Expanding torque possibilities: A skeletally anchored torqued cantilever for uprighting “kissing molars”

Several uprighting mechanics and devices have been used for repositioning tipped molars. “Kissing molars” (KMs) are an uncommon tooth impaction involving 2 severely tipped mandibular molars with their occlusal surfaces positioned crown to crown, with the roots pointing in opposite directions. Orthodontic uprighting of KMs has not been a usual treatment protocol, and it can be a challenging task due to the severe tipping and double impaction, requiring efficient and well-controlled uprighting mechanics. An innovative skeletally anchored cantilever, which uses the torque principle for uprighting tipped molars, is suggested. This torqued cantilever is easy to manufacture, install, and activate; it is a well-known torque that is effective for producing root movement. A successful treatment of symptomatic KMs, involving the first and second molars, was achieved with this cantilever. Thus, clinicians should consider the suggested uprighting mechanics and orthodontic device as a more conservative alternative to extraction of KMs, depending on the patient’s age, involved teeth in KMs, tipping severity, and impaction positions.

Highlights

  • “Kissing molars” (KMs) are uncommon tooth impactions involving 2 severely tipped mandibular molars.

  • An innovative skeletally anchored cantilever, which uses the torque principle, is proposed for KM treatment.

  • KMs were successfully treated, achieving an excellent occlusal balance.

  • Reasons and guidelines for orthodontic treatment of KMs are discussed.

Molar uprighting mechanics are frequently required to reposition mesially tipped and impacted molars or when the erupted molars tip toward an edentulous space because of loss or agenesis of an adjacent tooth. However, “kissing molars” (KMs) describe an unusual type of tooth impaction in which 2 mandibular molars are severely tipped and impacted with their occlusal surfaces positioned crown-to-crown and the roots pointing in opposite directions. Gulses et al proposed a radiographic classification of KMs into Class I, Class II, or Class III categories depending on the location of the teeth involved. If the impactions are between the first and second molars, they are classified as Class I KMs; between the second and third molars, Class II KMs; and between the third and fourth mandibular molars, Class III KMs. However, this classification does not set treatment guidelines.

KMs should be treated if they cause adverse symptoms, are associated with cystic pathology, or because they have a high risk of caries, periodontal complications, or progressive bone loss. Orthodontic mechanics for uprighting KMs have not been reported. Surgical treatment involving extraction of 1 or both KMs is the most common protocol. The reason for this includes the high severity of the ectopic positions inherent to KMs. When molar tipping is extremely severe, showing a vertically inverted position in a panoramic radiograph (ie, root apex positioned more occlusally than the tooth crown), and the exposure level of the molar crown does not allow placement of uprighting mechanics on its buccal surface, molar uprighting may be a challenging task. This report shows an orthodontic treatment option for Class I KMs, presents an innovative skeletally anchored cantilever to aid in uprighting severely tipped KMs, and discusses reasons and guidelines for orthodontic treatment of this anomaly.

Diagnosis and etiology

A girl, aged 10 years 9 months, sought treatment at the dental school at the Federal University of Rio Grande do Sul in Porto Alegre, Brazil, with a clinical history of recurrent pericoronitis involving the mandibular right molar region. The clinical examination was not enough to provide an accurate diagnosis ( Fig 1 ). Radiographically, the right first and second molars were severely tipped toward each other so that their occlusal surfaces were contacting crown to crown, whereas the roots pointed in opposite directions, in a typical KM impaction position ( Fig 2 ). The second molar was the most severely tipped, with a vertically inverted position and over 90° of long axis rotation in relation to the adjacent unaffected teeth ( Fig 2 ). The unerupted surfaces of the KMs presented an enlarged pericoronal space that communicated with the oral cavity, allowing food debris impaction, bacterial contamination, and chronic infection with acute episodes, leading to bone loss ( Figs 1 and 2 ). This difficult access for dental cleaning probably led to the development of a deep carious lesion in the first molar ( Fig 2 ). The patient’s parents reported a history of a cystic lesion related to the KMs, which had been surgically treated 3 years previously. Since the patient had no history of metabolic diseases, trauma, or fracture involving the KM area, the cystic formation may have contributed to the displacement of the adjacent teeth to the KM position.

Fig 1
Pretreatment facial and intraoral photographs.

Fig 2
Pretreatment, panoramic, and periapical radiographs. The second molar was the most severely tipped KM with a vertically inverted position (root apex positioned more occlusally than the tooth crown) and over 90° of long-axis rotation in relation to the long axis of adjacent unaffected teeth. Note that the distalization force vector is close to the center of resistance of the severely tipped second molar.

The premolar relationships showed a half cusp Class II malocclusion ( Fig 1 ). Distal tipping of the first molar, associated with mesial tipping of the second molar, caused arch-length shortening in the KM area. The pretreatment dentoskeletal and soft tissue cephalometric features are shown in the Table .

