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TOOTH PREPARATION
  FOR CAST METAL
   RESTORATIONS


       INDIAN DENTAL ACADEMY
    Leader in Continuing Dental Education


    www.indiandentalacademy.com
   INTRODUCTION
   DEFINITONS OF INLAY AND ONLAY
   BRIEF LOOK AT CASTING METALS
   INDICATIONS AND
    CONTRAINDIACTIONS
   ADVANTAGES AND DISADVANTAGES
   INSTRUMENTATION FOR TOOTH
    PREPRATION FOR CAST RESTORATION
   PRINCIPLES OF TOOTH PREPRATION
    FOR CAST RESTORATIONS
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    Types of margins, design features and functions
     of occlusal and gingival bevels.
    Types and design features of facial and lingual
     flares.
     TOOTH PREPARATION FOR INLAY CAST
     RESTORATION
  i) Indications
ii)  General shape
iii) Internal anatomy

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      TOOTH PREPARATION FOR ONLAY CAST
       RESTORATION
i)     Indications.
ii)    General shape.
iii)   Internal anatomy.
       TOOTH PREPRATION FOR CAST RESTORATIONS
       WITH SURFACE EXTENSIONS
i)     Skirt
ii)    Collar
      CONCLUSION.
      REFERENCES.
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INTRODUCTION
The cast metal restoration is versatile and the
  procedure requires meticulous care both in
  preparation and laboratory procedures.
      The practice of restorative dentistry
  improved permanently on cast metal restorations
  when it was first introduced by Taggart for cast
  gold restorations.
Today, cast metal restorations and its applications
  have become basic treatment modalities in
  dentistry both for strengthening the tooth
  structure and maintaining the functional value.
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DEFINITIONS
INLAY
      It is primarily an intracoronal
 cast restoration that is fabricated
 outside the oral cavity and placed in
 the prepared cavity.
ONLAY
     An onlay is combination of
 intracoronal and extra coronal cast
 restoration when one or more cusps
 are covered.
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Brief look at casting metals :
    Gold alloy is most commonly used, however due to its
  expense other metals which are in use are :

                 Noble      Noble      Base          Base
                 (Gold      (Palladium metals        metals
                 based)     based)     (Cobalt       (Nickel
                                       based)        based)
Major            Gold       Palladium  Cobalt        Nickel
constituents
    ‘’           Silver     Silver     Chromium      Chromium

    ‘’           Copper     Copper     Tungsten      Iron

     ‘’                    Gold         Molybdenum
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INDICATIONS FOR CAST RESTORATIONS
A) Extensive tooth involvement
        Ultimate in both efficiently replacing lost tooth structure
    and supporting remaining tooth structure.
B) As an adjuvant to successful periodontal therapy
          i) physiologically restoring the dimensions of the
    contact contour, marginal ridges and embrasures.
          ii) Splinting of teeth loosened by periodontities to a
    better bone supported teeth. The rigid connection of several
    cast restoration assures distribution of the applied forces to
    the best supported teeth and minimises force on disabled
    teeth.



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C) Correction for occlusion:-
               If any drastic change is planned for the occlusal
  table or occluding parts of a tooth, cast restorations are ideal.

D) Restoration of Endodontically treated teeth:-
               After endodontically treated, the tooth become
  brittle. Almost always the clinical crown portion of these teeth
  will need reinforcing restoration.

E) Support for and preparatory to partial or complete dentures:-
                Weather they are a clasp type, over denture type,
  bar attachment. Most removable prosthesis will need cast
  restorations.



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F) Low incidences of plaque accumulation or decay :
              patients to receive a cast restorations should
   have their plaque accumulation in rigid control.

G) Esthetics :
              Of all metal restorations properly fitted cast
  restorations enhance esthetic appearance.

CONTRAINDICATIONS :

a) Developing and deciduous teeth:
              Growth or resorption may be affected by the
   traumatic nature of the procedures of the cast restorations.

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b) High Plaque and caries indices :
                 Patients with rampant caries and
  poor oral hygiene should not be given cast
  restorations

c) Occlusal Disharmony :
                Cast restorations should not be
  used in patients with severe occlusal
  interference or other defects .

d)Dissimilar Metals :
                  Gold-based castings are avoided
  in patients already having silver restorations.

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Advantages and Disadvantages of cast metal
               Restorations
Better yield, compressive, tensile and   Being a cemented restorations,
sheer strengths of alloy.                interphase leading to leakage around
                                         and under cast restoration will be a
                                         common problem.
Reproduces precise form and minute       Extensive tooth involvement creates
detail.                                  hazards to vital tooth structures.
Metals that are usually used are not     The cathodic effect of dental alloys
significantly affected by tarnish and    towards other metals used in the same
corrosion .                              mouth will lead to galvanic
                                         deterioration.
Fewer voids, no layering effects, less   Lengthy procedures, requiring many
internal stress will lead to strong      visits, temporary coverage between
structure.                               visits, expense of alloy.
Cast restorations can be finished,  Some cast alloys exhibit high abrasive
polished or glazed outside the oral resistance which may lead to
cavity.
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                                    imbalance occlusion.
Instrumentation for tooth preparations for
               cast restorations
A) Removal of undermined enamel and
  gaining access:
    undermined enamel is easily
  removed with hand cutting
  instruments like chisel, hatchet,
  wedelstaedt.




B) Removal of caries dentin and placing
  intermediary basing :
       Decayed dentin is usually
  excavated using spoon excavators,
  cleared of the diseased tissue ,proper
  intermediary base is placed and
  locked in place.
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c) Defining the facial and lingual marginal and axial
  parameters of the extra coronal portion of the
  preparation :
         using #3,4, or 5 round bur or ball shaped
  diamond stone, gauge out the axial surface near
  contemplated circumferential tie, Several of these
  gougings may be made within the parameters of
  the extracororonal preparation. They will serve as
  guide lines in over all axial reduction.




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D. Bur no.271 : tungsten
   carbide tapering fissure with
   0.8mm width
E. Bur no. 169L tapering
   fissure with 0.5 mm
F. Preliminary Shaping:
            Tapered fissure burs
   or diamond stones with or
   without rounded ends, are
   used to reduce the axial
   surface to the depth of the
   gouges, cutting strokes
   should be preplanned in
   starting and ending points,
   their angulations and their
   direction of pressure.
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   G .Boxing up :
              Using a tapered fissure bur, wall
    proper, e.g., for cast alloy onlay, the
    inner(pulpal) half to two-thirds of the
    facial or lingual wall occlusally , the axial
    half of the facial to two-thirds of the facial
    or lingual walls proximally, and the axial
    half two thirds of the gingival floor
    proximally. Care is taken in this step as it
    retains the resistance and retention form
    and hence angulation of cutting tool is
    very influential.

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H. Establishing circumferential tie
    constituents:

        Gingival bevels are best created with
    gingival margin trimmers. primary and
    secondary flares are done so with chisels
    or hatchets. occlusal bevels are prepared
    with cone shaped aluminum oxide stone.
    A feather-edge finishing line is prepared
    with filamentous stone . A beveled
    shoulder is prepared with a tapered
    fissure bur and a GMT.


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A hallow-ground bevel
  can be prepared either
  with a torpedo-shaped
  stone or bullet shaped
  stone, followed by
  round bur. For the
  reverse secondary flare,
  the preparation can be
  done using taper end
  diamond stone followed
  by hand instrument
  hatchet or bi angle
  chisel.

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I)   Finishing and establishing the continuity
     between the circumferential tie
     constituents:
                   Smoothing of the tie can be
     done with hand instruments and 12 fluted
     or 40 fluted carbide burs. Also fine grit sand
     paper discs, if access allows can be used
     effectively.
          Establishing the continuity between the
     circumferential tie constituents is best done
     by wedelstaedt chisel, biangle chisel or any
     other sharp chisel.


