Abstract
The aim of this paper is to describe a technique for sinus floor augmentation with a 1-step crestal approach where the residual bone is ≤7.5 mm. 36 implants were installed in 25 patients in the atrophic posterior maxilla immediately after sinus floor elevation. Sinus floor elevation was performed with a crestal approach using either osteotomes and burs or piezosurgery. Standardized intraoral radiographs were taken prior to surgery and 1 year after surgery. The mean residual bone height was 5.61 mm (range 3–7.5 mm). The mean gain of sinus elevation was 6.78 mm (range 3.5–10 mm) at 1 year after surgery. Two patients dropped out of the study. Of the 23 patients completing the study, one implant failed, whilst the remaining 33 implants were stable 12 months after surgery (cumulative survival rate 97%). A statistically significantly higher bone height was achieved with tapered implants compared with cylindrical implants ( P < 0.05). No statistically significant differences were found in bone level using osteotomes or piezosurgery. Piezosurgery was considered to provide less discomfort for the patient and greater convenience for the surgeon.
In the posterior maxilla, implant insertion is often limited due to maxillary sinus extension, especially in atrophic maxillae . Sinus floor elevation is a well-recognized method of overcoming this problem and allows implant installation . The most widely used techniques for maxillary sinus floor elevation are the classical lateral antrostomy introduced by T atum in 1976 , which consists of the preparation of a bony window in the lateral maxillary sinus wall, and the more recent osteotome technique that utilizes a crestal approach, proposed by S ummers in 1994 .
According to traditional protocols, in cases of good quality bone and subantral bone height ≥5–6 mm the implant is installed simultaneously with the sinus floor elevation, with or without adding bone graft material . In contrast, in situations of poor quality bone or of subantral bone height <5 mm, lateral antrostomy is performed and the space under the elevated Schneiderian membrane is filled with bone graft material .
Lateral antrostomy may be performed using a 1- or 2-step approach. Implants are installed simultaneously with the bone graft (1-stage lateral antrostomy) or after a delay to allow for bone healing (2-stage lateral antrostomy). Residual bone thickness (whether it is greater or less than 5 mm) is the deciding factor between the two methods . The 1-stage procedure is less time-consuming for the clinician and patient, but its success depends on the amount of residual bone .
The most common intraoperative complication with these surgical approaches is perforation of the Schneiderian Membrane . W allace et al. state that the membrane perforation rate has been reduced from the average reported rate of 30% with rotary instrumentation to 7% using the piezoelectric technique.
Using piezoelectric ultrasonic vibration (25–30 kHz), the piezosurgery device precisely cuts only mineralized structures (bone) without cutting soft tissues, which remain undamaged even in case of accidental contact . The typical cavitation effect induces a hydropneumatic pressure in the physiological saline solution that contributes to atraumatic sinus membrane elevation .
Another advantage of piezosurgery is its precision . Compared with the oscillating micro-saw, the movement of the piezosurgery knife is very small, so the cutting precision is greater and causes less discomfort for the patient . The absence of macrovibrations makes the instrument more manageable and allows greater intra-operative control, with a consequent safer action in anatomically difficult situations . When using this instrument the clinician applies a very small amount of pressure which allows a very precise cut .
The piezosurgery device provides a clear surgical site, as it maintains a blood-free surgical field during bone cutting, due to the air–water cavitation effect of the ultrasonic instrument. This allows improved visualization of the surgical area.
The main advantage of the osteotome technique is that it is a less invasive procedure than lateral antrostomy . It improves bone density, which allows greater initial stability of implants. After progressive preparation of the bone, elevation of the sinus floor by several millimeters is obtained with a reduced operative time compared with other sinus graft procedures. The disadvantage of the crestal approach required with the osteotome technique is that initial implant stability has to be substantiated if the residual bone height is <6 mm and implants are installed simultaneously with elevation of the sinus floor . The chances of achieving a sufficient sinus floor elevation with the osteotome technique are limited. According to standard protocol, the osteotome procedure cannot be used to elevate the sinus membrane more than 5 or 6 mm . Favourable results have been reported in cases with a residual bone height of 3 mm treated with a crestal approach .
