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  • Review
  • Open Access

The effect of pacifier sucking on orofacial structures: a systematic literature review

Progress in Orthodontics201819:8

https://doi.org/10.1186/s40510-018-0206-4

  • Received: 4 November 2017
  • Accepted: 3 March 2018
  • Published:

Abstract

Background

Non-nutritive sucking habits may adversely affect the orofacial complex. This systematic literature review aimed to find scientific evidence on the effect of pacifier sucking on orofacial structures.

Methods

A search on MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, and Web of Science databases was conducted to find all pertinent articles published from inception until February 2018, based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The quality of the studies was evaluated using the risk of bias judgements in non-randomized studies of interventions (ROBINS-I).

Results

Among the 2288 articles found, 17 articles met the selection criteria: seven prospective cohort studies, nine cross-sectional studies, and one randomized clinical trial. Using ROBINS-I, 12 studies were evaluated to have a serious overall risk of bias and five, a moderate one.

These studies claimed a strong association between a pacifier sucking habit and the presence of an anterior open bite and posterior crossbite. Functional/orthodontic pacifiers were shown to cause significantly less open bites than the conventional ones.

Conclusions

High level of evidence of the effect of sucking habits on orofacial structures is missing. The available studies show severe or moderate risk of bias; hence, the findings in the literature need to be very carefully evaluated.

There is moderate evidence that the use of pacifier is associated with anterior open bite and posterior crossbite, thus affecting the harmonious development of orofacial structures.

Functional/orthodontic pacifiers reduce the prevalence of open bite when compared to the conventional ones, but evidence is needed concerning the effects on posterior crossbite. Well-designed randomized controlled trials are needed to further analyze the effects of functional/orthodontic and conventional pacifiers on orofacial structures.

Keywords

  • Malocclusion
  • Pacifier
  • Non-nutritive sucking habits
  • Orofacial structures
  • Overjet
  • Open bite
  • Posterior crossbite
  • Systematic review

Background

The use of pacifiers is widespread among babies and children throughout the world. Pacifiers are frequently used to calm crying babies, to increase the well-being of the parents and babies, and to prevent thumb or finger sucking [1, 2]. The use of pacifiers in some developed countries is so culturally established that the prevalence is up to 42.5% in young children by the age of 12 months [3]. Pacifier sucking is a common non-nutritive habit and has received considerable attention over many years [1, 2].

Pacifiers were cited for the first time in medical literature in 1473, being described by German physician Bartholomäus Metlinger in his book “Kinderbüchlein,” retitled on later editions as “Ein Regiment der jungen Kinder” (“A Guide on Young Children”) [4]. Pacifiers consist of a latex or silicone nipple with a firm plastic shield and handle and are available in different forms and sizes. There are many types of pacifiers such as the conventional pacifier NUK® [5], the functional pacifier Dentistar® [6], and the orthodontic pacifier Curaprox Baby® [7]. However, a proper definition for a functional or orthodontic pacifier is missing.

According to non-randomized studies, the use of conventional pacifiers may impair the development of orofacial structures, cause infections, shorten the duration of breast-feeding, and produce dental malocclusions [2, 8, 9].

The effects of the use of pacifiers is duration and frequency dependent [10].

However, the use of pacifiers has been described as having a protective effect against Sudden Infant Death Syndrome [2, 3], but the level of evidence is very low [9], since no RCTs are available that has reliably tested the above mentioned hypothesis [11].

Pacifiers designed to cause less side effects, the so-called orthodontic pacifiers, have been introduced into the market [1215] or have been used to correct an already existing pacifier-associated open bite and increased overjet [16]. A systematic review comparing conventional and orthodontic nipples could not show significant differences on their effects on the stomatognathic system [9]. However, a recent randomized controlled trial has shown that a thin neck nipple reduces the occurrence of anterior open bite and increased overjet [16].

The purpose of this study was to systematically review the evidence of the scientific literature on the effects of pacifier sucking on orofacial structures, including the evidence of differences between orthodontic and conventional pacifiers.

Materials and methods

Search methods

The present systematic review was conducted and reported according to the Preferred Reporting Items for Systematic reviews and Meta Analyses (PRISMA) guidelines for reporting studies to evaluate health care interventions and Cochrane studies method [1719]. The first phase of this systematic review involved the development of a specific protocol and a research question based on the Population Intervention Control Outcome (PICO) format [20]. The quality of the studies was evaluated using the risk of bias judgements in non-randomized studies of interventions tool (ROBINS-I) [21].

