Lecture 3, Principles of Cavity Preparation

8/3/2019 Lecture 3, Principles of Cavity Preparation

1/12


2/12

Principles of Cavity Preparation

Last lecture we stopped at burs , now we will continue :Burs are composed of three parts :

1) shank: which is fixed on the hand piece.

2) Neck : that connects the head to the shank and transmit the

force to the head.

3) Head : the working part of the bur.

When we put the bur in the hand piece the force come from the hand

piece to the shank then from the shank to the head by the neck.

Burs can be classified according to two things :1) Head of bur : As we call them in the lab , we have fissure

bur, round bur, pear shaped.2) Number : unfortunately we dont use the number.

We have a lot of burs but at this picture we just have the basic burs that

we use in the clinic and its important to know them, and to know that

most of them are made from Tungsten carbide.

The number of Pear

shaped bur is 330.


3/12

We have :1) Round : we have high-speed and slow-speed ( its head is

round )

2) Inverted cone : also we have high-speed and slow-speed.

(the tip is larger than the base so we call it inverted )

3) Pear shaped : because it looks like the pear.

4) Straight fissure : because its straight from both sides.

5) Tapered fissure : the base is broad and the apex is tapered.

Recommended burs

From left to the right : first four are round but they are differ from each

other by the size of the head ( , , 2 , 4 , 6, 8 ) .

Number 5 is inverted, number 6 is tapered, number 7 is straight , number

8 is tapered, the last is straight.*** Dont care about the number we just need the shape.

Finishing burs :

They are tungsten carbide also , but we call them finishing burs , we use

them to finish restoration ( composite , amalgam) , they come in several

size and shaped , we have :

1) Round

2) Torpedo3) Tapered


4/12

Instrument grasps

-Its very important because you will take the grasp like a habit so you

must learn the correct grasp .

-The more efficient grasp is the pen grasp ( we use it as the pen and we

use the rest of our fingers to rest so we will have more support and we

can control the hand pieces better and we will not harm the patients oral

cavity) .

-We have the palm and thumb grasp but its less supportive.So please any instrument in the lab use the pen grasp.

Now we are going to start the new lecture .

Principles of cavity preparation

1- Objective of tooth preparation

2- Factors affecting your tooth preparation

They come in mini/small size and have

more blades than normal so cutting

efficiency is more and we use them in

finishing and polishing.


5/12

3- Stages and steps of tooth preparation

Stages and steps of tooth preparation

The doctor now doesnt follow them because she has the experience but

for us we have to follow them to learn.

For example in the lab we drill all fissures in tooth preparation but in the

clinic we just include the fissures that contain the caries only so we will

be more conservative, but here we learn the ideal cavity preparation.

Definition of tooth preparation : The mechanical alteration of defective,

injured, or diseased tooth to best receive a restorative material that will

reestablish a healthy state for the tooth, including esthetic corrections

where indicated, along with normal form and function.

Why we do the cavity preparation ??

To remove the defect from the tooth whether this defect is caries, trauma,

or congenital defect of the tooth , so we want to remove this defect, and

put it in a form or a shape that will receive the restorative materials ( like

what we do in amalgam, we prepare the tooth with depth = 1.5mm if the

depth is less the amalgam will fracture) so we are prepare a certain shape

to receive the restorative material to return the tooth to its normal shape

and function ( like making fissures, grooves, slope of the cusps, line of

cusps.. ) and esthetic ( when we use composite its not just for function

but also for esthetic)

The objective :

1- Remove all defects & provide necessary protection to the

pulp.

2- Extend the restoration as conservatively as possible

( because once you remove the tooth structure you remove it fromthe residual of the tooth and you will in more danger when you areclose to the pulp).3- Form the tooth preparation so that under masticatory forces

the tooth or restoration will not fracture or the restoration will not


6/12

be displaced.( when we form tooth preparation we have two forms:resistance form and retention form )***Resistance form : to resist fracture of bone, tooth and

restoration.

***Retention form : to avoid removal of the restoration from thetooth.

4- Allow for functional & esthetic placement of restorative

material.

Factors affecting tooth preparation :

1) Diagnosis : I will not hold the burs and start drilling the

tooth without knowing the cause of the problem or knowing the

proper diagnosis of the tooth in the patients mouth in the patient

so we are treating the patient. The reason for placing the restoration in the tooth :

why we will do this cavity ? I want just to return thefunction ? or I care about the esthetic only ? to protect the pulp ?? you need to know the answers for thesequestions before doing the cavity!

Periodontal & pulpal status: its very important ( forexample if the tooth has a class 1 caries and needs cavity

preparation and restoration but at the same time this toothis hopeless for example it is moving because there is a

periodontal disease and its suppose that it will not lastmore than 2 months in the patients mouth, so we need tomake RCT after the restoration , we will drill therestoration again then make RCT. so we need to know the

status of the tooth before doing the cavity.

Esthetic factor:it depends on the patient.

Relationship with other treatment plans.

The risk potential of the patient for other dentalcaries

: some patients we considered them as high risk of caries

so we place any restoration that could release fluoride likemodified glass ionomer cement.

