Dental Impressions PDF

Dental Impressions Dr. M. El Halawani Impression An impression is a negative likeness or copy in reverse of the surface of an object; an imprint of the teeth and adjacent structures for use in dentistry. A negative imprint of an oral structure used to produce a positive replica of...

Dental Impressions Dr. M. El Halawani Impression An impression is a negative likeness or copy in reverse of the surface of an object; an imprint of the teeth and adjacent structures for use in dentistry. A negative imprint of an oral structure used to produce a positive replica of the structure to be used as a permanent record or in the production of a dental restoration or prosthesis.  Involves a Single tooth A quadrant An entire arch Can be with or without teeth Soft or hard tissue Positive Copy Gypsum or stone is poured into the impression to create a model of the oral structure that is a positive copy of the original structure. This model is referred to as a “Cast” Requirements of ideal impression Must be an exact record of all aspects of the prepared tooth. Include su cient unprepared tooth structure immediately adjacent to the margins —> for creating proper contours of tooth. No air bubbles. Clearly visible nish line. ffi fi  Requirements of ideal impression Su cient data from the rest of the arch should be obtained. Tray borders not in contact with teeth. Enough material beyond the prepared tooth. ffi Properties of ideal impression material Must be able to ow and adapt around structures — semi-liquid state Must harden into a solid state Rigid enough to withstand distortion Elastic enough to be removed from patient’s mouth Dimensional stability after setting Biocompatible and non toxic fl Properties of ideal impression material Accurate reproduction of details Viscosity —> high mucocompressive —> Low mucostatic Wettability —> ability of the liquid to cover the surface completely Hydrophobic Hydrophilic Properties of ideal impression material Have adequate working time — between start of mix and placement in the mouth. Have a reasonable setting time. Have acceptable taste, odor and appearance. Chemically compatible with the material used to create cast. Can be disinfected without changing properties Easy to manipulate.  Classification of Impression Materials In-elastic (Rigid) Elastic Hydrocolloids Elastomeric In-elastic Impression materials Original impression materials Not used so much today Can be brittle and break during removal Best for edentulous cases (minimal undercuts) 1- Plaster of Paris (type I gypsum) 2- Impression compound 3- Zinc oxide eugenol impression Elastic impression Materials Reversible hydrocolloid Gel Agar Hydrocolloid or Agar-Agar - a seaweed At higher temperatures (90o)— from gel to uid sol. Heating As it cools (lower than 50o)— sol to gel. Sol Advantages: Hydrophilic Cooling Low cost No custom tray needed Gel Can be reused fl Elastic impression Materials Reversible hydrocolloid Disadvantages: Needed speci c equipment for heating and cooling Speci c trays for water cooling fi fi Elastic impression Materials Reversible hydrocolloid Disadvantages: Poor tear strength Low stability —> must be poured immediately (within 30 minutes) Elastic impression Materials Irreversible hydrocolloid Alginate impressions Forms an irreversible gel when mixed with Sol water. Comes in di erent setting speeds. Water Gel ff Elastic impression Materials Irreversible hydrocolloid Advantages: Disadvantages: Rapid set Can only be used with stone casts Hydrophilic Less ner details than other materials Easy technique Exhibit some permanent deformations Low cost fi Elastic impression Materials Elastomeric materials Polysul des Condensation silicones Addition silicones Polyethers fi  Elastic impression Materials Elastomeric materials - 1) Polysul de polymer The oldest elastomeric impressions on the market. Supplied as a two tube paste system (base and catalyst) Di erent viscosity (light - regular - heavy) Brown in color — polymerized aided by lead peroxides ff fi Elastic impression Materials Elastomeric materials - 1) Polysul de polymer Advantages: High tear strength High elastic properties easy removal from patient Easy pouring Better stability than hydrocolloids - still has to be poured within an hour Least expensive elastomer fi Elastic impression Materials Elastomeric materials - 1) Polysul de polymer Disadvantages: