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effectiveness of twin blocks and extraoral maxillary splint thurow appliances for the correction of class ii relationships aim:the aim of this study was to evaluate the skeletal and dentoalveolar changes due to treatment with twin block and thurow appliances in patients with class ii occlusions method the sample consisted of 19 randomly selected patients in each group as well as 20 individuals in the control group all patients were treated during the prepubertal growth spurt for 12 months lateral cephalograms were analyzed at the beginning of active treatment and 12 months later all data were tested with the anova and bonferroni tests results and conclusion these tests showed that the twin block promotes a significant increase p .001 in the total length of the mandible as well as an increase in anterior facial height in contrast anb and napog were reduced in both treatment groups the maxillary incisors retruded significantly p .001 although more so in the twin block group in the thurow appliance group the mandibular incisors protruded significantly p .001 all other differences between the two treated groups were not significant world j orthod 2010;11:230­235 Álvaro francisco carrielo fernandes dds msc1 ione helena portela brunharo1 cátia cardoso abdo quintão dds msc phd1 myrela galvão cardoso costa dds md2 mickelson rio lima de oliveira-costa dds md phd3 key words twin blocks extraoral maxillary splint thurow appliance class ii occlusions keletal class ii occlusions are very common and vary in their structural configuration they can be caused by maxillary protrusion mandibular retrusion or a combination of the two the treatment of choice depends on the location of the problem often one of the many functional/orthopedic appliances is used for the correction of the skeletal and occlusal disharmony among functional appliances the twin block originally developed by clark 1 and the thurow appliance developed by thurow,2 seem to be viable options the twin block consists of a maxillary and mandibular plate with bite blocks s that force the mandible forward during closure.1,3 the thurow appliance is a rigid splint that engages all or just some of the maxillary teeth it inhibits the anterior and caudal displacement of the maxilla and its concurrent tooth movements.4 the best results with both appliances occur when the peak of mandibular and maxillary growth occurs in the treatment period the objective of the present study was to compare the skeletal and dento alveolar changes produced by twin blocks and thurow appliances in subjects with an angle class ii division 1 occlusion 1professor department of orthodontics rio de janeiro state university rio de janeiro rj brazil 2doctoral degree student rio de janeiro state university rio de janeiro rj brazil 3professor department of orthodontics bahiana school of medicine and public health salvador ba brazil correspondence dr myrela galvão cardoso costa department of orthodontics rio de janeiro state university rio de janeiro rj brazil email myrelacardoso@yahoo.com.br 230 © 2010 by quintessence publishing co inc printing of this document is restricted to personal use only no part of this article may be reproduced or transmitted in any form without written permission from the publisher.

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volume 11 number 3 2010 fernandes et al fig 1 lateral view of the twin block functional appliance used fig 2 occlusal view of the thurow appliance used methods and materials this study was approved by the relevant ethics committee the patients were selected from the orthodontic post graduate clinic of rio de janeiro state university after providing consent 58 patients were included in the sample they met the following criteria a skeletal class ii relationship anb 4.0 degrees a class ii molar relationship overjet 6.0 mm no previous orthodontic treatment and ascending segment of their individual pubertal growth spurt as identified by the hand and wrist indicators of hassel and farman.5 the twin block group consisted of 12 boys and 7 girls with a mean age of 9.5 years 8 months the thurow group was made up of 10 boys and 9 girls with a mean age of 10.0 years 6 months an untreated class ii division 1 group of 13 boys and seven girls with a mean age of 9.9 years 13 months was used as the control group the analysis of variance anova test verified the initial homogeneity of the sample the design of the twin block followed clark 1 with modifications by brunharo and quintão6 fig 1 all patients were instructed to wear their appliance fulltime and to document this in a compliance form the thurow appliance followed the design of thurow 2 fig 2 all patients were instructed to wear it at night approximately 10 hours per day the outer bows of the high-pull headgear ended in the region of the maxillary first molars the applied force was around 400 cn lateral cephalograms in centric occlusion were taken of all subjects at the beginning of active treatment t1 and 12 months later t2 these radiographs were subsequently scanned using the deskscan program hp with standard definition all cephalograms were analyzed by the same operator using the radiocef 2.0 memory studio software radiocef floresta a vertical reference line originating from s and perpendicular to s-n was constructed as previously described by brunharo and quintão 10 the analysis was based on measurements of the steiner,8 ricketts,9 and mcnamara analyses.18 the various reference points and lines as the measured angles and distances are represented in fig 3 to minimize possible errors every reference point was digitized by a single operator also the method error was evaluated in four randomly selected radiographs which were digitized 10 times by the same operator the intraclass correlation coefficient icc was calculated and a value of 0.88 was obtained descriptive statistics included the calculation of means and standard deviations the changes resulting from growth and treatment were evaluated using anova to test the differences among groups the bonferroni test was used a p value of .05 was considered significant 231 © 2010 by quintessence publishing co inc printing of this document is restricted to personal use only no part of this article may be reproduced or transmitted in any form without written permission from the publisher.

