cons sheet # 8 - Ala'a Hmdan

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cons sheet # 8 - Ala'a Hmdan

Post by Shadi Jarrar on 27/11/2010, 2:36 am

بسم الله الرحمن الرحيم

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Class II amalgam restoration


Slide 2:

Class II; any caries located at the proximal surfaces of molars & premolars (Mo, Do, Mod)


Slides 3-5:

Features of cavity preparation:

- The general outline form is box like (to include the caries which found at the proximal surface) with an occlusal extension.
(This is a standard cavity preparation but there are some modifications we will talk about them later).

Note;
Most of the pictures in the slides are about class II cavity preparation for upper molar, MO surface.


- Class II is a class I plus box in the proximal surface, so, all the guidelines which applied on class I also applied on occlusal surface of class II (length, width, depth … ect.).

- The occlusal margins of the preparation are equidistant form the center of the defective grooves, fissures, & pits (same as class I).


- The extremities of the buccal & lingual grooves & the portion of the wall that's adjacent to the distal marginal ridge are flared, prepared at 95 degree to the pulpal floor (same for class I except at the mesial surface there's no flare because it's opened to the box on the mesial wall).



Slide 6:

You can see the cavosurface angle from occlusal extension to external tooth surface, should be 90 degree.

- We measure this angle from the buccal or the lingual walls of the box to the tangent that drawn on the external tooth surface.

Slide 7:

- The mesial view shows :-

1. the lingual wall of the proximal box is parallel to the long axis of the tooth (straighter than facial)
2. facial wall is parallel to the facial surface (external surface)
3. Facio-gingival & linguo-gingival line angles are slightly rounded.




Slide 8:

- Gingival & pupal floors should be flat, parallel to the tooth surface, perpendicular to the long axis of the tooth surface, & the 2 walls must be in dentin.


Here we have 2 cases:
1. if we make the margins of the cavity purely in enamel in the occlusal extension, then that's very thin (any caries doesn't reach the dentin we can deal with it without make restoration>> by making demineralization because this is a reversible caries)
2. If the gingival wall purely in enamel then the cavity will be very weak & the restoration will be broken in the future.

Slide 9:

- Axio –pulpal line angle should be beveled. Because the sharp angle make stress concentration point – then the filling broken above this angle.


Q: what are the differences between class II & class I with lingual extension??
- In class I >> flare
- Class II >> bevel
- We are talking about 2 different things, at the beginning, bevel done in a 90 degree angle which located between 2 walls. But the flare is whole wall tilted upward.

- So , bevel angle:-

1. To remove a stress concentration point (to get strong filling).
2. To gain more thickness on the weak area which the junction between box & occlusal extension.

Q: when we make class I with lingual extension then we have a sharp angle. Why do we not make it beveled??
- Lingual extension doesn’t located at occlusal contact point >> no stress concentration point.


- After that remove any unsupported enamel from the gingivo- cavosurface.


- So, we make 2 bevels;
1. axio- pulpal
2. Gingival


Slide 10:

Retentive groove:

- We make it by (palm & thumb) & (inverted palm &thumb) grasps.

- We make retentive grooves on the linguo-axial & facio-axial line angles.


- Deepest at the gingival floor & the depth decreases as we move to the pulpal floor (almost disappear at the pulpal floor).

- These grooves are very important in order to make retention (to make the box retuned to the tooth). Mechanical interlocking to lock the amalgam inside the tooth.



Slide 11:

Measurements:
- At the occlusal extension same as to class I but when we come to the isthmus area in class II, the thickness of the instrument must be more than class I.
Isthmus is about 1.5mm.

- We talked previously, isthmus must be around 1.0mm but here at the connection between occlusal extension & the box we need more than 1.0mm, actually we need 1.5mm to accommodate for the extended width of the proximal box compared to the occlusal extension.

- Occlusal extension is a narrow extension, but the box is opened with wide dimension (to allow us making the right angle of cavosurface margins in the box) so, to accommodate these 2 extensions we must make the isthmus in this area about 1.5mm.

