Comparison Of The Headgear Activator And Herbst Appliance Biology Essay

SUMMARY The purpose of this survey was to measure the effects of the headgear activator ( HGA ) and Herbst contraption during active intervention and keeping and at followup in kids with a skeletal Class II malocclusion. The two groups comprised 16 back-to-back male patients ( average age 11.6 ± 1.42 old ages ) treated with a HGA and 16 male patients ( average age 12.6 ± 1.13 old ages ) treated with a Herbst contraption and Andresen activator ( HAA ) sampled from a larger pool utilizing similar choice standards. Growth informations were obtained for the two groups. Lateral cephalograms taken at the start, after 6 months of intervention, after 12 months of active intervention or 6 months of keeping, and at the 24-month followup were analysed.

The entire alterations over the whole observation period ( T0 – T3 ) did non differ signi. cantly between the groups ; there was, nevertheless, a statistically signi.cant addition in jaw prognathism ( P & A ; lt ; 0.05 ) and betterment of the grinder relationship ( P & A ; lt ; 0.05 ) in the HAA group as compared with the HGA group. During the initial intervention stage ( T0 – T1 ) , the overall intervention effects were statistically more marked in the HAA group than in the HGA group.

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Despite signi.cant differences in intervention effects and alterations between the two devices, there were no signi.cant overall alterations at follow-up except for the prognathism, i.e. maxillary prognathism decreased with intervention with the HGA while mandibulars prognathism continued to increase with HAA intervention.

Introduction

A big figure of functional contraptions of different designs, .xed and removable, have been used to rectify Class II division 1 malocclusions ( Graber et al. , 1997 ) . Two normally used devices are the Herbst contraption – a.xed functional contraption ( Pancherz, 1979 ) , and the headgear activator ( HGA ) – a removable functional contraption ( van Beek, 1982 ) .

The immediate intervention alterations reported with the usage of the Herbst were restraint of maxillary growing and enhanced growing of the mandible ( Pancherz, 1979, 1982a ) . It has been demonstrated that condylar and glenoid pit remodelling seemed to lend signi.cantly to the addition in inframaxillary prognathism when investigated utilizing a magnetic resonance imagination technique ( Ruf and Pancherz, 1998 ) . The betterment in occlusal relationship during Herbst intervention resulted about every bit from skeletal and dental alterations ( Pancherz, 1982a ) . The consequence of the Herbst contraption on the maxillary.rst grinder ( i.e. distalization and invasion ) was comparable with that of a high-pull headdress ( Pancherz and Anehus-Pancherz, 1993 ) .

After short-run followups, the upper jaw in Herbst patients has shown a period of catch-up growing, whereas the mandible demonstrated a period of minor decrease in growing ( Pancherz, 1981 ; DeVincenzo, 1991 ; Pancherz and Anehus-Pancherz, 1993 ) . It has besides been reported that the sum and way of temporomandibular articulation ( TMJ ) alterations were affected favorably but merely temporarily by Herbst intervention, as all desirable TMJ alterations reverted about 7 months after intervention ( Pancherz and Fischer, 2003 ) .

A long-run followup survey on headgear-Herbst intervention ( Wieslander, 1993 ) found that there was a signi.cant backsliding both in inframaxillary promotion and in the addition in inframaxillary length obtained during initial intervention, while another similar survey of the Herbst contraption ( Hansen and Pancherz, 1992 ) concluded that in malice of the betterment of the jaw – base relationship during initial intervention and long-run followup, Herbst intervention did non normalise the sagittal skeletal relationship at the terminal of the observation period.

The.ndings from surveies on the intervention alterations of the HGA are debatable. However, the general consensus is that there is a decrease of maxillary prognathism in patients treated with this regimen ( Ozturk and Tankuter, 1994 ; Cura et Al. , 1996 ; Bendeus et Al. , 2002 ) . Other immediate intervention alterations reported include sweetening of inframaxillary growing ( Cura et al. , 1996 ; Sari et Al. , 2003 ) and retrusion of the upper incisors ( Ozturk and Tankuter, 1994 ; Weiland et al. , 1997 ; Altenburger and Ingervall, 1998 ; Bendeus et Al. , 2002 ; Sari et al. , 2003 ) . A survey which followed a group of patients treated with HGAs for 5 old ages ( Lehman et al. , 1988 ) reported that one out of six topics experienced a backsliding of the treated Class II malocclusion.

A retrospective survey that compared the intervention result of the Herbst contraption and the Andresen activator ( HAA ) in footings of effectual TMJ growing alterations and their in.uence on the place of the mentum ( Baltromejus et al. , 2002 ) found that effectual TMJ and chin alterations were greater with both activator and Herbst intervention than in the control subjects. However, the Herbst contraption produced more favorable sagittally orientated intervention effects in a much shorter clip than the activator.

Although legion surveies have been conducted on the effects of the Herbst contraption and HGA in isolation, no comparing of the effectivity of the two therapies seems to hold been undertaken. Due to certain confining factors in the designs of probes, such as varied capable sampling processs and continuance of intervention, it is dif.cult to utilize bing surveies to pull a direct comparing between the two different intervention regimens.

The purpose of this survey was to measure and compare the effects of a removable and.xed functional contraption during active intervention and keeping and at followup in kids with a skeletal Class II malocclusion.

