Case Reports

0 downloads 0 Views 598KB Size Report
in the oral vestibule. The positioning of the miniplate served several purposes. Anteroposterior positioning in the region of the mesial third of the mandibular.
Case Reports

Double impact: Intrusion of two mandibular molars using an SAS— A case report Kartik D. Dholakia, BDS, MDS1 Shweta R. Bhat, BDS, MDS2

The size of the envelope of tooth movements using fixed mechanotherapy has been increased with the use of temporary anchorage devices (TADs). Orthodontic mini-implants, a form of TADs, have been successfully used for achieving a variety of tooth movements, such as bodily retraction, extrusion, protraction, and even intrusion of maxillary molars. However, the use of orthodontic mini-implants for intruding mandibular molars is questionable due to anatomical constraints. Skeletal anchorage systems (SASs), another form of TADs, overcome these limitations to give promising results for mandibular molar intrusion. The following case report shows the use of unilateral SAS for intruding two mandibular molars and extruding a maxillary molar of the same side to establish a stable occlusal plane. The amount of intrusion achieved in relation to mandibular molars was evaluated by comparing panoramic images. The mandibular left first and second molars were intruded by approximately 1.6 and 2.5 mm, respectively, in relation to the occlusal plane. Orthodontics (Chic) 2011;12:378–385. Key words: intrusion, mandibular molars, panoramic radiograph, SAS

T

he envelope of tooth movements using fixed mechanotherapy includes tipping, bodily tooth movement, torquing, extrusion, derotation, intrusion, and all possible combinations thereof. However, for biomechanical systems to be in equilibrium, there is always a reciprocal force system generated, which may sometimes have some undesirable effects. For instance, intrusion attempted on the anterior segment of the arch using fixed mechanotherapy has a reciprocal extrusion effect on the posterior segments, which may be unacceptable. This drawback can be overcome only to some extent by increasing the number of anchorage units (ie, molars). But when the molars themselves require significant intrusion, there needs to be a source of anchorage. The answer to this question can be TADs (temporary anchorage devices). Orthodontic mini-implants, a form of TADs, have proven to simplify and increase the envelope of tooth movements performed in conjunction with fixed mechanotherapy.1 Mini-implants have been successful in achieving even maxillary molar intrusion. But in cases of mandibular molar intrusion, the use of mini-implants is questionable due to anatomical constraints. These constraints include inadequate vestibule depth for placement of implants apical enough to deliver intrusive forces, thin interadicular and interdental bone limiting use of longer mini-implants for primary stability, and biomechanical ineffiencies if placed mesially or distally to the mandibular molars. A skeletal anchorage system (SAS), which is a stable TAD, is a miniplate that can be placed underneath the mandibular molars and derives its anchorage from the basal bone for intruding the molars.2–5

1Consultant

Orthodontist and Private Practice, Mumbai, India. 2Professor and Head, Department of Orthodontics, Nair Hospital Dental College, Mumbai, India. CORRESPONDENCE Dr Kartik D. Dholakia KD Orthodontics 502, C Wing, Shanti Vihar S.V. Road, Kandivali (W) Mumbai 400067 Maharashtra India Email: dholakia.kartik@ gmail.com

378

The Art and Practice of Dentofacial Enhancement

ORTHODONTICS  

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

The following is the report of a patient in whom unilateral mandibular molar intrusion along with maxillary molar extrusion was carried out using a single mandibular SAS.

Case report A 15-year-old Indian girl reported to the Department of Orthodontics, Nair Hospital Dental College, Mumbai, India, with the chief complaint of forwardly placed and malaligned maxillary anterior teeth. A detailed case history revealed a history of trauma in the mandibular anterior region 6 years prior, which led to the loss of three mandibular incisors, following which the patient undertook appropriate treatment. On clinical examination, a loss of space due to mesial migration of the adjacent teeth was observed (due to the missing teeth). It was also observed that the maxillary left first molar was infraerupted and mesially tilted, and the opposing mandibular first and second molars were extruded with some degree of mesial tipping of the first molar and distal tipping of the second molar. All diagnostic records were collected and analyzed (Figs 1 and 2). An intraoral periapical radiograph of the maxillary left first molar displayed some fuzziness in relation to the apical third; however, it was not conclusive of ankylosis (Fig 2). After analyzing all the diagnostic records, maxillary first premolar extraction was proposed to correct the maxillary anterior proclination. It was planned that space available in the mandibular anterior region would be restored with a prosthesis of a single incisor and both the mandibular canines and premolars would be recontoured to look like lateral incisors and canines, respectively. In the posterior segment, it was decided to intrude the mandibular left first and second molars using an SAS. The same anchorage system was planned to attempt extrusion of the maxillary left first molar. Fixed mechanotherapy using MBT brackets with 0.022-inch slots was used. Brackets were bonded as per the MBT bracket placement chart. The maxillary and mandibular first and second molars were banded. A continuous archwire was used in the mandibular arch only after the placement of the SAS to intrude the mandibular left molars. The maxillary archwire extended from the maxillary left second molar to the right second premolar. The maxillary left first and second molars were dealt with as a separate segment.

