Fixed Prosthodontics BDS4 Flashcards
Why do we replace teeth?
Improve aesthetics
Improve occlusal stability e.g. prevent eruption of opposing teeth
Improve function e.g. mastication, speech.
For periodontal splinting
Restoring OVD
Patient preference
What is a diagnostic wax up?
What are the advantages of a diagnostic wax up?
Wax is added to study casts in order to mock up the appearance of a fine restoration
Usually used for bridges, veneers, build-ups etc.
Facilitates communication as it gives a visual aid to show patient
Allows for greater accuracy and consistency
3D visualisation by patient and dentist
Allows for provisional trial
Incurs extra cost and time but can equally save costs and time in the long term
What are the various types of wax ups that can be sued in fixed pros?
Wax up is done on a study cast of patient Composite mock up done directly on teeth then impression sent to lab Wax up, then clear vacuum formed stent or putty matrix made to allow changes to be duplicated in the mouth Composite shell (lab constructed) to be temporarily placed in the mouth Computer imaging - may be idealistic but not achievable and very expensive
What is the diagnostic wax up technique?
Alginate impression for study casts
Good communication with lab asking them to construct study casts and add wax as prescribed
Explanation to patient, they can take wax up away with them to consider
Possible putty matrix construction or VFS may be carried out
What are extra-coronal preparations?
Give examples
It is when restorative material on a base or core is placed over the tooth to bring the tooth back into its functional or aesthetic normal structure
Crowns
On-lays
Veneers
What are the reasons for placing veneers?
Improve aesthetics
Change teeth shape/contour
Correct peg shaped laterals
Reduce/close proximal spaces and diastema’s
Align labial surfaces of in-standing teeth
When should you not use veneers?
Poor OH High caries rate Gingival recession Root exposure High lip lines Severely rotated/overlapping teeth Extensive tooth surface loss/Insufficient bonding area Heavy occlusal contacts Severe discolouration
What are the reasons for restoring teeth with inlays/onlays?
In tooth wear cases (increase OVD)
When there is fractured cusps
Restoration of root treated teeth
Replace failed direct restorations
Why do we treat tooth wear?
Aesthetic concerns from patient Symptoms of pain and discomfort Unstable occlusion Functional difficulties Excessively fast rate of tooth loss so prevention is key
What are the 5 factors that need to be taken into consideration when treating localised anterior maxillary tooth wear?
The pattern of tooth loss
Inter-occlusal space
Space requirements for restoration to be used
Quality and quantity of remaining hard tissue, especially the remaining enamel as this greatly affects success rate
Aesthetic demands of patient.
What are the 3 types of patterns observed in maxillary tooth wear?
Tooth wear limited to palal surfaces
Tooth wear involving palatal and incisor edges resulting in reduction of crown height
Tooth wear limited to labial surface
Why is there a lack of inter-occlusal space associated with tooth wear?
When teeth wear, there is no increase in freeway space but there is compensation for loss of tooth substance by dental-alveolar bone growth
This growth maintains masticatory efficiency but leaves no space for restorations to be placed
What is the Dahl technique?
It is a technique used to gain inter-occlusal space in cases of localised tooth wear without tooth reduction
Initially, an appliance is placed anteriorly increasing the OVD by 2-3mm
Over time, the posterior teeth erupt into occlusion
This creates space to allow for restorations of the anterior teeth
What is the technique used for treating localised anterior maxillary tooth wear?
Modification of Dahl Technique;
Mount study models with face bow registration
Open articulation by 1-2mm to create space to allow for incisor build-ups
Diagnostic wax up, starting with the canines and then continuing waxing up the rest of the teeth when the articulator is closed
What is the procedure for using a vacuum formed matrix in tooth wear cases?
Use PTFE tape to cover teeth adjacent to tooth being built up to prevent teeth sticking together
Try the matrix in place then remove
Cut a vent hole on incisor edge to allow extra composite to vent out of the matrix
Etch and bond tooth in question for build-up
Load matrix tray with composite and seat firmly, remove excess composite that comes out of the vent
Light cure composite
Remove matrix and trim
Remove dental dam
What special investigations do you carry out prior to placing extra-coronal restorations?
Sensitivity testing - thermal and EPT
Percussion and mobility testing
Radiographs (peri-apical)
Why do we require study casts for planning crowns?
To create a diagnostic wax up of patients teeth
For articulation, surveying and designing the crowns
To allow for facebow to be mounted - particularly if OVD is being changed
Occlusal registration and analysis
What are the different types of crowns that are available?
All metal restorations;
Precious gold or platinum
Non precious nickel, titanium and chromium
Metal-ceramic restorations;
Porcelain fused to metal
What are the advantages and disadvantages of metal-ceramic restorations?
