Accessory Retention Flashcards
When Do We Need Accessory
Retention?
Often used with large restorations
◦ Especially amalgam
Accessory Retention
(2)
◦ This just means additional retention
◦ More than the primary retentive features of your prep
Often used with large restorations
◦ Especially amalgam
(3)
◦ Amalgam relies completely on mechanical retention
◦ Accessory retention does NOT seal or increase strength!
◦ NO effect on resistance form
Accessory Retention
Required when the
residual tooth structure
does not provide
adequate retention
Indications for Pin Placement
(3)
To improve retention
Extensive preparations
Prognosis of a tooth is uncertain
To improve retention
◦ when more conservative methods can’t be used
Extensive preparations
◦ Especially those missing a cusp
Prognosis of a tooth is uncertain
(2)
◦ eg. perio prognosis questionable
◦ Sometimes it is the only treatment of choice if the tooth is sclerosed and we cannot access pulp canals for additional retention
Contraindications
(5)
Severe loss of tooth structure
Endodontically treated teeth
Large pulp canals
Difficult access
Tooth already serves as abutment for partial denture
Advantages of Pin
Placement
(4)
Economical
One appointment
Alternative to extraction
Pins remove minimal tooth structure compared to other
methods
Economical
(2)
◦ 70% of four surface amalgams are successful at 5 years compared
to gold crowns (84% success) (Martin & Bader, 1997)
◦ 72% of amalgam restorations survive for 15 years including those
with cuspal coverage (Smales, 1991)
Pins remove minimal tooth structure compared to other
methods
◦ less than slots, grooves and amalgapins
Disadvantages of Pin
Placement Introduces stresses in the dentin which can lead to
crazing and even fracture
The pin does not strengthen the amalgam
(2)
◦ its only function is to provide additional
retention and or resistance.
◦ Pins reduce the compressive and transverse strength
of amalgam
Disadvantages of Pin
(3)
Placement Possibility for perforation
Microleakage around pin
Anatomy harder to carve
Possibility for perforation
(2)
◦ Into pulp
◦ Into periodontal ligament
Types of Accessory Retention
Vital Teeth
(3)
◦ Pins
◦ Slots and grooves
◦ Amalgapins
Endodontically Treated Teeth –
Non-Vital
Do not use pins in non-vital teeth
(3)
◦ endodontically treated teeth are brittle
◦ Pins can concentrate stress
◦ Lead to fracture
Endodontically Treated Teeth –
Non-Vital
Do not use pins in non-vital teeth
◦ endodontically treated teeth are brittle
◦ Pins can concentrate stress
◦ Lead to fracture
Alternatives:
(2)
Amalgam Core
◦ Retention from pulp chamber
Post Retained Amalgams
◦ Post placed in actual canal, not dentin
Pin is always placed in
dentin
What Types of Pins are
Available?
