Five Years Follow-up of Short Implants Placed in Atrophic Maxilla with Simultaneous Sinus Floor Transcrestal Elevation

Abstract

Objective

Many authors have tried to face the anatomical limitations resulting from maxillary bone atrophy. Up to five millimeters bone height, the lateral sinus floor elevation is the most commonly used and validated strategy to achieve the prosthetic rehabilitation. However, the disadvantages of this technique are its invasiveness and delayed rehabilitation. The aim of this paper was to assess 5 years clinical outcome of implants placed with a technique that allows the percrestal sinus floor elevation and the immediate implant placement.

Materials and Methods

30 transcrestal sinus floor elevations with immediate implant placement were performed in severely atrophic maxillae. Implant survival, marginal bone level variation, harvested bone height variation and periodontal indices were assessed.

Results

After a five year follow up none of the thirty implants were lost. The mean value of vertical harvested bone loss was 5%. The mean crestal bone loss was -0.33 mm (Standard Deviation (SD) 0.11 mm). The mean value of periodontal indices was respectively: PD 1.22 mm (SD 0.72 mm), PI 17.47% (SD 15.01 mm), BOP 9, 87%.,(SD 19.17 mm).

Conclusion

The results obtained are comparable with success criteria in implant rehabilitation. The reported technique proved to be successful in the population observed, with minimal trauma and reduced invasiveness.

Introduction

The prosthetic rehabilitation in atrophic posterior maxilla is a current topic in dentistry. The biological and mechanical improvements of dental implants and reconstructive surgery have allowed surgeons to rehabilitate increasingly complex cases. Up to date, many techniques have been described in the literature to face the anatomical limitations and create the conditions for implants insertion (1). As shown by several studies, the sinus floor elevation has been demonstrated to be a predictable and well-documented strategy to overcome the maxillary atrophy (2). Nearly half of the studies present in the literature have been published in the last five years, thus showing the relevance and actuality of the current topic. Two techniques of sinus lift are largely used: the lateral sinus floor elevation (LSFE) and the osteotome sinus floor elevation (OSFE) (3, 4). The LSFE was reported firstly by Tatum in 1997 and modified over the years by various authors, using different materials, instruments or access designs (5-10). Despite its highly predictable and successful rate, the indications of LSFE are limited to the severe cases of atrophy (<5 mm residual vertical bone) because of its invasiveness and risks of complications (11).

The OSFE, described by Summers in 1994, is able to create the condition to place standard-length screw-implants and regenerate bone at the same time without a second surgical stage (12, 13). The success rate of this technique is comparable to LSFE procedure but with a more conservative approach which is less burdened by complications (14).

However, the use of this technique is limited by the availability of at least 5 mm of residual bone height (RBH) to ensure the stabilization of standard-length screw-implants (15, 16).

On the contrary, when RBH is less than 5 mm the lateral approach is a suggested option, but according to Smiler DG et al. the delayed implant placement is recommended (17). Although new bone could be obtained with this technique, it is difficult to assess the position and the total amount of graft material needed for the future implant placement in the first surgical stage. Furthermore, a longer treatment time is required. However, Peleg et al. (2006) concluded that the bone graft in LSFE and simultaneous implant placement is predictable even in case of 1-2 mm RBH, if “careful case planning and meticulous surgical techniques” are used (18).

In line with the abovementioned, and in order to reduce the treatment duration and risks of complications, it could be auspicious to use the technique that simultaneously combines the safeness of crestal approach and the possibility of immediate positioning of implant even in case of RBH <5 mm.

Fugazzotto (1998) described a crestal window approach and bone graft in case of RBH ranging from 1 to 2 mm. However, the implants were still positioned in the second stage (19). The same author described a crestal sinus augmentation using a trephine bur to design the window. In this case, the minimal RBH had to be 4-5 mm for technical reasons (the use of trephine bur) and the implants were delayed as well (20).

A recent systematic review supports the use of short implants as alternative solution to bone augmentation procedures (21). The survival rate of a short implant placed in atrophic bone is comparable to the procedure that involved bone manipulation to place standard length implants (22).

A great majority of authors believe that a short implant is a fixture long 8 millimeters or less, whilst an implant with a length of < 6.5 mm has been considered an extra-short implant (23). The use of a short implant could limit the amount of bone graft, thus reducing the invasiveness of the technique.