Subjects and methods

The original sample comprised of 20 back-to-back Caucasic male patients with a skeletal Class II division 1 malocclusion, treated with a HGA devised by new wave Beek ( 1982 ) for 12 months ( T0 – T2 ) and followed for 24 months ( T2 – T3 ; Bendeus et al. , 2002 ) . Four topics were excluded due to hapless conformity or uncomplete records. The choice standards were assorted teething, good form of the dental arches, mild to chair skeletal Class II ( ANB 4.5 grades ? 8.0 grades ) , inframaxillary plane angle ( NSL/ML ) greater than 39.0 grades, no old orthodontic intervention, and acceptable co-operation ( evaluated after 2 months ) . The initial mean overjet and overbite were 8.6 and 3.9 millimeter, severally. The 2nd sample consisted of 16 Caucasic male patients who received active intervention with a banded Herbst contraption ( Pancherz, 1985 ) for 7 months ( T0 – T1 ) followed by 6 months of keeping with an Andresen activator with moderate bite opening ( T1 – T2 ) , and were later followed for 24 months ( T2 – T3 ) . These topics were recruited from a big pool of patients treated with the Herbst contraption, whose records were obtained prospectively. The lengths of the observation intervals are given in Table 1. No keeping or farther intervention was provided between T2 and T3 in either group.

Growth informations were obtained for two groups of male topics, which were sampled utilizing similar choice standards. One group included 14 topics ( average age = 11.0 ±

1.5 old ages ) from the HGA group, and the 2nd consisted of 17 male patients ( average age = 12.9 ± 1.3 old ages ) taken from another prospective survey ( Nelson et al. , 1999 ) , who were comparable with the Herbst contraption group. The growing alterations in these topics were followed for 6 months before beginning of any active intervention. The information from both groups were pooled to obtain the 6-month growing alterations. Treatment effects were calculated by deducting the growing alterations from the intervention alterations.

Lateral cephalograms in centric occlusion were taken at the start of intervention ( T0 ) , after initial ( T1 ) and late ( T2 ) intervention, and at the 24-month followup ( T3 ; Table 1 ) . The HGA group was on norm 1 twelvemonth younger than the HAA group ( P & A ; lt ; 0.05 ) . Interpolations were made to obtain informations from both groups, stand foring precisely the same length of observation periods ( Table 1 ) . All sidelong cephalograms were analysed ( Figure 1 ) harmonizing to Bj & A ; ouml ; rk ( 1947 ) and Pancherz ( 1982a, B ) by one research worker ( PKLD ) twice, with a 1-week interval, and the two sets of informations were averaged in order to cut down the measuring mistake ( Miethke, 1989 ) . Using Pancherz ‘s method, superimposition was undertaken on the constructions of the anterior base instead than merely on the nasion-sella line.

Method mistake survey

Prior to the analysis, the intervention alterations for 10 patients were assessed twice with a 2-week interval to find the method mistake. A mated t-test was carried out and no systematic mistake was found. The size of the combined method mistake in placement, superimposing, and mensurating the

Table 1 Age at the start ( T0 ) , after 6 months ( T1 ) , and 12 months ( T2 ) of intervention, and 24 months of followup ( T3 ) , and continuance of observation periods of Headgear activator ( HGA ) group ( n = 16 ) and Herbst contraption and Andresen activator ( HAA ) group ( n = 16 ) .

T0/T0 -T1 T1/T1 – T2 T2/T2 – T3 T3 HGA HAA Diff HGA HAA Diff HGA HAA Diff HGA HAA Diff Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD

Age 11.6 1.42 12.6 1.13 ?1.0* 12.1 1.42 13.1 1.14 ?1.0* 12.6 1.4 13.7 1.20 ?1.1* 14.6 1.4 15.6 1.14 ?1.0* Duration 6.0 0.39 6.8 1.11 ?0.8* 6.1 1.00 6.3 0.73 ?0.2 23.7 1.20 23.8 0.99 ?0.1 35.8 0.80 36.9 1.30 ?1.1*** Adjusted [ 6.0 ] [ 6.1 ] [ 35.8 ] continuance

SD, standard divergence ; Diff, difference. * P & A ; lt ; 0.05 ; ***P & A ; lt ; 0.001.

K. L. D. PHAN ET AL.

Figure 1 Cephalometric variables: OLs ( OP, Maxillary occlusal shave, connection Is and the distobuccal cusp tip of the maxillary permanent.rst grinder ) , and OLp ( Occlusal plane perpendicular, mention line from S perpendicular to the maxillary occlusal plane ) . Sagittal – overjet ( millimeter ) , Is-OLp subtraction Ii-OLp ; maxillary prognathism: A-OLp ( millimeter ) , Linear place of maxillary base ; SNA ( & A ; deg ; ) , angular measuring of maxillary place ; inframaxillary prognathism: Pg-OLp ( millimeter ) , additive place of inframaxillary base ; SNB ( & A ; deg ; ) , angular measuring of inframaxillary place ; jaw base relationship: A-Pg ( millimeter ) , jaw – base relationship, A-OLp minus Pg-OLp ; ANB ( & A ; deg ; ) , sagittal jaw relationship ; A, B on OP ( millimeter ) , sagittal jaw relationship on occlusal plane measuring ; upper incisor: Is-A ( millimeter ) , alteration of maxillary cardinal incisor, Is-OLp minus A-OLp ; lower incisor: Ii-Pg ( millimeter ) , alteration of inframaxillary cardinal incisor, Ii-OLp minus Pg-OLp ; molar alterations: Ms-A ( millimeter ) , alteration of the maxillary permanent.rst grinder, Ms-OLp minus A-OLp ; Mi-Pg ( millimeter ) , alteration of the inframaxillary permanent.rst grinder, Ms-OLp minus A-OLp ; Ms-Mi ( millimeter ) , molar relationship, Ms-OLp minus Mi-OLp. Vertical – overbite ( millimeter ) , distance from Ii perpendicular to OLs, Ii-OLs ; lower face tallness: Me-MxPl ( millimeter ) , distance from MxPl perpendicular to Me ; incisor alterations: Is-NL ( millimeter ) , lower face tallness, distance from Is perpendicular to MxP ; Ii-ML ( millimeter ) , perpendicular place of inframaxillary cardinal incisor, distance from Ii perpendicular to MnPl ; molar alterations: Msc-NL ( millimeter ) , perpendicular place of the maxillary permanent.rst grinder, distance from Msc perpendicular to MxPl ; Mic-ML ( millimeter ) , perpendicular place of the inframaxillary permanent.rst grinder, distance from Mic perpendicular to MnPl ; rotational alterations: SN/MnPl ( & A ; deg ; ) , inframaxillary plane angle ; SN/MxPl ( & A ; deg ; ) , maxillary plane angle ; occlusal planes: OLs/NSL ( & A ; deg ; ) , maxillary occlusal plane angle ; OLi/NSL ( & A ; deg ; ) , inframaxillary occlusal plane angle.

