Fundamentals of Tooth Preparation (Operative Dentistry)

Dr. SARANG S HOTCHANDANI BDS BATCH 01 [email protected]

Fundamentals of Tooth

Preparation & Pulp Protection STURDEVANTS’S ART AND SCIENCE OF OPERATIVE DENTISTRY 6 TH EDITION

Table of Contents

Definition of Tooth Preparation. ........................................................................................................................................................ 0

Need/ Reasons for Restoration ......................................................................................................................................................... 1

Objectives of Tooth Preparation ....................................................................................................................................................... 1

Factors Affecting Tooth Preparation ................................................................................................................................................. 1

Nomenclature/ Terminology ............................................................................................................................................................... 2

STEPS OF TOOTH PREPARATION ..................................................................................................................................................... 4

INITIAL TOOTH PREPARATION STAGE ........................................................................................................................................ 4

STEP 1; Outline Form & Initial Depth ....................................................................................................................................... 5

STEP 2; Primary Resistance Form ............................................................................................................................................. 6

Step 3; Primary Retention Form ............................................................................................................................................... 7

STEP 4; Convenience Form ......................................................................................................................................................... 7

FINAL TOOTH PREPARATION STAGE .......................................................................................................................................... 7

STEP 5; Removal of Any Remaining Enamel Pit or Fissure, Infected Dentine, or Old Restorative Material, If

Indicated ........................................................................................................................................................................................ 7

STEP 6; Pulp Protection, if indicated. ...................................................................................................................................... 8

STEP 7; Secondary Resistance & Retention forms. ................................................................................................................ 9

STEP 8; finishing the External walls of Tooth Preparation. ............................................................................................... 11

STEP 9; Final Procedures; Cleaning, Inspecting, & Desensitizing. .................................................................................... 12

ADDITIONAL CONCEPTS IN TOOTH PREPARATION. ................................................................................................................. 12

DIFFERENCE B/W TOOTH PREPARATION OF AMALGAM V/S COMPOSITE....................................................................... 13

The End .................................................................................................................................................................................................. 14

Definition of Tooth Preparation.

It is the mechanical alteration of a defective, injured or diseased tooth such that placement of restorative material

re-establishes normal form, function and esthetics.

Principles of tooth preparation were given by J.V Black, but modifications have been done in the principles given

by him due to availability of;

o Improved restorative materials, instruments & techniques.

o Increased knowledge & application of preventive measures for caries.

Types of tooth preparation;


o Conventional tooth preparation

Require precise tooth preparation, specific wall forms, depths, and marginal forms

Used in amalgam, cast metal & ceramic restoration.

o Modified tooth preparation

Does not require precise tooth preparation, specific wall forms, depth, retentive features or

marginal forms.

Used in composites & GIC.

Fundamental concept relating to conventional and modified tooth preparation are same;

o Remove all unsupported enamel tooth structure (enamel without support of dentine).

o The fault, defect or caries is removed.

o The remaining tooth structure is left as strong as possible.

o Protect the pulp.

o Restorative material is retained in a strong, esthetic and functional manner.

Need/ Reasons for Restoration

Prevention & Repair of caries

Repair/ replacement of defective restoration.

Restore form and function of Fracture teeth

Restore form or function of congenitally malformed teeth.

Objectives of Tooth Preparation

Remove all defects and provide necessary protection to the pulp.

Extend restoration as conservatively as possible.

Make the tooth preparation in such a manner that under the forces of mastication, the tooth or the restoration will

not fracture or displace.

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

Factors Affecting Tooth Preparation

Pulpal, periodontal & occlusal problems & other treatments affect the design of tooth preparation and the choice

of material.

Dental Anatomy

o Direction of enamel rods

o Thickness of enamel/ dentine

o Size and position of the pulp

o The relationship of tooth to its supporting structures.

Patient factors play role in determining restorative treatment.

o Esthetic concerns

o Economic status

o Medical condition & Age

Require special position, shorter, less stressful appointment.

Old person mostly need restorative treatment on root.

