The Importance of Masticatory Muscle Function in Dentofacial Growth

Variability associated with maxillary infrazygomatic crest and palatal bone width, height, and angulation in subjects with different vertical facial growth types: a retrospective cone-beam computed tomography study

OBJECTIVES

To assess the infrazygomatic crest (IZC) and palatal bone width, height, and angulation in patients with different vertical facial growth types as potential miniscrew insertion sites.

MATERIALS AND METHODS

In this retrospective cone-beam computed tomography study, 162 subjects (81 males and 81 females, mean age 16.05 ± 0.65 years) were included. They were divided into three groups (hypodivergent, normodivergent, and hyperdivergent) based on the Frankfort mandibular plane angle. Ten buccal bone measurements were made at two different coronal sections: maxillary first molar mesiobuccal and distobuccal roots (bilaterally). Six palatal bone measurements were made on a sagittal section at the maxillary central incisors (bilaterally). A total of 32 measurements per subject were considered in the study.

RESULTS

No significant difference was observed for the IZC (width and angle) at the maxillary first molar mesiobuccal root. A comparison of normodivergent and hyperdivergent groups for buccal width at the distobuccal root of the first molar showed significant differences. Palatal bone thickness at the level of 2 mm distal to the apex of the central incisor was significantly higher for the hyperdivergent group (10.43 mm) compared with the normodivergent (7.58 mm) and hypodivergent groups (7.83 mm).

CONCLUSIONS

Hyperdivergent subjects tend to present a longer and deeper IZC and increased palatal bone thickness compared with other groups. The recommended insertion angle for the IZC mini-implant at 3 mm from the alveolar crest should be between 75.5° and 77°.

Three-dimensional radiographic assessment of the mandibular retromolar donor site in different vertical facial growth types

PURPOSE

To assess volumetrically, the impact of vertical facial growth types (VGFT) on the retromolar area as a bone donor site MATERIAL AND METHODS: 60 cone beam computed tomography (CBCT) scans of adult individuals were classified in three groups according to their SN-GoGn angle: hypodivergent group (hG) (33.33%), normodivergent group (NG) (30%) and hyperdivergent group (HG) (36.67%). Total harvestable bone volume and surface (TBV and TBS respectively), total cortical and cancellous bone volume (TCBV and TcBV respectively) and the percentage of cortical and cancellous bone volume (CBV and cBV respectively) were evaluated.

RESULTS

The whole sample showed a mean TBV of 1220.99±448.81mm³ and a mean TBS of 940.29±259.93mm². Statistically significant differences were found between the different outcome variables and the vertical growth patterns (p<0.001). TBS differs for the different vertical growth patterns with the highest mean of TBS observed in the hG group. TBV also significantly differs between the different vertical growth patterns (p<0.001) with the highest mean observed for the hG individuals. Significant differences in percentages of cBV and CBV were present between the hyper-divergent groups and the other groups (p<0.001) with the hyper-divergent group having the lowest percentage of CBV and the highest percentage of cBV.

CONCLUSION

hypodivergent individuals tend to have thicker bone blocks that can be used in onlay technique while thinner bone blocks harvested from hyperdivergent and normodivergent individuals can be used in three-dimensional grafting approach.

Commensal Microbiota Effects on Craniofacial Skeletal Growth and Morphology

Microbes colonize anatomical sites in health to form commensal microbial communities (e.g., commensal gut microbiota, commensal skin microbiota, commensal oral microbiota). Commensal microbiota has indirect effects on host growth and maturation through interactions with the host immune system. The commensal microbiota was recently introduced as a novel regulator of skeletal growth and morphology at noncraniofacial sites. Further, we and others have shown that commensal gut microbes, such as segmented filamentous bacteria (SFB), contribute to noncraniofacial skeletal growth and maturation. However, commensal microbiota effects on craniofacial skeletal growth and morphology are unclear. To determine the commensal microbiota's role in craniofacial skeletal growth and morphology, we performed craniometric and bone mineral density analyses on skulls from 9-week-old female C57BL/6T germ-free (GF) mice (no microbes), excluded-flora (EF) specific-pathogen-free mice (commensal microbiota), and murine-pathogen-free (MPF) specific-pathogen-free mice (commensal microbiota with SFB). Investigations comparing EF and GF mice revealed that commensal microbiota impacted the size and shape of the craniofacial skeleton. EF versus GF mice exhibited an elongated gross skull length. Cranial bone length analyses normalized to skull length showed that EF versus GF mice had enhanced frontal bone length and reduced cranial base length. The shortened cranial base in EF mice was attributed to decreased presphenoid, basisphenoid, and basioccipital bone lengths. Investigations comparing MPF mice and EF mice demonstrated that commensal gut microbes played a role in craniofacial skeletal morphology. Cranial bone length analyses normalized to skull length showed that MPF versus EF mice had reduced frontal bone length and increased cranial base length. The elongated cranial base in MPF mice was due to enhanced presphenoid bone length. This work, which introduces the commensal microbiota as a contributor to craniofacial skeletal growth, underscores that noninvasive interventions in the gut microbiome could potentially be employed to modify craniofacial skeletal morphology. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Orthodontic Retainers-A Critical Review

