What is an appropriate case for a lower incisor extraction?

Lower incisor extractions are indicated in the following presentations:

1.   Tooth size discrepancy of 4.5mm or greater (Klein, 1997)

2.   Mandibular tooth size excess (Matsumoto et al., 2010)

3.   Stable posterior occlusion

4.   Mild-moderate class 3 (Zhylich and Suri, 2011)

5.   Edge to edge anterior occlusion  (Zhylich and Suri, 2011)

6.   Localized crowding in the lower labial segment with reduced overbite and overjet.

7.   Discrepancy in the anterior arch form, with a U-shaped mandibular dental arch and a V-shaped maxillary arch, as this helps reduce the lower intercanine width.

What do I need to consider prior to treatment?

In order to assess the effects of lower incisor extractions on occlusal relationships, an evaluation of tooth sizes is required through the Bolton’s ratio. A manual or digital method can be used. Periodontal evaluation of the lower incisors will inform of their health, and can aid in selection of the incisor for removal.

What are the advantages?

The main advantage of lower incisor extraction is the shorter average treatment time, often 12-18 months, a reduction of the 7-12 months from the average premolar extraction case of 19-24 months (DiBiase et al., 2011). Due to anterior extraction the posterior occlusion remains relatively stable, and the anchorage demand is reduced on posterior teeth. Lower incisor extraction constricts the lower intercanine width, which can be advantageous in crossbite cases.

What are the disadvantages?

With an asymmetric extraction the lower midline will not coincide with the upper midline. The recommended approach is of the lower midline being in the centre of a lower incisor, achieving symmetry in the lower arch. Following extraction of a lower incisor there can be loss of the interdental papilla and a resulting open gingival embrasure or ‘black triangle’ forming at the end of space closure. Sometimes it can be challenging to achieve canine guidance; as canines are often lingual and in a narrower arch. Without planning for the TSD there can be an increased overjet and overbite. The patient also may be concerned of the aesthetics of a ‘missing tooth’ at the front of their mouths.

 What can you do to minimize complications?

The good news is that not all the disadvantages need to be addressed, non-coincident midlines have been shown to be of no functional or aesthetic consequence, however patients should be advised of the appearance of a black triangle (Duron Rivas and Tafoya Barajas, 2016). There is a likelihood of a tooth size discrepancy formed through the lower incisor extraction, this anterior discrepancy can be addressed through a variety of methods:

1.   Anterior maxillary interproximal reduction

2.   Distal crown tip of adjacent teeth (bends or bracket positioning)

3.   Preparation of the extraction site before extraction

4.   Swapping upper canine brackets (reduces upper 3-3 arch length)

5.   Proclination of lower incisors (e.g. class 2 elastics)

6.   Up righting of upper incisors (e.g. Andrews prescription)

7.   Achieve slightly class 3 canine relationships

The remainder of the blog will focus on the top 3 methods of minimizing the occlusal consequences of lower incisor extraction

Anterior maxillary interproximal reduction

With one lower incisor missing, the TSD can be balanced through removal of an equal amount of upper dental material, problem solved! Unfortunately, the maximum possible IPR between the upper canine to canine is 2.8mm, not enough to match the 5.5mm of a removed lower incisor. However, ‘case selection’ can be the solution. In a case of mandibular excess of 3.5mm the Bolton’s ratio is to 85%, the loss of 1 lower incisor then requires 2.5mm of upper IPR to achieve an ideal anterior Bolton’s ratio of 77.6%, resulting in ideal anterior relationships (Kerolos has checked my maths, and for a change it’s correct)

Distal crown tip

After a lower incisor extraction, the adjacent incisors have a want to get close to their new neighbours, however they tip excessively into the extraction site, exaggerating the black triangle. There are 3 ways to correct this:

1.   Gable bends: Distal crown tip bends in finishing and detailing will correct the mesial tip of the adjacent teeth to the extraction

2.   Sympathetic bracket positioning: Offsetting the rotation of the bracket on bonding via a mesial rotation will provide a distal tip through the archwire sequence

3.   Burstone geometry VI. Impossible to escape a conversation of biomechanics without mention of Charles Burstone’s geometries. A bend in the middle of the two adjacent teeth will provide a distal tip as space closure occur.

