Comparative Evaluation of Hyoid Bone Position and Tongue Area with Twin Block and Forsus: A Randomized Clinical Trial

Introduction: Class II div 1 malocclusion is most commonly presented with retruded mandible. This backward placement of mandible pushes the tongue posteriorly and inturn impairs the position of hyoid bone and total tongue area. Correction of retruded mandible with functional appliances is also considered to have positive effect on hyoid bone position and tongue area. Aim and Objectives: The objective of this study was to evaluate and compare the effects of Twin Block and Forsus on the hyoid bone position and tongue area in the treatment of Class II division 1 malocclusion. Materials & Method: A 2-arm parallel, randomized controlled trial was designed consisting of 24 Class II division 1 malocclusion patients indicated for treatment with functional appliances. 24 patients were randomized and equally divided among Twin Block (Group A) and Forsus (Group B) group. Preand post functional lateral cephalograms of both groups were traced and statistically analysed using paired t-test and T test of Equality of Means. ‘p’ value of less than 0.05 was considered as statistically significant. Result: A significantly upward and forward movement of hyoid bone was found with both the appliances. Tongue area also improved with Twin Block and Forsus group. On intergroup comparison insignificant results were observed between both the appliances indicating similar effect on tongue area and hyoid bone position. Conclusion: Twin Block has more skeletal effect than Forsus, still both Twin Block and Forsus are effective in improving tongue area and forward and upward displacement of hyoid bone position while correcting Class II malocclusion.


INTRODUCTION
Class II malocclusion is the most commonly encountered problem in orthodontic practice. 1  obstructive sleep apnea syndrome (OSAS). 3 Enache 4 found the significant positive correlation between AHI Dr Raksha Rajput, 1 Dr Suchita Daokar 2 1 and ANB suggesting that the patients with OSA had a retrognathic sagittal pattern with a class II anteroposterior relationship.
Khannna 5 study on Angle's Class II division 1 malocclusion with retrognathic mandible showed an inferoposterior displacement of hyoid bone and the position alteration was prevalent in skeletal malrelationship rather than dento-alveolar malocclusion. Johal 6 investigated that the hyoid bone is more inferiorly positioned in OSA patient.
The hyoid would tend to pull the tongue backwards, further narrowing the pharyngeal airway and thus could form a prognostic indicator for OSA severity.
Hence, this study was designed to compare the changes in skeletal, hyoid bone position and tongue area with Twin Block and Forsus.

MATERIALS AND METHOD
The present study was a prospective, double-blind,

In Vivo Study
The lateral cephalograms of the subjects were categorized into the following groups (gender and age equity)-Group A (Twin block group) & Group B (Forsus group).
Each group consisted of 12 subjects.

Randomization and Allocation Concealment
Once informed consent had been obtained, subjects were allocated to Group A or Group B using a block randomization determined by a computer-generated random number table. Block sizes of 2, 4, 6 were used within each group. The sequence of the block sizes generated by the computer was 4, 6 then 2. In the first block, they were numbered from 1 to 4, in the second block they were numbered 1 to 6 and in the third block from 1 to 2. Based on the randomisation list generated they were allocated to either group A or group B.
Same list were used to allocate the female participants to the group.   The FRD was engaged and continued until the Class II were corrected to edge to edge incisor relationship.
The patients were observed at 4-week intervals for a period of 6 months and appliances were activated as needed.

Cephalometric Analysis
Lateral cephalometric radiographs were taken before starting (T1) and after removal (T2) of the functional appliance therapy on the same machine with standardized head position and were traced and analyzed manually by the same operator. The readings were taken thrice and mean of which are taken so as to overcome any tracing errors.

Blinding
Blinding of participants in each group was done. As the primary investigator who performed the procedure could not be blinded, so both the co investigator who analyzed Finally, add the length of all offset lines and multiply the result times the distance that separate these lines.

Statistical Analysis
Statistical analyses were performed with software package SPSS (for Windows 7, version 16.0, SPSS). Pre versus post treatment values were analyzed and mean, standard deviation and paired t-test was carried.
Intergroup comparison of various parameters was performed using T test of Equality of Means.
A 'p' value of less than 0.05 was considered as statistically significant.
Similarly in group B significant increase in SNB angle from 73.67˚ to 74.58˚ (p= 0.001), effective mandibular length from 102.58mm to 104.58 mm (p=0.001), W angle from 50.00˚ to 51.67˚ (p=0.000), FMP angle from 20.75˚ to 22.75˚ (p=0.000) was observed. No significant difference was seen in SNA angle (p=0.586), effective maxillary length (p=0.674) after the treatment.
Inter group comparison between Twin Block and Forsus showed significant difference with SNA (p=0.001), SNB angle (p=0.000), effective mandibular length (p=0.004) and YEN angle (p=0.000) indicating Twin Block having greater skeletal changes than Forsus whereas no significant results were found with effective maxillary length (p=0.501), FMP angle (p=0.152).

