Gingival recession following intrasulcular incision in the area of maxillary central incisor (PFM crown)
Separation of the wound margins may occur within the first week after surgery. This complication may result from tissue failure rather or improper suturing techniques. The wound margins may be closed again or left to heal depending upon the margins extent and the surgeon’s judgment of the clinical scenario .
The presence of a periodontal disease may adversely affect the outcome of the endodontic surgery [24, 25] and is associated with higher risk of complications [6, 26, 27]. When performing endodontic surgery in teeth with periodontal lesions, the endodontic success rate may be less than 80%, compared to more than 90% for cases without periodontal lesions .
Gingival morphology has a significant impact on the risk of soft tissue-related complications following endodontic surgery. There are two types of anatomical “gingival biotypes” : “thin gingival biotype” is characterized by a highly scalloped marginal gingiva with slender teeth, delicate and translucent appearance, and with a narrow attached gingival [13, 17, 29]. “Thick gingival biotype” is characterized with a bulky scalloped marginal gingiva in short and wide teeth, broad attached gingiva, fibrotic and resilient tissue, flat soft tissue, and large amount of attached gingival [6, 13, 17, 29]. Patients with thin gingival biotypes may be at a higher risk for recession development following the surgery [6, 14, 17, 29]. On the other hand, patients with thick gingival biotype may be more prone to infra-bony defect formation and deeper probing pocket depth following the endodontic surgery [10, 12–14, 17, 28, 29].
Adequate incision design is crucial and several principles should be applied: horizontal and severely angled vertical incisions or incisions over radicular eminences should not be performed [27, 30, 31]; the incisions should facilitate flap repositioning over a solid bone [27, 31]; the incisions should avoid muscle attachments [27, 31]; the vertical incision extension should facilitate the positioning of the retractor during surgery on a solid bone without tension [1, 27, 31]; and the extent of the horizontal incision should enable adequate surgical access with minimal stretching of the soft tissue [1, 6, 27, 31].
The flap should be designed as “full thickness” to include the entire mucoperiosteal tissues. Full-thickness flaps maintain the supra-periosteal blood vessels and result in less tissue trauma and ensuing bleeding [1, 6, 27, 31]. It is recommended to minimize as possible the time of the operation and perform a short-duration surgery in order to prevent flap ischemia and necrosis .
9.1.2 Periapical Osteotomy and Curettage
The main goal of the osteotomy in endodontic surgery is to provide an adequate access for the surgical management of the apical part of the root [1, 2, 4–6, 18, 34]. However, when the size of the osseous defect is extensive, osseous regeneration of the wound may not occur, and the defect might heal by fibrous connective tissue [6, 18, 35, 36]. Enlarged osteotomy directed toward the coronal margin may potentially lead to perio-endo communication, endanger the adjacent anatomical structures, and cause a damage to neighboring teeth [1, 6, 24, 37]. With the modern microsurgical techniques, the size of the required osteotomy decreased, to about 4–5 mm in diameter, a diameter large enough to allow the surgical manipulations and at the same time reducing the potential risk [1, 6].
Excessive heat generated during osteotomy preparation may generate heat [38, 39], interrupting the blood flow, and may cause decreased osteoclastic and osteoblastic activity, dehydration, and desiccation, with resulting osteocytic degeneration and osteonecrosis [6, 38, 39]. The factors that may influence the amount of heat generation are the drill design, the drilling technique, and the bone characteristics [6, 40]. Only light brushing motions using a high-speed bur with the copious amount of irrigation should be applied for endodontic surgery .
Periapical curettage is aimed to remove pathological tissue and enable access to the surgical site. The curettage may potentially jeopardize adjacent anatomical structures such as the maxillary sinus, the nasal cavity, and neurovascular bundles . The inflammatory endodontic lesions (either cyst or granuloma) are the responses of the periradicular tissues to irritants from the infected root canal, and it is usually not necessary to completely curette all the involved periradicular tissues during the surgery [6, 41].
9.1.3 Complications During Root-End Management
Root-end management involves a root-end resection and retrograde preparation and filling of the apical part of the root canal .
Root–end resection was traditionally recommended in order to remove the contaminated apical part of the root canal and to provide access for retrograde cavity preparation and obturation [1, 43]. It was suggested that at least 3 mm of the root end should be removed . However, in some cases, excessive root-end resection may dangerously reduce the crown-to-root ratio (CRR) [44, 45]. Recent studies suggest that root-resected teeth are not prosthodontically compromised unless there is also periodontal bone loss. Therefore, preserving the suggested ideal 1:2 CRR must not compromise the main goal of the surgery [46, 47].
Missed root canals may compromise the success of the whole surgical procedure. Inadequate root resection or limited visualization of the root anatomy is the main cause of missed root canals .
Ultrasonic tips are used to prepare a retrograde cavity to a depth of 3–4 mm [16, 49]. However, during the use of ultrasonic endodontic tips, a fracture of the tip can occur, and dentinal cracks may develop . Therefore, light touch with moderate power setting and copious irrigations should be employed while operating the ultrasonic tips .
