Obliteration of the Nasopalatine Canal in Conjunction with Horizontal Ridge Augmentation

Simone Verardi, DDS, MSD; and Julie Pastagia, DDS, MSD

Root-formed dental implants are utilized routinely and to successfully replace missing teeth.¹ Good functional and esthetic results may also predictably be achieved with implantology.²

When treatment-planning implant surgery in the upper central incisor area, it is imperative to consider anatomical factors such as the location and morphology of the nasopalatine canal prior to the surgical phase. Implants placed within the canal may increase the risk of decreased osseointegration, due to possible lack of bone-to-implant contact (BIC). An increased incidence of implant failure might thus occur.

Very few reports in the literature offer suggestions for navigating around this anatomical structure for ideal implant placement in the anterior maxilla.^3,4 Furthermore, the upper central incisor area is critical for the patient’s esthetic satisfaction. Precise placement of the implant according to the restorative plan cannot be compromised.⁵ An adequate edentulous ridge must be present; if instead the ridge is atrophic, augmentation procedures must be considered. Avoiding the canal may not be an option if in doing so the esthetic outcome is affected. Sometimes the presence of a wide nasopalatine canal might also be associated with a deficient edentulous ridge. In these cases, bone augmentation techniques are used to facilitate ideal implant placement.

In this report, the author briefly reviews the anatomy of the nasopalatine canal and presents a technique for obliterating and grafting this canal with graft particulate material in conjunction with ridge augmentation prior to implant placement.

Anatomy of the Nasopalatine Canal

The face and the oral cavity develop between weeks 4 to 8 of intrauterine life, and the secondary palate is formed between weeks 8 and 12. In the midline between the primary and secondary palates, two channels—the incisive canals—persist. It is thought that the palatine processes partly overgrow the primary palate on either side of the nasal septum. Thus, the incisive canals represent passageways in the hard palate, which extend downward and forward from the nasal cavity. Just before exiting the bony surface of the hard palate (incisive foramen or incisive fossa), the paired incisive canals usually fuse to form a common canal in a Y shape, which is located just posterior to the central incisor teeth.⁶ The nasopalatine nerve and the terminal branch of the nasopalatine artery pass through these canals and provide sensation to the anterior palate, as shown in the Figure 1 schematic of anatomy/innervation.

In their 1998 report, Kraut and Boyden⁷ analyzed computed tomography (CT) scans and found that in 4% of cases the size of the nasopalatine canal did not allow implant placement. A 3-dimensional (3-D) analysis of the nasopalatine canal conducted by Mraiwa et al,⁸ which was published in 2004, showed a range in its diameter of 1.5 mm to 9.2 mm, even in the absence of canal pathology. They also showed the buccopalatal bone width anterior to the canal to range from 2.9 mm to 13.6 mm, suggesting that in anterior implant-treatment planning, the size and location of the nasopalatine canal, as well as the amount of bone buccal to the canal, are equally important in determining if implant placement is feasible.

Cases of regenerative procedures using autogenous bone chips or a mixture of demineralized freeze-dried bone allograft (DFDBA) and tri-calcium phosphate (TCP) have been reported in which a meticulous curettage of the soft-tissue contents of the canal was conducted prior to implant placement.⁴ Artzi et al³ proposed a surgical technique in which the placement of a bone graft to fit the foramen while pushing back the soft-tissue contents could enable implant placement without any sensory disturbances. More recently, Penarrachoa et al⁹ presented a technique in which the implant is placed in emptied nasopalatine canals of severely atrophic maxillae.

The technique presented here involves grafting an enlarged nasopalatine canal as well as augmenting the deficient buccal width of bone from the canal to facilitate ideal implant placement in three dimensions in order to achieve an appropriate final prosthesis. It is highly recommended that there be a distance of 1.5 mm from the implant to the root of the adjacent teeth, while two implants should ideally be at least 3 mm apart. It is also important to have at least of 1 mm of bone buccally and lingually to the implant.

Case 1

A healthy 19-year-old male patient was referred to the Department of Periodontics at the University of Washington School of Dentistry for implant placement in site No. 8. The patient had been in an automobile accident at the age of 7, at which time the developing tooth No. 8 was traumatized and surgically removed by his dentist. He underwent subsequent orthodontic treatment and had been wearing a removable partial denture ever since.

Upon examination, there was deficient buccopalatal width for proper implant placement in the No. 8 site. A periapical radiograph revealed an enlarged nasopalatine canal located in the site for implant placement. At this time, it was also noted that the mesiodistal width of tooth No. 9 was about 1 mm smaller than that of the No. 8 space. The decision was made to undergo minor orthodontic movement to facilitate a restoration that would have the same dimensions as that of No. 9 for a better esthetic result (Figure 2). It was also decided to bone-graft the nasopalatine canal and augment the edentulous ridge buccally in order to place the implant in the ideal restorative position.

