Microarchitectural study of the augmented bone following ridge preservation with a porcine xenograft and a collagen membrane: preliminary report of a prospective clinical, histological, and micro-computed tomography analysis

Abstract

Socket preservation using a combination of porcine xenograft and collagen membrane maintains the vertical and horizontal dimensions of the ridge. The aim of this study was to evaluate the microarchitecture of the grafted area by histological analysis and micro-computed tomography. Patients in the test group (group 1; nine patients) underwent socket preservation, while the sockets in the control group (group 2; eight patients) were allowed to heal without preservation. After a 6-month healing period, bone core biopsy samples were obtained and implants were placed in the augmented sites in the test group (12 biopsy samples) and the non-augmented sockets of the control group (12 biopsy samples). Analysis of the biopsy samples obtained from group 1 revealed that particles of the graft were surrounded by newly formed bone in eight cases and by granulation tissue in four cases. Micromorphometric data showed statistically significant differences in several parameters between the microarchitecture of the native bone and the newly formed bone within the augmented sites, which suggests that the xenograft particles interfere with the bony healing of the alveoli.

The alveolar ridge is a tooth-dependent structure of the jaw. Its development is induced by tooth eruption, and the loss of teeth results in resorption and atrophy of the alveolar ridge. During the first year after tooth removal, there is a 25% decrease in the volume of the ridge, and its width reduces by 40–60% in the first 3 years. Severe atrophy of the ridge prevents favourable prosthetic positioning of endosseous implants; therefore, ridge augmentation may be necessary for implant placement.

Preservation of the alveolus following tooth extraction predictably maintains the bone volume. Several techniques and biomaterials for alveolus preservation have been described in the literature. Studies have shown that the use of bone substitute materials with or without bioresorbable or non-resorbable barrier membranes significantly reduces the horizontal and vertical bone loss following extraction. There are reports of the successful application of several bone graft materials in ridge preservation, i.e. autologous bone, mineralized freeze-dried bone allograft (FDBA), demineralized freeze-dried bone allograft (DFDBA), alloplastic polymers, nanocrystalline hydroxyapatite bioactive glass, biphasic ceramic bone substitute, porous bovine bone mineral (PBBM), and other xenografts of bovine and porcine origin. However, all of these materials interfere with normal extraction socket healing. Autologous bone is the gold standard bone substitute material; however, morbidity related to the donor region is a disadvantage of the use of autologous bone.

A xenograft of porcine origin has recently been studied. It is a particulated, high-porosity, corticocancellous xenograft. The porcine bone undergoes thermal processing (maximum temperature 130 °C) to completely eliminate any pathogenic elements and to maintain the structure and composition of the natural collagen and hydroxyapatite. Type I collagen induces the osteoblastic differentiation of bone marrow cells. The processing of this biomaterial results in greater degradation of the granules compared to other xenografts.

Micro-computed tomography (micro-CT) has been used to analyze the internal structure of hard tissues in high resolution. Compared to histological sectioning, it is a quick, reproducible method that is also non-destructive, thus allowing further processing of the specimen. According to the literature, micro-CT analysis is a viable method to study the integration of bone augmentation materials.

The aim of this prospective study was to clinically examine and then investigate the integration of porcine xenografts used in ridge preservation by histological and micro-CT analysis. The aim was to determine whether socket grafting interferes with natural bone healing.

Materials and methods

Patients

Patients who were periodontally healthy, older than 18 years of age, able to sign an informed consent form, and who needed implant-supported restoration were included in this study. The exclusion criteria were as follows: history of systemic diseases that would contraindicate oral surgical treatment, unwillingness to return for follow-up examinations, smoking, and pregnancy. The procedures used in the study were explained thoroughly to the patients, and they signed informed consent forms. The study was approved by the Regional and Institutional Committee of Science and Research Ethics and the Hungarian Office of Health Authorisation and Administrative Procedures, and was conducted in accordance with the Declaration of Helsinki.

The patients were categorized into two study groups. The test group (group 1) consisted of nine patients who required ridge preservation to maintain sufficient bone volume for implant placement. These patients showed loss of buccal bone after tooth removal. Therefore, their sockets showed a three-wall bone morphology. The control group (group 2) consisted of eight patients who did not require ridge preservation in order to maintain the bone volume for implant placement. These patients showed an intact and thick buccal bone after tooth removal, and their alveoli presented a four-wall bone morphology.

Surgical treatment

All patients rinsed with 0.2% chlorhexidine solution for 1 min before surgery. The removal of teeth was performed in an atraumatic manner under local anaesthesia. The sockets were thoroughly debrided to remove all of the soft tissues.

Socket morphology was examined at this stage. If the buccal bone of the alveolus was missing and the socket presented a three-wall bone morphology, the socket was assigned to group 1 (test group). If an intact buccal bone wall was observed and the socket presented a four-wall bone morphology after tooth removal, the socket was assigned to group 2 (control group).

In group 1, an intrasulcular incision with or without crestal incision and two relieving incisions were made to raise a full-thickness flap. The corticocancellous porcine bone graft (Gen-Os; OsteoBiol, Tecnoss Dental, Torino, Italy) was packed into the socket and a porcine collagen membrane (Evolution; OsteoBiol, Tecnoss Dental) was used as the occlusive barrier. The buccal flap was mobilized to allow tension-free primary closure. The margins were stabilized with single interrupted sutures. The images presented in Fig. 1 show a preoperative radiograph and a cone beam CT image obtained after a 6-month healing period in one of the cases in group 1.

Fig. 1
Preoperative radiograph (left) and cone beam CT image (right) after a 6-month healing period in one of the cases in group 1.

In group 2, sockets were left to heal without the use of socket preservation techniques.