Slight contraction during polymerization (can be minimized by using custom tray) Long setting time (10 minutes) - humidity and temperature a ects setting time. Not liked by patients - color and odor Messy and can cause stains ff fi  Elastic impression Materials Elastomeric materials - 2) Condensation silicone Supplied as a base and catalyst Made of Dimethylsiloxane with reactive -OH groups. The higher the molecular wt the heavier the material Supplied as putty, heavy body, light body Reaction of material by condensation —> producing alcohol  Elastic impression Materials Elastomeric materials - 2) Condensation silicone Usually used in a 2-step impression (putty then light body) or used with custom trays. Advantages: Short setting time (6-8 minutes) Less a ected by high room temperatures Odorless ff  Elastic impression Materials Elastomeric materials - 2) Condensation silicone Disadvantages: Hydrophobic —> poor wetting capabilities Teeth and gingival sulci must be free of moisture completely Surfactant needed before pouring casts to avoid air bubbles Putty must be free of contaminants so not to prevent adherence of light body. Loss of alcohol and/or water may result in loss of dimensional stability over time Has to be poured immediately  Elastic impression Materials Elastomeric materials - 3) Addition silicone Also known as Polyvinyl Siloxane. Similar to condensation silicone except with much better stability —> no water or alcohol byproducts. After setting it is more rigid than polysul de. Originally hydrophobic materials. Supplied as normal set and fast set. fi  Elastic impression Materials Elastomeric materials - 3) Addition silicone Supplied in di erent consistencies: Putty Heavy body Regular body Light body ff  Elastic impression Materials Elastomeric materials - 3) Addition silicone New materials have hydrophilic properties for greater reproduction of details.  Elastic impression Materials Elastomeric materials - 3) Addition silicone Advantages: Dimensionally stable — some exhibit stability up to 1 week. Pleasant to use Short setting time Automix is available - less material waste - better mixing - less air bubbles  Elastic impression Materials Elastomeric materials - 3) Addition silicone Disadvantages: Hydrophobic in nature Hydrophilic materials can imbibe water Setting inhibited when using latex gloves — due to presence of Dithiocarbamates used in manufacture of such gloves. Some materials release H2 gas during polymerization —> air bubbles in cast —> wait 1 hour before pouring.  NEW — HYDROPHYLIC ADDITIVES Main new feature — Hydrophilic nature compared to other VPS materials === great detail reproduction  Elastic impression Materials Elastomeric materials - 4) Polyethers Base: on low molecular weight polyether containing ehtlene amine terminal groups. Catalyst: sulfonic acid When mixed together —> polymerization + cross linking —> sti polyether rubber ff  Elastic impression Materials Elastomeric materials - 4) Polyethers Advantages: It has the highest sti ness of all elastomeric materials. Together with PVS they have the best dimensional stability. Hydrophilic in nature —> best detail reproduction. Automix available ff  Elastic impression Materials Elastomeric materials - 4) Polyethers Disadvantages: The high sti ness can cause problems when removing from cast with undercuts. Has to be stored dry as it absorbs moisture by imbibition. Short working time — limit the use for smaller number of abutments. Some patients exhibit allergic reaction. ff  Elastic impression Materials Elastomeric materials - 4) Vinyl Polyethers A combination between Vinyl Siloxane and polyether Hydrophilic without the need for surfactants Great ow High tear strength and exibility Faster intraoral setting (75 secs) fl fl Choosing the correct impression tray Types of trays include - Stock trays (prefabricated) - Custom trays Choosing the correct tray Avoid flexible trays Stainless steel trays —> best Rigid plastic trays —> limited to open tray implant technique Tray should cover the occlusal surface of all the teeth in the arch Tray should be wide —> not touching soft tissues or teeth —> Can be easily moved from side to size Choosing the correct tray For retention of impression material Perforated trays Rim lock Rim Lock Tray adhesive Custom trays Improves accuracy of elastomeric materials—> limited material Can be made from Autopolymerizing