Sura H.khraisat cons– sheet #119/12

This lecture is about Class III cavity preparation for composite restorations for Dr. Suzan Hattar and as reference for this lecture you can back to “Sturdevant’s Art and Science” fifth edition chapter12 pages from (530-541).

First of all we know that there are differences between composite and amalgam restorations and the most important one that composites binds to the tooth structure rather than amalgam which needs a mechanical means like undercuts .

Now back to Class III:

**Where is the Class III occurring?

According to J.V black classification Class III cavity occurs at proximal surfaces of anterior teeth that not involve the incisal edge.

As we talked before about the Class II cavity preparation the access point (where we start) was from occlusal surface why? Because it is the strongest point and the buccolingual width of posterior teeth is so wide, so its not sense to cross all that width to reach the contact point which will weaken the tooth.

**but what we will do in the anteriors?

In anteriors we do the opposite exactly so the start point (access point) will be either facially (buccally) or lingually.

As all the caries which occur at the proximal surfaces it will exist below the contact point .why? Because this area where food and bacteria get there and it’s not cleanable easily

**How could the Class III been detected?

-By an explorer -Radiograph -transilumenation

Class III can be detected simply, so clinically you can detect it because the bucclingual width is small

As we know the caries are radio translucent and transilumenaton: which we put high light on surfaces so the class III will appear as dark or black area (transilumenation as ilumenation to the tooth)

For esthetic purposes, we couldn’t do Class III with amalgam restoration BUT there is one place where we could do an amalgam restoration which is at the distal surface of the lower canine and the cavity not involved the facial surface.

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** Tooth color restorations: - composite - Glass inomers

For Class III we use mainly composite which is the best choice, but it needs high degree of isolation and skillful operator and the Dr. will talk about composite in coming lecture in details.

** Access to the lesion:

Shall we go through lingual or buccal surface …..

We try as much as we can to through lingual surface to leave the buccal surface with natural enamel for esthetics. But sometimes we cannot go lingualy and we should go facially and these times are:

-If we have overlap between teeth for example between lateral and central which mean sometimes the lateral go down under the central so if we go lingualy to reach central we have to go through lateral which is not involved with lesion so we go thorough facial surface.

-If we have caries JUST on the facial surface.

-If we have old restoration which is located facially.

So, here the dr. was reading from slides

Facial approach advantages:

If the caries just exist facially and to preserve the lingual marginal ridge which is the centric stop (which is the point where the opposing teeth will stop and touching at the occlusion )and of course it’s better If we have tooth to tooth stop point rather than having tooth to restoration stop point .

Lingual approach advantages:

1- Facial enamel is conserved.2- Unsupported enamel may be left (not like amalgam where we cut out all undermined enamel)

because the composite binds to the tooth structure which gives the support.3- The difference in color will not be seen.4- We will avoid the discoloration later on.

**Initial steps:

1- Anesthesia 2- Occlusion analysis: with articulating paper to preserve contact points and to avoid putting the

cavosurface (the weakest area which is the margin between the restoration and the tooth structure) at these points.

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3- Shed selection: we do that at beginning of clinic because after the tooth has been isolated it will have some sort of changing in color due to isolation

4- Tooth isolation.

**Final steps:

- Out form -primary resistance -primary retention

**Types of cavity preparation for Class III:

1- Conventional Class III tooth preparation.2- Beveled conventional Class III tooth preparation.3- Modified Class III tooth preparation.

**Conventional Class III tooth preparation:

The primaryIndication for this type of Class III preparation isFor the restoration of root surfaces. Thus, it would be unusualTo have an entire Class III preparation of the conventionalType. More likely, only a portion of a toothpreparation-the portion on the root surface that has no

enamel margin-would be prepared in this manner

When preparing the conventional portion of a preparation(on the root surface), the form of the preparationwalls is the same as that of an amalgam preparation.The cavosurface margins exhibit a 90-degree cavosurfaceangle and provide butt joints between the tooth and

the composite material. Thus the external walls are prepared

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perpendicular to the root surface. In this conventionally prepared area of the tooth, which is apical of the cervical line, the external walls will be entirely of dentin and cementum.

These walls must be prepared to a sufficient depth pulpally to provide for the following:

1- adequate removal of the caries, old restorative material,Or fault, and sometimes

2- The placement of retention grooves, if deemed necessary.

This wall depth (depth to axial line angles) usually will be approximately0.75 mm into dentin, assuming no additional caries excavation

is required.

Combined cavity: This is a cavity that include the conventional cavity preparation on the root with beveled conventional cavity preparation on the crown which is the most common.

**Beveled Conventional Class III Tooth preparation:

The beveled conventional tooth preparation for composite restorations is indicated primarily for replacing an existing defective restoration in the crown portion of the tooth. However, it also may be used when restoring a large carious lesion for which the need for increased retention and/or resistance form is anticipated.

