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Introduction The root apex is of interest to endodontists because the stages of root development and the type 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 interrupt it correctly in radiogaphs, and to felt it through tactile sensation during instrumentation are essential for an effective rendering of the treatment of root canals. Achievement of a perfect oral at the apex using an invert filling material is the ultimate goal for every endodontist. Existence of apical 3rd: 1. Development of the root apices. 2. Pulpal tissue within. 3. Morphology and variance. 4. Ability to interrupt correctly. 5. Fell it through tactile sensation during instrumentation. All essential for a successful treatment of the root canal.

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Development of the root apex: 

The development of the root begins after the enamel and the dentin formation has reached the future cemento-enamel junction.

The enamel organ play an important part in the development by forming Hertwig’s epithelial root sheath, which molds the shape of the roots and initiates radicular dentin formation.

Hertwig’s root sheath consists of the outer and inner enamel epithelial 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 first layer of dentin has been laid down, the epithelial root-sheath loses its structural continuity and its close relation to the surface of the rooth.

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 malassez”.

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There is a pronounced difference in the development of Hertwig’s epithelial root sheath in teeth with one root and in those with 2 or more roots. 

Prior, to the beginning of root formation, the root sheath forms the epithelial diaphragm.

The outer and inner enamel epithelia bind at the future cement-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 and growth of the root.

The proliferation of the cells of the epithelial diaphragm is accompanied by proliferation of the cell of the connective tissue of the pulp, which occurs in the area adjacent to the diaphragm.

The difference of odontoblasts and the formation of dentin follow the lengthening of the root-sheath.

The free-end of the diaphragm does not grow into the connective tissue, but the epithelial proliferates coronally to the epithelial diaphragm.

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At the same time the connective tissue of the dental sac surrounding the root-sheath proliferates and divides the continous 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 it 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 lags 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 apposition 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 trunk 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. 4


2 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 ends of these horizontal epithelial flaps 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 openings, root development follows in the same way as described for single-rooted teeth.

Type I

:

A single canal extends from the pulp chamber to the apex.

Type II

:

2 separate canals leave the pulp chamber and join short of the apex to form are canal.

Type III

:

One canal leaves the pulp chamber, divided into 2 within the root, and then to exist as one canal.

Type IV

:

2 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 2 separate and distinct canals with separate apical foramina.

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Type VI

:

Two separate canals leave the pulp chamber, merge in the body of the root and redivide short of the apex as 2 distinct canals.

Type VII

:

One canal leaves the pulp chamber, divides and then regions within the body of the root and finally redivides into 2 distinct canals short of the apex.

Type VIII :

3 separate and distinct canals extend from the pulp chamber to the 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-VIII). Classification of the root apex is essential for endodontic practice, particularly when dealing with pulp-involved or pulpless teeth of children and young persons. As a general rule, as 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 the root apices. C.I. Eruption 6-8 Calcification 10-12

L.I.

Cused

7-9 11-12

10-12 13-14

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1st PM 2nd PM 9-11 11-12 12-14 13-14

1st M

2nd M

5-7 10-11

12-13 15-16


In young incompletely developed teeth the apical foramen is funnel shaped with the wider portion extending outward. The mouth of the funnel 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 pulps 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.

CI

LI

C

PM

M

2nd M

6-8

7-9

10-12

9-11

5-7

12-14

10-12

11-12

13-14

12-14

10-14

15-16

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. 7


Awareness of these is considered important for effective rendering of the treatment. The foramen can change in shape and location beucase of functional influences on the tooth for e.g. tongue pressure, or nasal pressure, mesial drift. Cementum resorption curve on the wall of the foramin fastest for the force apposition on the wall nearest the net result is 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 0.5-1mm from the anatomical apex. 

This distance is not-always constant and may increase as the tooth ages because of the deposition of 2° cementum on the outer surface of the root and 2° dentin on the walls of the root canal.

The apical foramen is not always located in the center of the root apex.

It may exist on the mesial, distal, labial or lingual surface of the rot, 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.

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An endo instrument protruding beyond the foramen on either buccal or lingual / palatal aspect cannot be discerned 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 pre molars.

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 AF located at the anatomic apex but it is not so always. AF located 0.5-1mm away from anatomical apex. Distance may vary with age either due to : Increased dentin, increased cementum deposition. 

In maxillary Class I, Class II, 1st premolar and mandibular 2nd premolar AF open may coincide and apex.

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But in all mandibular teeth (except mandibular 2 nd premolar) and maxillary molars opening does not coincide with anatomical apex.

Many believes the apical foramen to open at the center of the root apex but not so can open either M, D, B, C more often B/L.

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 0.5-1mm from the apical foramen.

Again, the portion of the apical constriction varies with age as deposits of 2nd dentin, within the root canal, site of the constriction 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.

