Impressions in Fixed Prosthodontics Lecture 1 PDF

Impressions in Fixed Prosthodontics Dr. Mahinour Ahmed  Accurate impressions are critical in fixed prosthodontics. Dental impressions are essential in: Creating accurate models(casts) Give precise dental restoration. After finishing preparation and starting to take...

Impressions in Fixed Prosthodontics Dr. Mahinour Ahmed  Accurate impressions are critical in fixed prosthodontics. Dental impressions are essential in: Creating accurate models(casts) Give precise dental restoration. After finishing preparation and starting to take impression……  A good impression not only captures the necessary details but also fosters a positive relationship between the dentist and the patient. Positive Experience. Trust Building. Bad Experience  Impression: A negative replica of the teeth and surrounding structures that used to obtain a cast, on which the planned restoration is fabricated. Positive replica (positive copy) A negative imprint of an oral structure used to produce a positive replica of the structure to be used in the production of a dental restoration. Gypsum or stone is poured into the impression to create a cast of the oral structure that is a positive copy of the original structure.  1. Primary (diagnostic) Types of impression in impression. fixed prosthodontics: 2. Secondary impression. 1. Primary (diagnostic) impression. Purpose: Diagnostic Construction of tray. Secondary impression Purpose: Obtain master (definitive) cast.  Tray A device that holds impression material. Types of Impression Trays  1.Stock trays (prefabricated): available in various sizes. Plastic/ aluminium trays Stainless steel trays (non-rigid) cause distortion (Rigid): avoid distortion  Stock trays (prefabricated) Metallic or Plastic. Perforated or Non-perforated. Full or sectional/ inter-arch tray (dual tray). Types of Trays Dual-Arch Trays: Capture both arches simultaneously.  For retention of impression material within the tray use: Perforated trays (to expand through the holes and so be held securely in place). Rim Lock Tray adhesive Types of Trays 2. Custom/ Special Trays: Individualized tray. Made on a diagnostic cast. More accurate adaptation. Custom tray - Fabrication Line is drawn to mark end of spacer. 3-5 mm from gingival margins. 2 layers of base plate wax used. Trimmed until the marked line. Custom tray - Fabrication Wax is removed to form tray stops. Best to make tray stops on non functional cusps Tin foil is adapted on the wax. Custom tray - Fabrication Resin is adapted to the cast. Excess material trimmed. Attach a handle. Trimming of the custom tray. Proper tray selection Ensure tray covers all surfaces of teeth. Tray Selection  Tray Selection Sufficient distance to the tray wall on both sides. Tray Selection  A tray that is too Tray narrow may prevent Selection adequate seating. Impression Materials Requirement for an Ideal Impression Material Biocompatible material. Patient Comfort. Have acceptable taste, odor and appearance. Ease of Use. adequate working and setting time. Can be disinfected without changing properties. Requirement for an Ideal Impression Material Have: Dimensional stability Accuracy and details reproduction. Tear resistance. Wettability.  Dimensional Stability: ability to retain its absolute dimensional size over time. Accuracy: ability to replicate the intraoral surface details. Tear Resistance ability to resist tearing in thin sections (such as the feather-edged material within the gingival sulcus.  ability of the liquid to cover the surface Wettability completely.  Hydrophilic VS Hydrophobic materials Hydrophilic materials have a high affinity for moisture (low contact angle), provide good surface wetting, and allow for a high degree of surface detail. Hydrophobic materials have a low affinity for moisture (high contact angle), provide poor surface wetting, and a lower degree of surface detail. Classification of Impression Materials 1. Non-elastic (Rigid). 2. Elastic. Non-elastic Impression materials 1- Plaster of Paris (type I gypsum). 2- Impression compound. 3- Zinc oxide eugenol impression. 4- Waxes. Not used so much today. Can be brittle and break during removal. Best for edentulous cases (minimal undercuts). Types of Elastomeric Impression Materials Agar Aqueous (reversible) Hydrocolloids Alginate (irreversible). polysulfide Non-aqueous - Condensation Silicone Elastomers - Addition Silicone Polyether Impression Materials Gel Aqueous Hydrocolloids: Agar (reversible) Heating Changes between sol Sol and gel based on temperature. Cooling Gel  Irreversible Hydrocolloid (Alginate) Advantage: Material of choice for diagnostic impression (primary impression). Easy of manipulation Rapid set. Hydrophilic material.  Imbibition: Syneresis: absorption of loss of water. water. Hydrocolloids Properties Factors affecting setting time of Alginate Hot water, cold water, water amount.  