THE EFFECT OF EARLY HEADGEAR TREATMENT ON THE DENTAL ARCHES

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KAUNAS UNIVERSITY OF MEDICINE

Viktorija Krušinskienė

THE EFFECT OF EARLY

HEADGEAR TREATMENT

ON THE DENTAL ARCHES

Doctoral Dissertation

Biomedical Sciences, Odontology (08 B)

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Dissertation preparation took place in Kaunas University of Medicine and Oulu University, Finland during 2005–2009 years.

Scientific Supervisor

Prof. Dr. Antanas Šidlauskas (Kaunas University of Medicine, Biomedical Sciences, Odontology – 08 B)

Consultant

Prof. Dr. Pertti Mikael Pirttiniemi (Oulu University, Finland, Biomedical Sciences, Odontology – 08 B)

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KAUNO MEDICINOS UNIVERSITETAS

Viktorija Krušinskienė

ANKSTYVOJO GYDYMO

IŠORINIU TEMPIMO APARATU

POVEIKIS DANTŲ LANKAMS

Daktaro disertacija

Biomedicinos mokslai, odontologija (08 B)

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Disertacija rengta 2005–2009 metais Kauno medicinos universitete ir Suomijos Oulu universitete.

Mokslinis vadovas

prof. dr. Antanas Šidlauskas (Kauno medicinos universitetas, biomedicinos mokslai, odontologija – 08 B)

Konsultantas

prof. dr. Pertti Mikael Pirttiniemi (Suomijos Oulu universitetas, biomedicinos mokslai, odontologija – 08 B)

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For those, who understand the meaning of Science

and for the Best Future

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ABBREVIATIONS

AC/IOTN – Aesthetic Component of Index of Orthodontic Treatment Need

CFB – cervical-pull facebow

HG – headgear appliance

LII – Little’s Irregularity Index PAR – Peer Assessment Rating Index RCT – randomized clinical trial RME – rapid maxillary expansion

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INTRODUCTION

The main aim of orthodontic treatment is to correct or improve the aesthetic appearance and function of the dentition and thereby enhance psychosocial functions and experiences for patients.

The most appropriate time for treatment of Class II malocclusions and methods to treat crowding in children are controversial. Orthodontists can agree on what is quality of orthodontic result, however, due to controversial scientific evidence they disagree on how to achieve the best result and what is a proper timing for it. Some clinicians strongly believe that the treatment started during mixed dentition before adolescence is advantageous, while others are convinced that early treatment is often waist of time and resources.

The term “early orthodontic treatment” is restricted to therapeutic mea-sures taken in deciduous dentition or in the early stage of mixed dentition. The goal is to facilitate the development of a normal intermaxillary rela-tionship with symmetric dental arches and a harmonious muscular balance, factors of importance for the further developmental processes in a young child. The aim of many clinicians providing early treatment is to reduce the time and complexity of fixed appliance therapy. It has been emphasized its benefits such as greater ability to modify skeletal growth, improved patient's self-esteem and satisfaction of parents, better and more stable result, less extensive therapy required later and reduced potential for iatrogenic tooth damage such as trauma, root resorption and decalcification [38].Advocates of early treatment argue that a large part of the growth of facial bones occurs by the age of 12–14 years and therefore might not be influenced anymore with orthopaedic appliances in later stages. Often the early treatment is resulting in two-phase treatment with the first phase intended for the orthopedic effects (influence on facial growth) and the second phase for the orthodontic (tooth movement) corrections when all permanent teeth have erupted [38].

Opponents of early treatment declare that up to 90% of all growing pa-tients can be treated successfully in one single phase by starting treatment in the late mixed dentition stage of development at the time of exfoliation of all deciduous teeth except the second primary molars [87].

There has been much debate over the appropriate treatment timeas well as the most suitable methods concerning crowding diagnosed during the early mixed dentition [86, 140, 150, 190]. Traditionally, one of the most popular treatment methods has favoured the extractionof primary canines. Later, the choice of treatment has in manycases led to the extraction of two

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or four premolars. The advantageof this method has been the early align-ment of the anterior teeth, which is thought to reduce treatment time with fixed appliances during subsequent therapy. As the trend in camouflage treatment of crowding has been to favour non-extraction methods,at least in borderline cases, the number of premolar extractionshas remained relatively low when compared with the situationdecades ago [189].

The evident consequence of the trend to avoid extraction of permanent premolars has been the need to expand the dentalarches. The ideal goal of expansion is to achieve a permanent result where good alignment of the dental arches is gained with all the permanent teeth in occlusion even at long-term follow-up. The key question in this treatment philosophy is, in additionto the stability of the treatment result, the appropriate timingfor the expansion of dental arches. According to the earlier well-adopted follow-up studies, permanent expansion of dental arches was considered uncertain and relapse after expansionwas evident, especially in the lower arch [139, 142, 216]. In spite of these results, expansion techniques have been widely used in orthodontics in order to facilitate the alignment of allpermanent teeth. Thus, a fundamental question,when the outcome of treatment is considered, is whether it is possible to maintain the expansion in dental arches if the expansion is well timed.

Patients and practitioners seek treatments that provide excellent outco-mes by simple and efficient methods. Ideally, treatment should be provided when it is the most effective and would produce the least disruption in the child’s and family’s lives. The goals and objectives must be clearly defined to prevent unnecessarily prolonged treatment that may “burn out” the patient’s cooperation in future [90].

For children with Class II problem, the debate is not just whether it can be corrected early or late because ample evidence from clinical practice sug-gests that it usually can be corrected at various stages of child’s develop-ment. Recent reports from several prospective trials clearly demonstrate that some improvement in jaw relationships can be achieved during early treat-ment with both headgear and functional appliances [85, 108, 114, 171, 240]. The important questions are: (1) does the treatment started during early mi-xed dentition, when followed by the second phase of treatment in early per-manent dentition, provide superior results to a single-phase treatment de-layed until adolescence? Additionally, (2) is there enough additional benefit for patients, parents, and practitioners to justify the greater burden of 2-pha-se treatment? and (3) do the changes repre2-pha-sent a permanent effect or simply a short-term response that will disappear with subsequent growth [240]?

These questions can be best answered by following children with similar initial problems, who did or did not have early treatment, to late adolescence

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after the completion of comprehensive treatment during the permanent den-tition.

The aim of the present longitudinal randomized study was to determine the long-term effects of early expanding HG treatmenton dental arches and craniofacial morphology, when treatment is started during the early mixed dentition. The objective is to analyze the possible benefits and stability of early treatment, when compared to camouflage treatment of dental crow-ding, using extractions done at the second phase. The hypothesiswas that with the early use of cervical HG it can be achieved well balanced position of the jaws, stable occlusion and significant increasesin dental arch dimen-sions.

