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Animal experiment: Histological analysis of the LPM reattachment2138IntroductionTotal temporomandibular joint replacement (TMJR) is an uncommon treatment that, is considered the final option in cases of end-stage temporomandibular disorders. Its indications are well described by both the American Association of Oral and Maxillofacial Surgeons (AAOMS)(1) and British National Institute for Health and Care Excellence guidelines.(2) The main purpose of joint replacement is to restore proper temporomandibular joint (TMJ) function, as well as to relieve the patient of pain and improve the overall quality of life. Current TMJRs can reduce pain and improve mouth opening. However, they lack the ability to restore proper masticatory function, due to the loss of protrusive and laterotrusive movements for tearing and grinding of food. In humans, the lateral pterygoid muscle (LPM) plays a crucial role in this process. It allows for protrusion through bilateral contraction and by unilateral contraction for laterotrusive movement.(3,4) The LPM can be divided into a superior and inferior muscle belly, of which the latter is subdivided into four components. Each of these parts play a role in either initiating or continuing through with protrusive and laterotrusive movements.(5,6) However, despite the distinct muscle bellies, their fibers variously insert into the muscle tendon, fovea, capsular ligament and disc, resulting in a ‘uniform’ insertion or attachment in the mandibular condylar area.(7) Because both the intra-articular disc and condyle are resected during the placement of a total TMJ prosthesis, the LPM insertion is effectively lost. This situation results in impaired laterotrusive and protrusive jaw function as shown by both Mercuri et al.(8) and Dimitroulis et al.(9). Additionally, because correct mastication occurs bilaterally, unilateral mastication results in an uneven load distribution over the two TMJs. This increased load can lead to further joint deterioration – for example, through articular disc damage and cartilage destruction – resulting in pain and limited function.(10–12)To prevent an increased load in the contralateral joint, as well as to retain LPM function in patients treated with a TMJR, Mommaerts(13) aimed to develop a new patient-specific additively manufactured TMJR, together Nikolas de Meurechy NW.indd 213 05-06-2024 10:14