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Space-maintaining management in maxillary sinus lifting: a novel technique using a resorbable polymeric thermo-reversible gel

Space-maintaining management in maxillary sinus lifting: a novel technique using a resorbable polymeric thermo-reversible gel



International Journal of Oral & Maxillofacial Surgery, 2017-05-01, Volume 46, Issue 5, Pages 648-654, Copyright © 2017 International Association of Oral and Maxillofacial Surgeons


Abstract

Several techniques have been proposed to achieve sinus floor elevation and the formation of new bone through the grafting of autologous, heterologous, or alloplastic materials. The grafted materials act as a scaffold for bone formation inside the maxillary sinus. This study investigated a non-graft sinus lifting procedure using a resorbable polymeric thermo-reversible gel. A space-maintaining approach to sinus lifting, using a resorbable polymeric thermo-reversible gel, was applied in 11 patients undergoing implant treatment in the atrophic posterior maxilla. After a healing period of 6 months, a total of 14 implants were placed; biopsies were taken and evaluated histologically and histomorphometrically. The parameters evaluated included the percentages of new bone formation, residual gel, and fibrous tissue. Histological examination showed the formation of new bone with no fibrous tissue or severe inflammatory cellular infiltration. The percentage of newly formed bone was in the range of 54–60%; this consisted of both lamellar and woven bone. No foreign-body reaction was observed. The mean quantities of both residual gel and connective tissue were small. This non-graft sinus lifting procedure using a space-maintaining gel appears to stimulate predictable bone formation; it is thus a useful technique for promoting bone formation in the sinus.

In attempting dental implant placement in the posterior zone of the maxilla, pneumatization of the maxillary sinus can cause difficulties. Furthermore, the progressive atrophy that often results from the extraction of one or more teeth means that the clinician must deal with an inadequate alveolar ridge and poor quality bone. Several surgical techniques have been proposed to achieve sinus floor elevation and thereby the formation of new bone, so as to enable optimal implant positioning. Most of these techniques involve elevating the Schneiderian membrane of the sinus, grafting autologous, heterologous, or alloplastic materials, and then positioning a titanium implant. The grafted materials act as a scaffold for bone formation inside the maxillary sinus, confirming the osteoinductive properties of the Schneiderian membrane.

However, the use of grafting materials is not a prerequisite for predictable bone formation: several clinical and experimental studies have reported maxillary sinus floor augmentation achieved simply by lifting the sinus membrane, without applying any graft materials. These studies employed different surgical methods, using either lateral or crestal approaches, and all achieved successful implant stability and adequate new bone formation. This type of bone augmentation procedure is thus clearly viable for an atrophic posterior maxilla, and may give predictable results.

Studies of guided bone regeneration have shown that good bone regeneration can be achieved with the use of blood clots alone, without inserting bone grafts. However, respiration produces air pressure in the maxillary sinus, which may cause the blood clot to shrink during the healing stages in non-graft sinus lifting. In an experimental study of sinus augmentation using blood clots alone, the clots were observed to collapse during the early postoperative healing period, leading to instability of the newly formed bone; the study reported only a small amount of new bone around the implants, and the vertical gain of new bone was insufficient for stability. The study authors attributed this poor result to the air pressure within the maxillary sinus that, with the respiration pattern, alters the blood clot, significantly reducing the augmented space, and leading to insufficient new bone formation. Further, if atrophy is severe, the implant cannot be placed; maxillary sinus floor augmentation must be performed prior to the insertion of the implants.

Considerable surgical skill is required in the use of space-maintaining devices. Furthermore, the devices currently available for this type of procedure are unstable and rigid, which may lead to membrane perforation.

