Class I Cavity Preparation for Amalgam Restorations PDF
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Delta University For Science And Technology
Basma Ahmed Mohamed Abdelmoneim
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This document provides a detailed explanation of Class I cavity preparation for amalgam restorations. It covers the preparation steps and considerations to protect the pulp and maintain tooth structure. Techniques for various cavity types and the importance of proper margins are also discussed.
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Class I Cavity Preparation For Amalgam Restorations Basma Ahmed Mohamed Abdelmoneim BDS, MDS (Operative Dent, Endodontics and Crowns & Bridges), PhD (Oper Dent) Senior Assistant Professor of Operative Dentistry Facult...
Class I Cavity Preparation For Amalgam Restorations Basma Ahmed Mohamed Abdelmoneim BDS, MDS (Operative Dent, Endodontics and Crowns & Bridges), PhD (Oper Dent) Senior Assistant Professor of Operative Dentistry Faculty of Oral and Dental Medicine Delta University for Science and Technology Conservative Class I Cavity Preparation For Amalgam Restoration Conservative tooth preparation is recommended: -To protect the pulp. -To preserve the strength of the tooth. -To reduce deterioration of the amalgam restoration. -To enhance marginal integrity and restoration longevity. Pits and fissures are frequently more retentive for food and susceptible to caries due to their defective structure. -Class I cavity preparation These are pit and fissure type cavities that involve: -The occlusal surfaces of molars and premolars. -The occlusal 2/3 of buccal and lingual surfaces of molars. -The palatal pits in maxillary anterior teeth. -These lesions are characterized by: A small surface opening which may remain unnoticed until the lesion becomes of a considerable size -The carious lesion has a conical spread in both enamel and dentin. Types of Class I -Simple include only one surface (occlusal, lingual, buccal or palatal). A -Compound include two surfaces (occluso-buccal or occluso-lingual). B,C -Complex include more than two surfaces (occluso-bucco-lingual). Cavity Preparation For Class I Cavity Preparation 1-Outline form Outline form for class I cavities should be very conservative. It is governed by: - The extent of caries in both enamel and dentin. - The amount of extension needed to eliminate pits and fissures to secure smooth margins. -Outline form varies in shape according to : number of cusps and orientation of pits & fissures. Operative procedure -Begin the Class I occlusal preparation by entering the deepest or most carious pit using the No. 1/2 carbide bur at high speed with air-water spray. -Extension of the cavity done with a suitable size fissure bur (No. 245 bur) -This bur has a head length of 3 mm and a tip diameter of 0.8 mm to prepare a conservative class I preparation. -The sides slightly convergent toward the shank produces occlusal convergence of the facial and lingual preparation walls for adequate retention form for the cavity preparation. -The slightly rounded corners of the end of this bur produce slightly rounded internal line angles to make the tooth more resistant to fracture from occlusal forces. - When the bur enters the pit, the proper depth of 1.5 mm (one half the length of cutting portion of bur) should be made. - The 1.5 mm pulpal depth is measured at the central fissure. - -The necessary cavity extensions through pits, fissures and deep developmental grooves are made by keeping the bur at right angle to the surface of the tooth. -Cavity Preparation in mandibular premolar (crown tilted lingually) cutting bur should be tilted so that its long axis is parallel to the long axis of the tooth crown - -The cavity preparation should include the faulty, defective occlusal pits and fissures, all carious and undermined enamel. -Extending around the cusps to conserve tooth structure. -Running in sweeping curves with a minimum width. -Cavity width = 1/3-1/4 intercuspal distance and terminating on smooth surfaces to preserve the strength and function of the cups but it must be wide enough to allow condensation of restorative material. -The mesial and distal margins are placed in midway between the bottom of the proximal fossa and the crest of the proximal ridges. -The mesial and distal walls should have slight divergence from the pulpal floor outward to avoid undermining the marginal ridges to preserve strength of marginal ridges. -Eliminating a weak wall of enamel by joining two outlines that come close together (less than 0.5 mm apart). -Extending the outline form to include enamel undermined by caries. -Using enameloplasty on terminal ends of shallow fissures to conserve tooth structure. -Establishing conservative depth of the pulpal wall. 2-Resistance and retention forms Resistance form achieved by: -Boxing the preparation. -Flat pulpal floor in sound tooth structure to resist forces directed in the long axis of the tooth and provide strong and stable seat for the restoration. -Minimal extension of external walls. -Strong, ideal enamel margins. -Sufficient depth (i.e., 1.5 mm) to result in adequate thickness of the restoration. Retention form achieved by: -Slight occlusal convergence of two or more opposing external walls. 3-Convenience form -Although conservation of tooth structure is very important, convenience form in some cases may require extent of the preparation to provide adequate access and visibility. 4-Removal of carious dentin -In small size cavities……..carious dentin should have been removed during making the cavity extensions. -In moderately deep and deep cavities……carious dentin is removed carefully using large spoon excavator or round bur. -Only light pressure in a direction parallel to that of the pulp is made. -This is continued until hard dentin floor is reached. -Resistance form improved with flat floor peripheral to excavated areas. 5-Pulp protection -If the cavity preparation is of ideal or shallow depth no liner or base is indicated (varnish application is sufficient). -In deeper carious excavations (remaining dentin thickness is judged to be 0.5 to 1.0 mm) place a thin layer of resin-modified glass-ionomer RMGI base. -In very deep cavities (less than 0.5 mm RDT) calcium hydroxide liner is placed then the resin modified glass ionomer base applied. 6- Planning of enamel walls -The enamel walls of the cavity should be finished without any undermined enamel to meet the tooth surface at a right cavo-surface angle. -Cavo-surface margins should be well defined and well supported in order to be easier to visualize and carve and to provide marginal integrity of the restoration. -This may be done by sharp chisels and hatchets, fissure burs, or stones. -All sharp corners in enamel must be rounded. 7-Toilet of the cavity --A sharp explorer is then used to check the details of the prepared cavity and to loosen the tooth debris which are then blasted out with air. -This facilitates adaptation of amalgam to the cavity and improves the physical properties of the restoration by elimination of void or foreign material. Buccal or Palatal pits preparation -These preparations are made with No. 245 bur. -If the lesion is very small……… No. 330 or 169 bur may be used. -Depending on the extent of the caries and the angulation of the walls, retention grooves may be added with No. 1/4 or 1/2 bur. Compound Class I Cavity Preparations -In case of occluso-buccal and occluso-lingual cavities extensions are made through the fissures and towards the respective surfaces. -The cutting is done in dentin at D.E.J using No. 56 bur by applying pressure in a gingival direction and at the same time moving the bur mesio-distally until the occlusal ridge is undermined and removed. -If the caries is still gingival to the level of the pulpal seat a step is indicated. -The axial wall should follow the contour of the buccal / lingual surface of the tooth. -It may be extended: *With step forming axial wall and gingival floor. *Without step in cases of extended caries or fissure at the level of the pulpal floor. *Rounding of axio-pulpal line angle to: - Prevent stress concentration. - Provide bulk to the restoration. *Axial wall direction should be parallel to the corresponding external tooth surface to: - Prevent pulp exposure. - Provide uniform thickness of the restoration. - Retention grooves (if needed) in dentin along the axio-mesial and axio-distal line angles (as secondary retention form).