DISCUSSION
In Class II patients with retruded mandible, backward placement of mandible may lead to inferoposterior position of hyoid bone, posteriorly positioned tongue and soft palate which may increase the chances of

Twin Block Forsus
Hy-MP Hy-NL impaired respiratory functions. The anteroposterior position of mandible has also effect on position of hyoid bone which is associated with important functions as deglutition, phonation, and respiration. Hoffman and Hoffman 7 believed that the hyoid bone was important for tongue position, since most of extrinsic muscle of no significant difference was seen. There was also increase in W and FMPA angle following treatment with both the appliances.
The so-called "head-gear effect" was seen with the Twin Block appliance with decreased value of the SNA angle demonstrating the inhibition in anterior development of the maxilla and posterior repositioning from cranial base. This result is in accord with Vinothet al 16 study. No significant change in SNA angle with Forsus was seen. This result showed significant difference between both the appliances in SNA angle.

Hyoid Bone Position
In present study, the results showed a significant upward & forward movement of hyoid bone following Twin Block & Forsus treatment. Brodie 21 brought attention to the suprahyoid muscles which suspend hyoid bone and tongue, since these muscles are attached to the symphysis of mandible, the hyoid bone passively follow the course of chin.

Intergroup comparison revealed insignificant results,
showing that the upward and forward movement of hyoid bone achieved by the two appliances are similar and changes in the effective mandibular length following the functional appliance treatment was seen in both the groups. As the mandible was advanced a balance is restored between the suprahyoid and infrahyoid muscles and the hyoid bone moved both upward & forward. Verma et al 22 reported that under the influence of Twin Block appliance treatment hyoid bone shifted forward in horizontal dimension and upward direction in vertical dimension.
The study of Ozdemir 23 found no change in hyoid bone position following Forsus which could be due to the fact that no skeletal effects on the mandible were reported. The Class II correction was achieved only by dentoalveolar changes, whereas in our study Class II correction was achieved with true skeletal changes (effective mandibular lengthening) following Forsus treatment.
In accordance with results, effect of Twin Block and Forsus, when compared they are insignificant, indicating similar effect on hyoid bone. This observation supported the concept that the hyoid bone moved in conjunction with adjacent anatomic structures when the mandible is advanced.

Tongue Area
Significant increase in tongue area was seen with both the appliances. This change in tongue area was a the tongue are attached to it and it also maintains the pharyngeal airway. Bucchieri 8 investigated that the altered hyoid bone position may influence the tongue position and upper airway patency. Hence, any change in position of mandible and hyoid bone can adversely affect the dimensions of airway. Grant 9 also reported difference in hyoid bone position, and found hyoid bone was higher in Class III than Class II subjects in relation to the cervical vertebrae. According to Thurow, 10 the geniohyoid muscle functions to adjust the anteroposterior position of the hyoid and to maintain the airway patency throughout the various movements of the craniofacial complex.
According to the Balter's 11 philosophy, Class II malocclusion are a consequence of backward position of a tongue, disturbing the cervical region. Thus, it is necessary to assess tongue in orthodontic diagnosis and treatment planning.
Peat 12 postulated the role of tongue in positioning of dento-alveloar structures. Not only the function, but also the growth, posture or function of tongue is of significance. Rakosi 13 proposed that abnormalities of either posture or function could possibly contribute to development of skeletal malocclusion.
Correction of retruded mandible with functional appliances also has positive effect on hyoid bone position and tongue area. Kalgotra 14 stated that as the body of the mandible lengthens, the attachments of the genioglossus and geniohyoid muscles move forward away from the oropharynx, increasing the pharyngeal space and found significant positive correlation between tongue position and Class II skeletal patterns. This study evaluated & compared hyoid bone position and tongue area changes with the Twin Block and Forsus appliances.

Skeletal Parameters:
The main skeletal change that results from our study is mandibular advancement. Nevertheless, this advancement is due to change in both mandibular length and effective mandibular length seen with both the appliances. A similar observations was made by Ghodke et al 15 and Vinoth et al. 16 SNB angle showed change in pre and post treatment values of Twin Block and Forsus and was in accordance with those of Bidayet al, 17 Vinoth et al, 16 Elfeky et al, 18 Ghodke et al 15