|Year : 2016 | Volume
| Issue : 5 | Page : 10-22
Lingual biomechanics, case selection and success
Director, Institute of Lingual Orthodontics, Indirapuram, Ghaziabad, Uttar Pradesh, India
|Date of Submission||07-Dec-2016|
|Date of Acceptance||15-Dec-2016|
|Date of Web Publication||18-Jan-2017|
Dr. Sanjay Labh
Institute of Lingual Orthodontics, Indirapuram, Delhi NCR, Ghaziabad, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Deeper understanding of lingual biomechanics is prerequisite for success with lingual appliance. The difference between labial and lingual force system must be understood and kept in mind during treatment planning, especially anchorage planning, and extraction decision-making. As point of application of force changes, it completely changes the force system in all planes. This article describes lingual biomechanics, anchorage planning, diagnostic considerations, treatment planning, and case selection criteria in lingual orthodontics.
Keywords: Case selection, diagnosis and treatment planning, lingual biomechanics
|How to cite this article:|
Labh S. Lingual biomechanics, case selection and success. J Indian Orthod Soc 2016;50, Suppl S1:10-22
| Introduction|| |
Proper understanding of biomechanics and its application in treatment improves the efficacy of appliance system and makes treatment simple. It is also required to improve force delivery and achieve more predictable tooth movement with minimal adverse effect in any appliance system.
Lingual appliance system is more difficult because of unpredictable lingual surface anatomy, no direct access to lingual surface, and different point of application of force. Key factor for successful orthodontic treatment is precise bracket positioning. Therefore, several indirect bonding procedures have been developed for lingual technique.
| Point of Force Application is Different and Dynamic|| |
Lingual biomechanics is different because force system is different. Tooth moves in response to applied force. Type of tooth movement depends on relationship between point of application of force and center of resistance (Cres) of tooth and manner of application of force. Point of force application (PF) in lingual appliance is different and its relation is dynamic with CR.
Relationship of Center of Resistance and point of force application
PF is different in lingual appliance. Relationship between Cres of tooth and PF produces different types of tooth movement.
In Labial Appliance, changes in bracket height and Changes in Tooth Inclination doesn't bring about much change in relation of Point of Force application and Cres. While in Lingual Orthodontics, changes in bracket height and Changes in Tooth Inclination and thickness of customized base of the Bracket, brings about major change in relationship between Cres and point of force application, leading to generation of different moment, and makes Lingual Biomechanics more DYNAMIC.
In general, PF is lingual to Cres of tooth as compared to labial PF in labial mechanics. There is inherent lingual tipping moment on anterior teeth with lingual mechanics. Every attempt in laboratory set up should be done to counteract this lingual tipping [Figure 1], [Figure 2], [Figure 3], [Figure 4].
|Figure 1: Distance between point of application of force and C res of tooth in sagittal plane|
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|Figure 2: Distance between point of application of force and C res of tooth in vertical plane|
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Different force vector
When same amount of retraction and intrusion force is applied to the incisors in Labial and lingual system, the resultant force vector in lingual system passes Lingual to CR, producing larger lingual tipping moment during treatment, retraction force should be minimized and intrusive force should be maximized to reduce residual lingual tipping moment from force system [Figure 5].
|Figure 5: The effect of bracket position and location of point of force application on resultant force vector|
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The primary changes induced by the lingual appliance can best be categorized as those dynamic effects on vertical, anteroposterior, and transverse planes.
Factors responsible for better anchorage control in lingual mechanics than labial mechanics are
- Lingual tipping moment generated on anterior tooth is transmitted to posterior teeth as distal tipping moment leading to distal uprighting of molars
- In horizontal plane, with application of retraction force, molars have tendency of mesial-out and distal-in rotation
- Cortical anchorage is established, in occlusion after placement of lingual brackets in molar teeth, usually lingual cusp of lower molars touches bracket on upper molar. As there occlusal forces are transmitted lingual to CR, it results in lingual crown tip and buccal root tipping and establishment of cortical anchorage
- Smaller arch perimeter on lingual side increases rigidity of lingual wire.