alterations of the different landmarks was calculated utilizing the

expression. The combined mistake did non transcend ±0.4 ( millimeter or grade ) for any of the variables investigated.

Statistical analysis

A Student ‘s t-test for odd sample and Welch rectification were used. The degree of statistically signi. cant difference was set at P = 0.05.

Consequences

Dentofacial morphology of the patient groups

There was a minimum statistically signi.cant difference in the dentofacial morphology at the start of intervention ( T0 ) between the two patient groups, except for the place of the maxillary incisors and.rst grinders in the sagittal plane ( Table 2 ) . After the initial intervention stage ( T1 ) , some statistically signi.cant differences in dentofacial morphology were observed, but these became less pronounced at T2 and had virtually vanished at T3, except for maxillary and inframaxillary prognathism, which became more marked in the Herbst group ( P & A ; lt ; 0.01 ) .

Growth alterations

Six months of growing resulted in statistically signi.cant alterations such as an addition of lower face tallness, maxillary and inframaxillary prognathism, betterment of jaw – base relationship, and some dental alterations ( Table 3 ) .

HGA intervention and followup

The statistically signi.cant intervention effects ( Table 3 ) during the entire intervention period ( T0 – T2 ) were a lessening of overjet and overbite, betterment of the jaw base and molar relationship, restraint of maxillary forward growing, addition of lower face tallness, retrusion of the maxillary incisors and grinders, bulge of the inframaxillary incisors, and gap of the occlusal planes ( Figure 2 ) . During T0 – T1, the intervention effects were more marked than at T1 – T2. During the follow-up period ( T2 – T3 ; Table 4 ) , the following statistically signi.cant alterations were noted in the sagittal plane: maxillary and inframaxillary prognathism increased ( without a statistically signi.cant betterment of the jaw base relationship and overjet ) and the inframaxillary incisors and maxillary grinders re-bounded. In the perpendicular plane, there was an addition in lower face tallness, eruption of the dentition, and shutting of the inframaxillary plane angle. During T0 – T3 ( Table 4 ) , there were statistically signi.cant alterations in the sagittal plane with a decrease of overjet, due to retrusion of the maxillary incisors, and betterment of the jaw base relationship ( the addition of inframaxillary prognathism was more marked than that of the upper jaw ) , with a decrease of the overbite, an addition in face tallness, and eruption of the dentition.

Herbst intervention and followup

The statistically signi.cant intervention effects ( Table 3 ) observed during the entire intervention period ( active intervention with Herbst and keeping with activator, T0 – T2 ) were a lessening of overjet and overbite, betterment of the jaw base and molar relationship, enhanced frontward inframaxillary growing, an addition of lower face tallness, retrusion of the maxillary incisors and grinders, bulge of the inframaxillary grinders and incisors, invasion of the maxillary grinders and

Table 2 Comparison of dentofacial morphology at start ( T0 ) , after 6 months ( T1 ) , and 12 months ( T2 ) of intervention and after 24 months of followup ( T3 ) between Headgear activator ( HGA ) and Herbst contraption plus Andresen activator ( HAA ) .

Variables T0 T1 T2 T3

HGA HAA Diff HGA HAA Diff HGA HAA Diff HGA HAA Diff ( n = 16 ) ( n = 16 ) ( n = 16 ) ( n = 16 ) ( n = 16 ) ( n = 16 ) ( n = 16 ) ( n = 16 )

Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD

Sagittal

Overjet ( millimeter ) 8.6 2.78 9.2 2.96 ?0.6 6.6 2.11 1.5 3.22 5.1*** 5.7 2.10 4.0 2.22 1.7* 5.0 1.39 4.2 2.15 0.9

Maxillary prognathism A-Olp ( millimeter ) 79.2 3.41 81.2 4.42 ?1.9 79.4 3.17 81.3 4.24 ?1.9 79.5 3.32 82.1 4.60 ?2.5 81.3 3.21 85.2 3.54 ?4.0** SNA ( & A ; deg ; ) 81.0 3.22 82.4 4.73 ?1.4 80.8 2.62 81.8 4.49 ?1.0 80.3 2.92 82.1 4.71 ?1.8 80.0 3.00 82.9 4.44 ?2.9*

