Special Tray And Base-plates Cnvvrt 1q5365

Special trays and Record bases in complete dentures.

INTRODUCTION IMPRESSION TRAYSA receptacle or device used to carry the impression material to the mouth, confine the material in apposition to the surfaces to be recorded and control the impression material while it sets to form the impression. Special trays are also known as: CUSTOM TRAYS/INDIVIDUALIZED TRAYS/TAILOR MADE TRAYS. It is defined as correctly fitting tray made on preliminary cast. Its main use is to make secondary or final impression of the jaw. REQUIREMENTS OF SPECIAL TRAYS o Must be strong & rigid. o Must have smooth & round borders. o Must have provision to retain the impression on its surface. o Its handle must be firmly attached & conveniently placed. o Must not distort during & after impression is made. o Flanges of the tray must not be adopted into undercuts. o Posterior borders of maxillary tray must be 1/8 of an inch beyond the junction of hard & soft palate. And posterior border of mandibular tray must cover the retromolar pad. o Borders must not impinge on the muscle attachment & should have proper relief for frenal attachments. o Borders of tray should be little short of the peripheral outlines. o Borders must never be overextended. TYPES OF SPECIAL TRAYS A: • CLOSE FITTING SPECIAL TRAYThis tray has not much room for impression material. The impression materiel is in thin layer as in wash impression.ZOE paste gives such impression due to thin consistency. • SPACER SPECIAL TRAY OR LOOSE FITTING SPECIAL TRAYThese trays have space for thicker consistency impression material like alginate & thick consistency ZOE paste.

B: MATERIALS FOR MAKING SPECIAL TRAY •

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NON METALLIC •

SHELLAC BASE PLATE

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NON BRITTLE IMPRESSION COMPOUND

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ACRYLIC RESIN

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1. SELF CURED

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2. HEAT CURED

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THERMO-PLASTIC RESIN SHEET

METALLIC •

SOFT ALLOY OF TIN & LEAD

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PLUMBERS SOLDERS

SPACER o Modelling waxOne sheet thick for thick consistency ZOE paste impression. Two sheet thickness for alginate impression o Piece of thick canvas

HANDLE o Same material as the tray o Metal wire TO RETAIN THE IMPRESSION MATERIAL IN THE TRAY o Perforations o Special adhesive solutions o Cotton wool threads spread over the surface of tray & fixed with sticky wax at 3 to 4 points.

SHELLAC SPECIAL TRAY Double thickness shellac baseplate material is essential for fabricating an impression tray.

Advantage •

Rapidity with which the shellac baseplate material can be adapted to the cast and the tray fabricated.

Disadvantage •

Lack of dimensional stability, especially during application of heat when border moulding the tray.

TYPES OF SHELLAC •

Plain

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Alluminium filled

TECHNIQUE •

Make an outline of the impression tray on the cast. Block out severe undercuts with a wet sheet of non asbestos casting ring lining material.

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Provide relief as required.

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Centre a sheet of double thickness shellac baseplate material over the cast and wilt it onto the cast with flame.

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Fold excess material at borders onto itself.

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Continue adaptation until shellac makes intimate with the cast.

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Form a handle from scrap shellac baseplate material, warm it and adapt it to the impression tray.

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Allow tray to cool, then remove it and trim the border outline.

PROBLEM WARPING OF IMPRESSION TRAY AND FAILURE TO LIFT

PROBABLE CAUSE SHELLAC BASEPLATE MATERIAL WARPED DURING COOLING.

SOLUTION READAPTING SHELLAC BASEPLATE MATERIAL. USING DOUBLE THICKNESS SHELLAC

CAST IMPRESSION TRAY TOO FLEXIBLE

SHELLAC BASEPLATE MATERIAL NOT RIGID ENOUGH , AND ANTERIOR RIDGE ON MANDIBULAR CAST FLAT. SHELLAC BASEPLATE MATERIAL OVERHEATED DURING ADAPTION.

BASEPLATE MATERIAL AND REINFORCING ANTERIOR RIDGE REGION WITH WIRE.

TRAY STUCK TO CAST.

WETTING CAST BEFORE HEATING SHELLAC BASEPLATE MATERIAL AND

NOT OVERHEATING AND CHARRING SHELLAC BASEPLATE MATERIAL.

