Tooth-width ratios are used diagnostically to
quantify the harmony between the mandibular
and maxillary arches. A number of analyses
have been developed to compare the tooth-width
ratios of malocclusions to standardized norms.1-4
The Ho-Freer Graphical Analysis of Tooth-
Width Discrepancy (GATWD) provides a simple
graphic description of tooth-width relationships
between the arches, a comprehensive representation
of tooth-width ratios in various arch segments,
and a method of localizing tooth-width
Although the GATWD is more comprehensive
than previous analyses, it is also more laborintensive.
Now, a personal-computer-based version
of the GATWD enables clinicians to incorporate
the analysis into their routine diagnosis
and treatment planning, as well as to identify
tooth-size mismatches that may develop toward
the end of treatment.
To generate baseline data, tooth-width measurements
were obtained from a sample of pretreatment
orthodontic study casts. Nine cumulative
percentage ratios relating maxillary teeth to
mandibular teeth were derived5 (Table 1), and a
template was created to show ranges of two standard
deviations from the means (Fig. 1).
A software engineer was hired to design a
computer version of the GATWD that permits
direct input of 24 tooth-width measurements per
patient from study casts, using digital calipers, or
manual input via the computer keyboard. The
program, developed using [foot]Microsoft Visual
Basic 3.0 for Windows[/foot], provides a quick calculation
of tooth-width ratios and tooth-width
excesses. In addition, it incorporates the template
of mean tooth-width ratios for comparison of any
malocclusion with the mean values. Reports such
as tooth-width ratios and tooth-width excesses
and a graphic display of the analysis can be printed
with the Windows Print Manager, and the
hard copies can then be placed in the patient?s
The beaks of a Mitutoyo 6"/150mm
Digital Caliper Zero Set (Fig. 2) are ground
down to tapered points to allow precise positioning
on the mesial and distal contact points of the
teeth. The digital calipers are connected to a
Mitutoyo Digimatic Mini Processor (Model No. DP-1HS) via a Mitutoyo Digimatic cable. An
RS-232C interface cable links the Mini Processor to an IBM-compatible personal computer.
The program has five main screens:
Patient details screen (Fig. 3): Basic patient
information is entered here. The malocclusion
line has a pull-down menu with choices of Class
I; Class II, division 1; Class II, division 2; Class
II indefinite; and Class III. A field is available to
indicate extraction or nonextraction treatment.
Pull-down extraction codes include four first
bicuspids; maxillary first and mandibular second
bicuspids; maxillary first bicuspids alone; four
second bicuspids; and maxillary second and
mandibular first bicuspids. Other extraction patterns
can be entered by typing in the ISO/FDI
tooth numbers. The patient information can be
used to generate overview reports on the practice?s
entire patient population.
Mesiodistal tooth-width measurement screen
(Fig. 4): Measurements of the 24 permanent
teeth from first molar to first molar are input
directly into the appropriate fields by pressing
the data key on the digital calipers. Editing is
possible by deleting the incorrect entry and manually
entering the tooth width.
Tooth-width ratio screen (Fig. 5): When the "Derived
Ratios" button is activated (Fig. 4), the program
performs the calculation of tooth-width
ratios. Tooth-width excess can then be viewed
tooth by tooth or in graphic form.
Tooth-width excess screen (Fig. 6): The amount
of tooth-width excess is displayed for each tooth.
Graphic display of tooth-width analysis screen
(Fig. 7): The graphic display, based on the template
shown in Figure 1, provides an immediate
visual assessment of any incompatible maxillary-
to-mandibular tooth widths. Tooth-width
ratios greater than two standard deviations above
or below the mean are readily recognizable.
In the Class I case with mandibular anterior
crowding demonstrated here (Fig. 8), the
GATWD indicated a significant tooth-width
excess in the mandibular anterior segment--about the width of a lower incisor. Therefore, the
mandibular left central incisor was extracted.
The post-treatment results show a harmonious
relationship with the 14 maxillary teeth occluding
on the 13 mandibular teeth (Fig. 9).
In a different case with a near-ideal Class I
occlusion (Fig. 10), the GATWD showed all
tooth-width ratios falling within two standard
deviations of the mean, indicating harmony
between the maxillary and mandibular tooth
widths (Fig. 11).
Orthodontic diagnosis should always
include an analysis of the relative sizes of maxillary
and mandibular teeth, especially in the anterior
region, where relative tooth sizes control the
amount of overbite, overjet, crowding, and spacing.
Tooth-width excesses of greater than 2mm
should be taken into account during treatment
planning. Maxillary-to-mandibular discrepancies
can have a pronounced effect on the occlusion
that may not become apparent until the finishing
stages of treatment.
Previous tooth-width analyses have required
mathematical calculations and reference
to standard tables or formulas to determine the
locations and amounts of tooth-width discrepancies.1-4 Now that the more comprehensive
GATWD5,6 has been incorporated into a computer
software program, these inconveniences can
The use of digital calipers with direct input
into the computer program can virtually eliminate
measurement transfer and calculation errors,
compared to analyses that require dividers,
rulers, and calculators. Although some measurement
error may be associated with the positioning
of the calipers on the mesial and distal surfaces
of the teeth, this method is certainly more
reliable than manual measurements. It provides a
diagnostic tool that is convenient, consistent, and
easy to operate.
ACKNOWLEDGMENT: This research was supported by the
Australian Dental Research Foundation.