Influence of pacifier design on pacifier-palate contact: a finite element analysis

Abstract

Objective

The study compares the contact pressure and pressure distribution of various pacifier shapes on the palatal surfaces of newborns and six-month-old infants using nonlinear finite element analysis (FEA). Additionally, it seeks to assess the extent and pattern of interaction between pacifier designs and the lateral and medial zones of the palates.

Materials and methods

3D finite element models of four pacifiers (A = NUK^®, B = MAM^®, C = BIBS^®, D = CURAPROX^®) of newborn and six-month-old palate and tongue were developed. The palate geometries were based on dental stone impressions of a neonate and six-month-old infant. The pacifier designs were digitized using computed tomography and analyzed in ANSYS Mechanical 2024 R1 (Ansys, Inc., Canonsburg, USA). Hyperelastic silicone rubber properties were used, while the palate and tongue were modeled as rigid and the mucosa as flexible. The interaction between different pacifier designs and the palate of a newborn was assessed through deformation, contact area, and contact pressure relative to the vertical tongue displacement in the anterior, medial, and lateral zones of the palates.

Results

Pacifier D exhibited the highest lateral and medial pressures on both the newborn and six-month-old palates with its broad-winged design. Pacifiers A and B showed moderate but steady increases in lateral pressure. In contrast, pacifier C showed concentrated pressure in the anterior zone with its distinct, rounded shape, particularly on the newborn palate. Pressure distribution patterns differed significantly between pacifier designs, with pacifier D showing the most extensive and uniform pressure distribution across the palate.

Conclusions

Pacifier design significantly influences palatal interaction, with broader shapes resulting in higher pressure concentrations on the lateral sides that may affect the transversal palate dimension. Understanding the biomechanical impacts of pacifier use is the first step in giving valuable insights to both clinicians and parents in making informed decisions regarding pacifier selection to support optimal oral development. Further clinical studies are needed to validate these findings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13005-025-00525-6.

Introduction

Pacifiers are widely utilized in infant care to soothe and satisfy the innate sucking reflex, which is crucial for early feeding and oral development [1]. Beyond their immediate calming effects, pacifiers have been associated with a reduced risk of sudden infant death syndrome (SIDS) when used during sleep [2]^,. However, concerns have emerged regarding prolonged pacifier use and its potential impact on oral and dental structures, particularly the development of malocclusions such as anterior open bite, posterior crossbite, and narrow palates [3]^, [4]^, [5]. These observations underscore the importance of understanding the interactions between pacifier designs and the developing orofacial structures of infants.

Various designs, materials, and shapes are available for commercially produced pacifiers intending to balance comfort and oral health considerations [6]^, [7]^, [8]. The so-called orthodontic pacifiers facilitate natural oral development by distributing forces evenly across the palate, thereby reducing the risk of dental malformations [7]^, [9]. In contrast, conventional pacifiers often prioritize comfort without incorporating specific design features to support palatal development. Despite the variety of designs available, there is a dearth of knowledge regarding the biomechanical interactions between these devices and the developing palate, particularly during periods of rapid growth [10]^, [11].

The infant palate is highly malleable, making it susceptible to deformation by external forces [12]. By six months of age, the process of ossification and growth increases the stiffness of the palate, altering its mechanical response to external pressure [13]. In addition, in newborn babies, the mid-palatal suture of the palate is not yet interdigitated, meaning that external influences can affect its development more easily than at later stages [14]. It is imperative to comprehend these developmental alterations to evaluate the long-term impact of pacifier utilization on oral health. Observational and clinical studies have identified correlations between prolonged pacifier use and dental malformations; however, the specific biomechanical mechanisms underlying these outcomes remain unclear [5]. This deficiency in the existing literature emphasizes the necessity for comprehensive biomechanical studies to inform evidence-based pacifier design and utilization guidelines.

Finite element analysis (FEA) can be used to investigate the biomechanical interactions between pacifiers and the infant palate [10]^, [15]. FEA allows for the simulation of deformation, stress distribution, and contact pressures and distribution on the palates of newborns and six-month-old infants without having to perform in vitro or in vivo testing [8]. Although FEA has been extensively applied in orthodontics to study appliances and craniofacial biomechanics, its application to pacifier-palate interactions remains underexplored [16]. Recently, studies have utilized FEA to evaluate the mechanical behavior of various pacifier designs, demonstrating its effectiveness in assessing functional mechanics and influencing recommendations for improved pacifier performance and safety [11]. Meanwhile, the thin morphology of the anterior portion of the pacifier has been found to cause less anterior open bite [17]. It is still unclear which pacifier morphology exerts lateral pressure. Verifying the best morphology that exerts pressure in the lateral direction is crucial, as using the pacifier may cause a narrow palate leading to crossbite. A high palatal vault has also been associated with SIDS [5].

