Palatal rugae morphology is associated with variation in tooth number

Abstract

This observational study compared palatal rugae morphology in adolescent subjects with normal tooth number and tooth agenesis. Maxillary dental study casts were used to compare rugae number, length and shape. Each study group contained 60 subjects (30 females and 30 males) mean age 13.4 (SD, 1.55) in control and 13.56 (SD, 1.54) years in tooth agenesis groups (p = 0.576). Mean number of missing tooth units in the tooth agenesis group was 2.1. Mean number of primary rugae in the whole sample was 4.35 (SD, 0.98) on the right and 4.33 (SD, 0.92) on the left with no significant differences (p = 0.236 and p = 0.404, respectively). However, the number of secondary rugae on the left (p = 0.006) and fragmentary rugae on the right (p = 0.004) was significantly increased in the tooth agenesis group. The shape of left primary rugae 2 and 3 also differed between groups, tending towards a wavy pattern in the control group and curved in the tooth agenesis group (p = 0.012 and p = 0.004, respectively). In addition, primary rugae 3 was more convergent (p = 0.008) whilst left primary rugae 3 and 5 were orientated in an antero-posterior direction (p = 0.04 for both rugae) in the tooth agenesis group. Subgroup analysis also identified significant associations between patterns of tooth agenesis and rugae number, in addition to shape of primary rugae. The identification of significant differences in rugae pattern between subjects with normal tooth number and agenesis suggests potential commonality in signal pathway disruption during establishment of these structures.

Figure 1

Morphological classification of primary rugae. Primary rugae were classified according to SHAPE, CONTINUITY and DIRECTION. SHAPE was classified as Straight (a straight line from origin to termination), Curved (a simple gently curving crescent shape), Wavy (a serpentine shape or the presence of any curve at the origin or termination of a curved rugae) and Circular (a definite continuous ring). CONTINUITY between rugae was classified as Convergent (a split origin in the midline and converging laterally), Divergent (a single origin in the midline and diverging laterally or Distinct (with no unification and as shown in SHAPE). DIRECTION was classified as Type I–IV according to the relationship between the midline origin and lateral termination in relation to the anterior–posterior axis of the palate midline. Type I (Posterior–Anterior) have an origin situated posterior to the termination; Type II (Perpendicular) have an origin and termination in the same plane; Type III (Anterior–Posterior) have an origin situated anterior to the termination and Type IV are Multi-directional. Vertical lines represent palatal midline. (a) anterior; (p) posterior.

Figure 2

Distribution of missing teeth in the tooth agenesis sample by dental quadrant. The x axis represents each tooth in the quadrant from: (1) central incisor; (2) lateral incisor; (3) canine; (4) first premolar; (5) second premolar; (6) first molar and (7) second molar. The y axis represents the total number of teeth missing in the tooth agenesis sample. upper right dental quadrant (URQ); upper left dental quadrant (ULQ); lower right dental quadrant (LRQ); lower left dental quadrant (LLQ).