The Invisalign System Flashcards
How are impressions from Invisalign digitized?
CT (computed tomography) scanning is used, avoiding the need for impressions to be poured
For Invisalign, is it better to scan directly in the patients mouth or to take an impression? Why?
The benefit of scanning the teeth directly in the patients mouth is the loss of slack between teh impression material and teeth.
It yields better accuracy
The manufactured thermoplastic has a better fit
Shortening of turnaround time
Information of the arches is sent without risk of distortions during shipping
What are the downsides of scanning patient’s teeth rather than taking a PVS impression?
It could take longer (assuming there are no retakes of the PVS impressions.
Scanning is done in 20 minutes on average
Pts mouth gets dried out when scanning
(Another benefit of scanning is the lack of mess created.
Why is it essential that the gingival margins of teeth are clearly obtained in the scan?
Trimming of the thermaformed plastic is done by robots and is guided by the level of the gingival margins
What are the steps after the scan has been sent to Invisalign?
1) segmentation (virtual cutting of the teeth)
2) final setup (the desired end result of orthodontic treatment)
3) staging (how to incrementally get to the final result)
4) design and placement of attachments guided by the software that analyzes the forces transmitted to the virtual tooth roots
5) review (inspection of clincheck by the clinician
6) fabrication (production of SLA models and thermoforming the plastic to fabricate the Invisalign aligner)
Practically, our current understanding of orthodontic biomechanics is limited to the first ___ of tooth movement. What affect the force systems which makes force analysis in orthodontics so difficult?
Millisecond
Movements of adjacent teeth
Nature of periodontal response to force
Precision of bracket placement
Wires
Attachments
Plastic
The way the patient handles the hardware
What conditions in the gingiva and bone affect tooth movement?
Thick or thin character of collagenous structure of gingival tissue affects tooth movement
Bone too is compliant, except in cases such as idiopathic osteoscerotis, obstruction from overgrown, cystic formations, lining of the maxillary sinus
True or false… teeth move faster when gingival tissues are inflamed and when the patient is pregnant.
True
Teeth move faster when the patient is pregnant due to the presence of the hormone relaxin in circulation. It relaxes collagenous tissues such as the PDL and sutures of adjoining bones
Thermoplastic materials are viscoelastic; thus their properties are __-dependent.
Time
Forces generated by the aligner decrease with time. This process is accelerated in a moist and warm environment
Does thicker aligner material yield better tooth movement?
Increasing the aligner material thickness does increase the stiffness. However, clinical trials provide no indication that a thicker aligner is better in finishing a case. Also, the increased thickness does not affect the quality of tooth movement during the active treatment phase.
What are some factors that precipitate tipping when using aligners?
Roots are in maxillary sinus (the lining of the sinus doesn’t remodel readily)
Depth of over bite
Crown-root ratio
Gingival resistance
Sclerotic bone
Occlusal contacts
Crown morphology
Indifference of the orthodontist to carefully study the ClinCheck images
True or false… complex attachement designs for teeth adjacent to extraction sites help reduce tipping, but, at present, sectional fixed appliances are necessary almost every time.
True
What are some issues with closing premolar extraction cases with aligners?
After the extraction space is closed, marginal ridges are not level
first and second molar marginal ridges rarely align properly
In premolar extraction cases, tipping of the ___ is most problematic and should not be allowed. To prevent tipping, the orthodontist may employ ___ attachments placed as ___ as possible.
Molars
Long and prominent molar
Mesially
____ between the plastic and tooth surfaces is the reason for the improved control of tooth movement, better tracking, and better finishing.
Intimacy of forces
For some movements, namely ___ and ___, attachments are required
Extrusion
Rotation
(Some movements need one attachment and some require two. There are some movements that require only a change in the shape of the aligner itself and no attachment)
What are the drawbacks to aligner treatment?
1) by far, the weakest link is patient compliance
2) extrusion of teeth, especially the maxillary lateral incisor
3) inability to move the root apex, however, the addition of power ridges, optimized attachments, and Smart Track made torquing and translational movements possible)
True or false… there are no reported studies of noticeable root resorption in patients treated with the Invisalign system
True.
This is probably due to less than 0.25mm of tooth movement per tray with mild forces. This distance does not obstruct the PDL blood flow, thus avoiding formation of necrotic regions
True or false… the amount of IPR performed with Invisalign should be about the same as with fixed appliances
True
Exceptions aside, IPR should be limited to instances of Bolton’s discrepancy. Need to simulate physiological tooth attrition. Need to camouflage a skeletal deformity without surgery. Necessity to alter the tooth morphology
True or false… IPR has shown to adversely affect dental and periodontal health
False
Initial concerns of root proximity, caries risk, and the like have not shown to be valid. Nonetheless a good depth of enamel must be present so that some of it could be removed.
True or false… it is best to perform IPR before the intraoral scan.
False… it is best to perform IPR during the course of treatment, rather than before the scan/impression.
In order to correct an anterior open-bite, the properly designed clincheck should exhibit a posterior openbite with about __-___mm of freeway space. Why?
This will not tangibly happen in the clinic, because the mandible will rotate forward and take up the room. Whereas clincheck images are static, the mouth is dynamic
The dynamic mindset of the orthodontist should envision that aligners might 1) block forces of the tongue on the lingual cingula of upper incisors, and 2) in the posterior segments, coverage of occlusal surfaces by the plastic trays aid in teh intrusion of posterior teeth
what is the protocol that has been proven successful to extrude a tooth?
An optimized horizontal rectangular attachment with a gingival bevel (for anterior teeth)
If the clinician desires extrusion of posterior teeth, one must specifically ask for horizontal rectangular beveled attachments where the beveled surface faces the gingiva
What are some special instructions that should be made to relate the Clincheck treatment plan for deep overbites with CAT?
Level curve of spee by extruding lower bicuspids for a total of 3mm and intruding the lower cuspid to cuspid a total of 4mm
Attachments on lower bicuspids: horizontal rectangular beveled gingival: 4mm wide, 1.5mm high, 1.25mm thick at the occlusal margin tapering to a thickness of 0.25mm at the gingival margin. Place as far occlusally without any interferences from the opposing arch
What is the advantage of Invisalign over fixed appliances in the case of deepbites?
They can star correcting the overbite on both arches from the very beginning. Most typically with fixed appliances, upper anteriors would have to be flared out or intruded to create adequate clearance to place the lower brackets.
What is the advantage of CAT over fixed appliances when treating cross bites?
The plastic covers the occlusal surfaces, so acting as a built-in bite raiser to disarticulate the occlusion during crossbite correction.
