Model analysis is the study of dental casts, which helps to study the occlusion& dentition from all three dimensions &analyze the degree & severity of malocclusion & to derive the diagnosis &plan for treatment Model analysis is an essential diagnostic record that helps to study the occlusion and the dentition from a three dimensional aspect.
The study ranges from the metric analysis of the arch form to the prediction of the sizes of the unerupted permanent teeth during the mixed dentition. They have been the “gold standard” in orthodontic diagnosis with the advantages ranging from being a routine dental technique, ease of production, inexpensiveness and ease in measurement to plaster casts being able to be mounted on an articulator for study in three – dimensions14.
Model analysis can be classified in the following ways1.Based on whether the analysis is on the permanent dentition or on the mixed dentitiona) PERMANENT DENTITION ANALYSES Ashley howe’s Carey’s / Arch perimeter Pont’s Linder Hearth’s Korkhau’s Bolton’s
Moyer’s Tanaka Johnston Hixon and Old father Staley kerber Huckaba’s Ballard and Willie
2.Based on the arch in which the analysis is carried out ,they can be classified as MAXILLARY ARCHPont’sLinder hearth’sKorkhau’sArch perimeter MANDIBULAR ARCHCarey’sHixon and Old fatherPeck and peckTotal space analysisStaley Kerber
3.Based on the Parameter determined by the analysis2 TOOTH SIZE ANALYSESBolton’s tooth ration analysisSanin Savara analysis RELATIONSHIP OF TOOTH SIZES TO THE SUPPORTING STRUCTURESAshley howe’sPont’sLinder hearth’sKorkhaus
SPACE ANALYSES DURING MIXED DENTITION Moyer’s Tanaka Johnston Ballard and willie Hixon and Old father
4)Based on principles of space analysisNON –RADIOGRAPHIC SPACE ANALYSES Moyer’s Tanaka Johnston Ballard and WylieRADIOGRAPHIC ANALYSES Nance’s Huckaba’sCOMBINATION OF RADIOGRAPHS AND PREDICTION CHARTS Hixon and Old father Staley kerber
After completion of the dental cast review, depending upon the age of the pt, a mixed dentition analysis can be completed. An early assesment of available space may permit early intervention /minimise development of malocclusion. Prediction of the M-D widths of the unerupted canines and the premolars is an essential part of the tooth size-arch length analysis during the mixed dentition period.
Following the eruption of the permanent incisors, the mandibular arch length and the width have achieved the adult dimensions for all practical purposes. A meaningful mixed dentition tooth size-arch length analysis depends on an accurate prediction of the mesio-distal widths of the unerupted permanent canines and the premolars1
Space analysis , using the study casts is valuable in evaluating the likely degree of crowding for a child in the mixed dentition ; and in that case,it must include the prediction of the size of the unerupted permanent teeth.
Mixed dentition period 6-12 years Indications- Nanda(1993)a. Premature loss of primary canine.b. Rotation or blocking of lateral incisor because of lack of space.c. Ectopic eruption of permanent first molars.d. Distal terminal plane relationships.
a) 1st permanent molar and permanent incisors are erupted.b) The succedaneous permanent teeth are forming.c) Size relationship between unerupted permanent teeth and primary teeth.d) There is size difference in primary canines and molars and the succedaenous teeth.e) M-D width of primary canines and molars is greater than perm’ sucessors (leeway space of nance) 2
Methods of space analysis
Basis- high co relation among groups of teeth , thus measuring one group of teeth, prediction of size of other group of teeth can be done1. Armamentarium-1. Dental cast2. Boley’s guage3. Probability chart
Procedure:1. Measure the widths of each of four permanent mandibular incisors .2. Total the M-D widths of mandibular incisors3. Using prediction chart for space available in mandibular arch,locate the value closest to the sum of four mandibular incisors.
3)On the study cast, determine and mark the midline of mandibular arch.4)Total the M-D widths of right mand’ incisors & set the boley’s gauge to this value. Measure from midline to right side. Place one point of the gauge at the midline bet’n the central incisor and let the other end lie along the line of the dental arch on the right side. Mark on the point where the precise point where the distal tip of boley’s gauge touched. Repeat for the left side.
5) Measure the dist betw the point marked on the cast to the mesial surface of perm’ 1st molar.Record that value and calculate the difference6) Repeat the process on the maxillary arch.
