cons sheet # 4- 3bd Alkareem

Instruments used in operative dentistry


Finishing and polishing stones
The most common one is green stone, it is used for polishing amalgams the stones could be in a form of points or cups and they made of rubber

-rubber cups are used with pumice for polishing amalgam restoration

-the shofu polishing kit for amalgams contains(greenies and brownies) which are rubber points and cups impregnated with pumice for polishing

When to replace burs ?

1) Burs life is affected by how it is used, the handpiece in which it is used cleaning and sterilization procedures
2) when cutting resins and porcelain
3) if the shank becomes bent, the bur should be discarded immediately otherwise the hand piece will be damaged

Accessory instrument:
1) spatulas : they have flat ends in both sides , we use it to mix cement impression material and apply the impression material
2)scissors : used for cutting dental dam material, retraction cords, and stainless steel crown
3) dappen dish: made of cup of glass (can be reuse) or plastic hold certain liquid dental material or amalgam during procedure

Control of cutting instrument:
High speed handpiece and burs remove tooth tissue with great efficiency, the grasp of the handpiece should be firm but the force used to cut the tissue should be light , similar to the action of fine paint brush.

-care must be taken to avoid damaging the patients gingival and oral tissue or both
-precise instrument control can be achieved by using the proper grasp of the instrument as well as finger rest which helps stabilize the instrument

Instrument holding techniques:

1) Modified pen grasp (most common used): you have the maximum tactile sensation the middle finger support the instrument and the other two small fingers resting on the oral tissue
2) Inverted pen grasp: used for lingual surface of maxillary teeth
3) Palm and thumb grasp: as if you holding a knife and remove the skin of orange, we use it to create a relative cuts in class 3 preparations
4) Modified palm and thumb grasp: the thumb is supporting the instrument and create a finger rest

Principles of cavity preparation:
Cavity preparation is the orderly procedures whereby a tooth is readied to receive and retain a restoration .

The aims of cavity preparation:
1)removal of defective tooth structure
2)establishing a form which meets the biochemical principles of restorative material.

- a constant requirements in cavity preparation is provision for the prevention of failure of the restoration through:
1)recurrence of decay
2) inadequate resistant to applied stresses

* conventional preparation = amalgam preparation


Steps of cavity preparation :
1)obtain the required form: it is the form of the area of the tooth surface to be included in a cavity or enamel margins of the finished cavity preparation, this defines the external boundary of the cavity preparation .
The rule for establishing the external out line is to extend all margins into sound tooth tissue

Factors influencing outline form :
a)local factors
b)general factors

local factors : 1) extent of decay, must be within the outline form
2)undermined enamel(enamel that is not supported by dentine),should be removed
3)extent of decalcification , should be within the outline form
4)aesthetics : if the cavity that we must do it on the mesial surface of the canine (high aesthetic area) we must minimize the out line
5) should be located on smooth cleanable tooth surface
General factor :
1)caries experience : if I want to do cavity preparation I must extend to nondeffictive fissures because caries may appear in this fissure (I can not conserve tooth structure), the rule is extension for prevention
2) oral hygien
3) mal- positioned teeth: we have to modified the outline according to mal- positioned teeth (the contact points are not normal)
4)accessibility


Features of the outline form :
a) preserving cuspal strength : if I have cavity preparation and the margin of the cavity reach half of the incline of the cusp (and it must be reach 1/3 of the incline) so the cusp is very weak , I must do cusp capping (remove the cusp and replace it with restorative material)

b) preserving marginal ridge strength
c) minimize faciolingual extension : there a risk to fracture if we increase faciolingual extensions
d)using enameloplasty : if we have a fissure and it is not easy to clean we make a u shape instead of fissure and it is easy to clean

e) connecting two close faults or cavities if it less than .5 mm apart


occlusal outline form :
where pits, fissures or other deep irregularities exist contiguous with caries. These should be removed .
maintain oblique and transverse ridge because it is important in maintain the strength of the tooth and the cavity outline should be smooth gently curved and free from deep irregularities.