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PRINCIPLES OF CAVITY PREPRATION
 I) Outline form:
     i) External outline form:
          The external outline for inlay should consists of
        straight lines and smooth flowing curves, avoiding
        any short angles.
          Enamel rods at the cavosurface margin should be
        supported by dentin and supported laterally by rods
        that lie within the preparation.
          The cavosurface margin is placed in sound,
        unbroken tooth tissue to obtain a well fitting casting.
          The placement of bevels make the outline form
        slightly wider for cast restorations.
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ii) Internal outline form:
               The Pulpal floor and the axial wall
  of the inlay preparation must be placed in
  dentin. Care must be taken to protect the pulp.
              Pulpal floor will be usually positioned
  0.5mm into dentin below the central groove.
             In shallow preparations, parallelism
  enhances the resistance and retention form of
  the preparation.
            line angles in both occlusal and
  proximal portions of the preparations should be
  well defined. The axio-pulpal line angle should
  be slightly rounded.
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 It is sometimes desirable to incline the cutting
  instrument so that it forms either an exaggerated taper
  from cavosurface to pulpal floor or a long bevel on that
  area of the wall.
 This procedure protects the thin wall of enamel that
  remains at the cavosurface by maintaining a supporting
  edge of dentin.

II) Resistance and retention forms :
               The preparation of the tooth for a cast
   restoration must be so designed that will resist dislodging
   forces of compression and tension.
Inlay taper:
             Cavity walls must diverge from the floor of the
   preparation externally forms a basic design for all cast
   restorations
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 Removal of wax pattern and insertion of the casting is
  facilitated by the taper.
 A range between 4 to 6 degrees is used as it provides
  adequate retention of the cemented casting.
 The axial length of the preparation will influence the
  amount of taper. longer preparations require taper in
  higher range, short preparations in the lower range.
 Pulpal and cervical floors ideally should be
  perpendicular to lines of force that will influence the
  restoration. Floors positioned perpendicular to these
  lines of force will absorb the stress over a broad area
  of the tooth.
 Well defined line angles are also important in obtaining
  resistance and retention form.
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 The occlusal interlock or dovetail is a major factor in
  resistance and retention form.
 Specially designed features like pinholes or postholes are
  placed parallel to the line of draw of the preparation and with
  appropriate concern for the pulp
 Tapered grooves extending from cervical floor to the
  occlusal surface, are sometimes placed in the dentin portion
  of the proximal walls to form a locking key to aid in
  preventing lateral dislodgement of the restoration.


III) Removing carious dentin :
        Removal of deeper carious lesion frequently precedes
  the establishment of resistance and retention form.

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IV) Convenience form :
 This form provides accessibility and visibility
  required to complete operative procedures
  thoroughly.
 Opening the preparation to its approximate final
  outline form establish an intact dentin enamel
  junction enhances access and visibility for
  removing carious dentin and old restoration.
 Extension, taper and flare of proximal walls to
  permits access for disking and bevel placement,
  and extension to allow proper finishing and
  adaptation of the margins of the restorative
  material are all examples of convenience form.

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V) Finishing enamel walls and margins
       If Coarse or medium grit diamond
  instruments have been used during cavity
  preparation the walls and margins should be
  finished with carbide finishing burs or fine
  abrasive discs.
           The cervical bevel of indirect
  preparation is most frequently placed with the
  flame shaped extra fine finishing bur or gingival
  marginal trimmers for convenience and they
  provide a steeper bevel to prepare for an
  effective adaptation of the metal margin.
          A bevel placed with a flame shaped
  rotary instrument will establish excellent cervical
  margin and will further blend together with the
  buccal andwww.indiandentalacademy.com
               lingual proximal finish lines.
 a bevel on the cervical margin of a box preparation
  for the direct technique should be uniform about 1/4
  to ½ of mesio-distal width of the cervical floor and
  must include the proximal cervical cavosurface
  angles. Such a bevel is placed with GMT prior to
  finishing the proximal enamel walls.


VI) Cleaning and inspection of the cavity :
      Upon completing the cavity preparation, the walls,
  floors, margins should be cleaned with water. after
  drying with cotton pledgets and a gentle stream of
  warmed air, the cavity should be scrutinized carefully
  for any imperfections.


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Primary tooth preparations are more less the same as
   mentioned above and the dissimilar features are ;
1.Path of insertion : (a) should be parallel to the long
   axis of the tooth. (b) should be opposite to the
   occlusal load, this helps the inlay to seat well in the
   cavity without rocking or to prevent any micro
   movements.

2.Taper :It is the preparation in which the walls of the
  cavity in intracoronal cast restoration is diverged to
  occlusal margin and in extracoronal, converged to
  occlusal margin. The amount of taper should be
  normally 2˚ to 5˚ for one wall, for both walls should
  not exceed 10˚.The sum of taper of both walls is
  called “cone angle taper” and should not exeed 10˚.
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Taper depends on :

 1.Length of the preparation: Longer the wall, increased
     taper and shorter wall, minimal taper and parallel
     the wall.

 2.Surface involvement of cavity : More complex the
     surface involved, less should be taper and more
     parallelism.

 3.Need for retention : reduce the taper to have
     maximum retention.


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Types of margins in a cast restoration

Bevel, Chamfer, Shoulder are commonly used
  margins for cast restorations, how ever
  other margins are feather edge, chisel
  edge, sloped shoulder, shoulder with
  bevel.




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Advantages and Disadvantages
Bevel           Removes            Extends
                unsupported        preparation into
                enamel, allows     sulcus if used
                finishing of       on apical
                metal              margin.
chamfer         Distinct margin,   Care needed to
                adequate bulk,     avoid
                easier to          unsupported lip
                control            of enamel
Shoulder        Bulk of            Less
                restorative        conservative
                material

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BEVELS
Bevels are the “flexible extensions” of a cavity
   preparation.
This peripheral marginal anatomy of the preparation
   is called “circumferential tie”, bevels, being the
   part of the circumferential tie, are one of the
   major retention forms for a cast restorations. and
    has following features:
a) Enamel must be supported in the sound dentin.
b) Enamel rods forming the cavosurface margin
   should be continuous with sound dentin.
c) Enamel rods forming the restorative material and
   angular cavosurface angles should be trimmed.
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FUNCTIONS OF BEVELS
1)To increase the bulk of the material at the margins of
   the preparation.
2)By increasing the bulk, burnishing of the cast
   restoration is possible.
3)The cement line is hidden or marked by the bevel thus
   preventing marginal leakage.
4)Discrepancy in the cavity preparation or cast
   restoration is marked by the bevel.
5)It improves the resistance of the tooth structure.
6)Improves retention –reverse bevel also called as
   flexible extension, i.e., any surface defect like attrition
   can be involved in the preparation.
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The bevels available for cast restoration

1)   Partial: it involves part of
     enamel
2)   Short: It involves entire
     enamel.
3)   Long: It involves all of
     enamel but one half of
     the dentinal wall.
4)   Full: This involves all of
     the enamel and dentinal
     wall.


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5)   Hollow ground: It is concave in
     form, truly it is not a bevel,
     some times given to increase
     retention.




5)   Inverted Bevel: It is indicated
     only in metal ceramics. it is
     given on the labial shoulder.




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7)   Counter bevel : in case of capping
     the cusps. It is started from inner
     dentine involves enamel with a flat
     plane on enamel and is taken back.
8)   Reverse bevel: bevel towards axial
     wall and slopping towards it, made
     of dentine fully, aids in retention
     and prevents proximal
     displacement.
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Types and design features of facial and
     lingual flares.

a) The Primary Flare:
        This is the conventional and basic part of the
    circumferential tie facially and lingually of the proximal box
    for an intracoronal preparation.
         It is very similar to the long bevel formed of an enamel
    and part on the dentin, on the facial or lingual proximal wall.
          Primary flares have 45 degree angulation to the
    dentinal wall proper.




