This study aimed to compare cephalometrically the pharyngeal airway, hyoid bone, and soft palate (SP) changes after Class II malocclusion treatments using Twin-block (TWB) and Forsus Fatigue Resistant Device (FFRD) (3M Unitek Corp, 3M Dental Products, Monrovia, Calif) during the postpeak growth period.
Forty-two patients with Class II malocclusion treated during the postpeak growth period were randomly and retrospectively included in this study. These patients were divided into 2 treatment groups: TWB and FFRD. The skeletal, dental, pharyngeal airway, hyoid bone position, and SP measurements were obtained from the lateral cephalometric radiographs taken at the beginning and at the end of the treatment. Paired-samples and independent-samples t tests were used for the intragroup and intergroup comparisons, respectively.
In the TWB group, the SNB (°), Md1-NB (mm), Md1-NB (°), and McNamara upper and lower pharyngeal airway dimensions significantly increased, whereas the ANB (°), AD1-Ba (mm), AD2-H (mm), adenoidal nasopharyngeal area, and SP angle decreased ( P < 0.05). In the FFRD group, the SNB (°), Md1-NB (mm), Md1-NB (°), Ptm-Ba (mm), and McNamara upper airway dimensions significantly increased, whereas the ANB (°), AD2-H (mm), and interincisor angle decreased ( P < 0.05). Moreover, there were statistically significant differences in the Md1-NB angles and SP thicknesses between the 2 groups ( P < 0.05).
The effects of TWB and FFRD treatment on the airway during the postpeak growth period were similar. However, the FFRD caused a greater mandibular incisor protrusion.
Effects of Twin-block and Forsus Fatigue Resistant Device were compared.
Devices had a similar effect on the airway during the postpeak growth period.
Forsus Fatigue Resistant Device caused a greater protrusion of the mandibular incisors than Twin-block.
Functional appliances are used to treat mandibular deficiency during the growth period to stimulate growth and elicit dental alveolar change by the forward positioning of the mandible. They increase the oropharyngeal dimensions by forcing the mandible, tongue, soft palate (SP), and hyoid bone forward. , Previous studies have reported that the early orthodontic treatment of mandibular retrognathia with a functional appliance may be helpful in preventing airway problems. ,
Several methods can be used to evaluate the upper airway, including cephalometry, , acoustic reflection rhinometry, fluoroscopy, nasopharyngoscopy, computed tomography (CT), cone-beam CT, magnetic resonance imaging, esophageal manometry, and bronchoscopy. Cephalometry is the preferred method based on its advantages such as routine usage, low cost, and minimal exposure to radiation, and it provides the opportunity to obtain sufficient information about SP and nasopharynx.
No previous studies comparing the effects of the functional appliances on the airway during the postpeak growth period are in the literature. Therefore, this study aimed to use cephalograms to evaluate the pharyngeal airway dimensions, hyoid bone positions, and SP measurements of patients with Class II malocclusions treated during the postpeak growth period with Twin-block (TWB) and Forsus Fatigue Resistant Devices (FFRD) (3M Unitek Corp, 3M Dental Products, Monrovia, Calif). The null hypothesis of this study is that there is no difference between TWB and FFRD appliance therapy regarding the effects on the pharyngeal airway dimensions.
Material and methods
This study was approved by the Regional Ethical Committee on Research of Selçuk University Faculty of Dentistry, Konya, Turkey (2017/15). The materials for this retrospective study were selected from the archives of the Department of Orthodontics at Selçuk University in Konya, Turkey, and they consisted of the pretreatment and posttreatment radiographs of patients treated with TWB and FFRD. To determine the sample size in our study, the mean and standard deviation values of the SPS (the distance of the midpoint of the line from posterior nasal spine (PNS) to the tip of SP to the horizontal counterpart on the posterior pharyngeal wall along the parallel line to Frankfurt horizontal plane) (FFRD, 1.06 ± 1.43 mm; control, −0.16 ± 0.01 mm) based on the study by Bavbek et al. were used. It was determined that 15 subjects in each group would yield more than 90% power at the α = 0.05 significance level to detect the significant differences, assuming a 1.2-mm SPS difference in the airway sizes. All of the patients’ files contained written informed consent for these regular procedures.
Forty-two patients with Class II malocclusions who had undergone orthodontic treatments during the postpeak growth period were randomly and retrospectively included in this study. These patients were divided into 2 groups: the patients treated with TWB and fixed orthodontic appliances were included in the first group (16 females, 5 males; mean age, 14.8 ± 2.1 years), and the second group consisted of those patients who were treated with fixed orthodontic appliances and FFRD (13 female, 8 male; mean age, 15.1 ± 1.8 years). TWB, which was developed by Clark, consists of maxillary and mandibular acrylic blocks with inclined planes at 70° to the occlusal plane. TWB design used in this study included maxillary labial bow and acrylic capping with ball-ended clasps on the mandibular incisors ( Fig 1 ). FFRD is a popular fixed functional appliance that was first described by Vogt. FFRD is an interarch spring composed of a spring module that attaches to the headgear tube and a push rod that attaches to the mandibular archwire distal to the canine ( Fig 2 ). Postpeak growth period was defined by hand–wrist (if available) and lateral cephalometric films. DP3u, PP3u, MP3u, and Ru growth periods were classified as postpeak on hand–wrist radiographs. CS4, CS5, and CS6 growth periods were classified as postpeak on lateral cephalometric radiographs according to the skeletal maturation method. Because the airway growth is complete at approximately 15 years of age, no untreated control group was used.