resin Thermoplastic resin Photopolymerized resin 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. Impression techniques Irreversible hydrocolloid Manipulation Correct powder/liquid ratio used Rubber mixing bowl Wide spatula with exible blade Alginate mixer can be used Used with stock perforated/rim-lock trays fl Impression techniques Irreversible hydrocolloid Manipulation Correct powder/liquid ratio used Rubber mixing bowl Wide spatula with exible blade Alginate mixer can be used Used with stock perforated/rim-lock trays fl Impression techniques Irreversible hydrocolloid The tray is loaded with the impression material — do not over ll Retract the mouth angle with the fore nger or using an intraoral mirror. The tray is introduced with the right hand at an angle. fi fi Impression techniques Irreversible hydrocolloid The tray is then rotated so the handle coincides with the midline of patient. Upper jaw —> the tray is rst pressed in the distal region, and then in the anterior region of the upper jaw. Lower Jaw —> the tray is rst placed in the anterior region and pressed in the distal region of the jaw. fi fi Impression techniques Irreversible hydrocolloid The impression is then held passively until complete setting of the material. 2 hand technique 1 hand technique Managing Gagging re ex Use the lease amount of material - ie do not cover palatal area with impression material Patient should be sitting upright Controlled breathing method Distraction techniques Topical anesthesia can be used Medication can be prescribed 1 hour before appointment - anticholinergics fl Impression techniques Elastomeric Materials 2 Step technique Putty or Heavy Body - Lightbody 1 Step technique Single Viscosity 2 Viscosities 2-step Impression technique Elastomeric Materials 2-step Impression technique Elastomeric Materials - Putty impression 2-step Impression technique Elastomeric Materials - Putty impression Remove material exceeding the tray rim Remove the lateral edges (undercuts) Remove interdental areas Remove undercuts Prepared teeth are not trimmed Carve escape channels for light body 2-step Impression technique Elastomeric Materials - Putty impression 2-step Impression technique Elastomeric Materials - Putty impression 2-step Impression technique Elastomeric Materials - Putty impression 2-step Impression technique Elastomeric Materials - Putty impression 2-step Impression technique Elastomeric Materials - Wash (light body) Tray with putty checked for easy seating Putty should be cleaned and air dried Light body should be applied evenly Tray reseated with pressure —> 3-5 seconds Impression kept in place —> passive pressure 2-step Impression technique Elastomeric Materials - Wash (light body) 1-step Impression technique Elastomeric Materials 1-step Impression technique Elastomeric Materials - Monophase A single viscosity of material is used. Usually regular/medium body. Impression is loaded into the tray. Can be injected on the abutment teeth. Used with non perforated trays. 1-step Impression technique Elastomeric Materials - Monophase  1-step Impression technique Elastomeric Materials - 2 Viscosities Same type of material - 2 di erent viscosities Putty/Heavy body —> used as a base Medium/Light —> wash/ corrective layer ff  1-step Impression technique Elastomeric Materials - 2 Viscosities Tray is lled with base layer — A groove is made in the base layer, where and lled with the corrective material. Intraoral mixing syringe or application syringe used to apply material directly on abutment. fi fi Impression techniques Elastomeric Materials - Removal of impression Closed mouth technique Elastomeric Materials Also called dual-arch technique - or - triple tray technique Impression made at maximum intercuspation Using High-viscosity polyether or polyvinylsiloxane Impression includes abutment tooth, adjacent teeth and opposing dentition + records them at MI. Eccentric relationships are not recorded —> modi cations will be needed during delivery. fi Closed mouth technique Elastomeric Materials Closed mouth technique Elastomeric Materials Closed mouth technique Elastomeric Materials Impression cleaning and disinfection Impression is thoroughly rinsed under running water. Then the impression should be disinfected before sending to the dental lab. Disinfectant used according to the type of impression material. Impression cleaning