Impression Tray Notes PDF

Notes in prosthodontics lecture (3) Impression tray BY; Dr/Ashraf.A. Attia.  IMPRESSION TRAY This topic include 1-impression (def –types,selection of impression matrial ) 2-cast (def-types) 3-trays (def-parts-...

Notes in prosthodontics lecture (3) Impression tray BY; Dr/Ashraf.A. Attia.  IMPRESSION TRAY This topic include 1-impression (def –types,selection of impression matrial ) 2-cast (def-types) 3-trays (def-parts-shape-types) 4-spacer 5-pouring of impression and requirement of cast Impression Def Negative registration of the entire denture bearing, stabilizing, and border seal areas present in the edentulous mouth. Types 1-Preliminary (primary) impression Is an impression of the edentulous mouth which is made for the purpose of producing a diagnostic cast upon which a custom impression trays will be fabricated * Done by stock tray and used to make study cast on which custom (special) tray is made * Give over all impression to tissues *Done by compound or agar agar or thick mix alginate 2- Final (secondary) impression Is a finally detailed impression which is used for construction of the master cast upon which the denture fabricated Done by custom tray(special tray) and used to make master cast on which denture is constructed *Give fine details to tissues and borders smooth rounded even thickness *Done by zinc oxide eugenol or rubber base or thin mix alginate Selection of impression mate rial Dentulous 1ry impression by alginate ,, 2ry by rubber base Edentulous 1ry impression if present undercut by alginate,, if none undercut use compound 2ry impression if undercut present use rubber base ,, if no undercut use zinc oxide eugenol Cast Def Positive reproduction of the form of tissues of the upper or lower arch Types (a) facial cast (facial model) done by impression to patient face used in maxillofacial prosthesis (b) dental cast(dental model) 1-study (diagnostic)(1ry) produced from the primary impression by casting with plaster of paris.It is used for study and treatment planning.Also it is used for construction of special tray. 2-master (secondary) is replica of prepared teeth and residual ridge, it is produced from the final impression by casting with dental stone. It is used for construction of the record blocks.Also it is used for processing the denture. 3-refractory cast is only used for construction of metallic denture framework. It is made from investment material by duplicating the master cast after preparation. 4-optical/digital imaged by camera to oral cavity, can make design on the computer 5-die positive replica to one tooth where crown is fabricated Impression tray Def Is a device used to carry, confine and control impression material while making and impression Parts of tray 1-Handle used to facilitate insertion and removal of tray, but not support impression where supported by dentist fingers upper place index finger at centre of hard palate till setting of impression material. lower place fingers bilateral at premolar area till setting of impression material 2- B ody consist of floor and flange. The upper tray has a vault part to cover the palatal area in the patient mouth. The lower tray has lingual flanges to allow free movement of the tongue Shape of tray Different according to type of patient 1-Dentulous( floor flat ) , ( flange long ) , ( handle in line with floor of the tray) 2-Edentulous (floor round) , (flange short) , ( handle at right angle with floor of the tray''L-shaped'to clear lip') 3-Partially edentulous "remaining anterior teeth" Floor anterior flat, posterior round flange anterior long , posterior short Type of the tray (a)stock tray (used for 1ry impression) (b)custom (special) tray(used for 2ry impression) (a)Stock tray Ready-made trays available in different sizes (No.1,2&3) 1-selection 2-type 3-modification * Used for 1ry impression (1)selection *According to (a)condition of patient (dentulous -edentulous –partially edentulous) (b)size of arch has different sizes 1 -2-3 detect by caliper placed at maxillary tuberosity or retromolar pad (c)shape of arch U shaped- V shaped- ovoid (d)impression matrial alginate use perforated to give mechanical retention to alginate or solid and use adhesive with it compound impression use closed"non perforated" retained by excess material over border  N.B may use perforated agar –agar use rim lock with water cooling system where supply agar by water to convert it from sol to gel state by cooling (2)types according to material a-metallic may be stainless steel,low fusing alloy and aluminium. b- plastics :autoclave able anatomical trays and non autoclavable (disposable)trays has different colors (3)modification After selection of proper size, form and shape of stock tray for the patient, some modification of the stock tray must be carried out to be individually adapted to the patient to achieve accurate impression.These modification includes: (a)bending: either open or close the flange with pliers to provide adequate space for the impression material (3-4mm between the tray and tissues). (b)cutting trimming by scissor to border if over extended N.B at labial frenum has v-shaped as labial frenum has restricted movement At buccal frenum has soucer shape as buccal frenum has more movement (c)building(addition) 1- if flange is short so add compound or wax 2-high palatal vault "v-shaped “add wax or compound at center of hard palate to stabilize tray in mouth  (b)custom "special"tray A special tray is defined as: A custom made device prepared for a particular patient constructed and fitted on preliminary cast to meet individual requirements and is used to carry, confine and control an impression material while making an impression. Requirement of special tray A special tray should be: 1-well fitted and accurately