Prof. Park, you conducted the first clinical study on how different compressive forces affect Ridge Preservation outcome. Why?
Prof. Park: When performing Ridge Preservation, we sometimes find that the bone particles are pushed out of the socket over time. That’s why we decided to compact the bone graft inside the socket. There were no previous studies on what compressive forces work best in Ridge Preservation or Guided Bone Regeneration. Thus, we decided to investigate the effects of extreme pressure versus low pressure.3
How was the investigation done?
Prof. Park: We included 20 patients who required the extraction of a single maxillary or mandibular molar tooth. After tooth extraction, the sockets were filled with 250 mg of Geistlich Bio-Oss® Collagen, applied with either very low pressure, 5 Newton, or with extreme pressure, 30 Newton. Then we covered the sockets with Geistlich Bio-Gide® membranes in a double layer technique and made a hidden cross suture on top.
What did you observe?
Prof. Park: Focus was on hard and soft tissue volume changes, implant survival and new bone formation. To investigate the latter, we analyzed histologies from core biopsies. While volume gain and implant survival were similar in both groups, we saw an increased amount of new bone formation in the sockets filled with higher compressive forces.
You did, however, not find differences in volume gain or implant survival.
Prof. Park: True. We already have a great success rate with common treatment planning, implants and bone graft biomaterials.
So, if everything works out so well, why should we care about compressive force? Though it may not make a big difference for all patients, compression may have a tremendous impact on patients with impaired medical conditions, such as osteoporosis or diabetes, or patients with major bone deficiencies.
Nik Stiefel, you follow the development in this field. Is the finding that compression can lead to more new bone formation surprising for you?
Nik Stiefel: Yes and no. Yes, because in dentistry it is recommended to apply particulate bone graft materials as gently as possible to not lose trabecular architecture and porosity of the graft. And no,
because compression increases the mechanical stability of a particulate graft and there is no reason why the principles of mechanobiology “more stability means more bone” should not apply in cranial bone formation.
Could you explain the positive effect of compression?
Nik Stiefel: According to mechanobiological laws, nearly no movement leads to bone formation while large amounts of movement lead to soft tissue formation. Because compression increases the mechanical
stiffness of the particulate material, less movements and by that less soft tissue formation and more bone formation are expected.
Is this a proven principle?
Nik Stiefel: Yes. We know that blood clot stability and overall stability of the wound play a crucial role in bone regeneration. For example in tibial mid-diaphysis fractures of rats certain types of strain lead to formation of cartilage instead of bone.4 And while contained bone defects do fully ossify during bone regeneration using particulate bone material5, mechanical stabilization is needed for vertical defects to enable bone formation.6 In addition, there is evidence that at tissue level mechanical strains and fluid movement affect relevant celltypes such as osteoblasts7, endothelial cells8 or human mesenchymal stem cells9 that are relevant for tissue regeneration.
Prof. Park: Several other factors might be involved. Mechanical transduction with integrin-beta signaling in osteocytes is a well-investigated principle. The facilitated formation of bony bridges in a densely packed cavity is another - we call it contact osteogenesis. Or the simple fact that via compaction we force the biomaterial into the most apical part of the socket. All we know currently is that when we put more force on the biomaterial we get more new bone, but we don’t know whether it’s this force that enhances bone formation or something else, for example the stability of the biomaterial.
Would you expect the same effect with another biomaterial?
Prof. Park: Our study was conducted with Geistlich Bio-Oss® Collagen where the collagen fibers might act as space maintainers between the bone particles and prevent crushing of the biomaterial.
With Geistlich Bio-Oss® particles, things might be different. Further variables need to be considered, like: the type of procedure (horizontal or vertical ridge augmentation vs ridge preservation), source of biomaterial (xenograft, allograft, synthetic graft), particle size (small vs large), quality of surrounding bone (e.g., 3-wall vs 1-wall defect). How should one decide? When thinking that compression is an important factor, a ton of questions appear.
But is there research going on in this field?
Prof. Park: There is a lot of research on how to enhance bone regeneration with growth factors, anabolic or anti-resorptive agents, etc. All these adjunctive therapies have side-effects. But by adapting a
routine clinical procedure only slightly, we can make a difference. And I, as a clinician, would do almost anything to have better and faster bony healing.