FUNDAMENTALS OF CAVITY PREPARATIONS - PowerPoint Presentation

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FUNDAMENTALS OF CAVITY PREPARATIONS

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INDEX

INTRODUCTION

OBJECTIVES OF CAVITY PREPARATION

FACTORS AFFECTING CAVITY PREPARATION

TERMINOLOGY

CLASSIFICATION

PRINCIPLES OF CAVITY PREPARATION

TOOTH PREPARATION-BEYOND G.V.BLACK

CONCLUSION

REFRENCES

ACKNOWLEDGEMENTS

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INTRODUCTION

Knowledge of basic cavity preparation essential

Physiological and psychological aspects of treatment to be considered

Understanding of relationship between restorative material and the cavity design is a prerequisite

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NEED FOR RESTORATIONS

Need to repair a tooth after destruction from a carious lesion

Need to repair a tooth due to destruction from non carious lesions e.g.abrasion,erosion,attrition,abfraction

Replacement or repair of restoration with serious defects e.g..gingival excess,improper contact,poor esthetics

Restore a fractured tooth to proper form and function

Restore congenitally malformed teeth

Enhance esthetics

As preventive measure for caries

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CAVITY PREPARATION

DEFINITION

It is the mechanical alteration of a tooth to receive a restorative material which will return the tooth anatomy to proper form,function and esthetics

OBJECTIVES

Remove all defects and give pulp protection

Locate the margins of restorations as conservatively as possible

Form cavity so that the restoration and tooth doesn’t fracture under masticatory load

Allow for esthetic and functional placement of a restoration

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FACTORS AFFECTING CAVITY PREPARATION

GENERAL

FACTORS

DIAGNOSIS

OCCLUSAL RELATIONSHIPS

ESTHETICS

RELATIONSHIP WITH OTHER TREATMENT PLANS

CARIES RISK

PATIENT

FACTORS

AGE

SOCIO ECONOMIC STATUS

DESIRE FOR HOME CARE

ISOLATION OF OPERATIVE SITE

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GENERAL FACTORS:

Diagnosis: Prior to any restorative procedure, a complete and thorough diagnosis must be made. There will be a reason to place the restoration in cavity such as caries, fractured tooth and esthetic need, etc. An assessment of pulpal and periodontal status will influence the potential treatment of the tooth, especially in terms of choice of restorative material and design of cavity preparation.

Occlusal relationships must be assessed thoroughly since these also affect the choice of restorative material and cavity preparation design.

The patient’s concern for esthetics should be considered.

The relationship of a specific restorative procedure with other treatment plans for the patient must be considered. Design of a restoration may need to be altered for a tooth, which is supposed to act as an abutment for a fixed or removable prosthesis.

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PATIENT FACTORS:

The patient’s knowledge and appreciation of good dental health will influence his/her desire for restorative care and the choice or restorative material.

The patient’s socio-economic status will be a factor in selecting the type of material.

Age of the patient is an important factor. Elderly patients are more prone to root surface caries.

Ability to isolate the operating site is another important consideration.

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TERMINOLOGY

CARIES TERMINOLOGY

location of caries: 1. Primary

2. Secondary

3. Recurrent

4. Pit & Fissure

5. Smooth surface

6. Backward

7. Forward

8. Residual

9. Root surface

10.Radiation caries

extent of caries: 1.Non cavitated

2. Cavitated

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CARIES TERMINOLGY:

Location of caries –

Primary caries: it is the original carious lesion of the tooth. Three types of primary caries are seen. They are: pit and fissure caries, enamel smooth surfaces and root surfaces caries.

Secondary caries: it indicates a carious focus, which is in no relation to the primary focus.

Recurrent caries: ideally it means reoccurring caries. It is caused mostly due to a focus of caries left either intentionally or otherwise under a restoration. It is mostly seen at the junction of the restoration and tooth and usually indicated micro leakage in the restoration.

