Dental Waxes

Transcript

Dental Waxes MANIVASAGAN.C PG STUDENT Dept of prosthodontics including crown & bridge & implantology Contents • • • • • • • • Introduction History Ideal properties Classification Characteristic properties Different waxes & their uses Conclusion References Introduction • Definition : One of several esters of fatty acids with higher alcohols, usually monohydric alcohols. Dental waxes are combinations of various types of waxes compounded to provide desired physical properties. (G.P.T. 8th Edn. 2005) History • Paraffin wax :parum = few or without affinis = connection or attraction most important natural wax • To protect themselves from adverse weather conditions, plants produce a layer of wax on their leaves & stems • Material from dead plants 100-700 million years ago accumulate large quantities & became buried beneath earth’s surface :: slow decay :: crude oil/petroleum formed :: refined to form clean, clear liquid, or solid milky white block :: WAX History • Bees wax : introduced in 1711 • It is actually a refinement of honey • It is used by honeybees in construction of their honeycombs • The wax appears in the form of small, irregularly oval flakes or scales over the abdomen of honeybees Ideal Properties • Should be tough & rigid at room temperature but not brittle • Should have a low softening temperature • Should flow easily • Should be dimensionally stable • Should have a melting point well below boiling point of water, so that wax can be removed under boiling water • Should have pleasant color & posses a color contrast to help during carving Classification I. According to source/origin : 1) Natural waxes i) Mineral waxes : paraffin microcrystalline bransdahl ceresin ozokerite monton Characteristic Properties 1) Melting range 2) Thermal expansion 3) Mechanical properties 4) Flow 5) Residual stress 6) Ductility Melting Range • Waxes have melting range rather than specific melting point Eg. Paraffin wax : 44-62o C Carnauba wax : 50-90oC • By varying compositions, it is possible to change melting ranges suitable according to use Thermal Expansion • Largest values of coefficient of thermal expansion (150-400x10-6/oC) • Contraction of wax pattern by 0.3-0.8% when cooled from 37oC to room temperature leading to inaccuracy of finished restoration • Poor thermal conductors :: suitable kneading & time is required to heat them uniformly & cool them to room temperature Mechanical Properties • Modulus of elasticity, proportional limit, flexibility & compressive strength are low & decreases with rise in temperature Flow • Flow increases as melting range of wax is approached • Depends upon temperature of the wax, external deforming force & the time the force is applied Residual Stress • Waxes tend to return to their original shape after manipulation :: elastic memory. • When wax is held under compression during cooling, atoms & molecules are forced closer together than when they are under no external stress. After it is cooled on room temp & load is removed, motion of molecules is restricted, & this restriction results in residual stresses in it. Residual Stress • When wax is heated, release of residual stresses adds to normal thermal expansion, & total expansion is greater than normal Ductility • Increases with an increase in temperature • Waxes with low melting temperatures have greater ductility than those with higher melting temperature Pattern Waxes • Used to prepare predetermined size & contour of an artificial dental restoration which is to be constructed of a more durable material such as cast gold alloys, Co-Cr-Ni alloys or poly methyl methacrylate resin • Types : Inlay waxes Casting waxes Base plate waxes Inlay Waxes • Used to prepare wax patterns of inlays, crowns, & bridges for the lost wax casting technique. • Dispensing : supplied as deep blue or purple rods or sticks of about 7.5cm length & 3mm diameter. Also supplied in the form of small pellets & cones. Classification • According to ADA specification No. 4 Type I : medium wax, used in direct technique Type II : soft wax, used in indirect technique Composition Ingredients 1. Paraffin wax 2. Carnauba wax 3. Ceresin wax Weight Functions % 60 % Used to establish melting point. Likely to flake when trimmed & does not give glossy surface 20 % Increases melting range, decreases flow at mouth temperature provides glossiness of wax surface 5% Improves carving characteristics & modifies Composition Ingredients Weight Functions % 4. Bees wax 5 % Reduces flow at mouth temperature & reduces its brittleness 5. Gum dammar 3% 6. Synthetic 2 % resins Improves surface smoothness, gives more resistance to flakiness & provides toughness Gives stable flow properties to the wax Desirable Properties • When softened, wax should be uniform • Color should contrast with die material or prepared tooth • There