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Year : 2014  |  Volume : 25  |  Issue : 5  |  Page : 662-666
Functional approach to a Class II patient with upper first molar impaction

1 Department of Orthodontics, University of Florence, Via Ponte di Mezzo 46, Florence 50125, Italy
2 Department of TMD of Univesity of Florence, Via Ponte di Mezzo 46, Florence 50125, Italy

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Date of Submission06-Jun-2013
Date of Decision18-Jun-2013
Date of Acceptance13-Mar-2013
Date of Web Publication16-Dec-2014


The lack of the left first molar maxillary and the left second molar maxillary, caused respectively by impaction and agenesis is a very rare case, which determines an important occlusal imbalance and asymmetrical mandible movement. A gnatologic and functional orthodontic approach were planned to improve the retrognathic mandible and the muscular activity using kinesiograph and electromyography.

Keywords: Class II, electromyography and kinesiograph, first molar impaction, functional orthodontic treatment, temporomandibular disorders

How to cite this article:
D'Orlandi G, Raguzzi L, Defraia E, Pierleoni F. Functional approach to a Class II patient with upper first molar impaction. Indian J Dent Res 2014;25:662-6

How to cite this URL:
D'Orlandi G, Raguzzi L, Defraia E, Pierleoni F. Functional approach to a Class II patient with upper first molar impaction. Indian J Dent Res [serial online] 2014 [cited 2021 May 7];25:662-6. Available from:
The role of jaw muscle function as a determinant of growth and development of the human craniofacial complex has been studied extensively. The first attempt to study muscular activity in orthodontics was reported by Moyers. [1],[2] He suggested that the inherent imbalance of the temporomandibular musculature, particularly the temporal muscle, was an etiologic factor of "true Class II cases" and that a different pattern of muscle activity seemed to be associated with a different type of occlusion. It has also been reported that the synergistic behavior of the masseter and temporal muscles varied with the occlusion of the teeth. Pancherz [2] postulated that the impaired muscle activity found in Class II cases might be attributed to diverging dentofacial morphology and unstable occlusal contact conditions. Many muscular studies were focused on treatment effects of functional appliances, especially the twin-block. Another aspect we have analyzed was the first left molar retention and one of the most studied aspects, even in non syndromic patients, in oral surgical pathology is teeth retention, especially when it affects multiple teeth and not just the third molars. The etiological factors responsible for tooth impactions may be divided in two main groups. Local factors include an increase in bone deposition, trauma, malposition, prolonged retention of primary teeth, and local pathosis. Systemic factors consist of conditions such as childhood diseases, hereditary factors, cleft palate and cleidocranial dysostosis. In their study Bereket et al. they found that the prevalence of impacted or retained first molar to be 0.03% (0.01% lower, 0.01% upper). [3] With regard to the impacted molars, there was a significantly higher incidence in males and a higher incidence on the right side. So this is a very rare case of tooth impaction of the left upper first molar in a female.

   Case report Top

A 9-year-old Caucasian female was referred to the Department of Orthodontics of the University of Florence for initial examination. The medical history of the patient was unremarkable, no abnormalities in general growth and development. The cephalometry was performed on the lateral teleradiography with 10% of enlargement and shows a skeletal Class II by mandibular retrusion and protrusion of maxillary incisor.

The panoramic radiography revealed the impaction of the left first molar and the agenesis of the left upper second molar [Figure 1].

The dynamic evaluation of jaw movement and muscle activity was performed by kinesiograph and electromyographic exams.

This study was performed using a K-7 Evaluation System, Myotronics-Noromed, Inc., surface electromyography (EMG) with disposable cutaneous electrodes EMG (Duotrodes and Myo-trodes SG). The K-7 Myotronic is an 80 channels EMG with a 15-430 Hz band-pass filter, containing a special 60 Hz notch filter to eliminate electrical noises from the recording environment. All the recordings were performed with patients in a sitting position. The subjects were asked to have a comfortable posture, to relax their arms by their sides, and to look straight ahead and make no head or body movements during the test. The electrodes, which determine to a large extent the quality of the recordings, were placed according to the  Atlas More Details of Cram and Kasman. [4] Before the electrodes were applied, the skin was thoroughly cleaned with alcohol. The EMG's activity of four muscles was studied bilaterally:

  • With neuromuscular mandible position
  • During maximal voluntary clenching
  • With the mandible in rest position
  • During clenching on cotton roll.