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fernandes et al world journal of orthodontics nssv line co s an n fig 3 linear and angular cephalometric measurements sna snb anb co­a maxillary length co­gn mandibular length 1/na angle and mm 1/nb angle and mm v-line a du6-vl dl6-vl b a b gn me go b a mu6-vl go pog gn me table 1 mean values and standard deviations sd of the various cephalometric parameters for the three groups at t1 and p values anova for repeated measurements parameter sna degrees co-a mm snb degrees co-gn mm anb degrees napog degrees ab ocp degrees gogn-sn degrees ans-me mm sn-gn mm s-go mm u1-na mm u1-na degrees l1-nb mm l1-nb degrees l1-gogn degrees u1-l1 degrees mu6-vl du6-vl dl6-vl twin block mean sd 82.5 92.9 75.7 111.1 6.8 13.0 5.9 33.7 65.2 68.1 69.6 3.3 27.8 6.4 28.9 99.4 116.6 33.0 22.8 30.5 4.2 3.7 3.7 4.0 1.7 4.3 3.2 5.6 5.2 4.3 4.5 2.7 7.1 2.6 5.7 6.3 8.2 5.3 5.3 5.7 thurow appliance mean sd 83.1 91.0 76.1 109.9 6.3 14.1 4.7 34.5 65.0 69.3 69.2 6.3 26.0 7.4 31.0 100.3 115.9 30.8 20.8 28.3 3.9 4.6 3.6 5.5 1.8 5.4 3.9 4.5 4.0 3.0 4.8 2.8 7.3 2.3 6.9 6.4 8.1 3.5 3.4 3.6 control mean sd 82.4 90.5 76.2 110.7 6.3 12.5 6.4 33.4 64.9 68.1 68.5 5.3 26.0 6.2 27.7 99.2 115.9 32.0 21.9 29.9 4.7 5.2 3.7 7.8 1.8 4.8 6.3 5.2 4.7 3.2 4.8 2.7 6.0 2.3 6.6 7.3 8.1 4.2 3.9 4.5 p .840 .230 .930 .818 .497 .556 .502 .773 .980 .479 .757 .502 .662 .276 .266 .860 .840 .325 .364 .320 results the cephalometric values for all three groups at t1 are listed in table 1 the parametric anova demonstrated that there were no significant differences among the groups anb was reduced in both treated groups but increased in the control group though a significant difference could be detected only between the twin block and control group p .01 table 2 napog was also reduced especially in the twin block group this led to a significant difference when compared to the control group p .05 co-gn indicated a length increase of the mandible in all patients with a significant difference between only the twin block and control group p .016 232 © 2010 by quintessence publishing co inc printing of this document is restricted to personal use only no part of this article may be reproduced or transmitted in any form without written permission from the publisher.