Mandibular prognathism Pg-Olp ( millimeter ) 80.1 4.10 83.4 5.59 ?3.3 81.2 4.17 86.0 5.99 ?4.9* 82.3 4.11 86.4 6.01 ?4.2* 84.9 4.10 90.5 5.86 ?5.7** SNB ( & A ; deg ; ) 75.8 2.47 76.9 3.55 ?1.1 76.1 2.43 78.1 3.76 ?2.0 76.5 2.67 78.2 3.79 ?1.7 76.6 2.42 78.8 3.77 ?2.2

Jaw base relationship A-Pg ( millimeter ) ?0.8 2.02 ? 2.3 4.46 1.4 ? 1.8 2.59 ? 4.8 4.11 2.9* ? 2.7 2.69 ? 4.4 4.33 1.6 ? 3.6 3.00 ? 5.3 5.20 1.7 ANB ( & A ; deg ; ) 5.2 1.24 5.5 2.29 ?0.3 4.7 1.07 3.6 2.14 1.0 3.9 1.31 3.9 2.36 0.0 3.4 1.37 4.1 2.60 ?0.7 A, B on OP ( millimeter ) 2.3 1.74 1.8 3.29 0.6 1.3 2.05 ? 2.7 3.11 4.0*** 0.6 1.98 ? 1.7 2.81 2.3* 0.1 1.65 ? 0.9 3.18 1.0

Upper incisor

Is-A ( millimeter ) 8.7 1.67 9.9 1.72 1.3* 7.9 1.27 7.5 2.02 0.4 7.8 1.47 7.9 1.74 ?0.1 7.1 1.54 7.9 1.84 ?0.8

Lower incisor

Ii-Pg ( millimeter ) ?0.8 2.82 ? 1.5 3.78 0.7 ? 0.5 2.76 1.3 3.27 ?1.8 ? 0.5 2.94 ? 0.5 3.75 ?0.1 ? 1.6 3.05 ? 1.6 3.97 0.0

Molar alterations Maxillary ?25.7 1.79 ? 23.4 2.09 ?2.3** ? 26.2 1.64 ? 25.5 2.42 ?0.7 ? 26.4 1.99 ? 24.8 2.12 ?1.6 ? 25.2 2.27 ? 24.7 2.41 ?0.5 molar ( millimeter ) Mandibular ?27.1 2.18 ? 27.6 3.29 0.5 ? 27.1 2.11 ? 26.1 3.38 ?1.0 ? 27.1 2.4 ? 26.2 3.31 ?1.0 ? 26.4 2.71 ? 26.7 3.41 0.2 grinder ( millimeter ) Molar 0.6 1.49 2.0 2.37 ?1.4 ? 1.0 1.91 ? 4.2 2.78 3.2*** ? 2.0 2.01 ? 3.0 2.60 0.9 ? 2.4 1.57 ? 3.3 2.67 0.9 relationship ( millimeter )

Vertical

Overbite ( millimeter ) 3.9 1.02 4.8 1.71 ?0.8 3.4 1.30 1.4 1.73 2.0*** 3.1 1.32 2.9 1.66 0.2 3.0 1.42 3.2 1.89 ?0.3 Me-MxPl ( millimeter ) 60.0 4.03 62.9 4.66 ?2.9 61.2 4.28 65.7 5.30 ?4.5* 62.6 4.19 65.6 5.09 ?3.0 66.6 4.88 68.8 6.28 ?2.2

Incisor alterations

Is-NL ( millimeter ) 28.3 2.74 29.9 3.25 ?1.6 28.3 2.73 30.1 3.18 ?1.9 28.5 2.99 30.6 3.16 ?2.1 30.1 3.02 31.6 3.52 ?1.5

Ii-ML ( millimeter ) 40.2 2.86 41.8 1.69 ?1.7 40.7 3.06 40.3 1.63 0.3 41.1 3.02 41.3 1.77 ?0.2 42.6 3.33 43.6 2.11 ?1.0

Molar alterations

Msc-NL ( millimeter ) 20.6 2.01 22.8 2.29 ?2.2 20.9 2.04 22.1 2.38 ?1.3 21.4 2.11 23.1 2.47 ?1.8* 23.5 1.87 24.5 2.73 ?1.0

Mic-ML ( millimeter ) 29.9 2.12 31.3 2.18 ?1.4 30.6 2.29 32.7 2.17 ?2.1* 31.1 2.24 33.1 2.29 ?2.0* 33.6 2.50 35.4 2.77 ?1.7

Rotational alterations

SN/MnPl ( & A ; deg ; ) 31.0 4.66 30.2 5.30 0.8 30.8 4.78 30.4 5.87 0.5 31.0 4.95 30.0 5.97 1.0 30.1 5.20 28.2 6.12 1.9

SN/MxPl ( & A ; deg ; ) 5.8 2.55 6.1 2.37 ?0.4 5.6 2.23 7.0 2.31 ?1.4 6.1 2.50 6.8 2.47 ?0.7 6.3 2.50 6.4 2.21 ?0.1

Occlusal planes

OLs/NSL ( & A ; deg ; ) 18.5 3.98 18.6 4.99 0.0 18.8 3.82 20.8 4.96 ?2.0 18.4 3.77 19.8 4.60 ?1.4 18.2 3.85 18.2 4.30 0.1

OLi/NSL ( & A ; deg ; ) 9.8 4.34 8.7 4.79 1.1 9.9 4.33 15.1 6.07 ?5.2** 10.2 5.27 12.7 5.78 ?2.6 10.3 5.24 10.6 5.44 ?0.2

SD, standard divergence ; Diff, difference. * P & A ; lt ; 0.05 ; **P & A ; lt ; 0.01 ; ***P & A ; lt ; 0.001.