and disinfection Interocclusal Records Interocclusal records Interocclusal records present the lab with the relationship between the maxillary and mandibular arches for mounting on the articulator. Centric Relation Maximum Intercuspation Lateral interocclusal records Centric Relation The relationship between the maxillary and mandibular arches that exists when the condyles are in their most anterosuperior position in the glenoid fossae. The maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective disks with the condyle-disk complex in the anterosuperior position against the articular eminences. It is a bone to bone relationship regardless of the position of the tooth contact. Centric Relation The centric relation is used when fabricating: RDP FDP For restoration of a signi cant portion of the occlusion. fi Centric Relation Techniques Accurate mounting of casts depends on precise manipulation of the patient’s mandible by the dentist. The condyles should remain in the same place throughout the opening-closing arc. Centric Relation Techniques Chinpoint guidance Bimanual manipulation technique (Dawson) —> easily repeatable Single handed manipulation technique Unguided method —> replies on muscle proprioception Centric Relation Techniques Chinpoint guidance Pressure on the chin while the patient is closing to guide the mandible into position. Posterior-superior position of the condyle. Impingement on the neuromuscular supply or retro-discal pad. Centric Relation Techniques Chinpoint guidance It might cause supra-occlusion of restorations. Centric Relation Techniques Bimanual Manipulation technique Described by Dawson It is a reproducible technique Patient is in reclined position Thumbs rest on the chin Fingers rest rmly on the inferior border of the mandible Thumbs —> gentle downward pressure Fingers —> upwards pressure fi Centric Relation Techniques Single-handed Manipulation technique Similar to the bimanual More di cult to ensure condyles are in place Frees one hand to hold the interocclusal record material ffi  Centric Relation Techniques Unguided method Depends on the neuromuscularature Produces a physiologic (muscle position) Di cult to achieve consistent results A leaf gauge can be used to separate the anterior teeth —> help eliminate direct proprioceptor response. The leaf gauge is increased in size until the patient disoccludes the posteriors ffi Anterior programing device Used in case of resistance in achieving CR. The rationale is to help the neuromuscular forget the re exed leading to MI position. The anteriors can be kept apart using Cotton rolls Leaf gauge Anterior programing device (Lucia jig) fl Anterior programing device Autopolymerizing resin is mixed and adapted to the maxillary central incisors. Thermoplastic material can also be used. Patient is guided into CR and stopped when posterior teeth 1 mm apart. Device is trimmed (using indentations as a guide). Avoid inclined contact area —> excessive retrusion of the mandible. Maximum Intercuspation Used when enough occlusal contacts are present. In cases needing a partial coverage restoration, single crown, short span FDP. The patient is requested to bite in MI and position is veri ed by the dentist. fi Materials Requirements of ideal bite registration material The materials should o er limited resistance before setting to avoid displacing the mandible during closure Accurately record the incisal and occlusal surfaces of the teeth Rigid enough with minimal dimensional changes Easy to manipulate Biocompatible ff Materials Wax —> reinforced Aluwax better than baseplate wax Zinc Oxide Eugenol Elastomeric materials —> most accurate Autopolymerizing resin Wax Squash Bite Wax Squash Bite Wax Squash Bite Wax Sheet Wax Sheet Wax Sheet Wax Sheet Wax Sheet Elastomeric Materials Can be injected in position. 2 separate quadrants are taken. Excess material should be trimmed. In case of CR a Lucia jig should be used to avoid overclosure. Zinc Oxide Eugenol Best used with a gauze mesh for reinforcement (3-way tray) The material is applied to the mesh. The patient is then guided to the position. Patially edentulous patients Lateral Interocclusal Relationship Done for the purpose of capturing the position of the condyles in their respective fossae. These records are then used to set the condylar guides to approximate the anatomic limits of the temporomandibular joints.