HERBST APPLIANCE

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LITHUANIAN UNIVERSITY OF HEALTH SCIENCES MEDICAL ACADEMY

Dalia Latkauskienė

TREATMENT OF ANGLE CLASS II MALOCCLUSION WITH THE CROWN

HERBST APPLIANCE

Doctoral Dissertation Biomedical Sciences, Odontology (07B)

Kaunas, 2012

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The dissertation was prepared at the Department of Orthodontics of Lithuanian University of Health Sciences 2004–2012.

Scientific Supervisor

Prof. Dr. Antanas Šidlauskas (Lithuanian University of Health Sciences, Medical Academy, Biomedical Sciences, Odontology – 07 B)

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LIETUVOS SVEIKATOS MOKSLŲ UNIVERSITETAS MEDICINOS AKADEMIJA

Dalia Latkauskienė

ANTROS KLASĖS SĄKANDŽIO ANOMALIJŲ GYDYMAS VAINIKĖLIAIS TVIRTINAMU

HERBSTO APARATU

Daktaro disertacija Biomedicinos mokslai,

odontologija (07B)

Kaunas, 2012

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Disertacija rengta Lietuvos sveikatos mokslų universiteto Ortodontijos klinikoje 2004–2012 metais.

Mokslinis vadovas

Prof. dr. Antanas Šidlauskas (Lietuvos sveikatos mokslų universiteto Medicinos akademija, biomedicinos mokslai, odontologija – 07B)

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ABBREVIATIONS

cHerbst – stainless steel crown Herbst CII:1 – Class II division 1

CII:2 – Class II division 2

BJFA – bite jumping functional devices

CVM – growth staging index according to cervical vertebrae RCT – randomized clinical trial

CCT – controlled clinical trial

ICC – intraclass correlation coeficiant

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INTRODUCTION

Class II is one of the most common orthodontic malocclusions, it occurs in about one third of the Lithuanian population [1] as well as in some European countries [2] and the United States [3]. Functional jaw orthopedics is a specific type of treatment for Class II dentoskeletal disharmonies associated with mandibular retrusion. A wide range of fixed and removable functional appliances is available for correction of Class II skeletal and occlusal disharmonies, however their modes of action are diverse. Among the various types of orthopedic and functional devices, the Herbst appliance has been proved to be effective for correcting Class II malocclusion [4-6].

The Herbst device has become increasingly popular worldwide during the last three decades mostly due to the compliance-free design of the appliance and clinical effectiveness.

Although the traditional banded Herbst has been shown to be clinically efficient [4-6] (Picture 1), it has several disadvantages, such as high break- age rate and frequent episodes of additional laboratory work during the active treatment [7-8].

Picture 1. Banded Herbst

Therefore several modifications of the appliance were presented. In 1980 Langford introduced the stainless steel crown Herbst (cHerbst) (Picture 2) [9].

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Picture 2. Crowned Herbst

In 1983 Howe and McNamara [10] described the current modification of the acrylic splint Herbst (Picture 3).

Picture 3. Acrylic Herbst

In 1984 Wieslander [11] presented the cast splint Herbst design (picture 4) in combination with headgear.

Picture 4. Cast splint Herbst

In 1989 Valant and Sinclair [12] introduced the Herbst appliance with a mandibular-acrylic splint and stainless steel crowns on maxillary first molars. Among those modifications the cHerbst appliance seemed to be simple to adjust and deliver to patients with reliable performance not involving extensive laboratory work.

Only a few studies on the effects of cHerbst are available in the literature [13-15]. Those studies on cHerbst reported the results after the fixed appliance therapy conducted immediately after the cHerbst, so the isolated effect of treatment with cHerbst device was not revealed [13,15]. Recent systematic review by Barnett et al [14] stated that still there were not enough good quality studies to evaluate immediate changes after the banded Herbst or cHerbst appliance were removed for growing individuals. No

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studies conducted on cHerbst reported the data on clinical success and complications of this appliance design.

AIM OF THE STUDY

The aim of this prospective study was to evaluate the mechanism of Class II correction in the sample of growing Class II patients treated with the cHerbst.

Tasks:

1. To evaluate the cHerbst effect in growing patients (who presented with stable Class I occlusion one year after treatment) immediately after treatment and at one year follow- up as the impact on the following dental and skeletal structures:

a) maxilla;

b) mandible;

c) upper incisors;

d) lower incisors;

e) upper first molars;

f) lower first molars.

2. To evaluate patients’ self-perception six months after treatment.

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THE ORIGINALITY AND PRACTICAL USE OF THE STUDY

This study is the first prospective clinical trial which evaluated Class II treatment with the cHerbst as a single appliance with one-year post treatment follow up period. The cephalometric investigation of the study patients evaluated unadulterated effects of the cHerbst treatment, because no additional orthodontic appliances (including retainers) were used during the treatment stage as well as during the 12 month follow-up period, so only isolated cHerbst appliance effect could be examined. Only a few studies on the effect of cHerbst are available in the literature [13-15]. Those studies on cHerbst reported the results after the fixed appliance therapy conducted immediately after the cHerbst, so the unadulterated cHerbst effect was not revealed [13,15]. The systematic review by Barnett et al [14] stressed that studies published on cHerbst device reported only delayed treatment results.

Recent systemized review by stated that still there had been not enough information of good quality to evaluate immediate changes after the banded Herbst or cHerbst appliance were removed for growing individuals.

To explain the mechanisms of Class II correction, the changes were compared with maturity matched Class II controls from a historical sample picked from University of Michigan and Denver growth studies. It would be desirable to have an access to a control material of the same quality as treated material, but for ethical reasons it is no longer possible to perform longitudinal rentgenological registrations of untreated patients with post- normal occlusion. As well all the patients were treated in a private practise, they payed for their therapy and wanted to proceed with the effective treatment, so no delay could take place. Because of these two reasons our clinical study was not a randomized clinical trial.

A considerable advantage of this prospective study is that the dropouts, complications, failure rates could be measured accurately. No other study had published failure rates of cHerbst before. As the result of the research, the orhodontists will receive a valuable message on the clinical aspects of the cHerbst and be able to inform the patients on the posible treatment outcomes as well as arrising complications.

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Another advantage of the research is that all the clinical part was mana- ged by the same investigator (D.L.) in the same private practice. Treatment was performed according to cHerbst protocol, being the same to all patients starting with the instalation of the appliance, activation and finishing with the follow ups and evaluation of occlusion.

