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Treatment of periapical pathology with Retrograde Endodontic Technique Atousa Rashedi

Institute of Odontology Karolinska Institutet Huddinge, Sweden

Summary The aim of this study was to review the definition, indication, and treatment possibilities and case presentations of a retrograde therapy. Definition of retrograde endodontic treatment is removal of periapical pathology due to failure of root canal treatment, root fracture, obliteration of the root canal or unidentified canals. The radiographic feature is radiolucency surrounding the bone at the apex of the root. A sinus tract will and therefore the pus will decrease the intensity of the pain. Retrograde endodontic treatment involves laying a mucoperiostal flap and remove of inflammatory tissue, to achieve optimum access to the root end. The reason is to make a root resection and sealing the cavity with apical sealant materials.

Introduction The definition of retrograde endodontic treatment, apexectomi, is removal of periapical pathology due to failure of root canal treatment. Non-healing periapical pathology associated with endodontically treated teeth is customarily managed by retreatment of the previous therapy. Root-end resection or retrograde endodontic treatment is less often the first optional treatment. The treatment might be the option after an unsuccessful retreatment or if retreatment is impossible.

Before, the term ¨conservative treatment¨ was used as a synonym for nonsurgical treatment. According to Chivan the term indicates that periapical surgery is radical but it should be considered that this procedure might save the tooth and therefore it cannot be counted as radical [1].

The cause of periapical pathology is infectious products from an infected pulp space or from the peiapical area. Microorganisms that colonize these areas release their product into the periapical tissue and causes a lesion in the bone. The severity of the destruction is depended on the amount of products as well as the resistance of the host. The inflammatory development might be acute, and leading to a periapical abscess or chronic with sign of a periapical granuloma or a cyst.

In the past century, endodontic surgery has been done frequently and was included in almost all cases of periapical pathology. The clinical experience and usage of different advanced techniques and materials, indicates that conventional re-orthograde endodontic treatment succeeds in a higher rate without a retrograde procedure and therefore the frequency of periapical surgeries are less than before.

Clinical and Radiographic Features The clinical and radiographic characteristics for acute periapical infections are:

1. Tenderness to percussion and palpation of the mucosa at the level of the . The tooth has no sensitivity to cold or electrical tests. The tooth is though tender to percussion at the level of root apex

2. In severe cases the patient experience spontaneous throbbing pain. A widening of the periodontal ligament might be shown on the x-rays. The reason for developing either

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acute or chronic periapical abcess, could be from an improper made root filling, a root fracture, an unidentified root canal or false obliteration.

Chronic periapical abscess can be developed from an acute periapical abscess or might have a quiet development. The chronic periapical abscess might develop even though the tooth has been endodontically treated. The accumulation of dead cells and consequent release of lysosomal enzymes produces pus, which is drained through a sinus. A sinus tract may open exrtraorally in the oral mucosa (Fig. 1.1), in the skin (Fig.1.2), or internally in maxillar-sinus, nasal-cavity or in the floor of the mouth and releases the symptoms as the pus is drained. Patients usually complain over bad taste in the mouth.

Fig. 1,1: mucosal sinus drainage Fig. 1,2: Extraoral sinus tract The radiographic feature is a radiolucency indicating inflammation and bone loss around the apical part of the root. This area is sometimes surrounded by a band of radiopaque sclerotic trabeculae, which is a chronic sign [2]. Removal of infected pulp tissue is a prerequisite fir successful healing. A conventional root canal treatment, instrumenting the root canal with endodontic files and irrigating with hypo-chlorite a solution and using antibacterial calcium-hydroxide in the canals as an inlay, before the final root-filling. If the above-mentioned treatment has failed a retrograde treatment might be the best option if an orthograde retreatment is impossible.

Retrograde endodontic procedure involves laying of flaps and removal of tissues from outside the root canal space, including bone, periodontal membrane, and periosteum [3]. After root end is exposed and detected with microscope, there are possibilities to examine and recognize the pathology behind the periapical pathosis, and thereafter a proper treatment. Retrograde endodontic surgery may induce postoperative pain, oedema and discoloration, which is all reversible.