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volume 11 number 3 2010 fernandes et al table 2 mean differences and standard deviations sd between t1 and t2 of the various cephalometric parameters and bonferroni significance test between paired groups twin block n 19 mean sd ­0.4 1.8 1.2 4.4 ­1.5 ­3 ­3.1 ­0.3 2.7 ­0.4 2.7 ­7.6 ­1.7 2.0 1.2 1.2 7.2 ­1.3 1.0 2.7 1.5 5.4 1.1 3.0 0.8 1.9 2.8 2.2 2.8 1.4 2.3 5.1 2.0 2.6 1.3 3.1 4.9 4.9 3.8 2.3 thurow appliance n 19 mean sd ­0.7 1.8 0.1 1.8 ­0.8 ­1.9 ­0.8 ­0.7 1.6 0.1 2.6 ­3.4 1.7 ­1.4 ­0.1 ­0.9 5.7 ­0.5 ­0.7 1.7 2.0 2.7 1.4 2.7 1.2 3.0 2.5 1.9 1.5 1.2 1.7 3.2 1.8 2.8 0.7 2.9 4.7 3.4 3.0 4.2 control n 20 mean sd 1.0 1.5 0.9 1.5 0.1 0.1 ­0.6 ­1.3 ­0.7 ­0.7 2.1 0.7 0.5 2.7 0.4 1.5 ­2.4 1.5 1.8 1.3 3.2 4.2 3.0 4.2 1.4 3.2 5.8 2.1 4.8 2.0 2.2 2.6 1.2 5.0 0.9 3.2 2.5 3.1 2.7 3.8 significance twin block thurow twin block control group control group thurow ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns parameter sna degrees co-a mm snb degrees co-gn mm anb degrees napog degrees ab ocp degrees gogn-sn degrees ans-me mm sn-gn mm s-go mm u1-na mm u1-na degrees l1-nb mm l1-nb degrees l1-gogn degrees u1-l1 degrees mu6-vl du6-vl dl6-vl ns not significant asterisk denotes statistically significant difference u1-na mm was significantly different for all three groups but for u1-na degrees a significant difference existed merely between the twin block and control groups as between the thurow and control groups p .01 l1-nb mm increased in the twin block and control groups and a significant difference became apparent between the thurow and twin block groups discussion after treatment the maxilla was retruded in the twin block and thurow groups sna thurow ­0.7 degrees twin block ­0.4 degrees whereas in the control group it increased sna 1.0 degree snb increased with no significant difference in any group twin block 1.2 degrees thurow 0.1 degrees control group 0.9 degrees which is in accordance with the relevant literature 11­15 similar to other studies co-gn increased in all three groups but only the difference between the twin block and control group was significant p .05 2,16­18 anb was reduced in both treated groups in comparison to the control group which is also supported by other studies.4,12­16,19­21 ans-me demonstrated an increase in both treated groups and a reduction in the control group trimming of the maxillary posterior blocks will allow the molars to erupt which will lead to an extra increase in posterior facial height that is favorable in patients with a deep bite u1-na was reduced especially in the twin block group this effect is likely due to the labial bow of the appliance because the force vector of the headgear in the thurow group ran through the center of resistance of the maxillary complex the maxillary incisors tipped less palatally in this group 233 © 2010 by quintessence publishing co inc printing of this document is restricted to personal use only no part of this article may be reproduced or transmitted in any form without written permission from the publisher.

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fernandes et al world journal of orthodontics l1-nb degrees increased during treatment in the twin block group whereas l1-nb mm/degrees became smaller in the thurow group these dentoalveolar changes are supported by many other studies.4,13­17,19,20 the molar relation in the control group did not show any improvement as previously found by ritter and almeida 14 instead the maxillary molars moved mesially in relation to the vertical reference line which aggravated the class ii relationship in the thurow group the class ii relation was improved because the maxillary molars were moved distally by the headgear.14,23­26 in the twin block group the maxillary molars moved 1.0 mm mesially in relation to the vertical reference line which differs entirely from other publications that reported a distal movement of the maxillary posterior teeth calling it the appliance headgear effect.16,18­20,27 the nonsignificant increase of the distance between the mandibular molar and vertical reference line in all groups contributed to the correction of the class ii relationship in 85 of all treated patients references 1 clark wj the twin block technique a functional orthopedic appliance system am j orthod dentofacial orthop 1988;93:1­18 2 thurow rc craniomaxillary orthopedic correction with en masse dental control am j orthod 1975;68:601­624 3 clark wj twin block functional therapy applications in dentofacial orthopedics zurin mosby-wolf 1995 28­79 4 seckin o sürücü r treatment of class i division 1 cases with a maxillary traction splint quintessence int 1990;3:17­23 5 hassel b farman a