Clinical Oral Implants Research

Association of transalveolar sinus floor elevation, platelet rich plasma, and short implants for the treatment of atrophied posterior maxilla

Authors


Abstract

Objectives

Assess the efficiency of transalveolar sinus floor augmentation in association with platelet rich plasma and short implants for the treatment of atrophied edentulous maxilla with a residual bone height (RBH) <5 mm.

Materials and methods

Atrophied posterior maxilla was treated with transalveolar sinus floor augmentation performed with conventional bone drills and autologous platelet concentrate. The space created below the Schneiderian membrane was filled with platelet rich plasma alone or in combination with a bone graft and followed by the insertion of short implants. Surgical complications, implant survival, and marginal bone loss were evaluated during the follow-up period.

Results

Forty-eight patients (average age: 55.98 ± 8.71 years) with 61 short implants were treated in this study. Schneiderian membrane perforation occurred in one maxillary sinus, and the initial RBH of 4.15 ± 0.53 mm was increased to 8.86 ± 1.60 mm. There was no significant difference between the grafting materials with respect to the gained bone height. The mean follow-up time of the implants was 10.81 ± 5.87 months (range: 2–28 months) since loading. The average bone loss was 0.59 ± 0.12 mm (loading time <6 months), 0.62 ± 0.16 mm (loading time between 6 and 12 months), and 1.00 ± 0.45 mm (loading time higher than 12 months). The use of wide implants was the only parameter that decreases significantly the marginal bone loss. Two implant failures occurred before loading, and the cumulative implant survival rate was 96.7%.

Conclusions

The proposed treatment protocol for transalveolar sinus floor augmentation could be efficient in the treatment of severe atrophy in the maxilla.

Introduction

Lateral maxillary sinus floor augmentation is a well-documented surgical technique to resolve insufficient bone height in posterior maxilla that impedes the placement of dental implants (Aghaloo & Moy 2007; Anitua et al. 2013). This approach requires the creation of a bone window in the lateral wall of the maxillary sinus to get access to the Schneiderian membrane and allows to obtain a gain in the bone height of 10–12 mm (Zitzmann & Scharer 1998). However, it is associated with significant surgical morbidity (nose bleeding, pain, and swelling) and higher risk of intraoperative Schneiderian membrane perforation that was reported to occur in 25–44% of the cases (Chanavaz 1990; Katranji et al. 2008). These complications have encouraged the development of more conservative alternatives that may result in a more predictable treatment.

A lesser invasive approach was first suggested by Tatum and involved a transalveolar access for sinus floor elevation with subsequent placement of dental implants. The technique was later modified by Summers who introduced the use of osteotomes to prepare the implant site (Tatum 1986; Summers 1994; Tan et al. 2008). Clinically, the transalveolar sinus lift is indicated when at least 5 mm of residual bone height is available (Del Fabbro et al. 2012) and has been shown to be more conservative than the lateral approach constituting lower risk of Schneiderian membrane perforation (about 2% of the cases) (Peleg et al. 2006; Del Fabbro et al. 2012). However, the sinus floor elevation and the placement of the bone grafts are performed blindly and thus increase the uncertainty of possible perforation of the Schneiderian membrane (Tan et al. 2008).

The clinical success of transalveolar bone augmentation in the maxilla has encouraged the study of the association of short implants and transalveolar sinus floor augmentation for the rehabilitation of atrophic edentulous maxilla. Pjetursson et al. (2009) reported that implant failure occurred more frequently when using short 6-mm implants and resulted in an implant survival rate of 57%. Whereas in another study, the 12-year cumulative success rate for short 8-mm implants was 88.9% (Ferrigno et al. 2006). However, recent studies have reported a comparable survival rate for implants <10 mm in length and longer implants. Kermalli et al. (2008) have indicated that the 5-year cumulative survival rate (CSR) of short implants was 96.49%, and Schmidlin et al. (2008) have found that the 2-year CSR was 100%. Nedir et al. (2013) reported that the 1-year CSR of reduced length implants in non-grafted augmentations was 100%. Taschieri et al. (2012a) in a prospective study of osteotomes sinus floor elevation in association with plasma rich in growth factors reported a survival rate of 100% of implants ≤8.5 mm in length with a mean follow-up period of 14.4 months since prosthetic loading.

