This document provides details on preparing Class II amalgam restorations involving only one proximal surface. It describes the initial and final tooth preparation stages, including entering the pit nearest the involved surface, establishing target depths, and visualizing the final locations of facial and lingual walls. It also discusses creating a proximal ditch cut, modifying preparations based on factors like gingiva location and condition, and designing resistance and retention forms to protect the restoration and remaining tooth structure.

1. CLASS II
AMALGAM
PREPARATION

2. DEFINITION
 Preparations involving the proximal surfaces of posterior teeth are termed
Class II.
 Involves the proximal, proximo – facial ( lingual ) , proximo – occlusal
preparation on molars and premolars.

5. C L A S S I I A M A LG A M R E S TO R AT I O N S
I N VO LV I N G O N LY O N E P ROX I M A L S U R FAC E
 Carious lesion on one proximal surface.
 STEPS IN PREPRARATION -
 1. Initial tooth preparation stage
 2. Final tooth preparation stage

6. 1. Initial tooth preparation stage -
A. Outline form -
 Enter the pit nearest the involved proximal surface with a punch cut using a No. 245
bur .
 Entering the pit nearest the involved proximal surface allows the mesial pit (in this
case) not to be included if it is sound.
 Viewed from the proximal and lingual (facial) aspects, the long axis of the bur and the
long axis of the tooth crown should remain parallel during the cutting procedures.

8.  As the bur enters the pit, a target depth of 0.1–0.2 mm into dentin should be
established (i.e., one-half to two-thirds the length of the cutting portion of a No. 245
bur); 1.5 mm as measured at the central fissure, and approximately 2 mm on the
prepared external walls such that the DEJ is identified

9.  While maintaining the same depth and bur orientation, the bur is moved to extend the
outline to include the central fissure and the opposite pit (the distal pit, in this
example), if necessary

10.  Isthmus width should be as narrow as possible, preferably no wider than one-quarter
the intercuspal distance.

11.  The amount of remaining tooth structure is more important to restoration longevity
than is the restorative material used.
 Occlusal convergence - provides favorable amalgam angles at the margins.
 The facial, lingual, and distal walls should be extended until a sound DEJ is reached.

12.  It may be necessary to tilt the bur to diverge occlusally at the distal wall if further distal
extension would undermine the marginal ridge of its dentinal support.

13.  The dovetail feature is not required in the occlusal step of a single proximal surface
preparation, unless a fissure emanating from an occlusal pit indicates it.
 Without a dovetail, however, the occlusal step should not be in a straight direction,
which may reduce the retention form. This type of retention form also is provided by
any extension of the central fissure preparation that is not in a straight direction from
pit to pit.

14.  Before extending into the involved proximal marginal ridge (the mesial ridge, in this
example), the final locations of the facial and lingual walls of the proximal box are
visualized. This action prevents overextension of the occlusal outline form (i.e.,
occlusal step) where it joins the proximal outline form (i.e., proximal box).

15.  The preparation is extended mesially, stopping approximately 0.8 mm short of cutting
through the marginal ridge into the contact area.
 The occlusal step in this region is made slightly wider faciolingually than in the Class I
preparation because additional width is necessary for the proximal box.

16. Proximal Outline Form (Proximal Box)
 The desired final location of the facial and lingual walls of the proximal box or the proximal
outline form relative to the contact area is visualized. The objectives for the extension
of the proximal margins are as follows:
 1. Include all caries, defects, or existing restorative material
 2.Create 90-degree cavosurface margins (i.e., butt-joint margins)
 3. Establish (ideally) not more than 0.5 mm clearance with the adjacent proximal surface
facially, lingually, and gingivally

17.  1. PROXIMAL DITCH CUT (two-thirds at the expense of enamel and one-third at the
expense of dentin )

19. . G, The faciolingual dimension of the proximal ditch is greater at the gingival
level than at the occlusal level.
H, To isolate and weaken the proximal enamel further, the bur is moved toward
and perpendicular to the proximal surface.
I, The side of the bur may emerge slightly through the proximal surface at the
level of the gingival floor.

20.  Clearance of the proximal margins (i.e., mesiofacial, mesiolingual, gingival) greater
than 0.5 mm is excessive, unless indicated to include any caries, undermined enamel,
or existing restorative material.
 Extending gingival margins into the gingival sulcus should be avoided, where
possible, because subgingival margins are more difficult to restore and may be a
contributing factor to periodontal disease.

