Is Residual Bone Height an Absolute Indicator for Simultaneous Implant Placement in Lateral Wall Sinus Grafting?

Lanka Mahesh, BDS, MS; Gregori M. Kurtzman, DDS, MAGD, DICOI; and Sagrika Shukla, MDS, DICOI

For implant placement, the posterior maxilla is the most problematic and difficult-to-treat intraoral area.1 Nonetheless, sinus grafting surgeries have become an integral part of implant treatment procedures, as thousands of patients annually undergo sinus augmentation to allow implant placement.¹ Placing an implant in the posterior maxilla often relies heavily on various procedures that increase the vertical dimensions of available bone. Pommer and colleagues² state that the minimum requirements to allow implant placement are bone that is at least 10 mm in height and 3 mm to 4 mm in diameter. Fortunately, a variety of options are available to modulate the quality and quantity of bone available, thus overcoming the intrinsic limitations of dental implant placement in this region.

Both anatomical structures and mastication contribute to the long-term survival rates of endosseous dental implants in the posterior maxilla.¹ However, many other variables also contribute to implant success, the foremost of which is the quality and quantity of residual bone present.³ In 1987, Misch³ developed a classification for the treatment of the edentulous posterior maxilla based on the amount of bone available below the antrum and the ridge crest, indicating the following treatment plan: SA1, adequate vertical bone for implants (ie, 12 mm) and no manipulation of the sinus is required; SA2, 0 mm to 2 mm less than the ideal bone height and may require surgical correction; SA3, only 5 mm to 10 mm of bone below the sinus; and SA4, less than 5 mm of bone below the sinus.

All the surgical protocols follow these guidelines. Implant placement with or without sinus augmentation or direct sinus lift with simultaneous implant placement depend on residual bone availability, which is done according to the aforementioned surgical protocol. With various bone graft substitutes now available and recent advancements having been made in technique, the question arises of whether residual bone height still remains an absolute indicator for simultaneous implant placement in lateral wall sinus grafting.

Case Report

A 44-year-old man presented with a missing maxillary left first molar and wanted the tooth replaced. A complete blood count indicated that the patient, who was a nonsmoker, had no systemic disease. Radiographic imaging showed an atrophic maxilla with 2 mm of bone available between the crest and the sinus floor (Figure 1). A direct sinus lift procedure with simultaneous implant placement was planned.

During surgery, after sufficient local anesthesia was achieved, a full-thickness mucoperiosteal flap was elevated in the region of interest and a lateral window was prepared using an SLA Kit (Neobiotech, neobiotechus.com) (Figure 2). Gentle elevation of the osseous window (Figure 3) and sinus membrane was achieved using sinus curettes (Figure 4). Osseous graft material was introduced into the elevated sinus, with 1 cc of cerabone^® (botiss biomaterials GmbH, botiss.com) being placed into the antrum. Approximately 75% of the graft material was placed before implant placement (Figure 5) to ensure that the implant would be surrounded by graft material without voids. The graft material used in this case is derived from the mineral phase of bovine bone and has a strong resemblance to human bone with regard to chemical composition, porosity, and surface structure. The porous network in the bone graft material particles enables a fast penetration and adsorption of blood and serum proteins and serves as a reservoir for proteins and growth factors as the graft matures.⁴

An osteotomy was created at the crest, through the native bone of the ridge and into the graft material. A Bioner Top DM implant 9 (Bioner, bioner.es), 4 mm x 11.5 mm, was inserted into the prepared site (Figure 6). The remaining bone graft material was packed over the implant to completely cover the lateral window on the ridge (Figure 7).

A resorbable membrane (Jason®, botiss biomaterials) was placed over the lateral osseous window of the grafted site (Figure 8). This membrane uses porcine percardium and consists of collagen. Porcine pericardium offers such advantages as low membrane thickness, easy manipulation (wet or dry), slow degradation because the type III collagen content provides a long-term barrier, and high tear resistance.5 The site was closed using resorbable 3-0 cytoplast sutures (Osteogenics Biomedical, osteogenics.com). A periapical radiograph was taken to document the graft and simultaneous implant placement (Figure 9).

The postoperative healing period was uneventful. A cone-beam computed tomography (CBCT) scan taken at 5 months to check the 3D fill of the graft around the implant revealed a well-integrated implant and good maturation of the bone graft (Figure 10). Apart from the CBCT, histological evidence is a time-tested method to validate bone graft maturation; however, in patients who have an implant placed simultaneously, as did this patient, a trephine core biopsy was deemed unnecessary. The implant cover screw was uncovered using a tissue punch, and impressions were taken for the implant restoration. Following conventional protocols,³ a screw-retained porcelain-fused-to-metal crown was fabricated and placed.

