Periapical lesions, when they grow big and stubborn

Inflammatory lesions of dental pulp infection origin are the most common periradicular lesions of the jaws. Endodontic lesions may be classified into periapical granulomas, chronic apical abscesses and periapical cysts. These three endodontic lesions are usually unilocular, periapical radiolucencies of varying in sizes and marginal definition.

The differential diagnosis for large endodontic lesions will include odontogenic keratocysts, ameloblastomas, lateral periodontal cysts, nasopalatine duct cysts and periapical fibrous scars.

Root canal treatment (RCT) or retreatment is the first line of treatment for large endodontic lesions. If these lesions do not resolve after RCT, then apical surgery would be indicated. Other indications of apical surgery include failed retreatment cases due to calcified canals, procedural errors, eg. separated instruments or any obstructions that prevent thorough biomechanical preparation of the root canal system, apical transportation, foreign body or excessive root filling material in the periapical lesion and/or the presence of post restorations. 

Periapical inflammation is a direct effect of bacteria infection of the root canal system (Kakeshashi et al, 1965; Moller et al, 1981). The inflammation is a result of interaction between bacteria in untreated infected root canal systems and the host’s defense or immune system. Inadequate infection control of the primary infection is the main reason for the failed RCT, leading to persisting periapical inflammation.

Studies have shown that non-surgical root canal treatment failed because bacteria can survive and maintain an infectious disease in periapical lesions, although the size of the lesions were not mentioned (Tronstad et al, 1987; Tronstad et al, 1990; Sunde at al, 2002). The microbiota of persistent apical periodontitis lesions is composed of various types of microorganisms with biofilm-forming capacity. The majority of the bacterial strains of extraradicular infection were facultative anaerobes (51.6%) and obligate anaerobic bacteria (38.7%). Bacteria were also found in abscesses and cysts of extracted teeth with lesions attached to the apices (Ricucci et al, 2006). Actinomycotic infections were found to be more common in periapical infections than previously believed and apical surgery including curettage of the infected area with resection of the involved roots is the treatment of choice.  

From a histological point of view, large periapical lesions may either be granulomatous or cystic. Both periapical granulomata and cysts have the same clinical and radiographic appearance. It is difficult to differentiate between the two lesions based on radiographic density of the periapical lesion. A very well defined lining on the radiograph only indicates a long-standing lesion that is slowly increasing in size, whereas a diffuse border indicates a rapidly expanding lesion. The size of the radiolucency is also irrelevant to the histological state of the tissue as both small and large lesions can be granulomata, abscesses or cysts.

The progression of apical periodontitis to periapical cyst may be seen as an end stage of an ongoing host defense response to root canal infection. A periapical cyst is believed to be a direct sequel of a periapical granuloma. The transition from granuloma to cyst is based on gradual increasing proportions of epithelium and development of a defined lumen. Although there are several theories proposed, little is known of the pathogenesis of cysts. The prevalence of periapical cysts among apical periodontitis lesions ranges from 8.7% to 37.7%, using different criteria in histological studies. Granulation tissue with epithelial proliferation without cavitation is an insufficient diagnosis of a cyst, and is classified as granuloma. Based on strict histological criteria used by Nair et al (1996), cystic formation are often in the minority and may constitute 15% of lesions studied, 9% true cysts and 6% periapical pocket cysts. As the pocket cyst is directly connected to the root canal system, healing is likely to occur after removal of intracanal bacteria during RCT. A true cyst is self-sustaining because the lumen of a true cyst is completely enclosed by the epithelium and there is no communication with the root canal system. Since the cyst is independent on presence of absence of irritant in the root canal, it is not likely to resolve by RCT and thus surgical intervention is necessary.

Retreatment was carried out prior to surgery.  Biomechanical instrumentation reduces microorganisms and their toxins in the root canal system. Together with a good quality root canal filling and a retrofill with a tight seal, the egress of microorganisms and their toxins from the canals into the periapical tissues will be kept to a minimum. This promotes healing and ultimately, reduce the incidence of healed lesions relapsing.

To ensure a good outcome of an apical surgery, the main treatment concepts are outlined below:

1.     Magnification and illumination using the dental operating microscope

The outcome of endodontic surgery was compared between the use of dental operating microscope and loupes or no magnification, in a meta-analysis of 101 articles from the endodontic literature (Setzer et al, 2012). The probability for success for endodontic microsurgery proved to be significantly greater than the probability for success for conventional root end surgery, providing best available evidence on the influence of high-power magnification rendered by the dental operating microscope or the endoscope.

2.     Achieving profound hemostasis

Hemostasis is essential for better visualization during apical surgery to create a dry surgical site to facilitate the insertion of root end fillings and reduce post-operative bleeding. Vasoconstrictors in local anesthetics reduce the blood flow at the surgical site. The use of 1:50000, or at least 1:80000 epinephrine (as in Articaine) is recommended. Cotton pellet with epinephrine and ferric sulphate can effectively control bleeding.

3.     Always resect the root and retrofill

Resection of 3mm of the root tip reduces more than 90% of the apical ramifications and lateral canals, without compromising on the strength and stability of the tooth. Root end fillings placed after root resection shows greater healing success compared to those with only root resection. The root end cavity preparation should be at least 3mm into the root dentin. The ultrasonic angled retrotips provide easier access to the root end.

4.     Choice of retrofilling material

This ideal root end filling material should be biocompatible, regenerates periapical tissues and has excellent sealing ability. Amalgam as the traditional retrofill material is unacceptable nowadays because its sealing ability is questionable, it corrodes and tattoos the gingiva or mucosa. Mineral trioxide aggregate (MTA) and zinc oxide eugenol containing materials, such as IRM, are the more commonly used materials. MTA is extensively researched in endodontics and it is shown to be biocompatible and bioactive when set and produces a high pH before setting, which results in regeneration of periapical tissues including cementum and periodontal ligaments. However, this material requires mixing and not easy to manipulate. The endodontic pre-mixed bioceramics (Totalfill BC RRM-Putty) contains calcium silicates, zirconium oxide, calcium phosphate, tantalum oxide and fillers; has excellent mechanical and biological properties; and easy to handle.

The resected tooth was checked for clinical signs of persisting infection in every six monthly review session. Radiographic signs of density change within the lesion, trabecular reformation and lamina dura formation are evidence of periapical healing. Scar tissue is a reparative response, producing fibrous connective tissue instead of bone. Scars occurred more frequently when both the buccal and lingual cortical plates are lost. Formation of the scar tissue should not be interpreted radiographically as an endondontic treatment failure or misdiagnosed as an infected lesion. A long-term review up to four years is essential to confirm successful outcome of the apical surgery of these teeth.