Do you mean tooth morphology proportions of a maxillary central incisor, such as crown height-to-width and the division of the crown into thirds?

Do you mean tooth morphology proportions of a maxillary central incisor, such as crown height-to-width and the division of the crown into thirds?

┌──────────────────────────────────────────────────────────────────────┐ │ MAXILLARY CENTRAL INCISOR: RATIOS & SEGMENT CALCULATIONS │ │ Using standard average anatomical dimensions: │ │ Crown length = 10.5 mm | Crown width (MD) = 8.5 mm │ │ Crown depth (labiolingual) = 7.0 mm | Root length = 13 mm │ │ Total tooth length = 23.5 mm │ ├──────────────────────────────────────────────────────────────────────┤ │ A. WHOLE-TOOTH RATIOS │ │ │ │ 1. Crown width : crown length │ │ = 8.5 : 10.5 = 0.81 : 1 │ │ = 81% │ │ Clinical esthetic target: about 75%-85%, often quoted 80%. │ │ │ │ 2. Crown length : crown width │ │ = 10.5 : 8.5 = 1.24 : 1 │ │ │ │ 3. Root length : crown length │ │ = 13 : 10.5 = 1.24 : 1 │ │ │ │ 4. Crown length : total tooth length │ │ = 10.5 : 23.5 = 0.447 = 44.7% │ │ │ │ 5. Root length : total tooth length │ │ = 13 : 23.5 = 0.553 = 55.3% │ │ │ │ 6. Mesiodistal width : labiolingual depth │ │ = 8.5 : 7.0 = 1.21 : 1 │ │ The crown is therefore about 21% wider MD than LL. │ ├──────────────────────────────────────────────────────────────────────┤ │ B. CROWN-THIRD CALCULATIONS │ │ │ │ Crown length = 10.5 mm │ │ Each horizontal third = 10.5 ÷ 3 = 3.5 mm │ │ │ │ • Incisal third: 3.5 mm │ │ • Middle third: 3.5 mm │ │ • Cervical third: 3.5 mm │ │ │ │ Each third = 3.5 ÷ 10.5 × 100 = 33.3% of crown length │ ├──────────────────────────────────────────────────────────────────────┤ │ C. ROOT-THIRD CALCULATIONS │ │ │ │ Root length = 13 mm │ │ Each root third = 13 ÷ 3 = 4.33 mm │ │ │ │ • Cervical root third: 4.33 mm │ │ • Middle root third: 4.33 mm │ │ • Apical root third: 4.33 mm │ │ │ │ Each third = 4.33 ÷ 13 × 100 = 33.3% of root length │ ├──────────────────────────────────────────────────────────────────────┤ │ D. CERVICAL-CONSTRICTION RATIO │ │ │ │ Maximum crown MD width = 8.5 mm │ │ Cervical MD width is about 1.5-2.0 mm less, approximately 7.0 mm │ │ │ │ Cervical width : maximum width = 7.0 : 8.5 = 0.824 : 1 │ │ = 82.4% │ │ │ │ Total narrowing = 8.5 - 7.0 = 1.5 mm │ │ Approximate narrowing per side = 1.5 ÷ 2 = 0.75 mm │ ├──────────────────────────────────────────────────────────────────────┤ │ E. GINGIVAL / INCISAL REFERENCE CALCULATIONS │ │ │ │ Visible crown height assumed = 10.5 mm │ │ • 1/3 from incisal edge = 3.5 mm │ │ • 1/2 of crown height = 10.5 ÷ 2 = 5.25 mm │ │ • 2/3 from incisal edge = 7.0 mm │ │ │ │ Contact-area guide: │ │ • Central-central contact: incisal third, extending toward middle │ │ • Central-lateral contact: junction of incisal and middle thirds │ │ │ │ This follows the usual anterior-tooth “50-40-30” contact-area trend: │ │ central-central about 50%, central-lateral about 40%, lateral-canine │ │ about 30% of the relevant clinical crown height. │ ├──────────────────────────────────────────────────────────────────────┤ │ F. SMILE-DESIGN / ESTHETIC RATIOS │ │ │ │ 1. Golden proportion, if used for visible frontal widths: │ │ Lateral incisor : central incisor = 0.618 : 1 │ │ If central visible width = 8.5 mm: │ │ Lateral visible width = 8.5 × 0.618 = 5.25 mm │ │ │ │ Canine : lateral = 0.618 : 1 │ │ Canine visible width = 5.25 × 0.618 = 3.24 mm │ │ │ │ 2. Golden percentage, total visible anterior width = 100%: │ │ • Right canine = 10% │ │ • Right lateral = 15% │ │ • Right central = 25% │ │ • Left central = 25% │ │ • Left lateral = 15% │ │ • Left canine = 10% │ │ │ │ Thus, both centrals together = 50% of the visible six anterior │ │ teeth. │ ├──────────────────────────────────────────────────────────────────────┤ │ G. CERVICAL-LINE CURVATURE │ │ │ │ Mesial CEJ curvature ≈ 3.5 mm │ │ Distal CEJ curvature ≈ 2.5 mm │ │ │ │ Mesial : distal CEJ curvature = 3.5 : 2.5 = 1.4 : 1 │ │ Mesial curvature exceeds distal by 1.0 mm, or 40%. │ └──────────────────────────────────────────────────────────────────────┘

Important: these are standard teaching averages, not fixed values for every patient. Crown width-to-height is the main practical ratio: aim near 0.80, while individual facial form, gingival level, age, wear, and ethnicity can alter the appropriate value. A 2025 systematic review found variation among populations but no significant sex-based difference in average anterior tooth width-to-height ratios (systematic review).

The average anatomical dimensions used here align with commonly described values of about 10-11 mm crown height and 8-9 mm mesiodistal crown width (anatomy reference). Natural right and left centrals also are often not perfectly identical (clinical measurement study).

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