Guided bone regeneration: materials and biological mechanisms revisited

Guided bone regeneration (GBR) is commonly used in combination with the installment of titanium implants. The application of a membrane to exclude non‐osteogenic tissues from interfering with bone regeneration is a key principle of GBR. Membrane materials possess a number of properties which are amenable to modification. A large number of membranes have been introduced for experimental and clinical verification. This prompts the need for an update on membrane properties and the biological outcomes, as well as a critical assessment of the biological mechanisms governing bone regeneration in defects covered by membranes. The relevant literature for this narrative review was assessed after a MEDLINE/PubMed database search. Experimental data suggest that different modifications of the physicochemical and mechanical properties of membranes may promote bone regeneration. Nevertheless, the precise role of membrane porosities for the barrier function of GBR membranes still awaits elucidation. Novel experimental findings also suggest an active role of the membrane compartment per se in promoting the regenerative processes in the underlying defect during GBR, instead of being purely a passive barrier. The optimization of membrane materials by systematically addressing both the barrier and the bioactive properties is an important strategy in this field of research.

Tissue dynamics and regenerative outcome in two resorbable non-cross-linked collagen membranes for guided bone regeneration: A preclinical molecular and histological study in vivo

OBJECTIVES

To investigate the molecular and structural patterns of bone healing during guided bone regeneration (GBR), comparing two resorbable non-cross-linked collagen membranes.

MATERIALS AND METHODS

Trabecular bone defects in rat femurs were filled with deproteinized bovine bone (DBB) and covered with either a membrane comprising collagen and elastin (CXP) or collagen (BG). Samples were harvested after 3 and 21 days for histology/histomorphometry and gene expression analysis. Gene expression analysis was performed on the membrane (at 3 days) and the underlying defect compartment (at 3 and 21 days).

RESULTS

At the total defect level, no differences in bone area percentage were found between the CXP and BG. When evaluating the central area of the defect, a higher percentage of de novo bone formation was seen for the CXP membrane (34.9%) compared to BG (15.5%) at 21 days (p = .01). Gene expression analysis revealed higher expression of bone morphogenetic protein-2 (Bmp2) in the membrane compartment at 3 days in the BG group. By contrast, higher Bmp2 expression was found in the defect compartment treated with the CXP membrane, both at 3 and 21 days. A significant temporal increase (from 3 to 21 days) in the remodeling activity, cathepsin K (Catk) and calcitonin receptor (Calcr), was found in the CXP group. Molecular analysis demonstrated expression of several growth factors and cytokines in the membrane compartment irrespective of the membrane type. Bmp2 expression in the membrane correlated positively with Bmp2 expression in the defect, whereas fibroblast growth factor-2 (Fgf2) expression in the membrane correlated positively with inflammatory cytokines, tumor necrosis factor-alpha (Tnfa) and interleukin-6 (Il6) in the defect.

CONCLUSIONS

The results provide histological and molecular evidence that different resorbable collagen membranes contribute differently to the GBR healing process. In the BG group, bone formation was primarily localized to the peripheral part of the defect. By contrast, the CXP group demonstrated significantly higher de novo bone formation in the central portion of the defect. This increase in bone formation was reflected by triggered expression of potent osteogenic growth factor, Bmp2, in the defect. These findings suggest that the CXP membrane may have a more active role in regulating the bone healing dynamics.

Lateral ridge augmentation with Bio-Oss alone or Bio-Oss mixed with particulate autogenous bone graft: a systematic review

The objective of this systematic review was to test the hypothesis of no difference in implant treatment outcomes when using Bio-Oss alone or Bio-Oss mixed with particulate autogenous bone grafts for lateral ridge augmentation. A search of the MEDLINE, Cochrane Library, and Embase databases in combination with a hand-search of relevant journals was conducted. Human studies published in English from 1 January 1990 to 1 May 2016 were included. The search provided 337 titles and six studies fulfilled the inclusion criteria. Considerable variation prevented a meta-analysis from being performed. The two treatment modalities have never been compared within the same study. Non-comparative studies demonstrated a 3-year implant survival of 96% with 50% Bio-Oss mixed with 50% autogenous bone graft. Moreover, Bio-Oss alone or Bio-Oss mixed with autogenous bone graft seems to increase the amount of newly formed bone as well as the width of the alveolar process. Within the limitations of this systematic review, lateral ridge augmentation with Bio-Oss alone or in combination with autogenous bone graft seems to induce newly formed bone and increase the width of the alveolar process, with high short-term implant survival. However, long-term studies comparing the two treatment modalities are needed before final conclusions can be drawn.

