This prospective study aimed to provide detailed clinical information on a sinus augmentation procedure, i.e., transcrestal sinus floor elevation with a bone block using the press-fit technique. A bone block is harvested with a trephine burr to obtain a cylinder. This block is inserted into the antrum via a crestal approach after creation of a circular crestal window. Thirty-three patients were treated with a fixed prosthesis supported by implants placed on 70 cylindrical bone blocks. The mean bone augmentation was 6.08 ± 2.87 mm, ranging from 0 to 12.7 mm. Only one graft failed before implant placement. During surgery and the subsequent observation period, no complications were recorded, one implant was lost, and no infection or inflammation was observed. This proof-of-concept study suggests that the use of a bone block inserted into the sinus cavity via a crestal approach can be an alternative to the sinus lift procedure with the creation of a lateral window. It reduces the duration of surgery, cost of treatment, and overall discomfort.
In resorbed posterior maxillary bone due to alveolar ridge resorption and maxillary sinus pneumatization, implant placement posterior to the first premolar requires bone grafting, a procedure that is well-documented in the literature. Following the creation of a window in the buccal side of the sinus, the Schneiderian membrane is elevated prior to bone placement to increase bone volume. The sinus augmentation procedure is associated with several complications. Membrane perforation is the most frequently reported complication, ranging from 0% to 58%, whether or not associated with sinusitis, which varies in severity. Graft loss also has to be considered a complication, since it modifies the treatment plan. Partial loss could modify implant placement, which could result in treatment failure related to aesthetics or function. Partial graft loss is found in 0–25% of cases, while total graft loss occurs in up to 2.6% of cases.
This graft loss can be explained in part by biological concepts. It has been demonstrated that subantral bone can be augmented in a space created concentrically from the sinus bone walls after placement of the blood clot with or without the addition of filling materials. Thus, to optimize the bone-forming capacity of the subantral tissues, it is important to preserve the osteogenic potential from the lateral bone walls and to make the lateral window as small and as high as possible. This biological concept may be in contradiction with sufficient visual control in areas that are difficult to access through a lateral window. Thus, the design of the lateral window is a potential cause of graft loss.
Whatever the design of the window, success can be described as the complete reossification of the reconstructive material based on osteogenic cell penetration, adhesion, and neovascularization to supply individual cells with nutrients and oxygen. The vascularization process continues over time in the host tissue, from the outer area to the core of the volume. Thus, the time required for the development of the vascular network to cover the entire graft volume depends on the grafted bone volume. As a consequence, cells located at the core of the graft die faster due to ischaemia in the central part, which can result in incomplete colonization, limited to the scaffold’s external layer or to some part of the scaffold, which does not permit appropriate implant placement.
To counter this potential problem, particularly for severely atrophic bone in the posterior maxillary region that requires a greater volume of filling material, the use of image-guided surgery to take advantage of the limited remaining bone volume or the placement of zygomatic implants has been proposed. Another option would be to reduce the size of the grafted volume to the implant dimension at the implant location. Draenert and Eisenmenger have described such a surgical strategy: a transcrestal elevation of the sinus floor and alveolar ridge augmentation with a cylindrical bone transplant with the press-fit technique. This method also reduces the lateral fenestration of the maxillary sinus and the preparation of the sinus mucosa. The method was tested successfully on 10 fresh porcine skulls and two fresh human cadavers. To our knowledge no in vivo results have been published.
The present prospective observational study was conducted to describe the clinical outcomes of this crestal approach with delayed implant placement. The objectives of this report are to describe potential graft complications and survival after a follow-up period of 2–13 years.
Materials and methods
Since 1998 we have performed the surgical approach presented herein as an alternative to the sinus lift with a lateral approach. Not every patient who matched the inclusion criteria was included, since very few patients were initially eligible until the follow-up observation period was considered sufficient to reuse the method.