The most immediate and readily apparent appliance-induced change is the bite opening resulting from the lower incisors occluding on the maxillary incisor bracket bite planes. This bite opening produces both positive and negative effects. In the low angle brachyfacial patterns, the bite opening is usually desirable. Many deep bite cases have low mandibular plane angles and benefit from posterior extrusion. The posterior disclusion, resulting from the anterior bite plane opening, permits a rapid eruption of the molars and bicuspids, with posterior occlusion reestablishing in approximately 3-4 months. In the mesiofacial and dolichofacial types, where bite opening may not be desirable, orthodontic mini-implants should be used in conjunction to control vertical dimension.
The posterior disclusion removes two prime anchorage factors - the inclined plane occlusion and musculature. The "bowing" occurs in the vertical direction, potentially causing loss of anterior torque control, tipping, and further bite opening.
In many instances, occlusal interferences, due to bracket coming in between upper and lower posterior teeth, always maintains some intrusive force on posterior teeth in lingual appliance, and hence vertical anchorage is conserved.
With the initial posterior disclusion, the expansive nature of the lingual appliance and a tendency to cause mesiobuccal molar rotation during space closure, intermolar dimension becomes more important to control. Therefore, transverse considerations gain additional importance. Retraction on resilient wire can produce several adverse effects, particularly in the transverse planes. Interarch retraction forces on more flexible wire can cause a "bowing" effect, resulting in the bicuspids being displaced buccally and the molars rotating to the mesiobuccal. Once the maxillary first molars rotate to the mesiobuccal, this can cause a functional interference between the molars, inducing additional vertical opening and further aggravation of the anteroposterior discrepancy.
Fortunately, most of these problems can be prevented by proper treatment planning and archwire sequencing as well as a degree of patience in allowing the more resilient archwires to exert their influence before proceeding to the next wire. Retraction and space closure with lingual must also follow well-established principles, requiring anchorage preparation and transition to archwires of sufficient stiffness.
Six keys for anchorage control in lingual sliding mechanics
- Extra palatal root torque in anteriors, molar tubes mesially placed, incorporate molar tie back, buccal root torque in molars
- Reduce friction with use of bidimensional archwire or dual slot system
- Posterior bite stops/blocks should be given if posterior separation is more than 2 mm
- Use light Class I, II, or III elastics for space closure
- Second molars should be included in anchor unit.
In lower arch, on lingual side, bond till first molar only. Bond buccal tube on buccal side of first and second molars and insert full size NiTi or TMA wire, to avoid patient discomfort
- Compensating curves should be given in archwire.
Tendency of buccal flaring of posteriors
Archwire should be passive in transverse plane to avoid buccal flaring of posterior teeth.
Difficult rotation correction
Small interbracket span, unibracket system, and small moment generation due to smaller distance of lingual bracket base to Cres are the factors leading to difficulty in rotation correction in lingual mechanics. Smith's rotation tie should be utilized for fast and efficient rotation correction.
Vertical bowing effect
Any retraction force will lead to lingual tipping of incisors and distal tipping of canines, if appropriate counter moment is not applied.
When lower anterior teeth come in contact with bite plane of upper anterior bracket, it leads to posterior disocclusion and loss of occlusal interlocking. It makes molar prone to forward movement/mesial tipping.
Finally, it leads to deepening of bite and lateral open bite in canine-premolar region.
Care must be taken to avoid this vertical bowing in lingual system [Figure 6].
Preventive measures to be taken are
In set up
- Overcorrection in torque of anteriors
- Overcorrection in canine mesial tip
- Overcorrection in distal tip of premolars and molars
- Vertical position of canine bracket gingival to normal position.