Irreversible Hydrocolloid (Alginate) Disadvantage: Poor accuracy and surface details. Low tear resistance. Not suitable for definitive casts. Should pour immediately (within 30 minutes). Limited shelf life.  Modified alginate Alginate modified by in corroborating silicone polymer (paste form) Advantage: Fine details production. Better tear resistance. better dimensional stability. Non-aqueous Elastomers  Polysulfide Brown in color — polymerized aided by lead peroxides. Different viscosity (light - regular - heavy). Supplied as a two-tube paste system (base and catalyst). Polysulfide Advantages: higher tear strength. least expensive elastomer. Disadvantage: unpleasant sulfide odor, Messy, long setting time in the mouth (about 10 minutes). Hydrophobic.  Condensation Silicone Supplied as putty, heavy body, light body. Advantages. Odorless, shorter setting time (6-8 minutes). Adequate tear resistance. Disadvantages. Hydrophobic so the prepared teeth and gingival sulci must be completely dried. Alcohol byproduct causes shrinkage. Should be poured immediately. Polyvinyl siloxane (PVS) Addition Silicone Supplied as (Putty, Heavy body, Regular body, Light body). Automix is available so, less material waste, better mixing and less air bubbles.  Polyvinyl siloxane (PVS) Addition Silicone Disadvantage: NO byproduct. High cost. the most accurate material, Hydrophobic. offering excellent dimensional Material setting can be inhibited by stability and tear resistance. sulfur in latex gloves N.B. vinyl or nitrile gloves can be worn for mixing.  Polyvinyl siloxane (PVS) Addition Silicone (now hydrophilic type is available).  Polyether Hydrophilic (best detail reproduction). no byproduct. Excellent dimensional stability. short setting time in the mouth (about 5 minutes). Automix available.  Polyether Disadvantages: The stiffness ------causes broken of stone cast when separated from the impression. Expensive. Should be stored dry as it absorbs moisture by imbibition. Polyvinyl ether silicone (PVES) A new elastomeric impression material which is a combination of vinyl polysiloxane (VPS) and polyether (PE) elastomers. Hydrophilic the highest accuracy. Great flow. High tear strength flexibility. Clinical steps Laboratory steps Examination and diagnosis, Primary impression Pouring of Diagnostic casts and mounting on (alginate impression) articulator. Sectional tray & index (with putty silicon impression). Tooth preparation abutment A. Provisional / temporary crown restoration for abutment A. Tooth preparation abutment B. Alginate impression. Temporary bridge. Provisional / temporary crown restoration for abutment A, B. Finalization of teeth preparations, gingival Pouring of master cast retraction and secondary impression. Die preparation and die trimming Shade selection. Fabrication of Wax pattern, Spruing, Investing and casting Trimming and Finishing Metal try in Porcelain build-up and glazing Insertion and cementation Thank you Impressions in Fixed Prosthodontics Dr. Mahinour Ahmed PREREQUISITES BEFORE TAKING IMPRESSION Gingiva Tissue health Saliva control displacement  Tissue health Careful evaluation of surrounding tissues (No tissue damage).  Tissue health Any inflammation must be treated and resolved before fixed prosthodontic treatment.  Tissue health Lead to this Gingivitis or periodontitis Tissue health PREREQUISITES BEFORE TAKING IMPRESSION Gingiva Tissue health Saliva control displacement Challenges Gingival tissues must be displaced laterally to allow access and to provide space for the impression material.  Mechanical Techniques for Displacement Chemical Surgical PREREQUISITES BEFORE TAKING IMPRESSION Gingiva Tissue health Saliva control displacement Saliva control 1. Conventional technique. 2. Recent (digital technique). Conventional Impression technique 1- Single copper band (impression compound). 2. For Irreversible hydrocolloid (Alginate). 3. For elastomer materials: a. One step / monophase technique (Single Viscosity) b. One Step Putty-Wash technique (two Viscosity applied at the same time). c. Double step Putty-Wash technique (two Viscosity applied in two steps). d. Closed mouth technique/ dual-arch or triple tray technique.  This means of carrying the Copper band impression impression material and a mechanism for gingival retraction. Impression technique Irreversible hydrocolloid (Alginate)  Impression Manipulation Do not overload the tray. Faulty tray placement can cause discomfort and trigger gag reflex.  Managing Gagging reflex do not cover palatal area with impression material. Patient should be sitting upright. Controlled breathing method. Distraction techniques. Impression technique 1- Single copper band (impression compound). 2. For Irreversible hydrocolloid (Alginate). 