Preparations

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Preparations ProvisionalsCompetency

• February 5, 2005
• USC School of Dentistry
• Brent Fung Saj Jivraj

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A Quote for the Day

• "What a man accomplishes in a day depends upon
  the way in which he approaches his tasks. When we
  accept tough jobs as a challenge. . . and wade
  into them with joy and enthusiasm, miracles can
  happen. When we do our work with a dynamic
  conquering spirit, we get things done." -
  Arland Gilbert

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Why are we here?

• To promote students dental skills.
• To provide students more consistent and complete
  feedback.
• To strive for higher levels of care.
• To challenge ourselves, review concepts, and/or
  maybe learn a new one or two.
• To provide a safe place for instructors to feel
  more comfortable and ask questions.

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Grading in General

• When grading, the work earns the lowest grade it
  receives in a category or, in the case of several
  minor errors (S grades), an M.
• Four R grades and one T grade in a category
  still earns an unacceptable grade of a T.

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Four Major Preparation Criteria

• Outline
• Covers the areas at or outside the margins the
  extent of coverage of the restoration.
• Damage to Adjacent Teeth, Separation from
  Adjacent Teeth, Proper Extension for Esthetics,
  Inclusion of Diseased Tooth Structure or Existing
  Restorations, Retention and Resistance are all
  covered in this area of evaluation.

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Four Major Preparation Criteria

• Internal
• This category evaluates the ability of the
  practitioner to properly reduce the tooth to
  allow adequate bulk for strength of restorative
  material, proper path of insertion, freedom of
  undercuts, and proper use of base and/or build-up
  materials.
• Technically, this is the most difficult of the
  categories to excel in due to the precision of
  the criteria and skill involved.

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Four Major Preparation Criteria

• Retention (and Resistance)
• This category evaluates the ability of the
  preparation to withstand dislodging forces placed
  on the final restoration including any
  supplemental retentive features.
• The four major contributing features are
• Parallelism of Retentive Features/Walls
• Height of Retentive Features/Walls
• Preparation Surface Area
• Preparation Surface Texture

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Four Major Preparation Criteria

• Cavosurface Margins
• This category evaluates the ability of the
  preparation to create a marginal seal while
  balancing the requirements for strength of the
  restorative material and tooth by utilizing
  proper geometry. It also evaluates the
  smoothness, continuousness, cleanliness, and
  accessibility of margins for impressions.
• Metal margins, here at USC, are typically
  prepared with a shoulder-bevel or chamfer finish
  line. Porcelain restorations are prepared with
  either a shoulder or differing depth chamfers.

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Grading the Outline

• Gingival Extension Preclinically, we extend to
  0.65 mm (range supragingival to 1.00 mm) from the
  exterior of the bevel to the gingival crest. We
  measure from line angle to line angle along the
  buccal and lingual surfaces.
• Clinically esthetics or pre-existing restorations
  may dictate where to place the margin.

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Grading the Outline

• To the left, the extension is even from the
  gingival crest and proper in dimension for an
  R.
• On the lower picture, the extension varies from
  supragingival to just over 0.65 mm for an M.

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Grading the Outline

• This preparation is underextended to well over 1
  mm (the upper limit for acceptability). This
  prep. would earn a grade of a T.
• In this canine preparation, the extension is
  evenly done, but only at 0.5 mm. Good control,
  but a variance in size for an S.

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Grading Outline

• Flares
• Flares should be measured at a point closest to
  the adjacent tooth ( 2/3 the way up the flare
  occlusal-gingivally) for extension.
• Maxillary MB Flares 0.5 mm (0.25 to 0.65 mm)
• All other Flares 0.75 mm (0.50 to 1.0 mm)

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Grading the Outline

• Access from Adjacent Teeth
• We want a minimum of 0.5 mm from the adjacent
  teeth after margins are placed to allow for an
  embrasure and bulk of impression material. There
  is no upper limit on separation. The tip of a
  Marquis Periodontal Probe measures 0.5 mm in
  width.

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Grading the Outline

• Damage to Adjacent Teeth
• Hopefully we wont incur any damage to the
  adjacent teeth during preparation. Teeth that
  are abraded or slightly flattened can still be
  acceptable if smoothed and the flattened area is
  small.

