jude20111.files.wordpress.com€¦ · Web viewSlides (1-3): For the posterior teeth we use class 2 cavity preparation. For the anterior teeth we use class 3 cavity preparation

26-10-2013 sheet # 6 Areej Hammad

Class 2 cavity preparation

Slides (1-3):

For the posterior teeth we use class 2 cavity preparation.

For the anterior teeth we use class 3 cavity preparation.

Keep in mind about class 2 prep is the location of caries that found in proximal areas, its start usually subcontact (just below the contact area) and this the hardest area to clean for the patient.

Note: (Understanding the start location of this caries is very important to understanding class 2 cavity designs.)

Slides (4-6):

Features of class 2 cavity preparation:

It's basically a boxlike cavity that is one part of your preparation , the other part is just like a class 1 cavity prep (occlusal extension) so the boxlike will include the caries that is inter proximally , we joint two cavities as one(the interproximal and occlusal) so for occlusal extention of your class 2 cavity preparation their feature design is exactly the same for class 1 so we talk about extension, outline, shape…everything is exactly the same as class 1 prep.

So now we will be talk about the box like cavity, something to keep in mind is where to extend your box, how much should you take from the proximal areas and where you should end your buccal and lingual walls. Keep in mind that we want enamel margins (interproximal margins) to be 90 degree, where we measured from? From the lingual wall with the tangent of the interproximal surface (in this case distal surface) so the tangent of that surface with the lingual wall of the cavity we should have 90 degree, keep in mind that the tooth is not flat it’s have a curve so you want to make sure that your margins end by having 90 degree angles and in order to achieve that in the inter proximal sides we tend to have flared walls, what we mean by flared? Means when we lock from occlusal to distal side they are flare they are not parallel, if they are parallel the buccal to the lingual they will not be 90 degree they will be less than90 it will be acute angle so it must be flared which will be end

by 90 degree .

Notes :

* For demonstration purposes, the cavity preparation will be a MO class II on a mandibular molar.


* There are two portions in this cavity preparation. The occlusal extension or outline is the same in class I.

*Generally the amount of remaining tooth structure is more important to restoration longevity than the restorative material used.

Slide 7:

Something U notice in Premolars is something called A reverse curve on the buccal wall of the cavity in class 2:

What mean by that?

Usually the caries start subcontactly, where is the contact located in premolars?

The contact area of the premolars are located (towards the occlosal) more buccally so I expect the caries to be shifted to the buccal side, so in order to get 90 degree margin on the buccal wall and still removing all the caries that is in between we have to come from central fissure toward the buccal wall with a curve, it should not be straight but when we go lingually from the central fissure we tend to have a straight line, we don’t get a curve.

So this feature is in premolars (in the box) of the buccal wall, we call it a reverse curve feature. Why do we do it? In order to conserve tooth structure and still have 90 degree margins on the buccal wall, and it’s especially in premolars, because in molars the contact area is more or less in the middle.

Slide 8:

-Now for the box itself (in Premolars as well) your lingual wall will be more or less parallel to the long axis of the tooth. However ur facial wall is parallel to the external or the buccal surface of the tooth, it will not be parallel to the long axis of the tooth, why is that? Again because the contact area is shifted more to buccal side. so ur lingual comes up straight but the buccal with a curve ( something to be attention to)

-The facio-gingival and linguo-gingival line angles are slightly rounded.

Slide 9:

Now the gingival wall is flat and perpendicular to the long axis of the tooth, the pulpal floor is also flat and its parallel to the occlusal plane of the tooth. So both should be horizontal and both should

be flat.)


Slide 10:

You have to have rounded or beveled axio-pulpal line angle and you have to have also beveled or angeled gingivo-cuvo-surface angle so it has to be beveled , why is that ? because if it is straight, fracture will happen, because the enamel rods cervically flare outward, so they’re divergent in that area, so if you make it 90 degree the enamel rods will be unsupported in this very end gingival floor, so you have to bevel it in order to follow the direction of the enamel rods and not to have unsupported enamel in that area . so you should remove that.