Despite the variety of pacifier designs available, there is still a significant lack of knowledge regarding how specific morphological features influence biomechanical interactions with infant palates at different stages of development. The objective of this study is to utilize FEA to assess the mechanical interactions between diverse pacifier designs and different areas of the palates of newborns and six-month-old infants. Null hypothesis (H₀): There is no significant difference in palatal pressure distribution patterns across the anterior, medial and lateral zones among different pacifier designs and geometries. Rejecting this hypothesis would suggest that pacifier morphology affects the magnitude and location of contact pressures exerted on the infant palate. The findings will contribute to formulating evidence-based guidelines for pacifier use, thus facilitating parental decisions and supporting manufacturers in optimizing designs for oral health.

Materials and methods

Pacifier design and digitization

Three distinct geometries were employed for each finite element model: the pacifier bulb, tongue, and palate. The palate geometries were derived from dental stone impressions obtained from a newborn and a six-month-old child using a soft silicone material. The impressions were taken by trained clinicians to ensure safety and comfort of the infants, and the technique did not require full mouth opening. Dental stone impressions were collected from clinically healthy, full-term infants with no congenital abnormalities: one newborn aged 0–2 weeks and one six-month-old infant. Only those with typical oral anatomy, normal birth weight, and no history of surgery or congenital defects were included. The selected models were gender-neutral in design; gender was not considered a variable in this biomechanical analysis, as the objective of the study focused on the influence of pacifier design rather than patient-specific anatomical variations. Exclusion criteria included structural anomalies of the palate or medical conditions known to influence orofacial development. The impressions mentioned above were subsequently digitized and are presented in Fig. 1 and Additional file 1: Video clip. As can be seen in Fig. 2, four different morphologies were chosen and characterized by:

Fig. 1.

Digitized top and side views of the palate models for newborn (left) and six-month-old (right) infants, with frontal (green), medial (blue), and lateral (violet) zones highlighted. Scale bar = 10 mm

Fig. 2.

Newborn pacifiers: (a–d) Isometric views of pacifiers A, B, C, and D; (e–h) inferior-to-superior views; (i–l) cross-sectional views showing the palate (mucosa in red, bone in ivory) and tongue (pink). Scale bar = 10 mm

• A.A thin, flat “neck” and a round, flat nipple (NUK^®).
• B.A thin, flat “neck”, but a spherical nipple (MAM^®).
• C.A round, non-flat “ neck” and a spherical nipple (BIBS^®).
• D.A thin, flat “neck” and a flat, rectangular nipple (or trapezoidal, in the case of morphology at 6 months, CURAPROX^®).

The pacifiers were digitized using cone beam computed tomography (CBCT) ProMax 3D Max (Planmeca, Helsinki, Finland). In the case of the newborn model, smaller-sized pacifier bulbs were employed for pacifier models A, B, and D.

Based on the CBCT scans, the pacifier shapes were segmented and converted into standard tessellation language (STL) files. The geometries, as mentioned earlier, were subsequently simplified and converted into ISO 10,303 Standard for the Exchange of Product model data (STEP) files utilizing the “Auto Skin” tool in ANSYS SpaceClaim 2023 R2 (Ansys, Inc., Canonsburg, USA). Figures 2 and 3(a–h) illustrate the finalized designs of the pacifiers.

Fig. 3.

Six-month-old pacifiers: (a–d) Isometric views; (e–h) inferior-to-superior views; (i–l) cross-sectional views showing the palate and tongue. Scale bar = 10 mm

Palate and tongue modeling

To eliminate the confounding variable related to the potential asymmetry of the palate, following the digitization of the models, the palate of newborns and 6-year-olds was made symmetrical by duplicating and mirroring one half of the palate.

In order to simulate the biomechanical interactions, the palate geometry was altered to include a mucosal layer of 1.5 mm over cancellous bone [10]. This was accomplished by displacing the upper surface of the palate geometry by a distance of 1.5 mm into the palate and subtracting it from the geometry. Furthermore, a tongue shape was designed to induce the deformation of the pacifier. A symmetry plane was introduced, and all models were sectioned in half and mirrored in order to reduce the computational demand (see Figs. 2 and 3(i–l)).