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Grading the Outline

• Slight Flattened, but smooth enough to provide a
  nice contact without changing the contours
  significantly. Still acceptable at an S or an
  M depending on area affected and degree of
  contour change.
• Significant contour change (including nicks and
  gouges) and roughness left on the adjacent tooth.
  All of these errors would grade to a T.
• Severe damage to the adjacent teeth requiring a
  restoration to repair damage would result in a
  V grade.

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Grading the Outline

• Clinically, one would also check that the
  preparation is extended to include
• Caries
• Decalcification (Clinical)
• Existing Restorations
• Termination of Finish lines on Finishable Tooth
  Structure
• Fissured Grooves

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Grading the Internal

• Occlusal Reduction
• Is measured at the reduced cusp tips to the
  opposing fossa or marginal ridge at an angle that
  parallels the opposing triangular ridges.
• Metal 1.5 mm (1.0 to 1.75 mm)
• Porcelain 2.0 mm (1.5 to 2.5 mm)

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Grading the Internal

• Round Condenser measures 1.5 mm and 2.0 mm on the
  small and large ends.
• Here instrument doesnt quite fit, so the
  occlusal reduction at this area is less than 2.0
  mm which is desirable for metal for an M grade.
  
• A 1.0 mm Hoe doesnt pass in centric occlusion
  showing under-reduction for a T Grade.

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Grading the Internal

• Clinically, the occlusal reduction can be checked
  with check bite wax. The difference in light
  transmission determines the amount of reduction.
• The wax can be calibrated by the use of Boley
  Gauge to graduated thicknesses.

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Grading the Internal

• Both of these preparations show inadequate
  reduction of less than 1.0 mm on the buccal
  cusps. These preparations would both earn a T
  grade.

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Grading the Internal

• The top picture shows an over-reduced preparation
  occlusally. It measures over the 2.5 mm maximum
  for porcelain for a certain T.
• The lower picture shows reduction within the
  range of acceptability that varies from
  cusp-to-cusp to earn the grade of an M.

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Grading the Internal

• Gingival Axial Reduction
• The gingival reduction is measured from the base
  of the 1st plane axial wall to the (extrapolated)
  external of the tooth perpendicular to the
  external surface. It looks smaller after the
  bevel if one is placed.
• Metal 0.65 mm (range of 0.5 to 1.0 mm (to 0.8 mm
  historically))
• Porcelain 1.0 to 1.3 mm ideally (1.0 mm to 1.5 mm)

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Grading Internal

• Box Form Axial Depth
• Box forms should have an axial depth of 1.3 mm
  (1.0 to 1.75 mm).
• They must create the internal corners of the box
  form with proper width to be retentive.

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Grading the Internal

• The top preparation is reduced 1.0 mm axially
  circumferentially for an M grade for porcelain.
• The bottom is reduced 0.65 mm where measured, but
  measured over 1.0 mm on the distolingual for a
  grade of a T.

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Grading the Internal

• Mid-Axial Reduction
• Mid-axial reduction is a function of the path of
  insertion and proper gingival reduction. When
  those two are acceptable, so will the mid-axial
  reduction.
• Metal 1.0 mm (0.75 to 1.25 mm)
• Porcelain 1.5 mm (1.0 to 2.0 mm)

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Grading the Internal

• The top picture shows too minimal a mid-axial
  reduction from a buccal path of insertion. This
  would be unacceptable T.
• The central preparation shows a nice mid-axial
  reduction thanks to a proper path of insertion
  and gingival axial reduction. This is R worthy.

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Grading the Internal

• Proper Path of Insertion
• A proper Buccolingual direction allows even
  reduction along the 1st planes from each surface
  directs the force down the long axis of the
  tooth. Mesiodistally, the path of insertion
  should allow the restoration to seat past the
  adjacent teeth. It also allows for multi-unit
  restorations to seat together.

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Grading the Internal

• Here two nicer paths of insertion are shown.
• In the top picture, the anterior bridge
  preparation will draw past the adjacent teeth.
• On the lower picture, the premolar prep has a
  slight lingual tilt to mimic the path of
  insertion of this tooth.

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Grading the Internal

• Freedom from Undercuts
• Preparations should be free from undercuts to
  allow a restoration to be fabricated. Undercuts
  so severe that a restoration cannot be fabricated
  will earn a T or V grade depending on the
  severity.

