Computer-aided design and manufacturing of bone- and tooth-borne maxillary protraction with miniscrews and Class III elastics: Can we contemporize Class III treatments in growing patients?

The purpose of this clinical report is to illustrate an innovative treatment plan for a patient with Class III malocclusion. The plan combined the versatility of computer-aided design and manufacturing technology with miniscrews. Maxillary and mandibular fully customized metal framework anchored to 4 miniscrews was digitally designed and constructed for a growing patient with midface hypoplasia and a skeletal Class III malocclusion. The patient wore Class III elastics between hooks on the maxillary and mandibular frameworks full time for 10 months. Overcorrection was obtained with limited dental side effects, and a significant improvement of the profile was achieved. With the advantages of computer-aided design and manufacturing technology and less invasive insertion procedure compared with miniplate surgery, this patient-specific treatment approach was simple and effective.

Highlights

  • CAD/CAM technology opens the door to new orthodontic treatment modalities.

  • An eleven-year-old patient had skeletal Class III malocclusion.

  • Bone- and tooth-borne maxillary protraction with miniscrews and Class III elastics were used.

  • Satisfactory results were achieved with minimal dental side effects.

  • Invasive surgery was not needed.

Class III malocclusion is well known as a polygenic condition that results from an interaction between susceptibility genes and environmental factors. According to previous studies, about two-thirds of subjects with a Class III skeletal relationship were due to either maxillary retrognathism or a combination of maxillary retrognathism and mandibular prognathism.

Maxillary protraction using an orthopedic facemask has been widely applied as a major treatment modality for Class III children. However, 25% to 30% of Class III skeletal patterns are known for relapsing into negative overjet. Patients with substantial mandibular prognathism require constant monitoring and may need further therapy.

To meet the challenges of Class III malocclusion, some authors have used skeletal anchorage for enhancing the maxillary protraction effects compared with facemask therapy. This made it possible to achieve a full-time protraction while increasing skeletal effects and reducing dentoalveolar compensations with good vertical control. , Indeed, Feng et al confirmed in a systematic review that bone-anchored maxillary protraction induced more maxillary advancement with minimal dental side effects when compared with tooth anchored appliances. However, although reliable maxillary protraction using miniplates has been confirmed, the insertion of miniplates requires a relatively invasive surgery with a flap, which, in most cases, needs the patient to be under general anesthesia. Moreover, the use of mandibular miniplates is not possible before the late mixed dentition stage, preventing an early intervention. To overcome this, Sar et al used maxillary jaw miniplates in conjunction with a facemask, which has the disadvantage of relying on patients’ compliance. Alternatively, Wilmes et al developed the mentoplate, which is attached subapical to the mandibular incisors and is used in combination with a hybrid hyrax in the mandibular jaw anchored to 2 miniscrews in the anterior palate. However, the mentoplate requires a very invasive placement surgery.

Therefore, alternatives producing similar effects with less invasive surgery would be very desirable. Computer-aided design and manufacture (CAD-CAM) technology could help overcome this challenge. This report aimed to describe an innovative treatment option for the treatment of Class III skeletal patterns by using a CAD-CAM framework anchored both on the teeth and on miniscrews, coupled with intermaxillary Class III elastics.

Clinical case

An eleven-year-old girl was seen at the postgraduate clinic, Department of Dentistry and Oral Health, Aarhus University, Aarhus, Denmark. At the age of 9 years, the patient had undergone an early phase of treatment using a hyrax and facemask, leading to satisfactory results. After that, a passive transpalatal arch was used to maintain the transverse relation. While waiting for the permanent dentition, the patient had a worsening of her Class III skeletal characteristics. At the age of 11 years, she presented with a flat profile, significant midface deficiency, and a negative lip step. The intraoral assessment showed severe maxillary crowding with high labial canines, an anterior crossbite of the maxillary lateral incisors, and an overbite and overjet of 1 mm, yet with retroclined mandibular incisors ( Figs 1 , 2 , and 3 ).

Fig 1
Pretreatment facial and intraoral photographs.

Fig 2
Pretreatment digital models.

Fig 3
Pretreatment panoramic x-ray and lateral cephalogram.

The treatment objectives were to improve the patient’s profile and to obtain a normalized overjet and overbite. After achievement of those objectives, the treatment plan would be revised: extractions and fixed appliances would further be considered to relieve the maxillary crowding and finalize the case with a stable occlusion.

Material and methods

In the first instance, 2 miniscrews 2.0 × 9 mm (PSM Medical Solutions, Tuttlingen, Germany) were placed in each jaw, on the palatal side between the first molars and the second premolars in the maxilla, and buccally between the first and second premolars in the mandible. Miniscrew insertion was followed by an intraoral scan (TRIOS; 3Shape, Copenhagen, Denmark) without the use of any transfer caps. The intraoral was sent directly from the TRIOS scanner to the dental technician, who designed the framework using the Appliance Designer software (3Shape) after the provided orthodontic prescription.

The appliance was composed of 3 parts: 1 in the maxillary arch, consisting of 2 circumferential bands on the first molars, with hooks on the buccal side, whereas on the palatal surface, 2 extended arms covering the palatal surface of both premolars were present. The 2 bands were connected with a transpalatal bar, in which 2 housings for the insertion sites of the miniscrews were present ( Figs 4 , A and B ). In the mandibular arch, on the buccal side, 2 similar parts covering the buccal surfaces of the first molars and first premolars were designed for the right and left sides; gingival clearance was left to facilitate cleaning. Those buccal parts presented 2 housing for the insertion of the miniscrews. An arm with a hook was extended to the canine region to achieve a 45° vector to the occlusal plane of the Class III elastic connecting the maxillary and mandibular hooks ( Figs 4 , C and D ). To increase the rigidity of the appliance and thus anchorage, we added a lingual bar connecting the 2 sides ( Fig 5 ).

Fig 4
Digital design using Appliance Designer software (3Shape, Copenhagen, Denmark): A and B, maxillary framework design; C and D, mandibular framework design.

Fig 5
CAD-CAM generated appliance after polishing and sandblasting the bonding surfaces.

The final metal framework design was printed by selective laser melting process (Concept Laser, Lichtenfels, Germany), using the material Remanium Star (Dentaurum, Ispringen, Germany). This material is produced in powder form and locally melted using a high-energy laser beam with high energy density. After cooling down, the appliance was electro-polished, and the bonding surfaces sandblasted ( Fig 5 ).

The appliance was bonded using the NOLA Dry Field System (Great Lakes Dental Technologies, Tonawanda, NY) to keep the teeth dry. Bonding surfaces were microetched using aluminum oxide ≤50 μ for approximately 3-4 seconds per tooth, followed by acid etching with 37% phosphoric acid gel for 30 seconds. After rinsing and air drying, RelyX Unicem (3M ESPE, St Paul, Minn) was used to cement the appliance to the tooth surfaces and was light-cured for 30 seconds. Finally, fixation screws were placed, and the patient was instructed to use 6 oz 3/16-in Class III elastics full time, to be replaced at least thrice a day.

Results

After 10 months of maxillary protraction, the sagittal skeletal relation significantly improved, increasing the Wits appraisal by 8 mm ( Figs 6 , 7 , and 8 ). The overjet increased from 1 mm to 4.8 mm. The anterior crossbite was corrected, whereas the vertical skeletal changes were negligible ( Table ).

Jan 30, 2021 | Posted by in Orthodontics | Comments Off on Computer-aided design and manufacturing of bone- and tooth-borne maxillary protraction with miniscrews and Class III elastics: Can we contemporize Class III treatments in growing patients?
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