0:00 Hello, this is Dr. Kim Jeong-il. Today, I will lecture about model analysis. What kind of malocclusion will be if the mandibular posterior teeth are mesial inclined? We easily think that it would be a Class III malocclusion. However, in some patients, as in the model, the right teeth of the mandible are mesial inclined, and the maxilla is also mesial inclined, and Class I malocclusion may be seen. Alternatively, in some patients, the right teeth of the mandible are mesial inclined, but the posterior movement of the mandible may result in Class II malocclusion.
0:53 In MEAW orthodontic, the mesial inclination of the posterior teeth, especially the mandibular posterior teeth, is closely related to the posterior occlusal plane. This can also be evaluated in model analysis. In general, when it comes to model analysis, many people evaluated crowding only. However, there are many things that can be evaluated in model analysis. What should we observe when we look at the Model? You may also have questions like: First, what can we get from model analysis? Second, how can we make a model so that we can analyze it accurately?
1:44 I have already lectured on model fabrication. Model analysis will include the following: It includes anteroposterior relationship, vertical relationship, left and right transverse relationship, tooth size, space analysis, Bolton analysis, and whether the tooth position is in a normal position. Based on these points, I evaluate six points: The first is Aesthetics, the second is the function, the third is the tooth size discrepancy, , the fourth is how to gain the space if you treat it with non-extraction treatment,
2:34 the fifth is which tooth extract if you treat it with extraction treatment, and the sixth is how to evaluate a midline deviation in a model analysis. Today, as part 1, I will mainly lecture on the first and second points. Many patients who want orthodontic treatment come to the hospital for aesthetics. Aesthetics can first be called a teeth arrangement. It should be first observe if there is a crowding or space in the anterior and posterior part etc. For proper arrangement, the lingual side of the mandible should be a smooth arc. And, you should observe whether the palatal side of the maxilla is also a smooth arc.
3:24 The first item to be evaluated is crowding. crowding is evaluated in two main ways. The first is Arch Length Discrepancy, the second is Irregularity Index. Arch length discrepancy is to observe the relationship between the patient's skeletal pattern and the teeth within the alveolar bone. In this way, Arch length is the space in which the teeth will be arranged. The distance from the contact point of one first molar to the contact point of the opposite first molar is called Arch length.
4:13 In other words, it is a line connecting from the contact point of one first molar to the contact point of the opposite first molar, through the buccal cusp of the premolar and the incisor edge of the anterior tooth. In the picture, the red line is the Arch length. First, the length of each tooth from the central incisor to the second premolar is marked and the value is added. Arch length discrepancy is the arch length minus the sum length of these teeth. If there is spacing, it is marked with +, and if there is a crowding it is marked with -.
5:02 This patient has crowded in the maxillary anterior teeth. Therefore, it is indicated that the maxillary anterior teeth have -14 mm crowding, and the mandibular anterior teeth have -8 mm crowding. This patient has space in the maxillary anterior teeth. However, the mandible has no space and no crowding. Therefore, arch length discrepancy is indicated by +5 mm for the maxilla and 0 mm for the mandible. Through this arch length discrepancy, we can know the degree of irregularity and even predict the extraction possibility. For example, if the crowding is less than 3 mm is not a severe case,
5:50 if the profile is not bad then it is much more desirable to reproximate (strip) the proximal tooth contact rather than the extraction. However, if the crowding is more then 8mm, it would be better to extract the first premolar. If it the crowding is 3~8 mm, it would be better to extract the second premolar. This is not an absolute indicator. It is only a guideline, please refer to it. Let's look at the disadvantages of arch length discrepancy. If it protrudes like this, the crowding is almost invisible. This patient Arch length discrepancy is -2 mm in the maxillary incisor and -2 mm in the mandibular incisor. Crowding is not severe, but it shows a severe protrusion.
6:43 This means that looking at arch length discrepancy alone, it is not easy to apply to treatment. Next, there will be a difference in the arch length measured by the red solid line and the red dotted line as in the photo. Depending on how you measure the arch length, different measurement values will appear. So I recommend selectively measuring only the crowding part like this. This patient has a crowding in the lateral incisor and canine area. You can calculate easily and conveniently,
7:32 when if you subtracting the measurement value of the length of teeth from the value of the measuring the available space of lateral incisor and canine area. Likewise, in the mandible, there is a crowding in the lateral incisor and the second premolar areas on the left. You can calculate the required length by measuring the available space of the crowding parts, measuring the length of the tooth, and subtracting the value. The next measurment value for evaluating anterior tooth crowding is the Irregularity Index (II). The Irregularity Index is specifically used to measure crowding of the mandibular anterior teeth. This is to measure the distance between contact points in the crowding areas.
8:20 If there is no crowding, the contact points on adjacent surfaces must match. This is the model just before. If there is crowding like this, the distance between all contact points is measured and added. The Irregularity Index is primarily used to assess crowding in front of the canine. The crowding of the lower anterior teeth is often rotated, or displaced lingually or labially.
9:05 At this time, you can measure the horizontal linear displacement distance, which calculates the amounts of displaced teeth in 5 areas of the 6 incisors of the mandible. However, this Irregularity Index does not include vertical discrepancy. Therefore, if the dentition between canines is perfectly arranged, the score is displayed as 0. The more severe the crowding looks, the bigger the score value will be. So, does the treatment become difficult because the score value increases?
9:52 Irregularity Index has the following problems. A large score means that one tooth or several teeth are rotated heavily. However, having this rotation does not mean that the treatment is difficult. This is because these indexes do not take into account other characteristics of malocclusion before evaluating the patient's score. However, the implications of the Irregularity Index are important.
