Maxillary sinus augmentation.

The placement of endosseous implants in posterior edentulous maxilla is normally a challenging task in implant dentistry due to maxillary sinus pneumatization. Various sinus augmentation techniques have been used with impressive success rates aimed at developing these sites for implant placement. Knowledge of anatomy of maxillary sinus guides us not only in proper preoperative treatment planning but also helps us to avoid the possible complications that may arise during sinus augmentation procedure. This topic attracts a rising number of publications with most of them reporting results that suggest, the patients with atrophic maxillae requiring implant treatment can benefit considerably from the use of sinus augmentation. This article explains the basic techniques, namely, direct and indirect techniques used for maxillary sinus elevation and augmentation.

INTRODUCTION

Maxillary sinus augmentation (also known as sinus floor elevation) procedures have become increasingly popular procedures before placement of dental implants in posterior maxillae that have suffered severe bone loss due to sinus pneumatization, alveolar bone atrophy, or trauma. In 1970s, Hilt Tatum used maxillary sinus cavity to increase available bone using graft material, which allowed greater implant to bone contact area once the bone graft matured.[1] The maxillary sinus lift grafting procedure that was designed and described by Boyne and James,[2] is not the same procedure that is performed today. After that, numerous articles have been published regarding different grafting materials and modifications of their technique.[34] The purpose of this review article is to enumerate all the techniques used for maxillary sinus elevation and augmentation.

Anatomical considerations

Having knowledge of sinus anatomy is a prerequisite for understanding the principles involved in making proper incisions and designing and managing the sinus elevation. Clinicians should also be familiar with other anatomic structures before performing sinus elevation. Diagnostic imaging is an essential component of treatment planning in oral rehabilitation in posterior maxillary region.[5] Cone-beam computed tomography (CBCT) provides more precise dimensions of the residual bone height and density.[6] It also provides information about maxillary sinus membrane, arterial passages in the lateral sinus wall, pathologies of maxillary sinus, and presence of septa.[7]

Sinus anatomy and dimensions

Maxillary sinus is the biggest pyramidal-shaped paranasal sinus. The average dimensions of the maxillary sinus are 36–45 mm in height, 23–25 mm in width, and 38–45 mm in length (anteroposterior axis). The average volume of the maxillary sinus is 15 ml.[8] Anterior wall extends from inferior orbital rim to the maxillary alveolar process containing infraorbital neurovascular bundle. Superior wall is the floor of orbit and is very thin. Posterior wall separates the maxillary sinus and pterygopalatine fossa which contains posterior superior alveolar nerve and blood vessels, the pterygoid plexus of veins and internal maxillary artery. Medial wall is the lateral wall of the nasal cavity which houses primary ostium. This ostium serves as the main channel for drainage of secretions. Lateral wall forms the buccal aspect of the sinus and contributes to the posterior maxillary and zygomatic process; this wall provides access for the lateral wall sinus graft procedure.

Maxillary sinus septa

Maxillary sinus septa were first mentioned by Underwood in 1910.[9] Based on their origin, septa can be further subdivided into primary septa, formed during maxillary development and tooth growth, or secondary septa which is acquired during the pneumatization of the maxillary sinus after tooth loss.[10] The majority of septa are located between the second premolar and first molar area.[11] Sinus augmentation is usually complicated by the presence of septa. If there is a full partition of the sinus by a septum, more than one lateral window is created as part of the sinus opening to circumvent the septa.[12]

Schneiderian membrane

Maxillary sinus is lined by the membrane called as Schneiderian membrane. This membrane is a pseudostratified columnar respiratory membrane ciliated epithelium formed by the basal cells, columnar cells, and goblet cells fixed to the basal membrane. About 100–150 cilia present on each columnar cell which vibrate at 1000 beats/min. Thickness of the membrane normally varies from 0.13 to 0.5 mm (average 0.8 mm thick).[13] The membrane should be freed totally from the caudal area to enable lifting of the sinus; however, the distal side of the sinus might extend considerably.[14] Chances of sinus membrane perforation depend on the angle between the lateral and the medial wall of the sinus. Greater than 60° angle has 0% chances of perforation; 30°–60° angle has 28.6% chances of perforation; and <30° angle has 62.5% chances of perforation.[15] Thus, narrow angles result in higher perforations. Overfilling of the maxillary sinus with the bone graft material may cause necrosis of the membrane as well as sinusitis and the potential loss of the bone graft into the sinus.

