RESTORATIVE DENTISTRY III

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RESTORATIVE DENTISTRY III

• STAINLESS STEEL CROWNS

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HISTORICAL PERSPECTIVES

• Stainless steel crowns for primary teeth were
  first marketed by Rocky Mountain Dental in the
  early 1950s. However, these early crowns had
  straight sides, that is, they were not preformed
  (festooned) to the primary tooth anatomy and
  required considerable chairside time and effort
  to trim, contour, crimp, and finish the crown in
  order to adapt it to the primary tooth.
• In the early 1960s, the Unitek corporation
  introduced an improved stainless steel crown.
  This crown was designed to require fewer
  alterations in clinical placement and was
  manufactured to match more closely the dimensions
  of the primary teeth. This crown was only
  slightly longer than the primary tooth crown, and
  the margins were festooned to correspond to the
  cervical aspect of the tooth. Although basically
  straight, the buccal and lingual walls were
  slightly contoured at the occlusal third to
  correspond to the anatomy of the tooth. The
  margins generally required trimming with
  subsequent contouring, crimping and finishing.

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HISTORICAL PERSPECTIVES

• In the late 1970s, the 3M Company began marketing
  a preformed posterior crown that was shorter in
  length, and was contoured and crimped in
  manufacture.
• These crowns more closely resemble the actual
  anatomic crown height and, therefore, require
  trimming less frequently.
• They are festooned, contoured in the middle third
  and crimped at the gingival margin.
• While they do require adjustments when being
  adapted to the childs tooth, they require fewer
  modifications, and therefore less chair time to
  place. This crown is the one generally employed
  in practice.

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HISTORICAL PERSPECTIVES

• Rocky Mountain Unitek 3M

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STAINLESS STEEL CROWNS
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STAINLESS STEEL CROWNS
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STAINLESS STEEL CROWNS
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INDICATIONS

• Restoration of a primary tooth with carious
  involvement such that a clinically acceptable
  amalgam or composite restoration cannot be placed
  which would last the life expectancy of the
  primary tooth.
• Interproximal caries which, when removed, would
  result in either wall of the proximal box of an
  intracoronal cavity preparation being extended
  beyond the anatomic axial line angles of the
  tooth.
• Caries on the mesial surface of the maxillary or
  mandibular first primary molar. The unique
  morphology of the mesial surfaces of these
  teeth, and the proximity of the pulp, make
  placement of an acceptable intracoronal
  restoration difficult.

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INDICATIONS

• Teeth so severely affected by the carious process
  that several surfaces have been destroyed.
  Enough tooth structure must remain to develop
  structurally sound walls for an intracoronal
  restoration. Caries on three or more surfaces
  generally dictates the placement of a crown.
  Typically three surface Class II restorations are
  not accomplished on primary teeth.
• Primary teeth with developmental defects.
  Aberrations in development such as amelogenesis
  imperfecta or dentiogenesis imperfecta will
  generally affect large surfaces of the primary
  tooth crown, thus requiring a stainless steel
  crown for restoration.

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INDICATIONS

• Stainless steel crowns are indicated following
  pulpal therapy. Subsequent to such procedures,
  the tooth tends to become brittle due to fluid
  loss and is likely to fracture. The placement of
  an extracoronal restoration protects against
  this.
• A stainless steel crown is indicated if the child
  has a high susceptibility to caries, manifested
  either by numerous, gross carious lesions or by
  rampant caries. Covering the clinical crown
  effectively prevents further assault of the tooth.

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NOT PREFERRED

• While stainless steel crowns have been advocated
  for the following circumstances, they are not the
  restoration of choice.
• Primary teeth in which conservative introcoronal
  restorations can be placed.
• Teeth to be exfoliated within six to 12 months.
  The cost-effectiveness of the restoration should
  be considered in treatment planning in many
  instances a temporary restoration can be places
  in molars approaching exfoliation.

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NOT PREFERRED

• Abutments for space maintainers. The preformed
  crown should be considered a means of restoring
  the tooth, not as a method of fabricating a space
  management appliance. The use of crowns to serve
  this dual role can result in poor adaptation of
  the crown to the tooth to accommodate the demands
  of the space maintainer. It is more appropriate
  to restore the tooth with a crown and then use a
  band over the crown as the abutment for the space
  management appliance.
• Stainless steel crowns are also manufactured for
  anterior primary teeth and permanent posterior
  molars. It is probable that alternative
  restorations, such as composite resin systems or
  bonded amalgams offer more appropriate strategies
  for restoration of these teeth.

