Tooth Morphology

DR Mazen D D

Master In Endodontics & Operative Dentistry

This Lecture Contains:1- components of the root canal system

2- Root canal anatomy3-Anatomy of the apical root

4- Objectives and guidelines for access cavity preparation

5- mechanical phase of access cavity preparation6- challenging access cavity preparation

7- errors in access cavity preparation8- Morphology and access cavity preparations for

individual teeth

- The optimal endodontic result is difficult to achieve if .the access is not properly prepared

-Careful evaluation of two or more periapical radiographs, exposed at different horizontal angulations of the x-ray cone, is mandatory

An important aid for locating root canals is the dental operating microscope (DOM), which was introduced into endodontics to provide enhanced lighting and visibility

the number of second mesiobuccal (MB-2) canals identified in maxillary molars increased from 51% with the naked eye to 82% with the microscope

(1)

COMPONENTS OF THE ROOT

CANAL SYSTEM

The entire space in the dentin where the pulp is housed is called the root canal system

Factors affecting root canal system:1- physiologic aging 2- pathosis3- occlusion all potentially modify its dimensions through the production of secondary and tertiary dentin and cementum

Root canal system is divided into two portions:

1-Pulp chamber

2-Root canal

A root canal begins as a funnel-shaped canal orifice, generally at or just apical to the cervical line, and ends at the apical foramen,which opens onto the root surface at or within 3 mm from the center of the root apex

Nearly all root canals are curved, particularly in a facio lingual direction

Angled views are necessary to determine their presence, direction, and severity.

A curvature may be a gradual curve of the entire canal or a sharp curvature near the apex

In most cases the number of root canals corresponds to the number of roots.an oval root may have more than one canal.

Accessory canals are minute canals that extend in a horizontal,vertical, or lateral direction from the pulp to the periodontium.

In 74% of cases they are found in the apical third of the root.

do not supply the pulp with sufficient circulationto form a collateral source of blood flow

Accessory canals

(2)

ROOT CANAL ANATOMY

a tapering canal and a single foramen is the exception rather than the rule .

Investigators have shown multiple foramina, additional canals, fins, deltas, intercanal connections, loops, C-shaped canals, and furcation and lateral canals in most teeth

The pulp canal system is complex, and canals may branch, divide, and rejoinThere are eight pulp space configurations, which can be

briefly described as follows: Type I: A single canal extends from the pulp chamber to the apex.

Type II: Two separate canals leave the pulp chamber and join short of the apex to form one canal.

Type III: One canal leaves the pulp chamber and divides into two in the root; the two then merge to exit as one canal.

Type IV: Two separate, distinct canals extend from the pulp chamber to the apex.

Type v: One canal leaves the pulp chamber and divides short of the apex into two separate, distinct canals with separate apical foramina.

Type VI: Two separate canals leave the pulp chamber, merge in the body of the root, and redivide short of the apex to exit as two distinct canals.

Type VII: One canal leaves the pulp chamber, divides and then rejoins in the body of the root, and finally redivides into two distinct canals short of the apex.

Type VIII: Three separate, distinct canals extend from the pulp chamber to the apex.

Specific types of canal morphology appear to occur in different racial groups.

compared with Caucasian patients, those of African descent have a higher number of extra canals in both the mandibular first premolar and the mandibular second premolar.

if only one canal is present, it usually is located in the center of the access preparation.

If only one orifice is found and it is not in the center of the root, another orifice probably exists.

How to explore an oval orefice

As the distance between orifices in a root increases,the greater the chance is that the canals will remain separate.If the first file inserted into the distal canal of a mandibular molar points either to the buccal or to the lingual aspect, the clinician should suspect a second canal .

If two canals are present, they will be smaller than a single canal.

When one canal separates into two, the division is buccal and palatal/lingual, and the lingual canal generally splits from the main canal at a sharp angle, sometimes nearly a right angle

(3)

Anatomy of the apical

root

funnel ‘or' crater

In root-end resections a bevel perpendicular to the long axis of a root exposes a small number of microtubules

a root resection with a 45-degree bevel exposes asignificantly greater number of tubules.

