Cavity Preparation: Objectives and Classification

Objectives of Cavity Preparation

• Define key terms in cavity preparation
• Discuss classification of cavities
• Discuss the objectives of cavity preparation
• Describe the principles of cavity preparation
• Describe the design and preparation of all classes of cavities
• Outline the steps in cavity preparation
• List the armamentarium utilized in cavity preparation

Classification of Cavities

• The G.V. Black Caries Classification ranges from Class I to Class VI.
• Dr. Greene Vardiman Black (G.V. Black), developed a system over 100 years ago, from (1836-1915)
• Dr. Black categorized carious lesions based on the tooth affected (anterior or posterior)
• He also assessed the location of the lesion (lingual, buccal, occlusal)

Class I Cavities

• Cavities in pits or fissures on the occlusal surfaces of molars and premolars
• Cavities on facial and lingual surfaces of molars
• Cavities on the lingual surfaces of maxillary incisors
• Class I corresponds to surfaces of a posterior tooth seen clinically: occlusal/lingual/buccal surfaces

Class II Cavities

• Cavities on proximal surfaces of premolars and molars
• Class II corresponds to surfaces of a posterior tooth you cannot clinically

Class III Cavities

• Cavities on proximal surfaces of anterior incisors and canines while not involving the incisal angle
• Class III corresponds to surfaces of an anterior tooth you cannot clinically

Class IV Cavities

• Cavities on proximal surfaces of incisors or canines which involve the incisal angle
• Class IV lesion is an extended version of Class III covering the incisal angle

Class V Cavities

• Cavities on the cervical third of the facial or lingual surfaces of any tooth
• Think of the neck of the tooth

Class VI Cavities

• Cavities on incisal edges of anterior teeth and cusp tips of posterior teeth
• Class VI corresponds to the very top surface of a tooth

Caries Classification Based on Severity

• Incipient Lesion extends less than halfway through the enamel
• Moderate Lesion extends more than halfway through the enamel but does not involve the dentino-enamel junction (DEJ)
• Advanced Lesion extends to the DEJ but does not extend more than half the distance to the pulp
• Severe Lesion extends through enamel and dentin, and more than half the distance to the pulp

What is Cavity Preparation?

• Cavity preparation is the mechanical alteration of defective, injured, or a diseased tooth.
• Cavity preparation is required in order to best receive a restorative material
• Cavity preparation can help reestablish that the tooth aesthetically looks normal
• Cavity preparation can also help normalize the function of the tooth as well

Purpose of Cavity Preparation

• Cavity preparation helps Restore integrity of the tooth surface and function
• It helps with removing diseased tissue from the tooth
• Cavity preparation can help Improve aesthetics
• Necessary to repair defective restorations
• Required to facilitate the Restoration of occlusion

Objectives of Cavity Prep

• Remove all defects and give the necessary protection to the pulp
• Locate the margins of the restoration as conservatively as possible
• Aim to form the cavity so that the tooth or the restoration will not fracture under forces of mastication and the restoration won't be displaced

Cavity Preparation Terminology

• Simple Tooth Preparation- only one tooth surface is involved
• Compound Tooth Preparation – two surfaces involved
• Complex Tooth Preparation – three or more surfaces involved

Cavity Walls

• Buccal, axial, lingual, pupal, and gingival

Principles of Cavity Preparation

• Gain access to the tooth
• Outline form to have the correct shape
• Resistance form by utilizing matrix bands
• Retention form to help resin hold
• Provide Convenience form for the dentist
• Removal of Remaining Caries
• Finishing Cavity Walls
• Cavity Toilet to ensure sanitary environment

Gain Access

• This refers to accessing the carious lesion, usually with the help of a round bur

Outline Form

• This is the desired shape and boundaries of the completed cavity
• The outline should include the carious lesion and may include areas that are more susceptible to carious lesions
• External outline refers to the marginal boundaries
• Internal outline refers to the shape of the internal form of the preparation

Outline Form Considerations

• All the circumference of carious lesions must be included within the outline
• Pits, fissures, grooves and retentive areas must be included in the outline
• The cavity margins should extend to sound tooth structure, without undermined enamel, and in a self cleansable area
• The outline form must be in curves to prevent caries recurrence, avoid stress concentration areas, and obtain better aesthetics
• Cavities nearing each other must be connected to avoid leaving a weak ridge between them which is prone to fracture

Class 1 Outline for Different Teeth

• Maxillary 1st molar- Kidney Shape (Mesial cavity)
• Mandibular 1st molar- Bat Shape
• Mandibular 1st premolar- Snake eye shape or Butterfly shape
• Mandi 2nd molar- Plus shape
• Mandi 2nd premolar- Y Shape
• Maxillary premolars-Butterfly shape

Resistance Form

• Shape and placement of cavity walls must be able to withstand pressure from masticatory forces
• The cavity preparation must extend far to include the entire carious area
• Must extend until unsupported enamel can be supported by dentin
• Enamel which is unsupported tends to fracture

Factors Affecting Resistance Form

• Amount of occlusal stress
• Type of restoration used
• Amount of remaining tooth structure

Resistance Form Principles

• Utilize the box shape with a relatively flat floor to resist load
• Keep extension of the external walls as small as possible
• Have round internal line angles to reduce stress
• Sufficient thickness of restorative material will prevent material fractures under load

Retention Form

• Shape and configuration of the cavity preparation is important
• It resists the displacement or removal of restoration during mastication

Dovetail

• Used in Class II Cavities where it provides resistance to lateral displacement

External and Internal Walls

• Listed as: Distal, Facial, Lingual, and Gingival

Overhanging Margins of Restorations

• Usually due to improper placement of a matrix band and wedge
• Leads to plaque retention and periodontal disease