The achievement of aesthetic, functional occlusion should not mark the end of the orthodontic intervention. To prevent relapse, retention needs advance planning, and may vary in duration. This review aims to present and comment on the available means of retention. The ever-popular, passive Hawley-like removable appliances are credible in maintaining the desired occlusion. Modifications are the removable appliance Wrap Around, having the labial archwire extending to the premolars; the translucent retainer, Astics, a unique aesthetic Hawley-type device; and the reinforced removable retainer, which features a metallic grid reinforcing the acrylic base. Vacuum-formed retainers are easy to fabricate and are readily prescribed. By contrast, fixed retainers are made of orthodontic wire and composite resin bonded on the lingual or palatal surfaces of the anterior teeth. Patient-related variables need evaluation to select the appropriate retainer, while patients ought to realize the importance of retention and comply with offered guidance. Overall, the orthodontist is responsible for keeping the patient informed on the properties and the duration of retention, even before starting active orthodontic treatment.

Orthodontic Retainers-A Critical Review

The achievement of aesthetic, functional occlusion should not mark the end of the orthodontic intervention. To prevent relapse, retention needs advance planning, and may vary in duration. This review aims to present and comment on the available means of retention. The ever-popular, passive Hawley-like removable appliances are credible in maintaining the desired occlusion. Modifications are the removable appliance Wrap Around, having the labial archwire extending to the premolars; the translucent retainer, Astics, a unique aesthetic Hawley-type device; and the reinforced removable retainer, which features a metallic grid reinforcing the acrylic base. Vacuum-formed retainers are easy to fabricate and are readily prescribed. By contrast, fixed retainers are made of orthodontic wire and composite resin bonded on the lingual or palatal surfaces of the anterior teeth. Patient-related variables need evaluation to select the appropriate retainer, while patients ought to realize the importance of retention and comply with offered guidance. Overall, the orthodontist is responsible for keeping the patient informed on the properties and the duration of retention, even before starting active orthodontic treatment.

Cephalometric effects of Twin-block and van Beek Headgear-Activator in the correction of Class II malocclusion

INTRODUCTION

The Twin-block (TB) and the van Beek Headgear-Activator (vBHGA) are indicated for patients with Class II malocclusion with a retrognathic mandible. Although the former is commonly prescribed for horizontally growing patients, the latter is often recommended for those growing vertically. This study aimed to compare the skeletal, dentoalveolar, and soft-tissue short-term effects of TB and vBHGA, taking growth patterns into account.

METHODS

Immediate prefunctional (T1) and postfunctional appliance (T2) lateral cephalometric radiographs were retrospectively obtained for vBHGA (n = 46), TB (n = 45), and untreated control (n = 45) groups. The interaction of several variables at T1, T2, and T2 - T1, as well as the resultant treatment effect, were analyzed using the analysis of covariance regression models at the 5% significance level.

RESULTS

Except for a greater reduction in Wits measurement (3.0 mm; P <0.0001) in the TB group, no anteroposterior (AP) skeletal difference was observed between the 2 appliances (ANB, 0.530; P = 0.07) (Harvold, 0.13 mm; P = 0.81). Both improved the AP skeletal relationship (ANB and Harvold) compared with the control (P <0.05). Although this mostly occurred because of the forward positioning of the mandible with the TB (SNB, 0.960; P = 0.01), the maxillary restriction was the main mechanism with the vBHGA (SNA, 1.590; P <0.01). Dentoalveolar compensations were more pronounced with the TB (IMPA, 1.92; P = 0.02), leading to greater overbite and overjet correction. Only the inclination of the maxillary incisors showed interaction with the growth pattern, with the TB horizontal growers experiencing more retroclination (U1-NA°. 3.620; P = 0.0067).

CONCLUSIONS

Both appliances produced similar modest AP skeletal changes that, together with dentoalveolar compensations, were able to correct the Class II malocclusion regardless of growth pattern.

