Lecture Twelve------------------------------------------------------------Operative dentistry
Restoration of endodontically
treated teeth
An endodontically treated tooth should have a good prognosis. It can
resume full function and serve satisfactorily as an abutment for a fixed or
removable partial denture. However, special techniques are needed to
restore such a tooth. Usually a considerable amount of tooth structure has
been lost because of caries, endodontic treatment, and the placement of
previous restorations. The loss of tooth structure makes retention of
subsequent restorations more problematic and increases the likelihood of
fracture during functional loading. Two factors influence the choice of
technique: the type of tooth (whether it is an incisor, canine, premolar, or
molar) and the amount of remaining coronal tooth structure. The latter is
probably the most important indicator when determining the prognosis.
Before restoration, existing
Endodontically treated teeth need to be assessed carefully for the
following:
 Good apical seal
 No sensitivity to pressure
 No exudates
 No fistula
 No apical sensitivity
 No active inflammation
CONSIDERATIONS FOR ANTERIOR TEETH
Endodontically treated anterior teeth do not always need complete
coverage by placing a complete crown, except when plastic restorative
materials have limited prognosis (e.g., if the tooth has large proximal
composite restorations and unsupported tooth structure). Many otherwise
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Lecture Twelve------------------------------------------------------------Operative dentistry
intact teeth function satisfactorily with a composite resin restoration.
Discoloration in the absence of significant tooth loss may be more
effectively treated by bleaching than by the placement of a complete
crown, although not all stained teeth can be bleached successfully.
Resorption can be an unfortunate side effect of nonvital bleaching.
However, when loss of coronal tooth structure is extensive or the tooth
will be serving as an FPD or RPD abutment, a complete crown becomes
mandatory. Retention and support then must be derived from within the
canal because a limited amount of coronal dentin remains once the
reduction for complete coverage has been completed.
Coupled with the loss of internal tooth structure necessary for endodontic
treatment, the remaining walls become thin and fragile often requiring
their reduction in height.
CONSIDERATIONS FOR POSTERIOR TEETH
Endodontically treated posterior teeth are subject to greater loading than
anterior teeth because of their closer proximity to the transverse
horizontal axis.
This, combined with their morphologic characteristics (having cusps that
can be wedged apart), makes them more susceptible to fracture. Careful
occlusal adjustment will reduce potentially damaging lateral forces during
excursive movements. Nevertheless, endodontically treated posterior
tooth should receive cuspal coverage to prevent biting forces from
causing fracture. Possible exceptions are mandibular premolars and first
molars with intact marginal ridges and conservative access cavities not
subjected to excessive occlusal forces (i.e., posterior disclusion in
conjunction with normal muscle activity).
Complete coverage is recommended on teeth with a high risk of fracture.
This is especially true for maxillary premolars, because complete
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Lecture Twelve------------------------------------------------------------Operative dentistry
coverage gives the best protection against fracture, since the tooth is
completely encircled by the restoration. However, considerable tooth
reduction is required, particularly when a metal-ceramic restoration is to
be used. When significant coronal tooth loss has occurred, a cast postand-core or an amalgam foundation restoration is needed.
Tooth preparation for endodontically treated teeth can be considered a
three-stage operation:
1. Removal of the root canal filling material to the appropriate depth.
2. Enlargement of the canal.
3. Preparation of the coronal tooth structure
PRINCIPLES OF TOOTH PREPARATION
1. CONSERVATION OF TOOTH STRUCTURE:
 Preparation of the Canal: When creating post space, great care must
be used to remove only minimal tooth structure from the canal. Excessive
enlargement can perforate or weaken the root, which then may split
during cementation of the post or subsequent function. The thickness of
the remaining dentin is the prime variable in fracture resistance of the
root. Nevertheless, it is difficult to enlarge a root canal uniformly and to
judge with accuracy how much tooth structure has been removed and
how thick the remaining dentin is. Most roots are narrower mesiodistally
than faciolingually and often have proximal concavities that cannot be
seen on a standard periapical radiograph.
 Preparation of Coronal Tissue.
Endodontically treated teeth often have lost much coronal tooth structure
as a result of caries, of previously placed restorations, or in preparation of
the endodontic access cavity. However, if a cast core is to be used, further
reduction is needed to accommodate a complete crown and to remove
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Lecture Twelve------------------------------------------------------------Operative dentistry
undercuts from the chamber and internal walls. This may leave very little
coronal dentin. Every effort should be made to save as much of the
coronal tooth structure as possible, because this helps reduce stress
concentrations at the gingival margin." The amount of remaining tooth
structure is probably the single most important predictor of clinical
success. If more than 2 mm of coronal tooth structure remains, the post
design probably has a limited role in the fracture resistance of the restored
tooth.
2. RETENTION FORM
Anterior Teeth:
Dislodgment of a post-retained anterior crown is frequently seen
clinically and results from inadequate retention form of the prepared root.
Post retention is affected by the preparation geometry, post length,
diameter, surface texture, and by the luting agent.
Posterior Teeth:
Relatively long posts with a circular cross section provide good retention
and support in anterior teeth but should be avoided in posterior teeth,
which often have curved roots and elliptical or ribbon-shaped canals. For
these teeth, retention is better provided by two or more relatively short
posts in the divergent canals.
When amalgam is used as the core material, it can be condensed either
around cemented metal posts or directly into short, prepared post spaces.
If more than 3 to 4 mm of coronal tooth structure remains, use of the root
canals for retention is not necessary, and this avoids the chance of
perforation. Using the canals for retention can provide good results,
although the strength of the tooth once a complete crown has been
provided is not dramatically influenced by differences in technique.
