|Year : 2012 | Volume
| Issue : 3 | Page : 218-226
Skeletal and Dentoalveolar changes concurrent to use of Twin Block appliance in Class II division I cases with a deficient mandible: A cephalometric study
AK Sharma1, V Sachdev1, A Singla2, BC Kirtaniya1
1 Department of Pedodontics and Preventive Dentistry, Himachal Dental College, Sunder Nagar, District. Mandi, Himachal Pradesh, India
2 Department of Orthodontics, Himachal Dental College, Sunder Nagar, District. Mandi, Himachal Pradesh, India
|Date of Web Publication||21-Dec-2012|
A K Sharma
Department of Pedodontics, Himachal Dental College, Sunder Nagar-174 401, Himachal Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Most of Class II malocclusions are due to underdeveloped mandible with increased overjet and overbite. Lack of incisal contact results in the extrusion of the upper and lower anterior dentoalveolar complex, which helps to lock the mandible and prevent its normal growth and development, and this abnormality, is exaggerated by soft tissue imbalance. The purpose of present study was to cephalometrically evaluate skeletal and dentoalveolar changes following the use of Twin-Block appliance in 10 growing children of age group 9-13 years (mean 11.1 year ± SD 1.37) of Class II division 1 malocclusion with a deficient mandible. Cephalometric pre- and post-functional treatment measurements (angular and linear) were done and statistically analyzed using student's paired t-test. The results of the present study showed that maxilla (SNA) was restricted sagittally (head gear effect) with marked maxillary dental retraction. Significant mandible sagittal advancement (SNB) with minimum dental protraction was observed with significant increase in the mandibular length. The maxillomandibular skeletal relation (ANB and WITS appraisal) reduced considerably which improved the profile and facial esthetics. Pronounced correction of overjet and overbite was seen. The present study concluded that Class II correction occurs by both skeletal and dentoalveolar changes.
Keywords: Cephalometric changes, class II division I malocclusion, retrognathic mandible, Twin block appliance
|How to cite this article:|
Sharma A K, Sachdev V, Singla A, Kirtaniya B C. Skeletal and Dentoalveolar changes concurrent to use of Twin Block appliance in Class II division I cases with a deficient mandible: A cephalometric study. J Indian Soc Pedod Prev Dent 2012;30:218-26
|How to cite this URL:|
Sharma A K, Sachdev V, Singla A, Kirtaniya B C. Skeletal and Dentoalveolar changes concurrent to use of Twin Block appliance in Class II division I cases with a deficient mandible: A cephalometric study. J Indian Soc Pedod Prev Dent [serial online] 2012 [cited 2020 Aug 10];30:218-26. Available from: http://www.jisppd.com/text.asp?2012/30/3/218/105014
| Introduction|| |
The most consistent finding in Class II malocclusion is mandible skeletal retrusion. Moyers in 1980  found the incidence of normal maxillae in combination with deficient mandible within the Class II population to be approximately 70%, a much higher figure than was formerly recognized. McNamara in 1981  while studying a group of 277 children with Class II malocclusion found that 60% of the group was having retruded mandibles.
Functional appliances are used to correct the abnormal function that induces abnormal growth and development of the underlying hard tissues. Altering and directing the neuromuscular activity of the oral cavity to normal limits is the major goal of applying this method of the treatment. When there is mandibular retrognathia, positioning the mandible forward is believed to enhance its growth. ,,,,
The most popular myofunctional appliance used for the correction of Class II malocclusion is the Twin-Block appliance which was developed by Dr. William J Clark.  So the present study have been designed to cephalometrically evaluate the skeletal, dentoalveolar changes concurrent the use of Twin Block appliance in Class II division 1 malocclusion with a deficient mandible.
| Materials and Methods|| |
The present study was carried out on 10 growing children of Class II division 1 malocclusion in the age group of 9-13 years (Mean 11.1 year ± SD 1.37) fulfilling the following criteria were delivered Twin Block appliance for 12 months. The inclusion criteria were;
Lateral cephalograms were taken at the start (0 month) and at the end (12 months) of the Twin-Block therapy. The landmarks as elucidated by Rakosi T  for functional therapy and Jacobson 1995  were identified on each cephalogram [Figure 2]. To evaluate whether the child is in active growing age or not, the criteria given by Julian Singer  was used.
