A Twin Block Study - Same Age, Same Malocclusion, Same Appliance, Different Sex Does the Effect Varies???

Abstract

Objective :The objective of this study was to compare the effects of twin block in two individuals of same age group(growing individuals), similar type of malocclusion(Class II division 1 ) treated with same appliance (twin block) but different sex.

Methodology: Case A was of a male patient 12 years 4months old with a Class II division 1 malocclusion with retrognathic mandible to whom a twin block appliance with an upper expansion screw was given. The total time wear was 15months followed by fixed mechanotherapy. Case B was of a female patient 12 years 7months old who was also given a twin block appliance with an upper expansion screw along with the tongue crib.

Results : The effect on maxilla was similar i.e. no growth of maxilla was seen. More amount of sagittal advancement was seen with Case B as compared to Case A. More amount of skeletal changes were seen with Case B i.e. increase in mandibular length , lower anterior facial height. Mandibular dental protraction was seen more with Case A.

Conclusion: More amount of skeletal changes were seen with Case B i.e. the female patient whereas more amount of dental changes were seen with Case A. this suggested that intercepting at the pubertal spurt produces more skeletal changes as compared to pre-pubertal spurt.

INTRODUCTION

Class II malocclusions are commonly occurring conditions in orthodontic practice. The component mostly involved in Class II malocclusion is mandible skeletal retrusion. Moyers in 1980 found deficient mandible within the Class II population to be approximately 70%.1 McNamara in 1981 found this to be 60% of the group having retruded mandibles.2

Various functional appliances have been proposed in literature for treating growing Class II with mandibular deficiency. Alteration of maxillary, mandibular growth and position, and change in dental and surrounding muscular envelope relationships are the expected effects of these appliances.

The most widely used functional appliance for the correction of Class II malocclusion is the Twin-Block appliance developed by Dr. William J Clark.3 The appliance works on the principle of correction of faulty inclined planes. The basic principle of twin block is 24hours wear to utilize the masticatory forces for mandibular growth stimulation. The current study aims at discussing the effects of twin block appliance in two growing individual a male and a female (developing Class II with mandibular retrognathism) of similar age group and comparing the changes brought about by the twin block therapy in same age but different sex.

Case A

A 12year 4months old male patient reported to the orthodontic clinic complaining of of forwardly placed upper front teeth.(Figure 1a)

Extraoral examination—the patient had a symmetrical mesoprosopic facial form with incompetent lips. The profile of the patient was convex with recessive chin. (Figure 1b)

Intraoal examination- all the teeth uptill 2nd molars were present in all the quadrants.(Figure 1e)The molar & canine relation was Class II bilaterally with an excessive overjet of 8mm and overbite of 5mm.(Figure 1d)

The study cast revealed upper arch was constricted in premolar region and there was a need for expansion in the upper arch.

Cephalometric analysis- revealed that patient was in a CVMI stage III(transition) with Skeletal Class II bases due to mandibular retrognathism , average angle case with proclined upper and lower incisors.(Figure 6)

Soft tissue profile revealed protrusive upper and lower lip with an acute nasolabial angle.

Treatment goals

1. To correct severe Class II skeletal base relationship.
2. To achieve and maintain Class I molar and canine relationship bilaterally.
3. To improve the soft tissue profile.
4. To align and level upper and lower arches.
5. To achieve normal overjet and overbite.

Treatment plan-

Since the patient was a growing individual a two phase treatment with Phase I growth modulation followed by Phase II fixed mechanotherapy for detailing of occlusion was planned.

Treatment progress-

In phase I a twin block appliance with an expansion screw in the upper arch was given (Figure 3a). Active period lasted for 9months followed by a support phase of 6months in which upper anterior inclined plane was given for establishing buccal segment occlusion.

The functional correction was followed by fixed mechanotherapy with 0.022×0.028 inch pre adjusted edgewise appliance using MBT prescription. Wire sequencing during the treatment was initial levelling and alignment with a sequence of 0.014’, 0.016”, 0.17×0.25 HANT wires followed by 0.17×0.25 SS wires upto 0.21×0.25 SS wires. Settling of the occlusion was done by giving settling elastics for a period of 2 weeks. The entire finishing phase after achieving post functional correction lasted for about 1 year.

Treatment results

After the functional correction, the patient's mandible was positioned forward, and the profile improved. (Figure 2b) The intraoral examination showed improvement of the deep overbite and large overjet, and correction of molar and canine relationship (Figure 2d-e).Facial profile changed from convex to straight. Lip protrusion also greatly improved. Neutrocclusion of the canines and the molars, good alignment and levelling of the maxillary and mandibular teeth, and correction of the dental midline were achieved. The cephalometric analysis depicted an increased mandibular length, a forward position of the mandible, restriction of maxillary growth.

Retention Plan The patient was given activator as a retentive appliance for 6 months followed by removable Hawley’s retainer for 6 months.

