DESIGN OF COMPLEX AMALGAM PREPARATION - PowerPoint PPT Presentation

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DESIGN OF COMPLEX AMALGAM PREPARATION

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Occlusal, axial and gingival walls in dentin. EXTENSIONS BEYOND IDEAL ... between pulp and external surface of root if gingival margin is in cementum ... – PowerPoint PPT presentation

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Title: DESIGN OF COMPLEX AMALGAM PREPARATION


1
DESIGN OF COMPLEX AMALGAM PREPARATION
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2
STANDARD PRINCIPLES
  • Margins 90 (perpendicular) to tangent to
    carvosurface
  • Proper clearance 0.25mm 0.5mm
  • Occlusal, axial and gingival walls in dentin

3
EXTENSIONS BEYOND IDEAL
  • Pulpal and axial extensions beyond ideal remove
    round burs or spoon excarvators only

4
EXTENSIONS BEYOND IDEAL
5
(No Transcript)
6
Extend beyond ideal depth around tooth at normal
depth
7
Provide vertical support for occlusal forces
  • Avoid inclined planes

8
Provide vertical support for occlusal forces
  • Convert inclined planes to steps

9
HANDLING EXTENSIONS
  • Disto-facial cusp of mandibular molars
  • Large disto-facial cusp
  • Small disto-facial cusp
  • Margin crosses cuspal eminance cap cusp
  • Capping disto-facial cusp

10
HANDLING EXTENSIONS
11
CAPPING DISTO-FACIAL CUSP
12
COVERING CUSPS WITH AMALGAM
  • OFFSETS THE MOST IMPORTANT SOURCE OF RESISTANCE

If no offsets are present, all the force must be
borne by the grooves or pin.
13
Reduce to obtain a minimum of 2mm thickness of
amalgam
Reduce flat, perpendicular to occlusal
forces. Leave dentin 0.5mm 1.0mm higher than
pulpal floor to prepare offset Remove all
undermined enamel (supported by 0.5mm of dentin)
14
RETENTION FEATURES Slot, pin,cove,well and
amalgapin
  • Slot a long, narrow retentive factor in a
    vertical or horizontal wall
  • Cove a shallow, round hole in the incisal of
    class III preparations
  • Well a short, deep hole (about 2.0x0.8x0.8mm
    deep
  • Amalgapin a large, deep hole (0.8-1.4mm D X
    1.3mm deep) used to replace pins in amalgam
    restorations

15
Slot ??
16
PINS IN RESTORATIVE DENTISTRY
17
HISTORY
  • Dr. Miles Markley in 1958 cemented threaded
    stainless steel wires, reporting as pin
    reinforcement and retention
  • Later studies showed that pins increased
    retention in amalgams, but decreased strength

18
TYPES OF PINS
  • Cemented pin is 0,002 smaller than the channel
  • Friction-locked pin is 0.001 larger than the
    channel
  • Self-threading (TMS) pin is 0.001-0.004 larger
    than the channel

19
General Principles
  • Pins must be stable.
  • Pins must not perforate into the pulp or
    periodontal membrane.
  • Tips of pins will be covered with at least 2mm of
    amalgam.
  • Pins will clear matrix brand laterally.

20
General Principles
  • Pins will not predispose to caring or fracture of
    tooth structure.
  • Place so pin is surrounded by 0.5mm-1.0mm of
    dentin. (Larger pins or non-vital teeth require
    1.0mm)

21
General Principles
  • If pin is close to the DEJ, or if tooth is
    non-vital
  • Use smaller pins regular Minim
    minikin - minuta
  • Use hand wrench to prevent over-torquing
  • Monitor torque and seat pin completely
  • Back off pin ¼ turn

22
General Principles
  • If pin is close to the DEJ, or if tooth is
    non-vital
  • Use cemented pins
  • Cut groove in pin and tapthreads in dentin

23
General Principles
  • Must provide flat seat and space around the pin
  • Allows more complete seating of drill
  • Allows maximum depth of pin channel
  • Allows amalgam to flow around the grasp pin
  • Choose pinhole direction parallel to external
    surface of tooth, not parallel to long axis of
    tooth or crown

24
General Principles
  • Choose proper location for pins
  • Place in area of greatest bulk of dentin
  • Place 0.5-1.0mm from the dej to prevent crazing
  • Place halfway between pulp and external surface
    of root if gingival margin is in cementum
  • Avoid furcations and depressions on roots

25
Preparation of pin channels
  • Prepare in a clean, dry, caries-free field
  • Use rubber dam to prevent swallowing or
    aspiration of instruments
  • Use slow speed, high torque (101 contra-angle or
    torque-increaser)
  • Keep drill rotating at all times. Never place a
    drill back into hole unless it is rotating.

26
Preparation of pin channels
  • Careful maintain the same direction
  • If pin channel cannot be completed quickly
  • Check direction of rotation
  • Use slightly more pressure
  • Confirm that you are not in enamel
  • Assume the twist drill is dull and replace

27
If self-threading pins strip and wont hold
  • Confirm that all caries has been removed in area
    of pin channel
  • Use the next larger drill and pin size
  • Minuta Minikin Minim regular
  • Drill the channel deeper (if direction is safe)
  • Drill to a 3mm depth
  • Use a 4-5mm twist drill, being very careful no to
    break
  • Change to a cemented pin

28
If self-threading pins strip and wont hold
  • Avoid the problem by maintaining same angle
    during drilling, and drill one time only (avoid
    re-entering the channel)

29
Accidents with pin
  • Perforation into pulp fill hole with CaOH and
    place a pin elsewhere
  • Perforation in periodontal membrane
  • Place pin flush with root surface using a hand
    wrench
  • Do a gingival flap and cut pin cut off flush with
    root surface
  • Fill channel with root canal sealer

30
Accidents with pin
  • Broken drill or pin
  • If pin is loose, remove it and proceed
  • If stable, leave the broken pin or drill in
    place, and place a new one in a different location

31
Avoiding breakage of twist drills
  • Use only 2mm depth-limiting twist drills
  • Use only sharp, new drills
  • Dont press too hard, especially with smaller
    diameter drills
  • Maintain same direction during drilling
  • Never place a drill into a hole unless is
    rotating
  • When using the longer (4-5mm) drills, follow all
    rules very carefully
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