- Orthognathic maxilla with a retrognathic mandible having a favorable growth pattern with ANB angle ≥4 degree
- Angle's Class II or end on molar relationships with well aligned dental arches without crowding or with minimal crowding.
- Overjet ≥6 mm, overbite ≥3 mm
- Normal or reduced lower facial height
- Positive VTO i.e., visual treatment objective
|Figure 1: Pre‑treatment (extra‑oral and intra‑oral) and post‑treatment (extra‑oral and intra‑oral) photograph of the patient following successful treatment outcome concurrent with Twin Block appliance|
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| Results|| |
The pre- and post-treatment lateral cephalograms were traced using the mentioned landmarks [Figure 3] and [Figure 4] and superimposed with S-N plane [Figure 5] as a reference plane [Figure 1]. Difference between cephalometric pre-treatment and post-treatment measurements was statistically analyzed using student's paired t-test (38 cephalometric, 2 clinical). The significance of P value was determined at 0.05 (*), 0.01 (**) and 0.001 (***) levels of confidence [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9].
|Figure 5: Cephalometric superimposition of the pre-treatment cephalometric (green color) and post-treatment cephalometric tracing (red color) with Sella -nasion as a reference plane|
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|Table 1: Cephalometric changes (Angular and Linear) in cranial base following the use of Twin Block|
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|Table 2: Cephalometric changes (Angular and Linear) in maxilla (Skeletal) following the use of twin block|
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|Table 3: Cephalometric changes (Angular and Linear) in maxilla (Dentoalveolar) following the use of twin block|
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|Table 4: Cephalometric changes (Angular and Linear) in mandible (Skeletal) following the use of twin block|
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|Table 5: Cephalometric changes (Angular and Linear) in mandible (Dentoalveolar) following the use of Twin Block|
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|Table 6: Cephalometric changes (Angular and Linear) in maxilla to mandible relationship (Skeletal) following the use of twin block|
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|Table 7: Cephalometric changes (Angular) and clinical changes (Linear) in maxilla to mandible relationship (Dentoalveolar) following the use of Twin Block|
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|Table 8: Cephalometric changes (Angular) in vertical relationship following the use of twin block|
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|Table 9: Cephalometric changes (Linear) in vertical relationship following the use of twin block|
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| Discussion|| |
The goal in the development of the Twin Block approach to treatment was to produce a technique that could maximize the growth response to functional mandibular protrusion by using an appliance system that is simple, comfortable and aesthetically acceptable to the patient. Rapid functional correction of malocclusion is achieved by the transmission of favorable occlusal forces to inclined planes that cover the posterior teeth. The forces of occlusion are used as a functional mechanism to correct the malocclusion. The results of present study are being discussed as;
Changes in cranial base
Saddle angle which signifies position of mandible with respect to the cranial base has decreased indicating that mandible is repositioned anteriorly.
The articular angle is a constructed angle between the upper and lower parts of the posterior contours of the facial skeleton. Increase in this angle suggested that downward and backward repositioning of mandible has taken place with opening of the bite, which is of clinical relevance in correction of deep bite.
The statistically significant increase in anterior cranial base length (Se-N) by 2.1 mm suggests that treatment had been carried out during active growth period. This increase was in accordance as annual incremental growth suggested by Rakosi T. 
Maxillary skeletal changes
Angle S-N-A expresses the sagittal relationship of the anterior limit of the maxillary apical base to the anterior cranial base. McNamara  has pointed out growth increment in this angle from 79.5° to 81.28° during 9-15 years of age. So increase in this angle is expected in children during growth.
But in the present study, there was decrease in SNA angle by mean of 0.5 ± 0.707° suggesting that forward growth of maxilla is restricted. When the mandible was postured forwardly by the Twin-Block appliance, a reciprocal force acted distally on the maxilla, which restricted the forward growth of maxilla (headgear effect). A situation where the normal forward growth of the maxilla is inhibited would be ideal for correction of a Class II skeletal discrepancy (Trenouth MJ  ).
