# Oral Impacts of Aligners versus Fixed Self-Ligating Lingual Orthodontic Appliances
## 1 Introduction  
In recent years, the demand for and the provision of aesthetic orthodontic treatment appliances have increased among patients. This trend reflects an acceptance that invisible orthodontic appliances, namely, clear aligners and lingual brackets, are preferable for adults, in terms of appearance, to more traditional orthodontic appliances [1; 2; 3]. The aesthetic advantages of these appliances over conventional buccal appliances have contributed to a shift in the demographic of the orthodontic patient population to increase the percentage of adults [1]. Nevertheless, adaptation difficulties may affect patient perception and compliance, and thus treatment outcome. Discomfort and pain, for example, are well-documented sequelae encountered during the course of orthodontic treatment. Approximately 90-95% of patients receiving orthodontic treatments experience these symptoms during the first weeks of treatment [4; 5]. Pain and the fear of pain discourage orthodontic treatment and are the main reasons for treatment discontinuation [6; 7; 8]. Recently, there has been growing interest in not just understanding pain and other symptoms experienced during treatment, but also the oral impacts of orthodontic treatment, such as the influence on quality of life. To this end, many oral health-related quality of life measures have been used to assess oral impacts [9; 10; 11; 12; 13; 14; 15; 16]. All measures assess key oral impacts: discomfort and pain, eating difficulties, speech disturbances and social activities. Different orthodontic treatment modalities function in different ways, making it imperative to assess the oral impacts of each treatment separately. Some studies have reported conflicting results regarding pain levels between different orthodontic appliances [17; 18; 19]. A recent systematic review concluded that orthodontic patients treated with Invisalign(r) appear to experience lower levels of pain than those treated with fixed appliances during the first few days of treatment; thereafter, (up to 2 months) no differences were noted [20]. However, it was pointed out that the malocclusion complexity level among the included studies was mild and the type of malocclusion was not comprehensively described, which may lead to controversial results. Thus, the level of certainty of this evidence was moderate. Moreover, different materials may affect pain levels too: the recently developed SmartTrack material has been favorably rated by the patients in regard to pain intensity and duration as well as overall comfort [18]. Regarding the effect of aligners on overall oral health-related quality of life compared to fixed appliance treatment, a recent systematic review concluded that information was limited, and effects were inconclusive with weak evidence that aligners might cause less eating disturbance [21]. A common critique by lingual appliance users is that the adaptability of lingual appliances takes a long period of time; therefore, the oral impacts should not be evaluated only in the short-term. Moreover, differences in plaque retention and composition are anticipated during orthodontic treatment with lingual brackets [22]. A systematic review compared lingual to buccal appliances and suggested that patients wearing lingual appliances have more pain, speech difficulties, and problems in maintaining adequate oral hygiene. No differences for eating and caries risk were identified [23]. Compared to children, adults have less speech adaptability due to muscle memory, and speech alteration may lead to reduced patient compliance [24]. The smaller the profile of the lingual appliance, the less pronounced are the impairments it induces [25]. To date, there has been no study comparing the oral impacts experienced by patients wearing the most discreet appliances available, namely, aligners versus lingual orthodontic braces over a 3-month period following the insertion of the appliances.