When a functional tooth has to be extracted, the obstacles that all clinicians have dealt with is how to manage extraction sites to prepare better site for the following dental implant placement or to minimize ridge shrinkage for a fixed or removable prosthesis delivery.[12] It is well documented that bone graft/substitute can contribute to reducing of the ridge dimensional changes or supporting implant placement after a tooth is extracted. Ideal bone graft/substitute materials should be able to fill irregular sockets, attach to the alveolar bone, provide a load-bearing property, and maintain biological support during new bone regeneration.[13] The superior handling characteristics of CPC have make it a promising candidate materials for application in implant dentistry. However, it is also widely accepted that there are still some crucial issues that need to be solved to satisfy real clinical requirements.[8]
Hardened CPC are intrinsically microporous with pore size in the range of submicro/micrometers, being conducive to tissue fluid impregnation into CPC, and help resorption and replacement of CPCs by bone. However, it is also desirable to create macropores of at least tens of micrometers in CPCs to favor bone colonization, accelerating the process of replacement of CPCs by bone. [14, 15] In our previous animal study, we proved collagen could be a bionic component to be integrated with CPC to improve its bio-compatibility, meanwhile create macro-porosity within CPC. The CPC-collagen composite had expanded inner surface area that could facilitate bone ingrowth.[10] In this study, we chose clinically available gelatin sponges and CPC to fabricate a uniform composite for both preclinical testing and clinical trail. By using a tissue homogenizer, the gelatin sponges were smashed and mixed with CPC paste forming a fusion product. After hardening reaction, the final CPC composite showed abundant macroporosity, which was architecturally similar to cancellous bones.
In this study, the novel CPC composite also presented other beneficial properties. Due to the evenly distributed gelatin sponges, we found the modified CPC paste had improved viscosity. Addition of cohesion promoters to CPC had been considered important because CPC pastes tend to disintegrate upon early contact with blood or other aqueous fluids, which inhibits the use of these materials for clinical use as for bone repair, reconstruction and augmentation.[8, 16] The improvement of paste viscosity could help maintaining the material’s early stability in fresh alveolar socket. Another main challenge facing CPC composites was their mechanical properties, including strength, toughness, brittleness and reliability.[17, 18] In this study, the novel CPC composite was a homogeneous material having a strength comparable to cancellous bone.[20] The overall mechanical properties of CPC composite made it a favourable packing material for dental implant in non-to-moderate load-bearing environment.
The fresh alveolar socket was a more complicated open environment, comparing with the closed bone cavity in rabbit’ femur.[21] Various socket bone wall defect and dynamic bone remodeling/resorption following extraction would influence the stability of packing materials. The chewing activity would create unexpected load-bearing during the healing process. Furthermore, without extensive flapping, the wound closure after tooth extraction would generally be secondary closure, also known as healing by secondary intention. This type of healing required more time.[22, 23] Based on the concerns above, alveolar ridge preservation without dental implant placement was designed to testing CPC composite in clinical case series. However, loss of materials from upper molar sockets occurred in two patients. Different from the traditional particle materials, the CPC composite set in situ as integrated material, whose stability largely depended on a tight contact with surrounding bone of the extraction socket. We suggested that additional fixation, instead of simple suturing of the extraction wound, should be necessary for CPC composite in upper large sockets with excessive bone defects. Further studies will be carried out.
The limitations of this study include a small cohort and time-limited observation. But the evidences provided by the preclinical study and clinical trial primarily confirmed the high osteoconductivity, appropriate mechanical properties and good surface chemistry of newly fabricated CPC composite, which make it a unique candidate for dental applications. The commercial product of CPC, gelatin and minocycline ointment are reasonably cheap. There is no need for barrier membrane guidance. Further researches will be carried out to find appropriate approach for severely damaged socket restoration by using CPC composite material allied with immediate dental implant placement.