_______________________________________________________________
Qualität des Behandlungsergebnisses bei nicht angelegten Unterkieferprämolaren und
kieferorthopädischem Lückenschluss durch Mesialisierung von Unterkiefermolaren ohne
Ausgleichsextraktionen im Oberkiefer
Dissertation
zur Erlangung des Doktorgrades der Zahnheilkunde in der Medizinischen Hochschule Hannover
vorgelegt von Elisabeth Klang aus Ibbenbüren
Hannover 2018
Angenommen vom Senat der Medizinischen Hochschule Hannover am: 01.04.2019
Gedruckt mit Genehmigung der Medizinischen Hochschule Hannover
Präsident: Prof. Dr. med. Michael P. Manns
Wissenschaftliche Betreuung: Prof. Dr. med. dent. Dr. h.c. Dirk Wiechmann
1. Referent: PD Dr. med. dent. Ingmar Staufenbiel 2. Referent: Prof. Dr. med. dent. Harald Tschernitschek
Tag der mündlichen Prüfung: 01.04.2019
Prüfungsausschuss
Vorsitz: Prof. Dr. med. Dr. med. dent. Frank Tavassol 1. Prüfer: Prof. Dr. med. dent. Michael Eisenburger
2. Prüfer: Prof. Dr. med. Dirk Scheinichen
Inhaltsverzeichnis
1. Publikation mit Literaturverzeichnis ... 1
2. Zusammenfassung ... 13
2.1 Einleitung ... 13
2.1.1 Hintergrund ... 13
2.1.2 Differentialtherapeutische Aspekte bei Nichtanlage des zweiten unteren Prämolaren ... 14
2.1.3 Der kieferorthopädische Lückenschluss ... 15
2.2 Diskussion ... 17
2.2.1 Studiendesign ... 17
2.2.2 Lückenschluss auf der Aplasie-Seite des Unterkiefers ... 18
2.2.3 Die Nullhypothese wurde widerlegt ... 18
2.2.4 Weitere qualitätsrelevante Parameter ... 19
2.3 Schlussfolgerung ... 23
2.4 Literaturverzeichnis ... 24
3. Anhang ... 30
3.1 Danksagung ... 30
3.2 Lebenslauf ... 31
3.3 Erklärung nach § 2 Abs. 2, Nrn. 7 und 8 ... 33
1
1. Publikation mit Literaturverzeichnis
R E S E A R C H Open Access
Quality of occlusal outcome following space closure in cases of lower second
premolar aplasia using lingual orthodontic molar mesialization without maxillary
counterbalancing extraction
Elisabeth Klang1*, Frauke Beyling1, Michael Knösel2,3,4and Dirk Wiechmann1,5
Abstract
Background:Controlled space closure in cases of isolated lower second premolar aplasia (ILSPA) without maxillary counterbalancing extraction is challenging. Anterior anchorage loss may occur during space closure resulting in
compromised occlusal results in terms of an absence of proper canine guidance during laterotrusive mandible movements.
In order to evaluate the effectiveness of Herbst telescope anchorage in combination with double-cable, pull mechanics and a completely customized lingual appliance for orthodontic space management in cases of ILSPA, we tested the null hypothesis that there is a significant deterioration in the sagittal canine relationship towards an Angle-Class-II occlusion expressed as a loss of anterior anchorage following space closure with molar mesialization.
Methods:Twenty-five consecutively de-bonded subjects (female / male 17 / 8; aged at T0 (start of MB Tx) 12.3 to 20.
6 years; mean age 15.0 / SD 1.7 years) were included in this retrospective analysis using the inclusion criteria of least of one lower second premolar aplasia; completed treatment with a totally customized lingual appliance (CCLA) in combination with Herbst telescopes. Exclusion criteria were the absence of counterbalancing maxillary extractions, as well as additional tooth aplasia other than lower second premolars. A total of 33 single, lower premolar aplasia space closures (right / left sided 17 / 16) were assessed using plaster casts and intra-oral photographs scaled to the plaster casts, at bonding (T0), Herbst insertion (T1), following gap closure (T2) and de-bonding (T3). Parallelism of roots was controlled by panoramic x-rays at T3.
Results:The mean aplasia space at T0 was 7.5 mm (SD 2.6). Complete space closure was achieved in all 33 situations. The null hypothesis was rejected. There was a significant improvement in the initial canine relationships (mean 3.5 mm distal occlusion at T0) to a mean 0.1 mm at T3. When evaluated against the individual treatment plan, the following amounts of planned improvements were achieved: space closure 100%, canine relationship 97.5%, overjet 93.9%, overbite 96.4%, parallel roots in space closure site 93.9%.
Conclusion:Herbst telescope anchorage in combination with double-cable pull mechanics and a CCLA for orthodontic space closure can deliver predictable, high-quality treatment results.
* Correspondence:eklang@kfo-badessen.de
1Private Practice, Lindenstraße 44, Bad Essen 49152, Germany Full list of author information is available at the end of the article
© The Author(s). 2018Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Background
Finding adequate solutions for space management and oc- clusal adjustments in cases of isolated lower second pre- molar aplasia (ILSPA) is a frequently encountered challenge in clinical orthodontics, implantology and prosthodontics.
The types of teeth affected by aplasia are most commonly second premolars, followed by maxillary lateral incisors and maxillary second premolars [1, 2]. In contrast to patients with multiple dental aplasia, patients with ILSPA and other- wise complete dentition, including third molars, may bene- fit more from orthodontic gap closure than opting for either prosthodontic solutions, auto-transplantation or im- plants [3,4].
Third molars, which are often extracted in patients with complete dentition, may be used in this situation to com- pensate for excess space in the premolar aplasia region.
Orthodontic space closure can be performed whilst the pa- tient is a teenager without having to wait for growth to be completed, as required in implantological or prosthodontic treatment approaches [3,4]. A choice between these treat- ment options requires that the orthodontist exercises dili- gence in informing the patient and / or his guardians. For underage patients, decisions are most often made by their guardians and the orthodontist, and it is worth mentioning that the chosen solution for restoring the edentulous space will affect the patient for a lifetime [3].
While it has been widely regarded as favorable to treat cases of ILSPA in combination with maxillary counterbal- ancing premolar extraction, in order to achieve a proper molar and canine Angle-Class I occlusion in a convenient manner, concepts for ILSPA space management without maxillary counterbalancing extraction have been suggested as an alternative and valid treatment option [5–7]. Particu- larly in cases where there is no crowding in the upper arch or even with spacing, a counterbalancing extraction may not be considered appropriate. However, as a loss of canine anchorage may occur during space closure, this treatment approach is challenging: compromised occlusal results mea- sured in terms of the absence of proper canine guidance during laterotrusive mandible movements, as well as mid- line shifts, may be a consequence of inadequate anchorage control and space closure mechanics [3,8]. Therefore, good clinical practice suggests increasing anchorage during ILSPA space management by making use of inter-maxillary elastics,−telescopes, or - springs, if this is compatible with individual sagittal requirements, such as the presence of an Angle-Class I or II malocclusion [9].