Antibiotics (1 g amoxicillin–clavulanate twice a day for 5 days, or in the case of side effects or a known allergy to penicillin, 300 mg clindamycin four times a day for 4 days), anti-inflammatory drugs (50 mg diclofenac three times a day for 3 days), and chlorhexidine mouthwash (twice a day for 21 days) were prescribed to the patients assigned to both groups. During the healing period, patients either received temporary prostheses that were in no contact with the surgical area or did not wear temporary prostheses at all.

After a 6-month healing period, a clinical examination was made and the surgical re-entry procedure was performed under local anaesthesia. A bone core biopsy was taken with a trephine with an external diameter of 3.5 mm and an internal diameter of 2.5 mm (330 205 486 001 025; Hager & Meisinger GmbH, Neuss, Germany) and implants of at least 4.0 mm in diameter were placed into the grafted alveolus, non-submerged. Final prosthetic restorations were cemented after 3 months. Patients were recalled for follow-up every 6 months.

The bone core biopsy samples were removed, pushed out of the trephine, and placed in sample holders filled with 4% formaldehyde solution in 0.1 M phosphate buffered saline (PBS), pH 7.3; these were stored at 4 °C. The image presented in Fig. 2 shows the bone core biopsy sample obtained from the augmented site of one of the cases in group 1.

Fig. 2
The bone core biopsy sample obtained from the augmented site in one of the cases in group 1.

Histological evaluation

Bone core biopsy material was fixed in 10% buffered formaldehyde solution. Following dehydration, the biopsy material was embedded in paraffin and 6-μm sections were prepared with a diamond knife (Diatome, Biel, Switzerland). The sections were stained with routine haematoxylin–eosin stain.

Micro-computed tomography analysis

The bone core biopsy samples were scanned using a micro-CT scanner (SkyScan 1172 X-ray microtomograph; Bruker, Kontich, Belgium). The X-ray tube potential (peak) was 70 kV and the X-ray intensity was 124 μA. Bone core biopsy samples were scanned in a 4% buffered formaldehyde solution. Scanning was carried out at 5.90-μm resolution. A 0.5-mm aluminium filter was used to remove image noise. The ring artefact correction was 10, and the beam hardening correction was 61%. The average scan duration was 25 min. After scanning, reconstruction of the three-dimensional microstructural image data was done using the SkyScan NRecon software. The reconstruction duration per slice was 1.59 s.

The morphometric variables calculated by the SkyScan software were the specific bone surface (BS/BV), bone surface density (BS/TV), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), trabecular number (Tb.N), trabecular bone pattern factor (Tb.Pf), structure model index (SMI), number of objects (Obj.N), number of closed pores (Po.N(cl)), volume of closed pores (Po.V(cl)), surface of closed pores (Po.S(cl)), closed porosity (percent) (Po(cl)), volume of open pore space (Po.V(op)), open porosity (percent) (Po(op)), and total volume of pore space (Po.V(tot)). The morphometric variables and their definitions are listed in Table 1 .

Table 1
Morphometric variables calculated by the SkyScan software. a
Abbreviation Variable Description Standard unit
BV/TV Bone volume fraction Relative volume of calcified tissue in the selected VOI. %
BS Bone surface Surface of the region segmented as bone. mm 2
i.S Intersection surface Surface of the VOI intersected by solid binarized objects, i.e., the part of the VOI boundary surface that runs through solid objects. mm 2
BS/BV Specific bone surface Ratio of the segmented bone surface to the segmented bone volume. mm 2 /mm 3
BS/TV Bone surface density Ratio of the segmented bone surface to the total volume of the region of interest. mm 2 /mm 3
Tb.Th Trabecular thickness Mean thickness of trabeculae, assessed using direct 3D methods. mm
Tb.Sp Trabecular separation Mean distance between trabeculae, assessed using direct 3D methods. mm
Tb.N Trabecular number Measure of the average number of trabeculae per unit length. 1/mm
Tb.Pf Trabecular bone pattern factor This is an index of connectivity of trabecular bone; it calculates an index of relative convexity or concavity of the total bone surface, on the principle that concavity indicates connectivity (and the presence of ‘nodes’), and convexity indicates isolated disconnected structures (struts). 1/mm
SMI Structure model index An indicator of the structure of trabeculae; the structure model index indicates the relative prevalence of rods and plates in a 3D structure such as trabecular bone. An ideal plate, cylinder, and sphere have SMI values of 0, 3, and 4, respectively. (Conversely, cylindrical and spherical cavities have SMI of −3 and −4, respectively.) None
Obj.N Number of objects The total number of discrete binarized objects within the VOI is reported. None
Po.N(cl) Number of closed pores The total number of discrete binarized closed pores within the VOI is reported. A closed pore in 3D is a connected assemblage of space (black) voxels that is fully surrounded on all sides in 3D by solid (white) voxels. None
Po.V(cl) Volume of closed pores The total volume of all closed pores within the VOI. mm 3
Po.S(cl) Surface of closed pores The total surface area of all closed pores within the VOI. mm 2
Po(cl) Closed porosity (percent) The volume of closed pores as a percentage of the total of solid plus closed pore volume, within the VOI. %
Po.V(op) Volume of open pore space The total volume of all open pores within the VOI is reported. An open pore is defined as any space located within a solid object or between solid objects, which has any connection in 3D to the space outside the object or objects. mm 3
Po(op) Open porosity (percent) The percentage open porosity is the volume of open pores as a percentage of the total VOI volume. %
Po.V(tot) Total volume of pore space The total volume of all open and closed pores within the VOI is reported. mm 3
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Dec 14, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Microarchitectural study of the augmented bone following ridge preservation with a porcine xenograft and a collagen membrane: preliminary report of a prospective clinical, histological, and micro-computed tomography analysis
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