IMPRESSION MAKING (IN COMPLETE DENTURES) DR ZURYATI AB GHANI BDS (WALES), Grad Dip Clin Dent (Adelaide), Doctor in Clinical Dentistry (prosthodontics), Adelaide, FRACDS 17.06.2007
Impressions An impression an imprint produced by the pressure of one thing upon or into the surface of another Active rather than passive role Making rather than taking Flawed impressions account for the majority of denture problems
Categories Primary impressions Conventional techniques Template techniques Definitive/secondary impressions Conventional techniques Selective pressure techniques Functional techniques Reline and rebases techniques
PRIMARY IMPRESSION Definition-an impression made for the purpose of diagnosis or for the construction of a tray
Tray selection for primary inpression stock trays (for edentulous ridge) metal or plastic, perforated or non perforated 2-33 mm clearance between stock tray and ridge tray should extend over tuberosity and hamular notch
Materials for primary impression Relatively high viscosity materials Alginate used with perforated trays (metal or plastic) Compound used in with non perforated trays
Primary impression Upper Sit patient upright Stand on one side and behind the patient (Your elbows level with patient s s upper jaw) Evert upper lip Hold the loaded tray inferior and anterior to the incisive papilla Insert the tray upwards and backwards to fill, first of all, the labial sulcus,, then left and right sulci before the palatal area is pressed into position Ensure the material record the right and left sulci Borders definition- ask pt to suck down into tray, move mandible side to side and then open wide.
Primary impression Lower Sit patient upright with your elbows level with patient s s lower jaw. Stand to one side and in front of the patient Rotate the tray within the pt s s mouth in a horizontal plane until it is in the center of residual ridge and press the loaded tray The labial, right and left sulci in turn being everted to permit the impression material to fill the functional width of the sulci ask pt to raise tongue, then border mould.
Once the material has set, the tray is removed in one motion Mark the borders of the custom tray to be made. Pour up impression
Secondary or definitive impression Definition Should record the entire functional denture- bearing area to ensure maximum support, retention and stability for the denture during use Primary purpose To record accurately the tissues of the denture bearing areas, in addition to recording the functional width and depth of the sulci
Special trays Close fitting tray 2mm even thickness Smooth Rigid material ( eg. Cold cure acrylic) 2mm short of sulcus 45 handle
2 impression (Conventional technique) Disinfect the trays Check for adequate extension (antero- posteriorly and bucco-lingually) Use pressure indicating paste Correct under extension with tracing compound Trim the tray if over extended Apply tracing compound to the posterior aspect of the upper tray to produce a posterior seal
Secondary impression making Upper and lower arches- follow primary impression taking Materials Zinc oxide eugenol (material of choice) - Polyether - Polyvinylsiloxane (PVS)
Anatomical landmarks of importance Upper arch Lower arch
Salient anatomical features of denture bearing areas
The Incisive Papilla Soft tissue pad Covering the incisive canal
The Incisive Papilla Nerves and blood vessels supplying the anterior part of the palatal mucosa Position relatively constant following the extraction of the natural teeth Useful guide when placing artificial teeth as the labial surface of the upper anterior teeth is usually 8-10mm 8 10mm in front of the centre of the papilla
Palatine Fovea/fovea Palatinae Two orifices (small depressions in the mucosal surface) one each side of the midline About 2mm posterior to the vibrating line Act as collecting ducts for a group of minor palatine salivary glands
Vibrating Line Imaginary line across the posterior part of the palate marking the division between the movable and immovable tissues of the soft palate Junction of the hard and soft palate This line should lie in the soft palate The posterior border of the denture usually finishes on the compressible tissue 1-2mm 1 posterior to the vibrating line. It must cover to the tuberosities and extend to the hamular notches.
Freanum A narrow fibrous submucosal membrane bridging the buccal,, labial, or lingual sulcus This picture shows an upper impression with a depression created by a buccal freanum
Retromolar Pad Triangular soft tissue elevation distal to the third molars Important for denture support and preventing distal denture displacement Bounded by tendons and raphes of muscles. Denture base should extend only one half to two third of the retromolar pad
THANK YOU Some of the materials are courtesy of Dr Adam Husein
References 1. Nallaswamy D. (2003). Textbook of Prosthodontics. Jaypee brothers medical publishers (p) LTD. New Delhi 2. Some illustration are courtesy Dr Adam Husein