INTRODUCTION S igns and symptoms of myoarthropathies of the masticatory system (MAP), i.e. , of craniomandibular disorders, are quite common. In approximately 3.6 to 7% of affected persons, the symptoms are severe enough to require treatment (Okeson, 1996). The MAP etiology appears to be multifactorial and includes structural overload and lack of tissue adaptation (Milam, 2006; Stegenga and de Bont, 2006). In clinical practice, oral splints are one of the most common treatment modalities, in addition to physical therapy, medication, psychological treatment, and, ultimately, surgery (Dionne et al., 2006). Splint treatment is non-invasive and reversible if correctly applied; however, its mechanism of action has not been elucidated, and controversial ideas exist about its clinical indication and functioning. These include placebo effect, changes in occlusion, improvement of jaw-muscle function, modification of oral behavior, recruitment of different motor units, behavioral intervention, and new positioning of the condyle and/or the articular disc (Dao and Lavigne, 1998; Al-Ani et al., 2004; Forssell and Kalso, 2004; Nilner, 2004; Turp et al., 2004; Schindler et al., 2006). Regardless of its mode of action, some randomized clinical trials and literature reviews have documented its therapeutic effectiveness (Kreiner et al., 2001; Ekberg et al., 2002; Kuttila et al., 2002). The literature is not conclusive on whether an occlusal splint increases the condyle-fossa distance, as shown by measurements performed on radiographs of the temporomandibular joint (TMJ) (Moncayo, 1994; Ekberg et al., 1998; Kuboki et al., 1999; Lau and Green, 2003). Dynamic stereometry facilitates a non-invasive, in vivo, three-dimensional, and person-specific analysis of the condyle-fossa distance during static positions and mandibular movements. The technique combines the three-dimensional reconstruction of the TMJ anatomy obtained by magnetic resonance (MR) images with jaw motion data obtained by tracking the jaw with 6 degrees of freedom (Palla et al., 2003; Gossi et al., 2004; Gallo, 2005). The aim of this study was to analyze, by dynamic stereometry, the effect of the insertion of an occlusal splint of 3-mm thickness on (1) the minimum condyle fossa-distance, (2) the condyle-fossa distance closest in maximum intercuspation, and (3) condylar rotation and translation. MATERIALS & METHODS Participants Ten healthy asymptomatic individuals (five males and five females; age range, 18 to 31 yrs) participated in the study after giving informed consent. They were free of signs and symptoms of a myoarthropathy, as revealed by history and clinical examination. Exclusion criteria were tenderness to palpation of masticatory muscles and TMJ area, painful jaw movements (maximum mouth opening < 40 mm, laterotrusion and protrusion < 7 mm), TMJ pathological signs ABSTRACT Occlusal splints are used for the management of temporomandibular disorders, although their mechanism of action remains controversial. This study investigated whether insertion of an occlusal splint leads to condyle-fossa distance changes, and to mandibular rotation and/or translation. By combining magnetic resonance images with jaw tracking (dynamic stereometry), we analyzed the intra-articular distances of 20 human temporomandibular joints (TMJs) before and after insertion of occlusal splints of 3 mm thickness in the first molar region. For habitual closure, protrusion, and laterotrusion in the contralateral joint, occlusal splints led to minor—yet statistically significant—increases of global TMJ space and to larger increases at defined condylar areas. Condylar end rotation and translation in habitual closure were reduced. Hence, the insertion of a 3-mm-thick occlusal splint led to a change in the topographical condyle-fossa relationship, and therefore to a new distribution of contact areas between joint surfaces. KEY WORDS : biomechanics, Magnetic Resonance Imaging, stress, mechanical, occlusal splints, temporomandibular joint disorders, temporomandibular joint. Received November 23, 2007; Last revision May 8, 2008; Accepted June 16, 2008 Stereometric Assessment of TMJ Space Variation by Occlusal Splints D.A. Ettlin*, H. Mang, V. Colombo, S. Palla, and L.M. Gallo Clinic for Masticatory Disorders, Removable Prosthodontics and Special Care Dentistry, Center for Oral Medicine, Dental and Maxillo-Facial Surgery, University of Zürich, Switzerland, Plattenstrasse 11, CH-8032 Zürich, Switzerland; *corresponding author, dominik.ettlin@zzmk.uzh.ch J Dent Res 87(9):877-881, 2008 RESEARCH REPORTS Clinical 877