1. Introduction

Periapical endodontic surgery (PES) consists of dental root resection and removal of periapical pathology. This operation is indicated in a case of confirmed bone damage at the periapical region of an endodontically treated tooth when the effectiveness of orthograde reassessment of the canals is questionable or when such treatment cannot be performed. Surgical intervention is oriented towards removing the infected part of the root and creating conditions for reliable apical sealing of the canal to prevent further penetration of bacteria and the products of their activity from the canal into the surrounding tissues.

When planning PES, it is necessary to take into consideration the initial clinical situation of the patient in general, and not only the "causative" tooth condition (the state of neighboring teeth, antagonists teeth), the type of future prosthetic construction. In different studies, the efficacy of an apicoectomy varies widely. The outcome of this type of treatment is influenced by the following factors: the tooth, the root (buccal, distal, mesial, or palatal); quality of the previously performed orthograde filling of the "causative" tooth canals; the possibility of preoperative reassessment of the root canals; selection of the material used for retrograde filling of the root canals, and operation technique. Some doctors attribute the intervention outcome to the size of the periapical lesion and to the tooth itself. Furthermore, the larger size of the pathology and the molar region are associated with less effective treatment.

The endodontic retreatment efficiency and surgical periapical intervention are currently assessed according to the generally accepted Rud classification: (1) Complete healing. Complete elimination of the radiographic dilution and formation of a new periodontal ligament, as well as the absence of any clinical symptoms. (2) Incomplete healing. Radiographic reduction in the size of the initial lesion, or the maintenance of its size, but with no clinical symptomatic evidence, and the presence of signs suggesting scar tissue formation in the pathological area. (3) Uncertain healing. Radiographic reduction of the initial lesion with more than twice the increase of the periodontal space relative to the normal, but with no clinical symptoms. (4) Unsatisfactory healing. Maintained or increased size of the radiographic field or presence of a clinical symptomatic periapical lesion.

Only a conservative approach (orthograde endodontic treatment) is fully justified in the absence of prior endodontic treatment and maximum conservation of the coronal part of the tooth. The decision to preserve the tooth should be based on the highest possible predictability of treatment outcomes. It is necessary to define the criteria for the assessment of a tooth with damaged periodontium and compare the prognosis of dental surgery and the prognosis of immediate implantation. According to Tang et al ^[1], in cases of normal healing and asymptomatic course after apicectomy 10 years following the intervention, failure of treatment reaches 43%. It is important to differentially regard the PES for different tooth types. The most common poor PES prognosis is associated with multi-rooted teeth. In contrast, single-rooted teeth may have a better long-term prognosis. The successful preliminary repeated endodontic intervention will increase the possibility of long-term single-rooted tooth retention after surgery^[1-4]. As a result, immediate dental implantation has significantly displaced PESs, especially in the premolar and molar areas. Doctors prefer to remove the tooth and immediately install the implant in the socket of the extracted tooth^[5-9].

It has also been reported that 23% of bone mass is lost in the first 6 months and 11% in the next 2 years following tooth extraction^[10]. Existing data suggest that up to 25% of the alveolar crest bone undergoes resorption within the first year after the tooth extraction in the buccolingual direction, and up to 30%–40% by the third year^[4]. As a result of resorption, the 6–8 mm wide alveolar crest size following a tooth extraction is often insufficient for implantation after a year. After three years from tooth extraction, implantation is often practically impossible without procedures directed to increase the volume of the alveolar crest.

According to the recent clinical observations, implant placement with simultaneous tooth extraction (immediate implantation) allows maximal preservation of both bone tissue and mucous membrane of alveolar processes^[11-14]. The outcome of this treatment is considered by many specialists to be stable over time in terms of functional and aesthetic parameters, as well as in terms of bone tissue preservation, compared to PES. Regardless of the system, there are more than 85% long-term success cases of the implantation in healthy patients with no local (insufficient bone volume, radiation therapy, etc.) and common risk factors (diabetes, immunity disorders, etc.)^{[10, 15-17]}.

