Patients

The examined group was composed of two major groups (Table 1). In this population-based study, the first group comprised 81 randomly selected children with age ranging between 6.3 and 10.6 years and an average age of 8.7 years. The examination was conducted in an elementary school in Germany.

Table 1.  Demographic Parameters of the Children's Group and the Adult Group Examined in the Present Study^a

View Fullscreen

The second group was composed of 67 randomly selected adults who ranged in age from 18 to 44 years, with an average age of 29.2 years. All adults had complete permanent dentitions with no missing teeth. The gender distribution of children and adults was equal.

All experiments were conducted by one examiner with the understanding and written consent of each subject. Before the instrumental functional analysis test was performed, the temporomandibular joints of all patients were examined according to the Modified Hamburg CMD-Screening craniomandibular dysfunction (CMD) Test.21 None of the children or adults had any symptoms of functional disorders. No pain was noted upon palpation, and no muscular pain was reported by any examinees. All subjects showed a neutral class I position with no orthodontic treatment history.

Instrumental Function Analysis

Condylar and mandibular movements were recorded with the JMA-System (Jaw Motion Analyzer, Zebris Medical GmbH, Isny, Germany), which is a contactless and remote from the joint ultrasonic registration system. Information on the accuracy and performance of this method has been introduced in previous publications.5722 Sequential ultrasonic pulses are transmitted at a frequency of 40 Hz23 between a sending device mounted on the lower anterior teeth with CronMix K Plus (Merz Dental GmbH, Lütjenburg, Germany) and a receiver mounted on the forehead (Figure 1).

View Figure

• Download as Powerpoint
• Download Figure

Before the registration process was started, the delineation of a reference plane for the WinJaw software program (Zebris Medical GmbH, Isny, Germany) was carried out. The kinematic center as described by Yatabe et al24 was chosen as a condylar reference because of the translatory and rotatory nature of mandibular movements.

In the functional analysis test, all subjects performed three maximum left and right lateral jaw movements that were not manipulated and tooth guided. Each movement was repeated more than once to allow for more accurate readings. Three-dimensional movements were calculated with WinJaw, version 10.05.03.

Statistical Analysis

Documentation and statistical analysis of recorded data were carried out with the Statistical Package for the Social Sciences (SPSS), version 15.0 for Windows (SPSS Inc, Chicago, Ill). Data were presented graphically by box and whisker-plots with the use of SigmaPlot 10.0 (Systat Software GmbH, Erkrath, Germany). Results were considered significant at P ≤ .05.

Maximum Laterotrusion

The maximum laterotrusion of the right and left sides in the group of children and in the adult group is shown in Table 2. The mean maximum laterotrusion in the children's group was 11.0 mm on the right side and 10.6 mm on the left side. As can be seen on the box-plots (Figure 2), the maximum laterotrusion in the adult group exceeded that in the group of children.

Table 2.  Descriptive Statistics for Right and Left Maximum Laterotrusion and Right and Left Maximum Retrusion (all measurements in mm) for the Children's Group and the Adult Group^a,b

View Fullscreen

View Figure

• Download as Powerpoint
• Download Figure

The mean maximum laterotrusion of the group of children on the right side was 90.2% of the mean maximum laterotrusion on this side in the adult group. On the left side, the mean of the group of children corresponded to 90.6% of the adult value. The Kolmogorov-Smirnov test showed a normal distribution of the data, and Levene's test showed no homogeneity of variances. Therefore, significance was tested with the Mann-Whitney U-test. A significant difference between the children's group and the adult group was found in maximum laterotrusion on the right (P < .001) and left (P = .001) sides.

Even though the maximum lateral movement was numerically bigger to the right side than to the left side, no statistically significant differences were identified between the right and left sides in children (U-test; P = .170) or in adults (U-test; P = .097) (Table 3).

Table 3.  Descriptive Statistics for Right and Left Maximum Laterotrusion and Maximum Retrusion (all measurements in mm) for the Children's Group and the Adult Group^a,b

View Fullscreen

Testing for gender specificities with the Mann-Whitney U-test revealed no significant differences in maximum laterotrusion between males and females independent of age group.

Maximum Retrusion

As is shown in Table 2 for the children's group, the mean maximum retrusion on the right and left sides was found to be 0.6 mm, with standard deviations of 0.6 mm on the right and left sides. As is evident on the box-plots (Figure 2), the mean maximum retrusion of the adult group was somewhat smaller than that of the children's group.

Because higher values for the mean maximum retrusion on the right and left sides were found in the children's group, the mean of the adult group corresponded to only 50% on the right side and 66.7% on the left side of the children's group.

The Kolmogorov-Smirnov test showed normal distribution of the data, and Levene's test showed no homogeneity of variances. Therefore, differences in maximum retrusion between the children's group and the adult group were tested for significance with the Mann-Whitney U-test. A significant difference between the children's group and the adult group was found in maximum retrusion on the right (P = 0.008) and left (P = .013) sides (Table 2).

Normal data distribution (Kolmogorov-Smirnov test) and homogeneity of variances (Levene's test) were found for comparison of the right and left sides. Therefore, Student's t-test was applied.

Student's t-test (Table 3) revealed no significant differences in maximum retrusion between the right and left sides for children (P = .654) or for adults (P = .084). The maximum retrusion to the left (0.4 mm) was slightly larger than that to the right side (0.3 mm) in the adult group.

Testing for gender specificities with the Mann-Whitney U-test revealed no significant differences in maximum retrusion between males and females.

