Let’s examine each of these separately:
- Incisal display — intrusion of the upper anterior teeth would be in- dicated in deep-bite cases with super-eruption of the upper incisors, but would be contra-indicated in deep-bite cases with insufficient in- cisal display.
- Gingival display — similar to incisal display, upper anterior intrusion may be beneficial in patients with vertical maxillary excess (VME) to reduce gummy smiles (image 5-1, 5-2).
- Gingival margins — intrusion or extrusion of key teeth may help to improve the symmetry of gingival margins. In patients with incisal wear and super-eruption of the worn tooth, anterior intrusion would be indicated to level the gingival margins prior to restoration of the tooth (image 5-3).
- Smile arc — when working up Invisalign treatment plans, we endeavor to create pleasing smile arcs where the curvature of the upper anterior incisal edges follows the curvature of the lower lip. Anterior intrusion or extrusion is a primary consideration in these cases (images 5-1, 5-2).
- Lower Curve of Spee — lower incisor intrusion and/or posterior extrusion are key components to correcting deep over bites. Some deep-bite cases requiring bite opening via posterior extrusion. For example, in patients with:
- Short lower facial heights
- Restorative cases with loss of vertical dimension
- Hypodivergent, skeletal deep bites
- CL II div.2 malocclusion
- Extrude the anterior teeth
- Intrude the posterior teeth, or
- A combination of the two.
- Incisal display — anterior open-bite cases with insufficient incisal dis- play may benefit esthetically from anterior extrusion, whereas those patients with normal incisal display would be more likely to benefit from closure of the open bite via posterior intrusion.
- Gingival display — anterior open-bite cases with excessive gingival display would not benefit esthetically from upper anterior extrusion, whereas those with insufficient gingival display would.
- Gingival margins — leveling gingival margins may in some cases re- quire extrusion.
- Smile arc — when an anterior open bite is related to a habit, the resul- tant reverse smile arc may be remedied with anterior extrusion.
RELATIVE VS. ABSOLUTE EXTRUSION/INTRUSION
Relative vs. Absolute Extrusion/Intrusion is another subheading in the vertical section of the ClinCheck list. Let’s examine these move- ments more closely:
Relative Extrusion or Intrusion — these are predictable movements, another “Invisalign free ride,” and you don’t need any specific attach- ments or major ClinCheck plan modifications to achieve relative extru- sion or intrusion.
In cases that require relative extrusion, we achieve it by simply tipping teeth lingually. When teeth tip lingually, the incisal edges of the anterior teeth travel along an arc and the bite naturally tends to deepen, as do Gilbert’s (from Chapter 3) UR2 and UL2 (images 5-4, 5-5). Again, this is a predictable movement, and no special ClinCheck plan modifications are required in open-bite cases where we desire closure of the bite. On the other hand, in deep-bite cases that present with flaring and spacing of the anterior teeth, retraction of the anterior teeth will also lead to relative extrusion, which would worsen the deep bite. In these cases, compensa- tory incisor intrusion should be built into the ClinCheck plan to coun- teract the bite-deepening effects of relative extrusion.
The same goes for relative intrusion. In deep-bite cases where the an- terior teeth are lingually inclined, labial proclination will tip the crowns forward, resulting in the incisal edges traveling in an arc away from each other (images 5-6, 5-7). It’s important to recognize cases requiring rel- ative intrusion or extrusion, as these movements are more predictable. Similarly, in open-bite cases that require proclination of the anterior teeth — to resolve crowding for example — the proclination will result in relative intrusion, which would make the open bite worse. In these cases, compensatory absolute incisor extrusion must be built into the ClinCheck plan.
Absolute Extrusion/Intrusion — are more challenging movements with Invisalign treatment — this doesn’t mean we can’t achieve it — how- ever it is important to “read” your ClinCheck plan and recognize teeth that are absolutely extruding or intruding. The superimposition tool can be helpful to determine absolute vs. relative movements. In certain cas- es, absolute extrusion requires specific:
- Attachment substitutions
- Over treatment moves, and/or
In cases of absolute extrusion, we are physically extruding a tooth or group of teeth relative to the alveolus. This requires “grip” — a lot of grip — most commonly on central and lateral incisors that have very smooth surfaces and minimal undercuts. In some cases that require absolute ex- trusion, optimized extrusion attachments will be placed automatically by the software. The presence of optimized extrusion attachments on the anterior teeth is a tip-off that absolute extrusion is occurring.