Although point A is a deep alveolar point in maxilla, but it is also influenced by the dentoalveolar changes. As in our study, the upper incisors are tipped significantly in a palatal direction (6.9°), and then the root apices will move more anteriorly. Thus point A may advance as a result of reshaping of alveolus. If angle SNA is not increased but decreased under these circumstances it could be postulated that more degree of maxillary restraint might have occurred but not detected because of dentoalveolar remodeling, distinguishing the true headgear effect achieved in the treatment.
The S-N-Pr angle was decreased by 0.6° indicating that position of premaxilla has also been restricted from moving forward.
Linear analysis of the effective midfacial distance (Cd-A) indicated that this distance had significantly increased during Twin Block appliance treatment. Similarly, the length of the maxillary base (PNS-ANS) was also found to be increased. These increases are to be expected in growing children and suggest that Twin Block appliance has little or no effect on these midfacial parameters, concurring with previous studies that report no restriction of midfacial growth following Twin Block appliance treatment. ,,,
Maxillary dentoalveolar changes
After the Twin Block treatment, the subjects demonstrated a mean reduction in the proclination of upper incisor (6.9°) which is both statistically and clinically significant, which is more than that reported by ,,,, and less as reported by Illing et al.,  (9.1°), Trenouth  (14.37°).
The contact of the labial bow on the upper incisors presumably together with the associated lip musculature resulted in final palatally retroclined position of the upper incisors.
This is an expected treatment outcome of functional appliance therapy due to their Class-II 'Traction effect' (Illing et al. ).
There was statistically highly significant reduction (5.000 ± 1.563 mm) in linear distance between the maxillary incisors in relation to facial plane (N-Pog line). This showed that relative prominence of upper incisors has decreased. This reduction after the Twin Block treatment can be attributed to the lingual tipping of the upper incisors and forward movement of the pogonion. The present results is in accordance with the results reported Clark ,, Lund and Sandler,  Mills and McCulloch,  O'Brien et al.,  Lee et al. 
Mandibular skeletal changes
After the treatment, the gonial angle and lower gonial angle has increased; however changes in the lower gonial angle are statistically significant. Although, the increase in the lower gonial angle has to some extent being compensated by the decrease in upper gonial angle (the forward movement of point N in upward and forward direction); thereby reducing the net gonial angle. We hypothesize that this increase in lower gonial angle has an effect on the increase of the mandibular plane angle.
Pancherz  found an increase in the gonial angle of the patients of the Herbst group. He determined that by changing the muscle functions or by sagittally directing condylar growth, there could be some resorption on the gonial region.
This growth modification as suggested by the increase in gonial angle have previously been described as "posterior mandibular morphogenetic rotation" a biological mechanism leading to greater increments in total mandibular length and, thus, efficiently improving the skeletal sagittal relationships in Class II malocclusion. ,
As in our study, the primary inclusion criterion was skeletal Class II division 1 malocclusion with a retrognathic (deficient) mandible; thus mandibular retrognathia improvement can be demonstrated by the increase in SNB angle. This SNB angle is increased significantly by a mean of 2.4 ± 1.174° due to the forward shift of point B. Thus, a statistically and clinically significant improvement has occurred in anteroposterior spatial position of mandible.
As point B is a deep alveolar point which is influence by dentoalveolar changes. As the lower incisors in this study were proclined by 1.1° and lingual movement of lower incisor roots could also allow alveolar remodeling, moving point B slightly lingually and reducing SNB.
This increase in SNB angle was in accordance with previously reported studies by Clark, ,, Illing et al.,  Lund and Sandler,  Mills and McCulloch,  Trenouth,  Sidlauskas. 
Changes in the length of mandible
One of the major controversies in functional appliance therapy is the effects of functional appliance on increase in size or acceleration of mandibular growth. Many researchers have claimed extra mandibular growth with Twin-Block appliance (Illing et al.,  Mills and McCulloch,  Lund and Sandler  ).
