Brain damage due to retraction was studied morphologically and physiologically in the dog brain. Two methods of retraction were compared using a retractor with a strain gauge: 1) continuous retraction; and 2) intermittent retraction. Total retraction time was 60 minutes for each method. Brain damage started to appear at a retraction force of 30 gm with continuous retraction, and increased in proportion to the force used. The power spectrum of the electrocorticogram showed full recovery after the release of retraction when the retraction force was less than 40 gm. With intermittent retraction, the damage was morphologically minimal with a retraction force of less than 50 gm, and recovery of the power spectrum of the electrocorticogram was prompt in comparison with continuous retraction. The results indicate the superiority of intermittent over continuous retraction.
