Bridge (dentistry)

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A bridge is a fixed dental restoration (a fixed dental prosthesis) used to replace a missing tooth (or several teeth) by joining an artificial tooth permanently to adjacent teeth or dental implants.

Types of bridges may vary, depending upon how they are fabricated and the way they anchor to the adjacent teeth. Conventionally, bridges are made using the indirect method of restoration. However, bridges can be fabricated directly in the mouth using such materials as composite resin.

A bridge is fabricated by reducing the teeth on either side of the missing tooth or teeth by a preparation pattern determined by the location of the teeth and by the material from which the bridge is fabricated. In other words, the abutment teeth--including portions which are otherwise perfectly healthy--are "reduced" in size using a high-speed rotary tool to accommodate the material to be used to restore the size and shape of the original teeth in a correct alignment and contact with the opposing teeth. The dimensions of the bridge are defined by Ante's Law: "The root surface area of the abutment teeth has to equal or surpass that of the teeth being replaced with pontics".

The materials used for the bridges include gold, porcelain fused to metal, or in the correct situation porcelain alone. The amount and type of reduction done to the abutment teeth varies slightly with the different materials used. The recipient of such a bridge must be careful to clean well under this prosthesis.

When restoring an edentulous space with a fixed partial denture that will crown the teeth adjacent to the space and bridge the gap with a pontic, or "dummy tooth", the restoration is referred to as a bridge. Besides all of the preceding information that concerns single-unit crowns, bridges possess a few additional considerations when it comes to case selection and treatment planning, tooth preparation and restoration fabrication.

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

1. Replacement of a single tooth or a small spanning space.
2. Good oral health status and motivation of patient to maintain oral health.
3. Periodontal status of remaining dentition at a stable and satisfactory level.
4. Abutment teeth of good quality with minimal restorations and enough surface area and enamel present for adhesion.
5. Splinting of periodontally compromised teeth to improve occlusal stability, comfort and decrease mobility. (Periodontally compromised teeth is also a contraindication).
6. As a way of fixed retention after orthodontic treatment or extraction.
7. 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

1. Size of saddle area too long.
2. Patients with parafunction e.g. bruxism.
3. Tooth mobility increases risk of de-bonding.
4. Malaligned teeth resulting in poor aesthetics and common path of insertion.
5. Abutment tooth quality inadequate for example may have a reduced surface area, reduced enamel or be heavily restored.
6. Increased risk of caries due to increased difficulty in maintaining oral hygiene around the bridgework.
7. Increased risk of loss of vitality.
8. Allergy to base metal alloys e.g. nickel 

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Types of bridge

Conventional bridge

Conventional bridges are bridges that are done with extensive tooth reduction, obtain primary retention through retentively shaped preparation and secondary retention by luting cement. Unlike conventional bridges, Resin Retained Bridges require little to none tooth reduction which is much preferred due to the irreversible damage caused by drilling of teeth. The 3 designs of conventional bridges are fixed-fixed, cantilever (spring cantilever as a subclass), and fixed-movable. They are named depending on the way the pontic (false teeth) is attached to the retainer (indirect restoration on the abutment teeth/tooth).

Fixed-fixed bridges

A fixed-fixed bridge refers to a pontic which is attached to the retainer at both sides with only one path of insertion. To achieve a single path of insertion, both abutment teeth must be prepared parallel to each other in the long axis and undercuts must be avoided.

Cantilever

A cantilever is a bridge where a pontic is only attached to a retainer only at one side. This type of bridge is rather similar to the resin bonded bridge as both have retainers on one side. This allows for conservation of tooth tissue as the other abutment tooth is spared.

Spring cantilever

Spring cantilever bridge are historical methods used when replacing an anterior tooth where the adjacent tooth are unrestored or there was anterior spacing. The anterior tooth replaced are usually attached to a molar teeth with a long spanning palatal connector.

Fixed-movable

A fixed-movable bridge are bridges with 2 attachable parts,

i) pontic which is firmly attached to a retainer at one end (major retainer)

ii) 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.

The Maryland bridge

An alternative to the tradition bridge is the Maryland bridge (also called an adhesive bridge). A Maryland bridge utilizes "wings" on the sides of the pontic which attach it to the abutment teeth, meaning that little or no damage is done to these teeth in the process. They are most often used in the front of the mouth and only if the abutment teeth are whole and sound (i.e., no crowns or major fillings). They are not considered as strong as conventional bridges, and unlike other tooth replacement options the Maryland bridge cannot be made translucent: their structure requires them to be completely opaque, making them look somewhat artificial in the mouth.

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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

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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.

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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.

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Benefits 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.

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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

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See also

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References

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External links

• Biomimetic crown

Source of the article : Wikipedia