(3)
Cemented Friction Lock Self-Threading
Self Threading (Going 1966) Pin hole is 0.002” smaller than pin
Pins self threads into dentin
◦ Use hand wrench or
◦ Latch grip on slow speed
5-6 times as retentive as the cemented pin
High crestal and apical stresses; Crazing and
microleakage
◦ Greater stresses in dentin
There should be at least 1.0 mm dentin around pin hole
Used at UMKC most frequently
Self Threading
Self threading pins are
self shearing
o They break off on their own as you turn them with hand wrench or slow speed
Multiple Pins
Advantage
◦ Increases retention
Multiple Pins
Disadvantages ◦ Increases dentin crazing
(4)
◦ Amount of available dentin between pins
is decreased
◦ Strength of amalgam restoration is
decreased
◦ More difficult to condense around the
pins
Pin Placement
Pins should be placed — apart from each other
MINIMUM of – apart
5mm
3 mm
Pins should be — from wall of prep
* MINIMUM — from wall
1mm
0.5mm
Pin should be — deep into the dentin
2mm
Factors Affecting Pin Placement
Type of pin: — most common 99% used, and
most retentive
self threading
Surface characteristics of pin:
depth of deformations on the
pin
◦ amalgam engages for retention
Orientation of Pins:
align pins vertically along long access of
tooth
◦ If using multiple pins, slightly angle in different directions
◦ Avoid bending, if possible
Factors Affecting Pin Placement
(2)
Diameter of Pin
Pin breakage
Diameter of Pin
◦ increased diameter= increased retention
Pin breakage
◦ If pins breaks, place another one 1.5 mm away from broken pin
Pin Hole Sizes
(4)
Regular
Minim 0.021
Minikin 0.017
Minutia 0.0135
Regular
◦ 0.027 inch in diameter
◦ Do not use unless hole is stripped
Minim 0.021
◦ Most frequently used threaded pin
◦ Start with a 0.021 and if you strip the hole, place a
0.027 pin
Minutia 0.0135
◦ not retentive enough in posterior teeth
General rule - Use one pin per
(3)
missing cusp, axial wall, or line
angle
Use no more than — pins/tooth
4
◦ VERY rarely use more than 1 or 2 pins
◦ Use composite
Place the pin in
line angles
◦ Greatest area of bulk
Twist Drill
Use in — head of handpiece
◦ Slow speed or electric on slow speed (5000 rpm)
— acts as a heat absorber
Minuta and minikin twist drill have a built-in wobble to
Discard after — uses (too dull)
LATCH
Aluminum shank
minimize dentin
crazing and breakage of the small drills
20
Latch Contra-angle
Drill the pin hole with the slow speed drill (300 rpm)
using air to cool* Pin placement raises the pulpal temperature 4oF - do not use excessive
speed
Pinhole Location Depends Upon
(2)
Pulpal anatomy
External tooth anatomy
Pinhole Location Depends Upon
Pulpal anatomy
External tooth anatomy
Determine using:
(2)
◦ radiograph
◦ perio probe around the tooth
Also consider patient age
◦ older teeth
◦ younger teeth
are more brittle
have larger pulp
Best Sites for Pin
Placement? Best site for placement are at the
line angles (DF, DL, MF, ML)
Sites to Avoid for Pin Placement
Avoid for pulp exposures
(3)
◦ Mesio facial corner of Max and Mand 1st molar
◦ Distal mand molars and max lingual of molars
◦ Mid-facial, mid-mesial and mid-distal furcations of Max 1st & 2nd
molars
Concavities to watch for
Mesial concavity over Max 1st PM
Mid-lingual and mid-facial of
Mand 1st and 2nd molars
Mid-facial, mid-mesial and
mid-distal furcations of
Max 1st & 2nd molars
Flat area Prepare a flat area prior to pin placement
(2)
◦ Otherwise the drill may slip and you may
inadvertently angle it into the pulp or periodontal
ligament
◦ Alternatively you may not drill the correct pin hole
height (generally 2mm in depth)
Distance from DEJ Place pin minimum of — inside DEJ
0.5 mm
◦ Preferably 1.0mm inside DEJ
◦ or pins should be a minimum of 1.0mm from the external surface
of the tooth, whichever is greater.
