• For gold crown: Functional cusp is 1.5 mm and
• For PFM: Functional cusp is 1.5–2.0 mm and
nonfunctional cusp is 1.0–1.5 mm.
• For all-ceramic crowns, there should be all round
Functional cusp bevel: Wide bevel is placed on the
functional cusp of the posterior teeth to provide
adequate structural durability.
• Functional cusp bevel is placed on the buccal cusp
of the mandibular teeth and palatal cusp of the
• Nonfunctional cusp should always be rounded to
• If functional cusp bevel is not provided, it may
result in overcontoured crown.
Adequate axial reduction should be done to provide
sufficient space for the restorative material or else
may result in overcontoured crown.
Structural durability in the preparation is improved
by providing sufficient space for the reinforcing
• Features that improve durability of the restoration
are occlusal shoulder, isthmus, incisal or occlusal
offset, proximal grooves, boxes, etc.
• In partial veneer crown, the incisal offset is joined to
the proximal grooves on the either side to improve
structural durability and give the ‘truss effect’ (Fig.
• Reinforcement in the MOD onlay is provided by
joining the isthmus with the proximal boxes.
Marginal adaptation of the restoration is of utmost
importance for its longevity in the oral cavity. It is
affected by the type of finish line and restorative
material used. Proper marginal adaptation and
complete seating of the restoration on the prepared
tooth is desirable for successful treatment. Bevels
may be given on the finish line to improve marginal
(V) Preservation of periodontium
• The location of the finish lines has direct bearing on
the health of the periodontium.
• The finish lines should be located supragingivally
• Subgingival finish lines should be avoided, as they
may result in gingival inflammation, periodontal
pockets or even loss of alveolar bone.
• The finish line should not violate the biological
• They should be smooth and easily cleanable.
• The crown or restoration should not be
overcontoured or undercontoured.
FIGURE 25-1 Functional cusp bevel on the buccal cusp of
FIGURE 25-2 The incisal offset connects the grooves to give
Finish line can be defined as ‘the terminal portion of the prepared tooth or
the peripheral extension of a tooth preparation’. (GPT 8th Ed)
Classification of Finish Lines
(iii) Margin at the crest of the gingiva
On the basis of configuration and margin design
Basic criteria for successful finish lines are:
• Acceptable marginal adaptation
• Sufficient bulk for restorative material
• Well tolerated by the tissues
• It is formed when external line angle of the
preparation is perpendicular to the long axis of the
• It is indicated for all-ceramic crowns (margin of
choice), injectable ceramic and facial margin of
• Gingival crest should be adequately supported with
the wide ledge which provides resistance to
functional forces and minimizes stresses that might
• It is should be 90° to the external surface and 1.2–1.5
• Flat-ended tapered cylinder bur is used to prepare
shoulder margin and is kept perpendicular to the
• Sloped shoulder (120°) is an alternative to 90°
shoulder for labial margin of a PFM crown.
• Sloped shoulder provides sufficient bulk for the
restorative material and minimizes the possibility
of unsupported enamel (Fig. 25-4).
• It provides adequate space for restorative material.
• It offers maximum aesthetics.
• It provides adequate space for gingival contour.
• It provides excellent strength.
• It resists distortion due to inherent bulk of metal at
• It is less conservative for tooth structure.
• Its sharp internal line angles are susceptible to stress
concentration and fracture of the tooth at margin.
• Bevel with rounded axial angle is believed to
improve marginal adaptation of the restoration on
the prepared tooth (Fig. 25-5).
• Small flame-shaped diamond bur is used in bevel
• Proximal box of inlays and onlays.
• Occlusal shoulder of onlays and mandibular threequarter crowns.
• Facial margins of PFM crowns where aesthetics is
• Preparation with short walls.
• It has improved marginal adaptation.
• It has better seal at the margin.
• It has minimal unsupported enamel.
• It provides adequate bulk of metal to resist
• It has a less conservative preparation.
• The preparation extends more apically into the
• It is possible to create sharp edge of metal at the
• It is a concave, obtuse-angled finish line.
• Torpedo diamond bur is commonly used to develop
• Less than half the diameter of the tip is used for
• About 0.5 mm of reduction is usually recommended
for chamfer finish line (Fig. 25-6).
• Heavy chamfer may be used to provide a 90°
cavosurface angle for a ceramic crown, if shoulder
• Margin of choice for metal crowns.
• Lingual margin in a PFM crown.