This study tested a resorbable polymeric thermo-reversible gel for maxillary sinus augmentation in patients with severe maxillary atrophy, and examined the clinical, radiographic, and histological outcomes. The gel used is a specific mixture of poloxamers (predominantly poloxamer 407). These materials are used primarily in pharmaceutical formulations as emulsifying, solubilizing, and stabilizing agents to maintain the clarity of syrups or elixirs. They can also be used as wetting and lubricating agents. The objective was to use the gel as a space maintaining device, with the goal of achieving stable elevation of the sinus membrane through a simple, economical surgical technique, exploiting the osteoinductive properties of the Schneiderian membrane.

Materials and methods

Protocol

The study included 11 patients (six male and five female; mean age 51 years, range 30–70 years). All patients enrolled in the study presented atrophy of the posterior maxilla and agreed to undergo implant-supported prosthesis placement. The patients were fully informed of the study methods and provided their written consent to participate. The institutional review board approved all study protocols. The study was conducted in accordance with the ethical principles of the Declaration of Helsinki and was approved by the local ethics committee.

Inclusion criteria were the following: atrophy of the posterior maxilla with healthy sinuses, with a minimum residual alveolar crest height of ≤4 mm ( Figs 1 and 2 ); no disease affecting the neighbouring teeth; non-smoker. Exclusion criteria were the following: diseases of the maxillary sinuses; uncontrolled systemic diseases such as diabetes; acute sinus infections; chemotherapy; radiotherapy within 12 months before surgery in the head and neck region.

CT slice of the maxilla at baseline (frontal section): note the severe bone resorption.
Fig. 1
CT slice of the maxilla at baseline (frontal section): note the severe bone resorption.

CT slices of the maxilla at baseline (sagittal sections): note the severe bone resorption.
Fig. 2
CT slices of the maxilla at baseline (sagittal sections): note the severe bone resorption.

Data on the residual alveolar crest height before and after surgery were recorded by computed tomography (CT).

Surgical procedure

Prophylactic antibiotics (4 g amoxicillin (Zimox) or 600 mg clindamycin (Dalacin)) were prescribed 1 day before surgery, and were continued at a lower dose for a week after the surgical procedure. Chlorhexidine mouthwash (0.2% for 2 min; Curasept ADS 020) was applied immediately before surgery. The two surgical procedures (sinus augmentation and implant placement) were done by the same surgeon. A buccal mucoperiosteal flap was elevated to expose the alveolar crest and lateral wall of the maxillary sinus. An osteotomy in the form of a trapezoidal bone window was cut in the lateral sinus wall using a 0.9-mm-wide cross-cut fissure bur. After removal of the bone window, the membrane was carefully detached from the sinus wall and lifted to allow gel placement. The sinus was then filled with thermo-reversible gel and the hole closed by replacing the bone window. The amount of gel used in each case was based on the specific anatomical structure of the sinus and on clinical requirements (one or two implants, initial bone height). The thermo-reversible material was placed with a syringe. This material is stored in the fridge at 10 °C and remains liquid until placed inside the sinus. At the higher temperature under the elevated mucosa it becomes denser and stable as a gel. Removal of the excess material was easy due to the consistency acquired at the higher temperature. The material was also useful for bleeding control, acting as a mechanical barrier.

Type D3, B bone, as per the Lekholm and Zarb index, was common in the maxilla.

Post-surgery

Patients were prescribed an analgesic (ibuprofen 600 mg; DOC Generici S.r.l., Milan, Italy) immediately after the surgical intervention, and then every 12 h for 3 days. They were also prescribed chlorhexidine solution 0.2% rinse (twice daily for 1 min). Sutures were left in place for 8–10 days. Implants were placed after 6 months.

The same type of implant was used in all cases (Global; Sweden & Martina SpA, Padova, Italy) with three different diameters (3.8, 4.3, or 4.8 mm) and two lengths (10 or 13 mm). At least half of each implant was positioned in new bone ( Tables 1 and 2 ). Definitive crowns were cemented in place 3–5 months after implant placement.

