The development of infants up to the age of 2 years is highly plasticity, and feeding during this period affects children's growth and development (Okeyo, 2018) and even their long-term health (Campoy et al., 2018). Inadequate complementary feeding habits, insufficient nutrient content of foods, and lack of complementary intake can lead to malnutrition, irreversible growth retardation, poor cognitive development, and craniomaxillofacial underdevelopment (Arikpo et al., 2018). Due to socio-economic development, there has been extensive research on the nutrient content, intake, and timing of complementary foods to prevent adverse consequences (Campoy et al., 2018, Dewey and Adu-Afarwuah, 2008, Kostecka et al., 2020). However, with the refinement of food, many families will provide infants with a soft diet for an extended period before transitioning to solid foods, which may be a new poor feeding habit. Because food characteristics also have a long-lasting effect on infants' food habits and growth (Blasko et al., 2023, Hübl et al., 2020). An early semi-liquid diet aligns with infants' dietary preferences, and providing appropriate foods during the weaning period promotes the gradual acceptance of a wider variety of food types and the development of healthy eating habits (Le Révérend et al., 2014). However, it is important to note that long-term soft food diets often have negative effects on the stomatognathic system (Karamani et al., 2022, Scheidegger et al., 2018), such as insufficient growth and poor mineralization of the jaws (Tsolakis et al., 2022), structural changes in the temporomandibular joints (Yan et al., 2021), and reduced activity of the masticatory muscles (Langenbach et al., 2003).

Most changes in the stomatognathic system are related to changes in masticatory behavior and reduced occlusal force due to soft food diets (Consolação Soares et al., 2017, Pereira et al., 2006). The development of teeth, the vital organs that fulfill the function of mastication, is also closely related to diet-related biomechanical factors. The introduction of complementary feeding is a critical period when children's teeth begin to erupt in the mouth and gradually complete the establishment of occlusion. During this period, food is gradually changed from liquid and mud paste to semi-solid and solid. The difference in food traits is often accompanied by the difference in bite force. A prolonged soft food diet causing a weakened bite may affect the development of tooth hard tissues. At the time of tooth eruption, the development of enamel has been completed, while dentin and cementum are still developing. It has been demonstrated that soft food diets can lead to dental osteogenesis imperfecta (Nakasone & Yoshie, 2011); however, few studies have reported the effect of soft food diets on dentin formation. Dentin, a hard tissue formed throughout life, serves a vital role in resisting external stimuli and protecting the pulp tissue (Bergenholtz et al., 2010). Physiologic dentin naturally forms in the absence of external stimuli, while dentin formed in response to external stimulation is referred to as restorative dentin (Arana-Chavez & Massa, 2004). Physiologic dentin formation is divided into 2 stages; primary dentin is formed during tooth development and secondary dentin is formed after root development is complete and occlusion is established. Both have similar mineral and organic content, but the rate of secondary dentin formation is greatly reduced to one-tenth that of primary dentin (Sloan, 2015). After establishing the occlusion, the maxillary and mandibular teeth come into contact with each other during masticatory movements, and the masticatory muscles contract to generate occlusal forces. Changes in occlusal forces before and after occlusion establishment may be an essential factor causing differences in the rate of dentin formation. It has been demonstrated that occlusal loading may affect the mechanism of secondary dentin formation, leading to the activation of adult dentin cells and the formation of a stronger secondary dentin layer (Nudel et al., 2021). No studies have been reported on the effect of occlusal forces on dentin formation during tooth development.

Teeth are at risk of caries as soon as they begin to erupt. Teeth in the eruption process cannot be closed to prevent caries, and Early childhood caries (ECC) affects half of the world's school-age children (Uribe et al., 2021). When it occurs, adequate primary dentin thickness helps to protect pulpal tissue, buying more time for caries treatment and preventing periapical disease. Therefore, the aim of this study was to investigate the effect of a soft diet on molar dentin formation during the occlusal establishment period and reveal the possible mechanisms by which occlusal forces affect dentin formation. This study will fill a gap in the literature in the related field and thus provide valuable insights for guiding the diet of young children to strengthen their tooth structure. In this study, we used a mouse masticatory model, which has been maturely applied to study the effects of occlusal forces on dentition and periodontal tissues. The mouse incisor is a continuously erupting tooth and the mouse molar is a finitely erupting tooth. The eruption of these teeth may be regulated by different molecules and mechanisms (Wise & King, 2008), with the latter being more similar to mammalian teeth in terms of morphology and function. Therefore, we chose the mouse molar as the object of study. In this experiment, we obtained food for the soft diet group by grinding ordinary mouse food and mixing it with sterile water in standard proportions to form a semi-liquid diet, in contrast to ordinary rat food for the hard diet group (Karamani et al., 2022). It mimicked the different consistencies of complementary foods during the establishment of the teething occlusion. We speculate that, as with the development of other oral tissues, a soft diet may be detrimental to dentin formation, and deciduous teeth obtain a weaker dentin layer, which is not conducive to the prevention and treatment of dental pulp disease.