Morphological features of the maxillary incisors roots and relationship with neighbouring anatomical structures: possible implications in endodontic surgery

Abstract

The purpose of this study was to investigate the relationship between the root apex of the upper incisors and neighbouring anatomical structures as well as the morphology of the root-end foramen after apicoectomy. Fifty-seven patients requiring endodontic surgical treatment for a maxillary anterior root were enrolled. A preoperative diagnostic computed tomography (CT) scan was analysed to determine: the distance between the anterior wall of the nasopalatine duct and the central (CI-ND) incisor root 4 mm from the apex; and the distance between the floor of the nasal cavity and the tip of either the central (CI-NF) or the lateral (LI-NF) incisor root. After apicoectomy, root-end foramen endoscopic pictures were taken in order to characterize their morphology. Fifty-nine central and 26 lateral incisors were evaluated. The average CI-ND was 4.71 ± 1.26 (SD) mm. The average CI-NF was 10.62 ± 2.25 mm. The average LI-NF was 13.05 ± 2.43 mm. The foramen shape after apicoectomy was ovoid to circular in about 90% of cases in both central and lateral incisors. A sound knowledge of the anatomical relationships at the surgical site is essential for the clinician to perform a safe endodontic surgical procedure.

The aim of root-end preparation techniques during endodontic surgery is to create a well-cleaned and shaped cavity to be filled, in order to seal the apical terminus of the root canal system .

The anterior maxilla is often considered a relatively safe site for oral surgical procedures. In 2007 J acobs et al. reported the increasing rate of surgical interventions in that area, and underlined the potential risks and the anatomical variations. M raiwa et al. highlighted the high variability of the nasopalatine canal, in terms of dimension and morphological appearance. The presence of a true neurovascular bundle in the anterior maxilla raises the risk of complications associated with the surgical procedure, including haemorrhage and sensory disturbances . Damage to neurovascular bundles can be prevented with careful surgical planning, using cross-sectional imaging as suggested by M raiwa et al. . L ofthag-Hansen et al. compared intraoral periapical radiography and 3D images for the diagnosis of periapical pathology and concluded that a high resolution 3D technique can be of value for the diagnosis of periapical lesions. V elvart et al. showed that the use of computed tomography (CT) for the detection of the endodontic lesion and its relation with important neighbouring anatomic structures, offers additional beneficial information that is not available from dental radiographs for treatment planning in apical surgery.

Anatomical studies demonstrated anatomic complexities and irregularities of the root canal system especially in the apical portion . The identification and treatment of these microscopic findings is key for effective periradicular healing . The significance of these anatomic complexities and the need for managing them, may have contributed to the genesis of modern apical surgery, which gained further acceptance amongst practitioners with the introduction of magnification and micro-instruments. The hard tissue repository of the human dental pulp takes on many configurations that must be known before endodontic treatment can begin.

Although many anatomic and radiographic studies have provided extensive information about root features, root canal and apex anatomy of the upper incisors, there has been limited disclosure about the characteristics of root-end foramen, obtained after apicoectomy .

This descriptive study was undertaken to investigate the morphology of the root apex of anterior upper incisors and its relationship with surrounding anatomical structures, as well as the features of root-end foramina after apicoectomy, to provide valuable information for periradicular surgery.

Material and methods

Fifty-seven patients (32 women and 25 men), who were referred for surgical treatment during a period of 60 months (from December 2002 to December 2007) in a university clinic and in a private practice setting were enrolled in the study. A single experienced surgeon (S.T.) performed all the interventions.

The following criteria were adopted for case selection: only central and lateral maxillary problems were taken into consideration: the tooth treated surgically showed a periradicular lesion of strictly endodontic origin, and the nonsurgical retreatment was either considered unfeasible or had previously failed; the tooth treated surgically exhibited adequate final restoration with no clinical evidence of coronal leakage; all the teeth treated had root fillings within 6 mm of the radiographic apex; the apical root canal had 6 mm or more without the presence of a post; the patient already had a CT scan that had been requested by the referring clinician for diagnostic purposes.

The following exclusion criteria were applied: teeth with pathology associated with vertical root fracture; teeth with perforation of the lateral canal walls; teeth with traumatic injuries; supernumerary teeth, fused teeth, or dens invaginatus.

Each patient received written information about the surgical procedure and the necessary follow-up care instructions. Patients signed a consent form before surgery and were also given the opportunity to withdraw from the study. A total of 85 teeth (59 maxillary central incisors and 26 maxillary lateral incisors) were included in the study. All teeth showed periapical lesions diagnosed clinically and radiographically.

A periapical radiograph of each tooth was taken during the preliminary visit. All the radiographs were taken using film holders, customized with impression material. The paralleling technique was adopted to ensure reproducibility. Upper incisors were evaluated preoperatively using a diagnostic CT scan (CT 9800, General Electric, Cormano, Milan, Italy) and analysed by computer software for 3D imaging (3Diagnosys, 3Diemme srl, Cantù, Como, Italy) ( Fig. 1 ). The following were assessed: deviation of the root apex from the main root axis; distance between the anterior wall of the nasopalatine duct and the central incisor root (CI-ND) detected 4 mm from the root apex ( Fig. 2 ); distance between the tip of the central incisor root and the floor of the nasal cavity (CI-NF) ( Fig. 3 ); and the distance between the tip of the lateral incisor root and the floor of the nasal cavity (LI-NF).

Fig. 1
Multiplanar 3D CT reconstruction of the surgical site of interest. The defect involving the periapical region of tooth 21 is clearly visible. The left central incisor shows an axial inclination between the crown and the root of a tooth.

