Effects of age and diet consistency on the expression of myosin heavy-chain isoforms on jaw-closing and jaw-opening muscles in a rat model.

BACKGROUND: Skeletal craniofacial morphology can be influenced by changes in masticatory muscle function, which may also change the functional profile of the muscles. OBJECTIVES: To investigate the effects of age and functional demands on the expression of Myosin Heavy-Chain (MyHC) isoforms in representative jaw-closing and jaw-opening muscles, namely the masseter and digastric muscles respectively. METHODS: Eighty-four male Wistar rats were divided into four age groups, namely an immature (n = 12; 4-week-old), early adult (n = 24; 16-week-old), adult (n = 24; 26-week-old) and mature adult (n = 24; 38-week-old) group. The three adult groups were divided into two subgroups each based on diet consistency; a control group fed a standard (hard) diet, and an experimental group fed a soft diet. Rats were sacrificed, and masseter and digastric muscles dissected. Real-time quantitative polymerase chain reaction was used to compare the mRNA transcripts of the MyHC isoforms-Myh7 (MyHC-I), Myh2 (MyHC-IIa), Myh4 (MyHC-IIb) and Myh1 (MyHC-IIx)-of deep masseter and digastric muscles. RESULTS: In the masseter muscle, hypofunction increases Myh1 (26, 38 weeks; p < .0001) but decreases Myh4 (26 weeks; p = .046) and Myh2 (26 weeks; p < .0001) expression in adult rats. In the digastric muscle, hypofunction increases Myh1 expression in the mature adult rats (38 weeks; p < .0001), while Myh2 expression decreases in adult rats (26 weeks; p = .021) as does Myh4 (26 weeks; p = .001). Myh7 expression is increased in the digastric muscle of mature adult rats subjected to hypofunction (38 weeks; p = <.0001), while it is very weakly expressed in the masseter. CONCLUSION: In jaw-opening and jaw-closing muscles, differences in myosin expression between hard- and soft-diet-fed rats become evident in adulthood, suggesting that long-term alteration of jaw function is associated with changes in the expression of MyHC isoforms and potential fibre remodelling. This may give insight into the role of function on masticatory muscles and the resultant craniofacial morphology.

The influence of altered functional loading and posterior bite-blocks on the periodontal ligament space and alveolar bone thickness in rats.

OBJECTIVES: Posterior bite-blocks are resin-based structures elevating the occlusion and creating intrusive force on the posterior teeth. Bite-blocks were applied to the molars of growing rats and a hard and soft diet was used to create altered functional masticatory forces. The aim of the present investigation was to study the effect of this appliance on the periodontal ligament space and alveolar bone thickness when combined with altered masticatory forces. MATERIAL AND METHODS: Fifty-two four-week-old rats were divided into two groups, hard and soft diet. Two weeks later, half of them received a bite-block appliance, creating four groups: control hard (CH), control soft (CS), bite-block hard (BH) and bite-block soft (BS). All were sacrificed at age of 10 weeks. Their heads were scanned by micro-CT and periodontal ligament space (PDL) width, cross-sectional alveolar socket surface and alveolar bone thickness were measured. Analysis of variance (ANOVA) was used to compare the groups. RESULTS: The PDL was 9.2% thinner in the CS group (p < 0.001) and 20.7% in the bite-block groups (p < 0.001) compared to the CH group. Within each of the four groups, the mesiodistal PDL space was larger than the palatobuccal. The alveolar bone was thinner by 5.8% (p = 0.018) in the CS group, 10.7% in the BH group (p < 0.001) and 16.7% in the BS group (p < 0.001) compared to the CH group. CONCLUSIONS: Young rats wearing posterior bite-blocks have narrower PDL space and thinner alveolar bone compared to controls. When fed a soft diet, the alveolar bone is even thinner but the PDL showed no difference.