Data collection and selection of studies

Two reviewers (KS, RK) independently searched the titles and abstracts of the following databases by using a standardized form: MEDLINE (via PubMed), EMBASE, Cochrane Central Register of Controlled Trials, and Web of Science. The keywords used to identify the relevant studies were pacifier, dummy, comforter, tooth, malocclusion, deciduous, tongue, swallowing, openbite, crossbite, myofunctional, muscle, and orofacial, and the different terms were combined using Boolean operators. Full texts of eligible studies were only obtained when both reviewers were in consensus.

Lack of agreement between the reviewers was resolved by discussion with a third reviewer who acted as an arbitrator. The selected studies and relevant articles were checked for cross references. The remaining articles were evaluated by reading the full text independently.

Selection criteria

The types of studies intended to be included in the search comprised randomized controlled trials (RCTs), cohort studies, intervention studies, case-control studies, and cross-sectional studies. No language restrictions were applied in this search. The minimum number of participants in the relevant subgroups of the study population was 30. There were no limitations on the date of publication or the place where the studies were carried out.

Type of participants

The participants of the reviewed articles included healthy babies and children who only had a pacifier sucking habit. The studies including subjects with craniofacial anomalies (e.g., cleft lip and palate), systemic diseases, or older infants undergoing or having had previous orthodontic treatment were excluded from this review.

Type of intervention

The studies which analyzed pacifier sucking effects on orofacial structures were included.

Type of outcome measures

The effects of pacifier sucking should have measurable documentation relating to any malocclusion and/or other anomalies in orofacial structures.

Data extraction

The two reviewers extracted data independently using a standardized form. The following factors were recorded when the information in the reviewed articles was available: study design, country where the study was performed, sample size, follow-up, age range, control group characteristics, examined dental and orofacial features with specific reference to anterior open bite, posterior crossbite, overjet, overbite, molar and canine relationship, and arch width. The level of evidence of each study was classified by means of the Oxford Centre of Evidence-Based Medicine [22]. The reviewers resolved any disagreement by means of discussion. In case of insolvable discrepancies, a third reviewer acted as an arbitrator.

Assessment of the risk of bias

The risk of bias was assessed according to the type of study available. Since only one RCT study was conducted on this topic, the assessment of the risk of bias was performed using the risk of bias in non-randomized studies of intervention (ROBINS-I) tool. It includes risk of bias due to confounding factors (lack of information on type of pacifier, start and finish of the habit, initial malocclusion, presence of digital or object sucking), selection of participants into the study, classification of interventions, deviations from intended intervention, missing data, measurement of outcomes, and selection of the reported results [21].

The reviewers ranked independently each included study and resolved any disagreement by reciprocal consulting.

Results

Results of the search

The initial electronic search resulted in 2288 studies after duplicates were removed. After screening the titles and abstracts, 2227 were excluded. From the remaining articles, 61 full-text articles were eligible for assessment. Seventeen articles published up to February 2018 could be included in this systematic literature review (Fig. 1): seven prospective cohort studies, nine cross-sectional studies, and one RCT [3, 8, 10, 1215, 2332]. Forty-four articles were excluded; 32 did not meet the inclusion criteria (non-healthy children included, undefined non-nutritive sucking habit, insufficient sample size, incorrect age group), 11 showed poor methodology (no control group, unclear measurement methods, unclear duration habit), and one was a finite element analysis. An overview of the most important data from the included studies is presented in Table 1.
Fig. 1
Fig. 1

Flowchart of the study selection process

Table 1

Summary of characteristics and results of the included studies

Study, year

Study design, country

Sample size

Follow-up

Age range (mean ± SD) in months

Characteristics of the control group

Examined orofacial structures

Results: Pacifier group

Results: Control group

Adair et al., 1995 [12]

Cross-sectional study, USA

218

No

24–59 (44 ± 9)

No sucking habits

AOB, PCB, overjet, molar and canine relationship

AOB: 16.7%**, PCB:15%*, overjet (≥ 4 mm): 20%*, class II primary canine relationship: 17.7%*, distal step molar relationship: 9.6%*

