This observational study aimed to evaluate the prevalence of poor oral habits and malocclusions among children after using an orthodontic type of pacifier. The sample (198 children, ranging between 3 and 5 years of age) is undoubtedly the most extensive report among the published literature, recording the data of children who have exclusively used an orthodontic pacifier. Thus, the collected data can be generalized for the population of children who use orthodontic pacifiers. In addition, previously, no study has looked into whether or how orthodontic pacifier sucking is interrelated with poor oral habits, mouth breathing and tongue thrust swallow.
In the present sample, the great part of children (78.28% of the whole sample) gladly started utilizing orthodontic pacifier during their first 3 months of life (78.79% of the whole sample), adopting it regularly throughout the night, in their first year of age (89.39% of the whole sample). Thus, the present data can confirm that orthodontic pacifier was generally well accepted by children, as this fact has already been reported in various literatures [6, 10, 20]. In addition, the collected data of the present study revealed that the 91.41% of the parent/guardians had been properly informed right from the beginning about the advantages of orthodontic pacifiers over the conventional types and also the risks related to its prolonged usage. This also has been outlined that a great number of children were given their pacifiers during the night (89.39% of the whole sample), following the recommendations of pacifier usage, i.e. that it should be used while the infant is sleeping and not reinserted if the child drops it during sleep  (today, the recommended usage would be for sleeping and for less than 4–6 h per day) . These data are in close agreement with the fact that an orthodontic pacifier is adopted by those mothers who are adequately informed concerning the risks of using conventional pacifiers. The present data also indicate that no significant correlation was detected between the duration of the pacifier sucking and the prevalence of recurrent otitis, as recurrent otitis was recorded only for 20 children out of 198 (10.10%). Differently from another previous report, which observed that pacifier sucking for a period exceeding 10 months, increases the risk of recurrent otitis .
Mouth breathing during the night was present in 71 children out of 198 (36.04% of the sample). The result of present study suggests that there exists a predominant pattern of nasal breathing among participated children. While, no relationship can be deduced between the breathing pattern and orthodontic pacifier sucking.
This result agrees with a recent survey from a sample of 1405 children between the ages of 2 and 7, (699 females and 706 males), in which oral breathing was present in 26.3% of the total children, concluding for the great benefits of an early interceptive treatment, as it is categorized as grade 2 of risk, requesting a periodical surveillance, and ear, nose, and throat evaluation for breathing problems. 
In a previous sample of 36 pre-school children with primary dentition using conventional pacifier, Nihi et al. found that 22.2% of them (8 subjects out of 36) had mouth breathing at rest, while only 8.3% (4 children out of 48) of pacifier non-users showed mouth breathing . According to Nihi et al. a higher prevalence of mouth breathing among pacifier users with respect to controls, may be associated to the altered position of the tongue in the mouth, which causes these subjects to keep their mouths open and consequently develop a mouth-breathing pattern. This explanation may be justifiable both for children using conventional as well as orthodontic pacifiers, although the present data seem to be insufficient to validate any correlation between pacifier sucking and mouth breathing. Therefore, it may be concluded that the pacifier sucking is not strongly related to breathing pattern during the night.
The result of present observational study, reveals that the tongue thrust swallow affected 16.16% of the sample (32 children out of 198), and no significant dependency could be established with pacifier sucking beginning or its duration. In the sample analyzed by Nihi et al., tongue thrust swallow was detected in 27.8% (10 out of 36 subjects), a percentage higher than that of the present study (16.16%; 32 children out of 198) . Nihi et al. associate the tongue thrust swallow with a prolonged pacifier-sucking habit, which delays maturation of the swallowing reflex. The present data suggest that an orthodontic pacifier thin neck nipple structure could be helpful to reduce the occurrence of tongue thrust swallow, as also hypothesized previously . With regard to the poor oral habits, 5.56% of the present sample (11 children out of 198) reported fingersucking/thumbsucking, but no relationship was detected between breastfeeding and fingersucking/thumbsucking. In addition, those children who began to use orthodontic pacifier very early - between 0 and 3 months of life – showed a lower risk to develop fingersucking/thumbsucking habit in respect to children who begin after 4 months (OR 0.13, 95% CI 0.04–0.47, p = 0.0004) (Table 3). This result is in an acceptable agreement with the recommendation of both Canadian and American Dental Associations, which suggest pacifiers out of finger/thumb sucking, as it would be more convenient for parents to control the sucking habit, as it is easier to wean a child’s habit from a pacifier, than from a thumb [25, 26].