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1. AIMS OF THE STUDY

The aim of this longitudinal randomized-controlled study was to assess the long-term effects of early expanding cervical HG treatment on dental arches and craniofacial morphology, when treatment started during the early mixed dentition and to compare it with the randomized control group. The objectives were:

1. To evaluate the dental arch changes using the linear measurements on dental casts

2. To evaluate skeletal changes by cephalometric analysis 3. To measure occlusal stability using occlusal indices

4. To monitor lower incisal area by measuring the irregularity 5. To assess the dental aesthetic outcome

6. To analyze the influence of permanent teeth extractions on dental arch changes and occlusal and lower incisor stability

Novelty of the study

To date there are only five Class II early treatment studies conducted as randomized clinical trials [85, 108, 114, 171, 240]. All of them have used different orthopedic appliances, treatment mechanics, timing of the treat-ment and inclusion criteria. The only study of these five has published long-term results evaluated after 7 years after initiation of early treatment [172]. When reporting the final results, most authors stated that the optimal timing for treatment of Class II malocclusion remains controversial. Thus it can be concluded that there is insufficient knowledge regarding early Class II treat-ment.

The aim of the current study is to elucidate the early Class II treatment topic by exploring long-term results evaluated after 13 years follow-up and to analyze the early cervical headgear treatment effects on dental and ske-letal structures.

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2. LITERATURE REVIEW

2.1. Morphological features of dental crowding, Class II malocclusion and possibilities to influence the maxillary growth

2.1.1. The problem of dental crowding

Crowding and irregularity are the most prevalent components of maloc-clusion in dental patients [138]. Prevalence of crowding has been reported from 5 to 80% in different populations [1, 2, 3, 4, 14, 82, 110, 112, 134, 145, 165, 169, 175, 178, 179, 192, 221, 232, 237]. In North American Afri-cans and Caucasians crowded malaligned teeth are the most common single contributors to malocclusion [191]. The extensive surveys conducted in the U.S. in 1960s found that 40% of children (aged 6 to 11 years) and 85% of youths (aged 12 to 17 years) have crowding problems [117, 118]. The U.S. survey data from 1988 to 1991 also indicate that crowding and irregularity is the persistent problem for children and adults [48]. Only 22% of the North American population had no mandibular incisor irregularity and 78% exhibited mandibular incisor crowding, ranging from mild to severe [49]. Crowding is also an aesthetic concern that causes many people to seek orthodontic treatment [63, 138].

The problem of crowding can be classified as simple or complex [164]. Simple crowding is defined as “disharmony between the size of teeth and the space available in the alveolus with no skeletal, muscular, or occlusal functional features”. It is often associated with Class I malocclusion, although it may be found with Class II malocclusions with maxillary dental protrusion and a normal skeletal pattern as well [164]. Complex crowding is defined as “crowding caused by skeletal imbalance, abnormal lip and tongue functioning, and/or occlusal dysfunction as well as disharmony between the size of teeth and the available space” [164].

Crowding may be categorized as an alignment problem based on the ex-tent of crowding. The crowding in the anterior regions of the dental arches may be measured as the Little’s Irregularity Index [138]. The millimeter distances of the contact point of the next incisor tooth are measured and obtained total value may be classified as ideal (0–1 mm), mild (2–3 mm), moderate (4–6 mm), severe (7–10 mm), and extreme (more than 10 mm) crowding [138].

The exact cause of crowding or malocclusion in general is unknown. Several researchers have suggested that the problem is hereditary and is associated with the evolutionary development of modern humans [45, 56, 57, 77]. Malocclusion and crowding is an increasingly common problem

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encountered in industrialized countries. It has been described as a “disease of civilization” because of its high prevalence in contemporary industriali-zed countries as compared to historic populations and even to isolated cultu-res that continue to subsist on less-processed diets [56, 58]. Skeletal remains show that the present prevalence of malocclusion is several times greater than it was millennium ago [191]. Some investigators attributed the main cause of crowding to a progressive reduction in the jaw size as compared with tooth size. There is also evidence of a secular trend towards deeper, longer, and narrower faces and an increased prevalence of malocclusion [45, 65, 246].

The study of Evensen and Øgaard (2007) performed on a sample of me-dieval Norwegians indicated a significant increase in both prevalence and severity of malocclusions in Norway during the last 400 to 700 years. Furthermore, females showed both higher prevalences of malocclusions and more severe malocclusions than males in the past. Only 36% of the medieval group had a professionally assessed need for orthodontic treatment compared with 65% of modern sample [77].

Mossey (1999) claimed that the trend towards narrower maxillary arches and greater crowding is compatible with a gene/environment interaction, where certain genetically determined craniofacial types tend to show a greater susceptibility to certain environmental factors. It is believed that there are true signs of hereditary and environmentally induced tooth-size/jaw-size discrepancy [160, 161]. Thus the etiology of crowding must be considered as multifactorial involving both genetic and environmental components [90, 96, 160, 161, 191]. Some environmental factors that may affect the development of a malocclusion are airway obstruction, tongue posture, muscle tonicity, head posture, and oral habits such as digit sucking and tongue thrusting, variation in size and position of the bony structures, and variation in tooth size and shape [96, 191].

Another study analyzed the primary dentition with and without spaces. “Primary spacing”, according to the author, occurs in maxilla among 70% of children and in mandible among 63% of children. It was found that the intercanine distance was by 1.7 mm in maxilla and by 1.5 mm in mandible larger in dentitions with spaces compared to that without spaces. The author concluded that a primary dentition without spaces is followed by crowding in approximately 40% of cases [15].

Berg (1986) in the longitudinal investigation analyzed whether subjects with crowding showed differences in dentofacial development compared with children having normal occlusion. The groups were: (1) normal occlu-sion group and (2) crowding group with measured lack of space at least 3.5 mm mesial to the first molars in either dental arch. The study showed that

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crowding developed between the ages of 6 and 12 years and that the differ-rence in space conditions of the dental arches of two groups was non-significant at the age of 6 years. General trend for larger mesiodistal tooth dimensions, lower values of intermolar distance, and larger intercanine distance as well as relatively great amount of mandibular retrognathism was observed in the crowding group [24].

Various authors have tested whether tooth size and arch length are risk factors for malocclusion [33, 57, 67, 156, 170, 182, 236].

Two groups of young adult white females from the Northeastern United States were compared. One group consisted of 45 subjects with “perfect” incisor alignment (no overlapping teeth or tooth rotations), while the second group consisted of 70 subjects selected without consideration for incisor alignment. None of the subjects had received orthodontic treatment, and two groups were considered comparable with except of the incisor alignment. Authors found that the mesiodistal diameter of the mandibular central and lateral incisors was significantly smaller in the “perfect” alignment group, while the buccolingual diameter was significantly larger. It was concluded that greater mesiodistal and lesser buccolingual tooth dimensions seemed to be associated with greater degree of lower incisor crowding [182].

Norderval et al. (1975) investigated mandibular anterior crowding in relation to mesiodistal crown widths, intercanine width, third molar presen-ce, and craniofacial morphology. Their sample consisted of 66 adults (48 males; 18 females) aged 20 to 30 years with Angle Class I occlusions. The sample was divided into two groups based on the presence or absence of anterior crowding: 27 subjects had sufficient or excess space, while 39 sub-jects had slight crowding. From their craniofacial findings, only the basal sagittal jaw relationship (ANB angle) and the mandibular inclination differ-red significantly between the groups. The group with crowding had signi-ficantly greater ANB angle, and the inclination of the inferior border of the mandible in relation to the palatal plane was also greater. They found that intercanine width and the prevalence of third molar were the same in the two groups. In the crowded group, mesiodistal widths of four mandibular incisors were significantly greater comparing to combined width of the six mandibular anterior teeth in the group without crowding [170].