should be no flakiness or surface roughening when wax is molded for softening • In Type I waxes, it should be sufficiently plastic at a temperature slightly above mouth temperature & become rigid at mouth temperature Desirable Properties • It should have a flow not less than 70% at 45oC & not more than 1% at 37oC • Wax should not pull or chip with the carving instrument when it is carved • After the mold has been formed, wax should burn out, forming carbon, which is later eliminated by oxidation of volatile gases • Wax pattern should be completely rigid & dimensionally stable at all times until it is eliminated. Properties of Inlay Wax • Flow • Thermal conductivity • Coefficient of thermal expansion • Wax distortion Flow • The flow of wax is a measure of its potential to deform under a small static load, even that associated with its own mass • Type I inlay wax exhibits marked plasticity or flow at a temperature slightly above mouth temperature • Maximum flow for Type I waxes at 37oC is 1% • Both Type I & Type II waxes must have flow between 70% & 90% at 45oC, i.e., when waxes are inserted into the prepared cavity Thermal Conductivity • Thermal conductivity of waxes is low, sufficient time is required both to heat them uniformly throughout & to cool them to body or room temperature Coefficient of Thermal Expansion • Inlay waxes have a high coefficient of thermal expansion • Linear expansion of 0.7% with increase in temperature of 20oC & contract as much as 0.35% when cooled from 37oC to 25oC • ADA specification No.4 contains no requirements for thermal expansion for Type II waxes. A maximum of 0.6% linear change in dimension is permitted for Type I waxes when they are heated from 25oC to 37oC Wax Distortion • Most serious problem Wax Distortion • Results from thermal changes & release of stresses that arise from : 1.Non-uniform contraction on cooling if wax is not held under uniform pressure 2.Occluded gas bubbles 3.Non-uniform heating during insertion in the cavity :: some parts of wax pattern may contract more than others when stresses are introduced 4.change of shape during molding, carving, & removal Wax Distortion • Methods to minimize wax distortion : 1. Proper selection of waxes (Type I for direct & Type II for indirect technique) 2. Soften the wax uniformly 3. Place the soften & molten increments quickly to bound with earlier increment 4. Invest the pattern immediately after removal from cavity (or store it in cold water in a refrigerator) Manipulation Direct technique (Type I wax) • Wax is softened with dry heat over a flame (rather than in water bath) taking care not to volatize it • It should be twirled until it becomes shiny • Kneaded together & shaped to the prepared cavity • Type I wax has adequate plasticity in a temperature range safely tolerated by the pulp Manipulation Direct technique (Type I wax) • Hold under pressure until it sets either with finger or by the patient biting on the wax • Allow it to cool gradually at mouth temperature (not by cold water) & invest the pattern as early as possible Manipulation Indirect technique (Type I wax) • Impression of prepared cavity is made with a rubber base impression material & die is made • Die is coated with a lubricant (containing wetting agent) • Melted wax may be added in layers with spatula or it may be painted on with a brush • Prepared cavity is overfilled, & and wax is then carved to proper contour • Wax pattern is removed & invested as early as possible Casting Wax • It is one of the pattern waxes used to prepare wax patterns for metallic framework of removable partial dentures • They are highly ductile • Mode of supply : Sheets : 0.4 & 0.32 mm thickness Readymade shapes : round rods (10 cm long) half round rods half pear shaped rods Bulk form : for sprues & vent sprues Preformed wax patterns : for cast RPD frameworks Composition Ingredients 1. Paraffin wax 2. Ceresin wax 3. Bees wax 4. Natural resins Functions To establish melting point Improves carving characteristics Reduces flow at mouth temp & reduces brittleness Gives suitable flow properties to wax Uses • To make metallic framework of removable partial dentures • To provide uniform minimum thickness in certain areas of partial denture framework Base plate wax • Also known as Modelling wax • Mode of supply : sheets of pink/red color width- 7.5 cm length- 15 cm thickness- 0.13 cm Composition Ingredients Weight Functions % 1. Ceresin wax 80 % Improves carving characteristics 2. Bees wax 12 % Reduces brittleness & reduces flow at mouth temp & gives glossy surface 3. Natural or 3% Gives stable flow synthetic resin properties 4. Microcrystalline 25 % To establish required wax melting point Classification • According to ADA specification No.24, they are classified as : Type I Soft - for building veneers Type II Medium – tried in mouths in