Implants Placed in the Nasopalatine Canal to Rehabilitate Severely Atrophic Maxillae: A Retrospective Study With Long Follow-up

The rehabilitation of atrophic maxillae with implant-supported prostheses is complicated by low bone quantity and quality.¹  After the loss of teeth, a vertical and horizontal resorption of the anterior maxilla occurs.²  The nasopalatine canal tends to lengthen and the neurovascular bundles inside may ultimately emerge from the ridge crest.^3,4  Even in cases of severe resorption, dense cortical bone remains anterior to this canal.²  In patients with severe maxillary atrophy, anchorage of implants in the bone remaining around the nasopalatine canal is an alternative to bone grafting that provides sufficient anterior support to enhance the biomechanics of the implant-supported prosthesis.

The incisive canal ranges in length from 4 to 26 mm and is related to maxillary bone height; it has an axis of 70° (57–89.5°). The nasal process of the maxilla rises 2 to 3 mm above the nasal floor; as a result, when 8 to 10 mm or above are present below the nasal floor, a large osteotome may be used, permitting the placement of a 10–13 mm-long implant.^2,5 

There are few references in the literature to implants placed in the nasopalatine canal. The technique was described by Scher²  and Misch;⁵  using a large round drill, the soft tissue from the canal site was curetted and then drills of progressively increasing diameter up to 2 mm were used coronal to the final depth of the canal until the implant osteotomy diameter was reached. The literature review performed in preparation for the present study also located 3 further studies.^6–8  Rosenquist and Nyström⁶ filled the incisal canals with autogenous bone in 4 patients who had lost 1 or both central maxillary incisors due to trauma. After a healing period of 4–5 months, implant surgery was performed; in all cases the canal appeared to have been replaced by cancellous bone and the implants were placed partially into the grafted area. After a 12-month follow-up none of the implants had been lost. Artzi et al⁷  reported the case of a patient with an enlarged incisal foramen; at the time of implant placement a corticocancellous block graft was adjusted to fit the foramen and the soft tissue was pushed back but not removed. Nine months later, solid bone support was observed embracing the implant body and although the size of the incisal foramen had decreased significantly, the nasopalatine branches were still evident. In a pilot study, Peñarrocha et al⁸  reported the use of implants inserted in the nasopalatine canal after removal of the neurovascular bundle to rehabilitate 7 patients with severely atrophic maxillae. After an observation period of 12 months, only 1 nasopalatine implant had been lost due to lack of osseointegration.

The aim of the present study was to make a retrospective analysis of the long-term (2 to 11 years) outcome of implants placed in the nasopalatine canal to rehabilitate patients with severe maxillary atrophy.

This clinical retrospective study was carried out at the Oral Surgery Unit of Valencia University Dental Clinic and analyzed patients treated between 2000 and 2009 with implants placed in the nasopalatine canal using the technique described in an earlier pilot study.⁸  Patients with class V of Cawood and Howell classification⁹  of maxillary atrophy were rehabilitated using implants placed in the nasopalatine canal supporting full-arch fixed prostheses, and monitored over a follow-up period of at least 24 months after loading. All patients gave written consent to take part, having been provided with full information about the treatment plan.

Preoperative radiographic examination included panoramic radiographs and computerized tomography (CT) scans in all cases to assess the bone available, the dimensions and configuration of the nasopalatine canal and any presence of sinus pathology (Figure a–c).

All surgeries were performed by the same surgeon under local anesthesia (4% articaine with 1:100 000 adrenaline; Inibsa, LliçaVall) and sedation with 1% propofol solution; the procedure included blood pressure, pulse and oximetric monitoring by an anesthetist.

Patient age, sex, relevant medical history and locations of the implants were registered (Table).

The first step in placing the implant in the nasopalatine canal was to identify the incisive foramen (Figure d), and evaluate the angle and depth of the bony canal with a periodontal probe. The nasopalatine neurovascular bundle was then removed using a curette. Preparation of the implant site was started with a round drill and a long 2.3 mm diameter drill (Figure e), and then Summer osteotomes of progressively increasing diameters were used until the final implant bed was completed (Figure f and g). Particles of autologous bone collected from the nasal spine or particles of β-tricalcium phosphate (KeraOs, Keramat, Coruña, Spain) were added and compacted using osteotomes to form a bone ceiling at the apex of the implant bed (Figure h and i). The implant was then inserted into the nasopalatine canal (Figure j). All implants placed in the nasopalatine canal achieved high primary stability (insertion torque of 45 Ncm). Other implants were placed in the canine buttress, in the pterygomaxillary area, in the zygomatic bone or using the standard procedure (Figure k). When present, peri-implant defects were covered with autologous particulate bone alone in combination with β-tricalcium phosphate (KeraOs; Figure l).

