Cavity preparation for dental

amalgam – part II

D-r I. Dimitrova

Main topics

II class cavity preparation – indications, basic design.

Characterization of basic cavity configuration.

Instruments and preparation techniques.

II class cavity preparation - indications

Class II cavities are the cavities essentially on the proximal surface of posterior teeth. These may be mesial, distal, mesio-occlusal (MO), disto-occlusal (DO), and mesio-occluso-distal (MOD) cavities in posterior teeth.

Caries lesion may be present in a proximal surface/mesial or distal/ of a molar or premolar.

Caries lesion may also be present in a proximal, involvingalso a occlusal surface of a molar or premolar.

Class II preparations involving only one or the two proximal surfaces.

II class cavity - basic components and functions

Proximal part - curative, preventive (against secondary caries and parodontopathologies) and static functions

Occlusal part - provides cavity retention, treatment and dental caries prophylaxis

Isthmus - the junction between the occlusal part and the proximal part, important for the obturation

strength

Proximal part of II class cavity - main components

Cavosurface margins - buccal, lingual and gingival floor margin

External walls - buccal, lingual and gingival floor

Internal wall - axial

Internal line angles - bucco-gingival, gingivo-lingual

Internal point angles -

bucco-axio gingival and linguo-axio

gingival

General characteristics of proximal part of II class cavity - main components

The buccal and lingual proximal margins are localized:

In the contact point in caries resistant patients;

Outside the contact point in carries active patients

Proximal part - cavosurface margins

The angle between

proximal buccal and

lingual cavosurface is

90°.

General characteristics of proximal part of cavity configuration – occlusal view

The following configurations can be viewed from the occlusal area:

Rectangular - within contact point

Trapezoid - Buccal and lingual proximal margins are outside of the contact point area

S shaped form - Buccal and lingual margins create S shaped curve from proximal surface to occlusal part of cavity

Proximal part configuration – proximal view

Trapezoid shape - buccal and lingual walls converge occlusally

Prismatic shape - buccal and lingual walls are paralell to longitudinal axis and between each other

Proximal part – gingival floor

The gingival floor of the proximal preparation may be flat and approximately perpendicular to the long axis of the tooth, or it may be curved and/or slanted.

The location of the gingival floor, therefore, should be determined by the gingival extent of the carious lesion.

Mesio-distal size of gingival floor is 1,5 mm minimal.

Proximal part – gingival floor

Parallel to the occlusal plane

Concave apically

Configuration in mesio-distal direction:

Flat and parallel to the occlusal plane

Tilted to the pulp

Tilted proximally – the most unfavourable for the statics of the

obturation. Solutions – leveling of ½or 1/3 of pulpal part of the gingival floor or groove dentin retention

Configuration in bucco-lingual direction:

Configuration of gingival floor in mesio-distal direction

Configuration in mesio-distal direction-flat and parallel to the occlusal plane - the best configuration

Tilted proximally – the most unfavourable

Configuration of gingival floor in mesio-distal direction

Configuration in mesio-distal direction

Tilted to the pulp

Proximal part – axial wall and internal angles

Axial wall - it is located between the gingival floor and the axial –pulpal margin

Flat, concave or convex

Internal angles are rounded

II class cavity form - occlusal part Retention types

The cavity consists of two parts: occlusal and prroximal

There are two configurations depending on the caries location: Mesio-occlusal or Disto-occlusal

The cavity consists of three parts: occlusal, mesial and distal

Occlusal part has a retention function.

Retention types:

- complete or partial fissures extension

- dovetail

- enamel-dentin retention grooves

- mesio-occlusal-distal retention

II class cavity - occlusal partDovetail retention with 3 parts:

1. area of the cups,

2. area of the triangular fossa,

3. and isthmus area.

The buccal-lingual size of the retention:

- is greater in the area of the triangular fossa

than the buccal-lingual size in the area of the

cups, but smaller than buccal-lingual size in the

isthmus area

II class cavity form - occlusal part-retention types

Retention types:

1. Partial or

2. Complete fissure extention

II class cavity form - occlusal part Retention type – complete extension

Occlusal fissures complete extention is performed in molars.

The cutting of oblique ridge is indicated only in following conditions:

- Ridge is undermined with caries,

- Ridge is crossed by a very deep carious fissure,

- When the caries lesion involves the whole central fissure.

The retention has the biggest buccal-lingual size in the isthmus and the minimal depth of 2 mm.

II class cavity form-occlusal part Retention type - partial

Partial fissure extension is indicated in caries resistant patients with good oral hygiene.