This paper describes and evaluates a procedure for maxillary sinus elevation with a crestal approach in cases with residual bone height of 7.5 mm or less. This is a 1-step approach in which implants are inserted simultaneously with sinus grafting. The technique uses either osteotomes and traditional burs or a piezosurgery device to perform the antrostomy osteotomies with a minimally invasive procedure.
The aim of this prospective study is to describe the above-mentioned technique for sinus floor elevation with a 1-stage crestal approach and to evaluate if there is any difference in bone level augmentation at 1-year post-implant installation when osteotomes are used compared with piezosurgery following this technique.
Materials and methods
From April 2002 to January 2008, 25 patients (14 women; 11 men), with a mean age of 48.25 years (range 27–72 years) were treated for sinus floor elevation, to install dental implants in the atrophic posterior edentulous maxilla. The patients selected were all considered to be in good general health with no contraindications for oral surgery and the related prosthetic protocols. Exclusion criteria included: an uncontrolled medical condition such as diabetes mellitus, immune suppression, bisphosphonate medication, oro-facial cancer, chemotherapy or head and neck radiotherapy; infarct during the preceding 6 months; a pathologic lesion in the sinus (benign/malignant tumour, mucocele, or active sinusitis); untreated active periodontitis in neighbouring teeth. Healing time since tooth extraction was longer than 12 months.
Opposing dentitions were natural teeth or fixed prostheses supported by natural teeth or implants. Subjects with opposing removable prostheses were excluded. The mean height of the alveolar process in the intended implant sites was 5.61 mm (range 3–7.5 mm). Alveolar height was measured from the alveolar bone crest to the sinus floor. Each patient had at least one, but no more than two implants installed into an edentulous area. In total, 36 implants were evaluated. Baseline radiographs consisted of intraoral peri-apical films obtained with the parallel long cone technique.
All the subjects involved in this research, which was approved by the Scientific Ethical Committee of the University of Genoa, provided informed written consent prior to starting the study. All the patients underwent pre-surgery screening and initial periodontal therapy. They agreed to return for the required recall appointments.
Immediately prior to surgery, the patients were asked to rinse their mouths using a chlorexidine digluconate solution 0.2% for 1 min. The surgical protocol ( Fig. 1 ) required a mucoperiosteal flap slightly palatal to the ridge crest, with two buccal releasing incisions. Full thickness flaps were elevated to visualize the bone crest.
In 17 implant sites (11 patients), traditional burs and the osteotome technique were applied. In the other 19 sites (16 patients) the osteotomy was performed using piezosurgery (27,000–30,000 Hz). Patients were randomly selected for one of the two groups. Two patients had both techniques at different sites.
In the first case, the perforation of the cortical bone was performed with a round bur with a diameter of 2 mm followed by the first spiral bur of the same dimension. The vertical dimension of the osteotomy reached a distance of 2 mm from the maxillary sinus ( Fig. 2 ). At this time, osteotomes (Summers™ osteotomes kit, 3i Implant Innovations, Palm Beach Gardens, FL, USA) were used in increasing order. The first was used with gentle percussion with a hammer and a rotatory action of the osteotome to obtain infraction of the sinus cortical plate. In sequence, the second and third osteotomes were used in the same way, with the apical addition of graft material to elevate the Schneiderian membrane. Osteotome number 1 has a diameter of 1.6 mm at its apex and gradually enlarges to a diameter of 2.4 mm at 10 mm length, to permit the introduction of the second osteotome that has a diameter of 1.9 mm at its apex and 3.1 mm at 10 mm length. At this point, it is possible to finish the site with the third osteotome (diameter 2.8 mm apically and 3.3 mm at 10 mm length) or to insert a 3.75 mm implant. All the osteotomes used have a conical shape, this is justified because an implant site underprepared with respect to the implant size allows improved lateral compactness, to obtain a better bone–implant interface. All the osteotomes used have a concave form, to drive the graft material apically.
In the clinical cases where piezosurgery was applied, the Piezosurgey ® device (Mectron Medical Technology, Carasco, Italy) was used. The osteotomy began with the conical insert OP5 (diameter 0.6–1.3 mm; granulometry 30 μm) to arrive at 2 mm from the sinus cortical floor. The following insert was the IM2 (diameter 2 mm) and the osteotomy continued with the OT4 insert (diameter 2.4; granulometry 150 μm). Finally, the osteotomy was completed with IM3 (diameter 3 mm) reaching about a 2 mm distance from the sinus cortical floor. With OT4 it was possible to perfect the preparation and come into contact with the sinus membrane. At this time, the bone graft material was inserted. Once the osteotomy was ready, an intraoral radiograph was taken as a control before implant installation.