Relation of sinus to dentition – Roots of maxillary premolars and molars have an intimate relationship with the inferior aspect of the maxillary sinus. Molars roots are closer to sinus than premolar roots.[16] Mesiobuccal root apex of the second molar is closest to the maxillary sinus wall (average distance of 0.83 mm), whereas lingual root apex of the first premolar is furthest from the sinus wall.[17]

Vascularization

Blood supply occurs by the branches of maxillary artery, namely, infraorbital artery, posterior lateral nasal artery, and posterior superior alveolar artery. Additional blood supply to the inferior part of the sinus may come from the greater palatine artery.[18] Infraorbital artery and posterior superior alveolar artery supplies the lateral wall of the maxillary sinus, while posterior lateral nasal artery supplies the medial wall of the sinus. Lateral wall of sinus has both extraosseous (in the buccal tissues) and intraosseous (within the buccal plate of bone) anastomosis that occurs between infraorbital and posterior superior alveolar artery. Extraosseous anastomosis is around 23–26 mm from the ridge. It may cause hemorrhage during flap preparation. Intraosseous anastomosis is around 16–19 mm from the ridge. When examining cross-sections of a CBCT scan, detection of radiolucency in the buccal plate denotes the presence of an intraosseous blood vessel. Thus, it may need to be managed during a lateral window preparation.[19]

Indications:

Inadequate residual bone height (<10 mm of vertical bone height)

Atrophic posterior maxillary alveolus.

Contraindications:

Acute active sinus infection

Recurrent chronic sinusitis

Severe allergic rhinitis

Neoplasm or large cyst of the sinus

Previous sinus surgery like the Caldwell–Luc operation

History of radiation therapy to maxilla

Presence of Underwood's septa/severe sinus floor convolutions

Uncontrolled diabetes mellitus

Alcoholic and heavy smoker

Psychosis.

DIFFERENT TECHNIQUES FOR MAXILLARY SINUS ELEVATION

The type of maxillary sinus elevation and augmentation that a surgeon chooses to use on a given patient depends on the surgeon's preference as well as patient anatomy. Patient anatomical factors include the residual bone height and amount of lift desired. There are two main approaches for maxillary sinus floor elevation: Direct and Indirect approach. Direct –lateral window technique and indirect – osteotome sinus floor elevation, bone added sinus floor elevation, minimally invasive transalveolar sinus approach, and antral membrane balloon elevation. But in this article, sinus augmentation using lateral window approach and osteotome sinus floor elevation are only described in detail.

Direct/lateral window technique

In this technique, sinus membrane is directly visualized and instrumented through the window created in the lateral wall of maxillary sinus.

Following are the steps of direct/lateral window technique:[20]

Anesthesia – Infraorbital, posterior superior alveolar, greater palatine nerve block; subperiosteal anesthesia through slow infiltration (speed 1 ml/min)

Incision – Soft-tissue incisions must provide adequate room for creation of the lateral window. Anterior vertical incision should be at least 10–15 mm anterior to the wall of sinus to ensure soft tissue over the bone. Next, a mid-crestal ridge/palatal incision with 15C blade is made connecting the vertical incision. It is desirable to make the horizontal incision in keratinized tissue to facilitate suturing. Full-thickness flap is reflected to access canine fossa just below the infraorbital foramen, buttress of the zygomatic arch, and posterior lateral maxillary wall. While elevating full-thickness flap, the elevator must be adherent to the bone surface, so that the periosteum remains unchanged