All patients received a post-surgical prescription of amoxicillin (Clammily, GlaxoSmithKline, Madrid, Spain) 500 mg / 8 hours for 7 days; ibuprofen (Bexistar, Laboratorio Bacino, Barcelona, Spain) 600 mg / 8 hours for 4 days; and 0.12% chlorhexidine rinses (GUM, John O. Butler/Sunstar, Chicago, Ill) 3 times a day for 7 days.

Patients were recalled after 7 days for suture removal. All implants were left submerged, and the second surgery was performed 12 weeks after implant placement. Twelve patients were rehabilitated with fixed screwed full-arch prostheses and 1 patient who had been referred by another dentist for implant surgery was rehabilitated with a fixed, cemented full-arch prosthesis (Table; Figure m–o).

Recall visits were scheduled in all cases at 1, 3, and 6 months after implant placement and annually after prosthesis placement.

A neurosensory evaluation of the anterior palate of each patient was performed using the pointed/blunt discrimination test: a ball burnisher and a pointed dental probe were pressed lightly and randomly on the palate to check the patient's ability to differentiate between pointed and blunt objects. All patients underwent evaluation 1 week (at the suture removal visit) and 1 month after implant placement. Those patients reporting neurosensory alterations were recalled weekly to check on progression until this had disappeared.

Twelve months after prosthesis placement and annually thereafter, patients were recalled for clinical and radiographic evaluation. Prostheses, with the exception of the single case treated with a cemented prosthesis, were removed to be thoroughly cleaned and allow better clinical examination of the peri-implant tissues. Paralleled digital intraoral radiographs were obtained to assess marginal bone levels around the implants (Figure p).

At the first annual control visit, patient satisfaction with the treatment was also assessed. Ten-cm visual analogue scales (VAS) were used to estimate patient satisfaction.^10–13  These measurements assessed general satisfaction with the implant-retained prosthesis, comfort and stability, ability to speak, ease of cleaning, aesthetics, self-esteem, and function. The anchor words were “totally dissatisfied” and “completely satisfied.” Patients marked the scale independently, although a research assistant was available to offer help or explanations when required.^10,12,13 

Implant success was assessed using clinical and radiologic criteria as described by Albrektsson et al¹⁴: (1) absence of clinical mobility of the implant, (2) absence of exudate, persistent inflammation, pain or bleeding, (3) absence of periapical radiolucency, and (4) absence of bone loss progressively greater than 0.2 mm annually after the first year of implant placement.

Thirteen patients, 5 men, and 8 women, with a mean age of 54.8 years (range 30 to 76 years) were treated. The average follow-up was 70 months (range 24 to 132 months). Three patients smoked less than 10 cigarettes per day and 10 were nonsmokers. Regarding systemic conditions, one patient had anhidrotic ectodermal dysplasia¹⁵  and 2 had epidermolysis bullosa;¹⁶  the remaining were healthy patients with severe maxillary atrophy – Class V of Cawood and Howell.⁹  The procedure for implant insertion in the nasopalatine canal was exactly the same for patients with ectodermal dysplasia or epidermolysis bullosa as for healthy patients. Soft tissue healing was uneventful in all cases.

A total of 78 implants were placed (5–7 per patient): 13 were anchored in the nasopalatine canal, 6 in the zygomatic bone, 12 in the pterygomaxillary region, 2 in the frontomaxillary region, and 45 in other locations. All implants used were Phibo implants with Avantblast surface (PhiboDental Solutions S.L., Barcelona, Spain; Table).

At the study endpoint, 6 patients reported a slight decrease in sensitivity in the anterior palate when the point/blunt technique was performed one week after surgery; this alteration had spontaneously disappeared completely in all cases within 6 weeks (Table).

Two early failures—during the osseointegration period—of implants placed in the nasopalatine canal occurred but there were no late failures following prosthesis placement. All surviving implants fulfilled the success criteria of Albrektsson et al,¹⁴  with implants in the nasopalatine canal yielding a success rate of 84.6%. Both failures occurred in healthy patients. None of the implants placed in other locations failed.

Average patient general satisfaction was 9.0 (range 8 to 10). All patients were satisfied with comfort and stability (mean VAS score 9.7; range 9 to 10), ability to speak (mean VAS score 9.5; range 8 to 10), function, esthetics, self-esteem (mean VAS 8.5; range 7 to 10) and ease of cleaning (mean VAS score 9; range 8 to 10).

