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Space closure and profile control in LO
Rafi Romano, D.MD, MSc., Israel
www.lingualnews.com, Volume 1, Number 1 - November 2002 |
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Orthodontic treatment involves many times a necessity for space closure mechanics. A crowding case treated with extractions or multiple space malocclusion face the orthodontist with a big challenge. It is well known today that aesthetics involve not only good and functional occlusion but also preservation or improvement of the patient's smile and face.
Diagnosis is an essential part of the spaced dentition and it should be done in 4 aspects: skeletal, dental, aesthetics and miscellaneous factors (like habits, personality type, financial possibilities and patient personal preferences and expectations) (Table 1). |
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Spaces should also be analyzed according to the following criteria:
Duration: Spaces that exist from the completion of the permanent dentition can indicate on discrepancy between teeth size and arch size, low frenum or missing teeth. Continuous opening of spaces can indicate on imbalance occlusal forces, tongue thrust habit or periodontic problems.
Size: Spaces over 4 mm can be considered as an extraction case since the closure mechanics may involve a change in the patient profile. Small spaces can indicate on Bolton discrepancy between the size of upper and lower teeth.
Teeth shape: Spaces can appear for example, when the teeth have a peg shape or when they were restored improperly. Triangular shape teeth (like in adults after periodontal intervention) may lead to "black triangle" appearance after all spaces are closed and therefore reshaping of the teeth should be considered. (Fig. 1)
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Fig. 1: Spaces between upper and central lateral incisors. Note the convergence of the upper central incisor near the gingival line around 2mm below the CEJ and the peg shaped lateral incisors |
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Papillae shape: Spaced dentition usually is involved with flat shape papillae or with total absence of papillae. It may also be involved with keratinized gingiva that will prevent, in some cases, from the orthodontist to close all spaces.
When choosing the proper treatment plan, the orthodontist should also determine the type of appliance to be used, wire properties, mechanics of space closure, anchorage requirements, and retention type. Prognosis of the end result should be determined since the tendency for reopening of the spaces is very high, especially when the musculature of the face and lips and the function of the tongue are imbalanced. Permanent retention with continuous follow-up documentations (x-rays, photos and cast models) and periodontal maintenance is prescribed after spaces had been closed.
Space closure mechanics is a big challenge for the orthodontist using Lingual Orthodontics (LO) appliance. The lingual bracket is almost always bonded palatally to the Center of Resistance (CR), which will cause a retroclination moment when retraction force is applied. (Fig. 2). |
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Fig. 2: A retraction force (F) is applied on anterior teeth with LO appliance. The distance between the force application (D) and the Center of Resistance (CR) create a retroclination moment (M). M=F X D. |
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The intrusion forces on the incisors that are caused by the contact between the lower incisors and the bite plane will cause in retroclined teeth to exacerbation of the retroclination moment (Fig. 3). Intrusion of the upper incisors is unwanted in the majority of the cases due to the current knowledge we have that indicate that lip position become low with aging and teeth will un aesthetically be covered in all various functions like smiling, speaking and in rest position. (Fig. 4)
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Fig. 3: An intrusion force (F) is applied on retroclined anterior teeth with LO appliance. Since the distance between the force application (D) and the Center of Resistance (CR) is negative, a retroclination moment is created which exacerbate the retroclination of the tooth. |
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4: A typical appearance of a 50 years old male during smile. Note the limited exposure of teeth and the thin upper lip. |
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Case A:
Class I malocclusion, mild spaced upper and lower anterior dentition, acceptable teeth exposure during smile and good smile line, distal angulation of upper incisors (2-2), small over-jet and over-bite, lack of upper and lower anterior papillae, alveolar bone loss, calculus, enlarged lower 1/3 of the face with normal tonus of the face musculature. (Fig. 5).
