Dental Impression Trays & Occlusion Blocks PDF

Dr: Sherin Donia Impression tray It is a device used to carry, confine and control impression material while making an impression. Dental impression It is a negative registration of the entire denture bearing area. Cast It is a positive reproduction of the form of the tissues. ...

Dr: Sherin Donia Impression tray It is a device used to carry, confine and control impression material while making an impression. Dental impression It is a negative registration of the entire denture bearing area. Cast It is a positive reproduction of the form of the tissues.  Preliminary impression Secondary impression Purpose To record dimensions of the arch. To record fine details of the arch. Tray used Stock tray. Special tray. Used for Pouring of primary cast & Pouring of master cast construction construction of special tray. of trial denture base & completion of the denture. Materials Impression compound or alginate. Plaster, Zno & E or rubber base. used Cast Plaster of paris Dental stone material Resulting Study (primary) cast Master cast cast Types of impressions  Impression Tray Handle BODY Floor Flange Flange Flange Floor Floor  Types of trays Stock trays T C+~~lr CYCllln· Special trays I-Stock trays: Ready made trays available in different sizes and forms. Supplied in different materials such as metal (aluminum or stainless steel) and plastic. Either perforated or non-perforated. Should conform to the shape and contour of residual ridge. Should provide approximately 4-6mm for impression material over the entire basal seat area. Stock trays  Component parts of a tray A tray consists of a body and a handle. The body consists of → floor and flanges. Shape of the body and handle differs according to the case whether it is dentulous, edentulous or partially edentulous.  For Dentulous patients: Trays have flat floor, long flanges and flat handle. For edentulous patients: Trays have rounded floor, short flanges and L-shaped handle.  For partially edentulous patients: In the dentulous area, the tray has flat floor and high flanges and in the edentulous area, the floor is rounded and the flanges are short. Stock trays may be classified according to: 1. Material of construction into: Stock trays may be classified according to: 2. Nature of impression material: 3. Size: Small, medium, large Or size1,2,3 …..etc.  Stock trays Perforated tray, non-perforated, water cooled tray with tubes to accept cold water influx and outflux.  Uses of Study cast ✓ Study cast is used to study the following: Ridge shape. - Palatal vault. - Denture bearing area. - Areas of undercut. - Relief areas. - Posterior palatal seal area. - Sharp bony edges. - Depth of the sulci. - Inter-arch relation and space. - b. Study cast is used for construction of special trays. II- Special trays (custom or individual trays): Advantages of special tray: 1- They fit accurately to the dental arches, (in comparison to stock trays) 2- Bulk of impression material is reduced and accordingly less dimensional changes are expected. 3- Less impression material is used. 4- More comfortable to the patient. II- Special trays (custom or individual trays): a. Self-cure acrylic resin b. Shellac base plate c. Swaged metal Advantages Of Acrylic Resin Special Tray 1. easily constructed. 2. More rigid than shellac trays. 3. Can accept thermoplastic border tracing material. 4. Can be easily trimmed.  Wax spacer or Wax shim: ❖ It is usually used in the minimal pressure impression technique. ❖ The shim should be of even thickness usually 2-3 mm. ❖ It should have three or four perforations “Tissue stops”, two in canine, and two in the molar region. Advantages of a spacer: 1- It provides a space of even thickness in the custom tray for the impression material So any dimensional change in the impression material will be equal throughout the impression. 2- In case of plaster impression material, the suitable thickness provided will help the fractured areas to be accurately assembled.  Techniques of final impression Muco-static impression technique (Minimal pressure impression technique) Muco-compressive impression technique (Definite pressure impression technique) Selective pressure impression technique  Muco-static impression Muco-compressive Selective pressure technique impression technique impression technique Other names Minimal pressure impression Definite pressure impression technique technique Mode of At rest At function, under biting force Selectively registration. Special tray Perforated with spacer Non-perforated, without spacer. Selectively relieved Tray with occlusion rims Impression Flowy impression material, e.g. Viscous impression material, Intermediate Plaster impression e.g. medium body rubber base material Indications Thin and wiry ridge Firm and healthy mucosa Ridges with sharp or Flabby ridge sensitive areas.  Muco-static impression Muco-compressive Selective pressure technique impression technique impression technique Procedure The impression is The impression is (open mouth achieved using achieved using patient’s technique) minimal finger biting force on Or (closed mouth prefabricated occlusion pressure while the technique) rims constructed to the patient is opening his approximate patient’s mouth (open mouth vertical dimension technique) (closed mouth technique)  Muco-static impression Muco-compressive Selective pressure technique impression technique impression technique Advantages 1.Stability during rest. 1. Denture is stable during 1. Denture is stable at rest 2.Less pressure. function. and function 2. Sensitive areas are 3.Open mouth allow 2. Denture covers the automatically relieved. visibility. maximum area. 3. Pressure will be directed towards primary stress 4.Suitable for flabby ridge. bearing areas. Disadvantages 1. Denture is not stable 1. No stability during rest. during function. 2. Continuous pressure on 2. The use of plaster needs the ridge. separating medium. 3. More bone resorption.  Boxing of impressions It is a building up vertical walls around the impression periphery, to produce the desired size, form of the base of the cast and to preserve the borders of impression.. Methods of boxing: 1- Wax bead boxing method. 