Influence of bone morphogenetic protein (BMP) signaling and masticatory load on morphological alterations of the mouse mandible during postnatal development.

OBJECTIVE: Bone homeostasis relies on several contributing factors, encompassing growth factors and mechanical stimuli. While bone morphogenetic protein (BMP) signaling is acknowledged for its essential role in skeletal development, its specific impact on mandibular morphogenesis remains unexplored. Here, we investigated the involvement of BMP signaling and mechanical loading through mastication in postnatal mandibular morphogenesis. DESIGN: We employed conditional deletion of Bmpr1a in osteoblasts and chondrocytes via Osterix-Cre. Cre activity was induced at birth for the 3-week group and at three weeks for the 9-week and 12-week groups, respectively. The conditional knockout (cKO) and control mice were given either a regular diet (hard diet, HD) or a powdered diet (soft diet, SD) from 3 weeks until sample collection, followed by micro-CT and histological analysis. RESULTS: The cKO mice exhibited shorter anterior lengths and a posteriorly inclined ramus across all age groups compared to the control mice. The cKO mice displayed an enlarged hypertrophic cartilage area along with fewer osteoclast numbers in the subchondral bone of the condyle compared to the control group at three weeks, followed by a reduction in the cartilage area in the posterior region at twelve weeks. Superimposed imaging and histomorphometrical analysis of the condyle revealed that BMP signaling primarily affects the posterior part of the condyle, while mastication affects the anterior part. CONCLUSIONS: Using 3D landmark-based geometric morphometrics and histological assessments of the mandible, we demonstrated that BMP signaling and mechanical loading reciprocally contribute to the morphological alterations of the mandible and condyle during postnatal development.

Long-Term Effect of Diet Consistency on Mandibular Growth within Three Generations: A Longitudinal Cephalometric Study in Rats.

BACKGROUND: This study investigated the effect of diet consistency on mandibular growth of Wistar rats through three generations. METHODS: A total breeding sample of 60 female and 8 male Wistar rats were used in this study. Measurements took place only on female animals. Twenty female Wistar rats at 30 days old and four male rats at 30 days old comprised the primary breeding sample of the first generation, and from these animals two different generations were reproduced. Lateral cephalometric X-rays were taken from all female rats at the age of 100 days. A total of 7 craniofacial landmarks were selected for the linear measurements, and 12 curves and 90 landmarks were selected for geometric morphometric analysis of the lateral X-rays. Bonferroni test and a permutation test were performed for the statistical analysis. RESULTS: Means of measurements of all soft diet groups compared to hard diet groups were significantly smaller. According to linear measurements, there was a significant difference only between the first-generation soft diet with the third-generation soft diet group. According to geometric morphometric analysis, the statistical differences appeared on the condylar process and the angle of the mandible. CONCLUSIONS: The soft diet could be responsible for less mandibular growth, and this information might be passing through generations.

Effects of Diet Consistency on Rat Maxillary and Mandibular Growth within Three Generations-A Longitudinal CBCT Study.

BACKGROUND: In this study, wistar rats were used to examine the impact of diet consistency on maxillary and mandibular growth over three generations. METHODS: In this investigation, a breeding sample of 60 female and 8 male wistar rats was used. Measuring was only performed on female animals. The first generation's primary breeding sample consisted of 20 female wistar rats that were 30 days old and 4 male rats that were also 30 days old; two subsequent generations were created from these animals. At the age of 100 days, CBCTs were collected of all male rats. Twenty-eight craniofacial landmarks were selected for the linear measurements on stl format extracted from the DICOM files. A Bonferroni test was performed for the statistical analysis. RESULTS: Means of measurements of all soft diet groups compared to corresponding measurements of the hard diet groups were significantly different. According to linear measurements, there was statistical difference on the maxillary measurements between the soft diet groups of the first and third generation, while the rest did not appear to have any statistical difference. There was significant difference for the mandibular dimensions only when the first generation soft diet group was compared with the third generation soft diet group. CONCLUSIONS: Food consistency has a significant impact on the growth and development of the maxilla and mandible. Soft diet habits may result in retrognathic mandible, and narrower maxilla.