For molars
• length of the gingival floor = 3-3.5mm
• height of the free gingival margin is about = 1.0mm
• width of the gingival floor = depth of the axial wall = 1.0 mm (from the external tooth surface to the axial wall)
• tooth surface is not a straight surface so when you go up at the level of pulpal floor the depth of the axial wall = 1.5 mm

These dimensions are conservative for ideal class II cavity preparation but actually we follow the caries extension.







Slide 13:

Cavity preparation:

- pencil the defective grooves on the occlusal surface of the tooth (only in the lab).

-With articulating paper record the occlusal contact of the opposing tooth.
In the slide there are 3 marks act as the contact area with the opposing tooth.
-The importance for determine the occlusal contact points is to avoid placing the margin of the cavity on these points of occlusal contact (move away from these points).
Move your outline to a safest margin because when we put it at occlusal contact points the margin will break.


Slides 14+15:

- Start at the pit that nearest to involved proximal surface with no. 245 bur tilted as illustrated in the slide.
(In this case we start at mesial pit)

- Incline the bur to the mesial surface & superficially move this bur among the distal surface when it moving to the distal surface it goes deeper.

- We move like this until the depth of point 2 in the slide become 1.5mm (at the distal pit).
That's mean we enter 0.2 -0.3mm from dentin, we come back later to the mesial side & modify it.



Slide 16:

- Move distally along fissures & grooves to make accurate occlusal extension, make sure that you keep the depth about 1.5mm & the bur is perpendicular to the tooth surface to avoid unnecessary cutting to a wall against other walls.

- In the previous slide, the bur doesn't appear perpendicular to the tooth surface, because intentionally we don’t need the bur to be perpendicular at this stage, but when you look from the mesial or distal surfaces you can see the long axis of the bur is perpendicular to the tooth surface, & when you look for it buccaly or lingually you can see the long axis of the bur tilted mesially. So, it's different views.





Q: what's the importance of the inclination??
1. We need some thickness around the defective marginal ridge, because we will enter again & make the box. We don't make establishment from the very first start to the mesial marginal ridge to be 1.5 mm, leave it with some more thickness. Ya3ni: you make the occlusal extension after you finish it you go to the proximal extension & make the box.
2. If you make 1.5 mm all over you can't make something called ditch cut on the proximal surface probably.(To conserve the adjacent tooth structure.)

To now we finish the occlusal extension approximately


Slide 17:

-At this stage we make 1.5mm depth mesially, we come close to the external tooth surface by 0.8mm (from the proximal contact area)

-As you approach the marginal ridge, direct the cut toward the center of the contact area (don’t go from the side)

-Don’t break through the mesial marginal ridge at this stage we leave it to a next step.


Slide 18:

The objectives for extension of proximal margins are to:
1. Include all caries, faults, or existing restorative material (if the caries extended buccally my cavity shifted buccally).
2. Create 90 degree cavosurface angles.
3. Establish (ideally) not more than 0.5mm clearance with the adjacent proximal surface facially, lingually, & gingivally.

-In natural teeth we have contact with adjacent teeth, to remove all the caries & to get hygienic margins we must get 0.5mm clearance with the adjacent tooth.

-Ya3ni: when you look from occlusal view you can't see any contact between your margin & the adjacent tooth .

-Tip of explorer = 0.5mm
So if the tip of explorer enters from buccal, lingual, & gingival then you have 0.5mm clearance & that's true.

-If the clearance more than 0.5mm this unnecessary cutting in the absence of the caries, but at the presence of caries that is correct.

Q: if we make the ideal box (3.5mm length & 1.5mm depth…etc).
Then the clearance less than 0.5mm what should we do??
-we talked that there are variations according to the height & width of the tooth, or if the tooth is molar or premolar, so 3-3.5mm this is estimated, we do it if there's no proximal contact, but when there's proximal contact we follow adjacent tooth, that means to make 0.5mm clearance more important than to make exactly 3.5mm of the box.



Slide 19:

-we should visualize final location of proximo–occlusal margins before (drawn with dotted line in the slide)

Note: this picture isn't very accurate because the lingual clearance is more than 0.5mm.