These results have motivated the use of short implants in combination with transalveolar sinus augmentation for the rehabilitation of edentulous maxilla when the residual bone height is <5 mm (Nedir et al. 2013). Nedir et al. (2013) have shown the efficiency of the osteotome technique and short implants in the rehabilitation of maxilla with residual bone height <3 mm. The mean survival rate after 1 year of implant placement was 94.6% (Nedir et al. 2013).

In a modification of the osteotome technique, Cosci & Luccioli (2000) introduced the use, in a specific sequence, of drills with varying lengths to permit a gentle abrasive removal of the cortical bone of the sinus floor without fracture. In a recent paper, this method was used for the rehabilitation of posterior maxilla with residual bone height <5 mm (Bernardello et al. 2011). The survival rate was 96.3% for implants ≥10 mm in length with an average follow-up time of 48.2 months (Bernardello et al. 2011).

Furthermore, Checchi et al. (2010) compared in split-mouth randomized clinical study the Cosci and the Summers techniques for transalveolar sinus floor elevation . No discomfort/complications were reported at sites treated with the Cosci technique, whereas 12 of 15 patients reported discomfort during the augmentation procedure at the side treated with the Summers technique. Perforation of the Schneiderian membrane occurred in the site treated with Summers technique in one patient. In the Summers-treated sites, headache was reported in 9 patients and swelling occurred in 3 patients. Lesser time was needed to place implants according to the Cosci technique (Checchi et al. 2010).

Both Cosci and Summers techniques required the acquisition of additional kits for performing the sinus floor augmentation than the instruments necessary to place a dental implant. The aim of this study is the presentation of a new protocol that further simplifies the transcrestal sinus floor augmentation and permits the use of conventional bone drills, used for implant site preparation, to perform the sinus augmentation. A new drill with frontal-cutting surface is employed to prepare the last 1 mm of the residual bone height. To the best of our knowledge, this is the first study where transalveolar sinus floor augmentation is associated with the use of bone drills, autologous platelet concentrates, and short implants to rehabilitate atrophied edentulous maxilla with residual bone height <5 mm.

Material and methods

Patient selection

Patients' records were revised to identify those who were eligible to participate in this retrospective study. The inclusion criteria consisted of the following parameters:

  • Residual bone height ≤5 mm.
  • Transalveolar sinus floor augmentation with bone drills.
  • The insertion of implants with a length ≤8.5 mm.
  • The use of Fibrin plug to separate and push apically the Schneiderian membrane.

Those patients who failed to meet any of the inclusion criteria were excluded from the study. For data analysis, the principal outcome was the gain in bone height after 5 months of surgery. The secondary outcomes were the occurrence of surgical complications, implants survival, and peri-implant bone loss.

Surgical protocol

Before surgery, each case was assessed by reviewing the medical and dental history, diagnostic casts, and radiographic evaluation (panoramic radiographs and cone-beam CT scan). The cone-beam CT scans were analyzed with diagnostic software (BTI Scan II, Biotechnology Institute, Vitoria, Spain) to identify the location of the posterior maxillary artery and to measure both the residual bone height and the bone density at future implants' sites. The latter was used to assess the bone quality (Lekohlm 1985) and to determine the sequence of bone drills for the preparation of implant socket (Fig. 1).

Figure 1.

Bone drilling sequence that was employed to prepare the implant bed of short implants in the posterior maxilla. The diameter of the final drill is determined by the bone density.

