Introduction

One of the reliable methods that enables implant insertion in a severely resorbed posterior maxilla is open maxillary sinus floor elevation with bone substitute grafts.(1) Implant stability has to be obtained during implant insertion and maintained over time. Achieving suitable implant stability in posterior maxillary grafted sites is challenging in comparison with non-grafted similar regions. However, recent studies have illustrated that this stability may be achieved in grafted sites.(2, 3) Resonance frequency analysis (RFA) offers a clinical measure for implant stability and presumed osseointegration.(4) Most studies have focused on implant stability in augmented posterior regions of maxilla after osseointegration(5).  Digedi et al. in 2007 perform a study to evaluate whether a good primary stability could be achieved in sites with history of  a sinus augmentation procedure and    the importance of different clinical factors in the determination of ISQ values at implant insertion. Sites treated with open sinus augmentation procedure could offer good primary stability after 6 months of healing. The length and diameter of the implants, together with the geometry of the implant used, were the most important factors for higher RFA values.(5).

Same authors in 2009 evaluated the ISQ values at 6 and 12 months from the implant insertion in sinus grafted and non-grafted sites. Sites treated with open sinus lift could offer good long-term stability. After 6 and 12 months, the geometric characteristics of the implant were no longer important to obtain high RFA values, and the bone–implant contact was determinant.(6).

At present, very few data are available regarding the monitoring of implant stability in augmented posterior maxillary regions versus non-augmented similar sites. This study aimed to evaluate and compare the time required to achieve good implant stability between implants inserted in sites that had undergone an open sinus augmentation procedure with implants inserted in non-augmented sites, with a particular focus on histological features.

Materials and Methods

Patients

Fourteen patients (8 females and 6 males) whose age ranged from 55 ± 10 years were selected who required posterior maxillary implantation. Written consent to use their data for research was obtained from each patient prior to their inclusion. The exclusion criteria were as follows: 1) any history of sinusitis or sinus surgery; 2) a history of localized radiation of the oral cavity; and 3) patients undergoing chemotherapy or who were otherwise immunocompromized. A total of 30 standard ITI implants (Straumann, Swiss) were distributed with 14 implants in the test group(site that had undergone open sinus augmentation) and 16 implants in the control group(Matched non-augmented posterior maxillary sites).

Surgical technique

In the test group, an open sinus lift procedure (trap door technique) was performed in patients with a residual bone height of less than 4 mm (Fig. 1). DFDBA (Tissue Regeneration Co., Iran) was used as the graft material. Antimicrobial prophylaxis was administered with 625 mg co-amoxiclav (Loghman Co., Iran) qds 2 days before surgery. A crestal incision was performed and a full thickness flap was reflected. A lateral window was created with a piezosurgery device (Mectron, Italy). Using a trap door technique, the sinus membrane was elevated and DFDBA was applied to the site. A resorbable membrane (Tutogen, Sweden) was placed and the flap was sutured. Six months postoperatively, implants were inserted according to a strict protocol following the manufacturer’s instruction in the augmented site. In the control group, the residual bone height was suitable for implantation and implants were inserted.

Figure 1. Residual bone height in a 53-years-old female before the open sinus lift surgery

ata collection

In the test group, before the sinus lift procedure, residual bone height was recorded by Cone Beam CT(CBCT). Six months postoperatively, a new CBCT was performed to measure the augmented bone height(Fig. 2). The diameter and length of implants was also recorded, and were found to be similar in both groups (diameter: 4.1 and 4.8 mm,   and length: 10 mm). The ISQ of each implant was measured with an Osstell device (Integration Diagnostic AB, Savedalen, Sweden) on the day of surgery (baseline, ISQ₀) and monitored in the first month (ISQ₁),second month (ISQ₂) and third month (ISQ₃) post-implantation in each group.

Figure 2. Augmented bone height in the same patient 6 months after the sinus lift surgery.

Histological evaluation

Ten bone samples were collected (7 samples from the test group and 3 samples from the controls). Each sample was approximately 4 mm in length and 2 mm in diameter, and was obtained during implant drilling with a trephine. The biopsies were placed in 10% formalin. The sections were ground and polished to a final thickness of 4 ± 10 µm. They were then observed under a light microscope after Hematoxylin and Eosin staining.

Statistical analysis

ISQ values in different groups and time points had normal distribution, so repeated measures ANOVA with external factor was used for statistical analysis. Due to observed interaction between groups and time, single analysis was performed using repeated measures ANOVA and two sample t test to compare ISQ in different time points in each group and   in each period of time between groups, respectively. The correlation between the ISQs and with other variables, such as implant diameter and residual and augmented bone height were carried out with Pearson correlation test.   A p-value

Results

No membrane perforations occurred during the sinus lift procedure. The implant survival was 100% after 3 months and no adverse reaction to bone materials was recorded. The mean residual bone height in the test group was 2.92 ± 1.46mm and 11.21 ± 1.23mm in the controls. The mean augmented bone height was 10.41 ± 1.46mm. The mean ISQ value in both groups is shown in Fig. 3. The difference between ISQ values in both groups was only significant at the baseline (p=0.023). The correlation between ISQ values and residual or augmented bone height were not statistically significant. No statistically significant correlations were found between ISQ values and implant diameter in both groups (Table 1 and 2). The correlations between the ISQ_0, ISQ_1, ISQ₂ and ISQ₃ values in each group were evaluated. In the test group, correlations between ISQ values were significant between ISQ₀ and ISQ₁ (r=0.690, p=0.006), ISQ₁ and ISQ₃ (r=0.569,p=0.034) and ISQ₂ and ISQ₃ (r=0.540,p=0.046). In the control group, the correlation was significant only between ISQ₀ and ISQ₁ (r=0.716, p=0.002).

Histological findings

No evidence of necrosis, inflammation or foreign body reactions were detected in each sample. In the test group, a trabeculated pattern was noted, interspersed with DFDBA particles (osteoconduction) (Fig. 4). In two samples, there was some evidence of osteoinduction detected by stromal mesenchymal cells with osteoblastic activity and some small bone trabeculae found in these areas (Fig. 5).

Figure 3. ISQ values in both the test and control groups in different time points (base line and after 1,3 and 6 months)

Figure 4. DFDBA materials and bone trabeculea are seen parallel to each other (H&E, ×40)

Figure5. Small bone trabeculae formed by the osteoinduction of DFDBA (H&E, ×100)

Table1. Correlation between ISQ and Implant diameter in different time points in test group

Table2. Correlation between ISQ and Implant diameter in different time points in control group