2) Knowledge of Dental Anatomy:

When you prepare the cavity we need to know the

dental anatomy ( enamel , dentin , pulp) , we need to know

that the thickness of enamel in the occlusal part is thicker

than in the cervical part, so when we are drilling 1.5mm in

the occlusal surface maybe we are not in the dentin but in the


7/12

cervical part we are sure that we are in the dentin and close

to the pulp.

Also when we prepare a tooth we will consider a

young patient differs from an old patient why?? Becausewith age we will have Recession for the pulp ( decreasing in

the size of the pulp) because we are having secondary

dentin, tertiary dentine so you are having more tooth

structure to work with in old patient because of the thickness

of dentin and the height of the pulp will be changed.

3) Patient Factors:

The patient knowledge & appreciation for good dental

health.( if the patient has more knowledge about oral hygieneso we will think about using a good restorative material whichcould be expensive, but if the patient doesnt brush his teeth ordoesnt know about the oral hygiene we will use a lessexpensive material) .

Patients economic status : you shouldnt make anytreatment or restoration before asking the patient and telling

him how much it will cost.

Gross picture of the tooth both

internally and externally must

be visualized.

The thickness of enamel,

dentin and position of the

pulp.

Relation to other supporting

tissues ( when we prepare tooth

near the supporting tissue like

deep class 2 or deep class 5 ) .


8/12

The patient age: related to the anatomy and to the lifeexpectancy, for example if the patient is very old and has a lotof health disease so we put a good restoration but not veryexpensive and could be for a short time ( for example if I have a

patient (70 years old) and has many medical problems andneeds MOD restoration so Ill not make a crown for him or useamalgam, I just use GIC because its less expensive and can beuseful for him and will not take a long time to use it ).

4) Conservation of Tooth Structure:

We want to make the cavity in a form that is proper for the

material but we should be conservative.

Preservation of the vitality of the tooth by avoiding

the application of poor or careless operative procedures onthe tooth .

Restorations should be made as small as possible :( should be convenient and restorative ; I mean as small as

possible and in the form of retention and restoration)

Small tooth preparations result in restorations thathas little effect on both inter-arch & intra-arch relationshipsas well as esthetics. : when we make a restoration as smallas possible it affects the adjacent teeth(adjacent teeth:intra-arch relationship), the opposing teeth(apposing teeth

: inter-arch relationship) and on the esthetic. when we drillthe occlusal surface we remove the fissures and grooves, soit has a little effect than if we replace a cusp; because asmuch as we do we will not return it to the normal shape ofthe tooth . we try to do that but we cant do it 100% . Inintra-arch when we do class 2 cavity then it will affect theadjacent tooth , if it is small the effect will be less but if itsbig the interference will be large. So when you make arestoration make it small as possible as you can to make

the interference less .

5) Restorative Material Factors:

Mainly we are talking about direct restorative materials.

Amalgam Vs resin composite. To some extend glass

ionomer cement. ( demands for cavity preparation for amalgam

will differ from the composite because the amalgam has a

mechanical retention but the composite has a micromechanical


9/12

retention ( can adhere to the tooth) so the criteria for preparing

the cavity will differ)

The ability to isolate the operating field.

The extension of the problem (i.e. caries).

Stages and Steps of Tooth Preparation

Stages and steps of tooth preparation

Initial Stage

Outline form & initial

depth.

Primary resistance form.

Primary retention form.

Convenience form.

final Stage5. Removal of any remaining

infected dentin.

6. Pulp protection if indicated

7. Secondary resistance &

retention forms.

8. Procedures for finishing

external walls .

9. Final procedures: cleaning,

inspecting & sealing.

You have to follow

these stages because

you are still a

student so when you

are doing the cavity

you need to visualizethese steps.


10/12

a)Initial Tooth Preparation Stage:

1. Outline form & initial depth:

Each cavity has its own out line form

Placing the preparation margins in the positions theywill occupy in the final preparation : Im drawing the outline

and he borders ( where Im going to stop)

Preparing an initial depth of 0.2 to 0.8 mm pulpally of

the DEJ position : I dont go to the full depth at the

beginning, I should go to the initial depth and this initial

depth is different when Im doing class 1 or class 5 because

the thickness of enamel is different, so in class 1 most of my

cavity preparation will be in the enamel but in class 5 it will

be in dentin.

Why 0.2 to 0.8 ??0.2mm inside DEJ when Im going to make class1 occlusaly,

0.8mm in class 5, thats mean Ill be in dentin in class 5 for

0.8mm but in class1 Ill be slightly in the dentine just for

0.2mm. ( look at the picture below)


11/12

3 principles to put the initial depth and the outline :

1. All weakened enamel should be removed.( because this

enamel maybe break in the future )

2. All faults should be included.( all grooves and fissure )

3. All margins should be placed in position to affordgood finishing of the margins of the restoration ( Ill not

leave the border of my cavity at a fissure but at smooth

surface so the finishing will be easier)

The end

Done by : Haneen Zuhdi Al-kwamleh

Thx a lot Walaa Khdour for the help


12/12

Walaa and Eman : Best

friends are like diamonds,precious and rare.

Documents

Lecture 3, Principles of Cavity Preparation