The Benefit System and its scope in contemporary orthodontic protocols

Maxillary molar distalization (Beneslider and pendulum B)

The treatment objective of upper molar distalization may be required frequently during correction of malocclusions. The most common indication is a dentoalveolar Class II malocclusion with increased overjet and/or anterior crowding. Another less frequent indication may be to correct dentoalveolar compensation in Class III patients that are undergoing surgery. Due to esthetic drawbacks and the length of time to be worn, molar distalization with a headgear is unpleasant for many patients.^[18,19] This has resulted in a tendency to favor purely intra-oral distalization appliances with minimal need for patient cooperation. Unfortunately, most of the conventional devices for noncompliance maxillary molar distalization show some unwanted side effects, such as anchorage loss, especially, when distalization forces are applied buccally.^[20] One possibility to reduce unwanted effects of reciprocal orthodontic forces is the use of palatal acrylic pads (Nance buttons). However, the anchorage stability of this soft-tissue borne element is not always certain. Moreover, oral hygiene is impaired due to the partial coverage of the palatal area. If the anchorage unit includes teeth, mesial migration and/or protrusion of the anterior dentition have to be considered as major drawbacks.^[21,22] The amount of the anchorage loss of conventional intra-oral devices ranges between 24% and 55%.^[23] Although indirect anchorage can be used to support the premolars during maxillary molar distalization, miniscrew tipping and wire deformation may result in anchorage loss and mesial premolar migration. Moreover, after molar distalization, the appliance must be refabricated for distalization of the premolars and anterior teeth. Therefore, direct anchorage is preferable.

To benefit from the advantages of direct anchorage mechanics and of the anterior palate as the most suitable mini-implant insertion site, the Beneslider^{[5,11,12,24,25]} device has been designed fixed on top of mini-implants with exchangeable abutments. The Beneslider utilizes sliding mechanics and has proved to be a reliable distalization device^[25] [Figure 8]. However, if frictionless mechanics is preferred and/or the molars are to be uprighted or derotated simultaneously during distalization, pendulum mechanics can be employed.^[26] Several authors introduced skeletally-supported pendulum mechanics to avoid anchorage loss.^[27-30] However, all described appliances require additional laboratory work. The pendulum B^[31] was designed to have the ability to adapt a skeletal borne pendulum device chair side immediately after mini-implant insertion without a laboratory procedure [Figure 9].

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Figure 8

Clinical example: Beneslider for upper molar distalization

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Figure 9

Clinical example: Pendulum B for upper molar distalization

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Maxillary space closure (Mesialslider)

Unilateral or bilateral missing upper teeth are diagnosed quite frequently: Congenitally missing lateral incisors/ second bicuspids, extremely displaced canines or a severe trauma of a central incisor are potential complaints that result in a reduced upper dentition. The two major treatment approaches are space closure or space opening to allow prosthodontic replacements either with a fixed prosthesis or single-tooth implant. Both of these treatment approaches may potentially compromise aesthetics, periodontal health, and function.^[32] In many cases, space closure to the mesial seems to be the favorable treatment goal, since treatment already can be completed as soon as the dentition is complete.^[33] Canine substitutions can be accomplished with good aesthetic outcomes by tooth reshaping and positioning, bleaching, and porcelain veneers. ^[34,35]

The more mesial the missing tooth is, the higher will be the demands for anchorage quality, especially in asymmetric cases with a midline deviation. If the central incisors are in the correct position (midline, torque and angulation are correct), a T-Bow^[11,12,36] can be bonded to the lingual surfaces of the central incisors to apply an indirect anchorage with the goal to avoid lingual tipping of the central incisors during space closure.^[11,12,36] As an alternative to the T-Bow (indirect anchorage), the Mesialslider^[11,12,37] as a direct anchorage device can be used. The Mesialslider enables clinicians to mesialize upper molars unilaterally or bilaterally. Since the incisors are not fixed, a midline deviation can be corrected at the same time. The Mesialslider can be used to close space in the upper arch from distal, e.g., for missing lateral incisors [Figure 10], canines [Figure 11], premolars [Figure 12] or molars. The Mesialslider can also be used for protrusion of the whole upper dentition to compensate a mild Class III occlusion.^[37]

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Figure 10

Clinical example with missing upper right lateral incisor: Mesialslider for unilateral upper mesialization

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Figure 11

Clinical example with missing upper right canine: Mesialslider for unilateral upper mesialization

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Figure 12

Clinical example with missing upper second bicuspids: Mesialslider for bilateral upper mesialization

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Asymmetric molar distalization and space closure (Mesial-Distalslider)

In many cases with unilaterally missing teeth, the midline is off. The favored appliance to correct the midline, to close the space on one side and to distalize the contralateral segment is a combination of the Mesialslider and a Beneslider, the Mesial-Distalslider^[38] [Figure 13].