Maximum Laterotrusion

In the adult group, the mean maximum laterotrusion to the right was found to be 12.2 ± 1.7 mm and to the left 11.7 ± 2.0 mm, which compares well with values previously published for adults. The readings were somewhat larger than those found by Buschang et al14 Ingervall,18 and Agerberg,13 but they fall within the ranges of values reported previously.

Ingervall18 found the maximal lateral movement of the mandible in adult females to be larger to the right (10.48 mm) than to the left side (9.82 mm). Buschang et al14 found in a study of 27 adult females with normal occlusion that during right laterotrusion, the incisors consistently moved a greater linear distance (11.45 mm) than they did during left laterotrusion (10.89 mm). Similar functional differences have been reported by other authors.6 In the present study, the maximum laterotrusion to the right was somewhat larger than to the left, but the difference was not significant. Intraindividual variation on both sides in this study varied between 7.7 mm and 15.7 mm and was thus slightly smaller than that reported by Ingervall18 (with a range of 5.5 mm to 14.8 mm in 20-year-old women) and those reported by Agerberg13 (5–6 mm).

The mean maximum laterotrusion of the children's group in the present study was found to be 11.0 ± 1.7 mm on the right side and 10.6 ± 1.5 mm on the left side and was significantly smaller than in the adult group. The values measured in the children's group corresponded to 90.6% on the left side and 90.2% on the right side of the adult group.

Very few studies were conducted for the purpose of examining the kinematic variables in children. The values in the present investigation are very similar to those found in 1970 by Ingervall,18 who studied the ranges of mandibular movement in boys and girls at the age of 10 years and compared them with those of women aged 20 years. As for maximum lateral movement, Ingervall18 found that the mandible in 10-year-old boys moved on average about 10.81 mm to the right and 10.41 mm to the left. The 10-year-old girls showed somewhat smaller values.

In accordance with the findings of Ingervall,18 lateral movement in our study was numerically larger to the right than to the left side in the children's group, although no significant difference was noted. Additionally, Ingervall18 found no differences in maximum laterotrusion between 10-year-old girls and women aged 20 years, suggesting that in girls, the range of movement of the mandible reaches adult level by 10 years of age. In this study, we found a significant difference in laterotrusion between the children's group and the adult group. This might be due to the age difference of the children's group between the two studies.

In the present investigation, intraindividual variation in the children's group ranged between 5.3 and 15.1 mm for the right laterotrusion; variation in the left laterotrusion was somewhat smaller at 8.4 to 15.7 mm. These values are similar to those reported by Ingervall,18 who found a range of 7.0 to 14.3 mm on the right side and 5.8 to 14.8 mm on the left side for 10-year-old children.

Even though Ingervall18 reported significantly larger lateral movement in 10-year-old boys than in girls, in the present study, maximal laterotrusion did not vary significantly according to gender specificity. Hirsch et al19 reported in a study of children aged 10 to 17 years a similar mean (right side, 10.2 mm; left side, 10.6 mm) for maximum laterotrusion.

Cortese et al20 examined a group of children with average age of 6.9 years and found somewhat smaller values of maximum laterotrusion (right side, 6.05 mm; left side, 6.13 mm). These smaller values might be due to the lower average age of the group of examined children.

Maximum Retrusion

In the present study, dorsal movement of the condyle was measured indirectly from ipsilateral laterotrusion. The mean registered value in the adult group was 0.3 mm on the right side and 0.4 mm on the left side with a standard deviation of 0.3 mm on the right and left sides. The current findings are close to the values reported by Gernet.25 He measured the distance from maximum intercuspation into maximum retrusion and reported values from 0.4 mm to 0.6 mm in more than 80% of adults. The values obtained in this investigation are smaller than those reported by Ricketts,10 who in a study of 50 patients found that the space between the posterior surface of the condylar head and the glenoid fossa in occlusion is about 2.56 ± 0.7 mm. This difference could be due to differences in the measuring technique and reference point used. The range of movement on the right side (0.0–1.1 mm) was smaller than that on the left side (0.0–2.0 mm) in the adult group.

To the best of our knowledge, no investigation has used kinematic measurements to assess the development of maximum retrusion in children. Ingervall26 recorded the retruded positions of the mandible in children with the aid of wax records and dental casts. The mean values of the present study are somewhat smaller but fall within the ranges reported by Ingervall.26

The mean maximum retrusion in children measured in this study was significantly larger than that of the adult group, with a value of 0.6 mm on the right and left sides.

Ricketts10 reported that the size of the fossa is maximum before the condyle reaches full size. This would indicate a provision for play in the condyle–fossa relationship during the growth period. In adulthood, the condyle continues to grow until it fills the fossa space, which consequently limits condylar mobility. Therefore, larger retrusive movement of the condyles may be expected in children compared with adults. This means that posterior border movement of the mandible is not established by early stages of childhood—between 6 and 10 years—but is developing further. In adults, when the size of the condyle is fully developed, less space is available for condylar retrusive movements, and smaller maximum retrusive values are noted.

The range of movement of both condyles was also greater in the children's group than in the adult group. This supports Ricketts' notion10 that condylar mobility in retrusive movement is larger in children and decreases during adulthood.

The mean maximum retrusion in the children's group was found to be equal at the right and left sides (0.6 mm). In the adult group, the maximum retrusion of the right side (0.3 mm) was slightly smaller than that of the left side (0.4 mm), but no significant difference was found.

In the present study, no significant differences in maximum retrusion were found according to gender specificities either. This is in accordance with the findings of Ingervall,26 who found the retruded contact position and the intercuspal position to be of the same magnitude in boys and in girls.