b 2

Conservation Presentation

Topic: Tooth preparation and maintaing pulp vitalityBy:Aqdas NiaziGuided by : Dr.Rauf sheikh (H.O.D)

Defination of tooth preparation:• Tooth preparation is the mechanical

alteration of a defective,injured,or diseased tooth such that placement of restorative material re- establish normal form and function,including esthetic correction, where indicated.

Need for restorations

Prevention from Dental caries often requires prophylactic restorative procedures.Caries progression may cause destruction of tooth structure which requires repair.Another common need is the replacement or repair of restoration with serious defects.

• Restorations are also indicated to restore proper form and funtion to fractured teeth.

• Teeth present with minor to major amounts of missing tooth structure or with an incomplete farcture " greenstick fracture"

Objectives of tooth preparation :Generally, the objective of tooth

preparation are to 1) remove all defects and provide

necessary protection to the pulp.2) extend the restoration as

conservatively as possible3) form the tooth preparation so that

under the forces of mastication , the tooth or the restoration will not fracture

4) Allow for the esthetic and functional placement of restorative material.

FACTORS AFFECTING TOOTH PREPARATION:

i)General factors => Diagnosisii)Knowledge of dental Anatomy iii) Patient factors iv)Conservation of tooth structure v)Restorative material factors

Tooth Preparation walls:

Internal wall:Is the prepared surface that does not extend to the external tooth surface.

Axial wall: Is the internal wall parallel to the long axis of the tooth.

Pulpal wall(Floor):Is the internal wall that is perpendicular to the long axis of the tooth and occlusal of the pulp.

External wall:Is the prepared surface that extends to the external tooth surface.Such a wall takes the name of the tooth surface(or aspect) adjacent to that wall.

Enamel wall: Is that portion of a prepared externl wall consisting of enamel.

Dentinal wall: Is that portion of a prepared external wall consisting of dentin.

Tooth preparation angle :

Line angle: A line angle is the junction of two planar surfaces of different orientation along a line.

Point angle: The point angle is the junction of three planar surfaces of different orientation.

Cavosurface angle and cavosurface margin:

The cavosurface angle is the angle of tooth stucture formed by the junction of a prepared wall and the external surface of the tooth.

The actual junction is referred to as a cavosurface margin.

STEPS OF TOOTH PREPARATION:The tooth preparation procedure is divided into

two stages, each with several steps:i)Initial tooth preparation stage:

step 1: outline form and initail depthstep 2: Primary resistance formstep 3: Primary retention formstep 4: convenience form

ii)Final tooth preparation stage: step 5: Removal of any remaining infected dentin or old restorative material step 6: Pulp protection, if indicatedstep 7: Secondary resistance and retention forms

step 8: procedure for finishing external walls

step 9: final procedure-cleaning, inspecting,

desensitizing.

STEP 1:OUTLINE FORM AND INITIAL DEPTH

Defination: Establishing the out line form means

1) placing the preparation margins in the positions they will occupy in the final preparation except for finishing enamel walls and margins.

2) preparaing an initial depth of 0.2 to 0.5mm pulpally of the DEJ position or 0.8 mm pulpally to normal root surface position

Principles :

The three general principles on which outline form is established

1)all unsupported or weakened(friable) enamel usually should be removed.

2)all faults should be included and 3) all margins should be placed in a

position to allow finishing of the margins of the restoration.

Factors:

In determing the outline form of a proposed tooth preparation, certain conditions or factors must first be assessed.These factors are extend of caries lesion, defect, or faulty old restoration affects the outline form of the proposed tooth preparation because the objective is to extend to sound tooth structure except in a pulpal direction.

Features :

Generally, the typical features of establishing proper outline form and initial depth are

1) preserving cuspal strength, 2)preserving marginal ridge strength

3) minimizing faciolingual extenstion 4) connecting two close (<0.5mm apart)

defects or tooth preparations. 5) restrictng the depth of the

preparation into dentin.

Step 2: Primary resistance formDefination:Primary resistance form may

be defined as the shape and placement of the preparation walls that best enables the remaining tooth structure and the restoration to withstand, without farcture,masticatory forces delivered principally in the long axis of the tooth.