The subjects were instructed to close their jaws in centric occlusion as forceful as possible. Movement patterns were conducted for at least three repetitions to ascertain stability according to the protocol developed by Donaldson and Donaldson. [5] The first movement patterns were eliminated as the "learning" sequence, as they were frequently observed as dissimilar to the other two repetitions. The third movement was considered the most stable.

The muscular areas tested were: Right and left masseter area, anterior temporal area, as masticatory muscles; sternocleidomastoid and digastric area. The EMG's recording time for each analysis was at least 15 s, and the values were expressed in microvolts/second (μV/s). In the single subject, all surface EMG data were the arithmetic means of three surface EMG's recordings. This was performed in an attempt to reduce the effects of nonstationary nature of EMG's signals. [6] parameters were also investigated The following kinesiographic parameters:

· Speed test of the open close cycle of the jaws

The difference between the maximal occlusal position and the neuromuscular position after transcutaneous electrical neural stimulation (TENS of cranial nerves v, vii, xi).

At T1, to establish a reference position to stick the electrodes in the same position compared with T0, great attention was given to position the electrodes according to the atlas of Cram and Kasman. The patient was observed at T0 at the age of 9 years and 5 months affected by a Class II with a mandibular retrusion and increased overjet (OVJ) of about 8 mm, Anb of 4, Snb of 75.3, protrusion of maxillary incisors at the cephalometry exam. The kinesiograph exam after TENS confirmed the mandibular retrusion: In fact there was sagittal retrusion of 2.1 mm, between the habitual occlusion and the neuromuscolar occlusion, and a left mandibular shift with an "italic S" path at the open cycle test due the lack of first upper left molar. The neuromuscolar path reported on the y-axis resulted in a 112° angle at T0 and at T1, hence the kinesiograph exam showed stability of the muscular path. The EMG exam confirmed the normodivergent pattern of growth because the value of clench decreases after an increase of posterior occlusal vertical dimension tested with cotton rolls and there was also a greater clenching force on the right side where there is the upper first molar. The atypical deglutition was evident clinically for the increased OVJ, and it was confirmed by the combination of electromyography and kinesiograph exam that revealed an activation of digastric muscle when there was no occlusal contact. The length of lateral movement of the mandible was asymmetrical: The left lateral movement was shorter than the right.

Treatment objectives

The orthodontic treatment objectives were to correct the skeletal Class II malocclusion (retrognathic mandible), improve the OVJ and overbite, and improve facial aesthetics. Cessation of the lip-biting habit was considered essential. The treatment plan was to apply a twin-block for correcting the Class II and the OVJ with a mandibular advancement.

The twin-block was constructed on the bite of a specific mandibular position obtained after the 1 h of TENS and the EMG and kinesiograph test that was named neuromuscular position.

Treatment progress

The twin-block appliance was used with the maxillary expander activated once a week after an adaptation period of 2 weeks. The patient was instructed to wear the twin-block appliance 24 h a day, especially during eating. The patient was initially seen 10 days after the first visit, then monthly so that the blocks could be adjusted for retention and stability as needed.

Treatment results

After 1-year (T1) new radiographic and kinesiograph exams were performed.

The clinical exam showed an improvement of facial esthetics with an important decrease of OVJ.

The cephalometry revealed an increase of mandibular growth of 1 mm, an occlusal Class I and Anb of 0. The kinesiograph exam after TENS revealed a decreased value of sagittal retrusion at 0.6 mm; so the habitual position was closer to the neuromuscular position [Figure 2].

The vertical distance OA-x was 4.2 mm and OA-x' was 2.1 hence the distance between the habitual position and neuromuscular position was reduced to 50%.

At the electromyography control the value of clenching was decreased, but anyway the increase of vertical dimension causes a decrease of the clenching force [Figure 3].

There was also a clenching force balancement between the left and the right side and a decrease in the left mandibular shift after the twin-block therapy.