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Functions and indications :
 Brings proximal facial and lingual
 walls to self cleansable and
 finishable areas.
 They are indicated for any facial
 or lingual proximal wall of any
 intracoronal cavity preparation. It
 is prepared on enamel and
 dentin.


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The secondary flare :
It is a flat plane superimposed
    peripherally to a primary
    flare. usually it is prepared
    on enamel , but sometimes
    may involve dentin. Unlike
    primary flare, secondary
    flare have different
    involvements, angulations
    and extent depending on
    their functions.



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Functions of secondary flare
In a very widely extend lesion bucco-lingually ,the buccal
   and lingual structure will be badly thinned, the primary
   flare will end with acute angled marginal tooth structure,
   here a secondary imposed flare will create the needed
   obtuse angulation of the marginal tooth structure without
   any sacrifice to resistance and retention form, because
   the wall proper and primary flare maintained at their
   proper location and angulations.




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In very broad contact areas, the
   primary flare will not bring facial
   and/or lingual areas to self
   cleansable areas, however a
   secondary flare placed
   peripheral to that primary flare
   will accomplish this without the
   change in a 45 degree
   angulation and the resistance
   and retention forms.


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Surface defects or decalcifications, facial
 or lingual to the primary flare’s facial
 and lingual margin respectively, can be
 involved in the preparation with the
 secondary flare without to extend or
 angulate the primary flare more than
 indicated.

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   In ovoid teeth peripheral margin
    undercuts esp. apt to be present
    occluso-apically on the facial and/or
    lingual peripheries of the cavity walls.
    Elimination of these undercuts via wall
    proper or primary flare extension will
    unnecessarily involve and weaken
    tooth structure. How ever a secondary
    flare superimposed on primary flare
    will eliminate these undercuts with only
    minimal sacrifice to tooth structure.




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Tooth Preparation for Inlay cast
restoration :
   Indications :
     cavity width does not exceed 1/3 inter cuspal
      distance.
     Strong self-resistance cusps remain.

     Indicated teeth have minimal or no occlusal facets

      and if present limited to occlusal surfaces.
     The tooth occlusion or occluding surfaces are not to

      be changed by restorative procedure.
   General shape :
              Outline of occlusal preparation is dove
    tailed. the proximal portion is usually boxed in
    shape.
   Location of margins :
                   In occlusal portions, the margins are
    located on inclined planes of corresponding
    cusps , triangular cusps or marginal ridges.
                  The most peripheral margins of the
    preparations are located away from contact with
    the opposing tooth surface during centric closure
    and extrinsic movements of the mandible.
                  All adjacent wear facets,
    supplementary grooves, areas of decalcification
    should be included in beveled portion of the
    cavity preparation only. The margins of this
    design fulfill all requirements of extension of
    prevention.
   Internal anatomy :
                           The wall
    proper-taper, should taper from
    either 2-5 degrees or be parallel to
    each other. Each wall should make
    right angles/slightly obtuse angle
    with pulpal floor. Preferably each of
    wall proper should be parallel to
    long axis of crown.
   The occlusal bevel : it is along bevel, almost one
    third of the facial and lingual (proximal) walls. This
    beveled outer plane of the walls will have
    angulations of 30-45 degrees to the long axis of
    the crown. This angulation should increase as the
    width of the cavity increases to accommodate
    more bulk of the cast alloy and to resist increased
    stress near the cusps on inclined planes.
   Pulpal floor : should be flat for
    most extent if this is not possible,
    atleast the peripheral portions
    should be flat .Generally should
    be 1 to 1.5mm from DEJ. The
    pulpal floor should meet all
    surrounding walls at definite line
    angle except its junction with the
    axial wall, where it should be
    rounded.
   Proximal portion: Axial wall should be flat or
    slightly rounded in bucco-lingual direction, either
    vertical or slightly divergent(5-10 degrees)
    towards pulpal floor in the gingivo-occlusal
    direction. The depth axially should be 1 to 1.5mm
    from DEJ. However different depths may be
    necessary according to carcinogenic pattern.
   Proximally facial and lingual walls : composed
    of two planes ,axial half and proximal half.
     Axial half (i.e. facial or lingual wall proper ) is
    completely formed by dentin and meets axial
    wall at right angle. This is main resistance and
    retention form of this part.
    Proximal half: Is formed of primary flare in
    enamel and dentin ,45 degree angle to wall
    proper.

    Secondary flare: Some times it is necessary to impose
    a third plane in the form of secondary flare, placed on
    the enamel peripherally .This simplifies impressions and
    wax patters techniques.
   The gingival floor: Proximally should be flat in the
    bucco-lingual direction, making a slightly obtuse angle
    with the buccal and lingual walls. The axio proximal line
    direction is formed in two planes, the axial half and
    proximal half. The axial half consists of gingival floor,
    being perfectly flat, formed of dentin making either right
    angle or slightly obtuse angle with the axial wall. The
    proximal half should be beveled in the form of a long
    bevel inclining gingivally. this bevel is usually angulated
    on the average of 30-45 degrees.
   The junction between the occlusal bevel and the
    secondary or primary flare proximally and also
    the junction between the primary and secondary
    flares proximally and the gingival bevel should
    be rounded and smooth.
Secondary modes of retention :


    1) Luting cement : fills gap between inlay and
       tooth giving a physio chemical bonding.
       Physical – Zinc phosphate, chemical : glass
       inomer + polycorboxylate. The exposed
       cement dissolves in the oral cavity and so
       should not be considered as main retentive
       factor.
2) Grooves : Place two
  grooves, one on bucco axial
  and other on lingual axial line
  angle with #165 bur. It is
  totally placed on dentine.
  Depth of groove should be
  0.3mm at the expense of
  buccal and lingual walls and
  never at expense of axial
  walls.
3)Reverse Bevel :
                    It is given on
  gingival seat. This bevel has
  generally three planes, i) reverse
  bevel plane where inclination is on
  gingivoaxial plane which prevents
  proximal displacement.
  ii) secondly, flat plane made of
  dentine.
  iii) thirdly ,plane which is sloping
  away from the axial wall made of
  enamel and dentine, this helps in
  proximal displacement.
4) Internal box:
                  made on the
  pulpal floor, which improves the
  retention by 4-5 times. this is
  on the uninvolved side. it
  should not have sharp line and
  point angles and definite walls.
  This prevents micromovement
  of the inlay. Internal box should
  always be reciprocated with a
  reverse bevel or groove to
  avoid micromovement.
5) External box : these are box
   shaped preparations opening to
   axial tooth surface .they can be
   proximal, facial or lingual. They can
   be either stepped occlusally or
   gingivally.
6) Roughening of pulpal floor : at
   specific areas of tooth preparation,
   esp. in pulpal floor, is done for
   more retentive and laterally
   locking. irregularities should have
   no frail or undermined enamel.
   Creating different levels out of flat,
   dished up, gingival or pulpal floors
   could change a mechanically
   negative situation into a positive
   one.
   7) Precementation grooves : after casting make
    grooves on the walls of the inlay and/or grooves
    on the cavity wall exactly opposite. This will
    house with solid mass of cement which helps in
    good retention
8)Electrolytic etching of inlay :

      This gives hinge like projections.

   Procedure : Protect proximal and occlusal surface
  with sticky wax and keep it in the electrolyte
  solution of 0.5 normal nitric acid.
               Inlay is kept in anode and metal with
  increased EMF as cathode.(316 stainless steel )
              current causes microporosities on fitting
  surface which enables the luting cement to flow
  into it for better retention. This process takes place
  for around 10 to 15 mins.
Tooth preparations for onlay cast
            restorations
  It is partly intracoronal and partly extra coronal type of
   restoration, which has cuspal protection as main feature.
Indications:
       1)cupal protection is to be considered if the lesion
   width is1/3 or ½ the intercuspal distance.
       2) cuspal protection is mandatory, if the width of the
   lesion exceeds ½ the intercuspal distance.
       3) In the tooth preparation. if the length:width ratio of
   the cusps is more than 1:1 but not exceeding 2:1, cuspal
   protection to be considered.
       4)if the length:width ratio is more than 2:1,cuspal
   protection is mandated.
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5) whenever there is a need to change the dimension, shape
   and interrelationship of the occluding tooth surfaces, onlay
   cast restorations are the ideal, most conservative
   restorations.
6) Onlays are ideal restorations for abutment teeth for a
   removal partial denture or fixed prosthesis.
7) Onlays are a ideal supporting restorations for remaining tooth
   structure, combined with conservative tooth involvement.
8) Onlays are indicated when it is necessary to include wear
   facets that exceed the cusp tips and triangular ridge crests
   facially and/or lingually.