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

If the constriction is destroyed by once-instrumentation and an apical stop is not developed the chances of long term success are greatly lessened. Repeated instrumentation extending beyond the constriction is

unwarranted. It causes peri-radicular inflammation and often destroys the biologic constriction of the root apex. Although same, 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.

Cemento dentinal junction: Intentional overextension of instruments post-treatment is warranted only when damage must be established the periradicular tissues such as in an acute apical abscess etc. According to Kutler (1958), the root canal is divided into a long conical dentinal portion and a short funnel-shaped cemental portion. 

The cemental portion is usually in the form of an inverted cone with its narrowest diameter at or near the cementodentinal junctions and its base at the apical foramen.



However, occasionally the cementum abuts directly on the dentin at the apex.

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

At times, the cementum extends for a considerable distance into the root canal, timing the dentin in an irregular manner.

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Apical Constriction: Narrowest portion of the canal coincides with the CDS location in relation to apical foramen. Usually located 0.5-1mm away from AF but this distance can change with age i.e. deposition of cementum, deposition of 2 nd dentin – as in cases of ortho treatment or perio disease. Shape of canal: Said to have a conical dentinal portion and inverted cone cemental portion. The apical constriction located at the narrowest opening of the inverted cone or at the cemento DS bases of inverted cone is at the apical foramen. Cementum seen to covered apex of root and sometimes extend into the root canal a considerable distance. Deposition of cementum varies on walls. Clinical sign: It is believed that the obturation and instrumentation within the root canal should be limited upto this apical constriction or CDS. As this AC acts like a artificial ledge and provides apical dentin matrix for condensation on gutta-percha. However over instrumentation beyond AC can lead to:

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-

Loss of biologic constriction.

-

Over extension beyond foramen and

-

Peri-radicular inflammation. Situations are especially likely to occur in periodontally positioned

teeth or in teeth which have been moved orthodontically. In those instances, the root canals as well as the apexes may almost become obliterate by heavy deposition of 2° cementum. The extent 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 tissues varies among the teeth of different patients.

No definite morphological pattern of the cementodentinal junction is found consistently.

The thickness of cementum around the apical foramen is inconsistent and varies greatly.

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Significance: The significance of the cementodentinal junction 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 0.507mm in young people and 0.784mm 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, Lateral canals: Cause: Any disturbance to the tooth during formation of the root apex results in discontinuity of epithelium in Hertwig’s epithelial RS. Hence failure of dentine formation and cementum deposition at that site leading to formation of a channel. These accessory canals usually located in the apical area and are continuous with the main canal. They end at access foramen.

Incidence: These accessory canals are usually seen in younger patients. As with age these channel close with cementum obturation.

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Certain cases accessory canals open at right angles to main chamber especially at furcation areas of molars or cervical region of roots. These are termed at lateral canals.

Significance: 1. These canals act as avenues for smear of infection / from infected pulp to pulp or vice versa i.e. endoperiolesions, microorganisms breakdown toxic products. 2. Instruments of these canals during endo treatment is impossible. Hence if necrotic debris left behind in channels can act as needus for reinfection. These channels are best delmided chemically with through filling and reaming. 3. Studies show these channels get obliterated with time if pulp vital. If non-vital pulp present these channels are filled with granulomatous tissue. The aim of endo treatment here would be to remove inflamed tissue and replace it by healthy connective tissue.

Accessory Canals and Foramina: 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

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Hertwig’s root sheath more frequently, this leading to the formation of many accessory canals and foramina in the apical third. These accessory canals branch off from the main root canal and end in accessory foramina. They are more common in young patients because they become obliterated by cementum and dentine 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 pulps may become inflamed or necrotic formation the presence of 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 a tooth does not appear to be a significant factor in success or failure of endodontic therapy in teeth with vital pulps. 17


If they are most endodontic therapy would fail The apical and accessory foramina provide an opening for microorganisms and / or 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 gingiva 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 necessary canals, when with thorough reaming and filing. 

Studies have shown that following endodontics 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 pulps, granulomatous tissue is found in the accessory canals prior to endodontic therapy. 18


The significance of the involved tissue remaining in the accessory foramina as a factor of failure of repair after endodontic therapy has yet been definitely determined.

Presumable,

following

endodontic

therapy,

the

inflammatory tissue should be resorbed and replaced with uninflamed connective tissue. (An accessory canal can also create a periodontic-endodontic 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 to the pulp. Denticles and Dystrophic Mineralizations: 

Selter et al; 1966 found dystrophic mineralizations in the apical pulp tissue of approximately 25% of anterior teeth.

Mineralization within:

-

and around the collagen fibres.

-

Rarely in the myline sheath of the nerves.

 -

Mineralization vary in appearance. Fine. 19


-

Diffuse.

-

Fibrillar variety.

-

Large denticles.

Young and old.

Pulp stones (Denticles): 

Compared of tubular dentin and alveolar mineralized material.

PS in – Apical 3rd – present in 15% of teeth.

