MAXILLARY SINUS AUGMENTATION USING DEPROTEINIZED BOVINE BONE (BIO-OSS®) AND IMPLADENT® DENTAL IMPLANT SYSTEM PART I. COMPARISON BETWEEN ONE-STAGE AND TWO-STAGE PROCEDURE

For many people the loss of teeth can mean the loss of jaw function, and can lead to poor oral aesthetics and severe emotional and psychological handicaps. Osseointegrated dental implants have made it possible to rehabilitate nearly all of these patients. Unfortunately, certain patients have been unable to take advantages of dental implants because of inadequate bone availability. The edentulous patient with a severely resorbed maxilla often requires bone grafting to enable implant insertion. The reason for this limited quantity of bone volume is related to the excessive resorption of the alveolar bone and/or the increased pneumatization of the maxillary sinuses that occur following teeth loss (10). The use of short implants in poor bone quality does not seem to be advisable. Jemt and Lekholm (4) reported failure rate of 24 % with implants 7 mm in length in the maxilla. Maxillary sinus elevation (sinus lift procedure) has become a well-accepted technique for increasing height of the bone in the posterior maxilla when inadequate bone exists for the placement of dental implants. In-fracture of the lateral wall of the maxillary sinus provides access for sinus mucosa elevation and graft placement (9,17). Implants can be placed into the grafted sinus in one-stage (simultaneously) or two-stage (delayed) surgical procedure. The determining factor has been appeared to be ensuring primary stability of the implants. In one-stage procedure, implant can be placed simultaneously with a sinus graft if adequate alveolar bone is available to stabilize the implant. In this case, the cortical bones of the crest and of the original sinus floor may be used to stabilize the implant, permit its rigid fixation, and prevent migration or even loss of implants during the early healing phase (11). On other side, in a delayed implant placement procedure, a graft is placed first and requires certain time to mature, after this time, the implant bodies are placed. This requires two waiting periods: the first for graft maturation and the second for implant osseointegration (15,16,22). The question of whether to place the endosseous implants simultaneously within the sinus graft, or whether a delayed approach should be utilized following augmentation, has been evaluated in a number of experimental and clinical studies. Simultaneous implant placement has been advocated by several authors (6,9,12,14,22); however, there are several advantages that tend toward the decision to delay implant placement (1,5,8,11,13,14,15). The aim of this retrospective study was to investigate whether any significant difference in implant survival could be detected between those implants placed in oneor two-stage procedure.


Introduction
For many people the loss of teeth can mean the loss of jaw function, and can lead to poor oral aesthetics and severe emotional and psychological handicaps. Osseointegrated dental implants have made it possible to rehabilitate nearly all of these patients. Unfortunately, certain patients have been unable to take advantages of dental implants because of inadequate bone availability. The edentulous patient with a severely resorbed maxilla often requires bone grafting to enable implant insertion. The reason for this limited quantity of bone volume is related to the excessive resorption of the alveolar bone and/or the increased pneumatization of the maxillary sinuses that occur following teeth loss (10). The use of short implants in poor bone quality does not seem to be advisable. Jemt and Lekholm (4) reported failure rate of 24 % with implants 7 mm in length in the maxilla.
Maxillary sinus elevation (sinus lift procedure) has become a well-accepted technique for increasing height of the bone in the posterior maxilla when inadequate bone exists for the placement of dental implants. In-fracture of the lateral wall of the maxillary sinus provides access for sinus mucosa elevation and graft placement (9,17). Implants can be placed into the grafted sinus in one-stage (simultaneous-ly) or two-stage (delayed) surgical procedure. The determining factor has been appeared to be ensuring primary stability of the implants. In one-stage procedure, implant can be placed simultaneously with a sinus graft if adequate alveolar bone is available to stabilize the implant. In this case, the cortical bones of the crest and of the original sinus floor may be used to stabilize the implant, permit its rigid fixation, and prevent migration or even loss of implants during the early healing phase (11). On other side, in a delayed implant placement procedure, a graft is placed first and requires certain time to mature, after this time, the implant bodies are placed. This requires two waiting periods: the first for graft maturation and the second for implant osseointegration (15,16,22). The question of whether to place the endosseous implants simultaneously within the sinus graft, or whether a delayed approach should be utilized following augmentation, has been evaluated in a number of experimental and clinical studies. Simultaneous implant placement has been advocated by several authors (6,9,12,14,22); however, there are several advantages that tend toward the decision to delay implant placement (1,5,8,11,13,14,15). The aim of this retrospective study was to investigate whether any significant difference in implant survival could be detected between those implants placed in one-or two-stage procedure.

Materials and Methods
From January-1998 to March-2000, seventy-seven consecutive patients (36 men and 41 women) who required sinus grafting of one, or both, of their maxillary sinuses for placement of endosseous implants in the posterior maxilla were evaluated clinically and radiographically in our center. The implants (Impladent ® , Lasak, Czech Republic) placed into sinus grafts were separated into 2 groups based on the surgical technique used. Group 1 included implants placed with augmentation material using a one-stage procedure, while those assigned a two-stage procedure classified as Group 2 (Tab. 1). Clinical evaluations were recorded and radiographs were taken prior to sinus augmentation and at second stage procedure.

