cavity preparation in primary teeth

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Principles of Operative Dentistry in primary

teeth

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ContentsDefinition of operative

dentistryIndication for

operative treatmentRationale of pediatric

treatmentGeneral consideration

regarding pediatric dentistry

Classification of dental caries

Principles of tooth preparation

Various materials used in pediatric restorations

Amalgam RestorationGIC restoration Resin based

compositesComparative studies

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Definition

Art and science of the DIAGNOSIS, TREATMENT, and PROGNOSIS of defects of teeth that do not require full coverage restoration for correction.

Treatment should result in the restoration of proper tooth form, function, and esthetics, while maintaining the physiologic integrity of the teeth in harmonious relationship with the adjacent hard and soft tissues.

All of which should enhance the general health and welfare of the patient

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Indications for Operative TreatmentCaries,Malformed, discolored, non esthetic, or

fractured teeth,Wearing of teeth (attrition, abrasion, etc.)Restoration replacement or repair.

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Basis of pediatric operative dentistry:Maintenance of arch length – preserve primary

teeth

Maintenance of healthy oral environment – transmissible factor

Prevention and relief of pain – conservative procedure

Maintenance and improvement of appearance – smile care

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General considerations for Restoration procedure in children Development status of dentition: Stage of root

development / resorption

Caries experience of the patient: Caries risk assessment based on history

Patient’s oral hygiene

Patient cooperation & parent compliance

Individually tailored treatment plan

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Difference in tooth morphology- Primary tooth is small, bulbous, bell shaped Definite cervical constriction Pulpal outline DEJ Pulp horns are highly placed Thin & uniform thick enamel

Symmetry of caries attack

Proximal decalcification in Cl-II lesions

Need for bitewing radiograph, if contacts are closed

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Consideration for efficient treatment:

Appointments – Single arch treatment

Positive attitude of the dental team

Four handed dentistry

Use euphemisms

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Classification of Cavity Preparation: [Primary & young permanent teeth]G.V. Black’s Classification

Class I – V , Class VI [ Simon’s modification]

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Finn’s modificationClass I: Cavities involving the pit and fissures of the molar

teeth and the buccal and lingual pits of all teeth.

Class II: Cavities involving proximal surface of molar teeth with access established from the occlusal surface

Class III: Cavities involving the proximal surfaces of the anterior teeth which may or may not involve a labial or a lingual extension

Class IV: A restoration of the proximal surface of an anterior tooth which involve the incisal angle

Class V: Cavities present on the cervical third of all teeth, including proximal surface where the marginal ridge is not included in the cavity preparation

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Sturdevant’s Classification: Simple Cavity- One surface

Compound Cavity- Two surfaces

Complex Cavity- + Two surfaces

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Baume’s Classification:

Pit & Fissure Cavities

Smooth Surface Cavities

Mount & Hume Classification:

Extent

SITE Minimal 1

Moderate 2

Enlarged 3

Extensive 4

Pit & Fissure 1

1.1 1.2 1.3 1.4

Contact Area 2

2.1 2.2 2.3 2.4

Cervical 3

3.1 3.2 3.3 3.4

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Conventional Concept of Cavity Preparation :

G.V. Black’s concept – “extension for prevention”

To prevent the recurrence of caries by placing the margins of restoration along self cleansing areas.

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CLASSIFICATION OF TOOTH PREPARATIONAccording to BLACK’S CLASSIFICATION:

1. Class I :- all pits and fissure restoration are class I , and are assigned to three groups.

Restoration on occlusal surface of molars and premolars.

Restoration on occlusal two thirds of the facial and lingual surfaces of molars.

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Restoration on lingual surface of maxillary incisors.

2. Class II :- Restoration on the proximal surfaces of

posterior teeth.

3.Class III :- Restoration on the proximal surfaces of anterior

teeth that do not involve the incisal angles.

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4. Class IV :- Restoration on the proximal surfaces of anterior

teeth that do involve the incisal edges.

5. Class V :-Restoration on the gingival third of the facial or

lingual surfaces of all teeth.

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6. Class VI :- Restoration on the incisal edge of anterior teeth

or the occlusal cusp heights of posterior teeth.

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INITIAL AND FINAL STAGES OF TOOTH PREPARATION

Initial tooth preparation: in this stage, the mechanical alterations of

the tooth extended to sound tooth structure while adhering to a specific , limited pulpal or axial depth.

Final tooth preparation: this stage includes excavating any

remaining ,infected carious dentin,removing old restorative material if indicated,protecting pulp.

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The stages and steps in tooth preparation are as follows:

Initial tooth preparation:-

Step 1. outline form and initial depthStep 2. primary resistance formStep 3. primary retention formStep 4. convenience form

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Final tooth preparation:

Step 5. removal of any remaining infected dentin or old restorative material,if indicated.

