A New Collector Device for the Immediate Use of Particulate Autogenous Bone Grafts

Featured Application

Autogenous particulate bone collector (chips) for bone repair and implantation.

Abstract

Autogenous bone grafts can be harvested from either intraoral or extraoral sources. Intra-oral sources include healing tooth extraction wounds, a bone from edentulous ridges, bone trephined from within the jaw using trephine drills, bone formed in wounds, and bone from the maxillary tuberosity, ramus, and mandibular symphysis. Extra-oral sources are the iliac crest, which provides cancellous bone marrow, and the tibia and calvaria. Autogenous bone grafting aids in probing depth reduction, gaining clinical attachment, the bone filling of osseous defects, and the regeneration of new bone, cementum, and periodontal ligaments in teeth. An innovative biomedical device is presented in the form of an autogenous bone collector that can fill defects of 96.91 mm³ with bone particulates, and may be used in bioengineered scaffolds. Experimental studies on synthetic bone have demonstrated the feasibility and applicability of the amount of bone obtained.

1. Introduction

Bone defects can be the consequences of congenital and developmental malformations or originate from tumour surgery, trauma, or infections. Functional and aesthetic bone defects are often a challenge to overcome, mainly related to the donor site and the size of the graft needed, as well as possible complications related to the procedures used to treat them. These can be autogenous transplants (from the same individual), allograft or allogenous transplants (from the same species, but different individuals), xenograft (from different species), and alloplast synthetic materials [1,2,3,4,5]. Bone transplant complications are mainly associated with the manipulation of grafts and the increased risk of contamination of the material collected or to be implanted, adverse reactions when autogenous transplantation is not used (allografts, xenografts, and alloplast), and the need for multiple surgical procedures, especially in cases of removal of bone material from the same individual (autogenous transplants). In these cases, often, the removal of the bone graft becomes a surgery of greater trauma than the procedure of bone implantation. The biological qualities of bone mean that transplantation with fresh autogenous bone still represents the gold standard for bone grafts [2,3,4,5,6,7,8].

Autogenous bone grafts can be harvested from either intraoral or extraoral sources. Intra-oral sources include healing dental extraction wounds, bone from edentulous ridges, bone harvested from inside the jaw using trephine drills, bone formed in wounds, and bone harvested from the maxillary tuberosity, ramus, and mandibular symphysis [9,10,11,12,13]. Extra-oral sources are the iliac crest, which provides cancellous bone marrow, and the tibia and calvaria. Extra-oral sources may cause post-operative infection, increased patient costs, and difficulty in finding donor material [9,10,11,12,13,14].

There are several techniques and devices for harvesting bone grafts, depending on the patient’s needs, location, and size of the bone defect. These include the bone scraper, which removes bone by scraping, rotary instruments such as drills or trephines, bone chisels, rongeurs, and piezoelectric devices [9,14]. Bone dust collected during the use of high-speed drills has several applications, and could be a useful source of viable osteogenic material in spinal, cranial, and craniofacial procedures, wherein a bone collection device can be connected to a standard aspiration circuit and used to collect this bone dust [15].

The development of a bone collection device with which autogenous bone is removed with a simpler and less traumatic procedure is desirable for surgeons and patients choosing the source and/or donor region of the bone graft. Surgery for dental implants has proven over the decades to be a safe procedure, and is well accepted by patients in relation to surgical trauma and its results. The use of a bone collection device in which the same procedures are applied in dental implantation makes the act itself similar the surgeon’s normal routine, and we can predict similar expected results in terms of the patient’s acceptance [1,3]. The new mechanical device, bioactive kinetic screw (BKS), described here is a simple multifunctional machine able to simultaneously drill and screw, measure the volume density of the material where it is applied, and compact the material inside [16,17,18,19,20]; here, we also describe another application, wherein the material collected in the device’s interior volume can be used for transplantation to other regions for bone filling, or be used as a stimulus of osteogenesis, osteoinduction, and osteoconduction in bone scaffolds. The idea of reusing bone from bone drilling during dental implant insertion creates the concept of the BKS model as a bone collector [8,16,17,18,19], which allows simultaneous drilling and screwing, and insertion of the cut material (bone chips) into the internal volume of this new BKS implant model, to then be transplanted.

