impressions in complete dentures

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Impressions in Complete Dentures : 

Impressions in Complete Dentures An imprint / negative likeness of the teeth &/or edentulous areas where the teeth have been removed, made in a plastic material which becomes relatively hard or set while in contact with the tissues. Impressions may be made of full complements of teeth, of areas where some teeth have been removed, or in mouth from which all teeth have been removed. A complete denture impression is a negative registration of the entire denture bearing, stabilizing & border seal areas present in the edentulous mouth.s

Classification : 

Classification Depending on theories of impression making Mucostatic / passive impression (Richardson & Henry L. Page) Mucocompression / functional impression (Carole Jones & Greene brothers) Selective Pressure impression (Boucher)

Classification : 

Classification Depending on the technique Open mouth / Closed mouth technique Hand manipulation for functional movements (Dynamic impression) Depending on type of tray Stock tray / Custom tray impression

Classification : 

Classification Depending on purpose of the impression Diagnostic / Primary / Secondary Depending on the material used Agar, Alginate, Impression Compound, Plaster, Wax, Silicone, Thiokol rubber impression.

Anatomical landmarks in Maxilla : 

Anatomical landmarks in Maxilla Limiting Structures Labial frenum, labial vestibule, buccal frenum, buccal vestibule, coronomaxillary space, hamular notch & posterior palatal seal area Supporting structures Primary stress bearing areas Hard palate (Jacobson & Krol) Postero-lateral slopes of residual alveolar ridge Secondary stress bearing areas Rugae, Maxillary tuberosity, alveolar tubercle

Anatomical landmarks in Maxilla : 

Relief areas Incisive papilla Cuspid eminence Mid-palatine Raphe Fovea palatina Anatomical landmarks in Maxilla

Anatomical landmarks in Mandible : 

Anatomical landmarks in Mandible Limiting Structures Labial frenum, labial vestibule, buccal frenum, buccal vestibule, lingual frenum, alveololingual sulcus, retromolar pads, pterygomandibular raphe. Supporting structures Primary stress bearing areas Buccal shelf area Retromolar pads Secondary stress bearing areas Residual alveolar ridge, genial tubercles

Anatomical landmarks in Mandible : 

Relief areas Crest of the ridge Mental foramen Torus mandibularis Labial & lingual inclines Anatomical landmarks in Mandible

Principles of impression making : 

Principles of impression making Oral tissues must be healthy Impression should include basal seat within limits Borders must be in harmony with anatomical & physiological limitations of oral structures Selective pressure tech. shd be used Sufficient space should be provided within impression tray for imp. material Guiding mechanism (tissue stops & handle) shd be provided for correct positioning of tray Imp. Shd be removed from mouth without damaging the mucosa Materials used shd be dimensionally stable External shape of impression shd be similar to ext. form of complete denture

Objectives of impression making : 

Objectives of impression making P – preservation of remaining natural structures R – retention E – esthetics S – stability S – support

Preservation of remaining natural structures : 

Preservation of remaining natural structures Muller De Van (1952): the preservation of that which remains is of utmost importance and not the meticulous replacement of that which has been lost Impression shd record details in appropriate form to prevent injury to the tissues Relief to non-stress bearing areas, thus preventing damage Avoid overextensions

Retention : 

Retention That quality inherent in the prosthesis which resists the force of gravity, adhesiveness of foods, and the forces associated with the opening of the jaws It is the ability of denture to withstand displacement against the path of insertion Factors affecting retention Anatomical ----size & quality of denture bearing area Physiological – viscosity of saliva (thick/thin) Physical -------- adhesion, cohesion, surface tension, capillarity & atmospheric pressure Mechanical ---- undercuts, retentive springs, magnets, adhesives, suction chambers/discs Muscular ------ Neutral zone

Stability : 

Stability The quality of a denture to be firm, steady, or constant, to resist displacement by functional stresses & not to be subject to change of position when forces are applied It is the ability of the denture to withstand horizontal forces. Factors affecting stability Vertical height of ridge -- resorbed ridge – poor stability Quality of soft tissue ---- firm / flabby tissues Quality of impression---- accurate, smooth, stable Occlusal plane ------------ should be parallel to ridge Arrangement of teeth --- balanced occlusion Contour of the polished surfaces

Support : 

Support The resistance to vertical forces of mastication, occlusal forces & other forces applied in a direction towards the denture bearing area. Achieved by covering as much area as possible This helps to distribute forces - snowshoe

Esthetics : 

Esthetics Thickness of flanges Impression should reproduce width & height of sulcus

Recording the Preliminary Impression : 

Recording the Preliminary Impression TRAY – A receptacle into which a suitable material is placed to make an impression A device which is used to carry, confine & control an impression material while making an impression Stock tray – metal / plastic, 2-3mm clearance, shd cover tuberosity & hamular notch Special tray – A custom made device prepared for a particular patient which is used to carry, confine & control an impression material while making an impression Material used shd be well adapted, stable, 2mm thick, contrast in colour & 2mm short in sulcus Adapt the relief wax (spacer) Fabrication of tray – shellac, self cure resin, thermoplastic resins, vacuum formed Vinyl or Polystyrene Storing the trays

Making the Secondary impression : 

Making the Secondary impression Border Moulding – Single step / Incremental Wash Impression – ZnOE / noneugenol, light body silicone Recording the posterior palatal seal - the soft tissues along the junction of hard & soft palates on which pressure within the physiological limits of the tissues can be applied by a denture to aid in the retention of denture Conventional approach Fluid wax technique Arbitrary scraping of master cast Extended palatal technique

Slide 18: 

Inspecting the impression Disinfecting the impression Remaking the impression