All-ceramic inlays, onlays, veneers, and crowns are
some of the most esthetically pleasing prosthodontic
restorations. Because there is no metal to block light
transmission, they can resemble natural tooth structure better in terms of color and translucency than
any other restorative option. Their chief disadvantage is their susceptibility to fracture, although this
is lessened by use of the resin-bonded technique.
The restorations may be fabricated in several
ways. The technique (first developed over 100 years
ago) originally called for a platinum foil matrix to
be intimately adapted to a die. This supported the
porcelain during firing and prevented distortion.
The foil was removed before cementation of the
restoration.
Today, popular fabrication processes for the
restorations include hot-pressing and slip-casting.
These options are discussed in Chapter 25.
create an esthetically pleasing restoration. Incisally,
a greater ceramic thickness may be required.
Only minor differences in tooth preparation design exist among the restorations fabricated with
the various techniques. Therefore, the hot-pressed
crown preparation is described in detail, and the
necessary variations are discussed when pertinent.
ADVANTAGES
The advantages of a complete ceramic crown include its superior esthetics, its excellent translucency (similar to that of natural tooth structure),
and its generally good tissue response. Lack of reinforcement by a metal substructure permits slightly
more conservative reduction of the facial surface
than is possible with the metal-ceramic crown, although the lingual surface needs additional reduction for strength. The appearance of the completed
restoration can be influenced and modified by selecting different colors of luting agent. However,
changing cement color under restorations that rely
on an opaque core for strength, such as the slip cast
alumina core system (InCeram*), will be ineffective.
COMPLETE CERAMIC CROWNS
Complete ceramic crowns should have relatively
even thickness circumferentially. For the hotpressed ceramic crown (IPS Empress* or Optimalt)
(Fig. 11-1) usually about 1 to 1.5 mm is needed to
DISADVANTAGES
The disadvantages of a complete ceramic crown include reduced strength of the restoration because of
the absence of a reinforcing metal substructure. Because of the need for a shoulder-type margin circumferentially, significant tooth reduction is necessary on the proximal and lingual aspects. Porcelain
brittleness, when combined with the lack of a reinforcing substructure, requires the incorporation of a
circumferential support with a shoulder. Thus, by
comparison, the proximal and lingual reductions
are less conservative than those needed for a
metal-ceramic crown.
Difficulties may be associated with obtaining a
well-fitting margin when certain techniques are
used. The "unforgiving" nature of porcelain, if an
*Ivoclar-AG: Schaan, Liechtenstein.
tjeneric/Pentron, Inc: Wallingford, Conn.
Fig. 11 -1. Recommended reduction for the all-ceramic
crown.
*Vita Zahnfabrik: Bad Sackingen, Germany.
262
Chapter 11 Tooth Preparation for All-Ceramic Restorations
inadequate tooth preparation goes uncorrected, can
result in fracture.
Proper preparation design is critical to ensuring
mechanical success. A 90-degree cavosurface angle
is needed to prevent unfavorable distribution of
stresses and to minimize the risk of fracture (Fig.
11-2). The preparation should provide support for
the porcelain along its entire incisal edge. Thus a severely damaged tooth (Fig. 11-3) should not be restored with a ceramic crown.
All-ceramic restorations are not effective as retainers for a fixed partial denture, although the
strongest of the slip-cast materials (In-Ceram zirconia) and the higher-strength pressed systems (IPS
Empress 2) may be suitable for anterior applications.
The brittle nature of porcelain requires that connectors of large, cross-sectional dimension (a minimum
of 4 x 4 mm is recommended) be incorporated in the
FPD design. Typically this leads to impingement on
the interdental papilla by the connector, with increased potential for periodontal failure.
Wear has been observed on the functional surfaces of natural teeth that oppose porcelain restorations. This also applies to teeth opposed by
metal-ceramic restorations, especially the mandibular incisors, which can exhibit significant wear over
time (see Fig 17-1).
I NDICATIONS
The complete ceramic crown is indicated in areas
with a high esthetic requirement where a more conservative restoration would be inadequate (Fig.
