Biomaterials in facial reconstruction

State-of-Art of Standard and Innovative Materials Used in Cranioplasty

Cranioplasty is the surgical technology employed to repair a traumatic head injury, cerebrovascular disease, oncology resection and congenital anomalies. Actually, different bone substitutes are used, either derived from biological products such as hydroxyapatite and demineralized bone matrix or synthetic ones such as sulfate or phosphate ceramics and polymer-based substitutes. Considering that the choice of the best material for cranioplasty is controversial, linked to the best operation procedure, the intent of this review was to report the outcome of research conducted on materials used for such applications, comparing the most used materials. The most interesting challenge is to preserve the mechanical properties while improving the bioactivity, porosity, biocompatibility, antibacterial properties, lowering thickness and costs. Among polymer materials, polymethylmethacrylate and polyetheretherketone are the most motivating, due to their biocompatibility, rigidity and toughness. Other biomaterials, with ecofriendly attributes, such as polycaprolactone and polylactic acid have been investigated, due to their microstructure that mimic the trabecular bone, encouraging vascularization and cell-cell communications. Taking into consideration that each material must be selected for specific clinical use, the main limitation remains the defects and the lack of vascularization, consequently porous synthetic substitutes could be an interesting way to support a faster and wider vascularization, with the aim to improve patient prognosis.

Use of Calcium Phosphate Cement Paste in Orbital Volume Augmentation

BACKGROUND

The development of calcium phosphate in cement paste form has made its application simplified and easy. In this study, the authors used an alpha-tricalcium phosphate/dicalcium phosphate dibasic/tetracalcium phosphate monoxide/hydroxyapatite injectable calcium phosphate cement paste to evaluate its potential use in orbital volume augmentation.

METHODS

Five New Zealand white rabbits were used in this study. In each rabbit, the right orbit was directly implanted with calcium phosphate cement in its injectable paste form, and a prehardened form was placed in the left orbit. The orbital roof was approached through a subciliary skin incision and the implant was placed posterior to the globe of the eyeball to push it outward. Measurement of proptosis and intraocular pressure was monitored before and after implantation. The animals were killed after 3 months, and orbit bone-implant samples were taken for histology and microradiography.

RESULTS

In both groups, proptosis was induced, 4.2 +/- 0.27 mm in the prehardened group and 3.8 +/- 0.22 mm in the injectable group. These values taken 1 week postimplantation were unchanged until the end of the experiment and were maintained without significant intraocular pressure changes. The implants were well tolerated, and no sign of infection, extrusion, or migration was noted. Histologic analysis showed good biocompatibility and osteoconductivity, and microradiography has confirmed a well-set cement with direct bone union to it.

CONCLUSION

These findings therefore indicate that calcium phosphate cement implant, when used as an injectable paste or in its prehardened form, can be a safe, effective material for orbital volume augmentation.

A 1-year study of hydroxyapatite-derived biomaterials in an adult sheep model: III. Comparison with autogenous bone graft for facial augmentation

BACKGROUND

The present study investigates onlay bone grafts and implants in a large-animal (sheep) model to determine whether there are composite biomaterials that can maximize long-term facial augmentation when compared with conventional bone grafts.

METHODS

Facial augmentation was performed in 10 adult sheep. First, 16.8 x 5-mm disks were prepared from autogenous calvarial bone, hydroxyapatite ceramic, ceramic composite of 60 percent hydroxyapatite and 40 percent beta-tricalcium phosphate (60 percent hydroxyapatite ceramic), and hydroxyapatite cement paste. Facial recipient sites were the body of the mandible (depository), the maxillary region (resorptive), and the frontal bone (depository). The volume of all bone grafts and implants was determined using computed tomographic scans, and the amount of bone formation was measured by means of backscatter electron microscopy 1 year postimplantation.

RESULTS

Cranial bone graft demonstrated a highly significant reduction in volume in all sites studied. Other than a slight decrease in volume of hydroxyapatite cement paste disks applied to the maxillary region, there was no significant change in volume of the biomaterials implanted in any of the remaining recipient sites. Bone replacement was greatest in hydroxyapatite ceramic (23.9 percent) followed by 60 percent hydroxyapatite ceramic (16.4 percent) and least with hydroxyapatite cement paste (4.2 percent). Minimal differences in bone replacement were noted between recipient sites.

CONCLUSIONS

This study demonstrates that the volume maintenance of onlay hydroxyapatite composites is highly predictable, whereas that of cranial bone graft is unpredictable. Minimal differences were seen in bone replacement within biomaterials between "depository" and "resorptive" facial recipient sites. Ceramic forms of onlay hydroxyapatite implants demonstrated significantly greater bone replacement than did the cement paste forms of hydroxyapatite.

Biomaterials in craniofacial reconstruction

Biomaterials have become an integral component of craniofacial reconstruction. Their increasing ease of use, long "shelf-life," and safety enables them to be used effectively and play an important role in reducing operating times. There are various biomaterials currently available and specific usages have been characterized well in the literature. This article reviews different biomaterials that can be used in craniofacial reconstruction,including autogenous bone, methyl methacrylate and hard tissue replacement,hydroxyapatite, porous polyethylene, bioactive glass, and demineralized bone.