The BKS can be manufactured in a variety of sizes to suit specific requirements and applications. These sizes can be modified internally (through flute length and width, diameter, and position in relation to the longitudinal axis of the through hole), as can the length and overall diameter of the screw. The larger the internal volume measurements of the BKS, the greater the bone collection capacity will be in proportion to the size of the total volume of BKS applied [19]. The choice of the amount of bone to be harvested, and therefore the size of the BKS, depends on the patient’s needs, the surgeon’s choice of the donor site, and the purpose of the graft (bone defect filling, or vertical or horizontal bone augmentation). In addition, the larger the width of the BKS flutes, the larger the size of the particles harvested [7,8].

To make it easier to correlate the results obtained and to describe the capacity of bone grafting for different purposes, this work uses the same model that has featured in previous studies, and in another application as a bone collector [16,17,18,19,20]. Approximately 96.91 mm³ of fresh autogenous bone, which can be used to fill gaps or stimulate bone formation in scaffolds, is obtained by compacting and collecting the entire BKS volume. The results described here demonstrate the simplicity and efficiency of the BKS for the collection of bone, and the low level of manipulation that is inherent to the technique presented here.

2. Materials and Methods

For this experimental study, a BKS device was machined from commercially pure titanium to a diameter of 4 mm and a length of 10 mm, and connected to a counter-angle motor adapter (Techdrill Equipamentos Ltda ME, Pompeia, Brasil) Surgical Motor-1 with 150 Watts of power, and a pre-set torque of 45 N/cm, as shown in Figure 1.

Synthetic bone in the form of a mandible (Synbones AG, Zizers, Switzerland) was selected for drilling and harvesting with the BKS Bone Collector to analyse the efficacy and feasibility of the technique proposed here. The technique described here for harvesting particulate bone is already used in several devices on the market [21,22,23], in which a drill adapted to a bone-harvesting or aspiration device stores the material to be transplanted later in another region. The innovation lies in the biomechanics of the BKS, in which the device itself collects and compacts the bone in its interior [19], without the need for another device to store the collected bone, thus reducing the manipulation of the material and its exposure to contaminating factors.

The method used in this experiment is the same as that used to insert and screw bone implants. The difference lies in the characteristics and properties of the new, simple BKS machine, which allows the material to be collected, compressed, and condensed inside it. When we removed the BKS after it had been fully inserted into the bone, the experiments showed that it was possible to remove the material contained inside it without direct manipulation. This procedure proved to be simple in its described technical execution, allowing the use of the bone particles for bone filling and, above all, for the activation of the bone scaffold in larger rehabilitations.

The technique consists of drilling into the bone with the BKS at low speed (60 rpm), as seen in Figure 1b, and after inserting the entire length into the bone, reversing the direction of rotation on the motor to remove the BKS completely from the bone donor bed. With the particulate bone in its internal volume, without directly manipulating the bone, the bone is removed from inside the BKS using tweezers or a dental explorer, and placed directly into the desired recipient bed, as seen in Figure 2.

Considering that synthetic materials such as hydroxyapatite are also used for bone grafting, the method applied here with synthetic bones can be described as experimentally valid for cases wherein synthetic bones are used in clinical rehabilitation due to the similarity of their application.

3. Results

The surgeon’s familiarity with the method used in the described technique is an advantage observed in the results of the experimental procedures compared to other bone-grafting techniques, making the predictability and execution of the proposed technique similar to what the professional performs in routine implant surgeries [2,3]. The innovation is mainly due to the unique characteristics of the new BKS model, which collects and compacts the bone in its internal volume in the same drilling procedure. This technique allows the procedure of removal without wasting the collected material, thanks to the presence of square threads that maintain the stability of the BKS.