inframaxillary incisors, bulge of the maxillary incisors and inframaxillary grinders, and gap of the maxillary and occlusal planes ( Figure 2 ) . During T0 – T1, the intervention effects included about all cephalometric variables, whereas during T1 – T2 practically all those variables re-bounded. During T2 – T3 ( Table 4 ) , the following statistically signi.cant alterations were noted in the sagittal plane. Overjet and maxillary and inframaxillary prognathism increased ( without a statistically signi.cant alteration in the jaw – base relationship ) , and the inframaxillary incisors uprighted. In the perpendicular plane, there was an addition in face tallness, eruption of the dentition, shutting of the maxillary and inframaxillary plane angles, and re-bounded occlusal planes. During T0 – T3 ( Table 4 ) , there were statistically signi.cant alterations in the sagittal plane with a decrease of overjet, due to retrusion of the maxillary incisors and betterment of the jaw base relationship ( the addition of inframaxillary prognathism was more marked than that of the upper jaw ) , and in the perpendicular plane a decrease of the overbite, an addition of face tallness, eruption of the dentition, and closing of the inframaxillary plane.

Comparison of HGA and Herbst contraption

The entire alterations from T0 – T3 ( Table 4 ) did non differ signi.cantly between the two groups, except that there was a greater addition in jaw prognathism and betterment of

K. L. D. PHAN ET AL.

Table 3 Dentofacial growing alterations of 31 topics, and intervention effects during initial stage ( T0 – T1 ) , late stage ( T1 – T2 ) , and both stages combined ( T0 – T2 ) of headgear activator group ( HGA ; n = 16 ) and Herbst activator group ( HAA ; n = 16 ) . Comparison of the dentofacial effects between HGA and HAA during the assorted intervention stages.

Variables

Growth alteration

HGA

HAA

HGA vs. HAA

6 months

T0 – T1

T1 – T2

T0 – T2

T0 – T1

T1 – T2

T0 – T2

T0 – T1

T1 – T2

Mean

South dakota

Mean

South dakota

Mean

South dakota

Mean

South dakota

Mean

South dakota

Mean

South dakota

Mean

South dakota

Mean

Mean

Sagittal

Overjet ( millimeter ) ?0.1 0.97 ? 1.9*** 1.54 ?0.8* 1.16 ? 2.7*** 1.98 ? 7.6*** 2.39 2.6*** 1.68 ? 5.0*** 1.70 5.7*** ?3.4*** 2.2**

Maxillary prognathism A-OLp ( millimeter ) 0.6** 1.02 ?0.5 1.00 ?0.4 0.96 ?0.9** 1.03 ?0.5 1.01 0.2 0.96 ?0.3 1.02 0.0 ?0.6 ?0.6 SNA ( & A ; deg ; ) 0.1 0.71 ?0.3 0.89 ?0.5* 0.71 ?0.9** 0.94 ?0.7** 0.73 0.2 0.71 ?0.5* 0.80 0.3 ?0.7** ?0.4

Mandibular prognathism Pg-OLp ( millimeter ) 1.1*** 1.03 0.0 1.18 0.0 1.36 0.0 1.49 1.6*** 1.41 ?0.7 1.53 0.9* 1.19 ?1.6** 0.7 ?0.8 SNB ( & A ; deg ; ) 0.3* 0.64 0.0 0.80 0.0 0.85 0.0 1.01 0.9*** 0.90 ?0.3 0.87 0.7** 0.71 ?0.9** 0.3 ?0.6 ( * )

Jaw base relationship A-Pg ( millimeter ) ?0.5* 1.02 ?0.5 1.10 ?0.4 1.38 ?0.9* 1.39 ? 2.0*** 1.39 0.9* 1.44 ? 1.2*** 1.09 1.5** ?1.3* 0.2 ANB ( & A ; deg ; ) ?0.2 0.69 ?0.3 0.74 ?0.6* 0.85 ?0.9** 0.92 ? 1.6*** 0.83 0.5* 0.79 ? 1.1*** 0.70 1.3*** ?1.0** 0.2 A, B on OP ( millimeter ) 0.3 1.21 ? 1.3*** 1.17 ? 1.0** 1.31 ? 2.3*** 1.50 ? 4.8*** 1.75 0.7 1.50 ? 4.1*** 1.37 3.5*** ?1.7*** 1.8**

Upper incisor

Is-A ( millimeter ) 0.1 0.88 ?0.9** 0.87 ?0.2 1.01 ?1.1** 1.25 ? 2.5*** 1.62 0.3 0.99 ? 2.2*** 1.45 1.6** ?0.5 1.1*

Lower incisor

Ii-Pg ( millimeter ) ?0.2 0.70 0.5* 0.83 0.1 0.68 0.7** 0.86 3.0*** 0.93 ? 1.6*** 0.78 1.5*** 0.75 ?2.5*** 1.6*** ?0.8*

Molar alterations Maxillary 0.2 1.13 ?0.7* 1.02 ?0.3 1.12 ?1.1** 1.12 ? 2.3*** 1.13 0.6 1.17 ? 1.7*** 1.09 1.6*** ?0.9* 0.6 grinder ( millimeter ) Mandibular 0.1 0.83 ?0.1 0.85 ?0.1 0.83 ?0.2 1.03 1.4*** 0.94 ?0.2 0.93 1.2*** 0.80 ?1.5*** 0.1 ?1.4*** grinder ( millimeter ) Molar ?0.4* 1.19 ?1.2** 1.28 ?0.6 1.26 ? 1.8*** 1.54 ? 5.7*** 1.64 1.7** 1.72 ? 4.1*** 1.34 4.6*** ?2.3*** 2.3*** relationship ( millimeter )

