Bone augmentation by replica-based bone formation

Abstract

Objective

The sources of iliac crest bone grafts are limited. Alternatives are evaluated due to the progress in biomaterial sciences. Synthetical hydroxyapatite (HA), ß-tricalcium phosphate (ß-TCP) or biphasic compounds, or even a mélange of HA and ß-TCP will replace bovine ceramics. The goal is maintenance of replica-based-bone formation (RBBF) for bone augmentation.

Methods

2 female and 2 male patients between 41 and 73 years with 5 sinus elevations were evaluated. Sinus elevations with lateral fenestration, trapezoidal-muco-periosteal flaps and filling with micro-chambered beads (1.5 mm) was performed. A porcine-collagenous membrane and the refixated flap covered the defect. A biopsy program over 20 months was confirm confirm the maintenance of the newly formed bone.

Results

A fast bone formation was pronounced. The biopsies revealed mature lamellar bone and full osseointegration of the ß-TCP implant. The biopsy after 20 months showed compact bone with osseointegration of minor rests of the ceramic implant. The defect revealed a mature bone stock already after 5 weeks.

Significance

The introduction of the replica-based-bone formation (RBBF) around micro-chambered beads will change the paradigm of bone augmentation. The next step of the ongoing study has to redefine the interval for implant insertion.

The clinical approach confirms the breakthrough to primary mature lamellar bone formation and will permit reduction of placement time for a dental implant.

Introduction

Autologous iliac crest bone-graft (ICBG) is still considered the gold standard for bone grafting. The amount of autologous bone which can be gathered from the iliac crest is defined and only accessible by surgeons. The arguments in favor of searching for alternatives are first, not to prolong the operation by a second intervention, and second, to avoid donor bed morbidity [ ]. The science of bone substitutes has made enormous progress, the results of which are approaching the success of autologous cancellous bone or are even surpassing it, if combined with growth factors or micro-chambered beads (MSCs) [ ].

The main objective of this study was to evaluate a bone graft substitute (BGS) which provides fast bone formation, full biocompatibility, no immune response, osteogenicity and osteoinduction as well as osteoconduction to replace ICBG, thus changing the paradigm. Another objective concerns the indication of hydroxyapatite (HA) or ß-tricalcium-phosphate (ß-TCP)? Do we need both or even a mélange due to their different biomechanical properties? Finally, which morphology and what’s about the combination with autologous morselized bone, growth factors or even MSCs?

The terminology is mainly influenced by the market. Starting with market research, we find the NIH definition of biomaterials : “Any substance (other than a drug) or combination of substances, synthetic or natural in origin, which can be used for a long time, as a whole or as a part of a system that treats, augments, or replaces any tissue, organ, or function of a body. The market can be segmented based on the material used for implants into metallic, ceramic, polymer and natural biomaterials”, including all arthroplasties and dental implants. The definition of orthobiologics is more restricted: “Orthobiologics mainly refers to products that combine both biology and biochemistry for replacement or regeneration of musculoskeletal structures. These products include allografts, bone and soft-tissue substitutes, tissue-engineered substances, and cell-based matrices” [Allied Market Research: Portland, OR 2018]. Demineralized bone matrix (DBM), as well as allografts are predominant products in US, whereas in Europe and especially in Asia, synthetic ceramics are common. Collagenous membranes and mixtures of collagen with calcium phosphates or sulfates, as well as bone-morphogenetic protein (BMP ) and MSC for local tissue engineering, play a more dominant role in those disciplines [ ].

The results with DBM are often reported as comparable to ICBG [ ]. In a study on sheep, comparing DBM with ß-TCP + BMP-7, delayed healing with clear signs of immune response were reported, whereas bone-healing processes, bone remodeling and even resorption of ß-TCP were enhanced by BMP-7 [ ]. rhBMP-2 and rhBMP-7 represent the most frequently studied growth factors for orthopedic and maxillo-facial indications [ ].

Side effects of BMP are not only heterotopic-bone formation, but also local edema and infection. Even osteolysis and antibody reactions were published [ ]. The risk of malignancy was considered more theoretically [ ]. In the Draenert et al. sheep study [ ], no heterotopic bone formation was observed due to the slow release from the carrier.

Mineralized cancellous-bone allografts are common in enhancing augmentations with autologous-cancellous bone; demonstrating good results and complete healing after a 14-year follow up [ , ]. Despite any histocompatibility matching [ ], allografts remain controversial with respect to delayed healing, transmission of tumors and infections [ ]. In summary, allografts are in fact unlimited with respect to the amount needed. There are, however, several arguments in favor of searching for bone substitutes which fulfill all of the criteria for replacing autologous and, particularly, homologous grafts.

Alloplasts and heteroplasts

The following materials are available on the market: HA and ß-TCP or biphasic materials combining both in a defined composition [ ]. FDA approved ceramic BGSs for dental, oral and maxillo-facial application are the synthetic Cerasorb®, a ß-TCP and Osbone® a synthetic hydroxyapatite, as well as the bovine HA Endobon® and BioOss®, mainly for augmentation or reconstruction of the alveolar ridge and filling of infra-bony periodontal defects and after root resection [ , ].

All ceramic BGSs on the market morphologically present scaffolds similar to cancellous bone, which implies that ingrown bone presents a replica of all bone marrow spaces, forming so-called bony balls, and needing remodeling during the following 4–6 months [ ].

