1. Dr. MohammedALMUZIAN Page 0
UNIVERSITY OF GLASGOW
Lower labial segment crowding
Personal notes
Dr. Mohammed ALMUZIAN
1/1/2013

2. Mohammed Almuzian, University of Glasgow, 2013 Page 1
Table of Contents
Terminology ................................................................................................................................ 2
Incidences....................................................................................................................................2
Classification of crowding............................................................................................................. 2
The risk factors............................................................................................................................. 3
The aetiological factors................................................................................................................. 3
Lower incisor crowding & Third molar debate................................................................................ 4
Treatment.....................................................................................................................................5
Factors that should be considered............................................................................................... 5
The treatment options................................................................................................................ 6
Evidences.....................................................................................................................................6

3. Mohammed Almuzian, University of Glasgow, 2013 Page 2
Lower labial segment crowding
Main article Richardson 1994 AJO and Richardson2002 Dental update
Terminology
 Tertiary Crowding,
 Late SecondaryCrowding,
 Post-AdolescentCrowding
Incidences
 Late crowding of the mandibular incisors beginning between the ages of 17 and
mid-twenties and progressing through into late adult life is common (Sakuda
1976).
 approximately 2/3 of adolescents with good alignment and “normal” occlusions
will develop incisor irregularity be early adulthood
 Richardson (1982) reported that patients with crowding of the early permanent
dentition are more likely to result in impaction of the third molars.
Classificationof crowding
Van der Linden 1974
1. Primary crowding refers to a discrepancy of tooth dimension and jaw size,
mainly determined genetically.
2. Secondarycrowding is caused by environmental factors, including local space
conditions in the dental arches and the position and function of the tongue, the
lips and the buccalmusculature.
3. Tertiary crowding occurs during adolescence and post-adolescencewith a
predilection for the lower labial segment.

4. Mohammed Almuzian, University of Glasgow, 2013 Page 3
The risk factors
1. Patients at pretreatment with excess overjet and/or excess overbite prone to
more relapse. (Little 1999)
2. Vertical facial growth also a risk factor for stability. (Little 1999)
3. Pre-existing tooth tissue discrepancy:
 Robinson (1981) demonstrated an association between the degree of lower labial
segment crowding in the early dentition and the degree of crowding in the late
adolescence, in a group of treated patients.
 The presence of LLS crowding increase the risk of posttreatment relapse. For each
1mm of LLS crowding there is a chance of 4-18% of relapse (Fudalej 2008).
4. Teeth morphology
 Peck and Peck 1976 found that crowding is slightly more common in persons
whose teeth have large mesiodistal dimensions than in those with smaller teeth
due to the theory of contact point slippage. However (Little 1999)found no
correlation.
5. PD compromised dentition
6. Extraction less than non-extraction
7. Orthodontic treatment: Teeth that have been moved orthodontically have a
natural tendency to return to their original (crowded) positions especially
excessive arch expansion in the canine region have a strong tendency to relapse.
The aetiologicalfactors
1. Lack of attrition:Begg (1954).
2. Soft tissue maturation:
 Van der Linden (1979) Late mandibular growth changes may bring the lower
incisors into a different soft tissue environment causing retroclination and
crowding

5. Mohammed Almuzian, University of Glasgow, 2013 Page 4
 Bench 1952 found that the hyoid bone and tongue descend with age, relative to
surrounding structures, causing imbalance between lip and tongue and resulting
in crowding
3. Late anterior growth and mandibular remodelling:
 Continued growth of the mandible after the cessation of maxillary growth may
cause lower incisors crowding (Moore, 1960).
4. Anterior component of occlusal forces:
 Van Beek (1979) the anterior component of the force of occlusion on mesially
inclined teeth,
 Occlusal changes may also be caused by restorations, tooth loss with drifting, or
the development of grinding habits
5. Mesial vectors of muscular contraction,
6. Degenerative periodontal changes allowing teeth to drift under light
pressures;
7. Mesial drift of posterior teeth by trans-septal fibres (Stephens and
Houston, 1984).
8. Toothsize and shape which can result in contact point displacement (Kahl-
Nieke et al, 1995)
9. The mandibular third molar: Mandibular third molars–presence and position.
Richardson in his study 1984 found that patient with impacted molars develops
more crowding and have bigger molars than non-impacted group.
Lower incisorcrowding & Third molar debate
Studies relating third molars to crowding
1. Jensen study (1960) they have examined 60 dental students (33 persons with
unilateral third molar aplasia in the maxilla and 30 in the lower. They have
found that in both maxilla and mandible there was a greater degree of crowding
on the side where the third molar was present.

