Existing therapies for symptoms related to painful clicking of the temporomandibular joint (TMJ) have rarely met with complete success and predicting prognosis remains difficult. Few studies have reported the efficacy of maxillary flat occlusal splints (MFOSs) for the treatment of painful clicking of the TMJ, and few studies have evaluated the predisposing factors that influence the clinical outcomes of MFOSs. The aim of this study was to investigate the treatment efficacy of MFOSs for painful clicking of the TMJ, and to determine the factors influencing TMJ therapy with MFOSs. We conducted a retrospective study of 109 patients suffering from unilateral clicking concurrent with preauricular area pain for at least 2 months between 2004 and 2008. Seventy-five patients were treated with an MFOS, while 34 patients did not receive MFOS therapy. Clicking score, pain-free maximal mouth opening, pain score, duration of the clicking sounds, age and bruxism were recorded during treatment and involved into the reviews. The degree of joint clicking was determined by a stethoscope placed in the anterolateral area of the external auditory canal and was divided into four grades. Data were analyzed using a Mann-Whitney U test, Fisher's exact test, and Student's t test. Results showed statistically significant differences in treatment outcomes between the MFOS-treated and control groups in clicking index, maximal mouth opening, pain and complete remission rates of symptoms within 1 year. Furthermore, for patients treated with MFOS, there were statistically significant differences in the clinical outcomes between those with a high clicking index and those with a low index before treatment. Factors significantly correlated with successful outcomes of MFOS included nocturnal bruxism, patient age and duration of clicking. MFOSs can be used to treat patients with painful clicking of the TMJ and related symptoms. The severity of clicking, bruxism, age and duration of clicking are all important factors influencing treatment outcomes with MFOSs.