In tissue engineering and regeneration, most everything of interest happens in the first 4 weeks. This post will discuss the clinical application of 3D-printed bone grafts for ridge augmentation and evaluate what is happening in the graft as it is converted into vital bone. We will discuss the surgical application of OsseoConduct βTCP 3D-printed ridges and assess what is happening in the graft material from day of surgery through 4 weeks.
3D-Printed Tissue Regeneration
When the implants are in place, the alveolar ridge is perforated to gain access to the regenerative cells. At that time, the area is covered with Socket Graft Injectable and the OsseoConduct 3D-printed ridge is placed over the implants. The implants are used to stabilize the 3D-printed ridge. Another layer of Socket Graft Injectable is placed over the printed ridge to encase the ridge in graft material.
2 weeks post op. The initial density of Socket Graft Injectable is reduced as regenerative cells and extracellular fluid invade the putty. At this time point, there is very little vascular supply in the graft. Osteoblasts and other cells involved with bone growth are migratory and the vascular cells are not, so the graft is populated by regenerative cells days before the vascular supply arrives. The putty is hydrophobic and blocks the bleeding and clot formation that inhibits and delays bone formation. In this radiograph, the membrane is evident under the gingiva and is separated from the OsseoConduct printed graft by mineralizing tissue that lines the membrane and covers the printed graft.
2 weeks post op. The surgical technique used in this case was mucosal incision with a secondary incision to raise the periosteum. However, the suture technique used was a single incision line to close both the periosteum and the mucosa. In this case, the membrane is exposed as noted in this photograph.
4 weeks post op. The density of the graft continues to reduce as it is replaced by early mineralization and the arrival of the vascular supply. Early mineralization is not radiopaque. A significant portion of the 3D-printed graft is now resorbed, and the printed graft is separated from the membrane by mineralizing tissue. The regenerative cells migrate to the membrane and form a remarkably tough layer of osteoid that is firmly bound to the d-PTFE membrane.
Mineralized bone covered with osteoid is present under the membrane. At this 4-week time period, the putty is resorbed and replaced with woven bone with vascular supply. No inflammation is present as the initial inflammation caused by the surgical trauma has resolved with the conversion of inflammatory M1 macrophages into M2 macrophages that direct the mineralization process. With the arrival of bone throughout the graft site, osteoclasts are joining with the osteoblasts, forming basic multicellular units that are resorbing the 3D print and replacing it with bone.
A note of correction needs to be made at this point. In previous posts describing the Simple Ridge Augmentation, the d-PTFE membrane was firmly attached to the bone and it was assumed the membrane separated into different layers when it was removed. The layer remaining over the bone was of equal toughness to the layer of Teflon that was removed. However, it is now believed that the membrane did not separate, but it was a very tough layer of osteoid that was firmly bound to the membrane. In future cases, histology of this layer will be done to confirm the composition of this membrane-like tissue.
Integration to the exposed surfaces of the implants has occurred by two weeks and mineralized bone covers the implants at 4 weeks. Integration to the exposed implant surfaces precedes integration to the preexisting bone because the surgical trauma caused by drilling the osteotomies damages the bone lining the implants and this layer of bone needs to be resorbed before integration can occur. Healing abutments are planned for 3 months post surgery.
The osteotomy has been prepared for the sinus augmentation and the sinus membrane is dissected. The OsseoConduct 3D-printed graft is tried in place while Sinus Graft is prepared for the sinus augmentation portion of the surgery. The osteotomy for the sinus augmentation is visible, apical to the OsseoConduct 3D-printed graft. The 3D-printed graft sits and contacts the bone precisely.
Sinus Graft is injected, and the sinus membrane is lifted hydraulically. The alveolar ridge is perforated to allow for regenerative cell migration from the pre-existing bone into the graft. Typically, the alveolar ridge cortex is perforated after the implant osteotomies and prior to implant placement.
A surgical stent is used to place the implants and when the implants are driven into place, Sinus Graft is expelled from the sinus osteotomy as noted on the buccal of the implants. The next step is to cover the implants with Socket Graft Injectable and set the printed graft in place over the implants. After the printed graft is in place, the graft is covered with Socket Graft Injectable and then covered with a d-PTFE membrane.
Two-week post-op radiograph showing the sinus filled with Sinus Graft. As we stated earlier, the radiopacity of the graft material decreases as the graft material is infused by extracellular fluid and regenerative cells migrate throughout the graft matrix. In the sinus, there is now a band of decreased radiopacity that has developed in the graft material lining the floor of the sinus. This radiolucency will move further into the sinus as the regenerative process continues and this radiolucency will turn radio-opaque as the mineralization process moves deeper into the sinus. Over time, you will see a radiolucent band migrate away from the sinus floor. The graft site is bedded with Socket Graft Injectable and after the 3D print is placed, it is then covered with Socket Graft Injectable. Socket Graft Injectable is hydrophobic, which blocks blood from entering the graft site. Bleeding into a graft material will cause the graft site to then go through the different stages of clot, granulation tissue, fibrous tissue, and then all of this needs to be removed before bone can form. When bleeding is allowed to fill a graft material, the fibrous tissue that is produced covers the implant surface and this is the reason why other bone grafts have been shown to not produce implant integration at the grafted site. Socket Graft Injectable blocks blood from entering the graft site which skips the normal healing process and results in osteoblasts reaching the implant surface first, which then results in integration to the implant in the area of the graft. If a fibroblast reaches the implant surface first, you get fibrous encapsulation of the implant which prevents osteointegration. If the osteoblasts reach the implant first, integration occurs.
Two-week post-op suture removal photo shows no membrane exposure and reconstruction of the atrophic ridge. The difference between this case and the preceding case was the suturing method used for closing. Both cases had mucosal incisions with dissection of the periosteum, but this case first closed the periosteum with resorbable sutures and then closed the mucosa with Vicryl and sealed with Oral Bond tissue adhesive. The difference in suturing has resulted in maintaining closure of the surgical wound.
At one month, the membrane in area #10 was exposed and removed. Healthy connective tissue is present covering the implant and graft. Gingival structures are rebuilt for an esthetic outcome. The knowledge and techniques used for traditional bone grafts do not translate into tissue engineering and regenerative medicine. The OsseoConduct 3D-printed ridges are now available for order. As a medical device manufacturer, we are required by the FDA to provide instruction on the use of our products. To achieve this for you, we have introduced a personalized 5 CE course on Tissue Engineering and Regenerative Medicine. The course consists of a 1 hour video and personalized consultation of two early implant placement cases. Our early implant protocol is a great primer on regenerative medicine. You will choose your two cases, at which point Dr. Steiner will review your cases and comment on the regenerative process as the cases mature and go to completion. The course is open to anyone but directed primarily to those who want to introduce the OsseoConduct 3D-printed ridge technology into their practice who do not have experience with our products. For information on our Tissue Engineering and Regenerative Medicine course and ordering 3D-printed grafts, please follow the link below:
American Society for Bone and Mineral Research (ASBMR) Tissue Engineering and Regenerative Medicine International Society (TERMIS)