Doris et al. (1981) compared mesiodistal tooth crown dimensions of orthodontically treated patients with marked dental crowding with a sample displaying little or no crowding. Eighty subjects (40 males, 40 females) aged from 11 to 18 years (mean age of 14.0 years) were divided into two groups based on degree of dental crowding. One group consisted of individuals with up to 4 mm of lower anterior crowding, while the other individuals had more than 4 mm of lower anterior crowding. They found that the

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mesiodis-tal crown diameters from the central incisors through second premolars were significantly larger in the crowded arch [67].

The dental arch size, mesiodistal and buccolingual crown diameters, and crown shape (ratio of mesiodistal and buccolingual crown widths) were in-vestigated in two groups of Taiwanese children in the primary dentition. Children with anterior crowding in both dental arches (n=27) were compa-red with children having spacing in both arches (n=34). Age of subjects ranged from 4 to 5 years. The investigator of study found that the crowded upper and lower dentitions had significantly narrower arch widths than dentitions with spacing. Additionally, he found that the mesiodistal and buccolingual crown widths of all maxillary teeth were consistently larger in the sample of crowded dentitions. It was concluded that inadequate arch width contributes most to crowding in the primary dentition [236].

Mills (1964) also found smaller arch widths associated with dental crowding. He conducted a study of 230 subjects to determine if well-aligned dental arches differed from crowded dental arches in arch width, arch length, or tooth crown size. All subjects were males aged 17 and 21 years without orthodontic treatment, crossbite, openbite, or missing teeth mesial to the second molars. Author found a significant association between mala-lignment of teeth and arch width. Specifically, the average width of both the maxillary and mandibular arches across the second premolar region steadily decreased in size as malalignment increased in severity. The correlation bet-ween arch length and malalignment was not significant. Likewise, there was no significant difference in mean mesiodistal crown width in presence of varying degree of crowding as compared to cases of no crowding [156].

Bishara et al. (1995) assessed changes in maxillary and mandibular crow-ding after complete eruption of deciduous dentition to the time of eruption of second permanent molars. They attempted to predict crowding in perma-nent dentition based on observations of deciduous dentition. Their sample consisted of 35 males and 27 females from the Iowa Longitudinal Growth Study. Each subject had a flush terminal plane or a mesial step relationship in second deciduous molars, 0 to 50% overbite, and 0 to 3 mm of overjet. Arch length, arch width, and mesiodistal widths of maxillary and mandi-bular deciduous and permanent teeth were measured. With exception of maxillary second molars, the sizes of all deciduous teeth were significantly correlated to their permanent successors. In other words, the mesiodistal widths of deciduous teeth were mostly predicting the mesiodistal widths of the permanent successors. They found that crowding was mainly due to decrease in arch length of both arches. No comments were in results regar-ding arch widths. The authors were unable to predict crowregar-ding in the perma-nent dentition from dental measurements in deciduous dentition [33].

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The other study tested whether mandibular incisor crown shape was asso-ciated with dental crowding. The sample consisted of 50 white subjects (25 males, 25 females) with comparable age among males and females (range from 17 to 29 years). All permanent teeth were present except third molars, and none of subjects had a history of orthodontic treatment. The authors concluded that the mandibular incisor mesiodistal or buccolingual crown dimensions have no predictive value for lower incisor crowding [214].

Bernabé and Flores-Mir investigated the mesiodistal and buccolingual tooth crown sizes in three groups that were labeled based on Little’s Irregu-larity Index as mild, moderate, and no crowding [138]. This study analyzed 200 Peruvian students aged 12 to 16 years. Crowding was defined as the difference in millimeters between the arch perimeter and sum of mesiodistal tooth sizes. Their results showed that mesiodistal crown sizes in moderate crowded arch were always larger than those in mildly crowded arch, and these were larger than in non-crowded arches. The most statistically significant differences were observed between those with no crowding and those with moderate crowding. When considering the mesiodistal tooth sizes, significant differences among crowding groups existed in all upper teeth, lower central incisor, second, and first premolar. The evaluation of crown proportions between groups indicated differences for both dental arches, though not as significant as that for mesiodistal tooth sizes [25].

A longitudinal study of 50 sets of Australian aboriginal dentitions (25 male) was conducted to see what role attrition played in tooth-arch discre-pancies. It was concluded that small jaws rather than large teeth were more likely responsible for dental crowding [57].

Some studies have attributed dental crowding to causes distinctly differ-rent from paradigm of „relatively large“ teeth simply erupting into „relative-ly small“ dental arches. Indeed, researchers have found that dental crowding increases in the absence of malocclusion simply as a function of age. Re-searchers have shown that even when teeth erupt into proper alignment, they frequently become crowded as arch dimensions change with age [159, 213].

Seipel (1946) investigated changes that accompanied development of dentition and growth of jaws in deciduous and permanent dentitions. His sample included 1500 subjects from Stockholm, Sweden. Data were collec-ted cross-sectionally from individuals at 4, 13, and 21 years of age (500 sub-jects in each age group with nearly equal distribution of males and females). He made about 50 measurements on each case including measurements related to tooth size, tooth position, transverse dimensions of dental arch, arch length, interarch relations, and cephalometric measurements. He found that (between ages of 4 and 13) the combined mesiodistal width of incisors increased by 30%, the degree of spacing decreased by more than 50%, and

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the frequency of lower anterior crowding increased by 37%. He also found that while the total tooth material increased by 65%t, the jaw size increased only by 20% from 4 to 13 years and by 30% from 4 to 21 years. He stated that the difference in dimensional changes between tooth and jaw materials is of considerable importance in positional changes of the teeth. A compa-rison of cephalometric measures led to conclusion that the jaw size is at the same time considerably smaller in cases with crowding [213].

In a longitudinal study, Moorrees and Reed (1965) found that arch length decreases 2 to 3 mm between ages of 10 and 14 years, when primary molars are replaced by permanent premolars. These authors also found a reduction in arch circumference of approximately 3.5 mm in mandible among boys and 4.5 mm among girls during the mixed-dentition period. It was conclu-ded that if crowding is evident during early mixed-dentition years, it will not improve with further growth and development [159].

Many studies confirmed a definite trend toward mandibular arch length decrease and anterior crowding in late adolescence and adulthood [33, 35, 37, 40, 78, 86, 100, 104, 143, 200, 216], even up to age of 50 years [32, 49, 52, 94, 95, 202]. Various factors have been discussed in relation to late mandi-bular crowding, such as eruption of third molars [111, 137, 201, 243], late mandibular growth [256], mandibular growth rotation [29, 200], muscle function and soft-tissue equilibrium [188, 229], mesial drift or anterior com-ponent of occlusal force [222], or mandibular incisor crown dimensions [182].