2- Plaster and pumice boxing method  1- Wax bead boxing method. Beading wax Boxing wax Beading wax Boxing wax 2- Plaster and pumice boxing method. Advantages of boxing: 1- It allows preservation of the impression borders. 2- A cast with a predetermined thickness of the base can be obtained. 3- Dense cast can be obtained as vibration gets rid of air bubbles. 4- Time and material are conserved. Occlusion Blocks Occlusion blocks: consist of occlusion rims attached to well fitting trial denture bases. Trial denture bases occlusion rims  The trial denture base (Base plate OR Record base) is that part of the occlusion block which is directly adapted to the master cast. Uses of trial denture base : 1- Carries the occlusion rims on which jaw relations are recorded. 2- Carries the teeth to help the try-in stage. 3- Checks the accuracy of the final impression.  Requirements of the Record Base: Must be rigid to withstand applied loads. Accurately adapted to master cast. Easy to construct and fully extended. It should be relieved from any undercuts. Must be of even thickness. They should be neat, clean and smooth Edges must be smooth and rounded to be comfortable Dimensionally stable to withstand clinical and laboratory procedures.  Special tray Trial denture base No handle Fully extended No spacer  Types of trial denture bases; a. Temporary trial denture base → replaced by P.T.D.B. b. Permanent trial denture base. Materials used for temporary trial denture base: 1. Hard base plate wax. 2.Shellac base-plate 3. Cold curing acrylic resin. 4. light curied acrylic resin. 5. Swaged tin.  Hard Base plate wax: The advantage Easy, rapid and thin to gain space to set teeth. The disadvantage: Lack of dimensional stability. Although reinforced with wire base plate wax (thermoplastic), it is subjected to warpage when warmed and rolled, They soften at body temperature.  Shellac base plates: These are thermoplastic plates adapted on the final cast by heat softening and finger manipulation. Care must be exercised in the application of excessive dry heat to avoid burning the material. Advantage: They have controlled uniform minimal thickness so that they can be used in cases showing limited inter-arch space.  Shellac base plates: Disadvantage: They have insufficient rigidity so that they cannot be used in cases of patients with heavy biting power. Several means of reinforcement of the shellac base plates can be achieved through: Thermoplastic plates adapted on the final cast by heat softening and finger manipulation. Care must be exercised in the application of excessive dry heat to avoid burning the material.  Swaged tin Three tin pieces of gauge 5 are swaged one above the other on a metal die made from the master cast and trimmed according to the predetermined outline. The layers of tin may be cemented together with a thin film of hard wax and the complete unit is re-swaged for final adaptation to the cast. Its advantage: ❑Is that it provides a uniform thickness of final denture ❑It is reasonably accurate ❑ Dimensionally stable in mouth temperature.  Autopolymerizing resin (Cold cure acrylic resin denture base, Tray Type): It is the most commonly used material as trial denture Advantages of resin trial denture bases over shellac bases: 1. Close and accurate fit to the cast. 2. Dimensionally stable in the mouth. 3. High strength to withstand biting pressure. II- Permanent Trial Denture Bases: The permanent trial denture bases constitute the bases of the final prostheses. Advantage Permanent Trial Denture Bases is → giving good idea about extension, retention and stability of the final denture. Disadvantage is → additional shrinkage on second processing when the teeth are added. Materials used for permanent trial denture base; 1. Heat cured acrylic resin. 2. Metal bases (Cast gold,Chromium-nickel alloy,Chromium-cobalt alloy. Heat cured A.R. : Advantages : 1-Strong & rigid. 2- Control thickness ( during waxing up ). 3-Minimizes dimensional changes. 4- trial denture base become part of the denture. 5- Requires minimal finishing & polishing. Disadvantages : 1-Time consuming. 2-Need to construct mounting casts. 3-Warpage → second processing to attach teeth.  Metal Bases : Advantages : 1- No acrylic warpage. 2-More strength. 3-More accurate. 4-Less tissue change under the base. 5-More hygienic.→ Less porosity. 6-Good thermal conductivity. 7-Less deformation in function. Disadvantages : 1-Cost 2-Difficulty in relining. 3-Time consuming. Stabilization of Recording Bases: Additional stabilization is sometimes required with temporary trial denture bases through relining with Zn & Eugenol impression material after adaptation of tin foil to the master cast. Stabilization of temporary trial denture base  Occlusion rims (record rim): Occlusion rims are generally made of pink modeling wax. Uses of occlusion rim: 1. Registration of jaw relationships. 2. Choice of the artificial teeth. i. Midline is determined on it. ii. High and low lip lines are determined on it to indicate the length of the teeth. iii. Canine lines → width of the anterior teeth. Distance between the canine line & the posterior end of the occlusion rim → M-D width of posterior teeth. 3. Setting-up of teeth. 4-Support for lip & cheeks. 5. Helps in proper try-in.  Special forms of occlusion rims: 1- Wax occlusion rims.( Most commonly). 2- Modeling compound occlusion rims. → Graphic tracing method. 3- Plaster and pumice rims. → Functional chew-in technique.  Wax dimensions 6-8 mm 8-10 mm 20-22 mm 16-18 45 degree mm bevel 2/3 retromolar pad 16--18 8-10 mm mm 6 mm  Special forms of occlusion rims: Modeling compound occlusal Plaster and pumice rims: rims: Such rims are selected when Disadvantages: recording the mandibular 1) Modeling compound takes movements using the functional longer time for trimming and generating path technique. adjusting. The surface of the occlusion rim is 2) Residual pigments can be easily shaped according to the path taken left in the final denture by the mandible during function.