To control the bias of the study, two independent examiners were invited to participate in the research: tracing of the cephalograms was accomplished by the investigator Gundega Jakobsone in Riga Stradins University, Latvia and maturity according to the lateral cephalograms was assessed as well as control group picked by another researcher Lorenzo Franchi in the University of Florence, Italy. Investigators in Latvia and Italy were not aware of the treatment progress of the study patients.

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1. LITERATURE REVIEW

1.1. The origin of Class II

The relative influence of genetics and environmental factors in the aetiology of malocclusion has been a matter for discussion and controversy in the orthodontic literature. General conclusions are that, while phenotype is inevitably the result of both genetic and environmental factors, there is irrefutable evidence for a significant genetic influence in many dental and occlusal variables. The influence of genetics however varies according to the trait under consideration and in general remains poorly understood.

Horowitz et al [16] studied fraternal and identical adult twin pairs using only linear cephalometric measurements, and he demonstrated highly significant hereditary variations in the anterior cranial base, mandibular body length, lower face height, and total face height. Fernex et al [17] found boys to show more similarities to their parents than girls. Facial skeletal structures were more frequently transmitted from mothers to sons than from mothers to daughters. Female twins showed greater concordance in facial features than male twins. While the profile outline coincided most frequently, this was not true of the cranial base and differences increased with age. Hunter et al. [18] found genetic correlation to be strongest between fathers and children, especially in mandibular dimensions (Picture 1.1).

Picture 1.1. Mother and daughter with similar facial features

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Malocclusion may be defined as a significant deviation from what is defined as normal or “ideal” occlusion [19]. Many components are involved in normal occlusion. The most important are: 1) the size of the maxilla; 2) the size of the mandible, both ramus and body; 3) the factors which determine the relationship between the two skeletal bases, such as cranial base; 4) the arch form; 5) the size and morphology of the teeth; 6) the number of teeth present; and 7) soft tissue morphology and behaviour, lips, tongue, and peri-oral musculature. The term ‘ normal occlusion’ is arbitrary, but is generally accepted to be Class I molar relationship with good alignment of all teeth and represents a situation that occurs in only 30–40 per cent of the population [3].

The Class II malocclusion often reflects on the disharmony in the jaw relationship. In Caucasians it has been reported that increased overjet is because of a retrusive mandible only more often [3]. Since the mandible is too far back or too small in most Class II patients, one sensible orthodontic treatment option in growing patients is to bring the mandible forward, aiming to enhance the growth of the condyle [6,20] and remodeling of glenoid fossa [21,22]. The mandibular and facial growth pattern varies within the Class II patients from favorable vertical-forward condylar growth direction and clockwise rotation of the mandible to unfavorable sagittal condylar growth direction and counter clock-wise rotation of the mandible as well as mandibular angle differences (Picture 1.2) [23].

Picture 1.2. Clockwise mandibular rotation with the short ramus of the mandible (left), counter-clockwise mandibular rotation

with the long ramus (right)

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The growth direction of the posterior cranial base varies and results in an open or closed skull base angle. Subsequently, the glenoid fossa can be in a more posterior or anterior position which decides the position of the mandible. Therefore, a retrusive mandible can be of normal size with its condyle in a glenoid fossa, which is located posteriorly, or of a small size and/or abnormal shape with its condyle in a glenoid fossa which is located more anteriorly. In conclusion, patients with severe overjet are not homogenous in either overall facial or mandibular morphology or growth pattern. This will at least to some extent explain the often considerable individual variations in response to various orthodontic treatment mechanisms, such as bite jumping therapy using functional appliances.

1.2. Dentoskeletal characteristics of Class II malocclusions:

differentiation between the subgroups

In dentofacial orthopedics a thorough knowledge of dentoskeletofacial morphology and growth is essential for the diagnosis and treatment planning, as well as for the evaluation of the results. The cephalometric characteristics of Class II malocclusions have been analyzed in a number of investigations [24-30]. The largest samples and the differentiation between the subgroups: Class II division 1 (CII:1) (Picture 1.3) and Class II division 2 (CII:2) (Picture 1.4) was performed by Pancherz et al [30].

Picture 1.3. Class II division 1 occlusion

Picture 1.4. Class II division 2 occlusion

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The differentiation of the subgroups is most important as CII:2 subjects may have a specific craniofacial morphology [31-33]. Pancherz et al [30]

investigated two age groups of patients: 8–10 years (representing early mixed dentition) and 11–13 years (representing late mixed dentition). The patients were devided into two subgroups: CII:1 and CII:2 and compared to the “normal” population [34-35]. The authors reported that mandibular retrusion was a common characteristic for both subgroups as confirmed by other studies [26-29]. Due to normal growth and development [34-35] the frequency of mandibular retrusion was expected to become lower with age.

This was true for the CII:1 sample only. Deep bite and retroclination of upper incisors could restrict the growth of the mandible in CII:2 subjects [30]. This assumption was confirmed by the observation that in these cases dentoalveolar development (Sella-Nasion-point B angle) in the mandible was restrained more than basal development (Sella-Nasion-point Pg angle) [30] (Picture 2.25).

This finding was supported by Arvystas MG observation [36]. Pancherz et al [30] also reported on the increase of low angle cases with age in both subgroups. Their data was in agreement with Bjork results on anterior mandibular growth rotation [37]. Another interesting finding by Pancherz et al [30] was that vast majority of cases (97-100%) in both subgroups had short lower facial heights. Similar results were reported on CII:1 [28,38] and CII:2 [32] samples by other researches. On the contrary, excessive vertical development of the lower face was found in the CII:1 samples studied by Hunter et al [39] and McNamara et al [27]. The mandibular incisor incli- nation as reported by Pancherz et al [30] differed between the subgroups.

The teeth were relatively more proclined in CII:1 subgroup and relatively more retroclined in CII:2 subgroup. The same findings were detected by Solow [40] as the result of dentolaveolar compensation in response to mandibular retrusion (CII:1) and maxillary incisor retroclination (CII:2). To conclude on dentofacial characteristics of Class II subgroups Pancherz et al [30] noted that no basic morphologic differences were detected that could influence the principles of orthodontic treatment of CII:1and CII:2. In other words the same Class II correctors can be selected to treat both CII:1 and CII:2 malocclusions.

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1.3. Conservative Class II treatment options

Since the late 19^th century many types of bite jumping functional devices (BJFA) have been advocated to treat Class II growing patients [41]. The fundamental principle of all BJFA is to keep the mandible in protrusive position in an attempt to evoke condylar and then mandibular growth, which in turn consolidates the repositioned mandible.