GENERAL SHAPE :
       Onlays are dovetailed internally and follow cuspal
  anatomy externally. Proximally box or cone shaped. The main
  feature of the design of the tooth preparations are capping of
  functional cusps and shoeing of the non-functional cusps.
                   www.indiandentalacademy.com
Onlay Tooth Preparation Procedure

Occlusal preparation:
           The initial entry is made in
  the central fossa to a depth of
  approx. 1.00 mm into dentin(2.5mm
  in the total depth of the tooth). In
  some cases this may be needed to
  extend to greater depth because of
  caries or pervious restoration .
           The occlusal outline form
  should be as conservative as the
  carious lesion permits. The bur is
  kept in the long axis of the intended
  depth of the insertion so that the
  taper of the bur provides the
  desired 3 to 5 degree divergence
  for each internal cavity wall.
                 www.indiandentalacademy.com
Proximal boxes:
         The boxes are created
on the proximal surface. The
facial and lingual walls should
exhibit a combined divergence
of 6 to 10 degrees from each
other as was provided in the
occlusal area of the
preparation.




             www.indiandentalacademy.com
The faciolingual dimension
  is likely to be
  determined by the
  presence of a
  restoration, caries
  lesion. The bevels will
  extend the preparations
  slightly beyond the
  proximal contact area so
  that the margins of the
  restoration will be
  accessible for finishing
  with a disk.


             www.indiandentalacademy.com
Cuspal Reduction:
                 A carbide bur
or diamond bur is used to
reduce the cusp. Depth cuts of
1.5 to 2 mm are made for the
centric cusp(s) and cuts 1.0 to
1.5 mm are made for the non
centric cusps.




              www.indiandentalacademy.com
After the depth cuts are
  placed, a uniform
  reduction of the cusps that
  parallels the generally
  anatomic contours of the
  occlusal surface is made.




              www.indiandentalacademy.com
The cuspal heights are
  reduced to the full extent
  of the depth cuts.
  Reduction of centric
  cusps generally needs to
  be greater than that for
  the non centric cusps
  because less occlusal
  force tends to be exerted
  against a non centric
  cusp.



                www.indiandentalacademy.com
Shoulder Preparation:
                   A shoulder is
prepared on the external surface of
the centric cusp to provide a band
of metal to protect the tooth. The
bur is held parallel to the external
surface of the tooth and a shoulder
about 1.0mm in height and 1.0 mm
in axial depth is cut.
                 The finish line
should extend gingivally at atleast
1.0mm beyond any occlusal
contacts. The occlusoaxial line
angles are rounded. There must be
adequate (1.0 to1.5mm) clearance
in all eccentric mandibular
movements.

              www.indiandentalacademy.com
Non centric cusp :
                 A chamfer
or long bevel is given
instead of shoulder in non
centric cusp(s). A barrel
shaped bur can be used to
create chamfer. The bur is
positioned at an angle of
approximately 45 degrees
to the axial surface .This
provides additional
protection of the cusp.


           www.indiandentalacademy.com
Gingival Bevel:
   A smooth and distinct bevel is
established on the gingival margins with
no.7901 finishing bur, a thin tapered
diamond, or a gingival margin trimmer.
               This bevel should be
approximately 0.5mm width and at angle of
approx.45 degrees to the external surface
of the tooth.




              www.indiandentalacademy.com
Shoulder Bevel:
            A 1.0 mm bevel is placed on the
shoulder with No.7901 or fine diamond bur. This
bevel is blend with proximal bevels. Any sharp
angles at the junction of the various bevels and
across the occlusoaxial line angles are
eliminated.
Proximal Bevels:
           The proximal bevel or flare is
established with greater disk, a fine tapered
diamond. Divergence is established from the
gingival floor occlusally. The proximal bevel
should blend smoothly with the gingival bevel,
the buccal and lingual bevels.


            www.indiandentalacademy.com
Retention grooves :
   If retention grooves are
needed, grooves are placed
in both proximal boxes. A
no.169 bur is used to bisect
the facioaxial and linguoaxial
line angles.
        The grooves must
diverge toward the occlusal
aspect faciolingually and be
aligned with the internal part
of insertion.


            www.indiandentalacademy.com
TOOTH PREPARATION FOR CAST
           RESTORATIONS WITH SURFACE
                   EXTENSIONS
   Modifications for basic onlay and inlay tooth
    preparations and restoration involving part or all of the
    axial surface(s), but short of veneer crown
    preparation.

    i) Skirt.

    ii) Collar.




                  www.indiandentalacademy.com
Skirt:
 It is more extensive surface extension. It is
  also superimposed on the basic intra-coronal
  inlay or onlay cavity preparation facially or
  lingually.
 Indications:
           Skirting is required to involve defects
  with more dimensions (especially depth). To
  impart resistance and retention on a cast
  restoration in lieu of missing or shortened
  opposing facial/lingual walls.
          www.indiandentalacademy.com
   When the contact areas and the contour of the
    proximal surfaces are to be changed in the
    contemplated restorations. They will allow
    sufficient cast material to be accommodated
    without sacrifice of facial and lingual walls.
              Facially/lingually tilted teeth in order to
    restore occlusal plane. They will allow for the
    bulk, resistance and retention of the additional
    occlusal cast material required in building the
    occlusal table when so indicated skirts should be
    prepared on side towards which the tooth is
    tilted

             www.indiandentalacademy.com
    Every effort should be made to have the axial
    reduction of skirt parallel to rest of the cavity
    preparation. If skirt is to be used to change the
    contact and contour of the tooth, it should be
    extended far enough on facial and lingual surfaces
    of teeth to create sufficient retention and avoid
    marginal over hangs and over contouring. Like
    wise, if the skirt is used to create a regular
    occlusal plane for tilted teeth it should be extended
    far enough on facial or lingual proximally, away
    from direction of tilting.

                This helps in minimize effect of
    displacing forces in tilted direction. And also
    accommodation of enough cast material.

             www.indiandentalacademy.com
Collar :

 Most involving  are surface wise and
  depth wise, it can be one of the two
  types.
 Cuspal collars- involve the facial or
  lingual surfaces of one cusp in a multi-
  cusped tooth.
 Tooth collars – entire facial or lingual
  surface of the tooth.

        www.indiandentalacademy.com
   Indications :
   They help in retention and resistance when an
    entire cusp is lost prior to tooth preparation or
    when it is necessary to remove it due to
    excessive undermining.
   They help retention in shortened tooth.
   They help in resistance and enhance support in
    endodontically treated tooth.
   They are used in situations where pins are
    contra-indicated for retention purposes.
   They are used for cast materials with low
    castability.


          www.indiandentalacademy.com
   With axial depth of 1.5mm to
    2 mm, collar surface extend
    gingivally in a beveled
    shoulder finishing line,
    making it most reproducible
    extension. Collars should
    have less taper toward the
    cavity preparations than
    skirts. This improves retention
    in the shortened tooth or cusp
    preparations.




             www.indiandentalacademy.com
 The peripheral beveled portion of the
 collar will have its angulation and extent
 dictated by same features as those
 governing the angulation and extent for
 gingival bevels of inlays and onlays as
 more the bevel angulation better will be
 the marginal seating of cast restorations.


         www.indiandentalacademy.com
Conclusion:
Cast metal inlays and onlays offer excellent restorations that
  may be utilized in dentistry. Even though the technique is
  long and posts multiple visits for patient, the resulting
  restoration is durable and long lasting. High noble alloys
  are advised for patients with allergy or sensitivity to other
  restorative materials. Cast metal onlays in particular, can
  be designed to strengthen the restored tooth structure
  than a full crown.