• Usually indicated for molars.
• It involves less tooth reduction.
• It provides adequate seal at the margin.
• It has a distinct margin; readily visible on the tooth,
• It provides adequate bulk for restorative material.
• There are chances of unsupported enamel.
• It is an acute angle thin finish line.
• It is not routinely used but may be indicated in
some situations as mentioned below.
• Lingual surface of tilted mandibular molar.
• Teeth with very convex axial surface.
• It conserves tooth structure.
• It is difficult to locate on the die.
• It is difficult to accurately wax and cast.
• It may result in overcontoured crown.
• It has potential for metal display.
• There are more chances of distortion.
• It is similar to knife-edge finish line.
• Although more conservative to tooth structure, it is
• It does not provide sufficient space for the bulk of
FIGURE 25-3 Shoulder finish line.
FIGURE 25-5 Shoulder with bevel.
FIGURE 25-6 Chamfer finish line.
Supragingival and subgingival finish lines
Supragingival finish lines are those margins that are located above the
gingiva. It is always desirable to prepare the margins above the
gingiva because they are easy to prepare accurately without injuring
the soft tissues. There are number of advantages to prepare the
margins supragingivally than subgingivally. Supragingival finish
• Are usually prepared on tooth enamel.
• Impressions can be easily evaluated.
• Are easier for the patient to clean and maintain.
• Restorations can be easily evaluated at recall appointment.
• Chances of plaque accumulation are less.
They are defined as ‘the restoration margin or tooth preparation finish line
that is located apical to the free gingival tissue’. (GPT 8th Ed)
• The concept of subgingival finish lines was based on the mistaken
belief that gingival sulcus is caries-free.
• Current research indicates that subgingival margins create protected
area which encourages rapid plaque accumulation resulting in
marginal and papillary gingivitis and may even progress to
• Subgingival finish lines should be avoided whenever possible and
supragingival margin should be preferred.
• However, there are instances when subgingival finish lines become
• Caries extending subgingivally.
• Old restoration or cervical erosion extending subgingivally.
• Aesthetics is the primary concern, especially in the maxillary
• Short crowns where additional retention is required.
• If axial contour requires modification.
• In cases where root sensitivity cannot be controlled by conservative
• In endodontically treated tooth, if cervical crown ferrule is prepared.
• When the proximal contact area lies in or near the gingival crest.
Factors that influence the extent of inflammatory changes
associated with subgingival margins.
There are four factors which primarily affect the degree and extent of
inflammatory changes associated with subgingival margins:
• Contour of the tooth or restoration that extends
from the base of the gingiva is called the emergence
• If the restorative margin extends subgingivally, the
emergence profile of the tooth is likely to be
• The resulting restorations have overcontoured
crown which encourages plaque accumulation
resulting in periodontal problems.
(ii) Improperly finished margin
• Margin which is placed subgingivally is difficult to
finish and forms a plaque-retentive area.
• Overhanging of the restoration with open margins
is commonly associated with subgingival finish
lines and results in chronic periodontal problems
(iii) Inadequate zone of attached margins
• Subgingivally placed margins can sometimes lack
band of firmly bound attached gingiva.
• Subgingival finish lines are contraindicated in
patients with little or no attached gingiva, as it may
result in gingival inflammation followed by
attachment loss (periodontal pockets) and gingival
(iv) Violation of biological width
• Any margin which is placed more than 0.5 mm
subgingivally will violate the biological width and
results in chronic periodontal problems and
eventually alveolar bone loss.
Porcelain jacket crown (PJC) produces best aesthetic results to replace
and restore anterior teeth. Originally PJC was made of feldspathic
porcelain which was susceptible for fracture. Recently aluminous
reinforcement porcelain is becoming more popular because of higher
strength but still uses of PJC is restricted to anterior teeth. As the
restoration is made entirely of ceramic, it requires adequate tooth
reduction to provide space for the bulk of ceramic to provide
adequate strength. It is one of the least conservative preparations and
the size and position of the pulp chamber should be thoroughly
evaluated before selecting this preparation. Various features of PJC
and their functions are listed in Table 25-1.
