APICAL THIRD AND ITS SIGNIFICANCE

01. Introduction.

02. Development of root structure.

03. Clinical correlation in endodontic therapy.

Apical foramen.

Apical pulp tissue.

Apical dentin (constriction).

Accessory foramina and lateral canal.

4. Denticles and dystrophic calcifications.

5. Aical resorptions.

6. Apical instrumentation.

7. Conclusion.

INTRODUCTION:

The root apex is of interest to endodontists because the stages

of root development and the types of tissue present within the roots

of teeth are significant to the practice of endodontics.

Also appreciable knowledge of the morphology of the root

apex and its variance, ability to interpret it correctly in radiographs

and to feel it through tactile sensation during instrumentation is

essential for an effective rendering of the treatment of root canals.

Achievement of a perfect seal at the apex using an inert filling

material is the ultimate goal of every endodontist.

In this seminar the importance of apical 1/3rd shall be

discussed under following sub-titles.

1. Development of root apices.

2. Pulpal tissue within.

3. Morphology and variance.

4. Ability to interpret correctly in radiographs.

5. Feel through tactile sensation during instrumentation.

DEVELOPMENT OF ROOT APEX:

The development of the root begins after the enamel and the

dentin formation has reached the future CEJ.

The enamel organ play an important part in root development

by forming Hertwig’s epithelial root sheath, which molds the shape

of the roots and initiates radicular dentine formation.

Hertwig’s root sheath consists of the outer and inner enamel

epithelia only (and therefore it does not include the stratum

intermedium and stellate reticulum).

The cells of the inner layer remain short and normally do not

produce enamel.

When these cells have induced the differentiation of radicular

cells into odontoblasts and the 1st layer of dentin has been laid down,

the epithelial root sheath loses its structural continuity and its close

relation to the surface of the root.

Its remnants persist as an epithelial network of strands or

tubules near the external surface of the root.

These epithelial remnants are found in the periodontal

ligament of erupted teeth and are called “cell rests of mallassez”.

There is a pronounced difference in the development of

Hertwig’s epithelial root sheath in teeth with one root and in those

with two or more roots.

Prior to the beginning of root formation the root sheath forms

the epithelial diaphragm.

The outer and inner enamel epithelium bend at the future

cemento-enamel junction into a horizontal plane narrowing the wide

cervical opening of the tooth germ.

The plane of the diaphragm remains relatively fixed during the

development of growth of root.

The proliferation of the cells of the epithelial diaphragm is

accompanied by proliferation of the cells of the connective tissue of

the pulp, which occurs in the area adjacent to the diaphragm.

The free end of the diaphragm does not grow into the

connective tissue, but the epithelium proliferates coronally to the

epithelial diaphragm.

The differentiation of odontoblasts and the formation of dentin

follow the lengthening of the root sheath.

At the same time the connective tissue of the dental sac

surrounding the root sheath proliferates and divides the continuous

double epithelial layer into a network of epithelial strands.

The epithelium is moved away from the surface of the dentin

so that connective tissue cells come into contact with the outer

surface of the dentin and differentiate into cementoblasts that

deposit a layer of cementum onto the surface of the dentin.

The rapid sequence of proliferation and destruction of

Hertwig’s root sheath explains the fact that is cannot be seen as a

continuous layer on the surface of the developing root.

In the last stages of root development, the proliferation of the

epithelium in the diaphragm lays behind that of the pulpal

connective tissue.

The wide apical foramen is reduced first to the width of the

diaphragmatic opening itself and later is further narrowed by

opposition of dentin and cementum to the apex of the root.

Differential growth of the epithelial diaphragm in multi-rooted teeth

causes the division of the root track into 2 or 3 roots.

During the general growth of the enamel organ the expansion

of its cervical opening occurs in such a way that long tongue like

extensions of the horizontal diaphragm develop.

Two such extensions are found in the germs of lower molars

and 3 in the germs of upper molars.

Before division of the root trunk occurs, the free end of these

horizontal epithelial flags grow towards each other and fuse.

The single cervical opening of the coronal enamel organ is

then divided into 2 or 3 openings.