The high degree of satisfaction and service derived from a
properly made cast metal restoration is a reward for the
painstaking application required.

             www.indiandentalacademy.com
References:
Art and science of operative dentistry –
  sturdevant – 4th edition.
Operative dentistry-modern theory and
  practice - M.A.Marzouk.
Fundamentals of operative dentistry-
  Richerd.s.Schwartz. -2nd edition
Text book of operative dentistry-vimal.k.sikri
Internet sources.
         www.indiandentalacademy.com
Thank you



www.indiandentalacademy.com

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Tooth preparation for cast metal restoration / endodontic courses by indian dental academy

  • 1. TOOTH PREPARATION FOR CAST METAL RESTORATIONS INDIAN DENTAL ACADEMY Leader in Continuing Dental Education www.indiandentalacademy.com
  • 2. INTRODUCTION  DEFINITONS OF INLAY AND ONLAY  BRIEF LOOK AT CASTING METALS  INDICATIONS AND CONTRAINDIACTIONS  ADVANTAGES AND DISADVANTAGES  INSTRUMENTATION FOR TOOTH PREPRATION FOR CAST RESTORATION  PRINCIPLES OF TOOTH PREPRATION FOR CAST RESTORATIONS www.indiandentalacademy.com
  • 3. Types of margins, design features and functions of occlusal and gingival bevels.  Types and design features of facial and lingual flares. TOOTH PREPARATION FOR INLAY CAST RESTORATION i) Indications ii) General shape iii) Internal anatomy www.indiandentalacademy.com
  • 4. TOOTH PREPARATION FOR ONLAY CAST RESTORATION i) Indications. ii) General shape. iii) Internal anatomy. TOOTH PREPRATION FOR CAST RESTORATIONS WITH SURFACE EXTENSIONS i) Skirt ii) Collar  CONCLUSION.  REFERENCES. www.indiandentalacademy.com
  • 5. INTRODUCTION The cast metal restoration is versatile and the procedure requires meticulous care both in preparation and laboratory procedures. The practice of restorative dentistry improved permanently on cast metal restorations when it was first introduced by Taggart for cast gold restorations. Today, cast metal restorations and its applications have become basic treatment modalities in dentistry both for strengthening the tooth structure and maintaining the functional value. www.indiandentalacademy.com
  • 6. DEFINITIONS INLAY It is primarily an intracoronal cast restoration that is fabricated outside the oral cavity and placed in the prepared cavity. ONLAY An onlay is combination of intracoronal and extra coronal cast restoration when one or more cusps are covered. www.indiandentalacademy.com
  • 7. Brief look at casting metals : Gold alloy is most commonly used, however due to its expense other metals which are in use are : Noble Noble Base Base (Gold (Palladium metals metals based) based) (Cobalt (Nickel based) based) Major Gold Palladium Cobalt Nickel constituents ‘’ Silver Silver Chromium Chromium ‘’ Copper Copper Tungsten Iron ‘’ Gold Molybdenum www.indiandentalacademy.com
  • 8. INDICATIONS FOR CAST RESTORATIONS A) Extensive tooth involvement Ultimate in both efficiently replacing lost tooth structure and supporting remaining tooth structure. B) As an adjuvant to successful periodontal therapy i) physiologically restoring the dimensions of the contact contour, marginal ridges and embrasures. ii) Splinting of teeth loosened by periodontities to a better bone supported teeth. The rigid connection of several cast restoration assures distribution of the applied forces to the best supported teeth and minimises force on disabled teeth. www.indiandentalacademy.com
  • 9. C) Correction for occlusion:- If any drastic change is planned for the occlusal table or occluding parts of a tooth, cast restorations are ideal. D) Restoration of Endodontically treated teeth:- After endodontically treated, the tooth become brittle. Almost always the clinical crown portion of these teeth will need reinforcing restoration. E) Support for and preparatory to partial or complete dentures:- Weather they are a clasp type, over denture type, bar attachment. Most removable prosthesis will need cast restorations. www.indiandentalacademy.com
  • 10. F) Low incidences of plaque accumulation or decay : patients to receive a cast restorations should have their plaque accumulation in rigid control. G) Esthetics : Of all metal restorations properly fitted cast restorations enhance esthetic appearance. CONTRAINDICATIONS : a) Developing and deciduous teeth: Growth or resorption may be affected by the traumatic nature of the procedures of the cast restorations. www.indiandentalacademy.com
  • 11. b) High Plaque and caries indices : Patients with rampant caries and poor oral hygiene should not be given cast restorations c) Occlusal Disharmony : Cast restorations should not be used in patients with severe occlusal interference or other defects . d)Dissimilar Metals : Gold-based castings are avoided in patients already having silver restorations. www.indiandentalacademy.com
  • 12. Advantages and Disadvantages of cast metal Restorations Better yield, compressive, tensile and Being a cemented restorations, sheer strengths of alloy. interphase leading to leakage around and under cast restoration will be a common problem. Reproduces precise form and minute Extensive tooth involvement creates detail. hazards to vital tooth structures. Metals that are usually used are not The cathodic effect of dental alloys significantly affected by tarnish and towards other metals used in the same corrosion . mouth will lead to galvanic deterioration. Fewer voids, no layering effects, less Lengthy procedures, requiring many internal stress will lead to strong visits, temporary coverage between structure. visits, expense of alloy. Cast restorations can be finished, Some cast alloys exhibit high abrasive polished or glazed outside the oral resistance which may lead to cavity. www.indiandentalacademy.com imbalance occlusion.
  • 13. Instrumentation for tooth preparations for cast restorations A) Removal of undermined enamel and gaining access: undermined enamel is easily removed with hand cutting instruments like chisel, hatchet, wedelstaedt. B) Removal of caries dentin and placing intermediary basing : Decayed dentin is usually excavated using spoon excavators, cleared of the diseased tissue ,proper intermediary base is placed and locked in place. www.indiandentalacademy.com
  • 14. c) Defining the facial and lingual marginal and axial parameters of the extra coronal portion of the preparation : using #3,4, or 5 round bur or ball shaped diamond stone, gauge out the axial surface near contemplated circumferential tie, Several of these gougings may be made within the parameters of the extracororonal preparation. They will serve as guide lines in over all axial reduction. www.indiandentalacademy.com
  • 15. D. Bur no.271 : tungsten carbide tapering fissure with 0.8mm width E. Bur no. 169L tapering fissure with 0.5 mm F. Preliminary Shaping: Tapered fissure burs or diamond stones with or without rounded ends, are used to reduce the axial surface to the depth of the gouges, cutting strokes should be preplanned in starting and ending points, their angulations and their direction of pressure. www.indiandentalacademy.com
  • 16. G .Boxing up : Using a tapered fissure bur, wall proper, e.g., for cast alloy onlay, the inner(pulpal) half to two-thirds of the facial or lingual wall occlusally , the axial half of the facial to two-thirds of the facial or lingual walls proximally, and the axial half two thirds of the gingival floor proximally. Care is taken in this step as it retains the resistance and retention form and hence angulation of cutting tool is very influential. www.indiandentalacademy.com
  • 17. H. Establishing circumferential tie constituents: Gingival bevels are best created with gingival margin trimmers. primary and secondary flares are done so with chisels or hatchets. occlusal bevels are prepared with cone shaped aluminum oxide stone. A feather-edge finishing line is prepared with filamentous stone . A beveled shoulder is prepared with a tapered fissure bur and a GMT. www.indiandentalacademy.com
  • 18. A hallow-ground bevel can be prepared either with a torpedo-shaped stone or bullet shaped stone, followed by round bur. For the reverse secondary flare, the preparation can be done using taper end diamond stone followed by hand instrument hatchet or bi angle chisel. www.indiandentalacademy.com
  • 19. I) Finishing and establishing the continuity between the circumferential tie constituents: Smoothing of the tie can be done with hand instruments and 12 fluted or 40 fluted carbide burs. Also fine grit sand paper discs, if access allows can be used effectively. Establishing the continuity between the circumferential tie constituents is best done by wedelstaedt chisel, biangle chisel or any other sharp chisel. www.indiandentalacademy.com