Table 1
Distribution of implants by position and dimension.
Implant position Implant dimension, diameter × length (mm) Total
3.8 × 13 4.3 × 10 4.3 × 13 4.8 × 10
Premolar 1 3 1 2 7
Molar 1 2 1 3 7
Total 2 5 2 5 14

Table 2
Bone height before sinus augmentation and at 6 months after sinus augmentation when the implants were placed.
Patient Bone height before sinus augmentation Bone height at 6 months after sinus augmentation Bone increment
1 4 14 10
1 4 14 10
2 2 11 9
2 3 12 9
3 3 10 7
3 2 10 8
4 4 13 9
5 3 11 8
6 4 13 9
7 4 13 9
8 3 11 8
9 3 10 7
10 4 11 7
11 3 11 8

One case was complicated by a failed previous sinus lifting operation with bone graft material (deproteinized bovine bone, Bio-Oss; Geistlich) and resorbable membrane (Bio-Gide; Geistlich). The failure was due to infection as, despite instructions to the contrary, the patient had used a removable partial denture 6 days after surgery. In this case, the infected sinus was surgically revised to remove the infected graft material, and the sinus was cleansed with rifampicin. The sinus was then filled with the thermo-reversible gel and the procedure completed as in the remaining cases.

Drilling of the implant placement sites (at 6 months after augmentation) followed standard procedures, except for under-preparation to achieve suitable insertion torque for the implant. The implants (Global; Sweden & Martina SpA) were inserted through the residual maxillary ridge and placed so that they protruded into the space created beneath the lifted sinus membrane and into the newly formed bone. No grafting material (autogenous bone or bone substitutes) was placed in the sinus.

Material: polymeric thermo-reversible gel

A specific mixture of poloxamers dissolved in water was employed (predominantly poloxamer 407; BASF ChemTrade GmbH, Burgbernheim, Germany). A significant characteristic of this mixture is that it remains liquid at 23 °C and becomes denser and then solid at higher temperatures (about 37 °C). The poloxamer mixture thus remains stably positioned on the surface of the mucous membrane, achieving a stable elevation of the sinus membrane. Poloxamers are included in the European Pharmacopoeia and in the National Formulary of the United States Pharmacopoeia (USP–NF). They are not metabolized in the body and have been demonstrated to be non-irritant and non-toxic. Poloxamers that are introduced into the body via routes other than dermal exposure are rapidly cleared from the body, suggesting that there would be no risk of reproductive and/or developmental toxicity.

Preparation of histological and histomorphometric specimens

Biopsy specimens were obtained from the alveolar crest at implant placement using a 3-mm trephine bur in all cases. Specimens were fixed in 10% formalin and decalcified with 10% formic acid. Four sections of each specimen were placed on glass slides and stained following the conventional protocol for haematoxylin and eosin staining (H&E). Tissue blocks were sliced into 3-μm-thick sections for routine histological examination with H&E. The slides were studied under a light microscope (BX51; Olympus, Japan) at 100× magnification. Inflammatory infiltration was recorded as minor, moderate, or severe; foreign-body reaction was recorded if observed.

Histological parameters evaluated

The parameters evaluated were the percentage of new bone formation, the percentage of residual gel, and the percentage of fibrous tissue. Bone formation was evaluated in terms of osteoblast activity, mineralization, and the extent of resorption. Bone structure was expressed via different indices: bone volume/tissue volume ratio (BV/TV), i.e. the percentage of cancellous bone tissue, consisting of mineralized bone and osteoid matrix, versus the total tissue examined; volume of mineralized bone (Md.V/TV), i.e. the percentage of mineralized bone versus the total, and corresponds to the bone volume, osteoid volume; total bone volume (TBV), i.e. the portion of bone (including cortical and cancellous bone) expressed as a percentage of the specimen examined.

An optical microscope was used for the measurements, with enlargement ranging from 2.5× to 40×; this made it possible to measure both the tissue and the bone cells. Special eye-pieces fitted with grids were used for this purpose, enabling the specimen to be evaluated quantitatively.

Clinical and radiographic follow-up

At 6 months after the sinus lifting operation, implants were inserted; the diameter and length of the implant, and any Schneiderian membrane perforation, were recorded.