The primary objective of operative dentistry is to repair the damage from dental caries or trauma while

preserving the vitality of the pulp

Choice of restorative material.


Nomenclature/ Terminology

Complete union of enamel lobes results in formation of grooves & fossae.

Incomplete union of enamel lobes results in formation of pits and fissures.

Backward caries

o When caries along DEJ exceed the caries in enamel. It extends from DEJ into enamel.

Forward caries

o Caries cone of enamel caries is larger or of same size of cone of dentine caries.

Residual caries

o It is the caries which remain in tooth after completion of tooth preparation by operator intention or by

mistake.

o Unacceptable types of residual caries remaining after tooth preparation;

At DEJ

On Enamel wall of cavity.

o Only affected dentine/ inner carious dentine near the pulp should be left in the cavity after tooth

preparation.

It is a zone of demineralization of intertubular dentine and of initial formation of fine crystals in

the dentinal tubule lumen. It is softer than normal dentine and contain intact collagen fibers

because it is the only mineral portion of dentine is damaged from acid of caries and does not

contain bacteria.

Incipient caries

o It is the first evidence of caries activity in enamel.

o Appear opaque white and is reversible.

o A demineralized lesion usually is either opaque white or shade of brown-black from extrinsic coloration,

has hard surface and appears the same whether dry or wet.

o No need of restoration.

Cavitated caries (irreversible)

o Enamel surface is broken, caries advanced into dentine.

o Remineralization not possible, that’s why called as irreversible.

o Need of restoration.

Grooves & fissures; fossae and pits

o Anatomic depression in enamel mark the location of the union of developmental enamel lobes.

When union is complete it is called as groove, they are;

Slightly involuted, Smooth, hard, shallow, and accessible to cleaning.

Incomplete union; termed fissure, they are;

Sharply involuted, narrow, inaccessible canal of varying depth.

o Fossa; non defective enamel lobe union.

o Pit; defective enamel lobe union.

Extension for prevention

o It was given by Black, which states that “restoration should be extended to areas that are normally self-

cleansing to prevent recurrence of caries also it include the extension necessary to remove pits and

fissures.

o However, this concept has been eliminated now a days because of preventive measures for caries, new

restorative materials.

Enameloplasty

o It is the removal of shallow fissures, pits, grooves or any surface enamel defects to create a smooth,

saucer shaped surface that is easily cleaned.

Prophylactic Odontomy

o It is no longer available and it is characterized by; minimal preparation and amalgam filling of the

structural imperfections such as pits, fissures & grooves to prevent caries.

Affected and infected dentine

o Carious dentine consists of two layers;


Outer; infected dentine

Inner; affected dentine

o Always remove infected dentine and preserve affected dentine because it has potential to re-

mineralize in vital tooth.

o Now, how to distinguish b/w affected and infected dentine clinically?

Well there are many approaches like;

Degree of discoloration

Hardness/ softness by instrument

Caries detecting dyes.

Caries detecting dye is not specific for infected dentine, coz it can stain slightly

demineralized dentine as well as normal dentine.

Fractures

o Incomplete fracture not directly involving vital pulp is also called as greenstick fracture.

Caused by excessive occlusal trauma

It is sensitive, but pt. cannot tell which tooth is damages

o Complete fracture not involving vital pulp.

It is painless, unless the fractured part of tooth is in gingiva.

o Fracture involving pulp

If tooth is restorable, then perform RCT, if not then extraction.

Non hereditary enamel hypoplasia

o Usually seen in anterior teeth & 1st molar.

o Caused by injury to ameloblasts during enamel formation.

o Caused by fluorosis or fever.

Tooth preparation

o Simple; one tooth surface

o Compound; two tooth surface

o Complex; three or more tooth surfaces

Walls of cavity (fig; 5-7 in Art & Science 6th Ed.)

o INTERNAL WALL; surface inside of cavity which does not meet with external surface of cavity.

Axial wall; wall that is parallel to long axis of tooth.

Pulpal wall; wall that is perpendicular to long axis of teeth and is above the pulp.

o EXTERNAL WALL; these are walls of cavity which meets with external surface of tooth.