Periapical microbiology There are many different ways for microorganisms to invade the dental pulp. Either through an open cavity, caused by dental caries, or by trauma that has removed the barrier of enamel and the dentine. Microorganisms are also able to penetrate into the pulp through the dental tubules, especially when the pulp has been injured. Their entry might be through the salivary contamination or during dental preparation. Another way is through the gingival sulcus or periodontal ligament. If the periodontal destruction develops to a sufficient degree, the canal might be exposed to microorganisms without any caries or trauma. Failure of root canal treatment or retreatment could be caused either by presence of bacteria in the root canal system, or occurrence on the apical part surface of and occasionally in the periradicular tissue near to the apical foramina [4].

The correlation between bacterial invasion and endodontics has been a basic science. Gram-negative anaerobic microorganisms are not clinically found in the synergistic nature. These organisms need specific nutrients for growth. Many species that are present in the

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normal, non-pathological oral flora may become invasive and produce toxins in another environment together with other microorganisms. Bacterial infection of the dental pulp may be the cause of a periapical pathosis.

The presence of E.faecalis from the root canals of teeth in which the previous treatment has failed is notable. According to a study made by Sundquist et al [5] the microbial flora was evaluated before and after orthograde endodontic retreatment and the presence of E.faecalis was shown in 9 cases of a total of 54 canals. The bacterial test was taken during three times, first when the gutta-percha was removed without any antibacterial irrigation and the canals were left empty to allow any surviving bacteria in the root canal to multiply to a level that would be detectable at the next appointment. A week later bacteriologic samples were taken without any use of antibacterial solution. After the final instrumenting the canals were filled with calcium hydroxide paste. The third appointment began with the bacterial test from the canals with sterile saline solution. The root canals were then filled with gutta-percha. A follow up examination was made yearly. In samples taken at the time of root filling, microorganism were found from six canals and four of these lesions did not heal. E.faecalis infected three of these 4 canals and the fourth tooth contained Actinomyces israelii. The success rate in this study between the teeth that had a positive bacteriological sample at the time of root filling was very low 33% in comparison to 80% from those that was not infected.

Cells in the periradicular lesion The size of a periradicular lesion is depended on the balance between microorganism and their toxins against the host defence. The zone of infection (A) in the periradicular lesion consists of PMNL-cells that are lined up as a membrane to prevent bacterial invasion (Fig 2). These cells are presented at the apical foramina and releases lysosomal enzymes, which causes necrosis [6].

Fig. 2: Different zones in the peri- radicular lesion

Next layer is the zone of contamination (B), affected by diffuse antigens and irritants from the root canal and is dominated by plasma cells and lymphocytes. Adjacent to this layer is the zone of irritation (C), were osteclasts and macrophages are the dominant cells. Macrophages are able to remove and destroy cellular debris in this zone due to lack of root canal antigens. Beyond this layer is the zone of stimulation (D). This zone consists of young fibroblasts and osteoblasts, which produce a fibrous capsule around the lesion [6].

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Examination and indication for retrograde therapy As mentioned above some cases of retreatment are better treated with a retrograde technique. This can only occur if the present root filling is prime and is extended to an adequate level. Such cases are those with recurrent exacerbations. Another reason for a retrograde therapy is when the root configurations have a sharp dilacerations. These teeth need to be instrumented as far as possible to clear the most apical part of the canal from necrotic pulp-tissue and bacteria to achieve a healing process in the inflammatory bone lesion. If the healing fails, the treatment should be done by root-end resection. There are other cases were the most convenient access is through the apex. Such cases are when the tooth previously was treated with a post-and-core and a crown, and trauma, which can cause calcific degeneration, and result in a microscopic obliteration. Even if a total obliteration is visually observed, this space is enough for the bacteria to survive in.

Contraindication Beside local contraindication there are general contraindications were the medical condition is complex and must be discussed with the patient's doctor. The local contraindications are; I) poor periodontal support, II) non-restorable tooth and III) poor access. I. Apicectomy is also contradicted where the root is too short, or there is an extensive

gingival recession, or extensive marginal periodontitis. II. If there are not any optional treatment because the tooth is carious or fractured. III. Another reason is if the access to the apical part of the tooth is severely restricted and

it is difficult to carry out endodontic surgery.

Retrograde endodontic treatment Though it appears that a relatively low number of cases require surgical treatment there are however, some cases where the retrograde therapy is the most important adjunct to a successful treatment. Orthograde retreatment versus apical surgery has specific advantages, clinical meaning, risks, and their selection involves a decision-making process [8]. According to Friedman et al the result of retrograde treatment of periapical pathosis on teeth were no endodontic treatment was done, may not be satisfactory. A conventional endodontic orthograde treatment is always required for removal of the necrotic pulp tissue, which infects the surrounding periapical tissue [9].