Surgical procedure
Horizontal incision was carried along the posterior alveolar crest; then small releasing incisions were made into the buccal vestibule of the tuberosity region. A releasing inci-sion was also made into the vestibule in the canine region extending anteriorly. Once the flap was sufficiently elevated, a large round bur was used at 2000 rpm, with copious irrigation, to outline a bony window in the lateral sinus wall. The lower border of this window was estimated to be 2 mm above the sinus floor. The bony wall was then assessed for mobility, if the osteotomy was complete and the window was mobile, blunt sinus curettes (HU-FRIEDY, USA) were used to gently elevate the sinus mucosa to the anterior and medial walls of the sinus as far, posteriorly, as necessary for implant placement. A mixture of Bio-Oss ® (deprotienized bovine bone), venous patient's blood, and sometimes, autogeous bone harvested from the maxillary tuberosity was packed into the void created in the sinus. The decision to use one-or two-stage procedure was taken after enough evaluation of different factors such as the available bone height, width, and quality and the implant type and diameter. In simultaneous implant placement, implant receptor sites were prepared after completion of the sinus floor elevation. The augmentation material was compacted against the sinus walls and around the implant bodies until the surgical void was filled ( Fig. 1 a,b,c). The healing time prior to implant uncovering was 9 months (Fig. 2 a). In delayed implant placement, implants were inserted after a healing period of 6 months, and were allowed to ossointegrate for 9 months more (Fig. 2 b). All patients were given appropriate antibiotic treatment for 1 week beginning 1 hour before the surgery.   Journal of Oral Implantology in 1991, in which success was defined as, "Survival: Any implant removed or one that would be removed by any reasonable and experienced implantologist is a failure. The remainders are reported as percent survival" (21). The following were investigated and subjected to statistical analysis: 1. Was a one-stage or two-stage procedure employed? 2. What was the failure rate of the implants? Implant mobility was determined with the aid of a Periotest ® (Siemens, Bensheim, Germany). Fisher's exact test was used statistically to compare our results.

Results
Two implants failed during the second stage (survival rate of 98.91 %) (Tab. 2). Both of them were in the same sinus, and were from Group 2. Out of the implants inserted using the one-stage procedure, all survived. No statistically significance was observed between the two surgical techniques (P = 0.498). At abutment connecting stage all of the surviving implants appeared well integrated and they tolerated the torque force (35 N cm) required to stretch the abutment's screws without any pain. Clinical evaluation of their stability using a Periotest ® instrument (Siemens, Bensheim, Germany) showed positive results. All implants were loaded prosthetically at the time of the investigation (no one was excluded for one reason or another).

Discussion and Conclusions
In our study the difference between the results of simultaneous and delayed placement procedures was not statistically significant. This result agrees with others have been reported by prior studies (3,13,18,23). However, some reports indicate a higher failure rate for implants inserted simultaneously than for those inserted using a delayed approach (5,11). Jensen (5) reported a success rate of 81 % with simultaneous placement and 93 % with the two-stage procedure. Misch and Dietsh (11) reported a failure rate of 1 % in delayed implantation cases and 10 % in simultaneous implantation cases. Valentini et al (19) reported 96.8 % implant survival in two-stage procedure and 92.8 % in one-stage procedure. Tidwell et al (18) published failure of 8.7 % occurred in one-stage procedure and of 2.6 % of two-stage procedure. In other direction, the bone graft-implant interface has to be further examined in clinical studies to allow conclusions to be drawn about which surgical technique is preferable. Quińones et al (13) demonstrated significantly greater direct bone graft-to-implant contact in the delayed implant placement than the simultaneous installation of implants in the augmented area. Zitzmann et al (23) noticed differences between the two techniques even in the potential gained bone. In their study the gain in bone height for the one-step procedure has a median of 10 mm, compared to a median of 12,7 mm for the two-stage surgery. Some investigations have preferred delayed implant placement, because it guarantees better implant position and angulation for the prosthetic reconstruction (1,4). Blomqvist et al (1) noticed that the implants inserted during one-stage procedure were angled more palatally compared with those placed with two-stage operation. This is explained by the fact that a surgeon choosing a one-stage procedure often needs to use a thicker and more rigid bone palatal at the top of the alveolar crest to acquire initial stability.
For most of the aforementioned authors the available preoperative bone was thought to be a prognosticator for whether a delayed or simultaneous technique should be used. The question how much alveolar bone is enough to stabilize the implants during the healing phase is still unsolved. It has been published that at least 3-4 mm of alveolus should be present (14,16). In each borderline case (bone height = 4 mm), the decision as to whether to perform a one-step or a two-step procedure is also influenced by the buccolingual width and the bone quality of the alveolar ridge (22). Jensen and Greer (6) demonstrated that minimal preoperative bone had been reported to be an important factor in the failure to establish or maintain osseointegration. There also seems to be a correlation between the amount of supporting residual bone and the loss of implants, irrespective of the kind of particulate graft used. In their study, the implant survival rate was only 29 % when the residual bone was less than 3 mm, while all implants were stable when the residual bone was 7 mm or more. Langer et al (7) recommended that simultaneous implant and graft placement in sinus with less than 5 mm of residual bone height appear to yield a greater number of implant losses than those with more bone. At the Sinus Graft Consensus Conference (2) they concluded that there appears to be a statistical difference in implant loss when available bone was 4 mm or less as opposed to 5 mm or greater. From 349 implants 20 were lost. Of the implants lost, 13 were initially placed in residual bone of 4 mm or less, 7 were placed in bone of 4 to 8 mm, and none of the implants placed in bone with a height greater than 8 mm were reported lost. However, presently, there are only a few reports that suggested the lack of preoperative bone as a factor in implant loss (5,6,12). Peleg et al (12) reported about one-stage procedure in cases where the residual alveolar bone height in the posterior maxilla was 1 to 2 mm, but with a special modification in the surgical technique. In our practice, we consider that there are different factors, other than the available bone height, which interface in the decision whether implant simultaneous placement can be done or not. This is variable depending on the patient's residual bone width, osseous structure of sufficient quality and 117 Number of failed Implant implant survival (%) One-stage procedure 0 100 % Two-stage procedure 2 97,31 %