The classical functional appliances for Class II correction were loose fitting (e. g. Andresen type activator (Picture 1.5), Bionator (Picture 1.6)).

Picture 1.5. Andresen type activator

Picture 1.6. Bionator

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During the past 35 years, several authors suggested that functional appliances should be attached to the dental arches with clasps (e. g. twin block (Picture 1.7)) in order to improve the stability of the appliance and the compliance of the patient.

Picture 1.7. Twin block

But the appliances still remained removable. The problem with the removable BJFA is that appliances are bulky and difficult to function with.

Nevertheless the patients are instructed to wear the removable BJFA for 9 to14 hours per day in order to achieve desired Class II correction.

Nowadays it is difficult to persuade the patients to wear appliances that interfere with the function and their daily life and duties [41]. The lack of clinical success of functional appliances has in some circumstances been attributed to lack of patient compliance in appliance wear [42]. Fixed BJFA might be attached to the multibracket systems or function relying on direct anchorage of upper and lower teeth with the help of bands or crowns. A variety of BJFA is incorporated into modern orthodontics. For fixed BJFA, the fundamental design and biomechanics are well represented by Herbst (Pictures 1–4) appliance. The telescope mechanism of Herbst creates a continuous mandibular protrusion. The Herbst appliance can be banded or splinted (acrylic or casted) to the dental arch, so the patient cannot remove the appliance and BJFA works for 24 hours per day. Unlike removable BJFA which require prolonged treatment duration of approximately two years [41], the fixed BJFA impose a shorter treatment time of 6-12 months and are not dependant on patient’s compliance and cooperation [43].

Prospective investigations on removable BJFA (twin-block) reported following drop-out rates – 17% [44] and 50% [45].O‘Brien et al [42]

reported that 12.9% of children had not completed the fixed BJFA Herbst treatment and 33.6% had failed twin block therapy in the same study. Due to

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good patient compliance and clinical results the popularity of Herbst has increased so much during the past three decades that it is now the most widely used BJFA in the United States [46]. In conclusion to this section it can be stated that fixed BJFA have certain qualities against the removable BJFA that are important in daily orthodontic practise. Herbst type appliances do not interfere with function (patient can chew, speak, swallow, breathe normally with the device in situ), this way better patient compliance could be achieved, besides fixed BJFA impose shorter treatment time than their removable counterparts.

1.4. Short historical background of the Herbst appliance

Emil Herbst introduced his device at the 5^th International Dental Cong- ress in Berlin 1909. In 1934 Herbst presented 3 articles in Zahnarztliche Rundschau on his positive long term experiences with the appliance. Emil Herbst was criticized by his colleague Martin Schwarz about the treatment method due to the possibility of the overload of the anchorage teeth with periodontal damage as a consequence. After 1934 the Herbst appliance was forgotten until it was rediscovered by Hans Pancherz in 1979 [47]. Possible modifications of the current Herbst appliance are presented in the introduction section.

1.5. Treatment timing for the functional therapy

The main objective of therapy with functional appliances such as cHerbst is to induce supplementary lengthening of the mandible by stimulating increased growth at the condylar cartilage. Additionally it is possible to impact the growth of the other parts of the mandibular bone. The rate of mandibular growth is not constant throughout the juvenile and adolescent periods, with the existence of a pubertal peak in mandibular growth described previously in classical cephalometric studies [23, 48, 49]. There is evidence which shows that the greatest effect of functional appliances occurs when the peak in mandibular growth is included in the treatment period. Investigations of Petrovic et al [50, 51] revealed that the therapeutic effectiveness of other Class II correctors – the Frankel appliance and Bionator was most favourable when these appliances were used during the ascending portion of the individual pubertal growth spurt. Hägg and Pancherz [52] found that sagittal condylar growth in patients treated with the Herbst appliance at the pubertal growth spurt was twice greater than that observed in patients treated 3 years before or 3 years after the peak. Baccetti

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et al [53] supported their data, concluding that the twin block therapy should be performed during the growth peak or slightly after in order to get larger increments in mandibular length and ramus height, more posterior condylar growth, leading to enhanced mandibular lenghtening. On the contrary O‘Brian et al [42] reported that the growth increments were not greater in the patient group treated during the growth spurt as compared to off-spurt group.

If we believe the theory that we can be more efficient „growing man- dibles“ during the growth spurt as suggested [50-53], we have to consider the methodology on how to differentiate and determine the time point of the growth peek onset.

Different rates of mandibular growth at puberty, as well as the peak in mandibular growth velocity, can be detected on the basis of several methods for the assessment of skeletal maturity. These biological indicators include increase in body height [54], skeletal maturation of the hand and wrist [55], dental development and eruption [56,57], menarche, breast and voice changes [58] and cervical vertebrae maturation [59,60]. With regard to this last method, stages in the maturation of the cervical vertebrae showed significant correlations with pubertal changes in mandibular growth, as demonstrated by O’Reilly and Yanniello [60]. The simplified version of the growth staging according to cervical vertebrae (CVM) was presented by Baccetti et al in 2005 [61]. In our study on the cHerbst therapy the stages of cervical vertebrae maturation were used to match the treated group and the untreated control group according to pretreatment and posttreatment skeletal maturity. The ratings were performed by one of the inventors of CVM methodology [61] – professor L.Franchi.

Another question is the clinical significance of the mandibular elongation as the result of Class II therapy in case we treat malocclusion in time (during the growth spurt). Most of the studies on Herbst appliance to prove the dentoskeletal impact of the device were presented by the same source [6, 47, 52, 62-77], so to be objective on the final statements we have to refer to systematic reviews and meta-analyses (to be discussed in the next section of literature review). Nevertheless, if the mandible really grows more as a result of Herbst therapy, what happens when the treatment is over? Hansen et al [77] revealed that the growth period in which Herbst treatment had been performed did not seem to have effect on the long term results.