Pit and fissure caries: caries occurring in the pits and fissures caused due to imperfect coalescence of the developmental lobes. The caries in enamel is minimal but spreads along the DEJ and into the dentine. It is expressed as 2 cones base to base, with apex of the enamel cone towards tooth surface and apex of dentinal cone towards pulp.

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Smooth surface caries: the caries begins, not because of an enamel defect, but due to a surface that is habitually unclean or usually, covered by plaque. Diagrammatically, the cones are apex to base. The enamel cone reverses direction and points towards the DEJ.

Backward caries: when the spread of caries in dentine far exceeds that in enamel, the caries passes along the DEJ from dentine to enamel.

Forward caries: is when the caries cone in enamel is larger or the same size as the dentine cone.

Residual caries: caries that remain in the completed tooth preparation, whether by intention or accident. Such caries is not acceptable if at the DEJ or on prepared tooth wall.

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Root surface caries: occurs on root surfaces exposed to the oral environment. It is generally more rapid than other forms of caries. Its prevalence is increasing due to increased retaining of teeth by older patients.

Radiation caries:seen in patients receiving radiation treatment for cancer.caused mostly due to xerostomia.

Occult caries:those caries which are not seen clinically but diagnosed in bite wing or iopa films.mostly a type of backward caries.

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Extent of caries also includes

Incipient

Advanced

Rate of caries

Acute

Chronic

Grooves,fissures,fossae,pits

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Extent of caries –

Incipient (reversible): it is the first evidence of caries activity in enamel. On smooth surfaces it appears as an opaque white lesion, when air-dried. Enamel surface is pretty hard and intact and remineralisation is possible if immediate corrective measures are carried out.

Cavitated (non-reversible): the enamel surface is not intact and usually the lesion has advanced into dentine. Tooth preparation and restoration is indicated.

Rate of caries –

Acute caries (rampant): it is seen when the disease is rapid in damaging the tooth. It is observed in the form of soft, light coloured lesions and is infectious. Lesser time for extrinsic pigmentation explains the lighter discolouration.

Chronic caries: it is a slowly progressive lesion. The lesion is discoloured and fairly hard. Arrested caries is typically open to debridement, dark and hard in nature. The dentine is sclerotic or eburnated in nature

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Groove: a complete union of enamel lobes results in a groove on the enamel surface.

Fissure: an incomplete union of the lobes causes a fissure, which acts as a trap for plaque and other elements that can cause caries.

Fossa: is a junction of two or more lobes of enamel and is usually restricted to a small area.

Pit: incomplete union of lobes results in a pit formation.

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NON CARIES TERMINOLOGY

Abrasion

Erosion

Abfraction

Attrition

Fractures: 1. Incomplete

2. Complete

(no pulpal involvement)

3. Complete

(pulpal involvement)

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Abrasion - it is the abnormal tooth surface loss resulting from direct frictional forces between teeth and external objects which maybe caused by faulty tooth brushing, habits like holding a pipe stem, tobacco chewing and vigorous use of toothpicks. It is usually seen as a V-shaped notch on the gingival portion of facial aspect of the tooth.

Erosion – it results in the loss of tooth structure by chemico-mechanical action. It is seen on the lingual surfaces of anterior teeth, mostly caused by habitual regurgitation of gastric products. Also seen on facial aspects due to habitual lemon sucking.

Abfraction – cervical, wedge shaped defects seen due to strong eccentric occlusal forces. Also termed as idiopathic erosion.

Attrition – it is the mechanical wear of the incisal or occlusal surface of teeth as a result of functional or para functional movement of the mandible.

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TOOTH PREPARATION TERMINOLOGY

Simple, Compound, Complex

Tooth Preparation Walls:

1.Internal

2. External

3. Floor

4. Enamel wall

5. Dentinal wall

Tooth Preparation Angles:

1. Line angle

2. Point angle

3. Cavosurface margin

4. Cavosurface angle

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Simple compound and complex cavities – a tooth preparation is termed as simple if only one tooth surface is involved, compound if two surfaces are involved and complex if three or more surfaces are involved.