Complications (infection at the wound site, maxillary sinusitis) were recorded throughout the follow-up period. Statistical analyses were used to compare the postoperative bone level with the residual alveolar bone height.

Statistical analyses

The implant survival rate was evaluated using Kaplan–Meier statistics. The unpaired t -test was used to compare differences in the postoperative alveolar crest height minus residual alveolar crest height between groups with and without Schneiderian membrane perforation. All statistical analyses were performed using IBM SPSS Statistics for Windows, version 20 (IBM Corp., Armonk, NY, USA), and P < 0.05 was considered statistically significant.

Results

Histological findings

Newly formed bone was visible around the residual biomaterial mass in all patients, and there was no fibrous tissue. This viable bone consisted of lacunae containing osteocytes. In all patients, the total amount of new bone was in the range of 54–60%, and this consisted of both lamellar and woven bone. The mean quantities of both residual gel and connective tissue were small. The extent of inflammation was determined by the number of inflammatory cells; distribution patterns were also evaluated. No severe inflammation was noted; inflammation was considered mild in two cases: chronic inflammatory cells, including lymphocytes, plasma cells, and small numbers of macrophages, were observed. No statistically significant differences in the numbers of inflammatory cells were observed between patients, and no foreign-body reactions were reported ( Fig. 3 ).

Histological evaluation after 6 months.
Fig. 3
Histological evaluation after 6 months.

Radiography

After 6 months, radiography showed that there was almost no vertical reduction compared to the situation immediately after sinus augmentation surgery; the height of new bone was more than 10 mm in all cases ( Table 2 ; Figs 4–6 ).

CT slice after 6 months (frontal section): note the good (>1 cm) bone regeneration achieved with the thermosetting gel. Note also the small radiopaque area at the apical level of the sinus, due to the presence of a small number of particles of deproteinized bovine bone remaining after surgical revision of the sinus, since they had already been included in the Schneiderian membrane. The surgeon decided not to remove them, so as to avoid any lesion to the sinus membrane.
Fig. 4
CT slice after 6 months (frontal section): note the good (>1 cm) bone regeneration achieved with the thermosetting gel. Note also the small radiopaque area at the apical level of the sinus, due to the presence of a small number of particles of deproteinized bovine bone remaining after surgical revision of the sinus, since they had already been included in the Schneiderian membrane. The surgeon decided not to remove them, so as to avoid any lesion to the sinus membrane.

CT slices after 6 months (sagittal sections).
Fig. 5
CT slices after 6 months (sagittal sections).

Bone level at baseline (yellow line). Radiograph immediately after sinus augmentation with bone graft material (Bio-Oss) and resorbable membrane (Bio-Gide) that failed after 1 week due to infection (red line). Radiograph after implant placement, showing bone regeneration achieved with the polymeric thermo-reversible gel after 6 months (blue line). (For interpretation of the references to color in this legend, the reader is referred to the web version of the article.)
Fig. 6
Bone level at baseline (yellow line). Radiograph immediately after sinus augmentation with bone graft material (Bio-Oss) and resorbable membrane (Bio-Gide) that failed after 1 week due to infection (red line). Radiograph after implant placement, showing bone regeneration achieved with the polymeric thermo-reversible gel after 6 months (blue line). (For interpretation of the references to color in this legend, the reader is referred to the web version of the article.)

Clinical outcome

All of the patients recruited were included in the study and treated successfully. The mean duration of postoperative follow-up was 22.5 ± 9.5 months (range 24–36 months). A total of 14 implants (length 10–13 mm) were placed in regions with a mean residual alveolar crest height of 3.3 ± 0.7 mm (range 2.5–4.0 mm). In no case did Schneiderian membrane perforation occur.

Only one of the 14 implants (7%) was unstable at the time of insertion; all implants were clinically stable at implantation. No implant failures occurred during loading or the follow-up period.

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