Interesting finding in their study was that after the 7 months of Herbst therapy the mandible had overgrown maxilla by an average 2.2 mm, after 6.6 years after the treatment the overgrowth had been 2.1 mm and in the total observation period the figure was 4.3 mm. Recent study by Zhi-Hao You et al [78] found no significant difference in mandibular growth between

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the Class II samples and the Bolton norms in their longitudinal study from childhood to early adulthood. Their results indicated that in the Class II subjects forward growth of the mandible was greater than that of the maxilla by 4.36mm on average. If we look at the forward maxillary-mandibular growth rates presented by authors [77, 78], these are very similar: 4.3mm against 4.6mm. This would suggest that the induced growth of the mandible during the Herbst therapy has vanished in long term and in the end of growth process the projection of the lower jaw is more or less the same, no matter, if the Class II patient was treated or not. Another interesting thought brought by Hansen et al [77] was a claim that a stable occlusion after the Herbst or any other therapy could be of greater importance for the long term stability, than the post-treatment growth pattern or the growth period in which the patients were treated. That conclusion helped us whilst creating treatment protocol for our study. Hansen et al [77] conclusion was an edition to the earlier statement of Pancherz and Fackel [70] and brought up even more discussion in Class II treatment topic. The Herbst appliance had only a temporary impact on the existing skeletofacial growth. After therapy maxillary and mandibular growth seemed to catch up with their earlier patterns [70]. In spite of relapse to Class II occlusion due to recovering growth changes, functional stability of occlusion remained due to tight Class I contacts that obviously counteracted occlusal relapses[70]. After almost a decade Bremen and Pancherz published the paper on CII:1 treatment efficiency [79]. Authors concluded that treatment of CII:1 was more efficient in the permanent dentition than in the mixed dentition, in other words the interdigitation of occlusion in permanent dentition could improve the stability comparing to interdigitation provided by the deciduous teeth.

After several papers [70, 77, 79], H. Pancherz and his team presented the new concept for conservative Class II treatment in adults [80]. In earlier [75] and later [81] papers Pancherz and his team claimed that Herbst appliance increased mandibular prognathism, additonally the skeletal and soft tissue profile convexity had been reduced in all the adults treated with Herbst appliance. In his recommendations Pancherz concluded that growth adaptive therapy with the Herbst appliance was possible even after the age of 20 and could thus replace surgery in milder skeletal Class II cases [80].

The conclusion to this section is that Herbst appliance as Class II corrector may be used for growth adaptation in children, adolesents, postadolescents, young adults and as a camouflage orthodontics in elderly adults [80]. So the treatment onset time-span is much larger than suggested for the removable BJFA [41]. Induced growth of the mandible during the Herbst therapy disappears in long term, but the Class II remains corrected due to stability of occlusion which counteracts the growth changes.

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1.6. The mechanism of skeletal Class II correction as a result of Herbst therapy

The mechanism of Class II correction is still in dispute. Although all the BJFA strive to cure Class II, most dentoskeletal findings after the therapy are diverse and difficult to explain. As it was stressed before, most of the data on Herbst comes from the same source and thus systematic reviews could help us to find the answer to the question of the century: do we grow the mandible or not?

Chen et al [82] published systematic review on the efficacy of functional appliances on mandibular growth and limited their search to randomized clinical trials (RCTs). Chen et al [82] developed and implemented a Medline search strategy for the years 1966 to 1999. For the systematic review, authors limited Medline search to studies performed on humans and written in English. The search was stratified for randomized control trials and meta-analyses, which were viewed as providing the highest level of evidence quality [82]. Reported results were inconclusive due to incon- sistencies in measuring treatment outcome variables, different treatment durations among studies. Besides treatment groups were compared with either untreated controls or subjects undergoing other forms of treatment. Chen et al [82] noticed that in the last ten years, there had been an increasing number of studies of Class II treatment, though it was stressed that there was still a need to conduct more randomized control trials to reduce the methodologic limitations. Authors concluded that once confounding variables such as discrepancies in age, treatment durations, lack of control-matched groups, patient compliance, and patient accountability were minimized, one could identify which patients might or might not benefit from specific treatment options. Although functional appliances could be used for other purposes, results suggested the need to reevaluate functional appliance use for mandibular growth enhancement [82].

To broaden the scientific information on functional appliances and in order to finalize the conclusions on BJFA, Cozza et al [4] suggested that the rational systematic review should include not only RCTs, but also longitudinal prospective and retrospective controlled clinical trials (CCTs), because of the ethical problems and other substantial reasons for the paucity of RCTs in orthodontics. Cozza et al [4] review had a limited search strategy that focused only on mandibular growth changes. Authors searched for meta-analyses, RCTs, prospective and retrospective CCT’s published from 1966 to 2005. Selected studies had to include growing patients, untreated Class II control groups and mandible length had to be measured on lateral cephalogram using point condylion. Exclusion criteria were as follows: case

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reports, case series and descriptive studies, review articles, opinion articles, abstracts, laboratory studies, studies of adults, studies performed on magne- tic resonance imaging, measurements of total mandibular length using point articulare, treatment combined with extractions, treatment combined with fixed appliances, surgical treatments, success of therapy (at occlusal and skeletal levels) as criterion for case selection. To give the reader a quantita- tive appraisal of modifications in mandibular dimensions and sagittal position in Class II patients treated with functional appliances when compared with untreated Class II controls, the following data were evaluated for each retrieved study: mandibular sagittal position (SNB), total mandibular length (co-gn or co-pg), mandibular ramus height (co-go), and mandibular body length (go-gn, go-me, or go-pg) (Table 2.3) [4]. Because most of the samples in the retrieved studies reported annualized mandibular changes (expressed as annualized mean differences between treated and untreated groups), annualization was applied to the data of the remaining samples (except for samples with a treatment duration that was too short for annualization – less than 9 months). The actual amount of supplementary elongation in total mandibular length after active treatment with the functional appliance was also analyzed. It is well known that different functional appliances require different treatment durations to reach the goal of Class II correction at the occlusal level [4]. Therefore, the review included an evaluation of both the effectiveness and the efficiency of different types of functional appliances in inducing a supplementary elongation of the mandible with respect to controls. Effectiveness could be defined as the ability of the appliance to induce a clinically significant supplementary elongation of the mandible with respect to the controls at the end of the overall treatment period. Because of the average number of patients enrolled in the examined studies (ie, to the power of the retrieved studies), clinical significance in mandibular dimensions was defined as at least a 2.0 mm difference between treated and untreated groups [4]. Efficiency consists of an effective treatment in the shortest time. An appraisal of efficiency was performed by dividing the supplementary elongation of the mandible during the overall treatment period with the functional appliance by the number of months of active treatment duration (coefficient of efficiency) [4].

