1. Pin-Retained Amalgam Preparations & Restorations

2. Overview Definitions Tooth preparation for pin-retained amalgams
General rules for using pins
Types of pins
Characteristics of Pins
Factors Affecting Retention of Pins in Dentin and Amalgam
Pin Placement Factors and Techniques
Pitfalls with Pins

3. Definition What is a “pin- retained restoration”?
Any restoration requiring the placement of one or more pins into dentin in order to provide adequate resistance and retention forms
You may use pins whenever adequate resistance and retention forms cannot be established using slots, locks, or undercuts
Remember: pins have been shown in some studies to have greater retention than only boxes or amalgam adhesive bonding systems

4. Caution when using pins…
Preparing pinholes and placing pins may create
Craze lines or fractures and internal stresses in dentin
May have little or no clinical significance
They can be important when minimal dentin is present
Pulp or perforating the external tooth surface
The use of pins decreases the tensile and horizontal strength of pin-retained amalgam restorations

5. Tooth Preparation for Pin-Retained Amalgam Preparations
Initial tooth preparation
Extensive caries will require cusp capping of cups prone to fracture
When the facial or lingual extension exceeds two-thirds the distance from a primary groove toward the cusp tip
Increases resistance form
Significantly diminishes the retention form by decreasing the height of the vertical walls
Vertical walls should be formed to converge occlusally
to enhance the primary retention form
Facial or lingual groove can be extended arbitrarily to increase the retention form
The pulpal and gingival walls should be relatively flat and perpendicular to the long axis of the tooth

6. Tooth Preparation for Pin-Retained Amalgam Preparations
Final tooth preparation
Removal of remaining infected dentin
Pulp protection
Preparation of pin holes and pin placement
Auxiliary retention and resistance form
Slots, coves retention locks

7. Types of Pins Three types: A: Cemented B: Friction locked
C: Self threading
TMS pin (Thread Mate System)
Most commonly used
Stabilok pin system
Used at UKCD

8. Types of Pins Retentiveness of the pin in dentin
Self-threading pin is the most retentive
Friction-locked pin is intermediate
Cemented pin is the least retentive

9. Stabilok Operative Pin System
What’s the
“shear point”
mean?

10. Thread Mate System (TMS)
Versatile
Wide range of pin sizes
Color-coded system
Highly retentive
Gold-plated stainless steel or titanium

11. Characteristics of Pins
Diameter of a pinhole is inches smaller than the diameter of the pin itself
What allows the threaded pin to be actively “engaged” into a hole of a smaller diameter?
The elasticity (resiliency) of dentin
Pulpal stress is maximum when a self-threading pin is inserted perpendicular to the pulp

12. Characteristics of Pins
Vertical and horizontal stresses generated in dentin can cause craze lines related to the size of the pin
Most textbooks advocate “backing off” 1/4 turn after fully seating a pin (using a hand wrench)
Why?
Decrease stress in dentin

13. Characteristics of Pins
Depth of pinholes vary from mm depending on the length of the pin used
Pin lengths > 2 mm are unnecessary and are actually contraindicated in order to preserve the strength of the amalgam
The threads of self-threading pins do not engage dentin for their entire width

14. Characteristics of Pins
pin rule
2 mm of pin drilled into the tooth
2 mm of exposed pin sticking out of the tooth
2 mm of amalgam covering the pin

15. Factors Affecting Retention of Pin in Dentin and Amalgam
1) Type ( self-threading ,etc.)
2) Surface characteristics (serrations or threads)
3) Orientation, number, diameter
- Parallel
- Non-parallel: increases pin retention
- More pins increases crazing of dentin
- Decreased dentin between pins
- Lower amalgam strength

16. Factors Affecting Retention of Pin in Dentin and Amalgam
If you increase number of pins, this will increase retention into the dentin, but
craze lines increase along with fracture potential
strength of the amalgam may actually decrease
If you increase diameter of the pin, this will also increase retention into the dentin, but
increase chance of pulpal perforation
if you increase the number of long pins, this will decrease the condensation efficiency of the amalgam

17. Factors Affecting Retention of Pin in Dentin and Amalgam
Bending pins can be undesirable:
interferes with condensing amalgam
may fracture the dentin
IF you bend a pin, bend it only to provide for an adequate amount of amalgam (at least 1 mm) between the pin and the external surface of the finished restoration

18. Factors Affecting Retention of Pin in Amalgam and Dentin
Use only a TMS bending tool
Using an incorrect bending instrument or incorrect bending in itself may create sharp bends in the pin (weakening the pin), fracture the dentin, or leave insufficient space for the amalgam
Where exactly do you bend the pin?

