Correction of Functional Shift in Mixed Dentition

The early detection of a functional shift and identifying any premature contacts is essential in the mixed dentition. If left uncorrected, the functional shift may develop into a severe skeletal discrepancy. Using a routine method such as the “Dawson bimanual technique” (Dawson 1995), will manipulate the patient into a relaxed centric jaw position, will locate the premature contact, and will identify the functional shift. The most commonly seen functional shift is a unilateral crossbite, either anteriorly, posteriorly, or both (Figure 12.5.1a).

An 11‐year‐old child in her late mixed dentition presented with concerns of a median diastema, a unilateral posterior crossbite, and an underbite. She had a Class III dental malocclusion on a mild skeletal 3 pattern with a normal direction of growth with no family history of large lower jaws. The child had a normal midface but a prognathic mandible. The upper and lower permanent incisors and the first molars were present and fully erupted. The deciduous canines were slightly mobile while the molars were firm. There was a unilateral crossbite on the right, the upper and lower dental midlines were non‐coincidental with the lower midline and chin point both deviated to the right side (Figure 12.5.1b). There was a functional shift detected with premature contact on tooth #21, which subsequently led the mandible to shift anteriorly, as well as laterally to the right. The panoramic radiograph demonstrated routine findings with a full complement of teeth, with the premolars, permanent second and third molars developing (Figure 12.5.1c).

Stage I interceptive orthodontic treatment was indicated to commence immediately. The primary treatment objectives were to eliminate the functional shift, correct the posterior crossbite, close the upper median diastema, co‐ordinate the arches to realign the dental midlines and mandible, correct the underbite, and to normalize her subsequent facial growth and development. The plan also included the redistribution of spaces along the dental arches to allow the uneventful eruption of the other remaining permanent dentition.

She was treated with clear aligners. The Invisalign First™ product allowed optimized attachment designs and velocity of dental movement for both deciduous and permanent dentition. With shorter clinical crown heights, it is essential to plan sufficient attachments to maintain good retention of the aligners in these mixed dentition cases. We requested for an “elastic simulation” in the ClinCheck plans and executed that clinically with Class II elastics on the right side and Class III elastic on the left side (Figure 12.5.1d). The aligners were worn full‐time with the exception of brushing, flossing, and eating and had a weekly change regime.

After 27 out of 29 active aligners and approximately 7 months of treatment, the posterior crossbite on the right side was corrected, the dental midlines were co‐ordinated, overjet, overbite was normalized, and the median diastema was closed (Figure 12.5.1e). New intra‐oral scans were done and additional aligners were ordered for final detailing to improve the occlusal contacts. The additional aligners were also changed weekly. The stage I treatment was completed in 12 months (Figure 12.5.1f, g). All primary objectives of the interceptive treatment were achieved. The functional shift was eliminated, median diastema closed, unilateral posterior crossbite, overjet, and overbite corrected. Most importantly, her facial balance and asymmetry, and the prognathic mandibular posture were normalized (Figure 12.5.1h). Upper and lower fixed retainers were placed on the incisors and an upper Hawley retainer was prescribed to be worn during her sleep hours.

Subsequent plans were to continue to monitor the child’s growth and development periodically 3–6 monthly, until she is in her full permanent dentition. Phase two treatment may then be indicated and planned if necessary.

Congenitally Missing Tooth in Teen Treatment

Congenitally missing tooth/teeth commonly contributes to the formation of an asymmetrical malocclusion (Fekonja 2017). Depending on the severity of the discrepancy, and which tooth/teeth are missing; it may affect the patient’s smile and facial symmetry remarkably. Cases may range from just a single missing tooth to multiple missing teeth associated with certain syndromes.

A 12 years 7 months old female in her permanent dentition presented with a congenitally missing upper right lateral incisor (tooth #12). It contributed to a Class II subdivision left‐sided dental malocclusion. There were upper dental spaces, the upper dental midline was deviated to the right side with a half‐unit Class II dental relationship on the right side, and a good Class I interdigitation on the left (Figure 12.5.2a, b).

The two obvious treatment options discussed with the child and the parents were to either (i) open and reestablish the #12 space for a future prosthetic tooth. Or alternatively, (ii) to close the space and substitute the #13 for the #12. This option would not require any future prosthetic replacements. The pros and cons of these options should be discussed intimately.