In the present study, the nasopalatine canal was used as an anatomic buttress in which residual bone allowed placement of dental implants. The technique of implant placement directly in the nasopalatine canal was first described by Scher in 1994²  and later mentioned by Misch⁵  in his 1999 book. However, Rosenquist and Nyström⁶  had published a previous report of the use of the nasopalatine canal for dental implant placement. These authors treated 4 patients with absent central incisors. The canal was filled with autologous bone graft and 5 months later implants were placed partially in the grafted area; no fixture was lost after 12–15 months. Artzi et al⁷  treated a patient with an implant in the nasopalatine canal without removing the neurovascular bundle. These authors adapted a corticocancellous bone block graft to the canal and, without removing the soft tissue, pushed the block backwards; the implant was placed in the same surgical procedure. No complications were observed during a 9-month follow-up. In a pilot study prior to the present study, Peñarrocha et al⁸  treated 7 patients with implants placed in the nasopalatine canal after removing the neurovascular bundle and preparing the implant site using drills and osteotomes. One early failure occurred 3 months after implant insertion but no late failures occurred, yielding an implant survival rate of 85.7%. In the present study, 13 implants inserted in the nasopalatine canal were monitored for 24 to 132 months (average 70 months); a total success rate of 84.6% was achieved.

The nasopalatine canal starts at a point situated towards the front of the floor of each nasal cavity. Each canal opens into the midline incisive foramen on the median plane of the palatine process of the maxilla, posterior to the central incisor and transmits the nasopalatine nerve and the terminal branch of the descending nasopalatine artery, branches of the maxillary division of the trigeminal nerve and the maxillary artery.¹⁷  Although the nasopalatine canal has been identified as an important anatomical landmark for the implant surgeon,¹⁸  the risks and clinical implications of damaging the canal and its neurovascular structures have not been addressed in the literature.¹⁹  Mraiwa et al²⁰  pointed out the variability of both the dimensions and the morphological appearance of the nasopalatine canal. To avoid disturbing the neurovascular bundles and cause any complications, this important dimensional variability should be taken into account when dealing with surgical procedures such as implant placement in the central incisor region.²¹  In the present study, cone beam CT scans were used to assess the nasopalatine canal, and in all cases the dimensions and morphology were considered adequate for implant insertion according to the results achieved in the earlier preliminary study.⁸ 

Lack of osseointegration and sensory alterations are the 2 main complications that have been associated with implant placement in this region. Implant contact with the neural tissue may result in osseointegration failure.²⁰  In the present study, the soft tissues of the nasopalatine canal were curetted, then the preparation of the implant sites began with the first drills of the implant system and finalized with osteotomes of increasing diameters that allowed bone particle condensing at the floor of the implant site. Two implants failed during the osseointegration period but none failed following prosthetic loading. This yielded a success rate of 84.6%, which was slightly low in comparison to success rates generally reported for dental implants placed using conventional techniques.

Removal of the complete soft tissue content in the incisive canal can result in possible sensory loss in the anterior palatal region; altered mucosal sensation following surgical trauma due to implant placement in the region of the mental foramen has also been reported.²²  However, this sensation in the anterior third of the palatine mucosa usually recovers within 2 to 3 months through the compensatory action of the branches of the greater palatine nerves.^8,23  Of the 13 patients treated in the present study, 6 experienced a slight loss of sensitivity, which disappeared completely without treatment. All patients had class V atrophy of Cawood and Howell's classification⁹  and this could explain why no sensory alterations occurred. Similarly, Artzi et al⁷  treated a patient with severe atrophy with the technique of the corticocancellous bone block in the nasopalatine canal and observed no loss in sensitivity in the anterior region of the palate. Filippi et al,²⁴  who surgically removed palatally displaced canines in 59 patients, reported damage to the nasopalatine nerve in all patients. During the first week after surgery, sensory disorders were found in all patients but after 4 weeks no neurologic deficit was detected in any patient. Magennis²⁵  studied sensitivity in 18 patients after the elevation of a palatal flap with or without sectioning the nasopalatine nerve. This author observed a temporary loss of sensitivity in 2 patients and no alteration in all the others.

Regarding patient satisfaction with the treatment, the visual analogue scale used made it possible to evaluate subjective parameters that would be difficult to standardize and analyze statistically by other means. Patients reported no problems with the ability to speak, comfort, function, esthetics, self-esteem, or ease of cleaning. Peñarrocha et al²⁶  assessed satisfaction of completely edentulous patients with and without severe maxillary atrophy rehabilitated with full arch fixed prostheses and found no differences between the 2 groups.

Residual bone is associated with the nasopalatine canal even in patients with severe maxillary atrophy. Favorable outcomes and no complications were associated with the placement of implants in this canal. The nasopalatine canal should therefore be considered a possible location for an anterior implant when rehabilitating patients with atrophic maxillae using implant-supported prostheses.

Abbreviations

CAS

computer-assisted surgery

CT

computerized tomography

ISQ

instability quotient

IT

insertion torque

ITV

insertion torque value

PTV

Periotest value

RFA

resonance frequency analysis

VAS

visual analog scale