10:39 If there is crowding of the anterior teeth, especially if the Irregularity Index is broken like this, you should be more careful when doing bracket positioning. Also, when removing the bracket, the irregularity index of the anterior teeth must be a smooth arc with 0. after than the bonding retainer will be possible. Clear aligner is used a lot recently. The main tooth movement direction of this clear aligner will also be the direction to improve the Irregularity Index.
11:24 How to measure this patient's irregularity index? It can be obtained by measuring the distance between the contact point between the first premolar in the maxillary canine, , the lateral incisor in the canine, and the central incisor and lateral incisor. We've been looking at aesthetics so far. As the second item, let's look at the function. The basis for function is to obtain canine guidance occlusion. What items are important when obtain canine guidance occlusion.? There are several items such as Class I canine relationship, Class I molar relationship, Overjet, Overbite, etc.
12:11 First is the evaluation of the relationship between the posterior teeth. The posterior relationship is evaluated by measuring the distance from the mesio-buccal cusp of the maxillary first molar on the left and right to the buccal groove of the mandibular first molar. At this point, you need to evaluate both sides. If the mesio-buccal cusp of the maxillary first molar is located in the buccal groove of the mandible, it is called a Class I molar relationship. If the mesio-buccal cusp of the maxillary first molar is located in front of the buccal groove of the mandible, it is called Full Class II. This middle is Half Class Ⅱ. This is also called End-to-end Class II, or Cusp-to-cusp Class II in other terms.
13:08 If the buccal groove of the mandible is located one tooth forward than the mesio-buccal cusp of the maxillary first molar, it is called Full Class III, and if it is located halfway forward, it is called Half Class III. Half Class Ⅲ is also called End-to-end Class Ⅲ or Cusp-to-cusp Class Ⅲ in other terms. In model analysis, it is necessary to discriminate whether the posterior relationship is Class I, Half Class II or Full Class II. This is indicated by + value for Class II malocclusion. On the other hand, Class Ⅲ malocclusion is marked as - value. This model shows a class I molar relationship. It will be 0 mm.
13:57 For other models, record the occlusal relationship of +3 mm for Half Class Ⅱ, +6 mm for Full Class Ⅱ, -3 mm for Half Class Ⅲ, and -6 mm for Full Class Ⅲ. Look at this patient, it is a Class I molar relationship. There are some large overjet. How is the canine relationship? It is not in Class I canine relationship. In Class Ⅰ canine relationship, the maxillary canine must be located between the canine and the first premolar of the mandible. This malocclusion is called Half Class Ⅱ canine relationship.
14:44 Half Class Ⅱ canine relationship is not well-matched with the premolar area, and the occlusal contact is also not good. When performing model analysis, what if both patients show a Class I molar relationship, but one patient has a Class I canine relationship and the other patient has a half Class II canine relationship? At this time, the patients that should be observed as important are those with Half Class II canine relationship, not posterior relationship.
15:32 Let's look at another model. One is Full Class II canine relationship and the other is Half Class II canine relationship. The normal canine relationship is the maxillary canine must be located between the canine, and the first premolar of the mandible. If the maxillary canine is located in front of the mandibulr canine, it is a Full Class II canine relationship. If the maxillary canine is located just above the canine of the mandible, it is a Half Class II canine relationship. The same goes for Full Class Ⅲ and Half Class Ⅲ. If the maxillary canine is located posterior to the maxillary first premolar cusp tip, it is Full Class Ⅲ.
16:23 If the maxillary canine is located slightly anterior to the maxillary first premolar cusp tip, it is Half Class Ⅲ. Model analysis for orthdontic treatment evaluates not only aesthetics but also function. In the mandible, the line connecting the incisor edge and buccal cusp tip, and the cusp tip of the posterior tooth is called Active Centric Line. The part of the maxilla that occludes here is called the Passive Centric Line. The goal of orthodontic treatment is to match the Passive Centric Line of the maxilla and the Active Centric Line of the mandible.
17:13 So, how should the two lines match? First, evaluate the active centric line of the mandible. The active centric line of the mandible is a line connecting the contact point of the second premolar and the first molar of the mandible, and the incisor edge, and the cusp tip of the first premolar and canine teeth, and it can be drawn as a single circle. The part where the contact point of the mandible second premolar and the first molar correspond is the center of the cusps of the maxillary second premolar. It is recommended that these two points closely match. Passive centric lines can be connected to the maxilla in this way.
18:00 Connect the second premolar to the first molar contact point in the mandible, and draw an Active Centric Line connecting the incisor edge and the premolar cusp tip. Based on this, you can draw a circle. At this time, there may be a way to make a circle with which tooth is extracted to become a small circle, or by moving the mandibular incisors outward to form a normal circle shape. Let's try to respond to the maxilla. In order for the active centric line of the mandible to become a large circle, it will be necessary to expand the maxilla when responding to the maxilla.
18:52 In other words, the passive centric line of the maxilla must be slightly expanded so that the patient can obtain a desirable occlusion. This is after treatment photo. You can see that the active centric line of the mandible and the passive centric line of the maxilla are matched, and the teeth are well aligned.
19:39 From the passive centric line of the maxilla to the aesthetic line of the anterior teeth are called the guiding area. If these parts are properly positioned, the mandible will also be able to achieve proper tooth movement without interference. Therefore, orthodontic treatment must consider these functional parts in order to obtain a desirable occlusion of the maxilla and mandible, and this can be analyzed through the model. Thank you for watching.