Principles :

The fundamental principles involved in obtaining primary resistance form include:

1)using a box shape with a relatively horizontal floor,which helps the tooth resist occlusal loading by virtue of being at right angles to the forces of mastication that are directed in the long axis of tooth.

2)restricting the extension of the external walls to allow strong cusp and ridge areas to remain with sufficient dentin support.

3) having a slight rounding of internal line angles to reduce stress concentration in tooth structure.

4)reducing and covering weak cusps and enveloping or including enough of a weakened tooth within the restoration in extensive tooth preparation to prevent or resist fracture of the toothby forces in the long axis and obliquely.

5) providing enough thickness of restorative material to prevent its fracture under load.

6) bonding the material to the tooth structure when appropriate.

Factors: foremost is the assessment of the occlusal contact on the restoration and the remaining tooth structure.The amount of remianing tooth structure also affects the need and type of resistance form.The type of restorative material also dictates resistant form needs.

Features: the design features of tooth preparation that enhance primary resistance form are as follows:

1) Relatively horizontal floors.2) Box-like shape3) Inclusion of weakened tooth structure4) Preservation of cusps and marginal

ridges5) Rounded internal line angles6) Adequate thickness of restorative

material7) Reduction of cusps for capping , when

indicated.

Step 3: Priamary retention formDefination: Primary retention form is the

shape or form of the conventional preparation that prevents displacement or removal of the restoration by tipping or lifting forces for nonbonded restorations.

Principles: Because retention needs are related to the restorative material used, the principle of primary retention form vary, depending on the material.For amalgam

restorations in most class I and class II conventional preparations, the material is retained in the tooth by developing external tooth walls that converge occlusally.

Step 4: Convenience form Convenience form is the shape or form of

the preparation that provides for adequate observation, accessibility, and ease of operation in preparing and restoring the tooth.

FINAL TOOTH PREPARATION STAGE:Step 5: Removal of any remaining enamel pit or fissure, infected dentin, or old restrative material, if indicated :

Definition: Removal of any remaining enamel pit or fissure, infected dentin, or old restorative material is the elimination of any infected carious tooth structure or faulty restorative material left in the tooth after initial tooth preparation.

Techniques: Removal of remining old restorative

material, when indicated also is accomplished with a use of a round carbied bur at slow speed with air and water coolant.The water spray(along with high-volume evacuation) is used when removing old amalgam material to reduce the amount of mercury vapor.

Step 6: Pulp protection, if indicatedThe reason for using liners or bases is to

protect the pulp recovery or both.Effective tubular sealing may prevent penetration of bateria into the tubules and limit the retrogarde diffusion of baterial toxins towards the pulp.

Liners: May include suspensions or dispersions of zinc oxide, calcium

hydroxide, or resin-modified glass ionomer(RMGI) that can be applied to a tooth surface in a relatively thin form.Liners may also povide

1.a barrier that protects the dentin from noxious agents from either the restorative material or oral fluids. 2.initial electrical insulation,or

3.some thermal protection.

Bases :

Bases are material, most commonly cements,that are used in thicker dimentions beneath permanent restorations to provide mechanical, thermal, electrical protection of the pulp. Examples of bases include zinc phospate, zinc oxide-eugenol, polycarboxylate and the most common , glass ionomer.

Step 7: Secondary Resistance and retention forms:After any remining enamel pit or fissure,

infected dentin,or old restorative material has been removed, and pulpal protaction has been provided by appropriate liners and bases, additional resistance and retention features may be deemed necessary for the preparation. The secondary retention and resistance forms are of two types:1)mechanical preparation

2)treatments of the preparation walls with etching,priming,and adhesive materials.

Mechanical features:A variety of mechanical alteration to the preparation enhance retention form,and these alteration require additional removal of tooth structure.

Retention grooves and coves:Vertically oriented retention grooves are used to provide additional retention for the proximal portion of some conventional tooth preparation.Retention coves are placed for the incisal retention of class III amalgams.