Slide 11:

Objectives in class 2 cavity preparation:

Include all caries, faults, or existing restorative material-.

Create 90-degree cavo-surface angles-.

-Establish (ideally) not more than 0.5 mm clearance with the adjacent proximal surface facially, lingually, and gingivally.

What does this mean?

This means (in the box prep.) when you try to measure the space between your cavity preparation and the adjacent tooth -the clearance- the amount of space should be there between the buccal wall and adjacent tooth is 0.5 mm, between the lingual wall and adjacent tooth is 0.5 mm ,and between gingival floor and adjacent tooth is 0.5mm, this is the minimal clearance . Can you have more? Yes you can, it depends on the extension of the caries. If we talk about most conservative cavity you cannot have less than 0.5 mm, (it make sense) why? For the amulgum u have to insert matrix bands and some kind of a ring on the tooth In order to be able to clean and condense your filling material properly you have to have 0.5 mm clearance in all sides buccally, lingually and gingivally . (this is very important).

Notes:

The 0.5 mm can be measured as the diameter of the explorer tip. -

-In the most conservative preparations the clearance with the adjacent tooth could be 0.2-0.3 mm.

-usually this is achieved with the use of hand instruments to plane and shape the proximal walls. If the 245 bur is used, more clearance will be achieved.


Slide 12:

The axial wall:

The axial wall should be parallel to the long axis of the tooth, and when you look at the axial wall from the occlusal view it should be parallel to the external tooth surface, so is the external tooth surface flat? No, it is curved so same for your axial wall it should be having the same curvature as external tooth surface , why is that ? Because if we do it curve or parallel to the external tooth surface you tend to have uniform thickness for your filling material in that area, if it was flat some areas will be shallow and other will be deep, and this is not good for resistance, so it has to follow external tooth surface, and if we have very deep area it may damage the pulp and you don't want to compromise the vitality of the pulp so make sure that you follow this outline.

Slide 13:

Retentive grooves:

We didn't talk about retentive grooves in the class 1 cavity preparation because we said that the retention in class 1 preparation comes from parallel walls and slightly under cut walls that’s should be much enough for class 1 cavity preparation because in class 1we have 4 walls: lingual, buccal , mesial and distal.

Now in class 2 we lose one proximal surface at least, and may be two proximal surfaces are missing .So the amount of surface area contact between your filling and the tooth surface is minimized in this case, so that’s why in some cases especially when your class II cavity prep. Is big, u may want to supplement your retention with retention grooves. We still going to do convergence on the occlusal and on the box, but it’s especially when u have big or extended cavity u may want to use the retention grooves.

So you want to make a retention especially when you have extended or big cavity, how to do the retention grooves there?

Basically small grooves that are placed in the axio-buccal and axio-lingual line angles they extend from this point angle all the way to the level of the pulpal floor , you don't see it from occlusal side, it's just basically inside the cavity, they don’t extend more than the height of the pulpal floor . and they are made in dentine we can't make retention groove in enamel it has to be in dentine because we don't want to make undermined in the enamel so it has to be in dentine and has to be following the curvature of the axial wall.


Slide (14-15):

Measurements of the prepared cavity:

-the isthmus width in class II (we will interest especially with isthmus which connects your class 1 to your box preparation) it should be wide enough, how much wide? 1.5 mm this is the minimal width and it is good to (have as 1.5 mm wide in order) to provide maximum retention for the amalgam in the box.

Note : For the very conservative preparation, the isthmus width should be as narrow as possible and no wider than one quarter the intercuspal distance.

-you try to place your gingival floor about 1mm supra gingival, (it’s a rough estimation) but in general, what determinate the level of your gingival floor is extension of the caries but in general

that is what you will try to do in the lab keep it almost 1 mm supragingival .