   Discussion Top

We analyzed the EMG's activity of the jaw muscles and used kinesiography to assess longitudinal changes in the mandibular rest position and during clenching, swallowing mastication, maximum opening, lateral shift, lateral excursion, and protrusion in these children with Class II division 1 malocclusion after functional treatment with the twin-block appliance [Figure 4], [Figure 5], [Figure 6], [Figure 7].
Figure 1: The panoramic radiograph show the agenesis of the second left maxillary molar and the impaction of the left first maxillary molar at T0 and T1

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Figure 2: Graphic of neuromuscular movements matched with habitual occlusion at T0 and T1

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Figure 3: OA habitual occlusion at T0, OA' habitual occlusion at T1, NM neuromuscular mandible position, OA-X freeway space at T0, OA'-X' freeway space at T1, X-X' mandibular protrusion

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Figure 4: Lateral teleradiography at T0

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Figure 5: Lateral radiography at T1

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Figure 6: Extraoral and intraoral photos at T0

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Figure 7: Extraoral and intraoral photos at T1

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A more symmetrical muscular condition was achieved after functional treatment. Similar to Ingervall and Thόer, [7] we did not find a decrease in the activity of the temporal muscles after functional treatment, although such a decrease has been described as a sign of forward displacement of the mandible during treatment with a functional appliance. [8]

We observed a decrease in the EMG's activity of the left Masseter during Maximal Clenching after functional treatment [Table 1] and [Table 2]. This finding was probably due to occlusal instability or a lack of occlusal contacts of teeth in the posterior region, caused by the changed tooth positions and the intermaxillary relationship after functional treatment. In their study Ingervall and Thόer they found a decrease in the maximal activity of the masseters muscles after functional treatment with an activator, and Aggarwal et al. [9] made the same observation after treatment with the twin-block appliance.
Table 1: Value of masticatory muscle on clenching and clenching on cotton rolls at T0

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Table 2: Value of masticatory muscle on clenching and clenching on cotton rolls at T1

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According to McNamara [8] there is a growth in the mandible of about 1.8 mm and an important reduction of OVJ.

The kinesiograph test after treatment showed a decrease of the left mandibular shift in the opening movement. The electromyographic exam of clenching confirmed a more symmetrical balancement in the muscular activity.

So the twin-block made with the neuromuscular position tends not also to correct the retrognatic mandible and but also to give a better symmetrical functional balancement to the stomatognatic system.

   References Top

Moyers RE. Temporomandibular muscle contraction patterns in Angle Class II, division 1 malocclusions; an electromyographic analysis. Am J Orthod 1949;35:837-57.  Back to cited text no. 1
Pancherz H. Activity of the temporal and masseter muscles in class II, division 1 malocclusions. An electromyographic investigation. Am J Orthod 1980;77:679-88.  Back to cited text no. 2
Bereket C, Çakir-Özkan N, ªener I, Kara I, Aktan AM, Arici N. Retrospective analysis of impacted first and second permanent molars in the Turkish population: A multicenter study. Med Oral Patol Oral Cir Bucal 2011;16:e874-8.  Back to cited text no. 3
Cram JR, Kasman GS. Introduction to Surface Electromyography. Gaithersburg, MD: Aspen Publishers; 1997. p. 102-15.  Back to cited text no. 4
Donaldson S, Donaldson M. Multi-channel EMG assessment and treatment techniques. In: Cram JR, editor. Clinical EMG for Surface Recordings. 2 nd ed. Nevada City, CA: Clinical Resources; 1990. p. 143-74.  Back to cited text no. 5
Christensen LV. Experimental teeth clenching in man. Swed Dent J Suppl 1989;60:1-66.  Back to cited text no. 6
Ingervall B, Thüer U. Temporal muscle activity during the first year of Class II, division 1 malocclusion treatment with an activator. Am J Orthod Dentofacial Orthop 1991;99:361-8.  Back to cited text no. 7
McNamara JA Jr. Neuromuscular and skeletal adaptations to altered function in the orofacial region. Am J Orthod 1973;64:578-606.  Back to cited text no. 8
Aggarwal P, Kharbanda OP, Mathur R, Duggal R, Parkash H. Muscle response to the twin-block appliance: An electromyographic study of the masseter and anterior temporal muscles. Am J Orthod Dentofacial Orthop 1999;116:405-14.  Back to cited text no. 9

Correspondence Address:
Giacomo D'Orlandi
Department of Orthodontics, University of Florence, Via Ponte di Mezzo 46, Florence 50125
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-9290.147120

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]

  [Table 1], [Table 2]


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