The inclusion criteria were as follows: having a skeletal Class II malocclusion (ANB >4°, SNB <78°), treated during the postpeak growth period, no Class II elastics or headgear used, no systemic diseases or syndromes, no history of nasal respiratory complex surgery at baseline and during treatment, no pharyngeal pathologies, and complete cephalometric radiographs with enough sharpness and contrast for good visualization and identification of the structures.
The lateral cephalograms were taken while the patient maintained a standardized head position with the same cephalometric x-ray unit (Planmeca ProMax Dimax 3 Ceph; Planmeca, Helsinki, Finland) by the same operator at the beginning and the end of treatment. Figures 3-7 show the reference points and lines used in the analysis, including the skeletal, dental, pharyngeal airway linear, pharyngeal airway area, hyoid bone position, and SP measurements. The linear and angular measurements were obtained using the Quick Ceph Studio software (Quick Ceph Systems, San Diego, Calif), and the area measurements were obtained using the Foxit Reader software (version 8.3; Foxit Software, Fremont, Calif). Summary of cephalometric landmarks and definitions used in our study, as defined by various authors, are shown in Table I .
|S||Midpoint of sella turcica (the center of sella turcica)|
|N||Nasion, the most anterior point of the frontonasal suture in the midsagittal plane|
|A||The deepest midline point on the anterior outer contour of the maxillary alveolar process|
|B||The deepest point on the anterior outer contour of the mandible|
|Mx1||Incisal tip of most anterior maxillary central incisor|
|Md1||Incisal tip of most anterior mandibular central incisor|
|Po||Pogonion, the most anterior point of the bony chin in the midsagittal plane|
|Go||Gonion, a point at the intersection of lines tangent to the posterior border of the ramus and the lower border of the mandible|
|Gn||Gnathion, the most anterior inferior point of the bony chin|
|ANS||Anterior nasal spine, anterior point on maxillary bone|
|PNS||Posterior nasal spine, posterior limit of bony palate|
|Ba||The most posterior limit of the lowest point in the midline on the anterior margin of the foramen magnum|
|AD1||Posterior pharyngeal wall along the line from PNS to Ba|
|AD2||Adenoid tissue along the line from PNS to H|
|H||Hormion, the point located at the intersection between the perpendicular line to S-Ba and the cranial base|
|Cv3ai||The most anterior point on the inferior margin of the outline of the body of the third cervical vertebra|
|Cv3pi||The most posterior point on the inferior margin of the outline of the body of the third cervical vertebra|
|aa||Anterior arch of the atlas, the most anterior point on the anterior arch of the atlas (C1) assumed to be in the median sagittal plane|
|Hyoid||The most superior point on the anterior surface of the outline of the body of the hyoid bone|
|T point||Tuberculum sella, the intersection point of the lower contours of the anterior clinoid processes and the contour of the anterior wall of the sella|
|W point||Wing points, the intersection of the contour of the ala majör with the jugum sphenoidale|
|P point||Lower tip of the uvula|
|SP1||Front of uvula at its thickest point|
|SP2||Back of uvula at its thickest point|
|SNA (°)||The angle between the lines Sella-Nasion and Nasion-A point|
|SNB (°)||The angle between the lines Sella-Nasion and Nasion-B point|
|ANB (°)||The angle between the lines Nasion-A point and Nasion-B point|
|Mx1-NA (mm)||Perpendicular distance of the incisal point of the maxillary incisor to the NA line|
|Mx1-NA (°)||Angle between maxillary incisor long axis and NA plane|
|Md1-NB (mm)||Perpendicular distance of the incisal point of the mandibular incisor to the NB line|
|Md1-NB (°)||Angle between mandibular incisor long axis and NB plane|
|Po-NB (mm)||Perpendicular distance of the pogonion to the NB line|
|SN-GoGn (°)||Angle between the SN plane and GoGn plane|
|Interincisor angle||Angle between long axes of maxillary and mandibular incisors|
|FH||Frankfurt horizontal plane, the line formed by joining the porion with the orbitale|
|FMA (°)||Angle between the Frankfort horizontal plane and the mandibular plane|
|FMIA (°)||Angle between the Frankfort horizontal plane and the mandibular incisor axis|
|IMPA (°)||Inclination of the mandibular incisors to the mandibular plane|