Out of 22 articles (4 RCTs, 2 prospective CCTs, and 16 retrospective CCTs), fulfilling the inclusion criteria, four articles were on Herbst appliance effects on growing indiivduals [6, 83–85]. Three of these articles reported treatment effects with the acrylic splint Herbst appliance [83-85] and one with the banded Herbst appliance (6). All 4 studies [6, 83-85] presented significant favourable effects on mandibular growth. No articles on cHerbst that could update the data of this systematic review were included. Authors

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concluded [4] that functional appliances produced a statistically significant annualized supplementary elongation in 23 of 33 samples for total mandibular length, in 12 of 17 samples for mandibular ramus height, and in 8 of 23 samples for mandibular body length, outcomes in terms of changes in mandibular position in relation to the cranial base (SNB angle) were not clinically significant in any article. Authors noted [4] that the SNB angle was a poor indicator of the effectiveness of functional jaw orthopedics since in most patients the initial correction of a Class II relationship involves not just posturing the mandible in a forward position: vertical opening of the bite typically was involved, and a deep overbite was corrected, so a millimeter of increased lower anterior facial height camouflaged a millimeter of increased mandibular length, in that way the advancement of the chin point at pogonion might not be evident if the vertical dimension is increased along with mandibular length [4].

The amount of supplementary growth of the mandible when compared with untreated Class II controls varied widely among the studies included in the review [4]. Two-thirds of the samples in the 22 included studies reported a clinically significant supplementary elongation in total mandibular length (a changes greater than 2.0mm in the treated group compared with untreated group), whereas some studies that were judged as medium-high quality by the authors couldn’t confirm the significant mandibular changes [42, 86–88]. It was an interesting finding for Cozza et al [4] that none of the 4 RCTs reported a clinically significant change in mandibular length induced by functional appliances. To further explain this finding authors suggested to analyze the influence of treatment timing (skeletal maturity at the start of functional therapy) on treatment results [4] since it had previously been demonstrated that the effectiveness of functional treatment of mandibular growth deficiencies strongly depended on the biological responsiveness of the condylar cartilage, which in turn depended on the growth rate of the mandible (expressed as prepeak, peak, and postpeak growth rates with regard to the pubertal growth spurt) [62, 63]. Only seven of the selected 22 studies in the review reported information about their subjects’ skeletal maturity with a biological indicator (e. g., hand-wrist analysis, cervical vertebral maturation method), the amount of actual supplementary mandibular growth induced by treatment (measured by co-gn or co-pg) was clinically significant (> 2.0 mm) in all the “peak” samples, meaning that patients were on a growth spurt, whereas none of the samples treated in the prepeak period had a clinically significant amount of supplementary mandibular growth. Authors suggested [4] that the inclusion of the pubertal growth spurt in the treatment period could be regarded as a key factor in the attainment of clinically significant supplementary mandibular growth with functional jaw orthopedics. Cozza et

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al [4] also concluded that the average coefficient of efficiency for functional jaw orthopedics (average amount of actual supplementary elongation of the mandible in treated subjects versus Class II controls after the overall treatment period divided by the number of months of treatment in each study) was 0.16 mm per month. The Herbst appliance, as fixed BJFA had a coefficient of efficiency of 0.28 mm per month, the coefficient for the removable BJFA such as following: Twin-block appliance was 0.23 mm per month, the coefficient for the bionator (0.17 mm per month) was equal to the average coefficient, for the activator, it was slightly lower (0.12 mm per month), the coefficient of efficiency for the Fränkel appliance, was the lowest (0.09 mm per month). Authors stressed the importance of the quality of the studies [4]: in the quality analysis, six of the 22 studies were judged to be of medium/high quality. Four of these six articles were RCTs. The reason for a medium/high quality score instead of a high score was that these studies had some methodological limitations [4] such as no statistical analysis for the mandibular skeletal changes or absence of blinding in measuring the cephalometric parameters. On the other hand, only two CCTs out of 22 were judged to be of medium/high quality, whereas most CCTs were judged to be of medium quality [4]. The use of blinding in performing cephalometric analysis of craniofacial skeletal changes was the main factor that accounted for a higher score for these two CCTs. Only three of the 22 studies were considered of low quality because they lacked both method error analysis and blinding in measurements [4]. Another problem whilst selecting the studies for the review was the lack of unification in measuring techniques [4]. Shen et al [89] stated that the parameters adopted to quantify the skeletal changes were often created and determined by the individual researches and were not of consistence and compatibility between studies, so the problem of finding the skeletal changes could be hidden in the cephalometric analysis used by the investigators. Besides mandibular length measurements in Cozza et al study [4] relied on point condylion (Table 2.3), which is known to be difficult to determine cephalometrically [90, 91].

Another recent systematic review by Barnett et al [14] in 2008 had purpose to assess the scientific evidence on the efficiency of crown or banded Herbst appliance in enhancing mandibular growth in growing Class II individuals. The main question of the review was: what maxillary and mandibular skeletal and relative dentoalveolar treatment effects were produced by crown or banded Herbst compared to a Class II malocclusion nontreated control group considering growing individuals? Authors considered [14] that there was little doubt that measurable dental changes such as reduced overjet or molar correction occured in a favorable manner with the continuous use of functional appliances, however, the degree of skeletal versus dentoalveolar

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change that underlied these treatment effects was still a source of debate. As the greatest controversy over the effectiveness of functional appliances as suggested by Barnett et al [14] was in part because of the method of analysis employed by the published reviews. Authors stressed [14] that ideally, the treatment effects of each appliance should had been examined individually, because each appliance had a theoretically different mechanism of action and application that would likely produce different movement based on the relative dental and skeletal changes. In other words the results of different appliances could not be pooled together. However, most reviews had analyzed several functional appliances simultaneously and had obscured the real effects of each individual functional appliance by combining all the effects [4, 82]. Another important issue considered by Barnett et al [14] that although both removable and fixed functional appliances had been used for decades, with various forms coming in and out of popularity, removable appliances such as activators, bionators, and twin blocks had different time duration of being worn by the patients whereas fixed functional appliances had the advantage of not relying on patient compliance because they were fixed in the mouth, thus always working, in that way fixed BJFA could not be compared with the removable BJFA and even worse if the results of both fixed and removable appliances were pooled together to represent the skeletal effets.

Barnett et al [14] detected four reviews on Herbst appliance. Three of them analyzed exclusively Herbst effects [73, 92, 93] and one reported Herbst effects individually while analyzing other functional appliances [4].

