Use of Orthodontic Mini-Implants for Maxillomandibular Fixation in Mandibular Fracture

Abstract

Orthodontic appliances for skeletal anchorage are becoming increasingly more common in clinical practice. Similarly, different terms such as mini-implants, microimplants, and miniscrews have been used. There is a wide array of appliances currently on the market, in different designs and sizes, diameters, degree of titanium purity, and surface treatment. These appliances have been used for a variety of indications, including tooth retraction, intrusion, and traction. This study aimed to report the clinical case of a 19-year-old patient with a fractured mandible and to propose a novel use of mini- implants: the perioperative placement of mini-implants as anchors for maxillomandibular fixation steel wire ligatures. We concluded that this appliance provides an effective maxillomandibular fixation in patients with mandibular fracture, with little increase in the cost of surgery.

Orthodontic appliances for skeletal anchorage are becoming increasingly more common in clinical practice [1,2]. Similarly, different terms such as mini-implants, microimplants, and miniscrews have been used. There is a wide array of appliances currently on the market, in different designs and sizes, diameters, degree of titanium purity, and surface treatment [3].

Orthodontic mini-implants are made of titanium and may range from 4 to 16 mm in length and 1.2 to 2.0 mm in diameter. Mini-implants may be divided into three distinct parts: head (coupling portion of the orthodontic appliance), transmucosal profile (portion for accommodating peri-implant soft tissue), and active tip in the intraosseous area (corresponding to implant screw threads) [3,4]. They may also be self-drilling or self-tapping, the latter not requiring drilling [5].

Radiographic assessment (periapical dental films or panoramic radiographs) is usually used for visualization and preoperative planning of mini-implant placement, thus minimizing the possibility of screw insertion into important anatomic structures [6].

Indications

Retraction of Anterior Teeth

Strategic placement of mini-implants simplifies treatment, especially in cases of Angle class II bialveolar protrusion or malocclusions [7].

Mesial Movement of Posterior Teeth

Mini-implants have proven useful as supporting elements in orthodontic treatment for space closure due to both tooth loss and class II and III corrections [8].

Incisor Intrusion

Skeletal anchorage provides incisor intrusion without undesired effects on other teeth, especially when patients show absence of posterior elements [9].

Intrusion of Posterior Teeth

This is regarded as perhaps the most difficult movement in orthodontics, and the literature has reported good results with the use of mini-implants [10].

Correction of Occlusal Plane

The use of orthodontic anchorage for correction of uneven teeth may indicate the replacement of an extremely complex procedure with a simpler alternative [7].

Distal Molar Movement

Generally used for correction of Angle class II and III malocclusions, with no need for tooth extraction [11].

Disimpaction and Vertical Molar Movement

Depending on the angle of inclination of the tooth in question, this movement may be very difficult without the help of mini-implants [12].

Posterior Cross-Bite Correction

Correction of this problem using intermaxillary elastics requires patient compliance and may cause unwanted movements [13].

Traction of Unerupted Teeth

Strategic placement of mini-implants may allow this type of movement with no need for fixed appliances [14].

Midline Correction

In cases of midline deviation without the posterior teeth, the placement of mini-implants distal to the space to be used improves the desirable tooth movement [11].

Several techniques have been described in the literature regarding the treatment of mandibular angle fractures. Champy et al. described a technique in which the superior mandibular border is subject to tension and the inferior border to compression. The transition zone between these areas is referred to as a “line of zero force”, running along the inferior alveolar nerve. Based on these biomechanical findings, Champy et al. recommended a noncompression plate on the superior border for mandibular angle fractures [15].

The objective of this study was to report a clinical case and propose a novel use of mini-implants: the placement of mini-implants as anchors for maxillomandibular fixation (MMF) steel wire ligatures in a patient with a fractured mandible.

