- NEED HELP? CALL US NOW
- +919995411505
- [email protected]
Model Analysis in Orthodontics
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 & derive the diagnosis & plan for treatment.
Some model analyses are
Some model analyses are
PERMANENT DENTITION MODEL ANALYSIS
CAREY’S Analysis- The arch length-tooth material discrepancy is the main cause for most malocclusions.
- This discrepancy can be calculated with the help of Carey’s analysis.
- This analysis is usually carried out in the lower arch.
ASHLEY HOWE’SANALYSIS
- Howe’s considered tooth crowding to be due to deficiency in arch width rather than arch length
- He found a relationship to exist between the total width of mesiodistal diameter of teeth anterior to the second permanent molar & the width of the dental arch in the first premolar region
PROCEDURE
Following measures have to be obtained
- percentage of PMD to TTM PMD X 100 /TTM
- percentage of PMBAW to TTM PMBAW X 100 /TTM
- percentage of BAL to TTM BAL X 100 /TTM
- If PMBAW > PMD :-indication that basal arch is sufficient to allow expansion of premolars
- If PMD > PMBAW :- can be three possibilities
1) contraindicated for expansion
2) move teeth distally
3) extract some teeth
- If PMBAW X100 / TTM
a) less than 37% require extraction
b) if 44% an ideal case extraction not require
c) if between 37-44% (border line case) may or may not require extraction
WAYNE A. BOLTON ANALYSIS
- Bolton pointed out that the extraction of one tooth or several teeth should be done according to the ratio of tooth material between the maxillary & mandibular arch
- to get ideal interdigitation, overjet, overbite & alignment of teeth
- to attain an optimum interarch relationship
- Bolton’s analysis helps to determine the disproportion between the size of maxillary & mandibular teeth
- the sum of mesiodistal diameter of the12 maxillary teeth & the sum of the mesiodistal diameter of the 12mandibular teeth are determined
- In same manner the sum of 6 maxillary anterior teeth & the sum of 6 mandibular teeth is determined.
- OVERALL RATIO:-
_____________________________________________________
sum of mesiodistal width of maxillary 12 teeth
MEAN = 91.3%
- ANTERIOR RATIO:-
____________________________________________________
sum of mesiodistal width of maxillary 6 teeth
MEAN = 77.2%
INFERENCES
- If the ratio is more than mean value, then the mandibular tooth material is excessive
- If the ratio is less than mean value, then the maxillary tooth material is excessive
- Bolton prefers to do proximal stripping on the upper arch if the upper anterior tooth material is in excess & extraction of lower incisor, if necessary, to reduce tooth material in the lower arch
- study was done on a specific population & ratio obtained need not be applicable to other population group
- the analysis doesn’t take into account the sexual dimorphism in the maxillary canine width
MIXED DENTITION ANALYSIS
TANAKA & JOHNSON ANALYSIS- Tanaka & johnson did a study to repeat Moyer’s observation to validate its equation on a new sample
- The possibility of secular changes with in the past20 yrs was to be examined & they found Moyer’s prediction table to be equally appropriate for contemporary population
- they have simplified Moyer’s 75% level of prediction table into a formula
RADIOGRAPHIC METHOD
PROPORTIONAL EQUATION PREDICTION METHOD If most of the canines & premolars have erupted & if one or two succedaneous teeth are still unerupted, an alternative prediction method can be used to estimate the mesiodistal width of the unerupted permanent tooth PROCEDURE- The width of an unerupted teeth & an erupted tooth is measured on the same periapical film
- The width of erupted tooth is measured on the plaster cast
- These three measurements comprise the elements of a proportion that can be solved to obtain the width of unerupted tooth on the cast
Y1= X1 x Y2/X2
Where
Y1= Width of the unerupted tooth whose measurement is to be determined
Y2= Width of the unerupted tooth on the radiograph
X1= Width of the erupted tooth,measured on the cast
X2= Width of the erupted tooth,measured on the radiograph
MCQs
1 .Anterior Boltan ratio is:a) 91.3%.
b) 100%.
c) 61.7%.
d) 77.2%.
Ans: D
MEAN = 77.2%
2. Unfavorable mixed dentition analysis is an indication for:
a) Space maintenance and space regaining.
b) Space maintenance and space supervision.
c) Space regaining and gross discrepancy cases.
d) Space supervision and gross discrepancy cases.
Ans : D
