thumb|250px|right|A three unit porcelain fused to metal bridge (PFM) made by a dental technician

thumb|250px|right|A semi-precision attachment between teeth #3 and #4, with the mortise on #4. Note the [[Commonly used terms of relationship and comparison in dentistry|lingual buttons extending, in the photo, upward on #2 (on the left) and downward on #4. These are used to grasp the crowns with a hemostat and make them easier to handle. They can also be used to aid in removal of the crown in case there is an excessive amount of retention during the try-in. They are cut off prior to final cementation.]]

thumb|250px|right|The proximal surfaces of the pre-solder index abutment and pontic, showing lab-processed grooves for added retention of the [[acrylic resin]]

thumb|250px|right|The abutment and pontic joined with acrylic resin in a solder index and reinforced with an old bur (lying horizontally across the occlusal surface of the copings)

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

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.

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.

Advantages and disadvantages of tooth replacement

{| class="wikitable"

|+

!Advantages

!Disadvantages

|-

|Restore aesthetics (particularly important for anterior edentulous areas)

|Loss of tooth tissue (tooth preparation of abutments often requires significant tooth preparation)

|-

|Restore function (mastication, speech)

|Pulpal damage (tooth preparation opens dentinal tubules providing a connection between bacteria in the mouth and the pulp. Deep preparations can cause pulpal injury)

|-

|Occlusal stability (prevent tilting, drifting, rotation and over-eruption of adjacent/opposing teeth)

| rowspan="2" |Secondary caries (around crown margins, under debonded retainer wings)

|-

|Patient preference

|}

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. This type of design has a rigid connector at each end which connects the abutment to the pontic. As the abutments are connected together rigidly, it is critical that during tooth preparation the proximal surfaces of the abutment teeth must be prepared so that they are parallel to each other. 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.

  1. Splinting of periodontally compromised teeth to improve occlusal stability, comfort and decrease mobility. (Periodontally compromised teeth is also a contraindication).
  2. Patients with parafunction e.g. bruxism. (also known as hygienic pontic or sanitary pontic)

A pontic aims to restore aesthetics, give occlusal stability and improve function. It is commonly used in provisional bridges following extraction of teeth to improve the emergence profile and helps in shaping the gingiva around the future fixed prosthesis.

Types of bridges according to durability

Bridges can either be provisional (temporary/interim) or permanent. The provisional bridge is a transitional restoration that protects the teeth that are weakened by the preparation, and stabilises the dental tissues until the fabrication of the final restoration, moreover, it can pave the way to the aesthetics of the future permanent restoration and its appearance, which can help the patient accept the final profile. Provisional restorations are designed to be used for a few weeks to months, they can be fabricated directly (by chair side), or indirectly ( in the dental laboratory). It is usually tried in a few times to check if it fits properly and if its margins are well adapting on the teeth surface and gingiva, it may need relining or a few adjustments. Dimethacrylate-based materials were found to be better than monomethacrylates for temporary restorations in terms of flexural strength and hardness.

Types of bridges according to material

  1. Metal based, noble based metals such as gold, or base metal alloys such as nickel chromium.
  2. Non-metal based. They can be either resin veneered, fibre-reinforced composite, porcelain fused to metal, or ceramics which are either silica, alumina, or zirconia. However, PFM restorations may show a grey colour at the cervical margins of the tooth showing the metal substructure.

IPs Emax

IPs Emax ceramics offer high aesthetic properties, which is why its use has been increasingly popular. However, there is insufficient evidence to determine the longevity of Emax in bridges; some reports have found fair short-term survival, but unfavorable medium-term survival. Failures of restorations were most reported in the posterior teeth region. IPs Emax is available as press ingots or as IPs Emax CAD/CAM system. Emax use in crowns or bridges is not recommended for patients who suffer from bruxism.

Zirconia

Zirconia is used in anterior, and posterior fixed bridges, and also on implants. Zirconia is fabricated using the dental CAD/CAM technology. It has high mechanical strength and it can withstand high occlusal forces compared to all-ceramic materials. in addition it can resist crack propagation in the core material; however, cracks often occur in the veneering material leading to its fracture whether in the tooth-supported or implant-supported bridges. Reports found that the 3×3 mm designed connectors in zirconia bridges increased the strength to resist fracture by 20%.

Although the use of ceramic based fixed prosthesis have been popular as it achieves a lifelike, highly esthetic appearance, a Cochrane Review found insufficient evidence to support or refute the effectiveness of ceramic materials for fixed prosthodontic treatment over metal-ceramic.

Clinical stages of bridgework

  1. Assessment: Clinical assessment of the patient's suitability for bridgework. Detailed history (including medical history), appropriate assessment of the suitability of the patient's oral environment (including occlusion, caries risk, periodontal risk, radiographic examination, sensibility testing), assessment of patient aims and motivation, abutment tooth selection and bridge design. 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. 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 it is because the spatial relationship between the 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 each fit individually, 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 PATTERN RESIN from the company GC America. 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. A study examined the gingival health around the fixed bridges after 14 days – 6 months post insertion found the surfaces were more plaque retentive, causing gingival inflammation regardless the material of fabrication of the bridge, unlike single crowns which did not show the same effect.
  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. Fracture in connectors of bridges at the gingival side is a common finding in most all-ceram bridges.

  1. 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.
  2. 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.

  1. Problems with abutment teeth: Abutment teeth affected by secondary caries, vitality loss or periodontal disease can all lead to bridge failure.