This is the first study (based on the authors’ literature review) that applies nonlinear, dynamic finite element analyses to calculate the area and force of palatal contact under peristaltic action of the tongue and intraoral pressure of NNS. The results give new insights into the need to define pacifier fit by using the metrics of both size (e.g., bulb width) and the design (e.g., geometric, mechanical, physiological) of the individual pacifier.
The tongue and pacifier bulb interact with the palatal vault, Tektal wall (lateral palatal shelves), and anterior and peripheral alveolar pads during NNS. Variations in size and design (conventional or orthodontic) cause different patterns of palatal support against the Tektal wall and the palatal vault.
Commercially available orthodontic pacifiers vary in size, shape, and physiologic design. For example, the TB and TT pacifiers are of different “orthodontic” design but, in general, behave similarly with respect to their palatal interaction. Their mechanical behavior, however, is substantially different from conventional pacifiers such as the Soothie.
The conventional size 1 S pacifier in the 0-month palate shows greater contact and force in the PV area by nature of its design and size in comparison to the TB and TT orthodontic pacifiers. Because the 0-month palate is small, all three pacifiers came into contact with the TW; however, the TT showed the greatest area of contact and force against the Tektal wall.
For the orthodontic size 2 bulbs in a 12-month palate, there is contact on the TW by the TT and TB pacifiers but no contact by the S pacifier. Both size and design have limited this contact. The force is predominantly distributed in the PV. A pacifier that is too small, regardless of the design, is one whose bulb does not contact in the TW (lateral palatine area) under peristaltic tongue movement and intraoral pressure.
For the orthodontic size 3 TB bulb in a 22-month palate (Fig. 7) the greatest contact area/force was seen in the TW. Surprisingly there is no contact of this bulb in the PV of the 12-month palate. This is due to the fact that the geometric angled design provided an observable fit profile in both FEA and image-collisions analysis . This observation highlights the need to evaluate the differences in design of one brand’s pacifier to another and shows that orthodontic pacifiers cannot be placed into a single stratified “orthodontic” pacifier grouping.
Most significantly, the fit of the pacifier in different-aged palates shows large differences in palatal contact and force when the same pacifier is evaluated in different-aged palates, as shown in Fig. 8. As growth of the palate progresses, contact area/force profiles change. The loss of any contact in the Tektal wall which favors contact in the palatal vault area may contribute to palatal atresia as seen in palatal grooving caused by oro-tracheal tubes . For example, a size 2 S pacifier in a 12-month palate resulted in no Tektal wall contact. Likewise, the size 1 TT has lost contact with the Tektal wall in the 22-month palate. This supports the concern that chronological age sizing may not present reliable recommendations across all brands.
The difficulty in making comparisons with previous FEA studies is due in part to the fact that size, design, and fit have not been inclusively evaluated using dynamic simulations; constitutive models have been limited to linearly elastic materials; and biometric size of the pacifiers have not been disclosed. In a broad-sense, however, our results concur with Levrini et al.  who used a palatal model of a newborn and found that different geometric designs (conventional, orthodontic, and cherry) have different stress–strain contact profiles. In agreement with this study, the pacifier contact area within the palate was shown to vary based on the geometric shape of the pacifier. The pattern of stress distribution can have a direct effect on the morphological development of the palatal structures. Levrini et al. did not assess the fit of the pacifier in the palate but did find that the position of the pacifier in the palate differed from one geometric shape to another. Their results support the premise that the pattern of stress distribution can have a direct effect on the morphological development of the palatal structures.
Freitas’ findings  that an orthodontic pacifier produced maxillary force both forward and to the sides toward the lateral supporting pillars concur with this study. Conversely, a conventional, symmetrical cylinder design pacifier (e.g., Super Soothie) promoted an upward deformation in the midpalatine suture, favoring development of a more atretic palate. Pacifier bulb dimensions were not reported in their study.
Although Maurya et al.  used a geometric model of a pacifier and palate, they did not provide data on dimensional fit into aged palates. Their investigation study used “only average dimensions of a human infant,” dentate and edentulos gum pads, and a uniformly applied “biting” pressure . No dimensional information or brand names were given for the pacifiers in their study. It is important to reiterate that previous FEA studies [16,17,18] were all limited to static loading and linear elastic materials.
It is recognized that results of comparison studies will vary based on initial positioning of the bulb with respect to the palate, the shape of the palate, and the nature of the loading (e.g., amplitude, frequency, and direction). For the conditions and loading used in this study, comparison of results relative to each other show that the orthodontic pacifiers provided more support in the TW area than the conventional, non-orthodontic pacifiers. It should also be noted that the palatal models used were representative of the age but there are normal deviations in each age group.
The findings of this study show that the size metrics, geometric, mechanical, and physiological design of the pacifier alter the functioning and mechanical behavior of pacifiers during NNS. Any parameter of pacifier fit that can contribute to the loss to transverse dimension or cause palatal atresia can lead to the development of posterior crossbites and other malocclusions. This is integral to oral facial growth dynamics which impacts not only the development of malocclusions but can also compromise the airway and result in abnormal oral myofunction.
These FEA results show how pacifier fit during growth stages can play a significant role in palatal development. When coupled with duration, frequency, and intensity of use, these results provide new insights into the development of malocclusions arising from NNS.