Lecture 03 - Primary Impressions PDF

Preliminary Impressions Prosthodontics/Preclinical-1 1603340 27-30/10/2024 First Semester 2024 Dr. Ibrahim Khatib DDS, MClinDent, Mpros 3  Lecture outline I. Introduction II. Diagnostic/Preliminary Impressions I. Purpose and Indications II...

Preliminary Impressions Prosthodontics/Preclinical-1 1603340 27-30/10/2024 First Semester 2024 Dr. Ibrahim Khatib DDS, MClinDent, Mpros 3  Lecture outline I. Introduction II. Diagnostic/Preliminary Impressions I. Purpose and Indications II. Trays III. Materials III. Impression Philosophies 2 Introduction 3  The objectives of impression making are to capture all potential denture-bearing surfaces and tissues to provide support, retention, and stability for the denture under function 4  Importance of Accurate Impressions Retention: Proper impressions capture the anatomical contours of the edentulous ridge, creating a close-fitting denture base that aids in retention by establishing good suction or adhesion between the denture and oral tissues. How is retention achieved: The main mode of retention is the peripheral seal which requires intimate contact between the denture and the denture bearing area. 5  Importance of Accurate Impressions Support: Dentures need support from the underlying tissues to bear masticatory forces. Accurate impressions ensure the denture base fully contacts supporting structures, distributing pressure evenly and preventing tissue trauma. 6  Importance of Accurate Impressions Stability: Impressions that accurately capture the functional form of the oral tissues help ensure the denture is stable, preventing horizontal or rotational movements during chewing or speaking. 7 Diagnostic/Preliminary Impressions 8  Purpose and Indications Purpose: Preliminary impressions provide a general overview of the edentulous arch, allowing for the creation of diagnostic casts. These casts help visualize anatomical landmarks and plan treatment. The casts are used to fabricate a custom tray 9  Purpose and Indications Indications: Used in the initial phase of denture treatment to produce study models. Helps fabricate custom trays that are adapted to the patient’s specific oral anatomy. Provides information about ridge shape, undercuts, and vestibular extensions that are crucial for further steps. 10 Impression Trays 11 Impression Tray a device used to carry, confine & control the impression material to and from the patient's mouth Stock or Custom Trays 12  Stock Trays Prefabricated trays available in standardized sizes and shapes, providing a generic fit Can be dentate or edentulous Metal or plastic Plastic are lightweight and disposable. Flex Metal are durable and usually reusable. Rigid Perforated or non-perforated (retention) Full arch or quadrant 13  Body Flange Handle Size 14 15 16 Partial stock tray Dentate trays are deeper and box shaped 18  Stock Trays - Selection Criteria Depends on material to be used and function Different materials require different space Choose the tray size that closely fits the patient’s arch with at least 3-5 mm of clearance between the tray and the tissues to accommodate the impression material. Maxillary and mandibular trays should extend fully into the vestibules to capture the entire denture-bearing area. 19  The dentist places the tray in the mouth and initially positions it by centering the labial notch of the tray over the labial frenum. In the maxilla, the distal extension covers to the vibrating line, allowing space and coverage of the tuberosities. The mandibular tray should extend to the ascending ramus. 20  If the tray is too large, it will distort the tissues around the borders of the impression and will pull the soft tissues under the impression away from the bone, distorting the dimensions of the sulcus in the process. If it is too small, the border tissue will collapse inward onto the residual ridge. This too will distort the accurate recording of the border extension of the denture and prevent the proper support of the lips by the denture flange 21  Stock Trays - Modifications Under-extended - Wax/compound to increase extensions Over-extended - Adjusted with acrylic bur It can also be heated to modify shape (flex) 22 23 Stock Trays Convenient Availability Cost effective Fit is not ideal Rarely fit the jaws without tissue distortion Limited control over material thickness May require modification 24 Custom Trays 25  Importance of Custom Trays Custom trays are individually fabricated to fit the patient’s specific oral anatomy, leading to more accurate impressions. They reduce the bulk of impression material and allow uniform distribution over the tissues. Custom trays provide better control over the extension and border molding process, helping capture the functional peripheries more effectively. rigid – increases accuracy Light cured acrylic 26  Fabrication guidelines Spacer Extensions Perforations (retention holes) Adaptation (blocking out undercuts) Material Handle 27  Custom Tray Improves fit Reduces material thickness and makes it uniform - improves accuracy Time consuming Increases cost 28  Trays – retention of the impression material Retention perforations Adhesive Rim lock 29 30 31 Rim Lock Rim Lock  Materials 34  Materials When the preliminary impression is made, it is advisable to select an impression material that has a relatively high viscosity, thereby allowing the material to compensate more easily for the deficiencies of the tray. The most suitable materials are alginate (irreversible hydrocolloid) impression compound PVS putty (silicone) 35  Alginate (Irreversible hydrocolloid) Characteristics: Alginate is a hydrophilic, elastic material commonly used for preliminary impressions. It is cost-effective and easy to manipulate. Can be fast or regular set. Advantages: Quick setting time, good initial detail, hydrophilic properties (captures moist surfaces well), and affordable. Disadvantages: Poor dimensional stability (must