11-4). Usually such a tooth has proximal and/or facial caries that can no longer be effectively restored
with composite resin. The tooth should be relatively
intact with sufficient coronal structure to support
the restoration, particularly in the incisal area,
where it is important not to exceed a maximum
porcelain thickness of 2 mm; otherwise, brittle failure of the material will occur.
Because of the relative weakness of the restoration, the occlusal load should be favorably distributed (Fig. 11-5). Generally this means that centric
contact must be in an area where the porcelain is
Fig. 11 -2. A sloping shoulder is not recommended for
the all-ceramic crown. It does not support the porcelain. Incisal loading will lead to tensile stresses near the margin.
Fig., 11 -3. Removal of an existing anterior crown. Defects in this tooth make it unsuitable for an all-ceramic
crown.
Fig. 11 -4. A, Inadequately fitting all-ceramic crowns
have led to recurrent caries and gingival recession around
these central incisors. The patient, a professional model,
had a high esthetic requirement. B, The gingival defect was
corrected by minor periodontal recontouring, the teeth
were reprepared, and new all-ceramic crowns were
provided.
Section 2 Clinical Procedures-Part I
Fig. 11-7. Armamentarium for an all-ceramic crown
preparation.
Fig. 11-5. The occlusion on an all-ceramic crown is critical for avoiding fracture. Centric contacts are best confined
to the middle third of the lingual surface. Anterior guidance should be smooth and consistent with contact on the
adjacent teeth. Leaving the restoration out of contact is not
recommended. Future eruption may lead to protrusive interferences, precipitating fracture.
Fig. 11-8. All-ceramic crown preparation. A, Labial
view. B, Lingual view. To prevent stress concentrations in
the ceramic, all internal line angles should be rounded. The
shoulder should be as smooth as possible to facilitate the
technical aspects of fabrication.
PREPARATION
Fig. 11 -6. Unfavorable occlusal loading such as this
edge-to-edge relationship on the lateral incisor is a contraindication to the all-ceramic crown, particularly in view
of the parafunctional activity of this patient.
supported by tooth structure (e.g., in the middle
third of the lingual wall).
CONTRAINDICATIONS
The ceramic crown is contraindicated when a more
conservative restoration can be used. Rarely are they
recommended for molar teeth. The increased occlusal load and the reduced esthetic demand make
metal-ceramics the treatment of choice. If occlusal
loading is unfavorable (Fig. 11-6) or if it is not possible to provide adequate support or an even shoulder
width of at least 1 mm circumferentially, a metalceramic restoration should be considered instead.
Armamentarium (Fig. 11-7). The instruments
needed for preparing a ceramic crown include the
following:
Narrow, round-tipped, tapered diamonds, regular and coarse grit (0.8 mm)
Square-tipped, tapered diamond, regular grit
(1.0 mm)
Football-shaped diamond
Finishing stones and carbides
Mirror
Periodontal probe
Explorer
Chisels and hatchets
High- and low-speed handpieces
Step-by-Step Procedure (Fig. 11-8). The preparation sequence for a ceramic crown is similar to
that for a metal-ceramic crown; the principal difference is the need for a 1-mm-wide chamfer circumferentially (Fig. 11-9).
Chapter 11 Tooth P reparation for All-Ceramic Restorations
6.
Fig. 11-9. Note the uniform chamfer width of 1 mm on
this all-ceramic crown preparation.
Incisal (Occlusal) Reduction. The completed
reduction of the incisal edge should provide 1.5 to 2
mm of clearance for porcelain in all excursive movements of the mandible. This will permit fabrication of
a cosmetically pleasing restoration with adequate
strength. If the restoration is used for posterior teeth
(rare), 1.5 to 2 mm of clearance is needed on all cusps.
1. Place three depth grooves in the incisal edge,
initially keeping them approximately 1.3 mm
deep to allow for additional loss of tooth
structure during finishing. The grooves are
oriented perpendicular to the long axis of the
opposing tooth to provide adequate support
for the porcelain crown.
2. Complete the incisal reduction, reducing half
the surface at a time, and verify its adequacy
upon completion.
Facial Reduction
3. After placing depth grooves, reduce the facial
or buccal surface and verify that adequate
clearance exists for 1 mm of porcelain thick
ness. One depth groove is placed in the middle of the facial wall, and one each in the
mesiofacial and distofacial transitional line
angles. The reduction is then performed with
a cervical component parallel to the proposed
path of withdrawal and an incisal component
parallel to the original contour of the tooth.