(4)

OBJECTIVES AND GUIDELINES FOR ACCESS

CAVITY PREPARATION

Objectives:The objectives of access cavity preparation are:

(1) to remove all caries (2) to conserve sound tooth structure

( 3)to completely unroof the pulp chamber( 4) to remove all coronal pulp tissue (vital or

necrotic) (5) to locate all root canal orifices (6 )to achieve straight- or direct-line access

to the apical foramen or to the initial curvature of the canal ,

(7) to establish restorative margins to minimize marginal leakage of the restored tooth.

1-visualization of the position of the pulp space in the tooth

2 -Evaluation of the Cementoenamel junction and Occlusal Anatomies(see next slide).

3- Preparation of the Access Cavity Through the Lingual and Occlusal Surfaces

4-Removal of All Defective Restorations and Caries Before Entry Into the Pulp Chamber

5-Removal of Unsupported Tooth Structure

6-Creation of Access Cavity Walls That Do Not Restrict Straight- or Direct-line Passage of Instruments to the Apical Foramen or Initial Canal Curvature

Laws of access cavity preparation:1-Law of centrality

2-Law of concentricity3-Law of the Cej

4-First law of symmetry5-Second law of symmetry

6-Law of color change7-First law of orifice location

8-Second law of orifice location9-Third law of orifice location

Slightly fewer than 5% of mandibular second and third molars did not conform because of the occurrence of C-shaped anatomy.

MECHANICAL PHASES OF ACCESS CAVITY PREPARATIONArmamentariaThe preparation of an access cavity requires the following equipment:

• Magnification and illumination• Handpieces

• Burs• Endodontic explorer (DG-16, DE-l7)

• Endodontic spoon• #17 operative explorer• Ultrasonic unit and tips

Magnification and illumination

Handpieces

Burs

Round carbide burs (sizes #2, #4, and #6) -Removal caries

-creating the initial external outline shape -penetrating through the roof of the pulp chamber

and for removing the roof

Burs

fissure carbide burdiamond bur with a rounded cutting

end

Burs

Fissure carbide and diamond burs with safety tips

safer choices for axial wall extensions

Burs

Round diamond burs (sizes #2 and #4)when endodontic access must be made

through porcelain or ceramometal restorations

A transmetal bur

Burs

Burs

If a tooth has a receded pulp chamber and calcified orifices,the clinician often must cut into the root to locate and identifythe canal orifices. Extended-shank round burs, such as the Mueller bur and the LN bur

Once the orifices have been located , they should be flared or enlarged. This process permits the intracanal instruments used during shaping and cleaning to enter the canal(s) easily and effortlessly.

Endodontic Explorer, Endodontic Spoon, # 1 7

Operative Explorer

DG-16 endodontic explorer (top);

jW-17 endodontic explorer (bottom)

Ultrasonic Unit and Tips

Ultrasonic Unit and Tips

1-Ultrasonic systems provide outstanding visibility compared with conventional handpiece heads ,which typically obstruct vision.

2-Fine ultrasonic tips are smaller than conventional round burs, and their abrasive coatings allow clinicians to sand away dentin and calcifications conservatively when exploring for canal orifices.

Access

Cavity Preparations

REMOVAL OF CARIES AND PERMANENT RESTORATIONSclinicians were about 40% more likely to miss fractures, caries, and marginal breakdown if restorations were not completely removed

INITIAL EXTERNAL OUTLINE FORM

1 mm

PENETRATION OF THE PULP CHAMBER ROOF

drop-in

The clinician should measure the distance from the incisal edge to the roof of the pulp chamber on a dimensionally accurate pretreatment radiograph and limit penetration to this distance. If the drop-in effect is not felt at this depth, the clinician should evaluate the situation carefully to prevent a gouge or perforation

PENETRATION OF THE PULP CHAMBER ROOF

The depth and angle of penetration should be assessed for any deviation away from the long axis of the root in both the mesiodistal and buccolingual dimensions

A little caution and concern at this stage can prevent an iatrogenic

mishap

COMPLETE ROOF REMOVAL

Once the pulp chamber has been penetrated, the remaining roof is removed by catching the end of a round bur under the lip of the dentin roof and cutting on the bur's withdrawal stroke

IDENTIFICATION OF ALL CANAL ORIFICES

This instrument is to the endodontist what a periodontal probe is to the periodontist

Used for:reaching, feeling, and often digging at the hard tissue, it is the tactile extension of the clinician's fingers. evaluate straight-line access

REMOVAL OF THE LINGUAL SHOULDER AND ORIFICE AND CORONAL FLARING

2 mm apical to the orifice

MORPHOLOGY AND ACCESS CAVITY PREPARATIONS FOR

INDIVIDUAL TEETH“Anterior teeth”

Maxillary

Central In

cisor

average time of eruption: 7 to 8 years average age of calcification:10 years

average length: 22.5 mm Root curvature (most common to least

common) :straight, labial, distal.the pulp chamber is wider mesiodistally than buccolingually.