  • 20. PRINCIPLES OF CAVITY PREPRATION I) Outline form: i) External outline form:  The external outline for inlay should consists of straight lines and smooth flowing curves, avoiding any short angles.  Enamel rods at the cavosurface margin should be supported by dentin and supported laterally by rods that lie within the preparation.  The cavosurface margin is placed in sound, unbroken tooth tissue to obtain a well fitting casting.  The placement of bevels make the outline form slightly wider for cast restorations. www.indiandentalacademy.com
  • 21. ii) Internal outline form:  The Pulpal floor and the axial wall of the inlay preparation must be placed in dentin. Care must be taken to protect the pulp.  Pulpal floor will be usually positioned 0.5mm into dentin below the central groove.  In shallow preparations, parallelism enhances the resistance and retention form of the preparation.  line angles in both occlusal and proximal portions of the preparations should be well defined. The axio-pulpal line angle should be slightly rounded. www.indiandentalacademy.com
  • 22.  It is sometimes desirable to incline the cutting instrument so that it forms either an exaggerated taper from cavosurface to pulpal floor or a long bevel on that area of the wall.  This procedure protects the thin wall of enamel that remains at the cavosurface by maintaining a supporting edge of dentin. II) Resistance and retention forms : The preparation of the tooth for a cast restoration must be so designed that will resist dislodging forces of compression and tension. Inlay taper: Cavity walls must diverge from the floor of the preparation externally forms a basic design for all cast restorations www.indiandentalacademy.com
  • 23.  Removal of wax pattern and insertion of the casting is facilitated by the taper.  A range between 4 to 6 degrees is used as it provides adequate retention of the cemented casting.  The axial length of the preparation will influence the amount of taper. longer preparations require taper in higher range, short preparations in the lower range.  Pulpal and cervical floors ideally should be perpendicular to lines of force that will influence the restoration. Floors positioned perpendicular to these lines of force will absorb the stress over a broad area of the tooth.  Well defined line angles are also important in obtaining resistance and retention form. www.indiandentalacademy.com
  • 24.  The occlusal interlock or dovetail is a major factor in resistance and retention form.  Specially designed features like pinholes or postholes are placed parallel to the line of draw of the preparation and with appropriate concern for the pulp  Tapered grooves extending from cervical floor to the occlusal surface, are sometimes placed in the dentin portion of the proximal walls to form a locking key to aid in preventing lateral dislodgement of the restoration. III) Removing carious dentin : Removal of deeper carious lesion frequently precedes the establishment of resistance and retention form. www.indiandentalacademy.com
  • 25. IV) Convenience form :  This form provides accessibility and visibility required to complete operative procedures thoroughly.  Opening the preparation to its approximate final outline form establish an intact dentin enamel junction enhances access and visibility for removing carious dentin and old restoration.  Extension, taper and flare of proximal walls to permits access for disking and bevel placement, and extension to allow proper finishing and adaptation of the margins of the restorative material are all examples of convenience form. www.indiandentalacademy.com
  • 26. V) Finishing enamel walls and margins  If Coarse or medium grit diamond instruments have been used during cavity preparation the walls and margins should be finished with carbide finishing burs or fine abrasive discs.  The cervical bevel of indirect preparation is most frequently placed with the flame shaped extra fine finishing bur or gingival marginal trimmers for convenience and they provide a steeper bevel to prepare for an effective adaptation of the metal margin.  A bevel placed with a flame shaped rotary instrument will establish excellent cervical margin and will further blend together with the buccal andwww.indiandentalacademy.com lingual proximal finish lines.
  • 27.  a bevel on the cervical margin of a box preparation for the direct technique should be uniform about 1/4 to ½ of mesio-distal width of the cervical floor and must include the proximal cervical cavosurface angles. Such a bevel is placed with GMT prior to finishing the proximal enamel walls. VI) Cleaning and inspection of the cavity : Upon completing the cavity preparation, the walls, floors, margins should be cleaned with water. after drying with cotton pledgets and a gentle stream of warmed air, the cavity should be scrutinized carefully for any imperfections. www.indiandentalacademy.com
  • 28. Primary tooth preparations are more less the same as mentioned above and the dissimilar features are ; 1.Path of insertion : (a) should be parallel to the long axis of the tooth. (b) should be opposite to the occlusal load, this helps the inlay to seat well in the cavity without rocking or to prevent any micro movements. 2.Taper :It is the preparation in which the walls of the cavity in intracoronal cast restoration is diverged to occlusal margin and in extracoronal, converged to occlusal margin. The amount of taper should be normally 2˚ to 5˚ for one wall, for both walls should not exceed 10˚.The sum of taper of both walls is called “cone angle taper” and should not exeed 10˚. www.indiandentalacademy.com
  • 29. Taper depends on : 1.Length of the preparation: Longer the wall, increased taper and shorter wall, minimal taper and parallel the wall. 2.Surface involvement of cavity : More complex the surface involved, less should be taper and more parallelism. 3.Need for retention : reduce the taper to have maximum retention. www.indiandentalacademy.com
  • 30. Types of margins in a cast restoration Bevel, Chamfer, Shoulder are commonly used margins for cast restorations, how ever other margins are feather edge, chisel edge, sloped shoulder, shoulder with bevel. www.indiandentalacademy.com
  • 31. Advantages and Disadvantages Bevel Removes Extends unsupported preparation into enamel, allows sulcus if used finishing of on apical metal margin. chamfer Distinct margin, Care needed to adequate bulk, avoid easier to unsupported lip control of enamel Shoulder Bulk of Less restorative conservative material www.indiandentalacademy.com
  • 32. BEVELS Bevels are the “flexible extensions” of a cavity preparation. This peripheral marginal anatomy of the preparation is called “circumferential tie”, bevels, being the part of the circumferential tie, are one of the major retention forms for a cast restorations. and has following features: a) Enamel must be supported in the sound dentin. b) Enamel rods forming the cavosurface margin should be continuous with sound dentin. c) Enamel rods forming the restorative material and angular cavosurface angles should be trimmed. www.indiandentalacademy.com
  • 33. FUNCTIONS OF BEVELS 1)To increase the bulk of the material at the margins of the preparation. 2)By increasing the bulk, burnishing of the cast restoration is possible. 3)The cement line is hidden or marked by the bevel thus preventing marginal leakage. 4)Discrepancy in the cavity preparation or cast restoration is marked by the bevel. 5)It improves the resistance of the tooth structure. 6)Improves retention –reverse bevel also called as flexible extension, i.e., any surface defect like attrition can be involved in the preparation. www.indiandentalacademy.com
  • 34. The bevels available for cast restoration 1) Partial: it involves part of enamel 2) Short: It involves entire enamel. 3) Long: It involves all of enamel but one half of the dentinal wall. 4) Full: This involves all of the enamel and dentinal wall. www.indiandentalacademy.com
  • 35. 5) Hollow ground: It is concave in form, truly it is not a bevel, some times given to increase retention. 5) Inverted Bevel: It is indicated only in metal ceramics. it is given on the labial shoulder. www.indiandentalacademy.com
  • 36. 7) Counter bevel : in case of capping the cusps. It is started from inner dentine involves enamel with a flat plane on enamel and is taken back. 8) Reverse bevel: bevel towards axial wall and slopping towards it, made of dentine fully, aids in retention and prevents proximal displacement. www.indiandentalacademy.com
  • 37. Types and design features of facial and lingual flares. a) The Primary Flare: This is the conventional and basic part of the circumferential tie facially and lingually of the proximal box for an intracoronal preparation. It is very similar to the long bevel formed of an enamel and part on the dentin, on the facial or lingual proximal wall. Primary flares have 45 degree angulation to the dentinal wall proper. www.indiandentalacademy.com