Study objective
The aim of this study was to evaluate the effectiveness of Herbst telescope anchorage in combination with double-cable pull mechanics and a completely custom- ized lingual appliance (CCLA) for orthodontic space closure in ILSPA. The quality of the occlusal outcome
was determined by the deviation of the final canine oc- clusion from an Angle-Class-I and its consequences for overbite and overjet. The null hypothesis was that there is a significant deterioration towards an Angle-Class II canine relationship following complete space closure using molar mesialization.
Subjects Ethical approval
This retrospective study received full approval from the ethics commission of the Hannover Medical School (MHH; # 7727_BO_K_2018) prior to the commence- ment of data collection.
Patient recruitment
All patients who were treated with a CCLA (WIN; DW LingualSystems; Bad Essen, Germany) in one orthodon- tic center (Bad Essen, Germany) and de-bonded during the observational period from October 1st 2014 to Feb- ruary 28 2018 were consecutively screened for potential eligibility for this retrospective analysis. All treatment plans were approved by the same clinicians (DW, FB) prior to initiation of orthodontic treatment.
Inclusion and exclusion criteria
All patients meeting the following inclusion criteria were considered as potentially eligible:
(I-1) completion of second dentition including eruption of second molars;
(I-2) unilateral or bilateral aplasia of the lower second premolar;
(I-3) a treatment plan for lower molar mesialization, because of existing third molar;
(I-4) completed treatment with a completely custom- ized lingual appliance (CCLA) in combination with a Herbst appliance.
Exclusion criteria were:
(E-1) additional mandibular tooth aplasia other than lower second premolar or third molar aplasia;
(E-2) maxillary tooth aplasia other than third molar aplasia;
(E-3) counterbalancing maxillary extractions.
To minimise the risk of bias, no patient was excluded from this study for any other reason; in particular, bad compliance or missing records. This procedure was followed in order to evaluate not only the feasibility but, first and foremost, the predictability of the method.
Patients included in the study
Of all CCLA treatments completed during the recruitment period (de-bonding between October 1st 2014 and Febru- ary 28 2018), 123 patients (7%) were treated with a combin- ation of a CCLA and a Herbst appliance. Twenty-five subjects with an age range of 12.3 to 20.6 years (mean age
15.0 years/ SD 1.7 years) at the beginning of fixed lingual orthodontic treatment were eligible for trial assessments. A total of 33 situations with lower premolar aplasia space clo- sures (right / left sided 17 / 16) were assessed. Eight pa- tients had a bilateral aplasia, with unilaterally missing second premolars apparent in 17 situations.
Time points of assessment
Metric assessments were performed at the following time points: T0, immediately prior to bonding of the fixed lingual appliance; T1, initiation of anchorage reinforcement by adding Herbst telescopes; T2, comple- tion of gap closure and removal of Herbst telescopes;
T3, de-bonding of the fixed lingual appliance.
The mean ages of the patients at the single treatment steps between T0 and T3 are given in Table1.
Methods
Mechanics used for orthodontic space closure
The treatment involved the use of a completely custom- ized lingual appliance (WIN, DW LingualSystems, Bad Essen; Germany) in combination with a Herbst appliance (modified MiniScope, American Orthodontics, USA) for anchorage reinforcement [10]. Second molar brackets were designed with occlusal pads to reduce antagonistic interference. Space closure was achieved by two power chains as a double-cable mechanic device (Morita Energy Chain, Rocky Mountain Orthodontics) attached both lin- gually from first premolar to second molar and labially from the Herbst attachment to a buccal cleat on the first molar (Fig.1f). Initial load was set at 150 cN (1.5 N) per power chain, equal to about 300 cN per protraction mech- anic. As the alveolar processus in the area of the gap was, in many cases, extremely thin, the goal was to protract es- pecially the first molar in a slightly mesio-rotated position, in order to prevent a gingival recession on its mesial root.
Herbst telescope activation was based on individual re- quirements in a step-wise manner.
Retention
In addition to the standard retention protocol of placing a fixed 3–3 retainer, a labial fixed retainer was bonded from lower 4–6 at the de-bonding appointment, in order to prevent the aplasia space re-opening, and another one from upper 6–7, in order to prevent elongation of the upper second molar. In cases of pronounced Angle-class
II canine relationship at the beginning of lingual treat- ment, an activator was prescribed for night-time wear, in order to support the retention of the anterior/posterior correction [11].
Assessment of space closure, canine relationship, overjet and overbite by plaster casts and plaster target set-up models (T0, T3)
Plaster casts routinely prepared at T0 and T3 were uti- lized to assess space closure, canine relationship, overjet, and overbite. Wax bites taken in the subject’s centric re- lation were used to correctly position upper and lower plaster casts. The plaster target set-up models were mounted in the articulator. Assessment of overjet and overbite was performed on plaster models using the maximal distances between the upper and lower incisor labial surface or the maximal vertical incisor overlap.
The sagittal canine relationship was determined by assigning a value of zero (0) mm to a neutral (Angle-- Class I) canine relationship, i. e., the cusp of the lower first premolar is in contact with the upper canine and the upper first premolar. Deviations from neutral sagittal canine occlusion in the posterior direction (i. e., distal or Angle-Class II occlusion) were taken using a sliding cali- per (Dentaurum, Münchener Modell, Ispringen, Germany), and defined as positive distances (+ mm);
conversely, deviations in the anterior direction (mesial or Angle-Class III occlusion) were defined as negative values (− mm). All metric assessments were performed manually by one operator (EK) using a sliding caliper.
Assessment of space closure, canine relationship, overjet, and overbite photographs (T1, T2)
Measurements of the gaps between the first premolar and the first molar, as well as the canine and incisor re- lationships, were recorded and assessed at time points T1 and T2 using digital, high-resolution, intra-oral pho- tographs (D200, with Nikkor 105 mm; Nikon, Tokyo, Japan). Space dimensions were measured on occlusal photographs perpendicular to the occlusal plane using dental mirrors with dimensions 10.5 × 7.5 cm. Photo- graphs used for assessing the canine relationship, as well as the overbite and overjet, were taken directly (perpen- dicular to the canine’s labial surface, to avoid any poten- tial errors by distortion), using cheek retractors (NOLA, Chicago, IL, USA), without using mirrors.