FEATURES OF PORCELAIN JACKET CROWNS
Shoulder finish line Marginal integrity, structural durability
Axial reduction Retention and resistance, structural durability
Rounded angles Structural durability
Vertical lingual wall Retention and resistance
Concave cingulum reduction Structural durability
The steps involved in preparing PJC are as follows:
• Before reduction, depth reduction index is made
with silicone putty. It is divided into facial and
lingual index by sectioning the putty along the
• Depth orientation grooves are placed on the labial
and incisal surfaces with flat end-tapered diamond
• Recommendation of the incisal reduction ranges
between 1.5 and 2.0 mm. Approximately 2.0 mm of
incisal reduction is considered adequate for
fabricating aesthetically pleasing restoration.
• Over-reduction of the incisal or labial reduction is
avoided, as it may increase the stresses on the labial
surface and may result in half moon fracture.
• Reduced incisal plane should be perpendicular to
• Incisal reduction is done at an angulation of 45°
(palatally) to the long axis of tooth in normal
• This provides a broad, flat surface which is capable
of tolerating the compressive forces of the opposing
• A long, thin, tapered diamond bur is used for axial
• During reduction, adequate precaution is taken not
to harm the adjacent tooth in any way.
• Usually, 2–5° of taper is given.
• Minimum 1 mm of shoulder width is uniformly
• It is done with flat end-tapered diamond bur.
• It is commonly done in two planes, namely, incisal
two-thirds and cervical one-third.
• The cervical one-third reduction is done by
positioning the diamond bur parallel to the cervical
portion of the labial surface (along the long axis of
• The incisal two-thirds preparation is done by
positioning the diamond bur parallel to the incisal
aspect of the labial surface (along the plane of the
• Incisal two-thirds reduction of the labial surface
should be lingually inclined to provide adequate
• Labial reduction is extended onto the axial surface
to prepare the shoulder finish line.
• Lingual reduction is done in two planes, namely,
vertical lingual wall and concave cingulum.
• The vertical lingual wall is reduced with flat endtapered diamond with 2–5° taper and 0.75 mm
• Wheel-shaped diamond is used to prepare the
• Concave reduction of the cingulum ensures
maximum clearance on the middle of the lingual
• Recommended lingual reduction is 0.5–1.0 mm.
• There should be adequate clearance on lateral and
• In the canine teeth, two concave areas are prepared
because of the presence of canine lingual ridge.
• A sharp chisel is useful in removing unsupported
• Uniform shoulder is prepared around the tooth
using end-cutting diamond bur (Fig. 25-7).
• Excessive incisal reduction should be avoided, as it
reduces the retention and resistance form.
• Taper should not be given excessively.
• Labial and lingual reduction should be done in two
• Excessive reduction of the labial surface should be
• Precaution should be taken to ensure that adjacent
tooth is not harmed in any way during tooth
• Undercuts in the preparation should be avoided.
• Adequate lingual reduction is necessary to provide
sufficient space for porcelain.
• Prepared tooth should be smoothened and finished
well before impression making.
• Sharp angles and unsupported enamel are
FIGURE 25-7 Completed porcelain jacket crown preparation.
Preparation of full cast crown
A full veneer crown preparation involves all the surfaces of the crown.
This type of preparation demands extensive tooth preparation and,
therefore, should be used with caution. Steps involved in preparing
full metal cast crown on a maxillary first molar are given below.
• Round end-tapered diamond is used.
• Depth orientation grooves are made on the triangular ridges and
• Recommended occlusal reduction for functional cusps is 1.5 mm
and for nonfunctional cusps, it is 1.0 mm.
• Functional cusps in the maxillary molar tooth are the lingual cusps
and nonfunctional cusps are the buccal cusps.
• Occlusal reduction is done preserving the occlusal morphology.
• Functional cusp bevel is given with the help of round end-tapered
• Occlusal clearance is checked using red utility wax and asking the
patient to bite in maximum intercuspation.
• The thickness of the wax is checked for thin spots.
Buccal reduction and lingual reduction
• Orientation grooves are placed on both the walls with round endtapered diamond.
• The grooves placed on both the walls should be parallel to the
proposed path of withdrawal of the restoration.
• These grooves are joined to each other to accomplice reduction.
• Torpedo diamond is usually used for buccal and lingual reductions.
• Chamfer finish line is the margin of choice for full veneer cast
• The buccal axial reduction is prepared as far into the interproximal
embrasure as possible without damaging the adjacent tooth.
• Lingual reduction is done with the same bur and should also extend
as far interproximally as possible.
• In case of lingually tilted mandibular molars, the chamfer finish line
may be less defined but adequate reduction of the lingual axial
surface is desired to avoid overcontouring of the crown.
