The use of the Herbst appliance as an anchoring tool and modification for various treatment tasks is hardly established in orthodontics and only rarely described in the literature [17,18].
The cast splint Herbst appliance belongs to the rigid, bimaxillary Class II mechanisms, which allow the mouth to be opened by means of a telescopic mechanism and the lower jaw to be held in the desired target position [1]. In this study, only cast splint Herbst appliances were used to allow modifications to the appliance itself. Due to its support on several anchor teeth in the upper and lower jaw, it can be used as a multifunctional anchoring tool. The Herbst appliance can also be used as a passive anchoring tool if a class II malocclusion is not present.
If additional correction of the class II jaw relationship is desired, the Herbst appliance is the most effective treatment device [7,11,16]. The ideal time for insertion of the Herbst appliance is indicated after the pubertal growth peak until the end of pubertal growth [10]. In this study, the mean age was 15.6 years (σ=5.6). This insertion period is supported by studies on treatment with the Herbst appliance also in early adulthood or later adolescence and produces comparable success for Class II correction as immediately after the pubertal growth peak [10,21].
The gender distribution also corresponds to previous studies on Class II treatment with the Herbst appliance [11,15].
Due to the multifunctionality of this cast splint Herbst appliance, which could be shown in this retrospective study, the patient's wish for as non-invasive a procedure as possible can be fulfilled. Furthermore, fixed dentures and implants can be avoided, for example, in the case of aplasia of teeth with previously performed orthodontic space closure (Fig. 5). In addition, compensation extractions can also be avoided due to a lack of experience on the part of practitioners with regard to the possibility of therapy with the Herbst appliance to close the space if the indication is correct and the ideal function and aesthetics are nevertheless achieved [22,23].
Springy, bimaxillary Class II mechanics such as the Forsus spring, Jasper jumper and Sabbagh Universal Spring (SUS and rigid Class II mechanics such as the andibular anterior repositioning appliance MARA leave little room for modifications to the appliance itself and thus the solution of multifunctional treatment tasks due to its design. Here, the delicate design and the resulting increased wearing comfort play a greater role for the patient and can be used almost exclusively for sagittal mandibular correction in the anterior direction if there is a transverse congruence of both jaws. [12]. Zimmer et al. describe in their study the use of Jasper Jumper for uni- as well as bilateral space closure in the mandible after anchorage loss in the anterior mandiblewith compression-tension mechanics and class II elastic bands [23]. These push-pull mechanics and class II rubber bands require a high level of patient cooperation and compliance. The use of the Herbst appliance as anchorage for space closure in the molar region of the lower jaw in combination with a Class II treatment was 65 % prevalent in the University Medical Center and 15 % in the orthodontic practice during the study period (Fig. 5). In the literature, the occurrence of aplasia of teeth is stated as approx. 6.7 %. This affects 41 % of the second lower premolars and 13 % of the first lower premolars [24]. Anchoring problems to close the space can thus also be solved in combination with a class II malocclusion. Studies on the use of the Herbst appliance for mesialization of molars in the mandible in combination with a lingual bracket system can be found [17]. Here, Metzner et al. were even able to determine significantly faster mesialization of mandibular molars with the Herbst appliance as anchoring tool and a lingual bracket system than with TADs as an anchoring tool [17]. If the indication is correct before the start of therapy, the patient can be spared an invasive, painful surgical procedure and additional costs [25]. On the other hand, there are numerous studies that use TADs as an anchoring tool for the mesialization of lower jaw molars and premolars to close spaces, for example [19, 25].
The use of the Herbst appliance in combination with a quadhelix in the maxilla was only used in the specialist practice during the study period (Fig. 6). A transversal problem in the upper jaw with a deficit > 4mm is treated in the Department of Orthodontics at the University Medical Center of the Johannes Gutenberg University Mainz with rapid maxiullary expansion (RME) before the insertion of the Herbst appliance. In his book "The Herbst Appliance", Pancherz and Ruf describe both possibilities, i.e. the Herbst appliance in combination with a quadhelix and an RME appliance before the Herbst appliance. In case of a large transversal deficit, treatment with an RME appliance should be performed before sagittal correction [18].
Due to the frequently expressed desire for a therapy concept that is non-invasive, preserves teeth and avoids prosthodontics, orthodontists are often confronted with the task of finding therapy solutions. This study aims to propose solutions for a multifunctional management of treatment tasks and to thus expand the orthodontic therapeutic spectrum.
The present retrospective study was prepared to investigate and present the frequency, prevalence and possible individuality of the Herbst appliance. The therapy result was not evaluated. Therefore, no statement can be made about the effectiveness of the different Herbst appliance modifications. This remains the subject of further investigations.