Preparation of autologous platelet concentrate

Plasma rich in growth factors was prepared using PRGF-Endoret Kit (BTI, Vitoria, Spain). Briefly, citrated venous blood was extracted in 4–6 tubes (9 ml in each tube) and centrifuged at 580 g for 8 min to separate blood components according to the density. Then, plasma column was fractioned into fraction 2 (F2) defined as the 2 ml of plasma just above the Buffy coat and fraction 1 (F1) defined as the plasma column above the F2. [Corrections added on 26 November 2013, after first online publication: The relative centrifugal force for citrated venous blood was corrected from ‘460 g’ to ‘580 g’ and the definition of F2 was corrected from ‘2mm of plasma just above the Buffy coat…’ to ‘2ml of plasma just above the Buffy coat…’] This gave a total of 8–12 ml of fraction 2, and the volume of the fraction 1 will depend on the hematocrit value of the patient. Activated fraction 1 (F1) was employed to prepare a fibrin membrane that covered the surgical area before flap closure, and activated fraction 2 (F2) was used to store bone particulate harvested during the drilling procedure, to be injected into the implant bed, and to humidify the dental implants before insertion.

Flap elevation and bone drilling

Patients received 1 g of amoxicillin 1 h before surgery and as analgesic they received 1 g of acetaminophen 30 min before surgery. Under local anesthesia, a crestal incision was practiced and full-thickness flap was reflected to expose the alveolar crest where sinus floor augmentation was required. Vertical incision was only performed if it was required to permit better visualization of the surgical area.

Fig. 1 showed the drilling sequence employed for the preparation of implant bed. Bone drilling had been performed in two phases; the first phase employed conventional twisted bone drills and the working length (drill penetration into bone) was set at 1 mm shorter than the residual bone height (Fig. 2). The laser marks on the drills positioned at 3, 5, 8.5, 10, 13, and 15 mm from the drill tip were helpful in controlling the penetration depth. Worth to mention, bone drilling was performed at low velocity (150 rpm) without irrigation to facilitate the recollection of bone particulate produced during drilling (Anitua et al. 2007). This particulate was stored in the fraction 2 of the plasma rich in growth factors (PRGF) till needed.

Figure 2.

Step-by-step approach of transalveolar sinus floor augmentation of atrophied posterior maxilla (a). (b) preparation of the transalveolar access (implant bed) with bone drills where the working length was set 1 mm shorter than the residual bone height (RBH). (c) the last 1 mm of the RBH was gently prepared with frontal-cutting drill. (d) when a small window was opened in the sinus floor, a fibrin membrane was introduced to separate the Schneiderian membrane. (e) The space beneath the membrane was filled with a plug of fibrin followed by the insertion of the dental implant. (f) If a biomaterial is to be used, then the grafts are inserted in the following order: fibrin membrane, biomaterial + plasma rich in growth factors (PRGF), and then autologous bone + PRGF.

The second phase of drilling was realized with a new bone drill that had a frontal-cutting surface to prepare the last 1 mm of the bone below the Schneiderian membrane (Fig. 2). The design of this drill permitted careful removal of the bone underneath the membrane and eliminated the risk of drill sinking. When a window (50% of the size of the alveolus) was opened in the sinus floor, a plug of very-well retracted fibrin membrane (fibrin retraction occurred at 37°C during 40 min) was inserted beneath the Schneiderian membrane and the frontal-cutting drill was used to continuo opening the access to the sinus membrane (Fig. 2). This was verified by visual inspection and/or gentle probing with blunt hand instrument if necessary. The extension of the bony window was adjusted according to the required amount of vertical augmentation.

A Valsalva maneuver was performed to verify the integrity of the sinus membrane. A fibrin membrane was then inserted into the socket and pushed apically with a blunt hand instrument to elevate the Schneiderian membrane (Fig. 2). A Valsalva maneuver was performed again to rule out the perforation of the Schneiderian membrane.

