cast analysis

orthodontic cast analysis

1. MODEL ANALYSIS

2. INTRODUCTION The study model provides a three dimensional view of the maxillary and mandibular dental arches in all three planes of space, i.e., sagittal, vertical and transverse planes.

3. A dvantages They are three dimensional records of the patients dentition. Occlusion can be visualized from lingual aspect. They provide a permanent record of the intermaxillary relationship. Helps to motivate the patients as they can visualize the treatment progress. They are needed for comparison purposes at the end of the treatment and act as a reference for post treatment changes. They serve as a reminder for the parent and the patient of the condition present at the start of the treatment. In case the patient has to be transferred to another clinician study model are an important record .

4. PARTS OF A STUDY MODEL Anatomic Portion - Consists of the actual impressions of the dental arch & its surrounding structures. Artistic Portion - Consists of the plaster base that supports the anatomic portion and helps in analysing the occlusion & orientation of the study models. The ratio of the anatomic portion to the artistic portion should be 3:1.

5. REQUSITES OF STUDY MODELS Should accurately reproduce all the teeth and soft tissues without any distortion. Should be trimmed symmetrical on either side. Posterior surface should be trimmed, such that when placed on their back they should reproduce the occlusal plane. Should reproduce the alveolar process as much as possible.

6. According to ABO (1990) Guidelines Lateral view of the study model 1. Base of the maxillary cast is trimmed parallel to the occlusal plane. 2. Upper & lower cast base should be parallel.

7. Maxillary occlusal view of study model

8. Mandibular occlusal view of study model

9. REQUIREMENTS TO DO MODEL ANALYSIS Well prepared study models Vernier calipers Divider Ruler 0.033” Soft Brass wire

10. CAST ANALYSIS CAST APART CAST IN OCCLUSION

11. CAST APART Arch form Arch symmetry Teeth present Teeth absent Crowding Spacing Buccoversion / linguoversion Supraversion / infraversion Torsiversion Transposition Proclined Retroclined

12. DEFINITIONS Buccoversion when the tooth is displaced bodily in a labial or buccal direction Linguoversion when entire tooth is displaced in a lingual or palatal direction Infraversion tooth that has not erupted enough in comparison to adjacent teeth Supraversion tooth that has over-erupted Torsiversion rotated tooth or tooth movements around its long axis Transposition when two teeth have exchanged their positions

13. TORSIVERSION LINGUOVERSION

14. BUCCOVERSION SUPRAVERSION

15. TRANSPOSITION

16. CAST IN OCCLUSION Incisor relationship Canine relation Molar relation Overjet Positive – Class II Negative – Class III Overbite Positive – Deepbite Negative - Openbite Crossbite Palatal Crossbite Buccal Crossbite – Scissors bite Dental midline

17. Molar and canine relationships

18. MIDLINES

19. CLASSIFICATION PERMANENT DENTITION MODEL ANALYSIS MIXED DENTITION MODEL ANALYSIS Arch perimeter analysis Moyer’s Mixed dentition analysis Carey’s analysis Tanaka and johnston analysis Ashley Howe’s analysis Nance mixed dentition analysis Pont’s analysis Huckaba’s mixed dentition analysis (Radiographic method) Linder Harth analysis Korkhaus analysis Bolton’s analysis

20. ARCH PERIMETER ANALYSIS Tooth Material and Arch Length Discrepancy (ALD) Many malocclusions occur due to discrepancy between arch length & tooth material It is done in the upper arch Two measurements are required for intra-maxillary analysis of space requirement: 1. Calculation of space required 2. Calculation of space available Arch perimeter is the geometrical dental arc formed by teeth at their incisal / cuspal edges

21. PROCEDURE DETERMINATION OF SPACE REQUIRED: M easure the mesiodistal dimension of all the teeth mesial to the first molar (54321│12345) DETERMINATION OF SPACE AVAILABLE: M easure the arch perimeter using brass wire. From mesiobuccal line angle of maxillary right first molar , pass the wire along the buccal cusp and incisal edges in the anterior region, ‘pass the wire on the left quadrant like a mirror image till the mesiobuccal line angle of the left maxillary first molar. Mark the wire and measure the wire, which gives the space available.

