[Estimation of mandibular premolar teeth length and mesiodistal width based on panoramic radiograph]

Statement of Problem: In diagnostic studies of dentistry, estimation of the mesiodistal width of the unerupted teeth and the required space for their eruption in relation to the space analysis and evaluation of the root-crow ratio is of great importance

Purpose: This study aimed to evaluate the ratio between the real and radiographic length and mesiodistal width of mandibular premolars and provide a formula for prediction of the teeth length and mesiodistal width

Materials and Method: Fifty six extracted teeth of mandibular first and second premolars of patients and their panoramic radiographs with good quality were collected. The extracted teeth were divided into four groups: T34 [lower left first premolar], T44 [lower right first premolar], T35 [lower left second premolar], and T45 [lower right second premolar]. Then the length and mesiodistal width of both the panoramic images and the extracted teeth were measured. All of the obtained data were analyzed through t-test, two tailed student and linear regression model

Results: It was shown that the vertical magnification of the mandibular first premolars was almost 11.4%-12.1% and that of the mandibular second premolar was almost 16%. The horizontal magnification of the mandibular first premolar was almost 15% and that of the mandibular second premolar was almost 26%. No statistically significant differences were found between the true and radiographic length and mesiodistal width and the magnifications of the left side premolars compared with right side premolars. To determine the real mesiodistal width and length size, some equations are introduced

Conclusion: The panoramic radiographs taken in this research by X-ray imaging machine are feasible and reliable for estimating the actual premolar teeth length and mesiodistal width using specific equations for each teeth in the lower jaw

[Determination of required space for canine and premolar eruption in mixed dentition using mesiodistal width of mandibular incisors]

Background and Objective: Determination of the relation between periphery of dental arch and teeth size which mostly done before eruption of some permanent teeth, is of important levels of diagnosis in mixed dentition. Determination of this relationship is not possible without prediction and distinct evaluation of unerupted permanent mesiodistal width [Permanent canines and premolars]. The aim of this study was to evaluate the required space for eruption of canine and premolars using total width of lower incisor in Iranian people by Tanaka and Johnston method

Methods: In this study mesiodistal width of permanent first and second premolar and canine in each quadrant also of 4 lower incisors were measured in 604 dental casts of under 20 year old people [In Mazandaran] using Koulis with accuracy of 0.02 millimeter and final measurements were illustrated in a table. Needed teeth for measurement were completely erupted, caries free and without fracture or restoration

Findings: The mean of mesiodistal width of lower incisors, total mesiodistal width of upper and lower canine and premolars and a and b indexes for Tanaka and Johnston equation [Y=aX+b], a=0.167, b=19.387 for mandible and a=0.195, b=18.723 for maxilla have been calculated. Meanwhile X is the sum of lower incisor mesiodistal width and Y is the sum of canine and premolar mesiodistal width in one side

Conclusion: In present study, equation of Tanaka and Johnston is recommended. So its dependence on race is obvious