Sign In Dental bridges are an important part of dentistry as they are used so commonly. Below we will discuss when they are indicated as well as contraindicated all the way to the different types of bridges that clinicians and students should be aware of.
Bridges can be broken down into 3 types:
1. Fixed fixed: Pontic retained and supported at both ends
2. Fixed moveable: Pontic is retained rigidly at one end, and loosely, by means of a stress breaker at the other end. The stress breaker prevents the retainer on the smaller abutment tooth becoming loose.
Types of stress breakers:
– Rod and tube
– Dove tail
3. Cantilever: Pontic is supported and retained at only one end.
Bridge components
Saddle: The edentulous area between abutment teeth. This influences pontic design.
Abutments: Teeth used to support and hold the retainers, usually on either side of the saddle
Retainer: Restoration to which the pontic is attached. Can be minor or major.
Pontic: The artificial replacement of the tooth. May be, porcelain, acrylic, metal or a combination.
Unit: Number of pontics add the number of retainers
Connector: The device that joins the pontic to the retainer. Can be a:
- soldiered joint
- cast structure
- long spring arm.
- stress breaker
- dove tail
- precision retainer
Saddle: The ability of the abutment tooth to bear the occlusal load on the restoration
a) Ridge lap
b) Modified ridge lap -most common
c) Ovate
d) Sanitary
Ovate – Modified ridge lap – Ridge lap
The design of a pontic should be based on:
- Cleanablity
- Strength
- Appearance
The pontics purpose is :
- Improve appearance
- To stabilise occlusion
- To improve masticatory function
| INDICATIONS | CONTRAINDICATIONS |
|---|---|
| Comfort – Replacement of missing tooth/teeth – No palatal or lingual connectors required – No movement will occur during mastication (unlike partial dentures) | Condition of dentition – Periodontal disease (and poor bone support) – Poor oral hygiene – Other gaps in arch (consider denture) |
| Aesthetics | Occlusion – Deep overbite – Parafunction – Existing over-eruption of opposing teeth |
| Function – Masticatory efficiency – Prevents tilting, drifting or over-eruption into the gap where the tooth is missing |
Assessing for retention
The crown should be of adequate height and have sufficient tooth surface area
Assessing for support
- Crown to root ratio: ideally should be 2:3, but 1:1 is acceptable
- Roots configuration: widely splayed roots provide more support than fused ones
- PDL surface area: ANTES LAW
- PDL surface area of the abutment teeth must be equal or greater than the surface area of the PDL of the teeth being replaced
Assessing taper and parallelism
- The taper should be 5 degrees
- The preparations should be parallel especially in the case of fixed fixed dental bridges.
- Manage tilted abutment teeth (see next section)
Poor periodontal condition
In such a situation fixed fixed bridge is indicated as it can behave as a splint for mobile teeth.
Priority, however should go to improving the periodontal condition before placement of a bridge, otherwise the dental bridge would not last if the abutment is not stable.
Tilted abutment
Dental bridges are cast restorations, so they must have a path of insertion without any undercuts, otherwise the bridge will not seat.
There must be no undercuts, within each individual tooth as well as between abutments in the case of a fixed-fixed bridge.
This is when the abutment tooth is tilted either mesially or distally, which leads to the abutment teeth no longer being parallel preventing the bridge from seating.
As shown in the diagram below the fixed fixed bridge would not seat as the path of insertion is not parallel for the two abutment teeth.
Tilted abutment tooth
There are 3 ways to overcome tilted abutment teeth:
1. Orthodontics treatment
An orthodontic appliance can be used to realign the abutment tooth so it is no longer tilted.
2. Telescopic crowns
This is where a the tilted abutment tooth is built with a core material in order to maker its crown appear parallel to the other abutment, allowing the dental bridge to seat.
Telescopic crown
As shown in the diagram above, a telescopic crown is used in order to overcome the mesially tilted abutment. Here, the molar would be prepared with a telescopic coping as indicated by the red line. This would make the crown parallel with the premolar abutment allowing the bridge to seat.
3. Precision attachment
This is a movable joint in a fixed movable bridge work.
The pontic is retained rigidly at one end, and loosely at the other end, by means of a stress breaker. The stress breaker prevents the retainer on the smaller abutment tooth becoming loose.
Types of stress breakers:
- Rod and tube
- Dove tail
Pier abutment
A pier abutment is an abutment tooth connected to a pontic on either side.
The challenges of a pier abutment is that it can act as a fulcrum in the middle resulting in failure at one of the terminal abutments, usually presenting as debonding of one of the retainers in the case of a fixed fixed bridge.
As shown in the diagram above when force is applied on the molar as indicated by the red arrow, the pier abutment will act as fulcrum, creating a force at the premolar end of the bridge increasing the chance of debonding. Similarly, when occlusal force is applied on the premolar it increases the chance of debonding at the molar end of the bridge as indicated by the green arrows.
Conventional Bridge
A conventional dental bridge is essentially where the abutment tooth is prepared for a crown (crown of your choice – see crowns).
The same clinical steps are taken as when you would be preparing the tooth for a crown.
The only difference is the lab is requested to make a bridge using the prepared tooth as an abutment. The lab will then send back a bridge that can be cemented on the abutment tooth/teeth.
Resin Bonded Bridge
Resin bonded bridges are also known as maryland bridges.