Distal wall; wall of cavity on distal surface of tooth

Facial wall; wall of cavity on facial surface of tooth

Lingual wall; wall of the cavity on the lingual surface of tooth

Gingival wall; wall of the cavity that is toward gingiva

Floor or Seat of cavity

o It is horizontal wall

o Perpendicular to occlusal forces and long axis of teeth.

o E.g. pulpal/ gingival wall

o They provide;

Stability to restoration

Distribute stress in tooth structure.

Increase resistance form of restored tooth against post-restorative fracture

Mechanical retention features are located in dentinal wall of cavity.

Internal line angle; line angle whose apex points into the tooth.

External line angle; line angle whose apex points away from tooth.

Cavosurface angle & Cavosurface margin

o Actual junction of prepared wall and the external surface of tooth is called as Cavosurface margin.

o Angle of tooth structure formed by junction of a prepared wall and external surface of tooth is called

as Cavosurface angle.


Enamel margin strength (Fig; 5-11)

o For strongest enamel margin following 2 features should be present;

Enamel margin should be formed by full-length enamel rods whose inner ends are on sound

dentine, means Cavosurface angle of 90 degrees.

Or, these enamel rods are buttressed on the preparation side by progressively shorter rods

whose outer ends have been cut off but whose inner ends are on sound dentine.

o Coz, enamel rods are mostly perpendicular to enamel surface, so for strong enamel Cavosurface margin

should be greater than or equal to 90 degrees.

If Cavosurface angle is less than 90 degrees, then that enamel is unsupported.

Intra-coronal & extra-coronal tooth preparation

o Intra-coronal preparation is “Box-like” having internal and external walls.

Example; daily routine cavity preparations for fillings.

o Extra-coronal preparation is “stump-like” having only walls or surfaces result from removal of enamel.

Example; tooth preparation of crown and bridges

Classification of tooth preparation;

o Class 1;

Occlusal surfaces of premolars & molars

Occlusal 2/3rd of facial & lingual surfaces of molars

Lingual surfaces of maxillary incisors.

o Class 2;

Proximal surfaces of posterior teeth

o Class 3;

Proximal surfaces of anterior teeth without including incisal edges.

o Class 4;

Proximal surfaces of anterior teeth including incisal edges.

o Class 5;

Gingival 3rd of facial/ lingual surfaces of all teeth

o Class 6;

On the incisal edges of anterior teeth

Occlusal cusp tips of posterior teeth.

STEPS OF TOOTH PREPARATION

Initial tooth preparation stage

o Step1; outline form & initial depth

o Step2; primary resistance form

o Step3; primary retention form

o Step4; convenience form

Final tooth preparation stage

o Step5; removal of any remaining infected dentine or old restorative material or both.

o Step6; pulp protection

o Step7; secondary resistance & retention form

o Step8; finishing of external walls

o Step9; cleaning, inspecting, desensitizing

INITIAL TOOTH PREPARATION STAGE It involves the extension of the external walls of the preparation/ cavity at a specified, limited depth.

Non carious fissures or pits at periphery of expected external wall is treated by Enameloplasty.

o Enameloplasty does not extend outline form of cavity. However;

o The thickness of restorative material at the enameloplastied margin (pulpal depth of the external wall)

is decreased.


o But, it is not necessary to perform Enameloplasty for non-carious pits and fissure in composite

restoration.

o If any of the fissure or pit (supplemental/developmental) is penetrating 1/3rd or less of the enamel

thickness, they perform Enameloplasty on that fissure or pit and do not include in cavity. But;

If it penetrate more than 1/3 of enamel thickness then remove that fissure/pit by extending

cavity in these fissure/pits.

o Enameloplasty confine the tooth preparation/ cavity to one surface and produce smooth union of the

tooth surface & restorative material

o If the shallow fissure that approaches or crosses lingual/facial ridge.

Perform Enameloplasty if is penetrated less than or equal to 1/3rd of enamel thickness.

If not, then extend the cavity in that fissure and terminate at that point when approx. 2mm of

the tooth structure remain b/w bur and lingual/facial surface to give strength to restoration.

