Complex Amalgam Restoration (PART 2)
Resistance/Retention (cont’d)
Pins,
Slots,
Peripheral Shelf,
Endodontically-Treated Teeth
Pins - Indications/advantages
o Extensive loss of tooth structure/coronal dentin (need retention)
o Sufficient O-G height (4 mm)
o Quicker/less expensive/more conservative than crown
Pins - Disadvantages
o Risk of pulpal/periodontal perforation o Stresses tooth – crazing/cracking o Extra equipment needed o Difficult to adequately condense amalgam o Weakens amalgum
Types of Pins
o Cemented, friction-locked, threaded (most common)
o Thread Mate System (TMS) – threaded, each size of pin has drill
▪ 4 Sizes: minuta, minikin, minim, regular (smaller =
less stress)
▪ Pin hole slightly smaller diameter than pin
o Max Pin – has shoulder stop
Pins - Placement
o Place 1 mm inside DEJ
o Allow space for small condenser all around (use cove prep)
o Within confines of future crown prep, on flat surface
o Place starter hole w/ 1⁄2 mm round bur (guide for drill)
o Drill 1 mm at a time (to 2 mm), keep drill straight, parallel ext. surface, 90° to
pulpal floor
o Place pin w/ slow speed, ccw direction, self-limiting depth (2 mm)
o Rule of 2’s: 2 mm of pin in dentin, 2 mm in amalgam, 2 mm bulk above
Pins - Place in line angles (corners) of tooth
o 1 pin per missing line angle
o Danger spaces: middle, mesial concavity of max. 1st
premolar, bifurcation of 1st/2nd molars
Pins - Interpin distance (>2 increases stress) – 3 mm for minikin, 5 mm for minim/regular
:) You’ve got this!!!
Pins - May need to bend pin to w/in restoration outline
Yay!!!
Pins - Cutting pins:
use high speed, #169 bur, come from side, brief contacts
Pins - Horizontal pins IDICATIONS
not need cusp reduction (keep facial cusp = esthetic)
Pins - Horizontal pins PREPARATION: same guidelines as vertical
▪ increases mechanical advantage if near occlusal surface
▪ minim/minikin pins only
Slots INDICATIONS
o minimum O-G height with horizontal bulk of dentin
o no extra equipment needed
o rapid to place
o less chance of pulpal/periodontal perforation
o does not stress dentin or weaken amalgam/tooth
Slots DISADVANTAGES (same as amalgapin)
o may fracture if matrix is moved (not stable) or removed too early
o risk of voids from inadequate condensation
o need more dentin thickness
o decreased tensile strength
Slots PREPERATION
o use inverted cone bur to full depth, then follow DEJ around tooth (retentive b/c channel is wider at the bottom)
***Amalgapins -
vertical bulk / Slot – horizontal bulk
Peripheral Shelf INDICATIONS/ADVANTAGES
o need additional resistance
o allows conservative prep if enamel lost w/o dentin or cervical
decalcification/restoration present
o no extra equipment needed
o does not stress dentin or weaken amalgam/tooth
Peripheral Shelf DISADVANTAGES
o unidirectional resistance only
o risk of voids from inadequate condensation
o time-consuming
o more external restoration/amalgam display
o no advantage over amalgapin/slot
Peripheral Shelf PREPERATION
use # 58 bur to guide 1.5 mm wide/deep shelf
Endodontically-Treated Teeth
Pulp chamber provides great retention
Amalgum bonding –
in addition to mechanical retention; must condense into amalgam well
Matrix
▪ Many types: Tofflemire, Automatrix, etc.
▪ Stabilize w/ wedges, bite registration, modeling compound