Slide 20:
• To estimate the depth of the box:-

-Use no. 245 bur in the stationary condition (not rotating) & put it in the buccal or lingual surface then you estimate how much 0.5 mm below gingival contact is.
-In the slide the tip of the bur is 0.5mm below the contact, so this is the length of the bur that you have to go inside the tooth to break the contact.
(In this step we don't remove the contact; we just imagine how much I should remove from the contact).

Q: if the teeth naturally far from each other then the clearance more than 0.5mm, In this case what should we do??

-In this case this rule isn't applicable.


Clearance space: is the space between the margin & the adjacent tooth.


Slide 21:

-We imagine how we will cut the margin, in this step we will start the real cutting of the box.
-We enter 1.5mm & leave 0.8mm from the mesial marginal ridge (external tooth surface).
-When we leave 0.8nn from the external tooth surface, the bur located 2/3 on the dentin & 1/3 on the enamel.

If > 0.8 – deep axial wall
<0.8 – shallow axial wall.


Slide 22:

-Start to go inward in the tooth; we apply slightly pressure directed gingivally.

-The bur slightly angled to the mesial; to preserve the tooth structure which I lift (imagine yourself making a groove inside the tooth).

-In the slide, the black area is a caries lesion if you notice that the bur located below the caries.

-Because the dentine is softer & cuts easier than the enamel, the bur should be held against the harder enamel to guide & create an axial wall that follows the outside contour of the proximal surface.

-Create an axial wall that follows the outside contour of the proximal surface. Mesial contour is convex, so the axial wall must be convex as well.

-The mesio–distal width of the completed proximal ditch cut (remaining enamel) should be 1/3 in enamel & 2/3 in dentin.

In the 3rd picture at point (a): width of the ditch is about 0.7mm>> 0.5-0.6mm in dentin & the remaining in enamel.

At point(c):

Width of the ditch 0.75- 0.8 all of it in dentin, that's why when you go more gingivally dentin thickness remain the same but the enamel thickness decreases.
That means if you have deep caries (point c), all the box located on the dentin & no enamel involved.
– If the caries in root, the thickness should be 0.7-0.8mm in dentin, to have amalgam structure durable (don't break & enough for the restoration).

So, Root >> 0.7 – 0.8mm in dentin
Crown >> 0.5 – 0.6 mm in dentin & the remaining in enamel.

Q: Is the axial wall straight??
-Axial wall should be straight & parallel to the long axis of the tooth.

-Parallel if you look to it buccally or lingually, but convex if you look to it occlusally.



Slide 23:

Occlusal view:

Class I on the occlusal surface, something like groove inside the tooth, & proximal ditch.




Slide 24:

-Remove the enamel ditch to open the box.

-We can break it by hand instrument, almost we used hatchet.

-We used hatchet to remove the proximal remaining enamel its better than bur (safest) to avoid damaging of the adjacent tooth.

-Cutting hand instrument has blade, when we enter it just apply planning scraping force to remove the remaining enamel then we have totally opened box.

Q: can we use chisel??
No,
- Chisel: straighter, used with push-pull motion, & has one blade at the tip.
-Hatchet easier to used because it has 2 blades one on the side and the other on tip.


Slides 25 + 26:

ما تركزو على الأرقام كتير
بس بالامتحان في اسئلة عليهم

-With the same hatchet you are smoothing the sharp angles found after removed the remaining enamel.

-Using planning scraping action.


Slide 27:

-Very important not to flare the buccal or lingual walls. (Actually there's a flare but we are talking about intentionally not to flaring these walls).

-We want 90 degree angles for cavosurface margins, if I make the walls more opened (flare) then very weak margins for amalgam result & it will break in future.
-Should maintain the 90 degree angle & that's achieved by minimal flare in the walls.

Slide 28:

-With gingival margin trimmer make slight bevel of the axio–pulpal line angle & for the gingival margin.

-We make bevel for the gingival margin in order to follow direction of the enamel rods >> because if we make sharp angle then we have undermined enamel (unsupported enamel )that cause breaking of the tooth structure, all that steps to preserve the adjacent tooth.

Slide 29-32:

-Make retentive grooves in the box (at the axio–buccal & axio- lingual line angles).