Fig. 2
The linear distance between the anterior wall of the nasopalatine duct and the central incisor root (CI-ND) detected 4 mm from the root apex is indicated by the red line and equals 3.6 mm. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)

Fig. 3
The linear distance between the tip of the central incisor root and the floor of the nasal cavity (CI-NF) is indicated by red arrows. The TC section on which the actual tooth apex was visible was chosen for measurement. In the case shown in this figure the distance was 9.5 mm. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)

Surgical procedure

Preoperatively, the patient rinsed his or her mouth with an antiseptic mouthwash (Curasept ® , Curaden Healthcare s.r.l., Saronno, Milan, Italy) to reduce the risk of contaminating the surgical field. Treatment was provided under local anaesthesia with lidocaine 2% and epinephrine 1:100,000. A full mucoperiosteal tissue flap was used. The flap was mobilized, reflected and carefully retracted during the root-end management. Surgical access to the root was made through the cortical bone using a round bur. Shaving the bone was performed with a brush stroke approach, low rotary speed and constant sterile water irrigation. The periradicular lesion was removed with sharp bone curettes and angled periodontal curettes. The curetted tissue was placed in 10% formalin solution for pathological diagnosis. All of these procedures were carried out using magnification loupes (4.3×) with a headlight. After exposure of the middle-third of the root, the surgical procedure was performed using an endoscope as a magnification device (Fiegert-Endotech ® ; Gänsäcker 42, Tuttlingen, Germany). Root-end management procedures were carried out with a setting magnification of 10× or 20×.The cutting distance was measured with a periodontal probe and marked using a surgical intra-oral marker. A straight fissure bur in a hand-piece was positioned perpendicular to the long axis of the root end, beginning from the apex, cutting coronally, 3 mm of the root-end was shaved away. Prior to root-end preparation, local hemostasis was achieved using bone wax. The root-end surface and root-end foramina were examined to identify their anatomical features. The root-end cavities were prepared using zirconium nitride retro-tips (Dentsply, Maillefer Instruments, Ballaigues, Switzerland) driven by an ultrasonic device unit (Piezon Master 600 ® , EMS, Nyon, Switzerland) at no more than half power, with constant copious sterile water irrigation to avoid over-heating. The retro-tips enabled a well-defined parallel preparation of 2.5–3 mm depth to be made. The root-end cavities were dried using paper points. A zinc oxide EBA-reinforced cement (Super Seal, Ogna Pharmaceuticals, Milan, Italy) was used as the root-end filling material. A final endoscopic inspection was conducted to verify the quality of the root-end filling ( Fig. 4 ). The bone wax was removed and the reflected tissues were re-approximated to their original position, compressed, stabilized and sutured with polyamide 6–0 (Ethicon Inc. Johnson & Johnson, Piscataway, NJ, USA).

Fig. 4
Four filled root ends showing irregular anatomy. The irregularity visible in (d) resembles a dentinal crack.

Evaluation

An image of each root-end foramen was produced during intra-surgical procedures. Digital pictures were taken, with the endoscope magnification at 30× or 40×, to detect the morphology of the root-end foramen. Eighty-five root-end foramina were analysed.

Two blinded examiners (G.R. and T.W.) independently evaluated the radiographs and the digital pictures. They were calibrated prior to the evaluation. Cohen’s k -score calculated on 15 measurements was 0.81, indicating a very good agreement between the two evaluators. In order to reduce the effect of evaluator fatigue as a confounding variable, 10 radiographs/pictures were viewed consecutively and then a 15-min break was taken before starting the following evaluation session. Student’s t test was used to compare CI-NF and LI-NF, considering P = 0.05 as the significance level.

Results

A radiographic assessment of surgical site showed that the root apex of the central incisor is placed on the labial aspect, closely approximating the external cortical plate, which facilitates surgical access to this root. The root has a slender shape, which tends to enlarge apically near the vestibular plate. In 92% of cases the root apex of the central incisors were located along the root axis. In three cases (5%) it diverged to a distal–palatal position with respect to the root axis. In two cases (3%) it was angled to the midline so that the root apex was tightly in contact with the nasal spine.

The root apex of the lateral incisor is relatively sharper than the central one, often displaying a deflection to the distal and palatal direction. In a high percentage of cases (85%) the apical portion of the lateral incisors was placed towards the palatal cortical plate. The root apex of the lateral incisors was displaced to a distal–palatal position with respect to the root axis in 21 cases (81%), in one case (4%) a real dilaceration (>90° deviation from the main root axis) was evident, whilst in four cases (15%) it followed the root axis.

Measurements of the CI-ND distance, performed 4 mm from the root apex, showed a mean value of 4.71 ± 1.26 (standard deviation) mm. The average distance between the apex of the LI-NF was 13.05 ± 2.43 mm. The average distance between the apex of CI-NF was 10.62 ± 2.25 mm. A significant difference was found between these two distances ( P = 0.01).

Table 1 summarizes the morphological features of root-end foramina as assessed with the endoscope after root-end resection ( Figs 5 and 6 ).

Table 1
Morphological features distribution for root-end foramina after apicoectomy.
Central incisor ( N = 59) Lateral incisor ( N = 26)
Foramen shape (see also Figs 5 and 6 )
Type I – ovoid to circular 53 (89.8%) 24 (92.3%)
Type II – triangular 2 (3.4%) 1 (3.8%)
Types IIIa and IIIb – irregular 3 (5.1%) 1 (3.8%) (IIIb)
Type IV – extremely large, ovoid (≥25% of root surface area) 1 (1.7%) 0
No. of foramina
1 58 (98.4%) 26 (100%)
2 1 (1.6%) 0
No. of lateral canals 1 (1.6%) 0
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Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Morphological features of the maxillary incisors roots and relationship with neighbouring anatomical structures: possible implications in endodontic surgery
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