Date of Award

Spring 2011

Document Type


Degree Name

Master of Science (MS)



First Advisor

Liu, Dawei

Second Advisor

Bradley, Thomas G.

Third Advisor

Bosio, Jose


Aim: To determine the marginal ridge thickness (MRT) of maxillary incisors in orthodontic patients and the possible correlation between MRT and Bolton Index.

Methods: 120 pre<–>orthodontic treatment dental casts were collected, following the inclusion criteria: Quality pretreatment upper and lower casts, age 10<–>16, full permanent dentition (except 2nd and 3rd molars), no obvious wear/attrition/abrasion, no proximal restorations or crowns. For each cast, the mesio (M<–>D)distal (M<–>D) widths of the upper and lower teeth from left 1st molar to right 1st molar were measured to calculate Bolton Index. The MRTs of the maxillary incisors were measured in the following method. Along the long axis of clinical crown mark a circumferential line for the maxillary incisors at the incisal one<–>third level, followed by the measurement of the labial<–>lingual thickness at the mesial and distal marginal ridges as well as at the center of the crown, perpendicular to the long axis of the crown. Descriptive analysis was applied to show the distribution of the MRTs of each upper incisor. Independent sample t<–>test or one<–>way ANOVA was used to test the significance of the differences of the MRT between genders, races, and among Class I, II and III malocclusions, respectively. Pearson correlation analysis was used to test the possible correlation between MRT index and Bolton index. Significance was considered when p value was less than 0.05.

Results: MRT discrepancy (>2SD) exists in 4<–>6% of orthodontic patients. MRTs are smaller in Caucasian than non<–>Caucasians, and larger in males than in females (except distal #9). MRT scores (from small to large): Class II > Class I > Class III (except mesial #9, between Class I and Class II). MRT and Bolton Index are highly correlated (R=0.652, p=0.000).

Conclusions: The MRT established in this study may be used as a tool in treatment planning and finishing orthodontic cases.

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