Than 1 stone normally found Attached

Embedded

Adherent (only part of it is attached to the dentin) Clinical Correlations: 

Apical 3rd – difficulty in RC instrumentation during reaming and filing.

Detached Impacted into the a foramen Rendering institution difficult.

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Apical Resorption: 

Shallow resorptions of the dentin in the apical portion by the root canal are normal cocurrence.

Resorption of the apex can occur due to several reasons. In periodontally involved teeth, the cementum and occasionally some apical dentin, is completely resorbed from the root apex.

A denuded, scalloped, funnel 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 “non-eaten appearance”, it is possible that the tooth, by accident was ripped loose from its ligaments and / or was replasted. Sometimes an unexplained lesions in the region strongly suggests a malignancy. When resorption has enlarged lesion in the region strongly suggest a malignancy.

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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 depositions. Clinical significance: Due to resorption apical opening enlarged because difficulty in obtaining seal because apical closure technique to be followed. 1) The coronal pulp tissues is more felamonous whereas apical tissue more fibrous. Hence efficiently remove pulp push troach almost past coronal pulp to apical pulp and from the twist in order to remove pulp in toto. 2) This fibrous nature of apical tissue or resists apical progression of inflmmation and supports blood ---- that enter the pulp.

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Apical pulp tissue: The apical pulp tissue differs structurally from the coronal pulp tissue. The apical pulp tissue is more fibrous and contains finer cells than the coronal pulp tissue. 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 endodotic therapy: A vital pulp extirpation involves severance of the pulp tissue somewhere in the apical region of the main canal. 

Actually, the plane of severance 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 seperation can occur anywhere in the root canal or even beyond the apical foramen, somewhere in the periodontal ligament.



When the latter types of severance occurs, the ensuring hemorrhage causes a painful pericementitis. 23


Clinical sign: 1. While extirpating pulp avoid severing pulp at the coronal radicular pulp function but remove in toto. 2. If pulp is secured at the apical pulp ply junction then leads to painful periomentitis reaction and hemorrhage. 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 third is confine cleaning and shaping procedures maintainance of the spatial integrity of the foramen and 2) smooth shaping of the original course of the canal.



Adherance to this principle 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. Do not instrument beyond apical constrction because mount integrity of foramen. 2. Follow the shape of the canal because this presents damage to periradicular tissues and transportation of foramena. 24


Normal transportation can be either: 1. External 2. Internal. External transportation: takes 2 forms and may occur when instrumentation is carried out beyond the apical dentin matrix. One result is the ripping of the apical end of the canal resulting 1. tear drop, 2. elliptical or 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 third of a curved canal. Even though 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. External transportation occurs during over instrument beyond the apical constriction leads to perforations in the apical denture matrix that are teardrop, elliptical, or zipped shaped. Internal transportation: due to use of layer instruments at the apical area leads to of curved canal: 1. Loss of constriction. 25


2. Change in relation between the apical preparation and apical foramen. 3. No perforation. Generally, both types of transportation of the apical foramen can be prevented by containing 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 denting shavings during instrumentation procedure 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).

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

Chances of apical ripping and shafting of foramen are less with step-back technique (Christie and Peikoff 1950).

Prevention of transportation both internal and external: 1. Use precurved instruments. 2. Do not excessively enlarge the apical 3rd. 3. Use volumenous irrigation. 4. recapitulation. Conclusion: The morphological variations and the technical challenges involved in the treatment of the apical third seems infinite. -

Resorptions, weeping apex, immature foramen are some of the areas which continue to invite fresh viruses from clinicians and researchers.

-

It has to be remembered while treating the apical third 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 3 rd of these teeth may lead to serious clinical implications.

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-

Science in endodontics has grown to a great height compared to how it was 2 decades ago.

-

Cases which were ill-understood and found difficult to treat than are presently managed with case and confidence.

-

The drawback which is yet to be tackled is the consumption of considerable chairside time.

-

With the introduction of high technology and advancement of science in endodontics, the problem is bound to be solved soon.

Reference: 2) Samule Seltzer (2nd edition) (Endodontology). 3) Grossman (11th Solution) Endodontic practice. 4) Parimeswaram (Current trends in Endodontology) 5) F.J. Harty (Endodontics in chemical practice). 6) Cohen (Endodontics). 7) Ingle (Endodontology).

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APICAL 3RD AND ITS SIGNIFICANCE CONTENTS 1) Introduction 2) Development of root structures 3) Chemical correlation in endodontic therapy 4) Apical pulp tissue  Clinical correlation in endodontic therapy 5) Apical dentin  Clinical correlation in endodontic therapy 6) Accessory foramina and lateral canal i)

Implication of accessory foramina and lateral canal in endodontic therapy

7) Denticles and dyostrophic calcifications 8) Cementoenamel junction – Periodontal involvement 9) 2nd dentin – Clinical significance 10) Resorptions 11) Periapical region 12) Reference

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Apical 3rd and its significance copy/ dental implant courses by Indian dental academy