On the pulpal surface of the dividing epithelial bridges, dentin

formation starts.

On the periphery of each opening, root development follows in

the same way as described for single rooted teeth.

Now that we know how various canal configurations are

formed. The different configurations are:

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 a canal.

Type-III: One canal leaves the pulp chamber divides into two within

the root and then to exit as one canal.

Type-IV: Two separate and 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 and distinct canals with separate apical

foramina.

Type-VI: Two separate canals leave the pulp chamber merges in the

body of the root and redivide short of the apex as two distinct

canals.

Type-VII: One canal leaves the pulp chamber divides and then

rejoins within the body of the root and finally redivides into two

distinct canals short of the apex.

Type-VIII: Three separate and distinct canals extend from the pulp

chamber to apex.

Generally, the roots have a single apical foramen and a single canal

(Type-I). However, it is not uncommon for other canal complexities

to be present and exit the root as one two or three apical canals

(Type II – VII).

Classification of the root apex is essential for endodontic practice,

particularly when dealing with pulp involved or pulp less teeth of

children and young persons.

As a general rule, root apex is completely formed about 2-3 years

after the eruption of the tooth.

The following table gives the approximate time in years of

eruption of the teeth and calcification of root apices.

CI LICuspi

d1st 2nd 1st 2nd

Eruption 6-8 7-9 10-12 9-11 11-12 5-7 12-13

Calcificatio

n10-12 11-12 13-14 12-14 13-14 10-11 15-16

In young incompletely developed teeth the apical foramen is

tunnel shaped with the wider portion extending outward. The mouth

of the tunnel is filled with periodontal tissue that is later replaced by

dentin and cementum.

Any injury occurring before its closure may result in changes

that may lead to formation of the blunderbuss canal.

Successful repair of inflamed dental pulp in teeth with

incomplete apical root closure is enhanced compared to that of teeth

with completed root formation possibly because of the unrestricted

metabolism in the former group.

Thus pulp capping and pulpotomy procedures have a better

chance for successful resolution in teeth with open apexes. Once

root end formation has been completed, complete endodontic

therapy has a better prognosis than pulp capping or pulpotomy

procedures.

APICAL FORAMEN AND APICAL CONSTRICTION:

Location and shape of the fully formed foramen vary in each

tooth and in the same tooth at different periods of life.

Awareness of these is considered important for effective

rendering of the treatment. The foramen can change in shape and

location because of functional influences on the tooth for e.g. tongue

pressure or nasal pressure, mesial drift.

Cementum resorption occurs on the wall of the foramina

farthest from the force, opposition on the wall nearest; the net

results in the development of the foramen away from the tissue

apex.

It is a popular misconception that the apical foramen coincides

with the anatomical apex of the tooth. This is an infrequent

occurrence and usually the apical foramen opens 0.5 – 1.0 mm from

the anatomical apex.

This distance is not always constant and may increase as the

tooth ages because of the deposition of secondary cementum on the

outer surface of the root and secondary dentin on the walls of the

root canal.

The apical foramen is not always located in the center of the

root apex.

It may exit on the mesial, distal, labial or lingual surface of the

root, usually slightly eccentrically.

Levy and Glaft (1970) found in their study that the deviation

occurred more commonly on the buccal or lingual aspect than on the

mesial or distal side.

An endo instrument protruding beyond the foramen on either

buccal or lingual / palatal aspect cannot be appreciated in X-rays and

may give a deceptive picture as true placement upto the apex.

Studies (Green 1955, 1956, 1960) have shown that the major

apical foramina are situated directly at the apexes more frequently

in the maxillary centrals, laterals, cuspids and first premolars and in

the mandibular 2nd premolars.

In the maxillary molars and all the mandibular tooth with the

exception of the 2nd premolar, the main apical foramina coincide with

apices less frequently.

LOCATION AND SHAPE OF APICAL FORAMEN:

Varies with different teeth and in same teeth.

In relation to anatomical apex:

Many believe that the apical foramen is located at the

anatomic apex but it is not so always. Apical foramen located 0.5 –

1.0 mm away from anatomical apex.

Distance may vary with age either due to

- Increased dentin.

- Increased cementum deposition.

