Fixed bridges

Question 1

What is a fixed dental prosthesis?

Answer 1

o “Any dental prosthesis that is luted, screwed or mechanically attached to natural teeth, tooth roots, and/or dental implant abutments providing the primary support for the dental prosthesis”.

Question 2

What are the different components of a bridge?

Answer 2

• Abutments
• Pontic
• Retainer

Question 3

What is an abutment?

Answer 3

• Abutments – teeth, or implants that are supporting the prosthesis. E.g. the molar and premolar tooth.
• Abutment – that part of a structure that directly receives the pressure, the abutments can either be natural teeth or abutment component in a dental implant.
• Single abutment – cantilevered fixed bridge
• Double abutment – fixed-fixed bridge.

Question 4

What is a pontic?

Answer 4

• Pontic – artificial tooth that is filling the space
• Pontic – an artificial tooth on a fixed dental prosthesis that replaces a missing natural tooth, restores its function, and usually fills the space previously occupied by clinical crown.

Question 5

What is a retainer?

Answer 5

• Retainer – component that goes over the abutment tooth which can be in the form of a crown, a ¾ crown or metal wing.
• Retainer – this is the part of the bridge which is cemented to the abutments. This could be in the form of a full crown, but also can be a ¾ crown, an inlay/onlay or metal wing of a resin retained bridge.

Question 6

What should you do before you design a bridge?

Answer 6

• Before you design a bridge and give that option to a patient, you need to evaluate the abutment tooth, how big is your pontic and which space will it be filling, and the type of your retainer.

Question 7

What are different pontic designs?

Answer 7

o Modified ridge lap – pontic is only in contact with the ridge buccally. Most common type. This is because it is aesthetic due to no gap being visible buccally, but is easier to clean as there is more space palatally.

o Ridge lap – where the pontic is directly contacting the ridge both buccally and lingually.

o Sanitary pontic – no contact with the ridge. Allows space under the pontic for cleaning, most hygienic.

o Ovate pontic – point contact with the ridge. Sinks the convex surface of porcelain into mucosa/requires soft tissue surgery to prepare the site. It is the most aesthetic design, mostly used to replace anterior teeth. Gives the emergence profile to mimic a natural tooth.

o Main purpose of having different designs of a pontic is to make it hygienic.

Question 8

What are the 2 types of conventional bridges?

Answer 8

• 1. Conventional fixed-fixed bridges – a fixed dental prosthesis in which the pontic is retained and supported by 2 abutments, one either side of the pontic.
• Conventional means there is conventional preparation to the abutment teeth.
• 2. Conventional Cantilever Bridges – the pontic is retained by a conventional crown (mostly), inlay or onlay.
• Abutment and retention is coming from one side only.

Question 9

What are the indications for conventional bridgework?

Answer 9

• Heavily restored abutments
• Well-motivated patient with excellent plaque control
• No active caries lesions
• Stable periodontium
• Able to clean and maintain the bridge work
• Small edentulous spaces – larger spaces will fail due to overload.
• Replacement bridge work.

Question 10

What are the contraindications for conventional bridgework?

Answer 10

• Unrestored abutments
• Poorly motivated
• Active caries
• Active periodontitis
• Poor manual dexterity to clean bridge
• Large edentulous spaces
• Contact sports player.

Question 11

What are ideal bridge abutments?

Answer 11

• 1s, 3s, and 6s, make ideal bridge abutment.
• Abutment teeth are taking on a big load. Takes the load of its own tooth in its position and the missing pontic tooth load.
• Need teeth with long roots or multirooted teeth or diverging roots.
• Also need sufficient tooth structure clinically in crown height to provide sufficient retention of the retainer of the bridge.
• Other teeth can be used but need to assess root length, bone support and tooth tissue that is available doe retention.

Question 12

Which teeth are not suitable for abutments?

Answer 12

• Heavily restored teeth with post crowns, endodontically treated teeth, heavily restored with posts.
• These teeth are already compromised so would be unfavourable to be overloaded with additional load from bridge.

Question 13

What resin retained bridges?

Answer 13

• Resin retained cantilever bridges – the pontic is retained by a metal retainer relaying mainly of the cement and maximum abutment coverage.
• Pontic is retained by a metal retainer which is cemented to abutment tooth. Attached to one side only.

Question 14

What are the indications for resin retained bridges?

Answer 14

• Sound, unrestored abutments
• Well-motivated patient with excellent plaque control
• No active caries lesions
• Stable periodontium
• Able to clean and maintain the bridge work
• Small edentulous spaces.

Question 15

What are the contraindications for resin retained bridges?

Answer 15

• Heavily restored abutments
• Lack of clinical crown height in the abutment teeth
• Poorly motivated patient
• Active caries
• Active periodontitis
• Poor manual dexterity to clean bridge
• Large edentulous spaces
• Contact sports player
• Bruxism and parafunctional habits.

Question 16

What design features are used in bridges?

