Hiroshi Tomonari

Expression of the basal cell markers of taste buds in the anterior tongue and soft palate of the mouse embryo

Although embryonic expression of Shh in the fungiform papilla placodes has a critical role in fungiform papilla patterning, it remains unclear whether its appearance indicates the differentiation of the basal cells of taste buds. To examine the embryonic development of the basal cells, the expression of Shh, Prox1, and Mash1 was determined in the anterior tongue and soft palate in mouse embryos by in situ hybridization. In the anterior tongue, Prox1 was coexpressed with Shh from the beginning of Shh expression in the fungiform papilla placodes at E12.5. Shh was expressed in the soft palate in a band‐like pattern in the anteriormost region and in a punctate pattern in the posterior region at E14.5. The number (21.4 ± 4.3, at E14.5) of locations where Shh was observed (i.e., spots) rapidly increased and reached a peak level (54.8 ± 4.0 at E15.5). Also in the soft palate, Prox1 was coexpressed with Shh from the beginning of Shh expression. These results suggest that basal cell differentiation occurs synchronously with the patterning of Shh spots both in the anterior tongue and in the soft palate. In contrast, Mash1 expression lagged behind the expression of Shh and Prox1 and began after the number of Shh spots had reached its peak level in the soft palate. Furthermore, immunohistochemistry of PGP9.5 and Shh revealed that epithelial innervation slightly preceded Mash1 expression both in the tongue and in the soft palate. This is the first report describing the time courses of the embryonic expression of basal cell markers of taste buds. J. Comp. Neurol. 509:211–224, 2008.

Gα-gustducin Is Extensively Coexpressed with Sweet and Bitter Taste Receptors in both the Soft Palate and Fungiform Papillae but Has a Different Functional Significance

To clarify the regional differences in the expression and functional significance of Gα-gustducin in soft palate (SP) and fungiform (FF) taste buds, we examined the coexpression of Gα-gustducin with taste receptors and the impact of Gα-gustducin knockout (gKO) on neural responses to several sweet and bitter compounds. Sweet responses from both the greater superficial petrosal (GSP) and chorda tympani (CT) nerves in gKO mice were markedly depleted, reflecting overlapping expression of Gα-gustducin and Tas1r2. However, although Gα-gustducin was expressed in 87% and 88% of Tas2rs cells in the SP and FF, respectively, there were no statistically significant differences in the CT responses to quinine-HCl (QHCl) and denatonium (Den) between gKO and wild-type (WT) mice. In contrast, GSP responses to these compounds were markedly reduced in gKO mice with an apparent elevation of thresholds (>10-fold). These results suggest that 1) Gα-gustducin plays a critical role in sweet transduction in both the SP and the FF, 2) other Gα subunits coexpressed with Gα-gustducin in the FF are sufficient for responses to QHCl and Den, and 3) robust GSP responses to QHCl and Den occur in the SP by a Gα-gustducin-dependent mechanism, which is absent in the FF.Like mammals, bird embryos are capable of chemosensory learning, but the ontogeny of their feeding preferences has not been examined. We tested if the timing of stimulation in chicken embryos modulates the impact of in ovo olfactory stimulation on later food preferences. We exposed chicken embryos to an olfactory stimulus for a 4-day period in the middle or toward the end of the incubation period. The chicks were tested for their preference between foods with and without the olfactory stimulus in 3-min choice tests and on a 24-h time scale. Regardless of the type of food (familiar or novel) or the duration of the test, the control chicks not exposed to the olfactory stimulus consistently showed significant preferences for non-odorized foods. Chicks that were exposed in ovo to the olfactory stimulus did not show a preference for odorized or non-odorized foods. Only those chicks that were exposed to the olfactory stimulus toward the end of the incubation period differed from the controls and incorporated a higher proportion of odorized food into their diets on a 24-h time scale. This result indicates that olfactory stimulation at the end of embryonic development has a stronger impact on later feeding preferences. Our findings contribute to the growing pool of recent data appreciating the impact of olfactory signals on behavior regulation in avian species.

