Title: DESIGN OF COMPLEX AMALGAM PREPARATION
1DESIGN OF COMPLEX AMALGAM PREPARATION
2STANDARD PRINCIPLES
- Margins 90 (perpendicular) to tangent to
carvosurface - Proper clearance 0.25mm 0.5mm
- Occlusal, axial and gingival walls in dentin
3EXTENSIONS BEYOND IDEAL
- Pulpal and axial extensions beyond ideal remove
round burs or spoon excarvators only
4EXTENSIONS BEYOND IDEAL
5(No Transcript)
6Extend beyond ideal depth around tooth at normal
depth
7Provide vertical support for occlusal forces
8Provide vertical support for occlusal forces
- Convert inclined planes to steps
9HANDLING 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
10HANDLING EXTENSIONS
11CAPPING DISTO-FACIAL CUSP
12COVERING 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.
13Reduce 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)
14RETENTION 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
15Slot ??
16PINS IN RESTORATIVE DENTISTRY
17HISTORY
- 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
18TYPES 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
19General 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.
20General 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)
21General 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
22General 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
23General 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
24General 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
25Preparation 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.
26Preparation 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
27If 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
28If 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)
29Accidents 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
30Accidents 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
31Avoiding 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