6. Mohammed Almuzian, University of Glasgow, 2013 Page 5
2. Richardson and Mills (1990) have compared the mesial drift and change in
crowding over a 5-year period in 30 subjects whose lower second molar were
extracted between age 11 and 17 years and 30 subjects whose lower second
molars were not extracted. They have measured the arch length on the dental
casts. They suggested that the presence of a developing third molar can, in some
cases, cause forward movement of buccal teeth with an increase in crowding
and that the extraction of second molar is effective in reducing the incidence of
late lower arch crowding and third molar impaction..
Studies indicating lack of correlation between third molars and
1. Ades at al., (1990)
4 study groups all a minimum of 10 years postretention (Washington group)
 Absent 8s
 Impacted 8s
 Erupted and functional
 Extracted at least 10 years before postretention records
No significant differences in mandibular growth or LLS crowding between any
of the subgroups.
2. Harradine et al., (1998)
RCT on patients randomly allocated into third molar extraction and non-
extraction groups. Found very small decrease in LLS irregularity in patients
who had had lower third molars removed, not statistically or clinically
significant.
Treatment
Factors that should be considered
1. OH

7. Mohammed Almuzian, University of Glasgow, 2013 Page 6
2. Clinical condition of the teeth
3. Patient and clinician preference must be taken into consideration.
4. Amount of the attached gingiva
5. Overjet and overbite
6. Degree and site of crowding
7. Canine inclination
The treatment options
1. Accept
2. Prophylactic measurement: IPS as prophylactic measure had been described by
Peck and Peck 1974
3. Permanent retainer (Sadowsky)
4. In the presence of significant malocclusion, incisor crowding is best managed as
part of a comprehensive orthodontic treatment plan either by IPS, extraction or
proclination with permanent retention.
5. Yu 2013 Cochrane review. In this review there are no trials published between
1950 and 2012 in which patients were randomly treated with either fixed braces,
removable retainers or no treatment.
Evidences
1. Gum recession:
 Aziz 2011, No association between appliance-induced labial movement of
mandibular incisors and gingival recession was found. Factors that may lead to
gingival recession after orthodontic tipping and/or translation movement were
identified as a reduced thickness of the free gingival margin, a narrow
mandibular symphysis, inadequate plaque control and aggressive tooth brushing
2. Relapse:
 Paquette et al (1992) also found that cases which had been treated with an
average of 2.8 mm. more lower incisor proclination than another matched group

8. Mohammed Almuzian, University of Glasgow, 2013 Page 7
of cases, finished with slightly greater irregularity (Little’s index) out of
retention. The difference in post-treatment relapse of irregularity between the
two groups was very small (0.6 mm), but the findings did suggest that labial
movement of lower incisors during treatment does, on average, increase the
chance of subsequentrelapse.
 Ackerman and Proffit (1997) proposean approximate limit of 2 mm for labial
movement of the lower incisors if antero-posterior stability is the main factor
influencing our decision.
 Johnston and Magnusson 2010 retrospectively found less LLS crowding in
extraction cases.
3. Retention:
 The work of Little and others quoted above has shown that although larger
lower incisor changes in position are less stable, lower incisor alignment tends
to deteriorate after retention whether or not the lower incisor position has been
maintained
 Rowland 2008 found PFR is more efficient in a maintaining the LLS position
postortho.