Increase Distance if Planning to Place
Crown
1.0-1.5 mm inside DEJ
◦ Want to avoid exposing the pin during future crown preparation
Distance from Axial Wall Pins should be a minimum of — mm from any wall to allow room for
condenser and condensation of amalgam around the pin
0.5
Self Threading Pins-
Procedure
(3)
- Determine ideal pin location and drill pilot hole with ¼
round bur into dentin (optional) - Drill pin hole using provided twist drill
◦ Place in latch head of electric handpiece - Line up pin in pilot hole
◦ Turn hand wrench OR slow-speed handpiece until pin self-
shears
◦ Non-electric handpieces should have torque converter added
Starting Pilot Hole
Use a 1/4 round bur prior to using the pin drill
Orientation of the Pin Drill
Follow External Tooth Anatomy
Use perio probe to check external surface alignment
Knowledge of the anatomy of tooth
◦ ie furcations, grooves etc
Align pin-drill with external surface to check alignment
Check angulation twice from various angles
When Using the Pin drill
Place the pin hole in one movement. ◦ Avoid stopping and starting
Continue to reverse the drill as the pin drill is removed
◦ this clears the dentinal shavings
After placing pin hole, check for bleeding
◦ if you perforate, you will usually see blood easily
◦ Can use a paper point (endo) if you suspect a perforation but do not see bleeding
Placing the Self-Threading
Pin
Use hand wrench or latch on slowspeed
Make sure you have a positive stop
Quarter turn reverse at the end
◦ count total quarter turns
◦ reduces stress
What if the Pin is Too Tall?
There must be — of amalgam over
the top of the pin,
◦ otherwise the amalgam may fracture
2mm
If too tall:
(2)
◦ Reduce with handpiece
OR
◦ Bend slightly using provided pin tool
◦ Comes with pin kit
Cutting the Pin
Stabilize the pin with a forceps and cut
away the excess with a bur
Cut perpendicular to pin
◦ if you cut parallel to pin the pin will unscrew and
become loose.
After any of these procedures - check
that the pin is still retained
◦ If it is loose - remove and use a larger
size pin
Bending the pin
- Pin bender helps avoid
excessive stresses on pin
when bending
Incorrect Pin Bending
Do not use a condenser or any other instrument to push on the
pin and flatten it.
◦ Bending the pin with a condenser will further concentrate
stresses in the crestal region of dentine.
1.0 mm of amalgam around bent pin.
Summary of Procedure for Drilling
Pinholes Place – mm inside DEJ
Place pilot hole with a – round bur
Confirm correct angulation
Continuous drilling
◦ in and out one time
Interpin distance
0.5
¼
(3-5 mm)
Important Points for Pin Placement
ALWAYS use rubber dam◦ But especially with pin placement
◦ Risk of
aspiration
When using hand wrench
◦ Tie floss around the neck of the hand wrench - even if you use rubber dam.
Aspirating Wrenches or Pins Patients have swallowed and even worse —
these hand wrenches
inhaled
Pulpal Perforation
Pulpal perforation is preferable to a periodontal ligament perforation
◦ extirpation of the pulp solves the problem
◦ It may also be possible to attempt to pulp cap the perforation with calcium hydroxide depending on the endodontic prognosis of the tooth
Periodontal Perforation A periodontal perforation
(3)
◦ usually results in an abscess
◦ treated by uncovering the perforation, removing the part of the pin that
extend through and/or plugging this area with amalgam
◦ less predictable prognosis.
Slots and Grooves
Placed in dentin – mm inside the DEJ
Slots
(4)
0.5
◦ Similar to grooves, but larger
◦ created with 33 1/2 inverted cone bur
◦ 0.5-1.0 mm wide and 1mm deep
◦ should be undercut slightly to provide retention
Locks:
(3)
- allow for restorative material to act as “pin”
- more tooth structure is removed
- BUT slots result in fewer microfractures compared to pins
Amalgam Pins (Shavell
1980)
Preservation and Restoration of Tooth Structure, Mount, GJ, Hume, WR,1998, Mosby, St. Louis, MO.
- Utilize #245 bur
- Drill hole 1mm wide,
2mm deep
-Condense amalgam into pin hole
Amalgam Advantages as Build Up
MaterialBuild up: restoration under crown
Amalgam benefits:
oCan visualize when preparing crown
oEase of manipulation
oGood mechanical properties
oNot as technique sensitive as composite resin
oGood dimensional stability
oGood wear resistance
oRelatively inexpensive
Combination
Slots, locks, grooves, amalgapins, and pins can all be
combined to provide retention and resistance for a complex
amalgam restoration
Place slots, locks, grooves before placing pinhole