Mandibular Skeletal Anchorage System (SAS)

The SAS consisted of a four-hole, I-shaped 316L stainless steel miniplate with 2-mm profile.5,6 A mesially facing slit was prepared in the most coronal portion of the miniplate (Fig 3). The slit was used to engage the ligature wires, hook, or elastics would deliver intrusive forces on the mandibular left first and second molars and extrusive forces on the maxillary left first and second molars. Volume 12, Number 4, 2011 © 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

379

Case Reports

Double impact: Intrusion of two mandibular molars using an SAS—A case report

a

b

d

c

e

f Fig 1   Intraoral photographs before starting orthodontic treatment. (a) Right lateral view, (b) frontal view, (c) left lateral view, (d) maxillary occlusal view, (e) mandibular occlusal view, (f) mandibular left lateral view. Note that the occlusal photographs have been modified and are not mirror images.

Fig 2   Intraoral periapical radiograph of the maxillary left first molar before starting orthodontic treatment. Fig 3 (right)  Miniplate with a mesially facing slit.

380

The Art and Practice of Dentofacial Enhancement

ORTHODONTICS  

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

Case Reports

Dholakia et al

Line B1

Line C1

Line A1

a

b

Fig 4   (a) Panoramic radiograph 1 just after SAS placement, (b) tracing 1.

The patient was treated under local anesthesia with sedation. The miniplate was contoured and fitted vertically to the basal bone of the mandible using three 6-mm monocortical screws. The most coronal hole was left exposed in the oral vestibule. The anteroposterior positioning of the miniplate was such that the most coronal hole with a slit would lie below the mesial third of the mandibular left second molar. The vertical positioning was such that the coronal-most part of the miniplate was at least 4 mm below the inferior border of molar tube and exposed in the oral vestibule. The positioning of the miniplate served several purposes. Anteroposterior positioning in the region of the mesial third of the mandibular left second molar provided relatively more intrusive force on the second molar compared with the first molar, distal tipping force on the first molar and mesial tipping force on the second molar, and distal tipping force on the maxillary right first molar. The vertical position of coronal-most part of the miniplate 4 mm apical to the inferior border of the molar tube gave enough clearance from the archwire molar tube to deliver intrusion forces to the mandibular first and second molars. Postsurgically, following resolution of edema and pain, a panoramic radiograph was taken (Fig 4a). A continuous 0.016-inch heat-activated nickel-titanium (HANT) wire was placed in the mandibular arch. There was no risk for extrusion of adjacent premolars, because the mesial end of the molar tube on the mandibular left first molar was relatively more gingival compared with that of the distal end (the tooth was mesially tipped). Strong stainless steel ligation was used from the coronal hole of the miniplate extending the segment of the archwire, extending the mandibular left first and second molars such that this length of wire is pulled down in an arclike fashion toward the bone plate. This method of ligation (Figs 5f and 5g) delivered long-term intrusive forces on the mandibular left first and second molars as well as simultaneous distal tipping force on the mandibular left first molar and mesial tipping force on the second molar, thus uprighting these teeth. Elastics were used between the bone plate and the maxillary left first molar to facilitate its extrusion and distal tipping. A 3-week recall schedule was planned for routine checkup, replacement of elastics, and activation of stainless steel ligation for the mandibular molar intrusion. After 1.5 months, the mandibular 0.016-inch HANT archwire was changed to a 0.016 × 0.022-inch HANT archwire. Three months from the start of intrusion of the mandibular molars, the mandibular left first and second molars were sufficiently intruded to the level of the occlusal plane of the remaining mandibular teeth. Photographs and panoramic radiographs were taken at this appointment to evaluate the amount of mandibular molar intrusion achieved (Figs 6 and 7). Volume 12, Number 4, 2011 © 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

