Characteristics of protrusive and lateral excursions of the mandible in children with the primary dentition

In vivo three-dimensional mandibular kinematics and functional point trajectories during temporomandibular activities using 3d fluoroscopy

OBJECTIVES

To measure in vivo three-dimensional kinematics of the mandible and associated end-point trajectories and to quantify their relationships during temporomandibular joint activities using 3D fluoroscopy.

METHODS

A novel fluoroscopy-based 3D measurement method was used to measure motions of the mandible and the associated end points (i.e. incisors and lateral poles of both condyles) during open close, lateral gliding and protrusion-retraction movements in healthy young individuals. The contributions of each of the rotational and translational components of the mandible to the end-point trajectories were quantified through experiment-based computer simulations.

RESULTS

The mandibular rotation was found to account for 91% of the maximal mouth-opening-capacity and 73% of the maximal lateral incisor movement, while the condylar translation contributed to 99% of the anterior protrusion distance. Incisor trajectories were nearly vertical within the first 60% of the maximal opening during the open-close movement.

CONCLUSIONS

Similar condylar downward rotation paths but with bilaterally asymmetrical ranges were used to perform basic mandibular movements of different targeted TI trajectories in three dimensions, that is, open-close, lateral-gliding and protrusion-retraction. Mandibular rotations contributed to the majority of the principal displacement components of the incisor, that is, vertical during open-close and towards the working-side-during lateral-gliding, while mandibular translation contributed mainly to the forward movement of the incisor during protrusion-retraction. Owing to the anatomical constraints, the freedom of mandibular translation is limited and mainly in the anteroposterior direction, which is considered helpful for the control and stability of the TMJ during oral activities.

Can mastication in children with cerebral palsy be analyzed by clinical observation, dynamic ultrasound and 3D kinematics?

The aim of this study was to explore the feasibility of the Mastication Observation and Evaluation (MOE) instrument, dynamic ultrasound and 3D kinematic measurements to describe mastication in children with spastic cerebral palsy and typically developing children. Masticatory movements during five trials of eating a biscuit were assessed in 8 children with cerebral palsy, spastic type (mean age 9.08years) and 14 typically developing children (mean age 9.01years). Differences between trials were tested (t-test) and the mastication of individual children with cerebral palsy was analyzed. MOE scores ranged from 17 to 31 (median 24) for the children with cerebral palsy and from 28 to 32 (median 31) for the typically developing children. There was an increased chewing cycle duration, a smaller left-right and up-down tongue displacement and larger anterior mandible movements for the trials (n=40) of cerebral palsy children (p<0.000 for all comparisons) compared to the trials of typically developing children (n=70). The MOE captures differences in mastication between individual children with cerebral palsy. The MOE items 'jaw movement' and 'fluency and coordination' showed the most similarity with the objective measurements. Objective measurements of dynamic ultrasound and 3D kinematics complemented data from the MOE instrument.

Jaw motion during gum-chewing in children with primary dentition

This study was undertaken to characterize jaw motion during mastication in children with primary dentition and to compare jaw motion with that in adults. The means and the variances of the traditional parameters for the chewing cycle, i.e., duration, excursive ranges and 3-D distances of travel at the lower incisor, molars and condyles were analyzed and compared in 23 children and 25 female adults. The duration of opening in children was significantly shorter than that of adults. Significant differences between children and adults were observed in lateral and vertical excursion of the incisor, lateral excursion at the molars, and vertical excursion at the condyles. Many of these measurements had larger between-subject and between-cycle variances in children than adults, suggesting that chewing motion in children has not yet matured. The results of this study indicate that chewing motion in children is different from that of adults.

Limites de movimentos mandibulares em crianças

TEMA: a determinação dos limites de movimentos mandibulares é um importante procedimento na avaliação do estado funcional do sistema estomatognático, porém poucos são os estudos que focalizam os parâmetros de normalidade ou desvios em crianças. Objetivos: definir as médias dos limites de movimentos mandibulares em crianças brasileiras de 6 a 12 anos de idade; verificar diferenças entre os gêneros, em cada faixa etária, e entre as faixas etária de 6 a 8 anos, 8:1 a 10 anos e 10:1 a 12 anos de idade. MÉTODO: participaram 240 crianças, escolares do interior do Estado de São Paulo. Com o auxílio de um paquímetro digital foram mensuradas a máxima abertura mandibular, a protrusão, a excursão lateral direita e esquerda e o desvio da linha média, quando presente. O teste T Student, a Análise de variância e o pós-teste Tukey foram considerados significantes para p < 0,05. RESULTADOS: as médias das medidas da amostra foram: máxima abertura mandibular 44,51 mm, excursão lateral direita 7,71mm, excursão lateral esquerda 7,92 mm e a protrusão 7,45 mm. Não houve diferença estatística entre os gêneros. Houve aumento gradual nos limites dos movimentos mandibulares com o aumento da faixa etária, com diferenças significantes principalmente entre as faixas etárias de 6 - 8 anos e 10:1-12 anos. CONCLUSÃO: durante a infância os limites de movimentos mandibulares aumentam e a idade deve ser considerada na análise desses dados para maior precisão no diagnóstico.

