A Modified Transalveolar Sinus Floor Elevation Approach With a Bilaterally Enlarged Osteotomy

The maxillary first and second molars are among the most commonly extracted teeth. Progressive pneumatization of the maxillary sinus and resorption of the alveolar ridge after tooth extraction reduces the height of alveolar bone in the edentulous posterior maxilla, decreasing the available bone for dental implant placement.¹ 

Sinus floor elevation using a crestal approach or a lateral window technique has been used to vertically augment the posterior maxilla.^2,3  The lateral window approach is a predictable method for sinus augmentation with the residual alveolar bone height of less than 5.0 mm.⁴  However, this relatively aggressive technique causes more postoperative discomfort, such as postoperative pain, swelling, and ecchymosis.⁵  Sometimes blood vessels in the maxillary sinus wall complicate the lateral window opening.⁶  In a transalveolar antrostomy, sinus floor elevation is done via the osteotomy prepared by the implant drill. Therefore, the transalveolar sinus floor elevation technique causes less trauma and takes shorter operative time, and hence there is less postoperative morbidity.⁷  However, via the osteotomy, the sinus cavity cannot be directly visualized, and the sinus membrane cannot be directly instrumented.⁸  Hence, this technique usually requires a residual bone height (RBH) of more than 5.0 mm to achieve predictable results.^9,10 

This article presents a modified technique of transalveolar sinus elevation on the severely resorbed (RBH <5.0 mm) alveolar edentulous ridge with a buccal-palatal width of more than 8.0 mm. In this technique, the osteotomy is buccal-lingually enlarged to a measurement of 8.0–10.0 mm to provide access of surgical curets in the sinus.

This report presents 3 cases of sinus floor elevation on severely atrophic alveolar bone (RBH <5.0 mm). To restore missing maxillary teeth, a modified transalveolar approach was carried out as follows:

1. Under local anesthesia, make a midcrestal incision and raise a full-thickness mucoperiosteal flap.

2. Locate the sites of the planned implants and use a drilling kit with drill stop to prepare an osteotomy to less than 1.0 mm from the sinus floor.

3. Buccal-lingually enlarge the osteotomy to a measurement of 8.0–10.0 mm and remove the sinus floor using the diamond bur with caution (Figure 1a).

4. Elevate the sinus membrane with different curets (Advanced Sinus Kit, DentiumUSA, Cypress, Calif) from various angles (Figure 1b).

5. Test the sinus membrane for perforations with the Valsalva maneuver (a conscious attempt at expiration while holding the nostrils closed and keeping the mouth shut).

6. Fill the preparation with the grafting material. Place implants and cover the exposed osteotomy site with a resorbable membrane (Figure 1c).

A 55-year-old male was referred to restore a previously extracted maxillary left first molar (Figure 2a). The tooth was extracted due to severe periapical infection 6 months prior to presenting for implant treatment. The adjacent teeth demonstrated good periodontal condition. Cone-beam computed tomography (CBCT) showed that the RBH was 3.0–4.0 mm and that the alveolar bone width was above 10.0 mm in the edentulous region (Figure 2). The patient wanted a conservative and comfortable way for his implant treatment.

After the elevation of a full-thickness mucoperiosteal flap, the modified transalveolar approach to crestal sinus elevation was carried out as described above (Figure 3 a and b). The prepared sinus was filled with grafting material (Bio-Oss, Geistlich Biomaterials, Wolhusen, Switzerland). An implant (∅4.5 × 10 mm, DentiumUSA) was placed (Figures 3c), and a resorbable membrane (Bio-Gide, Geistlich Biomaterials) was used to cover exposed osteotomy. Postoperative X ray showed that sinus membrane was elevated for more than 6.0 mm. After 6 months of healing without events, some high-quality bone covering the cervical aspect of the implant was removed to place the healing abutment. An all-ceramic crown was fabricated and delivered later. Panoramic X ray demonstrated stable bone level around the implant neck and remodeled bone grafts in the sinus 12 months after the restoration (Figure 4).

