Sinus lift

Maxillary sinus floor augmentation^[1] (also known as a sinus lift, sinus graft, sinus augmentation, or sinus procedure) is a surgical procedure to increase the amount of bone in the upper back part of the jaw (posterior maxilla). This is achieved by lifting the lower Schneiderian membrane and placing a bone graft.^[2]

X-ray showing a sinus lift in the left upper jaw

Sinus lift surgery, 3D Illustration

Indications

While there may be several reasons for increasing the bone volume in the posterior maxilla, the most common reason for the surgery is to provide sufficient bone under the maxillary sinus for dental implant placement.^[3]

A sinus lift is performed when the medial wall is too close to an area where dental implants are to be placed. This procedure is performed to ensure a secure place for the implants while protecting the sinus. Lowering of the sinus can be caused by long-term tooth loss without treatment, periodontal disease, or trauma to the tooth.^[4]

Patients who have the following may be candidates for sinus augmentation:^[5][6]

• Loss of more than one tooth in the posterior maxilla
• Loss of a significant amount of bone in the posterior maxilla
• Missing teeth due to genetics or birth defects
• Missing most maxillary teeth and requirement of a strong sinus floor for multiple implants.

It is not known if sinus lift techniques are more successful than short implants in reducing the number of artificial teeth or dental implant failures up to a year after their placement.^[7]

Technique

1) Edentulous area of two missing teeth is being prepared for future placement of dental implants with a lateral window sinus lift; incisions into the soft tissue are shown here.
2) The soft tissue is flapped back to expose the underlying lateral wall of the left maxillary sinus.
3) The bone has been removed with a piezoelectric instrument, exposing the underlying Schneiderian membrane, which is the lining of the maxillary sinus cavity.
4) Through careful instrumentation, the membrane is carefully peeled from the inner aspect of the sinus cavity.
5) The membrane has been reflected from the internal aspect of the inferior portion of the sinus cavity; one can now visualize the bony floor of the sinus cavity without its lining membrane (note the triangular ridge of bone within the sinus, known as an Underwood's septum).
6) The newly formed space within the bony cavity of the sinus yet inferior to the intact membrane is grafted with human cadaver allograft bone. The floor of the sinus will now be roughly 10mm or so more superior than it was before, providing enough room to place dental implants into the edentulous site.

Before undergoing sinus augmentation, diagnostics are run to determine the health of the patient's sinuses. Panoramic radiographs are taken to map out the patient's upper jaw and sinuses. In special instances, cone beam computed tomography is preferable to measure the sinus's height and width, and to rule out any sinus disease or pathology.^[8]

There are several variations of the sinus lift technique.

Traditional sinus augmentation or lateral window technique

The procedure is performed from inside the patient's mouth where the surgeon makes an incision into the gum. Once the incision is made, the surgeon then pulls back the gum tissue, exposing the lateral bony wall of the sinus. The surgeon then creates a "window" into the sinus, exposing the Schneiderian membrane. The membrane is separated from the bone, and bone graft material is placed into the newly created space. The gums are then sutured closed, and the graft is left to heal for 4–12 months.^[9]

The graft material can be either an autograft, allograft, xenograft, alloplast, synthetic variants, or combinations.^[10] Studies indicate that the mere lifting of the sinus membrane might result in new bone formation due to the principles of guided bone regeneration.^[11] The long-term prognosis for the technique is estimated at 94%.^[12]

Osteotome technique

As an alternative, sinus augmentation can be performed by a less invasive osteotome technique. There are several variations of this technique, and all originate from a technique pioneered by Dr. Hilt Tatum, which was first published by Boyne and James in 1980.^{[citation needed]}

Dr. Robert B. Summers^[13] described a technique that is normally performed when the sinus floor needing to be lifted is less than 4mm thick. This technique is performed by flapping back gum tissue and making a socket in the bone 1–2mm short of the sinus membrane. The floor of the sinus is then lifted by tapping the sinus floor with the use of osteotomes. The amount of augmentation achieved with the osteotome technique is usually less than what can be achieved with the lateral window technique.

