Korean J Orthod.  2013 Feb;43(1):3-14. 10.4041/kjod.2013.43.1.3.

Torque control during lingual anterior retraction without posterior appliances

• Mo SS
• Kim SH
• Sung SJ
• Chung KR
• Chun YS
• Kook YA
• Nelson G

• KMID: 2273463
• DOI: http://doi.org/10.4041/kjod.2013.43.1.3

Abstract

OBJECTIVE
To evaluate the factors that affect torque control during anterior retraction when utilizing the C-retractor with a palatal miniplate as an exclusive source of anchorage without posterior appliances.
METHODS
The C-retractor was modeled using a 3-dimensional beam element (0.9-mm-diameter stainless-steel wire) attached to mesh bonding pads. Various vertical heights and 2 attachment positions for the lingual anterior retraction hooks (LARHs) were evaluated. A force of 200 g was applied from each side hook of the miniplate to the splinted segment of 6 or 8 anterior teeth.
RESULTS
During anterior retraction, an increase in the LARH vertical height increased the amount of lingual root torque and intrusion of the incisors. In particular, with increasing vertical height, the tooth displacement pattern changed from controlled tipping to bodily displacement and then to lingual root displacement. The effects were enhanced when the LARH was located between the central and lateral incisors, as compared to when the LARH was located between the lateral incisors and canines.
CONCLUSIONS
Three-dimensional lingual anterior retraction of the 6 or 8 anterior teeth can be accomplished using the palatal miniplate as the only anchorage source. Using LARHs at different heights or positions affects the quality of torque and intrusion.

Keyword

C-retractor; Lingual; Miniplate; Anchorage

MeSH Terms

Displacement (Psychology)
Incisor
Splints
Tooth
Torque

Figure

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  Figure 1 A first premolar extraction case using the lingual biocreative therapy. A and D, Lingual en masse retraction forces are initiated. B and E, Seven months of en masse retraction. Triangular elastics were applied to the canine for vertical control. C and F, Post-treatment. The total treatment period was 13 months.

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  Figure 2 A second premolar extraction case using the lingual biocreative therapy. A to C, Pre-treatment photos show dens evaginatus on #15 and a malformed #25. D to F, One month after en masse retraction force is initiated. G to I, Four months of en masse retraction.

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  Figure 3 Pre- and post-lateral cephalograms. A and B, Low lingual anterior retraction hook (LARH) - the patient needed controlled lingual tipping; hence, a LARH vertical height of 4 mm was used. C and D, High LARH - the patient needed bodily tooth movement; thus, a LARH vertical height of 13 mm was used. E and F, Second premolars were extracted due to internal resorption, so the 8 anterior teeth were retracted using the lingual biocreative therapy.

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  Figure 4 Three-dimensional finite element mesh with teeth, periodontal ligament, alveolar bone of the maxillary dentition, and C-retractor with the low lingual anterior retraction hook (LARH).

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  Figure 5 Schematic representation of the coordinate system of the lingual biocreative therapy with the low lingual anterior retraction hook (LARH) at different positions. A, Condition 1: the LARHs, made of 0.9-mm round stainless steel, were placed between the upper central and lateral incisors with 6° of toe in angle. B, Condition 2: the LARHs were placed between the lateral incisors and canines with 15° of toe in angle. C, Condition 3: the LARHs were placed between the upper central and lateral incisors after second premolar extraction. D, Condition 4: the LARHs were placed between the lateral incisors and canines with 15° of toe in angle after second premolar extraction.

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  Figure 6 Comparison of the effects of the different lengths and positions of the low lingual anterior retraction hooks (LARHs) in the C-retractor in the three dimensional finite element model. Tooth axies graph (incisor, midpoint of incisal edge to root apex; canine, cusp tip to root apex) magnified tooth displacement 70 times. Solid line means before displacement and a dotted line means after displacement (circles, central incisor; squares, lateral incisor; canine, triangles). Condition 1, The LARHs were placed between the upper central and lateral incisors after first premolar extraction. Condition 2, The LARHs were placed between the upper lateral incisors and canines after first premolar extraction. Condition 3, The LARHs were placed between the upper central and lateral incisors after second premolar extraction. Condition 4, The LARHs were placed between the upper lateral incisors and canines after second premolar extraction.

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  Figure 7 Comparison of the vertical effects (Z-axis) of the different heights and positions of the low lingual anterior retraction hooks (LARHs) in the three dimensional finite element model.

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  Figure 8 Comparison of the sagittal effects (Y-axis) of the different heights and positions of the low lingual anterior retraction hooks (LARHs) in the three dimensional finite element model.

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  Figure 9 A, When the lingual anterior retraction hook is located distal to the central incisors (condition 1 or 3). B, Part of the extraction space is closed by C-retractor. C, The canine can be segmented from the C-retractor for detailing. D, Incisors and canines are decrowded with conventional bracket system.

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