Step 6. pulp protection, if indicatedStep 7. secondary resistance and retention

formStep 8. final procedures-cleaning ,

inspecting,sealing.

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OUTLINE FORM AND INITIAL DEPTH

Definition:

it is the placement of the preparation margins in the position they will occupy in the final preparation, except for finishing the enamel walls and margins.it also includes preparing an initial depth of 0.2-0.5 mm pulpally beyond the DEJ.

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PRINCIPLES:

1) Remove all friable or weakened enamel.

2) Include all faults

3) Place margins such that good finishing of the margins of the restoration is possible.

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FACTORS:

Certain factors affect the decision regarding the extent of the outline form . they are:-

Extent of the carious lesion, defect or faulty old restoration.

Esthetic requirements which may affect the choice of the restorative material and modify the cavity design.

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FEATURES:

Generally proper outline form may be established if the following features are incorporated:

1)Preserve cuspal strength.

2)Preserve marginal ridge strength.

3)Minimize faciolingual extension.

4)Use enameloplasty wherever possible.

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5)Connect two close faults or tooth preparation(less than 0.5 mm apart)

6)Restrict the depth of the preparation into dentin to a maximum of 0.2-0.5mm.

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RESTRICTED AND INCREASED EXTENSIONS:

Condition that may warrant consideration of restricted extensions for smooth surface caries are as follows:

i. Proximal contours and root proximity

ii. Esthetic requirements

iii. The use of some tooth preparations for composite restoration.

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Condition that may necessitates increased extensions for smooth surface caries are as follows

i. Mental or physical handicaps

ii. Advanced patient age

iii. Restoration of teeth as partial abutments or as units of splints.

iv. Need to adjust tooth contours.

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STEP 2: PRIMARY RESISTANCE FORM.It may be defined as

” the shape and placement of the preparation wall that best enables the restoration and the tooth to withstand, without fracture, masticatory forces delivered principally in the long axis of the tooth.”

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PRINCIPLES:

• THE FUNDAMENTAL PRINCIPLES INVOLVED IN PRIMARY RESISTANCE FORM ARE AS FOLLOWS:

1. To use box shape or mortise form with relatively flat floors.

2. Restrict the extension of the external walls.

3. To have slightly rounded angles.

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4. To cap weak cusps and envelope or include enough of a weakened tooth with in the restration.

5. To provide enough thickness of restorative material to prevent its fracture under load.

6. To bond the material to tooth structure when appropriate.

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Restorative material minimal thickness

Amalgam 1.5mm

Cast gold 1-2mm

Porcelain 2.0mm

Composite 1-2mm

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FACTORS:

• Certain factors affect the resistance form of the preparation:

1) Amount of occlusal contact

2) Amount of remaining tooth structure

3) Type of restorative material

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FEATURES:

• The following features enhance primary resistance form:

1) Relatively flat floors

2) Box shape

3) Including all weakened tooth structure

4) Preservation of tooth and marginal ridges

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5) Rounded internal line angles

6) Adequate thickness of the restorative material

7) Reduction of cusp for capping when indicated.

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STEP 3. PRIMARY RETENTION FORMIT is

“the shape or form of the conventional preparation that resists displacement or removal of the restoration by tipping or lifting forces.”

PRINCIPLES: the principles of primary retention form varies according to the restorative material used

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For amalgam:1. Occlusal convergence2. Occlusal dovetail

For composite resin:3. Acid etching and bonding4. Enamel bevels

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For cast metal1. Close parallelism of opposing walls with a

slight degree of occlusal divergence.2. Occlusal dovetail

For direct filling gold:1. Elastic compression of dentin during

condensation.

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STEP 4.CONVENIENCE FORM:It is

“ the shape or form of the preparation that provides for adequate observation , and ease of operation in preparing and restoring the tooth.”

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FEATURES:

1. Providing adequate width and lateral extensions for tooth preparation for all restorative materials.

2. Refining line and point angles.

3. Providing proximal clearance from the adjacent tooth.

4. Occlusal divergence for cast gold inlays.

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FINAL TOOTH PREPARATION STAGEWhen the extensions and wall designs have

fulfilled the objectives of initial tooth preparation, the preparation is inspected carefully for other needs.

For most conservative restoration at this stage itself may be complete except for final procedures.

However in case of extensive destruction additional steps required.

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STEP 5.REMOVAL OF ANY REMAINING ENAMEL PIT OR FISSURE,INFECTED DENTIN, OR OLD RESTORATIVE MATERIAL IF INDICATED

the elimination of any infected carious tooth structure or faulty restorative material left in the tooth after initial tooth preparation.

