in detail.
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