-1.5 mm the depth of your amalgam composite extension, (like in class 1 cavity prep.).

-Now very important measurement to keep it in mind, The width of gingival floor in the molar should be 1 mm, can it be more? Yes it can depends on the extension of caries, but can it be less? No , because it has to be supported in dentine so you have to go at least 1 mm in order to reach dentine, also we said about the resistant form we should have a thick enough filling to withstand the occlusal forces. (even though this is a low stress concentration, but it should have a 1 mm, because as we said before that, areas with high stress concentration, the depth should be 1.5 mm but in this area 1 mm is enough, but less than that it might be subject to fracture).

So in molar u have to measure ur gingival floor and make sure that’s either 1 mm or slightly more, in premolar is less and we are talking about 0.8 mm for gingival width.

I don't care if you don’t remember these measurements (the height of box it's usually 4 mm, the width of gingival floor facio-lingually is 3 mm). these are very rough estimation u don’t have to know them. What I want you to keep in mind is the 1 mm for molar, 0.8 mm for premolar and 1.5 mm for isthmus these are the most important measurements.

premolar


Slide 16:

The cavity preparation:

How to start your cavity preparation:

-Start to have an idea about where your cavity should be extended. Important thing to do is to mark your occlosal contacts before you start your cavity preparation, and why we should do that? To ty to avoid them and try to place your cavity margins away from the contact areas with the opposing tooth, why is that? Because if it was on contact area (it’s a weak inter-face between the filling and the tooth), & if there is an opposing tooth that’s keep hitting this area ( the junction between the filling and the tooth) it may break either the tooth or the filling. So you don’t want your junction or cavosurface margin to be right on the contact area with the opposing tooth, so u have to modify your outline depending on whatever you have from the opposing contacts.

-After you finish your class 1 cavity preparation, ( just a regular class 1 cavity), u start to have an idea what’s the extension of your box should be ( guideline – 0.5 mm clearance all around and 90 degree Margins-) , so that’s basically what you are looking for whenever you want to go interproximal areas.

Again—visualize the outer contour, and try to draw a line before you go into proximal areas, -the most challenging thing in class ǁ cavity prep. is to break the contact area with the adjacent tooth, without damaging the proximal area of the adjacent tooth). How to do that? Just don’t hold your bur in between the teeth, it should be exactly at the same tooth you’re doing cavity prep. on, the bur should never go in between the teeth because if you go in between the teeth, u will likely to take from the tooth you’re doing and the adjacent tooth as well. So keep your bur directly on the toot you’re preparing, and then start establishing when the bur should stop (usually 0.5 mm below

your contact area), so this is your gingival extension, for example here if u use #245 bur (3 mm –length of the cutting edge-) and if u have to go 0.5 mm that tells u that u have to go almost the full length of the bur (like in the pic), that’s how u measure, measure it before u start cutting (when the bur is off –not rotating-) hold it in between the teeth and have an idea how u should go from ur bur, (it differs if u are using another bur- cuz different

lengths- but the guideline is 0.5 mm below the contact area.

-Now after we finish the class one, and we have the idea where should we stop, we start going into the box (to do the box preparation)

two thirds of the bur should be supported into dentine and a third into enamel, so keep ur bur supported against the harder enamel not against the softer dentine , in order to guide u through the process.


-if u notice we are leaving a thin shell of enamel that’s un-cut at this point -we start going gingivally leaving a thin shell of enamel to the end ( like u are doing ditch cutting inside the tooth), we are creating a vertical groove in the tooth before we open up and break this contact area. So u go gingivally, and to include the caries at this point we are almost at the same level of the pulpal floor

and then we are going gingivally in order to include or reach that subcontact caries, so in general how much should u go into dentine ? the least is (0.5 - 0.6) mm ,BUT the caries may be extend way below the contact area, it may be reaching the cementum sometimes, so u have to extend your cavity to include all the caries, if u ended up in the root area , the depth of this cavity preparation should be about 0.7-0.8 mm because at this area we no longer have enamel, here we only rely on dentine so that’s why we allow more a

deeper cavity preparation in the root area

Ques.(student) If caries extend to that deep , it won’t affect other structures like gingiva?

