15: Noncompliance upper molar distalization and aligner treatment for correction of class II malocclusions

Benedict Wilmes, Jörg Schwarze

Upper molar distalization in aligner treatment

The distalization of the upper molars may be considered as a treatment option for patients with an angle class II malocclusion characterized with an increased overjet and/or anterior crowding. There has been an increasing trend in the clinical use of purely intraoral appliances, which require minimal need for patient cooperation. Unfortunately, most tooth-borne appliances for upper molar distalization produce an unwanted side effect of anchorage loss resulting in maxillary incisor proclination, reported to be 24% to 55% of observed tooth movement.¹ Pure bodily tooth movement with sequential plastic aligner therapy is challenging to achieve to a high degree of predictability. As a consequence, molar distalization is limited when relying on aligner movement alone. While there are limited reports of successful upper molar distalization of up to 2.5 mm in the literature,² a very long treatment time and high level of patient compliance are expected with requirement for intermaxillary class II elastics to be worn during the long period of the sequential upper molar distalization.³ Moreover, the potential side effects of class II elastics must be considered in terms of mesial shift of the lower anchorage teeth.

To minimize anchorage loss and need for class II elastics, mini-implants have been incorporated into the design of maxillary distalization appliances.⁴^,⁵ Mini-implants can be positioned intraorally with minimal degrees of surgical invasiveness, are readily integrated with concomitant biomechanical initiatives, and are relatively cost effective.^6–8 Various designs of implant supported distalization appliances have been published. The retromolar region is an unsuitable area for mini-implant insertion due to the unfavorable anatomic conditions (poor bone quality and thick soft tissue).⁹ Additionally, the alveolar process has also been shown to be inappropriate in cases of a desired molar distalization since the mini-implants are in the direct path of the moving teeth resulting in a failure rate that is much higher as compared to the anterior palate.¹⁰ Therefore, the palatal area posterior from the rugae (T zone¹¹) seems to be the preferred insertion site for mini-implants where the treatment objective is for distal movement of the maxillary molars without associated anchorage loss and maxillary incisor displacement. Furthermore, good bone quality with thin attached mucosa implies minimal risk of tooth-root injuries and a very high success rate in the anterior palatal region.⁹ In contrast to treatment strategies involving the interradicular positioning of mini-implants, the molar teeth can be distalized, and the premolars are free to move distally due to the stretch of the interdental fibers without any interference since the palatally positioned mini-implants are not in the path of moving teeth. Within the T zone, the mini-implants can be inserted in a median or paramedian orientation,¹¹ with both insertion sites showing a similar stability.¹²

Clinical procedure and rational of the Beneslider

The Beneslider 13–15 is a maxillary molar tooth distalization appliance, principally designed on the use of one or two mini-implants coupled in a median or paramedian orientation in the anterior palate (Fig. 15.1). By modifying the angulation of the 1.1-mm stainless steel wire, it is possible to achieve a simultaneous intrusion or extrusion of the molars.^16–18 The distalization forces are transferred to the molars by the use of bonded tubes. The advantages of a bonded tube are esthetics, and the adaptability and fit of the aligners is not undermined by the presence of stainless steel molar bands. The aligner material could cover this bonded connection (Fig. 15.2) or the aligner could be cut out in this connection area (“button cutout”) (Fig. 15.3).

Fig. 15.1The Beneslider appliance is based on one or two mini-implants with exchangeable abutments.

Fig. 15.2The aligners can cover the bonded connection like a big attachment. After distalization, steel ligatures are to modify the active Beneslider into a passive anchorage device.

Fig. 15.3The aligners can be cut out in this connection area (“button cutout”). Springs are removed in this case to modify the active Beneslider into a passive anchorage device.

It seems advantageous that the Beneslider appliance can be fitted directly without the requirement for adjunctive laboratory work in terms of welding or soldering, or the need to record an intraoral impression. Alternatively, the clinician has the choice to record an intraoral impression and transfer the clinical setup to a plaster cast model using an impression cap and laboratory analogue from the Benefit system.

Following distalization of the maxillary molar teeth, steel ligatures can be used (see Fig. 15.2) or springs removed (see Fig. 15.3) to modify the Beneslider from an active distalization device to a passive molar anchorage device. The primary objective is to stabilize the maxillary molar teeth during the retraction of the maxillary anterior teeth. Our experience in using the Beneslider appliance in conjunction with aligners commenced with a two-phase approach¹⁶: the initial phase involving molar distalization and the secondary phase for the final detailing of the occlusion with sequential thermoplastic aligners. With a two-phase approach, an impression (or scan) is recorded after distalization. To reduce the total treatment time, we now recommend simultaneous distalization with the Beneslider and alignment with sequential aligners. With a single-phase approach, the impressions for aligners are taken prior to distalization of the maxillary molars, and the anticipated tooth movement to be produced by the Beneslider appliance is programmed in the digital software platform. For distalization, either a sequential step-by-step distalization or an entire maxillary arch can be chosen since the stretch of the interdental fibers supports the simultaneous distal drift of maxillary anterior teeth.

If the aligner material should cover the connection area with the molars (see Fig. 15.2), the impressions for aligners should be done after the insertion of the Beneslider appliance. The Beneslider should be not activated prior to the delivery of the aligners. If the aligners have a cutout area (see Fig. 15.3), the impressions for aligners are able to be recorded either before or after insertion of the Beneslider appliance. Distalization forces can be applied to the first or second maxillary molar teeth. Our clinical experiences have shown that force application to the first molar is a superior approach, as direct force application to the second molar teeth is associated with precocious distalization of the second molars, leading to improper tracking and fitting of the sequential plastic aligners, a risk that is reduced if the maxillary first molar teeth are connected to the Beneslider.

Clinical case

A 39-year-old female patient presented with anterior crowding class II malocclusion (Fig. 15.4; Table 15.1). The maxillary teeth were migrated mesially, especially on the left side. Due to the absence of the second lower right molar, the upper second right molar was elongated.