Therefore the bone rebuilder should be functionalized and preserved by adequate bone stimulation according to the laws of Wolff and Frost (24, 25).

The aim of this study was to describe and evaluate a technique that allows a sinus lift via crestal window and immediate positioning of extra-short implant in case of RBH ranging from 1 to 3 mm.

Material and Methods

The study was conducted in accordance with the World Medical Association Declaration of Helsinki and approved by the Institutional Review Board (or Ethics Committee) of “Sapienza” University of Rome (protocol code 27/13.06.2013). All participants gave their informed consent. Implant-prosthetic treatments were carried out at the Oral Surgery Unit of the Department of Oral and Maxillofacial Sciences, “Sapienza” University of Rome.

Patients with posterior maxillary atrophy (Class Ch Misch-Judy) (26), were the target population. Consecutive enrolment was used to select the patients between 2013 and 2014, and a total of 102 patients were enrolled for the first stage. Clinical visit and radio-graphical analysis (orthopantomography and intraoral periapical Rx) were prescribed. If vertical atrophies were considered eligible for the treatment, a Cone Beam CT scan was prescribed (27).

The inclusion criteria were: single or multiple posterior maxillary edentulism, stabilized post-extraction alveolus (at least 6 months after extraction) (28); space available for prosthetic rehabilitation; residual bone height from 1 to 3 mm; horizontal residual bone at least 5 mm (intra-cortical).

The exclusion criteria were: uncontrolled oral diseases, maxillary sinus disease, uncontrolled systemic diseases and ASA classes III, IV and V, chemo/radio tumoral therapy, immunosuppressed and patients being treated with corticosteroid or bisphosphonates, smokers who smoked more than 10 cigarettes a day.

Before surgery, clinical examination was carried on evaluating soft tissues and the adjacent teeth condition.

Two different examiners measured the vertical and horizontal residual bone using Horos™ software (The Horos Project, 64-bit medical image viewer, GNU Lesser General Public Licence, version 3.0) for each Cone Beam CT scan. The calibration of measure was obtained using the CT software and CT scans were analyzed using the paraxial cross section at the center of the area selected for implant placement and mesial/distal of it. The three measures were used to achieve the mean residual bone height (mRBH). (Figure 1)

Figure 1.

Vertical and horizontal residual bone on CT scan.

Surgical procedures

All patients received 2g Amoxicillin with Clavulanic Acid 1 hour before treatment and 1g capsule every 12 hours for 6 days after the surgery. The surgery was performed under local anesthesia. A mid-crestal incision was designed, and releasing was made only if strictly necessary. Using the calibrated bone chisel, a window was designed smaller than the chosen implant, horizontally. The window was mobilized starting from the corners using the concave calibrated hand-osteotome of the same diameter of the chisel used. When mobilized, the window was displaced apically towards the Schneider’s membrane up to 8 mm from the bone crest. If necessary, gentle dissection of membrane was carried on with the sinus floor surgical detangler. The allograft material, synthetic Beta-Tricalcium Phosphate (Synthograft™, Bicon Implants LLC, Boston MA, USA) was inserted into the sinus and gentle compacted using the calibrated osteotomes till reaching the expected vertical dimension. The filling was checked by a periapical Rx.

The implant used, a short titanium biphasic implant, conometric-connected (Bicon Im-plants LLC, Boston MA, USA) was joined to the “sinus-lift abutment” (SLA) (Bicon Implants LLC, Boston MA, USA). The SLA is a healing submerged abutment larger than the antrostomy that prevents the displacing of the implant into the sinus. The SLA-Implant complex was positioned in the site tapping the abutment on the crestal bone. Primary stability was thus obtained by the friction between SLA and antrostomy. In order to obtain a primary closure of the flap, the wound edges were everted and simple knots were made, (Figure 2).

Figure 2.

Illustration of surgical technique.

Patients were instructed to take analgesic treatment (Paracetamol 1g) only if required. Oral and written postoperative instructions were given to all patients. It was recommended to avoid increasing the pression between the mouth and nose. Oral hygiene was performed as normal, except for toothbrushing around the implants site for 7 days. Sutures were daily deterged at home with chlorhexidine 0, 2% and removed 7-10 days after surgery.

Prosthetic rehabilitation

After 6 months the implant was uncovered, and the SLA was removed rotating the abutment with forceps. Subsequently, the healing abutment was transgingivally connected to the implant.