ACRYLIC RESIN SPECIAL TRAY •

ADVANTAGES •

More rigid & strong

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Unbreakable

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Do not distort

METHODS TO PREPARE ACRYLIC RESIN SPECIAL TRAY •

Finger adapted dough method

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Sprinkle on method

Sprinkle on method

o Most commonly used method for constructing acrylic resin special tray (McCracken,1964). o Areas that require relief should be provided by adapting a special tray wax 1mm thick over the areas. TECHNIQUE •

Make an outline of the impression tray on the cast. The borders of the tray are kept shorter of the vestibular reflections of the cast.

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Posterior border should be 2mm distal to the fovea palatina.

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Block out severe undercuts and adapt baseplate wax for relief

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Apply tinfoil substitute onto the stone cast and relief wax

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Sift powdered polymer onto the cast and relief wax, and saturate it with liquid monomer.

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Continue applying powder and liquid until there is uniform thickness of 2mm.

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Cure the tray under an inverted plaster bowl to reduce the porosity.

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Mix more resin in a paper cup and when it is in dough stage, form handles and adapt them to the impression tray.

Dresen, 1958 suggested one handle in the anterior portion of tray. Merkeley, 1959 suggested three handles or finger rests for mandibular impression trays. Position the handles in the first molar region and anterior region of tray. Handles should be 3-4mm thick, 8mm high. Horizontal grooves can be placed in the facial and lingual surfaces of the handle to enhance grip. Handles on the impression tray should approximate the position of the teeth on the finished denture. Adapt the resin dough to the approximate size of handle and wet the tray at the point of attachment with liquid acrylic monomer to facilitate chemical bonding. After setting, remove tray from cast and trim it. Polish the rough areas that can cause discomfort to the patient.

PROBLEM ENTIRE IMPRESSION TRAY TOO THICK

PROBABLE CAUSE TOO MUCH RESIN BUILD UP ON CAST FROM TOO GENEROUS APPLICATION OF POWDER AND LIQUID

IMPRESSION TRAY TOO THIN OVER RIDGES AND TOO THICK IN PALATE

IMPRESSION TRAY OR CAST BROKEN DURING SEPARATION IMPRESSION TRAY TOO FLEXIBLE

SOLUTION CONTROL APPLICATION OF POWDER AND LIQUID TO CREATE UNIFORM LAYER APPROXIMATELY 2MM THICK;CHECK THICKNESS OF RESIN WITH PERIODONTAL PROBE RESIN FLOW NOT TILT CAST WHILE SIFTING CONTROLLED BY TILTING RESIN TO MINIMIZE CAST DURING SPRINKLE POOLING. ON AND RESULTANT THIN PALATE WITH BUR . POOLING OF RESIN IN PALATE REGION UNDERCUTS NOT IDENTIFY THE BLOKED OUT TINFOIL UNDERCUTS AND BLOCK SUBSTITUTE THEM. CONTAMINATED OR NOT PAINT TINFOIL USED SUBSTITUE ON CAST IMPRESSION TRAY TOO USE PROPER POWDER THIN OR ANTERIOR LIQUID RATIO. RIGDE ON LOWER CAST FLAT

FINGER ADAPTED DOUGH METHOD o This method is quick and the resultant impression trays fit well and have acceptable dimensional stability. It is used extensively for making resin special trays. TECHNIQUE •

Make an outline of the impression tray on the cast.

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Block out severe undercuts and adapt baseplate wax for relief. Removal of 4mm squares of relief wax will expose the cast, thereby providing tissue stops.

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Apply tinfoil substitute onto the stone cast and relief wax.

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Proportion the powder liquid ratio and mix in a paper cup

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From that excess material handles can be made.

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Cure tray under an inverted plaster bowl.

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After setting , remove tray from cast and trim it.

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Polish the rough areas that can cause discomfort to the patient. PROBLEM

PROBABLE CAUSE

TRAY THICK IN SOME AREAS AND THIN IN OTHER AREAS.

RESIN OVERTHINNED OVER CONVEX AREAS OF CAST BY TOO MUCH FINGER PRESSURE.

EXERCISE CARE WHEN ADAPTING RESIN TO CAST,PARTICULARLY OVER RIDGES AND TEETH;USE ONLY ENOUGH PRESSURE TO ACHIEVE ADAPTION.