22. In case of proclined incisors, pass the brass wire in the cingulum region, and if the anterior teeth are retroclined , pass the wire labial to them like a smooth curve.

23. SPACE REQUIRED SPACE AVAILABLE

24. DETERMINATION OF THE DISCREPANCY The difference between the space required and space available gives the arch discrepancy or excess. If the tooth material is more than the arch length, the space available for alignment is not sufficient results in crowding. If the tooth material is less than the space then there can be spacing.

25. CAREY’S ANALYSIS The arch length-tooth material discrepancy is the main cause for most malocclusions. This discrepancy can be calculated with the help of Carey’s analysis. The analysis is carried out in the lower arch.

26. INTERPRETATION OF ARCH PERIMETER ANALYSIS ARCH LENGTH DISCREPANCY ALD INFERENCE 0 to 4 mm Proximal stripping can be carried out to reduce the minimal tooth material excess Avoid extractions 4 to 8 mm Patient can be treated with or without extractions depending on lip procumbency and other factors Greater than 8mm Extraction of teeth usually first premolar might be required

27. PONT’S ANALYSIS FOR ARCH WIDTH Pont in 1909, proposed a method of determining the ideal dental arch width in premolar and first molar area based on the sum total of mesio -distal widths of maxillary incisors Pont suggested that : The ratio of the combined upper incisor width to transverse arch width was ideally 0.80 in the premolar area and 0.64 in the molar area.

28. PONT’S ANALYSIS HELPS IN Determining whether the dental arch is narrow or is normal in the premolar and molar region for a given sum of widths of incisors. Determining the need for lateral arch expansion. Determining how much expansion is possible at the premolar and molar regions.

29. ANALYSIS DETERMINATION OF SUM OF INCISORS (SI) DETERMINATION OF MEASURED PREMOLAR VALUE (MPV ) DETERMINATION OF MEASURED MOLAR VALUE (MMV):

30. INFERENCE If the measured value is less than the calculated value, then the arch is narrow for the given sum of incisors width and expansion can be done. If the measured value is greater than the calculated value, the arch is wider and there is no scope for expansion.

31. CALCULATED PREMOLAR VALUE (CPV): or the expected arch width in the premolar region is determined by: CPV = SI X 100 80 CALCULATED MOLAR VALUE (CMV): or expected arch width in the molar region is determined by: CMV = SI X 100 64 Patient A: SI = 40mm CPV = 50 Measured Inter-premolar width = 42mm CMV = 62.5 Measured Intermolar width = 50mm Patient B: SI = 30mm CPV = 37.5 Measured Inter-premolar width = 40mm CMV = 46.8 Measured Intermolar width = 48mm

32. DRAWBACKS Maxillary laterals are the teeth most commonly missing from the oral cavity. Peg-shaped laterals can be seen. The analysis was done from the casts of French population It does not take skeletal mal-relationships into consideration.

33. LINDER HARTH ANALYSIS Linder Harth proposed an index very similar to that of Pont’s analysis. He made variation in the formula to determine the calculated premolar and molar values The calculated premolar value (CPV): CPV = SI X 100 85 The calculated molar value (CMV): CMV = SI X 100 64

34. BOLTON’S ANALYSIS Wayne Bolton considered the ratio of the tooth material of the maxillary arch to the mandibular arch i.e. M-D widths of upper & lower teeth by nature have predetermined proportions to maintain normal occlusal relationship. An alteration in this balance will lead to improper intercuspation , overjet or spacing

35. Measurements Sum of maxillary 12 Sum of mandibular 12 Sum of maxillary 6 Sum of mandibular 6 Overall ratio Anterior ratio

36. Overall Ratio = Sum of mandibular 12 x 100 Sum of maxillary 12 For establishing ideal overjet & overbite overall ratio should be 91.3% If the overall ratio is less than 91.3%, it indicates maxillary tooth material excess. The amount of maxillary tooth material excess is determined by using the formula The amount of mandibular t ooth excess is determined by: Determining Overall Ratio

37. The sum of M-D widths of the mandibular anteriors to the M-D width of the max. a nteriors should be 77.2% The anterior ratio is determined using the following formula: If < 77.2 , maxillary anterior excess If >77.2 , mandibular anterior excess Determination of Anterior Ratio :

38. Disadvantages of Bolton’s Analysis Does not take into account the sexual dimorphism in the maxillary canine widths. Study done on specific population.