Lateral window/antrostomy – After flap elevation, a sterile number 2 pencil is used to demarcate the outline of the lateral wall window on the buccal plate of bone. Position of the antrostomy is determined by the size and location of maxillary sinus. Coronal outline of the window will depend on the height of the graft, length of the implant to be placed, and location of posterior superior alveolar artery. Apical outline of the window should be approximately 3 mm above the sinus floor. Mesial outline of the window should be as close to anterior wall and distal outline will depend on the number of implants to be placed. Size of the window should be 20 mm mesiodistally and 15 mm apicocoronally which is sufficient to guarantee easy surgical access. When the surgeons experience level increases then he/she can easily elevate the membrane with reduced access and a smaller, more conservative access window can be made. This will retain a large source of blood supply to the lateral wall and enhance maturation of graft. High-speed handpiece with number 8 diamond bur is used to outline the window until bluish hue is visible with gentle brushing or paintbrush stroke. The shape of the window is usually oval and should not have sharp edges that may cause perforation of the membrane [Figure 1]. Bone tampers are used to in-fracture the sinus bony access window. Antrostomy can either be elevated or completely removed. It is elevated when there is good surgical access and the thickness of the cortical wall is <2 mm. It is completely removed when surgical access is difficult, in the presence of septa and in shallow sinus

Figure 1

Oval configuration of the antral lateral window

Sinus membrane elevation – Detach the sinus membrane with blunt instrument. Elevation should be preceded only when the membrane detaches.[21] Membrane should be elevated carefully starting on the sinus floor and then extending to the anterior and posterior walls with the help of sinus curettes [Figure 2]. The final elevation is up to the medial wall to the full height of the expected graft placement [Figure 3]. Sinus membrane integrity can be tested by asking the patient to breathe in deeply while observing the membrane lifting

Figure 2

Scrapping sinus membrane off the bone

Figure 3

Increased distance from the crest of the ridge to the elevated sinus floor

Preparation of implant site – If there is minimum of 3–4 mm of residual crestal bone of good quality, it is possible to place implants simultaneously or else place the implant after 4–6 months. Since the maxillary bone is a low-density bone, undersize the implant osteotomy site. Protect the sinus membrane with periosteal elevator to avoid damaging with drills

Graft placement – Sinus membrane should be protected with collagen membrane. Implants are placed in the prepared implant sites. Bone grafts are placed in the least accessible area first. Anterior and posterior recesses are filled first followed by the area along the medial sinus wall. Do not compact the bone graft too tightly as it prevents vascularization. But some authors showed that sinus lift can be performed using the lateral approach with whole blood as the sole filling material with promising results.[2223] Thus, sinus augmentation with simultaneous implant placement can be done using platelet-rich fibrin as a sole grafting[24]

Membrane placement – Resorbable membrane is placed over the window (collagen membrane adheres over the bone which does not require fixation screws and does not require removal)

Suturing/incision closure – Nonresorbable monofilament suture and horizontal mattress sutures are used to suture the flap (does not require any advancement).

The major drawback associated with lateral antrostomy is that it requires the raising of a large flap for surgical access. This approach is more technique sensitive and time-consuming. The procedure's success relies mainly on the amount of residual bone.

In 2001, Vercellotti et al. introduced the piezoelectric technique.[25] The advantage of piezoelectric osteotomy lies in being able to cut the bony window with great simplicity and precision while ensuring the membrane's integrity. This is due to the termination of the surgical action when the piezosurgery tips come in contact with nonmineralized tissue.[2627]

Indirect/osteotome technique/crestal approach/transalveolar approach

Transalveolar technique was first performed by Tatum.[1] Summers later described another crestal approach, using tapered osteotomes with increasing diameters. Indirect osteotome maxillary sinus floor elevation is generally indicated where the residual bone height is equal to or >6 mm.[28]

Following are the steps of osteotome technique:[29]

