Kim Analysis

The Kim analysis was introduced by In-Kwon Kim in 1978 as a systematic method for supporting one of the most consequential decisions in orthodontic treatment planning: whether a case requires extraction. It builds two composite skeletal indicators — the Overbite Depth Indicator (ODI) and the Anteroposterior Dysplasia Indicator (APDI) — from angles that are already part of most standard cephalometric tracings.

Because both indicators are derived purely from skeletal geometry rather than tooth position or arch length alone, the Kim analysis is often used as a cross-check against clinical impressions of crowding severity when deciding between extraction, non-extraction, and borderline treatment mechanics.

What It Evaluates

The Kim analysis evaluates the patient's vertical skeletal pattern (deep bite versus open bite tendency) and anteroposterior skeletal pattern (Class I, II, or III) using two independent angular sums, then combines them into a single score used to guide the extraction decision.

Learn more: Growth patterns and overbite depth indicators of long and short faces in Korean adolescents: Revisited through mixed-effects analysis — PubMed

Key Measurements

  • ODI (Overbite Depth Indicator) — the sum of the AB plane–to–Frankfort Horizontal angle and the palatal plane (ANS-PNS)–to–Frankfort Horizontal angle. Normal mean: 74.5° ± 6.07° (range 62.4°–86.6°). Higher values indicate a deep bite/hypodivergent tendency; lower values indicate an open bite/hyperdivergent tendency.
  • APDI (Anteroposterior Dysplasia Indicator) — the sum of three angles spanning the facial plane, the AB plane, and the palatal plane relative to Frankfort Horizontal. Normal mean: 81.4° ± 3.82° (range 73.8°–89.0°). Higher values indicate a Class III skeletal tendency; lower values indicate a Class II skeletal tendency.
  • Combination Factor (CF) — simply ODI + APDI, giving a single score that integrates both the vertical and anteroposterior skeletal patterns. Normal mean: 155.9° ± 6.24°.
  • Extraction Index — a clinical threshold applied to CF: below 149° favors extraction, 149°–155.9° is borderline (decided by other clinical factors), and above 155.9° favors non-extraction.

Learn more: Overbite Depth Indicator and Anteroposterior Dysplasia Indicator Cephalometric Norms for African Americans — PMC

Clinical Interpretation

A low ODI points toward a hyperdivergent, open-bite-prone skeletal pattern, while a high ODI points toward a hypodivergent, deep-bite-prone pattern. A low APDI points toward a Class II skeletal relationship, while a high APDI points toward a Class III skeletal relationship — in validation studies, APDI has correctly matched the anteroposterior molar relationship in roughly 88% of cases, and ODI has matched the clinical overbite in roughly 81% of cases.

The Combination Factor and Extraction Index translate these two patterns into a practical decision aid: a low CF (skeletal pattern trending toward open bite and/or Class II) tends to favor extraction to manage arch length and incisor position, while a high CF (deep bite and/or Class III tendency) tends to favor non-extraction. As with any single index, the Extraction Index is meant to support — not replace — clinical judgment regarding crowding severity, incisor inclination, and soft-tissue profile.

Learn more: Extraction decision and identification of treatment predictors in Class I malocclusions — PMC

References