The depth of these grooves should be approximately 0.8 mm to allow finishing. The
reduction is performed on half of the facial
surface at a time.
4. Do the bulk reduction with the round-tipped
tapered diamond (which will result in a
heavy chamfer margin). Be sure to maintain
copious irrigation throughout.
Lingual Reduction
5. Use the football-shaped diamond for lingual
reduction after placing depth grooves approximately 0.8 mm deep. The lingual reduc
tion is done like the other anterior tooth
preparations (see Chapters 9 and 10) until a
clearance of 1 mm in all mandibular excur-
7.
sive movements has been obtained. Adequate space must exist for the porcelain in all
load-bearing areas.
After the selected path of withdrawal has
been transferred from the cervical wall of the
facial preparation, place a depth groove in
the middle of the cingulum wall.
Repeat the shoulder preparation, this time
from the center of the cingulum wall into the
proximal, until the lingual shoulder meets
the facial shoulder. This margin should follow the free gingival crest and should not extend too far subgingivally.
Chamfer Preparation. For subgingival margins, displace the tissue with cord before proceeding with the chamfer preparation. The ultimate objective is to direct stresses optimally in the
completed porcelain restoration. This is accomplished when the chamfer or rounded shoulder
margin completely supports the crown; then any
forces exerted on the crown will be in a direction
parallel to its path of withdrawal. A sloping shoulder will result in unfavorable loading of the porcelain, with a greater likelihood of tensile failure. A
90-degree cavosurface angle is optimal. Care must
be taken, however, that no residual unsupported
enamel is overlooked, because it might chip off.
The completed chamfer should be 1 mm wide,
smooth, continuous, and free of any irregularities.
Finishing
8. Finish the prepared surfaces to a final
smoothness as described for the other tooth
preparations. Be sure to round any remaining
sharp line angles to prevent a wedging action, which can cause fracture.
9. Perform any additional margin refinement as
needed, using either the diamond or a carbide rotary instrument of choice.
CERAMIC INLAYS AND ONLAYS
For patients demanding esthetic restorations, ceramic inlays and onlays provide a durable alternative
to posterior composite resins. The procedure consists
of bonding the ceramic restoration to the prepared
tooth with an acid-etch technique. The bonding
mechanism relies on acid etching of the enamel and
the use of composite resin, as seen in the resinretained FPD technique (see Chapter 26). Bonding to
porcelain is achieved by etching with hydrofluoric
acid and the use of a silane coupling agent (materials
are identical to those marketed as porcelain repair
kits). A similar restoration uses indirectly fabricated
composite resin instead of the ceramic inlays.
Section 2 Clinical Procedures-Part I
I NDICATIONS
A ceramic inlay can be used instead of amalgam or
a gold inlay for patients with a low caries rate requiring a Class II restoration and wishing to restore
the tooth to its original appearance. It is the most
conservative ceramic restoration and enables most
of the remaining enamel to be preserved.
CONTRAINDICATIONS
Because these restorations are time consuming and
expensive, they are contraindicated in patients with
poor oral hygiene or active caries. Because of their
brittle nature, ceramics may be contraindicated in
patients with excessive occlusal loading, such as
bruxers.
ADVANTAGES
Ceramic inlays and onlays can be extremely esthetic
restorations. The restoration wear associated with
posterior composite restorations is not a problem
with the ceramics. Marginal leakage associated with
polymerization shrinkage and high thermal coefficient of expansion of the resin is reduced, because
the luting layer is very thin.
DISADVANTAGES
Accurate occlusion can be difficult to achieve with
ceramic inlays and onlays. Because they are fragile,
intraoral occlusal adjustment is impractical before
they are bonded to place. Therefore, any areas of adj ustment need careful finishing and polishing,
which is a time-consuming procedure. Rough
porcelain is extremely abrasive of the opposing
enamel. Castable glass-ceramics (see Chapter 25)
are less abrasive than the traditional feldspathic
porcelain. Wear of the composite resin-luting agent
can be a problem, leading to marginal gaps. These
will eventually allow chipping or recurrent caries.