Abbreviated descriptions of tooth preparations - for brevity in records and communication, the description of tooth preparation is abbreviated by using the first letter, capitalized, of each tooth surface involved. Example: Occlusal preparation is termed ‘O’; mesial and occlusal surface preparation is termed ‘MO’.

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Tooth preparation walls –

Internal wall: it is a prepared surface that does not extend to the external tooth surface. Example: axial wall and pulpal wall.

External wall: it is a prepared surface that extends to the external tooth surface and takes the name of the tooth surface towards which the wall is situated.

Floor: a floor or seat is a prepared wall that is flat and perpendicular to the occlusal forces directed occlusogingivally.

Enamel wall: it is that portion of a prepared external wall consisting of enamel.

Dentinal wall: that portion of a prepared external wall consisting of dentine.

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Tooth preparation angles -

Line angle: it is the junction of two planal surfaces of different orientation along a line. An internal line angle is that whose apex points into the tooth. An external line angle is that whose apex points away from the tooth.

Point angle: it is a junction of three planal surfaces of different orientation.

Cavosurface angle: it is the angle of tooth structure formed by the junction of a prepared cavity wall and the external tooth surface. The actual junction is referred to as the cavosurface margin

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- Dentinoenamel junction, Cementoenamel junction

- Enamel margin strength:

1. Full length enamel rods

2. Buttressing by dentin

Extension for prevention

Enameloplasty

Prophylactic Odontomy

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Dentino enamel junction – it is the junction of the enamel and junction.

Cemento enamel junction – it is the junction of the enamel and the cement and is referred to as the cervical line.

Enamel margin strength – it is an important concept in the principles of tooth preparation. It has 2 features:

It is formed by full-length enamel rods whose inner ends are on sound dentine.

These enamel rods are buttressed on the preparation side by progressively shorter rods whose outer ends are cut off but whose inner ends are on sound dentine.

Because enamel rods are usually perpendicular to the enamel surface the strongest enamel margin results in a cavosurface angle greater than 90 degrees.

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Diagram illustrating ‘Tooth Preparation Terminology’

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CAVITY CLASSIFICATION-by Dr. G. V. Black

Class I:

Occlusal surfaces of premolars & molars

Lingual surfaces of maxillary incisors

Occlusal 2/3

rd

’s of facial & lingual surfaces of molars

Class II:

Proximal surfaces of premolars & molars

Class III:

Proximal surfaces of anterior teeth not involving incisal angle

Class IV:

Proximal surfaces of anterior teeth involving incisal angle

Class V:

Gingival third of facial or lingual surfaces of all teeth

Class VI:

incisal edge of anterior teeth or occlusal cusp tips of posterior teeth

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Some areas in which caries occur have been overlooked.

These are:

Lesions at line angles of different teeth

Lesions on labial surfaces of anterior teeth other than cervical 1/3

rd

and pits

Lesions on lingual surfaces of anterior teeth other than cervical 1/3 and pits

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BASIC PRINCIPLES OF CAVITY PREPARATIONS

INITIAL CAVITY PREPARATION

Outline form

Resistance form

Retention form

Convenience form

FINAL CAVITY PREPARATION

Removal of infected dentine, old restorative material

Pulp protection

Secondary resistance & retention form

Finishing external walls

Cleaning, inspecting & conditioning the cavity

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ESTABLISHING OUTLINE FORM

DEFINITION

Establishing outline form means placing the cavity margins in the position they will occupy in the final preparation except for finishing enamel walls and margins and preparing an initial depth of 0.2-0.8mm pulpally of DEJ or normal root surface position

PRINCIPLES

All friable or weakened enamel should be removed

All faults should be included

All margins should be placed so as to afford good finishing of the margins of the restoration

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FEATURES

:

Preserving cuspal strength

Preserving marginal ridge strength

Minimizing facio-lingual extension

Using enameloplasty

Connecting two close faults(less than 0.5mm apart)or cavity preparations

Restricting the depth into dentin to 0.2mm for pit and fissure caries

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TECHNIQUE FOR CLASS I CAVITY PREPARATION

