77116199-Bevel

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BEVEL

´ Bevel ,in dictionary terminology, is defined as

³any other angle other than 90°between 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.

´ Now as they are placed at various surfaces of prepared teeth it is

defined as

³any 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

divided into six types of bevel :->

1) Partial bevel

2) Short bevel3) Long bevel

4) Full bevel

5) Counter bevel

6) Hollow ground(concave) bevel

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´ They can also be classified according to surface they

are placed :->

1) Gingival bevel2) Occlusal bevel

3) 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.

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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 ³boxed- 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(CONC AVE) BEVEL

´ This is the only form which is not in flat plane form.

´ This allows more space for cast material bulk , a design featureneeded in special preparations to improve material¶s castabilityretention 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 bevelledshoulder 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 lmm.

to provide a sufficient bulk of gold on these surfaces and toincrease the resistance form of the preparation

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³X¶¶-1/2 mm clearance of buccal cusps of maxillary posterior teethin lateral relalionship pnovides protection with minimal display of

gold. ³ Y ́ for minimum of lmm clearance of lingual cusps and

occlusal inclines of the tooth provides adequate thickness of gold.

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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 tippingmovements.

´ The hydrostatic pressure during cementing a cast restoration

can produce a rotational displacement of the castings with flat

gingival walls.T

his effect is resisted by the reverse bevelresulting 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 unnecessarilydestructive.

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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.

´ Awide bevel placed on thefunctional 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 :

1. Can cause a thin area or perforation.

2. May result in over contouring and

poor occlusion

3. Over inclination of the buccal surface

will destroy excessive tooth structure

reducing retention.

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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 helpin improving the fit of casting in this region.

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INL AY PREPARATIONS

´ Inlay preparations include of two types of bevel

Occlusal bevel

Gingival bevel

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OCCLUS AL BEVEL

A

n ideal intra-coronal inlay preparation , would includeapproximately one-third of the bucco-lingual width of the occlusal

surface of the tooth.

It is recommended that the occlusal bevel be about 15°beginning at

the occlusal one-third of the surrounding occlusal walls.

This design employs the principle of the cone to provide a snug fit

of the casting against the surrounding walls of the preparation.

Extremely short obtuse bevels are contra-indicated on the

surrounding occlusal walls of conservative intra-coronal

preparations.

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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 theoutline form and connect with axial flares.

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´ 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.

´ The desirable metal angle at the margins of inlay is 40°

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´ Angle of bevel is decreased with increase in steepness of the

cusps.

´ Increased bevel angulations is necessary for a direct wax patterns

as more marginal bulk is required.

´ Bevel angulations should be increased to include remotely located

defects, supplementary grooves or decalcifications on the occlusal

surface.

´ In wider cavities and in deeper ones, they are extended to improvethe taper and reduce frictional components for easier material

manipulation.

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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GINGIV AL BEVEL IN INL AY

It is desirable to place a bevel of

approximately 45 degrees on the

gingival wall of all inlay preparations.

The gingival bevel should include one-half (.5mm minimum)the width of the

gingival wall.

Gingival bevels greater than 45

degrees may result in over-extension of

the gingival and proximal margins, thus

increasing the difficulty of impression

making, fabricating the wax pattern and

finishing of the restoration.

(A) Represents a bevel of approximately 45

degrees.

(B) The dotted line illustrates a gingival

bevel steeper than 45 degrees which

may result in over-extension of the

gingival and proximal margins.

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´ The gingival bevels of the preparation should connect in a

graceful curve without undercuts.

´ These flares should be flat planes and should form a definite,sharp cavo-surface angle with the outside surface of the tooth.

´ The gingival margin trimmer is recommended as the most

ideal instrument for placing gingival bevels on inlay

preparations.´ The design of this instrument provides control in establishing

the angle of the gingival bevel without possibility of injuring

the adjacent tooth.

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´ The gingival bevels can be established with specially designed

diamond rotary instruments.

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Axio-pulpal line angle is slightly beveled to provide thicker and

stronger wax pattern.

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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 ondistal gingival margin.

´ When this no is 75 to 85, the pair is used to bevel on mesialmargin.

´ The 100 and 75 pairs are for inlay- onlay preparations with steepgingival bevels.

´ The 90 and 85 pairs are for amalgam preparations with gingivalenamel bevels that decline gingivally only slightly.

´ Axio - pulpal line angle can also be beveled with same instrumentto reduce the stress point for restorative material.

