TREATMENT
ASSESSMENT
Before
considering embarking on indirect restorations, patients
should be assessed to ensure that their periodontal condition
has been stabilised and their caries risk is low.
The
restorative assessment of the individual tooth involves:
•
sensitivity/vitality tests
•
long cone periapical radiograph
•
examination of the quality of any existing restorations
•
assessing whether the remaining tooth structure after preparation
will have sufficient strength
•
assessing the need for crown lengthening prior to treatment
•
occlusal considerations.
The
occlusal assessment should involve consideration of the
tooth position relative to the opposing as well as the adjacent
teeth, as this will influence preparation design. If there
are occlusal interferences, these may place such a crown
under high functional stresses and will require removal
at a prior visit.The surfaces of the crown will need to
be duplicated so that either the group function or canine
guidance occlusion is maintained. The tooth may be a key
unit in the arch, i.e. partial denture abutment, and the
shape of the surface should be modified to allow the subsequent
placement of the denture. In such situations, mounted study
casts are a useful aid in planning the preparation design
as well as carrying out the occlusal assessment. Any tooth
preparation for a crown should follow the appropriate biomechanical
principles below , and when planning replacement of a failed
indirect restoration, it is important to identify the cause(s)
of failure so that this may be corrected at the time of
preparation.
Biomechanical
principles of tooth preparation
•
Preservation of tooth structure and pulp vitality
•
Obtaining adequate retention and resistance form
•
Obtaining adequate structural durability of the restoration
•
Obtaining adequate marginal integrity
•
Preservation of periodontal health
•
Appropriate aesthetics
Common
causes of failure include:
•
poor preparation design/shape resulting in lack of retention
and/or resistance form
•
insufficient reduction or lack of support/thickness for
ceramic or composite
•
undercut preparations
•
failure to identify and/or correct occlusal problems
•
poorly fitting restorations resulting from poor impression
procedures or faulty laboratory technique
•
inappropriate prescription/planning; no preventive regime
•
incorrect shade.
•
Crown & Bridge basic
• Restoration Assessment
• Restoration choice
• Tooth preparation
