Bevels in Dentistry
Bevels in Dentistry
Bevels in Dentistry
Restorative Dentistry
By: Naghman Zuberi
BEVEL
Bevel, in dictionary means as:
any other angle other than 90between the planes or surfaces.
Earlier bevel was placed only on cavosurface margins and was defined as the
roundening off of cavosurface margins at an angle. But Now a days in most of the
direct filling techniques, we dont give bevel on Occlusal cavosurface margins.
Now, as they are placed at various surfaces of prepared teeth, so bevel is defined
as
any abrupt incline between the two surfaces of prepared tooth or
between the cavity wall and the cavosurface margins in the prepared cavity
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Types of bevel
According to shape and types of tissue involvement they are classified as:
Partial bevel
Short bevel
Long bevel
Full bevel
Counter bevel
Hollow ground(concave) bevel
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They can also be classified according to surface they
are placed as:
Gingival bevel
Occlusal bevel
Proximal walls bevel
Functional cusp bevel
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Partial bevel
This type of bevel involves part of the enamel wall , not exceeding two-thirds of
its dimension.
This is usually not used in cast restorations except to trim weak enamel rods from
margin peripheries.
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Short bevel
This includes the entire enamel wall, but not dentin.
This bevel is used mostly with Class I alloys specially for type 1 and 2 gold alloys.
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Long bevel
This includes all of the enamel wall and up to one half of the dentinal wall.
This is the most frequently used bevel for the first three classes of cast materials.
Its major advantage is that it preserve the internal boxed- up resistance and
retention features of the preparation.
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Full bevel
This includes all of the dentinal and enamel walls of the cavity wall or floor.
Although it is well reproduced by all four classes of cast alloys, it deprives the
preparation of its internal resistance and retention.
Its use is avoided except in cases where it is impossible to use any other form of
bevel .
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Counter bevel
When capping cusps to protect and support them, this type of bevel is used ,
opposite to an axial cavity wall , on the facial or lingual surface of the tooth,
which will have a gingival inclination facially or lingually.
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Hollow ground(concave) bevel
This is the only form which is not in flat
plane form.
This allows more space for cast material
bulk , a design feature needed in special
preparations to improve materials
castability retention and better resistance to
stresses.
These bevels are ideal for class IV and V
cast materials.
This is actually an exaggerated chamfer or a
concave bevelled shoulder which involves
teeth greater than chamfer and less than a
bevelled shoulder.
The buccal slopes of the lingual cusps and
the lingual slope of the buccal cusps should
be hollow ground to a depth of at least 1mm.
to provide a sufficient bulk of gold on these
surfaces and to increase the resistance form
of the preparation
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Functional and Non-Functional Cusps Bevel
Functional Cusp
Non-Functional Cusp
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Other bevels
Reverse bevel
It is placed at the dentinal portion
of the cervical wall towards the
axiogingival line angle.
Reverse bevel at gingival wall will
prevent tipping movements.
The hydrostatic pressure during
cementing a cast restoration can
produce a rotational displacement of
the castings with flat gingival walls.
This effect is resisted by the reverse
bevel resulting in even seating of
the cast restoration.
It is given on the labial shoulder of
metal ceramic crowns to effectively
improve the esthetics at the margin.
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Bevelled shoulder
A shoulder with a bevel can also be
used to create an acute edge of metal at
the margin but it is unnecessarily
destructive.
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Function Of Occlusal Bevel
Bevels satisfy the requirements for ideal cavity walls.
They are the flexible extensions of a cavity preparation , allowing the inclusion of
surface defects , supplementary grooves , or other areas on the tooth surface.
Bevels require minimum tooth involvement and do not sacrifice the resistance and
retention for the restoration
Bevels create obtuse-angled marginal tooth structure, which is bulkiest and the
strongest configuration of any marginal tooth anatomy, and produce an acute
angled marginal cast alloy substance which allows smooth burnishing for alloy.
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Bevels as part of circumferential tie , are one of the major
retention forms for a cast restoration as it increases possibility
of a direct retentive frictional component between the casting
and the tooth.
This makes it possible to decrease or eliminate the cement line
by bringing the cast alloy closer to tooth structure.
Bevels like hollow ground occlusal and counter bevels, are used
for resistance form of the tooth-restoration complex by
encompassing cusps.
In wider cavities, and in deeper ones, they are extended to
improve the taper.