Partial fissure extension is performed to the first oblique ridge.

The retention has the biggest buccal-lingual size in the isthmus and the minimal depth of 2 mm.

II class cavity form-occlusal partRetention type – mesio-occluso- distal

Mesio-occluso-distal (MOD) cavity with two proximal caries lessions, involving two occlusal surfaces.

Characteristics of MOD cavity: Buccal-lingual size of occlusal part

is ½ of inter cuspals distance at 2 mm depth.

II class cavity form - occlusal partRetention type

Dentin retention groove-in buccal, lingual and gingival walls. Starts at 0,5 mm from the gingival floor. The bur is moved occlusally until it reaches 1,5 mm to occlusal dentin-enamel junction.

II class cavity – basic configurations

Box form

Conventional form

Conservative form

Proximal-buccal, respectively proximal –lingual form

Proximal - occlusal - buccal or lingual form

Tunnel cavity form

II class cavity – box form. Indication

Small proximal caries lesion, not involving the occlusal surface.

The decay is restricted to proximal surface without the corresponding occlusal marginal ridges.

On the proximal surface of premolars or molars.

Small proximal caries lesion in contact point area below at least 2 mm from the occlusal marginal ridge, without undermining the corresponding marginal ridge.

Direct access to lesion – through adjacent carious lesion, missing tooth, or diastema, or rotation of the affected tooth.

Box form - main elements

External walls: occlusal, buccal, lingual and gingival floor

Internal wall – axial

Cavosurface margins: occlusal, buccal, lingual and gingival

Box form - location cavosurface margins

Occlusal margin is located at least 2mm away from occlusal marginal ridge and is parallel or convex to its occlusaly.

Buccal and lingual margins do not reach the axial crown margins.

Gingival margin is located supragingival, subgingival or at gingival level.

Box form - resistance and retention form

Resistance form - outline follows the direction of enamel rods. Cementum should be removed, as it can not be part of cavity wall.The minimal occlusal thickness for amalgam for appropriate resistance to fracture is 2 mm.

Retention form - dentin retention- groove

Preparation of a box form

Gain access - using a round bur with axial pressure and removing infected tissues.

Preparing proximal box only with minimum facial and lingual extensions.

Conservative form of II class cavity -indication

The decay is restricted to the proximal surface only and the occlusal surface is sound.

This form involves primary the proximal surface and very limited part of occlusal surface, but not extending beyond the adjacent triangular fossa

The patient exhibits good oral hygiene and low caries risk.

Conservative form of II class cavity

There are two parts /occlusal and proximal/

with and without a pulpal floor.

The lesions are with a limited size.

Conservative design helps in the preservation of oblique ridge or the transverse ridge.

Conservative form of II class cavity -outline form

This preparation is designed to involve primarily proximal surface and very limited part of the occlusal surface not extending beyond adjacent triangular fossa.

Conservative form of II class cavity – basic elements

Cavosurface margins: Buccal and lingual within dental contact or

outside Gingival floor - depends on the size of carious

lesion Internal axial wall can end in occlusal margin

or has axio-pulpul ridge.

Conservative form of II class cavity -configuration

Conservative form of II class cavity -helps in preservation of obligue ridge or transverse ridge and protects the cuspal strength.

Conservative form of II class cavity -internal anatomy

Converging or parallel buccal and lingual walls

Axial wall - with occlusal or axial-pulpal margin

Resistance and retention form

Dentin retention groove - in buccal, lingual and gingival walls. Starts at 0,5 mm from the gingival floor. The bur is moved occlusally until it reaches 1,5 mm to occlusal dentin-enamel junction.

Preparation of the conservative configuration

Occlusal part - cuts with depth 2mm and buccal-lingual size to 1/3 of untercups distance and does not reach the line connecting two cups.

Preparation of gingival floor is away from approximal surface of the adjacent tooth.

Dentin retention groove - in buccal, lingual and gingival walls. Starts at 0,5 mm from the gingival floor. The bur is moved occlusally until it reaches 1,5 mm to occlusal dentin-enamel junction.

II class cavity conventional configuration- indication

Caries lesion on one or two approximal surfaces in patients with high plaque and caries non resitant.

Lesion with medium or large size undermining the corresponding oclusal-approximal ridge.

II class cavity conventional configuration - main elements

Cavosurface margins of approximal and occlusal part of cavity.

Outer walls of approximal and occlusal part of cavity.

Internal wall – axial: one wall to mesio occlusal cavity or two walls to MOD cavity.

