Bevels In Dentistry 1c686b

Bevels in Operative and Restorative Dentistry By: Naghman Zuberi

BEVEL • Bevel, in dictionary means as: “any 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. But Now a days in most of the direct filling techniques, we don’t 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 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 material’s 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 10

Functional and Non-Functional Cusps Bevel

Non-Functional Cusp

Functional Cusp

“X’’-1/2 mm clearance of buccal cusps of maxillary posterior teeth in lateral relationship provides protection with minimal display of gold. “ Y ” for minimum of l mm 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 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. 12

• 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 encoming 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 .

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Lack of functional cusp bevel may produce several problems : 1. 2. 3.

Can cause a thin area or perforation. May result in over contouring and poor occlusion 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 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. •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. 21

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.

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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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Factors affecting bevel angle • 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 improve the taper and reduce frictional components for easier material manipulation.

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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. •The gingival bevel should include onehalf (.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.

Axio-pulpal line angle is slightly beveled to provide thicker and stronger wax pattern. 28

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. 29

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. • In these instances, the degree of bevel must also be considerably greater than 15 °. • In this manner, the direction of bevel will result in the forces of occlusion driving the margin of the casting into closer apposition to the tooth. • The lower bicuspid teeth offer the most common example of this exception. • It may be advisable in many instances to eliminate complete coverage of excessive extra-coronal facets on these teeth which result from excessive over-bite of the buccal cusp of the maxillary bicuspid teeth with no overjet.

A. Facets of Wear. Facets of wear occurring on Buccal surfaces are frequently quite extensive on the Buccal Cusps of lower Bicuspid and Molar Teeth. B. Recommended type of bevel to be used when the entire facet of wear is not to be covered with gold

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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. • This bevel should be established either at a right angle to the long 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 rough enamel and have ease in finishing.

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BEVEL IN COMPOSITES • Its has always been controversial whether bevel should be given in composite cavity preparation or not. Authors ing beveling advocate that by beveling:

• The surface area is increased and the mechanical retention is improved. • Marginal adaptability is improved • Removes the prismless layer of surface enamel. • Expose the ends of enamel rods for better etching. • The color matching is improved since the transition from tooth to composite is gradual. 36

• Authors not in favor of beveling illustrated : • 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 t.

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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. 40

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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. 45

Bevel in Amalgam Restoration • Gingival Bevel is given only in MOD or Class II restorations and only on Permanent Teeth. • Deciduous Molars don’t 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 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. 47

• This precaution eliminates the possibility of leaving a poorly ed 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. 48

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. 49

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. 50

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 52