Little et al. (1988) conducted a 20-year follow-up study to determine whether there exists the age of “final dental alignment stability.” Dental casts of 31 cases with 4 sets of complete records (pre-treatment, end of ac-tive treatment, a minimum of 10 years post-retention, and a minimum of 20 years post-retention) were evaluated with Little’s Irregularity Index [138]. They found mean incisor irregularity values of 7.4 mm for pre-treatment, 1.7 mm for post-treatment, 5.2 mm for 10 years post-retention, and 6.0 mm for 20 years post-retention. Indeed, only 10% of cases had clinically accep-table mandibular alignment at 20-years final stage of records. Moreover, they found that crowding continued to increase during the 10-year to 20-year post-retention phase but at a slower rate. They argue that the only way to ensure post-treatment alignment is the use of fixed or removable retention for life [141].

A longitudinal retrospective study comparing skeletal and dental changes in orthodontically treated versus untreated individuals was conducted to evaluate the relationship between skeletal changes and mandibular incisor crowding. Two time points were selected, (1) at the completion of orthodon-tic treatment or at an age “typical” for completion of treatment and (2) bet-ween 20 and 44 years. The sample consisted of 44 untreated subjects with

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an average age of 14 years at initial time point and 23 years at final time point. The treated group consisted of 43 patients (21 males, 22 females) with initial average age of 15 years and final age of 29 years. Cephalometric superimpositions and dental cast analyses were obtained. It was found that in both groups the significant growth occurred beyond the age when ortho-dontic treatment is typically completed. When two groups were compared at baseline, the mean anterior facial height (nasion to menton) was 6 mm shorter in untreated group, while SNA and SNB angles were 3 to 4° smaller in treated group. At the second time point, with exception of SNA, all skele-tal dimensions changed significantly in both groups. The anterior and pos-terior facial heights increased approximately 4 to 5 mm. The largest dental change observed in both groups was a 4 to 5 mm inferior displacement of lower incisor attributed to growth. It was also found that lower incisor irre-gularity increased in both treated and untreated subjects (mean increase by to 1.5 mm), although the increase was greater in untreated subjects [68].

Bishara et al. (1994) conducted a longitudinal study of 30 adults who had been a part of the Iowa Facial Growth Study. Cephalometric and dental cast analyses were used to measure dentofacial changes occurring with age in 30 adults (equally distributed according to gender) between 25 and 46 years of age. All individuals were orthodontically untreated. Data were assessed for males and females separately. In males, they found that all skeletal linear di-mensions increased with age. Both genders displayed increased dental crow-ding in both dental arches, although to greater degree in mandible. They concluded that these changes are part of normal maturation process and should be taken into account by orthodontists when planning treatment and considering retention options for adult patients [32].

The conclusion which may be drawn from the analyzed literature is that the crowding is an unpredictable multifactorial problem, increasing with the age and that might be associated with larger mesiodistal tooth dimensions and narrower dental arches.

Anterior crowding is an orthodontic problem that the public considers as significant aesthetic issue and it is obvious to patients, parents, and society as well as to dental professionals and it causes many people to seek orthodontic treatment [46, 63, 109, 138, 219, 226].

2.1.2. Occlusal features and development in untreated Class II malocclusions

In a modern population there is a trend for the increase of dental crow-ding [136]. Also a prevalence of Class II malocclusions of over 20% is re-ported in Caucasian populations of North America, Europe, North and South Africa [55, 71, 83, 99, 132, 133, 232, 237, 257].

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When Angle in 1890 first developed his classification of malocclusion, he focused entirely on dental relationships of upper and lower first molars. The aim for him was the Class I occlusion (the mesiobuccal cusp of upper first molar occluding in mesiobuccal groove of lower first molar). He defined a malocclusion as Class II when lower molar is positioned distal to normal position of the upper molar [191]. Angle’s classification method is still used today in orthodontics but it has been expanded to include skeletal and dental relationships. Thus the Class II malocclusion may or may not include a skeletal discrepancy [191].

Moyers et al. (1980) in a study of 697 North American white children divided Class II individuals into 6 horizontal and 5 vertical groups. He established 15 subtypes of Class II malocclusions. Analysis of these subty-pes revealed persistent skeletal characteristics for each group during growth periods. He concluded that 20% had a maxillary protrusion while over 50% had a mandibular retrusion with little, if any, maxillary protrusion [163].

In the other study of Class II individuals, investigators observed that maxillary protrusion occurred in males while the maxilla was in a relatively neutral position in females. No difference was noted in maxillary molar po-sitioning compared to the Class I control group. In addition, it was found that the mandibular length is within normal limits in males, while it was less than normal in females [72].

Renfroe (1948) studied facial patterns in Class II malocclusions and ob-served that maxilla was generally in a retrusive position in both genders with maxillary incisor protrusion and molar retrusion relative to Class I sample [194]. He noted that while some Class II individuals have a deficien-cy in mandibular size, others have well formed mandibles of normal size. However, these normal mandibles were in a retruded position due to poste-rior position of the glenoid fossae. He concluded that mandibles of Class II individuals were retrognathic relative to other craniofacial structures [194].

Through investigation of Class II individuals Riedel (1952) determined that the maxillary skeletal base was normally positioned in both genders but with maxillary incisor protrusion. It was also noted that the mandible was relatively retrusive when compared to average of Class I individuals [198]. Similar findings were reported by Hunter (1967) who additionally observed a slight increase in anterior facial height [107].

Henry (1957) developed a classification of Class II division 1 malocclu-sions. He selected his sample according to Angle’s classification system, and categorized four groups for this malocclusion: (1) maxillary alveolar protrusion; (2) maxillary basal protrusion; (3) micromandible; and (4) man-dibular retrusion. From cephalometric evaluation he noted an increased

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mandibular plane angle in Class II cases compared to Class I norms, sugges-ting an increase in lower facial height [101].

McNamara (1981) examined a series of Class II patients to determine the nature and frequency of specific contributing components. The study was a cross-sectional evaluation of lateral cephalograms of 277 children aged 8 to 10 years. From these records he assessed maxillary and mandibular skeletal and dental relationships. The most common findings were an excessive lo-wer facial height and mandibular retrusion [147].

This line of research indicates that there is considerable variation within the population of individuals with Class II malocclusion.

An indication of how to treat a malocclusion may be gained by observing how it changes with time.

In a follow-up study it was found that while growth continues into adult-hood, existing maxillomandibular relationships are maintained in a fairly uniform manner with only small variations [21].

Ngan et al. (1997) compared skeletal growth changes between Class II, division 1 and Class I females aged 7 to 14 years. Lateral cephalometric radiographs had been taken annually from 5 through 17 years of age. They observed that maxilla was no more protrusive at the older age in Class II sample when compared with Class I. In fact, there was a decrease in maxil-lary prognathism in Class II subjects during the pubertal growth period. The maxillo-mandibular skeletal difference (ANB) was significantly greater in Class II sample at age 7 and did not improve with age; consequently, skele-tal differences maintained a greater degree of facial convexity in Class II subjects. The authors stated that “those results suggest that the Class II skeletal growth pattern is established early and maintained throughout puberty unless altered by orthodontic intervention” [168].

