Pedo Lecture 16: Arch Length Analysis PDF

Lec 16 Dr. Rawaa B. Fadhil B.D.S M.Sc. ARCH LENGTH ANALYSIS  Tooth size and alveolar size are the primary factors that determine the status of permanent dental arch, if the tooth size and arch size are not balanced, the effect on permanent dental arch is crowding or spacing  Crowding is the most c...

Lec 16 Dr. Rawaa B. Fadhil B.D.S M.Sc. ARCH LENGTH ANALYSIS  Tooth size and alveolar size are the primary factors that determine the status of permanent dental arch, if the tooth size and arch size are not balanced, the effect on permanent dental arch is crowding or spacing  Crowding is the most common feature of dental arch malocclusion.  Only when the combined size of permanent teeth is balanced with the size of alveolar apical area is an ideal dental arch possible  Arch length analysis is done to estimate the space adequacy for succedaneous tooth and fairly predict how much space will be required for eruption and proper alignment in the dental arch VARIOUS ANALYSIS USED FOR ESTIMATING SPACE ADEQUACY ARE 1- Nance analysis This analysis compares the space required and space available to arrive at arch length discrepancy. It is used during mixed dentition period, as a result of comprehensive studies, Nance concluded:  the length of dental arch from mesial surface of one mandibular first permanent molar to mesial surface of corresponding tooth on the apposite side is also shortened during the transition from mixed to permanent dentition  in the average patient’s mandibular arch a leeway of 1.7 mm per side exists between combined mesiodistal widths of primary mandibular canine and first and second primary molars and the mesio distal length widths of corresponding permanent teeth, with the primary teeth being larger  the difference in the total mesio-distal width of corresponding three primary teeth in maxillary arch compared with the width of the three permanent teeth that succeed them is only 0.9 mm per side LIMITATION  The Nance arch length analysis is seldom used, partly because the involved procedure for this analysis require a complete sets of periapical radiographs  the clinical reliability of other analysis that doesn’t use radiographs is sufficient to determining major arch length inadequacies 2- MOYER’S MIXED DENTITION ANALYSIS There is high co-relation between sizes of different teeth in the same individual, thus making it possible to predict the size of unerupted tooth by looking at the teeth present in oral cavity, it is also used during mixed dentition period ADVANTAGES 1- it has minimal error and the range of possible error is precisely known 2- it can be done with equal reliability either by beginner or by an expert 3- it is not time consuming 4- it requires no special equipment 5- it can be completed in mouth as well as on casts 6- it may be used for both arches 7- the analysis is based on correlation of tooth size; one may measure a tooth or group of teeth and predict accurately the size of other teeth in the same mouth 8- the mandibular incisors , because they erupt early in mixed dentition and may be measured accurately, have been chosen for measurement to predict the size of upper as well as lower, posterior teeth 9- if the predicted value is greater than available arch length, crowding of teeth can be expected METHOD 1- measure the mesio-distal width of mandibular incisors 2- measure the space for maxillary cuspids and bicuspids from distal of aligned lateral incisor to mesial aspect of first permanent molar 3- measure the space for mandibular cuspids and bicuspids from the distal aspect of aligned lateral incisor to mesial aspects of first permanent molar 4- using Moyer’s probability chart find out sum total mesio-distal width of upper and lower cuspids and bicuspids for the given sum width of the lower central and lateral incisors at 75% probability 5- compare the space available and space required in all four quadrants to determine arch length discrepancy TANAKA AND JOHNSTON ANALYSIS Is a variation of Moyer’s analysis except that a prediction table is not needed. It is also used during the mixed dentition period. The method includes: 1- the sum of widths of mandibular permanent incisors is measured and divided by 2 2- for lower arch. 10.5 mm is added to the result 3- for the upper arch, 11 mm is added to the result to obtain the total estimated widths of canines and premolars. For example, if the width of lower incisors is 23 mm, divide by 2 and add 10.5 mm for lower arch, the result is 22 mm compared with 22.2 mm obtained from Moyer’s table 4- one can then take these tooth mass predictions and compare them with total measured arch length and obtain any inadequacies in the arch length 5- if the result is positive, there is more space available in the arch than is needed for the unerupted teeth 6- if the result is negative, the unerupted teeth require more space than is available to erupt into ideal alignment ADVANTAGES 1- the technique involve simple, easily repeated procedures and minimal material needs 2- it doesn’t use prediction charts 3- this method doesn’t require additional radiograph BOLTON ANALYSIS  Also called Bolton’s tooth size ratio analysis  Used during permanent dentition period  According to Bolton, a ratio exists between mesio-distal widths of maxillary and mandibular teeth  This analysis address tooth mass discrepancies between maxillary and mandibular arches 1- it can be used to compare the sum of mesio-distal widths of 12 maxillary teeth with that of 12 mandibular teeth, first molar to first molar and to compare the 6 maxillary teeth with 6 mandibular teeth, canine to canine 2- the Bolton analysis ratio measurement is as follows: Sum of mandibular /sum maxillary x 100 = tooth mass ratio  For the overall ratio (12 teeth versus 12 teeth), the ,mean is 91.3  For the anterior ratio (6 teeth versus 6 teeth), the mean is 77.2  When significant discrepancy with these ratio is noted, the clinician must assess where the tooth mass problem is located and decide on the best method to resolve it