skeletal maturation evaluation using cervical vertebrae am j orthod dentofacial orthop 1995;107:58­66 6 brunharo ip quintão ca o aparelho funcional twin block ­ confecção laboratorial e aplicação clínica revista brasileira de odontologia 2001 58:373­377 7 broadbent bh a new x-ray technique and its application to orthodontics angle orthod 1931 1:45­66 8 steiner cc cephalometric for you and me am j orthod 1953;39:729­755 9 ricketts rms a foundation for cephalometric communication am j orthod 1960;46 330­357 10 mcnamara ja a method of cephalometric evaluation am j orthod 1984;84:449­469 11 fotis v melsen b williams s vertical control as an important ingredient in the treatment of severe sagittal discrepancies am j orthod dentofacial orthop 1984;86 224­232 12 malmgren o Ömblus j treatment with an orthopedic appliance system eur j orthod 1985;15:205­214 13 orton he battagel jm ferguson r ferman am distal movement of buccal segments with en masse removable appliance­its value in treating patients with mild class ii division 1 malocclusions part ii the model measuring system and results am j orthod dentofacial orthop 1996;109:379­385 14 ritter de almeida ma tratamento precoce da maloclusäo de classe ii divisäo 1 com splint de traçäo maxilar estudo clínico prospectivo ortodontia gaúcha 2002;6:154­166 15 trenouth mj cephalometric evaluation of the twin block appliance in the treatment of class ii division 1 malocclusion with matched normative growth data am j orthod dentofacial orthop 2000;117:55­59 16 lund dl sandler pj the effects of twin-blocks a prospective controlled study am j orthod dentofacial orthop 1998;113:104­110 17 malmgren o Ömblus j hägg u treatment with an orthopedic appliance system in relation to treatment intensity and growth periods a study of initial effects am j orthod dentofacial orthop 1987;91:143­151 conclusion the following conclusions were drawn from this study · the position of the maxilla in both treated groups as compared to the control group changed significantly between the beginning of treatment and the follow-up 12 months later · the twin block group demonstrated significant mandibular growth which improved the sagittal relationship between both jaws in comparison to the control group · the anterior facial height increased in the twin block group as compared to the control group · the maxillary incisors were retruded significantly in both treated groups in comparison to the control group · the maxillary and mandibular molar position was not significantly altered during the evaluated time interval 234 © 2010 by quintessence publishing co inc printing of this document is restricted to personal use only no part of this article may be reproduced or transmitted in any form without written permission from the publisher.

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volume 11 number 3 2010 fernandes et al 18 toth lr mcnamara ja treatment effects produced by the twin-block appliance and the fr2 appliance of fränkel compared with untreated class ii sample am j orthod dentofacial orthop 1999;116:597­609 19 baccetti t franchi l toth lr mcnamara ja a treatment timing for twin-block therapy am j orthod dentofacial orthop 2000;118:159­170 20 mills cm mcculloch kj treatment effects of the twin block appliance a cephalometric study am j orthod dentofacial orthop 1998 114:15­24 21 Üner o yücel-eroglu e effects of a modified maxillary orthopedic splint a cephalometric evaluation eur j orthod 1996;18:269­286 22 baumrind s korn el isaacson rj west ee molthen r quantitative analysis of the orthodontic and orthopaedic effects of maxillary traction am j orthod 1983;84:384­398 23 baumrind s korn el patterns of change in mandibular and facial shape associated with the use of forces to retract the maxilla am j orthod 1981;79:31­47 24 burke m jacobson a vertical changes in highangle class ii division 1 patients treated with cervical or occipital pull headgear am j orthod dentofacial orthop 1992;102:501­508 25 cura n saraç m the effect of treatment with the bass appliance on skeletal class ii malocclusions a cephalometric investigation eur j orthod 1997;19:691­702 26 orton hs slattery da orton s the treatment of severe `gummy class ii division 1 malocclusion with the maxillary intrusion splint eur j orthod 1992;14:216­223 27 illing hm morris do lee rt a prospective evaluation of bass bionator and twin block appliances part i the hard tissues eur j orthod 1998;20:501­516 235 © 2010 by quintessence publishing co inc printing of this document is restricted to personal use only no part of this article may be reproduced or transmitted in any form without written permission from the publisher.

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