Assessment of infrazygomatic crest dimensions in different vertical facial growth types for miniscrew insertion: A cone-beam computed tomography study

INTRODUCTION

This study aimed to assess the depth and height of the infrazygomatic crest (IZC) located in the posterior maxilla at the junction with the zygomatic process in patients with different vertical facial growth types as a potential miniscrew insertion site.

METHODS

The sample consisted of cone-beam computed tomography scans of 117 patients (42 males and 75 females), with a mean age of 22.9 ± 2.7. The population was divided into 3 groups according to the measured SN-GoGn angle: Decreased facial proportions (n = 28), average facial proportions (n = 62), and increased facial proportions (n = 27). Bone depth was assessed at 5 levels: apex, 1, 2, 3, and 4 mm vertically from the apex. The measurements were performed on the mesiobuccal and distobuccal roots of the first molar and the mesiobuccal root of the second molar. Repeated-measure analysis of variance followed by univariates analyses and Bonferroni multiple comparisons were performed to compare the mean bone thickness between groups. The IZC height was assessed through a vertical line ranging from the furcation of the maxillary first molar to the sinus floor. Analysis of variance followed by Tukey (honestly significant difference) post-hoc tests was used to compare the mean height between groups.

RESULTS

Mean bone depth between the 3 groups were significantly different at the mesiobuccal root region of the first molar at all the measured levels. It was smaller for average, intermediate for decreased, and elevated for increased facial proportions. No statistical difference was shown at the distobuccal root of the first molar except for the apex level and the mesiobuccal root of the second molar except for the apex and 4 mm levels. The mean bone height was significantly different between subjects with increased facial proportions and the 2 other groups.

CONCLUSIONS

Subjects with increased facial proportions tend to present a longer and deeper IZC followed by decreased facial proportions, then average facial proportions.

Masseter muscle thickness and vertical cephalometric characteristics in children with Class II malocclusion

Background

Masseter muscle thickness and its relationship with vertical craniofacial morphology have been extensively studied in adults, but data on children are lacking.

Objective

To examine the association between masseter muscle thickness and vertical cephalometric parameters in a group of Class II malocclusion growing children.

Methods

The current study design was retrospective and cross‐sectional, looking at a sample of 211 growing children with Class II malocclusion between the ages of 6 and 15 derived from two centers. Ultrasonographic masseter muscle thickness measurements and vertical cephalometric variables, including the gonial angle, were evaluated before any orthodontic treatment had been carried out. Multiple linear regression analysis was used to examine the association between masseter muscle thickness and vertical cephalometric measurements, including age and patient origin as independent variables in the analysis.

Results

In the present sample, masseter muscle thickness was found to be independent of sex, but correlated with age, with older children presenting thicker masseter muscles. In the total patient sample, using multiple regression analyses, children with thicker masseter muscles had significantly smaller intermaxillary and gonial angles. No other cephalometric vertical characteristics showed associations with masseter muscle thickness.

Conclusion

In growing children with Class II malocclusion, those with thicker masseter muscles are more likely to display smaller intermaxillary and gonial angles respectively.

Wild versus lab house mice: Effects of age, diet, and genetics on molar geometry and topography

Molar morphology is shaped by phylogenetic history and adaptive processes related to food processing. Topographic parameters of the occlusal surface, such as sharpness and relief, can be especially informative regarding diet preferences of a species. The occlusal surface can however be deeply modified by wear throughout an animal's life, potentially obliterating other signals. Age being difficult to assess in wild populations, especially small rodents, experimental studies of wear through age in laboratory populations may constitute a powerful way to assess its impact on molar geometry and topography, and to validate descriptors of molar morphology that could mitigate this issue. Molar morphology was therefore quantified using 3D geometric morphometrics and topographic estimates in four groups of house mice: wild-trapped mice, lab-bred offspring of these wild mice, typical laboratory mice, and their hybrids. Three descriptors of the molar morphology were considered: the surface of the whole molar row, the surface of the first upper molar, and a truncated template of the first upper molar mimicking advanced wear. Increasing wear with age was demonstrated in the different groups, with a more pronounced effect in the wild-trapped population. The geometry of the molar row is not only modified by wear, but also by the relative position of the late developing molars on the jaw due to loading during mastication. As a consequence, the alignment of the molars is modified in wild mice, showing a qualitative difference between wild animals and their lab-bred offspring. Results obtained from the lab should thus be transferred with caution to the interpretation of differences in wild populations. Topographic estimates computed for the first upper molar seems to provide more stable parameters than those based on the whole molar row, because issues related to non-planar occlusal surface along the molar row are discarded. The truncated template was proven efficient in discarding the wear effect to focus on genetic differences, allowing an efficient characterization of the hybridization signature between wild and lab mice. Dominance of the wild phenotype for the first molar shape supports that the lab strain evolved in a context of relaxation of the selective pressures related to nutrition.