- Reduce retraction force
- Increase intrusive force
- Increase upper anterior torque by giving additional torque in the wire
- Gable bends and compensatory curves should be incorporated in the wire
- Do not attempt to engage severely displaced teeth in continuous all teeth in archwire.
Transverse bowing effect
With application of retraction force, posterior segment rotates mesially out and distally in [Figure 7].
Preventive measures to avoid transverse bowing:
- Retraction wire with compensating curve is made with curvature starting from distal to upper premolar such that the archwire is expanded by one cusp width in second molar region
- In addition, bracket/tube of molars should be placed slightly mesial to mesiodistal center of tooth
- Elastic/spring for retraction of anteriors may be attached from second premolar to hook in canine-lateral incisor region rather than from molar
- Reason: Retractive force will rotate molar distal-in, leading to constriction of arch in molar region, i.e., transverse bowing
- E-chain may be placed in circular fashion passing from lingual side of molar to lingual of canine, crossing over mesial surface of canine to pass over to labial side attaching to the buccal tube on the molar, thus preventing rotation of posterior segment.
Anterior bite plane effect
Inherent bite plane effect in lingual bracket system allows for bite opening [Figure 8].
Always establish torque in anterior segment before starting retraction
Unequal torque in anterior segment makes it difficult to move negative and interferes with retraction. Hence, it is mandatory to establish uniform torque before retracting anterior teeth.
Utilize en masse retraction
From esthetic point of view, it is not desirable to have dark spaces in anterior segment; hence, en masse retraction is preferred over separate canine retraction.
In terms of mechanics, because of inset bend in the archwire distal to canine, it is not possible to slide canine.
[Figure 9] and [Figure 10]
| Ligation Method in Lingual Appliance|| |
- Anterior leveling and alignment
- Initial leveling and alignment - 012" NiTi/TMA
016" copper NiTi.
- Partial canine retraction
- Done to eliminate crowding and create space for alignment of four incisors in both arches
- Following this, six anterior teeth are leveled with a full archwire
- Care must be taken to prevent vertical bowing effect
- Adequate space must be created for rotation correction.
- Rotation correction with Smith's rotation tie
Method: For a tooth rotated mesial-out and distal-in
- Engage 10 loops of E-chain in main archwire,
- Bring E-chain to labial side through mesial gingival embrasure,
- Again bring E-chain to lingual side through distal gingival embrasure,
- Pull E-chain and engage 3rd loop of E-chain on bracket of that tooth and cut rest [Figure 11].
- Establishment of torque
Wire: 17 × 25" TMA [Figure 12].
|Figure 12: Establishment of torque with compensating curve on 0.017 × 0.025 TMA|
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- En masse retraction
Wire: Lower - 016 × 022" SS (sliding), upper - 17 × 25"
TMA/16 × 22" SS/17 × 25" SS (sliding) [Figure 13].
Wire: 016" TMA/016 × 016" TMA [Figure 14].
Key to biomechanical success
- Use very light force/resilient wire
- First create space then attempt derotation/decrowding
- Establish torque before retraction
- Never retract on round/light wire
- Give proper compensating curves
- En masse retraction
- Use light wire for detailing.
| Diagnosis and Treatment Planning|| |
Case diagnosis is conducted in a manner similar to established procedures. The treatment plan is based on the diagnosis, advantages and limitations of the various modes of treatment, cost and time factors, and, of course, the patient's desires.
As with all orthodontic cases, the status of the periodontium must be carefully evaluated. This is more important with lingual and adult patients.
The likelihood of encountering more extensive restorative and prosthetic work is naturally increased in the adult patient. In cases where there is a loss of several teeth, extreme tipping, and multiple or complex bridgework, the comprehensive interdisciplinary planning must be done.
Lingual crown height
Lingual clinical crown heights on the average patient are approximately 30% shorter than the available crown on the labial surfaces. Short lingual clinical crowns can present a contraindication to optimum lingual bracket positioning.