Let’s take a closer look at the orientation of the optimized extrusion at- tachment. (image 5-8). These attachments, like all optimized attachments, are placed automatically by the software to place the specific force sys- tems on the teeth to achieve the desired tooth movement. It is important to understand that the forces will be perpendicular to the active surface of the attachment, and that the aligner surface interacting with the active surface will be pre-activated to create the proper forces. Furthermore, I strongly recommended that these attachments NOT be removed, despite the esthetic concerns of some patients. They are on the teeth for a reason — to achieve the desired movement — and if they are removed the likeli- hood of encountering a non-tracking situation increases.
There are clinical situations, most often on non-tracking maxillary lateral incisors, where I will reengineer the attachments to provide ad- ditional aligner grip to help keep the teeth extruding. In my experience, I have found that a modified 4mm-long, gingivally-beveled, rectangular attachment can be quite useful (image 5-9). I will use 3D controls to move the attachment close to the incisal edge, where the aligner plastic is stiffer. In my experience this allows for better “grip” and more pre- dictable absolute extrusion. Furthermore, I will use 3D controls to “roll” the bevel as gingivally as possible to create a bevel that blends smoothly into the labial surface of the tooth, to gain additional surface area on the attachment, and therefore more aligner “grip.”
In cases of absolute extrusion, I have had many doctors ask me, “Which way does the bevel go?” There are two options to answer this question: we can place the bevel incisally or gingivally.
Incisal — when we use this approach we can potentially get more “grip” where there will be a 90° ledge at the gingival aspect (image 5-10) that will engage the aligner. This makes sense because we’re going to get more aligner grip. However, there is a higher chance for failure mode. Failure mode occurs when the aligner loses tracking and becomes totally disengaged from the attachment. If this occurs, the aligner has the po- tential to place undesired lingual forces on the tooth, which can lead to inadvertent intrusion, just the opposite of what we want.
Gingival — if we bevel our attachments gingivally (image 5-9) we get somewhat less grip, but also we have less chance to encounter failure mode. This is my personal preference when I am looking to achieve abso- lute extrusion, and I find this attachment quite useful.
Invisalign G5 innovations were designed to specifically address the challenges of correcting deep overbites with Invisalign. G5 features include:
- Pressure areas to intrude upper and lower incisors — these pressure areas direct the forces of intrusion along the long axis of the tooth for more predictable intrusion.
- Optimized premolar anchorage attachments — provide additional posterior anchorage to support lower incisor intrusion and leveling of the lower Curve of Spee.
- Precision bite ramps on upper incisors — disocclude the posterior teeth to remove posterior bite forces that may work against deep-bite correction.
- Conventional bite ramps on upper canines — when the overjet is greater than 3mm, the lower incisors will occlude behind precision bite ramps. Conventional bite ramps on the upper canines in this sit- uation may be a better option.
When patients present with deep-bite problems, the doctor has choic- es to make toward correction. These choices include:
Anterior Intrusion — in cases requiring anterior intrusion, the G5 pressure areas are placed on any incisor requiring intrusion incisors au- tomatically. You do not have to request them.
Optimized anchorage attachments on pre-molars are also placed automatically. These attachments provide anchorage to support lower incisors intrusion. You may be asking, “Why do I need posterior anchor- age to support lower incisor intrusion?” Think Newton’s third law. For every action, there is an equal and opposite reaction. In cases requiring lower incisor intrusion, for example, the “action” force is placed by the lower aligner against the lower incisors to intrude them. The “reaction” is for the aligner to lift off the posterior teeth. Clearly, we don’t want this to occur. “Posterior lift off” will result in decreased intrusion force to the anterior teeth, and the deep bite may not correct. Optimized anchorage attachments help keep the aligners engaged on the premolars, resulting in more predictable deep-bite correction.
NOTE: A situation may arise where the optimized premolar anchor- age attachments don’t appear on your ClinCheck plan. If the software detects greater than 5° rotations on the lower premolars the patient will not get the optimized G5 anchorage attachment. Instead, an optimized rotation attachment will be placed. In my experience, the optimized rotation attachment does not provide sufficient anchorage to support intrusion of the lower anterior teeth. At this point, it would be time for substitution of attachments. Let’s take a look at the Clin Checklist.
The Attachment section of the ClinCheck list helps guide you through this decision. In cases where you deem deep overbite correction to have priority over premolar rotation, substitute 4mm-wide, occlusally- beveled rectangular attachments on the lower first and second premolars (image 5-15). These attachments provide additional “grip” to prevent the aligners from lifting off posteriorly, and are very effective at supporting the intrusion of the lower incisors.