Curs 2 Prep Cav Cls 1 (2)

8/3/2019 Curs 2 Prep Cav Cls 1 (2)

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The treatment of carious lesions


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Classification of cavities

Principles in cavity preparation Class I cavity


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Consists of:

Removing pathogen microorganisms from the hard

tissue, enamel, dentin, cement and preparing a cavitywith some precise characters

Purpose:

Restore the loss of dental tissue by applying a filling

material (restoration) which is able to:

restore the tooth morphology

reestablish the tooth functions


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Classification of carious lesions and tooth

preparations

Blackclassified carious lesions into groupsaccording to their location in permanent teeth

The same classification is used to refer to cavity

preparations

According to the location of carious lesion on theteeth we distinguishsix classes of cavities


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The first class cavity ( Class 1 )

Results by the treatment of carious lesions that occurs :

on the pits and fissures of the occlusal face of the molars

and premolars

in the pits and fissures of the facial and lingual face of

the molars and premolars lingual surfaces of maxillary anterior teeth

It affects only one surface


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The second class cavity (Class II)results after the treatment of carious lesions situated on the proximal faces of

posterior teeth (molars and premolars)

If a proximal surface of a posterior tooth is involved in a restoration it is a Class IIrestoration

Class II restoration can involve one face ( simple) or two faces of the

tooth(composed).


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The third Class cavity (Class III)

results after treating carious lesion that occurs on the proximalfaces ofanterior teeth without involving an incisal edge


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The fourth Class cavity (Class IV)

Results by treating carious lesions that occurs on the proximal surfaces

ofanterior teeth when the incisal edge requires restoration

By extension: fractures of incisal edges of incisors and canines.


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The fifth Class Cavity (Class V)

Results by the treatment of

carious lesions situated on

facial or lingual surfaces

of all teeth in the gingival

third


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The sixth Class Cavity ( Class VI)

Restorations on the incisal

edge of anterior teeth or the

occlusal cusp heights of

posterior teeth are Class VI.


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Nomenclature of cavities

Classification of prepared cavities

1. Simple cavities situated on one face of the

tooth, named after the face where it is

located (occlusal cavity)2. Composed cavities located on two faces of

the tooth, are named after the face involved

3. Complex cavities located on three ormore faces of the tooth


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General principles in teeth cavity

preparation

1. Remove all defects and provide protection to the

pulp.

2. Extend the restoration as conservatively as

possible

3. Form the tooth preparation so that under theforce of mastication the tooth or the restoration

or both will not fracture and the restoration will

not be displaced

4. Allow for the esthetic and functional placementof a restorative material.

Black postulated in 1908 7 principles in tooth

cavity preparation: the Black principles


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1. Creating the access

Gaining access into the cavity should:

Assure a good visibility by direct or indirect

vision, into the cavity

Permit the good access of instruments for

preparation and restoration

Should not be very wide extended


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There are three clinical situations :

a. The cavity is wide opened by the carious lesion.

In that case the first step in cavity preparation consists only in

removing the undermined enamel that covers the pathological dentine

For that we use astraight fissure burin the turbine handpiece.


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b. The opening made by the carious lesion is very small.

In her development the carious lesion undermined the enamel producing

its breakdown at some point, on a very small area.

In this situation it is necessary to enlarge the small opening produced by

caries, to allow the access of the instruments in to the cavity

For this purpose we will use a small straight fissure diamond bur


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c.The cariuos lesion undermined the enamel but did not produce its

breakdown.

(ex: a PM presents on the marginal ridge a chalky stain, which indicatesthat the enamel is demineralised and undermined but it is not destroyed).

In that situation it is necessary to create the access through the

marginal ridge


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2. Removing the pathological dentine

Purpose is to prevent the occurrence of recurrent caries (which appear

under the restoration) and the inflammation of the pulp

The pathologic dentine is soft and discoloured, beyond it there is areactive dentine which is brown and more hard

3. Creating the extension for prevention

Refers at placing the cavity margin in sound dentine, in area which are

accessible to self cleaning and artificial cleaning.

The self cleaning area are those that get cleaned during mastication andthe artificial cleaning areas are those that get cleaned by brushing.

This principle prevent the occurrence of secondary marginal caries

( lesions that appear at the limit tooth restoration).

