Accessory Retention Flashcards
accessory retention is often used with:
large restorations, especially amalgam
does accessory retention increase strength
no
when is accessory retention required
when the residual tooth structure does not provide adequate retention
what are the indications for pin placement
- to improve retention when more conservative methods cant be used
- extensive preparations, especially those missing a cusp
- if prognosis of a tooth is uncertain
what are the contraindications for pin placement
- severe loss of tooth strucutre
- endodontically treated teeth
- large pulp canals
- difficult access
- tooth already serves as abutment for partial denture
what are the advantages for pin placement
- economical
- one appointment
- alternatie to extraction
- pins remove minimal tooth structure compared to other methods such as slots grooves and amalgapins
how is pin placement economical
- 70% of four surface amalgams are successful at 5 years compared to gold crowns
- 72% of amalgam restorations survive 15 years including those with cuspal coverage
what are disadvantages of pin placement
- introduces stresses in the dentin which can lead to crazing and even fracture
- possibility for perforation into pulp or PDL
- microleakage around pin
- anatomy harder to carve
what is the pins function
to provide additional retention and or resistance
pins reduce the _____ and _____ strength of amalgam
compressive and transverse
what are the types of accessory retention in vital teeth
- pins
- slots and grooves
- amalgapins
what accessory retention should be used in endodontically treated teeth- non vital
- do not use pins in non vital teeth
- use amalgam core or post retained amalgams
why should you not use pins in non vital teeth
- endodontically treated teeth are brittle
- pins can concentrate stress and lead to fracture
where does the amalgam core get retention from
pulp chamber
where are post retained amalgams posts placed
in actual canal, not dentin
what are the steps in pin placement
- broken cusp
- drill pilot holes
- drill pin holes
- place pins
- place restoration
- prepare crown prep
- avoid perforation
pin is always placed in_____
dentin
what types of pins are available
- cemented
- friction lock
- self threading
describe self threading pins
- pin hole is 0.002” smaller than pin
- pin self threads into dentin
- use hand wrench or latch grip on slow speed
- high crestal and apical stresses; crazing and microleakage
- greater stresses in dentin
- should be at least 1.0mm of dentin around pin hole
self threading pins are ______ more retentive as the cemented pin
5-6 times
what pin is used at UMKC most frequently
self threading
self threading pins are _____. what does this mean?
- self shearing
- they break off on their own as you turn them with hand wrench or slow speed
what are the advantages of multiple pins
increases retention
what are the 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
how far apart should pins be placed from each other
5mm. minimum of 3mm
how far away should pins be from wall of prep
1mm. minimum 0.5mm
how deep should pins be into dentin
2mm
what are the factors affecting pin placement
- type of pin
- surface characteristics of pin
- orientation of pins
- diameter of pin
-pin breakage
what type of pin is the most retentive
self threading
what are the surface characteristics of the pin that affect pin placement
depth of formations on the pin
- amalgam engages for retention
how does the orientation of pins affect pin placement
- align pins vertically along long axis of the tooth
- if using multiple pins slightly angle in different directions
- avoid bending
increased diameter of pin = ______ retention
increased
what do you do if pin breaks
place another 1.5mm away from broken pin
use one pin per:
missing cusp, axial wall or line angle
use no more than ____ pins per tooth
4
where do you place the pin and why
in line angles because greatest area of bulk
describe the twist drill
- use in latch head of handpiece on slow speed or electric on slow speed 5000 rpm
- aluminmum shank acts as a heat absorber
- minuta and minikin twist drill have built in wobble to minimize dentin crazing and breakage of the small drills
- discard after 20 uses because too dull
how do you use the latch contra angle
- drill the pin hole with the slow speed drill 300 rpm using air to cool
- pin placement raises the pulpal temperaturee 4 degrees F- do not use excessive speed
pinhole location depends on:
- pulpal anatomy
- external tooth anatomy
- patient age
determine pulpal anatomy and external tooth anatomy using
- radiograph
- perio probe around the tooth
what are sites to avoid for pin placement
- MF 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 and 2nd molars
why are there specific sites to avoid in molars
to avoid pulp exposures
what are the 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 max1st and 2nd molars
why do you want to prepare a flat area prior to pin placement
- the drill may slip and yuo may inadvertently angle it into the pulp or periodontal ligament
- alternatively you may not drill the correct pin hole height- generally 2mm in depth
place pin _____ inside DEJ
minimum 0.5mm
- preferably 1.0mm inside DEJ
- or pins should be a minimum of 1.0mm from the external surface of the tooth, whichever is greater
what do you want to avoid during future crown prep
expose the pin
what do you do to the pins if planning to place crowns
increase distance
how far should pins be from axial wall
- a minumum of 0.5mm from any wall to allow room for condenser and condensation of amalgam around the pin
what is the self threading pins procedure
- determine ideal pin location and drill pilot hole with 1/4 round bur into dentin
- drill pin hole using provided twist drill- place in latch head of electric hand piece
- line up pin in pilot hole- turn hand wrench OR slow speed handpiece until pin self- shears.