adapted to the supporting tissues provided it must cover all the bearing tissue 2-dimensional stable 3-free of voids and projection 4-2-3mm thick sufficient to be rigid 5- with a handle 6-rigid even in thin section to avoid deformation during pressure application or removal away from the mouth 1-advantage 1-accurately adapted 2-allow even thickness of impression material(so decrease dimensional changes ) 3-give fine details 4-more comfortable to patient 2- types (a)Thermoplastic material (soften by heat and harden by cooling) 1-shellac base plate *Dis advantage 1-easy breakage 2-warpage by heat *Advantage 1-easy construction 2-inexpensive *Construction 1-draw tracing lines on cast a-line with depth of sulcus b-line represent border of tray "2mm away from sulcus"except 2 areas (RMP-PPS) 2 lines with each other. c-line represent border of spacer 1-2mm from border line d-line at mid line and extend to base of cast to help placement of handle of tray. 2-ready-made shellac, soften, adapted on cast, trim excess 3-bend borders to be double layer to be strong, but still weak reinforced by wire placed at P.P.S or lingual pouch 4-make handle and added to tray 2-modeling compound Take 1ry impression by it and use this 1ry impression as special tray this done in "selective pressure impression technique" (b) acrylic resin (self cure-heat cure-light cure-old denture) 1-self cure acrylic resin special tray (most common) construction Has 2 methods a-finger adapted dough method Marking the cast Indeliable pencil is used to draw a line 2mm above depth of the vestibule which represents tray periphery and another line is drawn above the first on by 1-2 mm representing spacer periphery. Construction of spacer and stopper (if needed): -Any deep undercuts are blocked out with wax, layer of modeling wax (2mm spacer) is adapted to each cast and the excess wax trimmed  -apply separating medium , layer of spacer on cast accord to lines ,make holes in it to be stopper (4 where 2 anterior and 2posterior OR 3 where 1 anterior and 2posterior). -mix acrylic till dough stage and applied to cast ,apply pressure by finger then trim excess by sharp instrument with support by finger over acrylic -finish of acrylic so borders are smooth ,round, even thickness Function of spacer: -The spacer allows the tray to be properly positioned in the mouth during border molding procedure -To allow the impression to have an even thickness Prevent distortion of the material at final stage b- sprinkle on method 1 -draw tracing lines on cast and block out of under cuts 2-apply separating medium on cast 3-apply powder of acrylic on cast then monomer then powder then monomer till complete formation Advantage 1 -more adapted Dis advantage 1-cause irritation to fingers by monomer 2- difficult to control thickness,but this method can be used for repair of fractured denture. 2-heat cure Layer of wax adapted to the cast as shellac. The layer is flasked and processed in heat cure acrylic Advantage: more fitted, adapted Dis advantage: time consuming 3-light cure acrylic As self acrylic ,but *In self cure short working "rapid polymerization reaction " *In light cure adapt acrylic ,trim excess,then curing by light in curing chamber ,then removed from cast and placed where fitting surface toward light "control working time" 4_old denture Used as special tray after 1-shorten border by 1mm 2- remove 2mm from fitting surface  (c)plastic sheet Construction 1-apply plastic sheet on vaccum pressure machine first Work heater to soften plastic then Work vaccum to press and adapt plastic on cast Advantage 1 -more fitted ,adapted "can be used for bleaching tray" Disadvantage 1 -need special machine 2-need more finishing So not widely used (d)metal (casted or swaged) Cast metal and swaged metal trays are rarely used Dis advantage 1 - difficult construction 2- time consuming So not widely used Spacer *function create space to make uniform thickness for impression * stoppers mentain space created by spacer * Affect type of impression where impression can be 1-mucostatic technique where use uniform thickness of spacer 2-mucocompressive technique no spacer used 3-selective pressure impression technique where no spacer at 1ry stress bearing area ,less thickness of spacer at secondary stress bearing areas ,more thickness of spacer at relieved areas Pouring of impression 1-convensional method *Place soft mix of plaster or stone in anterior part of impression and vibrate to spread to all the ridge *Apply some powder to make thick mix on glass slab and then invert impression over it ,make land area by our hand 2-boxing Def building up of vertical of impression tobe base on cast Aim 1 -produce size,form of base of cast 2-preserve anatomical landmark of impression Advantage 1 -strengthen cast 2 -preserve full depth of impression 3-accurate thickness of cast where control pouring to be economic Methods a-wax boxing method ' for plaster impression ,zno impression as wax stick to them ' 1- Place beading wax '3;4mm width' below border of impression by 3mm to be land area on cast 2- Place boxing wax '12mm in length 'stick to beading wax to be vertical walls b-plaster and pumice method 'for rubber base impression as wax not stick to them' surround impression as beading wax to be land area on cast then apply wax to be Vertical walls Apply separating medium between plaster of pouring and plaster and pumice 3-clay of children 'for irreversible hydrocolloids as (alginate)' *Surround impression as beading wax, then apply wax to be vertical walls * Not need separating medium with plaster of pouring 4- magnetic strips 'for all impression' * Height of strips 11; 12mm *Simple, efficient, inexpensive No need to stick strips to each other N.B to make cast more harder so placed in K-sulphate so resist its scrapping