A dental implant is placed in the socket formed at the time of the sinus lift procedure and left to integrate with the bone. Bone integration usually takes 4 to 8 months. The goal of this procedure is to stimulate bone growth and form a thicker sinus floor to support dental implants for teeth replacement.^{[citation needed]}

Sinus dimensions and shape significantly influence new bone formation after transcrestal sinus floor elevation. With this technique, the regeneration of a substantial amount of new bone is a predictable outcome only in narrow sinus cavities. During surgical planning, sinus width should be regarded as a crucial parameter when choosing sinus floor elevation.^[14]

Dr. Bruschi and Scipioni^[15][16] described a similar technique (Localised Management of Sinus Floor or L.M.S.F.) that is based on a partial thickness flap procedure. This technique increases the malleability of the crestal bone and uses not the bone directly below the sinus, but rather the bone on the medial wall, and thus can be used in more extreme cases of bone resorption that would normally need to be treated with the lateral wall technique. The healing period is reduced to 1.5 to 3 months. Recently, an electrical mallet^[17] has been introduced to simplify the application of this and similar techniques.

Complications

A major risk of sinus augmentation is that the sinus membrane could be pierced or ripped. Remedies include stitching the tear or placing a patch over it. In some cases, the surgery is stopped altogether, and the tear is given time to heal, usually three to six months. Often, the sinus membrane grows back thicker and stronger, making success more likely on the second operation.^[18] Although rarely reported, such secondary intervention can also be successful when the primary surgery is limited to the elevation of the membrane without the insertion of additional material.^[19]

Besides tearing of the sinus membrane, there are other risks involved in sinus augmentation surgery. Most notably, the close relationship of the augmentation site with the sinonasal complex can induce sinusitis, which may become chronic and cause severe symptoms. Sinusitis resulting from maxillary sinus augmentation is considered a Class 1 sinonasal complication according to Felisati classification and should be addressed surgically using a combined endoscopic endonasal and endoral approach.^[20] Beside sinusitis, other procedure-related risks include:

• Infection^[7]
• Inflammation
• Pain
• Itching
• Allergic reaction
• Tissue or nerve damage^[7]
• Scar formation
• Hematoma
• Graft failure
• Tilting or loosening of implants
• Bleeding^[7]

Recovery

It takes about three to six months for the sinus augmentation bone to become part of the patient's natural sinus bone. Up to six months of healing is sometimes required before implants are attempted. However, some surgeons perform both the augmentation and dental implant simultaneously to avoid performing two surgeries.^[21][22]

History

A sinus-lift procedure was first performed by Dr. Hilt Tatum Jr in 1974 during his period of preparation to begin sinus grafting. The first sinus graft was done by Tatum in February 1975 in Lee County Hospital in Opelika, Alabama. This was followed by the placement and successful restoration of two implants. Between 1975 and 1979, much of the sinus lining elevation was done using inflatable catheters. After this, suitable instruments were developed to manage the lining elevation from the different anatomical surfaces encountered in the sinuses. ^[23]

Tatum first presented the concept at The Alabama Implant Congress in Birmingham in 1976 and presented the evolution of the technique during multiple presentations each year until 1986 when he published an article describing the procedure. Dr. Philip Boyne was introduced to the procedure when he was invited by Tatum, to be "The Discusser" of a presentation on sinus grafting given by Tatum at the annual meeting of The American Academy of Implant Dentistry in 1977 or 1978. Boyne and James authored the first publication on the technique in 1980 when they published case reports of autogenous grafts placed into the sinus and allowed to heal for 6 months, which was followed by the placement of blade implants. This sequence was confirmed by Boyne before the attendees at The Alabama Implant Congress in 1994.^{[citation needed]}

Cost-effectiveness

The slightly higher effectiveness of the lateral sinus-lift technique needs to be considered due to the higher costs in comparison with the transalveolar sinus lift technique. From a patient perspective, the higher invasiveness of the lateral technique will also be an important decision criterion. However, the transalveolar approach is unlikely to be effective in cases of advanced levels of bone reduction at the implant site.^[24]