SLJO

Sri Lankan Journal of Orthodontics

MINISCREW IMPLANT SUPPORTED K-LOOP (MISK) SPRING FOR MOLAR DISTALIZATION

Prabhat Kumar Chaudhari1, Sandhya Maheshwari2, Saba Khan3, Om Prakash Kharbanda4

1. Assistant Professor, Division of Orthodontics and Dentofacial Deformities, Centre for Dental Education and Research (CDER), All India Institute of Medical Sciences (AIIMS), New Delhi- 110029. INDIA.

2. Professor, Department of Orthodontics and Dentofacial Orthopaedics, Aligarh Muslim University, Aligarh-202001, India.

3. Assistant Professor , Department of Orthodontics and Dentofacial Orthopaedics, Aligarh Muslim University, Aligarh-202001, India.

4. Professor and Head, Division of Orthodontics and Dentofacial Deformities, Centre for Dental

This paper deals with the introduction of a treatment modality for maxillary molar distalization using Miniscrew Implant Supported K-Loop (MISK) spring.  The MISK spring consist of one active unit and one anchorage unit. The active unit uses K-loop spring attached bilaterally or unilaterally as needed between first molar tube and first premolar bracket. The premolar arm of the K-loop spring extended vertically for its attachment with anchorage unit to provide anchorage for molar distalization. The anchorage unit uses miniscrew implant. A typodont model was prepared to evaluate the effectiveness of MISK spring. Subsequently, MISK spring was tested for efficacy in a case. It was found that the MISK spring is efficient in distalization of maxillary molars.

Key words: Molar distalization, K-loop spring, Miniscrew implant.

Introduction:

Non-extraction treatment with intra-oral maxillary molar distalization has been in practice with buccal or palatal approach. Recent systematic reviews1-2 concluded that Pendulum appliance is most commonly used appliance among all appliances for intraoral molar distalization with Nance button and its variation for anchorage reinforcement, but it was not enough to neutralize the side effects of the anchorage loss and anterior anchorage loss are always critical with molar distalization appliances. Net amount of molar distalization utilizing conventional anchorage ranges from 40 to 80%.3  Recent study by Kinzinger et al using miniscrew-supported periodontal anchorage of the skeletonized distal jet showed that skeletal anchorage allows greater molar distalization in the total movement as 86.56 to 91.71%.3 This study signifies the efficacy of skeletal anchorage for intraoral molar distalization as an treatment alternatives to conventional anchorage. Palatal intraoral molar distalizing appliance apply distalization force closer to centre of resistance of molars, the molar experience therapeutically undesired mesio-palatal and disto-buccal rotation.

By changing the movement to force ratio with K-loop4 spring it is possible to achieve control tipping, uncontrolled tipping or bodily movement of maxillary molar depending upon the requirement of each case. But anterior anchorage was always critical with K-loop spring appliance. We have modified the premolar arm of the K-loop spring by extending it vertically for its attachment with miniscrew implant to make an innovative anchorage design to provide absolute anchorage for molar distalization. Through this paper we have tried to highlight a treatment modality for maxillary molar distalization using Miniscrew Implant Supported K-Loop (MISK) spring for nonextraction treatment of patients with a Class II malocclusion without proclination and mesial movement of the anterior teeth.

Materials and Methods:

Fabrication of MISK-spring:

 The MISK spring consists of one active unit and one anchorage unit. The active unit uses K-loop spring attached bilaterally or unilaterally as needed between first molar tube and first premolar bracket. The premolar arm of the K-loop spring extended vertically for its attachment with anchorage unit to provide anchorage for molar distalization (Fig. 1A). The anchorage unit uses miniscrew implants in the buccal alveolar bone between maxillary first premolar and canine (or between premolars) for absolute anchorage to resist the anteriorly directed force on anterior teeth during molar distalization (Fig. 1A).