6)Compute the amt of space available. Measure the dist’ from the point marked on the cast to mesial surface of the 1st molar, and calculate space difference.
It is advocated for foll’ reasons: Has minimal systemic errors and the range of such errors is known. Can be done with equal reliability by the beginner and the expert as it does not presume sophisticated clinical judgement. Not time consuming, simple and easy to perform. Requires no special equipment or radiographic projections. It can be done with reasonable accuracy in the mouth although it is best done on the dental casts. It may be used for both the arches.
Advantages- It has minimal error. Can be done with equal reliability Not time consuming No special equipment required Can be done in mouth as well as on cast Can be used for both archesLimitations1. Moyer’s analysis is probability analysis2. It does not account for tipping of mandibular incisor either lingually or facially3. Maxillary tooth size is predicted by mandibular teeth
4. Moyers advised caution in using any analysis, as none was able to compensate for the biological variation in individuals during the transition from primary to permanent dentition3.5. Moyers equation does not mention the population group from which they were calculated 136. Moyer’s method of prediction may have population variations. For one to be sure of the accuracy while using Moyer’s method it may be safer to develop prediction tables for specific populations. Thus Moyer’s method cannot universally be applied12.
Armamentarium- Boley guage Study cast The prediction of the size of the unerupted canines and the premolars in contemporary orthodontic population can also be done with the Tanaka Johnston analysis. Tanaka and Johnston conducted a study on 506 orthodontic patients in Cleveland.
They believed that the Moyer’s equations and the size of his confidence intervals have never been validated on any other samples. Also that the possibility of secular changes during the past 20 years cannot be ruled out. Hence they undertook the study in the Orthodontic Department of Case Western University school of dentistry
They simplified the Moyer’s results and gave regressive equations of the form Y = A+B(X) Where Y = sum of the mesio distal widths of the unerupted canines and premolars X = sum of the mesio distal widths of the lower incisors A & B are constants. For the maxillary arch , Y = 11 + 0.5 ( X ) For the mandibular arch, Y = 10.5 + 0.5 ( X )
Advantages-• Technique involves simple, easily repeated procedure with minimum material requirement.• Prediction chart and radiograph is not required Limitations-• Error in predicted size if patients are not from North western European descent.• *John Y. K. Linga; Ricky W. K. Wong concluded constants for males (upper-11.5; lower-10.5) or females (upper-11.0; lower-10.0) for southern Chinese population
Iowa Facial Growth Study. Staley and Kerber in a later study conducted at the Iowa, significantly reduced the standard error of estimate when they generated a revised Hixon and Oldfather prediction equation. The co-efficient of correlation of the revised equation was significantly higher than that of the original equation.
The original equation was primarily obtained from the measurements of the teeth on the left side of the arch of each subject whereas the revised equation was derived from the means of measurements taken from both right and left side teeth in each subject.Armamentarium-• Boley guage• Study cast• Periapical radiograph• Hixon- old father prediction chart
Procedure( Stanley and Kerber, 1980) From the casts, on one side, measure the m-d widths of the permanent mandibular central and lateral incisor. From the periapical radiographs, measure the m-d width of unerupted first and second premolars Total the m-d widths of four(4) teeth. Compare the measured value to estimated tooth size from the Hixon- Oldfather chart. Repeat steps 1 to 3 for the other side of the arch.
Advantage- it is very accurate technique Limitation- Can be used only for lower arch. CHART Measured value Estimated tooth size 23mm 18.4mm 24mm 19.0mm 25mm 19.7mm 26mm 20.3mm 27mm 21.0mm 28mm 21.6mm 29mm 22.3mm 30mm 22.9mm
This analysis is similar to arch perimeter analysis of the permanent dentition Armamentarium Dental cast Boley gauge, millimeter ruler Peri-apical radiograph
SPACE REQUIRED: ◦ measure the mesio distal width of the erupted permanent teeth. ◦ Measure the width of each unerupted tooth, cuspids and bicuspids from the IOPA. ◦ The total mesiodistal width of all the teeth in each quadrant will indicate space required to accommodate the permanent teeth.
B = measurement of un-erupted caninesand premolars on radiograph
SPACE AVAILABLE: ◦ using brass wire, measure the arch perimeter from the mesial surface of permanent first molar to the mesial surface of the permanent first molar on the other side. ◦ Compare the space required and space available to arrive at the arch length discrepancy
ADVANTAGES It results in minimal errors It can be performed with reliability It allows analysis of both archesLIMITATION It is time consuming Complete mouth radiograph is needed.
