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Background: Everyday jaw functions such as jaw opening, chewing, and eating are highly important for oral and general health. In adults, these actions involve coordinated activity between the jaw and neck, with jaw opening typically accompanied by neck extension and jaw closing with neck flexion. This reflects an elaborate and synchronized integration between trigeminal and cervical sensorimotor function. However, there is a notable lack of studies investigating the presence of this integration in children, how it develops throughout childhood, and how it manifests during early adolescence. The primary aim of this thesis was to explore the integrated jaw-neck motor function in children and adolescents compared to adults. This was achieved through a detailed description and objective quantification of jaw-neck movement patterns using kinematic analysis.

Methods: The thesis is based on four studies conducted at the Motion Laboratory, Department of Odontology, Umeå University, Sweden. Study I assessed the accuracy of a 3D kinematic method and test-retest reliability of functional jaw range of motion observed in 17 pain-free adult participants. Study II explored jaw-neck movement integration during jaw motor tasks in 25 healthy 6-year-olds and 24 adults. Study III followed 20 of these 25 children at ages of 10 and 13 to evaluate developmental changes in jaw-neck motor function compared to adults. Study IV characterized initial jaw and head movement adjustments during jaw function in 20 healthy young adolescents and 20 adults. All participants underwent clinical examination of the jaw and neck system, followed by motion capture of jaw and head movements during jaw opening-closing and chewing tasks.

Results: The 3D kinematic method displayed high accuracy. Jaw movements in the horizontal plane showed higher variability, likely due to biomechanical complexity. Compared to adults, 6-year-olds exhibited integrated jaw-neck motor function, though their movement patterns remained immature, characterized by smaller magnitudes, increased variability in jaw-neck coordination, and greater relative contribution of head movements and longer cycle durations during jaw motor tasks. Between the ages of 6, 10 and 13, motor development progressed during functional jaw movements. At ages 6 and 10, movement variability and cycle durations were more pronounced than in adults. By age of 13, movement patterns more closely resembled those of adults; however, initial movement characteristics still differ between adolescents and adults.

Conclusions: This thesis mapped typical developmental changes in the jaw-neck motor function from childhood to early adolescence. The kinematic method used provides reliable measurements for capturing these changes. Significant differences in spatial and temporal movement parameters were observed between children, adolescents and adults. Between the ages of 6, 10 and 13, the movement pattern becomes more coordinated and increasingly resembles that observed in adults. However, a distinction between adolescents and adults persists during the initiation of a motor task, suggesting that jaw-head movement coordination continues to refine from early adolescence into adulthood. Normative values based on key jaw-neck movement events during typical development may be of great importance for identifying atypical development and may be valuable when assessing children and adolescents with pain and motor disabilities in the jaw-neck system.

Jaw-head movement coordination develops during adolescence. However, functional adjustments during this period remain poorly understood. This study aimed to characterize jaw and head movement adjustments in early adolescents and compare this to adults. Three-dimensional optical cameras captured jaw and head movements during maximum jaw opening-closing and chewing. Twenty (8 females, 12 males) adolescents (mean 13.5 yr, standard deviation [SD] 8 months) and 20 (9 females, 11 males) adults (mean 28.2 yr, SD 80 months) participated. Outcomes included jaw and head movement magnitudes, movement cycle time, time to first peak value, and initial phase. Functional data analysis and Wilcoxon rank-sum tests were employed. Adolescents showed larger head magnitude in jaw opening-closing and smaller jaw magnitude than did adults during chewing in the first movement cycle. Adolescents exhibited longer time to peak and time of first movement cycle during jaw opening-closing. During chewing, adolescents showed a longer initial phase, time to peak for consecutive cycles, and movement cycle time. For both age groups, the first cycle differed from consecutive cycles in jaw and head movement magnitudes and cycle times. Compared to adults, adolescents displayed pronounced spatiotemporal initial jaw-head movement adjustments during jaw function, particularly in the first movement cycle. Jaw-head coordination refines from early adolescence into adulthood.

Background: Three dimensional (3D) kinematic analysis based on motion capture can study synchronized data from the integrated jaw and neck motor system. Jaw function is commonly estimated on linear outcome variables of motion range. By combining jaw border movements in three planes the functional range of motion could be described by movement area and volume measures.

