Is procline torque required for 1st premolar extraction cases with anterior retraction biomechanics in orthodontics?

Procline Torque in First Premolar Extraction Cases with Anterior Retraction

FALSE - Procline torque is NOT required; rather, PALATAL ROOT TORQUE (lingual crown torque) is essential to prevent the bowing effect and maintain proper axial inclination during anterior retraction in first premolar extraction cases.

The Biomechanical Reality

During anterior retraction following first premolar extraction, the anterior teeth naturally tend toward:

• Lingual crown tipping (proclination loss) without proper torque control 1
• Extrusion of incisors during retraction mechanics 2
• Loss of proper axial inclination creating the "bowing effect" 1

The solution requires ANTI-PROCLINE torque (palatal root movement), not procline torque. This means applying forces that move roots palatally while maintaining or advancing crowns labially to preserve or increase the labial inclination of anterior teeth 3, 4.

Evidence-Based Torque Requirements

Normal Axial Inclination Cases (U1-SN = 105°)

When anterior teeth have normal inclination at the start of retraction:

• Translation movement is optimal, requiring significant palatal root torque to prevent lingual tipping 1
• The rotation center should be positioned at the center of resistance to achieve bodily movement 3
• Without adequate torque control, pure palatal tipping occurs, creating the bowing effect 1

Oversized Axial Inclination Cases (U1-SN = 110°)

When anterior teeth are already proclined:

• Less aggressive torque control is needed compared to normal inclination cases 1
• Some controlled lingual tipping may be acceptable as it corrects the excessive proclination 1
• The goal is to reduce axial inclination to normal during retraction 1

Clinical Application Methods

Lever Arm Mechanics

Applying retraction force at the center of resistance level produces optimal torque control:

• Lever arm hooks placed between lateral incisors and canines allow force application that favors palatal root movement 3
• This creates greater palatal root displacement compared to conventional crown-level retraction forces 3
• The mechanics simultaneously reinforce posterior anchorage 3

Mini-Implant Anchorage (Biocreative Therapy Type I)

Severe gable bends on utility archwires engaged directly to mini-implants generate anterior torque:

• C-implants provide stable anchorage to resist both intrusive and retraction forces 4
• This allows effective torque control during en masse retraction without posterior anchorage loss 4
• The resistance to rotational forces enables anterior intrusion during retraction 4

Clear Aligner Considerations

Power ridges must be carefully designed to prevent the bowing effect:

• For normal axial inclination (U1-SN = 105°), a power ridge height of 0.7 mm approaches translational movement 1
• For oversized inclination (U1-SN = 110°), a power ridge of 0.4 mm provides adequate correction 1
• Without torque control, pure palatal tipping inevitably occurs 1

Common Pitfalls to Avoid

The term "procline torque" in the question is misleading - it suggests moving roots labially (increasing proclination), which would worsen the bowing effect. The actual requirement is the opposite:

• Never apply forces that would increase proclination during retraction 1
• Always anticipate lingual tipping tendency and compensate with palatal root torque 3, 4
• Avoid crown-level retraction forces alone, as these create uncontrolled tipping 3

Laceback ligatures do NOT provide adequate torque control:

• Studies show lacebacks cause 0.83 mm greater mesial movement of molars (anchorage loss) 2
• They provide no significant difference in anteroposterior or vertical position of anterior teeth 2
• Lower incisors retrocline during leveling regardless of laceback use 2

The Anatomical Context

While first premolar sites have more favorable anatomy than anterior teeth (27.5% thick bone wall phenotype versus 4.6% in central incisors) 5, 6, this anatomical advantage relates to extraction site healing and implant placement, not to the torque requirements during orthodontic retraction. The biomechanical demands of anterior retraction remain constant regardless of extraction site anatomy.