Bone grafting

In all cases, the fibrin membrane prepared from fraction 1 of the PRGF-Endoret was firstly placed below the Schneiderian membrane. The following bone grafts were placed to fill the space underneath the Schneiderian membrane: a clot of PRGF, PRGF + autologous bone, PRGF + autologous bone + Bio-Oss, or PRGF + Bio-Oss. It is important to mention that when a combination of Bio-Oss and autologous bone was used, the grafts were introduced in the following sequence: a plug of Bio-Oss + PRGF was first placed and then autologous bone + PRGF (Fig. 2).

Implant placement

The insertion of the dental implant was carried out with a surgical motor at an insertion torque of 25 Ncm and then continued manually to finish the implant placement. The final insertion torque was registered in the patient's record. Additionally, resonance frequency analysis was performed to obtain the implant stability quotient (ISQ) value. For that, the transducer (Smartpeg; Integration Diagnostics AB, Göteborg, Sweden) was connected to the implant immediately after placement. The analyzer probe was located close to the Smartpeg, and ISQ value was given by the Osstell device.

After the surgical site was covered with a fibrin membrane, the flap was repositioned and closed with 5/0 monofilament suture. Activated fraction 2 of the PRGF-Endoret was injected at the incision borders. The time passed from the start of the surgery till the complete insertion of the dental implant was registered to the nearest minute.

Follow-up

Visits were scheduled after 10 days for suture removal, 1 month for clinical observation, and 5 months for the placement of provisional prosthesis for progressive occlusal loading. The definitive prosthesis was delivered after 8 months of implant insertion. Clinical examination of the patients was performed at 6 and 12 months during the observation period of the study.

Statistical analysis

The patient was the statistical unit for the description of demographic data, social habits, bruxism, medical history, and history of periodontal disease. Mean, median, standard deviations, and range were calculated for the age variable, while relative frequency was calculated for the rest of patient-related variables. The implant was the statistical unit for the statistical description of implant length, diameter, location, insertion torque, ISQ, and marginal bone loss. The patient was the statistical unit for the analysis of the bone height before surgery and 5 months after surgery. Bone gain is defined as the difference between post-surgical bone height and pre-surgical bone height. Mean, median, standard deviation, and range were also calculated. All implants were considered in the description of the values of insertion torque, ISQ, marginal bone loss. Relative frequency was calculated for implant length, diameter, and location.

The pre- and post-surgical bone height was measured on CBCT scans obtained before sinus floor elevation and 5 months later, respectively. Whereas marginal bone loss was measured on standardized panoramic radiographs, the known implant length was used as a reference to calibrate the linear measurements on the digital panoramic radiograph. The data of the marginal bone loss were then classified into three categories: implants with loading time ≤6 months, between 6 and 12 months, and more than 12 months.

The relation of pre-surgical residual bone height, insertion torque, ISQ, implant length, and implant diameter with the marginal bone loss was analyzed by conducting multiple regression analysis. For that, one implant was randomly selected per patient to have 48 independent implants. Pearson correlation was also performed to identify the correlation between implant length, diameter, insertion torque, and ISQ for implant placed in type II bone (one implant per patient, = 42). The statistical significance was set at P < 0.05. All the statistical analyses were performed using the SPSS v15.0 for Windows statistical software package (SPSS Inc., Chicago, IL, USA).

Results

Demographic outcome

Forty-eight patients with 61 short implants completed the inclusion criteria and were enrolled in this retrospective study. The analysis of the demographic data indicated that 56.3% of the patients were females, and the mean age was 55.98 ± 8.71 years (median: 56 years; range: 35–76 years). Only four patients reported to smoke 20 cigarettes or more per day, and bruxism was possible in two patients. About 94% of the patients presented acceptable periodontal health according to the classification of Armitage (1999). The Patients' medical history indicated the presence of cardiovascular diseases in seven patients, hypothyroidism in three patients, and hyperthyroidism in one patient. Three patients receive treatment to prevent osteoporosis, five patients receive cholesterol-lowering drugs, and one patient received anxiolytics.