Vertical

Overbite ( millimeter ) ?0.1 0.44 ?0.4* 0.59 ?0.3 0.57 ?0.7** 0.77 ? 3.3*** 0.85 1.6*** 0.58 ? 1.7*** 0.86 2.9*** ?1.8*** 1.0** Me-MxPl ( millimeter ) 0.9*** 1.07 0.3 1.06 0.5 1.08 0.8** 1.11 1.9* 3.34 ? 1.0*** 0.98 0.9** 0.99 ?1.6 1.5*** ?0.1

Incisor alterations Is-NL ( millimeter ) 0.1 1.02 ?0.1 0.96 0.2 1.03 0.0 1.11 0.2 0.94 0.4 0.88 0.6* 0.94 ?0.3 ?0.2 ?0.6 Ii-ML ( millimeter ) 0.5*** 0.63 0.3* 0.64 0.3* 0.57 0.0 0.70 ? 1.9*** 0.87 0.5** 0.59 ? 1.5*** 0.78 2.0*** ?0.5* 1.5***

Molar alterations

Msc-NL ( millimeter ) 0.5* 1.08 ?0.3 1.01 0.0 0.98 ?0.3 1.01 ? 1.2*** 1.01 0.5 1.08 ?0.7* 1.08 0.9* ?0.5 0.4

Mic-ML ( millimeter ) 0.4*** 0.63 0.2 0.80 0.6* 0.88 0.8** 0.95 0.9*** 0.59 0.0 0.66 1.0*** 0.70 ?0.7** 0.1 ?0.6*

Rotational alterations

SN/MnPl ( & A ; deg ; ) ?0.4* 0.88 0.0 1.23 0.7 1.31 0.7 1.43 0.5 0.96 0.1 0.92 0.5 0.96 ?0.3 0.5 0.2

SN/MxPl ( & A ; deg ; ) ?0.2 1.28 0.2 1.24 ?0.1 1.16 0.1 1.33 1.0** 1.12 0.0 1.12 1.0** 1.18 ?1.0* 0.7 ?0.3

Occlusal planes OLs/NSL ( & A ; deg ; ) ? 1.0*** 1.20 1.3*** 1.22 0.6 1.25 1.9*** 1.15 3.3*** 1.36 0.0 1.24 3.2*** 1.37 ?2.0*** 0.6 ?1.4** OLi/NSL ( & A ; deg ; ) ?0.6* 1.34 0.8* 1.32 0.9* 1.50 1.7** 1.88 7.0*** 2.02 ?1.7*** 1.48 5.3*** 2.07 ?6.2*** 2.6*** ?3.6***

SD, standard divergence. *P & A ; lt ; 0.05 ; **P & A ; lt ; 0.01 ; *** P & A ; lt ; 0.001.

molar relationship in the HAA than in the HGA group ( Tables 3 and 4, Figure 2 ) . During T0 – T1 ( Table 3 ) , the overall intervention effects were more marked in the HAA than in the HGA group. During T1 – T2 and T2 – T3, some intervention alterations re-bounded in the HAA group, and at that place was continuance of advancement in the HGA group, taking to the disappearing of about all the differences observed during the initial intervention at the terminal of the observation period.

Discussion

In this prospective survey, a sample of back-to-back immature male patients with skeletal Class II division 1 malocclusions was treated with a speci. hundred type of HGA ( van Beek, 1982 ) . Another group of immature male patients with similar cephalometric dentofacial morphology ( Table 2 ) treated with HAA was selected from a big prospective survey and compared with the former group. Linear cephalometric measurings are known to be more dependable than angular measurings ( Baumrind and Frantz, 1971 ; Bookstein, 1997 ) , but angular measurings were besides investigated to ease comparings with other surveies. Interpolations were carried out to equalise the observation intervals for both groups and to let direct comparing. An of import characteristic of this survey was the long follow-up period to enable

Figure 2 Accumulative alterations ( A ) upper jaw, ( B ) lower jaw, ( C ) jaw base, ( D ) lower face tallness, ( E ) maxillary incisors, ( F ) mandibular incisors, ( G ) overjet, and ( H ) overbite. Growth alterations: 6 months ; intervention alterations: 0 – 6 months ( T0 – T1 ) , 6 – 12 months ( T1 – T2 ) ; follow-up: 24 months ( T2 – T3 ) ; HGA ( headgear activator ) ; HAA ( Herbst 6 months and activator 6 months ) .

the lasting effects of the intervention to be adequately assessed. Most old surveies ( Pancherz, 1979 ; Dermaut et Al. , 1992 ; Cura et Al. , 1996 ; Wong et Al. , 1997 ; Altenburger and Ingervall, 1998 ; Illing et Al. , 1998 ; Du et Al. , 2002 ) merely reported the immediate intervention alterations, and did non see the long-run effects of intervention.