Research question: Can we ensure the accuracy, test-retest reliability, and intra-individual variability with 3D kinematic analysis for estimating jaw functional range of motion (ROM), including jaw movement area and volume and jaw and head linear measures?

Methods: Accuracy was estimated by applying the method to a set of beakers with known volume, based on the percentage deviation and Pearson correlation coefficient between target and estimated values. Test-retest reliability was then analysed on maximum jaw movements performed in a pre-determined movement sequence by 17 pain-free participants (25.4 years ± 2.4) to estimate jaw functional ROM. Intraclass correlation coefficients (ICC) were calculated, and Bland-Altman plots were constructed. Coefficient of variation (CV) tested the within session reliability.

Results: The accuracy in volume and area measurements were high with a percentage deviation (0.03±0.59) and (1.2±0.45), respectively, with a strong linear relationship (R²=0.99) between target and estimated values. The test-retest reliability showed moderate to excellent reliability, and Bland-Altman plots showed good agreement. Overall, CVs showed high repeatability, but jaw movements in horizontal directions were less reliable and presented higher variability.

Significance: The study with 3D kinematic analysis of jaw functional ROM, provides a methodological basis for accurate and reliable measurements. The study presents a new way to estimate jaw functional ROM measures, useful for evaluation in clinical intervention, for instance in pain and jaw dysfunction. Moreover, the natural biological movement variability and the complexity of the interplay of jaw-head movement will be emphasised.

BACKGROUND: A functional integration between the jaw and neck regions during purposive jaw movements is well described in adults, but there is a lack of knowledge of such integration during jaw function in children.

OBJECTIVES: To determine the movement integration between the jaw and neck during jaw motor tasks in 6-year-olds, whether there is a difference between children and adults.

METHODS: Jaw and neck movements were recorded with an optoelectronic 3D system in 25 healthy 6-year-olds (12 girls, 13 boys) and 24 healthy adults (12 women, 12 men) during paced jaw opening-closing and self-paced gum chewing. Jaw and neck movement amplitudes, intra-individual variation in movement amplitude, ratio between neck-jaw movement amplitudes and movement cycle time were analysed. Differences between children and adults were evaluated with Mann-Whitney U test for independent samples.

RESULTS: Compared to adults, 6-year-old children showed larger neck movement amplitudes (P = .008) during chewing, higher intra-individual variability in amplitudes of jaw (P = .008) and neck (P = .001) movements, higher ratio between neck-jaw movement amplitudes for jaw opening-closing (P = .026) and chewing (P = .003), and longer jaw movement cycle time (P ≤ .0001) during the jaw opening-closing task.

CONCLUSION: Despite integrated jaw-neck movements in 6-year-old children, the movement pattern differs from that of adults and may be interpreted as an immature programming of jaw-neck motor behaviour. The well-integrated movements observed in adults most likely develop over years, perhaps into adolescence, and needs further research including well-controlled longitudinal studies to map this development in order to provide appropriate age-related clinical treatment for functional disorders.

The clinical examination in diagnostic criteria for temporomandibular disorders (DC/TMD) is a strict procedure and comprises mandatory commands. However, learning and using these mandatory commands in general practice have proven to be difficult and their use of DC/TMD is minimal. To investigate whether reliability on a diagnostic level for DC/TMD diagnoses differs between examiners using the mandatory commands or not. Six examiners were divided into two groups: one using the mandatory commands in DC/TMD for the clinical examination and one who did not use the mandatory commands. A reliability assessment was performed twice, one occasion for each group of examiners. The assessment was performed according to the guidelines from the International Network for Orofacial Pain and Related Disorders Methodology. Each group of examiners thereby examined 16 subjects (11 TMD patients and 5 healthy individuals) each, and the diagnostic agreement (reliability) as compared to diagnoses derived by a reference standard examiner was calculated with Cohen' s kappa coefficient. The DC/TMD diagnoses myalgia, arthralgia and headache attributed to TMD were included in the reliability assessment. There was no significant difference regarding diagnostic agreement reliability between the examiners using or not using the mandatory DC/TMD commands. This study indicates that not using the mandatory commands in DC/TMD in general practice does not impair the diagnostic reliability regarding the diagnoses myalgia, arthralgia and headache attributed to TMD compared to including the commands.