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Title: RESTORATIVE DENTISTRY III


1
RESTORATIVE DENTISTRY III
  • STAINLESS STEEL CROWNS

2
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.

3
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.

4
HISTORICAL PERSPECTIVES
  • Rocky Mountain Unitek 3M

5
STAINLESS STEEL CROWNS
6
STAINLESS STEEL CROWNS
7
STAINLESS STEEL CROWNS
8
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.

9
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.

10
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.

13
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.

14
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

15
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.

16
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.

31
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

37
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.

38
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.

43
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.

44
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.

45
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.

48
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.

49
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.

53
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.

54
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..

55
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.

60
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.

61
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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