temperate climatic conditions Type III Hard – for trial fitting in the mouth in tropical climates Uses • To make occlusion rims, which is used on base plate to establish vertical dimensions, plane of occlusion & initial arch form in complete denture fabrication • To produce desired contour of denture after teeth are set in position • To make patterns for orthodontic appliances & prosthesis other than complete dentures • To check various articulating relations in the mouth & to transfer them to mechanical articulators White/Ivorian Wax • Used for making patterns to simulate a veneer spacing • For diagnostic wax-up Processing Waxes • Used mainly as accessory aids in construction of a variety of restorations & appliances either in the clinic or in the laboratory • These are : Beading & Boxing wax Utility wax Sticky wax Carding wax Blockout wax Carving wax Beading & Boxing Wax • Used mainly to bead & box the impression to produce desired size & form of the base of the cast • Mode of supply : Boxing wax :: Sheets of width- 3 cm length- 15 to 30 cm thickness- 3 mm Beading wax :: Ropes of thickness- 3 to 4 mm length – 20 to 30 cm Properties • Preserves the extensions • Controls the form & thickness of the base of cast • Can be adapted easily as it is pliable • Its tackiness allows it to attach to the impression • It conserves the dental stone Adaptation to the Cast • Beading wax is adapted around the periphery of the impression • Should be appx. 4 mm wide & 3-4 mm below the borders of the impression • Height is adjusted until a boxing wax strip extends appx. 13 mm above the highest point on the impression Uses • To build up vertical walls around the impression • To produce desired size & form of the base of the cast • To preserve certain landmarks of the impression Utility Wax • Consists mainly of bees wax, mineral wax & other soft waxes in various proportions • Can be molded at room temperature, as it is pliable • Its tackiness allows it to stick to the impression • Mode of supply : cakes, sticks & sheets Uses • To provide desirable contour to a perforated tray for use with hydrocolloids • To build up flange of tray & raise the palatal portion of the tray posteriorly in recording impression of patients with deep palate Sticky Wax • Also known as adhesive wax or model cement • Consists of yellow bees wax, rosin & natural resins such as gum dammar • It is sticky when melted & adheres closely to the surface upon which it is applied • At room temperature, it is free from tackiness & is brittle Uses • To assemble metallic pieces temporarily in position or to seal a plaster splint to stone cast in the process of forming porcelain facings • To join fragments of broken denture before repair • As it is brittle at room temperature, it will break rather than become distorted if the assembled pieces move– these pieces can then be rejoined in their proper relationship, rather than unknowingly using it in a distorted relationship Carding Wax • Used for attaching broken parts of the denture before denture repair procedure • Used to join metal pieces in soldering procedures • Used to attach artificial teeth Block out Wax • Used to fill voids & undercuts during fabrication of removable partial denture Carving Wax • Used for tooth carving procedures in dental anatomy, laboratory procedures Impression Waxes • Used to record non-undercut edentulous portions of the oral cavity & are generally used in combination with other impression materials like polysulfide, ZOE impression paste or impression compound • Important impression waxes are : corrective impression waxes bite registration waxes Corrective Impression Waxes • Used as a wax veneer over an original impression to contact & register the details of the soft tissues • Consists of paraffin, ceresin & bees wax • Flow at 37oC is 100 % (can get distorted while removing from the mouth) Corrective Impression Waxes • • 1) 2) 3) 4) These waxes are designed to flow at mouth temperature Four types of waxes can be used for this technique IOWA Wax , white , by Dr. Smith Korecta Wax No.4 , Orange , by Dr, O.C. Apllegate H-L physiologic paste , yellow-white, by Dr.C.S.Harkins Adaptol , green , by Dr. N.G.Kaye Corrective Impression Waxes • 1) 2) 3) 4) Advantages – It is a physiologic method displacing the tissues within their physiologically acceptable limits Overcompression is avoided They can be used as corrective material for imperfections in other impressions, particularly those of Zinc oxide – Eugenol paste They flow enough to prevent overdisplacement Corrective Impression Waxes • Disadvantages – 1) More time is necessary during the impression appointment 2) Difficulty in handling the materials 3) Added care has to be taken during boxing 4) Material not easily available 5) Special Armamenterium required for using the material Armamentarium for