A no. 245 carbide bur with head length 3mm and width 0.8mm is used

Outline of the bur is divergent endwise hence gives a slight convergence to the preparation which is desired

Rounded corners of the burs also provide rounded internal line angles which is desired

A no. 330 carbide bur is also used in some conservative preparations

Cutting is begun by entering deepest pit with punch cut with bur oriented parallel to long axis of tooth

Depth of 1.5-2mm is desired ie.half the bur length

Extension distally in marginal ridge area indicates slight tilting of the bur distally to create occlusal divergence thus preventing undermining of enamel

Include all fissures that radiate from the pit

Maintaining bur depth will result in a flat pulpal floor

Width of cavity ideally should be 1/4

th

of intercuspal distance

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Illustration showing ideal punch cut depth

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CLASS I CAVITY

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TECHNIQUE FOR CLASS II CAVITY PREPARATION

Outline form for occlusal portion is the same as that for a class I preparation

For a MO cavity preparation distal pit area is prepared and extensions made to include disto facial and disto lingual fissures to get a dovetail form

Before extending into the involved proximal portion,anticipate the final positions of the facial and lingual walls relative to the contact area

Extend the preparation stopping 0.8mm short of the adjoining marginal ridge

With same bur orientation,next to the marginal ridge make a ditch gingivally along exposed DEJ 2/3rds at the expense of dentin and 1/3

rd

at the expense of enamel

Pressure is directed gingivally and towards enamel moving the bur facially and lingually

Ditch cut is extended till just beyond caries or contact width,whichever is greater

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The proximal ditch is diverged gingivally to provide retention form and also to conserve the marginal ridge while extending the margins facially and lingually

Two cuts are made at each limit perpendicular to the proximal surface in order to remove the remaining tooth structure proximally.very often the wall breaks on its own.

Hand cutting instruments are then used to cleave away undermined proximal enamel,giving proper direction to the proximal walls and cavosurface angle of 90 degrees

Margins should clear the adjacent tooth by 0.2-0.3mm

For a maxillary molar,viewed occlusally,the mesiofacial enamel wall is placed parallel to enamel rod direction thus obtaining a REVERSE CURVE in the outline

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CLASS II CAVITY PREPARATION – OCCLUSAL VIEW

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CLASS II CAVITY

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TECHNIQUE FOR CLASS III CAVITY PREPARATION

Consider a cavity preparation on the distal surface of a mandibular canine

Enter the tooth with a no2 round bur on distolingual marginal ridge,with long axis of bur perpendicular to the lingual surface of the tooth

Pulpal depth of 0.5 –0.6mm pulpally of DEJ is recommended (0.75mm when in cementum)

Facial margin is extended 0.2-0.3mm into facial embrasure keeping a curved outline from incisal to gingival so as to have inconspicuous margin

Lingual margins should blend with the incisal and gingival margins in smooth curves with cavosurface angles being 90 degrees at all margins

The lingual wall meets axial wall at obtuse angle

Axial wall should follow the external tooth surface

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CLASS III CAVITY

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TECHNIQUE FOR CLASS V CAVITY PREPARATION

A tapered fissure bur is used to enter the lesion to have pulpal depth of 0.5mm from DEJ to 0.25mm from cementum

Burs alignment is such that it is kept perpendicular to external tooth surface at all times thus parallel to the enamel rods

Extensions made on all sides to have pulpal depth of 0.75mm at gingival wall and 1.25mm at the incisal wall

Axial wall follows the contour of the facial surface of tooth mesiodistally and thus is convex mesiodistally

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CLASS V CAVITY

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OUTLINE FORM FOR A CLASS II GOLD INLAY

The outline form is similar to that for an amalgam restoration with few differences

Punch cut with no271 bur to about 1.75 –2mm initially to establish depth of the cavity

A general rule is to maintain long axis of the bur parallel to long axis of the tooth