Effect of Diet Consistency on Rat Mandibular Growth: A Geometric Morphometric and Linear Cephalometric Study.

BACKGROUND: Our study intended to investigate the null hypothesis that there is no effect of diet consistency on rat mandibular growth. METHODS: A total sample of 24 female wistar rats, 30 days old, was used in this study. In the first group, the rats were fed soft diet and in the second group, they were fed hard diet for 60 days. On the 60th day, the rats were sedated and lateral cephalometric X-rays were taken. Lateral cephalometric X-rays were digitized with 7 craniofacial landmarks for the linear measurements, as well as with 12 curves and 90 landmarks, of which 74 were semilandmarks and 16 were fixed landmarks for morphometric analysis. These landmarks were exposed to Procrustes superimposition and Principal Component Analysis (PCA) to describe the shape variability of the mandible. RESULTS: Means measurements of the soft diet group compared to those of the hard diet group were significantly different in linear and morphometric analysis measurements. The soft diet group of wistar rats revealed significant changes on the condyle (smaller), the angle of the mandible, and on the body of the mandible. CONCLUSIONS: Diet consistency affects the craniofacial growth of rats. Soft diet could be responsible for less mandibular growth.

Effects of Multi-Generational Soft Diet Consumption on Mouse Craniofacial Morphology.

Variations in craniofacial morphology may arise as a result of adaptation to different environmental factors such as soft diet (SD), which lessens functional masticatory load. Prior studies have shown that changes in the masticatory muscle function associated with a switch to short-term SD led to changes in craniofacial morphology and alveolar bone architecture. However, the long-term effects of SD and the associated adaptive changes in craniofacial shape are unclear. Our novel study set out to profile prospective skull changes in mice fed with SDs over multiple generations using three-dimensional (3D) geometric morphometric analysis (GMA). Our results revealed that short-term SD consumption led to a significant decrease in craniofacial size, along with numerous shape changes. Long-term SD consumption over 15 continuous generations was not associated with changes in craniofacial size; however, shape analysis revealed mice with shortened crania and mandibles in the anteroposterior dimension, as well as relative widening in the transverse dimension compared to the average shape of all mice analyzed in our study. Moreover, changes in shape and size associated with different functional loads appeared to be independent - shape changes persisted after diets were switched for one generation, whereas size decreased after one generation and then returned to baseline size. Our study is the first to study the role of prolonged, multi-generational SD consumption in the determination of craniofacial size and shape.

Functional Analysis of Rhythmic Jaw Movements Evoked by Electrical Stimulation of the Cortical Masticatory Area During Low Occlusal Loading in Growing Rats.

The maturation of rhythmic jaw movements (RJMs) and related neuromuscular control has rarely been studied in animals, though this process is essential for regulating the development of stomatognathic functions. Previous studies have shown that occlusal hypofunction during growth alters masticatory performance. However, little is known about patterns of cortically-induced RJMs under conditions of soft-diet feeding during development. The aim of this study is to clarify the effect of low occlusal loading on the pattern of cortically induced RJMs and related neuromuscular responses in growing rats. Sixty-four 2-week-old male albino Wistar rats were randomly divided into two groups and fed on either a normal diet (control) or soft diet (experimental) soon after weaning. At 5, 7, 9, and 11 weeks of age, electromyographic (EMG) activity was recorded from the right masseter and anterior digastric muscles along with corresponding kinematic images in RJMs during repetitive intracortical microstimulation of the left cortical masticatory area (CMA). Rats in both groups showed an increase in gape size and lateral excursion until 9 weeks of age. The vertical jaw movement speed in both groups showed no significant difference between 5 and 7 weeks of age but increased with age from 9 to 11 weeks. Compared to the control group, the average gape size and vertical speed were significantly lower in the experimental group, and the pattern and rhythm of the jaw movement cycle were similar between both groups at each recording age. EMG recordings showed no age-related significant differences in onset latency, duration, and peak-to-peak amplitude. Moreover, we found significantly longer onset latency, smaller peak-to-peak amplitude, and greater drop-off mean and median frequencies in the experimental group than in the control group, while there was no significant difference in the duration between groups. These findings indicate that a lack of enough occlusal function in infancy impedes the development of patterns of RJMs and delays the neuromuscular response from specific stimulation of the CMA.