2. Materials and methods

2.1 Patient participants

The study included 183 patients between the ages of 24 and 63 who underwent surgery between 2012 and 2020. All patients had a general medical and dental history, complete clinical examination, and X-ray examination. Among the participants, 108 received PES. In group Ⅰ, PES was carried out in 36 cases in the area of the first molars and premolars, and in 72 cases in the area of incisors and canines. 75 patients in group Ⅱ received implants with 231 implants installed. Some patients had combination of immediate and delayed implants. Accordingly, 184 of the 231 cases were immediate implants.

The following were the exclusion criteria in the selection of patients for immediate implantation: (1) Chronic somatic diseases. Significant bone resorption in periapical tissues (radiographic size - greater than 5 mm in diameter); Significant interdental bone tissue resorption (radiographic distance from the cemento-enamel junction - greater than 4 mm); Bone height from the root tip of the tooth planned for extraction to the mandibular canal, maxillary and nasal cavities of less than 2 mm; (2) Poor oral hygiene; (3) Local and generalized periodontitis of moderate and advanced stages. Patients who were excluded from the study were provided with dental extraction treatment followed by delayed implantation.

2.2 Drug treatment

In both groups, amoxiclav (375 mg, 3 times a day) and mouthwash with 0.05% chlorhexidine (twice a day) were prescribed to patients two days before and five days after the surgery. In case of pain, ketanov was given, one tablet after a meal, within two days after the surgery.

2.3 Implantation protocols

The PES was conducted in a generally accepted manner. No surgery protocol is given in this article. Only retrograde sealing was carried out with the mineral trioxide aggregate (MTA) when necessary.

The protocol for immediate implantation is as follows. With the aid of the peristome and elevators, the tooth was extracted as atraumatically as possible and, depending on the bone quality, the implant bed was prepared with the aid of drills and bone compactors. The removal of the molars was preceded by the root separation using surgical spherical diamond bur.

Before the pilot fraise was submerged on the rear (lingual or palatal) wall of the alveoli at the level of the midpoint of its height, the round stone provided a diving point in order to prevent the pilot from pushing towards the bottom of the socket. The fraise must be tightly pressed against the back wall of the socket; otherwise, it can go in the direction of the socket, which is undesirable. This error can cause subsequent contact of the pilot fraise with the vestibular plate, or even to perforation of the vestibular plate, leading to its inevitable resorption and further aesthetic and prosthetic problems. This tactic applies to all teeth, except for the lower first and second molars. In the case of the first molars, the implant is preferably placed in the area of the inter radicular septum. Implant placement in one of the sockets of this tooth is acceptable. In the second molar region, the buccal wall is thicker than the lingual wall due to the oblique ridge. Moreover, often there is an undercut under the socket on the mandibular lingual surface. If the fraise is placed along the lingual wall of the socket, the bone can be perforated entering the submandibular space and damaging a.lingualis or n.hypoglosus. In the socket of the lower second molars, the fraise must be placed along the buccal wall, even with a slight lingual inclination, to avoid the above-mentioned intraoperative complications.

We do not recommend immediate implantation at the site of the mandibular central incisors when adjacent intact incisors are present. The subsequent bone remodeling can result in the implant fenestration (bone resorption) and the roots of the adjacent teeth. This is due to the thin buccal and lingual walls of the sockets of these teeth. Delayed implantation or other alternative prosthetic techniques are preferred in this region. The proximity of the maxillary sinus is also problematic. At a very close position of the bottom, immediate implantation was ruled out.

