Operative dentistry aje qualtrough, jd satterthwaite la morrow, pa brunton

Risk of fracture
When there is a significant risk of tooth fracture steps should be 
taken to reduce the possibility of fracture occurring. As an aspect of
their increased retention, bonded restorations provide support to
weakened cusps
1,2
; however some doubt exists as to the long-term
benefit. A more reliable method for preventing fracture in the long
term is to provide a restoration with cuspal/occlusal coverage in
order to protect the remaining tooth structure. Cuspal coverage can 
be provided by direct as well as indirect restorations
3
but, as indicated
above, it is extremely demanding to place large restorations so that
they fulfil all necessary criteria for a successful restoration with respect
to recreation of form and occlusal contacts. Given a situation in which
remaining cusps are thin and unsupported by a bulk of coronal 
dentine, an indirect restoration with cuspal coverage will reduce the
risk of cusp fracture. Although this treatment will involve removal of
some healthy tooth structure, it will act to preserve tooth substance by
preventing tooth fracture.
In addition to teeth with unsupported cusps, root-treated teeth are
also at risk of fracture. A consequence of root treatment of posterior
teeth is that the remaining cusps are weakened owing to previous loss
of tooth structure from earlier restorations and further loss of tooth
structure due to the endodontic access. Posterior teeth provide the
majority of support in the intercuspal position and any contact during
excursive movement produces high lateral forces. As such, an
endodontically treated tooth requiring more than an occlusal restora-
tion has a significant risk of cusp fracture. A tooth with an intact
marginal ridge has significantly more resistance to fracture than a
tooth that has a cavity/preparation involving the marginal ridge. 
In order to prevent cusp fracture, in most endodontically treated 
Principles of indirect restoration