Answer 16

• Abutment:
  o In most cases no preparation is advised to allow maximum bonding to the enamel layer.
  o Most recent research concluded that – “Resin-retained bridges made with minimal tooth preparation are shown to be superior in terms of longevity than those for which other types of tooth preparation is made. Patient satisfaction with their treatment was high”.
• Cover maximal surface area of the abutment tooth to maximise retention. Want cuspal coverage over occlusal surface where possible. Doesn’t matter if bite is high, the posterior teeth will overerupt and gain contact posteriorly. This happens 3-18 months.
• The younger the patient, the teeth would over erupt quicker, therefore patient won’t notice it over a few months. So it is acceptable to bond resin retained bridge high to maximise retention of the bridge, maximise retention to enamel, and maximising coverage.
• Use rigid, non-precious metal wing retainers (so it doesn’t flex) of at least 0.7-0.8mm thickness:
  o Pre-molars and molars use 0.8mm.
  o Anterior teeth use 0.7mm.
• Use cantilever designs for adhesive bridgework and keep the pontic out of excursive contacts. No contact laterally or in protrusive movements on the pontic. This is to reduce excursive forces which will reduce bonding to the bridge.
• Canines and molars can make ideal bridge abutments – large teeth, large surface that maximise retention.

Question 17

Why are fixed/fixed resin retained bridges not used?

Answer 17

• Want to avoid fixed/fixed resin retained bridges.
• Would use 2 metal wings extending mesially and distally from the pontic to retain the pontic.
• In theory you are bonding the pontic to 2 teeth, so should be more favourable in retention and longevity. However, issues noticed is that when these bridges fail, it is quite catastrophic.
• When fail, they fail at the winged tooth interface and normally, there is degradation of the cement and there would be a gap and caries start to develop.
• If this was only a cantilever, you would see it early on due to the bridge being loose and de-bond quickly.
• However, a fixed-fixed resin retained bridge, one abutment fails, the bridge remains in situ, attached by the other abutment, and when you see the failures, it is later down the line, and can be quite late, so caries extended significantly into the tooth structure, which may lead to unrestorable teeth.

Question 18

What are cantilever bridges?

Answer 18

• Fixed dental prosthesis in which the pontic is cantilevered i.e. is retained and supported only on one end by one or more abutments.

Question 19

What is the clinical workflow for conventional bridges?

Answer 19

• Following clinical assessment to see it’s suitable for the patient.
• 1. Primary impressions
• 2. Diagnostic wax up on study model (requested from lab to assess these). Looking for size of the pontic and checking the occlusion of the pontic. You want very light contact on ICP and no contact in lateral or protrusive movements.
• 3. Abutment preparation and master impression (silicon). Temporisation.
• 4. Bridge construction while mounted on an articulator
• 5. Bridge trail and cementation.

Question 20

What are some design considerations for conventional bridges?

Answer 20

o 1. Occlusion – keep pontic with light contact in ICP and no contact in lateral/protrusive movements

o 2. Share the bridge occlusal guidance with the natural teeth if possible.

Question 21

What is the clinical workflow for resin retained bridges?

Answer 21

• Following clinical assessment to see it’s suitable for the patient.
• 1. Primary impression
• 2. Diagnositc wax-up on study model – look at model to see it’s symmetrical, matches shapes of nearby tooth, make sure it matches emergence profile and occlusion.
• 3. Master impression (silicon). Minimal or no preparation.
• 4. Bridge construction while mounted on an articulator.
• 5. Bridge trail and cementation.

Question 22

What are the design considerations for resin retained bridges?

Answer 22

o 1. Occlusion – keep pontic with light contact in ICP and no contact in lateral/protrusive movements.

o 2. Share the bridge occlusal guidance with the natural teeth if needed.

o 3. Discuss wax-up with patient specially in anterior bridgework.

o 4. Explain to the patient that metal wing might show through the abutment.

Question 23

Why are fixed-fixed bridges not used very often?

Answer 23

• Not contemporary practice
• Destructive and long-term complications are mostly catastrophic including caries and endodontic failure of the abutment teeth.
• Nowadays mostly made as a replacement option of an old bridge if abutments are still sound.

Question 24

What are the complications for bridges?

Answer 24

• Things to think about for conventional bridges, is the survival of abutment teeth.
• Survival of pulps under crowns and bridges (MCC) are reduced with the preparation of the tooth as your removing tooth structure, so compromising tooth structure.
• 10-year survival of the pulp under a crown is 84%. 20% chance of losing vitality of tooth with that preparation.
• If that tooth is also acting as an abutment, the chances of loss of vitality is about 30%. Tooth survival is 70%.
• Most common failure for bridges is endodontic failure, followed by debonding and caries, and fracture of porcelain.
• Conventional canterliver bridge - 91% survival at 5 years, 81.8% at 10 years. Caries, endo, loss of retention.
• Resin retained cantilever bridge - 80.8% survival 5 years, 80.4% at 10 years, debonding.
• Conventional fixed-fixed - 94% survival at 5 years, 92% at 10 years. Caries risk, endo.

Question 25

What is important to consider for bridges?

Answer 25

* Well maintained teeth last a very long time. * Everything else that we do prosthodontically has consequences: biological, technical and replacement cycle with on going costs (restorative escalator). * Planning: diagnostic wax-up, select the occlusal scheme and guidance before you start. * Choose the least destructive technique possible. * Consider shortened dental arch concept. Patients are able to function with fewer posterior teeth.