The impact of dietary consistency on structural craniofacial components: Temporomandibular joint/condyle, condylar cartilage, alveolar bone and periodontal ligament. A systematic review and meta-analysis in experimental in vivo research.

OBJECTIVE: The aim of this systematic review was to provide a comprehensive synthesis of available evidence evaluating the effect of dietary loading on temporomandibular joint/condyle, condylar cartilage, alveolar bone of the mandible and the periodontal ligament in healthy mice and rats. DESIGN: Medline via PubMed, EMBASE and Open Grey databases were searched for published and unpublished literature. Search terms included "mandiblular condyle", "alveolar bone", "temporomandibular joint", "condylar cartilage", "periodontal ligament", "rat", "mice". After data extraction, risk of bias (SYRCLE) and reporting quality (ARRIVE) were assessed. Random effects meta-analyses were performed for the outcomes of interest where applicable. RESULTS: A total of 33 relevant articles were considered in the systematic review, while only 6 studies were included in the quantitative synthesis. Risk of Bias in all studies was judged to be unclear to high overall, while reporting quality was suboptimal. Comparing soft to hard diet animals, significantly reduced anteroposterior condylar length (4 studies, weighted mean difference: -0.40 mm; 95% CI: -0.47, -0.32; p < 0.001) and width (4 studies, weighted mean difference: -0.043 mm; 95% CI: -0.51, -0.36; p < 0.001) were found in rats. Decreased anteroposterior condylar dimensions were detected for mice as well (2 studies, weighted mean difference: -0.049; 95% CI: -0.56, -0.43; p < 0.001). CONCLUSIONS: Overall, there was strong evidence to suggest a significant effect of soft diet on reduced condylar dimensions in rodents; however, there is need for further high quality experimental studies to inform current knowledge on condylar cartilage, alveolar bone and periodontal ligament related outcomes.

Association of feeding behavior with jaw bone metabolism and tongue pressure.

In recent decades, the eating habits of children and adolescents have undergone many changes due to the diversification of lifestyles worldwide. Reduced masticatory function in growing animals results in changes in the mandible, including a decrease in bone mass. However, the influence of different eating behaviors on jaw bone metabolism (e.g., the palatal palate) during the growth period is not fully understood. In addition, recent clinical studies reported that masticatory performance is positively related to tongue pressure in adults, but no consensus has been reached regarding whether tongue pressure is related to masticatory performance in children. This review summarizes current findings related to these issues, focusing on the influence of different feeding behaviors on jaw bone metabolism, including the development of tongue pressure. Consumption of a soft diet had a negative impact on jaw bone metabolism in the maxilla and mandible of rats; however, mastication of a hard diet recovered the collapsed equilibrium of bone turnover caused by a soft diet during growth. Tongue pressure is closely associated with an increase in masticatory performance in children. Peak maximum tongue pressure is reached earlier in women than in men. Before reaching adulthood, women require intervention to increase their peak tongue pressure.

Cooking Methods for a Soft Diet Using Chicken Based on Food Texture Analysis.