  • 38. Functions and indications : Brings proximal facial and lingual walls to self cleansable and finishable areas. They are indicated for any facial or lingual proximal wall of any intracoronal cavity preparation. It is prepared on enamel and dentin. www.indiandentalacademy.com
  • 39. The secondary flare : It is a flat plane superimposed peripherally to a primary flare. usually it is prepared on enamel , but sometimes may involve dentin. Unlike primary flare, secondary flare have different involvements, angulations and extent depending on their functions. www.indiandentalacademy.com
  • 40. Functions of secondary flare In a very widely extend lesion bucco-lingually ,the buccal and lingual structure will be badly thinned, the primary flare will end with acute angled marginal tooth structure, here a secondary imposed flare will create the needed obtuse angulation of the marginal tooth structure without any sacrifice to resistance and retention form, because the wall proper and primary flare maintained at their proper location and angulations. www.indiandentalacademy.com
  • 41. In very broad contact areas, the primary flare will not bring facial and/or lingual areas to self cleansable areas, however a secondary flare placed peripheral to that primary flare will accomplish this without the change in a 45 degree angulation and the resistance and retention forms. www.indiandentalacademy.com
  • 42. Surface defects or decalcifications, facial or lingual to the primary flare’s facial and lingual margin respectively, can be involved in the preparation with the secondary flare without to extend or angulate the primary flare more than indicated. www.indiandentalacademy.com
  • 43. In ovoid teeth peripheral margin undercuts esp. apt to be present occluso-apically on the facial and/or lingual peripheries of the cavity walls. Elimination of these undercuts via wall proper or primary flare extension will unnecessarily involve and weaken tooth structure. How ever a secondary flare superimposed on primary flare will eliminate these undercuts with only minimal sacrifice to tooth structure. www.indiandentalacademy.com
  • 44. Tooth Preparation for Inlay cast restoration :  Indications :  cavity width does not exceed 1/3 inter cuspal distance.  Strong self-resistance cusps remain.  Indicated teeth have minimal or no occlusal facets and if present limited to occlusal surfaces.  The tooth occlusion or occluding surfaces are not to be changed by restorative procedure.
  • 45. General shape : Outline of occlusal preparation is dove tailed. the proximal portion is usually boxed in shape.
  • 46. Location of margins : In occlusal portions, the margins are located on inclined planes of corresponding cusps , triangular cusps or marginal ridges. The most peripheral margins of the preparations are located away from contact with the opposing tooth surface during centric closure and extrinsic movements of the mandible. All adjacent wear facets, supplementary grooves, areas of decalcification should be included in beveled portion of the cavity preparation only. The margins of this design fulfill all requirements of extension of prevention.
  • 47. Internal anatomy : The wall proper-taper, should taper from either 2-5 degrees or be parallel to each other. Each wall should make right angles/slightly obtuse angle with pulpal floor. Preferably each of wall proper should be parallel to long axis of crown.
  • 48. The occlusal bevel : it is along bevel, almost one third of the facial and lingual (proximal) walls. This beveled outer plane of the walls will have angulations of 30-45 degrees to the long axis of the crown. This angulation should increase as the width of the cavity increases to accommodate more bulk of the cast alloy and to resist increased stress near the cusps on inclined planes.
  • 49. Pulpal floor : should be flat for most extent if this is not possible, atleast the peripheral portions should be flat .Generally should be 1 to 1.5mm from DEJ. The pulpal floor should meet all surrounding walls at definite line angle except its junction with the axial wall, where it should be rounded.
  • 50. Proximal portion: Axial wall should be flat or slightly rounded in bucco-lingual direction, either vertical or slightly divergent(5-10 degrees) towards pulpal floor in the gingivo-occlusal direction. The depth axially should be 1 to 1.5mm from DEJ. However different depths may be necessary according to carcinogenic pattern.
  • 51. Proximally facial and lingual walls : composed of two planes ,axial half and proximal half. Axial half (i.e. facial or lingual wall proper ) is completely formed by dentin and meets axial wall at right angle. This is main resistance and retention form of this part. Proximal half: Is formed of primary flare in enamel and dentin ,45 degree angle to wall proper. Secondary flare: Some times it is necessary to impose a third plane in the form of secondary flare, placed on the enamel peripherally .This simplifies impressions and wax patters techniques.
  • 52. The gingival floor: Proximally should be flat in the bucco-lingual direction, making a slightly obtuse angle with the buccal and lingual walls. The axio proximal line direction is formed in two planes, the axial half and proximal half. The axial half consists of gingival floor, being perfectly flat, formed of dentin making either right angle or slightly obtuse angle with the axial wall. The proximal half should be beveled in the form of a long bevel inclining gingivally. this bevel is usually angulated on the average of 30-45 degrees.
  • 53. The junction between the occlusal bevel and the secondary or primary flare proximally and also the junction between the primary and secondary flares proximally and the gingival bevel should be rounded and smooth.
  • 54. Secondary modes of retention : 1) Luting cement : fills gap between inlay and tooth giving a physio chemical bonding. Physical – Zinc phosphate, chemical : glass inomer + polycorboxylate. The exposed cement dissolves in the oral cavity and so should not be considered as main retentive factor.
  • 55. 2) Grooves : Place two grooves, one on bucco axial and other on lingual axial line angle with #165 bur. It is totally placed on dentine. Depth of groove should be 0.3mm at the expense of buccal and lingual walls and never at expense of axial walls.
  • 56. 3)Reverse Bevel : It is given on gingival seat. This bevel has generally three planes, i) reverse bevel plane where inclination is on gingivoaxial plane which prevents proximal displacement. ii) secondly, flat plane made of dentine. iii) thirdly ,plane which is sloping away from the axial wall made of enamel and dentine, this helps in proximal displacement.
  • 57. 4) Internal box: made on the pulpal floor, which improves the retention by 4-5 times. this is on the uninvolved side. it should not have sharp line and point angles and definite walls. This prevents micromovement of the inlay. Internal box should always be reciprocated with a reverse bevel or groove to avoid micromovement.
  • 58. 5) External box : these are box shaped preparations opening to axial tooth surface .they can be proximal, facial or lingual. They can be either stepped occlusally or gingivally.
  • 59. 6) Roughening of pulpal floor : at specific areas of tooth preparation, esp. in pulpal floor, is done for more retentive and laterally locking. irregularities should have no frail or undermined enamel. Creating different levels out of flat, dished up, gingival or pulpal floors could change a mechanically negative situation into a positive one.
  • 60. 7) Precementation grooves : after casting make grooves on the walls of the inlay and/or grooves on the cavity wall exactly opposite. This will house with solid mass of cement which helps in good retention
  • 61. 8)Electrolytic etching of inlay : This gives hinge like projections. Procedure : Protect proximal and occlusal surface with sticky wax and keep it in the electrolyte solution of 0.5 normal nitric acid. Inlay is kept in anode and metal with increased EMF as cathode.(316 stainless steel ) current causes microporosities on fitting surface which enables the luting cement to flow into it for better retention. This process takes place for around 10 to 15 mins.
  • 62. Tooth preparations for onlay cast restorations It is partly intracoronal and partly extra coronal type of restoration, which has cuspal protection as main feature. Indications: 1)cupal protection is to be considered if the lesion width is1/3 or ½ the intercuspal distance. 2) cuspal protection is mandatory, if the width of the lesion exceeds ½ the intercuspal distance. 3) In the tooth preparation. if the length:width ratio of the cusps is more than 1:1 but not exceeding 2:1, cuspal protection to be considered. 4)if the length:width ratio is more than 2:1,cuspal protection is mandated. www.indiandentalacademy.com