A dental revolution: The association between occlusion and chewing behaviour

Dentistry is confronted with the functional and aesthetic consequences that result from an increased prevalence of misaligned and discrepant dental occlusal relations in modern industrialised societies. Previous studies have indicated that a reduction in jaw size in response to softer and more heavily processed foods during and following the Industrial Revolution (1,700 CE to present) was an important factor in increased levels of poor dental occlusion. The functional demands placed on the masticatory system play a crucial role in jaw ontogenetic development; however, the way in which chewing behaviours changed in response to the consumption of softer foods during this period remains poorly understood. Here we show that eating more heavily processed food has radically transformed occlusal power stroke kinematics. Results of virtual 3D analysis of the dental macrowear patterns of molars in 104 individuals dating to the Industrial Revolution (1,700-1,900 CE), and 130 of their medieval and early post-medieval antecedents (1,100-1,700 CE) revealed changes in masticatory behaviour that occurred during the early stages of the transition towards eating more heavily processed foods. The industrial-era groups examined chewed with a reduced transverse component of jaw movement. These results show a diminished sequence of occlusal contacts indicating that a dental revolution has taken place in modern times, involving a dramatic shift in the way in which teeth occlude and wear during mastication. Molar macrowear suggests a close connection between progressive changes in chewing since the industrialization of food production and an increase in the prevalence of poor dental occlusion in modern societies.

Skull Shape Diversity in Pet Rabbits and the Applicability of Anatomical Reference Lines for Objective Interpretation of Dental Disease

Acquired dental problems are among the most frequently encountered diseases in pet rabbits. However, early symptoms are often overlooked because the affected animals first appear completely asymptomatic. Alterations from anatomical reference lines according to Böhmer and Crossley applied to standard skull X-ray images, have been shown to be indicative of tooth health problems in pet rabbits. Despite its proven usefulness, there are exceptions in which the anatomical reference lines appear not to be suitable for application. We addressed this issue by quantifying the cranial morphology of a large data set of pet rabbit patients (N = 80). The results of the morphometric analyses revealed considerable diversity in skull shape among the typical pet rabbits, but variance in only a few parameters influences the applicability of the anatomical reference lines. The most substantial parameter is the palatal angle. Specimens in which the anatomical reference lines could not be applied, have a rather large angle between the skull base and the palatal bone. We recommend to measure the palatal angle before applying the anatomical reference lines for objective interpretation of dental disease. Pet rabbits with a palatal angle larger than 18.8° are not strictly suitable for the successful application of the anatomical reference lines.

Three-dimensional changes in the craniofacial complex associated with soft-diet feeding

BACKGROUND AND OBJECTIVES

The masticatory force affects craniofacial development. We aimed to quantify the topological deviation of the growing craniofacial structure due to soft-food diet feeding and to map the region where the phenotypes appeared on three-dimensional (3D) images.

MATERIAL AND METHODS

Mice were fed a powdered soft diet (SD) or conventional hard diet (HD) of regular rodent pellets at 3 weeks of age until 9 weeks of age. The heads, excluding the mandibles, were scanned by micro-computed tomography. The topographic deviation of the bony surface was quantitatively assessed by a wire mesh fitting analysis. The actual displacement and significant differences were mapped and visualized in each x-, y-, and z-axis on the 3D craniofacial image. On these reconstructed images, two-dimensional linear measurements between the landmark points confirmed the 3D skeletal displacement.

RESULTS

In the transverse direction, the zygomatic arches and the region in which the temporal muscle attaches to the parietal and temporal bones were narrow in the SD group. The temporal muscle attachment regions significantly shifted anteriorly, and consequently, the sagittal zygomatic arch shortened. Although the cranial sagittal length was not affected, the vertical height was also reduced in the SD group compared to the HD group.

CONCLUSIONS

Our 3D surface-based analysis demonstrated that SD feeding resulted in reduced 3D bony development at the region where the chewing muscles attach to the zygomatic arches and the temporal and parietal bones. Interestingly, SD feeding induced an anterior shift in the temporal and parietal bone regions, which can affect the skeletal inter-jaw relationship.

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.

Evaluating mandibular symphysis bone density according to various skeletal patterns with CBCT

OBJECTIVE

The aim of this retrospective study was to evaluate the bone density (BD) at the mandibular symphysis according to horizontal and vertical patterns using cone-beam computed tomography (CBCT).