Particular attention should be given in the following instances:
- Extreme brachyfacial types with short alveolar and crown height dimensions
- Partially erupted teeth in the young adolescent patient
- Crown heights that have been diminished by excessive wear, trauma, or restorative work
- Diminutive teeth, i.e., peg laterals.
Temporomandibular joint considerations
Many clinicians have reported relief of joint symptoms following lingual appliance placement. This apparently occurs because of the disarticulation of posterior interferences, creation of freedom of movement of the "locked" mandible, and changes in muscle position and length due to different posturing of the mandible.
Extraction versus nonextraction considerations
The lingual appliance lends itself well to expansion and bite opening. The broad range of cases that lend themselves to this mode of treatment, especially Class I deep bites, are excellent candidates for invisible braces. In Class II cases, or when an open bite tendency exists, extractions should be considered. With its unique biomechanics, extraction choices in lingual orthodontics often differ from those in labial orthodontics.
| Guidelines for Case Selection|| |
To summarize the patient selection criteria and influences of appliance design parameters on treatment planning, the following guidelines, based on our clinical experience thus far, may be of assistance in the case selection process:
Ideal lingual cases
- Deep bite, Class I with mild crowding, good facial pattern
- Deep bite, Class I with generalized spacing, good facial pattern
- Deep bite, mild Class II, good facial pattern
- Class II Division 2 with retruded mandible
- Cases requiring expansion
- Consolidation (diastema) cases.
- Class II, maxillary first bicuspid and mandibular second bicuspid extractions
- Maxillary first bicuspid only extractions
- Bimaxillary protrusions with four second bicuspid extractions.
Difficult lingual cases
- High angle/dolichofacial patterns
- Surgical cases
- Class III tendencies
- Class II, four first bicuspid extraction
- Cases with multiple restorative work.
Cases contraindicated for lingual therapy
- Unadaptable or demanding personality types
- Poor oral hygiene or unresolved periodontal involvement
- Short clinical crowns
- Acute temporomandibular joint (TMJ) dysfunction.
| Case Report 1|| |
A 32-year-old female patient with chief complaint of unpleasant smile, front teeth not touching together and spacing between front teeth.
H/o orthodontic treatment 10 years before involving extraction of 15, 25, 35, and 45.
A case of Angle's Class I malocclusion with bimaxillary protrusion and spacing and anterior open bite (AOB) with secondary tongue thrust.
- From lateral view, patient's profile was mild convex
- From frontal view, facial asymmetry was not recognized
- Flat smile was noticed
- Lip incompetency was noticed.
- Patient's mastication and TMJ function were normal
- Secondary tongue thrust was present.
- Angle's Class I
- Overjet + 4 mm, overbite - 4 mm
- Midline diastema 1.5 mm
- Spacing in upper and lower arch
- Flat smile arc
- Preextracted/missing 15, 25, 35, 45
- Normal upper labial frenum.
Dental cast examination
- Mandibular arch: Arch length discrepancy + 4 mm
- Maxillary arch: Arch length discrepancy + 7 mm
- Occlusion sagittal: Angle's Class I; Overjet + 4 mm
- Occlusion vertical: Overbite - 4 mm
- Occlusion transversal: Normal.
Pretreatment panoramic radiograph
- Preextracted/missing 15, 25, 35, 45
- Mesial tipping of 16, 26, 36, 46
- 11, 12, 13, 21, 22, 23 in infraocclusion
- Generalized alveolar bone loss (mild periodontitis).
Pretreatment cephalometric analysis
Sagittal skeletal relation
Sagittal relation between maxilla and mandible was in normal range as follows (A-N-Pg 2°, SNA 78°, SNB 76°).
Reduced value of SNA and SNB was due to abnormal position of nasion.
Vertical skeletal relations
Maxillary inclination (S-N/ANS-PNS), mandibular inclination (S-N/Go-GN), and vertical jaw relation (ANS-PNS/Go-Gn) show vertical growth pattern and a hyperdivergent face.
