Mandibular third molars and late lower arch crowding – the evidence base by BJORK U. ZACHRISSON ppt

1. Literature review
‫ميحرلا نمحرلا هللا مسب‬

2. Type of study Review and expert opinion
Author BJORK U. ZACHRISSON
Date of publication 2005
Name of Journal World Journal of Orthodontics, volume 6. Issue 2

3.  The etiology of late mandibular incisor crowding in both orthodontically treated and untreated persons
is multifactorial
 Richardson 1994 (AJODO) stated that the main causes of crowding are:
 Mesial drift, tipping or inclined teeth ( forward movement of the buccal teeth )
 Mesial vectors of muscles
 Developing of 3rd molars
 Late mandibular growth
Richardson 1994 (AJODO)

4.  Skeletal morphology or complex growth patterns
 Tooth morphology
 Soft tissue maturation
 Connective tissue changes
 Occlusal factors
 Expansion
 Incisors proclination due to orthodontic treatment
Richardson 1994 (AJODO)

5. j
 Weakness of presently available clinical 3rd molar research : direct evidence for significant cause-
and-effect relationships is extremely difficult to establish in a research project due to the many
possible variables involved in late mandibular arch crowding.
 Kaplan (1976), Ades, Little, Joondeph and Chapko (1990), stated that there is no association
between 3rd molars and late lower crowding also they mentioned that there is postretention
crowding with lateral expansion of intercanine width during orthodontic treatment whether 3rd
molars are present or not.

6.  Effect of erupting 3rd molars on eruption pattern of the 1st molars:
 Richardson and Schwarze stated that lower 1st molars continued eruption between 20-30 years
of age and eruptive pressure from lower 3rd molars cause forward movement of buccal segment
which lead to anterior crowding.
 Richardson stated that eruption of lower 3rd molar cause anterior crowding which can be
reduced by extraction 2nd or 3rd molars.

7.  Rickets, Bjork and Skieller: declared
as fact that the normal average
eruption of lower 1st molars is
upward and mesial direction and this
eruption continued until 3rd molars
emerging into oral cavity.

8.  Using measurement form 60-degree-angled cephalometric better than lateral one because it gives clear
picture of molar area on each side and also gives reliable structural superimposition
 Richardson and Mills: showed that extraction of 2nd molars lead to decrease mesial movement of 1st
molars.

9.  According to Richardson: in the early teenage years (12.5 - 15.5), patient with increased mandibular
incisors incisor crowding were due to more forward of 2nd molar and a greater increase in the interincisal
angle but less on patient without crowding.
 Based on Schwarze who used photo documentation and computer
analysis of 3 dimension tooth movement in relation to third palatine
rugae and he showed decreased of mesial movement of 1st molars in
patients with 3rd molars extracted between 12 – 22 years of age ( similar
to Richardson study) .

10.  How can 3rd molars affect the forward movement of the buccal segments:
 Accrding to Richardson: when there is a variable space due to extraction of carious lower 1st molars 
posterior teeth tend to move in the distal direction.
My patient

11.  How can 3rd molars affect the forward movement of the buccal segments:
 Also Richardson: stated when impacted 3rd molars are extracted  may affect the continued eruption
of lower 1st and 2nd molars in mesial and upward direction.

12.  How can 3rd molars affect the forward movement of the buccal segments:
 Based on Richardson: showed that pressure from erupting 3rd change the continued eruption
path of 1st molar to a more mesial upward direction, at the same time if incisors don’t move forward
due to 3rd molar pressure  1st molars continued eruption  will result in mandibular crowding.
 So it’s recommended to keep permanent fixed retainer in placed until 3rd molar have erupted
properly.

13.  Management strategy for 3rd molar removal:
 There are 2 ways of extraction 3rd molars associated with orthodontic treatment:
1. From 8-10 age (when germs located above the 2nd molars)  germectomy
2. From 20-25 age (when 3rd molars are erupted partially

14.  Management strategy for 3rd molar removal:
 In the time period between 10-20 age or older  if the germs are located below the 2nd molars 
their removal may be unnecessarily traumatic for the patient  impacted 3rd molars without
complication may safely be left in situ.
 In a mesioangulation of 60 degree or more in relation with 2nd molar (distal root of 2nd molar) + root
resorption in 2nd molar  early extraction of 3rd molar is recommended.

15.  Effect of germectomy of 3rd molars:
 When they extracted  this space can used for spontaneous or active uprighting of 2nd molar
and posterior segment.

16. Conclusion

17.  Conclusion:
1. A mesially directed force  increased mandibular arch crowding.
2. Developing or presence of 3rd molars without insufficient space  cause late mandibular arch crowding.
3. Early extraction of lower 3rd molars  lower posterior teeth erupt in a less mesial direction
4. Extraction of lower 3rd molars  this space can used for distal uprighting of mandibular buccal segment
in non-extraction therapy.
5. Impacted disease-free 3rd molar  may safely be left in situ.
6. All presently available studies  do not establish the true relationship between 3rd molar eruption
and increased mandibular crowding.