The occlusal features of Class II malocclusion during the transition from deciduous to mixed dentition in untreated subjects were recorded in study of Bacetti et al. (1997). During the observation period, cephalometric changes consisted of significantly greater maxillary growth increments and smaller increases in mandibular dimensions in Class II sample. In addition, investi-gators observed a downward and backward rotation of mandible over time with a subsequent decrease in gonial angle for Class II subjects. They con-cluded that “all occlusal Class II features were maintained or became exag-gerated during the transition to the mixed dentition” [9]. These findings are similar to those found by Fröhlich (1961) who reported that no improvement of Class II occlusal relationship occurs from 5 to 12 years of age [81] and Arya et al. (1973) who observed that all patients presenting a distal step relationship of second deciduous molars exhibit the Class II relationship in permanent dentition [8].

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Bishara (1988) conducted a cross-sectional and longitudinal evaluation of changes in mandibular length and maxillary-mandibular relationships in un-treated Class II subjects from deciduous to permanent dentition. These Class II samples were compared with matched “normal,” untreated individuals. Longitudinal comparisons of growth profiles indicated that the growth trends were similar between untreated Class II, division 1 subjects and nor-mal subjects [31].

Some studies suggest that the Class II malocclusion is related to deficien-cy in maxillary width [9, 34, 121, 241, 253] and it can be masked once the posterior teeth occlude in a narrower portion of maxilla, compensating for the axial inclination. Narrow maxilla is seen already in deciduous dentition and it is likely to be a key factor in the development of malocclusion [9]. The narrowness leads to interarch discrepancy and consequently to counter-clockwise rotation or functional retrusion of mandible without a marked effect on the size of mandible [27, 224, 234]. During the past few decades, there has been significant trend toward narrower maxillary transverse di-mensions [136]. The expansion of maxillary dental arch and maxilla itself may enable normal mandibular growth and its clockwise rotation upward and forward [27, 122, 218].

McNamara (2000) emphasized the importance of maxillary arch expan-sion in Class II treatment and reported that by expanding the maxillary arch, spontaneous forward repositioning of mandible and additional arch length gain in the maxillary arch could be achieved [148]. You et al. (2001) found that the effect of forward growth of mandible during adolescence, which could potentially bring the lower dentition forward, was negated because of intercuspal locking. With maxillary expansion, intercuspal unlocking can be achieved [256]. Without any intervention and maxillary widening, interarch discrepancy is expected to increase with age [168, 196]. This is due to maxillary and mandibular growth pattern.

The cited literature suggests that untreated Class II dental malocclusions do not “self correct” or improve with time. If anything, they tend to worsen with time.

2.1.3. Possibilities to restrain of maxillary growth

The understanding of growth events is of primary importance in the practice of clinical orthodontics. Maturation status can have a considerable influence on diagnosis, treatment goals, treatment planning, and eventual outcome of orthodontic treatment. Clinical decisions regarding the use of extraoral traction, functional appliances, extraction versus non-extraction treatment, or orthognathic surgery are, at least partially, based on growth

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guidance. For thorough understanding of changes that can occur when applying orthodontic devices to restrict the maxillary complex growth it is necessary to overview the normal growth of this area which takes place during the period of early treatment.

Growth of the nasomaxillary area is produced by passive displacement, created by growth in cranial base that pushes the maxilla forward and active growth of maxillary structures and nose [73]. Passive displacement of maxilla is an important growth mechanism during the primary dentition years but becomes less important as growth at synchondroses of cranial base slows markedly with the completion of anterior scull base growth at about age of 7 years. Then sutural growth is the only mechanism for bringing the maxilla forward [73]. As the downward and forward movement occurs, the space at sutures is filled in by proliferation of bone. The sutures remain the same width, while the processes of maxilla become longer. The maxilla grows downward and forward as bone is added in the tuberosity area posteriorly and at posterior and superior sutures, but anterior surfaces of the bone are resorbing at the same time [74]. Enlow (1990) described this movement as an expanding “V”. Another substantial contributing factor to the downward-for-ward growth of nasomaxillary complex is the increase in vertical height from eruption of permanent teeth together with growth of alveolar processes [73].

There are many investigations describing the growth mechanisms of maxilla, and the most important of these are Björk’s (1955, 1966) and Björk’s and Skieller’s (1972, 1974, 1977) implant studies [26, 27, 28, 29, 30]. It was observed that the increase in length of maxilla in a sagittal direction is due to sutural apposition towards palatine bone and apposition on maxillary tuberosities [26, 29, 30].Using metallic implants and cephalo-metric radiographs in 9.4 year old boys, the growth of maxilla was followed until 16–20 years of age. Mean posterior skeletal increase of 6.5 mm was found in the maxilla, as measured between implants placed in infrazygo-matic crest area. This increase was approximately three times greater than between anterior implants placed below the anterior nasal spine on each side of midpalatal suture. The width of maxillary dental arch from first molar to first molar increased by 2.0 mm on average from age of 7 years to adult-hood, while intercanine width increased only by 0.6 mm on average from age of 4 years to adulthood [28].

The growth of maxilla in a vertical direction appears by elongating of its processes. The downward and forward displacement of maxilla is due to various factors: apposition on floor of the orbits, resorptive remodeling on floor of the nasal cavity, and apposition on hard palate in the oral cavity [30].Finally, implant studies showed a differential amount of remodeling of

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maxilla, with greater resorption in anterior portion of the nasal cavity crea-ting varying degrees of vertical rotation [30].

Besides dentoalveolar process, the important sites of growth of maxilla, where it might be possible to alter the expression of growth, are the sutures that separate the middle of palate and attach the maxilla to zygoma, ptery-goid plates, and frontonasal area. Some of the first growth studies that examined the midpalatal suture as a site of transverse growth were con-ducted by Keith and Campion (1922).They stated that “the median palatal suture takes an active role in the transverse growth of the maxilla” [115]. The implant studies of Björk (1969),Krebs (1958; 1964), Björk andSkieller (1977),Skieller (1964) Korn and Baumrind (1990),and Snodell and Nanda (1993) showed that the transverse growth of maxilla at the median suture continued beyond puberty until completion of growth in other facial sutures [26, 30, 129, 130, 131, 217, 220]. After pubertal growth spurt, the changes in transverse dimension of maxilla are minimal, but statistically significant [30, 129].It is believed that growth at midpalatal suture continues until around the age of 13–15 years and then is followed by continuation of apposition until the age of 18 years [152].The mean increase in transverse growth of the median suture has been estimated to be 6.5 millimeters from the age of 4 to 7 years and 5 millimeters of growth occurring after the age of 7 years. This is an average rate of 0.2–0.4 mm per year [30].In contrast, the maxil-lary dental arch increases in width between the first molars only by 2 milli-meters on average after the age of 7 years. This has led to conclusion that after the age of 10 years the increase in dental arch width is only about 25% of the increase in midline sutural growth at the level of first molars [26].

Melsen (1975) analyzed palatal growth and midpalatal suture morpholo-gy in humans aged 0 to 18 years using tissue blocks from autopsy material. She found that at birth the suture is broad and slightly sinuous, but by the age of 10 years it has developed into typical squamous suture where the palatine part overlaps the maxillary portion with incipient interdigitation visible in the lower, broadest portion. After 13 to 14 years of age, the suture shortens and becomes more serpentine, thus narrowing the connective tissue sheet that connects the lateral parts of palate. After the ages of 15 years in females and 17 years in males, the sutures consist of a narrow sheet of con-nective tissue with inactive osteoblasts [152].