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Figure 13

Clinical example with missing upper right canine and midline shift: Mesial-Distalslider for unilateral upper mesialization and contralateral distalization

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Rapid palatal expansion and early Class III treatment

Rapid palatal expansion (RPE) is considered to be the first orthodontic procedure to achieve skeletal widening of the maxilla. Today, RPE is considered to be a method for sutural distraction osteogenesis. For the treatment of patients with a Class III caused by a retrognathic maxilla, RPE is combined with a facemask for the protraction of the maxilla. Since the orthopedic forces are transmitted to the skeletal structures via the anchor teeth, distribution of the forces to as many teeth as possible, as well as completion of root growth, are considered essential. However, besides the therapeutically intended skeletal expansion, side-effects such as buccal tipping of the anchor teeth, fenestration of the buccal bone, root resorptions, and gingiva recessions were reported in some cases.^[39,40] To avoid these complications caused by the tooth-borne character of the conventional appliances, some authors reported about pure bone-borne RPE devices. Several palatal distractors have been presented over the last decade.^[41,42] However, insertion and removal of these miniplate-borne distractors are invasive surgical procedures with the need of a flap preparation, risk of root lesions and infections.^[41,43] As a consequence distractors of this type could not establish themselves as standard devices for RPE. To minimize the surgical procedure, Harzer introduced the Dresden-Distractor that is borne solely on an implant and a mini-implant. ^[44-46] Due to the risk of a root lesion at the insertion of implants in the lateral posterior alveolar process and lack of available bone in the median posterior palate, we used the 1^st molars or 2^nd deciduous as posterior anchorage unit. In the anterior median palate, there is more bone available bone for mini-implants^[13] and the resulting appliance is a half tooth-borne half bone-borne RPE device called hybrid hyrax ^[5,11,47-49] [Figure 14].

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Figure 14

Hybrid hyrax. Anterior anchorage is provided by two 2 mm × 9 mm Benefit mini-implants, placed about 5 mm apart. Before and after rapid maxillary expansion and Class III treatment using a facemask

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The application of the hybrid hyrax is minimally surgical invasive compared with pure bone-borne RPE devices like distractors.^[41,42] To employ the first molars or second deciduous molars as posterior anchorage unit and mini-implants as skeletal anterior anchorage unit provides several advantages.^[47-49]

• Applicable in cases with low anterior dental anchorage quality due to missing deciduous molars or deciduous molar with short roots.

• Applicable in cases with immature root development of the premolars.

• No risk of impairment of root development (curved roots).

• Reduction of the dental side effects, that is, premolar tipping.^[48]

• Anterior dentition is not bonded during the retention phase, and thus regular orthodontic treatment could be started earlier.

• Advantageous in cases with need for early Class III treatment, where the RPE supports maxillary advancement by weakening the midface sutures.

• Avoidance of mesial migration of the upper dentition during application of a facemask or the Mentoplate,^[47] thus enhancing the skeletal effects.^[48]

Skeletal Class III malocclusions are relatively infrequent, and their genesis is usually associated with genetic factors.^[50,51] The Class III relationship may be caused by a retrognathic maxilla, a prognathic mandible or both.^[50,51] Treatment of young Class III patients with maxillary deficiency is mostly conducted with a facemask. Since the force is applied to the teeth, mesial migration of the dentition is inevitable and may result in severe anterior crowding.^[52] On the other hand, the desired skeletal effect of this commonly used approach often turns out to be less than expected.^[52] To overcome these drawbacks and to minimize mesial migration of the molars, sagittal skeletal support by the hybrid hyrax is very useful. Secondly, to facilitate the advancement of the maxilla, opening of the midface sutures by RPE is recommended.^[53] With the goal to avoid an extra-oral device (facemask) and to apply the forces directly to the skeletal structures, De Clerck introduced the use of four miniplates (two anterior in the lower jaw and two posterior in the upper jaw) in combination with Class III elastics.^[54] This represents a new purely skeletal approach to correct the skeletal discrepancy. In order to enhance the skeletal effect by opening the midface sutures, we employ the hybrid hyrax appliance in the upper jaw allowing simultaneous rapid maxillary expansion and skeletally borne maxillary protraction. In the lower jaw, the Bollard miniplates by De Clerck are usually inserted after the eruption of the canines. To allow earlier insertion of the miniplate in the mandible, we developed the Mentoplate [Figure 15].^[47] Since the Mentoplate is inserted subapically to the lower incisors, it typically can be used already at the age of 8-9 years. By means of the hybrid hyrax in combination with a facemask or a Mentoplate forces are applied to skeletal structures only with the goal to achieve an optimum skeletal effect [Figure 15].

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Figure 15

Skeletal born early Class III treatment using the hybrid hyrax and the Mentoplate

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