Accessory Retention Flashcards
_____ ______ is often used with large restorations
◦ Especially amalgam
◦ Amalgam relies completely on mechanical
retention
Accessory Retention
____ ____ does NOT seal or
increase strength!
◦ NO effect on resistance form
Accessory retention
_____ _____ is used To improve retention
◦ when more conservative methods can’t be used
Pin placement
t/f Pins are typically seen in extensive preps that often have a missing cusp.
true
The following are contraindications or indications for pin placement?
Severe loss of tooth structure Endodontically treated teeth Large pulp canals Difficult access Tooth already serves as abutment for partial denture
Contraindications
Economical ◦ 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) One appointment Alternative to extraction Pins remove minimal tooth structure compared to other methods ◦ less than slots, grooves and amalgapins
Advantages of pin placement
Introduces stresses in the dentin which can lead to crazing and even fracture
The pin does not strengthen the amalgam
◦ its only function is to provide additional retention and or resistance.
◦ Pins reduce the compressive and transverse strength
of amalgam
Possibility for perforation- Into pulp or into periodontal ligament
Pin Microleakage around pin Perforation
Anatomy harder to carve
Disadvantages of Pin placement
t/f: Do not use pins in non-vital teeth
true
Why do we not use pins in non-vital or endo treated teeth?
◦ endodontically treated teeth are brittle
◦ Pins can concentrate stress
◦ Lead to fracture
the following are alternatives to ___ _____:
Amalgam Core
◦ Retention from pulp chamber Post Retained Amalgams
◦ Post placed in actual canal, not dentin
Pin placement alternatives
Where is the pin always placed?
dentin
What are the three types of pins used?
Cemented
Friction Lock
Self-Threading
Which type of pin is used at UMKC
self threading
◦ Pin hole larger than pin (0.001 - 0.002” larger than pin) ◦ Cemented with zinc phosphate cement ◦ Pin must be 3-4mm in length for adequate retention ◦ Least retentive of available pins
Cemented
What type of pin is this?
◦ Pin hole is 0.001” smaller than the pin ◦ Pin is tapped to place - resiliency of dentine
retains pin ◦ 2-4mm long pin hole ◦ 2-3 times as retentive as cemented pins ◦ Dentin exhibits signs of stress
Friction lock
What kind of pin is this?
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
self threading
Do multiple pins increase retention?
yes
disadvantages of multiple pins?
◦ Increases dentin crazing ◦ Amount of available dentin between pins
is decreased ◦ Strength of amalgam restoration is
decreased ◦ More difficult to condense around the
pins
t/f: Pins should be placed 5mm apart from each other • MINIMUM of 3 mm apart
true
t/f: Pins should be 1mm from wall of prep • MINIMUM 0.5mm from wall
true
t’f: Pin should be 2mm deep into the dentin
true
t/f: Self-threading pins: 72.6 lbs of retention at 2 mm in the dentin.
true
Which type of pin is Type of pin: most common 99% used, and most retentive
self threading
T/f: Orientation of Pins: align pins vertically along long access of tooth
◦ If using multiple pins, slightly angle in different directions
◦ Avoid bending, if possible
true
t/f: ◦ increasing the number of pins increases retention up to a certain point.
◦ Too many pins reduces the strength of dentin and the restoration and may
cause dentinal fractures
true
What did the dentist say when Tiger Woods came in for an appointment?
You have a hole in one.
t/f: increased diameter= increased retention
true
If pins breaks, place another one __ mm away from broken pin
1.5
What pin size is this?
◦ Most frequently used threaded pin ◦ Start with a 0.021 and if you strip the hole, place a
0.027 pin
Minim 0.021
t/f: Use one pin per missing cusp, axial wall, or line angle. Use no more than 4 pins/tooth
true
t/f: Place the pin in line angles
◦ Greatest area of bulk
true
What sites should be avoided for pulp exposures
◦ 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
t/f: it is important to drill pin hole on a flat prepped area.
true
t/f:
Place pin minimum of 0.5 mm inside DEJ
◦ Preferably 1.0mm inside DEJ
true
When placing a crown….
_-__ mm inside DEJ
◦ Want to avoid exposing the pin
during future crown preparation
1.0-1.5
t/f: Pins should be a minimum of 0.5 mm from any wall to allow room for condenser and condensation of amalgam around the pin
so very true
t/f: There must be 2mm of amalgam over the top of the pin, otherwise the amalgam may fracture
true
If pin is too tall, you can do what two things?
reduce height with handpiece or bend slightly (avoid bending if possible)
What process is this?
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.
Check to see if the pin is loose.
Cutting the Pin
t/F: 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.
true, but I definitely did this on my prep.
t/f: always use a rubber dam with pin placement.
true otherwise could aspirate.
t/f: pulpal perforation is preferable to a periodontal ligament perforation
true
What kind of perforation?
◦ 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.
periodontal perforation
What type of accessory retention is this?
◦ 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
slot
What type of accessory retention?
• allow for restorative material to act as “pin” • more tooth structure is removed • BUT slots result in fewer microfractures compared to pins
locks
What kind of accessory retention?
- Utilize #245 bur - Drill hole 1mm wide,
2mm deep -Condense amalgam into pin hole
amalgam pin
All of the following are benefits for using (composite or amalgam) for build up material under crown?
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
Amalgam benefits:
t/f: Place slots, locks, grooves before placing pinhole
true