Anesthesia

Incision – crestal incision should be extended distally in some cases, to the tuberosity area where autologous bone needs to be harvested

Flap – to expose ridge crest, full-thickness mucoperiosteal flap is elevated

Drilling – start the osteotomy preparation with pilot drill of 2 mm diameter keeping it 2 mm short of the sinus floor. Here, confirmatory radiograph should be taken by inserting pilot drill. Either the widened drills or set of osteotomes of varying dimensions can be sequentially used to widened the osteotomy site to the same level, i.e., 2 mm short of sinus floor. In low-density bone (D3 and D4), osteotomes are preferred to laterally condensed the bone and to enhance the density of the bone

Grafting – once the largest osteotome has expanded the implant site, particulated bone substitutes (mixed with autogenous bone) are added to the osteotomy as the grafting material. Composite bone graft composed of 25% autogenous and 75% hydroxyapatite graft should be preferred. Graft is inserted in the osteotome site, before the in-fracture of the sinus floor

Fracture – an osteotome of lesser diameter than the implant body is inserted in the prepared osteotomy site and tapped gently to fracture up the sinus floor. Look out for the change in sound while in fracturing the sinus floor. When sinus floor fractures different pitch of sound can be heard

Sinus floor elevation– This is done by reinserting the largest osteotome in the implant site with the graft material in place. The added bone graft exert pressure onto the sinus membrane which elevates it further. Bone graft can be added and tapped to achieve the desired amount of sinus membrane elevation [Figure 4a-c]. Do not exceed the stretching limit of the membrane

Figure 4

Bone-added osteotome sinus floor elevation (a) osteotome instrumentation by malleting (b) fractured sinus floor and added bone graft in osteotomy (c) sinus elevation with simultaneous implant placement

Implant placement – Implant fixture to be placed should be slightly larger in diameter than the osteotomy created by the final osteotome.

Minimally invasive techniques

Other minimally invasive techniques for sinus augmentation have been introduced over the years. Modified trephine/osteotome technique was described in 1999 was modified by the simultaneous insertion of implants. The implant site is prepared using a 3 mm exterior diameter trephine bur at a distance of 1–2 mm from the sinus floor. Bone cylinder is then pushed apically to a depth of 1 mm less than the one made with the bur, using an osteotome of the same diameter as the trephine bur. The final preparation of the implant site is carried out using osteotomes of increasing diameters, always inserting them to the same depth. The implants are inserted at a speed of 30 rpm, causing controlled lateral movement of the bone cylinder inside the space created by the movement of the sinus membrane.[30]

Antral membrane balloon elevation procedure was given by Soltan et al. in 2012. This technique uses inflatable balloon to elevate the sinus membrane. The Zimmer sinus lift balloon was designed to lift the sinus membrane gently and evenly. This technique has been shown to reduce the chance of sinus membrane perforation.[3132] There is a metal shaft with a tip connected to a latex balloon which has the inflation capacity of approximately 5 cm.[3] For lateral window approach, angled design of balloon and for a crestal approach, the straight design balloon is used. There is popular micro-mini design also available which can be used for either of the approaches. Before the balloon is inserted, the osteotomy is enlarged to 5 mm. Osteotome of 5 mm is used to break the sinus floor after the addition of bone. The sleeve of the balloon is then inserted 1 mm beyond the sinus floor. The saline is injected slowly from the syringe into the balloon so that the balloon would inflate progressively. The desired elevation is determined by deflating the balloon and the process is again repeated till the desired sinus elevation. One cubic centimeter of saline is expected to raise 6 mm of the membrane.[33]

Minimally invasive transalveolar sinus approach (MITSA) elevation technique was given by Kher et al. 2014. In this procedure, calcium phosphosilicate putty is used for hydraulic sinus membrane elevation.[34] Drilling is done 1 mm short of the sinus floor and osteotomy completes till the last drill. Concave 3 mm osteotome is used to in-fracture sinus floor. Novabone gun cannula fits snugly in prepared osteotomy. The material gently lifts membrane due to its consistency. Thereafter, implant is placed. MITSA technique is minimally invasive as this technique uses osteotome only once so is less traumatic to the patient.