Advantages;
Good aesthetics
Good strength
Minimum palatal reduction
Disadvantages;
Appearance at cervical margin may be poor
Destruction of tooth tissue and risk of pulpal damage
Allergies to components used
Could be abrasive to opposing teeth.
Root fracture may occur
What types of full gold crowns are available?
Type I and II = better for onlays and inlays
Type III and IV = better for crowns, bridges and RPDs
What are the advantages and disadvantages of using full gold crowns?
Advantages;
Long history of success
Minimum reduction of tooth tissue
Similar hardness to enamel
Disadvantages;
Gold allergies
Aesthetics are poor
Much more expensive cost.
What are zirconium oxide core ceramics?
They are machine ceramics produced using CAD/CAM systems
It is an extremely strong and opaque core
It is cemented to the tooth
It is useful for fixed partial dentures
What are the 4 steps for indirect restorations?
Preparation
Temporisation
Impressions and registration
Cementation
What are the principles of crown preparation?
Preservation of tooth structure;
Avoid weakening tooth structure and damaging the pulp
Retention and Resistance;
Retention prevents removal of restoration along path of insertion
Resistance prevents dislodgement of restoration under occlusal forces
Ideal inclination of opposing walls is 6 degrees
Structural durability;
Restoration must contain bulk of material adequate to withstand forces of occlusion
Achieved through occlusal and axial reduction
Marginal integrity;
Prepare robust margins with close adaptation to minimise microleakage
Use of shoulder and chamfer margins
Preservation of periodontium;
Ensure margins accessible for OH
Aesthetic considerations;
Create sufficient space for aesthetic veneers where indicated
Colour of surrounding teeth
What are the stages of crown prep?
- Occlusal reduction;
Retain occlusal morphology
Reduce cusp heights
Use diamond tapered fissure bur or ruby ball shaped bur - Separation;
Use long tapered diamond bur to separate from adjacent teeth - Buccal reduction;
Prepare in 2 planes using diamond tapered shoulder bur
Ensure you avoid buccal pulp horn - Palatal or lingual reduction;
Use diamond chamfer bur - Shoulder and chamfer finish;
Finish shoulder and chamfer margins ensuring they are smooth - Check occlusal surface and clearance
What measurements are required during crown prep for metal ceramic crown?
Non-functional cusps = 2mm
Functional cusps = 2.5mm
Incisal = 2mm
Shoulder/chamfer = 1.2mm
How do you carry out gingival retraction?
Secure one end of knitted cord in gingival crevice and “walk” instrument tip around the crevice, pushing the cord further into the gingival crevice
Can use haemostasis aids if necessary
Two techniques;
Can use a single cord that appears too large
Or
Can use two cords, using fine one initially
How do you take an impression of a crown prep?
Remove retraction cord Dry and inspect preparation Check for haemostasis Syringe polyether around the prep Seat impression tray with alginate as normal
What are custom resin provisional crowns?
They are customisable provisional restorations that help to check that tooth preparation is satisfactory with sufficient reduction and no undercuts present
Made from chemically cured bis-acrylic composite resin. E.g. protemp plus
What are the advantages and disadvantages of preformed provisional crowns?
Advantages;
Useful when impressions haven’t been taken prior to tooth preparation e.g. trauma cases
Disadvantages; Unlikely to fit accurately Difficult to adjust Can only be used on posterior teeth Large bank of crowns required to accommodate variations between patients - costly
What is the method for carrying out the steps required for a provisional crown restoration?
- Sectional impression
- Prepare tooth for chosen restoration
- Syringe protemp material into sectional impression of tooth
- Relocate impression in patients mouth - ensure it is fully seated
- Remove the impression and remove the provisional completely from the tooth prep.
- Remove any flash or ledges of provisional using high speed bur
- Check marginal fit and occlusion with provisional in situ and adjust if required
- Check aesthetics
- Cement provisional restoration with temporary luting cement e.g. tempbond
- Trim away any excess and check interdental regions with dental floss
What types of preformed crowns can be used for anterior teeth?
Polycarbonate crowns;
Tooth coloured shells that are easily cemented with temporary luting cement
Clear plastic crowns;
Clear shells that are filled with bis-acrylic composite resin and seated over the tooth
Clear shell is then removed and filled area is temporarily cemented
What is try-in paste?
Used for veneers
The fitting surface of the veneer is etched and the try in paste is used to allow for the shade and fit of veneer to be checked in the patients mouth
To remove the paste, it can be washed off with water/acetone
What are the steps when carrying out a trial fit of a crown?
Pre-op evaluation of crown;
Check aesthetics and occlusion on model
Check marginal fit
Check for any defects or damage
Seating the crown;
Ensure airway protection in place
Removal provisional crown and cement (LA may be required)
Seat the crown
Evaluation of seated crown;
Check occlusion and aesthetics
Check proximal contacts with floss
Check marginal fit
What are the main reasons for a crown failing to seat?