Table 1Descriptive analysis of patients’ages at selected time points (T0, immediately prior to bonding of the fixed lingual appliance; T1, initiation of anchorage reinforcement by adding Herbst telescopes; T2, completion of space closure and removal of Herbst telescopes; T3, de-bonding of the fixed lingual appliance)
T0 T1 T2 T3
Age [years]: Mean 15.0 16.0 17.2 18.2
(SD; min.; max.) (1.7; 12.3; 20.6) (1.8; 13.3; 21.8) (1.8; 14.7; 22.9) (2.0; 15.5; 24.7)
In order to obtain the true dimensions of the assessed space magnitude, canines, and incisors on the digital pho- tographs, a calibration technique which had been pro- posed previously was employed [12]. The intraoral photographs were scaled to the corresponding plaster casts by adjusting the dimensions of the upper canine (for sagittal occlusion assessments in lateral view) or the lower first molar (for aplasia space dimension assessments in occlusal-view) and the incisors in the photograph to its corresponding dimensions taken from direct cast mea- surements. Deviations from neutral sagittal canine occlu- sion in the posterior direction (i. e., distal or Angle-Class II occlusion) were likewise taken using a sliding caliper.
Assessment of axial root inclination by panoramic x-rays Axial root inclination or the absence of parallelism of the roots was evaluated using panoramic x-rays directly following de-bonding (T3). Root angulation of teeth located in a mesial or distal juxtaposition to the site of aplasia (lower first premolars and molars) were judged using the index for root parallelism of the American Board of Orthodontics (ABO; [13]) which distinguishes between roots that are parallel, non-parallel, or contacting.
Method error analysis
In order to assess the method error for the measure- ments on plaster casts and intra-oral photographs, ten arbitrarily selected cases were evaluated at T0 (plaster casts) and T1 (please refer to photographs). These mea- surements were repeated after two weeks:
Me¼
ffiffiffiffiffiffiffiffiffiffiffi
Pd2
2n s
where d is the difference between the Measurements and n the number of assessments [14]. The results of the method error analysis are given in Table2.
Statistical data analysis
Measurement data were analyzed descriptively (mean, minimum, and maximum values with standard devia- tions). A comparison of dependent variables was carried out using the t-test.
The significance level was set toα= 5%. SPSS Statistics V_25 software for Windows 10 was used for all statis- tical tests (IBM, Armonk, NY, USA).
Fig. 1Presentation of a case: Initial situation prior to bonding of the fixed lingual appliance at T0 (a,b,c); Figs. A and B were taken following pre-treatment with removable functional appliances, hence the mandible is seen in a protruded sagittal position. Following leveling and aligning and initiation of anchorage reinforcement by adding Herbst telescopes at T2 (d,e,f), and at T3 following de-bonding of the fixed lingual appliance. Posterior maxillary 6–7 retainers aid in maintaining the vertical relation until lower third molars are brought into occlusal contact, while mandibular 4–6 retainers prevent re-opening of aplasia spaces (g, h, i). Panoramic x-rays show an adequate root parallelism after completion of aplasia space closure (j, k)
Results Space closure
On completion of fixed lingual orthodontic treatment (T3), all second premolar aplasia spaces were com- pletely closed, as planned in the target set-up, yield- ing a success rate of 100% (Table 3). With space closure and Angle-class II correction together, the molar relationship on the aplasia side was corrected on average by 10.9 mm.
Following leveling and aligning (T1, Table3), the mean aplasia space dimension was 6.5 mm. Overall duration of space closure produced a mean of 13.0 months (SD 5.5; min. / max. 3.6 / 25.7 months), equal to 0.57 mm per month (SD 0.26; min. / max. 0.11 / 1.35 mm). The differences between right and left sides were minimal (right-sided: 0.59 mm / months; SD 0.26; min. / max.
0.28 / 1.35 mm/ months; left-sided: 0.54 mm / months;
SD 0.26; min. / max. 0.11 / 1.25 mm/ months).
Canine relationship
On the aplasia side, at T0 (Table 3) a pronounced tendency for having a distal occlusion was observed, with a mean deviation of 3.5 mm. At T1, i. e., fol- lowing leveling and aligning, the mean extent of dis- tal occlusion increased insignificantly (p-value 0.064) to 4.3 mm, and dropped significantly following Herbst appliance removal (T2) (p-value 0.001) to a mean of 0.2 mm (Fig. 2). In 29 of the 33 canine re- lationships assessed, an Angle-class I sagittal canine relationship (0 mm) was achieved at T3, with an overall correction of 97.5% compared to the individ- ual treatment plan, the target set-up (Fig. 3). An im- provement in distal occlusion compared to T0 was
seen in all patients at T2. No significant changes in inter-canine relationships were noted between T2 and T3.
Overjet and overbite correction
At T0, the mean overjet was 4.0 mm (SD 1.6 mm) and increased highly significantly to a mean 5.1 mm (SD 2.3) following leveling and aligning (T1). It de- creased highly significantly to a mean 0.9 mm (SD 0.5) following the Herbst telescope treatment stage, with some sagittal overcorrection (0.9 mm, Table 3, Fig. 4) to address potential relapse in those patients who initially had distal occlusion. At T3, mean overjet was 1.9 mm (SD 0.4 mm). The mean overjet correction was 2.1 mm (93.9% of the planned movements).
Initial mean overbite was 4.4 mm (SD: 1.4, Table 3, Fig. 5). In all 25 patients, correction of deep bite was achieved by a mean 2.3 mm (SD: 1.2; min. / max. 0.5 / 4.5 mm) representing 96.4% of the planned movements.
There was a significant reduction in overbite during lev- eling and aligning (T1), with an additional reduction during Herbst treatment (T1-T2). Mean overbite at the end of treatment was 2.2 mm (SD 0.6).
Root angulation following space closure
In 31 of 33 cases (93.9%), the roots of the lower first pre- molars and those of the first molars were parallel follow- ing aplasia space closure. The roots adjacent to two aplasia situations (6.1%) were not parallel at T3. How- ever, contact between adjacent roots was not seen in any of the 33 cases.
