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TOOTH PREPARATION FOR CLASS II AMALGAM RESTORATION

Prepared by,

Reshma Rajasekhar

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CONTENT

HISTORY
INDICATION
CONTRAINDICATION
ARMAMENTARIUM
INITIAL TOOTH PREPARATION
OCCLUSAL OUTLINE FORM
PROXIMAL OUTLINE FORM
FINAL TOOTH PREPARATION
PULP PROTECTION

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SECONDARY RESISTANCE AND RETENTION FORM
PROCEDURES FOR FINISHING EXTERNAL WALLS
FINAL PROCEDURES LIKE CLEANING,INSPECTING,SEALING
VARIATION IN PROXIMAL SURFACE PREPARATION
CLASS II AMALGAM INVOLVING BOTH PROXIMAL SURFACES
DESIGNS FOR CLASS II PREPARATION
CONCLUSION

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Tooth preparation is the mechanical alteration of a defective , injured, or diseased tooth to receive a restorative material that re-establishes a healthy state for the tooth including esthetic corrections where indicated and normal form and function
(sturdevent’s 5^th edition)

Class II cavity preparation is the proximal,proximo-facial(lingual),proximo-occlusal(or combination thereof) tooth preparation.

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Objectives:

Remove all defects and provide necessary protection to the pulp

Extend the restoration as conservatively as possible

Form the tooth preparation that under the forces of mastication the tooth or the restoration or both will not fracture and restoration will not be displaced

Allow for the esthetic and functional replacement of a restorative material

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INDICATIONS FOR USING AMALGAM RESTORATION

Moderate-to-large restorations.
Restorations not in highly esthetic areas
Restorations that cannot be well isolated.
Restorations that have heavy occlusal loads.

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Restorations that extend onto the root surface
Foundations
Abutment teeth for RPD

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CONTRAINDICATION

Esthetically prominent areas of posterior teeth

Small to moderate class I and II restorations that can be well isolated.

Small class VI restorations.

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ARMAMENTARIUM

Mouth mirror
Explorer
High speed contraangle hand piece
No.245 , 330 bur
Gingival margin trimmer
Enamel hatchet
Wooden wedge
169 L bur
¼ round bur

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INITIAL CLINICAL PROCEDURE

Local anesthesia usually required

Occlusal evaluation

Rubber dam placement

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Occlusal outline form

Using high speed with air water spray ,enter the pit nearest the involved proximal surface with a punch cut using No.245

Long axis of the bur should be parallel to long axis of the crown

Initial tooth preparation

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Proper depth of the initial entry cut - 1.5-2mm.

The pulpal depth -0.1-0.2 mm in to the dentin.

bur is moved to extend the outline to include the central fissure and opposite pit ,if necessary.

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The isthmus width should be as narrow as possible, at least one –fourth the distance between the facial and lingual cusp tips^1,2

^{Pulpal floor should be flat}

^{rounded internal line angles}

1:Summit et al,Effect of grooves on resistance form of class 2 amalgams with wide occlusal preparations. Oper dent 1993; 18:42-47

2:Larson TD,et al : Effect of prepared cavities on the strength of the teeth ,Oper dent 6:1,1981

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If extension of distal margin may undermine marginal ridge of dentinal support ,bur is tilted to diverge occlusally at distal wall.

Dovetail prevents the proximal displacement of the restoration.

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Enameloplasty should be used where indicated to conserve tooth structure.

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Before extending into marginal ridge, the final location of the facial and lingual walls of the proximal box visualized

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While maintaining the established pulpal depth and with the bur parallel to the long axis of the tooth crown,

the preparation is extended mesially, stopping approximately 0.8 mm short of cutting through the marginal ridge into the contact area.

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REVERSE CURVE

When viewed from occlusal outline of class II cavity particularly in maxillary teeth the proximal contact lies toward buccal surface whereas groove line occurs in the central portion of occlusal table.This disparity necessitated occlusal outline with Reverse curve

Advantages

It preserves the triangular ridge of cusp
Facilitates formation of 90 degree angle b/w proximal wall & tangent of proximal surface

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Proximal outline form

The objectives for extension of proximal margins are to:
Include all caries, faults, or existing restorative material.
Create 90-degree cavosurface margins (i.e., butt joint margins).
Establish (ideally) not more than 0.5 mm clearance with the adjacent proximal surface facially, lingually, and gingivally

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Buccal and lingual cavity margins should have 90 degree angles,(Wright and Yettram,1978)since the edge strength of amalgam is reduced when marginal angle is less than 90 degree.