The beveled conventional preparation is characterized by external walls that are perpendicular to the enamel surface, with the enamel margin beveled.Usually, retention is obtained by bonding to the enamel and dentin and no groove retention is necessary.

So if we have been asked that in which cavity prep. We need retention grooves the answer will be: conventional one.

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**Clinically what we do:We use round bur (we couldn’t use fissure one because we want to go as possible as we can near to the adjacent tooth to go perpendicular on carious lesion so if we use fissure bur we will end up with row cavities) and with sized (1/4) or (1/2) or (1) or (2) it depends on carious region and the size of cavity.Before contacting the tooth, the bur is positioned for entry and rotated at high speed using air-water spray.Direct the cutting instrument perpendicular to the enamel surface, but at an entry angle that places the neck portion of the bur or diamond instrument as far to the adjacent tooth as possible.

Incorrect entry overextends the lingual outline into potential stress areas (marginal ridges) and unnecessarily weakens the tooth (see Fig.)

The axial wall depth at this initial stage of tooth preparation is limited to 0.2 mm inside the dentinoenamel junction (DEJ) (if no retention groove will be used), which means it will be approximately 0.75 to 1.25 mm deep (the larger being incisally where enamel is thicker). The axial wall will be outwardly convex, following normal external tooth contour and theDEJ, both incisogingivally and faciolingually.

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deal initial axial wall preparation depth. A, Incisogingival section showing axial wall 0.2 mm into dentin. B, Facioingual section showing facial extension and axial wall followingcontour of tooth.

Unless necessary please try not to involve the proximal contact area, the facial surface, sub gingival areas and margin ridges.Undermines enamel can be left in non specific areas however friable enamel should be removed.** undermined enamel: enamel that not supported by dentin **friable enamel: very thin irregular enamel (which will not fit with composite)And you can differentiate between them so easy which what will we see in clinic.

If retention grooves are to be placed it will placed at axiogingival and axioincisal line angles and so the minimal depth here will not be effective for putting the grooves ,so you have to increase the initial depth to 0.5 mm inside the dentinoenamel junction to put 0.2 mm .

As we know we started with high speed bur to pass through enamel then we switch to low speed bur inside the dentin.

Finally, we do bevels on enamel so we use high speed burs such as large round, fissure diamond burs to do roughness surfaces and it’s with 45 degree.

**The advantages of doing bevels:1- Increase retentions2- Esthetics blending: no sharp or straight angle between restorations and tooth

structure so it look like as natural one.3- Remove the fragile enamel and do your margin.

**Areas we shouldn’t do bevel on it:1- Root surfaces : no enamel there2- Cementoenamel junction : very thin enamel3- Areas of stress

So what we will do if the cavomargin between the restoration and the enamel is to be placed at centric stop (area of stress) …..We will shift the cavity by 0.5-1.0 mm away from this point (extend your outlines).

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Bevel width is usually 0.2-0.5 mm depends on how much retention I need and on the thickness of enamel that I have.

**How we do retention grooves:1- We use a low speed round bur sized (1/4).2- Then you go to the axioincisal and axiogengival line angle at an angle that bisects

your tooth wallAnd the length of the groove go paralleling with length of dentinoenamel junction.And as we said the initial depth will be 0.5 mm inside the dentinoenamel junction rather than 0.2 mm why?If I do 0.2 mm as initial depth and I want to put retention grooves the cavity will be very shallow so extent the depth of the wall to put grooves.

**advantages of retention grooves:1- Increase retention 2- Minimize potential negative effect polymerization shrinkage, when composite is

setting and polymerizing after a period there will be some sort of shrinkage which makes gap but when we increase the surface area with grooves we decrease the possibility to have gap.

3- Increase sealing between the composite and tooth structure.

**Modified Class III Tooth Preparation:This is the most common one.Small to moderate cavity on crown ,there will be NO rules in this cavity preparation where you find caries ,remove it without initial depth or perpendicular walls JUST follow the caries ( so it’s the most conservative one ) and we do bevels.

No effort is made to produce preparation walls that have specific shapes or forms other than external angles of 90 degrees or greater. The extension axially also is dictated by the extent of the fault or carious lesion and usually will not be uniform in depth. Weakened, friable enamel is removed while preparing the cavosurface margins in a beveled or flared configuration with the round diamond. Usually no groove (or cove) retention form is indicated because the retention of the material in the tooth will result from the bond created between the composite material and the etched peripheral enamel. Thus, the preparation design appears to be "scooped" or concave.

The last thing **differences from other types:That the design is detected by the extension of the caries and it approach from lingual surface (If possible)

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NO effort to do specific form for the walls .extension of axial wall is detected by the extension of caries and there is no certain depth.Weaken and friable enamel is removed No grooves are indicated and always there is bevels for this cavity.

Good luck Sura H. khraisat

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