Hyaluronan supports recombinant human bone morphogenetic protein-2 induced bone reconstruction of advanced alveolar ridge defects in dogs. A pilot study

BACKGROUND

Prosthetic-driven implant dentistry requires predictable procedures for alveolar ridge augmentation. The objective of this pilot study was to evaluate bone regeneration in mandibular, full-thickness, alveolar ridge, saddle-type defects following surgical implantation of recombinant human bone morphogenetic protein-2 (rhBMP-2) in a novel hyaluronan (HY) sponge carrier. This sponge was fabricated from auto-crosslinked HY.

METHODS

Alveolar ridge defects (approximately 15 x 10 x 10 mm), 2 per jaw quadrant, were surgically prepared in each of 3 young adult American fox hounds. Four defects were immediately implanted with rhBMP-2/HY. Three defects were implanted with rhBMP-2 in an absorbable collagen sponge (ACS) carrier (positive control). The rhBMP-2 solution (1.5 ml at 0.2 mg/ml) was soak-loaded onto the HY and ACS sponges. Three defects were implanted with HY sponges soak-loaded with buffer without rhBMP-2 (negative control), while 2 defects served as surgical controls. The animals were euthanized at 12 weeks postsurgery for histometric analysis.

RESULTS

Clinically, alveolar ridge defects receiving rhBMP-2/ACS exhibited a slight supracrestal expansion, while defects receiving rhBMP-2/HY were filled to contour. In contrast, the HY and surgical controls exhibited ridge collapse. rhBMP-2/HY-treated defects exhibited a dense bone quality without radiolucent regions observed in defects treated with rhBMP-2/ACS. The histometric analysis showed 100% bone fill for the rhBMP-2/ACS defects and 94%, 58%, and 65% bone fill for the rhBMP-2/HY, HY, and surgical control defects, respectively.

CONCLUSIONS

The conclusions are based on data from 2 of 3 animals in the study. In one animal, no response to rhBMP-2 was observed with either carrier, and the animal may have been a non-responder of unknown nature. With this limitation, the observations herein suggest that: 1) HY supports significant bone induction by rhBMP-2; 2) the rhBMP-2-induced bone assumes qualities of the immediate resident bone; 3) HY alone exhibits no apparent osteoconductive potential; and 4) HY appears to resorb within a 12-week healing interval in the absence or presence of rhBMP-2. Thus, HY appears to be a suitable candidate carrier for rhBMP-2.

Long-term evaluation of osseointegrated implants inserted at the time or after vertical ridge augmentation. A retrospective study on 123 implants with 1-5 year follow-up

The purpose of the present study was to evaluate retrospectively, after 1 to 5 years of prosthetic loading, 123 implants consecutively inserted at the time of vertical ridge augmentation in 4 clinics. At the time of the implant surgery, 3 different techniques were used: the implants were allowed to protrude 2 to 7 mm from the bone level and a titanium reinforced expanded-polytetrafluoroethylene (e-PTFE) membrane was positioned to protect either the blood clot (Group A, 6 patients), or an allograft (Group B, 11 patients), or an autograft (Group C, 32 patients). The annual implant evaluation was carried out according to a standard protocol utilized for long term studies with endosseous implants inserted in non-regenerated bone. Only 1 implant failed immediately after the second stage surgery and after 1 month it was substituted with a new implant. All the remaining implants appeared clinically stable, no signs of radiolucency were present at the bone-implant interface, therefore, they could be defined successfully osseointegrated. The radiographic analysis showed stable bone crest levels with a mean bone loss of 1.35 mm for the Group A, of 1.87 mm for the Group B and of 1.71 for the Group C during the period of observation. Only 2 implants demonstrated an increased crestal bone loss of 3.5 mm and 4 mm respectively at the first year examination. On the base of these results, we can confirm previous long term studies on regenerated bone and we can conclude that vertically augmented bone with GBR techniques responds to implant placement like native, non-regenerated bone.

Anterior implant-supported reconstructions: a prosthetic challenge

Recent investigations have demonstrated that the successful utilization of anterior implant-supported restorations in the maxilla is dependent upon the satisfaction of numerous surgical and prosthodontic criteria. Conservative treatment alternatives that use a provisionalization phase can provide clinical benefits for patients with partial edentulism by guiding tissue maturation following completion of a meticulous surgical procedure. This article demonstrates a series of prosthetic considerations that guide contemporary aesthetic restorations, and highlights the underlying surgical factors related to this treatment.

Anterior implant-supported reconstructions: a surgical challenge

Reconstructive procedures are able to provide improved aesthetics for implant patients who present with anatomical limitations (e.g., vertical or horizontal tissue loss) in the anterior maxilla. Aesthetic results, however, are directly related to the ability of the treatment team to reconstruct the lost bone and soft tissue, place the implant into its proper tridimensional position in the patient's arch, and use precise restorative techniques. This article presents comprehensive treatment steps for the utilization of single-unit and multiple-unit implant-supported restorations in the anterior maxilla.

