COMPOSITE (MIXED) BONE GRAFTS

The practice of creating a bone graft composite – a mixture of more than one component started with the need to bulk out autogenous bone.

The limited availability of autologous bone and the additional trauma associated with retrieving larger volumes create a need to add something else. (1) This additive can possess similar or different properties depending upon the indication and preference.

Typically we see proprietary biomaterials mixed with autogenous bone or in a similar way processed dentin or autogenous bone or proprietary biomaterials can be combined with blood, PRF, aqueous soluble medications or another material to change its form or function.

BULK OUT WITHOUT CHANGING PROPERTIES

When the additional trauma to collect sufficient autogenous bone to complete the full procedure is inappropriate adding a proprietary agent with similar properties is recommended. Powerbone (silicate substituted BetaTCP) autogenous substitute attracts cells, supports new bone healing and resorbs fully in line with remodelling. Processed allograft or xenograft are resilient to remodelling and their addition changes the properties of the composite and reduces the space for new bone regeneration. (see below)

CHANGE THE PROPERTIES TO PROLONG THE AUGMENTED VOLUME

Sometimes we need to maintain the volume of an augmented site. This can be when we graft outside the natural bony envelope or when preserving the long-term volume (9 months+) of a ridge after extraction – important when an implant is not scheduled. In these instances, autogenous bone or a fully adsorbing calcium phosphate is unsuitable as it resorbs too quickly.

Better to combine a slow-resorbing proprietary material of synthetic, processed allograft or xenograft type. The ideal synthetic for this is Powerbone Biphasic Granules and the optimal xenograft type is Ti-oss. Both offer high porosity for clot and cell retention with a resilience to remodelling. Powerbopne Biphasic contains no animal or human tissue. Ti-oss is a processed xenograft formed by bovine cancellous bone.

NOTE ABOUT ALLOGRAFT. Freeze-dried human cadaver graft adds cell inductivity when added to autogenous bone. However, allografts typically available to UK clinicians do not possess such characteristics. The chemical and heat processing stipulated to make them safe for human use denatures protein and changes the density of mineral structures as it does when processing animal-derived tissue. For this reason, adding processed allograft to autogenous bone achieves the same result as adding xenograft.

CHANGE THE FORM – CREATE A STICKY BONE

Combining autogenous bone shavings, KometaBio-prepared autologous dentin or proprietary autogenous substitute graft with a freshly prepared PRF membrane creates an osteoinductive sticky bone graft that offers handling and soft tissue healing advantages. (Protocol)

INCREASE THE BONE HEALING – MIX WITH PRF

Flowable Platelet-rich fibrin can be created at low centrifuge speeds by using tubes with an anticoagulant coating. Used alone, PRF shows quick resorption that does not sustain long-term bone volumes, yet combining with autogenous bone and autogenous substitute bone enhances bone growth in sockets and alveolar jaw defects.

DELIVER CHEMICAL OR MEDICINAL AGENTS

Synthetic calcium phosphates (eg Powerbone Granules) represent ideal carriers for aqueous (water) soluble agents. Controlled release of antibiotics offers a promising strategy to overcome implant-related infection (2). Other agents that can be added to calcium phosphates include anti-inflammatory agents, analgesics, anticancer drugs, growth factors, proteins and genes. (3,4) The advantages of Calcium Phosphate are that it is fully biodegradable, and its degradation ions – Ca+ and PO- already exist in the body in high concentrations. (5)

Fully adsorbing materials are recommended for revision cases.

Regeneration of bone in contact with a mechanically or chemically cleaned implant surface is best undertaken with a fully resorbing material, irrespective of the type, brand or origin. Slow or non-resorbing materials such as processed allograft, xenograft or biphasic synthetics are resilient to remodelling and reduce bone-to-implant contact. Moreover, they are more likely to be encapsulated in fibrous tissue as part of the natural foreign body reaction. If bacteria and viruses are present, this has the potential to help them survive for longer periods increasing the risk of re-infection. 

Contact Regen Store to discuss any of the products mentioned in this article.

ask@regen-store.co.uk

(1) Moy PK, Lundgren S, Holmes RE. Maxillary sinus augmentation􀇱 histomorphometric analysis of graft materials for maxillary sinus floor augmentation. Journal of oral and maxillofacial surgery. Journal of the American Association of Oral and Maxillofacial Surgeons.

(2) Sussman C, Bates-Jensen BM􀇱 Wound care a collaborative practice manual. Lippincott Williams & Wilkins.

(3) Ginebra M, Traykova T, Planell J. Calcium phosphate cement as bone drug delivery systems a review. Journal of Controlled Release.

(4) Kim K, Fisher JP. Nanoparticle technology in bone tissue engineering. J Drug Target.

(5) Wang S, McDonnell EH, Sedor FA, Toffaletti JG. pH effects on measurements of ionized calcium and ionized magnesium in blood. Archives of pathology & laboratory medicine.