381

Case Reports

Double impact: Intrusion of two mandibular molars using an SAS—A case report

a

b

d

c

e

Occlusal plane

f

g

HANT archwire

Stainless steel ligature extending from miniplate to HANT archwire

Fig 5   Intraoral photographs before starting intrusion of the mandibular left first and second molars. (a) Right lateral view, (b) frontal view, (c) left lateral view, (d) maxillary occlusal view, (e) mandibular occlusal view, (f) method of ligating stainless steel ligature from SAS to the length of archwire between the mandibular left first and second molars, (g) biomechanics along sagittal plane. Note that occlusal photographs have been modified and are not mirror images.

Results Measuring the amount of intrusion using superimposed serial lateral cephalograms would not be feasible, since intrusion was attempted unilaterally. Therefore, tracing of panoramic radiographs taken just after placement of the SAS (1: magnification factor = 34.82 mm / 29.62 mm = 1.175) were compared with those taken after 3 months of treatment (2: magnification factor = 35.91 mm / 29.62 mm = 1.212) to evaluate the amount of intrusion achieved (Figs 4 and 7). To do so, the magnification factor of each panoramic radiograph in the vertical plane along the length of the miniplate (SAS) was evaluated using following formula: Magnification factor = Length of miniplate on the panoramic radiograph / actual length of miniplate On tracing paper, lines were constructed. On panoramic radiograph 1 (Fig 4), line A1 was perpendicular to the length of the miniplate at the coronal-most point on the miniplate, line B1 was perpendicular to the length of the miniplate 382

The Art and Practice of Dentofacial Enhancement

ORTHODONTICS  

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

Case Reports

Dholakia et al

a

b

d

c

e

f Fig 6   Intraoral photographs after 3 months of treatment. (a) Right lateral view, (b) frontal view, (c) left lateral view, (d) maxillary occlusal view, (e) mandibular occlusal view, (f) mandibular left view. Note that occlusal photographs have been modified and are not mirror images.

Line B2

Line C2

Line A2

a

b

Fig 7   (a) Panoramic radiograph 2 after 3 months of orthodontic treatment, (b) tracing 2.

at coronal-most point on occlusal surface of the mandibular left first molar, and line C1 was perpendicular to the length of the miniplate at the coronal most point on the occlusal surface of the mandibular left second molar. On panoramic Volume 12, Number 4, 2011 © 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

383

Case Reports

Double impact: Intrusion of two mandibular molars using an SAS—A case report

Table 1   Perpendicular distance between the constructed lines Distance measured

Distance (mm) (a)

Magnification factor (b)

Actual distance (a/b) (c)

Radiograph 1 A1–B1

9.8

1.18

8.30

A1–C1

7.73

1.18

6.55

A2–B2

8.15

1.21

6.73

A2–C2

4.91

1.21

4.05

Radiograph 2

radiograph 2 (Fig 7), line A2 was perpendicular to the length of the miniplate at coronal most point on bone plate, line B2 was perpendicular to the length of the miniplate at the coronal-most point on the occlusal surface of the mandibular left first molar, and line C2 was perpendicular to the length of the miniplate at the most coronal point on the occlusal surface of the mandibular left second molar. The perpendicular distance between the lines was measured and divided by the magnification factor to give the amount of actual distance between the respective lines (Table 1). The amount of intrusion was then calculated. For the mandibular first molar: Actual distance (A1 – B1) – actual distance (A2 – B2) = 1.6 mm For the mandibular second molar: Actual distance (A1 – C1) – actual distance (A2 – C2) = 2.5 mm Simply superimposing tracings of panoramic radiographs 1 and 2 was not attempted for the following reasons: • Differences in magnification factor • Ratio of the amount of variations in repeated digital vernier caliper measurements (on panoramic radiograph tracings) used over smaller lengths is greater compared with that of longer lengths, leading to exaggeration of error (sensitivity of the digital vernier caliper used for measurements is 0.01 mm) Both the mandibular left first and second molars were found to be vital postintrusion after 3 months. With respect to the maxillary arch, no extrusion of the maxillary left first molar was observed. Another intraoral periapical radiograph of that region was taken. Fuzziness was noted in the apical third region of the maxillary left first molar roots. Due to the absence of any extrusive movement of the tooth, and ruling out other possible causes for its infraeruption (mesially tipped molar locked beneath the distal cervical third of the second premolar), ankylosis was assumed to be present. Partial luxation was attempted by an experienced oral surgeon, following which elastic traction extending from the miniplate was given to extrude the first molar. No improvement was observed, and we proposed restoring the first molar with a crown to establish occlusal contact. A continuous wire bypassing the maxillary left first molar, along with elastic traction from the miniplate, brought the maxillary left second molar into occlusion with the opposing teeth (Fig 6). 384