CASE B

A 12year 7months old female patient reported to the orthodontic clinic with the chief complaint of forwardly placed upper front teeth. (Figure 4a)
Extraoral examination: the patient had a symmetrical mesoprosopic facial form with incompetent lips and upper lip being anatomically short. The profile of the patient was convex with recessive chin. (Figure 4b)

Intraoal examination: All the teeth uptill 2nd molars were present in all the quadrants. (Figure 4e)The molar & canine relation was Class II bilaterally with an excessive overjet of 8mm and overbite of 4mm. (Figure 4d) The study cast revealed upper arch was constricted in premolar region and there was a need of expansion in the upper arch and a tongue thrust present.

Cephalometric analysis : revealed that patient was in a CVMI stage III(transition) with Skeletal Class II bases due to mandibular retrognathism , average angle case with proclined upper and lower incisors.(Figure 7) Soft tissue profile revealed protrusive upper and lower lip with an acute nasolabial angle.

Treatment goals:

1. To correct severe Class II skeletal base relationship.
2. To achieve and maintain Class I molar and canine relationship bilaterally.
3. To intercept developing tongue thrust
4. To improve the soft tissue profile.
5. To align and level upper and lower arches.
6. To achieve normal overjet and overbite

Treatment plan : Since the patient was a growing individual a two phase treatment with Phase I growth modulation followed by Phase II fixed mechanotherapy for detailing of occlusion was planned.

Treatment progress :In phase I a twin block appliance with an expansion screw in the upper arch along with a tongue crib was given.(Figure 3b) Active period lasted for 10months followed by a support phase of 6months in which upper anterior inclined plane was given for establishing buccal segment occlusion.

The functional correction was followed by fixed mechanotherapy with 0.022×0.028 inch pre adjusted edgewise appliance using MBT prescription. Wire sequencing during the treatment was initial levelling and alignment with a sequence of 0.014’’, 0.016’’, 0.17×0.25 HANT wires followed by 0.17×0.25 SS wires upto 0.21×0.25 SS wires. Settling of the occlusion was done by giving settling elastics for a period of 2 weeks. The entire finishing phase after achieving post functional correction lasted for about 1 year 2months.

TREATMENT RESULTS

After the functional correction, the patient's mandible was positioned forward, and the profile improved with competency of lips achieved.The intraoral examination showed improvement of the deep overbite and large overjet, and correction of molar and canine relationship.(Figure 5d-e) Facial profile changed from convex to straight. Lip protrusion also greatly improved. Neutrocclusion of the canines and the molars, good alignment and levelling of the maxillary and mandibular teeth, and correction of the dental midline were achieved. The cephalometric analysis depicted an increased mandibular length, a forward position of the mandible, restriction of maxillary growth.

Retention Plan The patient was given activator as a retentive appliance for 6 months followed by removable Hawley’s retainer along with tongue crib.

(Figure 5b)

DISCUSSION

The purpose for using a Twin block appliance is that as compared to other myofunctional appliances it is very patient compliant. Maximum changes are brought about in a rapid period of time allowing phonation, speech, adequate mastication and speech. Forces of mastication are the natural guiding forces that directs the teeth and the underlying skeletal bases into proper occlusion.

The results of this study suggest that twin block appliance had a distinct advantage in correcting the sagittal discrepancy of both the patients by bringing the mandible forward. Both the patients showed skeletal corrections when the treatment was initiated in CVMI transition stage but the findings of this study was in contrary to the study by O`Brien et al who found that treatment at this age simply increased number of patient attendances, duration and the cost of treatment , and resulted in poorer final occlusion.4 However they also stated that early treatment results in reduction of overjet, favourable change in skeletal pattern & meaningful improvement in the self esteem of the treated group.

All the cephalometric headfilms i.e. pre treatment, post twin block, post treatment and 1year post retention were superimposed using sella-nasion as a reference line. In addition to it a vertical reference line was constructed through sella tursica perpendicular to palatal plane and the horizontal measurements were made using this reference plane. 5 (Figure 8,9)

MAXILLARY SKELETAL

Maxillary skeletal in both the cases did not show any change i.e. in both case A and B the maxilla did not grow and remained the same even after phase II completion. (Table 1,2) None of the variables in both the cases showed any change in maxillary skeletal growth the findings of which are similar to study by Mills and Mc Culloch who found that there may be a trend of slightly less forward maxillary growth in growing individuals with twin block therapy.5

McNamara revealed increase in growth in this angle from 79.5° to 81.28° during 9-15 years of age. The forward posturing of mandible gives it an anterior thrust which through the appliance gets transmitted to maxilla and restrains its growth (headgear effect).6 This situation would be ideal for correction of a Class II skeletal discrepancy (Trenouth MJ).7

MANDIBULAR SKELETAL

Mandibular skeletal in both the cases showed a stimulation in growth. The parameters SNB, effective mandibular length, Go-Pog (body length), Ar-Go (ramal length) , mandibular plane angle increased in both the groups indicating a definitive accelerated growth of mandible after twin block therapy. (Table No.1,2) This increase in SNB angle was similar to previously reported studies by Clark , Illing et al., Lund and Sandler, Mills and McCulloch, Trenouth, Sidlauskas. 5,7-11