Peri-implant tissue response to pathological insults

With the increased use of osseointegrated implants and with many implants functioning for long periods of time, the soft tissue barrier around implants has become more important. This paper reviews the soft tissue response around implants under healthy and diseased conditions and presents the etiology of peri-implant tissue breakdown. Diagnostic techniques such as probing pocket depth, radiographic evidence, and microbial sampling have been analyzed and modified from the periodontal field and used during the maintenance phase of the dental implant. The long-term goal of implant maintenance is to prevent or to arrest the progression of disease, and to achieve a maintainable implant site. Recent reports indicate that peri-implant tissues can be treated with either non-surgical or surgical techniques.

Autogenous bone harvesting: a chin graft technique for particulate and monocortical bone blocks

The use of the mandibular symphysis for harvesting intraoral autografts in implant reconstruction cases is based on the ample supply of donor material, the proximity to the recipient site, and the ease of access to the tissue. This article discusses the technique of successful bone harvesting from the mandibular symphysis. As with other harvesting techniques, morbidity can occur. This report demonstrates a low morbidity rate and presents guidelines to help accomplish this.

Vertical ridge augmentation around dental implants using a membrane technique and autogenous bone or allografts in humans

This study investigated the effect on vertical bone regeneration of the addition of demineralized freeze-dried bone allograft or autogenous bone chips to a membrane technique. Twenty partially edentulous patients with vertical jawbone deficiencies were selected for this study. The patients were divided into two groups of 10 individuals. The 10 patients of Group A received 26 Brånemark implants in 10 surgical sites. The 10 patients of Group B received 32 implants in 12 surgical sites. Fifty-two out of 58 implants (22 in Group A and 30 in Group B) extended 1.5 to 7.5 mm superior to the bone crest. Titanium-reinforced expanded polytetrafluoroethylene membranes were used to cover the implants and, before complete membrane fixation, demineralized freeze-dried bone allograft particles were condensed under the membrane in Group A, and autogenous bone chips were used in Group B. At the reentry after 7 to 11 months the membranes were removed and a small biopsy was collected from 11 sites comprehending the miniscrews. The clinical measurements from Group A demonstrated a mean vertical bone gain of 3.1 mm (SD = 0.9 mm, range 1 to 5 mm) with a mean percentage of bone gain of 124% (SD = 46.6%). The measurements from Group B showed a mean vertical bone gain of 5.02 mm (SD = 2.3 mm, range 1 to 8.5 mm) with a mean percentage of bone gain of 95% (SD = 26.8%). Histomorphometric analysis of the present study clearly demonstrated a direct correlation between the density of the pre-existing bone and the density of the regenerated bone. The mean percentage of new bone-titanium contact was from 39.1% to 63.2%, depending on the quality of the pre-existing bone. Both the clinical and histologic results indicate a beneficial effect of the addition of demineralized freeze-dried bone allograft or autogenous bone particles to vertical ridge augmentation procedures in humans.

Localized bone reconstruction as an adjunct to dental implant placement

Advances in bone reconstructive techniques, including the potential of barrier membrane usage for osteogenesis, have increased the indications for implant placement. This review discusses the critical biologic and clinical criteria involved in achieving a predictable success with barrier membranes. Experimental and clinical findings have shown that the type of adjunctive grafting material used, healing time of the membrane site, type and size of bone defect, and membrane exposure all influence the end result. Small bony defects like implant fenestrations and intact extraction sites seem not to depend on the application of membranes to regenerate bone membranes. Large bone grafts used for ridge reconstruction purposes might benefit from membranes, because they reduce the inevitable resorption of bone grafts when used alone. New developments in material and tissue engineering have introduced the use of resorbable membranes, xenografts, and osteoinductive proteins, such as recombinant human bone morphogenic protein, that are likely to play a role in the treatment of localized ridge deficiencies.

Bone rehabilitation to achieve optimal aesthetics

Treatment involving oral implants has established a high success rate, including implant survival on a long-term basis. The challenge facing the clinicians today is to achieve an optimal long-term aesthetic result. To address this challenge, the volume of the underlying hard and soft tissue must be restored either prior to or simultaneously with the implant placement. The learning objective of this article is to review the critical biologic and clinical criteria essential in achieving a predictable success in aesthetic enhancement of the implant site. The article discusses the five phases of ridge reconstruction, utilization of bone grafts (with or without membranes), and the use of membranes alone. Soft tissue management and augmentation in aesthetic and nonaesthetic regions are differentiated and presented. Surgical complications are recognized as a clinical reality, and exposure of the membranes is evaluated and discussed. Four cases are used to describe and illustrate the clinical procedure.

