A bridge is a fixed dental restoration (a fixed dental prosthesis) used to replace one or more missing tooth by joining an artificial tooth definitively to adjacent teeth or dental implants.
A bridge will span the area where teeth are missing. They are attached to the natural teeth or implants that surround this space. The natural teeth or implants which support the bridge are called abutments. Depending on the type of bridge, natural abutment teeth may be reduced in size to accommodate the bridge to fit over them. An impression will be taken of the abutment tooth or implant and space to provide a mould to create the bridge. Using this, the bridge is then fabricated in a dental laboratory.
Video Bridge (dentistry)
Definitions
Fixed Bridge: A dental prosthesis that is definitively attached to natural teeth and replaces missing teeth
Abutment: The tooth that supports and retains a dental prosthesis.
Pontic: The artificial tooth that replaces a missing natural tooth.
Retainer: The component attached to the abutment for retention of the prosthesis.
Unit: Pontics and abutment teeth are referred to as units. The total number of units in a bridge is equal to the number of pontics plus the number of abutment teeth.
Maps Bridge (dentistry)
Case selection and treatment planning
Case selection
Appropriate case selection is important when considering the provision of fixed bridgework. Patient expectations should be discussed and a thorough patient history should be obtained. Replacement of missing teeth with fixed bridgework may not always be indicated and both patient factors alongside restorative factors should be considered before deciding if providing fixed bridgework is appropriate. The survival rate of bridgework can be affected by the span of bridge needed, the proposed position of the bridge, and the size, shape, number and condition of planned abutment teeth. Furthermore, any active disease including caries or periodontal disease should be treated and followed by a period of maintenance to ensure patient compliance in maintaining appropriate oral hygiene.
Selection and evaluation of abutment teeth
Multiple factors influence the selection of appropriate abutment teeth. These include size of potential abutment tooth, with larger teeth having an increased surface area preferable for retention, using teeth with a stable periodontal status, favourable tooth angulation, favourable tooth position and an adequate crown-root ratio.
Previously Ante's law, which states that the roots of abutment teeth must have a combined periodontal surface area in three dimensions that is more than that of the missing root structures of the teeth replaced with a bridge, was used in bridgework design. However, research has shown no evidence supporting Ante's law
Indications for use of fixed prostheses in replacement of missing teeth
- Replacement of a single tooth or a small spanning space.
- Good oral health status and motivation of patient to maintain oral health.
- Periodontal status of remaining dentition at a stable and satisfactory level.
- Abutment teeth of good quality with minimal restorations and enough surface area and enamel present for adhesion.
- Splinting of periodontally compromised teeth to improve occlusal stability, comfort and decrease mobility. (Periodontally compromised teeth is also a contraindication).
- As a way of fixed retention after orthodontic treatment or extraction.
- Patient unsuitable for implants. This may be due to inadequate bone levels, expense or patient not wanting to receive implants.
Contraindications for use of fixed prostheses in replacement of missing teeth
- Size of saddle area too long.
- Patients with parafunction e.g. bruxism.
- Tooth mobility increases risk of de-bonding.
- Malaligned teeth resulting in poor aesthetics and common path of insertion.
- Abutment tooth quality inadequate for example may have a reduced surface area, reduced enamel or be heavily restored.
- Increased risk of caries due to increased difficulty in maintaining oral hygiene around the bridgework.
- Increased risk of loss of vitality.
- Allergy to base metal alloys e.g. nickel
Types of bridge
Conventional bridge
Conventional bridges are bridges that are supported by full coverage crowns, three quarter crowns, post-retained crowns, onlays and inlays on the abutment teeth. In these types of bridges, the abutment teeth require preparation and reduction to support the prosthesis. Conventional bridges are named depending on the way the pontic (false teeth) is attached to the retainer..
Fixed-fixed bridges
A fixed-fixed bridge refers to a pontic which is attached to a retainer at both sides of the space with only one path of insertion.
Cantilever
A cantilever is a bridge where a pontic is only attached to a retainer only at one side.
Spring cantilever
The pontic and retainer are remote from each other and connected by a metal bar. Usually a missing anterior tooth is replaced and supported by a posterior tooth.
Fixed-movable
The pontic is firmly attached to a retainer at one end of the span (major retainer) and attached via a movable joint at the other end (minor retainer)
A major advantage of this type of bridge is that the movable joint can accommodate the angulation differences in the abutment teeth in long axis which enables the path of insertion to be irrespective of the alignment of the abutment tooth.
Adhesive bridge
An alternative to the tradition bridge is the adhesive bridge (also called a Maryland bridge). An adhesive bridge utilizes "wings" on the sides of the pontic which attach it to the abutment teeth. Abutment teeth require minor or no preparation. They are most often used if the abutment teeth are whole and sound (i.e., no crowns or major fillings).