AOB: 3.1%, PCB: 5.1%, overjet (≥ 4 mm): 10.2%, class II primary canine relationship: 9.3%, distal step molar relationship: 3.6%

de Sousa et al., 2014 [23]

Cross-sectional study, Brazil

732

No

36–60

No pacifier sucking habits

AOB, PCB

AOB: 38.6.9%***, PCB: 18.2%***, AOB ≥ 36 months pacifier sucking: 73.5% vs < 36 months pacifier sucking: 19.5%***, PCB ≥ 36 months pacifier sucking: 25.5% vs < 36 months pacifier sucking: 15.5%*

AOB: 5.2%, PCB: 5.7%

Dimberg et al., 2010 [24]

Cross-sectional study, Sweden

457

No

36 ± 3

No sucking habits

AOB, PCB, overjet, class II canine relationship

AOB: 66%***, PCB: 25%***, overjet (> 4 mm): 28%***, class II canine relationship: 34%***

AOB: 1%, PCB: 1%, overjet (> 4 mm): 4%, class II canine relationship: 2%

Duncan et al., 2008 [10]

Prospective cohort study, Great Britain

867

0–61 months of age (questionnaire after 15, 24, and 36 months of age, clinical examination after 31, 43, and 61 months of age)

31, 43, and 61

No sucking habits

AOB, PCB, spaced labial segment

Pacifier sucking at 15 months: presence of AOB at 31, 43, and 61 months**, presence of PCB at 31, 43, and 61 months***, spaced upper labial segment at 61 months***, spaced lower labial segment at 31 months***

Pacifier sucking at 24 months: presence of AOB at 31, 43, and 61 months***, presence of PCB at 31, 43, and 61 months***, alignment of the upper labial segment at 43 and 61 months**, alignment of the lower labial segment at 31 months***

Pacifier sucking at 36 months:

presence of AOB at 43 and 61 months***, presence of PCB at 43 and 61 months ***, alignment of the upper labial segment at 61 months***, alignment of the lower labial segment at 43 months***

No data in paper

Facciolli Hebling et al., 2008 [25]

Cross-sectional study, Brazil

728

No

60

No pacifier sucking habits

AOB, PCB

AOB: 81.5%***, PCB: 27.1***

AOB: 11.85%, PCB: 13.73%

Katz and Rosenblatt, 2005 [26]

Prospective cohort study, Brazil

305

1 year

At the beginning average age: 48 ± 5

No sucking habits

AOB

AOB: 72% of the AOB group was pacifier sucking (initial examination) and 59% in the final examination*

AOB: 16% of the AOB group had no sucking habits (initial examination) and 23% in the final examination

Lagana et al., 2013 [27]

Cross-sectional study, Albania

2617

No

84–180

No control group

Molar and canine relationship

Molar and canine relationship: no statistically significant correlation

 

Lima et al., 2016 [15]

Prospective cohort study, Brazil

220

Birth up to the age of 29 ± 2 months; T1: birth, T2: questionnaire after 12–24 months, T3: clinical examination at the age of 24–36 months

24–36 (29 ± 2)

No pacifier sucking habits

AOB, PCB, overjet, molar and canine relationship, deep overbite

AOB: 96.3%**, PCB: 88.9%*, overjet (> 2 mm): 67.5%***, distal step of primary molar: 77.8%***, mesial step of primary molar: 6%***, flush: 85.7%***, deep overbite: 77.8%***

AOB: 3.7%, PCB: 11.1%, overjet (> 2 mm): 32.5%, distal step of primary molar: 22.2%, mesial step of primary molar: 64%, flush: 22.8%, deep overbite: 22.2%

Melsen et al., 1979 [28]

Cross-sectional study, Denmark

723

No

120–132

No sucking habits

AOB, PCB, overjet, molar and canine relationship, swallowing (normal swallow (NSW), tongue-thrust swallow (TTS), teeth-apart swallow (TAS), deep overbite

AOB: 8.5%, NSW: 0.6%, TTS: 34%, TAS: 12.4%, PCB: 14.1%***, NSW: 12.4%, TTS: 14.9%***, TAS: 17.1%*, increased overjet: 23.3%, NSW: 13.9%, TTS: 51.1%, TAS: 26%, bilateral distal occlusion: 41.4%***, NSW: 24.5%, TTS: 74.5%, TAS: 56.3%, mesial occlusion: 1.9%**, NSW: 2.2%**, TTS: 1.1%, TAS: 1.9%, deep overbite: 32%, NSW: 34.1%*, TTS: 22.3%, TAS: 33.5%