(Wright KW,Yettram AL (1978). Finite element stress analysis of a class I amalgam restoration subjected to setting and thermal expansion. J Dent Res 57:715-723)

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Isolation of the proximal enamel by giving the proximal ditch cut.

The 0.8-mm diameter bur end will cut approx

0.5 to 0.6 mm into dentin and 0.2 to 0.3 mm into enamel.

The ditch is extended gingivally just beyond the caries or the proximal contact, whichever is greater.

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When extension places the gingival margin in cementum, the initial pulpal depth of the axiogingival line angle should be 0.7 to 0.8 mm (the diameter of the tip end of the No. 245 bur is 0.8 mm).

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Ideally the gingival margin should clear the adjacent tooth by only 0.5mm ,which may be measured with the side of explorer.
The diameter of the tine of a No.23 explorer is 0.5 mm,one-fourth inch(6.3 mm) from the tip

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The axial wall should follow the faciolingual contour of the proximal surface and the DEJ.

According to Mahler(1958) ,the restorations placed in cavities with sloping axial walls and a flat pulpal floor developed 30% lower tensile stress at the occlusal surface when subjected to two point occlusal loading,compared to restorations placed in cavities with vertical axial walls

(Mahler DB(1958),An analysis of stresses in a dental amalgam restoration.

Jdent Res 37:516-526)

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GINGIVAL SEAT:-

It is extended beyond the contact area or up to the proximal lesion whichever is more. This also help in providing a contact clearance gingivally.

It is made flat so that the masticatory forces are distributed equally.

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The width of gingival seat- 0.6-0.8mm(premolars)

0.8-1.0mm(molars)

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The proximal ditch cut may be diverged gingivally to ensure that the faciolingual dimension at the gingival is greater than at the occlusal.

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This gingival divergence :

Increases the retention form .
Provides desirable extension of the facial and lingual proximal margins to include defective tooth structure or old restorative material at the gingival level.
Conserve the marginal ridge strength.
Provides 90-degree amalgam

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In completing the proximal extensions, next make two cuts, one starting at the facial limit of the proximal ditch and the other starting at the lingual limit,

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The side of the bur may emerge slightly through the surface at the level of the gingival floor

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A matrix band may be used around the adjacent tooth to prevent marring its proximal surface.

The isolated enamel, if still in place, may be fractured out with a spoon excavator or by additional movement of the bur.

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This shell of enamel prevent accidental nicking,scarring /other damages to the adjacent tooth

According to study by Qvist V et al, found that proximal surfaces of adjacent teeth were damaged 69% of the time and they were three times likely to become carious as were undamaged surfaces

(Qvist V,Johannessen L, Brunn M. Progression of approximal caries in relation to iatrogenic preparation damage. J Dent Res 1992;71:1370-1373)

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To protect the gingiva and the rubber dam when extending the gingival wall gingivally, a wooden wedge should already be in place

Rounded toothpick wedge Triangular wedge
Indicated in deep gingival extension

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With the enamel hatchet,cleave away any remaining undermined proximal enamel,

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STUDY ON THE EXTENT OF OCCLUSAL WIDTH

Vale experiment(1956)

Vale prepared occluso proximal cavities with different crossing dimensions at the marginal and occlusal ridges with a standard depth.

The teeth were then subjected to measured occlusal loads and then compared with load requirement to split a sound teeth

Percentage loss of fracture resistance of the tooth

Inter cuspal distance	One marginal ridges involved	Two marginal ridges involved	Involving a crossing ridge
1/4	10%	15%	20%
1/3	30%	35%	35%
½	40%	45%	45%

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FINAL TOOTH PREPARATION

Removal of any remaining defective enamel and infected carious dentin

Infected carious dentin is removed ,not affected dentin

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PULP PROTECTION

It is desirable to have approx 2mm bulk beneath the pulp and metallic restoration which may be Dentin, Liner or a Base.