• Long, thin, tapered diamond is initially used to reduce the proximal.
• The thin tapered diamond is held upright against the buccal wall
and moved towards the contact area with light pressure.
• Up and down, sweeping motion is used to break the contact.
• Torpedo diamond is subsequently used, once the contact area is
• All the axial walls are finished with a torpedo diamond finishing
• All the line angles are rounded off.
• Nonfunctional cusp bevel is placed.
• Additional retentive features such as grooves or boxes are placed
• The seating groove should extend gingivally 0.5 mm short of the
chamfer finish line on the axial surface.
• Seating groove enhances the resistance and retention form (Fig. 25-
FIGURE 25-8 Completed full veneer preparation.
• Grossly damaged teeth due to caries or trauma.
• Tooth requiring maximum retention and resistance.
• Correction of occlusal plane.
• Retainers of long-span fixed partial denture where extensive
dislodging forces are expected.
• It has a high aesthetic demand.
• If less retention and resistance are required, more conservative
• It has better resistance and retention than other restorations.
• It offers freedom to modify axial contours.
• It allows easier occlusion modification.
• It involves extensive removal of tooth structure.
• It can affect the gingival tissues.
• It results in unaesthetic display of metal.
• Tooth vitality testing is unreliable after crown cementation.
• Marginal adaptation is time-consuming.
Preparation for partial veneer crown
Partial veneer crown preparation is conservative to tooth removal.
Anterior partial veneer crown was first developed by J.P. Carmichael
in 1901. The labial surface of the tooth remains intact whereas rest of
all the surfaces are prepared. These preparations are not indicted for
all the teeth and in all the patients. Patient selection is critical for the
success of the restoration. A thick, square anterior tooth with
sufficient labiolingual thickness is best suited for such preparations.
Anterior three-quarter crowns can sometimes be used as retainers for
short-span bridges provided they are healthy and caries-free. Various
features of partial veneer crown and their function are listed in Table
FEATURES OF PARTIAL VENEER CROWN
Lingual reduction Structural durability
Axial reduction Resistance and retention form, structural durability, preservation of periodontium
Proximal flare Marginal integrity
Incisal offset Structural durability
Proximal groove Retention and resistance, structural durability
Chamfer finish line Marginal integrity, preservation of periodontium
Steps involved in preparing maxillary canine for accepting partial
veneer crown are described in the headings below.
• Depth orientation grooves are made on the lingual surface to ensure
• A small wheel diamond bur is used to do a concave cingulum
• Occlusal clearance of 0.7 mm is required.
• Cingular reduction of canine is done in two planes with a slight
ridge extending incisogingivally.
• Two concave depressions are made on the lingual surface.
• Lingual axial wall reduction is done with a torpedo diamond bur.
• The diamond bur should be kept parallel with the incisal two-thirds
• Vertical lingual axial wall enhances retention.
• Chamfer finish line is created during reduction with the torpedo
• In tooth with short lingual wall, retention can be improved by
giving the bevelled shoulder finish line on the lingual surface and
• It is done with wheel diamond bur.
• It parallels the inclination of the incisal edge.
• The mesial and distal inclines of the canines are followed.
• About 0.7 mm of reduction is done at the incisal edge.
• Labioincisal line angle should not be touched during incisal
• Long thin tapered diamond and torpedo diamond burs are used.
• First long thin tapered diamond bur is used in a sawing motion.
• Precaution is taken not to damage the adjacent tooth.
• Contact with the adjacent tooth should be barely broken with
enamel hatchet and not diamond bur.
• Torpedo diamond is then used to create a definite chamfer finish
• These grooves are placed by making an outline onto the tooth with a
• Mesial groove preparation is started with No. 170 bur to a depth of
• Then the grooves are prepared gingivally in increments until it
• The bur should be parallel to the incisal two-thirds of the labial
• The grooves should be placed as far labially as possible.
• The distal groove is placed parallel to the mesial groove in order to
have a single path of insertion and removal.
• The grooves are prepared just short of the finish line.
• It is prepared by flame-shaped diamond on the labial aspect of the
• It is wider at the incisal end than at the gingival end.
• Flame-shaped carbide bur is useful in preparing a smooth flare with
• In case of incisors, enamel hatchet or chisel is useful to prepare the
• It is prepared on the lingual surface with No. 170L bur by joining
the proximal grooves on the either side.