Extension for Prevention

• This refers to extending the margins of preparations to areas that are self cleansing
• The goal is to prevent the recurrence of caries at the margins of fillings

Convenience Form

• This form facilitates and provides adequate visibility, access, and ease of operation during preparation and restoration of the tooth
• Allows access for caries removal
• The cavity preparation should be wide enough to facilitate use of instruments for placing restorative material

Removal of Remaining Caries

• Once the external and internal outline form has been established, any remaining caries should be removed

Affected vs Infected Dentin

• Affected Dentin: Does not contain micro-organisms, can be remineralized, and it is acceptable to leave
• Infected Dentin: Contains micro-organisms, cannot be remineralized, and should be removed

Removal Techniques

• Soft decay can be removed using a spoon excavator by flaking up the caries
• Hard decay heavily discoloured should be removed using a very low speed bur

Finishing of Enamel Walls and Margins

• The finishing of the enamel margins should be done irrespective of restorative material used
• Finishing entails the further enhancement of the cavosurface design
• Finishing results in better marginal seal, increased and stronger tooth structure and degree of smoothness

Cavity Cleaning & Toilet

• Refers to the removal of debris, cleansing, and drying preparation
• Removal of all debris from the preparation, especially on the margins
• Prevents contamination of cavity walls and the restorative material
• Deposits left behind can dissolve, resulting in micro leakage which further leads to secondary caries
• Operator can examine all steps
• Best to clean and dry before the insertion of filling material

Hydrogen Peroxide in Cleaning

• Highly effective because of its effervescent action
• Should be washed immediately with warm water to avoid thermal pulp shock
• Can also use water, since it is not a medicament
• A cotton pellet can dry the cavity to reduce the use of air stream
• Removal of remaining water by air for a short time

Armamentarium Used in Cavity Preparation

• This includes the Mouth mirror, Cotton pliers, Dental bur, Explorers, and Spoon excavator

Mouth Mirror

• Used to improve visibility and retraction
• The handle can be used to percuss teeth (helps locate painful tooth)

Cotton Pliers

• Dental instruments are designed to guide, grasp, and place items to and from the cavity
• They can hold, bend, contour, and shape various dental materials

Dental Burs

• These are used in conjunction with the dentist's handpiece
• Good for cutting away hard tissue such as tooth and bone
• There are Round burs, inverted cone burs, straight crosscut fissure burs, and tapered fissure burs

Explorers

• Used to detect caries and determine irregularities at the margins of restorations

Spoon Excavator

• Cleioid is oval in shape while discoid is circular in shape.
• Used mainly for removal of any remaining soft caries

Amalgam Carrier

• Used to carry and dispense amalgam filling materials in the cavity

Plugger/ Condenser

• Used to condense the amalgam
• Used for packing the amalgam into the cavity

Dycal Applicator

• Used to apply calcium hydroxide (rigid-setting) material
• Used for direct and indirect pulp capping and as a protective liner under dental filling materials, cements, and other base materials
• Dycal stimulates the formation of secondary dentine, is acid resistant, and of low solubility

Dental Cement Spatula

• Used to mix dental cements
• These instruments have a sturdy metallic (e.g., stainless steel) handheld instrument with a working distal tip
• One can use wider surface area helps in the mixing of cement powders with liquids and it is designed not to stick to the cement being mixed

Plastic Instrument

• Used for application of composites
• Used to shape composite to reproduce the morphology of a restored tooth

Carver

• Used to remove the excessive restoration material
• Used to reproduce the tooth morphology on the restoration

Burnisher

• Used to smooth amalgam after condensing
• Used to create occlusal morphology

Dental Matrix Retainer

• Used to hold matrix band in place
• Maintains stability of the matrix band during condensation of restorative material
• The parts are: Rod, Guide posts, Outer nut, inner nut, diagonal slot and locking vise

Tofflemire Type Matrix Bands

• Adult: Universal (No 1), Broad (No 2), and Narrow (No 3)
• Junior: Universal (No 13), Narrow (No 14), and Broad (No 15)

Wooden Wedge

• Used to form a tight contact on the matrix band, compress the gingiva, and hold matrix band in place,
• Also absorbs saliva

Mylar Strips

• Used to maintain proximal integrity of composite restorations
• Ideal to use with light curable materials due to its transparency

Micro Brush

• Small plastic instrument with a small fiber bristled head
• Used to apply etchant, primer, bond, sealant

Curing Light

• Used for the polymerization of light cure resin based composites
• Used on several different dental materials, such as bonding, composites, sealants, cements, and build up.

Bonding Agent

• Resin materials make a dental composite filling material adhere to both dentin and enamel

Etchant

• Used to prepare enamel for the attachment of a bonded restoration
• These acidic materials remove the outermost layer of the tooth surface and expose rough, porous layer

Dycal

• Protects the pulp and promotes the formation of secondary dentin
• Used for direct and indirect pulp capping and as a protective liner under dental filling materials, cements, and other base materials
• Use 1: 1 ratio for mixing the catalyst and base

Dental Composite

• Can be in syringe or composite tip which requires a composite gun
• Used as permanent restorative material

Glass Ionomer Cement (GIC)

• Can be used as a cavity base liner
• Often it is used in primary teeth (exfoliating soon)

Dental Amalgam

• Liquid mercury and metal alloy mixture
• Used in posterior teeth

Dental Varnish

• Used to prevent micro leakage and seals tubules

Intermediate Restorative Material (IRM)

• Used as a liner and temporary filling

Light Cure Liner

• It is to be Used with composite fillings

High Speed Handpiece

• Used to remove carious lesions and adjust Permanent restorations