AOB: 5.2%, NSW: 1.4%, TTS: 25%, TAS: 9.5%, PCB: 3.1%, NSW: 2.8%, TTS: 0%, TAS: 4.7%, increased overjet: 15.9%, NSW: 7.4%, TTS: 50%, TAS: 38.5%, bilateral distal occlusion: 24%, NSW: 14.9%, TTS: 62.5%, TAS: 38.1%, mesial occlusion: 0%, NSW: 0%, TTS: 0%, TAS: 0%, Deep overbite: 25%, NSW: 22.4%, TTS: 11.7%, TAS: 38.1%

Moimaz et al., 2014 [3]

Prospective cohort study, Brazil

80

Birth up to 30 months of age (questionnaire after 12, 18, and 30 months of age, clinical examination at the 30 months of age

30

No control group

AOB, PCB, overjet, overbite (> 3 mm)

AOB and overjet (> 3 mm): pacifier sucking stop at 12***, 18, and 30***months, PCB: pacifier sucking stop at 12, 18, and 30 months, overbite (> 3 mm): pacifier sucking stop at 12, 18, and 30** months

 

Scavone et al., 2007 [29]

Cross-sectional study, Brazil

366

No

36–72

No pacifier- and finger sucking habits

PCB

PCB: 20.4%**, pacifier sucking until 2 years of age: 17.2%*, pacifier sucking until 4 years of age: 16.9%*, pacifier sucking until 6 years of age: 27.3%**

PCB: 5.2%

Schlomer, 1984 [30]

Cross-sectional study, Germany

582

No

36–72

No sucking habits

AOB, PCB, overjet (no significance data in the study) (no significance data in the study at all)

AOB: 22.8%, PCB: 12.8%, overjet (> 3 mm): 13.2%, pacifier sucking (NUK) stop until 3 years: 3–4 years of age: AOB: 15.2%, PCB: 23.9%, overjet (> 3 mm):10.9%, 5 years of age: AOB: 9.6%, PCB: 11.5%, overjet (> 3 mm): 1.9%, 6 years pf age: AOB: 2.7%, PCB: 10.8%, overjet (> 3 mm): 5.4% (no statistical significance for all mentioned data)

AOB: 2.1%, PCB 0.7%, Overjet (> 3 mm): 12.2%

Tibolla et al., 2012 [31]

Cross-sectional study, Brazil

237

No

36–168: Deciduous: 36–60, Mixed: 72–120, Permanent: 132–168

No pacifier sucking habit

AOB

AOB: 36.5%***, deciduous dentition: 65%***, mixed dentition: 37.3%**, permanent dentition: 23.4%*, > 2 years pacifier sucking vs ≤ 2 years: in deciduous dentition: 83.3% vs. 11.5%***, mixed dentition: 47.6% vs. 11.7***, permanent dentition: 25.9 vs. 9.4%, no or/and only to sleep vs. all the time in deciduous dentition: 17.2% vs. 88.9%***, in mixed dentition: 15.7% vs. 44.4%**, in permanent dentition: 10.7% vs. 25%

AOB: 7.2%, deciduous: 0%, mixed: 11.7%, permanent: 3%

Wagner and Heinrich-Weltzien [16]

Randomized clinical trial, Germany

86

3, 6, 9, and 12 months

16–24 months (20.3)

Weaned of pacifier with a pacifier-associated open bite or overjet ≥ 2 mm

AOB, overjet

Overjet 2.7 ± 0.5 mm, AOB − 1.2 ± 0.3 mm

Overjet 2.4 ± 0.5 mm, AOB − 0.8 ± 0.8 mm

Warren and Bishara, 2002 [32]

Prospective cohort study, USA

372

Birth until 5 years (questionnaire after 3, 6, 9, 12, 20, and 24 months of age, after that yearly, clinical examination: 54–60 months age)

54–60

No control group

AOB, PCB, overjet, molar and canine relationship, vertical overbite, arch width

AOB: 24–36 months pacifier sucking: lower prevalence than < 12 months**, PCB: 24–36 months had a higher prevalence of PCB than ≤24 months**, overjet (≥4 mm): 24–36 months pacifier sucking: lower prevalence than < 12 months, class II canine relationship: 24–36 months pacifier sucking: slightly higher prevalence than < 12 months, arch width and depths measurements: only small differences between < 12 months and 12–36 months pacifier sucking, vertical overbite (mm): not statistically significant between pacifier sucking less than 12 months, 12 to 24 months, and 24 to 36 months.

