Korean J Orthod.  2021 Nov;51(6):407-418. 10.4041/kjod.2021.51.6.407.

Differences in the heritability of craniofacial skeletal and dental characteristics between twin pairs with skeletal Class I and II malocclusions

• Park HM
• Kim PJ
• Sung J
• Song YM
• Kim HG
• Kim YH
• Baek SH

• KMID: 2522503
• DOI: http://doi.org/10.4041/kjod.2021.51.6.407

Abstract

Objective
To investigate differences in the heritability of skeletodental characteristics between twin pairs with skeletal Class I and Class II malocclusions.
Methods
Forty Korean adult twin pairs were divided into Class I (C-I) group (0° ≤ angle between point A, nasion, and point B [ANB]) ≤ 4°; mean age, 40.7 years) and Class II (C-II) group (ANB > 4°; mean age, 43.0 years). Each group comprised 14 monozygotic and 6 dizygotic twin pairs. Thirty-three cephalometric variables were measured using lateral cephalograms and were categorized as the anteroposterior, vertical, dental, mandible, and cranial base characteristics. The ACE model was used to calculate heritability (A > 0.7, high heritability). Thereafter, principal component analysis (PCA) was performed.
Results
Twin pairs in C-I group exhibited high heritability values in the facial anteroposterior characteristics, inclination of the maxillary and mandibular incisors, mandibular body length, and cranial base angles. Twin pairs in C-II group showed high heritability values in vertical facial height, ramus height, effective mandibular length, and cranial base length. PCA extracted eight components with 88.3% in the C-I group and seven components with 91.0% cumulative explanation in the C-II group.
Conclusions
Differences in the heritability of skeletodental characteristics between twin pairs with skeletal Class I and II malocclusions might provide valuable information for growth prediction and treatment planning.

Keyword

Heritability; Twins; ACE model; Principal component analysis

Figure

• 

  Figure 1 Landmarks and reference lines used in the cephalometric analysis. Landmarks: S, sella; N, nasion; Po, porion; Or, orbitale; CD, condylion; Ar, articulare; Ba, basion; PNS, posterior nasal spine; ANS, anterior nasal spine; A, A point; B, B point; Pog, pogonion; Gn, gnathion; Me, menton; Go, gonion; Reference lines: SN plane; Frankfort-horizontal (FH) plane; palatal plane (PP); occlusal plane (OP); mandibular plane (MP); N perpendicular line; U1, long axis of the upper incisor; L1, long axis of the lower incisor.

• 

  Figure 2 Cephalometric variables. Anteroposterior characteristics: 1, SNA (angle between S, N, and point A); 2, SNB (angle between S, N, and point B); 3, ANB (angle between point A, N, and point B); 4, NA-Pog (angle between N, point A, and Pog); 5, FH-NPog (angle formed by FH plane and N-Pog line); 6, A-N perpendicular (perpendicular distance from point A to the N perpendicular line); 7, Pog-N perpendicular (perpendicular distance from Pog to the N perpendicular line); and 8, mandibular body length/anterior cranial base (ratio of the distance between Go and Me to the distance between S and N). Vertical characteristics: 1, FH-PP (angle formed by FH plane and palatal plane); 2, FMA (angle formed by FH plane and mandibular plane); 3, PP-MP (angle formed by PP and MP); 4, Bjork sum (summation of angles determined by saddle angle, articular angle, and gonial angle); 5, N-Me (distance between N and Me); 6, S-Go (distance between S and Go); and 7, N-ANS/ANS-Me (ratio of the distance between N and ANS to the distance between ANS and Me). Dental characteristics: 1, U1-FH (angle formed by upper incisor axis and FH plane); 2, U1-PP (angle formed by U1 and PP); 3, U1-OP (angle formed by U1 and OP); 4, IMPA (angle formed by lower incisor axis and MP); 5, L1-OP (angle formed by L1 and OP); 6, interincisal angle (angle formed by U1 and L1); 7, FH-OP (angle formed by FH plane and OP); and 8, OP-MP (angle formed by OP and MP). Mandible characteristics: 1, gonial angle (angle between Ar, Go, and Me); 2, upper gonial angle (angle between Ar, Go, and N); 3, CD-Gn (distance between condyle head and Gn); 4, Go-Me (distance between Go and Me); and 5, Ar-Go (distance between Ar and Go). Cranial base characteristics: 1, saddle angle (angle between N, S, and Ar); 2, cranial base angle (angle between N, S, and Ba); 3, S-N (distance between S and N); 4, S-Ar (distance between S and Ar); and 5, Ar-N (distance between Ar and N). See Figure 1 for definition of each landmark.

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