4. The retention formRetention is the property of a cavity to retain the filling material and to

prevent the displacement of the restoration in several direction of space.

Retention form may be obtained by mechanical shaping (convergent

walls) or via bonding procedures.


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5. The resistance form (to fracture or displacement)

Resistance of the remaining tooth structure must be designed in

cavity preparation, so that the restoration is resistant todisplacement, and both tooth and restoration are resistant to

fracture during function.

6. Finishing enamel walls and cavosurface margins

Finishing the margins means removing any unsupported and weak

enamel and making the margins smooth and continuous to facilitate

finishing of restoration margins.

7.Toilet of the cavityIt includes washing and scrubbing away any debris in the preparation anddrying the preparation.


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The Class I Preparation


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1.Creating the access this stage can be donein two ways depending on the dimensions of the

caries

In the carious lesions with

a wide opening we realise

the removal of the

undermined enamel.

In the carious lesions with

a small comunication

orrifice there is necesary

to gain the access into the

cavity.

Removing the carious tissue (avoiding the cusps ridges)

Create a sufficient space for the insertion of the filling material


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Instruments used for creating the access

Round bursStraight fissure burs or tapered fissure

Inverted cone with round angles

The burs are attached to the high speed handpiece with water or aircooling system, are made of stainless steel or diamond and have

diameter of0,8 1mm for minimum extension of the cavity.

With this burs we penetrate into the pits for1,8-2mm, and include in

the cavity all pits and fissures affected by caries.


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Instruments

position

During all this

movements the bur

needs to be parallel to

the long axe of thetooth or perpendicular

to the occlusal face

and the cusps will be

avoided.


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2.The removal of infected dentine

Is made with round stainless steel

burs attached to the low speed contra

angle handpiece ,orwith a small

spoon

First the infected dentine from thelateral walls of the cavity is removed,

the last one instrumented is the pulpal

wall, where exists the danger of

opening the pulp chamber

The dentine on the floor of the cavityhas to be sound ( hard on exploring),

except the situation of small amounts

of infected dentine, whom removal

would expose the pulp chamber


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3.Performing the extension for prevention

Extension means placing the cavity margins in

sound tooth structure, in areas that are exposed

to self-cleaning and artificial cleaning on the

cusps versants.

Also including all the pits and fissures whichpresent carious lesions.

If two occlusal cavities are separated by a

sound dentine ridge from at least 2mm, then

the cavities need to be restored in a separate

manner, if the ridge is less then 2mm or the

dentine is not sound the two cavities will be

united


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3.Extension for prevention

The preparation extension primarily is dictated by

the amount ofcaries, old restorative material, or

defect present. Adequate extension to provide

access for the tooth preparation, caries removal,

matrix placement,and amalgam insertion also must

be considered

The conservative Class I tooth preparation should

have an outline form with gently flowing curves

and distinct cavosurface margins. Therefore, when possible, the outline form should

be extended around cusps and avoid undermining

the dentinal support of the marginal ridge .


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4.Creating the retention form

The parallelism or slight occlusal convergence of two ormore opposing, external walls provides the primary

retention form.Usually the No. 245 bur is used.

Pulpal wall should be flat and perpendicular to those

occlusal forces that are directed occlusogingivally

(generally parallel to the long axis of the tooth). Such

floors may be purposefully prepared to provide stabilizing

seats for the restoration.If the pulpal floor can not be

prepared flat the form is of flat stairs or a base filling is

placed


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Well expressed angles between pulpal and vertical walls

Axe of the cavity perpendicular the intercuspidian plan


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5.Creating the resistance formOn this matter we differentiate tooth resistance and restoration resistance

Concerning tooth resistance this principles should be followed:

(1) maintaining as much unprepared tooth structure as possible (preserving cusps andmarginal ridges).

Minimally extended facial and lingual walls conserve dentin supporting the cusps as well as facial and

lingual ridges, thereby maintaining as much strength of the remaining tooth structure as possible. This

resistance is against obliquely delivered forces, as well as those in the tooth's long axis. IThe width of

a class I cavity should be 1/3 of the distance from the cusps heights. If the cavity is more

extended then the cusps should be carefully evaluated.If the extension from a primary groove includes one half

or more of the cusp incline, consideration should

be given to capping the cusp. If the extension is two

thirds, the cusp-capping procedure

Is most often the proper procedure,

which removes the margin fromthe area of masticatory stresses.