non electric handpieces should have what added
torque converter
describe the orientation of the pin drill
- follow the external tooth anatomy
- use perio probe to check external surface alignment
- knowledge of the anatomy of the tooth
- align pin drill with external surface to chekc alignment
- check angulation twice from various angles
what should the handpiece angulation be
follow long axis of the tooth
what should the pin placement be parallel with
external surface of tooth and with pulp, halfway between each
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
- after placing pin hole, check for bleeding
why do you continue to reverse the drill as the pin drill is removed
to clear the dentinal shaving
what do you use if you suspect a perforation but do not see bleeding
a paper point (endo)
when placing the self threading pin, make sure you have a ____
positive stop
what should you do at the end of placing the self threading pin and why
quarter turn
- count total quarter turns
- reduces stess
there must be ______ of amalgam over the top of the pin. why?
2mm; otherwise it may fracture
what should you do if pin is too tall
reduce with handpiece or bend slightly using provided pin tool
how do you cut the pin
- stabilize the pin with a forceps and cut away the excess with a bur
- cut perpendicular to pin
what do you do if you cut parallel to the pin
it will unscrew and become loose
what do you do if the pin is loose after cutting it
remove and use a larger size pin
what does the pin bender do
helps avoid excessive stress on pin when bending
describe 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 dentin
- 1 mm of amalgam around bent pin
what is the summary of procedure for drilling pinholes
- place 0.5mm inside DEJ
- place pilot hole with 1/4 round bur
- confirm correct angulation
- continuous drilling: in and out one time
- interpin distance 3-5mm
what are the important points for pin placement
- always use rubber dam
- when using hand wrench tie floss around the neck of the hand wrench- even if you use rubber dam
which is preferable: pulpal perforation or periodontal ligament perforation
pulpal
what solves the problem of pulpal perforatino
extirpation
- or possible to attempt a pulp cap with CaOH
a periodontal perforation:
- usually results in an abscess
- treated by uncovering the perforation, removing the part of the pin that extends through and/or plugging this area with amalgam
- less predictable prognosis
slots:
- similar to grooves but larger
- created with 33 1/2 inverted cone bur
- 0.5-1.0mm wide and 1mm deep
- should be undercut slightly to provide retention
where are slots and grooves placed
in dentin 0.5mm inside DEJ
locks:
-allow for restorative material to act as pin
- more tooth structure is removed
- but slots result in fewer microfractures compared to pins
amalgam pins:
- use #245 bur
- drill hole 1mm wide and 2mm deep
- condense amalgam into pin hole
what are amalgam benefits
- can visualize when preparing crown
- ease of manipulation
- good mechanical properties
- not as technique sensitive as composite resin
- good dimensional stability
- good wear resistance
- relatively inexpensive
matrix band should not shift during:
condensing and initial set of the amalgam
what features can be combined to provide retention and resistance for a complex amalgam restoration
slots, locks, grooves, amalgapins
when should you place slots, locks, and grooves
before placing pinhole