Surgical and prosthetic outcomes

The bone type at the implant site was retrieved from the bone density measured on the preoperative CBCT scan. Bone type II was available at 86.9% of the implant sites, while bone type III was present in 11.5% of the locations. Bone type IV was only available in 1.6% of the implant sites.

The grafting material in 34 transalveolar sinus augmentation (32 patients) was solely PRGF, whereas autologous bone + PRGF was placed in eight elevations (eight patients). Anorganic bovine bone + PRGF was employed in two sinus augmentations (two patients), and a combination of autologous bone and anorganic bovine bone was placed in seven elevations (six patients).

Implants primary stability was achieved by an insertion torque of 32.54 ± 17.74 Ncm (median: 30.00 mm; range: 5–75 Ncm) where the average value of the ISQ was 121.72 ± 10.68 (median: 125; range: 75–125). Worth to mention, two implants (6.5 mm and 7.5 mm long) were inserted at an insertion torque below 10 Ncm, and for these implants, the ISQ value was not measured as precaution to protect the stability of the implant. Extra-short implants with a length ≤6.5 mm represented 40.98% of the inserted implants. The short 7.5-mm implant was inserted in the 45.9% of the cases, whereas the 8.5-mm implant was placed in the 13.1% of the cases. As shown in Table 1, the most selected diameter was 5.5 mm. Twenty-seven implants were inserted in the right maxilla and 34 implants in the left maxilla. The 57.4% of the implants were inserted at the position of first molar (Fig. 3a).

Table 1. The diameter and length of the short implants placed in the posterior maxilla after transalveolar sinus floor augmentation
 Diameter (mm)Total
55.566.25
Length (mm)
5.522004
6.52141421
7.52194328
8.513408
Total7389761
Figure 3.

(a) The anatomical distribution of the short implants placed in the posterior maxilla after transalveolar sinus floor augmentation. (b) Implant survival rate.

The average time that was needed to finish the sinus augmentation and completely insert the implant was 17.9 ± 1.7 min calculated from the moment of making the incision.

An average of 4–5 months passed before the insertion of the provisional prosthesis. With the exception of two implants (failed during the osteointegration period), forty-eight short implants served as a pillar for 48 fixed partial dentures: 45 prostheses were screw retained, and three prostheses were cemented. Seven implants gave support to fixed complete denture, and four implants supported a single crown. Fig. 4 showed the treatment of atrophied posterior maxilla where transalveolar sinus floor elevation permitted the insertion of extra-short implants that gave support to screw-retained partial denture.

Figure 4.

(a) Residual bone height of 3.3 mm was available and indicated the need for sinus floor augmentation. (b) Transalveolar sinus floor augmentation was efficient to increase the bone height to 9 mm and permitted the placement of extra-short implant. (c) The osteointegrated extra-short implant served as a pillar for implant-supported fixed partial denture.

Patients were screened for prosthetic complications (screw loosening/fracture, abutment/implant fracture, ceramic chipping, and prosthesis fracture), and the results indicated the absence of such complications. The average follow-up time since implant loading was 10.81 ± 5.9 months (median: 10 months; range: 2–28 months) and since implant placement was 18 ± 7 months (median: 16 months; range: 5–38 months).

Outcomes of the statistical analysis

Primary variable

Gain in bone height

The measurements of pre-surgical residual bone height resulted in an average height of 4.15 ± 0.53 mm (median: 4.16 mm; range: 3.00–4.99 mm) (Fig. 5). The residual bone height (RBH) was between 3.0 and <3.5 mm in 13% of the cases, between 3.5 and 4.0 mm in 26.1% of the cases and higher than 4.0 mm and <5 mm in 60.9% of the cases. The described treatment protocol significantly increased the residual bone height to 8.86 ± 1.60 mm (median: 8.44 mm; range: 5.74–13.55 mm) achieving a bone gain of 4.73 ± 1.74 mm (median: 4.33 mm) with a range between 1.68 and 9.54 mm (Fig. 5).

