Class 4 cavity preparation:
It occurs at the proximal surface of anterior teeth involving the incisal edge. It is
commonly caused by the fracture of the incisal angle therefore it’s clinically
visible, while class 3 is mainly caused by caries and it’s not obvious.
Class 4 caries begins as a class 3 carious legion that undermines the incisal edge.
It might be the result of traumatic fracture which occurs at the anterior teeth of
children and young adults.
The differences between class 3 and 4:
Class 4 composite restoration has different shades; cervically we put a
dark shade, while incisally it should be translucent to mimic the incisal
Occlusion in class 4 is of high extent
high contact in the centric
occlusion and it increases in the protrusive movement so we should
increase the resistance to avoid the common fractures while eating for
occlusal assessments in class 4 are very important especially class4
Restorations, they may influence the outline form (place your margins in non-
contact areas). Retention and resistance forms should be well established
especially when there is heavy occlusion.
We increase the retention by using bevels; we use wider bevels in class4. We can
also use retentive grooves or dovetail, but the dovetail is not commonly used.
We increase the resistance by making conventional beveled cavity
floor to oppose the occlusal forces.
Esthetic consideration is more critical in class4 because it includes a large scope
of the tooth, so it could necessitate a combination of multiple shades and
Wider bevels are required for proper blending of composite and natural enamel
and to increase the retention as we said.
In class 3 we are not going to influence the contact area, but in 4 we should
establish a contact between the incisors by using matrix bands and pre-wedging.
Without wedging we will not establish a contact, even though we can see a
contact, but the patient feels the space which accumulates food while eating.
Pre-Wedging is mandatory to create your proximal contact.
we can’t use amalgam, glass ionomer or microfill
composite, instead we use hybrid composites.
we always use rubber dam with composite.
3 types as in class 3:
- 90 degrees but joints the cavosurface margin.
- Usually located on the root where there is no enamel so it’s not beveled or
- Minimal clinical application.
*Because it’s class 4 so it will never be conventional alone because it’s extended to the
incisal edge so it should involve the crown, therefore in the crown portion we use the
beveled conventional type (combined preparation).
-indicated for restoring large proximal crown cavities that include the incisal edge.
*The cavity design of class 4 carious legion follows the conventional form of class 3
including the incisal edge.
-we use high speed round carbide or diamond burs, high speed initially then low speed
later on. We start the rotation before contacting the tooth. Direct your cutting instrument
perpendicular to the enamel surface, use Light pressure with intermittent strokes to gain
access into the legion.
*The axial wall depth at this stage should be 0.5 mm into dentine to avoid undermine
ding the enamel because retentive grooves are most likely to be placed, but we still can do
it 0.2 mm if we will not put grooves.
-The grooves are placed gingivoaxially.
-The axial wall is convex following the dentino-enamel junction and the external surface
of the tooth. The walls are prepared as much as possible perpendicular or parallel to the
long axis of the tooth resulting in a design that provides greater resistance.
*All enamel margins are beveled with wider bevels incisally where the enamel is thicker
and the stresses are greater.
*Advantages of enamel bevels:
Removing fragile enamel.
Making the margins smooth.
*Cavosurface bevel is best prepared with high speed round or flame-shaped diamond bur
resulting in an angle which is approximately 45 degrees to the external tooth surface.
-The bevel width should be from 0.25-2 mm depending on the amount of structure
missing and the retention you want.
*Final tooth preparation
-We remove infected remaining dentine using round bur or excavator, some undermined
enamel could be left but we should remove the friable enamel.
-If we make retentive grooves they should be placed at the gingivoaxial line angle at an
angle that bisects the external wall with the axial wall using number ? bur at a distance of
0.2 mm inside the dentino-enamel junction and a depth of 0.5 mm.
-The groove extends on the length of the gingivoaxial line angle and slightly upwards
facio-axially and linguo-axially.
-No retentive grooves are usually needed at the incisal area where mostly enamel exists.
-A dovetail extension on the lingual surface is not often used because it’s not very
-Pins might be used, but we don’t use them because of:
The risk of perforation.
They decrease the strength of the restoration.
Corrosion due to microleakage might result in discoloration which is very
-Indicated for small to moderate class 4 cavities as well as fractures with no caries or
-It’s used to prepare as little as much of the tooth to be as conservative as much.
-Little or no initial preparation is indicated for a fractured incisal corner other than
roughening the fractured tooth surface.
-Cavosurface margins are prepared with a bevel.
-The extension axially is dictated by the extent of the caries and will not be uniform in
-Usually no groove or cove retention is indicated because retention is achieved by the
bond between the composite and tooth structure.
-No effort is made to produce preparation walls that have specific shape or form that are
perpendicular to the external surface.
-weakened friable enamel is removed during the preparation of the cavosurface margin
during the placement of the bevel.
Done by: Dina Al-Saidi