Cons # 6 - Safa' Mak7ool

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Cons # 6 - Safa' Mak7ool

Post by Shadi Jarrar on 16/3/2011, 3:33 pm

بسم الله الرحمن الرحيم

يحتوي هذا الملف على صور
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http://www.4shared.com/document/NJETf2xz/cons_sheet_6JUDe.html
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PIN-RETAINED RESTORATION

In the last lecture we talked about the grossly carious teeth and we said that we need to use retentive means to improve the retention and the resistance forms since there is loss in cusps and insufficient tooth structure, in addition to these retentive means we can make cusp capping.

The retentive means which can be used with composite or amalgam are : grooves , coves, locks, boxes, dove tails, pins, and posts.















Why do we put pins and posts in separate category?

Because in locks, coves and boxes … we make a cavity in the walls of the filling in cretin shape to improve the retention
While in pins and posts we have to add something…

Now we will talk about PINS only and the posts will be discussed next year inshallah.

Any restoration requiring the placement of one or more pins in dentine to provide adequate retention and resistance forms.


In the picture we have a tooth in which all the buccal wall is missing so we have to use the pins for retention of amalgam restoration then we make cusp capping by amalgam which means that we shorten the original cusps of the tooth
and we cap them by amalgam, but how do we know if these cusps are weak and need to be capped?
We have a general guide line, that when the cusps are less than specific measurements then it will be fractured and if it fractured there is a risk of becoming unrestorable tooth.. so we need to protect the tooth in advance.

Generally pins are placed whenever satisfactory retention and resistance forms can’t be established with other means of retention. So it’s favorable to use other means such as undercuts, grooves, slots, and acid itching of enamel and dentine.

Types of pins:
Cemented pins
-Was designed by Markley 1985.
-Threaded (or serrated) stainless steel pins.
-They are cemented into pinholes prepared 0.001 to 0.002 inch larger than the diameter of the pin.

The only pin hole that is prepared larger than the diameter of the pin.

-the cement which is used either zinc phosphate or poly carboxelate.
-The depth f the pin hole is between 3-4 mm.

Every pin has its own drill so you don’t have to measure any thing.

-It doesn’t cause stress or craze lines in dentine. Because it’s passive you have only to prepare the hole , lute the pin with the cement, then insert it in the pin hole.

-The least retentive of the three types

friction-locked pin

-described by Goldstein In 1966 .
-the diameter of the pinhole is 0.001 inch smaller than the diameter of the pin.
The pins are tapped into place, retained by the resiliency of the dentin. Since the pinhole is smaller we have to force them in using a special instrument or by tweezers to put them in place and that doesn’t need to apply a high force because the dentine is soft.

-2 to 3 times more retentive than cemented pins .


self-threading pin

-described by Going in1966.
-The diameter of the prepared pinhole is 0.0015 inch to 0.004 inch smaller than the diameter of the pin.
-The pin is retained by threads, we screw it in place to engage the dentin as it is inserted.
-The most retentive of the three types , although the threads do not engage the dentin for their entire width.
-5-6 times more retentive than the cemented pin .
-apical and lateral stresses, since we are screwing it inside then we create stresses, and if we apply a high force or if the pinhole is too small the craze lines will appear in the dentine.
-Several types, sizes, and systems are available. And each type or size has its own drills which can’t be used interchangeably.
-the most common system is the thread mate system.

The main problem or difficulty is placement of pins in posterior teeth, imagine if you wanna make this small hole into dentine , parallel to the long axis of the toot, and you have a distal cavity in the lower seven molar!! It’s a bit difficult.

Stresses are created in dentine causing lateral cracks perpendicular to the long axis of the pin and shearing forces apical to the leading edge of the pin.

When the pins are indicated for the use with amalgam restoration and when are they contra indicated?

As we said we need to use the pins to provide an adequate resistance form with other means such as under cuts, grooves and slots.

- The number of pins to be used:
It’s determined by the amount of missing tooth structure, usually one pin for
each missing cusp.
but if you increase the number of the pins, the stresses will increase and this may lead to failure.