The patient and his family were informed about the potential complications of this procedure, most notably, transient or permanent paresthesia and/or anesthesia of the anterior part of the palate. Other potential complications associated with this procedure include exposure of the membrane, infection, hemorrhage, and inadequate bone regeneration. A detailed informed consent that included these possible complications was signed.

The patient was given 2 g amoxicillin orally 1 hour prior to surgery, and rinsed his mouth for 60 seconds with a chlorhexidine 0.12% solution before the start of the procedure. Perioral skin, nose, and neck were disinfected with a 4% chlorhexidine solution. The patient was placed under conscious sedation with 15 mg of diazepam and 25 mg of meperidine given intravenously; then, using local-infiltration anesthesia (four cartridges of Lidocaine HCL 2% with epinephrine 1:100.000 [Xylocaine^®, DENTSPLY, www.dentsplypharma.com), the nasopalatine foramen was exposed after reflection of a palatal and buccal flap (Figure 3). The size of the canal at its emergence was approximately 3 mm. The content of the canal was removed using Goldman-Fox curved surgical scissors (Hu-Friedy, www.hu-friedy.com) and Lucas Surgical curettes (Hu-Friedy) and thoroughly irrigated (Figure 4). A small (approximately 3 mm) piece of collagen (CollaPlug^®, Zimmer Dental, www.zimmer.com) was placed in the most apical part of the canal to prevent contact with the remaining soft tissue and to favor hemostasis. A cancellous particulate allograft material (Puros^®, Zimmer Dental) was hydrated in saline and packed into the prepared recipient site. The buccal bone was perforated with a No. 2 round bur in order to facilitate blood supply to the area. Subsequently, the graft material was placed to gain horizontal ridge width (Figure 5). A porcine collagen resorbable membrane was placed over the top, covering the buccal and palatal grafts. Primary closure was attained by periosteal release, and the flaps were sutured with a 5-0 nylon suture. Amoxicillin 500 mg t.i.d. for 7 days postoperatively was prescribed. Ibuprofen 600 mg t.i.d. was prescribed for 7 days. The patient was also instructed to rinse with a 0.12% chlorhexidine gluconate mouthrinse b.i.d. for 2 weeks postoperatively.

Follow-up examinations were carried out at 1 week, 2 weeks, 6 weeks, 3 months, and 6 months postoperatively. Periapical radiographs were taken at 2 weeks, 3 months, and 6 months postoperatively. During the healing phase prior to implant placement, minor orthodontic movement was conducted to create ideal space for No. 8 implant placement and restoration.

At 6 months, one implant 4-mm in diameter and 13-mm in length (NobelReplace™, Nobel Biocare USA, LLC, www.nobelbiocare.com) was placed in the No. 8 site after reflection of a small flap (Figure 6). The bone looked and felt successfully regenerated and the implant could be placed in the ideal position. Six months after placement, the implant was uncovered with no complications. A provisional crown was placed (Figure 7).

Case 2

A 46-year-old woman presented with failure of a tooth-supported bridge. Nonrestorable caries was found on the abutment teeth, and the patient was interested in an implant-supported prosthesis to replace the bridge. Based on the restorative plan, implants would need to be placed in the Nos. 6, 8, and 9 sites. The patient was in good general health and had no medical contraindications to undergoing surgical treatment. The remaining abutment teeth would be utilized to support a temporary bridge during the transitional phase.

At clinical examination, the ridge appeared deficient in the buccolingual dimension. This deficiency (2.5-mm residual ridge was also apparent on the cone beam CT scan, which also showed a very wide nasopalatine canal that appeared approximately 5 mm in the mesiodistal dimension (Figure 8). In order to allow for implant placement in the central incisor area, a decision was made to graft the nasopalatine canal and perform a concurrent horizontal ridge augmentation procedure via guided bone regeneration (GBR).

The patient was premedicated with 2 g oral amoxicillin 1 hour before the bone grafting procedure. A chlorhexidine 0.12% mouthrinse was administered for 60 seconds while the perioral skin was disinfected with chlorhexidine 4%.

A midcrestal incision made on the edentulous ridge was extended into the sulci of Nos. 4, 11, and 12, both buccally and palatally. Vertical-releasing incisions were extended beyond the mucogingival junction from the distal aspects of Nos. 4 and 12. After elevating the flap, the nasopalatine canal was emptied of its bundle as described in the previous case (Figure 9). Also, in this case a collagen plug (CollaPlug®, Zimmer Dental) was placed at the bottom of the canal to prevent internal passage of graft particles, favor hemostasis, and avoid possible graft particle soft-tissue contact. The narrow bony ridge and large nasopalatine canal precluded implant placement at the time of bone grafting surgery, so a delayed protocol for implant placement was utilized instead.

