The Relationship Between the Mid-Point and Most-Prominent Point on the Labial Curve of Upper Anterior Teeth

OBJECTIVES: This study investigates coincidence of the most-prominent point and the mid-point on upper anterior teeth in relation to the use of straight-wire appliances. MATERIALS AND METHODS: Alginate impressions of the upper jaw were obtained from forty Caucasian patients. Impressions were cast using hard dental stone. The teeth on each upper study model (canine to canine) were marked along the facial axis of the clinical crown (FACC line) then separated using a very thin diamond disc. Each tooth was mounted on a glass slide using sticky wax and cut into two halves down this FACC line. Images were acquired of the sections and a straight line connecting the gingival margin and the incisal edge was drawn on the flat cut surfaces (now the proximal crosssectional view). From this line, perpendicular lines were drawn at the mid-point and most prominent point to the labial curve. Coincidence rate was calculated or whether the most prominent point was gingival or incisal to the mid-point. RESULTS: Approximately 80% of upper central incisors had coincident mid- and most-prominent points. Upper lateral incisors and canine teeth had approximately 50% coincidence. The vast majority of cases without coincidence showed the most-prominent point incisal to the mid-point for all tooth kinds with just 5% or less gingival. CONCLUSIONS: The high proportions of non-coincident examples found suggest that clinicians should be aware of individual variation and that this may possibly effect 3(rd) order alignment.