Table
Cephalometric data before and after orthodontic treatment
Variable Pretreatment Posttreatment Difference
SNA (°) 87.8 88 0.2
SNB (°) 84.1 85.3 1.2
ANB (°) 3.7 2.7 −1
Wits (mm) 2.3 0 −2.3
SN.GoGn (°) 24.9 26 1.1
FMA (°) 17.6 18.1 0.5
LAFH (mm) 54 59.2 5.2
Mx1-NA (°) 26.3 20 −6.3
Mx1-NA (mm) 3.6 2.7 −0.9
Md1-NB (°) 19.8 31.2 11.4
Md1-NB (mm) 1.6 4.4 2.8
Overjet (mm) 5 2 −3
Overbite (mm) 3.5 2.2 −1.2
Nasolabial angle (°) 113.7 112.4 −1.3
Upper lip to E-plane (mm) −0.9 −1.2 −0.3
Lower lip to E-plane (mm) −1.5 −0.2 1.3
Inter-KMs angle (°) 138.5 5 −133.5

Treatment objectives

The primary treatment objectives were to normalize the posterior occlusion on the KM side and the periodontal health and dental cleaning access, preventing progress of the side effects associated with this developmental anomaly, such as occlusal collapse and bone loss. Additional objectives included Class II malocclusion correction and establishment of a functional occlusion.

Treatment objectives

The primary treatment objectives were to normalize the posterior occlusion on the KM side and the periodontal health and dental cleaning access, preventing progress of the side effects associated with this developmental anomaly, such as occlusal collapse and bone loss. Additional objectives included Class II malocclusion correction and establishment of a functional occlusion.

Treatment alternatives

Based on the primary objectives, some treatment alternatives were considered. Extraction of both KMs is the most usual treatment reported. However, in this young patient, having Class I KMs, extraction of first and second molars would produce an extensive occlusal sequel and early need for rehabilitation.

Extracting only the second molar could be a more conservative and reasonable alternative, taking into account its considerable tip ( Fig 2 ). However, the first molar had a deep carious lesion and some root shortening compared with the contralateral tooth ( Fig 2 ). Furthermore, the potential replacement of the second molar with the third molar, which was in the early stage of cusp calcification, raised treatment success uncertainties regarding the third molar’s anatomic characteristics, including its shape, structure, and dimensions. Treatment time would also be greatly increased waiting for the eruption of the third molar, to adequately position this molar and close residual spaces. Finally, replacement of the second molar with a dental implant instead of the third molar could also be disadvantageous because the patient has a long growth period ahead, which contraindicates implant placement in the short term while risking bone loss in the extraction area.

An alternative and conservative approach would be to extract the damaged first molar, but this option must take into account that treatment success would depend on the less predictable results of uprighting an extremely tipped second molar. The previously mentioned drawbacks, such as developmental uncertainties regarding the third molar, increased treatment time, and need for closing the residual spaces also applied to this protocol, as well as to bone loss in case of an implant rehabilitation choice. Lastly, it must be considered that, unlike second molar extraction, first molar removal would require the difficult task of mesializing 2 molars.

The factors that influenced the decision to treat this Class I KM patient using a nonextraction protocol were the following: the patient’s young age, the need for immediate clinical intervention, the early development stage of the third molar, the moderate preservation of the dental structure of the KMs, and the parental reluctance to accept an extraction treatment plan. Thus, any of the previously discussed extraction protocols involving late third molar handling would still be available if for some reason the repositioning of the KMs proved to be unsuccessful.

Treatment progress

The orthodontic treatment began with a focused intervention on KMs because of the urgent patient need and because not all permanent teeth were erupted at this time. Due to the arch-space deficiency for first molar repositioning, KM correction was started with uprighting of the second molar. However, the position and exposure degree of the second molar crown was not favorable for conventional buccal uprighting mechanics ( Fig 1 ). In addition, uprighting mechanics that are based on distalization force vectors cannot produce an effective uprighting moment when the molar is extremely tipped because the line of force action lies close to the center of resistance of the tipped molar ( Fig 2 ). Consequently, some distal movement of the second molar roots could occur; this would be undesirable ( Fig 2 ). Thus, an innovative skeletally anchored cantilever made of stainless steel rectangular wire (0.019 × 0.025 in) was proposed. This cantilever was created to satisfy the clinical conditions and the mechanical objectives of this patient ( Fig 3 ). A mini-implant was inserted between the canine and the first premolar to prevent the undesirable side effects from cantilever intrusion force. Unlike the usual cantilever mechanics, this new uprighting device uses the torque principle to move the roots in a mesiodistal direction ( Fig 4 ). Torque is a twisting force traditionally used to produce tooth movement in a buccolingual direction. To achieve this new torque effect, an orthodontic tube was bonded with its slot buccolingually positioned on the erupted part of the occlusal surface of the impacted tooth ( Figs 3 , A and B , and 4 , B ). Thus, when this torqued cantilever is actively inserted into the molar tube, a mesiodistal moment of force is applied on the molar roots, producing an uprighting effect ( Figs 3 , C and D , and 4 ).

Dec 12, 2018 | Posted by in Orthodontics | Comments Off on Expanding torque possibilities: A skeletally anchored torqued cantilever for uprighting “kissing molars”
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