Fixed Prosthodontics BDS4

Question 1

Why do we replace teeth?

Answer 1

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

Question 2

What is a diagnostic wax up?

What are the advantages of a diagnostic wax up?

Answer 2

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

Question 3

What are the various types of wax ups that can be sued in fixed pros?

Answer 3

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

Question 4

What is the diagnostic wax up technique?

Answer 4

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

Question 5

What are extra-coronal preparations?

Give examples

Answer 5

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

Question 6

What are the reasons for placing veneers?

Answer 6

Improve aesthetics
Change teeth shape/contour
Correct peg shaped laterals
Reduce/close proximal spaces and diastema’s
Align labial surfaces of in-standing teeth

Question 7

When should you not use veneers?

Answer 7

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

Question 8

What are the reasons for restoring teeth with inlays/onlays?

Answer 8

In tooth wear cases (increase OVD)
When there is fractured cusps
Restoration of root treated teeth
Replace failed direct restorations

Question 9

Why do we treat tooth wear?

Answer 9

Aesthetic concerns from patient 
Symptoms of pain and discomfort 
Unstable occlusion 
Functional difficulties 
Excessively fast rate of tooth loss so prevention is key

Question 10

What are the 5 factors that need to be taken into consideration when treating localised anterior maxillary tooth wear?

Answer 10

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.

Question 11

What are the 3 types of patterns observed in maxillary tooth wear?

Answer 11

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

Question 12

Why is there a lack of inter-occlusal space associated with tooth wear?

Answer 12

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

Question 13

What is the Dahl technique?

Answer 13

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

Question 14

What is the technique used for treating localised anterior maxillary tooth wear?

Answer 14

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

Question 15

What is the procedure for using a vacuum formed matrix in tooth wear cases?

Answer 15

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

Question 16

What special investigations do you carry out prior to placing extra-coronal restorations?

Answer 16

Sensitivity testing - thermal and EPT
Percussion and mobility testing
Radiographs (peri-apical)

Question 17

Why do we require study casts for planning crowns?

Answer 17

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

Question 18

What are the different types of crowns that are available?

Answer 18

All metal restorations;
Precious gold or platinum
Non precious nickel, titanium and chromium

Metal-ceramic restorations;
Porcelain fused to metal

Question 19

What are the advantages and disadvantages of metal-ceramic restorations?

Answer 19

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

Question 20

What types of full gold crowns are available?

Answer 20

Type I and II = better for onlays and inlays

Type III and IV = better for crowns, bridges and RPDs

Question 21

What are the advantages and disadvantages of using full gold crowns?

Answer 21

Advantages;
Long history of success
Minimum reduction of tooth tissue
Similar hardness to enamel

Disadvantages;
Gold allergies
Aesthetics are poor
Much more expensive cost.

Question 22

What are zirconium oxide core ceramics?

Answer 22

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

Question 23

What are the 4 steps for indirect restorations?

Answer 23

Preparation
Temporisation
Impressions and registration
Cementation

Question 24

What are the principles of crown preparation?

Answer 24

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

Question 25

What are the stages of crown prep?

Answer 25

1. Occlusal reduction; Retain occlusal morphology Reduce cusp heights Use diamond tapered fissure bur or ruby ball shaped bur 2. Separation; Use long tapered diamond bur to separate from adjacent teeth 3. Buccal reduction; Prepare in 2 planes using diamond tapered shoulder bur Ensure you avoid buccal pulp horn 4. Palatal or lingual reduction; Use diamond chamfer bur 5. Shoulder and chamfer finish; Finish shoulder and chamfer margins ensuring they are smooth 6. Check occlusal surface and clearance

Question 26

What measurements are required during crown prep for metal ceramic crown?

Answer 26

Non-functional cusps = 2mm Functional cusps = 2.5mm Incisal = 2mm Shoulder/chamfer = 1.2mm

Question 27

How do you carry out gingival retraction?

Answer 27

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

Question 28

How do you take an impression of a crown prep?

Answer 28

``` Remove retraction cord Dry and inspect preparation Check for haemostasis Syringe polyether around the prep Seat impression tray with alginate as normal ```

Question 29

What are custom resin provisional crowns?

Answer 29

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

Question 30

What are the advantages and disadvantages of preformed provisional crowns?

Answer 30

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 ```

Question 31

What is the method for carrying out the steps required for a provisional crown restoration?

Answer 31

1. Sectional impression 2. Prepare tooth for chosen restoration 3. Syringe protemp material into sectional impression of tooth 4. Relocate impression in patients mouth - ensure it is fully seated 5. Remove the impression and remove the provisional completely from the tooth prep. 6. Remove any flash or ledges of provisional using high speed bur 7. Check marginal fit and occlusion with provisional in situ and adjust if required 8. Check aesthetics 9. Cement provisional restoration with temporary luting cement e.g. tempbond 10. Trim away any excess and check interdental regions with dental floss

Question 32

What types of preformed crowns can be used for anterior teeth?

Answer 32

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

Question 33

What is try-in paste?

Answer 33

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

Question 34

What are the steps when carrying out a trial fit of a crown?

Answer 34

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

Question 35

What are the main reasons for a crown failing to seat?

Answer 35

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

Question 36

What are the 5 types of conventional cements that can be used for crowns?

Answer 36

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

Question 37

Apart from conventional cements, what are the other 2 types of cements that can be used?

Answer 37

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

Question 38

What are the statistics on the longevity of a single crown?

Answer 38

95% of crowns will remain in the mouth for at least 5 years | Long term survival ranges from 50-80%

Question 39

What are the most common causes of crown failure?

Answer 39

``` Caries Periodontal problems Fracture of abutment teeth Endodontic problems Fracture of porcelain Loss of retention due to heavy occlusal forces ```

Question 40

What is a bridge?

Answer 40

A prosthesis which replaced a missing tooth or teeth and it attached to one or more natural teeth (or implants)

Question 41

What structures does a bridge consist of?

Answer 41

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

Question 42

What are the different types of bridges?

Answer 42

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

Question 43

What materials are used for conventional bridges?

Answer 43

All metal; Gold, nicker and cobalt chromium Metal ceramic; Most commonly used All ceramic; Good aesthetics Ceromeric

Question 44

What are the different types of pontics that can be used in a bridge design?

Answer 44

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

Question 45

When is conventional and minimum prepared required for a bridge? Give examples

Answer 45

Conventional prep; Fixed-fixed bridges Fixed cantilever bridges Minimal prep; Resin retained bridge Adhesive bridge

Question 46

How do you evaluate if an abutment tooth is suitable?

Answer 46

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

Question 47

What are the advantages and disadvantages of a fixed-fixed bridge?

Answer 47

``` 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

Question 48

What is a conventional cantilever bridge? What are the advantages and disadvantages?

Answer 48

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)

Question 49

What is a fixed-moveable bridge?

Answer 49

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

Question 50

What is a hybrid bridge?

Answer 50

It is when there is one retainer which has a conventional preparation and another retainer that has a minimal preparation and is adhesive retained

Question 51

What is spring cantilever bridge?

Answer 51

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

Question 52

What does holistic treatment planning involve?

Answer 52

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.