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GINGIVAL FINISH LINES OF CROWNS & BRIDGES
Sana Mateen Munshi
OUTLINE (Focusing on TYPES)
Introduction
Importance
Precautions
Types of margin placement and design
Criteria for selection of margin design
FINISHING LINE (RESTORATIVE MARGIN DESIGN)
“The peripheral extension of a tooth preparation.”
“The terminal portion of a prepared tooth.”
GPT
IMPORTANCE ???
Disrupt smooth surface thus vulnerable to plaque accumalation
leading to secondary caries & microleakage at the margins.
MARGINAL DISCREPENCIES!!!
AESTHETIC FAILURE!!!
INADEQUATE MARGINS….
MAPPING ……
BIOLOGICAL
Considerations
MECHANICAL
Considerations
AESTHETIC
Considerations
P R I N C I P L E S O F TO OT H P R E PA R AT I O N1
• 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
PRECAUTIONSUSE ROTARY INSTRUMENTS WITH CAUSTION!
Conservation of tooth structure!
Check Position of bur!
Unsupported enamel should be removed!!
PROPERLY SEATED- MINIMAL MARGINAL GAP WIDTHS!!
MARGIN PLACEMENT
SUPRAGINGIVAL MARGINS
SUBGINGIVALMARGINS
Biological width violation depends more on margin placement than on margin design
SUPRAGINGIVAL MARGIN (IDEAL) 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.
SUBG
INGI
VAL M
ARGI
N
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.
BASICS
FEATHER-EDGE/ SHOULDERLESS/ KNIFE EDGE:
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.
SHOULDER MARGIN / BUTT JOINT:
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.
It should form a 90-degree angle with the unprepared tooth surface.
CHAMPER MARGIN:CHAMPER: A finishing design line for crown preparation which makes an obtuse angle between the axial wall of the tooth surface and the prepared margin.
ADVANTAGES DISADVANTAGESParticularly 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.
SHOULDER MARGIN Cont’d
A 120-degree sloped shoulder margin is used as an alternative to the 90-degree shoulderfor the facial margin of a metal-ceramic crown. The sloped shoulder reduces the possibility of leaving unsupported enamel and yet leaves sufficient bulk to allow thinning of the metal framework to a knife-edge for acceptable esthetics
SHOULDER BEVEL MARGIN:
ADVANTAGES DISADVANTAGESRecommended 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.
BEVEL MARGIN:ADVANTAGES DISADVANTAGESA 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.
MARGIN DESIGNS SUMMARY
STEPS OF CROWN PREPARATIONI. 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.
The selected margin should provide a predictable level of marginal integrity.
To minimize plaque accumulation, the selected margin should present smooth materials to the gingival sulcus.
Margin should also must provide acceptable esthetics.
CRITERIA FOR MARGIN SELECTION
ShoulderShoulder bevelSlope shoulder
ShoulderShoulder bevel
Shoulder design with a porcelain labial margin.