A 45-year-old male presented with the loss of the first and the second right maxillary molars with RBH of 2.0–3.0 mm (Figures 5a). Two bilaterally enlarged osteotomies were made, and the sinus membrane was safely elevated with the modified transalveolar approach (Figure 5b). To avoid perforation of sinus membrane during implant insertion, elevated heights at 2 sites were measured with a gauge before 2 implants (bone level, 4.8 × 10 mm; Straumann USA LLC, Andover, Mass) were inserted. Postoperative panoramic radiography showed that the sinus membrane was elevated for approximately 8.0 mm. In 1-year follow-up, implants functioned very well (Figure 5c).

Transalveolar sinus elevation was performed for a 40-year-old female with loss of the second left maxillary premolar and the first and the second left maxillary molars that had resulted in about 2 mm of RBH (Figure 6a). Three bilaterally modified osteotomies were made at the implant sites. Membrane around 2 molars was elevated with curets through osteotomies without events (Figure 6b). However, perforation of membrane occurred at the second premolar because the curet failed to keep in contact with the bone due to limited size of the osteotomy at this site. The perforation was covered with a resorbable membrane (Bio-Gide), and the osteotomy was filled with gelatine sponges (Gelatamp, Coltene, Langenau, Germany). The preparation of 2 molars was filled with grafting material (Bio-Oss). Then 2 implants (tissue level, ∅4.8 × 10 mm, Straumann) were placed. After covering exposed osteotomy with a resorbable membrane (Bio-Gide), the flaps were sutured. Postoperative CBCT showed that the sinus membrane was elevated for over 8.00 mm (Figure 7a), and there was no complication during the following 6 months of healing. Then another implant was placed for the second premolar (Figure 7b) after sinus elevation with the traditional Summers approach.

Membrane perforation is one of the most commonly occurring intraoperative complications during sinus augmentation surgeries, with a prevalence rate of 7%–44%.¹¹  Different factors are associated with sinus membrane perforation, such as rotary instruments, RBH, thickness of the membrane, and smoking. Among these, short RBH is a significant risk factor, and perforation rate increases significantly when the lift height of the membrane exceeds 5.0 mm.^12,13 

Modifications of sinus lift focus on gentle elevation of the membrane. In the lateral approach, the perforation rate of sinus membrane is effectively decreased by keeping hand instruments directly in contact with the bone surface.¹⁴  However, direct contact of hand instruments to the bone can be difficult in a conventional transalveolar method. In this report, the shape of crestal osteotomy is modified to increase the access of surgical curets in the sinus. Through the enlarged osteotomies, surgical curets can be kept in contact with the underlying bony walls to avoid membrane perforation. In the cases presented herein, the cortical bone of sinus floor was removed with the diamond bur of the Dentium Advanced Sinus Kit. Additionally, the piezosurgery and osteotome technique can be used to remove the floor.

The modified crestal method in the present study can be used on alveolar ridges with RBH of 1.0–4.0 mm; however, it is skill sensitive due to the lack of a direct view of sinus membrane. In addition, this technique is recommended for alveolar ridges with a buccal-palatal width of more than 8.0 mm to guarantee the size of crestal osteotomy and the corresponding access of surgical curets. Therefore, membrane perforation occurred in case 3 at the second premolar site, where the alveolar ridge was deficient in width. Moreover, special attention needs to be paid to the primary stability of implants, and root-analogue implants are recommended to avoid falling into the sinus. Also, the thickness of Schneiderian membrane makes a difference in a sinus lift surgery. Some reports found that greater perforation rate may occur in cases with either thick membrane (>1.5–2 mm)^15,16  or thin membrane (0.84 ± 0.67 mm).^17,18  Therefore, how membrane thickness affects the sinus lift surgery with this modified crestal method remains to be investigated.

This clinical report of raising the Schneiderian membrane to facilitate subantral bone augmenation demonstrates a modified transalveolar technique to permit placement of implants in the severely atrophic alveolar ridge with a buccal-palatal width of more than 8.0 mm. This method is more conservative than the lateral-wall approach and more versatile and predictable than the traditional Summers approach.

Abbreviations

CBCT:

cone-beam computed tomography, a medical imaging technique consisting of X ray computed tomography where the X rays are divergent, forming a cone.

RBH:

residual bone height, the height of bone between sinus floor and alveolar bone crest.

The authors declare no conflict of interest.