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´ Esthetics, conservation of tooth structure, andrequirements for retention may demand that an

occlusal cavo-surface margin be left in a faceted areain the region of the height of the tooth cusp.

´ In these instances, the degree of bevel must also beconsiderably greater than 15 °.

´ In this manner, the direction of bevel will result inthe forces of occlusion driving the margin of thecasting into closer apposition to the tooth.

´ The lower bicuspid teeth offer the most commonexample of this exception.

´ It may be advisable in many instances to eliminatecomplete coverage of excessive extra-coronal facetson these teeth which result from excessive over-biteof the buccal cusp of the maxillary bicuspid teethwith no overjet.

A. Facets of Wear. Facets of wear

occuring on Buccal surfaces are

frequently quite extensive on the

Buccal Cusps of lower Bicuspid

and Molar Teeth.

B. Recommended type of bevel tobe used when the entire facet

of wear is not to be covered with

gold

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BEVELS IN TEETH WITH FACET

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BEVEL IN ONL AY

´ 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.

´ This bevel should be established either at a right angle to thelong axis of the tooth or in a slight reverse direction.

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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 roughenamel and have ease in finishing.

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´ Its has always been controversial whether bevel should begiven in composite cavity preparation or not. Authorssupporting beveling advocate that by beveling:

1) The surface area is increased and the mechanical retention isimproved.

2) Marginal adaptability is improved

3) Removes the prism less layer of surface enamel.

4) Expose the ends of enamel rods for better etching.5) The color matching is improved since the transition from tooth

to composite is gradual.

BEVEL IN COMPOSITES

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´ Authors not in favor of beveling illustrated :->

1) The orientation of prisms varies in different anatomical sites and

beveling each site accordingly will be practically difficult.2) Composite in thin sections is liable to fracture especially at the

stress bearing areas.

3) Optimum strength of restoration is achieved by providing butt

joint.

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F ACTORS ON WHICH BEVEL

DEPENDS

It depends on :->

´ Area required for etching

´ Area visible externally

´ Wherever color matching is mandatory´ Area prone to stresses

´ Accessibility and visibility

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´ In composite a short bevel at the enamel margin has been

advocated to promote better sealing by etching.

´ Enamel in proximal wall should be bevelled because prismdirection 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.

GENERAL FEATURES

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BEVELED CL ASS 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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CL ASS 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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CL ASS 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 restorationduring cementation procedures, as there

is a definite stop, and the resulting

improved adaptation of the veneer

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FULL VENEER CROWN

A gingival shoulder approximately 1mm. in width is placed under the free

gingiva on the labial or buccal surface of

the tooth and is extended to the mesio and

disto-axial walls.

The outer one-half of the shoulder is

beveled at about a 45" angle to provide a

margin that will insure a better fit of the

casting.

A small tightly wrapped strand of cottonyarn is tucked beneath the gingiva. This is

covered with a larger strand of cotton

which is tucked tightly over the smaller

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´ Both strands of cotton remain in position for a sufficient length of

time to prevent injury of the gingival crest during final

instrumentation.

´ The larger strand of yarn is removed and the outer one-half of the

shoulder is beveled at about a 45" angle with a short flame

shaped diamond stone.

´ In porcelain fused metal crown porcelain should never cover

bevel. Only metal should cover as this prevents porcelain fracture

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THREE QU ARTER CROWN´ T

he cavo-surface margin on the incisaledges 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 enamelrods.

´ These finishing bevels should be

established either at right angles to the

long axis of the tooth or in a slightly

reverse direction. 48

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´ T

his precaution eliminates the possibility of leaving a poorlysupported or weak enamel margin andwill establish an obtuse angle of toothstructure for strength.

´ The resulting acute angle of toughmalleable gold alloy can be readily

finished to this "finishing bevel"without danger of injuring the enamelmargin. The "finishing bevel" need be

no more than '/4 to 1/2 millimeter inwidth.

´ Overextension of the finishing bevelwill result in an unnecessary display of gold without any additional advantages.

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THE SEVEN-EIGHTHS CROWN

´ The seven-eighths crown design isespecially 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 estheticsand 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 restorationwhere 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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REFERENCES

´ Operative dentistry modern theory and practice by M.A.Marzouk ,

A.L. Simonton and R.D.Gross.

´ Art and science of operative dentistry by Sturdevant¶s.

´

Fundamentals of operative dentistry by Summitt.´ Textbook of operative dentistry by Vimal Sikri.

´ An atlas of cast gold procedures by Rex Ingraham.

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