Lab faults;
Over extension of crown interproximally and/or marginally
“Blebs” in fitting surface
Restoration resin expansion
Clinical faults;
Incomplete removal of temporary restoration
Gingival tissue encroachment due to poor temporary restoration
Distortion of previous impression
What are the 5 types of conventional cements that can be used for crowns?
Zinc phosphate cement;
Good default cement for conventional crowns and posts
Zinc oxide eugenol cement;
Not recommended as a definitive cement
Polycarboxylate cement;
Traditionally used for vital or sensitive teeth
Zinc polycarboxylate cement;
Not as acidic as zinc phosphate cement
Glass ionomer cement;
Recommended for high caries rate and alternative default cement
Apart from conventional cements, what are the other 2 types of cements that can be used?
Hybrid cements;
RMGI cements e.g. Vitremer
Not recommended for ceramic crowns
Resin cements;
E.g. Panavia
Material of choice for porcelain veneers and ceramic crowns
What are the statistics on the longevity of a single crown?
95% of crowns will remain in the mouth for at least 5 years
Long term survival ranges from 50-80%
What are the most common causes of crown failure?
Caries Periodontal problems Fracture of abutment teeth Endodontic problems Fracture of porcelain Loss of retention due to heavy occlusal forces
What is a bridge?
A prosthesis which replaced a missing tooth or teeth and it attached to one or more natural teeth (or implants)
What structures does a bridge consist of?
Abutment;
A tooth which serves as an attachment for the bridge
Pontic;
The artificial tooth which is suspended from the abutment tooth/teeth
Retainer;
The extra or intra-coronal restoration that is connected to the Pontic and cemented to the prepared abutment tooth
Connector;
Component which connects the Pontic to the retainer
Saddle;
Area of edentulous ridge over which the Pontic will lie
Pier;
Abutment tooth which stands between and supports two Pontics on either side
Unit;
Either a retainer or a Pontic
What are the different types of bridges?
Cantilever; (support from one side)
Conventional fixed
Adhesive/resin retained
Conventional; (support from both sides)
Fixed-fixed
Hybrid;
Fixed retainer and adhesive retainer
Fixed-moveable
Spring cantilever bridge
What materials are used for conventional bridges?
All metal;
Gold, nicker and cobalt chromium
Metal ceramic;
Most commonly used
All ceramic;
Good aesthetics
Ceromeric
What are the different types of pontics that can be used in a bridge design?
Wash-through Pontic;
Makes no contact with soft tissue
Functional rather than for appearance
Considered in lower molar areas
Dome/torpedo Pontic;
Useful in lower incisors and premolars
Modified ridge-lap Pontic;
Buccal surface looks like tooth but lingual surface has been cut away which can create problems with food packing
Ridge-lap Pontic;
Greatest contact with soft tissue
Can be cleansed if designed carefully
Ovate pontic
When is conventional and minimum prepared required for a bridge? Give examples
Conventional prep;
Fixed-fixed bridges
Fixed cantilever bridges
Minimal prep;
Resin retained bridge
Adhesive bridge
How do you evaluate if an abutment tooth is suitable?
Must be able to withstand occlusal forces that the previous missing tooth was able to withstand
Supporting tissues should be healthy and free of inflammation
Crown to root ratio of minimum 1:1
Low root configuration
No interference from angulation/rotation of abutment tooth
Ante’s Law = root surface area of abutment tooth should be equal to or greater than that of the tooth being replaced with a pontic
What are the advantages and disadvantages of a fixed-fixed bridge?
Advantages; Maximum retention and strength Abutment teeth are splinted together for support Can be used in long span designs Lab construction is straight forwards
Disadvantages;
Preparation if difficult
Removal of tooth tissue puts pulp in danger
Path of insertion may not be parallel
What is a conventional cantilever bridge?
What are the advantages and disadvantages?
This type of bridge provides support for the pontic at one end only
Advantages;
Conservative design
lab construction if straight forward
No need to ensure preparations are parallel
Disadvantages;
Can only be used for short span bridgework
Very rigid
Mesial cantilever is usually preferred to prevent occlusal forces on pontic causing it to tilt (which would be the case if cantilever was distal to the Pontic)
What is a fixed-moveable bridge?
This type of bridge has a rigid connector usually at the distal end of the pontic and a moveable connector mesially which allows some vertical movement at the mesial abutment tooth
What is a hybrid bridge?
It is when there is one retainer which has a conventional preparation and another retainer that has a minimal preparation and is adhesive retained
What is spring cantilever bridge?
This type of bridge carries one pontic which is attached to the end of a metal arm that runs across the palate to a rigid connector on the palatal side of a retainer
What does holistic treatment planning involve?
Look at the whole mouth and not just specific teeth
Have a back up plan
Always think about what the dentition will be like in 10 years time.