In one histological study, the palatal sutural closure was investigated in individuals aged 15 to 35 years [183]. The authors demonstrated that palatal sutures may show obliteration during the juvenile period, but marked degree of closure is rarely to be found before the third decade of life. The chrono-logical age does not seem to be sufficiently reliable for assessing the indi-vidual sutural status [183].

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For modification of excessive maxillary growth, the concept of treatment would be to add a force to oppose the natural force that separates the sutu-res, preventing the amount of separation that would have occurred. It is dif-ficult to measure the compression or tension within the sutures as well as to know what is required to alter growth. Clinical experience suggests that mo-derate amounts of force against the maxillary teeth can impede forward growth of maxilla, but heavier force is needed for separation of sutures and growth stimulation [191]. When force is applied to teeth, only a small frac-tion of pressure in the periodontal ligament is experienced at sutures, becau-se the area of sutures is so much larger and distant from the site of force ap-plication. For this reason, even the moderate forces recommended for rest-raint of forward maxillary growth tend to be heavier than those recommen-ded for tooth movement alone. During growth modification treatment, tooth movement is less desirable – the objective is to correct the jaw discrepancy, not so much to move teeth. Heavy continuous force can damage the roots of teeth and the periodontium. Heavy intermittent force is less likely to pro-duce damage, and intermittent force is a less effective way to inpro-duce tooth movement, probably because the stimulus for undermining resorption is di-luted during the time when the heavy force is removed. It logically follows that for minimization of damage to the teeth, full-time application of heavy force to the maxillary dentition is not suggested [53, 180]. For tooth move-ment there is definite threshold for duration of force: unless force is applied to tooth for at least 6 hours per day no bone remodeling occurs. It is un-known whether similar duration threshold applies to the sutures, but clinical practice suggests that it may [191].

It has been shown that in both experimental animals and humans, short-term growth is characterized by fluctuations in growth rates, even within a single day [191]. In growing children, growth hormone is released primarily during the evening and addition of a new bone at epiphyseal plates of the long bones occurs mostly – perhaps entirely – at night [41, 203, 227]. It is not yet known whether facial growth follows this pattern, but it is entirely possible that it does. It is also possible that tooth movement is more likely to occur during the time of active growth, since tooth eruption occurs then and recent animal experiments have detected differences in the rate of tooth movement at different times of the day [191, 203]. Growth hormone secre-tion begins in the early evening, so it is important to emphasize that the patient should begin wearing a functional appliance at that time [41, 191].

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2.2 Treatment and stability 2.2.1. Early Class II treatment

Early orthodontic treatment is defined as the treatment that is started and finished before all permanent teeth erupt into the mouth. A major decision facing an orthodontist today is when to start treatment in patients with Class II malocclusion.

Orthodontic clinicians have basically two options to correct Class II ske-letal malocclusions in children. One option is to wait until at least almost all permanent teeth erupt and to treat the case with fixed braces or functional appliances during the single phase of treatment. The other option would be to treat the children earlier, using functional devices in mixed dentition (phase I) and thereafter to treat with the fixed appliances in permanent dentition (phase II).

The early treatment’s goal is to reduce the time of second phase of ortho-dontic treatment, to reduce the need for extractions in permanent dentition when necessary, and to avoid root resorption, periodontal problems, impact-ted canines, and orthognathic surgery [38].

There is some evidence to support a theory that early growth modifica-tion therapy can lead to improvement, if not complete correcmodifica-tion, of Class II malocclusion [240]. The mechanisms by which the correction is achieved and whether early correction has advantages over correction during the phase II of treatment lead to fundamental questions: Is facial growth altered or is the correction due to dentoalveolar changes? Do the changes represent a permanent stable effect or simply a short term response that will be negated by subsequent growth? Is the mechanism of change acting on the maxilla, the mandible or both [240]? To address these important issues the analysis of published results of Class II early treatment based on RCTs is relevant.

There are only a few well-controlled studies in which the timing of Class II malocclusion orthodontic treatment has been studied [85, 108, 114, 171, 240].

In study of Jakobsson (1967), a group of 57 Class II mixed-dentition sub-jects (mean age – 8.5 years) were randomly and equally assigned to obser-vation, Andreasen activator, and Kloehn headgear groups. The author repor-ted that both appliances reduced overjet compared with control, with greater effect in the activator group. Both appliances restricted maxillary anterior displacement and had no effect on anterior mandibular growth compared with control. It was noticed that the headgear was more effective in restrai-ning maxillary advancement than the bionator. The study reported about

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early treatment effects obtained after 18 months, though the authors did not examine the patients in long-term after the completion of treatment, so it was unclear about the stability of the results [108].

Tulloch et al. (2004) have published reports from the University of North Carolina study of the benefits of two-phase versus one-phase Class II treat-ment. In this RCT, 166 children with a moderate to severe Class II maloc-clusion were randomly assigned to one of the three groups: headgear treat-ment (n=52), bionator therapy (n=53) or an observational group in which no early treatment was administered (n=61). The inclusion criteria for children were: overjet of 7 mm or more, mixed dentition, no previous orthodontic treatment, and at least 1 year before their peak pubertal growth. After 15 months records were taken, the groups were pooled together and each child was randomly assigned to one of four orthodontists for treatment with tradi-tional fixed appliances (phase II) therapy. Cephalometric radiographs were used to assess skeletal changes. The Peer Assessment Rating (PAR) was used to rate alignment and occlusion [192]. The results showed statistically significant differences although there was a substantial individual variation observed in both treatment groups, as well as in untreated control group. The change in jaw relationship (reduction in ANB angle) was favourable in 76% of the headgear group, in 83% of the functional appliance group, and in 31% of the controls. Reliable predictors for favorable growth response were not identified. The second phase of the study was designed to test whether these changes represented long-term differences. At the completion of treat-ment, the investigators found no significant differences among the groups regarding subjects’ skeletal relationships as determined by their cephalo-metric measurements. In addition, there were no significant differences in subjects’ occlusions measured by PAR score. The results of this study suggest that, on average, the skeletal changes that occur with early treatment are not sustained. The improvement in jaw relationships seems to represent a period of accelerated growth rather than a permanent change. Tulloch et al. (2004) also noted that the number of patients who required extractions of permanent teeth was greater in the bionator group than in the headgear or control groups, and that orthognathic surgery was offered more often (although not necessarily accepted) to patients in the control group than to patients in either of the two-phase groups. The authors concluded that for children with moderate to severe Class II malocclusion, early (phase I) treat-ment followed by conventional orthodontics later on (phase II) does not pro-duce skeletal or occlusal relationships that differ substantially from those produced by phase II treatment alone. Moreover, severity of the problem and total treatment time have no essential influence on final result, while variations in skeletal growth patterns seem to play an important role. In

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addition, two-phase treatment seemed to be inefficient in that it did neither reduce the average time with fixed appliances nor the complexity of later treatment (need for extraction or orthognatic surgery) [240].