SETTING AND SAMPLING

Three hundred nineteen untreated adults with a mean age of 24 years.

MATERIALS AND METHODS

CBCT images were converted into the lateral cephalometric images, and tracings were performed for categorizing the patients based on skeletal features. Cortical BDs at B point, pogonion (Pog), genion (Ge) and menton (Me), and cancellous BDs of the mandibular symphysis were measured using CBCT images. Statistical analyses were performed to evaluate the effects of horizontal and vertical skeletal patterns on BDs.

RESULTS

Females exhibited higher BD than males at the Me, Pog, Ge (P < .001). Hyperdivergent skeletal pattern showed significantly higher cortical BD than normovergent and hypodivergent skeletal patterns at Me (P < .001). Normovergent skeletal pattern showed significantly higher cortical BD than hypodivergent skeletal patterns at Me (P = .001). Class II skeletal pattern showed significantly higher cortical BD than Class I and III skeletal patterns at Me (P < .001) and Ge (P < .05). Class I skeletal pattern showed significantly higher mean cortical BD than Class III skeletal pattern at B point (P = .025). Cancellous BD was higher in Class III and hypodivergent skeletal patterns than others but showed no statistical significance.

CONCLUSIONS

Significant differences were identified across various skeletal patterns. Several mandibular symphyseal landmarks showed statistically significant differences in BD at Me, B point and Ge, with Me having the most statistically significant findings.

Asymmetric Protrusion of the Midface in Young Adults

PURPOSE

This study evaluated midfacial asymmetry using an alternative method that involved comparing bilateral patterns of the zygomaticomaxillary prominence in a young adult population.

MATERIALS AND METHODS

Three-dimensional reconstructed images based on computed tomography scans of 100 Koreans (mean age, 24.7 years) were evaluated with reference to lines spaced at 30° intervals and radiating from the center of an interporion line in a superior view. The surface inclination of the zygomaticomaxillary region was quantified on the same reference lines using a 3-dimensional ruler.

RESULTS

The 30°-interval line (at the level of the zygomaticotemporal suture) was longer on the left side than the right side in both males and females, whereas the left 60°-interval line (at the level of the zygomaticofrontal suture) was longer in females. Comparing the surface protrusion revealed that the zygomaticomaxillary region was more prognathic and inflated on the left side.

CONCLUSION

Functional deviations are considered to be causes of asymmetric craniofacial growth. Postnatal growth allometry across the circummaxillary sutures as elucidated by this study could be useful information in craniofacial surgery.

Proximity of the roots of posterior teeth to the maxillary sinus in different facial biotypes

INTRODUCTION

Orthodontists consider facial growth pattern and oral function when developing a treatment plan. Less attention is given to the relationship between the maxillary posterior teeth and the maxillary sinus. We aimed to evaluate the relationship between the roots of the maxillary posterior teeth and the floor of the maxillary sinus.

METHODS

Proximity of the roots to the maxillary sinus was scored for the left and right first and second premolars and molars (scores, 0-3). Mean scores per patient and per tooth type were calculated. The influences of age, sex, and facial biotype on mean scores per patient and tooth were analyzed.

RESULTS

The mean scores per patient and the second molar scores were significantly lower in the normodivergent subjects compared with the hypodivergent subjects, and in the hypodivergent vs the hyperdivergent groups, indicating that the hypodivergent biotype had significantly fewer second molar roots into the sinus than the normodivergent and hyperdivergent biotypes. Age had no effect on mean score per patient, but in the hyperdivergent group, the second molar score increased with age, meaning that second molar roots tend to be closer to the sinus floor.

CONCLUSIONS

In a young population (7-24 years), the positions of the apices of the maxillary second molar roots in relation to the maxillary sinus floor are associated with the facial biotype. In a hypodivergent biotype, the roots of the second molars are located farther from the sinus floor compared with the normodivergent and hyperdivergent facial patterns.