Surgery and associated data were recorded in a dedicated file at the time of surgery. For this reason the study can be considered a prospective case series. The files of all patients treated with the tested method in our department between 1998 and 2010 were screened thoroughly. All patients included in this study were contacted early in 2012 for a follow-up visit. No patient was lost to follow-up.
Patients were only recruited if they matched the following criteria: implant placement required to support a prosthesis; partially or totally edentulous maxilla associated with various degrees of alveolar ridge resorption and sinus pneumatization that did not allow the placement of adequately sized implants; age over 18 years. Exclusion criteria were as follows: the need for tooth extraction during the surgical procedure; signs of sinusitis recorded on the computed tomography (CT) scan; pregnancy at the time of evaluation; tobacco addiction, metabolic disorders, immunocompromised status, haemophilia or other bleeding disorders, drug or alcohol abuse, treatment with steroids, history of radiation therapy in the head and neck, psychiatric disorders, and inability to understand the procedure described.
Two trephine burrs (Zepf; Helmut Zepf Medizintechnik GmbH, Tuttlingen, Germany) were used for the procedure; for example, a larger 6-mm (inner diameter) burr for donor site drilling and a smaller 5.5-mm (outer diameter) burr for crest drilling. An associated bone socket former with a tapered shape, a smooth tip, and a maximum outer diameter of 5.5 mm was used. For all bone graft material used, bone was harvested with the larger trephine burr in order to obtain a cylinder of bone of a certain diameter depending on the dimension of the residual crest and the planned implant diameter. The cylinder diameter was required to be 2 mm more than the planned implant diameter and the length ideally greater than the planned implant length.
Autogenous bone or allograft bone (TBF Genie Tissulaire, Mions, France) was used. The choice was made by the practitioner, taking into consideration the amount of bone needed for appropriate reconstruction and patient compliance. Given the difficulty in harvesting large bone cylinders measuring 12 mm in length and 6 mm in diameter to place an implant 10 mm in length and 4 mm in diameter in one piece, allograft material was our first choice ( Fig. 1 ). Autogenous graft material was harvested upon patient request or for a small block. Two sites were selected, the ramus and symphysis.
For the ramus, after incision, we used a 6-mm inner diameter trephine burr mounted on a contra-angle under extensive saline irrigation. Sometimes the length of the cylinder was nearly 10 mm, other times it measured 6–8 mm (proximity of the dental alveolar nerve); in this case, two ramus bone cylinders were harvested in order to reconstruct a 10-mm-high cylinder. We closed the site as for third molar surgical extraction. A similar procedure was used when harvesting on an edentulous span.
For symphysis access, a 1-mm incision was made under the mucogingival line, generally half thickness for 5 mm and then full thickness, and the symphysis area exposed. The bone cylinder was removed carefully with the trephine, avoiding the incisors and the canine apex. The osseous holes could be filled with collagen sponge. Soft tissues were replaced and sutured.
Preparation of the allogeneic bone graft is simple: the trephine corresponding to the inner diameter of the graft site is used to manufacture a cylinder of allogeneic cancellous graft that perfectly fits the grafted site. Before drilling, it is important to moisten the osseous block with physiological serum.
Crestal sinus floor elevation and bone augmentation procedure
One surgeon performed all the surgical procedures. Antibiotic prophylaxis was administered to all patients (amoxicillin 500 mg or clindamycin 300 mg) starting the day of surgery and continuing for 6 days after surgery. Steroids at 40 mg per day for 4 days were also administered.
All patients were treated under local anaesthesia. A full-thickness flap was reflected to expose the top of the alveolar crest and a very limited amount of the buccal plate and the palatal curvature. The osteotomy was performed on the crest at the planned implant location using the 5.5-mm outer diameter trephine burrs mounted on a contra-angle under extensive saline irrigation. The drilling sequence was stopped 2 mm above the Schneiderian membrane and continued carefully with a bone socket former to preserve membrane integrity and to create a circular bone window ( Fig. 2 ). The bone thickness was assessed before surgery by radiological examination ( Fig. 3 ).