TRAY OR CAST BROKEN DURING REMOVAL OF TRAY FROM CAST

TEETH ON CAST NOT BLOCKED OUT ADEQUATELY ;AND UNDERCUTS ELSEWHERE ON CAST NOT BLOCKED OUT. TINFOIL SUBSTITUTE CONTAMINATED OR NOT USED. IMPRESSION TRAY MATERIAL OVERTHINNED BY FINGER PRESSURE OVER RESIDUAL RIDGES AND ALLOWED TO BECOME TOO THICK IN CONCAVE AREAS. RESIN NOT ROLLED TO UNIFORM THICKNESS PRIOR TO ADAPTATION .

COAT THE CAST WITH UNCONTAMINATED TINFOIL SUBSTITUTE.

RESIN PAST DOUGH STAGE BEFORE START OF FINGER ADAPTATION AND ADAPTATION INACCURATE. FINGER ADAPTATION DISCONTINUED TOO SOON.

START ADAPTATION WHEN RESIN IS IN DOUGH STAGE;DO NOT WAIT UNTILL RESIN IS RUBBERY CONTINUE ADAPTATION UNTILL RESIN BEGINS TO SET TO PREVENT REBOUND

IMPRESSION TRAY TOO THIN IN SOME AREAS AND TOO THICK IN OTHERS.

FAILURE OF TRAY TO FIT CAST.

SOLUTION

EXERCISE CARE DURING ADAPTATION TO AVOID EXERTING TOO MUCH PRESSURE ON RESIN OVER CONVEX PORTIONS OF CAST. USE ROLLER TO MAKE SHEET OF RESIN OF PROPER THICKNESS

IMPRESSION TRAY OR CAST BROKEN ON SEPARATION.

UNDERCUTS NOT BLOCKED OUT. TINFOIL SUBSTITUTE NOT USED.

CONTINUE ADAPTATION UNTILLS RESIN SETS. BLOCK OUT UNDERCUTS PAINT CAST WITH TINFOIL SUBSTITUTE.

Thermoplastic resin Special trays

o Thermoplastic resin sheets can make good impression trays. o These are available in a variety of colours & thicknesses as well as different degrees of flexibility. o Vacuum adapted method is used to prepare these trays. VACUUM ADAPTED METHOD

This method is quick and easy, but requires special equipment for adapting the resin sheet on the cast. TECHNIQUE •

Make an outline of the impression tray on the cast.

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Block out severe undercuts with a material that will not melt when heated such as a wet sheet of non asbestos casting ring lining material.

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Centre the cast on vacuum adapter plate

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Place a sheet of resin and rotate the heating unit into position.

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Continue heating until the material starts to sag

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Lower the frame and resin sheet onto the cast, and start vacuum adaptation.

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After adaptation is complete, allow the resin sheet to cool, and then remove it from the vacuum unit.

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Trim the excess material and remove tray from cast.

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Trim the borders and add handles made of autopolymerizing acrylic resin. PROBLEM

PROBABLE CAUSE

SOLUTION

CAST OR TRAY BROKEN ON SEPARATION.

UNDERCUTS OR TEETH ON CAST NOT BLOCKED OUT .

EXAMINE CAST CAREFULLY TO IDENTIFY UNDERCUTS;BLOCK THEM OUT.

TRAY NOT ADAPTED TO CAST IN SOME AREAS.

TRAY MATERIAL NOT HEATED SUFFICIENTLY

MAKE CERTAIN THE RECOMMENDED AMOUT OF

BEFORE VACCUM ADAPTATION STARTED.

SAG OCCURS IN TRAY RESIN BEFORE ACTIVATING VACCUM.

TRAY TOO FLEXIBLE.

STOCK MATERIAL IS TOO THIN

USE TRAY WEIGHT RESIN SHEET FOR ADEQUATE RIGIDITY.

IMPRESSION TRAY TOO FLEXIBLE.

IMPRESSION MATERIAL TOO THIN.

USE THICKER STOCK MATERIAL;REINFORCE IT WITH WIRE

CAST OR TRAY BROKEN DURING SEPARATION.

UNDERCUTS NOT BLOCKED OUT.

IDENTIFY AND BLOCKOUT UNDER CUTS BEFORE ADAPTATION.