Bone was harvested from the left external oblique line with a disposable bone scraper and mixed with bovine xenograft (Bio-Oss®, Osteohealth, www.osteohealth.com) at a 1:1 ratio. The bone was placed in the canal and on the buccal and crestal sides of the edentulous ridge. The area was covered with a titanium-reinforced expanded polytetrafluoroethylene (e-PTFE) barrier membrane (Figure 10) and sutured with a 5.0 e-PTFE suture after periosteal releasing. Postoperative appointments were scheduled at 1, 2, 4, and 8 weeks and then at 4 and 6 months. The area was inspected, and the patient never perceived any sensory deficiencies in the area.

After 7 months of healing, the area was re-flapped. After membrane removal, a copious ridge was present, and the nasopalatine canal was completely filled in with bone.

An implant 4.3-mm in diameter and 13-mm in length was placed in the No. 8 area, while a 4.3-mm x 11.5-mm (NobelReplace, Nobel Biocare USA, LLC) implant was placed in the No. 9 area (Figure 11 and Figure 12).

Discussion

In these cases, optimal implant placement was achieved by obliterating and grafting the nasopalatine canal as well as augmenting the buccopalatal ridge width utilizing the GBR techniques of bone graft and membranes. In this report, the same technique was used to regenerate bone and allow subsequent placement of dental implants in the central incisor area. However, in Case 2 a slightly more complicated option was used, as a mix of autogenous bone with a xenograft combined with a nonresorbable titanium-reinforced membrane, held in place with titanium tacks (Frios®, DENTSPLY Friadent, www.dentsply-friadent.com), was preferred. This was due to the wide edentulous area and because the horizontal bone resorption was severe. In these cases, nonresorbable titanium-reinforced membranes led to more bone formation.¹⁰ In Case 1, because it involved only a mild amount of bone loss and a more self-containing shape of the incisal foramen, it was preferred that an easier to handle combination of materials be used.¹¹

No infections or postoperative complications were noted. Although the contents of the nasopalatine canal were removed and the canal thoroughly curetted, the patients did not report any postoperative sensory loss in the anterior palate. This is most likely due to overlapping innervation of the greater palatine nerve on the anterior part of the palate.

This technique offers the possibility of placing implants in an ideal position, favoring a final esthetic result.

The successful outcome of the grafting of the nasopalatine canal has already been reported with different techniques.^3,4,9 However there is still a scarcity of reports on the possible permanent anesthesia of the mucosa of the anterior side of the palate.

Filippi reported damage to the nasopalatine nerve during impacted canines extractions. Four weeks postoperatively, all patients recovered from the sensory disorder that had been observed in their anterior palatal area.¹² Very similar results have been reported in patients who received flap surgery in the incisor palatal area.¹³

Of the two cases treated with grafting of the nasopalatine canal, the author noted slight numbness on one of the patients only. This effect was noticed at the 1-week postoperative appointment and was completely resolved at the 4-weeks appointment. The cases were followed for a minimum of 24 months and no complications were reported.

Overall, the authors believe that this is a reliable and predictable technique that can be utilized in conjunction with ridge augmentation in order to achieve correct, restoratively driven, 3-D placement of implants in the central incisor area.

Acknowledgment

The authors would like to thank Robert Walter, DDS, MSD; Traelach Tuohy, DDS, MSD; Yen-Wei Chen, DDS, MSD; and Prof. Dr. Pierluigi Rodella for their assistance with this article.

References

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6. Allard RH, van der Kwast WA, van der Waal I. Nasopalatine duct cyst. Review of the literature and report of 22 cases. Int J Oral Surg. 1981;10(6):447-461.

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8. Mraiwa N, Jacobs R, Van Cleynenbreugel J, et al. The nasopalatine canal revisited using 2D and 3D CT imaging. Dentomaxillofac Radiol. 2004;33(6):396-402.

9. Peñarrochoa M, Carrillo C, Uribe R, Garcia B. The nasopalatine canal as an anatomic buttress for implant placement in the severely atrophic maxilla: a pilot study. Int J Oral Maxillofac Implants. 2009;24(5);936-942.

10. Hämmerle CH, Jung RE. Bone augmentation by means of barrier membranes. Periodontol 2000. 2003;33:36-53.

11. Verardi S, Simion M. Management of the exposure of e-PTFE membranes in guided bone regeneration. Pract Proced Aesthet Dent. 2007;192(2):111-117.

12. Filippi A, Pohl Y, Tekin U. Sensory disorders after separation of the nasopalatine nerve during removal of palatal displaced canines: prospective investigations. J Oral Maxillofac Surgery. 1999;37:134-136.

13. Magennis P. Sensory morbidity after palatal flap surgery–fact or fiction? J Ir Dent Assoc. 1990;36(2):60-61.

About the Authors

Simone Verardi, DDS, MSD
Affiliate Assistant Professor
Department of Periodontics
University of Washington
Seattle, Washington

Private Practice
Rome, Italy

Julie Pastagia, DDS, MSD
Private Practice
New York, New York