Fundamentals in Tooth Preparation Dr. Ramesh Bharti Assistant Professor Conservative Dentistry &Endodontics King George’s Medical University Lucknow

Definition of Operative Dentistry Operative dentistry is the ART and SCIENCE of the diagnosis, treatment, prognosis of defects of teeth which do not require full coverage restorations for correction, such treatments should results in the restoration of proper tooth form, function, and esthetics while maintaining the physiologic integrity of the teeth in harmonious relationship with adjacent hard and soft tissue, all of which enhance the general health and welfare of the patient.

Objectives of Cavity Preparation Remove all defects and give the necessary protection to pulp. Locate the margins as conservatively as possible. Form the cavity so that both the restoration and tooth can withstand the load of mastication. Allow for the esthetic and functional placement of a restorative material.

Need of Restoration Caries Malformed, discolored or fractured teeth Restoration replacement

Factors affecting tooth preparation 1. General Factors Pulpal & periodontal status Occlusal relationship 2.Dental anatomy Direction of enamel rods Thichness of enamel /dentin Size and positionof pulp Relationship of tooth to its supporting tissues

3.Patient factors 4.Affected & infected Dentine Age Esthetic consideration Economic status Patients with high risk caries 4.Affected & infected Dentine 5. Restorative material factors

Approach of Operative. cont….. Cavity preparation Matrix application Preparation of materials Insertion and carving of materials Finishing and Polishing

Cavity Preparation The mechanical alteration of a defective, injured, or diseased tooth in order to best receive a restorative material which will re- establish a healthy state for the tooth including esthetic corrections where indicated, along with normal form and function.

Cavity Structure walls angles Floor

Classification of cavity Class II Class III Class IV Class V Class VI —G.V.Black in 1908

Cavity Simple cavity: only one tooth surface is involved. Compound cavity: two surfaces are involved. Complex cavity: three or more surfaces are involved.

Class 1 Class 6 Class 1 Class 4 Class 3 Class 2 Class 2 Class 5

Stages and Steps in Cavity preparation Initial cavity preparation stage Final cavity preparation stage

Initial cavity preparation stage Step 1 Outline form and initial depth Step 2 Primary resistance form Step 3 Primary retention form Step 4 Convenience form

Final cavity preparation stage Step 5 Removal of any remaining infected dentin if indicated Step 6 Pulp protection Step 7 Secondary resistance & retention form Step 8 Procedure for finishing external walls Step 9 Final procedures

Outline Form and Initial Depth Definition: placing the cavity margins in the positions they will occupy in the final preparation. preparing an initial depth of 0.2~0.8 mm pulpally of the dentinoenamel junction position or normal root surface position.

Maxillary Class Ⅰ outline form

Mandibular Class Ⅰ outline form

Maxillary Class Ⅱ outline form

Mandibular Class Ⅱ outline form

Common Error

Outline Form and Initial Depth Principles: all friable and/or weakened enamel should be removed all faults should be included all margins should be placed in a position to afford good finishing of the margins of the restoration. Margins of the preparation will be located on finishable, self –cleansing area.

Outline Form and Initial Depth Features: preserving cuspal strength preserving marginal ridge strength minimizing facio-lingual extension using enameloplasty connecting two close faults or cavities restricting the depth of the preparation into dentin.

Auxillary Factors Conservation Adjacent enamel cracks or decalcification could be involved in the preparation. Type of restorative material. Extension for access. anatomy and alignment. If possible, no margins will be in occlusion with opposing teeth. Esthetics

Outline Form and Initial Depth for pit and fissure cavities Controlled by three factors 1- Extension to which enamel has been involved by caries. 2- Extension to achieve sound and smooth margins. 3- Limited bur depth while extending the preparaton

Rules Capping of cusp should be done when cavity extension is two-third from central fissure to cuspal eminence. Include all fissures that cannot be eliminated by enameloplasty. Restrict the depth. Join two lesions if they are less than 0.5 mm apart.

Outline Form and Initial Depth for smooth surface cavities Extension of cavity. Sufficient access. Depth. Sufficient clearance with adjacent tooth.

Initial cavity preparation stage Step 1 Outline form and initial depth Step 2 Primary resistance form Step 3 Primary retention form Step 4 Convenience form

Primary Resistance Form Definition: The shape and placement of the cavity walls that best enable both the restoration and the tooth to withstand, without fracture, masticatory forces delivered principally in the long axis of the the tooth.

Primary Resistance Form Principles: To utilize the box shape with a relatively flat floor to resist occlusal loading by virtue of being at right angles to mastication force. To restrict the extension of the external walls (keep as small as possible) to allow strong cusp and ridge areas to remain with sufficient dentin support.

Primary Resistance Form Principles: To have a slight rounding of internal line angles to reduce stress concentration in tooth structure; The presence of sharp internal line angles in GOLD FOIL resist the movement of the restoration Sharp internal line and point angles in dentin serve as convenient “starting” points for compacting of direct gold. To provide enough thickness of restorative material to prevent its fracture under load.

Primary Resistance Form Feature: Box shape Relatively flat floors Inclusion of weakened tooth structure Preservation of cusps and marginal ridges Rounded internal line angles Adequate thickness of restorative materials Reduction of cusps for capping if indicated

Primary Resistance cont…. Designing the outline form so that minimal of restoration is exposed to occlusal stress. Seat on sound dentin.