Minimally invasive transcrestal-guided sinus lift technique was given by Pozzi and Moy.[35] This is a new procedure with computer-guided planning and a guided surgical approach to elevate the maxillary sinus. The use of computer-aided design/computer-aided manufacturing generated surgical template in combination with expander-condensing osteotomes, make this surgical technique minimally invasive.

Postoperative instructions and care

Following postoperative instructions should be provided to the patient with both verbal and written form:[36]

On first night after surgery, head should be elevated on 2 or more pillows

Liquid diet for 2 days and then soft diet for 2 weeks

Some nasal bleeding may occur during first day

Medications – Amoxicillin with clavulanate potassium 625 mg BID for 10 days; ibuprofen 600 mg and acetaminophen 500 mg QID for 3 days; oxymetazoline nasal spray for 7 days; 1.2% chlorhexidine mouth 30 cc BID for 14 days

Avoid chewing from the surgical site, blowing the nose for 2 weeks, smoking, balloon blowing, sucking liquid with straw, flying in pressured aircraft or scuba diving, carbonated drinks (minimum 3 days), heavy lifting of weights, and playing musical instrument that require blowing. Actions that create negative pressure (blowing of nose or sucking through straw) must be avoided by the patient during the first week after surgery. If the patient does sneeze, he or she must keep the mouth open, so that the pressure is not exerted within the sinus

Swelling – some bruising, facial swelling expected underneath the eye. Apply ice packs over the face; 10 min on and 10 min off.

COMPLICATIONS AND ITS MANAGEMENT

Sinus membrane perforation is the most common intraoperative complication, which occurs in 7%–35% of sinus augmentation procedures.[37] Factors that affect sinus membrane perforation during osteotomy include vigorous instrumentation during elevation and thickness of the sinus membrane. Sinus membrane perforation increases rates of postoperative sinusitis and graft failure. Vlassis and Fugazzotto proposed a classification system for elevation and treatment.[38] If a membrane is perforated when creating the lateral window outline, the osteotomy is extended several millimeters beyond the original window to reestablish contact with the intact membrane.[3940] If membrane perforation occurs during the lifting of sinus membrane and is a small defect of <2 mm it can be left to heal itself but if the perforation is more than 2 mm, the opening can be patched with a piece of hydrated resorbable collagen barrier that's large enough to cover the tear by several millimetres.

Bleeding can occur while performing an osteotomy. Bleeding from the sinus membrane can be controlled by placing gauze soaked with anesthetic solution containing 1:80,000 epinephrine directly onto the membrane. Bleeding from the bone requires application of direct pressure with an artery forceps, or it can be managed with a cautery unit. Another method for containing an intraosseous arterial bleeder is to displace the membrane and compress the bone with a mosquito hemostat, thereby crushing the bone and obstructing the bleeding blood vessel.[4142]

Dislodgement of implant into sinus can occur several days postimplantation, at abutment connection surgery, or years later. This may be due to positioning of implant in an unnecessary apical position or excessive pressure during placement or widening of the ridge due to overdrilling. Thus, careful treatment planning, patient selection, and the appropriate sinus augmentation technique are essential to minimize the risk of implant displacement into the maxillary sinus. Once the displacement is diagnosed and located in computed tomography scan/orthopantomogram, the implant must be removed as soon as possible.[43]

Other complications are related to the presence of preexisting antral pathologies, such as rhinosinusitis, odontogenic sinus diseases, pseudocysts, retention cysts, and mucoceles.[43]

CONCLUSION

Pneumatization of the maxillary sinus secondary to posterior maxillary tooth loss prevents implant placement in this region. Maxillary sinus elevation and augmentation provides predictable outcome of regenerating lost osseous structure in the posterior maxilla. This offers the patient many advantages for long-term success at implant sites.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.