  • 63. 5) whenever there is a need to change the dimension, shape and interrelationship of the occluding tooth surfaces, onlay cast restorations are the ideal, most conservative restorations. 6) Onlays are ideal restorations for abutment teeth for a removal partial denture or fixed prosthesis. 7) Onlays are a ideal supporting restorations for remaining tooth structure, combined with conservative tooth involvement. 8) Onlays are indicated when it is necessary to include wear facets that exceed the cusp tips and triangular ridge crests facially and/or lingually. GENERAL SHAPE : Onlays are dovetailed internally and follow cuspal anatomy externally. Proximally box or cone shaped. The main feature of the design of the tooth preparations are capping of functional cusps and shoeing of the non-functional cusps. www.indiandentalacademy.com
  • 64. Onlay Tooth Preparation Procedure Occlusal preparation: The initial entry is made in the central fossa to a depth of approx. 1.00 mm into dentin(2.5mm in the total depth of the tooth). In some cases this may be needed to extend to greater depth because of caries or pervious restoration . The occlusal outline form should be as conservative as the carious lesion permits. The bur is kept in the long axis of the intended depth of the insertion so that the taper of the bur provides the desired 3 to 5 degree divergence for each internal cavity wall. www.indiandentalacademy.com
  • 65. Proximal boxes: The boxes are created on the proximal surface. The facial and lingual walls should exhibit a combined divergence of 6 to 10 degrees from each other as was provided in the occlusal area of the preparation. www.indiandentalacademy.com
  • 66. The faciolingual dimension is likely to be determined by the presence of a restoration, caries lesion. The bevels will extend the preparations slightly beyond the proximal contact area so that the margins of the restoration will be accessible for finishing with a disk. www.indiandentalacademy.com
  • 67. Cuspal Reduction: A carbide bur or diamond bur is used to reduce the cusp. Depth cuts of 1.5 to 2 mm are made for the centric cusp(s) and cuts 1.0 to 1.5 mm are made for the non centric cusps. www.indiandentalacademy.com
  • 68. After the depth cuts are placed, a uniform reduction of the cusps that parallels the generally anatomic contours of the occlusal surface is made. www.indiandentalacademy.com
  • 69. The cuspal heights are reduced to the full extent of the depth cuts. Reduction of centric cusps generally needs to be greater than that for the non centric cusps because less occlusal force tends to be exerted against a non centric cusp. www.indiandentalacademy.com
  • 70. Shoulder Preparation: A shoulder is prepared on the external surface of the centric cusp to provide a band of metal to protect the tooth. The bur is held parallel to the external surface of the tooth and a shoulder about 1.0mm in height and 1.0 mm in axial depth is cut. The finish line should extend gingivally at atleast 1.0mm beyond any occlusal contacts. The occlusoaxial line angles are rounded. There must be adequate (1.0 to1.5mm) clearance in all eccentric mandibular movements. www.indiandentalacademy.com
  • 71. Non centric cusp : A chamfer or long bevel is given instead of shoulder in non centric cusp(s). A barrel shaped bur can be used to create chamfer. The bur is positioned at an angle of approximately 45 degrees to the axial surface .This provides additional protection of the cusp. www.indiandentalacademy.com
  • 72. Gingival Bevel: A smooth and distinct bevel is established on the gingival margins with no.7901 finishing bur, a thin tapered diamond, or a gingival margin trimmer. This bevel should be approximately 0.5mm width and at angle of approx.45 degrees to the external surface of the tooth. www.indiandentalacademy.com
  • 73. Shoulder Bevel: A 1.0 mm bevel is placed on the shoulder with No.7901 or fine diamond bur. This bevel is blend with proximal bevels. Any sharp angles at the junction of the various bevels and across the occlusoaxial line angles are eliminated. Proximal Bevels: The proximal bevel or flare is established with greater disk, a fine tapered diamond. Divergence is established from the gingival floor occlusally. The proximal bevel should blend smoothly with the gingival bevel, the buccal and lingual bevels. www.indiandentalacademy.com
  • 74. Retention grooves : If retention grooves are needed, grooves are placed in both proximal boxes. A no.169 bur is used to bisect the facioaxial and linguoaxial line angles. The grooves must diverge toward the occlusal aspect faciolingually and be aligned with the internal part of insertion. www.indiandentalacademy.com
  • 75. TOOTH PREPARATION FOR CAST RESTORATIONS WITH SURFACE EXTENSIONS  Modifications for basic onlay and inlay tooth preparations and restoration involving part or all of the axial surface(s), but short of veneer crown preparation. i) Skirt. ii) Collar. www.indiandentalacademy.com
  • 76. Skirt:  It is more extensive surface extension. It is also superimposed on the basic intra-coronal inlay or onlay cavity preparation facially or lingually.  Indications:  Skirting is required to involve defects with more dimensions (especially depth). To impart resistance and retention on a cast restoration in lieu of missing or shortened opposing facial/lingual walls. www.indiandentalacademy.com
  • 77. When the contact areas and the contour of the proximal surfaces are to be changed in the contemplated restorations. They will allow sufficient cast material to be accommodated without sacrifice of facial and lingual walls.  Facially/lingually tilted teeth in order to restore occlusal plane. They will allow for the bulk, resistance and retention of the additional occlusal cast material required in building the occlusal table when so indicated skirts should be prepared on side towards which the tooth is tilted www.indiandentalacademy.com
  • 78. Every effort should be made to have the axial reduction of skirt parallel to rest of the cavity preparation. If skirt is to be used to change the contact and contour of the tooth, it should be extended far enough on facial and lingual surfaces of teeth to create sufficient retention and avoid marginal over hangs and over contouring. Like wise, if the skirt is used to create a regular occlusal plane for tilted teeth it should be extended far enough on facial or lingual proximally, away from direction of tilting.  This helps in minimize effect of displacing forces in tilted direction. And also accommodation of enough cast material. www.indiandentalacademy.com
  • 79. Collar :  Most involving are surface wise and depth wise, it can be one of the two types.  Cuspal collars- involve the facial or lingual surfaces of one cusp in a multi- cusped tooth.  Tooth collars – entire facial or lingual surface of the tooth. www.indiandentalacademy.com
  • 80. Indications :  They help in retention and resistance when an entire cusp is lost prior to tooth preparation or when it is necessary to remove it due to excessive undermining.  They help retention in shortened tooth.  They help in resistance and enhance support in endodontically treated tooth.  They are used in situations where pins are contra-indicated for retention purposes.  They are used for cast materials with low castability. www.indiandentalacademy.com
  • 81. With axial depth of 1.5mm to 2 mm, collar surface extend gingivally in a beveled shoulder finishing line, making it most reproducible extension. Collars should have less taper toward the cavity preparations than skirts. This improves retention in the shortened tooth or cusp preparations. www.indiandentalacademy.com
  • 82.  The peripheral beveled portion of the collar will have its angulation and extent dictated by same features as those governing the angulation and extent for gingival bevels of inlays and onlays as more the bevel angulation better will be the marginal seating of cast restorations. www.indiandentalacademy.com
  • 83. Conclusion: Cast metal inlays and onlays offer excellent restorations that may be utilized in dentistry. Even though the technique is long and posts multiple visits for patient, the resulting restoration is durable and long lasting. High noble alloys are advised for patients with allergy or sensitivity to other restorative materials. Cast metal onlays in particular, can be designed to strengthen the restored tooth structure than a full crown. The high degree of satisfaction and service derived from a properly made cast metal restoration is a reward for the painstaking application required. www.indiandentalacademy.com
  • 84. References: Art and science of operative dentistry – sturdevant – 4th edition. Operative dentistry-modern theory and practice - M.A.Marzouk. Fundamentals of operative dentistry- Richerd.s.Schwartz. -2nd edition Text book of operative dentistry-vimal.k.sikri Internet sources. www.indiandentalacademy.com