II class cavity conventional configuration - main elements

External margins:

Cavosurface margin of approximal part of cavity:

1. Approximo-buccal

2. Approximo-lingual

3. Gingival floor

Cavosurface margin occlusal part of cavity

1. Buccal

2. Lingual

3. Mesial or distal

Internal margins – one or two axio-pulpal

Internal walls - Axial and pulpal

II class cavity conventional configuration - internal anatomy of proximal part

Buccal and lingual walls from:

Enamel and dentin in one plane to trapezoid form.

Enamel and dentin in two planes to S form.

Gingival floor-enamel and dentin in one or two planes or only dentin when cement removed.

Axial wall is parallel the longitudinal axis of the tooth and/or converges occlusally

Preparation of II class cavity conventional configuration with a occlusal fissure extension

Proximal part - use diamond cylinder bur - at borders between fossa triangularis and central fissure:

Buccal and lingual walls should be parallel.

Gingival floor is straight.

Preparation occlusal part:

Buccal and lingual wall at 1/3 to ½ of intercupspal

distance should be parallel at cups.

Cuts around the cups are symmetrical.

Proximal - buccal or lingual form II class cavity - indication

Small to medium sized proximal lesion is localized appically to contact area with intact marginal ridge and contact point.

Patients with good oral hygine.

Occlusal proximal marginal ridge is intact with significant volume of sound tissue.

Approximal - buccal or lingual form II class cavity-configurations

Two configurations: With one or two chambers.

With one or two axial walls.

One chamber – with a box or trapezoid shape at small carious lesions.

Two chambers - have approximal and buccal parts with two axial walls; cutting of axial ridge, leading to decrease of mechanical strength. Use dentin grooves.

One chamber

Proximal-buccal or lingual form II class cavity - main elements and localization

Main elements

Cavosurfaces margins:

Occlusal, gingival, lingual, mesial or distal

Outer walls:

Occlusal, gingival, lingual, mesial or distal

Internal walls

One axial or two axial walls at two chambers configuration

Internal anatomy

One chamber has 3 outer walls - оcclusal,lingual and gingival floor.

Proximal-buccal or lingual form II class cavity - preparation

Entering from buccal area in the enamel of axial margin.

Distal cavity margin is outlined parallel to the longitudinal tooth axis.

Proximal-buccal/lingual-occlusal II class cavity - indication

At one or two proximal large lesions, with affected adjacent axial ridge from the tooth crown, with destruction of parts of buccal or lingual surface as wells as cups destruction.

Cups could be completely missing.

Proximal-buccal/lingual-occlusal II class cavity - location

It has 3 parts - proximal-buccal, occlusal and slot retention.

Slot retention includes axial reduction of anatomical structures.

Lingual margin of the proximal-buccal part is in the lingual interdental surface.

Distal margin is in the buccal surface and is parallel with the longitudinal dental axis.

Gingival margin - not in contact with proximal surface.

Slot retention - between the two lingual cups.

Approximal-buccal/lingual-occlusal II class cavity - main elements

Cavosurface margins

Proximal part: approxo-lingual, bucco –distal and gingival.

Occlusal part: lingual,buccal, distal

Slot retention: mesial with occlusal and lingual or buccal part, distal with two parts – similar to the mesial but with a gingival ridge.

Outer walls

Proximal part - buccal, lingual, distal and gingival floor.

Occlusal part -lingual, buccal and distal or mesial.

Internal walls

Axial and pulpal.

Approximal-buccal/lingual-occlusal II class cavity - resistance and retention form

Resistance – flat surface prepared in the gingival floor and pulpal floor.

Retention – every part of the cavity to be secured with its own retention, slot retention, double chamber retention.

Tunnel cavity form - indication

Proximal carious lesion at molars and premolars with preserved morphology of the proximal occlusal margin ridge, intact proximal surface, normal tooth position.

Class II tunnel preparation cavity connecting the proximal lession with the occlusal surface. The cutting ofmarginal ridge is avoided and the caries which is presentonly on the proximal surface of the posterior teeth isremoved.

Tunnel cavity form - main elements

Cavosurface margins

Proximal: buccal, lingual, occlusal and gingival

Occlusal: buccal, lingual, medial and distal

Tunnel cavity form - main elements

Walls:

Buccal, lingual, occlusal, pulpal and gingival floor.

Tunnel cavity form - internal anatomy, resistance and retention

Tunnel like cavity is formed

Widening in buccal and lingual direction

Resistance – sufficient volume of dentin

Retention – by the tunnel form