Finite element model

A comprehensive finite element mesh was constructed, as illustrated in Fig. 4. For contact areas, a mesh resolution of 0.25 mm was used. The maximum mesh size for the tongue and pacifier models was 1 mm, while the palate and mucosa had a coarser mesh size of 2 mm.

Fig. 4.

(a) Cross-sectional and (b) isometric finite element mesh for newborn palate, mucosa, tongue, and D pacifier

Boundary conditions and simulation setup

The palate was fixed at its superior surface, and the extremities of the tongue and pacifier were constrained along the vertical (Y-) axis. The vertical movement of the tongue was simulated using a displacement-driven approach along the Y-axis, whereby the displacement was modeled as an upward remote displacement.

Material properties

As the pacifiers’ material composition was unknown, it was assumed that they were composed of conventional silicone. The material properties were modeled based on the specifications of ELASTOSIL^® LR 3038/40 K1 CN silicone rubber, as supplied by Wacker Chemie AG, Germany. A third-order Yeoh model was employed to incorporate hyperelastic and nonlinear material behavior, which is suitable for capturing the significant deformation characteristics of silicone elastomers.

The strain energy density function 𝑊 was defined as:

The material parameters were derived from the tensile data reported in the supplier’s material data sheet [18]. Material constants were C₁₀ = 4964.4 Pa, C₂₀ = 0.00319 Pa, and C₃₀ = −1.5551 × 10^(− 10) Pa. The palate and tongue were modeled as rigid bodies, meaning they were assumed to undergo no deformation under load. These structures contributed to contact interactions but did not experience internal strain or stress. The mucosa was assigned Young’s modulus of 1 MPa, a Poisson’s ratio of 0.45, and a density of 1100 kg/m³.

Data collection and output

The contact area and pressure during the vertical movement of the tongue were recorded and exported as comma-separated value (CSV) files for further analysis.

Results

Newborn palate-pacifier interaction

The interaction between various pacifier designs and the palate of a newborn was evaluated through an analysis of deformation, contact area, and contact pressure relative to the vertical tongue displacement. The data is presented in four panels in Fig. 5 (a, b, c, and d), each representing a different interaction aspect.

Fig. 5.

Newborn Palate: (a) Deformation (mm), (b) contact area (mm²), and (c) contact pressure (kPa) results for the pacifier interaction relative to the vertical tongue displacement for NUK^® (A), MAM^® (B), BIBS^® (C), and CURAPROX^® (D) pacifier bulbs. The frontal, medial, and lateral, zones of the palate are highlighted in green, blue and purple, respectively. In (d), each pacifier bulb’s contact pressure (kPa) is shown for specific palate zones: frontal, medial, and lateral, with a vertical tongue displacement of up to 7 mm toward the six-month infant palate. Additionally, the plot shows the total reaction force (red) required to achieve a maximum tongue displacement of up to 7 mm for each pacifier bulb

The pacifiers that undergo deformation are, in order, A, C, B, and D. The pacifiers B and D undergo more posterior deformation, while A and C undergo more central deformation. This deformation is reflected in the distribution of the palate contact area. The little anterior deformation of pacifier D generates insignificant anterior contact, becoming more present in pacifiers B, C and A, in that order. Significantly, pacifier A has large central and lateral contact areas, while pacifier C has no lateral and posterior contact areas. Pacifier B has a larger contact area in the posterior region, while pacifier D has more extensive lateral than posterior contacts.

The pressure exerted is most significant in pacifier A, followed by D, while C and B show almost half the pressure. As depicted in Figs. 5c and d, the relatively high pressure in pacifier D is exerted on the lateral aspect of the palate, whereas the other pacifiers showed more deformation towards the frontal palate. It must be noted that the pressure zones in pacifier C are mainly in the front area. The most significant difference between the pacifiers is found in the lateral pressure. Pacifier D already exerts lateral pressure after 2 mm of vertical activation and quickly reaches 5.5 kPa, remaining constant even at larger displacements. Pacifier A exerts the lateral pressure more gradually. Pacifiers B and D, in comparison, exert a considerably lower lateral pressure and higher vertical displacements of 4 and 5.5 mm, respectively.

The medial pressure in the palate is present after 3.5 mm of vertical displacement in pacifiers B, C, and D. It is approximately 1-1.5 kPa. In contrast, in pacifier A, it is present after 5 mm of vertical displacement but is twice as high.