Accuracy is important with these restorations, because accurately fitting restorations (marginal gaps
less than 100 u m) have been shown to reduce this
problem significantly. Finishing of the margins can
be difficult in the less accessible interproximal areas.
Resin flash or overhangs are difficult to detect and
can initiate periodontal disease.
Bonded ceramic inlays are a relatively new concept, and long-term clinical performance is hard to
judge. The patient should always be made aware
that unforeseen problems may surface over time
when a newer procedure is used.
PREPARATION (FIG 1
1 -10)
Armamentarium (Fig 11-11). As for metal inlays, carbide burs are used in the preparation, but
diamonds may be substituted:
• Tapered carbide burs
• Round carbide burs
• Cylindrical carbide burs
• Finishing stones
• Mirror
• Explorer and periodontal probe
• Chisels
Fig. 11 -10. Maxillary first molar preparation for an MOD ceramic inlay. A, Defective restoration.
B, The restoration and caries removed. C, Unsupported enamel removed and glass ionomer base placed.
D, The completed ceramic restoration.
(Courtesy Dr. R. Seghi.)
Chapter 11 Tooth Preparation for All-Ceramic Restorations
•
•
•
•
Gingival margin trimmers
Excavators
High- and low-speed handpieces
Articulating film
Step-by-Step Procedure. Rubber dam isolation
is recommended for visibility and moisture control.
Before applying the dam, mark and assess the occlusal contact relationship with articulating film. To
avoid chipping or wear of the luting resin, the margins of the restoration should not be at a centric
contact.
Outline Form
1. Prepare the outline form. This will generally
be governed by the existing restorations and
caries and is broadly similar to that for con
ventional metal inlays and onlays (see Chapter 10). Because of the resin bonding, axial
wall undercuts can sometimes be blocked out
with resin-modified glass ionomer cement,
preserving additional enamel for adhesion.
However, undermined or weakened enamel
should always be removed. The central
groove reduction (typically about 1.8 mm)
follows the anatomy of the unprepared tooth
rather than a monoplane. This will provide
additional bulk for the ceramic. The outline
should avoid occlusal contacts. Areas to be
onlayed need 1.5 mm of clearance in all excursions to prevent ceramic fracture.
2. Extend the box to allow a minimum of 0.6
mm of proximal clearance for impression
making. The margin should be kept supra
gingival, which will make isolation during
the critical luting procedure easier and will
improve access for finishing. If necessary,
electrosurgery or crown lengthening (p. 150)
can be done. The width of the gingival floor
of the box should be approximately 1.0 mm.
Fig. 11 -11 .
Armamentarium for the porcelain laminate
veneer preparation.
3.
Round all internal line angles. Sharp angles
lead to stress concentrations and increase the
likelihood of voids during the luting procedure.
Caries Excavation
4. Remove any caries not included in the outline form preparation with an excavator or a
round bur in the low-speed handpiece.
5. Place a resin-modified glass ionomer cement
base to restore the excavated tissue in the gingival wall.
Margin Design
6. Use a 90-degree butt joint for ceramic inlay
margins. Bevels are contraindicated because
bulk is needed to prevent fracture. A distinct
heavy chamfer is recommended for ceramic
onlay margins.
Finishing
7. Refine the margins with finishing burs and
hand instruments, trimming back any glass
ionomer base. Smooth, distinct margins are
essential to an accurately fitting ceramic
restoration.
Occlusal Clearance (for Onlays)
8. Check this after the rubber dam is removed.
A 1.5-mm clearance is needed to prevent fracture in all excursions. This can be easily eval
uated by measuring the thickness of the resin
provisional restoration with a dial caliper.
PORCELAIN LAMINATE VENEERS
Laminate veneering (Fig. 11-12) is a conservative
method of restoring the appearance of discolored,
Fig. 11 -12. Esthetic facial veneers. A, Discolored maxillary central incisors. B, Prepared for porcelain veneers.
C, The laminates etched before bonding. D, Restorations in
place.
(Courtesy Dr. C. Zmick.)