Thus, the conditions for immediate implantation are: (1) A traumatic tooth extraction without damaging the walls of the alveolar bone; (2) Unacceptable contact of the drill with the vestibular plate during the formation of the implant bed (in the area of the socket of the second mandibular molars-vice versa); (3) Unacceptable absolute dryness of the tooth socket. At the moment of the implant immersion it must be filled with blood; (4) The submarginal location of the implant (immersion of the implant 0.5 mm below the bone edge of the socket); (5) Initial stabilization of the implant; (6) Absence of contact of the precervical part of the implant with the wall of the socket, especially the vestibular bone wall; (7) Filling with a blood clot (at least) or with an osseous complexion (but not with a fibro-osseous material!) the gap between the socket wall and the implant surface; (8) Convergence of soft tissue edges around the gum or temporal crown (immediate non-functional load).

3. Results

In group Ⅰ, the duration of the post-operative radiographic examination was 1 month, 6 months, and 12 months. During the examination, the condition of the soft tissues around the surgically operated tooth, the strength of the restoration, and the radiographic condition of the bone tissue around the surgically operated root were assessed according to the generally accepted Rud classification^[3]. The injuries of 108 patients in the postoperative period and after one month all healed without complications. The X-ray pattern was consistent with the postoperative bone injury, i.e. with no apparent reduction in bone dilution. In the absence of restoration, it was started. In none of the 36 operated cases of premolars and molars was the final elimination of the X-ray dilution of bone tissue (Class 2 and Class 3 Rud) observed after 12 months. In 3 patients, the first mandibular molars were extracted within 6 to 12 months with immediate implantation (4th grade Rud). These patients were later assigned to epy Group Ⅱ. In incisors and canines (72 cases), only 27 (37.5%) cases were fully healed (Class Ⅰ Rud). In the other cases, the partial restoration of the radiographic area of bone dilution (Class Ⅱ Rud) was observed during the claimed period.

In group Ⅱ, of the 184 implants installed immediately after the tooth extraction, one was extracted 1 month following the implantation, which was placed in the socket of the tooth 25. In the remaining cases, all implants were successfully integrated with the subsequent manufacture of prosthetic constructions, and none was removed between 2012 and 2020.

Thus, we confirm the previous opinions that the complex implant (placed in the socket of the tooth immediately after its extraction) - bone - soft tissues - prosthetic construction stable over time in terms of functional and aesthetic parameters, preservation of bone tissue and mucosa.

4. Discussion

Concerning teeth with a chronic periapical destructive of bone tissue processes, we have developed the following approach to the choice between PES and immediate implantation: (1) Incisors and canines: when the coronal part is minimally destroyed and no endodontic treatment has been previously performed, only endodontic treatment is performed. (2) Incisors and canines: if the coronal part is minimally destroyed, previously performed endodontic treatment is present, the canals are reevaluated with the subsequent PES. (3) Incisors and canines: when the coronal part is destroyed and endodontic treatment has either been performed or no, the tooth is extracted, and subsequently immediate implantation is done. (4) Premolars and molars: only endodontic treatment is performed when the coronal part is minimally destroyed, and no endodontic treatment has been previously performed. (5) Premolars and molars: when the coronal part is destroyed and no endodontic treatment has been performed, the tooth is extracted, and then immediate implantation is done. (6) Premolars and molars: regardless of the destruction of the coronal part and the presence of the previously performed endodontic treatment, the tooth is extracted, and then immediate implantation is done.

Thus, the authors narrowed the indications for PES in the area of molars and premolars, giving preference to immediate implantation. Over time, immediate implantation has gradually replaced PES in the molars and premolars due to benefits, such as: less traumatic implantation, reduced treatment time compared to delayed implantation, the ideal position of the implant, minimal bone atrophy in remote observation times, minimum soft tissue shrinkage in remote observation periods, the ideal gingival contour in the remote observation periods after the completion of prosthetics and stability over time.

Conflicts of interests

Edita Margaryan is an Editorial Board Member of the journal. The article was subject to the journal's standard procedures, with peer review handled independently of this member and the research groups.

Ethical approval

This study was approved by the Local Ethics Comittee of Sechenov University(No.11-13), and all the patients have signed informed consents.