In case of mandibular posteriors,bur is angled 5-10 degrees lingually to maintain the lingual cusps

A divergent taper of 2-5 degrees is given.width of taper should be a third of buccolingual dimension

Care should be taken not to keep any undercuts in the cavity preparation

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CLASS II INLAY PREPARATION

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ENAMELOPLASTY

It refers to eliminating the developmental fault by opening it using the side of a flame shaped diamond stone leaving a smooth surface(a saucer shaped area)

If 1/3

rd

or less of the enamel depth is involved in a fissure,only then is enameloplasty indicated

It does not extend the outline form

Restorative material is not placed in the recontoured area

Procedure also applicable to supplemental grooves on cuspal inclines

Also indicated when a shallow fissure approaches or crosses a lingual or facial ridge

Surface left by enameloplasty should meet cavity preparation in a cavosurface angle of no more than 100 degrees,producing an amalgam margin of 80 degrees,no less

During carving of the amalgam, no restorative material should be left in the recontoured area

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ESTABLISHING RESISTANCE FORM

DEFINITION

It is defined as that shape and placement of the restoration walls that best enable both the restoration and the tooth to withstand,without fracture,masticatory forces delivered principally along the long axis of the tooth

PRINCIPLES

Obtain a box shape with a relatively flat floor

Restrict the extension of internal walls to allow for strong ridges and cusps with sufficient dentin support

Slightly round the internal line angles

Slide47

Provide for enough thickness of the restorative material to prevent its fracture under load(1.5mm for amalgam,1-2mm for cast metal)

Weak cusps should be capped or enveloped to prevent its fracture

The material should be bonded to tooth structure whenever possible

CUSP REDUCTION

Cusp reduction should be considered when outline form extends more than half distance from groove to tip of cusp

It is mandatory if the outline extends more than 2/3rds the distance from groove to cusp tip

Exception is when the operator judges the cusp support to be adequate and if a bonded restoration is to be used

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ESTABLISHING RETENTION FORM

DEFINITION

It is that shape or form of the prepared cavity that resists displacement or removal of restoration from tipping or lifting forces

For amalgam restorations,retention is achieved by maintaining an occlusal convergence and a dovetail retention pattern

In class III,IV and V cavities,retention is provide by accentuating the internal line angles,although actual retention is provide by secondary retention features

For an inlay preparation,cavity design is very important.

1. The correct taper of 2-5 degrees should be maintained

2. Line angles should be well defined

3. Occlusal dovetail is a must to resist lateral displacement

4. Keep pulpal and cervical floors perpendicular to line of forces

5. The luting cement also affords some amount of retention

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Differences in Retention form for Class II amalgam v/s Class II inlay preparation.

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FACTORS AFFECTING RETENTION

Magnitude of dislodging forces

Geometry of tooth preparation ie taper,surface area,stress concentration,type of preparation

Roughness of the surfaces being cemented

Materials being cemented

Type of luting agent

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ESTABLISHING CONVENIENCE FORM

DEFINITION

It is that form or shape of the cavity that provides for adequate observation,accessibility and ease of operation in preparing and restoring a cavity

For amalgam restorations,an ideal cavity preparation already provides for convenience form.To check for convenience,one should be able to reach all line angles of the cavity with a round condenser.

In inlay preparations,the cavity should provide access for disking the margins and to allow proper adaptation of the restoration

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REMOVAL OF ENAMEL PIT/FISSURE,INFECTED DENTIN,RESTORATIVE MATERIAL

On achieving an ideal cavity depth,if some amount of enamel remains,it is removed locally without lowering the entire pulpal floor

In removing infected dentin,the scooping should stop when a relatively hard but discolored surface is obtained.this is called affected dentin and can be left in the preparation

In case of removing old restorative material,following factors are to be considered:

If old material negatively affects the esthetics of new restoration

If old material will compromise the amount of retention needed by the new restoration

If radiographic evidence of recurrent caries is seen

If pulp was symptomatic pre operatively

If periphery of old material is not intact

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Hand instruments like spoon excavators and rotary instruments can also be used.

