Effect of two kinds of thin and thick intermediate surgical splints on determination of new position of maxilla in Lefort I maxillary surgeries

Impaction displaces the maxilla in the vertical dimension, increasing the distance from the mandible; autorotation compensates this distance in the articulator and the mouth. The aim of the present study was to compare two thin (with the mandibular autorotation) and thick (without autorotation) splints. In this clinical trial, 19 patients (6 males and 13 females) were evaluated. The casts were trimmed and transferred to an articulator with the use of a Gnathus facebow. Jaw relationship was recorded in CR position. A model maxillary surgery was carried out in the direction of impaction and depending on the incisal pin of the articulator two intermediate splints were produced: 1. a situation with no incisal pin displacement (thick splint); 2. a situation with incisal pin displacement (thin splint). After maxillary osteotomy, at first the maxillary position was determined using the thin splint and reference lines were drawn on the maxillary sinus wall perpendicular to the osteotomy line. Then the thin splint was replaced by the thick one and the position of reference lines was evaluated and recorded. Data was analyzed with ANOVA (α=0.05). The reference lines changed in 6 patients (31%) (mean = 1.3 mm) and in 13 patients (69%) they remained constant. In 13 patients the mean of impaction and incisal pin movement were 4.3 mm (3-6 mm) and 4.9 mm (2-8 mm) respectively; in 6 cases they were 7.5 mm (5-9 mm) and 9.8 mm (7-15 mm). The probability of displacement of reference lines after splint replacement was calculated 10.7-52.5% by probability test. There is a possibility that thin and thick splints will not place the maxilla in the same position; the probability increases as impactions increases. Changes in reference lines are under the influence of articulator incisal pin displacement rather than the extent of impaction.