Figure 1: Miniscrew implant supported K –Loop spring; A- Basic wire bending design placed on typodont model; B- Moment and force produce by MISK spring

Biomechanics of MISK spring:

K-loop spring consists of two vertical loops of 8mm length and 2mm in width separated by a ‘V’ bend in 0.017by 0.025 inch TMA wire. The legs of ‘K’ are bends down 20 degree. After compression of spring between 1st premolar and molar, it produces opposite forces on the molar and premolar below the centre of resistance of teeth. These forces produce the clockwise tipping on molar and the counter clockwise tipping on the 1st premolar. The 20 degree bend in the spring legs produce moments that counteract the tipping moments created by the force of appliance. These moments are reinforced by moment of ‘V’ bend in the spring as loop is squeezed into the place. Hence, molar is expected to undergo a translatory movement but no movement of premolar should occur as the premolar arm is attached to the miniscrew implant and the reciprocal forces are absorbed by miniscrew implant (Fig. 1B).

Typodont Study Model:

Typodont setup was prepared using prefabricated cold cure acrylic shells mounted on hinge articulator. Occlusion setup on typodont was done in wax with Class II molar and canine relation bilaterally and well aligned upper and lower teeth. The K-loop spring was placed between maxillary molars tube and 1st premolars bracket and the extended premolar arm of the K-loop spring is ligated in the bracket slot of miniscrew implants (Fig. 2 A-E). The typodont was seated in a box with a heat lamp for 30 minutes to soften the wax, to allow movement on the typodont. This process provides simpler control on wax softening than using a water bath. Pattern and amount of tooth movement was accessed on typodont and it was found that maxillary first molars were distalize on both side by 4 mm (Fig. 3 A-E) measured at marginal ridges of molar and premolar, however amount of tipping could not be accessed.

Clinical Report:

In this case (Fig. 4 A-B) the K-loop spring was placed between maxillary 1st molar tube and 2nd  premolar bracket and the extended premolar arm of the K-loop spring was  ligated with miniscrew implant between 1st and 2nd premolars. Under infiltration local anaesthesia, titanium alloy miniscrew of 1.5-mm diameter and 8-mm length (SK Surgicals, Pune, Maharashtra, India) was inserted into the buccal alveolar bone between the right maxillary first and second premolars because there was not enough space in buccal alveolar bone between 1st premolar and canine. Treatment was continued for four months. It was found that the MISK spring provided correction of Class II molar relationship (Fig. 4 C-F) by distalization of right maxillary molar by 4mm measured at marginal ridges of molar and premolar.

Figure 4: Photographs and radiographs showing maxillary molar distalization using MISK spring (A-F).

Results:

Based on typodont study (Fig. 2&3) and photographic (Fig. 4 A-D) and radiographic record (Fig. 4 E-F) of clinical case, it is concluded that the MISK spring effectively distalizes the maxillary molars to correct the Class II molar relationship by moving the maxillary molars distally.

Discussion:

In routine orthodontic practice Class II malocclusion is the one of the most frequently encountered malocclusion.  Various orthodontic appliances like functional appliances, headgears, and multibracket fixed appliances with Class II elastics have been used for non-extraction treatment of Class II malocclusion. But both headgear and removable appliance need patient co-operation for successful orthodontic treatment.5-6

Pendulum and distal jet appliances also have been used for distalization with successful results but they have disadvantages of more laboratory time and high cost. Despite the use of different component in the design of Pendulum appliance to minimize the anchorage loss, anterior anchorage loss has been a problem with their use.1-2, 7  In recent years, Miniscrew implants have been used with intraoral molar distalization appliances to avoid anchorage loss.3, 8-10 Combining the findings of our typodont study and clinical report, it is  suggested that MISK spring is effective in maxillary molar distalization without the disadvantages of anchorage loss associated with conventional molar distalization appliances. Regarding patient comfort, there was no complaint by patient using the MISK spring, apart from difficulty with tooth brushing.

The limitation of this study was that the results cannot be claimed as valid predictor, due to the fact that natural tissue could not be simulated by typodont and MISK spring used in a single case. Hence clinical trial with large sample size will be needed to confirm the results with the quantification of amount of bodily movement and tipping for molar distalization. Based on limited evidence provided by this paper future trials should be designed, carried out and reported according to the Consolidated Standards of Reporting Trials (CONSORT) guidelines for its wider application.11

Conclusion:

It is concluded that the MISK spring effectively distalizes the maxillary molars to correct the Class II molar relationship in both typodont and clinical model by moving maxillary molars distally.

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