Die sagittale Kompensationskurve - Eine Untersuchung ihrer Veränderung und Abhängigkeit von Zahnbogenlänge, -breite und -symmetrie anhand multipel erstellter Klasse-I-Verzahnungen

Abstract

Introduction: Dental literature contains clinical studies, that investigates the modification of the curve of spee (COS) based on their genesis, their occurrence during the growth or connection to other factors. Numerous variations of COS during dentition or in the course of life are affected by growth, craniofacial morphology, bite force, morphology of incisors, characteristic of occlusion and relative position of jaw joints to mandible and other factors. Aim: The aim of this study was an investigation of the variation of the COS in a new constructed plaster casts made by doctoral candidate (D) and students (S) in neutral position. In context of reflections on biomechanics, the question arises if and how the expression of COS changes despite using teeth with identical anatomy. After considerations to occlusion and morphology, theoretically there is just one possible variant of arch form and COS by using identical teeth. It should be investigated, if there is correlation between the expression of the curve with other elements such as length, width and symmetry of dental arch. It should be compared the mean depth of both sides of the jaw, the position of the lowest point and minimum and maximum values of COS. Casts of doctoral candidate (D) and students (S) should be compared. Material and method: The plaster casts (upper and lower jaw) of a selected patient case (original cast, final cast after orthodontic treatment, neutral position) was duplicated 65 times. All teeth were separated. The puzzle of occlusion had to be new constructed. The doctoral candidate created 20 casts and 45 students each one cast in neutral position. 58 of 65 resulted casts could be evaluated. Measures were taken of the depth of COS, arch width, arch length and symmetry of dental arch by using callipers, millimetre film and an individual measurement apparatus. For statistical evaluation correlation calculations, hypothesis tests (t- test/ Welch test) and boxplots for graphic display were accomplished. Results: A negative correlation (r = -0,61) of arch width with arch length was investigated. There were no other correlations of COS with other measured values greater than r= 0,6 or less than r= -0,6. The casts of the students had a wider basis than the casts of the doctoral candidate. The depth of COS of the D-casts were significantly lower in both quadrants. The totally of reconstructed casts showed deeper curves in the 4th quadrant than in the 3rd and a shorter 3rd quadrant. Viewed from the horizontal plane, dental arch proceeded steeper in the 4th quadrant. The deepest point of COS is the mesio-buccal cusp of first molar on both sides. Conclusion: No significant connection of depth of COS from other measurements were detected. By examining the reconstructed casts separately, diverse depth of COS, arch widths and lengths occurred in functional occlusion. The mean values of all measured casts (arch width and length) are almost identical to those of the original cast ( 1,0mm). The theory, that the arch form is determined by tooth shape, is partly confirmed. The mean values vary around the morphology of the original cast. The variation for the arrangement of the morphology and the range of the arch form is larger than firstly suspected. There must be further studies in this field, to examine the facts in detail. As one aim of orthodontic treatment, flattening a pronounced COS is suggested to set a neutral position. The orthodontist should have sufficient knowledge of the ideal characteristics of COS because of ensuring neutral molar position by using rigid arches during terminal treatment with straight-wire-technique.