Dental waxes.pdf

Dental waxes Dr. H Omar 1  Dental waxes are hydrocarbon materials and they are used as an integral part of many technical procedures. 2  Composition of dental waxes Waxes are organic polymers consisting of hydrocarbon...

Dental waxes Dr. H Omar 1  Dental waxes are hydrocarbon materials and they are used as an integral part of many technical procedures. 2  Composition of dental waxes Waxes are organic polymers consisting of hydrocarbons and their derivatives. Loading… 1.Natural waxes: 1.1- mineral waxes (paraffin) 1.2- Insects waxes (bee wax) 1.3- Vegetable waxes (resin, gums and Cranuba waxes). 2- Synthetic waxes 3- Additives:likepigmentsandfats. 3  properties 1- Thermal properties: - Dental waxes are thermoplastic materials which means that they melt by heat; the temperature at which the material changes from solid state to liquid state is called melting temperature. - Below melting temperature, some of dental waxes can be manipulated satisfactory without being flaked or torn; at this point it is named solid-solid transition temperature. 4  2- Dimensional stability: - Dental waxes are dimensionally unstable as a result of thermal changes. - Upon cooling, a contraction of paraffin wax (11-25%) occurs. Loading… - Upon solid-solid transition phase, a contraction (0.5%) occurs. - The cooling contraction results in dimensional changes, whereas the other types of contractions results in development of residual stress that later released and results in distortion. 5  3- Internal stresses: - Dental waxes are thermally low conductive which makes it difficult to achieve uniform heating. - If dental waxes are molded or adapted without adequate heating at solid-solid transition temperature, stresses will be generated in the dental wax resulting in distortion 6  4- Flow: - Flow is a property required in dental waxes and it is related to temperature. - Waxes deform when subjected to a load for a period of time, and this plastic deformation depends on temperature and is found to be low when the temperature is below the solid-solid transition temperature, but it increases as the temperature is raised above the transition temperature. 7  5- Ductility: - Dental waxes are ductile materials and ductility increases with increase of the temperature. 6- Mechanical properties: - The modulus of elasticity, compressive strength and proportional limit of dental waxes are low comparing with other dental materials 8  Classification of dental waxes according to their application 1- Pattern wax 2- processing wax 3- impression wax 9  1- pattern wax Used to form patterns of appliances prior to casting. Following the production of a stone model or die, the next stage in the formation of is the production of a wax pattern of the appliance on the model The wax pattern defines the shape and size of the resulting appliance 10 Methods of wax pattern construction Indirect technique: in dental lab (e.g. wax pattern for crown) Loading… Direct technique: made directly in the prepared cavity of patient mouth (e.g. inlay) Indirect-direct: made in dental lab and corrected in patient’s mouth 11 Indirect wax pattern tech. Direct wax pattern tech. 12  Types of pattern was 1- inlay wax: it is hard and brittle in order to fracture rather than to distort when removed from undercut areas. The wax is mostly blue in color. They are used to make inlay’s and crown’s patterns. 13 Inlay wax 14  There are 2 types of inlay wax: Type 1: for direct technique Type 2: for indirect technique 15  2. Denture casting wax: used to produce the metal components of cobalt – chromium partial denture. It is based on paraffin wax with bees wax to give softness necessary for molding and stickiness necessary to ensure adhering to an investment material. It is mostly green sheet. Properties: construction. 1-they are ready-formed polymeric patterns to 2-itsimplify should burn out from the mold without leaving residue. the process of partial denture 16 construction. 17  3. Modelling waxes (Denture base plate wax, sheet wax): It is used to form the base of the denture and in occlusal rims (used for bite registration and teeth setting) Modelling waxes are generally supplied in pink sheet form. Modelling waxes are tough enough to resist fracture when withdrawn from shallow undercuts. 18  Three types of material are available, Properties: 1. it should be easy to mould when softened, and not tear flake or crack. 2. it should be easy to carve. 3. it should be capable of being melted and solidified a number of times without change in properties. 19 20  4. White wax: to make pattern simulate veneer facing in crowns 21  2- processing wax used during processing of the appliance Types of processing wax: 1.Beading wax: used to make beading around the impression before pouring gypsum to protect the margins 22 23  2. Boxing – in wax: used to make box around the impression to make pouring gypsum into the impression easier and more perfect 24  3. Block – out wax: to block – out undercut areas on cast during processing of Co/Cr metal frame work 25  4. Sticky wax: used for temporarily joining two components of an appliance and join the broken pieces of the denture before repair. 26  3- impression wax They are previously used to make impression but distort when removed from undercut, they have high flow. 27  Methods of softening wax Methods for softening wax prior to using include: 1. a water bath 2. an infra-red lamp 3. a bunsen burner. The best way to soften the wax is to be held in the warm raising air above the flame and not in the flame itself. 28  While The ideal method for softening wax is to Wax distortion Distortion is one of the most serious problems faced when forming the pattern and removing it from the mouth or die specially in the direct technique Loading… 29  Reasons for wax Distortion 1- Thermal changes: using of the wax at not uniform temperature. Some parts of the wax pattern may thermally contract more than others when stresses are introduced. 2 Releasing of internal stresses: The stresses are induced from the natural tendency of the wax to contract 2. Releasing on cooling,of frominternal stresses: occluded gas bubbles,The stresses change are during of shape induced from moulding and the due tonatural carving, tendency of the wax to contract on 30 etc.  cooling, from occluded gas bubbles, 3. Distortion may also take place due to flow of wax under its own weight particularly at a higher temperature. 4. During carving operation: some molecules of wax will be disturbed and the stresses will be introduced. 5. Time and temperature of storage before investment may result in stress release. 6. If the wax has to be melted and added to the pattern in order to repair some parts that were not accurately obtained, the added wax will introduce stress during cooling. 7. If the wax is not held under uniform pressure during cooling 31  Avoidance of wax distortion: 1. Minimal carving 2. Minimal change in temperature. 3. Minimal storage of the pattern (Invest immediately). 4. Use warm instruments for carving. 5. Store in fridge if necessary 32