1-8 DENTAL MATERIALS

Size: px

Start display at page:

Download "1-8 DENTAL MATERIALS"

Junior Strickland
6 years ago
Views:

1 1-8 DENTAL MATERIALS

2 Dental materials NATURE OF DENTAL POLYMERS

3 Nature of Dental Polymers

4 Nature of Dental Polymers Polymer: Polymeric materials are formed of several large molecules (polymer chains) with high molecular weight. These molecules are formed when smaller molecules named monomer are connected together. Monomer: The unit structure of the polymeric materials. It is always in the form of single small molecules and the linkage of large number of these molecules together will result in the formation of large molecule named as polymer.

5 Nature of Dental Polymers

6 Nature of Dental Polymers Polymerization: Chemical reaction resulted in formation of large polymer molecule from smaller monomer molecules. Polymerization shrinkage: Contraction of materials volume at the time of their polymerization. By-product: at the time of condensation polymerization, Small molecules could be formed beside those larger polymer molecules.

7 Nature of Dental Polymers Free radical: It is a molecule containing single unpaired electron which is able to form a bond with any other single electron to reach the stable state. Accordingly this free radical is considered as the active growing center of the polymer. Homopolymer: It is a polymer structure that made of repeating monomer molecules of the same chemical type (name). Copolymer: It is a polymer structure that made of repeating monomer molecules of two or more different chemical types (name).

8 Nature of Dental Polymers Cross-linking: It is a chemical reaction that links the polymer chains together forming a three-dimensional polymer network. This result comes when a cross-linking agent is added to the final monomer compound before its polymerization. Plasticizer: Chemical molecules when added to the monomer compound before its polymerization helps the slippage of polymer chains over each other and makes the polymerized material softer.

9 Nature of Dental Polymers Multifunctional molecule: Monomer molecules that have the ability to give more than one free electron (have two or more double carbon bonds) and accordingly could bond to two or more of the other molecules and increased the rate of polymerization.

10 INTRODUCTION : - Currently, Polymeric materials are widely used in our life disciplines. In dentistry polymers with their different forms also share in many dental applications. -These materials are simply formed of organic (hydrocarbons) chains of simple repeating units (monomers) connected together with covalent bonds. - These chains interact with each other and unite through Van der Waal forces and some times cross-linked to make the polymer structure and determine the material physical form and properties.

11 Different applications of polymers in dentistry: Applications Example of polymers used 1. Denture Fabrication and repair Acrylic resin, composite resin 2. Denture teeth Acrylic resin, composite resin 4. Permanent filling materials Composite resin, compomers 5. Cementing materials Acrylic resin, composite resin, compomer 6. Die materials Epoxy resin, polystyrene 8. Impression materials elastomeric materials 10. Fissure sealant flowable composite 11. Endodontic filling materials Gutta percha 12. Protective mouth gaurd Vinyl polymers 13. Post and core Fiber-reinforced composites 15. Maxillo-facial prosthesis Acrylic resin, silicones 16. Examination gloves Latex rubber, vinyl rubber 17. Many dental instruments

12 CLASSIFICATION OF POLYMERIC MATERIALS Several methods could be utilized to classify polymeric materials, as shown in the following sections, and one can use more than one category of this classification to accurately describe a polymeric material. A. Based on the material s origin 1- Natural polymers : - Naturally occurring materials -They could be made by human, animal and plants such as; proteins (Polyamide, polypeptides), polynucleic acids (DNA, RNA), polysaccharides (Starch, agar, alginate) and polyisoprene (Rubber, gutta percha).

13 CLASSIFICATION OF POLYMERIC MATERIALS 2- Synthetic polymers : - Synthetic polymers are produced either in the industry or laboratories via chemical reactions. For example bakalite, nylon, terylene, and poly (vinyl chloride). - They are non-metallic compounds produced from organic compounds (i.e. they contains carbon, hydrogen and oxygen)

14 CLASSIFICATION OF POLYMERIC MATERIALS Physical properties: a. They can be molded into various forms and then hardened. Depending on the form and the morphology of the molecules the type of the polymer is determined as fibers, rubber-like, resins b. They are bad thermal conductor due to the presence of covalent inter-atomic bonding in addition to the Van de Waal forces

15 CLASSIFICATION OF POLYMERIC MATERIALS Based on the thermal behavior of the polymer : 1. Thermoplastic polymers is a polymer that becomes pliable or moldable above a specific temperature, and returns to a solid state upon cooling 2. Thermosetting polymers - Polymers that solidify during fabrication but can not be softened on reheating. - These products are more stable in storage in comparison to the thermoplastic ones.