In maxillary 1st premolar and 2nd premolar apical foramen often

may coincide with apex.

But in all mandibular teeth (except mandibular 2nd premolar) and

maxillary molars opening does not coincide with anatomical apex.

Many believes the apical foramen open at the center of the root

apex but no so, it can open either mesial, distal, buccal center

more often bucco-lingual.

APICAL CONSTRICTION:

The apical foramen is not always the most constricted portion

of the root canal.

Frequently the narrowest portion of the root canal, termed the

“apical constriction” occurs about 0.5 – 1.0 mm from the apical

foramen.

Again, the portion of the apical constriction varies with age as

deposits of secondary dentin, within the root canal; site of the

constriction is away from the apex.

Ideally, the root filling should stop at this constriction as it would

serve as “apical dentin matrix” (an artificially produced ledge in the

apical root canal, against which gutta-percha could be compacted

without the fear of its protrusion into the periapex).

If the constriction is destroyed by instrumentation and an apical stop

is not developed the changes of long-term success are greatly

lessened.

Repeated instrumentation extending beyond the constriction is

unwarranted. It causes periradicular inflammation and often

destroys the biologic constriction of the root apex.

Perforations of the floor of the nose, maxillary sinus or mandibular

canal as a result of excessive over extension of instruments can lead

to severe post treatment pain, delayed healing and ultimate failure.

Intentional over extension of instruments should only be done when

drainage must be established from the periradicular tissue such as in

acute apical abcess etc.

CEMENTO-DENTINAL-JUNCTION (CDJ):

According to Kuttler (1958) the root canal is divided into a long

conical dentinal portion and a short tunnel-shaped cemental portion.

The cemental portion is usually in the form of an inverted cone

with its narrowest diameter at or near the cemento-dentinal-

junctions and its base at the apical foramen.

However, occasionally the cementum abuts directly on the

dentin at the apex.

At times, the cementum extends for a considerable distance

into the root canal lining the dentin in an irregular manner.

CLINICAL SIGNIFICANCE:

It is believed that the obturation and instrumentation within

the root canal should be limited upto this apical constriction or CFJ.

As this apical constriction acts like a artificial ledge and provides

apical dentin matrix for condensation or gutta-percha. However,

over instrumentation can lead to.

- Loss of biologic constriction.

- Over extension beyond foramen and

- Periradicular inflammation.

Situations are especially likely to occur in periodontally

compromised teeth or in teeth, which have been moved

orthodontically. In those instances the root canals as well as the

apices may almost become obliterated by heavy deposition of

secondary cementum.

The extend of cementum deposition on each wall of the root

canal varies, one wall is usually covered with a greater quantity of

cementum than the other wall.

Occasionally, tissue, which resembles both dentin and

cementum, is seen. The quantity of this intermediate tissue varies

among the teeth of different patients.

No definite morphological pattern of the CDJ is found

consistently.

The thickness of cementum around the apical foramen is

inconsistent and varies greatly.

The significance of the CDJ lies in its implication by a number

of investigators (Grove 1930; Hall 1930; Kultzer 1958) as the precise

region to which the root canal should be filled.

Kultzer (1955) claimed that the distance between the CDJ and

the apical foramen averaged 0.507 mm in young people and 0.784

mm in older people, thereby enabling the clinician to measure more

precisely the distance to which the root filling should extend.

However, the evidence for this precise location for the

terminus of the root canal filling is lacking.

ACCESSORY CANALS AND FORAMINA / LATERAL CANAL:

The mild trauma to which the tooth is subjected during

development of the root apex, may cause disturbance or breakage in

the continuity of the Hertwig’s root sheath more frequently, thus

leading to the formation of many accessory canals and foramina in

the apical third.

These accessory canals branch of from the main root canal and

end is accessory foramina.

They are more common in young patients because they

become obliterated by cementum and dentin as the patient ages.

Accessory canals, which open approximately at right angles to

the main pulp cavity are termed “lateral canals” and are generally

found in the furcation area of the posterior teeth.

