Internal Sinus Membrane Elevation in Patients with Less Than 5 mm Residual Bone Height – Rationale and Protocols

Maxillary sinus surgery has been performed since the 19th century, as initially described by George Caldwell and Henri Luc.¹ It was primarily for the treatment of infectious and pathologic conditions. Today, several dentoalveolar procedures are performed that involve the sinus cavity, such as orthognathic surgery and trauma, removal of dislodged root fragments and foreign bodies, and dental implant placement.

The sinus floor of the maxilla is curvilinear and consists of the alveolar process of the maxilla. Its lowest point is around the first or second molars but often extends mesially to involve the maxillary premolars.² As aging occurs, the sinus floor can resorb and cause dehiscence around the roots of the teeth.³ It has been shown that after extraction of teeth, maxillary alveolar bone resorption continues to occur throughout life.⁴ Through this resorptive process and expansion of the maxillary sinus, decreased residual bone height (RBH) may occur in the posterior maxilla. Pramstraller and colleagues found that the majority of patients had 7 mm or less of RBH in the posterior maxilla.⁵ This anatomic consideration may necessitate a sinus membrane elevation procedure before or concurrent with placement of dental implants.

Sinus membrane elevation is a surgical maneuver that raises the sinus membrane away from the floor of the sinus, allowing for placement of a dental implant. Access through the ridge crest and elevating the floor of the maxillary sinus and the sinus membrane was initially described by Tatum⁶ in 1976 and then published by Boyne and James⁷ in 1980. Later, Summers developed a set of osteotomes that allowed for a less invasive, closed method of elevating the sinus floor, known today as the internal sinus membrane lift procedure.⁸

The sinus membrane elevation procedure can be accomplished through either a direct or indirect technique.^9,10 The direct technique, popularly known as the lateral window technique, allows for visualization of the sinus membrane through the removal of the maxillary bone lateral to the sinus cavity, which is then elevated and grafted, and the implant is placed. This method is extensively documented and can be performed with significantly decreased RBH, through either a one-stage (4 mm to 6 mm RBH) or a two-stage (1 mm to 3 mm RBH) technique.¹⁰ However, it has been reported that the risk for sinus membrane perforation can range up to 44%.^11-16 Additionally, this procedure increases surgical morbidity, treatment cost, and treatment time, precluding many patients from being able to benefit from implant therapy.⁸

The indirect or internal elevation technique lifts the sinus membrane by elevating it superiorly using osteotomes, with or without the use of grafting material. Rosen and coworkersreported internal sinus membrane elevation performed on patients with ≥5 mm RBH had an implant success rate of 96% versus an implant success rate of 85.7% with ≤4 mm RBH.¹⁷ A previous consensus conference recommended that internal sinus membrane elevation not be performed unless there was 7 mm to 9 mm RBH.¹⁰ These initial reports, however, did not mention the initial implant stability at which the implants were placed. Furthermore, they were reported before the era of modern implant designs and surfaces and when periapical radiographs were not standardized. This has reinforced the commonly accepted limit for internal sinus membrane elevation as 5 mm RBH.¹⁸

Internal sinus membrane elevation was historically performed using grafting material.¹⁰ Recent studies have shown that the use of bone graft material when simultaneously placing an implant is not indicated. A study by Si and colleagues placed 41 implants using the internal sinus membrane elevation technique.¹⁹ A total of 21 implants were placed using xenograft mixed with autogenous bone in patients who had on average a RBH of 4.67 mm ± 1.18 mm, and 20 implants were placed without grafting material in patients who had on average a RBH of 4.58 mm ± 1.47 mm. At 36 months follow-up, the patients who had received bone grafting had a bone gain of 3.17 mm ± 1.95 mm, whereas the patients who had not received grafting material had a bone gain of 3.07 mm ± 1.68 mm.¹⁹ This increase in RBH is of benefit to both the anatomy of the sinus and characteristics of the sinus membrane. An intact sinus provides vascularity, and the scaffold created by the implant works to stabilize a blood clot, which carries osteogenic potential.^20,21 One purported advantage of using bone graft material with internal sinus membrane elevation is the avoidance of a tenting effect of the sinus membrane localized to the implant position; however, the clinical significance of this effect is considered inconsequential.

In a recent breakthrough study, Nedir and colleagues, using an internal sinus membrane elevation technique, performed a randomized clinical trial in which 37 tissue-level, coronally flared implants (Straumann TE^® Tissue Level, Straumann, straumann.us) were placed in RBH of 4 mm or less.²⁰ This amount of RBH is below the previously accepted values for internal sinus membrane elevation. A total of 17 implants were placed without grafting material (test group), and 20 implants were placed with grafting material (control group). All implants were loaded at 10 weeks and followed-up for 1 year. The investigators found that two implants in the control group failed (1.4 mm and 1.2 mm RBH). Two additional implants rotated at loading; one was in the test group (0.9 mm RBH) and one was in the control group (1.5 mm RBH). These two implants were allowed to heal for 3 more months and were then loaded successfully. Based on the investigators' radiographs, these failures seem to have occurred in patients with minimal RBH, suggesting potentially fused cortices (alveolar crest and sinus floor). The overall success rate was 100% for the test group and 90% for the control group.²⁰ In a subsequent publication on long-term follow-up of implants, Nedir and coworkers reported that this procedure can be performed predictably.²¹

The purpose of this article is to describe an adaptation of the procedure performed by Nedir and colleauges^20,21 and its successful use in the University of Connecticut School of Dental Medicine Advanced Specialty Education Program in Prosthodontics. The specific adaptations include the use of a collagen plug inside the osteotomy after upfracture of the sinus floor¹⁸ and the allowance of a 4- to 6-month healing period (as opposed to 10 weeks) before loading of the implant.