The previously harvested bone cylinder was prepared with a conical shape and inserted until the top was approximately flush with the top of the crest. The conical shape in combination with the 0.5-mm underdrilled host site led to bone compression and improved the primary stability of the block. The top was then modelled to obtain a slight overcorrection of the crest. None of the blocks was attached with microscrews; particulate bone was never used to pack the recipient site, nor was a sheet used to cover the surgical site. Soft tissue management ensured tight flap closure with 3-0 silk or polyethylene sutures. This suture material was removed after 1 week. Postoperative instructions included mouth rinse (0.2% chlorhexidine) and paracetamol for analgesia.
After the healing period, a second-stage surgery was performed to place the endosseous implant. To ensure the placement of the implant within the bone block, two procedures were used: (1) an intraoperative X-ray was taken with the first burr in place, or (2) placement was image-guided. In some cases, the Summers technique was used at the time of placement to increase the recipient site dimension in order to place a longer or larger implant ( Fig. 4 ). Abutment connection and prosthetic loading of implants were performed 4 months after implant placement ( Fig. 5 ). Radiographic follow-up consisted of either panoramic or intraoral radiographs obtained immediately after the reconstructive procedure at the time of implant placement, at the time of prosthetic loading, and annually thereafter ( Fig. 6 ). In some cases, the bone gain was assessed before implant placement using CT ( Fig. 7 ).
Success criteria and data recorded
Control visits were conducted by a single surgeon in early 2012. Ethical approval was obtained to collect and analyze the data.
During the follow-up visit, the prostheses were not removed because most were cemented. Implant survival was evaluated according to the clinical and radiological criteria proposed by Buser et al. and modified as follows: absence of mobility in prosthodontics, absence of peri-implant suppuration, absence of continuous radiolucency around the implant, and absence of pain and subjective sensation.
Crestal bone thickness and width were assessed based on a CT scan obtained before implant placement ( Fig. 3 ). A line tangential to the bottom point of the crest was traced representing height zero. A line perpendicular to the zero line was traced passing through the bottom point. The distance between the intersection points of the perpendicular line with the first sinus point and with the zero line was used to calculate the residual bone height. A third line was traced parallel to the zero line passing through the above-mentioned first sinus intersection point. The distance between the first palatal point and the first buccal point on the third line was used to calculate the residual bone width.
Bone height was measured before implant placement on an orthopantomogram (OPG) or intraoral X-rays to determine the bone gain.
Intraoral X-rays were used to measure peri-implant bone loss, both at the marginal position and apex position. Radiographic assessment was carried out by a radiologist technician. For every patient, at every stage, radiography positioners were used, placing the bar parallel to the direction of the X-ray beam, perpendicular to the sensor. Marginal bone loss was measured based on the radiological criteria reported by Buser et al., modified as follows: two reference points were marked on the surface of the implant platform and joined with a line representing height zero. Two vertical lines were drawn perpendicular to the zero line up to the first implant bone mesial and distal contact points. Differences in length between these perpendicular lines on X-rays taken at the different time points were used to calculate bone loss. Bone loss was measured between implant placement and prosthesis placement, and between prosthesis placement and the control visit ( Fig. 8 ).
From 1998 to 2010, 33 patients were treated; they ranged in age from 23 to 80 years (mean 55.5 years). All patients attended the follow-up visit in early 2012. Seventy-seven cylindrical bone blocks were used for bone grafting for the placement of 70 implants. Twenty-seven patients were treated with an allograft bone block and six patients received an autogenous bone cylinder. Six blocks were not used for implant placement. They were placed close to another block to avoid the protrusion of only one block in the large sinus that could injure the membrane. One graft failed before implant placement ( Table 1 ).
|Year graft implanted||Number of patients||Donor site||Number of implants placed||Graft failure||Implant failure|
|2002||4||3 ramus, 1 allograft||11||N||1|
|2010||8||1 ramus, 7 allograft||20||N||N|