Ideally a technique that has minimal heat and pressure and which affords good instrument control should be used.

Use of round carbide bur in high speed hand piece used at stall speed with air cooling is considered the best technique

In large preparations with extensive soft caries,removal may be done in initial cavity preparation itself so that an assessment of type of treatment can be made

Slide54

CARIES CONTROL TECHNIQUE

This procedure is useful when numerous teeth with extensive caries are involved.

It also finds use in quadrant dentistry.

In the 1

st

appt,all caries is removed including all infected dentin and then temporary restorations are placed.

Then in the following appts,each tooth is individually assessed and treated accordingly.

This procedure is useful in stopping the progress of caries.

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PULP PROTECTION

Metallic restorations can cause thermal sensitivity while drinking hot and cold foods or beverages.Other restorations can cause chemical irritation also.This calls for the use of certain materials to protect the pulp against insult.

Pulpal irritants are as follows:

Some ingredients of various materials

Thermal changes conducted through restorations

Forces transmitted from restoration through dentin

Galvanic shock

Ingress of noxious products and bacteria through micro leakages

FUNCTIONS OF PULP PROTECTING AGENTS

Thermal insulation

Chemical insulation

Sealing against interfacial leakages

Also ,in some cases,caries prevention properties

Slide56

CAVITY VARNISH

It is a solution of one or more resins,which when applied to cavity walls,evaporates leaving a thin film which acts as a barrier between restoration and the dentinal tubules

Varnishes are composed of natural gums(copal,resin)which are dissolved in organic solvents such as ether,chloroform or acetone etc.

They form a coating on tooth by evaporation and effectively seal the dentinal tubules thus protecting the pulp from ingress of noxious products.

Usually applied in 2 coats in order to ensure proper wetting of cavity walls.It is done with the help of cotton pellet or a thin brush.

Use of varnish is contraindicated in adhesive restorations.

Slide57

CAVITY LINERS

A liner is used like a cavity varnish to provide a barrier against the passage of irritants from cements or other restorative materials and to reduce the sensitivity of freshly cut dentin.

Liners are placed in a thin layer(maximum allowed is 0.5mm)

The material used most often is CALCIUM HYDROXIDE.

The high pH of the material also acts to neutralize the acid content in the base thus offering additional pulpal protection.

The function of liners is also extended to include maintaining adhesion at tooth restoration interface.e.g..Glass Ionomer Cement(Fuji lining LC)

Other materials used as liners are reinforced Zinc Oxide Eugenol cement(IRM).

Slide58

BASE

It is a layer of cement placed under the permanent restoration to encourage recovery of injured pulp and to protect it against numerous types of insult,be it thermal,mechanical,chemical or galvanic.

HIGH STRENGTH BASES are used to provide mechanical support primarily.They have high compressive strength.

E.g..Zinc Phosphate,Zinc Polycarboxylate,Glass Ionomer Cement and Reinforced Zinc Oxide Eugenol Cement.

LOW STENGTH BASES are also used but have low compressive strength.used mainly to provide chemical insulation.

E.g. Calcium Hydroxide,Zinc Oxide Eugenol Cement.

Slide59

A cavity of ideal depth does not require a liner or base

If excavation is very close to the pulp,calcium hydroxide cement is indicated, to stimulate reparative dentin

In moderately deep carious excavations(dentin thickness 1mm or more)a thin layer(0.5mm) of Zinc Oxide cement is applied.it acts as an insulator and as an obtundent

Conventional theory advises the use of a Zinc Phosphate or other cements in thickness varying from 0.2 to 0.5mm on the pulpal floor.

RULES TO FOLLOW

There should be at least 2mm of either dentin,liner or base between pulp and restoration

In composite restorations,a Calcium hydroxide liner is indicated only if the cavity floor is within 0.5mm from the pulp

Slide60

SECONDARY RESISTANCE & RETENTION FORMS

The types of secondary resistance & retention forms are:

Retention locks

Grooves

Coves

Groove extensions

Skirts

Beveled enamel margins

Pins & Amalgam Pins

Slots

In case of composite restorations:

Beveling of enamel margins

Etching of enamel walls

Dentine treatment

For many complex & compound restorations, the presence of additional resistance & retention forms are needed. It is usually done after application of base or liner.

