Mini-implants : Mechanical resource for molars uprighting

Contact address: Susiane Allgayer PUCRS – Pontifícia Universidade Católica do Rio Grande do Sul Av. Ipiranga, 6681 – Prédio 06 – Sala 209 CEP: 90619-900 – Porto Alegre / RS, Brazil E-mail: susianeallgayer@gmail.com Introduction: The early orthodontic treatment allows correction of skeletal discrepancies by growth control, and the elimination of deleterious habits, which are risk factors for the development of malocclusions, favoring for the correction of tooth positioning later in a second treatment stage. During development of teeth and occlusion, the mandibular second molars commonly erupt in the oral cavity after all other teeth of the anterior region. In their eruptive process there may be a condition known as tooth impaction, which precludes its complete eruption and requires proper uprighting treatment. The temporary anchorage devices allow disimpaction and movement of these teeth directly to their final position, without the need of patient compliance or reaction movements in other parts of the arch. Objective: This paper aims at describing a case report of the treatment of a patient with Angle Class II malocclusion, performed in two phases, in which mini-implants were used for uprighting the impacted mandibular second molars.


Introduction:
The early orthodontic treatment allows correction of skeletal discrepancies by growth control, and the elimination of deleterious habits, which are risk factors for the development of malocclusions, favoring for the correction of tooth positioning later in a second treatment stage.During development of teeth and occlusion, the mandibular second molars commonly erupt in the oral cavity ater all other teeth of the anterior region.In their eruptive process there may be a condition known as tooth impaction, which precludes its complete eruption and requires proper uprighting treatment.The temporary anchorage devices allow disimpaction and movement of these teeth directly to their inal position, without the need of patient compliance or reaction movements in other parts of the arch.

introduction
Tooth impaction is a condition in which the eruption of a tooth is interrupted as a consequence of its contact with other tooth or teeth. 1 A tooth is considered impacted when, after completion of root formation, the tooth does not erupt in up to six months compared to the contralateral tooth. 2 The prevalence of impaction of mandibular second molars is relatively low, nearly 1 to 3 teeth in 1,000. 3,4,5,6The most probable causes of impaction of second molars seem to be related to the excessive size of these teeth, deficient mandibular growth, inadequate length of the mandibular arch or only due to an abnormal eruption pathway. 7,8[9][10] The utilization of temporary implants for orthodontic anchorage allowed a new perspective in the orthodontic treatment, especially in the permanent dentition.][13][14][15][16][17][18] Class II is the severe malocclusion most frequently found and is characterized by "distal positioning" of the mandibular teeth compared to the maxillary teeth, which may be caused by bone dysplasia or forward positioning of the alveolar process or maxillary dental arch, or even by the combination of skeletal and dental factors. 9his case report describes the orthodontic treatment of a patient with Angle Class II malocclusion with impaction of the mandibular second molars, in which two mini-implants were used as an anchorage aid for uprighting of the teeth, which were impacted on the distal aspect of mandibular first molars.

cASE rEPort
Caucasian patient of female gender sought for initial orthodontic treatment at the age of 9 years and 5 months.The general health status was good and there was no history of severe diseases or traumas.On the clinical examination, it was observed that the patient was in the intermediate mixed dentition and presented tongue thrusting and speech disorder.
The patient exhibited symmetric face with a slightly convex profile and competent lips.The facial thirds were proportional and the smile line was normal (Fig 1   During the eruption process, the mandibular second molars presented a marked mesial eruption pathway (Fig 6), leading to impaction on the irst molars.Surgical removal of third molars was indicated to enhance the uprighting of second molars.The same procedure comprised surgical exposure and bonding of a bracket on the cusp of these teeth and placement of mini-implants (Ortoimplante Conexão, 2.0 x 9.0, medium transmucous proile) for anchorage on the retromolar region, distal and occlusal to the second molars, using a mucoperiosteal lap 11 .This site was selected to allow support for orthodontic eruption of the impacted second molars in distal and occlusal direction (Fig 7A ). 2 mm in the mandibular arch, with mild crowding in both arches.Analysis of (Fig 3) and periapical radiographs revealed the presence of all permanent teeth, including the third molars, besides deciduous canines and molars still present in the oral cavity.The hand-wrist radiograph revealed that the patient was not in the pubertal growth spurt yet.

