TOPIC: IMPRESSIONS IN COMPLETE DENTURES
🎯 KEY POINTS :
🔹 Sublingual crescent is the crescent-shaped area on the anterior floor of the mouth formed by the lingual wall of the mandible and the adjacent sublingual fold. It is the area of the anterior alveololingual sulcus.
🔹 Retromolar pad consists of glandular tissues and the fibres of temporalis posteriorly, buccinator laterally and pterygomandibular raphe and superior constrictor medially. It should be covered in the denture to aid in posterior seal of the lower denture.
🔹 Peripheral seal is the contact of the denture border with the limiting structures to prevent the passage of air or food.
🔹Distobuccal border of the maxillary denture is limited by the coronoid process, ramus of the mandible and the masseter muscle.
🔹The purpose of boxing the impression is to give definite shape to the base of the cast and preserve the width of the border after border moulding.
🔹Aesthetics of the denture begins during the impression stage itself.
🔹 Mucostatic impression is the negative replica of the oral tissues on the state of rest.
🔹 Recording jaw relation is difficult in denture construction of patient with neuromuscular disorders.
🔹In the upper denture, the accurate adaptation of the labial flange and the positioning of the teeth influence the aesthetics.
🔹 Neutral zone concept was first proposed by Wilfred Fish.
🔎 DEFINITIONS :
🔸Impressions : Defined as ‘the negative likeness or copy in reverse of the surface of an object; an imprint of the teeth and adjacent structures for use in dentistry’. (GPT 8th Ed)
🔸Retention : Defined as ‘that quality inherent in the dental prosthesis acting to resist the forces of dislodgement along the path of placement’. (GPT 8th Ed)
🔸Stability : Defined as ‘the quality of a denture to be firm, steady or constant, to
resist displacement by functional horizontal or rotational stresses’.
🔸Neutral Zone : Defined as ‘the potential space between the lips and cheeks on one side and the tongue on the other side’.
🔸Support : Defined as ‘the resistance to vertical forces of mastication, occlusal forces and other forces applied in a direction towards the denture-bearing areas’.
🔎 Objectives of Impression Making :
🔸5 primary objectives of impression making.
🔸These are as follows:
- Preservation of remaining structures
- Support
- Stability
- Aesthetics
- Retention
🔎 IMPRESSION TECHNIQUES :
💡Impression techniques can be classified on the following basis:
(i) On the basis of pressure used during impression making:
🔸 Mucocompressive technique
🔸 Mucostatic technique
🔸 Selective pressure technique
(ii) On the basis of tray selection:
🔸 Stock tray impression
🔸 Custom tray impression
(iii) On the basis of type of impression:
🔸 Diagnostic impression
🔸 Primary impression
🔸 Secondary impression
(iv) On the basis of material used:
🔸 Reversible or irreversible hydrocolloids
🔸 Impression compound
🔸 Impression plaster
🔸 Impression waxes
🔸 Silicone impression
(v) On the basis of mouth opening:
🔸 Open mouth technique
🔸 Closed mouth technique
(vi) On the basis of hand-manipulated functional movements:
🔸 Dynamic functional movements
🔸 Passive functional movements
📌 Various materials commonly used for impression-making in complete dentures are as follows:
🔸 Impression plaster
🔸 Zinc oxide eugenol paste
🔸 Modelling plastic or impression compound
🔸 Reversible hydrocolloid
🔸 Irreversible hydrocolloid
🔸 Rubber base impression material
🔸 Impression waxes