**3.1 Sequelae of pulpal infection in immature root canal**

Caries exposure related to vital pulp can present clinically with mild to moderate symptoms. In this case, vital pulp therapy like pulp capping [25] or pulpotomy [26, 27] using calcium hydroxide [Ca(OH)₂] or Mineral Trioxide Aggregate (MTA) would allow full root maturation. In spite of this treatment approach, usually the pulp goes necrotic and presents with asymptomatic or symptomatic apical periodontitis.

Periapical radiolucency of the dental follicle in immature teeth makes it hard to diagnose periapical periodontitis from dental radiographs. For this reason, apical periodontitis should be confirmed with clinical examinations such as cold tests, percussion, palpation, swelling and the presence of sinus tract. Once the pulp is confirmed to be necrotic in an immature tooth, a regenerative procedure may allow normal root maturation.

#### **3.2 Dental anomalies that contribute to pathogenesis of pulp in immature teeth**

Among congenital tooth anomalies, dens evaginatus is the most prevalent anomaly that causes early pulp devitalization and subsequent pulp necrosis in immature teeth [9, 28]. Dens evaginatus is a developmental anomaly causes a formation of accessory cusp (tubercle) project in the tooth surface. This tubercle consists of enamel, dentin and pulp tissues. With normal physiological tooth wear, the pulp gets exposed, leading to asymptomatic pulp necrosis in immature teeth [29]. Nevertheless, pulp exposure can be avoided if the tubercle is discovered early. Simple occlusal adjustment and topical fluoride application increases the enamel hydroxyapatite which contributes to enamel remineralization. Another treatment option would be the use of flowable composite resin sealant or in the case of pinpoint pulp exposure shallow pulpotomy using layer of tri calcium silicate cement (MTA, Biodentine®) or calcium hydroxide would be a conservative solution in case of dens evaginatus and thus avoid early pulp devitalization. Dens invaginatus is described as the folding of enamel into dentine which increases the risk of caries development and pulpal involvement. However, pulpal exposure can be avoided by simple preventive measures such as a fissure sealant.

## **4. Endodontic regeneration in traumatized teeth**

Many studies have revealed some situations in which an immature root may regenerate pulpal tissue and dentine after trauma spontaneously. Kling et al. [30] monitored 154 replanted avulsed teeth (72 were immature teeth) radiographically for pulp revascularization.

In all mature teeth with apical foramen width 1 mm and smaller, revascularization did not occur, while 18% of the immature teeth (apical foramen width larger than 1.1 mm) revealed signs of revascularization. Instead, all teeth that did *Regenerative Endodontic Procedure in Immature Permanent Teeth DOI: http://dx.doi.org/10.5772/intechopen.96986*

not respond to pulp revascularization revealed signs of periapical lesions and/or external resorption. Post-operative systemic antibiotics did not have any effect on the probability of pulp/dentine revascularization in replanted avulsed teeth in this study. The same result regarding post-operative systemic antibiotic use after avulsed teeth replantation was found in a later study by Andereason et al. [31]. Two types of hard tissue formation were found in teeth with revascularized pulp. There was either normal root maturation in both length and thickness of the root, or radiopaque material separated from the root and continued to grow with alveolar bone, while the tooth length arrested [32].

#### **4.1 Effect of extra oral time of avulsed tooth on spontaneous regeneration**

Extra-alveolar time can be defined as the time that the avulsed tooth spends out of its original socket. Andersson et al. [32] Found that extra-alveolar time of avulsed teeth was less than 45 minutes, the probability of revascularization was 39%, compared to 11% in teeth with extra-alveolar time more than 45 minutes. 60 minutes of extra-alveolar time can cause necrosis of the Periodontal Ligament (PDL) membrane and cells, which leads to external root resorption and the inhibition of further root development. When avulsed teeth are implanted immediately or within 15 minutes, no resorption was noted. In addition to this, after 15 minutes, replanted avulsed teeth revealed some root resorption but not in a progressive pattern [32]. Extra-alveolar time of less than 45 minutes shows better root formation and less inflammatory resorption when compared to times longer than 45 minutes. There was no significant difference in regeneration and subsequent root formation between different extra-alveolar storage media (dry medium, wet media [saliva, tab water, etc.], and combination medium [dry then wet]) for the avulsed tooth. Although it is not significant, a dry extra-alveolar time of less than 45 minutes led to more frequent root formation and completion [33].

