Preparation for Master Impressions Flashcards
What are the four phases of any treatment plan
Immediate treatment
Initial (hygiene or preparatory) phase
Reconstructive (corrective) phase
Maintenance
What are the clinical stages of RPD construction (9)
Primary impressions Primary jaw registration (if required) Mounted, surveyed study casts Design denture Tooth preparation and definitive impressions Jaw registration Trial Delivery Review
What are the aspects of mouth preparation for master impressions (6)
Initial prosthetic treatment Pre-prosthetic treatment Periodontal treatment Orthodontic treatment Fixed prosthodontics treatment and endodontics Tooth preparation
Give examples of initial prosthetic treatment
Repairs and additions
Temporary relines
Occlusal adjustment
Treatment of denture stomatitis
How long do materials used for temporary relines last
2-4 weeks
When should inflammation caused by denture stomatitis be treated
Before impressions are taken
What advice should be given to patients with denture stomatitis
How to keep their denture clean
Remove it at night
Gently brush the roof of their mouth to get rid of any candidal hyphae
Sometimes antifungal medication is necessary
Give examples of pre-prosthetic surgery
Remove retained roots or unerupted teeth
Remove pathology - cysts
Improve contours of edentulous areas by reducing bony prominences and hyper plastic soft tissue
Eliminate prominent fraenal attachments - may interfere with flanges
Give examples of periodontal treatment prior to taking master impressions
Establish periodontal health Assess patient motivation Give detailed instruction in oral hygiene procedures Scaling and root planing Periodontal surgery
What is the purpose of orthodontic treatment prior to taking master impressions
To optimise space
To optimise abutment alignment
What patients are most likely to need orthodontic treatment
Cleft patients
Hypodontia patients
Periodontal patients who have lost teeth
When should fixed prosthodontic treatment occur
Should follow denture design and precede denture construction
What is the purpose of fixed prosthodontic treatment
Establishes clinical integrity of teeth before master impressions are recorded
So that you can request rests, guide planes and buccal shells for clasp retention etc
When is tooth preparation carried out
Before master impressions
Why is tooth preparation necessary
To provide rest seats
To establish guide surfaces
To modify unfavourable survey lines
To create retentive areas
What instruments should be used for tooth preparation
Slow speed instruments
Initially rotary diamond being careful not to take too much away
Can use different rubber wheels or impregnated stones to help smooth and polish any preparation
Why are rest seats necessary
To divert the forces down the long axis of the tooth
Produce favourable tooth surface for support
Prevent interference with occlusion
Reduce prominence of the rest
Describe a maxillary anterior rest seat and how they are made
Well-developed cingulum allows prep to stay within enamel
Use a cylindrical diamond stone with a rounded tip
Describe a mandibular anterior rest seat
Lingual surface too vertical and cingulum too poorly developed to avoid penetrating enamel
Incisal rest seats used instead
When is it possible to use an incisal rest seat on mandibular anterior teeth, that is good aesthetically
If teeth have worn down, you can use an incisal rest on the worn tip which isn’t visible from the labial aspect
What are alternatives from using an incisal rest on mandibular anterior teeth
Produce a rest seat in composite applied to the cingulum area
Bond a cast metal cingulum to the tooth - not likely nowadays
Describe a rest seat on a posterior tooth
Reduced marginal ridge
Saucer-shaped to allow horizontal movement and dissipation of occlusal forces
Deep enough to allow a rest of at least 1mm thick
How is a posterior rest seat prepared if there is no space occlusally for a clasp to extend buccal from the occlusal rest
The preparation must be extended as a channel onto the buccal surface
What are guide planes
Two or more parallel axial surfaces on abutment teeth which limit the path of insertion of a denture
They may occur naturally but more often need to be prepared
What is an axial surface
Surfaces parallel to the long axis of a tooth
What do guide planes provide
Increased stability
Reciprocation
Prevention of clasp deformation
Improved appearance
How should a guide plane be prepared
Guide surface should extend vertically 3mm but be kept as far from the gingival margin as possible
Not more than 0.5mm of enamel should be removed
What is the outcome of an unfavourable survey line
Clasp would be positioned too close to occlusal surface which would cause deformation of the clasp
How can an unfavourable survey line be fixed
Can add composite in a curve following the natural anatomy of the tooth to lower the survey line
Describe the clinical part of the master impression stage
Obtain an accurate impression of the denture-bearing area using an individual tray for the patient and an appropriate impression material
Describe the laboratory part of the master impression stage
Produce casts Produce casting (if cobalt chrome base) Produce record blocks Produce trial denture Produce finished denture
What are individual trays made of
Made from primary casts from heat cured or light cured acrylic
What should be done to the individual trays before taking the impression
Disinfect them, then place them in cold water and make sure they are rinsed and there isn’t any disinfectant left
What is the purpose of green stick
Will help to support the impression material to flow and give a nice sulcus form lingually
In upper it will compress the junction between the hard and soft palate and give a posterior seal
Describe green stick
Thermoplastic material
Part of the stick is cold and hard but part is heated in a Bunsen burner so the material starts to flow and it can be added to the flanges of the trays
What are common impression materials used in master impressions
Alginate
Polyvinylsiloxane eg - extrude
Polyether eg - Pentamix