- Maxillary incisors were severely proclined (1 - ANS-PNS: 129°)
- Position of maxillary incisor was protrusive in relation to A-Pg line
- Vertical position of maxillary Incisors was in infraocclusion
- Mandibular incisors were normally inclined (1- Go-Gn: 95°)
- Position of mandibular incisor was protrusive in relation to A-Pg line (+7 mm)
- Vertical position of mandibular incisors was normal.
- Molar relation Class I
- Overjet + 4 mm
- Vertical relation was AOB (overbite - 5 mm) caused mainly from
- Infraocclusion of maxillary incisors and bimaxillary protrusion
- Mesial tipping of molars was also contributing in AOB.
- Upper and lower lip was retrusive in relation to E-line
- Patient's profile was almost straight.
- To obtain anterior lip seal
- To control secondary tongue thrust habit
- To close AOB
- To get a good smile arc.
- Indirect bonding of both arches with lingual appliance (ORG brackets)
- Leveling and alignment
- Space closure
- Distal uprighting of upper and lower molars to
- Change the cant of both occlusal planes to close AOB
- Prolonged bonded fixed retainer in both arch.
Reappearance of AOB was due to relapse. One of the reasons for relapse was lack of any kind of retention. Moreover, because of lack of anterior lip seal, there was a secondary tongue thrust.
Correction of inclination of upper and lower incisors and closure of generalized spacing in both arches were needed to obtain normal incisor relation and normal anterior lip seal.
Distal uprighting of upper and lower molars was needed to change the cant of both occlusal planes to close AOB.
By its virtue lingual appliance in itself is a tongue thrust habit breaker, so no other habit breaking appliances were planned.
- At start: Pretreatment records taken, diagnosis, and treatment planning done
Indirect bonding to mandibular and maxillary arch with lingual brackets
0.014 Cu-NiTi wire in both arches.
- 5 month: Started initial space closure on 0.018 SS archwire in both arch with E-chain
- 7 month: Space closure continued on 0.017 × 0.025 SS wire with E-chain in both arches
- 1 year: Completion of space closure and closure of AOB
- 1 year 2 month: Distal uprighting of molars in all quadrant with tip back bend
Settling of posterior occlusion with elastics on buttons bonded on labial surface of molars
- 1 year 4 month: Detailing on 0.016 TMA in both arch
- 1 year 6 month: Removed the appliances:
Posttreatment records taken and retention started.
Posttreatment panoramic radiograph analysis
- Uprighting of 16, 26, 36, and 46
- 11, 12, 13, 21, 22, and 23 in line of occlusion
- No further alveolar bone loss
- No root resorption.
Posttreatment cephalometric analysis
Sagittal skeletal relation
Tooth movement related mild change in sagittal position. Maxillary and mandiblular dentoalveolus reduced by 1°. While sagittal relation was unchanged.
Vertical skeletal relations
Maxillary inclination (S-N/ANS-PNS), mandibular inclination (S-N/Go-GN) and vertical jaw relation (ANS-PNS/Go-Gn) remained unchanged.
- Maxillary incisors proclination significantly reduced by 14° (1 - ANS-PNS: 115°)
- Vertical position of maxillary incisors became normal
- Mandibular incisors inclination reduced by 5° (1 - Go-Gn: 90°)
- Mandibular incisors well positioned relative to Go-Gn line.
- Class I molar and incisor relation attained
- Overjet reduced by 2 mm and became normal
- AOB closed and overbite of 1.5 mm was attained
- Uprighting of molars noticed.
- Upper and lower lip was mild retrusive in relation to E-line.
- Patient's profile was straight.
- Patient's smile improved a lot
- AOB was closed
- Proclination of upper and lower anteriors corrected
- Generalized spacing in both arch closed
- Uprighting of posteriors
- Class I molar relationship
- Stable occlusion with good interdigitation
- Normal overjet and overbite
- Normalization of tongue posture and movement
- Retention: Prolonged fixed retainer in both arches [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20].
| Case Report 2|| |
A 28-year-old female orthodontist patient with chief complaint of inability to close lips at rest and increased tooth visibility.