Surgical procedure A successful treatment of a periapical surgery is depended on the hemostasis among other factors. Hemostasis is essential for better visualization and good environment for replacing of the retrograde filling material. A good hemostasis-agent makes the hemostasis easy to achieve and manipulate, is biocompatible, does not impair healing, is reliable and is relatively inexpensive. There are different ways to achieve hemostasis; one is through pre-surgical local anesthetic with 2-3 carpules of epinephrine with multiple infiltration sites, the other is during surgery. Putting a sterile cotton pellet dipped in epinephrine into the bony crept after removal of granulation tissue. Calcium sulphate is an alternative hemostasis agent, which is biocompatible and will be dissolved in 2 - 4 weeks. Another way to accomplish hemostasis is by using ferric sulphate solution or post-surgical compression for decreasing the bleeding and post-surgical swelling. [10,11]. When an optimum hemostasis is achieved the flap can be raised. There are three different incision-methods; a) intrasulcular flap, b)submarginal flap, c) semilunar flap or vertical incision.

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Intrasulcular Intrasulucular flap extends along the gingival sulcus of the tooth being treated. There is a vertical incision at each end, which should give sufficient access to the root end these two cuts are united with a sulcus incision. This flap provides a good visualisation for the surgeon and the blood supply to the flap is being kept. The flap is elevated and access to the apex foramina is achieved with an elevating instrument (Norbergs Raspatorium). Postoperative pain and swelling are usually minimal. A possible disadvantage is gingival recession, this is normally a concern in the anterior region [12,13]. Palatal flaps are only used for treatment of palatal roots of molars or premolars. The incision involves several teeth along their gingival sulcus. Here there is a need of carefulness to not damage the palatine neurovascular bundle.

Submarginal The submarginal flap is made in the attached gingiva and follows its contours. This flap cannot be used in the mandible because of restricted width of the attached gingiva. The reason of choosing this flap is when the gingival tissue should be undisturbed, particulary adjacent to a crown. The flap should be minimized as possible to prevent ischemia of the remaining attached gingiva. The semilunar incision is entirely in the alveolar mucosa and is curved at its ends. This method is not widely used because of the small surgical access and the cause of ischemia [14].

Vertical incision This is made vertically over the root and is reflected vertically over the apex. This does not cut the vessels off and could be used if the roots are long, but the surgical access is limited and the incision may directly lie over the blood clot in the bony cavity.

Root end resection If any reverse filling is to be done, the root tip has to be prepared to receive the filling material. In the past, the preparation was made with burs, diamond stone and carbide burs. In the beginning of 1990s the ultrasonic devices became available, which has become more and more effective and relevant in the apical surgery. There have been some reports of crack formation after ultrasonic root-end preparation. One study showed that the results of ultrasonic instrumentation produced significantly greater strain on average than that generated with the microhandpiece system [15,16].

Fig. 3: Ultrasonic tip

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The ultrasonic tip is smaller than the burs, that were usually used (Fig.3). This tips converse tooth structure and give more parallel preparation that makes the root end filling more precise and decrease the risk for microbacterial leakage. Parallelism, which is accomplished with ultrasonic machine, is an important issue during a retrograde preparation, and is achieved with an axial and lateral force. This allows an improved sealing [17]. The relevant clinical features about using ultrasonic devices, because of their various angled design and the small size of the retro-tips, are the greater access to the apical part of the root and it requires smaller osteotomy for surgical access [18]. The ultrasonic tips allows the operator to make very precise preparations, because of the ease which it removes old gutta-percha and the way it cleans and widen canals narrowed by reparative dentine to make an excellent shape for the apical sealant.

Two different types of preparation have routinely been used by endodontists. One is the "class I" and the other is, "slot" or "matsura type". Before the preparation of the apex, the root must be bevelled. Bevelling is obtained by use of fissure bur on a handpiece and the cut should have an approximately 45-degree angle to the long access of the tooth (Fig.4). This with the help of a specially designed mirror (Fig.5) allows a better visualization of the entire root face.