Undernutrition caused by difficulties in masticating is of growing concern among the elderly. Soft diets are often served at nursing homes; however, the styles differ with nursing homes. Improperly modified food texture and consistency may lead to further loss of nutritive value. Therefore, we developed a method to produce a soft diet using chicken. The texture-modified chicken was prepared by boiling a mixture of minced chicken and additive foodstuff that softened the meat. The best food additive was determined through testing cooking process, size after modification and texture. The optimum proportions of each component in the mixture were determined measuring food texture using a creep meter. Teriyaki chicken was cooked using the texture-modified chicken, and provided to a nursing home. The amount of food intake by elderly residents was subsequently surveyed. This study involved 22 residents (1 man and 21 women; mean age 91.4±5.3 y). Consequently, yakifu, which was made from wheat gluten, was the most suitable additive foodstuff. The hardness of the texture-modified chicken, with proportions of minced chicken, yakifu, and water being 50%, 10%, and 40% respectively, was under 40,000 N/m2. The intake amount of the texture-modified chicken of subjects whose intake amount of conventional chicken using chicken thigh was not 100% was significantly higher. These findings suggest that properly modified food textures could contribute to improve the quality of meals by preventing undernutrition among the elderly with mastication difficulties.

Effect of soft foods on primary human gingival epithelial cell growth and the wound healing process.

OBJECTIVES: Investigate the effect of soft diet foods on gingival epithelial cell growth, migration, and mediator secretion. METHODS: Human gingival epithelial cells were stimulated for various time periods with the following soft diet foods: orange juice, drinkable yogurt, and a nutritional drink. Cell growth was determined by an MTT assay and cell migration was investigated by a scratch assay and F-actin filament staining. Keratin production was analyzed by Western blot and wound healing mediators IL-6 and human ß-defensin 2 were quantified by ELISA. RESULTS: We demonstrate, for the first time, that certain soft diet foods increased the production of keratin 5, 14, and 19 by gingival epithelial cells. These proteins were known to be produced by proliferating cells. The soft foods tested also stimulated gingival epithelial cells to produce IL-6 and human ß-defensin 2. Soft foods are capable of promoting gingival epithelial cell migration by increasing F-actin production, which is part of the wound healing process. Results varied depending on the foods tested. CONCLUSION: Gingival epithelial cells interacted with the soft diet foods under study. This interaction was shown to upregulate keratin expression, as well as IL-6 and human ß-defensin 2 secretions. Furthermore, following cell wound, the soft foods upregulated post-scratch cell migration and F-actin production. Overall data suggest that the choice of foods in soft diets following oral surgery may influence the wound healing process of gingival epithelial cells.

Influence of differences in the hardness and calcium content of diets on the growth of craniofacial bone in rats.

OBJECTIVE: To examine the effects of a soft diet and a low-calcium diet on the craniofacial growth and bone architectures of the maxilla and mandible. MATERIALS AND METHODS: Male rats (n  =  20, 3 weeks old) were divided into four groups. Ten rats were given a normal-calcium diet, and the other rats were given a low-calcium diet. Each group was then divided into two subgroups, which were fed a hard or a soft diet. After 4 weeks, craniofacial growth and architecture in maxillary and mandibular bone were analyzed using cephalometry, micro-computed tomography, and histopathology. RESULTS: The low-calcium diet had no effect on serum calcium levels. The low-calcium diet had the greatest effect on craniofacial bone growth, while the soft diet affected the growth of several bone sites that are attached to the masseter muscle. A low-calcium diet resulted in the deterioration of the connectivity of the trabeculae in the furcation region of the maxillary and mandibular first molar, while a soft diet resulted in the diffuse disappearance of trabeculae in the central part of the furcation regions. In the midpalatal suture, a low-calcium diet resulted in inhibition of cartilaginous ossification, although the midpalatal suture had a normal cartilaginous structure. A soft diet resulted in narrower cartilage cell layers in the midpalatal suture. CONCLUSIONS: We demonstrated that a low-calcium diet and a soft diet resulted in a deterioration of bone structures in both the maxilla and in the mandible; however, the mechanisms underlying these effects differed between diets.