After termination of extension of cavity, perform Enameloplasty on the remaining end of

fissure.

o Enameloplasty can be done in those teeth in which no cavity preparation is being expected.

NOTE; No more than 1/3rd of enamel thickness should be removed in procedure of Enameloplasty.

STEP 1; Outline Form & Initial Depth

DEFINITION It is placing preparation/ cavity margins in the position they will occupy in the final preparation and preparing

the initial depth.

o Initial depth of 0.2 – 0.5 mm below DEJ position enamel. OR

1.5 mm from Central fissure/pit

2 mm from prepared facial/lingual walls.

o Initial depth should be 0.8 mm in cavity at the root surface.

PRINCIPLES 1) All unsupported or weakened (friable) enamel should be removed.

2) All faults should be included.

3) All margins should be placed in a position to allow finishing of the margins of the restoration.

a. This principle differ for pit/fissures cavity and smooth surface cavity.

FACTORS affecting outline form & its extension The extent of caries lesion, defect, or faulty old restoration.

o Always try to extend tooth preparation in sound tooth structure, except in pulpal direction.

o It is sometime, acceptable practice to have a margin of new restoration placed into an existing, sound

restoration of same tooth if the distance b/w them is less than or equal to 0.5 mm.

E.g. a new Mesio-Occlusal touching a sound Disto-Occlusal).

Esthetic conditions, affects;

o Choice of restorative material

o Outline form

Occlusal relationships

o Alteration of cuspal form for better occlusion.

Adjacent tooth contour

Cavosurface margins

o Beveled margins

If beveled margins are expected, try to make outline form in such a manner so that the cavity

should not extend after placement of bevel in finishing of cavity in final stage of tooth.

FEATURES (why we create outline form) A. Preserve cuspal strength.

B. Preserve marginal ridge strength.

C. Minimizing facio-lingual extension.


D. Connecting two close (0.5 mm apart) defects or cavities.

E. Restricting depth of the preparation into dentine.

STEP 2; Primary Resistance Form

DEFINITION It is shaping, placing & orienting cavity walls in such a manner to resist fracture of the tooth or restorative

material from masticatory forces which are directed parallel to long axis of tooth.

o It is the pulpal and gingival floors which resist this force of mastication and prevent fracture of tooth or

restoration.

PRINCIPLES 01) Using a box shape cavity with horizontal floor.

a. Horizontal floor resist the occlusal force by being at right angle to force of mastication.

02) Restricting external walls to allow cusp and ridge areas with sufficient dentin support.

03) Rounding of line angles to reduce stress concentration in tooth structure.

a. Rounding of internal line angle reduces fracture of tooth.

b. Rounding of external line angle reduce fracture of restoration.

04) Reducing & covering weak cusps (cusp capping) or extending the cavity to include weakened tooth within it.

a. To prevent forces in long axis and obliquely/laterally directed forces.

i. Most resistance to obliquely/lateral forces is attained later in the final tooth preparation.

05) Providing enough thickness of restorative material to prevent its fracture under load.

06) Bonding the material to tooth structure, when appropriate.

These resistance form principles are for conventional or beveled

preparations. While

Modified tooth preparation does not require uniform pulpal or axial

depth or minimal thickness for the material.

The pulpal wall follows the original occlusal surface contours and the

DEJ (Fig; 5-13) these roughly paralleling each other.

Rule for Cusp capping

o If extension from a primary groove toward the cusp tips is no

more than half the distance, no cusp capping should be done.

o If this extension is one half to two third of distance, consider

cusp capping.

o If the extension is more than 2/3rd of the distance, capping of cusp is strongly recommended.

FACTORS Occlusal contacts & force

o Greater the occlusal forces and contacts, greater is the potential for future fracture.

Amount of remaining tooth structure.

o As we know, we should always remove weak and unsupported enamel. But sometimes unsupported, but

not friable, enamel may be left usually for esthetic reasons in anterior teeth, especially on facial

surfaces of maxillary teeth where stresses are minimal and a bonded restoration is used.

