Korean J Orthod.  2012 Aug;42(4):182-189. 10.4041/kjod.2012.42.4.182.

Differences in molar relationships and occlusal contact areas evaluated from the buccal and lingual aspects using 3-dimensional digital models

• Jang SY
• Kim M
• Chun YS

• KMID: 1435412
• DOI: http://doi.org/10.4041/kjod.2012.42.4.182

Abstract

OBJECTIVE
The aims of this study were to use a 3-dimensional (3D) system to compare molar relationship assessments performed from the buccal and lingual aspects, and to measure differences in occlusal contact areas between Class II and Class I molar relationships.
METHODS
Study casts (232 pairs from 232 subjects, yielding a total of 380 sides) were evaluated from both the buccal and lingual aspects, so that molar relationships could be classified according to the scheme devised by Liu and Melsen. Occlusal contact areas were quantified using 3D digital models, which were generated through surface scanning of the study casts.
RESULTS
A cusp-to-central fossa relationship was observed from the lingual aspect in the majority of cases classified from the buccal aspect as Class I (89.6%) or mild Class II (86.7%). However, severe Class II cases had lingual cusp-to-mesial triangular fossa or marginal ridge relationships. Mean occlusal contact areas were similar in the Class I and mild Class II groups, while the severe Class II group had significantly lower values than either of the other 2 groups (p < 0.05).
CONCLUSIONS
Buccal and lingual assessments of molar relationships were not always consistent. Occlusal contact areas were lowest for the Class II-severe group, which seems to have the worst molar relationships - especially as seen from the lingual aspect.

Keyword

Digital models; Classification; Dental cast analysis; Class II

MeSH Terms

Molar

Figure

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  Figure 1 Guidelines used for classifying molar relationships from the buccal aspect. A, Class I; B, mild Class II (Class II-m); C, moderate Class II (Class II-m); D, severe Class II (Class II-s).

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  Figure 2 Sectioned images of 3-dimensional digital models showing the buccal and lingual surfaces of the first molars. These images were used to identify the position of the mesiopalatal cusp of the upper first molar with respect to the lower molar. A, Buccal aspect; B, lingual aspect.

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  Figure 3 Guidelines used for classifying molar relationships from the lingual aspect. A, Lingual 0; B, lingual 1; C, lingual 2; D, lingual 3. *The mesiopalatal cusp of the upper first molar.

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  Figure 4 Three-dimensional digital models, produced by the Rapidform XOR3® program, showing the intersection areas (red) of the upper and lower scanned mesh. A, Upper right side; B, lower right side; C, occlusal contact area.

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  Figure 5 Distribution of samples (n) classified by evaluations from the buccal and lingual aspects. Lingual 0, distal triangular fossa; 1, central fossa; 2, mesial triangular fossa; 3, anterior aspect of the mesial triangular fossa.

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