The stiffness of HA-implants results in slow osseointegration due to stress protection, whereas bone ingrowth into the more soluble ß-TCP is faster due to its decrease in stiffness as water is absorbed [ ]. As a result of several animal experiments, it was concluded that the bone-forming element takes the shape of a bead. A conglomerate of beads presents an osteoconductive replica of all bone-marrow spaces, thus providing primary formation of physiological-cancellous bone, or replica-based bone formation (RBBF) [ ].

Purpose

The purpose of this study is to evaluate RBBF with micro-chambered-beads®(MCB®) for bone augmentation specifying early mature bone formation in monthly steps and its maintenance for implant anchorage as a scientific basis for an ongoing clinical study to evaluate the earliest possibility for implant insertion. In order to achieve this, the strength of the newly formed bone at different postoperative intervals must be examined.

Material and methods

4 patients, requiring a total of 5 sinus elevations, were operated on: 2 female patients, aged 59, on both sides, and 73 underwent operations, as well as two male patients, aged 66 and 41, respectively ( Fig. 1 d). MCB® ( Fig.1 a), consisting of pure ß-TCP measuring 1.5 mm in diameter and providing high capillary forces, were implanted. In all cases, a porcine-collagen membrane was applied. Precise diamond-coated instrumentation was used for gathering biopsies. The inclusion criteria for this first follow up were sinus-floor augmentation for implant anchorage in otherwise healthy patients.

Fig. 1
(a) Micro-Chambered Bead® (MCB®); (b) and (c) MCB® suction in blood and bone marrow 1/20 cc; after coagulation, the MCB® – implant represents a stable implantation. (d) Cohort of patients (w = weeks, m = month, Y = year, FEMR = free-end maxillary ridge, TTAG = two tooth alveolar gap, OTAG = one tooth alveolar gap).

The indication was based on the panoramic radiograph measuring the bony-sinus floor less than 5 mm. Anesthesia was achieved by means of local vestibular anesthesia by infiltration in combination with block anesthesia of the major palatine nerve. The incision was started along the maxillary ridge with the small base of a trapezoidal muco-periosteal flap preserving the vascularization of the tissue. The bone fenestration comprised a longitudinal rectangle or ellipsoid of 15–20 mm × 10–15 mm and was performed with a round, water-cooled bur. The preparation of the Schneider membrane was performed until a satisfying cavity was formed for the beads. The still adherent bone cover was carefully placed craniomedially to form the apical roof of the cavity. The ceramic beads had been prepared in a bowl or in a syringe with blood and Ringer solution and then precisely inserted into the cavity without damaging the bead shape. A tight package was achieved by covering the defect with a wet sponge and gently injecting Ringer or physiological NaCl solutions to distribute the beads within the defect.

In all cases, the filled cavity was covered by a porcine collagenous membrane and the flap was repositioned and sutured with single-stich sutures. Wound healing was checked on a daily basis and the sutures were removed on the 7th day. The interval between sinus elevation and augmentation was between 4.5, 11 and 20 months, respectively, depending upon the patience of the recipients, thus fulfilling the study design. An examination of the bone quality at various intervals was conducted to confirm the strength of bone under unloaded conditions. The preservation of strong bone is referred to as its maintenance .

Results

3 beads of MCB® suctioned in 1/20 cc of blood and bone marrow ( Fig. 1 b,c). All interventions were performed uneventfully. There was a single one-tooth alveolar gap (OTAG), one two-tooth alveolar gap (TTAG) and three free-end maxillary ridge (FEMR) segments. The step-by-step operation was identical for all patients: ridge incision, trapezoidal-flap preparation, fenestration of the bone and preparation of the Schneider membrane, filling with MCB®, and packaging the sponge-covered beads with a jet. In all patients, bleeding was stopped by the MCB®. On the OTAG digital volume tomography (DVT), the augmented floor bottom was presented ( Fig. 2 a–d). Wound healing was uneventful in all cases, the suture material was removed after 7 days. After 5 weeks, the X-ray of the OTAG revealed an already complete osseointegration of the implant: new mature bone had formed extending from the adjacent alveoli ( Fig. 2 e, arrows), newly-formed bone had grown over the beads like a shell and had extended into the pores of the MCB®. Most of the ß-TCP ceramic had already been reabsorbed. Eleven weeks after the operation, newly formed bone had been reinforced ( Fig. 2 f) and the mineralization process had advanced. Three and a half months after the operation, the implantation was preplanned with a DVT. Minor residuals of the implant had not yet been reabsorbed. The implant could be inserted into a compact bone stock with a perfect seat ( Fig. 2 g,h).

Fig. 2
Sinus elevation No. 5.
(a, b, c) sagittal, frontal; horizontal projection.
(a–c) The sinus floor measured less than 5 mm and the indication for augmentation was given: The height could be augmented. The newly forming scaffold of MCB® was loaded by the close teeth on both sides.
(d) The end-result was a compact filling with MCB® (ß-TCP).
(e–f) From both natural teeth and their alveolar bone thick mature lamellar bone is growing deep into the scaffold of the osseointegrated implant (arrows); the ceramic beads are completely overgrown by mature and fully mineralized newly formed bone, surrounding the beads’ shape like shells. The trabeculae supporting the implant onto the alveolar bone have been further reinforced after 11 weeks (arrows).
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Jan 10, 2021 | Posted by in Dental Materials | Comments Off on Bone augmentation by replica-based bone formation
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