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5.Creating the resistance form

Marginal ridges

resistance form

2) having pulpal wall prepared perpendicular to occlusal forces

3) having rounded internal preparation anglesRounding internalline angles (those with apices directed internally) reduces the stress on the tooth, thus

resistance to fracture of the tooth is increased.

4) removing unsupported or weakened tooth structure


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5.Creating the resistance form for

restoration

1) adequate thickness of amalgam (1.5 to 2 mm inareas of occlusal contact and

2) marginal amalgam of90 degrees

3) boxlike preparation form, which providesuniform amalgam thickness

4) rounding external angles (those with apices

directed externally) reduces the stress on somerestorative materials (amalgam and porcelain),

thus increasing resistance to fracture of the

restorative material.


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6. Finishing the margins

The strongest enamel margin is one that is composed of full-length enamel rods

supported on the preparation side by shorter enamel rods, all of which extend to

sound dentin . The shorter enamel rods buttress the full-length enamel rods that

form the margins, thus increasing the strength of the enamel margin

line angles formed by the junction of enamel walls should be slightly rounded

whether they are obtuse or acute

the cavosurface angle of 90 degreesproduces maximalstrength for both the amalgam and the tooth. Thus, no bevels are placed at the cavosurface

margin. On occlusal surfaces for Class I and Class II amalgam restorations, the incline

planes of the cusp and the converging walls (for retentive purposes) of the preparation

approximate the desirable 90-degree butt joint junction, even though the actual

occlusal enamel margin may be greater than 90 degrees.


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Preparation of Class I cavities when the

carious lesion is situated in the occlusal 2/3 th

o

f the lateral teeth facialo

r lingual The ovale facialClass I when the carious lesion is in a deep facial fissure

Instruments used: 245 diamond or tungstene carbure bur attached to the

turbine

The preparation starts with a balanced occluso-gingival

movement on the facial surface

The form of the cavity: width mesio distal 1mm

occluso - gingival 3mm

the occlusal and gingival outlines are rounded and smooth

1,5 deep in the gingival area and 2mm deep in the

occlusal area

The retention form: the mesial and distal walls are paralell or slightly

convergent

cavosurface angle 90


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Preparation of Class I cavities when the carious lesion is

situated in the occlusal 2/3 th of the lateral teeth facial or

lingual

The round facial Class I cavitywhen the carious lesion is in a

deep facial pit without attacking the fissure

Instruments used: 245 diamond or tungstene carbure bur attached tothe turbine

The preparation starts with a round movement on the facial surface,

the bur is perpendicular on the facial surface

The form of the cavity: diameter1mm1,5 mm deep

The retention form: the walls are parallel or slightly convergent


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2. The Class I cavity preparation when the carious

lesion is located in the supracingular pits of the lingual

face of anterior teeth

Creating the acces and removing the infected dentine are made with a

round diamond bur attached to the turbine .

The retention is performed with a inverted cone bur also attached to the

turbine.

On this type of cavity extension for prevention and finishing of enamelmargins are not necessary.

The incisal wall is parallelwith the incisal margin of the tooth

The proximal walls are parallel to the marginal ridges and slightly

convergent on the surface. This convergence is possible because of the

inclination of the enamel rods on the marginal ridges of the lingualface. The cavity is located in the area between the two marginal lingual

ridges that need to stay intact.

The internal angles well defined

Outline form triangular, 1,5 mm deep.


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3.Preparation of Class I cavity with extension on

vestibularor lingual surface

It is a cavity extended on the V or L surface

Cavity Form: width mesio-distal 1mm

deepness 1,5-2mm

axio pulpare angle beveled

cavosurface angles beveled on a width of0,5mm at

45


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Cavity criteria's

Outline form: regular, smooth lines including all principalfissures

Deepness: 1,8-2mm ( measured half of the active part of the

bur)

Width: 1mm

Walls: Vand L parallel and parallel to the log axe of the tooth

The mesial and distal margins of the cavity are parallel with

the proximal ridges and these has to be a width of1,5 mm for

PM and 2mm for M

Pulpal wall or floor should be flat and perpendicular to the

functional forces

The junction of vertical walls and floor net angles

Documents

Curs 2 Prep Cav Cls 1 (2)