The Art and Practice of Dentofacial Enhancement

ORTHODONTICS  

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

Case Reports

Dholakia et al

Discussion It is evident that the mandibular left first and second molars were significantly intruded and uprighted to the level of the occlusal plane of the other mandibular teeth. These values indicate intrusion in relation to the occlusal plane along the direction of the skeletal anchorage device (miniplate) and are not a representation of absolute intrusion in relation to the centroid. No significant buccal tipping was observed with the mandibular left first and second molars, which otherwise would normally occur with any biomechanical system applying intrusive forces buccal to the center of resistance of the tooth. The miniplate was contoured and placed such that the coronal portion (kept exposed at the depth of the vestibule) was placed in close proximity to the buccal aspect of the mandibular left second molar to minimize buccally directed force vectors. Also, the thick cortical bone of the external oblique ridge in that region would offer good resistance to buccal tipping. This may be the reason for reduced buccal tipping of molars.

Alternate plan

Cases of extruded mandibular molars are a common occurrence due to the high incidence of missing maxillary molars as a result of caries and periodontal pathology. The use of continuous archwires for leveling the occlusal plane in the mandibular arch without any intrusive force component in the molar region will lead to canting of the occlusal plane. Therefore, this method of leveling the mandibular arch is not advisable. An alternate approach toward management of unilateral mandibular extruded molars will be intentional root canal treatment of extruded teeth followed by crown prostheses with relatively shorter vertical dimensions and occlusal surfaces at the level of the occlusal planes of the remaining mandibular teeth.

Conclusion Like orthodontic mini-implants, TADs have been effective in intruding maxillary molars. However, their use for the intrusion of mandibular molars is not as clear. This is due to the requirement of high forces to intrude mandibular molars against thick cortical bone, which, coupled with constraints of a placement site apical enough to deliver intrusive forces, makes orthodontic mini-implants unpromising for intruding mandibular molars. Use of SAS overcomes these constraints and has proven efficient in this patient by achieving approximately 1.6 and 2.5 mm of intrusion of the mandibular left first and second molars, respectively, thereby establishing a flat functional occlusal plane. However, SAS device placement requires the use of sedation or general anesthesia, which itself requires high patient compliance. Hence, its use for intruding a single molar needs to be weighed against the risk of subjecting the patient for additional surgical procedures under general anesthesia or sedation. In this case, we opted for an SAS, since it required intrusion of two mandibular molars and extrusion of two maxillary molars on the same side. Therefore, the maintenance of the longevity of teeth along with a proper functional occlusal plane was given the priority over intentional root canal treatment and subsequent crown prostheses.

Acknowledgments The authors wish to thank Dr Neelam Andrade, Professor and Head, Department of Oral and Maxillofacial Surgery, Nair Hospital Dental College, for placing the skeletal anchorage system.

References 1. Nanda R, Uribe FA. Temporary Anchorage Devices in Ortho­ dontics. St Louis: Mosby, 2009. 2. Umemori M, Sugawara J, Mitani H, Nagasaka H, Kawamura H. Skeletal anchorage system for open-bite correction. Am J Orthod Dentofacial Orthop 1999;115:166–174. 3. Sugawara J. Dr Junji Sugawara on the skeletal anchorage system Interview by Dr Larry W. White. J Clin Orthod 1999;33: 689–696. 3. Sugawara J, Baik UB, Umemori M. Treatment and post­ treatment dentoalveolar changes following intrusion of mandibular molars with application of a skeletal anchorage system (SAS) for open bite correction. Int J Adult Orthod Orthognath Surg 2002;17:243–253. 5. Sugawara J, Nishimura M. Minibone plates: The skeletal anchorage system. Semin Orthod 2005;11::47–56. 6. Park JB, Bronzino JD. Biomaterials: Principles and Applications. Boca Raton, Florida: CRC Press, 2000.

Volume 12, Number 4, 2011 © 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

385