trEAtMEnt oBJEctiVES
The treatment objectives were to correct the skeletal and dental Class II malocclusion and intercept the malocclusion, providing conditions for adequate growth of the bone bases, thus improving the dentoalveolar morphology.Therefore, it was necessary to control the maxillary protrusion by redirecting growth, to eliminate oral habits, to re-establish normal lip and tongue functions to correct the overbite, and to control the eruption of mandibular second molars, which presented a mesial eruption pathway.

trEAtMEnt ProGrESS
Initially, a maxillary appliance with tongue crib was used for six months, for tongue reeducation.After achievement of adequate overbite (Fig 3), correction of the skeletal discrepancy was initiated by redirecting maxillary growth with an extraoral traction appliance, during 10 months (Fig 5).
The fixed orthodontic appliance was placed using standard edgewise brackets, and the alignment and leveling stage was initiated.The affected teeth were gradually moved using chain elastics, improving their positioning (Fig 7B).The period required for uprighting was 18 months.The mini-implants did not present mobility and the patient hygiene was excellent.
The maxillary second molars did not erupt (Fig 7B).After surgical removal of fibrosis, they erupted with palatal tipping and the mandibular second molars were in buccoversion, which caused a crossbite that was treated by placement of a contracted lingual archwire, besides expansion of the maxillary arch.Simple cross vertical elastics were also used on brackets bonded on the palatal aspects of maxillary right and left second molars and buccal aspect of the mandibular right and left second molars.After 18 months, they presented good inclination in the bone base (Fig 7C ), were included in the archwire, the lingual arch and mini-implants were removed and corrective fixed appliances were placed for treatment finalization.There was resorption of the distal root of the mandibular right first molar, which was followed up radiographically (Figs 7C and D).
The total treatment time with the fixed appliances was eight years, due to the period elapsed to wait for eruption of the maxillary and mandibular second molars.After orthodontic finishing and improvement of occlusion, the appliance was removed and a wraparound removable orthodontic retainer was placed in the maxillary arch, as well as a mandibular 3x3 bonded lingual retainer.Both mini-plates and endosseous implants are costly and difficult to be removed. 13,18,25owever, skeletal anchorage has surely been an important tool in Orthodontics.These treatments require minimum patient compliance and a good oral hygiene can be more easily maintained.Even in patients who do not need prosthetic rehabilitation, recent studies have used the retromolar, palatal and alveolar regions for the placement of implants only for orthodontic purposes, for induced movement of teeth or segments. 16

trEAtMEnt rESuLtS
At treatment completion, the facial outcome was excellent.The intraoral analysis revealed Class I molar and canine relationship, adequate overjet and overbite, coincident midlines and adequate intercuspation between the dental arches, including the second molars.The panoramic radiograph evidenced correct parallelism between the roots, and the cephalometric tracing and superimposition on the cephalogram revealed the dental and skeletal changes achieved at treatment completion (Figs 8 -11, Tab 1).