After two weeks an impression was made and the implant was restored with a prosthesis called Integrated Abutment Crown (IACTM). The restoration was made of the Morse taper abutment and a composite crown fused together, one piece, for direct application on the implant. The abutment was made of Titanium alloy (Ti V6 A14) and the resin material used for the crown was a highly filled polyceramic resin composite (Shofu Inc. Kyoto Japan) (Figure 3). Intraoral x-ray was performed (Figure 4).

Figure 3.

Integrated Abutment Crown (IACTM).

Figure 4.

Intraoral x-ray showing the osteointegrated implant with its prosthetic rehabilitation..

Follow ups

After prosthetic rehabilitation, follow-up visits were scheduled at 1, 6 and 12 months during the first year of function, and annually thereafter. At each recall, clinical and radiographical (periapical) examination was carried out to evaluate the following: implant survival; marginal bone level; periodontal indices. Evaluations made at one month of follow-up were considered the baseline values.

In the follow-up evaluations, only the patients, who in the period of one year and five years from the implant placement needed a 3-dimensional investigation for other reason not linked to this study, were considered. In line to this, only 26 out of 102 patients (30 implants) were considered for the follow-ups evaluations. CBCT scans were evaluated in order to assess the mean bone height after prosthetic restoration (mARBH), (Figure 5).

Figure 5.

Five Years CT cone beam scan.

Implant survival was defined as being symptom free and stable without mobility or radiographic evidence of severe bone loss (more than 2 mm). No inflammation or infection should affect hard and soft tissues. Two different examiners analyzed the implants using a blind analysis technique, and by giving univocal (yes/not) responses.

Marginal Bone Lost (MBL) is defined as the maximum distance from the implant-abutment junction (IAJ) to the marginal bone. Digital periapical radiographs were taken at each follow up and images were analyzed using the software (Dentsply, Sirona). Calibration was achieved using the software tools and using the implant length as control. Mesial and distal values (expressed in millimeters) were recorded for each implant. A positive value was assigned if the bone was over the IAJ, while a negative value was assigned if bone was below IAJ. The zero score was given when bone level was at IAJ. Mean value of the two measures was obtained for each implant. Two different examiners, who were independent of the surgeons, were enrolled to evaluate radiograms. The mean value of mesial and distal measure was obtained.

Mean values of MBL at baseline (1 month) were compared with values at the last follow up (five years) obtaining the marginal bone level variation (MBLv).

At each follow-up visit, a clinical evaluation was carried out in order to record the pocket depth (PD), the O’Leary plaque index (PI), and bleeding on probing (BOP) around implants.

PD was measured with a CP12 probe on six sites: three vestibular (mesial, vestibular, and distal) and three lingual (mesial, lingual, distal). The values, expressed in millimeters, were used to achieve the mean PD value for each implant and finally for all the implants.

PI was measured on six sites (three vestibular and three lingual) around each implant. Data were collected for all implants and were expressed as percentage of plaque sites (% PI) (number of surfaces with plaque/total number of sites examined x100).

BOP was also measured on six sites (three vestibular and three lingual) around each implant and evaluated altogether. Data are expressed as percentage of bleeding sites (% BOP) (Number of bleeding sites/total number of sites examined x100).

Two different examiners, independent of the surgeons, were enrolled to value implants.

ARBH is defined as the distance from the crest to the top of grafted bone after the surgery. It is achieved in the same way as mRBH using the CT scan software tools. Calibration was achieved using the software tools and using the implant length as control. The mean value (mARBH) was obtained for each implant by three measurements, one at the implant center and two mesially and distally of 2 mm on paraxial sections. The value of mARBH measured at 1 year of follow-up was compared to data at 5 years follow-up. The difference between the two values was the objective of this study and it has been called mARBH variation (mARBHv).

Some adverse events were recorded.

Results

A total of 30 implants were inserted in 26 patients. The population sample included 20 female and 6 male subjects. The average age of participants was 50.5 years (min 35 years and max 65 years). The dental sites treated were: 10 second upper premolar; 15 first upper molar; 5 second upper molar. Three implant measures were used (diameter X length in mm): 5x6 (13); 5x5 (7); 6x5 (7); 6x6 (3). The mean RBH of population was 2.13 mm with a minimum of 1.1 mm and a maximum value of 3 mm.

• Implant survival:

All the implants survived until the last follow-up.