 

Zimmer et al., 2011 [13]

Prospective cohort study, Germany

121

0–26 months

16 ± 4

No pacifier sucking habit

AOB, overjet

AOB: NUK-group: 38%***, Dentistar group: 5%, overjet (mm): NUK-group: 1.7 ± 1.4, Dentistar group: 1.3 ± 1.0

AOB: 0%, overjet: 1 ± 1 mm

Zimmer et al., 2016 [14]

Prospective cohort study, Germany

121

12 months

20–36

No pacifier sucking habit

AOB, overjet, molar and canine relationship, deep overbite

AOB: NUK-group: 50%, Dentistar group: 6.7%, increased overjet: NUK-group: 19%, Dentistar group: 31.1%**, class II primary canine and molar relationship: NUK-group: 11.1%, Dentistar group: 4.8%, deep overbite: NUK-group: 2.4%, Dentistar group: 6.7%,

AOB: 0%, increased overjet: 5.9%, class II primary canine and molar relationship: 2.9%, deep overbite: 8.9%

AOB anterior open bite, PCB posterior crossbite, NSW normal swallow, TTS tongue-thrust swallow, TAS teeth-apart swallow

*p < 0.05; **p < 0.01; ***p < 0.001

Risk of bias of included studies

The risk of bias judgements in ROBINS-I including pre-, at-, and post-intervention domains are depicted in Table 2. Eleven non-randomized studies were evaluated to have an overall serious risk of bias, and four non-randomized studies and one RTC study had a moderate overall risk of bias.
Table 2

ROBINS-I (risk of bias judgements in non-randomized studies of interventions)

 

Confounding

Selection of participants

Classification of interventions

Deviations from intended interventions

Missing data

Measurement of outcomes

Selection of reported results

Overall

Adair et al., 1995 [12]

Serious

Serious

Moderate

Moderate

Moderate

Low

Low

Serious

de Sousa et al., 2014 [23]

Serious

Serious

Moderate

Moderate

Moderate

Low

Low

Serious

Dimberg et al., 2010 [24]

Serious

Low

Moderate

Moderate

Moderate

Moderate

Moderate

Serious

Duncan et al., 2008 [9]

Serious

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

Serious

Facciolli Hebling et al., 2008 [25]

Serious

Serious

Moderate

Serious

Moderate

Moderate

Moderate

Serious

Katz and Rosenblatt, 2005 [26]

Moderate

Serious

Moderate

Moderate

Low

Low

Moderate

Serious

Lagana et al., 2013 [27]

Serious

Serious

Moderate

Serious

Moderate

Moderate

Moderate

Serious

Lima et al., 2016 [15]

Moderate

Moderate

Low

Moderate

Moderate

Low

Moderate

Moderate

Melsen et al., 1979 [28]

Serious

Serious

Moderate

Serious

Moderate

Moderate

Moderate

Serious

Moimaz et al., 2014 [3]

Moderate

Moderate

Low

Low

Low

Low

Low

Moderate

Scavone et al., 2007 [29]

Moderate

Serious

Moderate

Moderate

Moderate

Moderate

Moderate

Serious

Schlomer, 1984 [30]

Serious

Serious

Serious

Serious

Serious

Serious

Moderate

Serious

Tibolla et al., 2012 [31]

Serious

Serious

Serious

Serious

Serious

Moderate

Moderate

Serious

Wagner and Heinrich-Weltzien, 2016 [16]

Low

Low

Low

Low

Moderate

Low

Moderate

Moderate

Warren and Bishara, 2002 [32]

Low

Low

Low

Low

Moderate

Low

Low

Moderate

Zimmer et al., 2011 [13]

Moderate

Moderate

Low

Moderate

Moderate

Low

Low

Moderate

Zimmer et al., 2016 [14]

Serious

Moderate

Moderate

Moderate

Moderate

Low

Low

Serious

Low comparable to a well-performed randomized trial, Moderate sound for a non-randomized study, but not comparable to a rigorous randomized trial, Serious presence of important problems, Critical too problematic to provide any useful evidence on the effects of intervention, Overall risk of bias equal to the most severe level of bias found in any domain

Effects of pacifier on anterior open bite (AOB)

The prevalence of AOB in children using pacifier varies between 8.5 [28] and 96.3% [15]. It is worth mentioning that not all studies analyzed the same age groups nor the same type of pacifiers (Table 1).