diScuSSion
Tooth impaction may be caused by factors as heredity, malposition of the tooth germ, overretention of deciduous teeth, localized pathological lesions, reduced arch length and deficient growth of the mandibular ramus. 9The mandibular second molars may be impacted or severely malpositioned and are often blocked under the distal convexity of permanent first molars.Their early repositioning is usually advantageous during active root development. 9,10,19he utilization of mini-plates was initially suggested as orthodontic anchorage for distal movement of mandibular molars, which was necessary in cases like this.The placement and removal require invasive surgery, which may lead to infection. 13,18The utilization of endosseous implants as anchorage in retromolar, 21,22 palatal and edentulous areas has been successfully described in the literature, 11,16,23,24 however they require osseointegration before the orthodontic force is applied, thus increasing the treatment time, besides the limited sites for placement.
Different from the aforementioned resources, the mini-implants are easy to insert and remove, may be used immediately, are less costly and may be placed in several sites, increasing their versatility. 12,15,25The anchorage using mini-implants is as effective as the aforementioned mechanisms and has the advantages of being minimally invasive, the insertion technique is simple and facilitates the surgical procedure, providing reduced surgical time. 16For these reasons, in several clinical situations, they are preferred as a skeletal anchorage method 25 .
The site for fixation of the orthodontic miniimplant should present sufficient quantity of cortical bone tissue to assure immediate mechanical stability, minimum discomfort to the patient, safety to anatomical structures, as well as to allow the application of adequate biomechanics.The retromolar region 21,22 is indicated to promote the uprighting of molars because it increases the distal force component.When mini-implants are placed at this region, it is also possible to achieve extrusion forces with a distal component, another reason for selecting this treatment. 26ne of the goals of orthodontic treatment is to achieve a harmonious arch shape.Transverse problems should be corrected soon after diagnosis to prevent bone deficiencies. 27When a tooth presents crossbite, it rarely presents alterations only in its axial inclination.The opposing tooth in the other arch is often also malpositioned.Thus, the mandibular tooth may be in buccoversion and the maxillary tooth in palatoversion.In these cases, both should be corrected and simple cross elastics are indicated.In the present case, brackets bonded on the surfaces of molars were used to position the elastics to correct the crossbite.The technique is relatively easy, but requires patient compliance. 28Combined to elastics, a contracted lingual archwire soldered to the bands on the mandibular right and left second molars was placed, because they presented with marked buccoversion.
Similar to the aforementioned problem, deleterious habits should be interrupted as early as possible, to reestablish the normal lip and tongue functions in order to allow a correct overbite.In the present case, a maxillary removable appliance fabricated with clear acrylic and a tongue crib fabricated with 0.7mm stainless steel wire was used for tongue reeducation.This appliance -which is easy to be made and is ixed in the oral cavity using Adams clasps in the molars and Kennedy clasps in the canines -intercepted the local factors that precluded tooth eruption in their normal position and allowed stable outcomes during treatment.
External root resorption is a common complication of orthodontic treatment.The esthetic and function improvement oten compensate the treatment risks. 29eduction of the root length does not reduce the longevity or functional capacity of the afected teeth; ater the force is removed, there is the repair process and reestablishment of the periodontal ligament. 30In the present case, resorption of the mandibular right irst molar observed during treatment was controlled by radiographic follow-up and force control.Considering the large movement of the second molar, repair of the periodontal ligament of the mandibular right irst molar and reestablishment of the normal functions of the two teeth, resorption of the irst molar was clinically acceptable (Figs 7C and D).
Ultimately, the mini-implants provide biomechanical advantages that allow an easier and more effective treatment, without the need of patient compliance. 17,26The preference of clinicians for a certain treatment modality must not be necessarily followed.After deciding that the utilization of mini-implants is safe and necessary for the treatment, the area of insertion should be selected considering the accessibility, conditions of soft and hard tissues, biomechanical utility in orthodontics, comfort to the patient and possibility of irritation of the adjacent oral tissues. 26ncLuSion Disimpaction of the mandibular second molar, comprising extraction of the third molar, exposure of the crown of the impacted tooth for bonding of orthodontic bracket followed by orthodontic mechanics demonstrated to be a safe and effective approach with minimum discomfort to the patient.The mechanics required only two mini-implants placed at the retromolar region, which allowed correct positioning of the second molars impacted in the dental arch.Good results were obtained and the orthodontic treatment objectives were achieved; also, the Class II molar relationship and open bite were corrected, thus yielding an occlusion with excellent function and esthetics.

Figure 11 -
Figure11-Superimposition of cephalometric tracings at pretreatment (black) and posttreatment (red), with parallel Sella-Nasion lines and register at Sella for growth analysis.The redirection of maxillary growth combined to the favorable mandibular horizontal growth corrected the malocclusion.