Barnett et al [14] criticized the oldest review by Pancherz [73] for not being systemized and therefore influenced by bias. Flores-Mir et al [92] review concentrated on soft tissue changes. A more recent review by Flores-Mir et al [93] analyzed the effects produced by the splint type Herbst, which had different mode of action due to partially removable design and interocclusal layer of acrylic. The selection process by the year 2007 was also applied in the next selection stage searching for full articles on Herbst appliance. Out of pontentially relevant 80 clinical trials identified by the database searches Barnett et al [14] had found only 3 articles to fulfill the additional inclusion criteria [6, 94, 95]. The additional criteria that minimized the number of selected articles were: comparable Class II control group, randomized or consecutively treated cases, measurements taken soon after appliance removal and no concurrent use of any orthodontic appliance during the evaluation period. Author pointed out that Pancherz H articles [6, 94] reported the same group of subjects, but different measurements and the study by De Almeida et al [95] had a very young cohort, treated prior growth spurt. Eva- luating the skeletal effects reported in the selected studies, Barnett et al [14]

concluded that minimal effects were demonstrated on the maxilla, as only

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two of the seven maxillary sagittal measured variables showed statistically significant changes, whereas several significant (and nonsignificant) increa- ses were seen in mandibular length as compared to the untreated controls. It appeared that the magnitude of the mandibular change lied in the 2 to 3 mm range, depending on which measurement was considered, nevetheless, how much of this effect was an artifact of mandibular posturing had not been evaluated. Authors suggested using open-mouth cephalograms to help in the identification of condylion, the point on which relied most of the measurements. Barnett et al [14] stressed that the lack of a headgear effect on the maxilla was noteworthy. Considering dentoalveolar effects: maxillary incisors were retroclined, despite the fact that no appliances were used directly on them in any of the studies included in this review, it was confirmed that those findings were similar to ones seen elsewhere with Herbst appliances [14]. There was no doubt for that statement, because the movement of the upper front teeth was influenced by the fact that all cases used in Barnett at al review were Class II division 1 and thus were already quite proclined prior to treatment, which was not the case for all studies in the literature, whereas mandibular incisors showed a definite proclination, which was not surprising given the force vectors involved with Herbst treatment.

Maxillary first molar position showed small but statistically significant amounts of intrusion, though authors questioned the clinical significance of this movement as well the upper first molar was also moved distally within the maxillary alveolus: this distal movement could account for the retroclination of the maxillary central incisors via transeptal fibers [14]. Mandibular first molars showed an extrusive and anterior direction of movement that could be accounted for by the relative intrusion of the opposing maxillary first molar, allowing for that small but significant amount of eruption [14].

Barnett et al [14] stated that still there was not enough information of good quality to evaluate immediate changes after the banded or crown Herbst appliance was removed for growing individuals. Because of the limited number of finally selected studies and the heterogenity of their methodology, authors did not attempt to do a meta-analysis with the data. They concluded that there were mixed findings as to mandibular sagittal length and position, but also reported the proclination and anterior movement of lower incisors and improved first molar relationship, reduced ANB angle and increase in the mandibular plane angle, also no significant changes in the maxillary base position were noted as an immediate result of Class II treatment with the Herbst appliance. In order not to overlap with information, the literature review on dentoskeletal changes as the result of the Herbst therapy will be touched in the discussion section of our study as the comparison with the data we have received.

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2. METHODOLOGY

2.1. Study subjects

Prospective study on cHerbst appliance started in 2006 and ended in 2010. Study subjects were selected from the patients referred to Kaunas Ortodontijos Centras clinic for orthodontic treatment. All the patients were diagnosed, consulted and treated by the same orthodontist (Dalia Latkauskienė) at the same orthodontic office. Subjects fulfilling below listed inclusion criteria were asked to participate in the study and were given the subject consent forms in order to describe the purpose, procedures, benefits, risks, possible discomforts and precautions of the study and provide other details that may be important for the patients, such as the possible side effects, withdrawals from the study and the use of personal data (supplement no1). In case the patient decided to be part of the study, he or she was asked to sign a consent form (supplement no2). In case the patient was a minor, the consent form was signed by the parents or caregivers. By signing the consent form, patients confirmed the voluntary participation in the study and agreed to follow all the further instructions on treatment given by the doctor (D.L). Patients also received additional information on cHerbst protocol prior to treatment (supplement no3), all the possible questions and comments were answered by the doctor (D.L.).

2.1.1. Inclusion criteria

To be included in this prospective study patients had to present with:

 at least end-to-end Class II molar relationship bilaterally or more severe;

 permanent dentition;

 no active hard tissue lesions;

 no previous orthodontic treatment or tooth extractions;

 no bone level problems detected in panoramic x-ray;

 no TMJ complaints;

 no tooth size, form and number anomalies;

 no facial development or mental syndroms (such as Down, Treacher Collins, Crouzon, etc);

 no pregnancy.

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2.1.2. Diagnostic tools

Initial records were taken for each patient before the treatment onset:

 medical history (in order to find out about being pregnant, previous orthodontic treatment, complaints on TMJ, development or mental syndroms- patients were asked during the consultation and the information was outlined into the patient‘s data card);

 intraoral examination to detect the occlusion, teeth anatomy and hard tissue lesions (all patients were referred to their dentists for a check-up prior to orthodontic treatment in order to solve lesions of the hard dental tissues);

 dental casts as primary diagnostic source of teeth anatomy and occlusion;

 panoramic x-ray in order to evaluate the bone level (bone level in panoramic x-ray considered as normal if it starts from the enamel- cementum junction of tooth down to the apex, all along the dental arches from second molar to second molar with no visible defects as inspected by D.L.);

 lateral cephalogram, it will be used to measure treatment results after cHerbst therapy. Cephalograms were taken with the Frankfurt horizontal parallel to the floor with teeth in occlusion and lips relaxed. At least four cervical vertebrae had to be present in the x- ray in order to evaluate growth stage of the patient. Additonal lateral cephalograms were performed immediately after cHerbst treatment for all patients that finished therapy and at one-year follow–up time point in case the patient was included into the final study group of stable Class I patients. All three lateral cephalograms were taken with the same equipment.

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2.1.3. Unification of the study patients

Prior to cHerbst all CII:2 patients received 022 slot MBT prescription braces on the upper front eight teeth to convert the malocclusion into CII:1 (Pictures 2.1, 2.2). Alignment started with 016 nickel titanium wire and progressed up to 18 by 25 nickel titanium wire (Ormco, 1717 West Collins Avenue, Orange, CA 92867). Braces either stayed for the whole active cHerbst treatment period or were removed after aligning- in that case a retainer was bonded on four upper front teeth. For CII:2 patients the first diagnostic lateral cephalogram was performed after the upper front teeth were aligned.