Fig. 4: Root tip Bevelled 45-degree

With good bevelling technique of the root tip no significantly reducing root length is accomplished. After bevelling, the configuration of the root is either round, oval or 8 shaped as shown in Fig. 6. It is essential not to leave unclean space in the root end preparation, therefore the preparation should be extended to a well-condensed gutta-percha filling. Class I preparation is very similar to the occlusal class I preparation, only in a miniature form. If the root end canal has an oval or 8 shape, the proper preparation will be using a tip on the ultrasonic device and make it round, but touching preparations. The slot or Matsura preparation is used when it is inconvenient to utilize the other mentioned technique. This preparation requires much less periapical bone removal. Therefore the slot technique is used in cases where removal of tooth structure will lead to an insufficient root ratio crown, such examples are maxillary bicuspid and molars near the maxillary sinus and mandibular molars near the mandibular canal. The preparation is started at the apex of the root, and the bur is brought towards the cervical margin and then with help of an ultrasonic device or smaller burs the corners of the preparations are sharpened to provide undercut for retention of the root end sealant [19,20].

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Fig. 5: Miniaturemirror Fig. 6: Root end Table. 1: Comparison of 12- month success rate for the treatment methods [21]. Groups treatment of retrograde cavity success rate Group 1 Microbur and IRM sealant 52 cases 65% Group 2 Microbur, IRM sealant and CO2 laser 54 cases 67,5% Group 3 Ultrasonic device and IRM sealant 76 cases 95% Group 4 Ultrasonic device and CO2 laser 72 cases 90% A 4-year study that included 320 cases compared different root-end material and techniques are presented in table I [21]. Group 2 and 4 received CO2 laser treatment on the exposed radicular dentine with 1 W intensity (CO2 is a laser-melted hydroxy apatite). On the other two groups IRM sealant was used and polished. This study reported that there were no significant differences between uses of CO2 laser and IRM sealant. The only difference was between the use of micro-burs or ultrasonic devices.

Magnifying glasses Use of loupes and magnifying glasses have been common among dentist for a long time. Recently operating microscopes have been introduced as an endodontic support during operating theatres. In addition this makes the surgery better and has given the ability to take photos of high quality and magnification for use in presentation and articles. Some questions that can be discovered if the dentist is using the surgical operating microscope are: 1. Should a reverse filling be placed or is the existing filling sealed? 2. Is there a septum between the two major canals that should be addressed? For example in the mesial roots of mandibular molars and mesiobuccal roots of maxillary molars. 3. Is there an additional canal or is there a fracture line?

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4. Evaluate the last therapy and why it didn't succeed.

Root-end filling materials The purpose of a root-end-seal material is to prohibit bacterial invasion from the remaining intra-radicular pulp-tissue into the periradicular space and to prohibit intrusion of blood serum into the apical foramina. [22]. Other functions of an optimum apical seal are, insolubility in the tissue fluid and high dimensional stability. It should also adhere and adapt to the dentine walls of the preparated root end, prevent leakage of microorganism and be biocompatible.

A great variety of different materials have been suggested as apical sealants; amalgam, glass ionomer cement, gutta-percha, zinc oxide-eugenol based matrix, composite resin, MTA, cavit (eugenol-free temporary filling) and gold foil. Some of these materials are presented down below.

Amalgam Amalgam has been documented with good clinical results. When amalgam is used as a restorative material, its seal improves with time as a result of the accumulation of corrosion particles [23]. Its potential disadvantages are; initial leakage, secondary corrosion, release of mercury and tin, moisture sensitivity, microleakage as a result of needing an undercut preparation, staining of hard and soft tissue and management control of particle scatter. Amalgam is known to undergo corrosion intraorally, and will also appear intraradiculary. But there has been some reported cases, were some patients have developed discoloration of the oral mucosa adjacent to the apical part of the tooth [24,25].

Glass ionomer cement This cement has been suggested to be more sensitive to contamination with saliva and blood than amalgam [26]. The Chemfil powder has to be mixed with equal parts of distilled water containing calcium aluminium silicate and polyacrylic acid. The differences in periapical healing according to Jesslèn et al after using either amalgam or glass ionomer cement are presented in table 2. Of the 82 teeth included in this study 41 were sealed with amalgam and 41with glass ionomer cement. A 5-year evaluation should exhibited statistically significant differences in success or failure rates [27]. Table. 2: Differences in periapical healing when amalgam or glass ionomer cement are used as apical sealant after apical surgery [27]. Number of teeth_________________________ Classification 1-year follow up 5-year follow up____ of healing amalgam glass ionomer amalgam glass ionomer Complete healing 18 19 20 28 Improvement 19 18 15 7 No improvement 1 1 0 1 Failure 3 3 6 5

Gutta-percha For being able to use gutta-percha, the surgical access has to be excellent and therefore cases must be carefully selected. The gutta-percha could either be softened by heat, cold condensed, softened by chloroform (Fig.5). The use of gutta-percha has been limited in the clinical use, because of the tissue reaction is not favourable as in use of eugenol containing sealant [27].