be poured soon after), less accuracy for fine details, weight of the stone may be sufficient to distort the borders of the impression if they are not supported by the tray 36  Impression Compound Characteristics: A thermoplastic material that can be softened with heat and molded in the patient’s mouth. Supplied in cake or stick form. Can be used for preliminary impressions or border moulding Advantages: More stable and adaptable to specific areas, allows better control in capturing difficult anatomy. Disadvantages: Technique-sensitive, requires reheating and re-adaptation if deformed, non elastic 37  Polyvinyl siloxane Putty Consistency Characteristics: High viscosity silicone that is dimensionally stable. Supplied as base and catalyst and hand mixed. Advantages: good dimensional stability, easy to manipulate, can support itself, elastic Disadvantages: lower detail reproduction, limited flow, expensive 38 Taking the impression 39  To make an ideal impression, the following concepts should be adhered to, irrespective of the selected technique: 1. The tissues of the mouth must be healthy. 2. The impression should extend to include the entire denture bearing area 3. Proper space for the selected impression material should be provided within a properly fitting impression tray. 4. A guiding mechanism should be provided for correct positioning of the impression tray in the mouth. The preliminary impression should be as accurate as possible and overextension of peripheral borders is preferred to under-extension. 40 41 42 43 44 Impression Philosophies 45  The oral mucosa is compressible particularly during function Compression of the tissues supporting the denture during function may lead to denture instability These tissues may also be compressed during impression taking. If the tissues are recorded under compression, the denture will compress the tissues when it is fully seated even when not under function! 46  Some impression techniques are intended to record the shape of the tissues with minimum displacement; others are intended to displace the border tissues to a predetermined extent Impressions that record the tissues with minimum displacement are described as mucostatic, whereas those that displace the tissues are classified as mucodisplacing. 47  Introduction to different philosophies Mucostatic Mucocompressive Selective pressure technique 48  Impression Philosophies - Mucostatic Records tissues in their non-displaced, resting position. Often used when minimal pressure on the tissues is desired (e.g., for fibrous tissues). Suitable for patients with minimal residual ridge or when functional loading is not needed. 49  Impression Philosophies - Mucocompressive Tissues are recorded under functional pressure, simulating the forces applied during chewing. Often used to capture tissues under functional load. May result in better denture stability in patients with firm, healthy tissues. 50  Impression Philosophies – Selective Pressure A hybrid approach that applies pressure selectively to certain areas (e.g., the primary stress-bearing areas) while avoiding excessive pressure on other sensitive areas. This philosophy enhances retention and comfort by balancing compression and relief where needed. 51  How can we control pressure? Spacer - increasing the space between the tray and the tissues reduces the pressure on the tissue. Larger space - mucostatic Impression material viscosity - viscous materials will displace the tissues more easily More viscous - Mucocompressive Vent holes Reduces pressure - mucostatic Open tray (window) Similar to vent holes but has greater effect 52 53 54 55 56 57 58 Common Errors and Troubleshooting 59  Under-Extended Common Errors Impressions Common Causes: Under-Extended Impressions Tray not covering the entire denture-bearing area. Insufficient material in theor Voids tray. Air Bubbles in the Impression Tray seated improperly Improper Impression Centering Incorrect tray size or extension Distorted Impression 39 38 60  Under-Extended Impressions Common Causes: Tray not covering the entire denture-bearing area. Insufficient material in the tray. Tray seated improperly Incorrect tray size or extension 39 61  Under-Extended Impressions Troubleshooting: Tray Selection: Ensure the tray covers all critical anatomical landmarks and provides 3-5 mm of space for impression material. Wax Extensions: Add wax or compound to the periphery of the tray to improve coverage if the vestibular areas are not captured Recheck Positioning: Ensure correct seating of the tray (from posterior to anterior in maxilla, and proper alignment with the midline). 40 62  Voids or Air Bubbles in the Impression Common Causes: Trapped air while seating the tray (Rapid seating of the tray) Insufficient material flow into the vestibules Troubleshooting: Apply adequate material and seat the tray slowly and firmly to ensure the material flows into all areas without air entrapment. If small voids are present in non-critical areas, you can reheat impression compound and reapply it in those areas. 41 63  Improper Impression Centering Common Causes: Incorrect tray positioning. Tray moves during the impression-setting process. Troubleshooting: Correct Tray Alignment: Ensure that the tray handle aligns with the patient’s facial midline (nose) before seating. Firm Hold: Hold the tray steadily in position until the material is fully set. 42 64  Distorted Impression Common Causes: Removing the tray too early before material sets. Flexing or moving the tray during the setting process Troubleshooting: Wait for Full Set: Wait at least one minute after the material hardens at the periphery to ensure complete set before removing the tray. Swift Removal: Remove the impression with a single, swift motion to minimize distortion. 43 65 66 67  ? Q&A Thank you 68  References Prosthodontic Treatment for Edentulous Patients Chapter 8 Treating the Complete Denture Patient Chapter 2 Lab Brief 02 69