3. For elastomer materials: a. One step / monophase technique (Single Viscosity) b. One Step Putty-Wash technique (two Viscosity applied at the same time). c. Double step Putty-Wash technique (two Viscosity applied in two steps). d. Closed mouth technique/ dual-arch or triple tray technique. Monophase technique Single Viscosity (usually medium viscosity of polyether and addition silicones). Advantages Reduced waste of the material. Less time consumption. Disadvantages Relatively high viscosity and reduced flow of the monophase materials, makes their injection onto the preparation more difficult to control. Putty-Wash Impression One step One step. 2 Viscosities. Putty-Wash Impression One step Low viscosity elastomer (light body) and high viscosity elastomer (putty body) are recorded at the same time. Disadvantages of one Step Putty-Wash Impression improper blending and setting of putty & wash phases (uneven polymerization shrinkage). Procedures: difficult to control the thickness of the impression material. higher viscosity material displaces the low viscosity material. So, critical areas are captured in putty rather than light body. Two Step (double) Putty-Wash Impression Techniques 2 viscosity, 2 steps. A. Higher viscosity material (Putty ) B. low viscosity (light body). Two Step (double) Putty-Wash Impression Techniques Advantages: Improved Accuracy: more accurate reproduction of fine details due to the putty material providing a stable base. Enhanced Detail Capture: The second wash layer is typically of a lower viscosity and flows better into critical areas like gingival margins and undercuts, ensuring superior detail capture. Easier Seating of Tray: The initial putty layer reduces the amount of wash material needed and makes it easier to seat the tray properly. 2-step Impression technique (Fort elastomeric) Putty impression “Onion skin” structure of the set silicone resulting from insufficiently mixed-in activator. Premix base material and activator in circling movements, take up the mixture with the spatula and spread it out widely. Trimming of the Remove material exceeding the tray rim Remove the lateral edges (undercuts) initial impression  Cut the palate part. - Prepared teeth are not trimmed - Carve escape channels for light body  No material residues or loose material flags should be left the impression is thoroughly cleaned with the air syringe. The wash material is applied into the initial impression prior to syringing the prepared teeth. The setting reaction of the material proceeds more slowly outside the mouth than in the warm oral cavity.  Exertion of pressure only in the initial 3 – 5 seconds, afterwards the impression is kept in place without pressure  Removal of the impression Release of the impression tray from vestibular. The thumb serves as protection for the teeth of the opposing jaw. Do not simply pull at the tray handle, but alternately exert pressure on the tray rim from vestibular until the impression releases. Assessment of the impression Cleaning of the impression under running water Disinfection Protocols Use of 2% Glutaraldehyde for 10 min soak except polyether or additional silicone. Iodophors and chlorine compounds are effective. Protocol: Rinse, immerse, and rinse again before pouring. Closed mouth technique/ dual-arch or triple tray technique : Capture both arches simultaneously. dual-arch or triple tray technique, is popular for making impressions for single units. Closed mouth technique  DISADVANTAGES OF CURRENT IMPRESSION TECHNIQUES Errors in tray selection. Limitations in the impression material’s flow and hydrophilicity. Patient movement. Tearing and deformation of the impression during removal. Dimensional instability of the set impression overtime. Inadequate wetting and voids when pouring the cast. Messy materials. Discomfort to patient. CAD/CAM refers to the integration of Computer-aided design (CAD) and Computer-aided manufacturing (CAM).  The first digital oral scanner with CAD/CAM system for restorative dentistry (1984) Dr. Werner Mőrmann and Marco Brandestini CEREC Chairside Economical Restoration of Esthetic Ceramics. It used a video camera and reflective powder to create a 3D model of the teeth. PRE-REQUISITES OF DIGITAL IMAGING 1. Digital camera to capture the scan data in the patient’s mouth. Advanced scanners use multiple cameras to capture different angles simultaneously, ensuring comprehensive coverage. Light Source The operating methods of intraoral scanners  The operating methods of intraoral scanners Image stitching scanners record individual images, they have a field of view in the form of a cone, so they cannot collect information from those hidden surfaces, hence necessary to make several shots of the same area to collect all the information. Video-sequencing Scanners record the scanned areas working similarly as a video camera through sequential short videos at high speed.  PRE-REQUISITES OF DIGITAL IMAGING 2. Software to create image, design restoration using Computer-aided design (CAD) & export the data as STL file. PRE-REQUISITES OF DIGITAL IMAGING 3. Milling unit to fabricate the prosthesis (in clinic or in lab). PRE-REQUISITE OF DIGITAL IMAGING Milling unit to fabricate the prosthesis (in clinic or in lab).  