The anterior pressure in the latter and pacifier B is already exerted after 1.5 mm vertical tongue movement, whereas in A, this occurs after more than 3 mm. No anterior pressure is detected in pacifier D. The magnitude of the maximum anterior pressure exerted by pacifier A and C is 3.5 kPa, equivalent to 5 g of force.

Six-month-old infant palate-pacifier interaction

The interaction between different pacifier designs and the palate of a six-month-old infant was assessed through deformation, contact area, and contact pressure relative to the vertical tongue displacement. The data is presented in Fig. 6(a, b, c, and d), each illustrating different aspects of the interaction.

Fig. 6.

Six-month-old palate: (a) Deformation (mm), (b) contact area (mm²), and (c) contact pressure (kPa) results for the pacifier interaction relative to the vertical tongue displacement for NUK^® (A), MAM^® (B), BIBS^® (C), and CURAPROX^® (D) pacifier bulbs. The palate’s frontal, medial, and lateral zones are highlighted in green, blue, and purple, respectively. In (d), each pacifier bulb’s contact pressure (kPa) is shown for specific palate zones: frontal, medial, and lateral, with a vertical tongue displacement of up to 7 mm toward the six-month infant palate. Additionally, the plot shows the total reaction force (red) required to achieve a maximum tongue displacement of up to 7 mm for each pacifier bulb

The maximum deformation location in pacifier A is more anterior, while it is more posterior in pacifier D, which also has the least deformation in the anterior zone.

The contact areas with the palate are distributed in a circle in pacifiers A and B, with larger areas in pacifier B. Pacifier C, on the other hand, has the most extensive contact areas, mainly medial and anterior. An opposite pattern is shown in pacifier D, with broad lateral contact areas, followed by less wide median and absent anterior areas.

The pacifier exerting the greatest pressure is D, reaching approximately 0.25 N reaction force at 7 mm vertical tongue displacement, followed by A, B, and C. The most significant pressure in pacifier C is exerted in the lateral areas, starting at 2 mm of vertical displacement and maintaining a plateau up to 5 mm, then increasing rapidly. Lateral pressure is also present in pacifiers A and B after minimal vertical displacement of the tongue but does not reach amounts comparable to D. Pacifier C exerts no lateral pressure. Pacifier C also shows low medial pressures and only at high vertical tongue displacements. In contrast, pacifier B reaches the same amount of medial pressure (approx. 1 kPa) at 4 mm. A higher medial pressure is shown in pacifier A, but only at 5 mm upward tongue displacement and reaching max. 2.5 kPa.

Both pacifiers A, B, and C exert anterior pressures, but pacifier C already exerts it at minimal vertical movements, followed by pacifiers B and A. The latter, however, at 3 mm vertical activation, exerts a higher anterior pressure than B and C. Pacifier D exerts almost no anterior and medial pressure, except after 6 mm of vertical activation.

Discussion

The interaction between pacifiers and the developing palate represents a critical factor in understanding their potential impacts on oral health, particularly for the changes in palate shape and the development of malocclusions. The two major malocclusions provoked by pacifiers are open bite and posterior transversal deficit of the maxilla, leading to posterior crossbites [9]. In comparison, the literature confirms that a thin neck morphology can create a reduced anterior open bite [4]. A morphology that can generate less transversal deficit has not been investigated yet.

FEA is a valid and reliable method that has been previously used in the analysis of mechanical behavior of pacifiers [6]^, [7]^, [8]^, [11]. Since scientific validation of the pacifiers placed on the market to support oral health prevention policies is necessary, quantification through an FE analysis is beneficial for assessing the pacifier biomechanics. This is the first FEA study in which a pacifier morphology able to exert transversal forces has been investigated. Our study analyzed the deformation, contact area, and contact pressure on the palate at two different ages, specifically focusing on different palate areas. Since the localization of the deformation causes different malocclusions (anterior open bite or transversal crossbite), this approach enabled us to identify morphologies that potentially influence the occurrence of one malocclusion rather than another. The findings demonstrate discrepancies between pacifier designs with regard to their pressure exertion and distribution, which could have long-term ramifications for orthodontic development and oral health.

Our study showed that pacifiers D, which have a flat and trapezoid morphology, exert more lateral pressure on the palate than the other pacifiers, aligning better with the infant palate growth, which is from 0 to 6 months more significant in the transversal dimension [14]. The flat and trapezoid morphology of pacifier D aids in the even distribution of pressure across the palate, which supports the expected growth of the maxillary arch and reduces the likelihood of developing malocclusion [12]. In contrast, pacifiers with narrower designs, such as pacifiers A and C, exert pressure more localized anteriorly and medially, which may contribute to malocclusions like anterior open bite or posterior crossbite [4].

