dental practice July 2009
Tooth Prep with Paul Tipton
www.dental-practice.org
Part 4: three-quarter crowns
CPD
T
HE partial veneer crown is a • Reduced laboratory fee (versus PFM) Sandblasting also improves the ability
more conservative restoration • Maintenance and reparability of the clinician to assess the occlusion
then the more traditional full • Better periodontal health both prior to and after cementation.
crown. Further advantages of the However, the retention of the partial The standard three-quarter crown
partial veneer crown are: veneer crown is less, and the demands for a maxillary premolar or molar tooth
• Evaluation of fit on the clinician in his or her is one where the buccal surface is left
• More complete seating preparation skills and visualisation are unprepared (except for the cusp tips).
• Pulp testing much greater. However, the mandibular posterior
• Better aesthetics (in some situations) Partial veneer crowns are indicated three-quarter crown is much more
in those situations where there is an visible as the occlusal surface will often
FIG 2 – reduce the occlusal surface by
intact facial surface, minimal tooth show during speech and the buccal
approximately 1mm and depth slightly less as you
approach the buccal cusp tip, depending on whether
destruction, and aesthetic demands of preparation has to include and go
the tooth is in guidance or not. Keep the correct
the patient are not high. The metal will beyond the functional cusp. The
cuspal inclines
not be invisible, but it will often be preparation differs significantly in that
unnoticeable in normal conversation if more gold is shown, so it is therefore lasting of all posterior preparations if
placed on maxillary posterior teeth. not as often used in the lower jaw. performed well.
This can be further reduced by In the author’s opinion, the posterior It does require, however, an
sandblasting the restoration and maxillary partial veneer crown is not increased skill level in preparation and
FIG 1 – prepare UR4 for three-quarter gold
especially the buccal cuspal margins. used often enough and is the longest is often not taught at undergraduate
crown
level in some dental hospitals. Because
of its minimum tooth preparation, it is
was first carried out in this case laterals. However, this malformation
often an ideal restoration for the less
(Figure 4). can affect either the crown or the root
aesthetic-conscious, more mature
It was thought that the large area of any tooth, which may have a
patient.
provided by this method allowed dramatic effect on the management.
conduction of cold to the adjacent Teeth with such anomalies may have
Preparation
teeth via the orthodontic wires, thereby thin root walls and often open apices,
Tooth preparation begins with
giving a false positive vitality reading. complicating matters especially when
occlusal reduction and depth grooves
Application of Endo Ice with Endo- the pulp is non-vital. The long-term
cut with a straight round-ended bur
Frost pellets (Figure 5) to 22 (and 12) prognosis can therefore be poor in
to 1mm depth (width of the bur).
did not cause this effect because the certain cases.
Continued on page 18
sponges provide a significantly The highest priority for 12 is to
improved control to limit the area of preserve its vitality with prophylactic
application of the refrigerant to the treatment. 22 requires conventional
enamel surface. root canal treatment. An additional
FIG 4
How should this case be managed? It radiograph is often necessary to
is important to examine teeth before improve the diagnosis.
embarking on complex treatment. Every periapical lesion should first
There seems to a remarkably high rate be treated conservatively and then
of dental anomalies recorded in monitored to see if there is a reduction
orthodontic cases
1
. Therefore in size.
FIG 3 – angle the bur so that it prepares the
orthodontists in particular should Remember that for the diagnosis of a functional cusp bevel at approximately 45 degrees
examine teeth for developmental cyst no correlation exists between the to the long axis of the tooth
anomalies. radiographic diagnosis and histological
That recorded here usually affects findings. It is also worth remembering
maxillary incisors, particularly the that specialist practitioners should not
start complicated dental treatment
before primary disease has been
FIG 5
controlled. This patient’s plaque
control and diet needs immediate and risking further damage.
improvement with the addition of a The demineralisations usually result
fluoride mouthwash. in the formation of white spots lesions,
As there is caries and which are a significant clinical and
FIG 4 – make sure your margin is just
demineralisation around the brackets aesthetic problem. Enamel supragingival
particularly cervical on 11, the demineralisation has a recorded
bracket(s) should be removed and the prevalence of up to 96 per cent of
tooth restored. cases undergoing fixed appliance
It could be argued in this case that therapy.
these findings are an indication for an Products such as Select Defense
early de-bond, irrespective of the stage (available from DB Orthodontics, see
of orthodontic treatment. www.dbortho.com) may reduce the
If a patient’s teeth are decaying as a incidence of this problem.
consequence of wearing a fixed
1 Uslu O, Akam MO, Evirgen S and Cebeci
appliance, it is preferable to remove the
I. Prevalence of dental anomalies in various
FIG 5 – place the chamfer finish line
appliance and accept the malocclusion
malocclusions. Am J Orthod Dentofacial Orthop
supragingivally. Finish with fine diamond or
FIG 3
rather than persisting with treatment 2009; 135(3): 328-335.
carbide bur
17
DP July 09 8, 10, 12-20, 22.indd17 17 24/6/09 13:39:16
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