19. How Does A Pin Bender Work?
Simply insert the pin inside the slot and turn the instrument slightly
Once again…don’t bend the pin at the level of the tooth surface
…and don’t leverage against the tooth surface to bend a pin

20. Pin Placement Factors and Techniques
Different pin sizes
Four sizes of TMS pins (i.e. Regular, Minim, Minikin, Minuta) and they’re self- threading
Regular size TMS pin (.031 inch) is normally not used because it may introduce stress lines, crazing, or cracking into the enamel and dentin during insertion
One size available at UKCD with Stabilock pins

21. Pin Placement Factors and Techniques
How many pins should I use? depends on:
amount of tooth structure missing
amount of dentin available to receive pins
amount of retention required
size of the pins
General rule: 1 pin per missing axial line angle pin per missing cusp

22. Pin Placement Factors and Techniques
Fewest pins necessary is best
When 2-3 mm of the occlusal/gingival height of the cusp is removed, consider using an amalgapin
More pins…more retention but too many pins…can weaken the restoration

23. Pin Placement Factors and Techniques
Location: How do I know where to place the pin holes?
you must have a knowledge of normal pulp anatomy and external tooth contours
use current radiographs
use a periodontal probe to determine angulation and alignment of the tooth and root
patient’s age is a consideration
Why?

24. Pin Placement Factors and Techniques
Sturdevant’s rule: in the cervical 1/3 of molars & premolars, place the pin hole at the line angles of the tooth
Pin holes should be no
closer than mm to the DEJ
or no closer than mm to the external surface of tooth (whichever is greater)

25. Pin Placement Factors and Techniques
Allow enough room to condense amalgam
a minimum of 0.5 mm clearance around the circumference of the pin for adequate condensation of amalgam
When using 3 or more pins, try to place them at different levels on the tooth surface

26. Pin Placement Factors and Techniques
With 2 or more pins, allow inter-pin distance
the more distance between pins, the less stress in dentin
minimum distance?
3-5 mm
Maximal inter-pin distance results in lower levels of stress in dentin

27. Pin Placement Factors and Techniques
Recognize anatomic features which could get you in trouble
Drilling over a bifurcation, such as over the lingual of a mandibular molar in this instance may cause you to perforate the side of the root

28. Pin Placement Factors and Techniques
Pin holes should be placed on a flat surface to optimize the amount of amalgam condensed around the pin & engage the tooth completely
Textbook of Operativ Dentistry, p. 404

29. Pin Placement Factors and Techniques
Use No. 1/4 (or 33 ½ ) burs for placement of a pilot hole
Kodex drills used to drill pin holes have an aluminum shank
Note the depth-limiting drills

30. Pin Placement Factors and Techniques
Twist drill too dull after 20 pin holes
Dull twist drills cause an increase in frictional heat and therefore cracks in dentin
Watch the anatomic contours of the teeth!
Care must be exercised when preparing pinholes in mesially tilted molars to prevent external perforation on mesial surface (A) and pulpal penetration on the distal surface (B).

31. Preferred Locations for Pin Placement
Preferred areas are dotted (preferably at line angles)
White areas should be avoided because of concavities, furcations, or thin dentin
Lined areas - place with caution because of the angulation of the roots
preferred

32. Preferred Locations for Pin Placement

33. How do you align the pin hole drill?
Use a periodontal probe to “sight-in” the drill alignment
Hold the pinhole drill parallel to the adjacent external tooth surface
How far did we say we needed to be from the DEJ? mm
Fundamentals of Operative Dentistry, p. 328.