The bone-implant interface of dental implants in humans on the atomic scale

Osseointegration of dental implants occurs on a hierarchy of length scales down to the atomic level. A deeper understanding of the complex processes that take place at the surface of an implant on the smallest scale is of interest for the development of improved biomaterials. To date, transmission electron microscopy (TEM) has been utilized for examination of the bone-implant interface, providing details on the nanometer level. In this study we show that TEM imaging can be complemented with atom probe tomography (APT) to reveal the chemical composition of a Ti-based dental implant in a human jaw on the atomic level of resolution. As the atom probe technique has equal sensitivity for all elements, it allows for 3 dimensional characterizations of osseointegrated interfaces with unprecedented resolution. The APT reconstructions reveal a Ca-enriched zone in the immediate vicinity of the implant surface. A surface oxide of some 5nm thickness was measured on the titanium implant, with a sub-stoichiometric composition with respect to TiO₂. Minor incorporation of Ca into the thin oxide film was also evident. We conclude that the APT technique is capable of revealing chemical information from the bone-implant interface in 3D with unprecedented resolution, thus providing important insights into the mechanisms behind osseointegration.

STATEMENT OF SIGNIFICANCE

Osseointegration of dental implants occurs on a hierarchy of length scales down to the atomic level. A deeper understanding of the complex processes that take place at the surface of an implant on the smallest scale is of interest for the development of improved biomaterials. To date, transmission electron microscopy (TEM) has been utilized for examination of the bone-implant interface, providing details on the nanometer level. In this study we show that TEM imaging can be complemented with atom probe tomography (APT) to reveal the chemical composition of a Ti-based dental implant in a human jaw on the atomic level of resolution. Correlative microscopy ensures the accuracy of APT reconstructions and helps provide both chemical and structural information of the bone-implant interface on the smallest of length scales.

Guided bone regeneration using resorbable membrane and different bone substitutes: Early histological and molecular events

Bone insufficiency remains a major challenge for bone-anchored implants. The combination of guided bone regeneration (GBR) and bone augmentation is an established procedure to restore the bone. However, a proper understanding of the interactions between the bone substitute and GBR membrane materials and the bone-healing environment is lacking. This study aimed to investigate the early events of bone healing and the cellular activities in response to a combination of GBR membrane and different calcium phosphate (CaP) materials. Defects were created in the trabecular region of rat femurs, and filled with deproteinized bovine bone (DBB), hydroxyapatite (HA) or strontium-doped HA (SrHA) or left empty (sham). All the defects were covered with an extracellular matrix membrane. Defects were harvested after 12h, 3d and 6d for histology/histomorphometry, immunohistochemistry and gene expression analyses. Histology revealed new bone, at 6d, in all the defects. Larger amount of bone was observed in the SrHA-filled defect. This was in parallel with the reduced expression of osteoclastic genes (CR and CatK) and the osteoblast-osteoclast coupling gene (RANKL) in the SrHA defects. Immunohistochemistry indicated fewer osteoclasts in the SrHA defects. The observations of CD68 and periostin-expressing cells in the membrane per se indicated that the membrane may contribute to the healing process in the defect. It is concluded that the bone-promoting effects of Sr in vivo are mediated by a reduction in catabolic and osteoblast-osteoclast coupling processes. The combination of a bioactive membrane and CaP bone substitute material doped with Sr may produce early synergistic effects during GBR.

STATEMENT OF SIGNIFICANCE

The study provides novel molecular, cellular and structural evidence on the promotion of early bone regeneration in response to synthetic strontium-containing hydroxyapatite (SrHA) substitute, in combination with a resorbable, guided bone regeneration (GBR) membrane. The prevailing view, based mainly upon in vitro data, is that the beneficial effects of Sr are exerted by the stimulation of bone-forming cells (osteoblasts) and the inhibition of bone-resorbing cells (osteoclasts). In contrast, the present study demonstrates that the local effect of Sr in vivo is predominantly via the inhibition of osteoclast number and activity and the reduction of osteoblast-osteoclast coupling. This experimental data will form the basis for clinical studies, using this material as an interesting bone substitute for guided bone regeneration.

Comparative maxillary bone-defect healing by calcium-sulphate or deproteinized bovine bone particles and extra cellular matrix membranes in a guided bone regeneration setting: an experimental study in rabbits

OBJECTIVES

The aim of this study was to histologically compare the dynamics of bone healing response between calcium sulphate (CaS) and deproteinized bovine bone mineral (DBBM) particles in guided bone regeneration utilizing an extracellular matrix membrane (ECM) as barrier.

MATERIALS AND METHODS

Eighteen rabbits were used in thisstudy. 5 × 5 mm defects were created in the edentulous space between the incisors and molars in the maxilla. The CaS and DBBM particles were placed in the defects, with or without the placement of a membrane by means of random selection. Healing was evaluated at 2, 4 and 8 weeks by histology.

