Guided Bone Regeneration by a Thermoplastic Poly(L-lactic acid) Barrier Membrane

 Introduction: Surgical treatments for dental occlusion and masticatory functions with various implants have been tried as the highly reproducible odontotherapy. However, when there is significant resorption and atrophy at the target alveolar bone, it is practically practically difficult or impossible to perform the implant placement. Therefore, the membrane properties to prevent the soft tissue invasion, and have the thermoplasticity that can be applied to the bone defect and the mechanical strength that resists the function pressure, are necessary for GBR.

In this study, various thermoplastic membranes for guided bone regeneration (GBR) are prepared from PLLA with different molecular weights. We examine the mechanical strength of membrane and their cell proliferation. In addition, the application of PLLA membranes onto the pariental bone of rabbits, the bone formation was evaluated histologically.

 Materials and Methods: The PLLA with the molecular weight 100,000 (PLLA Mw:100,000) and PLLA with the molecular weight of 380,000 (PLLA Mw:380,000) samples were dissolved in chloroformto give the concentration of 8 and 4 wt%, respectively. Various volumes of PLLA chloroform solution were cast into a glass petri dish with 33 mm in diameter, followed by leaving at room temperature overnight until to the complete evaporation of chloroform.

The compression strength, the temperature and time to formulate was measured. Moreover, pH test and the cells cytotoxicity on the membrane by MTT assay were measured. In vivo experiments, to measure the volume of bone tissue newly formed, the H-E stained tissue section 12 weeks after implantation was viewed.

 Results and Discussion: The membrane prepared from PLLA Mw:380,000 showed excellent thermoplasticity at 75-80 °C and the compressive strength equal to that of titanium meshes, in contrast to that of PLLA Mw:100,000 and poly(lactic acid-co-glycolic acid (PLGA). Upon placing in the aqueous solution, the solution pH was significantly changed for the PLLA Mw:380,000 membrane and the cytotoxic activity was not observed. The membrane of dome shape was applied onto the parietal bone of rabbits to evaluate the bone formation. The membrane of PLLA Mw:380,000 induced new bone formation with the dome shape remaining.

 Conclusions: It is concluded that the PLLA membrane with the molecular weight of 380,000 is promising for GBR of a vertical bone augmentation.

 References:

�m1�nDahlin C, et al., Int J Oral Maxillofac Implants., 1989, 4(1), 19-25.

�m2�nSchwarz F, et al., Clin Oral Implants Res., 2008, 19(4), 402-415.