Extraction site preparation (Vilhjalmsson and Proffit 2019)

This idea is to tip the lower incisor tooth that needs to be extracted lingually first, this helps maintain the alveolar crest height that supports the interdental papillae, and was found effective at reducing the black triangles. Extraction site preparation is done in 2 steps:

1.   Orthodontically tipping the incisor that is to be removed lingually to a safer location for its removal

2.   Closing most of the space in front of it before it is extracted. This moves the new extraction site away from the delicate crestal bone and usually preserves the height of the alveolar crest where the tooth used to be. It also addresses the possible patient concern about the aesthetic effect of removing an anterior tooth.

How to select the tooth to be extracted?
 

Selecting the incisor to be removed can sometimes be difficult. One would want to remove a tooth that has enamel decalcification or has been shortened by attrition. But the main factor in preventing black triangles is to select for extraction the incisor with the greatest bone height around its cervical neck. If the height of the crestal bone is about the same around all the incisors, then it is usually easiest to select an incisor that is already lingually inclined. If the crowding is worse on one side, then it is sensible to select a tooth where the crowding is worst. Selecting an incisor that is labially inclined and in the front of the other incisors is tempting but is a bad decision, as these teeth often have the worst bone height. If more space is needed, then a lateral incisor is the tooth to select as it is usually wider (0.5-0.6mm).

What does the literature say?

There is a scarcity of research around this topic, there is 1 Systematic review:  Zhylich 2011 which showed the indications for lower incisor extractions:

·      Mild-moderate class 3

·      Edge to edge anterior occlusion

·      Crossbite with mild anterior mandibular excess

So, is it worth it?

Ideal dynamic and static occlusion are possible with lower incisor extractions; however, this can only be achieved through an assessment of tooth ratios (Bolton’s analysis), case selection and the likelihood of tooth reduction in the upper arch Rivas 2016. An orthodontic educator once said, excellence in orthodontics is knowing and managing the counter-effects of our decisions, the above is intended to inform the reader of the counter effects of lower incisor extraction, and suggested methods to manage them

A quote from Joseph Valinoti 1994 on the topic of lower incisor extraction

 “This middle of the road approach is indicated in carefully selected cases, especially where space requirements and facial aesthetics do not call for greater dental movements”, a succinct summary to end the blog.

Contributions

• Contents by Kerolos AlHakeem 
• Contents by James Andrews 
• Edited and contents by Farooq Ahmed

We hope you have enjoyed this blog, This blog started with a conversation between Kerolos AlHakeem, Farooq Ahmed and James Andrews, to follow more conversations, clinical tips and commentaries on orthodontics please check us out on Instagram:

Kerolos AlHakeem’s Instagram page @dr_al_hakeem

James Andrews’ Instagram page @dr.jamesandrews

Farooq Ahmed’s Instagram page @farooqahmed_orthodontist

References

DIBIASE, A. T., NASR, I. H., SCOTT, P. & COBOURNE, M. T. 2011. Duration of treatment and occlusal outcome using Damon3 self-ligated and conventional orthodontic bracket systems in extraction patients: a prospective randomized clinical trial. American journal of orthodontics and dentofacial orthopedics, 139, e111-e116.

DURON RIVAS, D. & TAFOYA BARAJAS, E. U. 2016. Extraction of a lower incisor as a treatment alternative in orthodontic treatment. Case report. Revista Mexicana de Ortodoncia, 4.

JANSON, G., BRANCO, N. C., FERNANDES, T. M. F., SATHLER, R., GARIB, D. & LAURIS, J. R. P. 2011. Influence of orthodontic treatment, midline position, buccal corridor and smile arc on smile attractiveness: A systematic review. The Angle Orthodontist, 81, 153-161.

KLEIN, D. J. 1997. The mandibular central incisor, an extraction option. American journal of orthodontics and dentofacial orthopedics, 111, 253-259.

MATSUMOTO, M. A. N., ROMANO, F. L., FERREIRA, J. T. L., TANAKA, S. & MORIZONO, E. N. 2010. Lower incisor extraction: an orthodontic treatment option. Dental Press Journal of Orthodontics, 15, 143-161.

ZHYLICH, D. & SURI, S. 2011. Mandibular incisor extraction: a systematic review of an uncommon extraction choice in orthodontic treatment. Journal of Orthodontics, 38, 185-195.

VILHJÁLMSSON, G., ZERMENO, J. AND PROFFIT, W., 2022. Orthodontic treatment with removal of one mandibular incisor: Outcome data and the importance of extraction site preparation.