Ballard and Wylie were so concerned about the distortions of the X- ray films that they devised a scheme for estimating the widths of the mandibular canine and the premolars on the basis of the combined widths of the four lower incisors. Using the plaster models of 441 cases, they measured and recorded the widths of all the mandibular teeth including the first molars. On the average, the sum of the four permanent lower incisors were 23.84 +/- 0.08 mm. The average sum of the canine,first and the second premolars turned out to be 21.97 +/- 0.06mm
Although not particularly high, the co-efficient of correlation of +0.64 seemed sufficiently high to justify a predicton. They modified the equation as Y = 9.41 + 0.527 ( X ) Testing these calculations on 60 cases , Ballard and Wylie came to a conclusion that their method had only 2.6% error as compared to the 10.5% error when using only the X-rays. They do indicate that good X rays should be used and suggest that their method was an adjunct to the Nance’s method.
This analysis makes use of a radiograph and study cast to determine the width of unerupted teeth Armamentarium Dental cast Boley gauge, millimeter ruler Periapical radiograph
With any type of radiograph, it is necessary to compensate for enlargement of radiographic image. This can be done by measuring an object that can be seen both in the radiograph and on the cast, such as primary molar tooth. It is possible to determine the measurements of un- erupted teeth by studying the teeth that have already erupted in a radiograph and on a cast
A simple proportional relationship can be established as follows:
Hixon and Oldfather: most accurate Tanaka and johnston : most practical Radiographic Radiographic method: for population other method: for population other than Caucasians
They did a review of Methods that have been proposed for mixed dentition analysis , Studies comparing the different methods have shown that the method of Hixon & Oldfather (1958), as refined by Staley & Kerber (1980), is the most accurate.* Mixed dentition analysis forms an integral aspect of orthodontic diagnosis to determine whether the treatment plan is going to involve serial extraction, space maintenance, space gaining or simply periodic observation of the patient.
Examine and compare the accuracy of the Moyers and Tanaka & Johnston mixed dentition analyses and to evaluate its applicability to Indian Marathi population. Developed regression analysis- Y = a + b (X) where , X= independent variable (mandibular incisors measurements) Y = dependent variable (sum of canine and premolars). For mandibular teeth- Y = 10.830 + 0.563 (X) For maxillary teeth- Y = 12.143 + 0.481 (X)
They concluded thata) Both Tanaka Johnson and moyers have comparable standard errors of estimate,thus their accuracy is fairly comparable.b) Moyers chart at 50% confidence level gives more realistic estimate of width of unerupted canine and premolars as compared to 75% confidence level for Marathi population.c) Sugessted the use of newly developed regression equations is suggested.
1) Mathewson R, Primosch R. Fundamentals of pediatric dentistry.3rd ed;30-332) Marwah N. Textbook of pediatric dentistry. Jaypee. 299-3073) Irwin R, Herold J, Richardson A. Mixed dentition analysis: a review of methods and their accuracy. IJPD 1995;5:137-1424) Orthodontics-the art and science- S.I. Bhalajhi – III edition5) Textbook of Pedodontics-Shoba tandon I edition6) Handbook of Orthodontics – Robert E Moyers – 4th edition7) Contemporary Orthodontics – William Proffit – 4th edition
8) Ballard,Murray L and Wylie, Wendell L : Mixed dentition case analysis :Estimating the size of the unerupted permanent teeth : Am Jol Ortho & Oral Surg : 1947 : 33: 754-7599) Textbook of Orthodontics-Hitchkock , Perry H10)Text book of orthodontics- Samire E Bishara11)Hixon EH,OldFather RE ,Estimation of the sizes of the unerupted cuspid and the bicuspid teeth : Ang Ortho : 1958:28:236-24012) Buwembo W, Luboga S.Moyer’s method of mixed dentition analysis: a meta-analysis.African Health Sciences2004;4: 63-6613) Sonawane S, Bettigiri A, Soni V. Comparison of two non-radiographic techniques of mixed dentition analysis and evaluation of their applicability for marathi population; Scientific Journal 2008;vol 2.14) Textbook of Orthodontics-Gurkeerat Singh – 2nd edition