## 1 Introduction  
The relationship between malocclusions and pacifier use is a much-debated issue. Although no definite conclusions that are consistent with the principles of evidence-based medicine have been drawn, the general consensus regards pacifier use as harmful if it does not comply with the recommended timing and modalities [1, 2, 3, 4]. Suction is an innate reflex that appears in the prenatal stage and is one of the first muscular coordination abilities of a fetus [5]. A pacifier stimulates this reflex. Its use is described as \"non-nutritive suction behavior\", comparable to finger suction. Infants have a natural suction instinct that is considered to be the first feeding instinct. If this instinct is not completely satisfied by the maternal breast or feeding bottle, the baby will experience feelings of frustration. This does not happen if the baby engages in a non-nutritive suction habit [6]. It is no coincidence that, in English, this object is called a pacifier, underlining its effectiveness in soothing the baby. Pacifiers also have some benefits, as follows:  
They reduce the perception of pain and the state of agitation in babies under 6 months old, whether born full term or prematurely, or enduring minor procedures in the Emergency Room [7]. In premature babies, they facilitate the development of a nutritive suction habit and improve digestion at the intestinal level, thus reducing hospitalization time [8]; they also reduce finger suction habits [9]. Pacifiers are also associated with possible risks, as they can cause dental misalignment and malocclusions if used by children older than two years [10]; hinder breastfeeding if used during the first month after birth, before breastfeeding has been consolidated [11]; and lead to the risk of otitis media, especially in children over one year of age [12]. The guidelines published in 2016 included pacifier use among the protection factors against Sudden Infant Death Syndrome (SIDS) during the first year of life [13]. Various hypotheses have been drawn on the role of a pacifier in reducing the risk of SIDS, for instance, preventing \"rebreathing\" by preventing the direct contact of the face with the sheets; lowering the threshold of awakening; and causing a greater arousal in the case of hypoxia [14]. The use of a pacifier also keeps the tongue in the anterior position, modifying the aerial spaces and keeping the airways open [15]. These positive effects seem to be unaffected by the possible loss of the pacifier during sleep. One study [16] showed that pacifier use in preterm infants is associated with a small, but significant and persistent forward movement of the jaw, which enables the upper airways to expand. This theory was confirmed by another study [17] that showed that a pacifier facilitates an adequate airflow, and therefore an adequate peripheral oxygen saturation, through the oral cavity in the case of nasal airway obstruction. In a previous paper, we demonstrated that pacifier use is correlated with a statistically significant reduction in the number of pathological apneas/night (AHI), and with an improvement in the average SpO2 as well as in the value of the minimum SpO2 detected during sleep in children with a history of Apparent Life-Threatening Events (ALTEs) [18]. The effects of pacifiers on the variations in peripheral oxygen saturation during wake time are unclear. One study [19] compared different sleeping positions in relation to changes in cardio-respiratory parameters. The positions studied were prone, supine, and lateral. While the prone position seems to be ideal for premature infants with mechanical ventilation, the same cannot be said for spontaneously breathing premature infants. In addition, due to the association between the prone sleeping position and SIDS [13], all hospitalized infants placed in the prone position must be continuously monitored in terms of SpO2 levels. [PERSON] et al.