Figure 5.

Residual bone height and the new bone height after 5 months of transalveolar sinus floor augmentation.

We further analyzed the bone height before and after surgery according to the type of grafting material. For that, the data of bone height were classified into two groups: PRGF alone (32 patients) or PRGF + bone graft (16 patients). The pre-surgical bone height in the PRGF group was 4.03 ± 0.51 mm (median: 4.07 mm; range: 3.00–4.92 mm) and in the PRGF + bone graft group was 4.36 ± 0.51 mm (median: 4.39 mm; range: 3.00–4.99 mm). The Student's t-test found a statistically significant difference between groups (= 0.045). Both graft types increased the bone height after 5 months of surgery to 8.66 ± 1.53 mm (median: 8.44 mm; range: 5.74–12.11 mm) and 9.23 ± 1.73 mm (median: 8.72 mm; range: 6.76–13.55 mm), respectively. The difference in the post-surgical bone height did not reach the statistical significance (Student's t-test; > 0.05). The bone gain was similar in both groups (Student's t-test; > 0.05) and had a value of 4.64 ± 1.68 mm (median: 4.33 mm; range: 1.68–9.54 mm) and 4.88 ± 1.89 mm (median: 4.1 mm; range: 2.36–9.22 mm) for PRGF group and PRGF + bone graft group, respectively.

Additionally, we compare the data of bone height where extra-short (19 patients) and short implants (29 patients) had been placed. The pre-surgical residual bone height did not differ significantly (Student's t-test; = 0.447) between the extra-short and short implants and had a value of 4.07 ± 0.54 mm (median: 4.10 mm; range: 3.00–4.92 mm) and 4.20 ± 0.52 mm (median: 4.31 mm; range: 3.00–4.99), respectively. The post-surgical bone height was 8.58 ± 1.80 mm (median: 8.44 mm; range: 5.74–12.11 mm) and 9.04 ± 1.47 mm (median: 8.46 mm; range: 7.53–13.55 mm), respectively, and the difference was not statistically significant (Mann–Whitney U-test; P = 0.392). The bone gain was similar in both groups (Mann–Whitney U-test; P = 0.333) and had a value of 4.53 ± 2.08 mm (median: 3.86 mm; range: 1.68–9.54 mm) and 4.85 ± 1.51 mm (median: 4.55 mm; range: 3.30–9.22 mm) for extra-short and short implants groups, respectively.

Secondary variables

Surgical complications

Perforation of the Schneiderian membrane occurred in only one maxillary sinus where the residual bone height was about 3 mm. In such case, the treatment was continued by opening a window in the lateral wall of the maxillary sinus, and a fibrin membrane was placed to manage the perforation.

Implant survival

Two implant failures were registered in two patients before the insertion of provisional prosthesis. A history of periodontitis was available in one patient where implant failure was registered. Both implants had a diameter of 5.5 mm and were 6.5 and 8.5 mm in length. They were inserted at the position of first molar in type II bone with a residual height of about 3.9 mm. The insertion torque was 45 and 55 Ncm for the 6.5-mm- and 8.5-mm-long implants, respectively. Thus, the Kaplan–Meier analysis displayed an implant survival rate of 96.7% up to 38 months (Fig. 3b).

We further studied the relation between insertion torque, initial ISQ, diameter, and length of the implant. This analysis was only performed for implants inserted in bone type II present in 87% of the implant sites. The results of the regression analysis indicated the absence of significant correlation between any of these parameters.