34. Pin Placement Factors and Techniques
2-2-2 rule
if pin length is > 2 mm after placement, use a No. 1/4, 1/2, 169L, 330 bur to shorten the pin by cutting perpendicular to the pin
stabilize the pin with a hemostat or cotton pliers (and I mean hold it firmly!)

35. Horizontal Pins Why use horizontal pins?
1) Reinforces free standing cusp
2) Cross splinting of max premolars
Place pins .5-1 mm from the DEJ into the thickest part of the dentin
Depth channel of mm may end up contacting enamel

36. Clinical Example Favoring Horizontal Pins
This complex amalgam failed with the lingual cusps fracturing away
A load “split” the restoration away causing a failure due to lack of distribution of resistance and retentive features

37. Clinical Example Favoring Horizontal Pins
Placing two vertical and two horizontal pins in a “cross- splinting” fashion could have averted failure of this restoration

38. Pitfalls with Pins Pitfalls can occur at five locations:
a) within the restoration (fracture)
b) interface between pin and restoration (separation)
c) within the pin (fracture)
d) interface between the pin and dentin (separation)
e) within the dentin (fracture)

39. Pitfalls with Pins
Failure is more likely to occur at the “pin-dentin interface” rather than the “pin-restoration interface”

40. What if the pinhole drill or the pin breaks off in the tooth?
What causes?
Drill breaks if it is stressed laterally or allowed to stop rotating before it is removed from the pinhole.
Use of sharp twist drills helps eliminate the possibility of drill breakage.
Pins also can break during bending
Best solution for these problems is prevention!!!
Broken drills and broken pins is to choose an alternative location and prepare another pinhole
at least 1.5 mm remote from the broken item
Removal of a broken pin or drill is difficult, if not impossible, and usually should not be attempted!

41. What if the pin is loose and “wiggles” because the dentin in the pin hole is “stripped out” from my drilling?
The pin should be removed from the tooth and the pinhole re- prepared with the next largest size drill, and the appropriate pin should be inserted (when using
Preparing another pinhole of the same size 1.5 mm from the original pinhole also is acceptable.

42. Pitfalls with Pins You’ve just drilled the pinhole into the pulp?
How can you tell ?
Drop in resistance to drill
What do you do now?
1) Remove pin (if possible)
2) Control bleeding
3) Place CAOH over site
4) Most importantly , INFORM patient

43. Pitfalls with Pins Not wise Good chance of sensitivity
“Should I ever consider leaving the pin in place if it enters the pulp?”
Not wise
Good chance of sensitivity
Probably complicate endo tx

44. Pitfalls with Pins
Whoops! Now you’ve drilled the pinhole and placed the pin into the periodontal ligament space (PDL) or the external surface of the tooth?

45. Pitfalls with Pins

46. Pitfalls with Pins
What if the pin penetrates into the periodontal ligament space (PDL) or the external surface of the tooth?
how can I tell?
First thing…you need to determine if the pin perforation is occlusal or apical to the gingival attachment by visual examination, periodontal probing or radiographic examination

47. Pitfalls with Pins
If the pin is occlusal to the gingival attachment (and you can actually see it), then your options include:
1) cut off the pin flush with tooth and do no further treatment
2) cut off the pin flush with tooth and prepare the tooth for a cast restoration extending your crown margin gingivally beyond the perforation site
3) remove the pin, enlarge the pin hole, and restore it preferably with amalgam
Surgical access and reflecting a gingival flap (if you can’t see it clearly) may also be an option

48. Pitfalls with Pins
If the pin is apical to the gingival attachment, then your options include:
1) surgically reflect the gingival tissue (flap), remove bone and pin fragment, enlarge the pin hole, and restore the perforation with amalgam
2) do a periodontal crown lengthening procedure, and place the crown margin of a cast restoration gingival to the perforation
As with the pulpal perforation, you must inform your patient!

49. What’s going on here?

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51. In your 1st-year dental kit…
…is your pin hole drill and your pins!

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Remember the rule and bend the pins “in” toward the tooth!

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