The present study also showed a statistically significant increase in mandibular length following Twin-block treatment by 7.1 mm. This 7.1 mm increase in effective mandible length is combined effect of normal growth increment, effect of forward posturing of the mandible by appliance (effect of appliance) and downward and backward rotation of mandible (posterior mandibular morphogenetic rotation).
There is also significant increase in length of mandible base and ascending ramus by 2.7 mm (P value ≤ 0.001) and 3.1 mm (P value ≤ 0.01) respectively suggesting significant increase in size following treatment.
Study by Lund and Sandler  found 2.4 mm extra mandibular growth between articulare and pogonion (total increase is 5.1 mm in Twin Block group; 2.7 mm in control group) during a 12-months period of Twin-Block treatment.
Mills and McCulloch  also found a greater mandibular growth (4.2 mm) with Twin Block therapy (total increase is 6.5 mm in Twin Block group; 2.3 mm in control group).
Toth and McNamara  found 3.0 mm additional increase in condylion to gnathion length during a standardized 16-months period of Twin-Block therapy as compared to 1.9 mm increase in Frankal group (total increase is 5.7 mm, 3.6 mm, 2.7 mm in Twin Block group, Frankal group and control group, respectively).
Jena AK et al.,  has found 1.65 mm and 1.05 mm extra mandibular growth following in the Twin Block and bionator group respectively compared with controls (total increase in mandible length was 5.02 mm in Twin Block group and 4.42 mm in bionator group, 3.37 mm in control group).
Mandibular dentoalveolar changes
The position of lower incisors in Class II correction with functional appliances is critical. Excessive labial tipping of lower incisors should be limited as it reduces the potential for orthopedic change. After Twin Block treatment, there was proclination of lower incisor in relation to mandibular plane (-1.1°) which was not statistically significant. Some authors reported significant lower incisor proclination during treatment with Twin Block appliance: Lund and Sandler  -7.9°, Mills and McCulloch  - 5.2°. Some studies, as this study, found that lower incisor remained comparatively stable after Twin-Block therapy (Trenouth  reported 1.4°, Toth and McNamara  by 2.8°, Sidlauskas A  by 3.2°).
This could be explained by the Twin-Block design as in the present study, the acrylic cover was used for lower incisors capping and eyelet clasps that provides rigid retention in the lower labial segment same as it was the case with the use of Sounthend clasps in the Trenouth  study and lower incisor acrylic coverage in the Sidlauskas A. 
Lund and Sandler,  Mills and McCulloch  used ball clasps and labial bow respectively and could not keep lower incisor stabile.
A significant increase in the linear distance of lower incisor to facial plane is seen which is in accordance with the findings reported by Illing et a1,  Lund and Sandler,  Mills and McCulloch  and could be attributed due to some increase in IMPA and additionally by downward and backward rotation of mandible.
Changes in maxilla to mandible relationship skeletal changes
The ANB angle is used to measure the change in skeletal maxillomandibular relationship. A highly statistically significant reduction was observed in angle ANB by 2.9° following treatment mainly because of increase in SNB (+2.4°) which is increased significantly by anterior positioning of mandible and slightly with a small reduction in angle SNA (-0.5°) due to restraint of forward maxillary growth. Thus the resultant reduction in the severity of maxillomandibular discrepancy was mainly mandibular skeletal changes and so called headgear effect was purely minimal. Since, all patient included in present study were having class II malocclusion with a retrognathic mandible and so are benefited from correction in mandibular discrepancy.
This finding is in agreement with results reported by Clark ,, Trenouth,  Illing et al.,  Lund and Sandler,  Mills and McCulloch. 
To rule out any bias going to occur with Nasion as reference point, the maxilla-mandibular apical base changes were analyzed with WITS appraisal.
WITS appraisal is reduced by 3.9 mm following Twin Block appliance treatment which is statistically and clinically highly significant. This reduction is attributed to restraining effect on the maxilla and anterior displacement of point B indicative of skeletal correction.
