Presentation on theme: "Dr. Gaurav Garg ( M.D.S.) Lecturer, College of Dentistry Al Zulfi, M.U. CLASS I CAVITY PREPARATION FOR AMALGAM Asalaam Alekum Date: 8/09/2015."— Presentation transcript:
Dr. Gaurav Garg ( M.D.S.) Lecturer, College of Dentistry Al Zulfi, M.U. CLASS I CAVITY PREPARATION FOR AMALGAM Asalaam Alekum Date: 8/09/2015
Contents Introduction Material qualities and properties of amalgam Indications for amalgam restoration Contraindications Advantages Disadvantages Clinical technique for class I amalgam cavity preparation
Introduction Class I amalgam restorations: Occlusal surface of posterior teeth Occlusal two thirds of the facial and lingual surface of molars Lingual surfaces of maxillary anterior teeth
Material qualities and properties of amalgam Strength Longevity Ease of use Clinically proven success Marginal seal improves with time Less susceptible to moisture contamination
Indications Moderate-to-large restorations Restorations that are not in highly esthetic areas of the mouth Restorations that have heavy occlusal contacts Restorations that cannot be well isolated Restorations that extend onto the root surface Foundations Abutment teeth for a removable partial denture
Contraindications Esthetically prominent areas of posterior teeth Small-to-moderate Classes I and II restorations that can be well isolated Small Class VI restorations
Advantages Ease of use and the simplicity of the procedure Low Cost Can be placed where isolation is compromised Placing and contouring of amalgam restorations are generally easier than that for composite restorations.
Disadvantages More complex tooth preparation required for an amalgam restoration compared to a composite restoration Less conservative tooth preparation compared with composite/GIC restorations Unaesthetic appearance
Initial Clinical Procedures Local Anesthesia ( if required) Isolation ( Rubber dam Recommended)
Instruments Bur: A No. 245 bur with a head length of 3 mm and a tip diameter of 0.8 mm or a smaller No. 330 bur is recommended Sides slightly convergent toward the shank (this produces an occlusal convergence of the facial and lingual preparation walls, providing adequate retention form for the tooth preparation). The slightly rounded corners of the end of the No. 245 bur produce slightly rounded internal line angles that render the tooth more resistant to fracture from occlusal force. The No. 330 bur is a smaller and pearshaped version of the No. 245 bur. It is indicated for the most conservative amalgam preparations No. 245 bur ( carbide) 3 mm 0.8mm
Initial Tooth Preparation Initial tooth preparation is defined as establishing the outline form by extension of the external walls to sound tooth structure, while maintaining a specified, limited depth and providing resistance and retention forms
Outline form The outline form for the Class I occlusal amalgam tooth preparation should include only the faulty, defective occlusal pits and fissures (in a way that sharp angles in the marginal outline are avoided).
Outline form Extending around the cusps to conserve tooth structure and prevent the internal line angles from approaching the pulp horns too closely Keeping the facial and lingual margin extensions as minimal as possible between the central groove and the cusp tips Extending the outline to include fissures, thereby placing the margins on relatively smooth, sound tooth structure Minimally extending into the marginal ridges (only enough to include the defect) without removing dentinal support
Outline form Eliminating a weak wall of enamel by joining two outlines that come close together (i.e., less than 0.5 mm apart) Extending the outline form to include enamel undermined by caries Using enameloplasty on the terminal ends of shallow fissures to conserve tooth structure Establishing an optimal, conservative depth of the pulpal wall (1.5 mm)
Procedure Begin the Class I occlusal tooth preparation by entering the deepest or most carious pit with a punch cut using the No. 245 carbide bur at high speed with air-water spray. A punch cut is performed by orienting the bur so that its long axis parallels the long axis of the tooth crown and then the bur is inserted directly into the faulty pit. When the pits are equally faulty, enter the distal pit which provides increased visibility for the mesial extension. As the bur enters the pit, the proper depth of 1.5 mm (measured from central fissure, one half the length of the cutting portion of the bur) should be established. The desired pulpal depth is usually 0.1 to 0.2 mm into dentin.
Procedure Maintaining the bur's orientation and depth, extend the preparation mesially following the DEJ creating a flat pulpal floor. When the central fissure has minimal caries, one pass along the fissure at the prescribed depth provides the desired minimal width to the isthmus. Ideally the width of the isthmus need be no more than the diameter of the bur or ¼ th of intercuspal distance. the distance from the margin of the extension to the proximal surface should not be less than 1.6 mm or two diameters of the end of the No.245 bur for premolars & 2mm for molars
Procedure Maintaining the bur's orientation and depth, extend the preparation distofacially or distolingually to include any fissures that radiate from the pit. Care should be taken not to undermine the marginal ridge. Correct
Procedure Remaining fissure which is no deeper than one quarter to one third the thickness of the enamel can be eliminated by Enameloplasty Enameloplasty refers to eliminating the developmental fault by removing it with the side of a flame-shaped diamond stone, leaving a smooth surface This procedure frequently reduces the need for further extension into the fissures with the No. 245 bur, thereby conserving tooth structure
Procedure The cavosurface angle should be 90- 100 degree which will provide a 90 degree butt joint between tooth structure and amalgam The strongest and ideal enamel margin should be made up of full-length enamel rods resting on sound dentin, supported on the preparation side by shorter rods, also resting on sound dentin
Resistance form Flat pulpal floor in sound tooth structure to resist forces directed in the long axis of the tooth and provide a strong, stable seat for the restoration Minimal extension of external walls, which reduces weakening the tooth Strong, ideal enamel margins Sufficient depth (i.e., 1.5 mm) to result in adequate thickness of the restoration, providing resistance to fracture and wear
Final tooth preparation Removal of remaining defective enamel and infected dentin on the pulpal floor Pulp protection where indicated Procedures for finishing external walls final procedures of cleaning and inspecting the prepared tooth Base application. A, Inserting RMGI with Williams periodontal probe. B, In moderately deep excavations a base (b) thickness of 0.5 to 0.75 mm is indicated. A B
Class 1 outline for different teeth Maxillary premolars-Butterfly shape Mandibular 1 st premolar- A. Snake eye shape B. Butterfly shape A B Mandi 1 st molar- Bat shape Mandi 2 nd molar- Plus shape Mandi 2 nd premolar- Y Shape Maxi 1 st molar Kidney Shape( Mesial cavity)
References & Suggested reading 1. Art and science of operative dentistry- Sturdevent’s,2006 2. Principles of Operative Dentistry- A.J.E. Qualtrough,2005