|VRL||Vertical reference line, perpendicular line passing through the T point|
|HRL||Horizontal reference line, the line passing through the T and W points|
|PNS-AD1||The distance from PNS to AD1|
|AD1-Ba||The distance from AD1 to Ba|
|PNS-AD2||The distance from PNS to AD2|
|AD2-H||The distance from AD2 to H|
|PNS-Ba||The distance from PNS to Ba|
|Ptm-Ba||The distance from Ptm to Ba|
|PNS-H||The distance from PNS to H|
|McNamara upper pharyngeal dimension||Minimum distance from the SP to the nearest point of the posterior pharyngeal wall|
|McNamara lower pharyngeal dimension||Minimum distance from the point in which the posterior tongue contour crosses the mandible to the nearest point on the pharyngeal wall|
|Lower pharyngeal dimension||The distance between the anterior and posterior pharyngeal wall through the line between Cv3ai and Cv3pi points|
|PL||The palatal line, the line passing through ANS and PNS points|
|SpL||Sphenoid line, tangent to lower border of sphenoid registered on basion|
|AAL||Anterior atlas line, perpendicular line to PL passing through aa point|
|PML||Pterygomaxillary line, perpendicular line to PL registered on Ptm|
|Np||Area Describe the 4 sides of a trapezoid which defines the nasopharyngeal area|
|Aerial area||Part of Np area that is consisting of air|
|Adenoidal area||Part of Np area that is consisting of soft tissue|
|Oropharyngeal area||PL and the Cv3ai-Cv3pi line were accepted as the upper and lower borders of the oropharyngeal area|
|Hyoid-SWpoint||The distance from hyoid to the horizontal reference line|
|Hyoid-VRL||The distance from hyoid point to VRL|
|Hyoid-CV3ai||The distance from hyoid to Cv3ai|
|SP length||The distance between PNS and P points|
|SP thickness||The distance between SP1 and SP2 points|
|SP angle||Angle between the ANS-PNS line and PNS-P line|
All statistical analyses were performed using SPSS statistical software (version 21.0; IBM Corp, Armonk, NY). The Shapiro-Wilk test and Levene test were used, showing that the data were normally distributed and variance homogeneity existed between the groups. A paired-samples t test was used for the intragroup comparisons, and an independent-samples t test was used for the intergroup comparisons. A P value of <0.05 was considered to be statistically significant.
To evaluate the tracing errors and examiner reliability, 15 radiographs were selected randomly. All the measurements were retraced and remeasured 2 weeks after the first evaluation. A paired-samples t test was then applied to the first and second measurements. There were no statistically significant differences between the first and second measurements ( P >0.05).
The treatment duration of the TWB group was 23.1 (standard deviation [SD], 3.4) months, with a 12-month treatment period. The treatment duration of the FFRD group was 22.8 (SD, 4.1) months, with a 9-month treatment period.
The means and SDs were calculated for the pretreatment and posttreatment values. The pretreatment and posttreatment cephalometric descriptive values and change comparisons within each group are presented in Table II .
|Variables||TWB group (n = 21)||P value||FFRD group (n = 21)||P value|
|Skeletal dental measurements|
|Interincisor angle (°)||129.01||12.58||124.27||5.55||0.119||129.50||11.61||123.10||7.32||0.017∗|
|Pharyngeal airway linear measurements|
|McNamara upper (mm)||10.57||3.67||13.88||2.72||<0.001∗∗∗||12.75||4.34||15.22||3.18||0.004∗∗|
|McNamara lower (mm)||9.90||3.09||10.16||2.87||0.539||11.18||3.09||11.09||2.92||0.873|
|Lower pharyngeal dimension (mm)||12.74||3.56||14.34||3.63||0.047∗||14.51||2.94||14.89||3.92||0.684|
|Pharyngeal airway area measurements|
|Adenoidal area (mm 2 )||349.86||85.93||280.52||84.09||0.003∗∗||343.89||81.88||307.88||85.33||0.071|
|Aerial area (mm 2 )||344.32||76.37||376.00||93.70||0.097||338.31||90.76||378.58||84.52||0.098|
|Pharyngeal area (adenoidal + aerial) (mm 2 )||694.17||90.49||656.51||120.59||0.083||682.20||125.80||686.46||118.39||0.874|
|Oropharyngeal area (mm 2 )||691.21||176.29||731.29||188.64||0.237||731.54||163.51||712.23||192.26||0.632|
|Hyoid bone position|
|Hyoid-SW point (mm)||94.45||6.22||94.44||7.74||0.988||96.87||8.47||97.07||8.22||0.819|
|SP length (mm)||32.09||4.61||32.50||3.68||0.614||30.48||3.35||30.47||3.28||0.986|
|SP thickness (mm)||7.40||1.19||7.75||1.34||0.257||8.58||1.68||8.10||1.49||0.096|
|SP angle (°)||137.90||5.27||135.80||4.27||0.047∗||138.04||6.46||135.72||7.92||0.101|