# Study Models Analysis > Study model analysis for NEET-MDS Orthodontics: Bolton and Pont indices, Carey and Howe analyses, mixed dentition prediction by Moyers and Tanaka-Johnston. - Canonical URL: https://prepelephant.com/topics/neet-mds/orthodontics/study-models-analysis - Exam / course: NEET-MDS · Subject: Orthodontics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Study Models Analysis", PrepElephant, https://prepelephant.com/topics/neet-mds/orthodontics/study-models-analysis ## Direct answer Plaster models quantified properly decide the extraction debate before any wire is placed. Model analysis falls into three families: space analysis comparing arch length available against tooth material required (Carey's analysis with a brass wire), tooth-size analysis comparing maxillary to mandibular widths (Bolton's overall ratio 91.3 ± 1.91 per cent, anterior ratio 77.2 ± 1.65 per cent), and arch-width analysis comparing measured against predicted transverse widths (Pont's index, premolar width = sum of upper incisors × 100/80; molar width = sum × 100/64). In the mixed dentition, unerupted canine and premolar widths are predicted — from Moyers' probability tables at the 75th percentile, or Tanaka-Johnston's arithmetic (half the lower incisor sum plus 10.5 mm per mandibular quadrant, plus 11 mm for the maxilla). ## What you must remember - **Bolton analysis:** overall ratio (sum of 12 mandibular teeth ÷ sum of 12 maxillary teeth) 91.3 ± 1.91 per cent; anterior ratio 77.2 ± 1.65 per cent — a maxillary anterior excess of more than about 1.8 mm forces stripping, extraction of a lower incisor or composite build-ups. - **Pont's index (1909):** premolar arch width = SI × 100/80 and molar arch width = SI × 100/64, where SI is the sum of the four maxillary incisor widths; Linder and Harth modified the divisors to 85 and 65 for broader arches. - **Carey's analysis:** brass wire contoured from the mesial of the first permanent molar through the contact points; discrepancy under 2.5 mm — proximal stripping; 2.5–5 mm — extract second premolars; above 5 mm — extract first premolars. - **Ashley Howe's analysis:** ratio of premolar-diameter mesiodistal widths to the premolar basal arch width (PMBAW); above 44 per cent extraction is unnecessary, 37–44 per cent is borderline, below 37 per cent crowding stems from a deficient basal arch and extraction is indicated. - **Mixed dentition prediction:** Moyers' charts read at the 75th percentile using the sum of the four mandibular incisors; Tanaka-Johnston: mandibular quadrant = SI/2 + 10.5 mm, maxillary quadrant = SI/2 + 11 mm. - **Diagnostic setup (Kesling, 1956):** teeth sawn off the cast and repositioned in wax to rehearse extraction and space-closure outcomes — the intellectual ancestor of the clear aligner setup. - **Model requirements:** casts poured in hard stone, trimmed so heels and bases are symmetric with the occlusal plane parallel to the base, and the posterior border perpendicular to the mid-sagittal line. ## A mixed dentition case worked on paper A 9-year-old with a full Class I molar relationship and crowded lower incisors sits in front of you. The four mandibular incisors total 22 mm. Tanaka-Johnston gives 22/2 + 10.5 = 21.5 mm as the expected canine-plus-premolar segment per quadrant; Moyers' table at the 75th percentile agrees closely. The brass-wire perimeter from first molar to first molar measures 39 mm against 43 mm of tooth material in both quadrants — a 4 mm discrepancy, moderate by any grading, and Carey's thresholds point toward second premolar extraction if the profile permits. Now run Bolton before committing: if the anterior ratio computes to 79 per cent, the lower anterior segment is relatively excessive and a stripped or extracted lower incisor changes the plan entirely. Finally Pont: an SI of 30 mm predicts a premolar width of 37.5 mm (Pont) or 35.3 mm (Linder-Harth); an actual intermolar width far below both tells you the arch is transversely deficient and some crowding may dissolve with expansion rather than extraction. The arithmetic takes ten minutes and converts opinion into a defensible plan. ## How the exam frames the numbers MCQ writers love reversed attributions: Pont is French, derived from a early twentieth-century European sample, and later surveys in many populations — Indians included — report that Pont's predicted widths tend to run large, so a "deficient" arch by Pont may be average in reality; say so and you earn the viva mark. Moyers must be read at the 75th percentile by convention, because the 50th under-predicts and risks a late space shortfall. The most common Carey error is quoting the stripping cut-off as 5 mm — the classical figure is 2.5 mm. And when asked "which analysis judges crowding due to a small basal arch?", the answer is Howe's, tested through the PMBAW-to-premolar-diameter ratio, not Carey or Pont. ## Frequently asked questions ### What are Bolton's normal overall and anterior ratios? Overall 91.3 ± 1.91 per cent and anterior 77.2 ± 1.65 per cent; deviations beyond two standard deviations create finish-line discrepancies that no wire can fix. ### State the Tanaka-Johnston prediction for one quadrant. Mandibular canine plus premolars equal half the sum of the four lower incisors plus 10.5 mm; the maxillary quadrant uses the same half plus 11 mm. ### What does Carey's analysis recommend at different discrepancies? Under 2.5 mm, proximal stripping; 2.5–5 mm, second premolar extraction; above 5 mm, first premolar extraction. ### How is Ashley Howe's ratio interpreted? A PMBAW-to-premolar-diameter ratio below 37 per cent means the basal arch is too narrow for the teeth and extraction is indicated; above 44 per cent the arch can accommodate them. ### What is a Kesling diagnostic setup? Teeth are sectioned from a duplicate cast and repositioned in wax to simulate the planned result, letting the clinician and patient preview extraction and space closure before treatment begins.