The Journal
Material and Methods
Used Pubmed to search electronic databases
in English, with keywords such as "Invisalign",
"Clear aligners", "Thermoplastic appliances",
"Clear plastic appliances", "Sequential
removable orthodontic appliances ", “ Clear
aligners tooth movement” and using filters
“Clinical trial” . After reading through the
abstracts, articles in English that related to the
effectiveness of clear aligners, the accuracy of
clear aligners and the factors related to the
effectiveness of clear aligners were selected.
Finally, the articles of the clinical studies
including prospective, retrospective,
randomized studies were chosen.
Results
Optimum force levels for orthodontic tooth
movement should be just high enough to
stimulate cellular activity without completely
occluding blood vessels in the PDL. Both the
amount of force delivered to a tooth and the
area of the PDL over which that force is
distributed are important in determining the
tooth movement.
There are many different forces that can be
used for tooth movement; like translation [70-
120gms], uprighting [50-100gms], rotation [35-
60gms], extrusion [35-60gms, tipping [35-
60gms], and intrusion which needs lighter
amount of force [10-20gms].
Tipping needs only a single force, while bodily
movement needs two or more force systems.
The use of plastic, transparent polyurethane
aligners as a solution to replace fixed
orthodontic therapy raises questions about its
effectiveness in moving the teeth as well as the
accuracy of the software that simulates and
predicts the tooth movements.
The Clear aligner therapy is complicated by the
uncertainty of where the exact point the forces
reach and its coverage over all surfaces of the
4
teeth, so the point of force application depends
on the tooth geometry, the materials‟
properties, the fit over the teeth and
programmed activation.
1. How accurate is the prediction.
In these three clinical studies[ 5,8,9 ] the accuracy
of tooth movements was measured by
comparing predicted with actual achieved
outcomes. While the ClinCheck software
program predicts the movements of the teeth,
achieved outcomes could not be exactly the
same. The average accuracy of tooth
movements for anteriors was found to range
from 41% 9 to 56% 5 . The amount of
concordance was only 14.3% when comparing
the predicted outcomes with the achieved
outcomes 11 .
2. Types of tooth movement
A. Expansion
Expansion is used to create the space needed
for orthodontic treatment. Sometimes
transverse maxillary expansion and protrusion
on the anteriors can create enough space for
orthodontic treatment without the need of
extraction.
The change of transverse dento- alveolar width
by self- ligating braces was found to be
statistically better results than Invisalign in the
study of Pavoni et al. In the Invisalign group, the
first intermolar widths (lingual and cusp), the
second intermolar widths (lingual) and the
intercanine widths (lingual and cusp) showed
no statistically significant change. In general, no
significant expansions in maxillary arches in all
of the measurements were shown in Invisalign
group 11 .
On the contrary, the Invisalign treatment of
crowded anteriors showed satisfactory success
in all subjects by protrusion on the anteriors,
distalization, and IPR in the study by Krieger et
al.2012. Noteworthy finding was that 47% of the
mandibular crowding subjects were treated
successfully by a combination of IPR and
protrusion 13 .
Vol. 14 No. 1
Jan-Apr 2018