DESIGN OF COMPLEX AMALGAM PREPARATION

STANDARD PRINCIPLES

Margins 90 (perpendicular) to tangent to carvosurface Proper clearance: 0.25mm 0.5mm Occlusal, axial and gingival walls in dentin

EXTENSIONS BEYOND IDEAL

Pulpal and axial extensions beyond ideal; remove round burs or spoon excarvators only

EXTENSIONS BEYOND IDEAL

Extend beyond ideal depth around tooth at normal depth

Provide vertical support for occlusal forces

Avoid inclined planes

Provide vertical support for occlusal forces

Convert inclined planes to steps

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

HANDLING EXTENSIONS

CAPPING DISTO-FACIAL CUSP

COVERING CUSPS WITH AMALGAM

OFFSETS THE MOST IMPORTANTSOURCE OF RESISTANCE

If no offsets are present, all the force must be borne by the grooves or pin.

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)

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

Slot

PINS IN RESTORATIVE DENTISTRY

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

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

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.

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)

General Principles

If pin is close to the DEJ, or if tooth is nonvital

Use smaller pins: regular Minim minikin minuta Use hand wrench to prevent over-torquing

Monitor torque and seat pin completely Back off pin turn

General Principles

If pin is close to the DEJ, or if tooth is nonvital

Use cemented pins Cut groove in pin and tapthreads in dentin

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

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

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 (10:1 contraangle or torque-increaser) Keep drill rotating at all times. Never place a drill back into hole unless it is rotating.

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

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

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)

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

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

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