9.2 Bleeding in Endodontic Surgery
A damage to blood vessels during the surgical procedure may lead to hemorrhage [51–55]. While a severe hemorrhage is rare in endodontic surgery, when happens it may cause serious systemic complications [53, 56]. In patient with bleeding disorders, excessive bleeding may occur even if only small blood vessels were damaged during the surgical procedure [6, 53, 56].
In cases when the bleeding is not penetrating the oral mucosa or the skin, a localized collection of the blood in the oral mucosa or facial tissues may cause a discoloration resulting in the formation of hematoma. Hematomas can last for up to 2 weeks and usually require no treatment . Rarely, an excessive hematoma developed in the floor of the mouth may even lead to potentially life-threatening scenarios .
Mild hemorrhage is relatively common during endodontic surgery, and although it is usually not life threatening, it may cause complications and may even compromise the prognosis of the treatment . Adequate bleeding control is therefore essential since it improves visualization of the surgical site, minimizes the operating time, and enables the dry field for proper placement of retrograde filling materials [6, 52, 55]. Minor bleeding is still common and should be controlled by a variety of means such as digital compression, gauze tamponade, cauterization, suturing of the bleeding vessel (ligation), and by adjunct topical hemostatic agents [1, 6, 52, 54, 55, 58–61].
The goals of local anesthesia during endodontic surgery are to achieve profound anesthesia that is necessary for the patient comfort and cooperation, together with proper hemostasis, achieved by administrating a local anesthesia agent with vasoconstrictor [1, 51, 54, 55, 60]. Usually, 1:100,000 epinephrine concentration should be sufficient to achieve proper hemostasis [6, 27].
Occasionally, a secondary bleeding phase is observed after an infiltration of local anesthetic with vasoconstrictor. This phenomenon, termed “the rebound phenomenon” , may last for hours, and it is usually impossible to reestablish hemostasis by additional injections . Thus, the more complicated and hemostasis-dependent procedures (such as the root-end management) should be done first [6, 31, 63].
9.3 Nerve Injury During Endodontic Surgery
Most routine surgical procedures may lead to nerve injury [1, 6, 64, 65]. In addition, nerve injuries may be caused indirectly by postsurgical pressure increase applied on the nerve bundle by the development of an intra-alveolar hematoma, or edema inside the mandibular canal, or by a prolonged pressure increase from neuritis . However, direct trauma to the nerve bundle during surgery is the most frequent cause of nerve injury and may occur through nerve compression, stretching, cutting, overheating, and accidental puncture [6, 67–71]. Most cases of inferior alveolar nerve (IAN) injuries have been reported in second mandibular molars [1, 6, 64, 72].
The use of cone-beam CT (CBCT) may facilitate the evaluation of the true extent of the periapical (PA) lesions and the relationship of the PA lesions and root apices to anatomical landmarks such as adjacent neurosensory structures, thus enabling a more predictable surgical approach [73–79]. Following surgical procedure, the practitioner needs to detect any possible signs of altered sensation [69, 71, 72, 80]. Early symptoms that may suggest possible nerve injury are acute pain during or after the surgical procedure or neurosensory alterations, such as paresthesia [6, 81].
The long-term prognosis of altered sensation following endodontic surgery is not fully elucidated, but it may be related to the type and extent of injury and to the intervention protocol and timing [64, 71, 72, 82–84]. It seems that most patients, especially those with a relatively low extent of injury, whom were treated immediately and properly, tend to improve with time . When nerve injury is suspected, a timely mannered clinical approach aimed to prevent permanent damage and to enable a better clinical and medicolegal response is of outmost importance [6, 64].
9.3.1 Maxillary Sinus Complications
The roots of maxillary premolars and molars may lie in proximity to the maxillary sinus floor . In many cases, it is the periapical granuloma or cyst extending into the sinus cavity, causing sinusitis of dental origin. This was shown for the first time in a study by Bauer  and later was termed “endo-antral syndrome” (EAS) by Selden . The reported frequency of sinusitis of dental origin varies considerably, between 4.6 and 47%  of all sinusitis cases. These represent risk factors for perforation of the Schneiderian membrane during periapical surgery.
Frequencies of Schneiderian membrane perforations vary from 9.6 to 50% . Sinus membrane perforations could be detrimental, causing inhibition of ciliary activity, thereby reducing the resistance to infection . Clinical signs and symptoms include nasal bleeding, sinus obstruction, and acute or chronic sinus infections . However, Ericson et al.  and then Watzek et al. (1997)  found no significant difference in the healing rate between patients with and without intraoperative sinus exposure. Moreover, later on, it was also demonstrated that as long as foreign materials and root apex are not allowed to enter the sinus cavity during root-end preparation, a Schneiderian membrane perforation is not detrimental to the clinical outcome .
9.3.2 Postoperative Pain, Swelling, and Infection
Postoperative pain and swelling are common complications of surgical procedures , and their intensity depends on the degree of tissue damage and inflammatory response. Inflammation may occur due to the surgical wound alone or as a result of the tissue injury combined with surgical site infection [6, 94].