Types of Pontic
1. Wash-through Pontic
2. Dome Pontic
(also known as bullet or torpedo shaped)
3. Ridge Lap Pontic
(also known as Full Saddle Pontic)
4. Modified Ridge-Lap Pontic
5. Ovate Pontic
Clinical stages of bridgework
1. Tooth Preparation: This should be completed with reference to radiographs and study casts obtained during treatment planning. For conventional bridges, tooth preparation should aim to conserve tooth tissue, ensure a parallel path of insertion, achieve clearance in the occlusion and ensure well defined preparation margins. The taper of each preparation on the abutment teeth must be the same. This is known as parallelism among the abutments and allows the bridge to fit onto the abutment teeth. Adhesive bridges require minimal preparation.
2. Master impressions: An accurate impression should be made of the prepared teeth, along with an impression of the opposing arch. The master casts are used to provide accurate information about the occlusion to the laboratory and construct the prosthesis.
3. Occlusal registration: An occlusal registration is needed when providing extensive bridgework to allow the opposing casts to be related accurately. This may not be necessary if only a small number of teeth are to be restored.
4. Temporary restoration: Temporary restorations should be fabricated if possible to protect and maintain the prepared teeth until placement of the final restoration.
5. Try in: Confirm the clinical acceptability before cementing definitively. Assess the prosthesis on the master casts and identify the cause of any problems if present. A period of temporary cementation to assess clinical acceptability prior to definitive placement is sometimes used.
6. Final placement: Once satisfied the prosthesis is clinically acceptable, cement and bond the bridgework definitvley.
7. Review: Assess the bridgework and manage any post operative issues.
Restoration fabrication
As with single-unit crowns, bridges may be fabricated using the lost-wax technique if the restoration is to be either a multiple-unit FGC or PFM. Another fabrication technique is to use CAD/CAM software to machine the bridge. As mentioned above, there are special considerations when preparing for a multiple-unit restoration in that the relationship between the two or more abutments must be maintained in the restoration. That is, there must be proper parallelism for the bridge to seat properly on the margins.
Sometimes, the bridge does not seat, but the dentist is unsure whether or not it is only because the spatial relationship of the two or more abutments is incorrect, or whether the abutments do not actually fit the preparations. The only way to determine this is to section the bridge and try in each abutment by itself. If they all fit individually, it must have simply been that the spatial relationship was incorrect, and the abutment that was sectioned from the pontic must now be reattached to the pontic according to the newly confirmed spatial relationship. This is accomplished with a solder index.
The proximal surfaces of the sectioned units (that is, the adjacent surfaces of the metal at the cut) are roughened and the relationship is preserved with a material that will hold on to both sides, such as GC pattern resin. With the two bridge abutments individually seated on their prepared abutment teeth, the resin is applied to the location of the sectioning to reestablish a proper spatial relationship between the two pieces. This can then be sent to the lab where the two pieces will be soldered and returned for another try-in or final cementation.
Advantages of bridges
Dental bridges offer several advantages.
They can usually be completed in only two dental appointments, restore the tooth back to full chewing function, require no periodic removal for cleaning, have a long life-expectancy and are aesthetically pleasing.
Bridge failures
Common reasons for bridge failures
1. Poor oral hygiene: As with any fixed prosthesis including bridges, maintaining good oral hygiene to prevent plaque formation around the bridge is key. This will ensure prolonged performance.
2. Mechanical failures: These failures can occur due to loss of retention of the bridge due to improper cementation, construction or preparation. Fracture of the metal coating or pontic can also lead to mechanical failures.
3. Biological failures: These can occur due to caries in the tooth (one of the commonest causes of crown and bridge failures ) or due to pulpal injury. Problems with abutment teeth such as tooth fracture, secondary caries or periodontal disease can cause discomfort and put pressure on surrounding soft tissues to also cause a biological failure of the bridge.
4. Aesthetic failures : These can occur at the time of cementation and include; colour mismatch, roughness of margins or improper tooth contour. Aesthetics failures can also occur over a period of time including through wear of teeth, gingival recession or drifting of teeth.
5. Problems with abutment teeth: Abutment teeth affected by secondary caries, vitality loss or periodontal disease can all lead to bridge failure.
Oral manifestations of bridge failures
Bridge failures result in clinical complications and patients can present with:
i) Pain in the oral cavity
ii) Sensitivity, bleeding and inflammation of the gums
iii) Foul breath and taste disturbances
Bridge failure management
Management of bridge failures depend upon the extent and type of failure and these can be prevented through forming a thorough treatment plan with the patient as well regularly emphasising the importance of maintaining a very good level of oral hygiene after the bridge has been placed. The importance of cleaning underneath the pontic, through the use of interdental cleaning aids, should also be reinforced as plaque control around fixed restorations is more difficult.
Management options include:
i) Keeping the bridge under observation/review
ii) Repairing, replacing or removing the fault
See also
References
External links
- Biomimetic crown
- Pros and Cons of Dental Bridges
Source of article : Wikipedia
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