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Open Access Publications from the University of California

Forecasting Tooth Size Discrepancy: A Novel Approach Utilizing 3D Laser Technology and Andrews Models

  • Author(s): Bailey, Emil
  • Advisor(s): Johnson, Earl
  • et al.


To describe a novel approach (UCSF Johnson/Nelson/Miller/Bailey Analysis) to forecasting tooth-size discrepancies, as a more relevant and accurate method to detect and measure existing tooth-size discrepancies as they pertain to occlusal relationships. The aim of this study is test the Bolton analysis on an ideal sample and then to describe and determine ideal norms for an accurate way to measure tooth size and arch length discrepancies via novel 3D CAD/CAM technology.


Dr. Larry Andrews' 141 ideal non-orthodontically treated models were scanned with the OrthoInsight 3D Laser scanner. A measurement algorithm was fabricated by the lead engineer at OrthoInsight per specifications and landmarks of our research team. It was debugged and tested by the lead investigator. The models were then measured and analyzed using the OrthoInsight software. Measurements were manually verified by the investigator.


Bolton's analysis grossly over-estimated the tooth size disharmony (TSD) in a large sample of ideal occlusion. Its Anterior Ratio analysis showed a significant TSD in 17% of the sample. Ideal ratios were developed and described using the ideal model data creating the new UCSF Johnson/Nelson/Miller/Bailey Analysis.


Bolton's Analysis was not sufficiently accurate when applied to an ideal sample. A new analysis was described to more accurately and relevantly describe TSDs as they pertain to occlusal relationships. Future studies are needed to determine the cut-off points for clinically significant TSDs utilizing norms vs cohort of known TSD cases.

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