Changes in condylar path inclination during maximum protrusion between the ages of 6 and 12 years

The purpose of this study is to quantify the changes in sagittal condylar path inclination during mandibular protrusion between the ages of 6 and 12 years. A total of 172 children (82 males and 90 females) ranging in age from 6.5 to 12.9 years were divided according to their chronological age into five subgroups with mean ages of 7.1, 8, 9, 10 and 11.4 years respectively. The control group consisted of 41 adults with a mean age of 28 years. All subjects had a normal temporomandibular joint function and neutral occlusion. Five maximum protrusion-retrusion movements were recorded with six degrees of freedom in each subject using an ultrasound (JMA) jaw-tracking system. Initially, condylar path inclination angle (CPIA) was calculated stepwise for each millimetre distance, for the first 10 mm of protrusive tracing path on both sides. A single mean value was then assigned for the entire protrusive path. One-way analysis of variance proved to be significant among the five subgroups of children. Linear regression analysis showed that condylar path had a tendency to become steeper with age, although it was statistically weak. The data indicated that the mean CPIA is 43 degrees -44 degrees at the age of seven, increases annually by 1.2 degrees -1.3 degrees and reaches an average of 49 degrees -50 degrees by the age of 12 at which time it attains around 83-85% of its adult level. In subgroup V, the female population had significantly steeper condylar path on the left-hand side than the male population. Condylar path inclinations indicated a symmetrical growth pattern of the articular eminence.

Changes in the masticatory cycle after treatment of posterior crossbite in children aged 4 to 5 years

INTRODUCTION

The aim of this study was to analyze the dynamics of the masticatory cycle after occlusal adjustment through coronoplasty on deciduous teeth (selective grinding) and composite resin occlusal guidance for posterior crossbite correction.

METHODS

Nineteen children, aged 4 to 5 years, with functional posterior crossbites diagnosed at their clinical examinations, were selected. Analyses of masticatory cycles, including lateral excursive movements, were performed before and after treatment by using kinesiographic examinations in the 3 reference planes (frontal, horizontal, and sagittal). The examinations were done during bubble-gum chewing. The data were submitted to sign, Mann-Whitney, and paired t tests concerning the variables: left maximum lateral movement, right maximum lateral movement, total lateral movement (LM), vertical movement (VM), anteroposterior maximum movement, maximum lateral movement (MLM), and total maximum lateral movement (TMLM).

RESULTS

The treatment produced increased TMLM, a significant increase of the MLM opposite the crossbite, no statistically significant difference of the crossbite side, and a significant decrease of LM. Left crossbite children showed significant decreases in the LM after treatment; right crossbite children showed significant increases in VM after treatment.

CONCLUSIONS

Functional crossbite treatment with selective adjustment and occlusal guiding changed masticatory cycle patterns, producing larger horizontal and vertical planes. The cycles became more symmetric in the frontal plane, increasing the tendency of bilateral alternate mastication.

Longitudinal observation of basic mandibular movements: report of a case

Sound development of mandibular function during childhood is indispensable to establishing healthy function in adults. To examine this developmental process, longitudinal recordings of basic mandibular movements were done using an optoelectronic analysis. Mandibular movements were recorded on five separate occasions in one boy, from an age of six years and five months to 14 years and five months. The incisor pathways during protrusion and lateral excursion were initially shallow, with more anterior than inferior movement, but as he grew the amount of inferior movement and the amount of rotation both increased. Similarly, at his first recording there was very little hinge-like rotation during mouth closing, but rotation increased markedly after eruption of his permanent second molars. These findings suggest that mandibular movements change from being relatively simple with more translation in younger children to more complex movements with more rotation once the permanent dentition is established.

Improvement in jaw motion following treatment of unilateral crossbite in a child with primary dentition: a case report

This case report examines jaw motion during both habitual opening-closing and gum chewing in a young (3 years, 10 months) patient with unilateral crossbite at the primary dentition stage. Jaw motion was measured three times: 1. before treatment; 2. after active treatment; and 3. after retention. The abnormal habitual open-close pathway seen prior to treatment was improved after retention. Prior to treatment, movement of the affected-side condyle preceded movement of the non-affected-side condyle during opening. After retention, the movement of the condyles was better coordinated. The chopping type chewing pattern, with less lateral movement, before treatment changed to a more grinding type pattern on the affected side after activation. This study suggests that the prescribed treatment effectively improved both the patient's morphology and function. However, neither the open-close pathways nor the chewing patterns were completely normal after retention. The results in this case suggest that early treatment of functional unilateral crossbite can be effective.

Occlusal contacts during lateral excursions in children with primary dentition

The presence of non-working occlusal contacts in adults is considered abnormal and may initiate parafunctional activity. Few studies have looked for non-working occlusal contacts in children with primary dentition. The purposes of this study were (1) to prove the existence of non-working-side occlusal contacts, and (2) to quantify their area during lateral excursion in children with primary dentition. To achieve this purpose, we developed a measurement system that combined a tracking system for mandibular movements with a three-dimensional digitizer for tooth shape. Ten children were selected for this study. Estimated occlusal contact area of the primary second molar on the non-working side was 0.8 mm2, in contrast to 2.0 mm2 on the working side, at 3.0 mm of movement of the lower incisor. All children examined had some occlusal contacts on the non-working side during the first part of lateral excursion.