Liner/Base- Mechanical, Chemical, Thermal Pulp protection and act as a barrier that protects the dentin.

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RDT>2mm – varnish/dentin bonding agent
RDT (0.5-2 mm)- Bases
RDT<0.5mm- subbase and base

Reduction in the RDT of preparations increasingly sensitize the pulp to cavity preparation injuries ,cytotoxic injuries from effects of acid etching ,air drying, restorative material. This is probably because of the decreased buffering properties of the dentin to potential sources of injury.

( Interactions between cavity preparation and restoration events and their effects on pulp vitality;Kessiri et al; Internation journal of periodontics&restorative dentistry, Vol 26,No.6,2006)

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SECONDARY RESISTANCE FORM AND RETENTION FORM

Using the gingival margin trimmer to bevel or round the axiopulpal line angle.

Proximal retention locks:

A retention lock is a prepared groove whose length is in a vertical plane
and which is in dentin.

Placed on axiofacial and axiolingual line angles.

Terminate at axiopulpal point angle.

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Prepared with No. 169L bur

There are four characteristics or determinants of proximal locks: (1) position, (2) translation, (3) depth, and (4) occlusogingival orientation

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Position refers to the axiofacial and axiolingual line angles of initial tooth preparation

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Translation refers to the direction of movement of the axis of the bur

Depth refers to the extent of translation (i.e., 0.5 mm at gingival floor level).

Occlusogingival orientation refers to the tilt of the No. 169L bur, which dictates the occlusal height of the lock, given a constant depth.

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Circumferential slots:

Slot is retentive groove in dentin whose length is in horizontal plane

Outhwaite et al introduced

Prepared with No.33^1/2 inverted cone bur
0.2 to 0.5 mm deep inside DEJ
2-3 mm length faciogingivally

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Indicated in tooth with short clinical crown and in cusp that have been reduced 2-3mm for coverage with amalgam

Coves
Coves are used for additional retention in preparation that utilizes pins and slots

Prepared with ¼ bur.

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Pins:
Pin retained restoration defined as any restoration requiring the placement of one or more pins in dentin

A)Cemented
B)Friction locked
C) Self threaded

As a rule one pin per missing axial angle should

be used .

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Amalgapins:

Proposed by Shavel

Depth of 1.5 to 2mm is adequate
Diameter 0.8 to 1mm
Prepared with No.35 inverted cone burs

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PROCEDURE FOR FINISHING EXTERNAL WALLS

There should be no unsupported enamel and marginal irregularities present.

There should be a butt joint relation between the tooth & amalgam

Cavosurface bevel [20°] at the gingival margin can be given by G.M.T , to remove the unsupported enamel rods.

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FINAL PROCEDURES LIKE CLEANING,INSPECTING,SEALING

Cleaning is to free the preparation of visible debris with warm water from syringe and then to remove moisture with a few light surges of air syringe.

Varnishes should be applied on all the preparation walls to prevent the microleakege.

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GLUMA desensitizer can also be used to reduce the postoperative sensitivity.

Disinfection of the preparation walls can be done by s phenol,ethyl alchol (short duration).

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VARIATION IN SINGLE SURFACE PROXIMAL PREPARATION

Mandibular First Premolar
Maxillary First Molar
Maxillary First Premolar
-

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Variation of single proximal surface preparation

1)Mandibular first premolar
The support of the small lingual cusp may be conserved by preparing the occlusal step more at the expense of tooth structure facial to the central groove than lingual.

The lingual cusp may need to be reduced for capping if the lingual margin of the occlusal step extends more than two thirds the distance from the central fissure to the cuspal eminence

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Sloping pulpal floor
When preparing occlusal portion,one tilts the bur slightly linguallly to establish the correct pulpal wall direction.

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2)Maxillary first molar
Extension into the enamel oblique ridge is avoided whenever possible to maintain the cross-splinting strength it provides to the tooth

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Cutting through the oblique ridge is indicated only if:
(1) the ridge is undermined with caries,
(2) it is crossed by a deep fissure, or
(3) occlusal portions of the separate MO and DO outline forms leave less than 0.5 mm of tooth structure between them.