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Grading the Internal

• This preparation is so far undercut that a
  restoration couldnt be made. The lingual margin
  is not visible when citing down the buccal 1st
  plane for path of insertion. This certainly
  would receive an unacceptable grade of a T
  maybe a V?

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Grading the Internal

• Coincident Paths of Insertion
• Multi-unit restorations need to have a similar
  path of insertion between the preparations. If
  the paths of insertion are divergent, the final
  restoration may not seat.

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Grading the Internal

• Proper Planes of Reduction
• Second and Third Planes may be indicated
  depending on the first plane axial direction and
  the desired contour of the restoration. These
  would insure proper bulk of restorative material.

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Grading the Internal

• The top picture shows a second plane that may not
  provide ideal bulk for an esthetic restoration
  incisally.
• The lower picture shows a prominent second
  lingual plane. Maybe a bit wide and
  over-angulated, but it would certainly provide
  adequate bulk.

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Grading the Internal

• Occlusal Surfaces Reduced to Allow Proper Anatomy
  and Bulk at the Marginal Ridges.
• Preparations should somewhat reflect the occlusal
  anatomy (triangular ridges, grooves, pits) and
  clearance adjacent to the marginal ridges.

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Grading the Internal

• Using the groove in the adjacent molar as a guide
  for triangular ridge tilt, notice that the
  central groove area isnt prepared with the same
  bulk as the cusp tips to allow for even thickness
  of restorative material.

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Grading the Internal

• The occlusal anatomy although slightly changed
  from the original is still featured, but the
  marginal ridge areas are under-reduced (lt1.0 mm)
  for a T grade.
• The lower preparation has totally inadequate
  reduction on the occlusal surface (and cusp!) as
  the probe placed from adjacent marginal ridges
  touches the buccal triangular ridge of the
  preparation! It grades a V.

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Grading the Internal

• Internally, wed also consider whether any caries
  remains on the tooth and the proper indications
  for base or build-up materials.

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Grading Retention

• Parallelism has been shown to maximize at 6
  degrees of taper (range of parallel/zero to 15
  degrees).
• First plane axial wall height of 3 mm minimally
  (at the tallest point) is ideal.
• Supplemental retention can be effective at 2.5 mm
  of first plane wall and longer.

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Grading Retention

• Parallelism/taper of this preparation can be
  determined by transferring the probe from an
  opposing surface and determining the angle formed
  by the probe and the first plane axial wall.

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Grading Retention

• Relatively parallel preparations are difficult to
  grade in general. Sometimes a provisional or
  surveyed cast is a good way to determine if it is
  parallel or undercut. Parallel is an M.
  Undercut is a T.

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Grading Retention

• Over-tapered preparations are easier on the eyes
  for grading.
• The top preparation is too over-tapered and would
  earn a T.
• The lower preparation is in the acceptable taper
  range for an M grade.

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Grading Retention

• First Plane Axial Wall Height
• The longest wall height on these mesial walls
  clears the 3 mm ideal figure.
• Obviously, lingual axial first planes on anterior
  teeth dont fit into these criteria.

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Grading Retention

• The molar preparation only has about 2.5 mm of
  first plane axial on the lingual surface, so
  supplemental retention is desirable.
• Wall height along with parallelism with this
  preparation doesnt require any supplemental
  retention.

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Grading Retention

• Surface Area and Surface Texture also contribute
  to the retention and resistance.
• Surface area is dependent on the existing tooth
  conditions and should be maximized for each
  situation.
• Surface texture is added by the use of Diamond
  Burs while preparing.

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Grading Cavosurface Margins

• Marginal configuration is dependent on the
  restorative material. It maximizes the materials
  ability to close the marginal gap and leaves the
  tooth and restorative material in strong
  configurations.
• Metal 45 (30- 60) with width of 0.65 mm (0.5
  1.0 mm (0.8 mm historically)) for bevels
• Porcelain 90 (75- 105?) with width determined
  in Axial Reduction

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Grading Cavosurface Margins

• Bevel Width is measured along the angle the bevel
  is placed as shown here.
• Bevel Angulation is compared to the external of
  the tooth. Interproximally, this bevel has
  acceptable angulations.