With option (i), the mechanics and treatment duration for the orthodontics could be simpler and shorter, respectively. Dentally, the end result could potentially be more symmetrical and aesthetically pleasing. However, we have to wait for the child to complete her vertical dentoalveolar growth before the placement of a prosthetic tooth such as an implant. That age is usually about 18 years old (Oesterle et al. 1993). The space has to be maintained with an aesthetic temporary solution in the meantime. This could be in the form of resin‐bonded bridge or a denture. There would also be the chance of vertical and/or bucco‐lingual bone loss during this time (Dietschi and Schartz 1997). Further bone augmentation might then be required before the dental implant is inserted. Such potential complications and surgical procedures need to be made known to the patient as part of informed consent prior to the commencement of the orthodontic treatment.

Option (ii) may offer a less esthetically balanced end result. The shape, color, and size of the #13 substituting as the #12 may require a certain degree of cosmetic enhancement and camouflage. The orthodontic treatment duration and mechanic designs might be longer and more complex. The final occlusion will be a therapeutic Class II relationship on the right while maintaining the Class I relationship on the left. However, this option would negate the need for any future surgery and dental prostheses. In this particular case, after much deliberation and considering all factors, treatment option (ii) was chosen.

The ClinCheck plan was set up with a simultaneous staging pattern, optimized, and conventional attachments were designed (Figure 12.5.2c). This plan was supported with concurrent wear of Class II and Class III elastics on the right and left sides, respectively. The patient was instructed to wear her aligners full time with a 2‐weekly change regime. She was reviewed at every 8–10 weeks intervals. During these review appointments, ensure to not only check on the compliance of the patient’s aligner wear, but also to remove the aligners, get the patient to bite down to check on the dental midlines and the sagittal correction done so far. The clinician needs to adjust the strength and consistency of elastic wear in order to achieve the desired outcome. Progressive records showed the gradual correction of the dental midlines (Figure 12.5.2d). The anchorage design was mainly the judicious adjustment of strength and length of wear of the dental elastics.

With conventional fixed appliance therapy, prolonged use of asymmetrical elastics may contribute to the canting of the occlusal plane and/or opening of the vertical occlusal dimensions. The benefit of the clear aligner system is that the aligners cover the occlusal surfaces of the dentition throughout treatment. This allows a biased distribution of force, diverting the forces from the elastics to a more horizontal vector, and suppressing the vertical component. This phenomenon makes the clear aligner system the appliance of choice when such mechanics need to be applied.

Due to the therapeutic Class II completion on the right side, the molar relationship on the right side was completed to a full unit Class II (Figure 12.5.2e, f) (Nangia and Darendeliler 2001). The active treatment completed in 18 months. Upper and lower fixed retainers, and upper and lower vacuum‐formed retainers were prescribed to maintain the orthodontic correction. The upper and lower dental midlines were aligned to restore some degree of dental symmetry. The #13 was judiciously adjusted to mimic the appearance of a lateral incisor (Figure 12.5.2g). There would be an option for the patient to have some dental whitening to further lighten the color of #13 in the future, if she chooses.

Dental Correction in Adult Treatment

Many dental asymmetries in adults are caused by either congenitally missing teeth or teeth that were previously extracted. The reasons for extraction usually include severe dental crowding, irreversible dental decay, or periodontal problems (Cahen et al. 1985; Morita et al. 1994; Richards et al. 2005). The loss of such teeth may lead to the asymmetrical collapse of the dental arch toward the extraction site. Non‐coincident dental midlines, asymmetrical archforms, uneven occlusal contacts, and dental crossbites are the usual consequences. These may further contribute to irregular facial muscular changes and other jaw joint‐related problems if left untreated (Pirttiniemi et al. 1990; Thilander 1986).

Class II Correction

An adult female patient presented with concerns of a deep dental overbite and she would like to improve her smile (Figure 12.5.3a). She had teeth #14 and #44 previously extracted due to crowding when she was young and her dentition had slowly drifted over the years. She presented as a Class II division 2 dental malocclusion on a mild skeletal 2 base. The OPG radiograph showed a normal healthy periodontium with all the wisdom teeth previously removed (Figure 12.5.3b). There was a deep dental overbite with evidence of increased wear and attrition on the anterior teeth. The upper dental midline was deviated to right with the Class II dental relationship was more severe on the left.