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PRINCIPLES:

The deeper portion of carious dentin may generally exhibit two distinct areas:

1. INFFECTED DENTIN: this is more superficial layer which is soft and leathery.

• High concentration of bacteria and collagen is irreversibly denatured.

• Must be removed.

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2. AFFECTED DENTIN: this is the deeper layer,hard in consistency.

• It does not contain bacteria and is reversibly denatured.

• Therefore this layer must be preserved.

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Removal of any old-restoration is indicated if:

1) It would affect the esthetics of the new restoration

2) It may compromise the retention of new restoration

3) There is evidence of secondary caries

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5) The pulp is symptomatic

6) There is marginal deterioration of the old restoration.

This may be done with a round carbide bur in an airotar handpiece with air water spray at low speed

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STEP6.PULP PROTECTION, IF INDICATED This is actually not a step in tooth preparation

in the strict sense but since it is a step in adapting the preparation for receiving the final restoration it s considered under final tooth preparation.

This step is achieved by the use of cavity varnish,liners,bases or bonding agents.

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The choice of the pulp protection agent is based on:

1)Extent of tooth destruction and proximity of preparation to the pulp.

2) Type of restorative material to be used

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Liners and bases are applied without pressure in exposure areas. It is recommended to have approximately a 1mm thickness of calcium hyroxide over near or actual exposure areas.

The varnish prevents penetration of material into the dentin and helps to prevent micro leakage.

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STEP 7. SECONDARY RESISTANCE AND RETENTION FORM

This step is necessary in case of compound and complex cavity preparation where additional preparational features are required to improve resistance and retention form.

Secondary resistance and retention form features are of two types:

1. Mechanical features2. Conditioning procedures

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1) Mechanical features: these include the following:-

Retention grooves and coves

Groove extention

Skirts

beveled enamel margins

Pins, slots, steps and amalgam pins

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2) conditioning procedures:

These include etching and bonding.

These are employed for bonded restoration like glass ionomers, composite or ceramic restoration.

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STEP 8.FINISHING THE EXTERNAL WALLS OF THE PREPARATION

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

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OBJECTIVES:

1. To allow a smooth marginal junction between the restoration and the tooth.

2. To provide close adaptation between the restoration and the tooth structure so that marginal seal is maintained.

3. To provide maximum strength for both the tooth and the restorative material at and near the margins.

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FACTORS:

Certain factors decide the type of finishing necessary for the external walls:

1) The direction of the enamel walls

2) Support of enamel rods at the DEJ and at preparation side

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3) Choice of the restorative material

4) Location of the margin

5) Degree of smoothness desired.

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FEATURES: this vary according to the type of restorative material employed:

1)design of the cavosurface angle

For amalgam:- cavosurface or butt joint recommended.

For composite:- bevels are indicated.

.

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2)Degree of smoothness or roughness of the wall-

this also vary with the type of restorative material used

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Morphologic considerations for pediatric operative dentistryShape of crown

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Enamel and dentin thickness

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Contact area between primary teeth

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Inclination of enamel rods

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Location of pulp horns

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Class I RestorationsAll pit-and-fissure restorations are Class I,

and they are assigned to three groups, as follows.

Restorations on Occlusal Surface of Premolars and Molars

Restorations on Occlusal Two Thirds of the Facial and Lingual Surfaces of Molars

Restorations on Lingual Surface of Maxillary Incisors.

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AAPD, 2008Dental amalgam is recommended for: 1. Class I restorations in primary and permanent teeth;

2. Class II restorations in primary molars where the preparation does not extend beyond the proximal line angles;

3. Class II restorations in permanent molars and pre- molars;

4. Class V restorations in primary and permanent poste- rior teeth.

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AAPD, 2008Glass ionomers can be recommended as:

1. luting cements; 2. cavity base and liner; 3. Class I, II, III, and V restorations in primary

teeth; 4. Class III and V restorations in permanent teeth in

high risk patients or teeth that cannot be isolated; 5. caries control with:

a. high-risk patients; b. restoration repair; c. ITR; d. ART.

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AAPD,2008 Resin-based composites are indicated for:

1. Class I pit-and-fissure caries where conservative pre- ventive resin restorations are appropriate;

2. Class I caries extending into dentin; 3. Class II restorations in primary teeth that do not ex- tend beyond the

proximal line angles; 4. Class II restorations in permanent teeth that extend approximately

one third to one half the buccolingual intercuspal width of the tooth; 5. Class III, IV, V restorations in primary and permanent teeth; 6. strip crowns in the primary and permanent dentitions.