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Grading Cavosurface Margins

• This top preparation has an acceptable bevel
  width of minimally 0.5 mm to earn an M grade.
• The lower preparation shows a bevel, but the
  width at the left is less than 0.5 mm and would
  grade a T.

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Grading Cavosurface Margins

• Porcelain Shoulder
• Porcelain is strongest at a 90 to the exterior
  of the tooth.

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Grading Cavosurface Margins

• Lipping Unsupported Enamel
• Oftentimes, lipping can occur at the transitional
  line angles of porcelain shoulders. The mesial
  side of this preparation shows a lipped area.

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Grading Cavosurface Margins

• Continuous Smooth Finish lines
• No matter which finish line(s) you have, margins
  should be smooth and continuous.
• The top bevel would earn an R.
• The bottom one is too rough and earns a T
  grade. Areas without a finish line earn a T or
  V.

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Grading Cavosurface Margins

• Both of these finish lines show roughness and
  irregularity.
• The top one is acceptable , an M, in this
  regard.
• The lower finishline may be too irregular to have
  a nicely fitting restoration for a T grade.

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Grading Cavosurface Margins

• Flares
• Flares should increase in size as they move
  occlusally.
• The angle formed to the tooth is still 45 to
  the external of the tooth.

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Grading Cavosurface Margins

• Clinically, wed also evaluate the preparation
  and adjacent teeth for cleanliness.
  Accessibility for impressions is also a
  consideration. Pre-clinically, we ask for the
  students to end equi-gingivally at the lowest.
  Clinically, this is obviously a very different
  situation.

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Preparation Errors
The next section will illustrate some preparation
errors. These preparations had been completed
as part of a pre-clinical exam. The Molars had
been prepared for a CVC and the premolar Prepared
for a PFM with metal occlusion. See if you can
visually evaluate the preparation and note the
error
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Examination Errors

• NOT ADHERING TO CRITERIA

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Overtapered
Lip
1.2mm above gingiva
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Occlusal anatomy flat
2mm above gingiva
Damage to adjacent tooth
Perio surgery
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Flat occlusal surface
Sharp angles and taper
Rough irregular margins, Too close to gingiva
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Very close to the gingiva
Overtapered mesially
Lip
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Too close to gingiva
Underreduced
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Undercut
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FILTHY
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Overtaper
Debris
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Interproximally, too much supragingival Not
sufficient clearance from adjacent teeth.
Overtaper
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Undercut
Undercut
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NO MARKS ON TOOTH HAND BACK CLEAN
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Irregular margins some too close
Occlusal overreduced
Short distal wall
Under-reduced and flat top
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Taper, lips in proximal area, too close to the
gingiva
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Lip
Wall height and taper
Over-reduced occlusally
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Overtaper, lipping at mesial proximal and damage
of adjacent tooth
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Overtaper
Under-reduced
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Very parallel, over 1mm above the gingiva,
under-reduced Occlusally 15
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Uneven prep
Axially Over-reduced
Shoulder on lingual
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UNECESSARY REMOVAL OF TOOTH STRUCTURE
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Buccolingual Undercut
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Rough margins
Sharp angles
Too parallel
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Margin too supra-gingival
Under-reduced
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UNDERCUTS
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SHORT WALLS
LIP
OUTLINE FORM
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EXCESSIVE SECOND PLANE
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EXCESSIVE SECOND PLANE
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INADEQUATE SECOND PLANE
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FLAT OCCLUSAL REDUCTION
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INADEQUATE CLEARANCE
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Occlusal Reduction Retention form Axial Wall
length Second Plane facial
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CONCEPTS CORRECT
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LACK OF CONCEPT
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Errors in Anterior Preparations
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OUTLINE
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No Clearance
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Interproximal Clearance
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INTERNAL
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Path of Insertion
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Lingual Clearance
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Lingual Clearance
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6.5 hoe should easily pass through
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Lingual Clearance
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There should be sufficient reduction at the TLA
for esthetics
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Excessive destruction of tooth tissue
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Excessive destruction of tooth tissue and Debris
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IDEAL
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Undercut on Canine as a result of wrong
angulation of bur During preparation
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Contours of preparation should follow contours of
adjacent tooth
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RETENTION
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MARGIN
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LIPPED MARGIN
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Look at slope of interproximal shoulder
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Slope of Interproximal Shoulder Incorrect not 90
degrees to EST
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Lipping
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DEBRIS
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PROVISIONALS
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Four Major Provisional Criteria

• Surface
• This category evaluates both the internal and
  external surface of the provisional for polish,
  smoothness, surface texture, adaptation, voids,
  debris, and density of acrylic resin.
• In this category, commonly seen errors include
  roughness, voids, poor adaptation, and debris.

