Influence of two barrier membranes on staged guided bone regeneration and osseointegration of titanium implants in dogs. Part 2: augmentation using bone graft substitutes

Porous polymeric membranes: fabrication techniques and biomedical applications

Porous polymeric membranes have shown great potential in biological and biomedical applications such as tissue engineering, bioseparation, and biosensing, due to their structural flexibility, versatile surface chemistry, and biocompatibility. This review outlines the advantages and limitations of the fabrication techniques commonly used to produce porous polymeric membranes, with especial focus on those featuring nano/submicron scale pores, which include track etching, nanoimprinting, block-copolymer self-assembly, and electrospinning. Recent advances in membrane technology have been key to facilitate precise control of pore size, shape, density and surface properties. The review provides a critical overview of the main biological and biomedical applications of these porous polymeric membranes, especially focusing on drug delivery, tissue engineering, biosensing, and bioseparation. The effect of the membrane material and pore morphology on the role of the membranes for each specific application as well as the specific fabrication challenges, and future prospects of these membranes are thoroughly discussed.

Comparison of a polyethylene glycol membrane and a collagen membrane for the treatment of bone dehiscence defects at bone level implants-A prospective, randomized, controlled, multicenter clinical trial

OBJECTIVES

The aim of the present randomized, controlled clinical multicenter trial was to compare a polyethylene glycol (PEG) and a native collagen membrane (BG) for simultaneous guided bone regeneration at bony dehiscence-type defects around bone level titanium implants.

MATERIAL AND METHODS

The study enrolled 117 patients requiring implant treatment in the posterior maxilla or mandible with expected buccal bony dehiscence-type defects at the placed titanium implants. According to a parallel groups design, defects were filled with a synthetic bone filler and randomly assigned to either PEG or BG membrane. As primary parameter, the relative vertical bone fill was assessed at baseline and at re-entry after 6 months of healing. As secondary parameters, the marginal bone level (MBL) was assessed radiographically and soft tissue conditions were recorded up to 18 months postloading.

RESULTS

Both groups showed comparable vertical bone fill revealing a relative change in defect height of 59.7% (PEG) and 64.4% (BG). The absolute mean reduction in defect size was 2.5 mm in the PEG group and 3.2 mm in the BG group. Although both groups revealed a statistically significant mean defect reduction (p < .001), a comparison between the two groups did not show statistical significances. The non-inferiority test with inferiority limit of -5% could not be rejected, based on the 90% confidence interval of the differences of the two means with lower limit -15.4%. After 18 months, an MBL increase of 0.45 ± 0.43 mm in the PEG group and 0.41 ± 0.81 mm in the BG group was detected (p < .001). Soft tissue complications were observed in both groups without showing statistical significance.

CONCLUSIONS

Both membranes supported bone regeneration at dehiscence-type defects and obtained vertical bone fill with a relative change in defect height of 59.7% (PEG) and 64.4% (BG); however, the non-inferiority of PEG could not be shown.

Staged implant placement after defect regeneration using biphasic calcium phosphate materials with different surface topographies in a minipig model

OBJECTIVE

To assess the influence of biphasic calcium phosphate materials with different surface topographies on bone formation and osseointegration of titanium implants in standardized alveolar ridge defects.

MATERIALS AND METHODS

Standardized alveolar ridge defects (6 × 6 mm) were created in the mandible of 8 minipigs and filled with three biphasic calcium phosphate materials (BCP1-3, 90% tricalcium phosphate/10% hydroxyapatite) with different surface properties (micro- and macroporosities) as well as a bovine-derived natural bone mineral (NBM) as a control. At 12 weeks, implants were placed into the augmented defects. After further 8 weeks of healing, dissected blocks were processed for histological analysis (e.g., mineralized (MT), residual bone graft material (BS), bone-to-implant contact (BIC)).

RESULTS

All four biomaterials showed well-integrated graft particles and new bone formation within the defect area. MT values were comparable in all groups. BS values were highest in the NBM group (21.25 ± 13.52%) and markedly reduced in the different BCP groups, reaching statistical significance at BCP1-treated sites (9.2 ± 3.28%). All test and control groups investigated revealed comparable and statistically not significant different BIC values, ranging from 73.38 ± 20.5% (BCP2) to 84.11 ± 7.84% (BCP1), respectively.