BENEFITS OF MAKING SPECIAL TRAYS o A tray of even thickness can be made o Even of the impression material o Control over the flow of the material o Reduced discomfort for the patient o Economic use of impression material

RECORD BASES o Also known as BASEPLATE TEMPORARY BASE TRIAL BASE o A temporary form representing the base of a denture. PURPOSES OF BASEPLATES o To act as carriers for occlussal rims on which jaw relations are recorded. o To hold the teeth in the wax set up far the try-in stage. o To check the accuracy of the prviously recorded rocords. REQUIREMENTS FOR BASEPLATES ELDER(1955) gave the following requirements for base plates1. The baseplate should adapt to the basal seat area as the finished denture base. 2. The baseplate should have same border form as the finished denture base. 3. The baseplates should be sufficiently rigid to resist biting force. 4. The baseplate should be dimensionally stable 5. The baseplate as constructed should permit its use as a base for setting up teeth. 6. It should be possible to construct baseplates quickly, easily, and inexpensively. 7. Baseplate should have no undesirable colour. BASEPLATE MATERIALS •

AUTOPOLY-MERIZING RESINS

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SHELLAC BASEPLATE MATERIAL

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THERMO-PLASTIC RESINS

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HEAT CURING RESINS

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BASEPLATE WAX

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METAL

AUTOPOLYMERIZING RESIN BASEPLATES Autopolymerizing resins (cold cure or self curing) require an activator & a catalyst for polymerization & no external heat. They areo o

Serviceable Economical

METHODS FOR CONSTRUCTING AUTOPOLYMERIZING RESIN SHEETS •

SPRINKLE ON METHOD

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FINGER ADAPTED DOUGH METHD

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CONFINED DOUGH METHODS 1. STONE MOLD METHOND 2. WAX CONFINED METHOD

SPRINKLE ON METHOD TECHNIQUE •

Examine the cast & block-out severe undercuts with baseplate wax & others with self curing autopolymerizing resin.

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Paint tinfoil substitute on the wet cast.

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Sift the conventional autopolymerizing resin powder on the cast & soft curing resin, & saturate it with the liquid.

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Tilt the cast laterally while applying the resin to prevent pooling the liquid & powder in the palate of maxillary cast which can cause an excessively thick palate.

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Make it to the desired thickness of 2 mm.

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Cure the baseplate under an inverted plastic bowl or in a pressure pot under warm water for 20mins at 20 psi.

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Examine the cured baseplate on the cast to evaluate its adaptation.

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Trim the resin flash around the borders.

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Smooth the borders and any dough space on the borders.

PROBLEM

PROBABLE CAUSE

SOLUTION

Baseplate unable to remove from cast. Baseplate broken during removal. Cast chipped or broken during removal Both cast and baseplate broken during removal. Completed baseplate too flexible

Undercuts not properly blocked out. Cast not coated with uncontaminated tin foil substitute

Block out undercuts with wax.

Improper ratio Baseplate removed too soon (polymerization not complete)

Using proper powder liquid ratio Allow adequate time for baseplate set.

Porous baseplate

Some areas allowed to dry when resin is applied on cast.

Failure of baseplate to fit the cast

Baseplate removed before poly merisation Baseplate heated by grinding and polishing Baseplated stored in dry environment.

Keep all areas moist with monomer to prevent drying when applying resin. Adequately cure resin before removing Donot overpolish….use slow speeds Store in water.

Coating the cast before adding resin.

FINGER ADAPTED DOUGH METHOD TECHNIQUE •

Examine the cast and identify the undercuts and block them.

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Apply tinfoil substitute to the cast.

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Proportion and mix the resin powder and liquid.

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When the mixture is in dough stage, form the resin into a roll, and adapt it to the cast.

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Continue finger adaptation until the resin, being well adapted to the cast, does not spring away or rebound.

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Place the baseplate on the cast under the plaster bowl or in a pressure pot.

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After curing, remove the baseplate from the cast, trim it and smooth it.

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Replace the baseplate on the cast, and evaluate the adaptation and border thickness.

PROBLEM Failure of baseplate to fit the cast.

PROBABLE CAUSE Resin beyond dough stage. Discontinuing finger adaptation too early.

SOLUTION Adapt in dough stage Adapts untill it no longer springs from the cast.

Baseplate too thin ir thick in some areas.

Convex areas too thin as a result of finger pressure. Resin not rolled to desired thickness before applying on cast.

Do not applying too much presssure in covex areas Roll the resin uniformly.

CONFINED DOUGH METHODS

Elder(1955)-applied pressure with modelling plastic. Lavere and freda(1974)-confined the resin with wax. Assadzadik and yarmond(1975)-made a stone index to mold the base plate. ADVANTAGES • • •

Offers excellent control over thickness Reduces finishing time Minimal porosities

DISADVANTAGES • •

More time required to make the mold Tendency to form voids in baseplate