Study Title: Investigation of the Effects of Tongue, Lip, and Cheek Pressures on the Development of Upper Jaw Narrowness

Introduction and Hypothesis The structure of our face and the alignment of our teeth are influenced not only by our genetics but also by the surrounding soft tissues, such as the lips, cheeks, and tongue. These muscles exert constant pressure on our teeth and jawbones. According to the "Equilibrium Theory," teeth stay in their proper positions when the inward pressure from the lips and cheeks is balanced by the outward pressure from the tongue.

The hypothesis of this study is that individuals with a narrow upper jaw (maxillary constriction) may have different muscle pressure patterns compared to those with normal jaw widths. We believe that identifying these pressure differences will help dentists and orthodontists better understand why jaw narrowness occurs and how to achieve more stable results after treatment.

What is Being Measured? To measure these delicate pressures, we use a specialized, high-tech device called the Iowa Oral Performance Instrument (IOPI). This device uses a small, air-filled balloon (bulb) that the patient presses with their tongue or lips. It allows us to measure muscle strength and endurance in "kilopascals" (a unit of pressure) without any pain or discomfort.

Study Procedure

This study will involve patients aged 12 to 25 who are seeking orthodontic treatment at Van Yüzüncü Yıl University. We will divide the participants into two groups:

Patients with a narrow upper jaw.

Patients with a normal upper jaw width (the control group).

Before any orthodontic braces are applied, we will measure:

Tongue Pressure: How hard the tongue can push against the roof of the mouth.

Lip Pressure: The strength of the upper and lower lips.

Cheek (Buccal) Pressure: The pressure exerted by the cheeks during rest and function.

Importance of the Study While many studies have looked at how these muscles affect the forward or backward position of teeth, there is very little research on how they affect the width of the jaw. By comparing these two groups, we hope to discover whether "weak" or "overactive" muscles contribute to a narrow palate. This information could lead to new treatment methods that focus not just on moving teeth, but also on training the oral muscles to ensure that the beautiful smiles created by orthodontists last a lifetime.