Fifteen out of the reviewed 17 articles showed a strong association between AOB and the use of a pacifier when compared with the children not using the pacifier [3, 10, 1216, 2326, 28, 3032]. Duration and frequency of pacifier sucking played an important role [10, 23, 31, 32]. The use of pacifier for more than 36 months was associated with AOB [10, 23]. Two studies showed that children who used a pacifier for more than 2 years were more likely to develop an AOB than children who used it for less than 2 years [10, 31]. One study showed that discontinuing the use of pacifier at 1 year of age may still result in an anterior open bite; however, this study had a serious risk of bias (Table 2) [3]. Tibolla et al. found that the presence of anterior open bite was statistically significantly higher in children using a pacifier during the day and night when compared to use at nighttime only [31]. However, Dimberg et al. could not support the above mentioned finding [24].

Effects of pacifier on posterior crossbite (PCB)

The PCB prevalence in children using pacifier varies between 12.8 [30] and 88.9% [15]. The use of pacifiers can lead to posterior crossbite according to nine of the reviewed articles [10, 12, 15, 2325, 2830]. However, Moimaz et al. could not find a statistically significant difference concerning posterior crossbite between the patients that used and those who did not use a pacifier at 12, 18, and 30 months except when the posterior crossbite was associated with finger sucking [3]. According to Scavone et al., the children who discontinued pacifier sucking by 2 years of age presented a lower prevalence of posterior crossbite (17.2%) than the ones that continued the pacifier sucking until 4 to 6 years of age (27.3%) [29]. De Sousa et al. showed that 25.5% of the children who used a pacifier for more than 36 months developed posterior crossbite compared to only 15.5% of the children who stopped pacifier sucking before 36 months of age [23]. However, both latter two studies presented a severe risk of bias.

According to Dimberg et al., 17% of the children who used a pacifier during the day had a posterior crossbite, compared to 23% of the children who used it at night and 31% of the children who used the pacifier during both day and night [24].

Effects of pacifier on overjet

Studies with severe and moderate risk of bias have shown that the prevalence of overjet is increased in children using a pacifier when compared with children who do not use a pacifier. Dimberg et al. found that an overjet of more than 4 mm was present in 28% of the pacifier users, compared with only 4% of children without any sucking habits [24]. Adair et al. reported that pacifier users had a higher average overjet of 4 mm (20%) than the group without a pacifier sucking habit (10.2%) [12]. A higher prevalence of overjet was associated with a pacifier sucking habit at 12, 18, and 30 months after birth [3]. Lima et al. found that the prevalence of overjet (> 2 mm) was higher in children with a pacifier sucking habit (67.5%) than in children who did not use a pacifier (35.5%) [15]. Other studies also found an association between pacifier sucking and increased overjet [13, 28, 32].

Effects of pacifier on molar and canine relationships

A distal molar and canine relationship was found in patients using a pacifier [12, 15, 24, 28]. Adair et al. and Dimberg et al. showed that distal molar and canine relationship had a statistically significant higher occurrence in patients using a pacifier than in children without using one [12, 15], whereas two studies have not found any strong association [14, 32].

Sagittal canine relationship showed no statistically significant differences in patients with a pacifier sucking habit when grouped according to habit duration [32].

Effect of pacifier on the dental arch

Warren and Bishara examined the effect of the duration of pacifier use on different dental arch measurements and found a statistically significant increased mandibular canine arch width and a statistically significant decrease in palatal depths [32].

Effect of pacifier on swallowing

The only study dealing with swallowing pattern was the one of Melsen et al. that presented a severe risk of bias. They found that the prevalence of abnormal swallowing patterns was higher in children with a pacifier habit. The majority of subjects using a pacifier had a normal swallowing (56.2%), whilst simple tongue-thrust occurred in 16.3% and complex tongue thrust in 27.5%. In the non-pacifier group, 69.8% of the children presented with a normal swallowing pattern and simple tongue thrust occurred only in 8.3% and complex tongue thrust in 21.9% [28].