Slide61

RETENTION LOCKS

Used mainly in classII restorations to provide additional retention to proximal portion of the restoration.

These are made with a small taper or round bur and drawn on the axiofacial or axiolingual line angles gingivo occlusally.

GROOVES

They are linear horizontal undercuts prepared prepared mainly in classIII or IV cavities and in root surface cavities

COVES

They are undercuts placed at point angles mostly and are used as additional retentive features in classIV or V cavities.

GROOVE EXTENSIONS

Includes involving the facial or lingual grooves in order to add vertical walls to the cavity preparation hence aiding retention.

Done mainly on molar teeth for cast restorations.

Slide62

SKIRTS

Used mainly in cast restorations

Skirts extend the preparation around some if not all the line angles of the tooth.

They provide additional retention by providing additional vertical walls.

They also aid in resistance form of the tooth.

BEVELED ENAMEL MARGINS

Used in cast restorations and composite restorations.

They may slightly aid in retention but major use I to provide better junction between tooth and restoration.

In composite restorations,they aid retention by providing more enamel surface for etching and bonding.

ETCHING OF ENAMEL WALLS

Used in composite and porcelain restorations.also in cases of bonded amalgam restorations.results in a roughened surface to which the bonding material is mechanically interlocked.

Slide63

CLASS II CAVITY

Proximal locks: axiofacial and axiolingual line angles

Slots: gingival floor in case of wide proximal box

Pot holes:gingival floor or pulpal floor

CLASS II INLAY CAVITY

Slots ,potholes and skirts are used in extensive restorations and when capping is indicated.

CLASS III CAVITY

Resistance form is provide by

90 degree marginal angle

Sufficient bulk of amalgam

No sharp line angles

Retention form is provided by

Gingival retention groove

Incisal retention cove

Lingual dovetail

Slide64

CLASS V CAVITY

Using no ¼ round bur and placing 2 retention grooves,one directed depth wise most occlusally and one most gingivally at gingivoaxially line angle increases the retention

Placing 4 retention coves at 4point angles is another conservative alternative.

Angle former or no.33 ½ bur can also be used to form retentive grooves.

For larger cavities,retention grooves can be placed circumferentially

Dentin and enamel adhesive systems can further increase resistance and retention.

Slide65

PROCEDURES FOR FINISHING EXTERIOR WALLS

DEFINITION:

Finishing the preparation walls is the further development, when indicated, of a specific cavosurface design and degree of smoothness or roughness that produces maximum effectiveness of the restorative materials being used.

OBJECTIVES:

To create the best possible marginal seal

Afford a smooth junctional margin

Provide maximum strength to both, tooth and restoration

Slide66

FACTORS TO BE CONSIDERED:

Direction of enamel rods

Support of enamel rods, both at DEJ & preparation side

Type of restorative material used

Location of margin

Degree of smoothness or roughness desired

For cast metal restorations, smooth walls are required.

Composite restorations require rough surface.

For amalgam, walls are not required to be as smooth as that for cast restorations.

Slide67

BEVELS & FLARES

DEFINITION:

A bevel is any abrupt incline between the two surfaces or between cavity walls and cavosurface margins in prepared cavity.

FUNCTIONS:

Strong enamel margin of 140-150 degree is created.

Weak enamel is removed.

It results in 30-40 degrees marginal metal that is burnishable.

Bevels reduce the error factor (of space between cast & tooth substance) by 3 or more folds at the margins.

Provides a lap sliding fit (at gingival margin).

Indirect improvisation of retention form.

Slide68

PRIMARY FLARE:

Similar to a long bevel formed of an enamel and part of dentine on facial and lingual proximal wall. It has 45 degree angulation to the inner dentine wall proper.