This finding appears to disagree with what is generally believed for conventional pacifiers, i.e. that if conventional pacifiers are given to infants in the early postpartum period, when they are learning to suck from their mothers’ breasts, its use may act as a favour for a later fingersucking/thumbsucking habit development . In agreement with this statement, Ling et al. reported, from a sample of 1034 Asian children aged 2 to 5 years old, that children who use conventional pacifiers “daily” have significantly higher chances of developing fingersucking/thumbsucking habits , while the present study does not confirm this association in the case of orthodontic pacifiers. The present data states the opposite concept, i.e. children who began to use orthodontic pacifier during the first 3 months of life are less likely to develop fingersucking/thumbsucking with respect to children who had begun after 4 months (OR 0.13, 95% CI 0.04–0.47, p = 0.0004). It must be noted that Ling et al. report data on conventional pacifiers, and did not analyze the beginning of the pacifier sucking, but only its frequency (a “daily” use or “not daily” use) (OR 2.136; 95% CI 1.11–4.10) . These factors provide satisfactory explanation concerning the different conclusions between the two studies. To the authors best knowledge there is no published work on the relationship between pacifier sucking and fingersucking. The only study performed is the one reported in 1977, the author came to the conclusion that there exists an inverse relation between two habits  this is quite compatible with the results obtained in the present study.
Thus, it is not difficult to draw a conclusion that the infants who begin early to use orthodontic pacifiers may experience a kind of satisfaction and this can reduce the urge for further addiction, preventing the development of other poor oral habits.
About the other poor oral habits, the proportions of children having the habits of lip biting, tongue interposition between dental arches, or nail biting were 5.56% (11 children out of 198), 12.63% (25 children out of 198) and 15.15% (30 children out of 198), respectively. In addition, the use of an orthodontic pacifier for more than 2 years seems not to favor the acquisition of additional poor oral habits, even when used for more than 2 years. These percentages appear low and acceptable, if compared with a general population of 1405 preschool children between the ages of 2 and 7 (699 females and 706 males), similar to recently analyzed study in which a percentage of 27.5% of children having bad oral habits was observed. 
In addition, no association was detected between the duration or the beginning of orthodontic pacifiers sucking, and the frequencies of these poor oral habits. These data suggest that orthodontic pacifier sucking doesn’t cause the dependency to other poor oral habits. Only a few studies in literature had analyzed the relationship between pacifier sucking and other poor oral habits. About the tongue interposition between dental arches at rest, it was previously investigated in a sample of 36 pre-school children with primary dentition using conventional pacifiers, and it was observed in 38.9% of children (14 subjects out of 36) , a percentage higher respect to the present study of 12.63% (25 children out of 198).
In general, the low frequencies of poor oral habits in the present sample could indicate that the use of orthodontic pacifiers do not represent a promoting factor. Despite what reported about conventional pacifiers, it could be hypothesized that infants could experience improved safety and satisfaction due to the unrestricted sucking, as previously reported for breastfeeding  and thus no other sucking actions are needed, leading to a low frequency of fingersucking/thumbsucking and other poor oral habits in children using orthodontic pacifiers.