Vale Experiments 1 MR at 1/4th ICD -10% Loss of FR 1 MR at 1/2 of ICD -40% Loss of FR 2 MR at ½ of ICD -45% Loss of FR

Initial cavity preparation stage Step 1 Outline form and initial depth Step 2 Primary resistance form Step 3 Primary retention form Step 4 Convenience form

Primary Retention Form Definition: The shape or form of the prepared cavity that resists displacement or removal of the restoration from tipping or lifting forces.

Primary Retention Form Principles: depending on the materials Amalgam restoration: developing external cavity walls that converge occlusally and dovetail design

The devotail design provide retention form to the occlusal portion of the cavity. The occlusal convergence of the walls offers retention in the proximal portion of the cavity against displacement occlusally.

Primary Retention Form Principles: depending on the materials Composite restoration: a mechanical bond between the material and conditioned, prepared tooth structure.

Dentin etched with 32% phosphoric acid Collagen exposed by the acid.

Bonding of resin to dentin, using a "total-etch" technique FIG Bonding of resin to dentin, using a "total-etch" technique

16 Bonding to dentin using a self-etching primer.

Scanning electron micrograph of the transition between composite resin (C) adhesive (A), adhesive-hybrid layer (H), and hybrid layer-dentin.

Initial cavity preparation stage Step 1 Outline form and initial depth Step 2 Primary resistance form Step 3 Primary retention form Step 4 Convenience form

Convenience Form Conception: The shape or form of the cavity that provides for adequate observation, accessibility, and ease of operation in preparing and restoring the cavity.

Convenience Form Principles: Allow access for caries removal Allow access for restoration placement Allow access to margins for finishing, evaluation and cleaning

Convenience Form

Final cavity preparation stage Step 5 Removal of any remaining infected dentin if indicated Step 6 Pulp protection Step 7 Secondary resistance & retention form Step 8 Procedure for finishing external walls Step 9 Final procedures

Removal of any remaining infected dentin if indicated Definition: The elimination of any infected carious tooth structure or faulty restorative material left in the tooth after initial cavity preparation.

Removal of dentinal caries using round burs and spoon excavators A: use of a round carbide bur, with air coolant and slow speed. B: use of spoon excavators. Removal of dentinal caries using round burs and spoon excavators

Pulp protection Using liners or bases to protect the pulp or to aid pulpal recovery or both. If the infected dentin more than 2 mm deeper from the initial pulpal or axial wall then a Liner is indicated.

Final cavity preparation stage….. Step 5 Removal of any remaining infected dentin if indicated Step 6 Pulp protection Step 7 Secondary resistance & retention form Step 8 Procedure for finishing external walls Step 9 Final procedures

Secondary resistance and retention forms Most compound and complex cavity preparations require additional resistance and retention form. The exception being those preparations that are very conservative.

Secondary resistance and retention forms Mechanical forms Cavity wall conditioning form

Mechnical form: Proximal locks Proximal slots

Proximal locks

Slot on gingival wall

Final cavity preparation stage…. Step 5 Removal of any remaining infected dentin if indicated Step 6 Pulp protection Step 7 Secondary resistance & retention form Step 8 Finishing external walls Step 9 Final procedures

Finishing the external walls Definition: Finishing the preparation walls is the further development of a specific cavosurface design and degree of smoothness that produces the maximum effectiveness of the restorative material being used.

Finishing the external walls Objectives: To create the best marginal seal possible between the restorative material and tooth structure; To afford a smooth marginal junction; To provide maximum strength of both the tooth and the restorative material at and near the margin.

The strongest enamel margin is that margin which is composed of full-length enamel rods that are supported on the cavity side by shorter enamel rods, all of which extend to sound dentin.

Finishing the external walls The design of the cavosurface angle The degree of smoothness of the wall

The design of the cavosurface angle depending on the material: Amalgam: 90° Composite: beveling 30°~ 40°

Final cavity preparation stage…….. Step 5 Removal of any remaining infected dentin if indicated Step 6 Pulp protection Step 7 Secondary resistance & retention form Step 8 Procedure for finishing external walls Step 9 Final procedures

Final procedures cleaning inspecting varnishing conditioning

Multiple Choice Questions Q.1. In cavity prepartion cavo-surface margin will be a junction between : a) Cavity wall/floor and adjacent tooth surface. b) Cavity wall and floor. c) Floor of the occlusal box and aproximal box d) Axial wall and occlusal floor.

Q.2 Toilet of the cavity is: a) Removal of debris by washing with water b) Removal of debris by cold air c) Removal of debris by hot air d) Washing the cavity with water.

Q.3 Most common fracture seen in amalgam restoration at: a) Cavosurface margin. b) Contact area c) Isthmus area d) Proximal box

Q 4 G. V Black concluded that following area of tooth surface are relatively non-selfcleansing: A) Pit and fissures B) Tips and cusps C) Fossa D) Marginal ridge

Q.5 Class III amalgam restorations areusualy prepared on: a) Distal surface of anterior teeth b) Mesial surface of canine c) Distal surface of canine c) Mesial and distal surface of all teeth.