Bone formation utilizing titanium-reinforced barrier membranes

Advances in bone reconstructive techniques have increased the indications for implant placement in sites previously thought to be unsuitable. This clinical study evaluated a new surgical technique for the treatment of a variety of localized bone defects in four patients utilizing a titanium-reinforced membrane. The membrane material was developed to maintain a large protected space between the membrane and the bone surface without the need for a supportive device. Healing was uneventful in all sites, and the membranes were retrieved after 6 to 12 months. No residual defects were noted, resulting in an average change of implant exposure of 8.2 +/- 2.3 mm for sites with buccal dehiscences and from 5 to 6 mm ridge enlargement in localized bone defects. The quality of the regenerated tissue under the titanium-reinforced membrane appeared as bone structure with a superficial fibrous layer. This fibrous layer was more pronounced in sites treated with a membrane alone but was more than compensated by the quantity of new bone under the soft tissue. The results demonstrated that the use of a reinforced membrane appears to be a viable alternative for the clinical treatment of non-space-maintaining implant/bone defects. Further clinical and experimental investigations are recommended.

Supracrestal bone formation around dental implants: an experimental dog study

To test the osteopromotive activity in large non-spacemaking alveolar bone sites, a total of 20 titanium dental implants were placed superior to a previously modified mandibular alveolar process in five adult beagle dogs. The supracrestal implant position resulted in a mean buccal dehiscence of 5.1 +/- 1.03 mm and a mean supracrestal bone deficit of 2.69 +/- 0.45 mm. Three treatment groups were randomly assigned: group I, ten implants treated with a titanium-reinforced expanded polytetrafluoroethylene (ePTFE) membrane (TR); group II, six implants treated with a standard ePTFE membrane (ST); and group III, four implants that received no membrane (control). Before mucoperiosteal flap closure, the bone surface was perforated and peripheral blood was injected around the implants and underneath the membranes. Clinical evaluation of submerged implant sites showed evidence of complete regeneration of the peri-implant bone defects in groups I and II, minimal bone formation in control group III, and a widening of the ridge in group I. Corresponding histologic examination of undecalcified sections demonstrated large amounts of newly formed bone beneath both types of membranes with a superficial layer of loose connective tissue. Mean gain of supracrestal regenerated bone amounted to 1.82 +/- 1.04 mm (TR group), 1.90 +/- 0.30 mm (ST group), and 0.53 +/- 1.34 mm (control group). Mean bone regeneration at the buccal dehiscences was 3.33 +/- 1.44 mm (TR group), 2.46 +/- 0.51 mm (ST group), and 2.76 +/- 0.84 mm (control group). The TR membranes showed evidence of increased alveolar bone width compared to ST membranes and control sites. These results suggest that supracrestal bone regeneration can successfully be enhanced by a submerged membrane technique in the dog model and that the titanium-reinforced membranes were able to maintain a large, protected space for blood clot stabilization without the addition of bone grafts and produced a larger bone quantity when compared to standard membranes.

Diagnosis and treatment of peri-implant disease

With the increased use of osseointegrated implants and with many implants functioning for long periods of time, various complications have been reported. This paper reviews progressive loss of peri-implant bone--one of the major concerns during the function period of implants. The recognition and treatment of peri-implant bone loss around functioning implants is a major challenge for the clinician. Diagnostic techniques, such as probing pocket depth, radiographic tools, and microbial sampling have been modified from the periodontal arena and used during the maintenance phase of the dental implant. The long-term goals in the treatment of peri-implant disease are to arrest the progression of the disease and to achieve a maintainable site for the patient's implant. Recent reports indicate that peri-implant bony defects can be treated with either nonsurgical or surgical techniques. Bone regeneration is possible in selected peri-implant bony defects when appropriate surgical techniques are used, implant surface preparation is achieved, and the cause is eradicated.

The management of peri-implant breakdown around functioning osseointegrated dental implants

Peri-implant tissue breakdown can be the result of microbial action as well as of biomechanical and occlusal overload. The long-term goal of the treatment of peri-implant breakdown is to arrest the progression of the disease and to achieve a maintainable site for the patient. Peri-implant bony defects around functioning implants can be treated with either non-surgical or surgical (resective or regenerative) techniques. Bone regeneration is possible in selected peri-implant bony defects of functioning implants if appropriate surgical techniques are utilized and the etiologic cause is eradicated.

Osteopromotion as an adjunct to osseointegration

Osteopromotion to enhance the formation of bone approximating implant surfaces can be obtained using bone regeneration techniques with polytetrafluoroethylene membranes. Treatment of dehiscences and other deficiencies of bone volume allows implants to be successfully placed in regions previously thought to be unsuitable. Bone regeneration is possible in peri-implant osteitis defects if appropriate surgical techniques are used.

Dental implant abutment resembling the two-phase tooth mobility

Natural teeth and dental implants have differing degrees of mobility thus causing a potential biomechanical problem when connected by fixed bridgework. The clinical follow-up often discloses marginal bone loss around an implant neck probably due to high stress factors. An implant with a built-in compliance resembling the tooth mobility could be advantageous for stress distribution. With axial loading the proposed 'elastic'-test model accomplishes this demand. By means of theoretical and experimental studies this 'elastic'-test model is optimized and compared with a stiff implant-model. The results show a 20 times reduction of stress accumulation in bone with the 'elastic'-test model.