(cavity margin should be away by 2 mm from the alveolar crest , 3la 7asab kol el clinical situations that guideline u should keep in mind, if it’s less than 2 , that’s when u have to do something extra ( surgical procedures – tsheel el gingival, tnzel el bone , t3ml exclusion lal sen in order to maintain these 2 mm (which we call the biological width) , just keep in mind that sometimes we have to reach the pulp in order to remove caries , but still we’re maintaining the healthy relationship between the cavity margins and the gingiva.

When u do that, like u see (the pulpal floor and , and this is our ditch cut that we did and we went down and we lift that thin shell of marginal ridge intact ,and then u expand ur cavity u go buccaly and lingually to include ur contact area , as we said we want it to extend 0,5 mm buccally and 0.5 mm lingually to the contact areas.

-now after u done that , the thin shell of enamel that we left we can break it just with a hand cutting instrument we just flick it off, u can easily break it with a hand instrument , if u do this way u will not have any trauma to the adjacent tooth not even a single micron, if u don’t do that if u go immediately into the box and don’t leave any shell of enamel u will end up having trauma to the adjacent tooth ( if the trauma is minor sometimes can be smoothen with finishing strips or finishing burs, u can get away doing that, but sometimes the trauma is very deep, so in this case do u have to do another class 11 on the adjacent tooth to close the trauma that u did, that’s why we try to avoid that by doing this technique.


If u don’t have hand instrument u still can still break this thin shell of enamel by a probe or even with the bur itself but very gently u will have much much less chances of trauma .

Now we can see the buccal and lingual walls of the box especially 3l premolars they are convergent , so they do have undercuts just like the occlusal extension and that’s aid in retention , so u have to have undercuts in buccal and lingual walls of the proximal.

-Now after u broke the contact area u can go with the hatchet and make sure that u have nice 90 degree margins all around ( buccaly, lingually and gingivally).

-for gingival floor again if u leave it flat, when u do the initial cutting in the beginning we will have flat floor, which is unsupported gingival enamel rods , what u have to do is just basically get a hand cutting instrument (gingival margin trimmer- this is the perfect hand instrument to use in this case) it basically transforms this acute angle on the gingival floor into a more of a 90 degree angle and bevels the gingival floor in order to get rid of the unsupported enamel on the gingival floor, so u can use gingival

margin trimmer which is the best thing to use in this case if u don't have it just use a regular bur and be careful not to hit the adjacent tooth. Again why this direction u can see from the pic the direction of enamel rods and the unsupported rods and the parallel ones that we did so u should have something like this.

-Now how to do retention grooves? u can do them by a bur #169 (it’s a tapered fissure bur) use It with a low speed hand piece and start with the tip of the bur and at the point angle at lingu-gingivo-axial u start at this point angle and then u drag ur bur upward till u reach the pulpal floor level. So if u take a cross section ur groove will be looking like this (the pic), again the grooves should be entirely located in dentin (how deep, what’s the diameter of the

grooves)? It’s 0.5 , u don’t need more than that diameter, that should be enough.

So u would see the grooves down below near the line angle they are like 0.5 and they fade out – start decreasing in diameter- as the go to the pupal floor, and u don’t see them from the occlusal surface.

(we don’t do retention grooves in the lab but sometimes clinically u do have to do them, usually if u have conservative cavity u don’t need retention grooves in class II, but if u have an extended cavity

(large cavity) very likely u will need to do retention grooves.)


how far away should they (retention grooves) be from the DEJ? It’s 0.2mm, 0.2 mm axial to the DEJ is enough as a location for the grooves, remember that if we went deeper u may likely to expose the pulp, so 0.2 is the perfect distance from the DEJ, and also we don’t want it exactly on DEJ because we undermind enamel.

