‘Butterfly’: a residual bone independent technique for one-stage sinus lift

Abstract

A 29-year-old woman with an extreme pneumatisation of the maxillary sinus and a missing molar was treated with one-stage sinus lifting and implant placement in a novel surgical approach.

Background

Maxillary sinus pneumatisation is a continuous physiological process that may affect the available subantral alveolar bone. Due to this consequence of tooth loss, in many cases, implant placement is not possible without performing an additional sinus-lift procedure. Traditionally, when less than 4 mm of alveolar bone height is present, the indication is to perform sinus lifting and implant placement in two different stages. However, some authors encouraged the idea to perform sinus lifting with simultaneous implant placement, even in cases with 1 mm to 4 mm of alveolar bone height, as long as convenient primary implant stability was achieved.^{1 2} Therefore, we look to introduce a new concept, marked by the fact that one-stage sinus lifting with simultaneous implant placement can be predictably performed, independently of the subantral alveolar bone height. This case report has the purpose to exemplify such a case scenario and its management using the ‘Butterfly’ technique. Additionally, a comprehensive description of this novel procedure is delineated.

Case presentation

We report a case of a 29-year-old woman who presented to our clinic, expressing the desire to replace her missing upper right first molar (figure 1A). The patient was a non-smoker, without any other previously diagnosed medical diseases.

Figure 1.

(A) Clinical aspect, (B) preoperative panoramic X-ray and (C, D) preoperative CBCT. CBCT, cone beam computed tomography.

Investigations

The preliminary radiographic analysis consisted panoramic radiography (figure 1B) for general evaluation of the amount of bone available; a panoramic X-ray investigation was supplemented with a three-dimensional evaluation with a preoperative cone beam computed tomography (CBCT, figure 1C, D). In a CBCT examination, a significant pneumatisation of the sinus could be assessed. Due to resorption, the remaining subantral bone was less than 1 mm on the position of the upper right first molar. Routine preoperative blood tests were performed. All the blood test results were within normal range.

Treatment

Antibiotic prophylaxis was initiated 1 hour before surgery (2 g of amoxicillin + clavulanic acid).

Two cartridges of 1.7 mL of 4% articaine with an epinephrine concentration of 1:100 000 (Ubistesin Forte 3M ESPE, Seefeld, Germany) were injected into the mucobuccal fold and palatal area adjacent to the right maxillary first molar. After anaesthesia was performed, a full thickness trapezoidal mucoperiosteal flap was elevated. A diamond round bur, at a speed of 1000 rpm with copious irrigation with normal saline solution, was used to prepare antrostomy in the lateral wall of the maxillary sinus. The position of the window was approximately 3 mm from the sinus floor. The lateral bone window was removed with a periosteal elevator and the Schneiderian membrane was carefully elevated without any intraoperatory complication. After the implant site was marked with a lance drill, a 3.3 mm drill was used (300 rpm with copious saline irrigation) in order to create the osteotomy for implant placement. The lifting height was determined by the insertion of the implant depth gauge through previously prepared osteotomy site. Undetected perforation of the Schneiderian membrane is one of the most common complications during sinus-lift procedures. This complication can be managed using a resorbable collagen membrane. Even though in this particular case no perforation was detected, a resorbable membrane (Collprotect Membrane, Botiss biomaterials GmbH, Germany) was placed under Schneiderian membrane as an extra safe-way element. Deproteinised bovine bone mineral particle (Cerabone, Botiss GmbH, Germany) mixed with 2 mL of metronidazole B solution (5 mg/mL) was used as a grafting material. Since sinus contamination by anaerobic bacteria seems almost unavoidable during bone graft surgery, the local use of of metronidazole could provide more security when performing sinus-lift procedures.³ After the grafting material was packed, a 4.0/11.5 mm tapered implant (Anyridge, Megagen Implant Co, Korea) was placed with the surgical motor (at 35 rpm), until approximately 3 mm of the implant remained supracrestally (figure 2A). The implant carrier was removed. Whenever necessary, implant holding tweezers may be used in order to facilitate the removal of the connector without modifying the implant angulation. A 2 mm cuff height screw (I-Gen Kit, Megagen Implant Co, Korea) was connected to the implant. A ‘Butterfly’ shape titanium mesh was designed using surgical scissors, accordingly to the mesiodistal distance between the neighbouring teeth. The titanium mesh used in this particular case was an I-Gen Membrane (I-Gen Kit, Megagen Implant Co) but a different titanium mesh could be used as an alternative, as long as it was properly adapted. It was crucial to leave at least 1.5 mm distance from the margin of the mesh to the neighbouring teeth, in order to facilitate the biological sealing between periosteum and native alveolar bone, and such preventing a dehiscence. With a surgical or anatomical forceps, the ‘Butterfly’ mesh was placed above the screw (previously connected to the implant), and a second cover screw (I-Gen Kit, Megagen Implant Co) was used to attach it to the first screw. This step of the procedure was performed with digital clockwise movements, until the ‘Butterfly’ wings reached the surface of the bone. Angulation of the implant is controlled by hand while clockwise rotation movements are performed. Since there are two titanium wings, as soon as the implant is screwed in the final position and the wings come in intimate contact with the bone, the angulation will be maintained. In order to avoid clockwise rotation of the mesh, forceps were used to stabilise it, by holding (or pressing) one wing against the alveolar bone. Two 1.5/3 mm self-drilling membrane fixation screws were used in order to stabilise the mesh together with the implant. The self-drilling screws were placed through the mesh, one from the labial aspect and one from the palatal aspect, without interfering with the neighbouring teeth (figure 2B, C). The implant had no contact with the native bone, being totally ‘immersed’ in the grafting material. The initial stability of the implant could be obtained by the accurate cortical engagement of the ‘Butterfly’ mesh with two self-drilling screws. Autologous cortical, lid previously removed, was placed back in order to cover the grafting particles (figure 2C). The flap was then secured with 5/0 non-resorbable horizontal mattress and interrupted sutures (figure 2D).