Table 2Error analysis for the two methods used
Method error Space magnitude Canine relationship Overjet Overbite
T0 [mm] plaster cast 0.19 0.27 0.35 0.16
T1 [mm] photograpy 0.49 0.47 0.30 0.53
Table 3Occlusal features: Descriptive analysis of space magnitude and sagittal inter-canine relationships for the aplasia side, overjet and overbite at the selected assessment time points
T0 T1 T2 T3
Space magnitude [mm]: Mean 7.5 6.5 0.0 0.0
(SD; min.; max.) (2.6; 2.5; 11.0) (2.3; 1.5; 11.5) (0.0; 0.0; 0.0) (0.0; 0.0; 0.0)
Canine relationship [mm]: Mean 3.5 4.3 0.2 0.1
(SD; min.; max.) (2.2; 0.0; 7.0) (2.2; 0.5; 7.7) (1.0;−1.2; 3.3) (0.3; 0.0; 1.0)
Overjet [mm]: Mean 4.0 5.1 0.9 1.9
(SD; min.; max.) (1.6; 2.0; 8.0) (2.3; 1.1; 10.2) (0,5; 0.0; 1.8) (0.4; 1.0; 3.0)
Overbite [mm]: Mean 4.4 3.0 1.0 2.2
(SD; min.; max.) (1.4; 2.0; 6.5) (1.2; 0.9; 6.0) (0.9;−1.1; 3.1) (0.6; 1.5; 4.0)
Deviations from neutral sagittal canine relationship towards an Angle-Class II were defined as positive distances (+ mm); conversely, deviations in the anterior direction towards an Angle-Class III were defined by negative values (−mm). All values are given in mm
Treatment duration
Total mean duration of treatment with the fixed lin- gual appliance (T0-T3) was 38.4 months (SD 7.6;
min./max. 19.6 months; 52.4 months). Leveling and aligning (T0-T1) took a mean 12.0 months (SD 3.4;
min./max. 7.6 / 21.9 months), while Herbst treatment
(T1-T2) stage took a mean 13.8 months (SD 4.1;
min./max. 3.6 / 21.6 months), with active aplasia space closure durations of 13.0 months. Further oc- clusal adjustments following space closure (T2-T3) took a mean 12.6 months (SD 5.0; min. / max. 4.6;
22.3 months).
Fig. 2Canine relationship development during treatment at the site of aplasia. The deviation from a canine-Angle Class-I is given in mm. See text for details
Fig. 3Success rate for canine relationship correction compared to the individual treatment plan (target set-up)
Discussion
To the best of our knowledge, the present study is prob- ably the first study to provide evidence regarding the rarely addressed subject of molar mesialisation using Herbst appliance anchorage in cases of lower aplasia gap closure without counterbalancing extractions. Clinical rec- ommendations have been based on case reports [3,8] and
retrospective studies on a smaller number of patients, treated for 2.2–3.1 years, with push-and-pull mechanics [5,7] or Jasper-Jumper [6].
Study design
This study had a retrospective design. However, all patients who were de-bonded within the time frame
Fig. 4Overjet development (in mm) during treatment. In cases with an initial Angle-Class II-malocclusion, the sagittal incisor relation has been temporarily over-corrected into an edge-to-edge relation at T2
Fig. 5Overbite development (in mm) during treatment
of forty-one months prior to starting any assessments were screened for eligibility. In order to evaluate the predictability of the concept, no subject who met the inclusion criteria was excluded because of a lack of compliance, missing records, insufficient oral hygiene, or similar reasons.
Method error
The reproducibility of the methods used here is judged to be adequate for assessing the occlusal changes in this study, as the variation in repeated plaster cast measure- ments varied between 0.16 and 0.35 mm, and for the photograph method between 0.3 and 0.53 mm (Table2).
Null hypothesis
The null hypothesis that there would be a significant deteri- oration in the inter-canine relationship towards an Angle-Class-II occlusion, in terms of a loss of anterior an- chorage following space closure by molar mesialization, was rejected. There was not only no deterioration in the initial mean sagittal canine relationships (mean 3.5 mm de- viation at T0), but instead a highly significant (p< 0.001) reduction to a mean 0.1 mm at T3 (Tables3and4).
Difficulties in achieving proper canine guidance in cases of ILSPA– mainly due to biomechanical require- ments - have been described previously [3, 6]. Pure mesialization is desired in cases of ILSPA in combin- ation with Angle-Class I occlusion, but reciprocal effects of common space closure mechanics contribute to a typ- ical loss of anchorage and resulting midline shifts [8].
Moreover, an Angle-Class II occlusion in combination with ILSPA elevates the treatment difficulty level clearly.
Therefore, Herbst appliance or Jasper-Jumper anchorage has been proposed to limit the reciprocal effects of space closure on sagittal occlusion [6, 12]. This appears to be advantageous compared to mini-screw anchorage, not only in terms of space closure durations, but particularly in cases in which there is an existing Angle-class II oc- clusion [12].
Speed of space closure
The mean speed of space closure was found to be 0.57 mm / month, which is slightly (12%) increased compared to those reported by Metzner et al. (0.51 mm / month) [12]. This may be explained by this study
having utilized a Herbst telescope system (WIN appli- ance, DW Lingualsystems, Bad Essen, Germany) which is less susceptible to appliance fractures or failures [10]
than the appliance of the type used by Metzner et al. (In- cognito appliance, 3 M Top Service für Lingualtechnik, Bad Essen, Germany) [12,15]: When using a Herbst ap- pliance or a Jasper-Jumper as anchorage during molar mesialisation, it is crucial to keep the rate of appliance fractures low, in order to achieve reduced treatment dur- ation by a continuous space closure strictly from a pos- terior direction, without anchorage or interruption of fixed treatment. The Herbst appliance in combination with the CCLA used here is considered to be suitable for this purpose, based on previous research outcomes [10]. The telescopes of the Herbst appliance are not dir- ectly connected to the lingual appliance, thereby avoid- ing arch-wire fractures which would otherwise produce additional repair appointments.
Overjet and overbite correction
Successful overjet reduction with a satisfying sagittal inter-incisal relation was accomplished in 24 of 25 pa- tients. Reductions in overjet by Herbst therapy has been reported to vary from 3.1 to 6.9 mm. However, the pur- pose of these studies was to achieve sagittal mandibular enhancement and they were based on samples with lar- ger initial overjets [16–18]. In our study, the Herbst tele- scopes were used primarily for anchorage reinforcement and, because of the inclusion of patients with initially neutral occlusion, the sample taken may have had less pronounced overjets compared to studies on the subject of Angle-Class II-correction effectiveness.
Deep overbite has been reported to be commonly asso- ciated with aplasia [19, 20]. Deep overbite corrections in this study were observed to have a mean of 2.3 mm (min.