Peri-implant bone loss

The data of marginal bone loss around dental implants were represented according to the loading time as shown in Fig. 6. Twenty-nine implants with a loading period up to 6 months showed a mesial bone loss of 0.57 ± 0.08 mm (median: 0.45 mm) and a distal bone loss of 0.61 ± 0.09 mm (median: 0.57 mm). In the case of the 16 implants with a loading period between 6 and 12 months, a mesial bone loss of 0.50 ± 0.10 mm (median: 0.48 mm) and distal bone loss of 0.75 ± 0.11 mm (median: 0.73 mm) were observed. A total of 14 implants with a loading period higher than 12 months showed a mesial bone loss of 1.29 ± 0.43 mm (median: 0.83 mm) and a distal bone loss of 0.71 ± 0.12 mm (median: 0.71 mm).

Figure 6.

Peri-implant bone loss represented in function of the implant loading time.

Regression analysis was performed to verify factors that may affect the mesial and distal marginal bone loss around the implants placed after transalveolar sinus augmentation. The analyzed factors were pre-surgical residual bone height, insertion torque, ISQ, length, and diameter of the implant. For that, one implant was randomly selected per patient to have independent data. The analysis was first realized by stratifying the time variable into three categories (up to 6 months, between 6 and 12 months, and higher than 12 months). The results showed that no variable reaches the statistical significance. The low number of subjects per group could limit the power of the statistical analysis. For that, we repeated the analysis without stratifying the time variable. The implant length showed a significant relation with mesial bone loss (= 0.000) and the implant diameter was the only parameter that had a significant relation with the distal bone loss (= 0.000):

display math

Where L is the implant length in mm.

display math

Where Φ is the implant diameter in mm.

The results of the other factors did not reach the statistical significant. This does not mean necessarily the absence of relationship with the marginal bone loss as the lower number of subjects included in this study could limit the power of the study.

Discussion

The purpose of this investigation was to determine the efficiency of transalveolar sinus augmentation with bone drills in association with short implants for the treatment of atrophied edentulous maxilla. Fibrin scaffold was employed in the present study to facilitate the elevation of sinus floor membrane and also as a grafting biomaterial (Sanchez et al. 2009).

Several studies have observed better post-operative recovery (less inflammation and pain) after maxillary sinus augmentation when autologous PRGF was employed (Anitua et al. 2012; Del Fabbro et al. 2012). Taschieri et al. (2012a,b)described the use of PRGF in the management of Schneiderian membrane perforations and concluded that the use of PRGF may be helpful in reducing complications following sinus lift surgery. Furthermore, the management with PRGF of Schneiderian membrane perforation during endodontic surgery significantly improved patients' quality of life (swelling, bad breath, and taste). Taschieri et al. (2013) Functional activities were less impaired, and pain was significantly lower during the first 6 days after surgery . In the present study, the sole use of PRGF clot as grafting material was efficient to promote new bone formation after sinus floor augmentation. The statistical analysis showed similar bone gain when PRGF was used with/without bone graft (autologous bone, anorganic bovine bone, or combination of the two).

Thus, the use of PRGF in transalveolar bone augmentation would facilitate the handling of bone graft, enhance the post-operative recovery, and promote the formation of new bone.

Another important aspect of the described treatment protocol is the possibility to use the same bone drills used in the preparation of implant bed to perform the transalveolar sinus floor augmentation (Fig. 4). This was possible as the last 1 mm of bone beneath the Schneiderian membrane was gently removed by a frontal-cutting drill. This drill is usually used to give the apical part of the implant bed a cylindrical form that matches the form of extra-short implant (Anitua et al. 2013). The distance from the drill tip is laser marked on the shaft of the drill, and by knowing the residual bone height, one can control the insertion depth and avoid the perforation of Schneiderian membrane. Additionally, fibrin scaffold was condensed below the cortical floor of the sinus to help in the apical displacement of the Schneiderian membrane. The time needed to perform the transalveolar sinus augmentation and place the dental implant was about 18 min.