Resistance form:
Ideally severely weakened teeth should be placed by cast restoration.
You may use retentive means and amalgam filling but sometimes it’s not the definitive restoration, because you need to use the cast restoration , like for example: the buccolengual width of your filling is too wide so the cusps will become undermined and can’t withstand the forces of occlusion “they may fracture” so that you will use the cast restoration in such case to protect the cusps.

In selected cases pins are placed before the placement of the amalgam and can function to improve the resistance form.

Status and prognosis of the teeth:
Teeth that are sensitive or symptomatic should be treated with a filling (which we called “the control amalgam filling” last lecture) ..wait till the symptoms subside, then go to the definitive treatment which is the cast restoration for example.

Contraindications:
-The placement of non cemented pins in root canal treated teeth should be avoided , because if you have a root canal treated tooth it’s better to use the chamber for retention or you can use posts as they provide a better surface area than the pins , so there is no need to use the pins as they may cause perforation and stresses.

-Pins are contra indicated in teeth where the gingival margins are so deep where the application of the matrix band is difficult or impossible.
Always before you make a filling, you have to assure having a good isolation even if you need a perio surgery if the margin is beneath the gingiva.

The role of the tooth in the overall treatment plan:

Occlusal requirement:
Pins are contra indicated in teeth that require elaborate occlusal alteration.
i.e. if there is an over eruption or tilting in the in the teeth , in this case you can’t use the pins as definitive treatment you need to make crown.
So if your treatment plan is to change the occlusion then you need to make crowns.


Esthetic requirements:
When esthetics are of prime concerns pins retained amalgam could be contra indicated, you can use composite in this case.
We rarely use pins with composite because it can provide enough retention but if it doesn’t, then the tooth is root canal treated tooth in most of the cases , so choose another option.
but not the pins because they tend to show through composite.


Cost;
When cost is a major factor, the pin retained amalgam is appropriate to provide an acceptable restoration. It may cost only 30 JD to make a pin retained amalgam restoration but it cost at least 70JD to make a crown!!

Age of the patient:
If the patient is too old you can’t make a crown because that needs many visits and since he is too old he may not be able to do so.
On the other hand if the patient is young (16 years) for example , you also can’t make a crown because there is a high chance of pulp exposure or irreversible pulpitis.
At the same time remember that in this age group (17 and below) you should be careful where to put the pin because it would be easy to penetrate the pulp.

Advantages of Pins retained amalgam restoration:
- tooth preparation is more conservative than other restorations because the pinhole measurements is too small compared to the slots or grooves.
- Gingival margins could be healthier than indirect restoration (such as crowns , they must be applied on the 4 surfaces of the tooth, while amalgam can be applied on 1 or 2 surfaces)
- Less time consuming and could be finished in one visit.
- Relatively economic compared with indirect means.
- Retentive form is significantly improved.
- In selected cases, resistance form is also improved. ( when using pins and making cusp capping both forms will be improved)



Disadvantages of Pins retained amalgam restoration:
- proper contours and occlusal contacts are difficult to be achieved, you have to be highly talented to be able to retrieve the anatomy of the tooth.
- Drilling the pinhole and placement of pin could create internal stresses in dentine.
- Micro leakage around all types of pins have been demonstrated but it’s not greter than the micro leakage at the tooth restoration interface.
- Pins don’t reinforce the amalgam, therefore they don’t increase the strength of the restoration. There is no increase in compressive strength , but they cause significant decrease in the tensile force. “so no increasing, but decreasing of the forces”
- Increase risk of perforation into the pulp or the external tooth structure.


Factors Affecting the Retention of the Pin in Dentin and Amalgam:

1- Type of the pin  the self-threading pin is the most retentive the friction locked pin is intermediate, and the cemented pin is the least retentive.

2- Surface characteristics retention of the pin in the amalgam restoration.
The shape of the self-threading pin gives it the greatest retention value , then the friction locked, the least is the cemented type.

3- no bonding between the amalgam and the pin pure mechanical retention,, amalgam doesn’t bind to anything

4- Orientation of the pins putting the pin not parallel to each other would enhance the retention of amalgam, but sever bending should be avoided.