Like I said the deepest point of the groove which is near line angle is 0.5 and start to fade out as it goes to the pulpal floor level.

-Use the same method to create the facial groove.

**The grooves should follow the curvature of the facio-axial wall and they must not extend occlusally beyond the height of the pulpal floor.

.

Just the extra information (as written in the sheet) !!

* If we don’t have an adjacent tooth we can go directly from the proximal surface like in class v.

* The deeper the cavity the closer to expose the pulp tissue so we need to keep it conserved.

* we break the remaining of the proximal enamel which is called “the enamel shell “ by hand instrument .(it's not found in the lab so we could use the bur but you should be very careful .the hand instrument prevent traumatizing the adjacent tooth but using the bur there will be a large possibility in causing trauma to the adjacent tooth.

* Because we don’t have the gingival marginal trimmer we could replace it with the bur.

* We use bur no.1691in the conventional speed hand piece and we can use the rounded bur.

* while making the retentive grooves always stay away from the pulp that’s why we place them on the line angle of the axio-buccal and axio-lingual but more to the buccal/lingual rather than going in straight direction in the axial wall.

Slide 35:

Where dose Resistance form in class II cavity prep. Comes from?

1 -The pulpal and gingival walls being relatively flat and perpendicular to forces directed with the long axis of the tooth.

2-Restricting extension of the walls to allow strong cusps and ridge areas to remain with sufficient dentin support.


3-Restricting the occlusal outline form (where possible) to areas receiving minimal occlusal contact .

4-The reverse curve optimizing the strength of both the amalgam and tooth structure at the junction of the occlusal step and proximal box .

5-Slightly rounding the internal line angles to reduce stress concentration in tooth structure (automatically created by bur design, except for the axiopulpal line angle).

6-Providing enough thickness of restorative material to prevent its fracture under mastication .

Where Retention comes from.?

-Occlusal convergence of buccal and lingual walls of the occlusal and proximal extensions. So they both should be convergent or on occlusal parallel is fine.

-Dovetail design of the occlusal outline.

-Retention looks or grooves. (When u have big cavity).

Special considerations:

Some modification to the regular guidelines that we talked about

Slide 38: Mandibular 1st premolar :

**The occlusal plane of this tooth is not coinciding with the occlusal planes of the rest of the teeth, because the lingual cusp is very small in size, so the occlusal plane of this tooth is inclined lingually, we said always the initial penetration should be perpendicular to the occlusal plane, so The bur should enter the occlusal surface when it is perpendicular to the occlusal plane of the tooth itself in order to preserve the lingual cusp and not to expose the buccal cusp horn. if u go vertically u will cut too much from the lingual cusp.

Notes (in slide) :

-This tooth is morphologically different from the other molars and premolars because of the diminished size of the lingual cusp. The bur should enter the occlusal surface when it is perpendicular to the occlusal plane of the tooth, i.e lingually tilted.

-Incorrect preparation would lead to either undermining the lingual cusp or exposure of the facial pulp horn.


When u start ur cavity, we said in regular class II we start with occlusal extension then we go proximally, but in this case u have to do the reverse. The proximal box is prepared before the dovetail occlusal extension for retension. That is done to preserve the transverse ridge and the lingual cusp of the tooth.

-Mesial and distal pits on this tooth are usually separated by a prominent transverse ridge. Therefore, a class II cavity in the mesial would not cross over to the distal pit. If caries is present in the distal pit, then two separate cavities should be prepared

**In this tooth, there is a very prominent transverse ridge, and the caries usually starts at mesial or distal pits (and we said btla3o two small cavity around the ridge in class 1 ) so it’s basically the same idea, when we made a box on mesial surface (for example) for a premolar we just make a small extension for retention on the mesial pit but we don’t cross over the transverse ridge to the distal pit because we will be compromising the tooth, let’s say there is caries in distal pit, what I should do? Two separate cavities ( class II and one cavity on distal pit) so we don’t connect them.