21.  If the proximal ditch cut is entirely in dentin, the axial wall usually is too deep.
 The ideal dentinal depth of the axial wall of the proximal boxes of premolars and
molars should be the same (two-thirds to three-fourths the diameter of the No. 245 bur
[or 0.5–0.6 mm]).
 The proximal ditch cut may diverge gingivally to ensure that the faciolingual dimension
at the gingival aspect is greater than at the occlusal aspect .

22.  The gingival divergence contributes to the retention form and provides for the
desirable extension of the facial and lingual proximal margins to include defective
tooth structure or old restorative material at the gingival level, while conserving the
marginal ridge and providing for 90-degree amalgam at the margins on this ridge.

27. A P P L I C AT I O N S O F T H E G E N E R A L P R I N C I P L E S O F
C AV I T Y P R E PA R AT I O N TO C L A S S I I L E S I O N S
 1. Outline form -
o Extension for convenience or access – For most molars and premolars with
proximal lesions , the occlusal surface should be included for access purposes .
o Few cases in which proximal cavity can be prepared from the facial or lingual
embrasure.

28.  Location and condition of the gingiva -
 A –Young teeth and high cariogenic activity
 B – Crest of free gingiva
 C- Recession – Supragingival margins

29.  Condition of the marginal ridge -
o If the proximal lesion can be instrumented from the buccal or
lingual embrasure , the integrity of the ridge occlusally
and proximally evaluated.
o If it is not undermined , a proximal cavity can be prepared or
occlusal and proximal cavity prepared separately with the marginal
ridge separating them.

30.  Location and extent of the contact areas -
o Purpose of class 2 restoration – to replace the diseased tissue and correct the
local conditions which initiated caries.
o Proper relationship b/w 4 anatomic landmarks – Marginal ridge , contact
areas, embrasures, gingiva – modify the outline form accordingly by
overextension or underextension .

31.  Modifying factors influencing the outline form -
1. Masticatory loads – inversely proportional to bucco lingual extent of cavity
2. Generalized plaque index - directly proportional to extent of cavity
3. Localized cariogenic factors – greater activity – greater extent of cavity into
self cleansable areas
4. Esthetics – minimize the facial extent of cavity esp. In mesiofacial margins of
premolars and first molars.
5. Tooth position – malaligned tooth , rotation

32. 2. RESISTANCE FORM -
 Concept is based on the reaction between the restoration and the remaining
tooth structure.
 Nature of this reaction - development of internal stresses – can lead to
structural failure.
 So tooth and restoration must resist failure by designing the cavity which is
best able to withstand the distribution and magnitude of stresses on tooth and
restoration.

33.  Occlusal loading – Tensile stresses at axiopulpal line angle ( isthmus) and
compressive stress in the underlying dentin and shear stress at junction of bulk of
proximal part and its self retained part.

34. Premature contacts by the amalgam will
exaggerate the stresses normally induced in
that area.
Can lead to mechanical and biological
failure.
Eliminate pre existing premature contacts
before treatment.

35. A. Design features to protect the mechanical integrity of the restoration -
1. Slanting the axial wall towards the pulpal floor.
2. Rounding of axio pulpal line angles
3. Flat pulpal and gingival floor
4. Every part of cavity self retentive
5. Avoid marginal excess – can fracture because of low tensile
Strength of amalgam – avoid feather edge margins – butt joint

36. B. Design features to protect the physio mechanical integrity of remaining tooth
structure -
1. ¼ to 1/5 of intercuspal distance – width at isthmus – avoid excess width
2. Occlusal cavity – rounded line angles , perpendicular facial , lingual walls at
isthmus
3. Ideal length to width ratio in cuspal wall surrounding a cavity – 1:1 ( flat table )

37.  When facial or lingual wall from occlusal surface
meet the proximal surface , should form right angles
.
 These walls must terminate past the contact areas in
the embrasures.
 Reverse S curve design - involvement of contact
area, 90 degrees cavosurface margin and termination
of facial and lingual walls in embrasure ,
preservation of tooth structure.

38.  Reverse S curve – mainly on facial wall, minimal lingually.

39. C . R E T E N T I O N F O R M -
1. Primary , secondary retentive features