The Effect of Lip, Cheek, and Tongue Muscle Pressure on Maxillary Transversal DevelopmentObjective: This study aims to investigate the influence of lip, cheek, and tongue muscle pressures on maxillary transversal development.Methodology: Quantitative, randomized clinical study.Research Question: Do lip, cheek, and tongue muscle pressures have a significant effect on maxillary constriction?Scientific Background and ValidityThe tongue is a primary component of the oral cavity. Due to its capacity to deform and move in all directions (anteroposterior, mediolateral, and cephalocaudal), it plays an extensive role in mastication and deglutition. Clinical studies investigating how the tongue supports swallowing have led to the development of significant literature documenting tongue structure and strength in both dysphagic and non-dysphagic subjects. The tongue is essentially a three-dimensional mass of muscle fibers occupying not only the oral cavity but also the oropharynx. Logemann reported that the tongue structure during swallowing can be divided into two parts: the oral part located in the oral cavity (tip, anterior two-thirds, anterior, middle, and posterior) and the base of the tongue (tongue root and epiglottis) located in the pharyngeal space.Recently, various approaches have been reported to evaluate oromotor skills and measure tongue-palate compression during swallowing. Tongue-palate pressures can be measured using air-filled bulbs placed between the tongue and the palate. Various forms of orolingual manometry equipment are currently available or under development. Models vary based on the size and number of pressure sensors used and whether the sensor placement is fixed. The Iowa Oral Performance Instrument (IOPI) and the KayPentax Swallowing Signals Lab Orolingual Manometry module are currently the most widely used tools.Perioral structures play a crucial role in the development of normal occlusion or malocclusion. Soft tissues, such as the lips, cheeks, and tongue, influence hard tissues and orthodontic treatment outcomes through perioral pressures, muscle forces, and periodontal attachments. Therefore, soft tissue constraints should be precisely evaluated by orthodontists, considering not only genetic but also environmental factors. According to the Equilibrium Theory defined by Weinstein et al., teeth are balanced internally by the tongue and externally by the lips and cheeks. Furthermore, even if the magnitude of the force is low, it can induce tooth movement when applied for a sufficient duration . Graber noted that observed changes in muscle functions could alter normal morphology or exacerbate existing malocclusions. Evaluations regarding soft tissues are critical for determining the etiology of malocclusion and the stability of orthodontic treatment.Environmental factors associated with the lips, cheeks, and tongue have been reported to be responsible for the etiology of various malocclusions . Some studies have indicated that the lips and cheeks are more significant environmental factors than the tongue regarding tooth position . For stable treatment results, the effects of these factors on malocclusion must be determined. It has been stated that lower lip resting pressure is more influential on the position of the upper incisors than the upper lip. In individuals exposed to significantly higher resting lip pressure compared to those with Class I malocclusion, a high lower lip line and pressure have been shown to be associated with the retroclination of upper incisors in Class II division 2 malocclusion.In the evaluation of soft tissues, it is possible to examine electromyographic or electrodynamic measurements in addition to thickness or volume measurements. The application of electrodynamic measurement techniques with strain gauges is a reliable method for assessing soft tissue forces and pressures . Lindeman and Moore compared three different methods for evaluating perioral pressure and force, arguing that the lips cause fluid-like pressure and should therefore be evaluated using pressure-sensitive devices rather than force-sensitive ones. The IOPI is a reliable tool that measures perioral pressures from the lips, cheeks, and tongue. Additionally, thanks to disposable measurement bulbs, there is no need for extra laboratory procedures and no risk of contamination.There is no consensus yet on the relationship between malocclusion types and perioral pressures. Lapatki et al. stated that upper incisors in Class II division 2 malocclusion are exposed to higher resting lip pressure compared to Class I occlusion. Conversely, another study showed that maximum lip pressure was lowest in individuals with Class II division 2 malocclusion. In a study including both young and adult individuals, the change in Upper Lip Pressure (ULP) between Class I and Class II malocclusions showed no significant difference. Additionally, Lambrechts et al. stated that no significant difference was found in tongue pressure across malocclusion types. While the relationship between sagittal anomalies and perioral muscle pressures has been examined in the literature, no study has investigated the relationship between maxillary transversal width and perioral muscle pressure. Therefore, examining this relationship is expected to contribute significantly to the literature.Study Protocol and ProceduresThis study will include skeletal Class I patients with maxillary constriction who will undergo treatment at the Van Yüzüncü Yıl University, Faculty of Dentistry, Department of Orthodontics.Inclusion Criteria:No prior orthodontic treatment.Skeletal Class I relationship.Presence of maxillary constriction.Absence of any systemic diseases.Age range between 12 and 25 years.Literacy (to evaluate the informed consent form).Voluntary participation.A detailed anamnesis will be obtained from the patients before treatment. They will be informed about the procedures, and written consent will be obtained. Patients will be divided into two groups of 20 individuals each, based on the presence or absence of maxillary constriction. Muscle pressures will be measured and recorded using the IOPI Pro Deluxe Kit before the bonding process.The IOPI aims to quantify pressure endurance and tongue, lip, and cheek pressures in kilopascals (kPa). The device consists of an air sensor, lingual sensor (bulbs), a connection tube linking the sensor to the gauge, and a meter that visualizes the force applied to a syringe for pressure control.Tongue pressure will be measured by placing the bulb in the retro-incisal region of the patient's mouth. The patient will be asked to lift their tongue and apply maximum pressure against the palate. Measurements will be taken three times with 30-second rest intervals, and the average will be recorded. To evaluate perioral pressure, measurements will include: upper lip pressure, lower lip pressure, vertical lip pressure, left buccal pressure, right buccal pressure, swallowing tongue pressure, and maximum tongue pressure. These measurements will be compared between the groups with and without maxillary constriction.Statistical AnalysisVariables within the groups will be expressed as numbers and percentages; descriptive statistics will be presented as mean and standard deviation. For comparisons of continuous variables according to categorical variables, One-way Analysis of Variance (ANOVA) will be performed. Following ANOVA, the Tukey post-hoc test will be used to identify differences between groups. Correlation analysis will be used to determine relationships between continuous variables, and the Chi-square test will be used for categorical variables. The level of statistical significance will be set at 5% (p < 0.05), and all calculations will be performed using the SPSS statistical software package.

Inclusion Criteria:Participants aged between 12 and 25 years.Diagnosed as Skeletal Class I (ANB angle: $0^\circ$ to $4^\circ$).Experimental Group: Clinical and radiographic diagnosis of maxillary transversal constriction.Control Group: Normal maxillary transversal width with no crossbite or constriction.Permanent dentition (excluding third molars).Good oral hygiene and no active periodontal disease.Ability to understand and follow instructions for the IOPI measurement protocol.

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Exclusion Criteria:Previous orthodontic or orthognathic surgical treatment.

History of craniofacial anomalies or syndromes (e.g., cleft lip and palate).

Neuromuscular disorders or systemic diseases affecting muscle function.

History of trauma to the jaw or facial region.

Congenitally missing teeth (hypodontia) or extensive prosthetic restorations.

Macroglossia or severe tongue-tie (ankyloglossia).

Use of medications that may influence muscle tone (e.g., muscle relaxants).

Presence of large tonsils or adenoids that significantly obstruct the airway.

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De-identified individual participant data that underlie the results reported in the final publication (including demographic data, cephalometric measurements, and orolingual pressure values measured via IOPI) will be made available to qualified researchers. Access will be provided following a methodologically sound proposal and after the signing of a data access agreement to ensure ethical compliance and participant anonymity

Data will be available beginning 6 months and ending 36 months following article publication

Data requests should be submitted to the corresponding author's institutional email. Requests will be evaluated by the principal investigator and the ethics committee of the hosting university. To gain access, data requestors will need to sign a formal data access agreement to ensure ethical usage and protect participant confidentiality.

Not applicable. This is an open-label study where both the investigator and the participants are aware of the group assignments due to the nature of the anatomical conditions being studied. However, data analysis will be conducted using anonymized patient codes to ensure objective statistical evaluation.