/ max. 0.5 / 4.5 mm; SD 1.2), which is in line with previous reports on Herbst appliance therapy [21,22]. With the ex- ception of two patients who had a normal overbite by the start of treatment, overbite reduction was finally achieved in all 23 other patients. At T3, three patients had a slightly increased overbite, as a trend, with overbites of 3 or 4 mm, respectively. Although the initial overbite of the lat- ter was, with a value of 6.5 mm, distinctively more pro- nounced compared to the mean initial overbite of the sample (Table3), inadequate deep bite correction may be
Table 4Space magnitude, sagittal inter-canine relationships, overjet, and overbite: Non-parametric comparison of dependent samples using the t-test
p-Value T0–T1 T0–T2 T0–T3 T1–T2 T1 - T3 T2–T3
Space magnitude 0.01 < 0.001 < 0.001 < 0.001 < 0.001 n. s.
Canine relationship n. s. < 0.001 < 0.001 < 0.001 < 0.001 n. s.
Overjet 0.002 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001
Overbite < 0.001 < 0.001 < 0.001 < 0.001 0.003 < 0.001
attributed to a lack of proper upper and lower incisor third order control and underlines the need for choosing arch-wires with adequate dimensions or third order over- corrections in cases of ILSPA.
Root angulation following space closure
Parallelism of the roots of the first molar and those of the first premolar following gap closure was observed in 31 out of 33 situations. In two situations a mesial angulation of the premolar roots was observed and this is most likely due to using elastic chains with an under-dimensioned, incom- pletely slot filling 0.016 × 0.024“steel arch-wire (slot dimen- sions: 0.018 x 0.025”), with some proportion of a vertical bowing effect. Bracket slots with larger mesio-distal dimen- sions may reduce this problem.
Treatment duration and clinician’s experience
Despite the existence of several reports on the orthodontic treatment of ILSPA, information about treatment duration is scarce [5–7]. Zimmer and Rottwinkel [6] reported a duration of mean active ILSPA space closure treatment of 3.1 years (37 months)(min. / max. 2.4 / 3.1 months), which is similar to our results, although the extent of molar mesialisation during orthodontic space closure reported by those authors was smaller than in our patients. Ortho- dontic treatment duration in those cases of ILSPA assessed by this study had a mean of 39.3 months, thereby distinctly exceeding average treatment durations of con- ventionally / labially bonded orthodontic cases without the need for space closure by congenitally missing teeth (20.02 mo; [23]). Levelling and aligning required a mean 12.0 months in the actual study cases. However, we ob- served a decrease in average treatment duration with in- creasing experience collected while treating the first patients of this study. The experience of the clinician seems to have an influence and Fig.6provides some evi- dence of the effect of an increasing training curve, reflected in a manifest reduction in mean treatment times of patients bonded later during the observation time
frame. Based on the experiences gained whilst treating these patients, it is advisable to use elastic chains between lower first premolars early in treatment, in order to reduce the time until incorporation of the Herbst telescopes.
Also, the use of steel ligatures early in treatment is consid- ered to be helpful in angulation control of lower canines and may indeed speed up treatment.
Alternatives to aplasia space closure
ILSPA gap management can be addressed by a variety of di- verse treatment approaches, each of which having both ad- vantages and disadvantages [3]. Potential treatment options mostly involve abundant mesio-distal enamel reduction of deciduous second molars, in order to prepare these teeth for a premolar-shaped crown. The disadvantages of this ap- proach may be the risk of damaging the pulp during reduc- tion and the questionable long-term prognosis for milk molars with distinctively shorter roots [3,24]. On the other hand, this approach provides a much quicker solution than orthodontic space closure. Other viable treatment options include the use of bridges, implants, or auto-transplants [3, 25]. A success rate of auto-transplanted third molars to re- place premolars has been reported to be 85% after 3.3 years, but also requires subsequent orthodontic treatment to pre- vent increased failure rates due to persistent infra-occlusion and ankylosis [25,26], which are also the typical problems maintained primary molars [3]. The advantage of protract- ing molars into edentolous areas would be a much better long-term prognosis and, in the case of the presence of third molars, the opportunity to close the gap without using ma- terial that may require renewal at some point in the future.
One should bear in mind that ILSPA patients presenting to orthodontists are mostly under-aged and unable to fully evaluate the consequences of the various treatment options.
The method proposed by this study offers a sustainable so- lution for replacing deciduous molars without utilizing ex- traneous material whilst preserving third molars [5], and also provides for adequate control of typical side-effects, such as anchorage loss or incomplete space closure.
Fig. 6Treatment duration related to start of CCLA treatment: The learning curve as a trend line is indicated in red
Conclusion
Based on the results of this retrospective study on ILSPA gap management using Herbst anchorage reinforcement and a double-cable pull mechanic with a completely cus- tomized lingual appliance, the following conclusions can be drawn:
Space closure was achieved in all cases.
Loss of anchorage during space closure is clinically well controllable, as Herbst anchorage seems to compensate distalizing forces of the double-cable mechanic, thereby providing the basis for adjusting an adequate inter-canine relationship in accordance with the Angle-Class-I occlusion concept.
The proposed technique is therefore considered to be a clinically viable treatment option for ILSPA gap management.
The experience level of the clinician appears to have an influence on treatment duration.
Acknowledgements
The authors would like to thank Sabine Ruf and Hans Pancherz for their re-introduction of Herbst appliance treatment to the orthodontic community and their fundamental evaluation of this important scientific concept.
Funding
The project did not receive any funding.
Availability of data and materials
All data and materials are available upon request at the following address:
Private practice Prof. Dr. Wiechmann & Dr. Beyling & Kollegen; Lindenstraße 44, 49,152 Bad Essen, Germany.
Authors’contribution
EK and DW initiated the investigation. EK, MK and DW designed the study.
FB, EK and DW supervised the treatment and treated the patients. EK collected and analysed the data and wrote the manuscript. MK and DW revised the manuscript. All authors read and approved the final manuscript.
Ethics approval and consent to participate
This retrospective study received full approval from the ethics commission of Hannover Medical School (MHH; # 7727_BO_K_2018) prior to the commencement of data collection.
Consent for publication
All patients signed a written consent form.
Competing interests
DW is the inventor of the completely customized lingual appliance WIN and owner of the DW LingualSystems, Bad Essen, Germany. All other authors don’t have any competing interests.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Author details
1Private Practice, Lindenstraße 44, Bad Essen 49152, Germany.2Department of Orthodontics, University Medical Center UMG, Robert-Koch-Straße 40, 37075 Göttingen, Germany.3Department of Orthodontics, Universidad de La Frontera UFRO, Avenida Francisco Salazar, 01145 Temuco, Chile.4Private Practice, Lübecker Straße 128, Hamburg 22087, Germany.5Department of Orthodontics, Hannover Medical School MHH, Carl-Neuberg-Straße 1, 30625 Hannover, Germany.