The mean increase in the difference between the effective mandible length and the midfacial length is 4.9 mm, which is significant statistically and is attributed to the significantly more increase in the effective mandibular length (CdGn) following treatment as compared to the increase in midfacial length showing that the mandible has outgrown the maxilla significantly in length by 4.9 mm.
The interincisal angle increased significantly by 7.0° following Twin Block treatment. This change is attributed mainly to upper incisor retroclination (6.9°) achieved during study and also greater inhibition of lower incisor proclination (1.1°) and is in accordance as found by Illing et al.,  by 8.6°.
A highly significant decrease in the degree of overjet was observed. The overjet correction was a combined effect of maxillary incisor retroclination and slight mandibular incisors proclination with marked skeletal contribution (forward growth of mandible) at the end of the treatment. This is supported by results shown by Weiland,  Illing et al.,  and Mills and McCulloch. 
Overbite reduced by 4.2 mm following the Twin Block treatment which is statistically highly significant. This reduction in overbite is because of combined effect of downward and backward rotation of mandible along with selective eruption of molars.
Our findings are supported by different studies of Clark. ,, Vergervik and Harvold,  Lund and Sandler,  Tumer and Gultan. 
Changes in vertical relationship
Control of the vertical dimension is one of the proposed benefits of the Twin-Block appliance (Clark  ). Clark  has stressed selective removal of acrylic to allow an increase in the vertical dimension as an important component of Twin-Block therapy. The significant increase in lower anterior facial height and mandibular plane angle observed was because of this type of acrylic contouring.
After Twin Block treatment base plane angle (Pal- MP angle), palatal plane to occlusal plane angle, mandibular plane angle (SN/GoGn), Frankfurt mandibular plane angle (FMA) has significantly increased by 2.6°, 2.3°, 2.2°, 2.3°, respectively.
The increase in these angles by the use of different functional appliances has been shown in many studies. ,,,,,,,,, indicated that at the end of activator treatment, the height of the posterior mandibular alveolar processes and the eruption of the teeth in the buccal segment show an increase and as a result, a posterior mandibular rotation occurs.
After the Twin Block treatment, there is a significant increase in the posterior facial height, total anterior facial height and lower anterior facial height by 3.4 mm, 5.5 mm and 4.4 mm respectively. Out of all these the increase in anterior facial height and more so the anterior lower facial height was statistically and clinically highly significant. This finding is in accordance with studies done by Clark, ,, Illing et a1.,  Lund and Sandler,  Mills and McCulloch,  Toth and McNamara,  Sidlauskas A,  Lee RT et al. 
Due to clinically significant rotation of mandible in clockwise direction, there is decrease in overbite and increase in facial height (mainly lower anterior facial height) which is a desirable outcome in Class II Division 1 patients having deep bite and reduced lower anterior facial height.
McNamara  has shown that every millimeter of increased lower anterior facial height camouflages a millimetre of mandibular length increase by causing the chin point to rotate downward and backward.
In present study, concurrent with significant changes in vertical relationship, there was statistically and clinical significant improvement in forward positioning of mandible as evidenced by increase in SNB angle and effective mandibular length.
| Conclusion|| |
The present study concluded;
Thus in present study conclusive evidence of skeletal, dentoalveolar changes leading to correction of Class II Division 1 malocclusion with Twin Block functional appliance have been established. However, further studies with a longer period of follow-up, with a large sample are required to substantiate the result of the present investigation.
- Maxilla (SNA) was restricted sagittally (head gear effect) with marked maxillary dental retraction because of labial bow incorporation in upper arch of Twin Block appliance design.
- Significant mandible sagittal advancement (SNB) with minimum dental protraction was observed because of modification of Twin-Block appliance by acrylic extension to cover edges of lower incisors.
- Significant increase in the mandibular length along increase in lower anterior facial height with opening of deep bite.
- The maxillomandibular skeletal relation (ANB and WITS appraisal) reduced considerably which improved the profile and facial esthetics.
- Pronounced correction of overjet and overbite was seen.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9]