Ghafari et al. (1998) conducted another randomized clinical trial on the effectiveness of early treatment in the correction of Class II malocclusion. The inclusion criteria were: Class II, Division 1 malocclusion associated with bilateral distoclusion (unilateral Class I excluded) and a minimum ANB angle of 4.5°; no prior orthodontic treatment. In this study, conducted at the University of Pennsylvania, 63 patients with Class II malocclusion aged 7–13 years were randomly assigned to either a straight-pull headgear group (n=35) or a Fränkel therapy group (n=28). As a result of treatment, the sagittal discrepancy was reduced in both groups. Similar to results of the University of North Carolina [248], the results of the Pennsylvania study showed that the headgear correction was primarily due to its effect on maxilla, while the Fränkel therapy had its greatest influence on mandibular position. Regarding the dentition, improvements in molar and canine rela-tionships were greater in the headgear group, while overjet correction was better in the Fränkel therapy group, although this difference in overjet correction was not statistically significant. These occlusal differences were probably due partly to greater influence of the headgear on posterior denti-tion and the palatal force exerted on maxillary incisors by the labial bow of the Fränkel appliance. To address the issue of treatment timing, the investi-gators further categorized the experimental groups on the basis of emer-gence or non-emeremer-gence of permanent canines, premolars, and permanent second molars. None of the changes mentioned above was influenced by these stages of dental development. As reported by Ghafari et al. (1998), Class II treatment seems to be just as effective in late childhood as it is at an earlier age [85].

Keeling et al. (1998) reported findings from a similar randomized clinical trial conducted at the University of Florida. The inclusion criteria were: bilateral half cusp or more of Class II molars, or if one side is less than half cusp Class II, the other side should be more than half cusp Class II; fully erupted permanent first molars; emergence of not more than 3 permanent cuspids or bicuspids. A group of 249 children, aged 9.6±0.8 years at base-line, were randomly assigned to control (n=81), bionator (n=78), and head-gear/biteplate (n=90) treatments. Their data showed that both the headgear (cervical or occipital anchorage with acrylic intraoral bite plane) and the bionator treatments in preadolescent children can result in short-term skeletal changes. Subjects in both treatment groups demonstrated enhanced mandibular growth compared with subjects in the control group. One-year follow-up after completion of treatment in this study showed that the

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skeletal changes were stable; however, some of the dental movements re-lapsed [114].

O’Brien et al. (2003) have conducted multicenter trial which was carried out in the United Kingdom. This study evaluated the effectiveness of early orthodontic treatment with the Twin-block appliance for Class II Division 1 malocclusion. The inclusion criterion was at least 7 mm of overjet. A total of 174 children, aged 8 to 10 years, with Class II Division 1 malocclusion were randomly allocated to treatment with a Twin-block appliance (n=89) or to an untreated, control group (n=85). This study used 14 hospital-base orthodontic specialists and treatment was provided outside of a controlled university setting where treatment is carried out in selected populations. The authors wanted to see how effective early Class II treatment is in the normal orthodontic practices outside dental schools. Results showed that early treat-ment with Twin-block appliances resulted in reduction of overjet, correction of molar relationships, and reduction in severity of malocclusion. Most of this correction was due to dentoalveolar change, but some was due to favo-rable skeletal change. Early treatment with the Twin-block appliance seems to be effective in reducing overjet and severity of malocclusion. The small change in skeletal relationship might not be considered clinically signifi-cant. This study reinforces the findings of other, similar randomized contro-lled trials that suggest that early functional appliance treatment does not, on average, influence the Class II skeletal pattern to clinically significant degree [171].

All above mentioned studies [85, 108, 114, 171, 240] have used different orthopedic appliances and treatment mechanics. In addition, the timing of treatment and inclusion criteria for RCTs has been different. Thus, Class II early treatment still remains a controversial issue. Much of the discussion concerning the effectiveness of early treatment has been concentrated on the timing and suitable methods of intervention in Class II malocclusion subjects. The individuals who received phase I early treatment had signifi-cant reduction in the severity of Class II discrepancy compared with con-trols. However, results published after phase II indicated that both I- and II-phase subjects underwent skeletal and dental changes that left them essen-tially indistinguishable at the end of treatment, and thus little was to be gai-ned from precisely timed early treatment. In those studies it was not possible to identify any predictive factors, which of the children would benefit from early intervention. When reporting the final results, most authors stated that the optimal timing for treatment of Class II malocclusion remains controver-sial and that the decision for early treatment should be based on individual indications for each child. It also remains unclear if these study results can be fully applied to children with moderate crowding and Class II tendency.

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2.2.2. Treatment effects produced by cervical HG

Over the years numerous techniques and appliances have been introduced in orthodontics in order to produce predictable treatment of Class II maloc-clusions. These techniques vary in terms of their approach, complexity, variability, and effectiveness. Many of these include fixed appliances, func-tional appliances, headgear, intermaxillary elastics, distalizing appliances, selective extraction patterns, and finally surgical correction.

In the field of healthcare, efficiency can be described as the production of desired results with minimum waste of time, money, effort, or skill [225]. Perhaps the most popular of all orthodontic extraoral maxillary traction appliances is the orthodontic headgear (HG) because it is cheap, efficient and easy to produce. The appliance, simplistic in its concept and design, consists of three basic components: facebow, strap, and force module. The facebow is made up of two parts, the inner bow that is designed to engage maxillary molars via special attachments placed on orthodontic bands, and the outer bow to which an extraoral vector of force is applied. The strap, commonly made of flexible material to fix to the back of patient’s neck or head, is used to reciprocate the tension produced by force module. The force module, a link between strap and facebow, may be composed of various materials ranging from elastic to nickel titanium, and is able to transfer the range of forces to maxillary molars via facebow [191].

Theoretically the force produced by HG is transmitted in posterior and superior direction via the teeth through maxilla to compress the circum-maxillary sutures, limiting or redirecting circum-maxillary growth [191].

Use of extraoral forces to modify the growth of maxilla has a long history, dating back to the work of Kingsley in the 19th century [248]. Interest in extraoral traction was decreased during the first half of the 20th century, but was revived by Oppenheim [176] and later by Kloehn [125, 126, 128]. Kloehn's original design featured a facebow, the inner bow of which was attached to maxillary first molars, with the outer bow connected by elastics to an occipital anchoring device. Later he modified that design to include only a cervical neck strap. The method of attachment and angulation of the outer bow of facebow could be altered to determine the direction of pull [128].

Kloehn understood that during the normal growth, the alveolar develop-ment and teeth are moving forward. If orthodontist could interrupt this movement in Class II patients, the mandible could follow its normal growth until reaching a favorable relation to maxilla [128].

There is a great variation in the direction and force of traction [80]. Kloehn advised that the outer face bow be long enough to extend well be-hind the first permanent molar attachment for the inner bow. He further

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re-commended that the outer bow be bent upwards off of horizontal plane, to prevent excessive tipping and extrusion of molar teeth. With his protocol, an excellent control over occlusal, palatal, and mandibular planes was achieved with little, if any, adverse effect on vertical dimension, while accomplishing the intended improvement in anteroposterior dimension [127].