The accessory and lateral canals are avenues for interchange

of metabolic and breakdown products between the pulp and

periodontal tissues. Pulp may become inflamed or necrotic from the

deep periodontal pockets, which cause exposure of the orifices of

the canals, thereby permitting the ingress of toxic products into the

pulp.

Conversely, breakdown products of inflammatory pulp lesions

may have an effect on the periodontal tissues via these canals

causing inflammatory changes.

The number of accessory canals in the root does not appear to

be a significant factor in success or failure of endodontic therapy in

teeth with vital pulps.

If they were more endodontic therapy would fail.

The apical and accessory foramina provide an opening for

microorganisms and for toxins to diffuse into the apical periodontal

space, setting up an acute or chronic apical periodontitis. This

irritation or infection may then follow the path of least resistance,

which may be in a coronal direction along the lateral root surface,

initiating a marginal gingivitis or periodontitis.

The inflammatory process may occur in the opposite direction

from the gingival and along the periodontal ligament space to the

apical and accessory foramina and into the pulp space to establish

pulp inflammation and its sequelae.

It would be difficult, if not impossible, by our current

techniques to instrument and cleanse the accessory canals when

with thorough reaming and filing it is possible.

Studies have shown that following endodontic therapy in teeth

with vital pulps (Hess et.al. 1983) the lateral and accessory canals

tend to become obliterated by the deposition of cementum with the

passage of time.

In teeth with totally inflamed / necrotic pulp, granulomatous

tissue is found in the accessory canals prior to endodontic therapy.

The significance of the involved tissue remaining in the

accessory foramina as a factor of failure or repair after endodontic

therapy has yet been definitely determined.

Presumable following endodontic therapy the inflammatory

tissue should be resorbed and replaced with inflamed connective

tissue.

(An accessory canal can also create a perio-endo pathway of

communication and possible portal of entry into the pulp if the

periodontal tissues lose their integrity).

In periodontal disease the development of a periodontal pocket

may expose an accessory canal and thus allow microorganisms or

their metabolic products to gain across the pulp.

DENTICLES AND DYSTROPHIC MINERALISATION:

Seltzer et.al. 1966 found dystrophic mineralisation in the apical pulp tissue of approximately 25% of anterior teeth.

Mineralisation within:

- and around the collagen fibers.

- Rarely in the myline sheath of the nerves.

Mineralisation vary in appearance:

- Fine.

- Diffuse.

- Fibri1llar variety.

- Large denticles.

(Seen in both young and old.)

PULP STONES (DENTICLES):

Comprised of tubular dentin and alveolar mineralized material.

In apical 1/3rd _ present in 15% of teeth.

Normally found as – attached, embedded, adherent (only part of it is attached to the dentin).

CLINICAL CORRELATIONS:

Pulp stones in apical 3rd causes

Difficulty in root canal instrumentation during reaming and filing.

If detached gets impacted into the foramen rendering instrumentation difficult.

APICAL RESORPTION:

Shallow resorption of the dentin in the apical portion of the root canal are normal occurrence.

Resorption of the apex can occur due to several reasons; in periodantally involved teeth the cementum and occasionally some apical dentin is completely resorbed from the root apex. A denuded, scalloped tunnel shaped structure remains.

The root ends may be resorbed during orthodontic tooth movement of the teeth. The root apex may be obliquely resorbed or have a cupped out appearance.

Most resorption are repaired by cementum.

In any event, if apical resorption has taken place, the apical

foramen will be in the center of the root.

If the root resorption has a “moth-eaten appearance” it is possible

that the tooth, by accident was loose from its ligaments or more

replanted.

Sometimes an unexplained lesions in the region strongly suggest

a malignancy.

When resorption has enlarged apical portion of the canal, apical

closure techniques should be used to ensure a better prognosis

for endodontic therapy (non-surgical).

CAUSES OF APICAL RESORPTION:

1. Periodontally involved teeth.

2. Orthodontic treatment.

3. Accident / trauma.

Almost all resorptions can be repaired by cementum deposition.

CLINICAL SIGNIFICANCE:

Due to resorption apical opening is enlarged so it is difficult to

obtain proper seal. Therefore apical closure technique is to be

followed.

Apical pulp tissue:

The apical pulp tissue differs structurally from the coronal pulp

tissue.