For avulsed teeth kept in a wet storage media (saliva, tap water, etc.), the survival of the pulp is significantly greater when it is kept for less than 5 minutes. This is because only part of the pulp that communicates with the storage medium is the pulpal tissue in the apical foramen; the body of the root protects the rest of the pulp. However, if the apical foramen were to be contaminated with bacteria due a longer duration of storage, the vascularization process as a whole would be jeopardised [31].

The extent of root maturation is related to the pulp revascularization; in healing pulp, more root maturation is found compared to necrotic pulp. Immature roots with large apical foramen had more tendencies toward pulpal tissue regeneration; large apical foramen facilitates the flow of apical papilla stem cells into root canal easier than a mature, narrow apical foramen.

#### **4.2 Factors that could contribute to REP in traumatized teeth**

A factor that had a strong correlation with pulp regeneration in avulsed teeth is the length of the pulp canal (the distance between the apical foramen and pulp chamber). Since pulp regeneration may be arrested by infection process, the longer the distance to be regenerated, the more chances there are of an infection occurring, and thus less chance for the pulp to regenerate [34]. The correlation between the length of the pulp canal and the probabilities of pulp revascularization has also been found in another study of revascularization of auto-transplanted 370 premolars [35].

Partial or arrested root formation is generally followed by bone ingrowth and formation of internal PDL tissues. Hertwig's epithelial root sheath (HERS) is

presumed to prevent the invasion of bone and PDL derived cells inside the canal and thus reduce disturbance to root development. This presumption is explained by a partial or total loss of HERS being accompanied by partial or arrested root development. In case of pulpal necrosis, root development and maturation may occur because HERS can tolerate trauma to avulsed tooth and damage by extra-alveolar time [33].

The predominant root resorption found in replanted avulsed teeth is external replacement resorption (Ankylosis), followed by inflammatory root resorption and finally, external inflammatory surface resorption. Inflammatory root resorption is most common in immature roots, while replacement resorption (ankyloses) is found more in mature roots [36]. Although bone remodelling is higher in young adolescents, rate of resorption in general is not affected by age. However, if the HERS and PDL are viable, age would not make a difference in the rate of resorption. In addition, Root Canal Treatment within the first three weeks (usually the third week) after tooth replantation can reduce the rate of resorption [32].

## **5. Follow up**

In follow-up visits, clinical and radiographic outcomes should be evaluated. Clinical evaluation includes absence of pain on percussion and palpation, no presence of soft tissue swelling and disappearing of sinus tract if present before treatment. The tooth response to sensibility tests (cold and EPT) should be recorded, but the absence of response does not indicate treatment failure. Radiographic evaluation includes: resolution of pre-treatment periapical radiolucency if it was present, further root length maturation and an increase in canal wall thickness.

There is no standard follow-up protocol after endodontic regenerative procedures as of yet. Nevertheless, in the published endodontic regenerative case reports, the follow-up ranged from 6 months [37] up to 60 months [38] after completing treatment. The European Society of Endodontology recommends follow-up and recall appointments every 3, 6, 12, 18 and 24 months, with annual recall after the follow-up period for the next 5 years [39].

In most endodontic regenerative cases, enhancement or resolution of periapical lesion is expected in the first 6 months. Wiggler et al. [40] endorse a recall every three months in the first year after completion of treatment and then every six months, unless symptoms developed.

#### **6. Conclusions**

In conclusion, regenerative endodontic procedure is a non-invasive treatment that restores the dentin/pulp complex in necrotic immature teeth, and is now an essential part of the endodontic speciality. In many case reports it shows a promising potential for saving necrotic immature teeth and helping the continuation of root maturation. Unlike conventional MTA or calcium hydroxide apexification, it tends to promote further root development and increases root canal wall thickness, which will improve the overall survival of the tooth.

*Regenerative Endodontic Procedure in Immature Permanent Teeth DOI: http://dx.doi.org/10.5772/intechopen.96986*