A Novel Method to Detect 3D Mandibular Changes Related to Soft-Diet Feeding

Craniofacial morphology varies among individuals, which is regulated by the interaction between genes and the environment. Soft-diet feeding is a widely-used experimental model for studying the association between the skeletal morphology and muscle-related loading on the bone. Traditionally, these studies have been based on linear and angular measurements provided on two-dimensional (2D) radiographs in the lateral view. However, 2D observation is based on simplification of the anatomical structures and cannot detect three-dimensional (3D) changes in detail. In this study, we newly developed a modified surface-based analysis with micro-3D computed tomography (CT) to examine and detect the 3D changes in the mandible associated with soft-diet feeding. Mice at 3 weeks of age were fed a powdered soft-diet (SD) or hard-diet (HD) of regular rodent pellets until 9 weeks of age. Micro-CT images were taken at age 9 weeks to reconstruct the anatomical architecture images. A computer-generated averaged mandible was superimposed to directly visualize the morphological phenotypes. Gross observation revealed the apparent changes at the posterior body of the mandible, the angular process and the condyle between HD and SD mice. Significant differences in the mapping indicated the regions of significant displacement in the SD mice over the averaged 3D image of the HD mice. This map revealed that vertical displacement was most evident in 3D changes. We also noted a combination of vertical, transverse and anteroposterior directions of displacement in the condylar growth, resulting in complicated shape changes in the whole condylar process in SD mice. In contrast, transverse displacement was more significant in the coronoid process. The map analysis further showed the significant outward displacement of the inner surface of the alveolar process, which consequently resulted in thinning of the alveolar process.

Agenesis of Third Molars among Turkish Children between the Ages of 12 and 18 Years: A Retrospective Radiographic Study

PURPOSE

The aim of this study was to investigate the agenesis of third molars (M3) in children with permanent dentition in a limited population in the province of Izmir, Turkey.

STUDY DESIGN

The panoramic radiographs of 773 patients (457 females, 316 males) were evaluated retrospectively at the Dental Hospital of Ministry of Health in İzmir, Turkey. The patients' ages ranged from 12-18 years. The agenesis of M3 teeth was investigated according to maxilla and mandible and right and left distribution.

RESULTS

In 593 of the patients (76.7%), all of the M3 teeth were present in the mouth; while in the other 180 (23.3%) patients, agenesis of a varying number of M3 teeth was identified. In 31 patients (4.0%), total M3 tooth agenesis was observed. A statistically significant relationship was not found between gender and M3 teeth (p=0.091). A statistically significant relationship was found between congenital M3 tooth agenesis and the maxilla (14.3%) and mandible (9.6%) (p<0.001). However, a statistically significant difference was not found between the right-left area of the jaw (p=0.100).

CONCLUSION

As a result, while all M3 teeth were present in 76.71% of the population studied in the province of Izmir, agenesis of one or more than one M3 tooth was found in the other 23.29% of the patients studied.

Developmental instability and its relationship to mental health in two historic Dutch populations

This study aimed to assess the magnitude and patterns of fluctuating asymmetry as an indicator of developmental instability between two urban archeological Dutch populations. The sample comprised of 209 adult individuals representing the general population of Alkmaar, the Netherlands, dating to the 18th to early 19th century (Grote Kerk, n=134), and a psychiatric hospital sample of the 19th to early 20th century (Meerenberg, n=75). Fluctuating asymmetry was assessed from left and right measurements recorded from various traits on the cranium, mandible, and dentition. Three non-specific skeletal indicators of stress were documented to aid in the interpretation of the differences in asymmetry. No significant difference in developmental instability, as reflected by fluctuating asymmetry, was apparent between the two populations. However, individuals who presented with skeletal lesions indicative of stress were significantly more asymmetric than individuals who did not present with any of the lesions. The observed frequencies of the pathological changes and socio-economic history suggest that the two populations experienced similar levels of stress, even though the source and duration of the stress might have been different. The possibility that the mentally institutionalized are not as developmentally unstable as suggested by previous research should be considered.

Prevalence of Third Molar Agenesis: Associated Dental Anomalies in Non-Syndromic 5923 Patients

The aim of this study was to investigate the prevalence of third molar agenesis and other associated dental anomalies in Bangladeshi population and to investigate the relationship of other dental anomalies with the third molar presence/agenesis. A retrospective study was performed using panoramic radiographs of 5923 patients, who ranged in age from 10 to 50 years. All radiographs were analyzed by Planmeca Romexis® 3.0 software (Planmeca Oy, Helsinki, Finland). Pearson chi-square and one way ANOVA (Post Hoc) test were conducted. The prevalence of third molar agenesis was 38.4%. The frequency of third molar agenesis was significantly higher in females than males (p <0.025). Third molar agenesis was significantly more prevalent in maxilla as compared to mandible (p <0.007). The prevalence of other dental anomalies was 6.5%, among them hypodontia was 3.1%. Prevalence of third molar agenesis varies in different geographic region. Among the other dental anomalies hypodontia was more prevalent.