Marginal bone level variation:

The difference of the mean bone level measured at each implant at 1-month follow-up and the mean value at 60 months of follow up (five years) resulted on average -0.33 mm (Standard Deviation (SD) 0.11) in the population observed (minimum -0.12 and maximum -0.52).

• Mean Bone Height After Prosthetic Restoration (mARBHv):

The mean value registered at 1 year was compared to the mean value registered at 60 months. The bone harvested resorption was on average -0.4 mm (DS 0.26) in the population observed, with a minimum loss of -0.06 mm and the maximum loss of -1.11 mm. The bone loss could be expressed as percentage, mean 5% of vertical harvested bone loss (max -11%; min - 1%).

• Periodontal indices at the last follow up (5 years):

The probing depth measured in the six sites for each implant was used to achieve the mean PD for the entire population. The mean value was 1.22 mm (DS 0.72) with values ranging from 0 and 3 mm.

Plaque and bleeding were recorded among the implant group at the last follow up. Thirty-two sites were positive to plaque and eighteen sites were positive to bleeding among the 180 sites analyzed. The relative mean percentage of Plaque Index was 17.47% (DS 15.01), while the mean percentage of Bleeding on Probing was 9.87% (DS 19.17).

The principal data on the five years follow-up are listed in Table 1.

Table 1. Schematic representation of the principal final data with respective mean values and standard deviations (SD).

Principal final data
Implant survival	100%
Mean MBLv	-0.33 mm (SD 0.11)
Mean PD	1.22 mm (SD 0.72)
Mean PI	17.47% (SD 15.01)
Mean BOP	9.87% (SD 19.17)
Adverse events	0
ARBHv	-0.4 mm (SD 0.26) on average (5%)

Discussion

The maxillary atrophy is a challenge for prosthetic rehabilitation. Over the years, many techniques were recommended to gain the adequate bone volume to place dental implants (1). The sinus floor elevation is the most documented treatment option and various techniques have been described. Many authors have questioned the best approach for each condition (2). The vertical residual bone height has been considered the crucial parameter in choosing the best strategy. When the amount of residual bone is at least 5 mm vertically, the immediate implant positioning is allowed (11), while the lateral approach for sinus floor elevation and delayed implant positioning is suggested in case of 4mm or less of residual vertical bone (17).

The objective of this study was to evaluate the long-term performance of a sinus floor elevation technique that allows immediate implant positioning in case of residual bone height less than 3 mm.

The population observed showed a good maintenance of crestal bone after the prosthetic restoration (mean -0.33 mm of crestal loss after 5 years). The stability of crestal bone could be explained by the subcrestal placement of the conometric implant-abutment junction. The mechanical and biological seal joined to the epicrestal stimuli carried by the abutment could be considered the key factor. The good health condition is confirmed by good values of periodontal indices registered.

The findings of this paper could be considered satisfactory according to the results presented in the literature (29).

As previously reported, socio-economic status and patients’ compliance are crucial in order to achieve implant success (30). All patients in care at Oral Surgery Unit of the Department of Oral and Maxillofacial Sciences of “Sapienza” University of Rome have been regularly followed over the years. In our study, after 5 year of function, we noted a reduction of grafted bone of 5% (mean value) in the interval between one year and five year follow up. The value is considered acceptable according to the results present in the literature (29, 31).

In authors’ opinion, the substantial stability of grafted bone volume depends not only on the osteoconductivity of the bone allograft but also on the formation of haversian bone following the functional stimulation carried out by the implant design. As reported by histological studies, the plateau macrodesign of those implants allows a direct bone formation (32). The healing chamber is filled by the blood clot, promoting the contact with fibrin and osteogenic cells, leading to bone formation (33).

Moreover, in reference to our case, Daher S. (2019) reported a histological analysis of a human retrieved functioning implant which was placed using Beta-Tricalcium Phosphate (34). The specimen analyzed showed no discernable differences between the original host bone and a new bone in terms of lamellar and osteonic structure.

Eventually, the use of short implants could reduce the time of rehabilitation, thus providing faster prosthesis even in case of extreme atrophy, when compared to traditional bone graft procedures.

Conclusions

This technique is considered safe for the patient and less invasive if compared to LSFE. Incidents and compliances are inevitable in every surgical procedure, even more in these advanced cases. The worst complication is a displacement of the fixture into the sinus. Anyway, if the case is carefully selected and the procedure carefully performed, the main complications are avoided.

Although more casuistry is needed, with its limitations, this research validated the viability of the technique presented.