-We used bur no. 169, its tapered bur; we make the grooves at the tip of the bur only.

-Start at axio–buccal–gingival point angle (internal point angle) & goes up, the deepest point in the groove is near the gingival & the depth decreased when you go up until disappear at pupal floor. Depth is about 0.5mm (small but significant) at the gingival floor.

-To make the grooves, the bur must title toward line angle not parallel to the long axis of the tooth.

-Grooves are cone shaped in cross section.

-Grooves located at critical area = near the pulp (axial wall located near the pulp).

So, you shouldn't preparing the grooves at the extent of buccal wall, or even toward safest wall, in bucco–axial case we make the groove slightly toward the buccal wall because the axial wall at risk of exposing the pulp.

Q; can we make retentive groove between axial & gingival walls??
-No, it won't be retentive because it with the long axis of the tooth & with the long axis of occlusal forces.

Slide 33:

-we go back to the occlusal surface & make some modifications:
Flare, smoothening … ect.


Slide 35-38:

**1st picture:
• 90 degree angle between the facial & lingual walls of the proximal box & the tangent.
• The proximal margins should be free by 0.5 mm from adjacent tooth.
• Axial wall always should be parallel to the long axis of the tooth.
• Gingival floor is beveled in the way that is sloped with the long axis of enamel rods in that area.
• From occlusal view the axial wall has the same convexity to the tooth.
• You can see in slide 38 the retentive grooves in a cross section.


Slide 39:

Measurements for the premolars:

- Length of the gingival floor = 3.0mm (an average number).
-Depth of the axial wall at the gingival floor =0.8mm
-Depth of the axial wall at the pulpal floor = 1.0mm


Slide 40:

-90 degree angle to the margins

Slide 41:
Read it from slides.


Slide 42:

-You should make retention form in both occlusal & proximal (box) extensions.

Slide 43+44

• in the mandibular 1st premolar there are some considerations:

- Occlusal surface is tilted lingually
-Lingual cusp is very small.
-So the bur in our cavity preparation must be perpendicular to the occlusal surface not parallel to the long axis of the tooth.

*If we go too much lingually >> undermined enamel at the lingual cup.
*If we go too much buccally >> expose the buccal pulp horn
(This is a very common mistake for mandibular 1st premolar).

-In the picture we didn't cross to the opposite pit (if you start with mesial pit, you don’t reach distal pit) because there's a strong transverse ridge, & usually no fissure crossing through the ridge so, there's no caries found in the transverse ridge.

-If you found a caries lesion at the distal pit, then you make 2 separate cavities.

-Same steps of cavity preparation.


Slide 45:

• maxillary 1st molar:-

-To preserve the oblique ridge.
-In some cases the caries extending to the buccal & lingual surfaces.
-In other cases the caries extending below the oblique ridge >> in this case, we extent the outline form to even go through oblique ridge.


Slide 46:

* Maxillary 1st premolar:
• One important consideration & its esthetics.
• The mesial aspect of the maxillary 1st premolar appears during smiling, so if we make amalgam restoration then it makes bad esthetics.
• To solve this problem:
1. You have limited the extension of the facial wall of the box.
Instead of 0.5mm we can go 0.2 – 0.3mm (clearance with the adjacent tooth)

2. Make the lingual & buccal walls in the box straight to shows less amalgam.
3. Nowadays we make it with composite.


Slide 47:

-we must do occlusal extension even we don't have caries, in the case of big class II at the proximal surface without enough retention form, here occlusal extension act as dovetail.

-But if we have small class II at proximal surface, broad facio_lingual contact, & low caries risk, here we can include the proximal surface without occlusal extension.

-Dimensions of this box are the same for what we discussed, except for the retentive groove which goes as the same from gingival to occlusal surface to get more retention.

The end

I wish every thing is clear

كل عام وانتم بألف خير بمناسبة عيد الأضحى المبارك, وبالتوفيق للامتحانات المتبقية.




Done by: Ala'a Hmdan.
Con. Lec. No. 8
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Shadi Jarrar
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عدد المساهمات : 997
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تاريخ التسجيل : 2009-08-28
العمر : 26
الموقع : Amman-Jordan

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