Gingival outline form :
Best to keep margins supra gingival (out of the sulcus ) because it is hygienic
As a general rule, extending cavity margins in to caries susceptible area such as supgingival may jeopardize the longevity of the restoration and there will be no guarantee against recurrent decay



Interproximal outline form :
At posterior teeth contact area should be removed at buccul, lingual, and gingival margins , the distance should be .5mm between two adjusent teeth and we do that to allow the restoration margins to be kept clean with a tooth brush or floss.
In anterior caries if I open the contact area labially and lingually I will compromise the aesthetic, so in the anterior caries lesions the contact area can be avoided particularly as it is more incisally placed .however in the larger lesions totally including the contact area would both jeopardize the aesthetic and weaken the incisal angle. The out line is thus extended only so far as is necessary to remove the decay



Class I :
There is five walls , all of the walls are external except the pulpal floor
Line angle : the junction between two walls ,it could be external or internal according to the walls that form it , there is 8 line angles in class one
Point angle : the junction between three walls it takes three letters , it is always internal , in class one there is 4 point angles


Class II :
Point angles = 6
Line angles = 11 because there is an axial wall, so we have two internal wall axial floor and pulpal floor


Class III :
The cavity triangular in shape
4 walls : facial, lingual, gingival, and axial floor
The axial wall is internal and the other are external
6 line angles
3 point angles


Class IV :
8 walls
11 line angles
6 point angles

Class V :
5 walls : mesial, distal, incisal , gingival, axial
8 line angles
4 point angles


Step 2 : obtain the required retention and resistant forms:

Resistant form: is the shape and placement of the cavity walls that:
a) resists fracture of the tooth structure due to forces of mastication
b)resists fracture of the restoration due to forces of mastication

the cavity design should include :
flat walls and floors and slightly rounded internal line angles (not rounded outline)to form a box, it is important because if there is occlusal force at the side of the filling, it distributes to a compressive and tensile force, in this case I do not have any kind of rotation to the filling.

Cavity walls meeting cavosurface margins of right angled. *

Adequate bulk bulk to the restorative material *

*Preservation of cusps and marginal ridges

Removal of weakened tooth structure like undermined enamel.*


Retention form : it is the shape in cavity design which prevents the dislodgment of the restoration due to tipping or pulling forces .

The cavity design may include:
a) parallel or slightly under cut walls that fix the material in the cavity
b) dovetails or occlusal locks
c) retentive groove
d) retentive pins


step 3 : obtain the required convenience form

step 4 : removal of remaining carious dentine :
carious dentine is removed completely during the shaping of the cavity. when carious dentine remains in the pulpal or axial wall it was removed at this stage.

Step 5 : finish of enamel wall :
Finishing of cavosurface enamel margins is necessary to :
a)assure sound supported enamel
b) assure strong fracture resistant restoration margins
c) obtain a smooth , well defined margin and facilitate the finishing of restorative material.

Factor to consider for finishing enamel margins:
1) the direction of the enamel rod : the enamel rods mostly perpendicular to the outer surface except the cervical margins and cusp tips.
2) support of the enamel rods both at the DEJ and laterally (preparation side)
3)the type of the restorative material to be placed in the preparation
4)the location of the margin
5) the degree of smoothness or roughness desired

Enamel walls must parallel to the direction of enamel rods (perpendicular to the external surface of the tooth) and be supported by sound dentine

Example of correct and incorrect treatment of enamel walls in cavity preparation :
Direction of enamel wall parallel to rods = correct

Oblique direction of enamel wall but rods well supported by dentine = acceptable for amalgam

Oblique direction of enamel wall and rods left unsupported = incorrect

Step 6 : toilet of the cavity

This is the final step which includes the final removal of debris by thoroughly cleaning the preparation.
The preparation should be thoroughly washed and dried.
There should be no blood or saliva present, which could contaminate the restorative material and result in failure of the restoration .

The operating field should be kept clean and dry during cavity preparation as well in order to have good visibility while working.