RESULTS

A total resorption of the CaS material was seen already at 2 weeks. Only minor resorption could be seen of the DBBM particles. The CaS group showed significantly more bone regeneration at all three healing periods compared to the DBBM group. The addition of an ECM membrane demonstrated significant additional effect on bone regeneration. The CaS group showed significant increased amounts of blood vessels compared to the DBBM group.

CONCLUSIONS

Thisstudy showed that CaS in combination with an ECM membrane provided synergistic effects on bone regeneration, seemingly due to stimulating angiogenesis in the early healing process.

Host tissue reactions of non-demineralized autogenic and xenogenic dentin blocks implanted in a non-osteogenic environment. An experimental study in rabbits

Dentoalveolar ankylosis with osseous replacement is often seen after replantation of avulsed teeth, and this process may be used for preservation of alveolar crests after trauma. Its exact mechanisms with regard to osteoinductive properties are not yet fully understood and need to be systematically investigated. Dentin can possibly act as a slow-releasing carrier of bone morphogenic proteins (BMP), and this property of dentin has been proposed to be used as an alternative or supplement to bone grafting in the maxillofacial region. We aimed to initially asses host tissue reactions to dentin by implanting dentin blocks of autogenic and xenogenic human origin in rabbit connective tissue of the abdominal wall and femoral muscle. Animals were sacrificed after a period of 3 months, and histological processing, sectioning and examinations were carried out. Bone formation, cell counts and thickness of capsule surrounding the grafts were evaluated. Only minor signs of heterotopic bone formation were seen. There were no significant differences between autografts and xenografts or grafts implanted in connective tissue or muscle with regards to tissue reactions except for a significant difference (P = 0.018) in findings of more local inflammatory cells in relation to grafts placed in connective tissue in the autograft group. We conclude that during the time frame of this study, non-demineralized dentin, whether autogenous or xenogenic did not have the potential to induce bone formation when implanted in non-osteogenic areas such as the abdominal wall and abdominal muscle of rabbits.

Early biocompatibility of poly (ethylene glycol) hydrogel barrier materials for guided bone regeneration. An in vitro study using human gingival fibroblasts (HGF-1)

OBJECTIVES

To evaluate the early cellular attachment and viability to modified polyethylene glycol (PEG) hydrogels with the influence of arginine-glycine-aspartic acid (RGD) in an in vitro model system.

MATERIAL AND METHODS

Human gingival fibroblasts (HGF-1) were cultured on 6 different modalities of PEG hydrogel in hydrophobic polystyrene wells. A total of 7500 cells/well (10,000 cells/cm(2)) were dispersed over the PEG filled wells and incubated in triplicates for 24 h, 7 and 13 days. Cell numbers were calculated by means of a NucleoCounter. Cell viability was determined by measuring lactate dehydrogenase (LDH). For statistical analysis, nonparametric Kruska-Wallis test followed by Dunetts T3 test were used.

RESULTS

All PEG modifications showed good biocompatibility, as demonstrated by low LDH values per cell at the earlier two time points. After 13 days, all PEG modifications showed significantly lower number of cells compared with the controls, and the MX60 configurations demonstrated significantly higher LDH/cell values compared with the other hydrogels.

CONCLUSIONS

Modifications of the physio-chemical properties of PEG hydrogels and the addition of RGD and spacers influenced the initial cellular response of cultured HGF-1 cells. With the exception of MX60 after 13 days, all PEG formulations performed similarly well. Early cellular response should be considered when developing PEG-based material for clinical purposes.

One-year results of a clinical and radiological prospective multicenter study on NEOSS® dental implants

BACKGROUND

NEOSS® (Neoss Ltd., Harrogate, UK) dental implant system was introduced on the clinical arena in 2003. It is important that novel implant systems are systematically evaluated in a multicenter setting.

PURPOSE

The aim of this study was to follow a large number of consecutively treated patients, with NEOSS dental implant system, both clinically and radiographically. The current report constitutes the 1-year data of a planned 5-year study.

MATERIALS AND METHODS

The study included a total of 177 patients treated with 590 NEOSS implants at 13 clinics in Sweden. The material was composed of 72 males and 105 females treated for single, partial, and total edentulism. Clinical, radiographic, and subjective evaluations were performed.

RESULTS

Out of 590 implants, 13 early failures have been reported, corresponding to a 1-year cumulative survival rate (CSR) of 97.8%. Evaluation of function and esthetics at the 1-year visit resulted in 100% success for function and 98% success for the esthetic outcome. The mean marginal bone loss was 0.6 mm (SD 1.1) after 1 year in clinical function. No adverse effects of the NEOSS dental implants were reported, and complications were few and similar to those reported for implant treatment in general.