Image quality, accuracy, detail Capture A comparison of the same patient scanned with multiple scanners.  Design and Size: Smaller, lightweight scanners tend to enhance patient Patient comfort, especially for longer Comfort procedures.  Scanning the Opposing Arch Capturing the Bite After scanning both arches, you'll need to capture the patient's bite. Ask the patient to bite down in their natural, comfortable position.  Accuracy: High precision in capturing details. Reduced patient discomfort and gag Advantages of reflex due to the elimination of messy Intraoral impression materials Scanning Immediate Feedback: Instant visualization of the digital model. Efficiency: Faster turnaround time for restorations.  Cost: High initial investment for equipment. Limitations: May struggle with certain anatomical areas. Disadvantages of Intraoral Technical Issues: Potential for software or hardware malfunctions. Scanning Presence of saliva or blood which do not allow the prober of digital impression capturing. Learning Curve: Requires training to master the technology. Impression evaluation  Requirements of ideal impression Complete coverage Free of voids No distortions or tear Proper depth Exact duplicate Accuracy Clear and defined finish line  1. Inadequate Marginal Detail 2. Internal Bubbles Impression Errors 3. Marginal Tears 4. Inconsistent pressure 5. Inadequate Impression Material Mixing 6. Tray Selection 7. Separation from the Tray 8. Surface Contamination 9. Rotation 10. Dimensional Instability due to Wrong Disinfection 11. Dimensional Instability due to Wrong Storage  Inadequate Marginal Detail Voids at margins due to insufficient retraction or fluid accumulation. Solved by using retraction cord and hemostatic paste.  due to insufficient material. Improper wetting. Voids Blood and saliva contamination around preparation. Improper retraction. improper syringe technique. Inconsistent pressure When applying the material, use your fingertips to evenly distribute it across your dental arch, ensuring it covers both gums and molars. Check for complete coverage front and back. Show-through of tray Streaking Inadequate impression material mixing Separation from the Tray  Thin Walls caused by: insufficient retraction, Insufficient proximal reduction. Tears caused by: Premature removal of the impression before fill setting of the impression material. Insufficient tissue retraction. Presence of deep undercuts in the prep. Tears Caused by: Vinyl Polysiloxane materials: Inhibition of setting due to contact with sulphur from latex gloves with tissue, tooth, or impression material.  Pulls caused by: The tray is inserted when the impression material has exceeded its working time. Removing the heavy-body tray before the material is fully set. Movement of teeth during the process. If the tray shifts, it can distort the impression. Securely hold the tray to prevent movement for a reliable impression. Surface contaminant  Damming and blocking out impression trays Dorsal damming inhibits leakage of the impression material from the tray in the distal region. Also, it prevents that impression material to flows into the throat and induces a gag reflex. conclusion  3.Choose appropriate tray 2.Ensure adequate retraction 1.Ensure healthy tissue and wash material viscosities and hemostatic procedure, if (complete periodontal as well as setting versions 4.Use proper fitting, rigid, necessary. If retraction agents treatment prior to (regular or quick) according to impression tray. are used, rinse and dry prosthodontic restoration). impression technique and thoroughly. indication. 8.Avoid air entrapment during 5. Assure a uniform and 7.Use gloves that do not Making an accurate homogeneous mix of 6.Fill tray sufficiently with impression material. inhibit the setting of the intra-oral syringing of the wash material by immersing and detailed material. impression material. tip into the material. impression is one of the most important steps in creating 9.Apply controlled pressure 10.Avoid any movements that superior prosthetic upon seating the tray to avoid could shift the position of the 11.Stay within working time of 12.Follow setting time before removing impression from contact between teeth/tissue tray and may lead to tray and wash material. restorations for your and bottom of tray. distortions. mouth. patients. In order to make a good impression you 14.Check if preparation 16.Check for proper blend should consider the 13.When removing tray from margins are captured entirely: 15.Make sure that the tray between tray and wash mouth avoid unilateral no voids, tears, following: rotation. displacements, and flow does not show through. materials as well as proper bond to the tray. defects. 19.Exact brand of impression 18.Rinse impression after 17.Disinfect impression material and disinfection disinfection with water and according to manufacturer’s protocol must be dry before sending it to the instructions for use. communicated to the dental lab. laboratory.