Anatomical, functional, physiological and behavioural aspects of the development of mastication in early childhood

Mastication efficiency is defined as the efficiency of crushing food between the teeth and manipulating the resulting particles to form a swallowable food bolus. It is dependent on the orofacial anatomical features of the subject, the coordination of these anatomical features and the consistency of the food used during testing. Different measures have been used to indirectly quantify mastication efficiency as a function of children's age such as observations, food bolus characterisation, muscle activity measurement and jaw movement tracking. In the present review, we aim to describe the changes in the oral physiology (e.g. bone and muscle structure, teeth and soft tissues) of children and how these changes are associated with mastication abilities. We also review previous work on the effect of food consistency on children's mastication abilities and on their level of texture acceptance. The lack of reference foods and differences in testing methodologies across different studies do not allow us to draw conclusions about (1) the age at which mastication efficiency reaches maturity and (2) the effect of food consistency on the establishment of mature mastication efficiency. The effect of food consistency on the development of children's mastication efficiency has not been tested widely. However, both human and animal studies have reported the effect of food consistency on orofacial development, suggesting that a diet with harder textures enhances bone and muscle growth, which could indirectly lead to better mastication efficiency. Finally, it was also reported that (1) children are more likely to accept textures that they are able to manipulate and (2) early exposure to a range of textures facilitates the acceptance of foods of various textures later on. Recommending products well adapted to children's mastication during weaning could facilitate their acceptance of new textures and support the development of healthy eating habits.

Effects of masticatory muscle training on maximum bite force and muscular endurance

OBJECTIVE

This study evaluates the effects of chewing training on strength and endurance of the masticatory muscles.

MATERIALS AND METHODS

Of the 49 healthy young adults included in the study, nine served as controls for a baseline measurement of bite force. The 40 participants who actively trained their masticatory muscles were randomly divided into a 'continuous training group' (CTG) and an 'intermittent training group' (ITG). The participants performed oral motor training by clenching silicon tubes (Chewy Tubes(™)) according to a designed protocol. The muscular strength was studied in terms of maximum bite force. Muscular endurance was evaluated by measuring the duration for which the participants held 50% of their maximum bite force value.

RESULTS

Both the maximum bite force and the muscular endurance capacity increased after intensive training for both groups. After 2 months, the ITG stopped training for 1 month. At this point, a significant difference was identified both in the mean bite force values and the mean muscular endurance duration: the ITG exhibited lower values. For both groups, the highest values were attained after 3 months of training. The maximum bite force values and the muscular endurance duration were observed to follow similar patterns. The effects attained decreased rapidly in both groups when the training stopped.

CONCLUSIONS

For both the continuous and intermittent training groups, 4 months of chewing exercises strengthened masticatory muscles, but such effects diminished gradually for both groups when the exercises stopped.

Morphological integration between the cranial base and the face in children and adults

The primary aim of the present study was to assess morphological covariation between the face and the basicranium (midline and lateral), and to evaluate patterns of integration at two specific developmental stages. A group of 71 children (6-10 years) was compared with a group of 71 adults (20-35 years). Lateral cephalometric radiographs were digitized and a total of 28 landmarks were placed on three areas; the midline cranial base, the lateral cranial base and the face. Geometric morphometric methods were applied and partial least squares analysis was used to evaluate correlation between the three shape blocks. Morphological integration was tested both with and without removing the effect of allometry. In children, mainly the midline and, to a lesser extent, the lateral cranial base were moderately correlated to the face. In adults, the correlation between the face and the midline cranial base, which ceases development earlier than the lateral base, was reduced. However, the lateral cranial base retained and even strengthened its correlation to the face. This suggests that the duration of common developmental timing is an important factor that influences integration between craniofacial structures. However, despite the apparent switch of primary roles between the cranial bases during development, the patterns of integration remained stable, thereby supporting the role of genetics over function in the establishment and development of craniofacial shape.

Effects of restriction of fetal jaw movement on prenatal development of the temporalis muscle

Jaw movement affects masticatory muscles during the postnatal period. Prenatal jaw movement has also been implicated in the development of the temporomandibular joint; however, its effect on prenatal development of the masticatory muscles has not been extensively analysed. In the present study, we examined the effects of the restriction of fetal jaw movement on the temporalis muscle, a major masticatory muscle, in mice by suturing the maxilla and mandible (sutured group) using an exo utero development system. We compared the morphology of the temporalis muscle between sutured, sham-operated and normal in utero groups. At embryonic day (E) 18.5, the volume of muscle fibres, but not that of connective tissue, in the temporalis muscle was decreased in the sutured group. The E18.5 temporalis muscle in the sutured group appeared morphologically similar to that of the E17.5 in utero group, except for frequent muscle fibre irregularities. By transmission electron microscopy, in the sutured group, the myofibrils were immature and scattered, the nuclei appeared comparatively immature, the mitochondria were expanded in volume with fewer cristae, and cytoplasmic inclusion bodies were frequently observed. Expression of Myf-6, a late myogenic transcription factor, by real-time RT-PCR was not significantly different between the sutured and sham-operated groups. These findings demonstrated approximately 1-day delay in the morphological development of the temporalis muscle in the sutured group, and some abnormalities were observed, although Myf-6 level was not affected in the sutured group. The present study revealed that the prenatal jaw movement influences the development of the temporalis muscle.