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TECHNIQUE

• Removal of carious lesion
• Preparation of the tooth
• Selection and seating of the crown
• Adaptation of the crown to the tooth
• Cementation of the crown

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CARIES REMOVAL

• After gaining profound anesthesia and applying
  the rubber dam, all of the carious lesion should
  be removed from the tooth.
• In the event of a carious exposure, appropriate
  pulpal therapy is completed at this time.
• This sequence is recommended as frequently
  preparation of the tooth for the crown will
  result in cutting of the rubber dam material,
  thus compromising your ability to maintain a dry,
  clean operating field in which to perform what
  ever pulpal protection or therapy necessary.
• Frequently it is desirable to initiate occlusal
  reduction of the tooth along with caries removal
  in order to improve access to the carious lesion.

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PREPARATION OF THE TOOTH

• .
• A 69L or 169L bur is used to reduce the occlusal
  surface by 1.5 - 2.0 mm, following the cuspal
  outlines and maintaining the original contour of
  the cusps.

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PREPARATION OF THE TOOTH

• The depth of the reduction can be guided by
  cutting grooves of 1.5-2.0 mm depth through all
  of the fissures on the occlusal surface, and then
  removing the tooth structure of the cuspal
  inclines to connect all of the grooves.

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PREPARATION OF THE TOOTH

• The bur is used on its side with the end pointing
  toward the central groove.
• The cusps are reduced by sweeping the bur back
  and forth mesiodistally.
• In severely carious teeth, much of the occlusal
  surface has already been destroyed. Only that
  amount of the occlusal surface necessary to bring
  the surface 1.5-2.0 mm below its original level
  should be reduced. This can best be judged by
  comparison with the maginal ridges of the
  adjacent teeth.

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PREPARATION OF THE TOOTH

• The proximal surfaces of the tooth are now
  reduced.
• Wooden wedges should be placed in the
  interproximal embrasures prior to proximal
  reduction. This provides some separation of the
  teeth thus increasing access and visualization,
  and minimizing the risk of damaging the adjacent
  tooth enamel.
• Additionally, a wedge will provide for increased
  retraction of the rubber dam and the gingival
  tissues, reducing the potential for cutting the
  dam and lacerating the gingival tissue.

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PREPARATION OF THE TOOTH

• The bur is swept bucco-lingually across the
  proximal surface, beginning at the marginal ridge
  and at an angle slightly convergent to the
  occlusal surface.
• The bur should follow a path tangential to the
  proximal surface.

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PREPARATION OF THE TOOTH

• The depth of the the proximal slice should be
  sufficient to break contact with the adjacent
  tooth.
• Care must be taken to extend the preparation
  gingivally far enough to avoid the development of
  a ledge, which would make it difficult to seat
  the crown properly.
• Because of the cervical constriction of the
  primary tooth, adequate depth of the proximal
  preparation will result in a knife-edge finish
  line.

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PREPARATION OF THE TOOTH

• The depth of the proximal slice must be
  sufficient to develop a finish line cervical to
  any existing carious lesion.

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PREPARATION OF THE TOOTH

• Completed Proximal Slice

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PREPARATION OF THE TOOTH

• Note Preparation of a second primary molar
  for a steel crown, when the first permanent molar
  has not yet erupted, that is, before age six,
  still requires that the distal proximal surface
  of the second primary molar be prepared as
  indicated even though there is no approximating
  tooth.

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PREPARATION OF THE TOOTH

• All line angles created by the occlusal and
  proximal reductions are now rounded.
• The occlusal-buccal and occlusal-lingual line
  angles are rounded with a broad bevel by moving
  the bur at a 45 degree angle to the occlusal
  preparation.
• Note that there is NO reduction of the direct
  buccal or lingual surfaces. The only exception
  to this is the elimination of the an especially
  prominent buccal bulge on the mandibular first
  primary molar, when it is found to exist.

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PREPARATION OF THE TOOTH

• Completed occluso-buccal and occluso-lingual
  bevels

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PREPARATION OF THE TOOTH
The distolingual and distobuccal surfaces and
the mesiolingual and buccal surfaces are rounded
slightly into the proximal preparations to
eliminate sharpness.