Upper molar distalization using clear aligners is a common and effective mechanism in correcting Class II dental malocclusions. Corrections of up to a half‐unit dental relationship are usually predictable. Sequential staging pattern is the default staging pattern in upper molar distalization in the correction of a Class II dental relationship using Invisalign® clear aligners. The terminal molars are first moved followed by the premolars, canines, and the anterior teeth, sequentially. This staging pattern could be time consuming, while the posterior teeth are being distalized, the anterior crowding is usually not corrected until the later stages of treatment. This may contradict our patients’ chief concerns, which usually is the anterior crowding. To overcome this roadblock, clinicians may request for an “aesthetic start” while planning the ClinCheck treatment. This allows the commencement of simple alignment of the anterior teeth while the terminal molars and premolars are distalizing (Chan and Darendeliler 2021).

When a sequential staging pattern is engaged (Figure 12.5.3c), the aligners have a “stopped arch” effect and this cross intra‐arch anchorage, supported clinically with inter‐arch Class II elastics contributes to the efficiency of this mechanism (Figure 12.5.3d). It is important to ensure minimal resistance to the upper molar distalization by removing any upper wisdom teeth. Start the clinical use of Class II elastics early in the treatment. First, commence with a lighter force and as treatment progresses and as the distance between the points of engagement of the elastics decreases, change to an elastic of a smaller diameter to maintain the strength of the traction. Understanding the variation of the biology of tooth movement is essential. Commence with 2‐weekly aligner change and if patient compliance is good and the teeth are tracking well, the clinician may indicate a gradually switch to a 10‐day or a 7‐day aligner change regime. At each 8–10 weekly appointment, the clinician needs to check the aligner fit, remove the aligners, and check the occlusion in maximum intercuspation. Monitor the progress of the molar distalization and the direction of the midline correction (Figure 12.5.3e). Increase or decrease the strength and intensity of the elastics where necessary.

With an uneven number of premolars on the left and right side of the arches, it is still possible to complete the case with a balanced occlusion and a good dental interdigitation. The key reference is an ideal overjet, overbite, coincident midlines (dentally as well as facially), and a socked‐in Class I canine relationship (Figure 12.5.3f). Once these are achieved, the buccal segments will usually fall into a good interdigitated occlusion.

Class III Correction

Molar distalization in correcting Class III dental malocclusion can be less compelling. The mandibular alveolar bone has a higher density and offers a greater resistance to this mechanism of correction. Movements can be less predictable (Chugh et al. 2013; Roberts 2005). However, with the right candidate, good biological response and good compliance from the patient, it can still be well managed.

A male adult patient had the upper right second premolar (tooth #15) previously extracted when he was younger. He presented with an asymmetrical occlusion; the upper dental midline was deviated to right, and the lower dental midline off to the left. There was an anterior crossbite at the lower right canine region with Class III canine relationship on the right side. There were mild and moderate degrees of upper and lower dental crowding, respectively (Figure 12.5.4a). The OPG radiograph showed a full complement of teeth, including lower impacted #38 and #48, and overly erupted #18 and #28 (Figure 12.5.4b). The treatment plan required the removal of all wisdom teeth. Using Invisalign® clear aligners, the ClinCheck plans involved mechanics with lower right and upper left molar distalization, asymmetrical use of Class II and Class III elastics (left and right sides respectively), and asymmetrical reduction (IPR) to achieve the desired results (Figure 12.5.4c).

The monitoring of treatment progress involved regular reviews every 8–10 weeks, with close monitoring of dental midlines, canine, and molar relationships (Figure 12.5.4d). The strength of the elastics was adjusted accordingly to the biological response of the patient, and the amount of dental movement achieved. Aligners were worn full‐time with a 2‐weekly change regime. Additional aligners worn at the later stage of treatment were changed weekly. The final occlusion achieved showed a therapeutic Class II molar and Class I canine relationship on the right side, Class I molar and canine relationships on the left side, coincident dental and facial midlines, and an ideal overjet and overbite (Figure 12.5.4e, f). The total treatment duration was 16 months. Overall and regional superimpositions of this case showed a successful 2–3 mm of molar distalization achieved for the lower right quadrant (Figure 12.5.4g). It is important to note that the absence of any wisdom teeth in such cases reduces the resistance of dental movement, allowing a more efficient molar distalization.