CONCLUSION

All bone graft materials facilitated new bone formation and osseointegration after 12 + 8 weeks of healing.

Effects of methods of hydration of a biphasic ceramic graft on bone regeneration of extraction socket defects

BACKGROUND

Alveolar volumetric changes are inherent to the healing process after tooth extraction and filling of the extraction site with biomaterials can reduce these volumetric changes and provide a more favorable environment for the future prosthetic restoration with implants. Among the biomaterials available, biphasic ceramic compounds have shown promissing clinical results, however, histologic evaluation of bone tissue response to different hydration and incorporation methods are limited. The objective of this study was to comparatively evaluate in vivo the osteoconductive potential of the biphasic ceramic bone substitute (SBC) composed of beta-tricalcium phosphate and hydroxyapatite after different hydration methodologies in rat extraction sockets.

METHODS

Wistar rats (n = 20) were randomly distributed in two subgroups (G1, G2) according to the hydration methods used. After extraction of the right upper central incisor the alveoli were filled with SBC hydrated by two different methods. Group 1: biomaterial hydrated in blood; Group 2: biomaterial hydrated in physiologic saline. The animals were euthanized after 1 and 6 weeks for removal of the bone blocks containing the biomaterial and were submitted to histologic processing. Five-μm-thick demineralized sections of the samples were stained with hematoxylin and eosin (HE) and subjected to histomorphometric analysis.

RESULTS

Bone formation was limited 7 days after the extraction procedure and increased in both groups between 7 and 42 days from surgery, demonstrating a time dependent increase of bone volume throughtout the experimental period (p < 0.05).

CONCLUSIONS

The hydration of SBC with saline significantly increased new bone formation and reduced connective tissue volume after 42 days demonstrating that hydration method may significantly influence bone healing in such defects, and, thus should be carefully performed.

Biodegradable Polymer Membranes Applied in Guided Bone/Tissue Regeneration: A Review

Polymer membranes have been widely used in guided tissue regeneration (GTR) and guided bone regeneration (GBR). In this review, various commercially available membranes are described. Much attention is paid to the recent development of biodegradable polymers applied in GTR and GBR, and the important issues of biodegradable polymeric membranes, including their classification, latest experimental research and clinical applications, as well as their main challenges are addressed. Herein, natural polymers, synthetic polymers and their blends are all introduced. Pure polymer membranes are biodegradable and biocompatible, but they lack special properties such as antibacterial properties, osteoconductivity, and thus polymer membranes loaded with functional materials such as antibacterial agents and growth factors show many more advantages and have also been introduced in this review. Despite there still being complaints about polymer membranes, such as their low mechanical properties, uncontrollable degradation speed and some other drawbacks, these problems will undoubtedly be conquered and biodegradable polymers will have more applications in GTR and GBR.

Key aspects on the use of bone substitutes for bone regeneration of edentulous ridges

OBJECTIVES

To review the histological and clinical outcomes of the use of bone substitues in different oral bone regenerative procedures: socket preservation, immediate implant placement, lateral and vertical bone augmentation.

METHODS

Histological animal studies and clinical trials regarding the performances of bone substitutes, either allogenic, xenogeneic or alloplastic, have been evaluated. Different procedures examined separately and evidence-based results were provided.

RESULTS

The use of deproteinized bovine bone mineral (DBBM) seems to be effective most clinical indications, due to their osteoconductivity, space maintenance characteristics and slow resorption. The combination of Hydroxyapatite and Beta Tricalcium Phospate (HA/TCP) has also reported similar histological evidence and clinical outcomes. The use of autogenous block grafts is still the method of choice in clinical situations in need of vertical bone augmentation.

CONCLUSIONS

The use of bone substitutes is the standard of therapy in current modalities of lateral bone augmentation, mainly when used in conjunction with implant placement.

Immunohistochemical analysis of staged guided bone regeneration and osseointegration of titanium implants using a polyethylene glycol membrane

OBJECTIVES

This study aimed to immunohistochemically evaluate staged guided bone regeneration and osseointegration of titanium implants using two bone graft substitutes in combination with a polyethylene glycol (PEG) membrane in a dog model.