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3)Maxillary first premolar
A Class II preparation involving the mesial surface requires special attention because the mesiofacial embrasure is esthetically prominent.

The facial extension of the mesiofacial proximal wall should be minimal and margins may be placed lingual to the facial contact.

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MODIFICATION IN CAVITY DESIGN

Simple box preparation
Slot preparation for root caries
Rotated teeth
Adjoining restoration
Unusual outline form
Abutment tooth for Removable Partial Denture

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MODIFICATION IN CAVITY DESIGN

1)Simple box preparation
A proximal box that is prepared without occlusal step.

restoring a small, cavitated, proximal lesion in a tooth with neither occlusal fissures nor a previously inserted occlusal restoration

Indicated in narrow proximal contacts

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2)Slot preparation for root caries

When caries is present in the proximal aspect without involving the marginal ridge.

Indication
gingival recession having root surface caries gingival to the proximal aspect.
When the adjacent tooth is missing.

Preparation for Class II restorations with facial or lingual access are sometimes referred to as Key Hole Preparations.

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3)Rotated teeth

-Preparation follows the same principles as for normally aligned teeth

-If tooth is rotated 90 degrees and the proximal lesion is on the facial or lingual surface, the preparation may require isthmus that includes the cuspal eminence

-If lesion is small, slot preparation should be done

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4)ADJOINING RESTORATIONS

Where the two restorations adjoin, care should be taken that the outline of the second restoration does not weaken the amalgam margin of the first.

The intersecting margins of the two restorations should be at
right angles as much as possible.

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5)UNUSUAL OUTLINE FORM

Usually seen in mandibular third molars having unusual groove pattern.

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6)ABUTMENT TEETH FOR REMOVABLE PARTIAL DENTURE

-if a tooth is an abutment for a R.P.D., the occluso proximal outline form adjacent to the edentulous region need additional extension if a rest seat is planned.
-Rest seat can be prepared in amalgam with encroaching the occlusal margin
-There should be a minimum of 0.5mm of amalgam between rest seat & the margins.

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CLASS II AMALGAM RESTORATION INVOLVING BOTH PROXIMAL SURFACES

A moderate to large sized lesion involving both the proximal boxes in which it becomes imperative to involve the occlusal box for proper accesibility of proximal lesion.

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CUSP CAPPING

The small distal cusp of mandibular first molars, the distolingual cusp of maxillary molars, and the lingual cusp of some mandibular premolars (especially first premolars) may be weakened when normal preparations of surrounding areas of the tooth are included.

This requires capping of these cusps

Cusp capping increases the resistance form of the tooth .

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CONCLUSION

Black’s designs of tooth preparation have been largely replaced by more conservative preparations.

Black’s concept of extention for prevention is now changed to constriction with conviction

Advancement in the field of instrumentation has paved way for a more conservative tooth preparation

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THANK YOU!

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REFERENCES

Sturdevents art and science of operative dentistry-5^th edition

Operative dentistry-modern theory and practice –MA Marzouk

Summitt’s Fundamentals Of Operative Dentistry,A Contemporary Approach-4^th edition

Vimal sikri – 4^th edition

Journal of History of Dentistry-vol 53,No.2,July 2005

Critical Reviews On Oral Biology and Medicine 9(4);469-479(1998)

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-Summit et al,Effect of grooves on resistance form of class 2 amalgams with wide occlusal preparations. Oper dent 1993; 18:42-47

-Larson TD,et al : Effect of prepared cavities on the strength of the teeth ,Oper dent 6:1,1981

-Wright KW,Yettram AL (1978). Finite element stress analysis of a class I amalgam restoration subjected to setting and thermal expansion. J Dent Res 57:715-723

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-Mahler DB(1958),An analysis of stresses in a dental amalgam restoration Jdent Res 37:516-526

-Qvist V,Johannessen L, Brunn M. Progression of approximal caries in relation to iatrogenic preparation damage. J Dent Res 1992;71:1370-1373

-Interactions between cavity preparation and restoration events and their effects on pulp vitality;Kessiri et al; Internation journal of periodontics&restorative dentistry, Vol 26,No.6,2006