39. BOLTONS ANALYSIS Ideal Value for Overall Ratio = 91.3% Ideal Value for Anterior Ratio = 77.2% Patient A Overall Ratio = 94% Patient B Anterior Ratio = 81% Patient C Overall Ratio = 88% Patient D Anterior Ratio = Sum of Mand 6/ Sum of Max 6 = 38/45 =

40. MIXED DENTITION ANALYSIS

41. AIM Methods of analysis of archlength during mixed dentition Those in which the sizes of unerupted cuspids and premolars are estimated from radiographic images Those in which the sizes of cuspids & premolars are derived from the knowledge of already erupted permanent tooth in the mouth.( Probability Tables ) Combination of the above two method

42. HUCKABA’S MIXED DENTITION ANALYSIS (RADIOGRAPHIC METHOD) This analysis makes use of a radiograph and study cast to determine the width of unerupted teeth. Advantages: Easy, practical & relatively accurate. Disadvantage: Chances of distortion of radiographic image.

43. PRINCIPLE It is based on the principle that if we measure an object, which can be seen both in radiograph as well as on a cast, then we can compensate for the enlargement of the radiographic image A simple proportional relationship can be established as follows:

44. SPACE AVAILABLE: the arch is divided into segments which are approximately straight lines. The dimensions in each of the segments is measured and added up. SPACE REQUIRED: for the un-erupted teeth is calculated from the radiographs. The discrepancy is calculated segment wise

45. MOYER’S MIXED DENTITION ANALYSIS It is based on the premise that there is a reasonably good correlation b/w the size of erupted permanent incisors and the unerupted canines & premolars This is because a person with large teeth in one part of the mouth will have large teeth elsewhere also, as their development is controlled by the same genetic mechanism. Here the lower permanent incisors are measured and the mesio -distal widths of unerupted permanent upper and lower canines and premolars is derived from the probability chart. The mandibular incisors are chosen for measuring as they are the first teeth to erupt in the mixed dentition period.

46. PROCEDURE SPACE REQUIRED- measure the mesio -distal dimension of all four lower incisors and sum it up. Using the Moyer’s probability chart find the total mesio -distal width of upper and lower canine and premolars from the upper and lower charts at 75% probability for the given lower incisor dimension.

47. TANAKA AND JOHNSTON ANALYSIS (1974) They developed a method to predict the width of un-erupted canine and premolar using the width of lower incisors . This methods has good accuracy despite a small bias towards over- estimating the un-erupted tooth size. They have simplified Moyer’s 75% prediction table into a formulas Predicted width of maxillary canine & premolars / quadrant= Sum Of Mandibular Incisors/2 +11 Predicted width of mandibular canine & premolars / Quadrant Sum of Mandibular Incisors + 10.5 2

48. Predicted width of maxillary canine & premolars / quadrant= Sum Of Mandibular Incisors/2 +11 Predicted width of mandibular canine & premolars / Quadrant Sum of Mandibular Incisors + 10.5 2 Patient A Sum of Mandibular Incisors = 24mm Predicted width of maxillary canine & premolars? Predicted width of maxillary canine & premolars? Patient B Sum of Mandibular Incisors = 19mm Predicted width of maxillary canine & premolars? Predicted width of maxillary canine & premolars?

49. RECENT ADVANCES IN MODEL ANALYSIS

50. Cast analysis by E Models/ 3D Digital Models

51. ADVANTAGES OF COMPUTERIZED ANALYSIS More Accurate Easy More information: Arch form Determine asymmetric Arch Space analysis Rotation Prediction

52. QUESTIONS?