Various guidelines are recommended to perform this indirect sinus membrane elevation procedure in situations with less than 5 mm of RBH. A summary of the guidelines is as follows: First, the procedure requires use of pretreatment cone-beam computed tomography (CBCT), and the choice of implant must be decided before surgery. Careful drilling is done without perforation of the sinus floor or membrane. A flat sinus floor, free of any septum, with sufficient width is needed. Depth stops on sinus elevation (concave tipped) osteotomes are used to fracture the sinus floor. No bone graft material is used, a collagen plug is placed into the floor of the osteotomy, and a coronally flared tissue-level type implant is used. The procedure employs single-stage implant therapy. Post-surgical sinus precaution instructions are given to the patient, and healing time is at least 4 months.

A preoperative CBCT scan is necessary to obtain an accurate measurement of the RBH and ridge width, as well as to evaluate the sinus anatomy of the patient. A flat sinus floor that is free of any septum in the area for implant placement is necessary as is a ridge with sufficient width that does not require significant horizontal ridge augmentation. If these anatomic factors are not satisfied, internal sinus membrane elevation may be contraindicated.^8,20,21

In the present case, the patient is receiving an implant to replace tooth No. 3 (Figure 1 and Figure 2). A full-thickness mucoperiosteal flap is first raised, exposing the bony crest, to prepare an implant osteotomy using standard drilling protocols (Figure 3). The length and height of the osteotomy must be restricted to the available RBH and stop short of the sinus floor to avoid any perforations. The osteotomy is then widened to the appropriate diameter of the planned implant by sequential drilling and cooling using chilled saline. A sinus membrane elevation osteotome with a depth stop is then lubricated with saline and carefully inserted into the prepared osteotomy. The sinus floor is carefully up-fractured, and the membrane is gently elevated to the appropriate height using further depth stops on the osteotome (Figure 4). A ligated guide pin also can be used to gently elevate the membrane instead of an osteotome instrument.

A 10-mm x 20-mm collagen plug (Zimmer Collagen Plug, Zimmer Biomet, zimmerbiomet.com) is then placed in the osteotomy (Figure 5). This may help to protect against any micro-tears in the sinus membrane while having no deleterious effects.¹⁸ No bone graft material or collagen membrane is placed inside the osteotomy. A tissue-level (transmucosal) coronally flared implant is then placed (Straumann Tissue Level or Straumann TE Tissue Level Implant) with good primary stability (Figure 6), followed by a healing abutment. The mucoperiosteal flap is then sutured using a single-stage surgical protocol. The patient is then instructed to follow standard postoperative sinus precautions for 3 weeks, and the implant is allowed to heal for at least 4 months, depending on bone density (Figure 7 through Figure 11).

Several additional examples of this procedure are presented in Figure 12 through Figure 19 to elucidate different scenarios with successful application of the protocol.

The internal sinus membrane elevation technique presented here has been documented extensively in the literature.^19,22-24 While not novel, the procedure offers a unique amalgamation of advantages previously described.^8,18-20,24 These advantages, along with disadvantages, are summarized in Table 1.

Use of a coronally flared implant is critical to the success of this technique for two reasons. First, along with a coronally flared implant geometry, this type of implant may have a shorter pitch distance and aggressive thread design that allow good primary stability to be attained. In a patient with decreased RBH, primary stability is especially important because of the risk of implant failure if the bone density in the posterior maxillary region is poor (type IV). Secondly, the coronally flared implant prevents potential loss of the implant superiorly into the sinus cavity, either during surgery or during the healing period before secondary stability is achieved. Furthermore, a widened healing abutment can be placed for additional security against dislodgement of the implant into the sinus cavity. Failure to use a coronally flared implant may significantly increase the risk of the procedure.

Although internal sinus membrane elevation may allow for a less invasive treatment, it is important to note that this technique is not meant to replace the traditional direct sinus membrane elevation technique. Nevertheless, as evidence emerges for minimally invasive procedures, clinicians should carefully consider the alternative internal sinus membrane elevation protocol before pursuing the more invasive approach of direct sinus membrane elevation.

Indirect sinus membrane elevation for patients with less than 5 mm RBH affords many advantages for implant placement in the posterior maxilla. It allows for less surgical morbidity and fewer surgical complications, decreased treatment time and cost, and reduced number of surgical procedures. It also offers a graft-less option while maintaining similar or better implant survival rates compared with direct sinus membrane elevation. The success of this treatment, however, is dependent upon strict adherence to the protocol, particularly the use of a coronally flared implant for achieving good primary stability and safeguarding against loss of the implant superiorly into the sinus cavity.

Tyler J. Thomas, DMD, MDSc
Former Resident, Post-Graduate Prosthodontics, University of Connecticut School of Dental Medicine, Farmington, Connecticut; Fellow, American College of Prosthodontists

Avinash S. Bidra, BDS, MS
Clinical Associate Professor and Director, Post-Graduate Prosthodontics, University of Connecticut School of Dental Medicine, Farmington, Connecticut; Fellow, American College of Prosthodontists