• It is inverted V-shaped on the maxillary canine and a straight line
• Incisal offset enhances the structural durability and provides the
truss effect, i.e. the metal occupying the offset tends to reinforce the
• About 0.5 mm bevel is placed on the labioincisal edge.
• Flame-shaped diamond is used to prepare the bevel.
• The bur is placed perpendicular to path of insertion on the mesial
• Contrabevel can be placed on the distal incline of the canine but
should never be used on incisors due to aesthetic reasons (Fig. 25-9).
FIGURE 25-9 Completed partial veneer crown preparation on
• Healthy tooth with adequate crown length.
• Intact labial surface which does not require contour modification.
• Patient with good oral hygiene.
• Extensive destruction, decalcification
• It results in the preservation of tooth structure.
• It has an ease in cleanability of the margins for patient.
• Complete seating of the restoration can be verified.
• It has a good seating, as it provides easy escape for cement.
• Electric vitality testing is possible.
• It is a less retention and resistance form than complete veneer
• A limited adjustment of the path of removal is possible.
• Display of metal is possible in the incisal edge.
PFM is useful to restore teeth requiring aesthetic replacement in the
posterior region. The maxillary premolar usually lies in the
appearance zone where aesthetics is a concern. Apart from maxillary
premolars, mandibular premolars and mandibular first molars also lie
Steps in the preparation of maxillary first premolar to receive PFM
Before preparation, an index is formed using silicone putty on the
labial, lingual and occlusal surfaces. The polymerized index is cut in
the centre of the occlusal surface to separate the facial and lingual
• Depth orientation grooves are made on the occlusal surface with
• About 1.5–2.0 mm of reduction is recommended in the areas
• Reduction is done in definite planes reproducing general basic
geometry of the occlusal surface of tooth.
• Functional cusp bevel is given on the lingual inclines of the
maxillary lingual cusp and buccal inclines of mandibular buccal
• About 1.5 mm reduction is recommended for metal coverage and
2.0 mm reduction for porcelain coverage.
• All the planes of occlusal reduction are smoothened with No. 170L
• Long thin tapered diamond is used.
• The bur is used in up and down or sawing motion.
• Reduction should not be overtapered.
• Torpedo diamond is used for lingual reduction.
• Chamfer finish line is created.
• Chamfer finish line and axial surfaces are smoothened with torpedo
• Flat end-tapered diamonds are used for buccal reduction.
• Shoulder finish line is created which extends lingual to the proximal
• Junction of the shoulder and chamfer on the lingual finish line
• Shoulder finish line or shoulder with bevel is recommended on the
buccal wall for PFM preparation.
• In those preparations where metal collar is recommended, the finish
line is placed within the sulcus to hide the metal (Fig. 25-10).
FIGURE 25-10 Completed metal–ceramic preparation on
• It has better aesthetics than cast metal crown.
• More tooth reduction is required to accommodate porcelain.
• There are increased chances of fracture of brittle porcelain.
• It has inferior aesthetics as compared with all-ceramic crowns.
• It is more expensive than cast metal crown.
• Functional cusp bevel is given on the lingual inclines of the
maxillary lingual cusps and buccal inclines of the mandibular
• Finish line of choice in cast metal is chamfer, in all-ceramic is
shoulder, in PFM is shoulder with bevel on labial surface and
chamfer on lingual and proximal surfaces, shoulder with bevel is
proximal box of inlay and onlay.
• Knife-edged finish line is advocated in lingually tilted mandibular
• Truss effect is provided to enhance the structural durability.
• All-ceramic crowns should be avoided in edge-to-edge occlusion
• Disadvantage of porcelain is high firing shrinkage.
• In winged preparation for PFM, the shoulder finish line should be
lingual to the proximal contact.
• Porcelain bonded to metal is strongest when it is fired under
• Proximal grooves in anterior partial veneer crown should be placed
parallel to the incisal two-thirds of the facial surface.
• In posterior partial veneer crown, the proximal grooves should be
parallel to the long axis of the tooth.
• Grooves should have definite lingual walls to resist displacement
• Reverse three-quarter crown is used on mandibular molars to
preserve intact lingual surface in cases of severe lingual inclination.
• Proximal half crown is a three-quarter crown which preserves the
distal surface as the tooth is rotated by 90°.
• Vertical lingual wall in anterior partial veneer crown is essential for
• In partial veneer crown, contrabevel is never placed on the incisor
• Minnesota ditch is a ‘V’-shaped groove at the junction of axial wall
and gingival floor in proximo-occlusal inlays used to enhance
resistance to displacement by occlusal forces.
