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o clean both under it and under the connector. This requires considerable dexterity by the patient. A number of spring cantilever bridges have failed because of periodontal disease on the palatal side of the abutment teeth.
The pontic may also traumatize the gingival papillae on either side of it because the springiness of the bar allows the pontic to move up and down slightly in use. The design of the bridge requires retention of the abutment preparations to be very good.
Inexperienced operators should not fall into the trap of using spring cantilever designs because they lack the confidence to prepare sound anterior teeth and prefer to practise bridgework using posterior abutments only. The design chosen should be the best one in the patient' s interest, and if the operator is not sufficiently experienced to carry it out he should refer the patient to a colleague or seek guidance in designing and making the bridge.
ADVANTAGES
Fixed-fixed
∙Robust design with maximum retention and strength
∙ Abutment teeth are splinted together, may be an advantage, particularly when teeth are uncomfortably mobile following bone loss through periodontal disease
∙The design is the most practical for larger bridges, particularly when there has been periodontal disease
∙ The construction is relatively straightforward in the laboratory
∙ Can be used for long spans
Fixed-moveable
∙Preparations do not need to be parallel to each other, so divergent abutment teeth can be used
∙Because preparations do not need to be parallel, each preparation can be designed to be retentive independently of the other preparation (s)
∙More conservative of tooth tissue because preparations for minor retainers are less destructive than preparations for major retainers
∙ Allows minor movements of teeth.
∙Parts can be cemented separately, so cementation is easy.
Cantilever
∙The most conservative design when only one abutment tooth is needed
∙ If one abutment tooth is used there is no need to make preparations parallel to each other; if two or more abutment teeth, so it is easier to make the preparations parallel.
∙ Construction in the laboratory is relatively straightforward
DISADVANTAGES
Fixed-fixed
∙ Requires preparations to be parallel and this may mean more tooth reduction than normal,
endangering the pulp and reducing retention; the strength of the prepared tooth may also
be reduced
∙Preparations are difficult to carry out, particularly if several widely separated teeth are involved; the preparation is slow and the parallelism has to be constantly checked, or alternatively (and wrongly) the preparations are over-tapered to ensure that there are no undercuts and so retention is lost
∙ All the retainers are major retainers and require extensive, destructive preparations of the abutment teeth.
∙Has to be cemented in one piece, so cementation is difficult.
Fixed- moveable
∙ Length of span limited, particularly with mobile abutment teeth
∙ More complicated to construct in the laboratory than fixed-fixed
∙Difficult to make temporary bridges
Cantilever