Preparation extension:

Additional retention of the restorative material may be obtained by arbitrarily extending the preparation for molars onto the facial or lingual surface to include facial or lingual groove.

Skirts: Skirts are preparation features used in cast gold restorations that extend the preparation around some, if not all,of he line angles of the tooth.When properly prepared, skirts provide additional,opposed vertical walls for additional retention.

Beveled enamel margins: The bevels for metal cast may improve

retention form slightly when opposing bevels are present but are used primarily to afford a better junctional relationship between the metal and the tooth.

Placement of etchant,primer, or adhesive on prepared walls:

Inaddition to mechanical alteration to the tooth peparation,certain alteration to the preparation walls by actions of various material cause increase retention and resistance to fracture.

Step 8:Procedure for finishing the external walls of the tooth preparation:

Defination:Finishing the preparation walls is the further development, when indicated, the degree of smoothness or roughness that produces the maximum effectivness of the restorativematerial used.

Objective:The objectives of finishing the prepared walls are to

1.create an optimal marginal junction b/w the restorative material and the tooth structure.

2.afford a smooth marginal junction 3.provide maximal strength of the tooth

and the restorative material at and near the margin.

The following factors must be considered in the finishing of enamel walls and margins:

1.the direction of the enamel rods2.the support of the enamel rods at the

DEJ and laterally.3.the type of restorative material to be

placed in the preparation.4.the location of the margin5.the degree of smoothness or roughness

desired.Features: Finishing of external walls has

two primary features:1.The design of the cavosurface angle2.The degree of smoothness and

roughness of the walls.

The restorative material used is the primary factor dictating the desired smoothness or roughness of an enamel wall.

Step 9: Final procedure :Cleaning, inspecting and desensitizing:-

The usual procedure in cleaning is to free the preparation of visible debris with water from the syringe and then to remove the visible moisture with a few light bursts of air from the air syringe.

Occlusion of the dentinal tubules limits the potential for tubular fluid movement and

resultant sensitivity.Desensitizers are effective disinfectants,provide crosslinking of any exposed dentin matrix and occlude the dentinal tubules by crosslinking tubular proteins.

Factors to consider before tooth preparation

Extent of caries extent of defect

Occlusion pulpal protection

Pulpal involment contours

esthetics economics

patients age patients risk status

patient's home care bur design

gingival status radiographic assessment

anesthesia other treatment factors

bone support patient co operation

patients desire fracture lines

material limitations tooth anatomy

operator skill ability to isolate areas

enamel rod direction

extent of old restoraive material

Instruments and equipment for tooth preparation/restoration preparation:-

Categories: The hand instruments used in the dental operatory may be categorized as

1. cutting (excavator, chisels and others)

2.non- cutting (amalgam condensers,mirrors, explorers,probes)

Design:

Most hand instruments,regardless of use,are composed of three parts: handle,shank, and blade

Excavator:

The four subdivisions of excavator are 1)ordinary hatches 2)hoes

3)angle-formers 4)spoons.Chisels: Chisels are intended primary for

cutting enamel and may be grouped as: 1.straight,slightly curved,or bin-angle.

2.Enamel hatches. 3.Gingival margin trimmers.

Hand instruments techniques:Four grasps are used with hand instruments:1.modified pen. 2.inverted pen. 3.plam and

thumb, and 4.modified palm and thumb

Dental burs:The term bur is applied to all rotary cutting

instruments that have bladed cutting head.Shapes: The term bur shape refer to the

contour of the head.The basic head shapes are :-

Diamond abrasive instruments :The second major category of rotary

dental cutting instruments involes abrasive cutting rather than blade cutting.Abrasive instruments are based on small,angular particles of a hard substance held in a matrix of softer material.

Terminology : consist of 3 parts 1.a metal blanks, 2.the powdered diamonds abrasive 3.a metallic bonding material that holds the diamond powder onto the blank.

Demerits of cutting instruments:1.Loss of control.2.More pain.3.Prolong time for operative procedures.4.Reduce the quality and precision of

tooth perparation.5.Heat generation if water or air coolants

are not used.