Since introduction of standardized cephalometric radiographs, many clinical studies have demonstrated that maxillary growth can be altered with the use of HG [13, 17, 18, 19, 20, 23, 47, 59, 60, 80, 105, 108, 125, 153, 157, 185, 186, 196, 199, 250, 251].These clinical data have been supported by primate studies demonstrating that extraoral orthopedic force directed against maxilla attenuates forward growth and alters bone apposition at ma-xillary sutures [44, 69, 70, 151, 223, 233, 235, 254].There are some studies that suggest that mandibular growth may be enhanced as well [11, 50, 93, 146, 155, 185, 210]. Since the HG is a toothborne appliance, there is some maxillary dental retraction that accompanies the skeletal change. Another dentoalveolar effect is the attenuation of maxillary molar eruption, resulting in anterior and superior mandibular rotation [64].

Studies have shown that the cervical traction usually employed in correc-tion of Class II is effective in redirecting the maxillary growth inferiorly and posteriorly [18, 187]. Extraoral force against maxilla decreases the amount of forward and downward growth by changing the pattern of apposition of bone at sutures. The Class II correction is obtained as the mandible grows forward normally while similar forward growth of maxilla is restrained [16, 17, 19].

Melsen and Enemark (1969), using the implant method, studied the effect of cervical-pull HG on craniofacial complex, in part to determine whether the specific angulation of the outer bow relative to occlusal plane was clini-cally significant. In one group of children, the outer bow was bent 20° above occlusal plane and in the second group – 20° below occlusal plane. In the first group with the outer bow bent upward, only slight tooth movement was observed, but the entire maxillary complex moved posteriorly and inferiorly relative to anterior cranial base. In the second group, more extensive tooth movement was observed, particularly a distal tipping of upper first molar [154].

A primary treatment effect of extraoral traction is the restriction of maxil-lary skeletal growth. There is virtually general agreement that, as a result of treatment, Point A is repositioned posteriorly relative to the remainder of face, resulting in a reduction in maxillary prognathism [50, 89, 103, 119, 124, 125, 128, 157, 158, 167, 187, 196, 199, 210, 252]. Wieslander (1963) has shown that this technique also influences the cranial base by producing

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a counterclockwise tilting of spheno-ethmoid plane during 3 to 4 years of treatment with HG [250].

An opening of mandibular plane angle has been reported by many inves-tigators [47, 93, 146, 155, 250, 252]. An opening of bite and an increase in lower anterior facial height also has been a frequent finding [16, 17, 124, 187, 209, 211, 212]. Klein (1957) and Ricketts (1960) reported that extra-oral force tends to open the Y axis angle and lengthen the face more than would occur with normal growth [124, 196]. In contrast, Ringenberg and Butts (1970), Baumrind (1978) and Hubbard et al. (1993) reported a closure of mandibular plane angle with treatment [16, 106, 199], whereas others reported no change [17, 39, 50, 119, 125, 204, 210, 245].

The studies on changes in transverse dimension with extraoral traction have been limited. Ghafari et al. (1994) conducted a comparative study of straight-pull HG and appliance of Fränkel. The inner bow of facebow was ad-justed at every appointment “to avoid any constriction or major expansion of the intermolar distance” resulting in a total expansion of the inner bow by 1.5 to 2.0 mm. The increases were noted not only in intermolar distance, but in intercanine distance as well. These investigators hypothesized that the change in intercanine distance, a region not directly affected by facebow, may have been a result of a shielding effect by the inner bow on lip and cheek muscu-lature, an indication of the influence of buccal and labial musculature on tooth position [84]. Ricketts et al. (1979) mentioned cervical HG expansive effect on maxillary dental arch with intentional expansion of inner bow. According to Ricketts et al. (1979), the expansive effect of cervical HG derives from anatomical configuration of maxillary complex and mechanical adjustment of the inner bow of HG [197]. One condition for this to occur is that the applied force should be of sufficient magnitude to overcome the bioelastic strength of sutural elements [22]. The expansion of the inner bow of cervical HG has been shown to be efficient during the mixed dentition [79, 121, 122].

Long-term follow-up studies of skeletal Class II patients treated with cer-vical HG are rare in the literature. Melsen (1978) reported only temporary influence of cervical HG on skeletal growth pattern and a recovery of expec-ted amount of growth in maxillary complex. She used maxillary and mandi-bular implants to study the effects of extraoral forces. It was noticed that during the treatment the maxilla grew downward and backward, the maxil-lary molar extruded and the mandible rotated posteriorly. When observed 7 to 8 years later, the growth direction of both maxilla and mandible was found to have changed dramatically. The maxilla had grown forward and downward, on average more forward than expected in a typical population, and similarly the growth direction of mandible had changed to a more for-ward direction in all but a few patients [153].

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Investigators have reached contradictory conclusions regarding the effects of extraoral traction therapy. These differences can be explained, in part, by specific treatment protocols used by the practitioner. The type of extraoral traction device, as well as the magnitude of the force applied and the direction of pull have been shown to be important considerations. The direction and force of traction have varied greatly, and high-pull, straight-pull, cervical-pull HGs, or combinations with different forces have been used [42, 43, 80, 241]. Although the use of HG is quite popular in orthodontics, the literature is ambiguous considering the amount of force necessary for effective and predictable outcome in molar distalization. The forces reported vary from 300 g to as much as 1000 g per side [245, 251]. Forces from 150 to 200 g may be used to move teeth, while forces over 450 g are assumed to surpass the tooth-moving threshold and have been used to control dental anchorage [42, 43, 90, 193]. Strong forces are needed to produce orthopedic skeletal effects on maxilla, which are essential in the treatment of Class II malocclusion [6, 90, 92, 124, 158, 185, 196, 210, 250]. The structure of the inner and outer bow has varied. The inner bow may be used with or without expansion and it may or may not bear on the upper incisors [23, 197]. The length of the outer bow and its angle against the inner bow has also varied [42, 43]. There is also ambiguity on the amount of time the appliance is to be worn to achieve desired effect. Armstrong (1971) and Badell (1976) suggest continuous HG wear (24 hours a day) to achieve optimal orthodontic results, while others prefered intermittent wear [6, 12]. A significant treatment effect usually requires that the HG be worn 12 to 16 hours per day [191].

There is also a broad inconsistency in the treatment duration which varies from several months to several years [80, 245, 250].

Furthermore, in many studies the HG therapy has not been used alone, but with fixed or functional appliances and with or without tooth extractions [85, 241, 247]. Therefore, it is difficult to compare different results of the HG therapy, and it is important to recognize what kind of HG therapy is studied. In addition, the malocclusion itself may result from various maxillary and mandibular skeletal and dental relationships [36, 51, 147, 163, 205]. This heterogeneity of Class II malocclusion adds some variability to the results.

Proffit et al. (2007) presented general recommendations on optimal “force prescription” for HG to restrain maxillary growth in patients with Class II problems [191]:

• Force of 500 to 1000 g total

• Force direction slightly above the occlusal plane (through the cen-ter of resistance)

THE EFFECT OF EARLY HEADGEAR TREATMENT ON THE DENTAL ARCHES

Viktorija Krušinskienė