Effect of different types of pacifier on orofacial structures

Among the five studies that assessed the effect of different types of pacifiers on the orofacial structures, three were classified as having a moderate overall risk of bias [13, 15, 16] and two a serious one [12, 14]. Functional orthodontic pacifiers seem to cause less dental malocclusion than conventional ones (Table 3) [1216].
Table 3

Effects of different types of pacifiers on orofacial structures

Study

Age of examination in months

Pacifier type 1

Pacifier type 2

Examined orofacial structures

Results (%)

Statistical significance (p value)

Pacifier type 1

Pacifier type 2

Adair et al., 1995 [12]

24–59 (43.9)

Functional exerciser

Conventional pacifier

AOB

13.4

23.7

0.19

   

PCB

15.9

13.2

0.79

   

Overjet (≥4 mm)

23.2

13.2

0.23

   

Class II primary canine relationship

26.8

5.3

0.01

   

Class II primary molar relationship

15.9

2.6

0.04

Lima et al., 2016 [15]

24–36 (29.0 (±2.0 SD))

Orthodontic pacifier

Conventional pacifier

AOB

44.3

55.7

0.03

   

PCB

37.5

62.5

0.72

   

Overjet (> 2 mm)

42.9

57.1

0.11

   

Class II primary molar relationship

28.6

71.4

0.78

   

Flush of primary molar relationship

41.7

58.3

0.78

   

Deep overbite

64.3

35.7

0.23

   

Diastema

55.6

44.4

0.32

   

Crowding

66.7

33.3

> 0.999

Wagner and Heinrich-Weltzien, 2016 [16]

16–24 months (20.3)

Thin neck pacifier (TNP)

Conventional or physiological

AOB

Overjet (≥2 mm)

−1.2

2.7

−2.2

3.2

< 0.001

< 0.001

Zimmer et al., 2011 [13]

15.9 (± 3.9 SD)

Dentistar

NUK

AOB

5

38

< 0.001

   

Overjet (mm), mean ± SD

1.3 ± 1.0

1.7 ± 1.4

> 0.05

Zimmer et al., 2016 [14]

20–36 months

Dentistar

NUK

AOB

6.7

50

0.00

   

Increased overjet

31.1

19.0

0.23

   

Class II primary canine and molar relationship

4.8

11.1

0.29

   

Deep overbite

6.7

2.4

0.47

AOB anterior open bite, PCB posterior crossbite

Wagner et al. found that the use of a thin neck pacifier decreases the occurrence of open bite and increased overjet [16]. The prevalence of anterior open bite was higher in children who used a NUK® pacifier compared to the Dentistar® pacifier, the latter having a thin neck [13, 14]. The same authors found an increased overjet in 31.1% of the children who used a Dentistar® pacifier and only in 19% of probands using the NUK® pacifier [14]. Lima et al. showed that the prevalence of anterior open bite, overjet, posterior crossbite, and distal step of primary molars were larger in children who used conventional pacifiers compared to orthodontic pacifiers [15]. Children using a conventional pacifier presented an increased prevalence of anterior open bite when compared to children using a functional exerciser. However, no statistically significant differences were found in the prevalence of posterior crossbite between these two groups of pacifiers. The prevalence of an overjet of 4 mm or more and the occurrence of distal primary molar and canine relationships was higher in children using a functional exerciser when compared to the group of children using a conventional pacifier [12].

Self-correction of malocclusion

In a cross-sectional follow-up study, Katz and Rosenblatt found that 23 out of 30 children who discontinued the non-nutritive sucking showed a self-correction of the open bite. However, self-correction of an open bite was observed also in children (6 out of 17) without non-nutritive sucking habits [26].

Discussion

This systematic review revealed a lack of high-quality evidence in publications dealing with the effects of pacifier sucking habits on orofacial structures.

In the hierarchy of evidence, the randomized controlled trials are on the top, cross-sectional studies come in the middle, and retrospective studies are at the bottom [11]. A single randomized clinical trial was found in the literature showing an improvement of the overjet and overbite in children presenting a pacifier-associated open bite and increased overjet when using a thin neck pacifier, when comparing with children still using the usual pacifier or discontinuing the habit [16]. In our review we needed to include non-randomized cohort studies and cross-sectional studies due to the lack of sufficient number of randomized controlled trials examining the association between pacifier sucking and its effects on the orofacial structures. We considered as cohort studies also those without a control group, as defined by Dekkers et al. [33]. The risk of bias of non-randomized cohort and cross-sectional studies was assessed to be from moderate to serious, and the conclusion of those studies has to be considered with substantial caution when analyzing the findings of the studies included in this systematic review of the literature (see Table 2).