Mandibular premolars and molars with a reasonable amount of remaining
coronal tooth structure, when coupled with a circumferential cervical
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Lecture Twelve------------------------------------------------------------Operative dentistry
band of tooth structure with restricted taper of about 2 mm, can often be
restored with amalgam directly condensed into the chamber. Core
buildups in molars with one or more missing cusps will benefit from one
or more cemented posts around which the amalgam can be condensed.
The posts provide the additional retention, which was compromised
because of the missing tooth structure. In mandibular molars, the larger
distal canal is recommended for post placement. In maxillary molars, the
palatal canal is used.
Types of posts:
A- Prefabricated Posts
1. Enlarge the canal one or two sizes with a drill, endodontic file, or
reamer that matches the configuration of the post. When using rotary
instruments, alternate between the Peeso-Reamers and twist drills that
correspond in size. In the case of a threaded post, the appropriate drill is
followed by a tap that prethreads the internal wall of the post space.
Parallel-sided posts are more retentive and distribute stresses better than
tapered posts, but they do not conform well to the shape of a canal that
has been flared to facilitate condensation of gutta-percha.
In this situation, it may not be possible to enlarge the canal sufficiently to
provide adequate retention for the post; in that case, a tapered custommade post is preferred.
2. Use a prefabricated post that matches standard endodontic instruments.
A tapered post will conform better to the canal than a parallel-sided post
and requires less removal of dentin to achieve an adequate fit. However,
it will be slightly less retentive and will cause greater stress
concentrations, although retention may be improved by controlled
grooving.
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Lecture Twelve------------------------------------------------------------Operative dentistry
3. Be especially careful not to remove more dentin at the apical extent of
the post space than is necessary.
NOTE: If careful measurement techniques have been followed,
radiographs are not normally required to verify the post space
preparation.
Most of the time a preformed parallel-sided post will fit only in the most
apical portion of the canal. Modified posts are available with tapered
ends, and these conform better to the shape of the canal although they
have slightly less retention than parallel sided posts do, particularly the
shorter ones.
In the absence of a vertical stop on sound tooth structure, such posts can
also create an undesirable wedging effect.
B- Custom-made Posts:
1. Use custom-made posts in canals that have a noncircular cross section
or extreme taper. Enlarging canals to conform to a preformed post may
lead to perforation. Often very little preparation will be needed for a
custom-made post. However, undercuts within the canal must be
removed, and some additional shaping usually is necessary.
2. Be most careful on molars to avoid root perforation. In mandibular
molars the distal wall of the mesial root is particularly susceptible. In
maxillary molars the curvature of the mesiobuccal root makes mesial or
distal perforation more likely.
Direct Procedure
1. Lightly lubricate the canal and notch a loose fitting plastic dowel. It
should extend to the full depth of the prepared canal.
2. Use the bead-brush technique to add resin to the dowel and seat it in
the prepared canal. This should be done in two steps: Add resin only to
the canal orifice first. An alternative is to mix some resin and roll it into a
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Lecture Twelve------------------------------------------------------------Operative dentistry
thin cylinder. This is introduced into the canal and pushed to place with
the monomer-moistened plastic dowel.
3. Do not allow the resin to harden fully within the canal. Loosen and
reseat it several times while it is still rubbery.
4. Once the resin has polymerized, remove the pattern.
5. Form the apical part of the post by adding additional resin and
reseating and removing the post, taking care not to lock it in the canal.
6. Identify any undercuts that can be trimmed away carefully with a
scalpel. The post pattern is complete when it can be inserted and removed
easily without binding in the canal. Once the pattern has been made,
additional resin or light-polymerized resin* is added for the core.
Indirect Procedure
Any elastomeric material will make an accurate impression of the root
canal if wire reinforcement is placed to prevent distortion.
1. Cut pieces of orthodontic wire to length and shape them like the letter
J.
2. Verify the fit of the wire in each canal. It should fit loosely and extend
to the full depth of the post space. If the fit is too tight, the impression
material will strip away from the wire when the impression is removed.
3. Coat the wire with tray adhesive. If subgingival margins are present,
tissue displacement may be helpful. Lubricate the canals to facilitate
removal of the impression without distortion (die lubricant is suitable).
4. Using a lentulo spiral, fill the canals with elastomeric impression
material. Before loading the impression syringe, verify that the lentulo
will spiral material in an apical direction (clockwise). Pick up a small
amount of material with the largest lentulo spiral that fits into the post
space. Insert the lentulo with the handpiece set at low rotational speed to
slowly carry material into the apical portion of the post space. Then
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Lecture Twelve------------------------------------------------------------Operative dentistry
increase handpiece speed and slowly withdraw the lentulo from the post
space. This technique prevents the impression material from being
dragged out. Repeat until the post space is filled.
5. Seat the wire reinforcement to the full depth of each post space,
syringe in more impression material around the prepared teeth, and insert
the impression tray.
6. Remove the impression, evaluate it, and pour the working cast.
NOTE: Access for waxing is generally adequate without placement of
dowel pins or sectioning of the cast.
7. In the laboratory, roughen a loose-fitting plastic post (a plastic
toothpick is suitable) and, using the impression as a guide, make sure that
it extends into the entire depth of the canal.
8. Apply a thin coat of sticky wax to the plastic post and, after lubricating
the stone cast, add soft inlay wax in increments. Start from the most
apical and make sure that the post is correctly oriented as it is seated to
adapt the wax. When this post pattern has been fabricated, the wax core
can be added and shaped.
9. Use the impression to evaluate whether the wax pattern is completely
adapted to the post space.
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