Basic and patient-oriented research
Examination of Masticatory Movement and Rhythm Before and After Surgical Orthodontics in Skeletal Class III Patients With Unilateral Posterior Cross-Bite

https://doi.org/10.1016/j.joms.2009.04.027Get rights and content

Purpose

We examined the movement of the mandible in skeletal Class III patients with a unilateral posterior cross-bite to clarify whether the correction of the cross-bite caused conversion of the masticatory movement from a reverse to a grinding pattern.

Materials and Methods

We studied 10 adults with mandibular prognathism who had been treated with surgery. The masticatory movement and rhythm (cycle time) during gum chewing were recorded before and after treatment.

Results

The results before treatment demonstrated a high frequency of patterns IV, VI, and VII and a low frequency of patterns I, II, and III on the cross-bite side. After treatment, the masticatory movement on the cross-bite side showed different patterns than from before treatment. The high frequency of pattern VI (reverse pattern) before treatment was significantly reduced, and patterns I and III had significantly increased in frequency after treatment. No significant changes were seen in cycle time, opening phase, occlusal phase, or the closing phase before and after treatment.

Conclusions

These results suggest that correction of a unilateral posterior cross-bite induces conversion of the masticatory pattern from the reverse pattern to the grinding pattern.

Section snippets

Patients

Ten adult patients (2 men and 8 women, mean age 26.1 years) with mandibular prognathism, who had been treated orthognathically at Tsurumi University Dental Hospital, were included in the present study.

The inclusion criteria were the diagnosis of skeletal Class III malocclusion with a unilateral posterior cross-bite and the lack of periodontal disease, signs or symptoms of trismus, or extensive dental work, and no current dental treatment. Patients with cleft lip and palate and those with

Masticatory Patterns

The examination of the masticatory movement at T1 demonstrated characteristic masticatory patterns on the cross-bite side. Although subjects with normal occlusion have a high frequency of patterns I, II, and III (grinding pattern),5, 11, 14, 15 most patients in the present study had different masticatory patterns. In the T1 data of the cross-bite side, a high frequency of masticatory patterns IV, VI, and VII and a low frequency of patterns I, II, and III were seen (Table 1, T1). The masticatory

Discussion

Several classifications have been done of the analysis of masticatory movement.4, 5, 11, 15 Proschel and Hofman5 analyzed the masticatory movement in detail and classified it into 196 patterns. It would have been difficult, however, to classify the 10 strokes counted in the present study into 196 patterns. In contrast, Akiyama et al14 proposed a more simple and practical classification system. Their system consists of 2 opening paths, 2 closing paths, regular or irregular, and 8 patterns (Fig 1

References (20)

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    Malocclusion with skeletal Class III is characterized by Angle Class III, anterior crossbite, compensatory inclination of incisors for skeletal discrepancy and uni- or bilateral posterior crossbite due to the transverse maxillary deficiency. Several studies have demonstrated that patients with skeletal Class III malocclusion show disorders of masticatory function associated with the malocclusion and jaw deformity; muscle activity,1–3 jaw movement,2–5 masticatory efficacy,1 and bite force.2 However, the effect of the severity of skeletal discrepancy on masticatory functional disorder is not yet clear.

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    Transverse maxillary deficiency with a uni- or bilateral crossbite is frequently identified in patients with mandibular prognathism.21 The posterior crossbite was found to play a role in the high frequency of reverse and reverse-crossing chewing type13 and correction of the posterior crossbite was associated with a significant decrease in the high prevalence of reverse chewing type in patients with posterior crossbite.19 On the other hand, previous studies suggested that orthognathic surgery improved the chewing pattern in patients with mandibular prognathism though it remained incomplete, compared with the control.4,14

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    The three-dimensional jaw movements during mastication can be analyzed by means of several specific spatiotemporal parameters of each masticatory cycle, as maximum range of motion, total cycle area, opening and closing maximum velocity, cycle duration, vertical, posterior, and right and left jaw movements (Buschang, Hayasaki & Throckmorton, 2000; Ferrario et al., 2006; Lepley, Throckmorton, Parker, & Buschang, 2010; Radke, Kull & Sethi, 2014). Also, the opening and closing phases of the chewing cycles have been subjectively classified in various characteristic patterns, according to the shape and direction of the trajectory, suggesting the existence of relations between the representative types of mandibular trajectories and malocclusions, and even with the presence of TMD (Kobayashi et al., 2009; Naeije & Hofman, 2003; Takeda et al., 2009). Considering the potential ability of selected descriptors of chewing cycles to differentiate among normalcy and various pathologies, but also the variability inherent in each subject, different methods have been used to study within-subject variability, which include the selection of “representative” cycles and the use of statistical approaches (Buschang, Hayasaki & Throckmorton, 2000; Ferrario et al., 2006; Shiga et al., 2009; Wintergerst, Throckmorton, & Buschang, 2008; Wintergerst, Buschang & Throckmorton, 2004).

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