Alloplastic grafts have become more and more popular due to their high productivity and ability to act as a scaffold while growth factors develop. This chapter examines the need for an alloplastic graft, its limits, clinical practice application, and the creation of a future-focused strategy to get around them.

1. Alloplastic graft need

The following are the requirements for an alloplastic graft, per the consensus put forth by the World Congress of Biomaterials.

• Inter-connected macroporosity
• The microroughness of the surface
• Beta-TCP, HA, and calcium silicate combined

2. Alloplastic grafts' attributes and range

Different approaches were taken in the development of alloplastic bone, from manufacturing to microstructure. OsteonTM (Genoss), a Korean-made alloplastic bone substance, is an illustration of their evolution. With pore sizes ranging from 300 to 500 μm, Osteon I (the original model of Osteon), which corresponds to the hydroxyapatite (HA) scaffold created using the replica approach, demonstrated 77% porosity. This had little usage in particle form but shown great qualities in block form when released with a tricalcium phosphate (TCP) covering.

Osteon II changed into a reinforced microstructure with tiny pores (less than 250 μm) and interconnective porosity. The sacrificial template method was used to create this biphasic scaffold (HA-TCP), which contained 70% resorbable TCP. However, it was challenging to totally eliminate the contaminants in the production process; as a result, more development is required. The identical biphasic scaffold, Osteon III, was produced with enhanced bone production by a more straightforward air-bubble approach.

From a clinical perspective, an alloplastic bone graft's long-term maturation is crucial. A block-form graft in the first generation (Osteon I) produced a satisfactory result, demonstrating a steady result in preserving the volume with a non-resorbable composition of HA27. However, because the first generation was hard to employ in particulate form, the second generation (osteon II) was created. Particulate Osteon II may be utilized for ridge augmentation, sinus grafting, and socket preservation. The substance was a biphasic scaffold made of β-TCP and HA combined. At first, the material's radiopacity was minimal, but when it reached the crest region, its density rose. However, due to the composition of β-TCP, Osteon II had a lower aspect in relation to the first generation in terms of volume. It would be simple to get around this by building up as much as the expected absorption. When creating the next generation, a modification to the production process raised the relative quantity of HA in order to counteract this absorption propensity.

Osteon III, the third generation, had a composition of 60% HA and 40% β-TCP with improved interconnectivity, which resulted in increased porosity and interconnection. By raising the sintering temperature to compensate for the decreased strength, the particulate form of osteon III demonstrated superior interconnectivity and enhanced crystallinity. In an animal (rabbit calvaria) study, the material demonstrated superior scaffold qualities in terms of its osteoblast and osteoclast activity when compared to a traditional alloplastic bone graft. In contrast to a xenograft (Bio-OssⓇ), a combination of resorbable membrane (BioGideⓇ) and alloplastic graft could result in superior bone regeneration in a dog model35. Therefore, Osteon III alone, which had the benefit of superior interconnective porosity, might be used to obtain satisfactory results in peri-implantitis without a membrane in addition to horizontal and vertical GBR.

3. Alloplastic graft clinical uses and limitations

Because alloplastic grafts lack osteoinductivity, their use has historically been restricted to minor or confined abnormalities. It is necessary to ascertain the long-term effects of functional bone formation. In an alloplastic graft, the particle size is particularly significant. The absorption of the surrounding tissue during the modeling phase may be impacted if the size is too tiny. The most appropriate size was determined to be between 0.5 and 1 mm. The size of the alloplastic graft was restricted to 0.5 to 1 mm, and it was made using pig collagen, which may be absorbed in as little as two weeks, due to its disadvantage of moldability when compared to other bone replacements. Given its exceptional moldability and volumetric stability, contouring augmentation may be a sign of an alloplastic bone graft for a suitable volume. Numerous studies have documented excellent outcomes for sinus transplant and socket preservation using an alloplastic graft. The benefits of bioabsorption and long-term replacement with autogenous bone have led to the ongoing use of alloplastic grafts.

There are two approaches to contouring augmentation: covering with a collagen membrane and applying directly to the graft sites without hydrating them. The process was primarily carried out without a membrane in the past, but in recent years, the membrane has been widely used to stabilize wounds. Every graft, even an alloplastic one, had unique benefits based on its makeup. Compared to particulate bone with a certain shape, collagen-composited bone showed a greater rate of bone development. Thus, the newly suggested procedure was to cover the grafts with a membrane and apply Osteon III to the first layer next to the implant beneath the contour augmentation using Osteon III collagen. The collagen-enriched bone exhibited outstanding volumetric stability but sluggish osteogenesis—roughly 1.5 times slower. The use of alloplastic bone grafts has been expanding. One example is ridge augmentation, which involves using an implant fixture to create a tenting effect with a lengthy healing period to build up the collagen-enriched bone covering the membrane.

4. Future alloplastic graft development

Block bone alloplastic grafts have also been created and can be employed as a tenting function with screw-on augmentation for major deformities. In this instance, it ought to be produced in a way that makes it simple to drill, trim, and fasten screws for operation. For these reasons, several grafts with a collagen coating have been created. Furthermore, because it is more difficult to secure alloplastic block bone with a traditional screw than autogenous block bone, an anchoring device, such as a screw type, would need to be developed.

If the technology develops further, a 3D printed bone graft is anticipated, and a tailored design using alloplastic graft materials for different alveolar abnormalities may be accessible based on the CT data. After 3D printing, a reinforced tailored graft structure with sintering could be produced. Numerous attempts have been made to improve bone quality by adding DNA or glycoprotein in order to get around the drawbacks of an alloplastic graft. The healing process on angiogenesis may be accelerated by the addition of elements like polydeoxyribonucleotide (PDRN), which is DNA with anti-ischemic and anti-inflammatory properties. Although a recent study on rabbit calvaria suggested that regeneration could be accelerated, the effect was not as strong as that of rhBMP-2. Combining these growth factors with the creation of tailored grafts may be the best course of action. Before this kind of transplant can be employed in clinical settings, more data will need to be gathered as technology advances.