Apical Coronal

More fibrous. More filamentous.

Contains fewer cells.

This fibrous structure appears to act as a barrier against the

apical progression of pulp inflammation.

It also supports the blood vessels and nerves, which enter the

pulp.

CLINICAL CORRELATION IN ENDO THERAPY:

A vital pulp extirpation involves separation of the pulp tissue

somewhere in the apical region of the main canal.

Actually, the plane of separation of the pulp tissue from the

periodontal ligament is not under the complete control of the

operator, especially when a barbed broach is used to extirpate the

pulp.

The separation can occur anywhere in the root canal or even

beyond the apical foramen somewhere in the periodontal ligament.

When the latter types of separation occurs, the ensuring

haemorrhage causes a painful pericementitis.

CLINICAL SIGN:

1. While extirpating pulp avoid separating pulp at the coronal and

radicular pulp but remove in total.

2. If pulp is separated at the apical pulp beyond periodontal

junction then it leads to painful pericementitis reaction and

haemorrhage.

INSTRUMENTATION:

Time spent on the proper preparation of the apical portion greatly

simplifies the subsequent canal preparation.

The general principles to be adhered to while preparing the apical

3rd is confine cleaning and shaping procedures maintaining the

spatial integrity of the foramen and smooth shaping of original

course of the canal.

Adherence to these principles prevent violation of the

periradicular tissues. This principle is evident when foramina are

transported (i.e. moved) during excessive apical instrumentation.

Points to be remembered while enlarging apical 1/3rd are:

1. Do not instrument beyond apical constriction therefore maintain

the integrity of the foramen.

2. Follow the shape of the canal because this prevents damage to

periradicular tissues and transportation of foramina.

Normal transportation can be either (1) External (2) Internal.

EXTERNAL TRANSPORTATION takes place two forms and may

occur when instrumentation is carried out beyond the apical dentin

matrix.

One is the ripping of the apical end of the canal resulting (1)

tear drop (2) elliptical (3) zipped foramen.

In its grosser form, external transportation leads to an outright

perforation of the root.

INTERNAL TRANSPORTATION: can also occur when excessively

large instruments are used in the apical 3rd of a curved canal.

Eventhough a perforation may not have occurred, there is a

definite loss of the narrowing apical preparation and the spatual

relationship of this preparation to the apical foramen.

Internal transportation due to use of larger instruments at the

apical area of curve canal leads to;

1. Loss of constriction.

2. Change in relation between the apical preparation and apical

foramen.

3. No perforation occurs but internal transportation (ledge).

Generally, both types of transportation of the apical

foramen can be prevented by confirming cleaning and

shaping procedures within the canal system by;

1. Using precurved instruments.

2. By resisting the temptation to excessively enlarge the apical

portion of the canal.

3. By using voluminous irrigation.

4. By preventing a build up of dentin shavings during

instrumentation.

5. Preparing by frequent recapitulation.

METHODS OF PREPARATION:

Preparation design has an influence upon the final seal.

Step-back or flaring type of preparation of the apex is found to be

advantageous over the conventional method (Alison et.al. 1979).

Flared preparation provides a strong apical dentin matrix (Weine,

1982).

Chances of apical ripping and shafting of foramen are less with

step-back technique (Christie and Peikoff, 1950).

CONCLUSION:

The morphological variations and the technical challenges

involved in the treatment of apical 3rd seem infinite.

Resorption, weeping apex, immature foramen are some of the

areas which continue to invite fresh techniques from clinicians and

researchers.

It has to be remembered while treating the apical 3rd that the

proximity of the apices of certain teeth are in close association with

important structures like maxillary sinus and inferior alveolar nerve.

Inadequate attention and improper handling of the apical 3rd of

these teeth may lead to serious clinical implications.

With the introduction of high technology and advancement of

science and endodontics, the problem is bound to be solved.

RE FERENCES;

1. Textbook of Endodontology by Samuel Seltzer.

2. Endodontic Practice by Grossman.

3. Pathways of the pulp by Cohen.

4. Endodontics in clinical practice by F.J.Harty.

5. Current Trends in Endodontology by Parameswaran.