H/O orthodontic treatment 10 years before with twin block appliance and fixed orthodontic appliance involving extraction of 14, 24, 34, 44.
- Skeletal Class II and dental Class II
- Prognathic maxilla
- Convex profile
- Incompetent lip
- Overjet >6 mm and deep bite
- Severe crowding in lower arch
- Increased incisal display
- Retreatment case - all 4's already extracted and no space remaining.
- Nonsurgical, no further extraction except 8's (if any)
- Torque control of maxillary incisor with bracket base customization
- Intrusion of maxillary incisor - utilizing bite plane effect
- Maxillary complete arch distalization with torque angulation device (TAD)
- Vertical control of molars with occlusal build ups.
Treatment started with pretreatment survey of cast. Tip and torque and height correction were planned for each and every tooth with the help of TAD. Brackets were customized by incorporating desired specific values in its base, with the help of bracket positioning device.
Indirect bonding done in both arches.
Alignment and leveling
- Lower arch - expansion loop made in 0.014 NiTi for space creation for 3 months
Followed by 0.014 × 0.025 Cu NiTi for 9 months
- Upper arch - 0.014 × 0.025 Cu NiTi in for 1 year for complete torque expression.
Maxillary arch distalization
- Stage 1: Started with E-chain on 0.017 × 0.025 SS wire to TAD, placed in posterior palate
- Stage 2: 12 mm long power arm placed on main archwire and retraction continued from different PF, making line of action of force pass through CR. With change in inclination of teeth in lingual system relative relation of lingual bracket (PF) and CR changes substantially leading to change of force system, point of application of force has to be changed accordingly during treatment.
- Straightening of profile
- Correction of maxillary prognathism
- Skeletal and dental Class I
- Maxillary incisor intrusion reducing display at rest and smile
- Overjet and overbite reduced to normal [Figure 21], [Figure 22], [Figure 23].
| Case Report 3|| |
A 25-year-old female with chief complain of gummy smile and increased tooth display
- Vertical maxillary excess
- Short upper lip
- High FMA
- Gummy smile
- Increased incisal display
- Bimaxillary prognathism.
Nonsurgical, extraction of 15, 25, 35, and 45.
Maxillary anterior brackets were customized with 10° of additional lingual root torque. Super elastic wires were kept for long time for torque expression. Vertical height of upper anterior lingual brackets was planned such that lower incisors were touching the inclined plane of upper brackets, converting occlusal force into intrusive force. Retraction of maxillary anteriors, coupled with intrusive force and lingual root torque force helped move premaxilla upward and backward, correcting vertical maxillary excess. Vertical control of molars was maintained with occlusal buildups. With extraction of second premolar, mesialization of molars was also allowed which reduced mandibular plane angle and improved profile.
Mild spacing and right side Class II molar relation were maintained.
- Complete correction of gummy display at rest and during smile
- Normal incisal display
- Straightening of profile
- Competent lips
- Reduced FMA
- Pleasing smile arc [Figure 24], [Figure 25], [Figure 26].
| Case Report 4|| |
- 21-year-old male
- Skeletal and dental Class I
- Convex profile
- Upright to retroclined maxillary anteriors
- Severe crowding in lower arch (tooth size arch length discrepancy >8 mm)
- Complete labial displacement of 42
- Reduced overjet
- Increased overbite.
- Treatment mechanics
- Nonextraction, noninterproximal reduction
- Torque correction of maxillary anteriors
- Creation of space in lower arch with dentoalveolar expansion
- Co-ordination of arches.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20], [Figure 21], [Figure 22], [Figure 23], [Figure 24], [Figure 25], [Figure 26], [Figure 27], [Figure 28], [Figure 29]