The presence of reduced residual bone height (4.15 ± 0.53 mm) was the reason to use short and extra-short implants in the described clinical protocol. Reduced length implants would simplify the treatment by reducing the amount of vertical bone augmentation needed to achieve. The success of short implants is based on the fact that the majority of stress transmitted to the peri-implant bone is concentrated in the crestal bone (the first 2–3 mm of implant length) regardless of the implant design (Pierrisnard et al. 2003; Anitua et al. 2010; Nissan et al. 2011). Esposito et al. (2011)reported that short implants are a minimally invasive alternative to surgical bone augmentation that permit the completion of treatment at lesser surgical morbidity, at lower cost and in a shorter time. In the present study, 40% of the placed implants had a length ≤6.5 mm (extra-short implants) and the rest of the implants were 7.5 mm and 8.5 mm in length. The cumulative survival rate was 96.7% after follow-up period of 18 ± 7 months since implant placement. This value of implant survival is comparable to survival data reported in other studies where osteotomes were used to perform the transalveolar sinus augmentation (Nedir et al. 2013).

The described treatment protocol was efficient to increase the residual bone height to 8.86 ± 1.60 mm obtaining a bone gain of 4.73 ± 1.74 mm (range: 1.68–9.54 mm) (Fig. 5). The osteotome technique permitted the gain of 3–4 mm of bone height (Bernardello et al. 2011; Nedir et al. 2013), a value which is comparable to the bone gain reported in the present study. The simple treatment protocol described herein was efficient for the rehabilitation of atrophied edentulous maxilla with residual bone height of 3–5 mm. This would widen the indication of transalveolar sinus floor elevation beyond the requirement of the availability of at least 5 mm of residual bone height to perform the technique (Del Fabbro et al. 2012). Rosen et al. (1999) reported that the implant failure rate increased with reduced residual bone height . The implants survival rate was 96% when the residual bone height was 5 mm or more but decreased to 85.7% when the residual bone height was ≤4 mm (Rosen et al. 1999). Our results are in line with the conclusions of Nedir et al. (2013) and Bernardello et al. (2011) that transalveolar sinus floor augmentation may be successfully performed when <5 mm of bone height is available. This could be related to the improvements in the surface and design of the implants and to the development of minimally invasive surgical techniques that preserve at most the residual bone (Nedir et al. 2013; Taschieri et al. 2012a,b).

The results of the regression analysis indicated significant correlation was not reached between any of the following parameters: insertion torque, initial ISQ, diameter, and length of the implant. Implant's primary stability is the net outcome of quantity and quality of hosting bone, the design of the implant, and the surgical procedure (drilling technique) (Rabel et al. 2007). In the scientific literature, discrepancy exists between studies on the correlation of the insertion torque and the ISQ (Friberg et al. 1999; Barewal et al. 2012). Such discrepancy is due to differences in the working principles of both techniques: the insertion torque measures the rotational stiffness of the implant–bone interface, while the resonance frequency analysis evaluates the axial stiffness of this interface (Barewal et al. 2012).

The retrospective type of the study implies that patients were not randomly assigned to type of grafting nor to the type of implant placed. This will limit the capacity to reduce the heterogeneity between groups and in addition to the low number of subjects would strongly affect the results of the statistical analysis.

Conclusions

This article reports a new treatment protocol for the performance of transalveolar sinus augmentation with conventional bone drills and a drill with frontal-cutting surface. The use of plasma rich in growth factors was efficient to promote new bone formation beneath the Schneiderian membrane. The adopted protocol in association with short implants was efficient in the treatment of reduced residual bone height and could constitute a conservative alternative that reduce the surgical morbidity, and save time and cost.

Acknowledgements

The authors acknowledge the support for MHA from the Program of Torres Quevedo, Ministry of Economy and competitively co-founded by the European Social Fund (PTQ-11-04711). Authors of the manuscript are researchers in Biotechnology Institute I + D (Vitoria, Spain).

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