CONCLUSION

The CSR in the present study was 97.8%. No adverse effects of the NEOSS implants were reported, and complications during the study period were few and similar to those reported to for other well-documented implants system. Based on the present data, we conclude that NEOSS dental implant is a safe and predictable implant system. However, the high number of dropouts in the radiological evaluation must be considered when interpreting the data.

Iliac crest autogenous bone graft versus alloplastic graft and guided bone regeneration in the reconstruction of atrophic maxillae: a 5-year retrospective study on cost-effectiveness and clinical outcome

BACKGROUND

Reconstruction of the atrophic maxillae with autogenous bone graft and jawbone-anchored bridges is a well-proven technique. However, the morbidity associated with the concept should not be neglected. Furthermore, the costs for such treatment, including general anesthesia and hospital stay, are significant. Little data are found in the literature with regard to a cost-benefit approach to various treatment alternates.

PURPOSE

The aim of this retrospective study was to compare from a health-economical and clinical perspective the reconstruction of the atrophic maxillae prior to oral implant treatment either with autogenous bone grafts harvested from the iliac crest or the use of demineralized freeze-dried bone (DFDB) in combination with a thermoplastic carrier (Regeneration Technologies Inc., Alachua, FL, USA) and guided bone regeneration (GBR).

MATERIALS AND METHODS

A total of 26 patients (13 + 13) were selected and matched with regard to indication, sex, and age. The study was performed 5 years after the completion of the treatment. Implant survival, morbidity, and complications were analyzed. Furthermore, a detailed analysis of the total cost for the respective treatment modality was performed, including material, costs for staff, sick leave, etc.

RESULTS

The study revealed no statistical difference with regard to implant survival for the respective groups. The average total cost, per patient, for the DFDB group was 22.5% of the total cost for a patient treated with autogenous bone grafting procedures.

CONCLUSIONS

The study concluded that reconstruction of atrophic maxillae with a bone substitute material (DFDB) in combination with GBR can be performed with an equal treatment outcome and with less resources and a significant reduced cost in selected cases compared with autogenous bone grafts from the iliac crest.

Postoperative Morbidity in Traditional versus Coblation Tonsillectomy

Objectives

The aim of this study was to compare levels of postoperative pain after traditional (cold steel with bipolar cautery) and Coblation tonsillectomies.

Methods

Patients with recurrent or chronic tonsillitis, including tonsillar hyperplasia, were randomized to undergo tonsillectomies using either a traditional cutting technique or the Coblation technique. Patients and staff on the relevant wards were blinded regarding patient allocation. Pain, odynophagia, and activity limitations were recorded on a visual analog scale. Analgesics were self-administered, and daily analgesic consumption by patients was reported. All complications were also registered.

Results

Fifty-seven patients (between 6 and 57 years of age) completed the study. No significant difference was found between the two techniques with regard to reported pain, odynophagia, activity limitations, or use of analgesics. A slight tendency toward decreased pain and decreased use of analgesics in the Coblation group reached statistical significance only when the adult patients were analyzed separately. Two cases of hospital readmission occurred because of postoperative bleeding following Coblation tonsillectomies.

Conclusions

Overall, the two methods are equivalent in terms of postoperative pain, including the use of analgesics. The risk of postoperative bleeding after the Coblation method requires further evaluation with specifically designed studies.

Postoperative morbidity in traditional versus coblation tonsillectomy

OBJECTIVES

The aim of this study was to compare levels of postoperative pain after traditional (cold steel with bipolar cautery) and Coblation tonsillectomies.

METHODS

Patients with recurrent or chronic tonsillitis, including tonsillar hyperplasia, were randomized to undergo tonsillectomies using either a traditional cutting technique or the Coblation technique. Patients and staff on the relevant wards were blinded regarding patient allocation. Pain, odynophagia, and activity limitations were recorded on a visual analog scale. Analgesics were self-administered, and daily analgesic consumption by patients was reported. All complications were also registered.

RESULTS

Fifty-seven patients (between 6 and 57 years of age) completed the study. No significant difference was found between the two techniques with regard to reported pain, odynophagia, activity limitations, or use of analgesics. A slight tendency toward decreased pain and decreased use of analgesics in the Coblation group reached statistical significance only when the adult patients were analyzed separately. Two cases of hospital readmission occurred because of postoperative bleeding following Coblation tonsillectomies.

CONCLUSIONS

Overall,the two methods are equivalent in terms of postoperative pain,including the use of analgesics. The risk of postoperative bleeding after the Coblation method requires further evaluation with specifically designed studies.