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Brad Beaudoin
Research proposal
Precision of Dental Cast Analysis: Digital model verses plaster model comparison.
Stone dental models have been the cornerstone of orthodontic treatment planning and
documentation for the past century. However as technology advances, there is a trend
toward digitalization of information and the many benefits that come along with it.
Indeed, with digitalized dental records the clinician or researcher can pull up records of
every class II div I patient they’ve ever treated with one keyword; a similar task that
would have taken years of spelunking through dusty stacks of illegible patient charts in a
basement or storage facility. This means that for the first time in orthodontic history, the
totality of a clinicians experience may survive past that one clinician’s lifespan and exist
in a usable format that can provide insight for the next generation of clinicians and the
procession as a whole. When the best continuing education is said to be critical review of
past treated cases, it logically follows that any process that will facilitate the creation of a
database to learn and reflect on, is worthy of consideration.1
However, before we all throw out our plaster and cleanout our basements, ample
unbiased and independent research is needed to assess how digital models compare to the
current gold standard, plaster. It’s previously been shown that there is no significant
difference between measurements taken on digital models verses plaster models in terms
of accuracy.2 A recent comprehensive review of the literature comparing dental casts and
digital models has failed to show any significant differences in the accuracy of recordings
of tooth size, transverse dimensions, irregularity index, arch width, crowding, Bolton
ratio, occlusal indices or inter-arch occlusal features.3 Indeed the literature seems to agree
that digital models are very accurate with respect to their plaster counter-parts.
One area that has not been specifically addressed in the literature to date is the issue of
measurement precision of plaster models verses digital models4. For example, consider a
single premolar tooth from a dental cast said to be 7mm in width. Studies to date have
shown that whether it is measured on a stone caste or digitally, the measurements are on
average likely to be the same. But consider if the same researcher measured that same
tooth again at some later date. The former may record 8mm for the first reading and 6mm
for the second reading. On average this would still equal 7mm, the true width of the
tooth. Likewise, the researcher may have measured 7.1mm and 6.9mm instead and again
the average would still be 7mm. Its clear that in this example the second measurement
method is superior as it consistently is closer to the true measure of the object in question;
it is more precise. The purpose of my study is to evaluate the null hypothesis that there is
1
Kockich. The Best Continuing Education. American Journal of Orthodontics & Dentofacial Orthopedics
Volume 141, Issue 2 , Page 131, February 2012.
2
Leifert. Comparison of space analysis evaluations with digital models and plaster dental casts Am J
Orthod Dentofacial Orthop 2009;136:16.e1-16.e4
3
Fleming PS, Marinho V, Johal A. Orthodontic measurements on digital study models compared with
plaster models: a systematic review. Orthod Craniofac Res 2011;14:1–16
4
Fleming PS, Marinho V, Johal A. Orthodontic measurements on digital study models compared with
plaster models: a systematic review. Orthod Craniofac Res 2011;14:1–16
no significant difference in precision of dental cast measures between stone and digital
models.
Materials and Methods:
A sample of 50 consecutively treatment planned cases from the Vanderbilt Orthodontics
department’s graduate department will be entered into the study.
Inclusion criteria: original dental casts must be available in addition to the digital models
scanned into OI3D model scanner software.
Exclusion criteria: cleft palate patient casts as malformations in arch-form and tooth
position preclude traditional arch length analyses that will serve as measures of this study.
Each model will be measured 25 times no sooner then 1 day apart.
-Stone models will be measured with a digital caliper(name, mfg)
-Digital models will be scanned with OI3D model scanner and measured with their
proprietary software(name, version, mfg)
-all measures will be rounded to nearest .01mm.
Measures:
1. individual tooth mesial-distal widths
2. arch lengths measured from the mesial of 6-6 measured through the contact points
of each tooth
3. anterior 3-3 Bolton ratios
4. arch length discrepancies
All data will be analyzed with researcher blinded as to which group is the stone or digital.
Appropriate statistical tests will be preformed to test if there is any significant differences
between:
1. measures of dental casts verses digital (accuracy)
2. degrees of variance within each measurement (precision)