The type of restorative material

o The minimal occlusal thickness for resistance to fractures is;

Amalgam; 1.5 mm

Cast metal; 1-2 mm

Ceramics; 2 mm

Composite; the thickness of composite depends on occlusal wear which is greater for posterior

teeth than anterior teeth.

Bonding a restoration to tooth

FEATURES Horizontal floors


Box-like shape

Include weak tooth structure in cavity

Preserve cusps and marginal ridges

Rounded line angles

Adequate thickness of restorative material

Reduce cusps for cusp capping, if indicated.

Step 3; Primary Retention Form

DEFINITION It is the form or shape of preparation/cavity that prevents displacement or removal of the restoration by tipping or

lifting forces for non-bonded restoration.

PRINCIPLES Principles of primary retention form depend on the material used.

For amalgam restoration in class 1 & all class 2

o Vertical external walls of proximal and occlusal portions converge occlusally.

Occlusal convergence should not be excessive which would result unsupported enamel.

Amalgam restoration in class 3 & class 5

o Vertical external walls diverge outwardly.

o Preparation of retention coves (concavities) or grooves in dentinal wall of cavity.

Composite restoration

o These are retained in the cavity by micromechanical bond b/w material and etched & primed tooth.

o Additional retention may be accomplished by beveling or flaring enamel margin at greater than 90

degrees.

Cast metal (gold alloy) intra-coronal restoration

o Parallel vertical walls of cavity for retention

o 2-5 degree of divergence per wall should be present in those walls which contain path of insertion/ line

of draw.

The greater the vertical height of the walls, the more divergence is recommend in walls of path

of insertion.

Inlay and onlay preparations

o Opposing walls diverge outwardly but only few degrees to each other.

o Wall of insertion path or line of draw is perpendicular to floor.

Close parallelism of the prepared walls is a principal retention form for cast metal restoration, another is luting

agent.

STEP 4; Convenience Form It is the shape or form of the preparation that provides for adequate observation, accessibility, and ease of

operation in preparing and restoring the tooth.

Procedures for obtaining convenience form;

Occlusal divergence of vertical walls for class 2 cast restoration

Extending proximal preparation beyond proximal contacts.

FINAL TOOTH PREPARATION STAGE

STEP 5; Removal of Any Remaining Enamel Pit or Fissure, Infected Dentine, or Old

Restorative Material, If Indicated

DEFINITION It is elimination or excavation of any infected carious tooth structure or faulty restoration which is left after initial tooth

preparation.


Allow affected dentine to remain in a prepared tooth.

o The use of color alone to determine how much dentine to remove is unreliable.

Coz, soft, acute/rapid caries is similar in color to normal dentine.

o Decision for differentiating b/w affected and infected dentine is by experience.

o It is not necessary to remove all dentine which is invaded by microorganisms.

We can remove major portion of dentine and retain smaller portion coz subsequent sealing of

the preparation with remaining dentine destroy those microbes or reduce them to inactivity or

dormancy.

o But, never leave carious dentine at DEJ as mentioned above.

Any remaining old restorative material should be removed if any of the following conditions are present;

o Old material affecting the esthetics of new restoration.

E.g. old amalgam under new composite.

o Old material affecting retention of new material.

E.g. GIC have low bonding to tooth than composite.

o Caries is present under old restorative material.

o The tooth pulp was symptomatic pre-operatively.

o Periphery of restorative material is not intact.

If none of these conditions are present leave the remaining old material to serve as base, rather than risk un-

necessary excavation nearer to pulp, which may result in pulpal irritation or exposure.

TECHINIQUE Removal of remaining caries in initial stage of tooth preparation is indicated in following conditions;

o Extensive caries

o Caries involving multiple teeth

In one appointment, infected dentine is removed and temporary filling is placed to stop the

progression of caries, after removal of all caries from teeth, permanent filling is then placed.

There are different methods proposed for removal as mentioned under;

o Spoon excavators

o Round steel burs at very low speed

o Round carbide bur at high speed

Frictional heat from burs can damage the pulp

Pressure from excavator can force microorganisms into pulp.