Slide 39: Maxillary 1st molar:

Again preserve the oblique ridge and don’t cross it unless there’s caries u can cross it, sometimes it can have a lingual extension and sometimes buccal extensions, usually the more common to see is the lingual extension because of the presence of palatal (lingual) pit.

Notes from the slides

Preserve the oblique ridge whenever possible. It is very important for the strength of the tooth .

Lingual or buccal fissures if involved may be included in the outline form.

Slide 40: Maxillary 1st premolar:

The upper 4 among all the posterior teeth is the most esthetically concerning tooth, just behind the premolar most of us (if not all) we show the 4 when we smile.

So in the box (we said to have retention the box walls should be convergent) if u do that convergent below u will have the amulgurm showing (right distal to the canine) u will have that shiny metal due to that convergent , so in order to restrict the outline form and preserve good esthetics in that area even with an amulgum restoration instead of having a convergent buccal wall, u do it straight. So

this a modification in upper 4 in order to preserve the esthetics .

Notes from the slides


In a MO class II cavity preparation on the upper 4, the facial wall of the box should be prepared parallel to the long axis of the tooth instead of converging occlusally. That is because it is more

esthetic, and shows less of the amalgam color .

The facial extension of the box should be kept to the minimum to clear the contact.

Slide 41: Box-only preparation:

Sometimes when we have just a proximal caries and all the fissures are clean (no caries), u don’t have to have an occlusal extension u just do the box like preparation, so u remove the caries in that area. How to get retention ? u still doing the convergent of the buccal and lingual walls but it’s better to supplement ur cavity with retention grooves.

In this case retention grooves are different from that we talked about before ( within class II with occlusal extension) because in this case the grooves have to go all the way to the occlusal surface, so when u lock at the occlusal surface u will see the grooves on the external surface, they are also 0.5 mm in diameter , and 0.2 mm away from the DEJ exactly the same but doing that will supplement ur retention a lot.

Notes in slides:

Employed when restoring a small proximal lesion in a tooth with no carious fissure or previous defective restoration .

To maximize retention buccal and lingual walls are prepared parallel or slightly convergent. Retention looks or grooves are essential here. They are prepared 0.5 mm in depth near the gingival and about 0.3 mm at the occlusal surface. Unlike in preparation with occlusal extension start s 0.5mm and will fade away toward the pulpal floor but in box-only preparation it starts as 0.5mm and ends 0.3mm won’t fade away.

Again ,, the convergence of the lingual and buccal wall are going to prevent the dislodgment of the filling material in what direction? Vertically , what will prevent the dislodgment laterally ? retention grooves. (that’s why u have to have retention grooves)

Slide 42 : MOD preparation:

The thing that in MOD because we lost 2 proximal surfaces and we have a cavity in the middle, they tend to wedge in between the cusps, so the wider ur cavity gets u have to shift ur plan from simple direct filling into indirect filling and do cuspal coverage (protect the cusp by covering the cusp with a restorative material(direct or indirect)) , so keep that in mind whenever ur cavity gets big especially

in MOD.


Same like the class II cavity but here it’s open at both sides (mesial & distal), so whatever applies to one surface applies to the other surface,.

And as we said the lingual wall of the cavity is straight and the buccal wall curves (reverse curve) to serve for the resistance and remove the caries and still get 90o margins .

Slide 43:cavity prep. To sum up!

Go perpendicular to the long axis of the tooth and create a punch cut ,, go buccally and lingually to open up and include the contact area , at this point u made the box but u didn’t break that thin shell of enamel , which u can remove with a hand instrument (make sure u have nice 90 degree margins all around ,, then retention groove.

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jude20111.files.wordpress.com€¦ · Web viewSlides (1-3): For the posterior teeth we use class 2 cavity preparation. For the anterior teeth we use class 3 cavity preparation