Posterior scissors-bite: masticatory jaw movement and muscle activity

Scissors-bite is a malocclusion characterised by buccal inclination or buccoversion of the maxillary posterior tooth and/or linguoclination or linguoversion of the mandibular posterior tooth. This type of malocclusion causes reduced contact of the occlusal surfaces and can cause excessive vertical overlapping of the posterior teeth. This case-control study is the first to evaluate both masticatory jaw movement and masseter and temporalis muscle activity in patients with unilateral posterior scissors-bite. Jaw movement variables and surface electromyography data were recorded in 30 adult patients with unilateral posterior scissors-bite malocclusion and 18 subjects with normal occlusion in a case-control study. The chewing pattern on the scissors-bite side significantly differed from that of the non-scissors-bite side in the patients and of the right side in the normal subjects. These differences included a narrower chewing pattern (closing angle, P < 0.01; cycle width, P < 0.01), a longer closing duration (P < 0.05), a slower closing velocity (P < 0.01) and lower activities of both the temporalis (P < 0.05) and the masseter (P < 0.05) muscles on the working side. In 96% of the patients with unilateral posterior scissors-bite, the preferred chewing side was the non-scissors-bite side (P = 0.005). These findings suggest that scissors-bite malocclusion is associated with the masticatory chewing pattern and muscle activity, involving the choice of the preferred chewing side in patients with unilateral posterior scissors-bite.

Influence of maximum bite force on jaw movement during gummy jelly mastication

It is known that maximum bite force has various influences on chewing function; however, there have not been studies in which the relationships between maximum bite force and masticatory jaw movement have been clarified. The aim of this study was to investigate the effect of maximum bite force on masticatory jaw movement in subjects with normal occlusion. Thirty young adults (22 men and 8 women; mean age, 22.6 years) with good occlusion were divided into two groups based on whether they had a relatively high or low maximum bite force according to the median. The maximum bite force was determined according to the Dental Prescale System using pressure-sensitive sheets. Jaw movement during mastication of hard gummy jelly (each 5.5 g) on the preferred chewing side was recorded using a six degrees of freedom jaw movement recording system. The motion of the lower incisal point of the mandible was computed, and the mean values of 10 cycles (cycles 2-11) were calculated. A masticatory performance test was conducted using gummy jelly. Subjects with a lower maximum bite force showed increased maximum lateral amplitude, closing distance, width and closing angle; wider masticatory jaw movement; and significantly lower masticatory performance. However, no differences in the maximum vertical or maximum anteroposterior amplitudes were observed between the groups. Although other factors, such as individual morphology, may influence masticatory jaw movement, our results suggest that subjects with a lower maximum bite force show increased lateral jaw motion during mastication.

First molar cross-bite is more closely associated with a reverse chewing cycle than anterior or pre-molar cross-bite during mastication

A posterior cross-bite is defined as an abnormal bucco-lingual relationship between opposing molars, pre-molars or both in centric occlusion. Although it has been reported that patients with unilateral posterior cross-bite often show unique chewing patterns, the relationship between the form of cross-bite and masticatory jaw movement remains unclear in adult patients. The objective of this study was to investigate masticatory jaw movement among different forms of cross-bite. One hundred and one adults were recruited in this study: 27 had unilateral first molar cross-bite (MC group); 28, unilateral pre-molar cross-bite (PC group); 23, anterior cross-bite (AC group); and 23, normal occlusion (control group). Masticatory jaw movement of the lower incisor point was recorded with six degrees of freedom jaw-tracking system during unilateral mastication. Our results showed that the reverse chewing ratio during deliberate unilateral mastication was significantly larger in the MC group than in the PA (P < 0.001), AC (P < 0.001) and control (P < 0.001) groups. These findings suggest that compared to the anterior or pre-molar cross-bite, the first molar cross-bite is more closely associated with a higher prevalence of a reverse chewing cycle.

Influence of surgical orthodontic treatment on masticatory function in skeletal Class III patients

Skeletal Class III patients exhibit malocclusion characterised by Angle Class III and anterior crossbite, and their occlusion shows total or partially lateral crossbite of the posterior teeth. Most patients exhibit lower bite force and muscle activity than non-affected subjects. While orthognathic surgery may help improve masticatory function in these patients, its effects have not been fully elucidated. The aims of the study were to evaluate jaw movement and the electromyographic (EMG) activity of masticatory muscles before and after orthognathic treatment in skeletal Class III patients in comparison with control subjects with normal occlusion. Jaw movement variables and EMG data were recorded in 14 female patients with skeletal Class III malocclusion and 15 female controls with good occlusion. Significant changes in jaw movement, from a chopping to a grinding pattern, were observed after orthognathic treatment (closing angle P < 0.01; cycle width P < 0.01), rendering jaw movement in the patient group similar to that of the control group. However, the grinding pattern in the patient group was not as broad as that of controls. The activity indexes, indicating the relative contributions of the masseter and temporalis muscles (where a negative value corresponds to relatively more temporalis activity and vice versa) changed from negative to positive after treatment (P < 0.05), becoming similar to those of control subjects. Our findings suggest that orthognathic treatment in skeletal Class III patients improves the masticatory chewing pattern and muscle activity. However, the chewing pattern remains incomplete compared with controls.