So, the ideal method for removal of this infected carious material is in which minimal pressure is exerted, frictional

heat is minimized and complete control of instrument is maintained. So for this we should use;

o Round carbide bur in slow or high speed hand piece with air coolant and slow speed.

After removal, examine the area with explorer

o Avoid use of excessive pressure to prevent perforation of pulp.

Ideally, removal of infected dentine should continue until the remaining dentine hardness approaches that of

normal dentin

Removal of old restoration is also accomplished by use of;

o Round carbide bure, at slow speed with air or air-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 indicated. It is done by using LINERS & BASES which seal the dentinal tubules.

Pulpal irritation during or after operative procedure result from;

o Heat generated by rotary instruments

o Some ingredients of various materials

o Thermal changes conducted through restorative material

o Force transmitted through materials to the dentine

o Galvanic shock


o Ingress of noxious products and bacteria through micro leakage (MOST COMMON Reason)

LINERS; suspensions of;

Zinc oxide

Calcium hydroxide

Resin-modified glass ionomer (RMGI)

o Applied as thin film

o Provide;

Barrier from noxious agents from restorative material or oral fluids.

Initial electrical insulation

Some thermal protection

Sedation to pulp & stimulate reparative dentine formation in case of trauma to tooth.

Specific pulpal response desired dictates the choice of liner.

o No Liner is indicated; if the removal of infected dentine does not extend deeper than 1-2 mm from initial

depth.

If the distance b/w pulp and pulpal floor is less than or equal to 0.5 mm, then use Calcium hydroxide liner to

stimulate reparative dentine formation.

o ZOE, CaOH liners in thickness of approx. 0.5 mm or more resist condensation force of amalgam and

provide protection against short term thermal changes in amalgam filling.

o CaOH liners must always be covered with RMGI to prevent decomposition of the liner over time when

used under amalgam restoration or composite restoration

It is recommended that at least 2mm of distance should be present b/w pulp and metallic restoration. And this 2

mm separation can be achieved by;

o Natural dentine present b/w them

o Liners or bases

Indirect Pulp Capping; procedure done on unexposed pulp with thin dentine above it.

Pulp Capping; it is technique to prevent dental pulp from dying after being exposed or nearly exposed during

cavity preparation.

Direct pulp capping; when pulp is exposed;

o Material of choice; calcium hydroxide

BASES; mostly cements;

Zinc phosphate

Zinc oxide eugenol

Polycarboxylate

RMGI (most common)

Bond chemically or micromechanically to tooth. That’s why retentive features are not

required

Release fluoride

Sufficient strength

Easily placed & contoured

o Applied as THICK film

o Provide mechanical, chemical & thermal protection to pulp

o The thickness of base should not decrease the cavity depth to so much that thickness of restorative material

get decrease and resulting decreased strength.

Liners or bases in exposed areas should be applied without pressure.

STEP 7; Secondary Resistance & Retention forms. When a tooth preparation includes occlusal and proximal surfaces, each of those areas should have independent

retention and resistance.

Many preparation features that improve retention form also improve resistance form, and the reverse is also true.

There are two mechanisms of secondary resistance & retention forms;


o Mechanical methods

o Placement of etchant, primer or adhesive on cavity walls.

MECHANICAL METHODS They require additional removal of tooth structure and include;

o Retention grooves and coves

o Preparation extensions

o Skirts

o Beveled enamel margins

o Pins, slots, steps & amalgam pins

RETENTION GROOVE & COVES In vivo studies do not prove the necessity of these grooves or coves

They are recommended for;

o Extensive tooth preparation for amalgam

o Cusp capping

Proximal portion of conventional cavity preparation require;

o Vertically oriented grooves

Class3, class 5 & root surface cavity preparation require;

o Horizontal oriented retention grooves.

Retention coves are placed for the incisal retention of class 3 amalgams.

In class 2, these grooves or coves;

o Prevent the movement of material caused by creep.

o Resist fracture of restoration at the junction of proximal and occlusal portions.