Received: 3 July 2018 Accepted: 18 September 2018
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13
2. Zusammenfassung
2.1 Einleitung
2.1.1 Hintergrund
Nichtanlagen von einzelnen oder mehreren Zähnen stellen den am häufigsten vorliegenden Befund im Bereich der dentofazialen Fehlbildungen dar [1]. Hierbei unterscheidet man die Phänotypen der Hypodontie, Oligodontie und Anodontie, wobei die dritten Molaren in der Definition nicht berücksichtigt werden [2-4]. Eine Hypodontie liegt vor, wenn bis zu sechs Zähne fehlen. Sind mehr als sechs Zähne nicht nachzuweisen, so spricht man von einer Oligodontie [5]. Davon abzugrenzen ist die Anodontie, das komplette Fehlen der Dentition.
Bei Hypodontien können nicht-syndromale Formen von syndromalen Formen unterschieden werden. Weiterhin sind kongenitale von erworbenen Formen abzugrenzen. Die Ursachen für nicht-syndromale Hypodontien können genetischen Ursprungs sein: Hier werden Mutationen der Gene MSX1, PAX9, AXIN2, PITX2, FGFRI, TGFA, EDA als mögliche Ursachen beschrieben [6-9].
Auch bei Patienten mit Lippen-Kiefer-Gaumenspalten treten vermehrt Nichtanlagen auf [10, 11]. Äußere Einflüsse wie Chemotherapeutika [12-14] und Pharmaka, beispielsweise Thalidomid [15, 16], oder ionisierende Strahlung [17, 18] können ebenfalls zur Zahnunterzahl führen. Hypodontien können auch mit der Ektodermalen Dysplasie, dem Apert- oder Down-Syndrom assoziiert sein und werden damit dem syndromalen Formkreis zugesprochen [19, 20].
Die am häufigsten vorkommende Nichtanlage ist die des zweiten Prämolaren im Unterkiefer, gefolgt vom Fehlen der lateralen Oberkieferinzisiven und der zweiten Oberkieferprämolaren [4, 21-25]. Die Prävalenz der Nichtanlagen in Bezug auf Geschlecht und Rassenzugehörigkeit unterscheidet sich deutlich. So sind Frauen häufiger von Aplasien betroffen als Männer [3, 25-28].
14 2.1.2 Differentialtherapeutische Aspekte bei Nichtanlage des zweiten unteren Prämolaren
Bei einer Nichtanlage des zweiten unteren Prämolaren kann der zweite Milchmolar als Interimslösung im Sinne eines Platzhalters für eine spätere prothetische oder implantat-prothetische Versorgung belassen werden. Ein derartiges Vorgehen ist aber nur sinnvoll, wenn keine Ankylose des Milchmolaren vorliegt, die eine Wachstumshemmung des Alveolarfortsatzes in diesem Bereich induzieren kann [29, 30]. Ist der Milchmolar kariesfrei und seine Wurzel gut ausgebildet, ergibt sich zumeist eine gute Prognose. Ein Verbleiben im Mund ist aber häufig höchstens bis in die dritte oder im äußersten Fall bis in die vierte Lebensdekade möglich [31-33].
Da die mesio-distale Breite der zweiten Milchmolaren etwas größer ist als die ihrer natürlichen Nachfolger, können sie im Rahmen einer kieferorthopädischen Behandlung durch mesiale und distale Schmelzreduktion in ihrer Größe angepasst werden, um eine gute Verzahnung zu erreichen [34]. Ist im betroffenen Quadranten ein Weisheitszahn angelegt, so muss dieser allerdings häufig später aus Platzgründen entfernt werden.
Ist der zweite Milchmolar nicht mehr erhaltungswürdig, stehen neben der konventionellen prothetischen Versorgung in Form von Brücken auch implantat- getragene Einzelkronen als Langzeitversorgung zur Verfügung. Insbesondere bei kariesfreien Nachbarzähnen hat die implantat-getragene Einzelkrone Vorteile [34-36]. Die Implantation sollte aber erst nach dem Wachstumsabschluss erfolgen [37-39].
Auch eine Autotransplantation von Weisheitszähnen kann durchgeführt werden, um einen fehlenden Zahn zu ersetzen [40]. Sogar Prämolaren des Oberkiefers können in den Unterkiefer autotransplantiert werden [41, 42]. Hierbei ist der Erfolg der Autotransplantation maßgeblich vom Wachstumsstand der Wurzel des zu transplantierenden Zahnes abhängig. Sind erst 50-75% des Wurzelwachstums abgeschlossen, können Erfolgsquoten von über 90% erreicht werden [43, 44].
Eine derartige Vorgehensweise erfordert im Regelfall eine kieferorthopädische Vor- und/oder Nachbehandlung.
15 2.1.3 Der kieferorthopädische Lückenschluss
Im Rahmen einer kieferorthopädischen Behandlung kann es sinnvoll sein, einen kieferorthopädischen Lückenschluss vorzunehmen. Folgende Aspekte sollten bei der Therapieplanung berücksichtigt werden:
- Platzverhältnisse (Platzüberschuss, Platzmangel)
- Zahnzahl (Anlage von dritten Molaren, weitere Nichtanlagen) - sagittale Relation (Neutral-, Distal- oder Mesialokklusion) - Gesichtsprofil (Ästhetiklinie, Nasolabialwinkel)
- Mittellinienübereinstimmung (Ober- und Unterkiefermitte zueinander und zur Gesichtsmitte)
- Inklination der Inzisiven im Ober- und Unterkiefer (norminkliniert, rekliniert, prokliniert)
- skelettaler Wachstumstyp (horizontal, vertikal, neutral)
Bei nicht angelegten zweiten Unterkieferprämolaren kann abhängig vom Gesamtbefund der kieferorthopädische Lückenschluss in Kombination mit Ausgleichsextraktionen in den nicht betroffenen Kieferquadranten durchgeführt [45-47]. Diese Therapiemöglichkeit ist insbesondere gegeben, wenn ein ausgeprägter Engstand im Oberkiefer-Zahnbogen vorliegt. Zum Lückenschluss werden festsitzende kieferorthopädische Apparaturen eingesetzt, weil nur diese die notwendigen, dreidimensional kontrollierten Zahnbewegungen ermöglichen, die für eine derartige Zahnstellungskorrektur erforderlich sind. Diese Apparaturen können bukkal und auch auf der Zahninnenseite (lingual) angebracht werden, was insbesondere bei jugendlichen Patienten neben den offensichtlichen ästhetischen Vorteilen auch aus kariesprophylaktischer Sicht günstig ist [48-55]. Zudem lassen sich linguale festsitzende Apparaturen relativ unkompliziert mit einer Herbst- Apparatur als Verankerungseinheit zum Lückenschluss kombinieren, die dann zeitgleich mit ihren Teleskopen an den vestibulären Zahnflächen der zweiten Prämolaren und ersten Molaren des Oberkiefers und den Eckzähnen und ersten Prämolaren des Unterkiefers jeder Seite befestigt wird. Herbst-Apparaturen werden in der Kieferorthopädie in erster Linie zur Behandlung eines Distalbisses eingesetzt, können aber auch gleichzeitig oder ausschließlich als selektives
16 Verankerungsinstrument dienen [56-62]. Da die Herbst-Apparatur ebenfalls festsitzend ist, erfolgt die Distalbisskorrektur beziehungsweise die selektive Verankerung patientenunabhängig, was das Erreichen des Behandlungsziels im Sinne einer bilateral gesicherten Okklusion begünstigt und so die langfristige Stabilität der Okklusion unterstützt [63, 64].