152
Four Major Provisional Criteria

• Marginal Integrity
• This category evaluates the provisionals ability
  to create a marginal seal with the tooth the
  gingival contour of the provisional.
• Oftentimes, sub-marginal or excess margins are
  found. Students should be encouraged to salt
  and pepper areas where inadequate marginal
  coverage exists and remove excess margin from
  beyond the margins.

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Four Major Provisional Criteria

• Occlusion
• This category evaluates the function and occlusal
  form of the provisional using articulating paper
  and silver mylar (shimstock) to evaluate centric,
  lateral protrusive movements, and visual
  inspection of the occlusal form for cuspal
  heights anatomic form.
• On the Panadent articulator, we place two fingers
  on the maxillary members screw with firm (not
  heavy) pressure to check centric occlusion.
  Clinically, that pressure would be determined by
  the patients bite force.

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Four Major Provisional Criteria

• Axial Contours and Contacts
• This category evaluates the provisionals contour
  to be in harmony with the emergence profile of
  the tooth and the other teeth in the arch, the
  interproximal contacts, pontic to tissue contact,
  embrasure form, and, if applicable, pontic form.
• Probably the most commonly seen problem here is
  open proximal contacts and over-contouring.

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Grading Surface

• External Surfaces
• Are evaluated for smoothness, freedom from pits,
  voids, debris, polish.

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Grading Surface

• The top provisional shows general slight pitting
  of the axial surfaces and should be graded to an
  M.
• This provisional is still fairly smooth although
  it looks like the salt and peppered area is
  rough, it isnt. This could earn an S for
  minor roughness.

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Grading Surface

• External Errors
• This interproximal area is too rough and needs
  additional trimming polishing and is
  unacceptable for a T.
• This pontic displays roughness partially
  polished areas which would still accumulate
  plaque for a M.

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Grading Surface

• Internal Duplication
• Internal surfaces are judged on adaptation,
  detail reproduction, voids affecting structural
  integrity, and debris.
• These are nicely adapted clean.

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Grading Surface

• Internal Errors
• The pencil marks are considered debris as are
  polishing agents, articulating paper marks, and
  otherwise.
• This provisional shows a void in the connector
  area that would compromise the structural
  integrity.

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Grading Surface

• These two show voids internally.
• The upper picture shows a minor void and is
  acceptable for an S.
• The lower picture shows a large void on the
  functional side which compromises strength for a
  T.

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Grading Surface

• The Resin Mixture is also evaluated in this
  category. It is different than the surface
  pitting in that it is through and through the
  provisional.

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Grading Marginal Integrity

• Marginal Integrity
• Beveled preparations should have the provisional
  end somewhere on the bevel.
• Shoulder finish lines should be covered no more
  than 0.5 mm sub-marginal to be acceptable.

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Grading Marginal Integrity

• The margin on the mesial-gingival is open you
  can see the axial wall.
• The same applies on the buccal axial surface of
  the lower provisional bridge, the provisional
  doesnt cover the bevel.

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Grading Marginal Integrity

• This provisional shows slight marginal excess on
  the mesial gingival area. It wouldnt affect the
  gingiva with supragingival margins, and earns a
  slightly lowered grade of an M due to the
  amount of area over-contoured.

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Marginal Integrity
Overhang
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Grading Marginal Integrity

• The gingival contours on the upper mimic the
  emergence profile of the teeth for an R.
• The lower provisional doesnt allow any room for
  papilla and is totally unacceptable for a V.

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Grading Occlusion

• ALWAYS CHECK OCCLUSION WITH AND WITHOUT
  PROVISIONAL, CONTACT ON ADJACENT TEETH SHOULD BE
  THE SAME

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Grading Occlusion

• Occlusion
• Is always judged to the existing occlusion before
  the provisional is seated with two fingers of
  pressure on the maxillary retaining screw.
• We evaluate the occlusion with both mylar and
  articulating paper.

