CLINICAL FEATURE
usually resolves off tracking and the teeth would begin to track after two weeks. If teeth are tracking at that stage, move onto the next aligner. Moderate off-tracking: Off-tracking > or equal to 1mm of space between the aligner and occlusal/incisal surface of tooth/ teeth is considered moderate. Back track 2-3 aligners with a five-day reversal protocol. A chewie can be used for 5mins three times daily changing each aligner every five days. If there is no improvement, the patient should be sent for refinement. If improvement noted, the patient moves forward to the next aligners on a 10-day change. POSTERIOR OPEN BITE AT END OF TREATMENT By far, this is one of the most common finishing problems. There are four main reasons for a posterior open bite (POB) at the end of treatment. The first step is to determine the aetiology for the open bite. Determine reason First, the POB may arise from premature contact at the incisor region due to poor intrusion of the incisors during aligner treatment. To minimise this, it would be useful to instruct the technicians to finish treatment with heavy interocclusal contacts on posterior teeth and light or no contact during the treatment simulation stage (except for cases of anterior open bite).
Second, POB could arise from insufficient palatal root torque on upper incisors. To minimise this possibility of under-expressed palatal root torque during incisor retraction, it would be prudent to finish with an additional 5-10° palatal root torque for cases where incisors are retracted due to extraction of premolars, IPR or generalised multiple diastema. Last, POB might arise from lateral expansion beyond 2mm per side. Expansion > 2mm may lead to buccal crown tipping resulting in the palatal cusp extrusion leading to a premature interference with lower teeth and hence POB. To avoid this, limit expansion to < or equal to 2mm buccal expansion on posterior teeth. This limitation also prevents potential gingival recession especially in cases of thin biotype or pre-existing gingival recession. Determine severity and treatment After determining the reason for the POB, the severity of the open bite needs to be determined for the appropriate treatment. First, if the severity is < or equal to 1mm, the most common treatment is to section the aligners at the posterior teeth starting from the terminal molar, moving forwards towards premolars if necessary for non-extraction cases.
per day (night time wear only) and review after one month. If during the one-month review, the premolars are also in a mild open bite (<1mm POB), section off the aligners at the premolars as well.
For anterior teeth exhibiting poor tracking, refinements are likely to be needed.
If the severity is more than 1mm, where the anterior teeth are aligned with good overjet and overbite: a) Section off the posterior molar portion of the last aligners, bond a button from upper posterior tooth to the corresponding lower posterior tooth, and use vertical elastics (3/16” 3.5oz full time) to extrude the teeth into occlusion (Fig. 1). In cases of premolar extractions, it is best to keep the last aligner on full time (but make button cut-outs to accommodate the button) and to use vertical elastics on a full-time basis (20-22hrs per day) to extrude the molars in open bite. b) Where molars/premolars appear tipped more than 20°, which is sometimes seen in extraction space closure, but with anterior teeth tracking well and overjet and overbite in desired result, refinement aligners may find it hard to upright teeth and tip the roots into optimal positions. More often than not, patients are better off with a sectional fixed brace from canine to molar.
Next, wear the last set of sectioned aligners of the molar areas as a retainer for 10-12 hrs
Buttons and up-down elastics (Only occlusal OTM needed)
POB at end of treatment
POB > 1mm
Sectional fixed braces (if teeth are tipped)
Poor Alignment
Good Alignment
Only Occlusal movements needed. Section aligners on posterior teeth and wear last aligners for 10-12hrs for one month
POB < 1mm
Refinements
Equilibrate incisor premature contact
POB resolved
Retainer and offboarding of patient
Dr Lew’s workflow for troubleshooting POB at the end of treatment
36 DENTAL ASIA SEPTEMBER / OCTOBER 2024
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