Contraindications:Resin-based composites are not the restorations of choice in the

following situations: 1. where a tooth cannot be isolated to obtain moisture control; 2. in individuals needing large multiple surface restora- tions in the

posterior primary dentition

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Treatment modalities for Pit and fissure caries

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Prophylactic odontomyRecommended by Hyatt (1923)

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Pit and fissure selants and PRR

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Conventional cavity preparationAmalgam

Primary and permanentComposite restorationsGlass ionomer restoration

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Amalgam restoration in primary dentition

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Outline form: Include all carious pits and fissures

Include deep susceptible pits and fissures

Overdestruction of cusps not acceptable

Isthmus- ¼ to 1/3

Resistance form-Class I- atleast 0.5 mm below DEJ

Flat pupal floor when ever possibleRounded internal line anglesCavo surface margin- 90o

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Cavity preparation for 1st primary molar- amalgamCavity- conservativePreserve central ridgeTry not to enter dentin

untill involvedSlightly convergent

wallsMesial pulp horns

approximating DEJ

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2nd primary molar- MandibularOcclusolingual or occlusobuccal

cavity may be formed

Preserve if possible- separate buccal and lingual restorations

If buccal /lingual extension made- converging occlusally with square external line angles

Extension should be cut 0.5 mm into dentin

Include buccal developmental groove

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2nd maxillary primary molar- amalgamUsually carious attack limited to central pit,

distal pit, mesial pit and grooves seperating them.

Avoid crossing oblique ridge

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Tooth coloured adhesive restorative materials in primary tooth

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Occlusal lesions in enamel only-Incipient cariesIncipient pit & fissure

lesions can be prepared by using a no. 2 small, round or a no.330 bur to carefully remove the carious enamel.

¼, 1/8 or 1/16 size according to the size of carious lesion-

For enameloplasyAir abrasion can also be

used

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Conditioning of enamelGel/liquid etchant placedWashed with air water sprayEnamel dried throughly (moist for acetone

based adhesive)Primer and adhesive placedPlacement of resin based composite:

flowable composite preferred over pit and fissure sealant

Pit in centric occlusion restored with resin based composite

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Occlusal lesion involving superficial to middle third of dentin depth

Preparation design:Outline- extent of lesion

Carious dentin at base of lesion should be visible-convenience form

Underlying enamel can be preserved

Carious dentin removed using round bur and spoon excavator

Sharp line angles avoidedFlat ended fissure burs

contraindicatedDisclosing agents might be used

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Choice of materialGIC- indicated in active lesions Primary focus towards removal of soft cariesFluoride releasing properties consideredMinimal tooth destruction

RMGI or composite resin restorations indicated- Larger lesions

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Conditioning of enamelEnamel should be dried- frosty white

appearenceComplete dehydration of dentin not

recommendedGIC base might be used as dentin

replacement- to be place immediately after etchant befor bonding agent is placed

Bonding agent- thin film, avoid pooling at base

Placement of composite or compomer2mm increment- 20 sec curing

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Occlusal lesion Involving deep dentin

Indirect pulp capping might be required

Calcium hydroxide base placed –confined to near exposure site

If GIC used- Enamel conditioned using phosphoric acid

Dentin conditioned using polyacrylic acid

Final bevel placed after GIC base placement

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Resin based Composite or compomer placed

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Rebonding of restorationAfter polymerization any remaining pits

and fissures might be filled using sealants or flowable composites.

Resin based composites and compomers in primary molars-DCNA 2000

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Rationale for use of various material

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ConclsionTherefore , since the form of cavity

preparation in primary teeth is partly governed by their anatomy , newer materials with better adhesive properties are recommended so that minimal destruction of the tooth structure is required.

The more ideal materials are expected to have better fluoride releasing properties , better aesthetics and a more functionally appropriate stress bearing strength

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ReferencesPediatric Dentistry:  A Clinical Approach by Goran

KochKennedy's paediatric operative dentistry by Martin

E. J. Curzon, J. F. Roberts, David Bernard Kennedy 4th ed

http://www.aapd.org/media/Policies_Guidelines/P_CariesRiskAssess.pdf

FDI statement. Minimal intervention in the management of dental caries. FDI general assembly 1 October 2002

Kreulen CM, van Amerngen et al. Two yeas results with box only resin compposite restorations.J Dent Child 1995;Nov-Dec:395-39

Murdoch-Kinch C A, McLean M E. Minimally invasive dentistry. J Am Dent Assoc 2003(Jan); 134:87-95

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Mount GJ and Hume WR: Preservation and restoration of tooth structure. Mosby 1998; 121-154

Mount GJ, Hume WR. A revised classification of carious lesions by site and size. Quintessence Int 1997;28:301-303

Mount GJ. Minimal intervention dentistry: rationale of cavity design. Operative dent 2003;28:92-99

Mount GJ. Minimal treatment of the carious lesion. Int Dent J 1991;41:55-59

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