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FUNCTIONAL CUSP BEVEL
An integral part of occlusal
reduction is the functional
cusp bevel.
A wide bevel placed on the
functional cusp provides
space for an adequate bulk of
metal in an area of heavy
occlusal contact.
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Lack of functional cusp bevel may
produce several problems :
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Functions of Gingival Bevel
Weak enamel is removed.
Bevel results in 30 angle at the gingival margin that is burnishable because of its
angular design.
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A lap sliding fit is produced at the gingival margin which help
in improving the fit of casting in this region.
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Inlay preparations
Inlay preparations include of two types of bevel:
Occlusal bevel
Gingival bevel
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Occlusal bevel
An ideal intra-coronal inlay preparation , would include
approximately one-third of the bucco-lingual width of the occlusal
surface of the tooth.
This design employs the principle of the cone to provide a snug fit
of the casting against the surrounding walls of the preparation.
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The occlusal bevel of 15 degrees beginning at the
occlusal '/3 of the surrounding occlusal walls should
be continuous and always include all the outline form
and connect with axial flares.
22
If the cusp inclines are so steep that the diamond instrument ,when positioned at
40 to the external enamel surface, is parallel with the enamel preparation wall, no
bevel is indicated.
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Factors affecting bevel angle
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Bevel on the occluding surface of the tooth produces thin
feather edges in gold casting which are subject to injury by
attrition and excessive forces during mastication.
As conditions require the occlusal width of the preparation to
be extended bucco-lingually, the degree of the occlusal bevel
must be increased.
This increase will result in the forces of occlusion driving the
margin of the casting into closer apposition to the tooth
structure.
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Gingival bevel in inlay
It is desirable to place a bevel of
approximately 45 degrees on the
gingival wall of all inlay preparations.
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The gingival bevels can be established with specially designed diamond rotary
instruments.
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Instrument used
The gingival marginal trimmer is designed to produce a proper bevel on the
gingival enamel margins of proximo-occlusal preparations.
When second no has formula of 90 to 100 , the pair is used on distal
gingival margin.
When this no is 75 to 85, the pair is used to bevel on mesial margin.
The 100 and 75 pairs are for inlay- onlay preparations with steep gingival
bevels.
The 90 and 85 pairs are for amalgam preparations with gingival enamel
bevels that decline gingivally only slightly.
Axio - pulpal line angle can also be beveled with same instrument to reduce
the stress point for restorative material.
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Bevels in Teeth With Facets
Esthetics, conservation of tooth structure, and
requirements for retention may demand that an
occlusal cavo-surface margin be left in a faceted area
in the region of the height of the tooth cusp.
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Bevel in onlay
The term "shoeing" refers to a veneer coverage of the cusp of a
tooth with only a slight finishing bevel on the crest of the cusp.
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In this manner the rule for establishing an obtuse angle of tooth structure on all the
margins of a preparation for greater strength and resistance of cavo-surface
margins is fulfilled.
It should be pointed out that in instances where the buccal cusp of a maxillary or
the lingual cusp of a mandibular tooth has been greatly weakened due to loss of
tooth structure, this finishing bevel should in these instances be established in a
reverse direction to tie the structural elements of the crown together.
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When the lingual cusps of a maxillary posterior tooth or the
buccal cusps of a mandibular posterior tooth is extensively
involved, a BEVELLED shoulder may be used instead of a
chamfered finish line in capping these cusps.
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Bevels in direct filling gold restorations
In cavities specifically class III, IV ,V bevels are made with wedelstedt chisel and
cavosurface is bevelled to remove rough enamel and have ease in finishing.
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BEVEL IN COMPOSITES
The orientation of prisms varies in different anatomical sites and beveling each
site accordingly will be practically difficult.
Composite in thin sections is liable to fracture especially at the stress bearing
areas.
Optimum strength of restoration is achieved by providing butt joint.
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Factors on which bevel depends
It depends upon :
Area required for etching
Area visible externally
Wherever color matching is mandatory
Area prone to stresses
Accessibility and visibility
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General Features
In composite a short bevel at the enamel margin has been advocated to promote
better sealing by etching as more enamel prisms will be exposed.
Enamel in proximal wall should be bevelled because prism direction is at -12 to
20 angles to the surface.
Bevels are recommended on labial surfaces of anterior teeth so as to merge the
color of the composite and the enamel.
