Objective: The present study was undertaken to determine the tooth whitening effectiveness of trays with no reservoirs (Invisalign aligners or Vivera retainers used as bleaching trays), initially with a finite element analysis (FEA) and subsequently with a clinical study using spectrophotometry. Materials and methods: The FEA technique was used to determine the ideal distribution of bleaching gel between teeth and aligners in vitro. Three sample areas of gel application on the maxillary central incisors (the incisal edge, the middle part, and the gingival edge) were analyzed. Spectrophotometry was used to ascertain the clinical effectiveness of the bleaching gel as it related to the results of the FEA. More specifically, the chromatic variation obtained by the bleaching gel on teeth 41 and 32 (control teeth, with reservoirs) was compared with that on teeth 31 and 42 (study teeth, without reservoirs). Results: The FEA results showed that the optimal gel distribution is reached when 2 mm3 of gel is applied to the center of the vestibular face of the tooth in the tray. As regards the clinical study, there were no relevant differences of whitening effectiveness between the teeth with reservoirs and those without. In both cases, the whitening was effective and the patients were completely satisfied with the results. Conclusions: The advantages for patients to receive dental bleaching during orthodontic treatment with aligners are evident. The procedure is not time consuming and requires less financial expense. Further clinical studies are required to assess the effectiveness of the procedure.