Picture 2.1. Class II:2 before alignment of the front teeth

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Picture 2.2. Class II:2 after alignment of the front teeth

2.1.4. Evaluation of the skeletal maturity

In order to control the bias of the study two more examiners were invited to participate in the study, one of them - Professor Lorenzo Franchi (University of Florence, Italy), the inventor of the CVM index which was used in this research [61]. Another examiner was invited to examine the lateral cephalograms of the selected patients. Both examiners were not informed on the patient sample and treatment progress.

Since one of the objectives in Class II treatment is to correct skeletal relationships which happens best during the active growth [61], the estimation of skeletal maturity in examined individuals at the time of treatment onset and discontinuation should be taken into account. According to CVM maturity index [61] of pre-treatment (T1) and post-treatment (T2) lateral x-rays, patients were divided into two groups by investigator (L.F.) : Group 1 – growing patients who either started cHerbst treatment as prepubertal or pubertal (CS2 or CS3) and finished postpubertal (CS4 or CS5), patients who started postpubertal (CS4 or CS5) and finished postpubertal or adults (CS5 or CS6), Group 2 – patients who started and finished Herbst treatment as adults (CS6). Illustrations to legends below (Pictures 2.3–2.5).

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Picture 2.3. Cervical stage 3 (CS3):

two clinical examples- pubertal patients

two clinical examples- postpubertal patients

two clinical examples- adult patients

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2.1.5. Protocol for cHerbst instalation and active treatment

A standard bite jumper (cHerbst) (Ormco, 1717 West Collins Avenue, Orange, CA 92867) was used as the only appliance for all patients. CHerbst was delivered within one month of the patient‘s initial records and no other appliances were used during the functional treatment phase. CHerbst appliance was produced and delivered in three visits:

 During the first visit separation of the lower first premolars was performed (Picture 2.6).

Picture 2.6. Separation of lower first premolars

 During the second visit in one week upper first molars were separated and lower first premolar crowns were fitted (Picture 2.7), alginate impression with the crowns in it was taken to the laboratory to produce welded lingual arch (Picture 2.8).

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Picture 2.7. Lower first premolar crowns fitted

Picture 2.8. Welded lingual arch

 During the third visit in one week, the lingual arch with the premolar crowns was cemented with Ketac-Cem glass-ionomer cement (3M Espe Dental Products, St.Paul, MN 55144-1000), occlusal rests on lower first molars were secured with flowable composite (Picture 2.9), upper first molar crowns were fitted and fixed with the same glass-ionomer cement (Picture 2.10).

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Picture 2.9. Cemented lingual arch

Picture 2.10. Cemented upper first molar crowns

Appliance was activated edge-to-edge incisor relationship (Picture 2.11), function of lateral movements of the mandible checked (Picture 2.12) and active treatment phase started (T1) No additional anchorage for the upper first molars was created.

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Picture 2.11. Appliance activation edge-to-edge, facial profile immediate change after the instalation of the cHerbst

(appliance in situ on the lower photograph)

Picture 2.12. Lateral movements of the mandible

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Patients were seen once every four to six weeks to evaluate the appliance status and the need for activation. The activations were performed by placing collars on pistons to make sure that the cusp of upper first premolar was projecting in between the lower first and second premolars to help natural vertical occlusion settling process (Pictures 2.13, 2.14).

Picture 2.13. Activation to allow vertical settling of occlusion:

vertical contacts immediately after cHerbst removal

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Picture 2.14. Stable occlusion 12 months after treatment

The appliance was removed after 12 months of active treatment (T2) and lateral cephalograms were taken on the same day.

2.1.6 Follow-up period

After cHerbst removal, no appliance to retain the occlusion was provided and the patients were asked to come for a check-up visit after six months (T3).

At T3 natural settling of occlusion in Class I relationship was checked and a treatment evaluation questionnaire was given to the patients (Picture 2.15).

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Picture 2.15. Questionnaire to evaluate cHerbst treatment.

If occlusion was slipping back to Class II relationships at T3, the patients received either an Andresen activator or started fixed appliance therapy (Pictures 2.16–2.19).

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Picture 2.16. Occlusion before treatment

Picture 2.17. Occlusion immediately after treatment

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Picture 2.18. Relapse to Class II malocclusion six months after treatment

Picture 2.19. Retention device provided for patients with unstable occlusion

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If occlusion was settling in Class I relationship, the patients were asked to come for the final checkup after six months (T4). If the occlusion at T4 was stabilized in Class I relationship, final lateral cephalogram was performed. In case of relapse at T4, the patients received an Andresen activator or started other treatment if agreed.

A patient with stable Class I occlusion one year after treatment with cHerbst is presented in Pictures 2.20–2.22.

Picture 2.20. Patient with stable occlusion one year after cHerbst treatment: before treatment

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Picture 2.21. Patient with stable occlusion one year after cHerbst treatment: immediately after cHerbst removal

Picture 2.22. Patient with stable occlusion one year after cHerbst treatment: one year after cHerbst removal

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2.1.7. Patient flow chart and final study group consolidation

The flow chart of the patients throughout cHerbst treatment and observation periods is shown in Picture 2.23.

Picture 2.23. Flow chart of the treated patients

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Out of the 180 patients who started treatment five patients (2.8%) did not finish the active phase: four patients due to numerous appliance breakages while one patient complained for increased episodes of migraine after insertion of the appliance. All 175 patients who finished the active phase of treatment attained Class I occlusal relationship. During the six-months follow-up period, 20 patients (11.4%) dropped from the study for several reasons not associated with treatment while 56 patients (32%) started fixed appliance treatment due to esthetic reasons. At T3 (six months after the end of the active phase of treatment) a total of 99 patients received a check up visit. During the 12-month follow-up period, 19 patients (19.2%) received an activator due to relapse, two patients (2%) were treated with fixed appliances due to esthetic reasons, and four patients (4%) did not show up for the 12-month check up visit.

At T4 (12 months after the end of the active phase of treatment) a total of 74 patients received a check up visit. Out of these 74 subjects, two patients (2.7%) received an activator due to relapse. Thus as a result of the cHerbst appliance used as a single appliance for a single phase therapy on a sample of 175 patients, 72 patients (41.1%) achieved and maintained stable Class I relationships at a one-year follow-up observation while 21 patients (12%) showed relapse. Other 58 patients (33.1%) passed to the second phase of treatment with fixed appliances and in all cases a stable Class I relationship was achieved.

Seven of 72 stable patients refused to take the final cephalogram, thus lateral cephalograms of 65 patients with stable Class I occlusion were available at the following observation periods: before treatment (T1), after active phase of treatment (T2) and at one year follow up (T4).