Study by Lund and Sandler found 2.4 mm additional growth between articulare and pogonion during a 12-months period of Twin-Block treatment.10

Mills and McCulloch also found a greater mandibular growth (4.2 mm) with Twin Block therapy.5

Toth and McNamara found 3.0 mm additional increase in condylion to gnathion length during a 16-months period of Twin-Block therapy as compared to 1.9 mm increase in Frankel group .12

Cephalometric superimposition revealed that more amount of skeletal change was found in Case B as compared to Case A. The possible reason for this difference can be attributed to the difference in timing of spurt for two individuals. The peak growth velocity would be expected around age 12 years in girls and around age 14years in boys henceforth more skeletal changes were seen with Case B over Case A.

McNamara & Baccetti et al stated that when compared to treatment performed before the peak, late Twin-block treatment produces more favorable effects that include: (1) greater skeletal contribution to molar correction, (2) larger increments in total mandibular length and in ramus height, and (3) more posterior direction of condylar growth.13

MAXILLARY DENTAL

Maxillary incisors in both the cases showed some retrusion. (Table No.1, 2) The contact of the labial bow on the upper incisors with the surrounding 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'.9

The present result is in accordance with the results reported Clark Lund and Sandler, Mills and McCulloch, O'Brien et al., Lee et al. 4,5,8,10,14

The amount of retrusion was seen slightly more in Case B as compared to Case A and the possible reason which can be attributed to this change could be more amount of skeletal change with Case B so more mandibular advancement resulting in more forward thrust of mandible leading to more reciprocal effect on maxillary dentition through the labial bow of the twin block appliance.

Table No. 1

Case A

Cephalometric changes pre treatment –post treatment

Table No. 2

Case B

Cephalometric changes pre treatment –post treatment

MANDIBULAR DENTAL

Mandibular dental showed a mesializing effect in both the cases. The lower incisors proclined in both the cases along with some mesial movement of lower molars. (Figure 8). Few studies have reported significant lower incisor proclination during Twin Block therapy: Lund and Sandler -7.9°, Mills and McCulloch - 5.2°.5,10 Some studies, found lower incisor remained comparatively stable after Twin-Block therapy (Trenouth reported 1.4°, Toth and McNamara by 2.8°, Sidlauskas A by 3.2°).11,12,15

This explanation to this could be Twin-Block design , the acrylic cover along with eyelet clasps were used for providing retention in the lower labial segment as with the use of Sounthend clasps in the Trenouth study and lower incisor acrylic coverage in the Sidlauskas A. 12,15

Lund and Sandler, Mills and McCulloch used ball clasps and labial bow respectively but stability was compromised.5,10

The dental change was seen more with Case A as compared to Case B. The reason that could explain this phenomena would be the difference in timing of spurt. Case B with 12years 7months of age (girl) during the treatment is at the peak of the spurt so maximum skeletal changes were seen as compared to Case A (boy) which was in a pre-pubertal stage. Studies have shown that appliance at the time of spurt tends to bring about more skeletal changes. 13

Changes in maxilla to mandible relationship skeletal changes

The resultant reduction in maxillomandibular discrepancy was mainly mandibular skeletal changes as the maxillary changes were minimum. This findings were similar to those reported by Clark, Trenouth, Illing et al., Lund and Sandler, Mills and McCulloch.5,7,8,9,10

The overjet reduced in both the cases due to mandibular forward movement, lower incisor proclination and retrusive effect on maxillary incisors.(Figure 8) This is in accordance with findings shown by Weiland, Illing et al., and Mills and McCulloch.5,9,16

The overbite also reduced due to downward growth of mandible and some amount of lower incisor proclination. Our findings are supported by studies of Clark , Vergervik and Harvold, Lund and Sandler, Tumer and Gultan. 8,15,17,18

Soft tissue profile showed that the convexity reduced in both the cases, protrusive lips corrected in both the cases and both the patients ended up with a pleasant profile.

Post treatment the results obtained were stable and were retained one year after.

CONCLUSION

• Maxilla (SNA) restrained (head gear effect) with the effect similar in both the cases
• Significant mandible sagittal advancement (SNB) was seen in both the cases more with Case B as compared to Case A
• Significant increase in the mandibular length , lower anterior facial height with opening of bite in both the cases; more with Case B
• The ANB and WITS appraisal reduced considerably which improved the profile and facial esthetics.
• Mandibular dental protraction was seen more in Case A.
• Maxillary dental retraction was seen in both the cases but was seen more with Case B
• Pronounced correction of overjet and overbite was seen in both the Cases

From the above study it can be concluded that more amount of skeletal corrections were seen with Case B(female) which was at the peak of the spurt whereas more amount of compensatory dental changes were seen with Case A(male) in a pre-pubertal spurt.

REFERENCES