With regard to the prevalence of malocclusions, in the present study, all the various types of malocclusions hypothetically correlated to poor oral habits were summarized together in a unique variable (i.e. “malocclusions”). The logistic regression failed to evidence any correlation between orthodontic pacifier sucking and the presence of malocclusions in the present sample, as only the gender and the breastfeeding variables were significantly related to the prevalence of malocclusion (Table 2). Also, the duration of using orthodontic pacifier was not associated to the prevalence of malocclusions. This could be considered an interesting finding, as malocclusion in the deciduous dentition represents a risk factor for the necessary orthodontic treatment of permanent dentition .
In the present sample, 36 children out of 198 (18.18% of the sample) showed a posterior crossbite (28 children showed unilateral crossbite, and 6 children showed bilateral crossbite). The prevalence of posterior crossbite in children using conventional pacifiers varies from 12.8 to 88.9%, as evaluated in a recent systematic review . But in a sample of 55 children using orthodontic pacifiers, Lima et al.  reported only 4 cases out of 55 having posterior crossbite (7.27%). To explain the difference with the present sample, we should consider that Lima et al. recorded a very low prevalence of crossbite (6 children out of 55, i.e. less than 10% of the sample) even among children using conventional pacifiers. Thus, the results observed from Lima et al.  could be associated not only to the type of pacifier, but probably to the lower mean age of children, that was 28.2 ± 1.9 months (with an initial age range for selection of subjects indicated as 12–24 months) in their sample, while in the present study the age of the children ranged between 3 and 5 years. Furthermore, Lima et al. excluded subjects with enlarged adenoids or respiratory problems, with history of finger sucking, lip sucking, lip biting and lingual interposition, while in the present sample these exclusion criteria were not adopted. Thus, the percentage observed in the present sample appear more generalizable to the population of children adopting orthodontic pacifiers.
From the present data, no significant correlation was found out between the beginning of using orthodontic pacifier, its duration, and the frequency of crossbite. Previous literature based on conventional pacifiers, strongly correlates the posterior crossbite with the duration of the habit, until 4–6 years of age , and with the use of a pacifier for more than 36 months , more than 2 years , more than 15.5 months , or more than 1 year . The present observation suggests that the design of the orthodontic pacifier doesn’t promote the occurrence of posterior crossbite, even when used for more than 2 years.
Most of the previous literature state that with a long duration and high frequency of conventional pacifier usage, there is a tendency to hyperfunction of the buccinator muscle, which causes a deficiency in transverse growth of the maxilla and increased frequency of crossbites. Differently, orthodontic pacifiers are designed to avoid hyperfunction of the buccinator muscle. However, some previous studies on conventional pacifiers failed to evidence for an association between posterior crossbite and pacifier sucking. For example, Moimaz et al. could not find any statistically significant difference concerning posterior crossbite between the patients with or without previous usage of a pacifier at 12, 18, and 30 months, except when the posterior crossbite was associated with fingersucking [32,33,34]. The present data did not reveal any relationship between the orthodontic pacifier sucking and the posterior crossbite, even when associated with fingersucking/thumbsucking. The present findings suggest that the use of an orthodontic pacifier should be not correlated to the prevalence of malocclusions in primary dentition, differently from what reported in literatures concerning the usage of conventional pacifiers.
At the end, this fact could be substantiated that contrary to popular belief regarding pacifier usage, an orthodontic type of pacifier has no effect on neither development of malocclusion, nor poor oral habits, this can be one of the considerable points to make orthodontic pacifier more preferable to the conventional ones.
Limitations of the study
This observational study was subjected to some limitations. A longitudinal design with an additional follow-up would be useful, especially for monitoring those children that used the pacifier for more than 2 years. Anyway, it should be noted that the present report did not indicate any higher risk of malocclusion for children with more than 2 years of pacifier usage with respect to those children with less prolonged usage, that confounders were reported, and adjustments for non-nutritive sucking habits were performed, trying to avoid biased results. It should also be considered that owing to its design, this study could be susceptible to recall bias. Finally, as parents are unable to monitor their children for 24 h per day, there may be an underestimation of the true level of poor oral habits.