• Principle of substitution is used to compensate for mutilated or
missing cusps or when clinical crown length is inadequate.
• Shade tabs should be moistened during shade selection.
• First all-ceramic crown was developed by Charles H. Land in 1886
• Dicor was the first commercially castable ceramic material used.
• Dr Charles Pincus first used porcelain veneers to improve
• Periodontal bridge is the most common cause of missing tooth in a
• Full veneer crown has the maximum retention among all the
• Richmond crown was the first crown on which porcelain facing was
• Davis crown is an all-ceramic crown which is attached to the tooth
Various Methods of Gingival Retraction during
Techniques Used for Gingival Retraction, 380
Importance of Impression Making in Fixed
Various Impression Techniques Used in Fixed
Post-space Impression Technique, 385
Successful restorative procedures demand dry operating field and
clear visibility. For that, fluid control is essential.
Fluid control provides the following:
• It provides a dry, clear operative field.
• It improves accessibility and visibility.
• It is comfortable for both the operator and the patient.
• It aids in impression making.
There are essentially two methods of fluid control, namely,
mechanical and chemical methods.
• Local anaesthetics (adrenaline)
• It was introduced by S.C. Barnum.
• This is the most effective isolation method.
• It is used during tooth preparation of inlays and onlays, post and
core fabrication, cementation and pin-retained amalgam.
• It should not be used with polyvinyl siloxane impression material
because it inhibits its polymerization.
• It is very useful during crown preparation.
• It is used effectively by assistant.
• It is an excellent lip retractor.
• It is not used during impression making or cementation procedure.
• It is most useful when used as an adjunct to high-volume
• It can be used alone for maxillary arch during impression making
• It is placed at the corner of mouth, opposite to the quadrant being
treated and head of patient is tilted towards it.
• It is used for isolation of the mandibular arch.
• It consists of metal saliva ejector with attached tongue deflector.
• Cotton rolls can be used along with it during cementation or
• It is most effective when the patient is upright.
• Accessibility to lingual surface of lower teeth is limited.
• It should not be used in patients with mandibular tori.
• Metal component may injure the soft tissues in the floor of the
• These drugs are helpful in controlling the salivary flow (e.g.
methantheline bromide and propantheline bromide).
• These are gastrointestinal (GI) anticholinergics which act on the
smooth muscles of the GI tract, urinary or biliary tract and produces
• Hypersensitivity to this drug, glaucoma, asthma, congestive heart
failure, patient on corticosteroids.
Another drug used effectively as antisialagogue is clonidine
hydrochloride. It is an antihypertensive agent and should be used
with caution in hypertensive patients taking other medications. Its
side effects are dry mouth and drowsiness.
Various methods of gingival retraction during
impression making in fixed prosthodontics
Indirect restoration, such as cast crowns, partial veneer crowns,
complete all-ceramic crowns, porcelain fused to metal crowns, inlays
or onlays demand accurate impression with defined cervical margin
for accurate fit. Gingival retraction is essential to accurately capture
the cervical margins. The primary aim of gingival retraction is to
displace the gingival tissues at the margins reversibly in order to
allow the impression material to capture the marginal detail.
Methods of gingival retraction
• The gingiva is physically displaced to ensure adequate reproduction
• Common mechanical methods are copper band, cotton cord and
• It serves as a receptacle to carry impression material as well as
• The copper band is contoured and trimmed according to the
• The band or tube is then loaded with impression compound or
elastomeric impression material and placed along the path of
• Impression is poured with die stone or electroplated metal.
• It is used when multiple abutments are prepared and their
impressions are made individually for more accuracy.
• Its disadvantage is that it may injure the gingiva.
FIGURE 26-1 Copper tube impression.
• Plain cotton cords are used to displace the gingiva physically.
• Its effectiveness is limited because it is based on pressure
application, which is not enough to control the sulcular
• It is used when limited number of teeth in a quadrant are prepared.
• The preparation should not extend too far subgingivally.
• The wings of the bow and clamp are blocked out and modified trays
• Elastomeric impression materials should not be used with rubber
dam as they interfere with its polymerization.
Mechanico-chemical method (retraction cord)
• This is the most commonly used method for gingival retraction.
• In this method, the chemical action of the material is combined with
pressure cord to control the sulcular fluid and reversibly enlarge the
Comments
Post a Comment
اكتب تعليق حول الموضوع