Kombiniert man die linguale Apparatur mit der Herbst-Apparatur, ist es möglich, im Bereich der Unterkiefernichtanlagen einen Lückenschluss durch Mesialisierung der Molaren zu erzielen. In diesem Fall könnte ein kieferorthopädischer Lückenschluss ohne Ausgleichsextraktionen in den anderen Quadranten erfolgen.
Trotz der offensichtlichen Vorteile eines solchen Konzeptes wird es von Kieferorthopäden nicht oft angewandt und noch seltener nachuntersucht [65-69].
Ein Grund hierfür ist sicher die Befürchtung eines Scheiterns des Behandlungsplans aufgrund einer insuffizienten Verankerung. Diese wäre zu erkennen an einer deutlichen Verschlechterung der Eckzahnbeziehung auf der betreffenden Seite.
Aus dieser Überlegung ergibt sich direkt die Fragestellung der vorliegenden Untersuchung. Die Nullhypothese lautet: Ein einseitiger Lückenschluss von distal ist zuverlässig und reproduzierbar nicht möglich, ohne die Eckzahnbeziehung auf der betreffenden Seite in Richtung einer Distalokklusion zu verschlechtern.
Um ein umfassenderes Bild über die Qualität der Behandlungsergebnisse zu erlangen, wurde in der vorliegenden Studie zusätzlich die Größe des horizontalen und vertikalen Überbisses bestimmt. Abschließend wurde auch die Parallelität der Wurzeln nach erfolgtem Lückenschluss beurteilt.
17 2.2 Diskussion
2.2.1 Studiendesign
Für die Studie wurden die Behandlungsunterlagen von 25 konsekutiv in der Therapie abgeschlossenen Patienten einer kieferorthopädischen Fachpraxis (Prof.
Wiechmann und Dr. Beyling, Bad Essen, Deutschland) retrospektiv ausgewertet.
Der Initialbefund zeigte eine Aplasie von einem oder beiden zweiten Prämolaren im Unterkiefer bei gesicherter Anlage des dritten Molaren auf der Aplasie-Seite.
Bei acht Patienten waren die Nichtanlagen beidseitig, bei den anderen 17 Patienten einseitig. Es konnten somit 33 Quadranten mit jeweils einer Aplasie beurteilt werden. Der Behandlungsplan sah vor, im betroffenen Quadranten beide Unterkiefermolaren (6-Jahr-Molar und 12-Jahr-Molar) zu mesialisieren und somit einen vollständigen Lückenschluss von distal zu erzielen. Bei keinem dieser Patienten erschien nach Auswertung der Anfangsdiagnostik eine Ausgleichsextraktion in den nicht betroffenen Quadranten indiziert. Alle Patienten wurden mit der vollständig individuellen lingualen Apparatur (VILA) WIN (DW Lingual Systems, Bad Essen, Deutschland) in Kombination mit der Herbst- Apparatur behandelt [70].
Zur Auswertung wurden Gipsmodelle vor Eingliederung der VILA und am Ende der aktiven Behandlung (T0 und T3), sowie hochauflösende intraorale Fotos vor dem Einsetzen der Herbst-Apparatur und nach dem Entfernen der Herbst- Apparatur (T1 und T2) herangezogen. Mittels der routinemäßig in der Praxis erstellten Behandlungsunterlagen wurden zu den jeweiligen Zeitpunkten die Lückengröße auf der Aplasie-Seite, die Eckzahnbeziehung sowie der horizontale und vertikale Überbiss gemessen und ausgewertet. Da zur Herstellung vollständig individueller lingualer Apparaturen immer ein individuelles Set-up erstellt wird, um das Behandlungsziel zu definieren, ist es zudem bei der Ergebnisbeurteilung möglich, die durchgeführten Zahnbewegungen mit den auf dem Set-up geplanten Zahnbewegungen zu vergleichen [71].
Zur Beurteilung der Parallelität der Zahnwurzeln des ersten Prämolaren und des ersten Molaren nach erfolgtem Lückenschluss wurde die Panoramaschichtaufnahme am Ende der Behandlung ausgewertet [72].
18 2.2.2 Lückenschluss auf der Aplasie-Seite des Unterkiefers
Nach der Nivellierungsphase, unmittelbar vor dem Einsetzen der Herbst-Apparatur (T1) betrug die durchschnittliche Lückengröße auf der Aplasie-Seite 6,5 mm (SD:
2,3 mm; min: 1,5 mm; max: 11,5 mm). Am Behandlungsende waren in allen 33 Quadranten die Lücken im Bereich der Aplasie vollständig geschlossen. In diesem Punkt konnte das Ziel-Set-up zu 100% umgesetzt werden. Studien zu VILAs im Rahmen der Versorgungsforschung beschreiben eine ähnliche Umsetzbarkeit der Behandlungsplanung, allerdings bei andersartigen Behand- lungsaufgaben [65, 73-76]. Die Dauer des Lückenschlusses betrug im Mittel 13 Monate (SD: 5,5 mm; min: 3,6 mm; max: 25,7 mm) bei einer durchschnittlichen Lückenschlussgeschwindigkeit von 0,57 mm pro Monat (SD: 0,26 mm; min: 0,11 mm; max: 1,35 mm). Der Lückenschluss konnte somit etwas schneller (0,51 mm pro Monat ) als in einer vergleichbaren Studie durchgeführt werden [65], was sowohl auf eine geringere Reparaturanfälligkeit als auch auf die größere Erfahrung der Behandler zurückgeführt werden kann [70].
