By Dr. Tony Pious
1St yr orthodontics
INTRODUCTION TO MODEL ANALYSIS
Model analysis is the study of dental casts, which
helps to study the occlusion & dentition from all three
dimensions & analyze the degree & severity of
malocclusion & to derive the diagnosis & plan for
The question of reduction of tooth structure as a
treatment procedure in orthodontics has been a
The decision to extract must be preceeded by a
great deal of thought and study.
Esthetics is also an important consideration.
Many malocclusions occur as a result of discrepancy between
arch length and tooth material.
Arch perimeter analysis helps in determining the extend of
this discrepancy in maxillary arch.
Same method on the upper arch is called ' ARCH
PERIMETER 'Analysis method.
Arch length anterior to first permanent molar is
measured by using a soft brass wire.
The wire is placed touching the mesial surface of the
first permanent molar and is passed over the buccal
cusps of premolar and along the anterior and is
continued on the opposite side.
In case of proclined anteriors the wire passed along
the cingulum of anterior teeth.
And in retroclined anterior it passes along the labial
to the teeth.
If discrepancy is
0-2.5 mm minimal tooth material excess,proximal
reduction can be carried out
2.5 – 5 mm need to extract second PM
> 5 mm need to extract the first PM
Segmental analysis involves an indirect assessment of dental
The dental arch is divided into six straight line segments of
two teeth per segment, including first permanent molars, the
record the mesiodental width of the teeth and sum them for
each segment and add them up for net discrepancy.
The difference between the actual and ideal arch length, on
the alignment of the teeth is determined by amount of dental
crowding and antero-posterior positioning of incisors in
relation to the facial skeleton.
Performed on both arches.