PREPARATION EXTENSION In this, extension of cavity occurs to non-carious grooves or pits.

Example; extending the preparation for molars onto the facial or lingual surface to

include facial or lingual groove.

SKIRTS It is extension of cavity or preparation into one of the line angles of cavity.

Used in cast gold restoration

BEVELED ENAMEL MARGINS Required in Cast metal & composite restorations.

In cast metal, beveled enamel margins improve retention very little but the main role of beveling enamel margins

in cast metal is it causes better junctional relationship b/w metal and tooth.

In composite, beveled margins increase surface area for etching resulting maximized bonding b/w restorative

material & tooth.

PINS, SLOTS, STEPS & AMALGAM PINS

Pins; are thin shafts of metal that are either cemented or screwed in tooth. Types are;

o Cemented pins

o Friction locked pins

o Self-threaded pins

Slots; these are box like grooves prepared into dentine to increase surface area.

They are 1.0 – 1.5 mm deep box like grooves.

Amalgam pins; these are vertical posts of amalgam anchored in dentine.

o Posts are thicker shafts of metal or composite.


PLACEMENT OF ETCHANT, PRIMER, OR ADHESIVE ON PREPARED WALLS

ENAMEL WALL ETCHING Uses in restorations involving bonding material, in this enamel surface is etched with acid in which bonding material

mechanically attach with roughness created by acid.

DENTINE TREATEMENT By use of dentine bonding agents.

STEP 8; finishing the External walls of Tooth Preparation. Cavosurface margin/angle onto root surface should be;

o 90 degrees for amalgam, composite or ceramic restoration.

o Beveled for cast metal restorations

DEFINITION It is the further development of Cavosurface design & degree of smoothness or roughness that produce maximum

effectiveness of the material.

OBJECTIVES A. Create optimal smooth marginal junction b/w restorative material & tooth structure.

B. To get maximal strength of tooth and the restorative material at the margin.

Following factors must be considered in finishing the cavity walls;

Direction of enamel rods

The support of enamel rods at DEJ & laterally

Type of restorative material

Location of cavo surface margin

Degree of smoothness/roughness needed

In general, rods converge toward the center of grooves, while they diverge towards the height of cusps. Coz, rods

converge toward concave surface and diverge towards convex surface.

In gingival third of smooth surfaces, rods incline slightly apically approx. 15-20 degrees (gif; 5-16)

Rods of occlusal enamel are harder than axial enamel (mesial, facial, distal, lingual) coz of twisting of rods caused

by convergence (gnarled enamel) towards occlusal surface. While there are straight rods in axial enamel.

Enamel walls should be oriented in such a manner that the inner ends of enamel rods should be on DEJ. If it does

not happen, V shaped ditch will be created along the Cavosurface margin.

The strongest enamel margin is one, in which full length of enamel rods are supported on the cavity side by shorter

rods whose inner ends are on DEJ.

Line angles should be made around slightly (Fig; 5-17)

FEATURES of Finishing Tooth preparation The Design of the Cavo Surface Angle.

Design of Cavosurface angle depends on restorative material.

90 degree for amalgam & ceramic because of low edge strength.

o Beveling is contraindicated in amalgam except only at gingival floor of class 2 cavity.

It still produces 90 degree despite beveling (fig; 5-16)

o It is inclination of cusps and the converging walls for retention make the 90-degree butt joint.

Beveling of external walls occurs in;

o Cast gold or cast metal

o Composites

Purpose of beveling in cast metal restoration;

o Produce strong enamel margin

o Permits a marginal seal in slightly undersized castings

o It provides marginal metal that is more easily burnished and adapted

o It assists in adaptation of gingival margins of castings that fail to seat by a slight amount.


Purpose of beveling in composite

o Increased retention by increasing surface area of enamel for etching.

o Adjacent minor defects can be included with beveling

o Enhancement of esthetic by bevel creating an area of gradual thickness from the margin to the bulk of

the restoration

o Enhancement of marginal seal

The Degree of Smoothness or Roughness

Can be done by;

o high speed hand pieces using burs or

plain fissure burs

finishing carbide burs

fine diamond stones

o Hand instruments.

o Sandpaper disks

Side effects of using high speed hand pieces

o Less tactile sensation

o Rapid removal tooth structure

These above factors can lead to over extension of margins, grooved walls, rounded Cavosurface angles.