the fluid wax technique Fluid Wax Technique Uses • Functional impression of distal extension partial dentures • To record posterior palatal seal • Functional impression for obturators Bite Registration Wax • Used to record the occlusal relationship of opposing quadrants • Consists of beeswax, paraffin wax & ceresin wax • Flow at 37oC ranges from 2.5 % to 22 % • Mode of supply : U-shaped thin sheets, which are sometimes matallised or foil laminated eg. Aluwax Bite Registration Wax • Bite Registration Wax is interposed between the teeth & patient is asked to bite in the position of jaw relation recording • The indentations thus formed on the wax are used to place the cast in position & then transfer it to the articulator. SPECIAL WAXES White wax • White wax is used for making patterns to simulate a veneer facing for aesthetic restorations Blockout• Wax Applications:  Fills undercuts, covers sharp edges and corrects draw on dies with non parallel walls. May be applied to the die prior to or after coating with hardener and spacers. • Properties:  - hard - easy flow when molten -excellent carvability for smooth contouring on die surfaces. Hardness holds carved edges and high fusing temperature prevents adhesion to coping wax. DISCLOSING WAX • Disclosing wax is sometimes known as pressure indicator paste • Used to determine unequal pressure points in a denture • Located by painting the wax on tissue side of the denture base and holding the denture in place under pressure in the mouth. • The wax flows away from the points needing relief. • • • • • • • LASER-WAX Laser reading for the CAD/CAM technique Advantages Laser readable Appropriate for all laser scanning systems Good Modeling capacity Pleasant color (pastel shade) Can be milled Extremely opaque Redi-Form Pontic • Eliminate tedious wax buildup. • Eliminates need to individually place singlepontic forms, reducing wax-up time dramatically. • When softened allows the four pontic section to be carved, narrowed, or bent to fit even the most complex case without loss of anatomical detail. • When cooled, the fourpontic section becomes rigid ALUWAX • ALUWAX dental wax is composite material which contains powdered aluminium • Increase the integrity of the compound • Better heat retention properties needed for efficient modeling Retention pearls RETENTION PEARLS ARE SPRAYED ON TO THE WAX PATTERN FOR ADDED RETENTION S-U-CERAMO-WAXES • Purest special waxes for pressceramics. • Absolutely purest raw material • Organic components only • Immediate recognition of secondary contamination • Finest filtration of the raw material used • Protected against contamination by an acrylic coping. • Optimum for pressed all-ceramic Review of literature Randa Diwan, BDS, Yousef Talic, BDS, B Noura Omar, BDS, And Walid Sadiq, BDS, Msc The Effect Of Storage Time Of Removable Partial Denture Wax Pattern On The Accuracy Of Fit Of The Cast Framework J Prosthet Dent 1997;77:375-81, • This study - effect of storage time of the wax pattern before casting and the influence of the palatal major connector design on the accuracy of its fit on the master casts. • Two designs -24 hours, 1 week and 1 month The storage time of wax patterns on the refractory cast had a significant effect on the accuracy of fit of the connector. Modified Palatal Plate And Anterior Posterior Palatal Strap Design Conclusions • Greatest Inaccuracies – 1 Month Storage Time • Greatest Discrepancies- Modified Palatal Plate Major Connector Design • RPD wax pattern -invested as soon as possible -1 hour or less. M. Krane, Dds,a A. Patyk, BS, DDS, Phd,b And L. W. R. Kobes, Prof Drc Study On The Surface Of Resins That Burn Without Residues In The Lost-wax Procedure(J Prosthet Dent 1998;79:389-92.) • In this study, the surface structure of the residue-free resins examined were in a range acceptable for the dental casting technique. • An increased application of residue-free resins in dental casting technique is therefore recommendable. • These resins could not only complement waxes or wax/resin compositions, but could even, in whole or in part, replace them. Conclusion • Waxes find great utility in dentistry from blocking undercuts, making rims, impressions, wax patterns to casting • Wide variety available for different uses • Handling of wax is an art • Its not only removing of unwanted but also building-up of what is wanted References • Anusavice : Philips’ Science of Dental Materials Xth & XIth Edn. • Craig : Dental Materials : Properties & Manipulation VIth, VIIth & VIIIth Edn. • J. F. McCabe : Applied Dental Materials VIIth Edn. • Jack Ferracane : Materials in Dentistry Principles & Application • O. Applegate : Essential of R.P.D. References • S. Winkler : Essentials of Complete Denture Prosthodontics IInd Edn. • Johnston : Modern practice in Crown & Bridge Prosthodontics IIIrd Edn.