2.2.3 Die Nullhypothese wurde widerlegt
Zur Einordnung der Nullhypothese ist eine genaue Betrachtung der Eckzahnbeziehung zu den verschiedenen Zeitpunkten erforderlich. Ein kompletter Lückenschluss im Unterkiefer entspricht zwar der initialen Behandlungsplanung, er sollte aber idealerweise ausschließlich von distal erfolgen. Ein auch nur geringfügiges Schließen der Lücke von mesial hätte zwangsläufig eine Verschlechterung der Eckzahnbeziehung in Richtung eines Distalbisses zur Folge und würde die Nullhypothese bestätigen.
Bei keinem Patienten kam es während der Behandlung zu einer Verschlechterung der Eckzahnbeziehung. Zu Behandlungsbeginn lag in unserem Untersuchungsgut ein Distalbiss von durchschnittlich 3,5 mm (SD: 2,2 mm; min: 0,0 mm; max: 7,0 mm) vor. Eine Verschlechterung (p-Wert: 0,064) des Distalbisses zum Zeitpunkt T1 auf 4,3 mm (SD: 2,2 mm; min: 0,5 mm; max: 7,7 mm) war zu erwarten, da nach Einsetzen einer VILA und vor Einsetzen der Herbst-Apparatur eine Aufrotation des Unterkiefers nach kaudal und dorsal auftreten kann. Nach Entfernung der Herbst-
19 Apparatur zeigte sich die sagittale Eckzahnbeziehung auf im Mittel 0,2 mm (SD: 1,0 mm; min: -1,2 mm; max: 3,3 mm) und damit höchst signifikant (p-Wert < 0.001) verbessert. Am Behandlungsende betrug die sagittale Eckzahnbeziehung 0,1 mm (SD: 0,3 mm; min:0,0 mm; max: 1,0 mm). Es konnte also nicht nur eine Verschlechterung der Eckzahnbeziehung verhindert werden, es wurde sogar eine Verbesserung erzielt. Damit wurde die Nullhypothese widerlegt.
Beim Vergleich mit dem Ziel-Set-up wird eine 97,5 %ige Umsetzung der angestrebten Korrektur der Eckzahnbeziehung deutlich.
In anderen Untersuchungen wurde ein Lückenschluss primär durch den Einsatz von intermaxillären Gummizügen angestrebt [66, 67, 77]. Für den Behandlungserfolg ist dabei aber, anders als beim Einsatz einer Herbst-Apparatur, die Mitarbeit des Patienten die wesentliche Voraussetzung.
Auch die Verwendung von Minischrauben zur Mesialisierung von Unterkiefermolaren stellte sich in der Vergangenheit nicht als wirklich zuverlässige Verankerungsmethode dar [65]. Zudem kann durch den Einsatz von Mini- schrauben beim Lückenschluss eine zu Beginn der Behandlung bestehende distale Eckzahnbeziehung nicht verbessert werden. Auch hier müsste dann wieder ein patientenabhängiger Einsatz von intermaxillären Gummizügen mit der oben beschriebenen Problematik erfolgen, um eine gesicherte Interkuspidation einzustellen. Diese ist besonders für ein langfristig stabiles Ergebnis erforderlich [78, 79].
2.2.4 Weitere qualitätsrelevante Parameter
Korrektur des horizontalen Überbisses (Overjet)
Zu Behandlungsbeginn lag der durchschnittliche Wert für den horizontalen Überbiss bei 4,0 mm (SD: 1,6 mm; min: 2,0 mm; max: 8,0 mm). Mit der Ausformung der Zahnbögen und teilweisen Aufrichtung der Frontzähne stieg dieser Wert auf 5,1 mm (SD: 2,3 mm; min: 1,1 mm; max: 10,2 mm) vor Insertion der Herbst-Apparatur an. Nach der Herbst-Phase standen die Frontzähne von Ober- und Unterkiefer aufgrund der geplanten Überkorrektur zur
20 Rezidivprophylaxe in Kopfbissposition. Über die gesamte Behandlung konnte der horizontale Überbiss im Mittel von 4,0 mm auf 1,9 mm (SD: 0,4 mm; min: 1,0 mm;
max: 3,0 mm) verringert werden. Das entspricht 93,9% der auf dem Ziel-Set-up angestrebten Korrektur und ist Ausdruck einer höchst signifikanten Verbesserung (p-Wert <0,001). Es ist zu berücksichtigen, dass bei Klasse II/2-Patienten nicht nur ein Distalbiss vorliegt, sondern auch eine deutlich reklinierte Oberkieferfront. Für die Einstellung einer Neutralokklusion ist nicht nur die sagittale Bisslagekorrektur durch die Herbst-Apparatur notwendig, sondern es ist zusätzlich auch die Aufrichtung der Oberkieferfrontzähne erforderlich. Eine unzureichende Aufrichtung würde entsprechend eine Distalokklusion im Seitenzahnbereich zur Folge haben.
Des Weiteren muss die linguale Apparatur den Torque der Oberkieferfrontzähne kontrollieren und in der Regel auch verbessern, da der Einsatz der Herbst- Apparatur eine Reklinierung der Oberkieferfrontzähne und eine Proklinierung der Unterkieferfrontzähne induziert. Die vollständig individuelle linguale Apparatur kann diese Anforderungen aufgrund der präzisen Slotdimension und der präzise hergestellten Bögen erfüllen [74-76].
Korrektur des vertikalen Überbisses (Overbite)
Bei allen 23 Patienten, die neben der Nichtanlage auch einen zu großen vertikalen Überbiss aufwiesen, konnte dieser in Richtung des Normwertes verbessert werden. Zwei Patienten hatten schon zu Beginn der Behandlung einen normwertigen Überbiss, so dass hier keine therapeutische Bisshebung erfolgen musste. Im Planungsmodell wurde dies entsprechend berücksichtigt. Zum Zeitpunkt T0 betrug der vertikale Überbiss im Mittel 4,4 mm (SD: 1,4 mm; min: 2,0 mm; max: 6,5 mm) und verbesserte sich auf durchschnittlich 2,2 mm (SD: 0,6 mm;
min: 1,5 mm; max: 4,0 mm). Drei der 25 Patienten wiesen bei Behandlungsbeginn einen extremen Tiefbiss mit Werten von 5 mm bis 6,5 mm auf. Auch bei diesen Patienten konnte der vertikale Überbiss auf Werte von 3,0 mm bis 4,0 mm reduziert werden. Im Vergleich zum Ziel-Set-up konnte im Mittel 96,4% der angestrebten Korrektur klinisch umgesetzt werden.
Bei einer Tiefbisskorrektur mit festsitzenden Apparaturen wird die sagittale Kompensationskurve durch eine Extrusion der Seitenzähne und Intrusion der Frontzähne nivelliert. Hier zeigen vollständig individuelle linguale Apparaturen im