16 CLASSIFICATION OF POLYMERIC MATERIALS Based on the polymeric spatial (physical) structure - Normally, the spatial structure of the polymer will determine its properties, for example, the cross-linked polymers flow at higher temperatures than linear and branched polymers. Also, they are less liquid absorbable than both the linear and the branched types. 1. Linear polymers : The monomers are connected together forming long, linear chains

17 CLASSIFICATION OF POLYMERIC MATERIALS 2. Branched polymers - The monomers are connected together forming a tree-like (Branched) polymer chain.

18 CLASSIFICATION OF POLYMERIC MATERIALS 3. Cross-linked - Several polymer chains are connected together to form a three-dimensional network.

19 CLASSIFICATION OF POLYMERIC MATERIALS Based on the molecular chemistry 1. Homopolymers - When single type of monomer contributes in the formation of polymer structure, the formed polymer is named homopolymer. 2. Co-polymers - The polymeric material is composed of many types of compatible monomers; these materials are usually named copolymers - The co-polymerization is usually used to combine the properties of all monomers enrolled in the polymerization (formation of polymer) process.

20 CLASSIFICATION OF POLYMERIC MATERIALS Based on the type of their structure units (monomers) : - The polymer is named according to its unit structure, for example, methyl methacrylate monomer when polymerize give polymethyl methacrylate polymer.

21 REQUIREMENTS OF DENTAL POLYMERS A. Biological and chemical properties - The material should be tasteless, odorless, none-toxic and none-irritant - The material should be impermeable to fluids to prevent the development of taste or odor - The material should be able to obtain smooth surface for better esthetic and to help in preventing both the mechanical irritation to oral tissues and the colonization of microorganisms over material s surface

22 REQUIREMENTS OF DENTAL POLYMERS B. Interfacial properties : - If the polymer is used as filling material, it should bond to the natural tooth structure to prevent any possible microleakage and bacterial ingress along the restoration/tooth interface - Surface energy of the polymer should not be encouraging for plaque retention

23 REQUIREMENTS OF DENTAL POLYMERS C. Chemical properties - The material should not degrade (insoluble) in either oral saliva or other fluids - Materials should be dimensionally stable under all conditions D. Mechanical and physical properties - Polymeric materials should have adequate strength to resist the impact as well as the biting and chewing forces - Materials should be wear resistant - Low specific gravity (Low weight) especially if the material used for constructing upper dentures.

24 REQUIREMENTS OF DENTAL POLYMERS E. Esthetic properties - Material should have the ability to be pigmented and tinted in order to provide the same color as the natural tissue to be replaced. - Maintain the smooth surface to give optical characters (light reflectivity, light refractivity and translucency) near or similar to those of the natural tissues - Materials should be color stable and not easy to be stained by foods and fluids

25 REQUIREMENTS OF DENTAL POLYMERS F. Practicability - Economic and easy to repair - Easy and safe manipulation and handling (Materials should not release and toxic perfumes at the time of its manipulation. At the same time, it should be easily mixed, packed and shaped.)

26 FORMATION OF POLYMERS - Polymers are formed through a series of (repetitive) intermolecular reactions that are capable to proceed indefinitely. - These reactions result in forming macromolecules (polymer) from the micromolecules (monomer). - Polymers can be formed either from single type of monomer molecules (homopolymer) or several types of monomer (Copolymer). - Polymers could also be formed from inorganic elements as in case of silicone dioxide network. - Monomer units connected to each other in the polymer chain by covalent bonds.