Similarly to our study, Tesini et al. compared through an FE Analysis the mechanical behavior of pacifiers of different designs and sizes using age-specific palatal models subjected to tongue function, including so-called orthodontic and conventional pacifiers [11]. They, too, have found that it is the design and size of the pacifier that determines the contact (area and force) between the pacifier and palate during peristalsis and under intraoral pressure, and the so-called orthodontic pacifier exerts more force in the lateral sides. Differently from Tesini et al., we did not use the definition provided by Hoff et al. [12] since we specifically wanted to focus on the anterior, median, and lateral sides. We added in our simulation one substantially different morphology compared to other pacifiers, observing that the more flat and trapezoid morphology can exert forces that are less anteriorly and more laterally located, especially in the 6-month-old morphology where the pressure is more significant and widely spread on the lateral areas. We could also confirm that the round, symmetrical cylinder morphology [7]^, [8], provoking the so-called “round passage,” exerts a more upward directed force and pressure also localized in the anterior area, differently to the pacifier with a thin neck, the so-called “thin passage” that exerts less anterior pressure. Such latter morphology is prone to cause a less open bite [17]. The lesser the round morphology, the more the forces are exerted laterally, as shown in Fig. 6. Of particular interest is that the only morphology that can exert a significant amount of lateral force at vertical excursions of the tongue of more than 4 mm is the one of pacifier D, having, therefore the most important potential of generating less transversal discrepancy. Generating a constricted upper arch is of particular concern when considering the relationship between pacifier design and sudden, unexpected infant death. Narrower palates have been observed in infants who succumb to SIDS, underscoring the critical need for pacifiers that support proper palatal development [19]^, [12]^, [20]. Pacifiers with varying nipple diameters influence tongue movement and affect palate development [14]. Pacifiers with broader, more flexible, and flat nipples, as in D, would probably force the tongue less caudally compared to the round ones, allowing the tongue to move freely and promoting proper tongue-palate movement.

Strengths and limitations of this study

1. This analysis is performed using different vertical tongue displacements, simulating the dynamic process related to the rhythmic displacement of the pacifier against the palate. The movement of the tongue has been considered mainly vertical, since the sucking movements in NNS is mainly vertical. Compared to nutritive sucking, in fact, where the anterior-posterior movement is necessary to effectively reduce the success of the milk from the nipple, the NNS sucking movement is predominantly rhythmic and vertical (Additional file 2: Video clip).

2. Analysis related to different areas of the palate to identify possible side effects (anterior open bite or crossbite) according to the morphology of the nipple. These results guide the practitioners and the parents in making an informed choice.

3. The limitations are those typical of a finite element analysis. Individual anatomical variability cannot be considered. Only one dental stone impression was used for each age group (newborn and six-month old), which limits the ability to account for inter-individual anatomical variability. In our simulation, to focus attention solely on the morphology of the nipple, we made the models of the palate symmetrical to eliminate variables related to the variability present not only between subject and subject but also within the same individual. Additionally, we assumed that all pacifiers were made of the same silicone material. This assumption may not be entirely accurate, as variations in material composition and mechanical properties could influence the deformation behavior. A more detailed material characterization would be necessary to verify whether differences in silicone formulations affect the mechanical response observed in our simulations.

4. Although extraoral models were used, they were based on real infant impressions to ensure anatomical relevance. In vivo validation is required in future to confirm clinical applicability.

Conclusion

Our results in the study emphasize the necessity of evaluating pacifier design to ascertain its potential influence on oral health. The results of this study indicate that the more flat and trapezoid morphology can exert forces that are less anteriorly and more laterally located. This may facilitate a more balanced interaction with the palate and promote healthy oral development in infants. The evidence highlights the necessity for further clinical studies to validate the biomechanical findings and refine recommendations for pacifier use in infant care.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Author contributions

M.M. and P.N. conducted investigations and experiments, wrote the main manuscript, and prepared all figures and videos. C. V. and F.M.T. participated in the conceptualisation, reviewing, and supervision of the experiments. All authors reviewed the manuscript.

Funding

Open access funding provided by University of Basel. Open access funding provided by University of Basel. The study received no funding.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Informed consent

Not applicable.

Competing interests

The authors declare no competing interests.