• Occlusal view of rounded proximo-buccal and
  lingual line angles

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PREPARATION OF THE TOOTH

• Mesiodistal section and buccolingual
• section of prepared tooth

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CLINICAL CRITERIA FOR SUCCESSFUL PREPARATION

• Occlusal surface is reduced 1.5-2.0 mm
• Occlusal surface contour maintained
• Interproximal contact broken
• No interproximal ledges
• Buccal occlusal and lingual occlusal bevels exist
• No reduction of buccal and lingual surfaces
• Mesio-buccal and mesio-lingual, and distal-buccal
  and disto-lingual line angles rounded.

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SELECTION AND SEATING OF THE CROWN

• Six sizes of stainless steel crowns (1-6) are
  available for adaptation to the tooth.
• The crown must be large enough to fit over the
  height of contour of the tooth and around the
  cervical, but not so large that crimping of the
  crown will not result in a tight fit.
• The crown must also approximate the mesiodistal
  width of the tooth before it was prepared.

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SELECTION AND SEATING OF THE CROWN

• Typically crowns are inserted over the tooth
  preparation from lingual to buccal.

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SELECTION AND SEATING OF THE CROWN

• Although both the mesio-distal width of the crown
  and the crowns circumference are necessary
  considerations, the circumference of the crown is
  the major consideration.
• The mesiodistal dimension of the tooth and the
  space available for crown placement is frequently
  altered by the carious process. Interproximal
  caries is a significant cause of loss of arch
  circumference.
• Adjustments to the stainless steel crown can be
  made to compensate for this loss, as will be
  discussed subsequently.
• The circumference of the tooth at the gingival is
  relatively unaffected by the loss of space
  through carious destruction of the crown,
  therefore priority in crown selection must be
  given to a crown which fits the tooth at its
  cervical circumference.

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SELECTION AND SEATING OF THE CROWN

• It is generally advisable to initially select a
  medium sized crown, such as a 4, and progress to
  a larger or smaller crown as required. A 4 is
  the most commonly employed crown.
• The properly selected crown will approximate the
  mesiodistal width of the tooth and will be large
  enough to completely envelope the circumference
  of the tooth. It will have been placed with some
  resistance.
• The properly seated crown will not be rotated on
  the tooth, will not be canted either to the
  buccal or lingual, and its marginal ridges will
  correspond to the marginal ridges of adjacent
  teeth.

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ADAPTATION OF THE CROWN

• Because contouring and crimping of the 3M
  crown have been accomplished in manufacture,
  relatively few adjustments are required of the
  crown IF he preparation is ideal, and if there
  has been relatively minor destruction of the
  tooths crown has occurred, that is, there has
  been no loss of arch circumference due to the
  caries. When either of these circumstances exist
  considerable crimping and adaptation may be
  required.

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ADAPTATION OF THE CROWN

• Generally the adjustments that are necessary can
  be made with the 137 (Gordon) pliers, or a 110
  (Peeso) pliers.
• Adjustments usually involve modifying the buccal
  aspect of the crown in the cervical third and at
  the margin to adapt it more closely to the tooth
  structure.
• Fine adjustments at the proximal margins must
  sometimes be made to ensure a tightly fitting
  crown.

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ADAPTATION OF THE CROWN

• The crown should adapt to the walls of the tooth
  on the buccal and lingual surfaces. Recall that
  there is no reduction of these walls in the
  preparation.
• Instability of the crown can be corrected by more
  closely adapting the crown to these walls of the
  tooth.
• Crowns will be more difficult to place, that is,
  require more adjustments, on teeth that have lost
  considerable amounts of coronal tooth structure.

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ADAPTATION OF THE CROWN

• Generally contact with the adjacent teeth will be
  restored in the process of placing the crown. If
  it is not, this can be accomplished by enhancing
  the proximal contour(s) of the crown with a 112
  ball and socket pliers.

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ADAPTATION OF THE CROWN

• Buccolingual section of adapted stainless steel
  crown

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CLINCIAL CRITERIA FOR PROPERLY ADAPTED CROWN

• Margins are 1mm subgingival
• Crown fits tightly does not rock on tooth
• Resists occlusal displacement forces when applied
  at the margin
• Margins adapted to the cervical of the tooth
• Marginal ridge height coincides with adjacent
  teeth
• Crown not canted to buccal or lingual
• Crown not rotated to buccal or lingual
• Interproximal contact restored
• Occlusion satisfactory when judged by
  interdigitation of adjacent and contralateral
  teeth.