Case Report

A 19-year-old male patient, in good general health, presented at our Dental Department at São Francisco de Paula University Hospital, Brazil, with a 45-day history of late mandibular fracture related to the lower left third molar. Routine radiographic examination for planning the removal of tooth 38 detected the fracture. Intraoral examination revealed good general condition of the teeth and periodontium. It was noteworthy that, despite the fracture, the patient had little occlusal interference, no pain on chewing, and little or no mobility in the fractured area.

During surgical planning, we decided on the placement of screws originally designed for orthodontic anchorage between teeth 12 and 13, 22 and 23, 33 and 34, and 42 and 43 (Figure 1). Placement sites were defined after the analysis of a panoramic radiograph of the patient. Screws of 1.6 mm in diameter and 9 mm in length (NEODENT^®; Curitiba, PR, Brazil) were used. These are self-tapping and self-drilling screws, made out of grade V titanium alloy, with torque resistance up to 20 N · cm, according to information provided by the manufacturer.

The fractured area was then approached and refractured, and local fibrosis (due to interfragmentary mobility) was removed. Tooth 38 was extracted, MMF was performed (Figure 2) to adjust occlusion, and the fracture was fixed with a four-hole 2.0 miniplate and spacer and four monocortical screws, inserted into the external oblique line, in the tension region. The Champy technique was chosen because it seemed appropriate to the case.

Postoperative care included a soft diet for 45 days, a strict oral hygiene regimen, and regular evaluations every week for at least 90 days. Return to solid diet was determined based on the evaluation of a control radiograph taken 90 days postoperatively. We decided not to remove the locking fixation screws at the first moment because they could be used again if any complications occurred in the postoperative period.

Discussion

MMF techniques have evolved over the years, from the use of splints and Erich arch bars, among others, to MMF screws, designed specifically for this purpose. The use of MMF screws results in shorter operating time, allowing good stabilization of the occlusion before the placement of rigid internal fixation devices. Given the current notion that early restoration of function contributes to the ossification process in the fractured area, MMF methods are less likely to be used postoperatively, and early return to function, although in a careful and monitored manner, has been stimulated among patients [16].

In the present case, the use of screws originally designed for skeletal anchorage in MMF was determined by their ease of application, high tensile strength, improved patient tolerance, good mechanical perform- ance, and low cost [16].

In orthodontics, these screws are inserted into the jaws and a significant orthodontic force is exerted over them. Thus, one may speculate whether these screws could be used in facial trauma, being used only during surgery to stabilize occlusion prior to the placement of rigid internal fixation devices [17].

Surgeons have improved their skills in handling these screws, because orthodontists increasingly makes use of these devices to optimize orthodontic treatment [18]. Prolonged periods with these screws in the oral cavity have been observed, and the screws appear to be well tolerated and to allow proper oral hygiene, without causing trauma to tissues, and over time, patients may not even realize their presence in the mouth. Such advantages are due to the features of these devices, including the small screw size and rounded head, with no sharp corners that may cause trauma to oral soft tissues. Similar to MMF screws, mini-implants for skeletal anchorage have a screw head neck capable of holding a locking wire and also a hole with a diameter appropriate for passing a ligature wire inside [3,19].

A significant advantage for the popular usage of mini-implants is the low cost. In Brazil, these screws cost about U.S. $34.00 each, cheaper than MMF screws, which allows their use in low-income patients, or those without health insurance, because the procedure could be provided at an affordable cost in private practice. Because these are smaller and therefore more fragile screws, they should be used in carefully selected cases, in which there is little bone or tooth displacement, well- balanced occlusion, and good patient compliance [20]. Specific MMF screws are larger and more resistant and may therefore be used in more complex cases. However, the larger diameter of MMF screws hinders their use in cases of reduced interdental space, especially when patients have dental crowding, leading to their insertion in areas more distant from the alveolar bone [16,21].

Conclusions

Good techniques do not have to be complex or expensive. Therefore, we believe that screws for skeletal anchorage may be used for MMF in carefully selected cases, such as the one reported here, as a simple, rapid, and inexpensive alternative.

After some minor adjustments, these screws may be used more widely in the management of oral and maxillofacial trauma, with no significant increase in treatment costs.