Korean J Orthod.  2009 Oct;39(5):330-337.

What determines dental protrusion or crowding while both malocclusions are caused by large tooth size?

• Sun MK
• Kim JH
• Cho JH
• Kim JM
• Hwang HS

Abstract

OBJECTIVE
To examine the differences in lateral cephalometric characteristics between patients with dental protrusion and crowding in order to determine what factors affect dental protrusion or crowding while both malocclusion types are caused by large tooth size.
METHODS
Twenty nine individuals with dental protrusion and 22 individuals with dental crowding were enrolled in this study. All subjects had larger teeth than average and Class I molar relationships. Craniofacial characteristics and hyoid bone positions were determined from lateral cephalograms and compared between the two groups.
RESULTS
In the comparisons of craniofacial characteristics, the measurements indicating maxillary length and facial convexity showed greater values in the protrusion group than in the crowding group. Comparisons of hyoid bone positions showed that the hyoid bone was positioned more anteriorly and superiorly in the protrusion group than in the crowding group.
CONCLUSIONS
The results of the present study indicate that some craniofacial characteristics and tongue position may affect the development of dental protrusion or crowding; when an individual has large teeth, dental protrusion or crowding might be determined according to maxillary growth and tongue position.

Keyword

Dental protrusion; Dental crowding; Cephalometric characteristics; Tooth size

MeSH Terms

Humans
Hyoid Bone
Malocclusion
Molar
Tongue
Tooth

Figure

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  Fig. 1 Cephalometric landmarks and tracing used in this study. S, Sella; Po, porion; Ar, articulare; N, nasion; Or, orbitale; Ptm, the eleven o'clock position of the pterygomaxillary fissure; Ptm', the perpendicular point from Ptm along palatal plane (ANS-PNS plane); ANS, anterior nasal spine; PNS, posterior nasal spine; A, point A; A', the perpendicular point from A along palatal plane; B, point B; Pog, pogonion; Me, menton; m, the most posterior point on the mandibular symphysis; Go, gonion; cv2tg, the most posterior point on the odontoid process of the second cervical vertebra; cv4ip, the most posteroinferior point on the corpus of the fourth cervical vertebra; cv2ia, the most anteroinferior point on the corpus of the second cervical vertebra; cv4ia, the most anteroinferior point on the corpus of the fourth cervical vertebra; hy, the most anterosuperior point on the body of the hyoid bone; hy', the perpendicular point from hy along the mandibular plane; apw2, the anterior pharyngeal wall along the line intersecting cv2ia and hy; apw4, the anterior pharyngeal wall along the line intersecting cv4ia and hy; U1, the tip of the upper central incisor; U1R, the root apex of the upper central incisor; L1, the tip of the lower central incisor; L1R, the root apex of the lower central incisor.

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  Fig. 2 Measurements for hyoid bone position used in this study. 1, The perpendicular distance from hy to S-N plane (hy-SN); 2, the perpendicular distance from hy to palatal plane (hy-PP); 3, the perpendicular distance from hy to mandibular plane (hy-MP); 4, the perpendicular distance from hy to cervical vertebrae tangent (hy-CVT); 5, the distance from hy to m (hy-m); 6, the distance from hy' to Go (hy'-Go); 7, the distance from hy to apw2 (hy-apw2); 8, the distance from hy to apw4 (hy-apw4).

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