A recent randomised clinical test ( RCT ; O’Brien et al. , 2003 ) that studied the differences in intervention result after intervention with Twin Block and Herbst contraptions concluded that there were no differences in skeletal and dental alterations between the contraptions at completion of the 2nd stage of intervention with.xed contraption therapy. Although it was reported that there was no difference in entire intervention clip ( functional stage plus.xed contraption stage ) between the contraptions, a closer examination of the survey design revealed that there was a statistically signi.cant difference in the continuance of intervention in the functional stage. This lasted

11.2 months with the Twin Block contraption and 5.8 months with the Herbst ( P & A ; lt ; 0.001 ) . Furthermore, in the instance of the Herbst contraption intervention, one time the overjet was to the full corrected the contraption was removed and intervention was continued with a.xed contraption. No considerations were used to keep the rectification achieved and let the occlusion to settle before the beginning of the 2nd stage with.xed contraptions. It has been demonstrated that 90 per cent of occlusal backsliding occurs during the.rst 6 months post­treatment ( Pancherz and Hansen, 1986 ) , and an experimental survey ( Chayanupatkul et al. , 2003 ) has shown that suf.cient clip is required for freshly formed bone to maturate into more stable bone. Furthermore, this RCT merely reported on the immediate intervention alterations, and presented no follow-up informations to re.ect the true result of intervention. The present survey dramatically demonstrates the importance of followup, as the immediate intervention effects differed markedly between the two curative groups, but after a period of keeping and settling the eventual differences at followup were limited to merely chew the fat prognathism ( Table 2 ) . Therefore, the decisions of a retrospective survey that compared the effects of the HAA ( Baltromejus et al. , 2002 ) are besides questionable, as the continuance of intervention with the two contraptions differed signi.cantly ( 2.6 old ages for activator versus 0.6 old ages for Herbst contraption ) , and the analysis of the intervention effects of the Herbst contraption was undertaken instantly after intervention, before a period of keeping to let for stabilisation and subsiding of the occlusion to take topographic point.

The built-in failing of the present survey is the little size of the groups. However, the topics were all males, and it has been shown that the growing rate between the genders differs signi.cantly closer to the pubertal upper limit ( Pancherz and H & A ; auml ; gg, 1985 ) . However, the age difference between the groups at the start of intervention was 1 twelvemonth which might bespeak that the basic growing differed slightly between the two groups. The ground for the age difference was chiefly due to the fact that the Herbst group was more dentally mature, since anchorage required the.rst bicuspids to hold erupted to the full ( Pancherz, 1985 ) . By comparing the effects of intervention instead than intervention alterations merely, this job might hold been reduced since effects of a certain intervention seem to be consistent and non straight related to growing position ( H & A ; auml ; gg et Al. , 1987 ) .

The two contraptions investigated in this survey produced different intervention effects on maxillary and inframaxillary growing ( Figure 2 ) . At T2, there was restraint of maxillary growing in the HGA group ( P & A ; lt ; 0.01 ) , but non in the HAA group. After initial intervention ( T 0 -T 1 ) , the sum of maxillary growing restraint was statistically insigni.cant ( ?0.5 millimeter ) with both HGA and Herbst contraption. Six months of keeping with the Andresen activator in this survey did non impact maxillary growing, which seemed to hold re-bounded to the normal degree. However, the Andresen activator has been shown to keep maxillary growing when used for active intervention for 12 months ( Jakobsson and Paulin, 1990 ) , and after an extended period of keeping following early intervention with the Herbst contraption ( Wieslander, 1993 ) . Previous surveies of HGA with active intervention of 9 – 11 months have shown restraint of maxillary forward growing ( Lehman et al. , 1988 ; Dermaut et al. , 1992 ; Altenburger and Ingervall, 1998 ) . In general, this. nding is in understanding with the consequences from two surveies on headgear intervention, which reported a pronounced addition in the intervention alterations on the upper jaw in patients treated for 2 old ages compared with those treated for about half as long ( Ghafari et al. , 1998 ; Tulloch et Al. , 1998 ) . By extrapolating the consequences from two old surveies of the Herbst contraption ( H & A ; auml ; gg et al. , 2002, 2003 ) , it was demonstrated that 6 months of intervention with a conventional Herbst did non signi.cantly affect frontward growing of the upper jaw, but after an extra 6 months of intervention there was a statistically signi.cant consequence. The combination of headdress and a. xed functional contraption, headgear-Herbst contraption, farther enhanced the restraint of maxillary growing, and the effects were already apparent after 6 months of intervention ( H & A ; auml ; gg et Al. , 2003 ) . These.ndings seem to bespeak that the length of intervention is an indispensable factor in the modi.cation of maxillary growing with headgear and functional contraptions.

Mandibular growing was accelerated ( P & A ; lt ; 0.01 ) during Herbst intervention ( T0 – T1 ) , but tended to go slower than normal during the keeping period ( T1 – T2 ; P = 0.08 ) , but the addition in inframaxillary growing at T2 was still statistically signi. buzzword ( P & A ; lt ; 0.05 ; Table 3 ) . Consequently, the usage of an Andresen activator as a consideration for a 6-month period after active intervention with the Herbst contraption for 7 months merely indicated that the Andresen activator was unable to keep the intervention consequence achieved by the acceleration of inframaxillary growing, or even the normal rate of inframaxillary growing to forestall slowing of growing after active intervention. A old survey of Herbst intervention showed that acceleration of inframaxillary growing merely occurred during the initial 6-month stage of intervention, and after 6 more months

K. L. D. PHAN ET AL.

of extended intervention inframaxillary growing did non differ from normal growing, a degree which was maintained during 6 months of keeping with a HGA ( H & A ; auml ; gg et Al. , 2003 ) . A recent experimental survey demonstrated that suf.cient clip after frontward positioning with a.xed jumping device was necessary to let the freshly formed condylar bone to maturate and go stable, and therefore enable normal growing to be maintained post-treatment ( Chayanupatkul et al. , 2003 ) . By contrast, inframaxillary growing appeared to be unaffected by intervention with the HGA ( Table 3 ) . This might be because the activator is a removable device which holds the mandible in a forward place for portion of the twenty-four hours merely. This.nding is besides consistent with the consequences of 12 months of intervention with an Andresen activator, which besides had no consequence on the mandible ( Jakobsson and Paulin, 1990 ) . However, other surveies utilizing the same HGA for 9 – 11 months have reported that inframaxillary growing was enhanced ( Lehman et Al. , 1988 ; Dermaut et al. , 1992 ; Altenburger and Ingervall, 1998 ) . Difference in conformity may partially account for these results, and it is besides possible that the mention values of normal growing in the surveies concerned were non obtained in a similar manner for the treated samples, as in the present probe.