5- number of pins  increase the number will increase the retention, but don’t increase the number too much because –again- this will cause stresses in dentine.

6- Diameter of the pin  with the limits, increase the diameter will increase the retention. But we can’t increase it because it’s pre fabricated.

7- the length of the pin into dentine and restorative material with the cemented pins retention increased linearly with increasing the pinhole depth. But with friction locked and threaded pins there is no real benefit in increasing the hole depth beyond 2mm other wise the stresses of the pin become the limiting factor.

Failure
Failure could happen in any of five deferent locations;
a. within the restoration itself.
b. at the interface between the pin and the restorative material , the material could pull off the pin.
c. within the pin; it can fracture when stressed beyond its limit.
d. at the interface between the pin and dentine.
e. within the dentine itself.

With the exception of friction locked pins, failure is more likely to occur at the pin – dentine interface(d) rather than the pin- restorative material interface.


Problems of pin retained restoration:
1- broken drills and broken pins:
if stressed laterally or allowed to stop before removing from the hole ; usually we insert and remove the drill rotating whatever you are preparing whether a cavity , crown or a post. If the pin broke:
- Choose a safe location at least 1.5 mm away from the broken piece.
- Removal of the broken piece is difficult and shouldn’t be attempted.. usually if the piece was broken we just leave it there.
- Prevention is the best solution.

2- loose pins:
-Usually loosening happens in cemented pins.
-it’s caused by the improper engagement with dentine or a very large sized pinhole, (even though each type of pins has its own drills but if we over do drilling, a larger hole will result)
-the pin should be removed by one of the following procedures:
- The pinhole is prepared with the next largest size drill
- The depth is increased




-pins could be loosened in attempt to shorten them with a bur , removed by rotating counter clock wise and insert a new pin or do as before . . i.e. if you put the pin and found that it’s too long and it will interfere with occlusion and you tried to shorten it using a bur it will get loose.

Penetration or perforation
If the tooth is tilted and you are drilling in a wrong way, you may penetrate the pulp or go to the external surface of the tooth.
“penetration into the pulp, perforation in the external tooth surface”
-hemorrhage in the pinhole following removal of the drill.
-usually operators can tell through by their tactile sensation.
When the doctor becomes well trained he can recognize that he is working in enamel or in dentine by his tactile sensation.
-observation of the angulation of the drill should indicate whether a pulpal or external perforation.

Radiographs
-can help us to know if we make penetration or perforation.
If there is sound dentine between the pulp and the pin  no pulpal penetration
But any view projecting the pin in the same region as the pulp doesn’t necessarily mean pulpal penetration because the radiograoh is 2 dimentional photo for a 3 dimentional structure in reality.

Sooo… if the radiograoh shows that there is no dentine between the pulp and the pin we can’t make sure that we penetrate the pulp.

-any radiograph showing the pin projecting outside the tooth confirms external penetration, however , any radiograph showing the pin inside the projected outline of the tooth doesn’t confirm an external perforation.

Meaning that if we put the pin more labial or more lingual or we take a radiograph in angle,, the result will be as if the pin is projected outside the tooth so it can’t confirm external perforation.

In asymptomatic tooth a pulpal penetration is treated as any other mechanical exposure, if there is no bleeding all you have to do is direct pulp capping.





Perforation into the external wall of the tooth:
examine clinically or by radiographs to determine the location of
- if the perforation is located occlusal to the gingival attachment:
- Cut the pin flush with the tooth surface.
- The pin is removed and the pinhole is restored.
- The tooth is prepared beyond the perforation.. if you prepare a crown before the perforation it will be leaky.

-if the perforation is located apical to the gingival attachment:
- Reflect the gingiva surgically
- Expose the pinhole, enlarge and restore it.
- Perform a crown lengthening and place the margins of the restoration gingival to the perforation.




BEST WISHES


Done by: Safa’a Makhool
Cons sheet #6
Date of the lec. 14/3/2011
Dr. Yara
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Shadi Jarrar
مشرف عام

عدد المساهمات : 997
النشاط : 12
تاريخ التسجيل : 2009-08-28
العمر : 26
الموقع : Amman-Jordan

http://jude.my-rpg.com

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