Section 2 Clinical Procedures-Part I
pitted, or fractured anterior teeth. It consists of
bonding thin ceramic laminates onto the labial surfaces of affected teeth. The bonding procedure is the
same as that for ceramic inlays.
ADVANTAGES AND INDICATIONS
The main advantage of facial veneers is that they are
conservative of tooth structure. Typically only about
0.5 mm of facial reduction is needed. Since this is
confined to the enamel layer, local anesthesia is not
usually required. The main disadvantage of the procedure relates to difficulty in obtaining restorations
that are not excessively contoured. This is almost inevitable in the gingival area if enamel is left for
bonding. Currently, little has been reported about
the effect of the restorations on long-term gingival
health and whether or how often they will need replacement over a patient's lifetime.
Esthetic veneers should always be considered as
a conservative alternative to cemented crowns. In
many practices they have largely replaced metalceramic crowns for the treatment of multiple discolored but otherwise sound teeth.
PREPARATION
Armamentarium. The instruments needed for
preparing a porcelain laminate veneer include the
following:
1-mm round bur or 0.5-mm depth cutter
Narrow, round-tipped, tapered diamonds, regular and coarse grit (0.8 mm)
Finishing strip
Finishing stones
Mirror
Periodontal probe
Explorer
Step-by-Step Procedure (Fig. 11-13). The gingival third and proximal line angles are often overcontoured with these restorations. Therefore, maximum reduction should be achieved with minimum
penetration into the dentin.
1. Make a series of depth holes with a round
bur to help avoid penetrating abnormally
thin enamel. The required amount of reduc
tion will depend somewhat on the extent of
discoloration. A minimum of 0.5 mm is usu-
C,D
E
Fig. 11 -13. Porcelain facial veneer preparation. A, The proximal contact areas and incisal edge are
preserved, and the preparation is limited to enamel. Normally a reduction depth of about 0.5 mm is recommended, but making a series of depth holes with a round bur will guard against penetrating thin
enamel. B, Tetracycline-stained teeth. Composite resin veneers were placed earlier but failed to mask the
discoloration satisfactorily. Six maxillary porcelain labial veneers will be provided. C and D, Completed
tooth preparations. E, Provisionals made directly with composite resin, which are retained by etching
small areas of enamel (see Chapter 15).
Chapter 11 Tooth Preparation for All-Ceramic Restorations
2.
3.
ally adequate. The reduction should follow
the anatomic contours of the tooth.
Place the "long chamfer" margin (Fig. 11-14).
This design has an obtuse cavosurface angle,
which exposes the enamel prism ends at the
margin for better etching. The margin should
closely follow the gingival crest so that all
discolored enamel will be veneered without
undue encroachment on the gingival sulcus.
Wherever possible, place the preparation
margin labial to the proximal contact area to
preserve it in enamel. However, slight clearance for separating the working cast and for
accessing the proximal margins for finishing
and polishing is essential. A diamond finishing strip helps create the necessary clearance.
Sometimes the proximal margins are extended lingually to include existing restorations. This can necessitate considerable tooth
Fig. 11 -14. The recommended margin ("long chamfer")
for facial veneers has an obtuse cavosurface angle so the
ends of the enamel prisms will be exposed for differential
etching.
4.
5.
reduction to avoid creating an undercut.
Some authorities advocate placing the ceramic margin on composite rather than extending the preparation to enamel, but this
is not recommended. Extensive existing
restorations are a contraindication for porcelain laminate veneers.
If possible, do not reduce the incisal edge
(Fig. 11-15); this helps support the porcelain
and makes chipping less likely. If the incisal
edge length is to be increased, the preparation should extend to the lingual. Care is
needed to avoid undercuts with this modification. Visualizing the path of insertion of the
restoration is important, because an undercut
will prevent placement of the veneer.
To prevent areas of stress concentration in the
porcelain, be sure that all prepared surfaces
are rounded (see Fig. 11-13, C, D).
Fig. 11 -15. The preferred design for porcelain laminate
veneers maintains part of the incisal edge in enamel. If the
edge is to be lengthened, a modified preparation with lingual extension will be needed (dotted line).
Section 2 Clinical Procedures-Part I
Chapter 11 Tooth Preparation for All-Ceramic Restorations