The document discusses various considerations for margin placement in tooth preparations, including biological, mechanical, and aesthetic factors. It describes advantages and disadvantages of different margin types such as supragingival and subgingival margins. Common margin designs like shoulder, bevel, and chamfer margins are explained. Guidelines are provided for reducing tooth structure during preparation in a systematic manner.

3. “The peripheral extension
of a tooth preparation.”
“The terminal
portion of a
prepared tooth.”

9. BIOLOGICAL
Considerations
MECHANICAL
Considerations
AESTHETIC
Considerations
1
• Conservation of tooth structure
2
• Prevention against damage
3
• Harmonious Occlusion
4
• Protection against Tooth fracture
5
• Considerations affecting future dental
health
i. Axial Reduction
ii. Margin Placement
iii. Margin Adaptation
iv. Margin Geometry
v. Margin Designs

11. MARGIN PLACEMENT
SUPRAGINGIVAL
MARGINS
SUBGINGIVAL
MARGINS

12.  Easier to prepare accurately
without trauma to the soft tissues.
 Usually situated on hard
enamel.
 They can be easily finished.
 They are more easily kept clean.
 Impressions are more easily
made, with less potential for soft
tissue damage.
 Restorations can be easily
evaluated at recall appointments.

13.  Dental caries, cervical erosion, or
restorations extend sub-gingivally, and a
crown lengthening procedure is not
indicated.
 The proximal contact area extends to the
gingival crest.
 Additional retention is needed.
 The margin of metal ceramic crown is to
be hidden behind the labiogingival crest
 It is also used to produce a cervical crown
ferrule on endodontically treated tooth.
 Root sensitivity cannot be controlled by
more conservative procedures, such as the
application of dentin bonding agents.
 Modification of the axial contour is
indicated.

15. ADVANTAGES DISADVANTAGES
Conservation of
tooth structure.
Fail to provide
adequate bulk at
margins (to enable
the wax pattern to be
handled without
distortion and to give
the restoration
strength and, when
porcelain is used,
esthetics).
This margin is
used for full
veneer metal
crowns , small
crowns and
already designed
margins by
previous dentist.
Over contoured
restorations.

16. ADVANTAGES DISADVANTAGES
Allows room for
porcelain 
recommended
for facial part of
the metal
ceramic crowns.
An acute angle is
likely to chip.
Placement of
margin deep into
the gingival
sulcus.
It is less
conservative of
tooth structure.

17. n.
ADVANTAGES DISADVANTAGES
Particularly suitable for
cast metal crowns and
the metal-only portion of
metal-ceramic crowns.
Tilting it away from the
tooth will create an
undercut; angling it towards
the tooth will lead to over-
reduction and loss of
retention.
Distinct and easily
identified, provides room
for adequate bulk of
material.
Marginal accuracy depends
upon having high quality
diamond and a true running
hand-piece.
Can be placed with
precision, although care
is needed to avoid
leaving a ledge of
unsupported enamel.
Chamfer should never be
prepared wider than half
the tip of the diamond 
an unsupported lip of
enamel can result.

20. ADVANTAGES DISADVANTAGES
Recommended for facial surface
of a metal-ceramic restoration
where a metal collar (as opposed
to a porcelain labial margin) is
used.
Less preferred to
shoulder or sloped-
shoulder for
biologic and
esthetic reasons.
Removes unsupported enamel
and allows some finishing of the
metal.
Allows improved esthetics
because metal margin can be
trimmed down a knife-edge and
hidden in the sulcus without the
need for positioning the margin
closer to the epithelial
attachment.

21. ADVANTAGES DISADVANTAGES
A beveled margin, under certain
circumstances, is more suitable
for cast restoration  particularly
if a ledge or shoulder already
exists.
When access for
burnishing is
limited, there is
little advantage in
beveling.
The objective in beveling is three
fold:
•To allow the cast metal margin to
be bent or burnished against the
prepared tooth structure.
•To minimize the marginal
discrepancy caused by a complete
crown that fails to seat
completely.
•To protect the unprepared tooth
structure from chipping (e.g. by
removing unsupported tooth
enamel).
In cases of gingival
margins  beveling
would lead to
subgingival
extension of the
preparation or
placement of the
margin on dentin
rather than on
enamel.

24. I. Guiding grooves or depth orientation grooves (on
both facial and incisal surfaces).
II. Labial reduction (first gingival third and then incisal
third).
III. Incisal or occlusal reduction (if required).
IV. Proximal reduction (not beyond contacts).
V. Lingual reduction (enhances mechanical retention
and increases surface area for bonding).
VI. Finishing of all prepared surfaces.

27. Shoulder
Shoulder bevel
Slope shoulder
Shoulder
Shoulder bevel
Shoulder design
with a porcelain
labial margin.