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Grading Occlusion

• Evaluating Occlusion
• Two fingers of pressure are placed on the
  Maxillary Retaining Screw.
• Mylar Holds in solid contacting areas. Mylar
  cannot be removed with added force.

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Grading Occlusion

• Evaluating Occlusion
• Mylar Drags in areas of close proximity. Mylar
  will become taut and be removed with added force
  in a drag.

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Grading Occlusion

• Proper Occlusion
• Notice that prior to the provisional seating that
  the premolars are contacting in centric
  occlusion. In the lower picture, the premolars
  still contact with the provisional seated.

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Grading Occlusion

• Hyperocclusion
• These provisionals are hyperoccluded and dont
  allow the premolars to contact with the
  provisional seated.
• The upper is less hyperoccluded and a T.
• In the lower, the front teeth are open by a
  couple of millimeters for a V.

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Grading Occlusion

• Hypoocclusion
• Provisionals are allowed to HOLD 4 thicknesses of
  mylar and still be acceptable M.
• Dragging 4 sheets of mylar is not acceptable, or
  a T.

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Grading Occlusion

• Lateral and Protrusive Interferences
• Articulating paper marks show centric in black
  and interferences in red. Notice the slight
  non-working interference in the central pit area
  of 19.

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Grading Occlusion

• Occlusal Cusp Heights and Anatomy
• Cusp heights should reflect harmony with the arch
  and concepts of Curve of Wilson and von Spee.
• Anatomy should be in harmony with the other teeth
  in the arch.

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Grading Occlusion

• Anatomy in these provisionals isnt well-defined,
  but functional. These provisionals would both
  receive an M solely for their anatomy.

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Grading Axial Contour Contacts..

• Axial Contour Contacts
• Proximal Gingival Contacts, Pontic Design,
  Axial Contours, and Embrasure Form are also
  evaluated here.
• This area is graded visually and with mylar.

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Grading Axial Contour Contacts..

• Open Contacts
• Mylar will pass directly through an open contact
  area without offering any resistance.

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Grading Axial Contour Contacts..

• Open Contacts
• Visually, you may be able to see light all the
  way through the contact area. Sometimes, the
  contour of the provisional may look like it
  contacts, but trying different angles may yield
  an open contact.

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Contacts
Contact snaps floss but does not drag mylar
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Contacts
FLOSS IS NEVER USED TO GRADE INTERPROXIMAL
CONTACTS
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Contact
What if provisional drags two mylar or even three
mylar
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Contact
1 Mylar strip is the criteria, if it drags two or
three it is open
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Grading Axial Contour Contacts..

• Pontic Design
• Posterior pontic designs have favored Modified
  Ridge Lap at USC. The outlined area should
  challenge the tissue.
• Ovate pontics have been favored for anterior
  restorations or esthetic reasons.

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Grading Axial Contour Contacts..

• Pontics
• The top picture shows a pontic that doesnt
  contact the tissue or edentulous ridge which
  traps food and is unacceptable for a T.
• The lower picture shows a Saddle pontic which is
  less hygienic than the modified ridge lap.

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Grading Axial Contour Contacts..

• Axial Contours
• These provisionals show nice axial contours and
  would both fit in the S category for slight
  over- and under- contouring.

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Grading Axial Contour Contacts..

• The upper picture shows generalized slight
  over-contouring for an acceptable M grade.
• The mesial axial of the premolar is generally
  over-contoured and borders on unacceptable.

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Grading Axial Contour Contacts..

• Gingival Embrasures
• Gingival Embrasures here are opened for optimal
  gingival health in both cases.
• Overly opened embrasures weaken the connector
  areas and strength of the restoration (not
  pictured).

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Grading Axial Contour Contacts..

• Closed Gingival Embrasures
• These embrasures arent properly opened for
  gingival health or hygienic access. Both of
  these embrasures would earn a T grade.

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Remember

• It is not JUST a provisional
• It is a blueprint for the final restoration.
• Must satisfy all requirements that a final
  restoration should apart from color stability.
• If you find an unsatisfactory provisional work
  with the student and make the corrections.

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Sincere Thanks to

• Dr. Kimberly Foon, Dr. Hubert Chan, Dr. Boris
  Keselbrener, Dr. Richard Kahn, Dr TJ Ahn and the
  DDS Classes of 2005,2006 and 2007 for their
  contributions to this presentation.