Masticatory muscle activity in children with a skeletal or dentoalveolar open bite

SUMMARY

The aim of this study was to compare the electromyographic (EMG) characteristics of masticatory muscles in children with either a skeletal or dentoalveolar open bite, compared with a control group (CG). Forty-five children (31 boys and 14 girls), aged 6-11 years, were included in the study, 15 with a skeletal anterior open bite (SAOB), 15 with a dentoalveolar anterior open bite (DAOB), and 15 with a normal occlusion (CG), defined by clinical evaluation and lateral cephalograms. EMG recordings of the temporal and masseter muscles were performed under maximal voluntary clenching and during chewing. Analysis of variance was used for inter-group analysis, followed by the Tukey post hoc test. A Student's t-test for paired data was used for intra-group analysis. There were statistically significant differences among the three groups (P < 0.05), with the mean EMG being highest in the CG and lowest in children with a SAOB. The percentage EMG activity during chewing in relation to that during maximal voluntary clenching was more than 100 per cent in the SAOB group. The CG and DAOB groups presented higher EMG activity during clenching compared with chewing (P < 0.001), as well as a greater difference between tasks. In the SAOB group, the neuromuscular system appeared to have a lower capacity to produce EMG activity according to the task, while that in the DAOB group suggests that their functional capacity during growth should also be carefully observed.

Deformation of nasal septal cartilage during mastication

The cartilaginous nasal septum plays a major role in structural integrity and growth of the face, but its internal location has made physiologic study difficult. By surgically implanting transducers in 10 miniature pigs (Sus scrofa), we recorded in vivo strains generated in the nasal septum during mastication and masseter stimulation. The goals were (1) to determine whether the cartilage should be considered as a vertical strut supporting the nasal cavity and preventing its collapse, or as a damper of stresses generated during mastication and (2) to shed light on the overall pattern of snout deformation during mastication. Strains were recorded simultaneously at the septo-ethmoid junction and nasofrontal suture during mastication. A third location in the anterior part of the cartilage was added during masseter stimulation and manipulation. Contraction of jaw closing muscles during mastication was accompanied by anteroposterior compressive strains (around -1,000 muepsilon) in the septo-ethmoid junction. Both the orientation and the magnitude of the strain suggest that the septum does not act as a vertical strut but may act in absorbing loads generated during mastication. The results from masseter stimulation and manipulation further suggest that the masticatory strain pattern arises from a combination of dorsal bending and/or shearing and anteroposterior compression of the snout.

The adaptive response of jaw muscles to varying functional demands

Jaw muscles are versatile entities that are able to adapt their anatomical characteristics, such as size, cross-sectional area, and fibre properties, to altered functional demands. The dynamic nature of muscle fibres allows them to change their phenotype to optimize the required contractile function while minimizing energy use. Changes in these anatomical parameters are associated with changes in neuromuscular activity as the pattern of muscle activation by the central nervous system plays an important role in the modulation of muscle properties. This review summarizes the adaptive response of jaw muscles to various stimuli or perturbations in the orofacial system and addresses general changes in muscles as they adapt, specific adaptive changes in jaw muscles under various physiologic and pathologic conditions, and their adaptive response to non-surgical and surgical therapeutic interventions. Although the jaw muscles are used concertedly in the masticatory system, their adaptive changes are not always uniform and vary with the nature, intensity, and duration of the stimulus. In general, stretch, increases neuromuscular activity, and resistance training result in hypertrophy, elicits increases in mitochondrial content and cross-sectional area of the fibres, and may change the fibre-type composition of the muscle towards a larger percentage of slow-type fibres. In contrast, changes in the opposite direction occur when neuromuscular activity is reduced, the muscle is immobilized in a shortened position, or paralysed. The broad range of stimuli that affect the properties of jaw muscles might help explain the large variability in the anatomical and physiological characteristics found among individuals, muscles, and muscle portions.