Modulation of the masticatory path at the mandibular first molar throughout the masticatory sequence of a hard gummy jelly in normal occlusion.

Objective: In this study, the authors investigated the modulation of the masticatory path at the mandibular first molar during natural chewing of a hard gummy jelly in adults with normal occlusion. Methods: The unilateral mastication sequence was divided into three stages, and the masticatory path of the mandibular first molar on the working side was analyzed at 2.0, 3.0, 4.0, and 5.0 mm vertical slice levels below the intercuspation in the frontal and sagittal views. Results: In the frontal view, the closing and opening angles and cycle width of the final stage at 3.0, 4.0, and 5.0 mm slice levels were smaller and narrower than those of the initial stage, although those at the 2.0 mm slice level were little changed. Discussion: Masticatory paths of the mandibular first molar at slice levels greater than 3.0 mm were evidently modulated to adapt to the changing properties of the food, and those at the 2.0 mm slice level remained stable throughout the masticatory sequence.

Replacement of a first molar and 3 second molars by the mesial inclination of 4 impacted third molars in an adult with a Class II Division 1 malocclusion.

This case report presents the successful replacement of 1 first molar and 3 second molars by the mesial inclination of 4 impacted third molars. A woman, 23 years 6 months old, had a chief complaint of crowding of her anterior teeth and linguoclination of a second molar on the left side. The panoramic radiographic images showed that the maxillary and mandibular third molars on both sides were impacted. Root resorption on the distal surfaces of the maxillary second molars was suspected. The patient was given a diagnosis of Angle Class II Division 1 malocclusion with severe crowding of the anterior teeth and 4 impacted third molars. After we extracted the treated maxillary second premolars and the second molars on both sides, the treated mandibular second premolar and the second molar on the left side, and the root canal-filled mandibular first molar on the right side, the 4 impacted third molars were uprighted and formed part of the posterior functional occlusion. The total active treatment period was 39 months. The maxillary and mandibular third molars on both sides successfully replaced the first and second molars. The replacement of a damaged molar by an impacted third molar is a useful treatment option for using sound teeth.

Relationships between the root-crown ratio and the loss of occlusal contact and high mandibular plane angle in patients with open bite

OBJECTIVE To determine the root-crown (R/C) ratio and dental root length of teeth in patients with open bite and seek any relationships with occlusal contact (OC) and the mandibular plane (Mp) angle. MATERIALS AND METHODS Thirty-one patients with open bite with negative overbite of at least four anterior teeth and 31 control patients with clinically normal overjet and overbite were enrolled. R/C ratios, dental root length, OC, and Mp angle were measured using panoramic radiographs, dental casts, and cephalograms, respectively. Mean differences between the groups, and variations between the R/C ratio or root length and Mp angle in patients with open bite were statistically analyzed. RESULTS R/C and OC ratios from the incisors to premolars were significantly lower for patients with open bite than for controls, and some teeth had short dental roots. Relationships between low R/C ratio or root length and high Mp angle were significant in patients with open bite. CONCLUSION Patients with open bite, especially those with a high Mp angle, have an unfavorable R/C ratio and short dental roots in some teeth, which may be related to the loss of OC.

Factors associated with the stability of miniscrews as orthodontic anchorage: Analysis of published clinical trials

We reviewed clinical studies to examine the factors associated with the stability of miniscrews as absolute anchorage in orthodontics. On May 31, 2011, the PubMed electronic database was searched for articles. We used these 4 selection criteria: (I) the original article about the stability of miniscrews published in journals with impact factor; (II) the human clinical research performed; (III) sample sizes of 100 miniscrews or more; (IV) the data on factors related to the length and diameter of miniscrews, the method and location of the miniscrew placement, the timing of the application force, and the ages and skeletal patterns of patients for correlation with the success rate of miniscrews. As a result, 17 articles were selected for this study on the basis of the above-mentioned criteria, and these articles included 4654 miniscrews, with a mean overall success rate of 86.3%. These rates may be affected more by the diameter than by the length of the miniscrews, and more than 1.2 mm in diameter was considered appropriate for clinical application. With respect to the placement protocol, the self-tapping and self-drilling methods were both broadly applied. To obtain the appropriate insertion torque, one should select the placement protocol showing the appropriate site for placement and the properties of miniscrews. An analysis of the optimal timing of the application force suggested that immediate or early loading within 4 weeks after placement seems to have little effect on the stability of miniscrews. Further, some studies have shown that the failure rates of implantation were higher in the mandible and in young patients than in the maxilla and in adult patients, respectively. Therefore, to increase the success rates of miniscrews, the above-mentioned countermeasures should be considered properly.