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Sinus Lifting: Direct vs. Indirect Approach

Introduction

Implant placement in the posterior edentulous maxilla poses a considerable challenge in implant dentistry, primarily due to severe bone loss resulting from sinus pneumatization, alveolar bone atrophy, or trauma. To address this issue, multiple sinus lifting techniques have been employed, demonstrating noteworthy success rates in preparing these sites for implant placement. A thorough understanding of the maxillary sinus anatomy not only aids in meticulous preoperative treatment planning but also plays a crucial role in preventing potential complications during sinus lifting procedures. Clinical studies indicate that patients with resorbed maxillae requiring implant treatment can significantly benefit from sinus augmentation. This article delves into the fundamental techniques—direct and indirect—utilized for maxillary sinus elevation and augmentation.

Things to Consider in Relation to Maxillary Sinus Anatomy

Understanding sinus anatomy is crucial for clinicians in order to make accurate assessments and effectively plan and manage sinus lifts. Diagnostic imaging plays a vital role in treatment planning for oral rehabilitation in the posterior maxillary region. Cone-beam computed tomography (CBCT) offers precise measurements of residual bone height and density, along with valuable information about the maxillary sinus membrane, vascularization in the lateral sinus wall, existence of pathologies, and whether or not septa are present.

ِAnatomical Landmarks

Located para-nasally, the maxillary sinus is the largest pyramid-shaped sinus averaging 36–45 mm in height, 23–25 mm in width, and 38–45 mm in length. With an average volume of 15 ml, its anterior wall extends from the inferior orbital rim to the maxillary alveolar process, housing the infraorbital neurovascular bundle. A thin superior wall serves as the floor of the orbit. The posterior wall acts as a barrier between the maxillary sinus and the pterygopalatine fossa, accommodating the posterior superior alveolar nerve and blood vessels, the pterygoid plexus of veins, and the internal maxillary artery.

The medial wall aligns with the lateral wall of the nasal cavity, featuring the primary ostium, which functions as the primary secretory drainage channel. The lateral wall forms the buccal aspect of the sinus and is adjacent to the posterior maxillary and zygomatic processes. It’s the lateral wall which provides access for the lateral wall sinus graft procedure.

Maxillary premolars’ and molars’ roots are closely adjacent to the inferior aspect of the maxillary sinus. Molars’ roots are nearer to the sinus than premolar ones. Mesiobuccal root apex of the second molar is closest to the maxillary sinus wall, whereas lingual root apex of the first premolar is furthest from the sinus wall.

Sinus Septa

Maxillary sinus septa can be categorized based on their origin, with primary septa developing during maxillary growth and tooth emergence, and secondary septa acquired during maxillary sinus pneumatization following tooth loss. Predominantly, septa are situated between the second premolar and first molar region. The existence of septa often complicates sinus lifting procedures. In cases where a septum fully partitions the sinus, creating more than one lateral window as part of the sinus opening becomes necessary to navigate around the septa.

Schneiderian Membrane

The Schneiderian membrane lines the maxillary sinus ranging in thickness from 0.13 to 0.5 mm. Complete separation of the membrane from the caudal area is necessary for effective sinus lifting. That said, caution is advised as the distal side of the sinus may extend significantly. The likelihood of sinus membrane perforation is contingent upon the angle between the lateral and medial walls of the sinus. Narrower angles are associated with a higher risk of perforation.

Overfilling the maxillary sinus with bone graft material may lead to membrane necrosis, sinusitis, and potential graft loss into the sinus. Therefore, careful consideration of these factors is essential for successful maxillary sinus procedures.

Vascularization

The blood supply to the maxillary sinus is facilitated through maxillary artery branches, specifically the infraorbital, posterior lateral nasal, and posterior superior alveolar arteries. Additionally, the greater palatine artery may supply blood to the inferior part of the sinus.

The lateral wall of the maxillary sinus is supplied by the infraorbital artery and the posterior superior alveolar artery, while the medial wall is served by the posterior lateral nasal artery. In the lateral wall, both extraosseous (in the buccal tissues) and intraosseous (within the buccal plate of bone) anastomoses occur between the infraorbital and posterior superior alveolar arteries. 

The extraosseous anastomosis is situated approximately 23–26 mm from the ridge, posing a risk of hemorrhage during flapping. The intraosseous anastomosis is positioned around 16–19 mm from the ridge, and the detection of radiolucency in the buccal plate on the CBCT scans indicates the presence of an intraosseous blood vessel. This may require careful handling during lateral window preparation.

Indications and Contraindications of Sinus Lifts

Indications

  • Insufficient remaining bone (i.e. vertical bone height of less than 10 mm)
  • Resorption in the posterior maxillary alveolar bone

Contraindications

  • Acute or chronic sinus sinusitis
  • Severe allergic rhinitis and usage of topical decongestant and vasoconstrictor medications such as Oxymetazoline
  • Neoplasm or large cyst of the sinus
  • Previous sinus surgery (e.g. Caldwell–Luc operation)
  • History of radiation therapy to maxilla
  • Presence of septa
  • Uncontrolled diabetes mellitus
  • Alcoholism or heavy smoking
  • Psychosis

Sinus Lifting Techniques

The choice of maxillary sinus elevation and augmentation method is determined by both your preference as a clinician and your patient’s anatomy. Patient-specific anatomical factors, such as residual bone height and the desired amount of lift, play a crucial role in this decision-making process. 

