Bone-borne rapid maxillary expansion distraction devices are used to achieve a more skeletal expansion and to avoid dental side effects of conventional expanders such as tipping of anchorage teeth. In this article, we report the use of a prefabricated expander fixed on 2 mini-implants in the anterior palate. This allows for the insertion of the mini-implants and the expander to occur without the need for an impression or any laboratory procedures. Especially when aligners are going to be used, the use of a mini-implant-borne expander seems to be reasonable because the expander can be left in place as a skeletal retainer during the aligner finishing.
Highlights
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If a mini-implant borne expander is used, dental side effects in terms of tipping of teeth can be avoided.
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A pre-fabricated expander allows a single appointment for insertion of mini-implants and the expander.
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The use of a mini-implant borne expander is also reasonable since the expander can be left in place as a skeletal retainer during aligner finishing.
Maxillary transverse deficiency is a common orthodontic problem, and it is often associated with a unilateral or bilateral posterior crossbite. Rapid maxillary expansion (RME) is considered the optimal procedure to achieve a skeletal widening of the maxilla. , Because the forces are usually transmitted to the skeletal structures via the anchor teeth, distribution of the forces to as many teeth as possible and completion of root growth are considered essential. However, besides the therapeutically intended skeletal expansion, side effects such as tipping of the teeth, root resorption, decrease in buccal bone thickness or dehiscence, and loss of marginal bone height resulting in gingival recessions may occur.
To reduce the unwanted side effects of tooth-borne maxillary expansion, several maxillary expansion appliances have recently been introduced, which share the load between the anchorage teeth and 2-4 mini-implants. Wilmes et al have introduced the hybrid hyrax expander in 2007 using 2 mini-implants in the anterior palate and 2 (deciduous) molars. Similar hybrid expanders were published in the following years by Garib et al in 2008, Lee et al in 2010, and Moon et al in 2015, called the mini-implant assisted rapid palatal expansion. The T-Zone in the anterior palate provides a safe insertion area for the mini-implants away from tooth roots and blood vessels while providing the best quality cortical bone. Many studies have shown the advantages of mini-implant assisted rapid palatal expansion compared with tooth-borne expanders inducing less tipping of anchorage teeth, a more skeletal expansion, , less decrease of the buccal bone thicknesses of anchorage teeth, a significantly higher nasal airway flow and less root resorption of anchorage teeth. A disadvantage of skeletal borne expanders is the need for local analgesia and the insertion of mini-implants. However, there seems to be no difference between pain intensity and discomfort during RME treatment with a conventional hyrax appliance vs a mini-implant anchored appliance.
The conventional procedure for the use of the hybrid hyrax is first to insert mini-implants, take an impression, or scan, manufacture the appliance in a laboratory and then insert it in a subsequent appointment. To avoid this 2-step procedure, a prefabricated expander borne on 2 mini-implants was designed, which can be inserted in the same appointment immediately after mini-implant placement. This expander is prefabricated in 3 different sizes (on the basis of the distance of the mini-implant centers: 6, 8, 10 mm) and can be adapted directly chairside. After insertion of 2 mini-implants in optimal insertion sites in the anterior palate (T-Zone), the appropriate expander size is chosen and additionally adapted to the distance of the 2 mini-implants by pre-turning of the expansion screw. The expander can be activated over a distance of 10 mm, which means even if the maximum pre-turning distance of 2 mm is done, 8 mm are still available for maxillary expansion.
An increasing number of orthodontic patients present seeking invisible or esthetic orthodontic treatment with clear sequential thermoplastic aligners. A treatment objective of bodily tooth movement with aligner therapy exclusively can prove challenging to achieve with a high degree of predictability. , This is especially true when attempting a significant amount of expansion in the maxillary arch. Houle et al and Zhou and Guo reported severe tipping of the teeth instead of a desired bodily tooth movement when aligners only were used for expansion. Consequently, it seems beneficial to combine a mini-implant borne expander and aligners to treat patients with a maxillary transversal deficiency and wish for invisible treatment.
Case report
A 13-year-old female patient presented with a severe maxillary transversal deficiency ( Fig 1 ). Intraoral examination showed a bilateral crossbite in the permanent dentition. The panoramic radiograph revealed the presence of all third molars. Pretreatment lateral cephalometric analysis showed a mild skeletal Class III (Wits, −1.2 mm; ANB, 0.5°) with a slightly prognathic mandible (SNB, 83.2°; Table ). The relative merits, shortcomings, and risks of each treatment modality were clearly explained to the patient and her parents. They made an informed decision to proceed with a treatment using a mini-implant borne expander for the maxilla and aligners for leveling of the teeth afterward.
| Measurements | Pretreatment | Posttreatment |
|---|---|---|
| NSBa | 122.3° | 126.6° |
| NL-NSL | 6.8° | 7.8° |
| ML-NSL | 26.9° | 27.3° |
| ML-NL | 20.1° | 19.5° |
| SNA | 83.7° | 84.3° |
| SNB | 83.2° | 83.2° |
| ANB | 0.5° | 0.7° |
| Wits | −1.2 mm | −1.9 mm |
| U1-NL | 115.0° | 114.6° |
| L1-ML | 88.5° | 89.7° |
| U1-L1 | 136.4° | 136.2° |
| Overjet | 2.1 mm | 2.8 mm |
| Overbite | 2.0 mm | 1.8 mm |
The treatment started with the insertion of 2 mini-implants (2 × 9 mm) in the anterior palate under local anesthesia ( Fig 2 , A ). A prefabricated expander ( Fig 2 , B ; 8 mm, BMX expander, psm North America, Inc, La Quinta, Calif) was first adapted by pre-turning the expansion screw directly chairside and fixed with 2 fixation screws ( Fig 2 , C ). Expansion activation was initiated by performing 1 activation per day for a total of about 0.2 mm expansion per day. After 4 weeks of activation, the maxilla was expanded by approximately 5.5 mm ( Figs 3 and 4 ). Subsequently, scans were taken for the aligner finishing (Clear Correct, Round Rock, Tex; Fig 5 ). The BMX expander stayed in place for skeletal retention and was substituted during the aligner finishing by a miniplate to achieve higher patient comfort ( Fig 6 ). The aligner treatment ( Fig 7 ) comprised 22 aligners (2-week change), including 1 refinement and was finished after 10 months ( Fig 8 ). The whole treatment duration was 12 months (1 month of expansion, 1 month for aligner manufacturing, and 10 months of aligner finishing). For retention, removable vacuum-formed retainers were prescribed. The occlusion improved because of the settling of the teeth during the retention period of 6 months ( Fig 9 ).
