What Is Kim's Analysis?
Kim's analysis was introduced by In-Kwon Kim in 1978 as a systematic approach to the extraction-versus-non-extraction decision in orthodontic treatment planning. Its core insight is that the extraction question cannot be answered by arch length discrepancy alone — it must incorporate both the vertical skeletal pattern and the anteroposterior skeletal pattern, because both influence how much space is available, how teeth will move, and what the final soft tissue profile will look like.
The analysis produces four values: the Overbite Depth Indicator (ODI), which quantifies the vertical skeletal tendency; the Anteroposterior Dysplasia Indicator (APDI), which quantifies the anteroposterior skeletal class; the Combination Factor (CF), which is simply ODI + APDI; and the Extraction Index, a clinical threshold system based on CF that categorises cases as extraction, borderline, or non-extraction.
Unlike analyses such as Steiner or Downs that focus primarily on describing skeletal and dental relationships, Kim's analysis is explicitly prescriptive — it is designed to inform a treatment decision. This makes it particularly useful during the treatment planning phase after the skeletal classification has already been established.
Measurements, Formulas & Norms
Overbite Depth Indicator (ODI)
The ODI is computed as the sum of two angles: the angle between the AB plane and the Frankfort Horizontal (FH), and the angle between the palatal plane (ANS-PNS) and the Frankfort Horizontal. When the palatal plane is tipped downward anteriorly (as in many hyperdivergent cases), the second component is measured as a negative contribution.
Geometrically, a high ODI reflects a steep AB plane (B point inferior to A) combined with a relatively horizontal palatal plane — the skeletal configuration associated with deep bite and hypodivergent patterns. A low ODI reflects the opposite: an open bite, hyperdivergent skeletal configuration.
Anteroposterior Dysplasia Indicator (APDI)
The APDI sums three angular components: the facial plane angle (FH to N-Pog, equivalent to the Downs facial angle), the AB to facial plane angle (equivalent to the Downs A-B plane angle), and the palatal plane to FH angle. This formulation means that APDI captures anteroposterior dysplasia across all three levels — cranial base, jaw bases, and palatal orientation.
A high APDI reflects a prognathic mandible, anterior B point position, and/or a reverse-tipped palatal plane — all consistent with a Class III skeletal pattern. A low APDI reflects the opposite Class II configuration.
| Measurement | Mean Norm | SD | Clinical Range | High Value | Low Value |
|---|---|---|---|---|---|
| ODI | 74.5° | ± 6.07° | 62.4° – 86.6° | Deep bite / hypodivergent | Open bite / hyperdivergent |
| APDI | 81.4° | ± 3.82° | 73.8° – 89.0° | Class III skeletal | Class II skeletal |
| CF (ODI + APDI) | 155.9° | ± 6.24° | 143.4° – 168.4° | Non-extraction favoured | Extraction indicated |
Norms from Kim IK (1978, 1987). Sample: Korean adults with Class I occlusion.
Extraction Index Thresholds
Kim derived extraction decision thresholds based on the CF value. These thresholds were developed from analysis of treated cases and represent population-based guidance — they are not absolute rules, and clinical judgment remains essential.
| CF Value | Category | Clinical Interpretation |
|---|---|---|
| < 149.0° | Extraction | Skeletal pattern strongly favours extraction; space creation typically needed to achieve facial harmony |
| 149.0° – 155.9° | Borderline | Decision depends on arch length discrepancy, profile, incisor position, and patient preference |
| > 155.9° | Non-extraction | Skeletal pattern favours non-extraction; space can typically be created without profile compromise |
Important: The Extraction Index addresses the skeletal contribution to the extraction decision. It should always be integrated with arch length analysis, incisor proclination, profile assessment, and patient-specific factors. A borderline CF with severe crowding may still require extraction; a low CF with minimal crowding may be treated non-extraction with expansion.
Landmarks Required for Kim Analysis
Kim analysis requires landmarks for the Frankfort Horizontal plane, the facial plane, the maxillary base, the mandibular base, and the palatal plane. These overlap heavily with the landmark sets used in Downs and Tweed analysis, so if you are running multiple analyses, the same landmark placements serve multiple modules in BCeph.
Sign convention note: In digital cephalometric software running on screen coordinates (where y increases downward), the sign conventions for the AB plane angle and the B-point-to-facial-plane distance must be computed geometrically — testing B point's actual position relative to the N-Pog line — not simply from the vector direction of A to B. BCeph implements this correctly to prevent false Class III classifications in low-angle Class II cases.
Clinical Interpretation of Kim Analysis
Integrating ODI and APDI Separately
Before combining ODI and APDI into the CF, each measurement should be read independently. A patient with a low ODI (open bite tendency) but normal APDI (Class I anteroposterior) has a primarily vertical problem — the extraction question may be secondary to vertical control strategies. A patient with low APDI (Class II) but normal ODI has a primarily anteroposterior problem — camouflage, growth modification, or orthognathic surgery may be more relevant than the extraction question alone.
The combination is most informative when both measurements deviate in the same direction. A patient with low ODI (hyperdivergent) and low APDI (Class II) has a genuinely complex skeletal pattern where extraction is frequently indicated to avoid profile flattening and to manage the vertical dimension.
CF and the Extraction Decision in Context
A CF below 149° should prompt a serious extraction discussion, but it does not mandate it. Clinical factors that may support non-extraction despite a low CF include: mild arch length discrepancy, severely retroclined lower incisors where proclination is planned, a class III molar relationship in a growing patient with remaining class III correction potential, and strong patient preference with full informed consent regarding profile outcomes.
Conversely, a CF above 155.9° (non-extraction zone) does not preclude extraction if there is significant crowding, excessive incisor proclination already present, or a profile that cannot tolerate further dental compensation. Kim's Index is a starting point for the extraction conversation, not the final answer.
Kim Analysis Alongside Other Modules
Kim analysis works best when interpreted alongside the vertical measurements from Björk-Jarabak analysis (posterior-anterior facial height ratio, sum of posterior angles) and the anteroposterior measurements from Steiner analysis (SNA, SNB, ANB). The Wits appraisal provides an independent check on the anteroposterior relationship that is not dependent on the cranial base reference.
Run Kim Analysis Free in BCeph
BCeph implements Kim analysis with all four outputs — ODI, APDI, CF, and Extraction Index classification — computed automatically from landmark positions. The sign conventions for the AB plane angle and the B-point position relative to the facial plane are handled correctly for screen coordinate systems, addressing a common source of error in manual implementations.
Kim analysis in BCeph is part of a complete multi-analysis workflow. The same landmark set used for Kim overlaps with Downs, Tweed, and Wits, so running multiple analyses requires no additional landmark placement. All data stays on your device — no cloud upload, no subscription, no per-case fees.