During T2 – T3, there was no signi.cant difference in growing alterations in either the mandible or the upper jaw between the two groups ( Table 4 ) . There was less addition in maxillary and inframaxillary prognathism during the 3-year observation period ( T 0 – T 3 ) in the HGA than in the HAA group. Apparently the lessening in maxillary prognathism during active intervention with HGA had a permanent consequence, and this might besides hold contributed to possible sub-normal growing of the mandible. In the HAA group, maxillary growing had already re-bounded during the keeping period. Despite some slowing of inframaxillary growing in the HAA group during T1 – T2, the addition in inframaxillary prognathism during the entire observation period appeared to be near to that expected from normal growing. Consequently, there seemed to be a impermanent acceleration of inframaxillary growing during intervention with the Herbst contraption, which was followed by a possible sub-normal or slowing of growing in the sagittal plane. Deceleration of normal growing is improbable, since the male patients during the follow-up period ( T2 – T3 ) were on mean 12.6 – 14.6 old ages of age and

13.7- 15.6 old ages in the HGA and HAA groups, severally, which were near to the pubertal upper limit of inframaxillary growing ( Bj & A ; ouml ; rk, 1972 ) . Another possibility was that inframaxillary growing became sub-normal after functional contraption intervention in both groups. Two recent studies on intervention with the Twin Block ( O’Brien et al. , 2003 ; Banks et al. , 2004 ) showed that the maxillary and inframaxillary intervention alterations were so really similar in the topics treated with a Twin Block for 7 months merely, compared with the sample that had 22 months of intervention with the Twin Block followed by comprehensive orthodontic intervention. This would bespeak that limited growing occurred after the initial stage of functional contraption intervention in the ulterior sample. In other words, growing could hold become sub­normal or close to zero after the initial stage of functional contraption therapy, or the growing way became ‘ strictly ‘ perpendicular during the ulterior stage of intervention with.xed contraption.

It was reported from a RCT ( Tulloch et al. , 2004 ) that there was no difference in the.nal result between the one- and two-phase intervention groups. The. gures published in two separate studies ( Tulloch et al. , 1995, 2004 ) were used in the present survey in order to cipher the alterations in mandibular ( SNB ) and maxillary ( SNA ) prognathism in the three ‘ experimental groups ‘ which would stand for the alterations displayed over an full estimated observation period of 40 – 50 months, and compared them with those obtained from the two groups investigated in the present survey over a period of 36 months ( Table 5 ) . In the present survey, the.ndings showed that maxillary prognathism in the HGA group tended to diminish ( P = 0.052 ) , but there was no pronounced alteration in the HAA group. The difference between the two groups was marginally statistically signi. buzzword ( P = 0.056 ) . Mandibular prognathism tended to increase in the HGA group ( P = 0.052 ) but increased even more markedly in the HAA group ( P & A ; lt ; 0.001 ) , the difference between the two groups being statistically signi. buzzword. The deliberate.gures from that RCT survey con.rmed that the

Table 5 Comparison of the differences of maxillary and inframaxillary prognathism at the start and terminal of the present survey and in the randomized controlled test ( RCT ) by Tulloch et Al. ( 1995, 2004 ) . ( HGA, headgear activator ; HAA, Herbst contraption + Andresen activator ; 1-Phase, one-phase.xed contraption ; 2-Phase B, bionator + .xed contraption ; 2-Phase HG, headgear + . xed contraption ) .

Variables

Present survey

RCT

HGA

HAA

1-Phase

2-Phase B

2-Phase HG

Diff

P value

Diff

P value

Diff

P value

Diff

P value

Diff

SNA ?1.0 0.052 0.4 0.207 ?0.8 0.281 ?0.6 0.496 ?1.5 0.028 SNB 0.8 0.052 2.0 0.001 1.1 0.123 1.9 0.035 0.5 0.439

headgear group ( two-phase intervention ) had reduced maxillary prognathism ( P & A ; lt ; 0.028 ) with no addition in inframaxillary prognathism. The bionator group ( two-phase intervention ) experienced an addition in inframaxillary prognathism ( P & A ; lt ; 0.035 ) but no alteration in maxillary prognathism, whereas in the.xed contraption group ( one-phase intervention ) there was no signi.cant alteration in jaw prognathism. Hence, these.ndings contradict the decision of the writers of the RCT ( Tulloch et al. , 2004 ) that there was no difference between the results of the three different intervention regimens. Based on the deliberate.gures from the old RCT survey ( Tulloch et al. , 1995, 2004 ) and the.ndings from the present probe, prognathism of the jaws was affected otherwise in the short and the long footings, depending on which intervention device was used.

Decisions

Maxillary prognathism decreased with intervention with the HGA, while inframaxillary prognathism continued to increase with HAA. This might bespeak that the usage of headdress besides has an indirect restraining consequence on inframaxillary prognathism.

Address for correspondence

Dr Urban H & A ; auml ; gg Orthodontics, Faculty of Dentistry The University of Hong Kong Prince Philip Dental Hospital 34 Hospital Road Hong Kong SAR China E-mail: euohagg @ hkusua.hku.hk