The performance of 3D printed resorbable bone implants in the mandible of pigs

New paper: Comparison of off-the-shelf b-tricalcium phosphate implants with novel resorbable 3D printed implants in mandible ramus of pigs

3D printed patient specific implants derived from CAD/CAM-based technologies are presented as an alternative to preformed bone graft substitutes. Yet, today, clinicians must still choose between patient specificity or implant properties that are favorable for bone remodeling, leading to off-the-shelf solutions such as the β-tricalcium phosphate granules and preformed blocks that are used today.

Ideal patient specific Implants not only exhibit exact fitting, porosity, density, and volume but are also insoluble, osteoconductive, osteoinductive, have resorption properties that resemble native bone, and allow ingrowth and formation of new bone tissue. These are properties which, in combination, are not found in commercially available patient specific implants (Thygesen et al, 2022).

The resorbable properties of P3D Bone has previously been investigated in several studies (Jensen 2020, Jensen 2018, Slots 2017). In this pilot study, the 3D printed P3D Bone has been directly compared to a commercially available preformed β-tricalcium phosphate implant in relation to defects in the mandible ramus of pigs. The aim of the study was to analyze the performance of the implants that fulfill the aforementioned requirements in a clinically relevant implantation model where the implant, defect and bone are similar in size to what would be expected in human patients.

The results of the study showed that the preformed off-the-shelf implant and the 3D printed P3D Bone performed equally well with predicted osteointegration medially and laterally and minimal gaping between the implants and native bone.

The study

The purpose of the study was to directly compare the P3D Bone implant with an off-the-shelf implant made from β-tricalcium phosphate. Empty voids were used as controls to showcase the natural ability of the pigs to mend a defect of that size.

Eight pigs were anesthetized, and a predetermined hole was dissected in the mandible in each side of the pig. Hereafter the P3D Bone implant was inserted on one side. On the other side either the control implant was inserted, or the hole was left as a void. The pigs were stabled individually for six months before evaluating the performance of the implants by CT-scanning and histology of jaw sections

Figure 1: CT-scans representative of voids and implant sites 7- and 180-days post op.

CT findings

Six months after the surgical procedure, the pigs were CT-scanned, and the analysis of the CT images showed promising results in regard to integration and ossification around the P3D Bone and control implants as well as to the resorption of implants.

The analysis showed various degrees of integration, resorption, and ossification of the voids – furthermore, bone integration and ossification at the perimeters and middle of the P3D Bone implant resembled natural bone presenting with a cortical surface and spongious-like bone within the implants.

Histological analysis

The findings from the CT-scan were supported by the histological analysis which showed that most of the P3D Bone implant was resorbed leaving only a few and small pieces of the original implant. As β-tricalcium phosphate does not degrade on its own inside the body, it is likely that the disappearance of the implants after six months was due to resorption by osteoclasts, the bone degrading cell type of the body.

The histology slides also revealed that the inside of the P3D Bone implants was filled with soft tissue, muscle tissue and bone tissue, with bone tissue being dominant. The bone tissue was dense with small canals of soft tissue containing blood vessels, and comparison of the P3D Bone implant site with native bone suggested that the newformed bone was mature. Meanwhile, the negative control voids were filled with adipose tissue, fibrous/connective tissue, and muscle tissue with no bone tissue.

Figure 2: Histological images of the P3D implant perimeter (A) and core (B–C) and of the off-the-shelf implant cores (D) and the resected non-treated voids (E–F) after 6 months.

Concluding remarks

The study showed that the P3D Bone implants performed at least equally as well as the commercially available off-the-shelf implants and that newly formed mature bone was integrated within the implants after three and six months. Furthermore, the study concluded that the P3D Bone implants are highly biocompatible and supports natural cellular and systemic responses.

Conduct your own in vivo studies using Ossiform Research Line

The P3D Bone graft substitute has not yet reached the market. However, Ossiform's research product line enables you to perform implant studies with the company’s material and technology.

The P3D Scaffolds are made of the same material as the P3D Bone and are 3D printed to cater to your research needs. They are approved for animal studies and previous studies demonstrate their usability in mice (Jensen et al, 2020).

The P3D Scaffolds are also suitable for in vitro research, thereby opening a world of opportunities for you and your research. For instance, the P3D Scaffolds enable you to seed selected cell cultures on the scaffold prior to implantation, making them advantageous for cancer modelling and various other studies, where the gap between in vitro and in vivo research may seem unbridgeable.

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