MATERIALS AND METHODS

Saddle-type alveolar ridge defects were prepared in the lower jaws of 12 foxhounds and randomly filled with a natural bone mineral (NBM) or a biphasic calcium phosphate (SBC) and covered with an in situ gelling PEG membrane. After a healing period of 8 and 12 weeks (six animals each), modSLA titanium implants were inserted to heal in a submerged position. At 8 + 2 and 12 + 2 weeks, respectively, dissected blocks were processed for immunohistochemical analysis [osteocalcin (OC)].

RESULTS

After 8 + 2 weeks, mean OC values (%) tended to be higher in the NBM group (NBM, 32.7 ± 8.9%), but failed to reach statistical significance over the SBC group (SBC, 24.4 ± 6.6%). After 12 + 2 weeks, mean OC values decreased in both groups and was almost identical in both groups (NBM 1.6 ± 1.2%/SBC 2.1 ± 1.4%).

CONCLUSION

It was concluded that all augmentation procedures investigated were characterised by a comparable OC activity during the process of bone regeneration and osseointegration of modSLA titanium implants.

Shell technique using a rigid resorbable barrier system for localized alveolar ridge augmentation

OBJECTIVES

To assess the safety and efficacy of a rigid synthetic barrier system in a shell technique for localized alveolar ridge augmentation.

MATERIALS AND METHODS

Saddle-type defects (n = 4 each) were prepared in the lower jaws of six fox hounds. At two defects, the outer contours were reconstructed using polylactic acid (D and L isomers) (PDDL) pins welded to PDDL plates by ultrasound vibration and the defect area filled using either a natural bone mineral (NBM) or NBM + autogenous bone (AB) and covered by a native collagen membrane (CM). While the third defect was augmented using NBM+AB+CM, the fourth site was left untreated. At 14 weeks, dissected blocks were processed for histomorphometrical analysis [e.g., augmented area (AA)].

RESULTS

AA values (median in mm(2)) were significantly increased in all guided bone regeneration (GBR) groups [NBM+PDDL+CM (19.74) > NBM+AB+PDDL+CM (16.98) > NBM+AB+CM (16.66)] when compared with the untreated control sites (7.34). Histological analysis has pointed, in the absence of any foreign-body reactions, to biodegradation of both PDDL plates/pins and CM.

CONCLUSIONS

(i) All GBR procedures investigated equally supported bone regeneration, (ii) the application of PDDL+CM may be associated with increased mineralized tissue MT and subsequently AA values than CM alone, and (iii) AB may not improve healing at NBM+PDDL+CM-treated sites.

Accuracy of peri-implant bone thickness and validity of assessing bone augmentation material using cone beam computed tomography

OBJECTIVES

The aim of this study was to evaluate the accuracy of measuring bone thickness surrounding dental implants and the reliability of assessing existence and completion of osseous integration of augmentation material using a cone beam computed tomography (CBCT) system.

MATERIALS AND METHODS

In jaws of foxhounds, artificial defects were regenerated by guided bone regeneration and then dental implants were placed. After putting down the dogs, the jaws were separated from the bodies and exposed in a CBCT system. The bone thickness was measured on both buccal and oral sides of the implants at different levels. Every examiner evaluated existence and integration of bone augmentation materials (BAM) and the completeness of marginal implant covering. The same measurements and evaluations were performed at digital images of the corresponding histological sections.

RESULTS

The mean and the standard deviation of the differences between radiological and histological measurements of peri-implant bone thickness were -0.22 mm and 0.77 mm, respectively. Sensitivity and specificity were 0.77 and 0.60 for existence of BAM, 0.59 and 0.74 for completed integration, and 0.39 and 0.71 for full covering of the implant surface.

CONCLUSIONS

The present study indicates that the PaX Duo3D(®) CBCT system allows measurements of peri-implant bone thickness at an accuracy of half a millimeter, and--within limits--assessing the existence and integration of BAM. It is not possible to evaluate whether the implant is covered completely by hard tissue.

CLINICAL RELEVANCE

Peri-implant bone thickness is a key factor for obtaining initial implant stability. The accuracy of its measurement has clinical impact. Radiological assessment of existence and integration of BAM would be of great benefit to the evaluation of augmentation procedures.