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SPECIAL CIRCUMSTANCESDECREASE IN ARCH
CIRCUMFERENCE

• Frequently, considerable proximal tooth structure
  will have been lost through caries. This loss of
  interproximal contact causes adjacent teeth to
  shift into the space normally occupied by the
  tooth be be restored.
• When this occurs, the crown required to fit over
  the height of contour and at the cervical aspect
  will be too wide mesiodistally to be placed.
• Sometimes the crown can be seated, but only if it
  has been rotated on the tooth to the buccal or
  lingual aspect to compensate for its width.
• A crown selected to fit the available mesiodistal
  space will be too small in circumference.

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SPECIAL CIRCUMSTANCESDECREASE IN ARCH
CIRCUMFERENCE

• When this occurs, a large crown, one which fits
  the tooth at the cervical is selected and reduced
  mesiodistally to fit the existing space.
• This is accomplished by grasping the crown with
  the Howe utility pliers at its marginal ridges,
  and squeezing the crown, thereby reducing the
  mesiodistal dimension.
• Care must be taken not to exert excessive
  pressure or the proximal walls will collapse.
• The reduction of the mesiodistal dimension will,
  of course, expand the crown buccolingually, and
  will necessitate considerable recontouring of the
  crown to the buccal and lingual walls of the
  tooth, as well as to the cervical circumference..

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SPECIAL CIRCUMSTANCESADJUSTING CROWN LENGHT

• It is sometimes necessary to adjust the length of
  the stainless steel crown. The crown may be too
  long, extending more than 1mm below the gingival
  crest and impinging on the ginginal attachment.
  This is manifest by blanching of the gingival
  tissues.
• When this occurs it is necessary to trim the
  excess. The gingival crest is scratched on the
  crown with an explorer. The crown length is then
  reduced to 1mm below this mark.
• The excess crown length is removed with a
  heatless stone. Alternatively, crown and bridge
  scissors may be used.
• Because this leaves the margin of the crown
  somewhat ragged and rough, the margin must be
  returned to a knife edge with a green stone, and
  then polished with a rubber wheel and fine
  abrasives, such as tripoli on a soft bristle
  brush, and rouge on a felt wheel.

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SPECIAL CIRCUMSTANCESADJACENT CROWNS

• When restoring multiple primary molars in the
  same quadrant, it is advisable to reduce the
  adjacent proximal surface of the teeth being
  restored more than when only one tooth is
  restored.
• This greater reduction will ease the placement of
  the crowns and the interproximal approximation.
• The more severe tooth reduction is necessitated
  by the loss of arch circumference which occurs
  when the proximal surfaces of two adjacent teeth
  are affected.

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CEMENTATION

• The crown can be cemented to place using either
  polycarboxylated cement (Durelon), a glass
  ionomer cement (Ketac), or zinc phosphate cement.
• The crown is slightly overfilled with the cement
  and placed on the thoroughly dried tooth.
• Cement should be expressed around all the
  margins, ensuring that all the space between the
  crown and tooth has been completely filled by
  cement, thereby effecting a good seal.
• When partially set, the excess cement is removed
  with an explorer or excavator.
• The interproximal area is cleaned of excess
  cement by typing a knot in a piece of waxed
  dental floss and drawing it through the
  interproximal.
• Air and water are used to flush the area and
  clean the crown.

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CEMENTATION

• Ideally, cementation can occur with the rubber
  dam in place. This is simply a safety precaution.
  With the rubber dam in place there is protection
  from the child swallowing (or in the worst case
  scenario, aspirating) the crown while it is being
  taken in and out of the mouth.
• This is most important when the behavior of the
  child is problematic or unpredictable.
• However, if the occlusion is questionable, then
  the rubber dam should be removed and the
  occlusion checked with the adapted crown in place
  before cementation.
• The most reliable prediction of the occlusion,
  absent removing the rubber dam, is the alignment
  of the marginal ridges of the crown with adjacent
  teeth.

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CLINICAL CRITERIA FOR SUCCESSFUL CEMENTATION

• The crown is cemented as adapted and continues to
  meet the adaptation criteria.
• No excess cement remains.

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