Principles of Cavity Preparation PDF

Principles of cavity preparation By Dr.Marihan Ibrahim Elgayar Principles of cavity preparation is originally recommended by G.V.Black, it include: a-mechanical principles b-biological principles A- Mechanical principles This include the fo...

Principles of cavity preparation By Dr.Marihan Ibrahim Elgayar Principles of cavity preparation is originally recommended by G.V.Black, it include: a-mechanical principles b-biological principles A- Mechanical principles This include the following steps: 1-Outline form. 2- Resistance form. 3- Retention form. 4- Convenience form. 5- Removal of decay. 6- Finishing enamel margin and the internal part of the cavity. 7- Debridement of the cavity. 1-Outline form Definition: The location that the peripheries (margin) of the completed tooth preparation will occupy on the tooth surface It is the perimeter of tooth preparation in width, length and depth. The location that the peri  Principles of outline form: 1-include all pits & fissures 2 remove decalcified enamel 3-remove undermined enamel 4- extend the margins to self cleansing areas 5- intracoronal preparation must be extended pulpally or axially to include DEJ:  Avoid seating the restoration on sensitive D.E.J. Give bulk to restoration. Allow the restoration to take advantages of dentin elasticity 6- connecting two cavities ≤ 0.5 mm Factors affecting outline form: 1- Conservative approach o Preserving cuspal stresses. o Preserving marginal ridge. o Minimizing the extension. o Enameloplasty. 2- Type of restorative materials  3- Esthetics How to achieve esthetics: Use esthetic materials. Margin in a hidden location. Margin not reflect the light. Definite outline. Biologically smooth surface.  Place surface landmarks. 4-cavosurface margin of restoration 5 -unusual anatomy 6- occlusion 7- protect critical and important anatomy 8-type of caries 9-abnormal cleansing capability: Mental retardation Physical handicaps 2-Resistance form Definition The shape of the cavity walls that enables both the restoration and the tooth to withstand the forces of mastication without fracture Mechanical prinicples: Forces directed to flat surface Flat horizontal surface is more resistance to occlusal force by being at right angle to forces. The box form or the mortise form with flat floor help the tooth to resist occlusal forces The cavity walls must be parallel Advantages of box-shape: 1- Ideal seating of restoration to resist force without fracture. 2- Maximum adaptation. 3- No lateral forces. 4- Prevent splitting cusp. 5-Cavity more convenient The inverted trauncated form is more resistant to occlusal forces Definite and rounded internal line angles to: 1-Reduce stresses on Restoration. 2- Reduce stresses on tooth. 3- Increase bulk of Restoration. 4- Good adaptation Conservative approach Design the outline with minimum exposure of restoration to occlusal forces Enough thickness of restorative material Enamel walls must be parallel to enamel rods Floor parallel to occlusal plane Remove undermined enamel Ending the margins at non-stress bearing areas The stress bearing areas are: a- Distal side of canine. b- Marginal ridge. c- Incisal edges. d- Functional cusps Bonding the restoration to tooth structure either : mechanical chemical 3-Retention form Definition: Shaping of the walls of the cavity preparation to enable the restoration to withstand lifting and lateral displacement forces. Retention means are divided according to efficiency into: a- Principal means of retention b- Auxillary means of retention Principal mean of retention 1- Frictional retention a-surface area b-opposing walls c-parallelism d-proximity e-occluso cervical length f- type of cement 2-Elastic deformation of dentin 2- Inverted trauncated cone or undercut 3- Definite point & line angles 4- Depth of the cavity Auxillary means of retention 1- Grooves or boxes 2- Post 3- Pins 4- Etching 5- Beveling Retention means are divided according to location into: 1- Intracoronal 2- Extracoronal 3- Extra means of retention 4- Intraradicular 4-Convenience form Definition: Widening the walls of the cavity to gain adequate access and good condensation  Shaping the walls of the cavity to be convienently seen, examined , approached & restored 5- Removal of caries Mechanism of caries removal Removal of soft caries using excavation Removal of hard chronic caries by large blunt low speed round bur 6- Finishing enamel margins The purpose of finishing and smoothening the enamel wall and margin: 1- To give marginal seal. 2- Maximum enamel strength Several considerations: 1- Direction of enamel rods. 2- Unsupported enamel. 3- Type of restorations. 4- Location of the margin. 7-cavity debridement It is the cleaning process of the cavity from saliva ,debris and micro organisms Methods of debridement: 1- Water and air. 2- Cavity cleaners. 3% H2O2, citric acid ethyl acetate, NaOCl 3- Disinfectant solution 0.2%EDTA 4- Scraping with sharp instrument b-Biological principles 1- Pulp exposure 2- Heat generation 3- Physical irritation 4- Chemical irritation 5- Deep cavity