27 POLYMERIZATION REACTION It is a repetitive intermolecular reaction in which monomers will change into polymer. Certain features characterize this kind of chemical reactions such as : 1. Affected by all factors that affect any chemical reaction such as temperature, reactants ratio, accelerators and retarders etc. 2. Heat generation (exothermic reaction) 3. Volume contraction (Polymerization shrinkage)

28 POLYMERIZATION REACTION Types of the polymerization reaction : 1. Condensation polymerization reaction 2. Addition polymerization reaction

29 POLYMERIZATION REACTION Condensation polymerization reaction The condensation polymerization reaction is formed of series of simple chemical reactions between two or more molecules to form a large molecule, with elimination of smaller molecule called by-product such as water, ammonia, halogen or acid.

30 POLYMERIZATION REACTION Condensation polymerization reaction 1. Examples of the condensation polymerization reaction a. Formation of biological polymers such as DNA, RNA, and Collagen b. Polymerization of old denture base materials (Valcanite) c. Polymerization of the polysulfide impression material HS-R-SH + HS-R-SH + PbO 2 à HS-R-S-S-R-SH + H 2 O I I I I SH SH SH SH Mercapten + lead dioxide polysulfide rubber + water as by-product

32 POLYMERIZATION REACTION Characters of the condensation polymerization reaction : a. Slow reaction because it goes in steps staring from monomer, dimer, trimer, tetramer, pentamer etc till reaching polymer state b. This reaction results in the formation of small molecular weight polymer chains (Mol. wt.= ) and it is not capable of forming longer chains because, as the chain grows, they become less mobile. Stiffness

33 POLYMERIZATION REACTION Addition (free-radical) polymerization reaction: - It is a chemical reaction between two similar or dissimilar molecules to form a larger molecule, with no elimination of a smaller one (i.e. no by- product is formed). - This kind of reactions required the presence of unsaturated carbon bond in the structure of the reactant molecules. - These unsaturated bond could be in the form of double carbon bonds (C=C) and some times included within a ring structure ( ).

34 POLYMERIZATION REACTION Examples of addition polymerization reactions : Most of dental resins, such as denture base acrylics and composite filling materials, addition polymerization reaction of impression materials.

35 POLYMERIZATION REACTION Characters of the addition polymerization reaction: a. No change in the composition of the reactants. The monomer just added to each other b. The reaction could produce giant polymer molecules and almost with unlimited size c. The reaction only stops when the reactive center is destroyed by one of the termination reactions d. The reaction occurs in four successive steps named induction (activation and initiation), chain growth, termination and chain transfer.

36 Steps of the addition polymerization reaction a. Induction (Activation and initiation) - An initiator (the starter of the polymerization reaction) should be added to the composition of each final monomer compound. - The initiator is responsible for providing the first active polymerizing centers (unpaired electron or freeradical) of each polymer chain. - To release these first free-radicals the initiator itself should be activated by exposing it to one or more of the three known methods (Heat, visible or ultraviolet light, or adding other chemical).

37 Initiation mechanism Initiator Activator -e Free radical Monomer molecule C =C Initiation of the addition polymerization reaction C -e C New free radical

38 Types of Activators 1. Heat activation : - Certain types of initiators such as Benzoyl peroxide will decompose at low temperature (50-100oC) releasing two free radicals per one molecule. - This method is used to activate the polymerization of denture base acrylic

39 Types of Activators - 2. Chemical activation : - Certain chemical compounds such as Tertiary amine or B-toludine sulfinic acid, could be utilized at the room temperature to decompose the benzoyl peroxide initiator in order to release free radicals able to proceed in the addition polymerization reaction. - This method is used to activate self-curing (auto-curing) acrylic resin, auto-curing composite resin, and silicone impression materials.

40 Light activation 3-Light activation - Other initiators (Photoinitiators) are sensitive to the different spectra of light 1- ultraviolet light 2- visible light 3- laser The light photons activate the initiator to generate radicals that are able to start the polymerization reaction

41 Light activation 1/3 : Ultraviolet light (UVL) - It has been used in the past to activate the polymerization of certain composite filling materials those contains UV absorbers, but several drawbacks of using this light have been discovered. - UVL has bad effects on the eye retina and on the pigmented oral tissues. - UVL has limited penetration depth, it could activate just mm material deep.