If hand piece is used, then use plain-cut fissure bur.

Degree of smoothness depend on the restorative material used;

o Smooth surfaces for inlay or onlay

o Rough surfaces for composites is required which can be done by coarse diamond rotary instrument

o Slightly rough surface for amalgam lead to improvement of resistance to marginal leakage.

STEP 9; Final Procedures; Cleaning, Inspecting, & Desensitizing. Remove the visible debris with water from triple syringe and remove moisture with air from triple syringe.

Debris attached to walls can be removed by explorer or small cotton pallet.

Do not dehydrate the tooth by overuse of air to avoid damage to odontoblasts.

Disinfection of cavity can be performed by;

o Chlorohexidine 2wt%

It can also stabilize the hybrid layer in composites by inhibiting enzymes (for explanation read

text on page 161 in Art & science)

o Germicidal action or restorative materials or cements.

E.g. Zinc oxide eugenol

o Fluoride content of some material also protect the tooth

o Corrosion in amalgam also prevent the ingress of fluid and subsequent pulp damage by preventing

marginal leakage.

Desensitizer used in non-bonding restoration & dentine bonding agents in bonding restorations decrease the post-

operative sensitivity.

o These are also used as dis infection purpose.

o Crosslink the exposed dentine matrix

o Occlude dentinal tubules by crosslinking tubular proteins.

Cavities for amalgam should be desensitized with a solution containing;

o 5% glutaraldehyde

o 35% hydroxyethyl methacrylate (HEMA)

ADDITIONAL CONCEPTS IN TOOTH PREPARATION.

Amalgam box only tooth preparation

o It shows that if the cavity is need on proximal surface only and no occlusal surface is involved then create

appropriate box and specific retention form is provided.

o Normally retention to proximal cavity is obtained by extension of cavity on occlusal surface.


Amalgam tunnel tooth preparation

o In this occlusal lesion and proximal lesion is joined by a prepared tunnel under the involved marginal

ridge.

o In this marginal ridge is intact but its strength is controversial because dentine support is lost and;

o There is lack of access to cavity and visibility.

Adhesive amalgam restoration

o In this technique, amalgam is bonded to cavity by an adhesive resin. By following steps;

o Prepare tooth like conventional amalgam tooth preparation, except retain weakened tooth structure.

o Apply adhesive resin

o Condense amalgam before polymerization of adhesive

However, there is no any long-term difference in adhesive amalgam or non-bonded amalgam.

DIFFERENCE B/W TOOTH PREPARATION OF AMALGAM V/S COMPOSITE.

FEATURE AMALGAM COMPOSITE Outline form Include defect, extend to include proximal

contact & include adjacent suspicious area for prevention.

Include defect, extend to include proximal contact & no extension further to suspicious areas.

Pulpal Depth 1.5 mm & uniform Remove defect

Axial depth 0.2-0.5 mm inside DEJ Remove defect

Cavosurface margin

90 degree butt joint ≥90 degrees

Bevels None, except gingival wall in class 2 In large preparation, esthetics & seal

Texture of prepared walls

Smoother Rough

Cutting instrument

Burs Burs or diamonds

Primary retention form

Convergence occlusally Roughness or bonding

Secondary retention form

Grooves, slots, pins, bonding Bonding

Resistance form Horizontal floors, rounded angles, box shaped (floors perpendicular to occlusal forces)

Same for large preparation in composites

Base indications Provide 2mm b/w pulp & amalgam Not needed

Liner indications Calcium hydroxide for pulp capping procedure, GIC for deep amalgam cavity.

Same as for amalgam

Desensitizers Solution of 5% glutaraldehyde + 35% HEMA Bonding system


The End

Fundamentals of Tooth Preparation (Operative Dentistry)

Education

Transcript of Fundamentals of Tooth Preparation (Operative Dentistry)