There are two primary approaches for maxillary sinus floor elevation: the direct approach, which includes the lateral window technique, and the indirect approaches, encompassing osteotome sinus floor elevation, bone-added sinus floor elevation, minimally invasive transalveolar sinus approach, and antral membrane balloon elevation. For the purposes of this article, we will focus on the lateral window and osteotome sinus floor elevation techniques.

Lateral Window Technique

The sinus membrane is exposed and operated on through the window created in the lateral wall of maxillary sinus.

Surgical Steps

  1. Local anesthesia: infraorbital, posterior superior alveolar, greater palatine nerve block; subperiosteal anesthesia through slow infiltration.
  2. Incision: to create the lateral window, it is essential that soft-tissue incisions allow sufficient space. An anterior vertical incision should be positioned in front of the sinus wall to ensure soft tissue coverage over the bone. Then, a connecting mid-crestal ridge/palatal incision is made (preferably in keratinized tissue to facilitate suturing). A full-thickness flap is then reflected to access the posterior lateral maxillary wall.
  3. Lateral wall: the outline of the lateral wall window on the buccal plate of the bone is delineated. The window’s coronal outline is contingent upon the graft’s height, the length of the to-be-placed implant, and the location of the posterior superior alveolar artery. The size of the window should be adequate to achieve easy surgical access. With experience, membrane elevation can be achieved using a smaller (i.e. more conservative) window. The antrostomy can be either elevated (if surgical access is adequate and the cortical wall is less than 2 mm thick), or completely removed (in cases of inadequate surgical access, presence of septa, and sinus shallowness).
  4. Membrane elevation: the sinus membrane is detached and only then it can be elevated with care starting on the floor of the sinus and then extending to the anterior and posterior walls. To test membrane integrity, you can ask the patient to breathe in deeply while you observe the membrane.
  5. Implant placement: immediate implant placement can be done if there’s a minimum of 3-4 mm of residual crestal bone of good quality, otherwise, implants can be placed after 4-6 months. Guided placement of the implant through the surgical guide’s sleeve protects the membrane from the drills and minimizes the risk of perforation.
  6. Bone grafting: bone grafts are placed in the least accessible area first followed by the area along the medial sinus wall. In order not to limit vascularization, bone graft material shouldn’t be condensed too tightly.
  7. Membrane placement: resorbable membrane is placed over the window. Collagen membrane adheres to the bone and does not require fixation screws or removal.
  8. Suturing: nonresorbable monofilament suture and horizontal mattress sutures are recommended.

A significant disadvantage of the lateral window technique is that it requires a large flap to be raised in order to gain surgical access. It’s a technique-sensitive and time-consuming approach, and the success thereof is determined by the amount of available bone.

Osteotome Sinus Floor Elevation Technique

Footage courtesy of 3Sixty Academy Speaker, Dr. Nathan Doyel

Also known as transalveolar or crestal approach, this technique is generally indicated if the residual bone is 6 mm or more in height. Tapered osteotomes with increasing diameters are used to indirectly lift the maxillary sinus.

Surgical Steps

  1. Anesthesia
  2. Incision: if autogenous bone is needed, you should extend the incision distally to the tuberosity to harvest bone from the area.
  3. Flapping: full-thickness mucoperiosteal flap is reflected to expose the crest of the ridge.
  4. Drilling: use a pilot drill to prepare the osteotomy stopping 2 mm short of the sinus floor. Continue using progressively wide drills or a set of osteotomes (preferred in low-density bone) to widen the osteotomy.
  5. Bone grafting: after the largest osteotome (or widest drill through the surgical guide) has been used, bone grafting material of choice is applied.
  6. Fracture: an osteotome or drill of lesser diameter than the implant is introduced and tapped gently to fracture up the sinus floor. There’s a distinct sound that can be heard when the sinus floor is broken in.
  7. Sinus floor elevation: reintroduce the largest osteotome/drill into the osteotomy site with the graft material in place. The bone graft pushes into the sinus membrane further elevating it. You can add and tap the bone grafting material to reach the optimal sinus membrane elevation level without overstretching the membrane. ​
  8. Implant placement: place the implant using the surgical guide. Implant diameter has to be slightly larger than that of the last drill/osteotome used.

Conclusion

Maxillary sinus pneumatization occurring after posterior tooth loss in the maxilla complicates implant placement in this area. Reconstructing lost bone through sinus lifting and bone augmentation offers consistently predictable treatment outcomes. This enhances the long-term implant treatment success for many patients.

Minimally invasive transcrestal-guided sinus lift technique represents a novel procedure incorporating computer-guided planning and a guided surgical approach for maxillary sinus lifting. Utilizing CAD/CAM surgical guides, in conjunction with expander-condensing osteotomes or drills, is the more conservative approach.

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