The ROBINS-I assessment tool is based on the Cochrane RoB tool for randomized trials and was used due to the fact that we found in our search only one study that was a true randomized trial. Other studies were defined as randomized according to the authors, but a thorough review revealed in reality severe risks of bias. The ROBINS-I assessment tool uses the domain-based assessment and has a comprehensive manual in which users can interpret the results in a similar way, thus reducing the risk of subjective evaluation.

Our assessment is in accordance with the findings of Dogramaci and Rossi-Fedele [8], despite the fact that we focused only on the effect of pacifiers and not on non-nutritive sucking habits in general. They concluded that the use of pacifiers in the deciduous dentition is cause of malocclusions [8]. Our review, although with moderate and serious overall risk of bias, shows that the use of pacifiers seems to be associated with anterior open bite [1215, 2326, 30, 31] and posterior crossbite [10, 12, 15, 2325, 2830].

We focused specifically on the influence of pacifiers on orofacial structures, since the so-called functional/orthodontic pacifiers seem to be a promising tool to limit their negative influence on the occlusion [7, 13, 14, 16]. However, the lack of sufficient number and quality of randomized clinical trials on the effect of pacifiers on the occlusion weakens the evidence. On the other hand, it has to be taken into consideration that well-designed randomized clinical trials might raise ethical concerns and interactions with other factors may make the control of concomitant variables difficult [34]. The only systematic literature review available on the difference between conventional and orthodontic nipples was not able to draw any conclusion due to the low level of evidence of the available studies [9]. However, Wagner and Heinrich-Weltzien have recently shown in a randomized clinical trial that a thin neck nipple reduces the occurrence of open bite and increased overjet [16]. The effect of the nipple on the transverse dimension was assessed by Adair and Lima et al. who found that the functional/orthodontic pacifiers under investigation do not induce less posterior crossbites than the conventional ones [12, 15].

The duration and frequency of pacifier sucking was not examined in all the studies, although playing a role in the developing of malocclusions [10, 23, 31, 32]. The data regarding the duration often relies on the information provided by parents or guardians, and therefore, the uniformity of data collection could be affected. Tools able to quantify the duration of pacifier use should be developed in order to properly control the time factor on the generation of malocclusion traits.

Different studies disagreed on the correlation between pacifier use and increased overjet [3, 12, 13, 15, 24, 28, 32], and the majority of them showed a serious overall risk of bias.

Conclusions

A high level of evidence on the effects of pacifier habits on orofacial structures is non-existent.

However, there is moderate evidence that the use of pacifier is associated with anterior open bite and posterior crossbite, thus affecting the harmonious development of orofacial structures.

Taking into consideration the present evidence, it seems that pacifiers with thin neck induce less open bite than the conventional ones. Functional/orthodontic pacifiers investigated in the literature seem not to reduce the occurrence of posterior crossbite. New nipple shape and texture are needed to counteract the narrowing of the palate.

Randomized controlled trials are strongly needed to further analyze the effect of conventional and functional/orthodontic pacifiers on orofacial structures.

Abbreviations

AOB: 

Anterior open bite

PCB: 

Posterior crossbite

PICO: 

Population Intervention Control Outcome

PRISMA: 

Preferred Reporting Items for Systematic reviews and Meta Analyses

RCT: 

Randomized controlled trials

ROBIN-I: 

Risk of bias in non-randomized studies of interventions

Declarations

Acknowledgements

We are grateful to Dr. J. Ball for her valuable support while proofreading the language.

Authors’ contributions

KS, RK, PN, and CB reviewed the information of the article. KS, PN, and CB drafted the manuscript. CV contributed to the conception of the study and critically edited the manuscript. All authors have read and approved the final paper prior to its submission.

Ethics approval and consent to participate

Not applicable

Consent for publication

Not applicable

Competing interests

The authors declare that they have no competing interests.

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Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors’ Affiliations

(1)
Department of Orthodontics and Pediatric Dentistry, University Center for Dental Medicine Basel, Hebelstrasse 3, 4056 Basel, Switzerland

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