Figure 2.

(A) Implant transitional position, (B) titanium mesh stabilised with cortical screws, (C) clinical aspect before wound suture, (D) wound closure and (E) postoperative panoramic X-ray. CBCT, cone beam computed tomography.

Outcome and follow-up

The patient was prescribed antibiotics (amoxicillin + clavulanic acid, 2 g daily for 7 days in total) and analgesics (ibuprofen 600 mg, two times per day for a maximum of 3 days). Oral rinses with 0.12% chlorhexidine solution, 2 times per day over 1 week, were also prescribed. No severe facial swelling and pain after surgery was mild. On the 10th day postoperatively, the mucosal wound healed uneventfully and the sutures were removed and a panoramic X-ray was performed (figure 2E). The surgical site was clinically evaluated (figure 3A) and subjected to CBCT scanning after 8 months (figure 3B, C). New bone formation was radiologically evaluated as optimal. A midcrestal incision was performed to expose the previous surgical site (figure 3). The two self-drilling membrane fixation screws were removed in order to detach the cover screw, titanium mesh and the 2 mm cuff height screw that facilitated implant placement (figure 3E). A smart peg was connected to the implant in order to assess the biological stability of the implant (figure 3F). The biological stability was 75 ISQ, corresponding to an optimal value for occlusal loading. A healing abutment was placed and the wound was sutured with 5/0 non-resorbable suture. The patient was recalled 10 days after healing abutment placement and the sutures were removed. Six weeks later, the final crown was delivered.

Figure 3.

(A) Clinical aspect 8 months after surgery, (B, C) 8 months postoperative CBCT, (D) intraoperative aspect before mesh removal, (E) implant intraoperative aspect and (F) biological stability measurement using Ostell ISQ. CBCT, cone beam computed tomography.

At 2-year recall appointment, both clinical and radiographic evaluations, showed the optimal status of the previously regenerated bone, dental implant and final crown (figure 4).

Figure 4.

Two years postoperative panoramic X-ray.

Discussion

Adequate quality and quantity of bone represent prerequisite criteria for a successful outcome in implant dentistry. Sinus pneumatisation is a continuous physiological process that may limit the available bone volume necessary for convenient implant placement in the lateral area of the maxilla. Nowadays, maxillary sinus augmentation is a frequently used procedure to increase the vertical height of the alveolar bone followed prior to or at the time of implant placement. There are many approaches and techniques that evolved through the 40-year history of sinus lifting. Conventionally, the moment of implant placement is decided in relation to the ability of the subantral alveolar bone to offer optimal implant primary stability.

According to the existing literature, if adequate vertical volume of the alveolar bone exists for obtaining optimal primary stability, the dental implants can be placed simultaneously with the sinus augmentation. Sinus lifting with simultaneous implant placement was first described by Tatum in 1986.⁴ According to most of the authors, simultaneous and delayed procedures display similar survival rates.^{1 2 5}

The Report of the Sinus Consensus Conference of 1996 asserted that in a class D scenario (1 mm to 3 mm residual bone height), a lateral approach involving a bone grafting material and delayed implant placement is recommended.⁶ However, several authors stated that even in less minimal residual alveolar bone height, simultaneous implant placement may be performed with similar survival and success rates. Cha et al reported that residual alveolar bone height was not a factor that impacts the outcome in a statistically significant manner. According to his study the cumulative survival and success rate (98.91%) for cases with 1 mm to 4 mm of alveolar bone height was similar to cases with 5 mm to 8 mm subantral bone (96.54 %).² Similar results were displayed by Felice et al.¹

In the present case report, the subantral alveolar bone was less than 1 mm in height and, therefore, was both class D and SA 4, according to Misch and Judy classification.⁷ Therefore the recommended treatment protocol according to the last 40 years of practical guidelines, would be to perform sinus augmentation and implant placement in a delayed approach. However, due to the novelty of this technique that involved additional implant components that would facilitate implant stabilisation, author’s choice was to perform one-stage procedure in cases with extreme alveolar bone resorption.

The advantage of the ‘Butterfly’ technique over multiple other procedures previously described is that in this protocol, implant placement is not conditioned by the primary stability enabled by the height of the available subantral bone. Placing the implant at the time of grafting minimises the overall treatment time, reduces the costs and brings an increased acceptability from the patients’ perspective since the morbidity is lowered. To date the procedure described has proved to be predictable and with a significant success rate.

Patient’s perspective.

Since I had a wisdom tooth extraction 3 years before, I was psychologically prepared for a more complicated procedure. Fortunately, my expectations were wrong.

Learning points.

• One-stage sinus lifting with simultaneous implant placement can be performed even in cases with less than 1 mm subantral alveolar bone height.

• ‘Butterfly’ technique can significantly save time, costs and reduce morbidity.

• Patients’ acceptance is high due to the reduced treatment time and to the fact that in one surgery, both alveolar bone reconstruction and implant placement are performed.