This is a technique for tooth replacement which requires minimal tooth removal.
The pontic is attached to the abutment tooth using a metal ‘wing’ rather than a traditional extra-coronal restoration e.g. crown.
For anterior RRB’s where that has been little or no prep the retention is solely from the bond between the enamel – active cement and active cement – metal wing.
The wing is made from non-precious metals mainly nickel-chromium or cobalt-chromium.
The fit surface of the wing is particle blasted with aluminium oxide and bonded to etched enamel using a chemically active resin cement.
RRB’s have a 80% survival after ten years.
However, mode of failure (75%+) is usually de-bonding of the retainer.
The problem with a fixed-fixed designs is that one retainer wings often will de-bond from the abutment, but the restoration will stay in place due to the other wing still being bonded. Over time, recurrent caries will occur under the de-bonded wing.
| INDICATIONS | CONTRAINDICATIONS |
|---|---|
| Minimal tooth preparation required – conserves tooth tissue | Can only be provided if enamel is present |
| No real potential for pulpal trauma | Risk of debonding and difficulty of recementation |
| Temporary not required | Technique sensitive cementation |
| Easy impression taking | Can be difficult to remove if required |
| Supragingival margin – easy to prepare as well as take impression of | Metal wing can ‘shine through’, compromising the aesthetics of the abutment tooth |
| Reduced chairside time | Good alignment of abutment teeth is required |
| Reduced lab time | Connector height can compromise aesthetics |
| Reduced chair time | Reduced restoration longevity compared to conventional prep |
See also Crowns
- Replacement of missing anterior teeth (especially in young patients)
- Short spans
- Unrestored abutment
- Significant clinical crown length of abutment
- Adequate enamel!
- Excellent moisture control can be achieved
- Lack of/or poor-quality enamel
- Long spans
- Restored or damaged abutments
- Difficult to achieve moisture control
- Short crown length of abutment
- Active periodontal disease and/or bone support
- Parafunctional habits
- Nickel allergy
- Significant pontic width discrepancy
- Deep vertical overlap
- Compromised enamel
1. Tooth preparation
- Increased tooth preperation is associated with bridge failure
- Any preperation other than into enamel is associated with a two-fold failure rate
2. Occlusion
Anterior:
- Static and dynamic occlusion should be maintained on the abutment wing.
- Risk of failure increases when intercuspal contact lies at or close to the junction of the retainer and tooth.
- Ideally occlusal scheme should provide intercuspal contacts on the retainer and light contact on the pontic, but in excursive movements the pontic should be free of antagonist teeth. Occlusion on the retainer wing is fine as long as it is not on the wing-tooth junction.
Posterior:
- Light intercuspal contact on pontic and none in excursion/protrusion. Again occlusion should not be on the wing-tooth junction.
3. Design
Single abutment, cantilevers are the most successful design – significantly more than fixed fixed designs.
Fixed-fixed may be more appropriate in the following circumstances:
- Periodontal splinting
- Large pontic spans
- Retention in post orthodontic fixed appliance treatment
4. Pre-existing restoration
- Presence of existing restoration results in decreased longevity
- Recommendation is to replace existing amalgam restorations with complete resin.
5. Cementation
- Those cemented under rubber dam are twice as likely to fail
- Panavia is the gold standard
6. Location
- Anterior have a higher survival rate than posteriors
- Maxillary have a higher survival rate than mandibular (easier to achieve moisture control in the maxilla)
- Distal facing cantilevers (abutment is anterior to pontic) carry higher risk of failure than mesial facing cantilevers
The aim of tooth preparation is to provide:
- As a great surface area of enamel as possible for bonding
- A single path of insertion
- Provide resistance form to the prep
- Allow accurate seating of the restoration
- Direct stress away from the adhesive
- No contact on the pontic in lateral excursions
- Light contact on the pontic in ICP (intercuspal position)
Design features:
- Must be in enamel
- 0.5mm cingulum reduction for the space for the wing
- Aim for 0.5 mm–1.00 mm occlusal clearance (not always necessary as the bite will adjust and the lowers will infra-occlude)
- Achieve 180 degree wrap around (preperation should involve 180 degrees of the tooth)
- Palatal supragingival chamfer
- Consider mesial and distal guide-planes to create a single path of insertion
- M and D grooves to provide resistance
- Short of the incisal edge to prevent shine through of the metal
- Should be cantilever design, as fixed fixed can lead to one wing becoming debonded leading to recurrent caries
Note: Tooth preparation is not always required
The opposing teeth should be in contact with only metal in all positions and movements. Avoid opposing tooth in contact on the metal tooth interface (i.e. the junction between the metal and the natural because if occlusion occurs here it is like to cause the dental bridge to fail). The opposing teeth should not contact the pontic in any excursive movements and should only be in light contact in ICP.
- Only in enamel
- 1-1.5 mm reduction of occlusal palatal/lingual cusp – to allow space for the metal wing without affecting the bite
- Mesial and distal rest seats and/or coverage of the entire palatal/lingual cusp (rest adjacent to pontic is more important)
- Gingival finishing line only needed if lab will be unable to locate the gingival margin
- Palatal/lingual reduction is only needed if you need to create a path of insertion due to a large bulbosity (path of insertion must be vertical due to the rest sets)
Posterior cantilever RBB with mesial and distal rest seats
Note: Tooth preparation is always required
