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Metallic bone plates have been shown to affect radiation in vitro. Although no damage has ever been demonstrated in vivo these plates may cause dose enhancements and shielding of the adjacent tissue. Resorbable high molecular weight as-polymerized poly(L-lactide) (PLLA) bone plates have recently been used for reconstruction in the maxillofacial area. To determine their influence on dose distribution, a 4-hole bone plate and screws of PLLA were exposed to electron and photon beams. A tissue-equivalent phantom of perspex was irradiated and measurements were made with LiF thermoluminescent dosimeters. No significant changes in dose deviations could be determined when the dose distribution in the homogeneous phantom was compared with that of the phantom in which the PLLA material was placed. From this study it can be concluded that the PLLA material can be regarded as tissue-equivalent and can, thus, be safely used for fracture fixation of bone fragments when postoperative irradiation is anticipated.

Bio-absorbable plates and screws were used for internal fixation of artificially created mandibular fractures in 6 dogs. The plates and screws were fabricated from a block of poly(L-lactide) (PLLA), with a high molecular weight. The material is microporous and has excellent mechanical properties. Plates and screws were inserted in accordance with Champy's principles on internal fixation. Clinical and radiographical follow-up and examination of the fracture site under general anesthesia showed that all fractures healed without callus and without complications. The plates or screws did not fail, despite the tensile strength of the PLLA used is less than stainless steel or any other metal. An explanation for their successful application may be the high impact resilience of this material. The proprioceptive mechanisms, however, that keep the dogs from maximal loading of their broken mandibles, may also play a role. Plates and screws of this bio-absorbable PLLA appear to be an attractive alternative for internal fixation of mandibular fractures and certainly for less loaded fractures of the human skeleton. The necessity to remove metallic osteosynthesis can be avoided.

In order to create artificial fractures in animals resembling those which occur naturally, a new technique for fracture production was developed. Using a specially designed clamp, artificial fractures were produced in the mandibular body of seven sheep and 12 dogs. Radiographical analysis of the effects of the clamp on the mandibular body showed simple, single vertical fractures in the buccal cortex, inferior border and the alveolar process comparable to those which occur naturally. Using the technique described it was possible, in all cases, to carry out treatment with the use of 4-hole poly(L-lactide) plates and screws.

Poly (L-lactide), a polymer of lactic acid (PLLA), with an extremely high molecular weight (Mv up to 1 x 10(6] has been synthesised under strictly controlled conditions resulting in a new microporous material with excellent mechanical properties. Bone-plates and screws machined from PLLA were used for fixation of two artificial mandibular fractures in sheep effected by a specially designed bone clamp. Fracture healing was uneventful without visible callus formation. Plates and screws of PLLA gave good stability over a sufficiently long period to enable normal fracture healing. Application in humans seems to be justified.