Minimally Invasive Transcrestal Sinus Floor Elevation Procedure in Severely Atrophic Ridge: A Case Report

Preoperative cone-beam computerized tomography (CBCT) view. The axial slice is drawn through the subantral bone parallel to the adjacent teeth and, more importantly, to the proposed angle of osteotomy preparation. This is an important detail because improper measurement angulation can contribute to significant under- or overestimation of the actual dimension of subantral bone, complicating osteotomy formation endeavors by risking membrane perforation.

Figure 2. Preoperative measurements. Subantral bone dimension measured as 1.7 mm in the apicocoronal dimension relative to the proposed drilling angle (faciopalatal dimension was measured as 6.9-mm wide, although not shown here so as not to obscure the image). A consequential yet often overlooked point is that this calculated apicocoronal dimension of the subantral bone represents the center of the proposed osteotomy, which may differ significantly from the apicocoronal dimension of bone at the periphery of the osteotomy. It should be noted that multiple measurements (ie, center of the osteotomy, as well as both mesial and distal peripheries) should be calculated because the subantral bone is not necessarily of uniform height for the entire osteotomy footprint. It is important to drill all the way through to the membrane (allowing some bone to remain can complicate membrane elevation and implant placement) but not through the membrane (which would introduce a perforation that would interfere with membrane elevation, introduction of graft material, and subsequent implant placement). Figure 3. Palatalized midcrestal incision with sulcular incisions placed at adjacent teeth for a full-thickness flap toward the facial. The palatalized incision puts the eventual palatal soft-tissue margin up against the eventual healing abutment and preserves valuable keratinized tissue from the occlusal aspect of the ridge. The eventual facial soft-tissue margin can then be placed up against the facial aspect of the healing abutment, thus providing an increased zone of keratinized tissue. Figure 4. A 2.8-mm crestal approach sinus (CAS) drill with 2-mm safety stopper. The 2.8-mm-diameter CAS drill with the color-coded drill stopper, both off the drill (at left) and on (at right). The kit includes CAS drills in various diameters and stoppers that permit the drill to extend from 2 to 12 mm. Figure 5. Intact Schneiderian membrane immediately after osteotomy formation with 2.8-mm-diameter CAS drill fitted with a 2-mm stopper. This point in the surgery is a good opportunity to clinically visualize the potential discrepancies between the heights of the subantral bone around the osteotomy and in relation to the center of the osteotomy as measured on the cone-beam computerized tomography. Care should be taken to not perforate the membrane with a perio probe during this undertaking.

Figure 6. Hydraulic elevation tool. The rubber valve (green tip) connects via a tube to a syringe. Although the device is provided by the manufacturer with a 1-mL syringe, a larger syringe can be fitted to the tube, such as this 2-mL syringe. Depending on the length and diameter of the tube, the amount of fluid that remains within the tube during injection can vary, but it is certain that the entire volume of fluid that leaves the syringe will not enter the osteotomy to contribute to membrane elevation. To calculate how much fluid is needed to fill the tube and is never seen by the membrane, the tube can be filled prior to inserting the tip into the osteotomy and the measurement markings on the syringe noted. Figure 7. The rubber tip is placed just slightly into the osteotomy for introduction of NaCl under the sinus membrane. The rubber tip can be secured either by hand or with the aid of an instrument such as a hemostat. A metal tip inserts into the rubber safety tip to prevent the hemostat from clamping the rubber tip and interfering with the flow of fluid. Figure 8. Elevated membrane, with displacement of the membrane visible through the osteotomy. Although the membrane appears different than it did before elevation, visualization of an apparently intact membrane confirms neither a favorable elevation nor a lack of tears in another portion of the membrane. Figure 9. Placement of the fixture. A Thommen SPI Element 4.5- × 11-mm fixture with external hex connection was placed (with its 0.5-mm polished collar remaining supracrestal) into a 2.8-mm-diameter osteotomy with 1.7-mm high native subantral bone. Initial stability was 30 Ncm. Figure 10. Postoperative measurements. The grafted area measures 14-mm high and 12-mm wide and appears well contained within the elevated Schneiderian membrane. Figure 11. Surgical site immediately postoperative. The soft tissue was stabilized with 6-0 nylon sutures around the 3.2-mm-tall healing abutment.

Figure 12. Soft tissue at 6 months postoperatively, after removal of the healing abutment. The photo was taken just before placement of the impression coping for restorative impression. Keratinized tissue is abundant and healthy. Figure 13. Final restoration: single-piece screw-retained crown immediately after placement. Figure 14. Periapical follow-up radiograph. This radiograph was taken 24 months after sinus elevation and implant surgery and 18 months after implant restoration. It reveals what appears to be ideal bone formation around the fixture where the sinus elevation and bone grafting occurred. It also demonstrates approximately 1.5 mm of crestal bone loss from the rough/smooth border, which must have occurred late enough for the fixture to have retained primary stability during healing. Figure 15. Radiographic follow-up. Sagittal section of cone-beam computerized tomography (CBCT) taken 30 months after sinus elevation and implant surgery and 24 months after implant restoration. It reveals no more crestal bone loss compared with the radiograph taken 6 months earlier. Figure 16. Radiographic follow-up. Axial slice (cross section) of the CBCT taken 30 months from sinus elevation and implant surgery and 24 months after implant restoration. It reveals 3-dimensional bone formation to the implant apex but slightly less on the facial aspect.