SECONDARY FLARE:

It is a flat plane superimposed peripherally to a primary flare usually prepared solely in enamel but may involve dentine.

FUNCTIONS:

Creates needed obtuse angulation of marginal tooth structure.

Extends margins into embrasures so that they become self-cleansing.

Results in a burnishable 30-40 degrees marginal metal.

Useful in avoiding over-cutting in proximal region.

Removes unsupported inner enamel.

Slide69

CLASS II INLAY PREPARATION(showing bevels and flares)

Slide70

CLEANING, INSPECTING & SEALING

Cleaning of the cavity is usually done by directing warm water from the syringe followed by removing moisture with a gentle stream of air.

For amalgam, apply two layers of varnish with the help of a cotton pellet or a small brush. This reduces micro-leakage.

For composite restorations, etching of the preparation and placing a dentine bonding agent is required.

Slide71

STERILISING THE CAVITY

Previously various agents like Phenols, Ethyl Alcohol and Silver Nitrate were used. Now their use is debated due to their effect on pulp.

Modern practice indicates the use of dentine bonding agents and/or sealers universally in order to eliminate bacterial penetration into dentine.

Slide72

CHANGES IN OPERATIVE DENTISTRY – BEYOND G.V.BLACK

Over a 100 years have passed since G.V. Black formulated his classification.

His classification was based mainly on the type of restorative material used.

Since then there has been considerable progress in the understanding of the carious process and also in the type of materials used.

The advent of adhesives in dentistry has resulted in a change in cavity preparation.

Hence it only seems logical to change or modify the classification to suit the needs of the newer materials.

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A newer classification, referenced from Mount & Hume, has been designed to recognize carious lesions at different stages.

It can be used successfully for replacement dentistry as well as minimal intervention dentistry.

A cavity, if left untreated, is likely to progress from the early stage (at which it can be re-mineralized) to the point at which the tooth is badly broken down.

These stages should be identified and recorded because methods of treatment and material used are likely to vary.

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CLASSIFICATION BY MOUNT & HUME

Size

No Cavity

Minimal

Moderate

Enlarged

Extensive

Site

0

1

2

3

4

Pit/Fissure

1

1.0

1.1

1.2

1.3

1.4

Contact

Area

2

2.0

2.1

2.2

2.3

2.4

Cervical Area

3

3.0

3.1

3.2

3.3

3.4

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Lesion site:

Site 1 – pits and fissures on occlusal surface of posterior teeth and other defects on otherwise smooth enamel surfaces.

Site 2 – contact areas between two teeth, anterior or posterior.

Site 3 – cervical areas related to gingival tissues, including exposed root surfaces.

Lesion size:

Size 0 – initial lesion, no surface cavitation, re-mineralization possible.

Size 1 – smallest minimal lesion requiring operative intervention.

Size 2 – moderate sized cavity, sufficient sound tooth structure remaining.

Size 3 – cavity needs ot be modified and enlarged for protecting the remaining crown against occlusal load.

Size 4 – extensive cavity, loss of cusp from posterior tooth or incisal edge from an anterior tooth.

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SALIENT FEATURES OF THE CLASSIFICATION

Blacks classification just provided the site of the cavity or lesion,whereas this also provides for the lesion size.

Blacks classification is based on amalgam as the restorative material and since it requires bulk for success,it cannot record an incipient lesion,which the newer classification has provided for.

The Mount and Hume classification also provides for teeth involved in trauma.e.g. an incisal angle fracture of anterior teeth is assigned no. 2.4 according to this classification.

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CONCLUSION

The only real constant in life is change, and dentistry is no exception. In the past 100 years there has been considerable change in methods for caries control; be it equipment, techniques or materials, but in spite of all this, there has been one constant in this profession – the G.V. Black system of classification.

While there was no valid reason or justification for change in the first 75 years, the advance of long-term adhesion and now, bio active restorative materials, offers a serious challenge to the profession and opens the way for change.

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THANK YOU