A periapical radiograph taken 2 years after restoration (Figure 11) showed stable crestal bone levels and the entire implant, including the apical portion, surrounded by dense bone.

Discussion

The posterior maxilla poses various clinical challenges. After tooth extraction, up to 25% bone loss occurs in the initial 6 months, and bone continues to resorb in the absence of a tooth or implant in the site.⁶ The maxillary sinus increases with age and its increased pneumatization^7,8 makes implant placement difficult, especially when the site has been edentulous for a period of time. With various modifications of the traditional sinus lifting procedures and bone grafting, however, this treatment has become not only an easy procedure but a predictably successful^9-12 method of tooth replacement with an implant.

The Report of the Sinus Consensus Conference of 1996¹⁰ clearly stated that in a class A scenario (residual bone height > 10 mm), classical implant protocol could be followed. When a class B (7 mm to 9 mm residual bone height) was present, simultaneous implant placement along with bone-added osteotome sinus floor elevation could be done. With a class C (4 mm to 6 mm residual bone height), a lateral approach involving a grafting material with immediate or delayed implants is advocated. Finally, with a class D (1 mm to 3 mm residual bone height), a lateral approach involving a bone grafting material and delayed implant placement is recommended.¹⁰

In the present case report, the ridge was only 2 mm in height and atrophic and, therefore, was both class D and in the SA⁴ category of the Misch³ classification. Consequently, ideal treatment would be a lateral approach involving a bone grafting material and delayed implant placement. The literature suggests that, in ridges with lower heights (< 10 mm), a two-phase procedure is recommended.^10,13,14 In 2010, however, Lambert and coworkers¹⁵ suggested that simultaneous implant placement and sinus grafting procedures could be performed on severely atrophic ridges, which decreased morbidity, costs, and the total time of treatment considerably, showing it to be a more desirable treatment option. The present case was consistent with many studies done in which similar surgical protocols were followed with success rates of 90% to 95%.^{7, 14-17}

In a study, Peleg and colleagues14 reported a 100% success rate of 55 hydroxyapatite-coated implants placed in 20 simultaneous sinus lifts in patients with only 1 mm to 2 mm of residual bone. Manso and Wassal,¹⁶ in a 10-year longitudinal study, reported on 160 implants placed in severely atrophic posterior maxilla, concluding that advanced posterior maxillary resorption with extensive expanded sinus (SA4) can be safely treated by a simultaneous sinus lift approach and implant insertion with survival and success rates up to 98.05% and 94.85%, respectively. Chiapasco and coworkers,⁷ after performing 9,052 sinus lifts in different categories of ridge resorption, stated that maxillary sinus floor elevation and grafting with autogenous particulated bone via a lateral approach is a safe and predictable procedure that also allows implant placement in severely resorbed posterior maxillae. In another study, Peleg and coworkers¹⁷ evaluated atrophic posterior maxillae for which only the simultaneous approach was used in a 9-year longitudinal study with 2,123 implants placed and reported a survival rate of more than 97% (44 implants failed).

Considering recent scientific advancements, the authors suggest that residual bone height is not an absolute contraindicator for simultaneous implant placement in lateral wall sinus grafting, which was clearly not the case in previous decades. Since the publication of a sinus lift procedure in 1980 by Boyne and James,¹⁸ implant surfaces, grafting materials, and sinus lift procedures have advanced considerably.¹⁹ Reviewing the literature, the results of sinus lift procedures are difficult to compare because different graft materials were used; many publications lacked well-defined criteria for the success rates of reconstructive procedures; and well-defined parameters of the initial clinical situation were rarely presented.⁷

In a systematic review, however, Wallace and Froum¹⁹ determined the efficacy of sinus augmentation procedures and compared the results. They reported that the survival of implants in augmented sinuses via a lateral window procedure varied from 61.7% to 100%, with an average survival rate of 91%. Further, they reported that sinuses augmented with particulate showed a higher survival rate compared with sinuses augmented with bone blocks and that the survival rate increased when the lateral window was covered with a membrane.¹⁹ In the present study, however, the authors wish not to comment on bone graft substitutes because the emphasis of this case report is that implants can be placed in a severely atrophic posterior maxilla and still be successful.^7,9-14,20

Conclusion

Though not a case series demonstrating consistent reproduction of results, this single case report showed successful implant placement in a severely atrophic posterior maxilla and that residual bone height is not an absolute indicator for simultaneous implant and grafting procedures. The main criteria for simultaneous implant placement are the surface treatment on the implant, the primary stability of the implant, and the vascularity of the area.

About the Authors

Lanka Mahesh, BDS, MS
Private Practice
New Delhi, India

Gregori M. Kurtzman, DDS, MAGD, DICOI
Private Practice
Silver Spring, Maryland

Sagrika Shukla, MDS, DICOI
Private Practice
New Delhi, India

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