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Super EBA and Zinc oxide-eugenol Because of these disadvantages other materials have and the advantage of the expansion capacity of Zinc Oxide-Eugenol, it has been advocated as root end filling materials. Such example is Super EBA, which is zinc oxide-eugenol based cement. The disadvantages with super EBA, are moisture sensitivity, irritation of vital tissue, solubility in tissue fluid and clinical handling difficulties [25].

Composite resin Composite in combination with saucer preparation and excellent moisture control has achieved good results over both short and longer period of time [28].

Mineral trioxide aggregate An experimented material, mineral trioxide aggregate (MTA) has been reported to seal all of the pathways of communication between the root canal and the periradicular tissue. MTA root repair material is a powder consisting of fine hydrophilic particles that set in the presence of water. Hydration of the powder creates a colloidal gel that solidifies to form a strong barrier. The principles of the compound are tricalcium silicate, tricalcium aluminate, tricalcium oxide and silicate oxide [25]. MTA has several advantages over existing root end materials, it is easy to mix and is not essential to use in a dry field. A possible disadvantage would be the long setting time. The physical and chemical compounds of MTA are presented in table 3.

Fig. 7: Radiograph of a MTA root end filled maxillary incisor 2 years after placement.

MTA material is indicated for use as; a) root-end filling material (Fig.7) ; b) for the repair of root canals as an apical plug during apexification; c) for repair of root perforations during root canal therapy; d) as a pulp capping material Table. 3: Physical and chemical properties of MTA [29]. Characteristic Description Physical state solid (powder) Colour grey Odour no special odour pH in water 12-13 Boiling point > 1000º C Solubility in water slightly soluble (0,1 -1,0%)

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Complications After surgical treatment, patient can have symptoms such as postoperative pain, swelling and discoloration. Most of these patients are absent from work after the surgery and they consume self-prescribed analgesics. While patients treated with an orthograde retreatment usually are asymptomatic after the procedure. A study made in Gothenburg indicated that retrograde therapy brought greater indirect costs than nonsurgical retreatment [30].

Case reviews

Case I; surgical incision 1. Need of a preoperative radiograph using parallel technique. (Fig 8.1) 2. Pain control after an adequate analgesia. 3. Incision design, vertical and sulcus incision. (Fig. 8.2 - 8.3) 4. Flap reflection, removal of granulation tissue and root end resection. (Fig. 8.4) 5. Sealing the apical cavity with above-mentioned materials. (Fig. 8.5) 6. Suturing of the flap. (Fig. 8.6) 7. Postoperative control and removal of sutures. (Fig.8.7)

Fig. 8,1: Pre surgical x-ray Fig. 8,2: Pre-surgical planning

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Fig. 8,3: Sulcus and vertical incision Fig. 8,4: Flap reflection

Fig. 8,5: Suturing Fig. 8,6: Post-surgical X-ray

Case II

1. Re-examine the access to the pulp chamber. 2. Re-evaluate canal preparation. Are there any canals that have been missed? Fig 9.1 3. Redress the canal with calcium hydroxide after irrigating with Sodium hypochlorite

solution. 4. Obturate the canal with gutta-percha and re-evaluate the treatment. 5. In the absence of periapical healing after retreatment, consider periapical surgery. The

cause might be intraradicular or extraraducular infection that cannot be accessed by conventional orthograde endodontic treatment. As shown in fig. 9.2 the apical delta prevented an adequate treatment.

6. Root-end resection, involving curettage and cleaning of the root apex with ultrasonic device obturation made with amalgam (Fig.9.3).

7. Almost complete healing after 6 months (Fig. 9.4).

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Fig. 9,1: Pre-operative Fig. 9,2: Residual infection.

x-ray.

Fig. 9,3: Postoperative Fig. 9,4: Healing 6 months

x-ray. after apical surgery.

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