Another important result observed in the technique was the low speed of rotation (60 rpm), which provided larger bone chips, as seen in Figure 2b, than those found at high speeds (over 300 rpm). With larger bone particles, it is easier to manipulate the graft without much waste during bone grafting from the receptor bed to the donor bed, and the larger particles favour the vitality of the transplanted bone [24]. The amount of bone harvested is limited to the size of the internal volume of the new BKS device, which can be designed with different geometries that increase its capacity for bone grafting in proportion to its volume, the size of the drilling grooves, the distance of the through-hole from the apex of the BKS, its length, and its overall diameter. In this study, the bone collection capacity was approximately 96.91 mm³, considering that this was the total volume of the BKS placed in the bone and its internal volume, as shown in Figure 3, in our previously published work [19].

Considering that the experiment was performed on synthetic bone, there was minimal loss of particulate bone, mainly in the removal of the BKS after its insertion during collection in the retromolar region of the mandible, as seen in Figure 2a. The time measured between the beginning of the technique and the end with the removal of the bone from inside the BKS was shorter than usual in dental implant surgery, considering that the procedure was a single perforation and removal. On average, a dental implant surgery requires four to seven perforations before the implant is screwed in.

4. Discussion

Bone grafts in maxillofacial surgery are used to correct or replace the quality or quantity of bone. Bone defects can be the result of either congenital and developmental malformations, tumour surgery, trauma, or infection. There are also many other indications for bone grafting in functional and aesthetic surgery [25,26,27,28,29,30,31]. When it comes to the biological properties of bone substitutes for bone transplants, fresh autogenous bone remains the gold standard of all available graft materials. This is the main feature of the innovative BKS device, which is used as a bone graft collector for transplantation, to use fresh autogenous bone in a simplified and controlled manner, according to the surgeon’s planning and needs. It can be used directly as a local bone filler or to activate scaffolds to support bone formation within the scaffold [27,28,29,30,31,32,33,34].

Some techniques use aspirators to collect bone particles during drilling. Despite these bone dust aspiration techniques and the preoperative use of chlorhexidine mouthwash, bacterial contamination of aspirated bone collected with these bone collector models is to be expected. In addition to the physiological bacteria of the oral flora, microorganisms commonly associated with implant failure may be found. Rinsing the bone collector with 200 mL of 0.1% chlorhexidine solution significantly reduces microbial contamination, but its effect on bone vitality is unknown [22]. The limited evidence available on the use of bone collectors suggests that the resulting graft material is less than ideal. Until other methods of avoiding bacterial contamination or other device designs are developed, clinicians should be cautious in the use of bone collectors [23,28,29,32,33,34,35].

The use of mineral bone graft materials such as hydroxyapatite is routine in bone implant surgery, with satisfactory clinical results; however, these results are still inferior to those obtained with autogenous grafts. Although this experiment was carried out on synthetic bone, the concept will be applied in vivo in future studies wherein the bone harvested is autogenous, thereby increasing the chances of success of the bone graft [1,2,3,4,5,6,7,8,9].

In this paper, an experimental study on a synthetic human mandible using the new biomechanical device BKS [16,17,18,19,20] was presented; the device removed bone from the mandible like a rotary instrument and immediately, without direct manipulation of the bone graft, removed it from the BKS internal volume and used it to fill the bone-deficient region or scaffold with autogenous bone [32,33,34,35]. With this technique, there is less manipulation of the bone graft, and the particulate bone is stabilized according to the surgeon’s plan. The results described here will be compared with in vivo experiments in ongoing studies.

5. Conclusions

The use of the new BKS device as a bone collector for autologous transplantation proved feasible, and the proposed technique simple and efficient. The amount of bone harvested is limited to the volume of the BKS, so proper planning should be carried out to correctly indicate this technique. The minimal manipulation of the bone graft reduces its exposure time, especially to the oral environment, and brings less chance of the contamination that occurs with most other devices available in surgical practice. The proposed technique is similar to the routine used by dental surgeons, and can therefore be adopted efficiently. Future work will assess the biological quality of the transplanted bone, its suitability for use in the filling of bone defects, and its suitability as a biological activator for scaffolds.