Asalaam Alekum
Date: 8/09/2015
CLASS I CAVITY PREPARATION
FOR AMALGAM
Dr. Gaurav Garg ( M.D.S.)
Lecturer, College of Dentistry
Al Zulfi, M.U.
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
CLINICAL TECHNIQUE
Initial Clinical Procedures
 Local Anesthesia ( if required)
 Isolation ( Rubber dam Recommended)
Instruments
No. 245 bur ( carbide)
 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
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
Retention form
 Occlusal convergence ( Facial &
Lingual walls)
 Proximal dovetails
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
A
B
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.
Class 1 outline for different
teeth
Maxi 1st molar
Kidney Shape( Mesial cavity)
A
Mandi 1st molar- Bat shape
B
Mandibular 1st premolar- A. Snake eye shape
Mandi 2nd molar- Plus shape
B. Butterfly shape
Mandi 2nd premolar-Y Shape
Maxillary premolars-Butterfly shape
References & Suggested reading
1. Art and science of operative dentistry- Sturdevent’s ,2006
2. Principles of Operative Dentistry- A.J.E. Qualtrough ,2005