Each part of the bridge should be designed individually, but within the context of the overall design. The components of a bridge are retainers, pontics and connectors.
Major or minor
Fixed-fixed , cantilever and spring cantilever bridges have only major retainer(s).
Fixed-movable bridges have a major retainer at one end of the pontic and a minor retainer (carrying the movable joint) at the other.
A major retainer for a conventional posterior bridge should not be less than an MOD inlay with full occlusal protection.
For incisor teeth it is usually a complete crown, although partial crowns are still sometimes used.
Minor retainers do not need full occlusal protection: a minor retainer may be a partial crown or a two – or three-surface inlay without full occlusal protection.
Minimal-preparation minor retainer(s) are also used for minimal-preparation where the occlusion is favourable.
The Choice Between Complete Crown, Partial Crown,
Intra-coronal or Minimal-preparation Retainers
Criteria for choosing a suitable retainer includes:
- Alignment of abutment teeth and retention
- Condition of abutment teeth
- Conservation of tooth tissue
The principles guiding the design of the pontic are :
All surfaces of the pontic especially the ridge surface, should be made as cleansable as possible. This means that they must be smooth and highly polished or glazed. and should not contain any junctions between different materials.
In a metal-ceramic pontic the junction between the two materials should be well away from the ridge surface of the pontic.
It is important too that the embrasure spaces and connectors should be smooth and cleansable. They should also be as easy to clean as possible. Access to them and the patient’s dexterity should be taken into account in designing pontics.
Where the full length of the pontic is visible. It must look as tooth-like as possible.
All pontics should be designed to withstand occlusal forces.
The longer the span, the greater the occlusal-gingival thickness of the pontic should be .
Metal-ceramic pontics are stiffer and withstand occlusal forces better if they are made fairly thick and if the porcelain is carried right round them from the occlusal to the ridge surface leaving only a line of metal visible on the lingual surface or none at all.
Classification of pontic design
Pontic designs are classified into two general groups:
Mucosal contact & Non-mucosal contact based on the shape of the gingival side of the pontic.
A) Mucosal contact:
- Ridge lap
- Modified ridge lap
B) No mucosal contact:
- Sanitary (hygenic)
- Modified sanitary (hygenic)
Patient must be instructed in how to clean the gingival surface of the pontic with floss
Sanitary or Hygenic Pontic
The design of the sanitary pontic allows easy cleaning, because its tissue surface remains clear of the residual ridge.
This hygienic design permits easier plaque control by allowing cleaning devices to be passed under the pontic.
Its disadvantages include entrapment of food particles, which may lead to tongue habits that may annoy the patient.
The hygienic pontic is the least “toothlike” design and is therefore reserved for teeth seldom displayed during function (i.e., the mandibular molars).
A modified version of the sanitary pontic has been developed . Its gingival portion is shaped like an archway between the retainers. This geometry permits increased connector size.
Saddle or Ridge Lap Pontic
The saddle pontic has a concave fitting surface that overlaps the residual ridge buccolingually.
Saddle or ridge lap designs should be avoided because the concave gingival surface of the pontic is not accessible to cleaning with dental floss, which will lead to plaque accumulation.
Modified Ridge-lap Pontic
The modified ridge lap pontic combines the best features of the hygienic and saddle pontic designs, combining esthetics with easy cleaning.
The modified ridge lap design overlaps the residual ridge on the facial (to achieve the appearance of a tooth emerging from the gingiva) but remains clear of the ridge on the lingual.
It should be as convex as possible from mesial to distal (the greater the convexity, the easier the oral hygiene).
Tissue contact should resemble a letter T whose vertical arm ends at the crest of the ridge.
The modified ridge lap design is the most common pontic form used in areas of the mouth that are visible during function.
Often called egg-shaped, bullet-shaped, or heart-shaped.
The conical pontic is easy for the patient to keep clean. It should be made as convex as possible, with only one point of contact at the center of the residual ridge.
This design is recommended for the replacement of mandibular posterior teeth where esthetics is a lesser concern.
The ovate pontic is the most esthetically appealing pontic design. Its convex tissue surface resides in a soft tissue depression or hollow in the residual ridge.
Socket-preservation techniques should be performed at the time of extraction to create the tissue recess from which the ovate pontic form will emerge. When an adequate
volume of ridge tissue is established, a socket depression is sculpted into the ridge with surgical diamonds or electrosurgery.
Advantages include its pleasing appearance and its strength. its emergence from the ridge appears identical to that of a natural tooth. In addition, its recessed form is not susceptible to food impaction.
Disadvantages: Meticulous oral hygiene is necessary to prevent tissue inflammation resulting from the large area of tissue contact. Other disadvantages include the need for surgical tissue management and the associated cost.
The occlusal surface
The occlusal surface of the pontic should resemble the occlusal surface of the tooth it replaces. Otherwise it will not serve the same occlusal functions.
The approximal surfaces
It is important that the embrasure space between the connector and the gingival tissue be as open as possible to ensure that there is good access for cleaning. particularly if the pontic is a ridge-lap or saddle pontic.
The buccal and lingual surfaces
The buccal and lingual surfaces of a pontic will be designed as a result of deciding the ridge surface.
There are three types of fixed connector:
A) Cast connectors
They are made by wax patterns of the retainers and pontics connected by wax being produced so that the bridge is cast in a single piece.
This has the advantage that a second soldering operation is not required. Cast connectors are stronger than soldered connectors.
B) Soldered connectors
They are used if the pontics and retainers have to be made separately .
This is necessary when they are made of different materials. for example a complete gold crown retainer with a metal-ceramic pontic.
C) Porcelain connectors
They are used only in conjunction with all-porcelain bridges.
Movable connectors are always designed so that the pontic cannot be depressed by occlusal forces.
This means that the groove or depression in the minor retainer (the female part of the attachment) always have a good base against which the male part of the attachment can seat.
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