Maxilla

ry la

tera

l Incis

or

-This pulp chamber is wider mesiodistally than buccolingually.

-A cross-section at the CE] shows a pulp chamber centered in the root, and its shape may be triangular ,

oval, or round-Normally only one root canal is present,

but two and three canals have been reportedaverage time of eruption: 8-9years

average age of calcification:11 years average length: 22 mm

Root curvature (most common to least common) :Distal-straight.

Maxilla

ry ca

nine

-This pulp chamber is wider buccolingually than mesiodistally

-it has no pulp horns- The pulp chamber outline at the CEj is oval.

- A lingual shoulder is present. -Usually one root canal is present, although two canals

have been reported-The external access outline form is oval or slot

shaped-- The incisal extension often approaches to within 2 to 3

mm of the incisal edge

average time of eruption: 10-12years average age of calcification:13-15 years

average length: 26.5 mm Root curvature (most common to least

common) :Distal-straight-labial

Maxillary Firs

t Premolar

- The pulp chamber of the maxillary first premolar is considerably wider buccolingually than mesiodistally

- The palatal orifice is slightly larger than the buccal Orifice and kidney shaped.

- From the floor, two root canals take on a round shape at mid root and rapidly taper to their apices.

- The palatal canal usually is slightly larger than the buccal canal.

- may have one, two, or three roots and canals; it most often has two

Average time of eruption: 10 to 11 years average age of calcification: 12 to 13years

average length: 20.6 mm .Root curvature )most common to least common(:buccal root: lingual, straight, buccal.

palatal root:straight, buccal, distal.single root:straight, distal, buccal.

Maxillary se

cond Premolar

-The root canal system of the maxillary second premolar is wider buccolingually than mesiodistally

- may have one, two, or three roots and canals

-Two or three canals can occur in a single root.

- Apical curvature is common - if two canals are present, they are nearly

parallel to each other.

Average time of eruption: 10 to 12 years average age of calcification: 12 to 14years

average length: 21.5 mm .Root curvature )most common to least common(:Distal, bayonet, buccal, straight

Mandibular C

entral

and La

teral Incis

ors

- a lingual shoulder must be eliminated to allow direct line access

- The shoulder conceals the orifice to a second canal that, if present, is found immediately beneath it.

- the pulp outline of the mandibular incisors is wider labiolingually

- At the Cej the pulp outline is oval till midroot- Often a dentinal bridge is present in the pulp

chamber that divides the root into two canals. The two canals usually join and exit through a single apical foramen

- On occasion one canal branches into two canals which subsequently rejoin into a single canal before reaching the apex

20.7

-The external outline form may be triangular or oval,depending on the prominence of the mesial and distal pulp horns

Root curvature (most common to least common):

straight, distal, labial

Mandibular canine

- root canal system is very similar to that of the maxillary canine, except that the dimensions are smaller

- the root and root canal outlines are narrower

in the mesiodistal dimension - occasionally has two roots and two root canals

located labially and lingually

- The access cavity for the mandibular canine is oval or slot shaped

25. 6 mm.

mandibular First Premolar

- They have a high flare-up and failure rate -wider buccolingually than mesiodistally

- At the cervical line the root and canal are oval -this shape tends to become round as the canal

approaches the middle of the root -If two canals are present, they tend to be

round from the pulp chamber to their foramen -a single, broad root canal may bifurcate into

two separate root canals -The mandibular first premolar sometimes may

have three roots and three canals -oval external outline, buccal extension can

nearly approach the tip

21.6

mandibular second Premolar

The mandibular second premolar is similar to the first premolar, with the following differences:

1- the root and root canal are more often oval than round

2 -the pulp chamber is wider buccolingually3- two, three, and four canals and a lingually

tipped crown

22.3