Consolidation of the final study group of growing subjects: forty patients (20 male, 20 female) with the mean age 13.6 ± 1.3 were judged as growing and included in the final study group, used to evaluate cHerbst effects immediately after treatment and at one year follow up. The patients started treatment either at puberty (CS3 n = 26) or at postpubertal stages (CS4 or CS5, n = 14) and they finished treatment either at a postpubertal stage (CS4 or CS5 n = 26) or at the end of active growth (CS6 n = 14). Twenty five patients out of 65 were judged as adults at T1 and collected to a non- growing group of patients which was not analyzed cefalometrically in the current study.

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2.2. Control group

It would be desirable to have an access to a control material of the same quality as final study group material, but for ethical reasons it is no longer possible to perform longitudinal rentgenological registrations of untreated patients with post-normal occlusion. Besides as it is stressed in the literature [61], functional appliances work best during the pubertal growth spurt, it would unethical to delay the treatment for the Class II patients in order to use them as controls. Examiner D.L. aimed to find the comparable control group of Class II patients matched as to skeletal maturity to the treated sample. Most of the European growth studies either present normative data as Bhatia and Leighton sudy or the lateral cephalograms are perfomed in time points different from that in our study (such as growth studies in Norway and Poland). On the contrary, the Michigan Growth Study and Denver Growth Study are comprised of annual records and the subjects in the study are primarily of Northern European ancestry. In the overall sample, there is a bias toward Class II malocclusion. There are 18 boys and 30 girls with longitudinal records taken at the intervals of 12 months deemed ideal as judged by the American Association of Orthodontists (www.aaoflegacycollection.org).

As reported by professor James JA. McNamara, who is the curator of the data, on the Michigan Growth study web page (www.aaoflegacycollection.org):

based on the study two major atlases were published, in addition, there have been 66 papers published in refereed journals and well as eight other books or chapters in books written by the curator and his colleagues that have used data form the Michigan Growth Study, as well as Denver growth study that was copied and infiltrated into the Michigan Growth Study.

Pofessor J. JA McNamara has kindly agreed and allowed examiner D.L. to pick the controls from the Michigan Growth Study records.

The control group consisted of 18 subjects (11 males, 7 females) who were selected from the longitudinal records of the University of Michigan Elementary and Secondary School Growth Study and Denver Growth Study. The mean age of the control group was 13.9 ± 1.6 years. The control group was matched to the treated group as to skeletal maturity at T1and T2 observation periods by the independent examiner L.Franchi. Attempts to increase the number of controls confronted the insufficient quality of lateral cephalograms at certain timepoints and limitations to select Cl-II patients with three lateral cephalograms performed in exact 12 month intervals (the same intervals as in our study).

There was no statistically significant difference in age between the groups at any of the time points. Pretreatment characteristics and demographics of

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the treated and control groups are summarized in Tables 2.1and 2.2 (explanation of points outlined in Table 2.3). Treated subjects presented with more proclined upper incisors as well as shorter midfacial length, significant difference comparing to the control group.

Table 2.1. Demographics for the treated and untreated Class II Groups

Mean (SD) N Female Male

Age at T1, y Age at T2, y Age at T3, y cHerbst group 40 20 20 13.6 (1.3) 14.8 (1.4) 15.9 (1.4) Control group 18 7 11 13.9 (1.6) 14.7 (1.4) 15.7 (1.4)

Table 2.2. Pretreatment characteristics of the study subjects compared with matched untreated Class II individuals. Mean values and standard devia- tions (SD) in parenthesis

Variable Study Group (n = 40) Control Group (n = 18) P value

Overjet (mm) 5.5 (2.2) 5.5 (2.4) 0.130

Overbite (mm) 5.6 (1.3) 4.5 (2.0) 0.758

SNA (degrees) 81.5 (2.9) 81.1 (3.8) 0.605

SNB (degrees) 76.7 (2.4) 76.6 (3.2) 0.910

SNpg (degrees) 78.1(2.6) 78.0 (3.3) 0.886

ANB (degrees) 4.8 (1.9) 4.5 (1.5) 0.449

co-A (mm) 86.6 (4.7) 83.6 (6.6) 0.045

co-gn (mm) 108.1 (5.4) 105.8 (7.3) 0.187

is to T-FMN (degrees) 111.5 (8.2) 104.4 (8.2) 0.003

ii to ml (degrees) 99.8 (7.0) 98.7 (7.6) 0.599

co-go-me (degrees) 121.5 (4.9) 119.8 (4.1) 0.178

2.3. Cephalometric analysis

Assistant professor Gundega Jakobsone (Riga Stradins University, Latvia) was invited as the second independent expert, not related to treatment process. G.Jakobsone hand traced the cephalograms perfomed at T1,T2,T3 on acetate paper. The tracings were digitized with Dentofacial planner Plus software (Dentofacial Software, Toronto, Canada) on a compu-

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ter with a digitizing screen (Numonics Cooperation, Montgomeryville, USA). All cephalograms were matched according to enlargement.

A modified Pancherz cephalometric analysis was applied (Picture 2.24).

Explanation of points used in cephalometric analysis outlined in Table 2.3.

Picture 2.24. A modified Pancherz cephalometric analysis

Table 2.3. Explanation of points used in cephalometric analysis

Abreviation Explanation

FMN Frontomaxillary nasal suture

T The most superior point of the anterior wall of sella turcica, at the junction with tuberculum sellae

Co Condylion.The most superior midline point on the condyle of the mandible.

Go Gonion. A point on the curvature of the angle of the mandible located by bisecting the angle formed b ylines tangent to the posterior ramus and the inferior border of the mandible.

Pg Pogonion. The most anterior point of the chin.

Me Menthon. The lowest point of the sympheseal shadow of the mandible seen on a lateral cephalogram.

Gn Gnathion. A point located by taking the midpont between pogonion and menthon.

S Sella. The geometric centre of the pituitary fossa.

HERBST APPLIANCE

Dalia Latkauskienė

TREATMENT OF ANGLE CLASS II MALOCCLUSION WITH THE CROWN

HERBST APPLIANCE

Dalia Latkauskienė

ANTROS KLASĖS SĄKANDŽIO ANOMALIJŲ GYDYMAS VAINIKĖLIAIS TVIRTINAMU

HERBSTO APARATU

CONTENTS

ABBREVIATIONS

INTRODUCTION

AIM OF THE STUDY

THE ORIGINALITY AND PRACTICAL USE OF THE STUDY

1. LITERATURE REVIEW

2. METHODOLOGY