Lingual bevels are avoided as it may lead to stress and color merging is not of
importance.
NEVER GIVE BEVEL ON THE OCCLUSAL CAVOSURFACE AREA OF
POSTERIOR TEETH.
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Beveled class III
Beveled conventional tooth preparation for composite restorations is indicated
primarily for replacing an existing defective restoration in the crown portion of the
tooth.
It also can be used when restoring a large carious lesion for which need for
increased retention or resistance form or both is anticipated.
It is characterized by the external walls perpendicular to the enamel surface, with
the enamel margin beveled.
If part of tooth to be restored is located on the root surface, a conventional
cavosurface configuration should be used in this area resulting in combination of
two tooth preparation designs- a conventional type in the root portion and a
beveled conventional type in crown portion.
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Class IV
Beveled conventional class IV tooth preparation is indicated for restoring large
proximal areas that also include the incisal surface of an anterior tooth.
In addition to etched enamel margin retention of the composite restorative material
in conventional beveled Class IV preparation can be obtained by grooves, dovetail
extensions, threaded pins or combination of these.
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CLASS V
Beveled conventional class V is indicated for replacement of an existing,
defective class V restoration that initially used a conventional preparation or for a
large new carious lesion.
The beveled conventional class V initially exhibits 90 degree cavosurface margins
which are later beveled.
In Class V restorations bevels are given on all walls surronding the cavity.
Bevel is accomplished by flame shaped or round diamond instrument in
approximately 45 degree to the external tooth surface and prepared to width of .25
to .50 mm.
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Veneer preparation
Incisal edge coverage with porcelain
provides a better result.
With a beveled incisal edge or more
extensive overlap design, the incisal
edge is replaced in porcelain.
Covering the incisal edge in porcelain
can provide an esthetic, translucent
edge.
It becomes easier to seat the restoration
during cementation procedures, as there
is a definite stop, and the resulting
improved adaptation of the veneer
avoids marginal discrepancies.
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Bevel in Amalgam Restoration
Gingival Bevel is given only in
MOD or Class II restorations and
only on Permanent Teeth.
Deciduous Molars dont need
gingival bevel as the enamel
prisms at gingival floor, in these
teeth are directed occlusally.
NEVER GIVE BEVEL ON THE
OCCLUSAL CAVOSURFACE
AREA.
Three quarter crown
The cavo-surface margin on the incisal
edges of the anterior teeth and the crest of
the buccal cusps of the posterior teeth
must be given special attention.
Not only must these fragile margins be
protected from injury with a sufficient
bulk of gold (1/2 to 1 millimeter
thickness), but also the nature and
direction of the bevel must be favorable to
the direction and support of the enamel
rods.
These finishing bevels should be
established either at right angles to the
long axis of the tooth or in a slightly
reverse direction.
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This precaution eliminates the
possibility of leaving a poorly supported
or weak enamel margin and will
establish an obtuse angle of tooth
structure for strength.
The resulting acute angle of tough
malleable gold alloy can be readily
finished to this "finishing bevel" without
danger of injuring the enamel margin.
The "finishing bevel" need be no more
than '/4 to 1/2 millimeter in width.
Overextension of the finishing bevel
will result in an unnecessary display of
gold without any additional advantages.
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The Seven-Eighths Crown
The seven-eighths crown design is
especially effective either as a single
tooth or an abutment restoration on
maxillary molar.
These are teeth where both proximal
surfaces are involved with the disto
buccal surface of the tooth.
In many instances, the mesio -buccal
cusps of maxillary first and second
molars can be preserved for esthetics
and still provide adequate extension to
include extensive areas of destruction
with help of beveling.
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The Proximal One-Half Crown
The proximal one-half crown preparation can be
employed where the distal surface of the crown
of the tooth is free from caries or other
involvements.
It is most useful as an abutment restoration
where there has been excessive drifting of the
tooth with tipping.
If the crown is to serve as a bridge abutment it
is desirable that the occlusal margin of the
preparation in distal part is extended or bevelled
to include the crest of the intact marginal ridge
in such a manner that
occlusal forces from the opposing teeth will tend
to drive the casting tighter to the preparation.
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conclusion
Though bevel contributes a little part in cavity preparation , it holds
important role in retention , sealing, distributing occlusal forces and
most importantly in conserving the tooth structure.
Therefore a proper knowledge of bevels and its functions is essential
for every practitioner.
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Thanks a lot
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