42 2/3 : Blue visible light (BVL) -Visible light with wavelength ranges from nm (Blue light zone) could be used to activate certain types of photoinitiators -VBL is able to penetrate materials mm. deep. -Mainly these type of initiators are utilized in the curing (polymerization) process of single-component resin pastes (e.g. VLC composite, VLC acrylic, VLC rubber impression materials)

43 2/3 : Blue visible light (BVL) -This method of light activation could also affected by certain factors listed below; Intensity of light source. Distance of light source from the material surface. Materials color shade and pigments. Materials filler content. Time of exposure to light. The tooth structure itself in case of direct curing and the cast material in case of indirect curing.

44 3/3 : Laser 3/3 : Laser (Light amplification series by emitted radiation) - Recently, lasers have the same wavelength range of VL have been recently tried to activate the polymerization of polymeric dental materials such as VLC composites, VLC acrylic and VLC impression materials. - Lasers provide the maximum depth of cure of 3-12 mm, however certain drawbacks were noticed such as heat generation, tooth pulp damage, burning of soft tissue and eye problems. - Improved lasers with safety eye glasses are now available and clinically used.

45 Light activation Recently : The two main dental curing lights are the halogen and LED Tungsten halogen curing light Light emitting diodes curing light

46 Initiation mechanism Initiation mechanism : 1. When the monomer compound is exposed to the activator, mainly fragment of large initiator molecule split, and exists unpaired electron. 2. Presence of this unpaired electron makes the radical very reactive and when approaches the monomer double carbon bond, it pairs with one of its sharing electrons leaving the other free. 3. Respectively, the monomer molecule becomes a free radical itself and its free electron of the monomer carbon bond is now able to pair with another from a new carbon bond of a new monomer molecule

47 Initiation mechanism Initiator Activator -e Free radical Monomer molecule C =C Initiation of the addition polymerization reaction C -e C New free radical

48 Initiation period Initiation period : The initiation period is the time during which the initiator molecules become activated forming free radicals those are able to interact with the monomer molecules. This time is influenced by the purity of the monomer (presence of impurities increases the initiation time) and the temperature (higher temperature reduces the initiation time).

49 Steps of the addition polymerization reaction B - Propagation (chain growth or chain reaction) - The initiation process is followed by rapid addition of other monomer molecules to the free radical and shifting of the free electron to the end of the growing chain - The formed polymer chains are responsible for providing the strength and consistency of the polymerized material. - Always this step is accompanied with evolution of heat (N.B. the reaction is exothermic)

50 Steps of the addition polymerization reaction C - Termination - During this stage the growth of the polymer chain will be stopped and the chain reaction will be terminated. - This termination could be happened as a result of one or more of the following causes; 1. Exchange of hydrogen atom from one growing chain to another. This hydrogen atom will bond with the active growing center of the chain (free electron) to form an inactive bond.

51 Steps of the addition polymerization reaction C - Termination 2. Coupling of two growing chains together. The free electron of each chain bond with that of the other to form an inactive double bond. 3. Presence of such kind of impurities within the chemical compound could react with the free radical of the growing chain and inactivate the growing center.

52 Steps of the addition polymerization reaction D- Chain transfer The already terminated polymer chain could be activated again by a process known by chain transfer. During this process the active state transfers from activated radical to the inactive polymer

53 Packing of mixed acrylic resin Advantages - - Easy denture base fabrication in short time. - - Higher flexure strength than the heat cured acrylic (both the residual monomer content and the absorbed water act as plasticizers). Disadvantages - - Lower mechanical properties such ad creep resistance and stiffness - - Higher porosity - - Color instability - - Higher residual monomer content that could irritate the patient's soft tissues

Lecture No. (1) Introduction of Polymers

Lecture No. (1) Introduction of Polymers Polymer Structure Polymers are found in nature as proteins, cellulose, silk or synthesized like polyethylene, polystyrene and nylon. Some natural polymers can also