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Case B:
Class I malocclusion, severe spaced upper and lower dentition, moderate teeth exposure during smile, distal angulation of upper incisors (2-2), small over-jet and over-bite, almost lack of upper and lower anterior papillae, normal lower 1/3 of the face with hypertonic of the face musculature. (Fig. 6).
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Case C:
Class III malocclusion, moderate spaced upper and lower anterior dentition, very small teeth exposure during smile, negative over-jet and open bite tendency, enlarged lower 1/3 of the face with normal tonus of the face musculature, pragmatic chin, small upper maxilla with retrusive upper lip. (Fig. 7). |
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Controlling incisor position during space closure
Cases A and C have a great tendency for bite opening and in case B,C incisor exposure is very small. Teeth position can be monitored in LO by adding torque in the laboratory stage (up to 10 degrees of extra torque or 24 degrees in total) or by applying more torque on the wire. Extra torque creates also an extrusive force on the incisors and an intrusive force on the molars (1)( Fig. 8a-b ). The best wires for torque control in LO are.017x.017 Copper. NiTi,.0175x.0175 TMA, .017x.025 TMA (Ormco) and .018x.018 Titanol (lancer). Due to the small interbracket space in LO, wires with similar properties will apply much more force and therefore S.S wires are rarely used for torque control. Wire should be left in slot tied with steel ligatures for around 4-5 months to enable the torque to be expressed.
Adding lingual root torque to the incisors create a distal crown angulation. described as as the "Wagon Wheel Effect" (2) This tendency is even more pronounced in LO where the interbracket space and the arch perimeter are a lot smaller then in Buccal Orthodontics (BO). Case A, B has distal crown angulation, and therefore bracket position should be monitored on the laboratory stage by adding more over correction angulation values to the teeth to ensure that they will be upright after space is closed. |
Case C is a minimum anchorage case. Minimum anchorage is difficult to control with LO since researches show better anchorage value for the posterior teeth in LO cases compared to BO. Stiff wires (like .016x.022 S.S) should be used for long span movement and resilient wires (like .017x.025 TMA) in case of torque problems and open bite tendency. A combination of .018" Slot for the anterior teeth (3-3) and .022 slot for the posterior teeth is also used to diminish the friction during sliding mechanics for space closure and maintain the anterior torque on the same time.
Class III elastics were used in case C for advancement of upper and retraction of lower teeth. Class II elastics were used in Case B to help in extruding the anterior teeth directing the patient to wear them in a more vertical direction, between the upper cuspid and the lower molar.
Lack of papillae can be an aesthetic problem. Adequate alveolar bone height, upright teeth angulation, root proximity and square tooth shape are essential for papillae preservation or regeneration. Proper laboratory prescription for indirect bonding with careful and frequent oral hygiene control had lead to regeneration of the papillae in all cases A, B. and C. |
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Fig. 8: A: Lingual root torque is added to the wire on the upper anterior central. B When the wire is incorporated to the slot, an intrusion force is applied on the molar and consequently an extrusion force is applied to the central causing a clockwise canting of the occlusal plane. |
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Conclusion:
3 cases with spaced upper and lower dentitions were presented. 2 were treated with LO in both arches (Cases B and C) and one with lower buccal appliance and upper Lingual appliance (Case A). Each case demonstrates a different diagnosis, different mechanics and different etiology. All cases showed improvement in aesthetics of the face and the smile, spaces were closed and good occlusion was achieved. (Figs. 9-10-11). |
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Fig. 9-11: Completion of space closure in cases A, B, C. Smile and profile has improved tremendously and good occlusion was achieved. |
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References
1. Mulligan TF. Common Sense Mechanics Part 2, JCO, 1979 October (676 - 683).
2. Andrews L.E.The six keys to normal occlusion Am. J. Orthod. 1972, 62:296-309). |
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www.lingualnews.com
Adult and Lingual Orthodontics
EDITORS:
Dr. Silvia Geron D.M.D., M.Sc
Dr. Rafi Romano D.M.D., M.Sc
Dr. Pablo Echarri D.M.D., M.Sc
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