The graft material used was BiOss (Geistlich Pharma AG, Wolhusen, Switzerland) mixed with autologous bone and antibiotic (hydrochlorate tetracycline, Ambramicina, Scharper SpA, Italy). The composite graft consisted of 50% autogenous bone and 50% BiOss.
Osseotite ® implants (Biomet 3i, Palm Beach Gardens, FL, USA) were installed. Implants with an internal (Osseotite ® Certain™) and an external hexagon (Osseotite ® Standard) were used. The implant diameter varied between 3.75 and 5 mm and the lengths were 10 or 11.5 mm, depending on the amount of bone available ( Table 1 ). The insertion torque for implants was 30–32 N cm.
| 10 mm | 11.5 mm | |
|---|---|---|
| Cylindrical implants | 9 | 15 |
| Tapered implants | 5 | 7 |
When the residual bone was poor in quality and in vertical and horizontal dimensions, tapered implants (Osseotite NT) were inserted. In the other cases, cylindrical implants (Osseotite STD) were used in the hope of providing less trauma to the sinus membrane. Implant restorative platforms were placed at the level of the osseous crest.
All the implants were assigned specific codes for blinding. The first number of the code (from 1 to 25) indicated the patient, the second indicated the implants inserted in a single patient. For each patient, the implants were numbered starting from the distal region of the first quadrant up to the distal part of the second quadrant, with no distinction between tapered and cylindrical implants.
Antibiotics (amoxicillin 1 g, twice a day) were prescribed for 6 days and analgesics as required. All patients were instructed to rinse twice daily for 10 days with chlorhexidine 0.2% solution (Curasept 0.2; Curaden Healthcare Srl, Saronno, VA, Italy).
Recall appointments were scheduled 7 days after surgery for reevaluation and 15 days after surgery for removal of any remaining sutures.
The second surgical phase for abutment connection and the impression for the provisional prosthesis were performed 7 months after implant insertion.
Radiographic examinations assessed the increase in sinus elevation at the 1-year follow-up appointment. The radiographs were recorded using a long-cone paralleling technique with fast speed films (Ultra-Speed Kodak, Eastman Kodak Company, Rochester, NY, USA). The distance between the implant shoulder and the new sinus floor was measured on the distal and mesial aspect of the implant. A comparison of this radiograph with the preoperative film provided a quantitative assessment of the newly formed mineralized tissue. A radiologist independent of the study performed the radiographic readings, using a diaphanoscope and magnifying lens.
An implant was classified as surviving if it fulfilled its prosthesis supporting function, it was clinically stable when tested individually and no pain or signs of infection were detected during clinical examinations. Bone–implant contact had to be present on the radiographs, with no evidence of radiolucency at the bone–implant interface. An implant-supported prosthesis was classified as surviving if it was functioning, had no fractures and provided the patient with adequate masticatory, aesthetic and phonetic function.
Statistical analysis
For statistical analysis of the data, the SPSS program (15.0 Version, SPSS Twc, Chicago, IL, USA) was used, based on the evaluation of the amount of bone level at 1-year post-implant installation. The null hypotheses, stating that no differences existed between the two different implant shapes (cylindrical vs tapered) nor between the two techniques adopted (osteotomes and burs vs piezosurgery), were tested by the bilateral method. The alpha risk of error was maintained under 5% and the beta was maintained under 20%.
Results
In the present investigation, the mean height of the alveolar process in the intended implant sites was 5.61 mm (range 3–7.5 mm; 5.79 mm for the osteotomes group; 5.48 mm for the piezosurgery group). 11 of the 36 implants analyzed were installed in sites with an initial subantral bone height <5 mm and five implants were placed in sites with an initial subantral bone height equal to 5 mm.
The mean elevation of the sinus membrane was 6.78 mm (range 3.5–10 mm; 6.507 mm for the osteotomes group; 6.989 mm for the piezosurgery group) at 1 year after implant placement ( Fig. 3 ). The relationship between residual bone and grade of sinus floor elevation at 1 year is illustrated in Fig. 4 .
