17
Arch Length Discrepancies
Arch length discrepancies result in crowding or spacing of the teeth. As most cases of dental crowding show a higher prevalence for the anterior region, clinicians need to have efficient methods of relieving dental crowding, such as arch expansion, proclination of the anterior teeth, sequential distalization, tooth extraction or interproximal enamel reduction. The method used will be determined by the amount of crowding, facial profile, and patients’ age.
This chapter will cover crowding management by interproximal reduction (IPR), mainly on the anterior segment. This is a safe clinical procedure involving the reduction, anatomical recontouring and protection of interproximal enamel surfaces of permanent teeth. For patients with mild or moderate crowding (4–8 mm): this is a really good alternative to dental extraction.
Fig. 17.1 Interproximal reduction has to be performed carefully in order to avoid tooth intrusion caused by insufficient space inside the aligner.
Apart from crowding there are some other indications for IPR on adults, such as Bolton Index discrepancy, changes in tooth shape and dental aesthetics (e.g. macrodontia), normalization of gingival contour and elimination of black gingival triangles.
Fig. 17.2 Interproximal reduction might improve the shape and size of teeth, reducing unaesthetic black triangles.
There is also another clinical point to this as, after creating proper interdental contacts, the risk of loss of alveolar bone or root cement is decreased.
Fig. 17.3 Interproximal reduction in cases of crowding might improve contact points thereby reducing alveolar bone or root cement, so it has clear indications for periodontal patients.
Tooth spacing, which might be related to tooth shape or size, also needs to be considered. In some cases we might perform IPR on the opposite arch to compensate the Bolton discrepancy or go for restorative treatment alternatives such as ceramic or composite veneers to re‐establish the ideal size of teeth.
Spacing can also be related any clinical conditions other than tooth size, which will need a specific clinical approach to obtain the best clinical and aesthetic results with the aligners technique.
Fig. 17.4 Spacing cases are usually related to abnormal tooth size, which leads to a need for aesthetic planning, which will be covered in chapter 25.
Key to this, as we will see in the clinical cases review, is adding extra palatal root torque (PRT) to teeth in which we are closing space, so crown retraction is accompanied by a root movement, creating an ‘en masse’ retrusion to close the space.
Fig. 17.5 Palatal root torque is seen on the ClinCheck Pro as blue areas on the superimposition areas in which the roots were previously placed.
17.1 Spacing
17.1.1 Spacing, Case 1
Fig. 17.6 Skeletal class I with spacing.
Diagnosis
A 45‐year‐old, symmetric, normodivergent patient presented with dental class I with missing 14/25/37 and 46 and an implant in 44. The patient had upper and lower diastemas, which were bigger in the upper arch, with abrasion on the incisal edges of upper incisors. A Bolton discrepancy with microdontia of lateral upper incisors was also found. First right upper molar was slightly extruded because of a missing missing 46.
Treatment Plan
- Distribute the upper and lower spaces to place implants for the missing teeth
- Centre both midlines
- Intrusion of the 16, which was slightly extruded, leaving final spaces of 0.5 mm distal to lateral incisors for their posterior reconstruction
Requirements for the Technician
- In order to correct upper diastemas, increase the overjet (requested on special instructions in the prescription form)
- IPR in the lower arch and leave upper diastemas distal to lateral upper incisors for the posterior composite veneers on lateral incisors to correct Bolton discrepancy
- In the upper arch a strong posterior anchorage is needed to create a movement of retrusion, intrusion and lingual root torque of upper incisors
- Third molars not to be moved in order to have posterior anchorage to retrude upper and lower incisors
Treatment Summary
- Treatment was completed in 20 months
- The patient wore a first set of 34 aligners with 10‐day change intervals and one set of additional aligners. Upper and lower diastemas were successfully closed
- Class I occlusion was maintained
- 16 was intruded and levelled with the occlusal plane
- The patient did not use intermaxillary elastics during treatment.
- A panoramic radiograph at the end of treatment shows root parallelism and the implants placed for the missing teeth
- The patient is still waiting to have the crown for 14 and the implant for 46 placed as well as the distal reconstruction in 12 and 22
Fig. 17.7 Pretreatment views.
Fig. 17.8 Pretreatment panoramic X‐ ray, teleradiograph and cephalometry.
Fig. 17.9 Upper CC superimposition and instructions to CAD designer.
Fig. 17.10 Lower CC superimposition and instructions to CAD designer.
Fig. 17.11 Front CC view.
Fig. 17.12 Front intraoral picture.
Communication with the Technician
Fig. 17.13 Right ClinCheck view, initial situation.
Fig. 17.14 Left ClinCheck view, initial situation.
Fig. 17.15 Post‐treatment views.
Fig. 17.16 Pretreatment and final smile.
Fig. 17.17 Post‐treatment panoramic and lateral X‐rays.
17.1.2 Spacing with Frenulectomy
Fig. 17.18 Skeletal class I with spacing.
Diagnosis
A 20‐year‐old, symmetric patient who presented with a dental class I and a gummy smile. The patient had a large upper diastema. Short clinical crowns on upper incisors were also found.
Treatment Plan
- Closing spaces and maintain anterior torque by adding extra lingual root torque
- Perform a frenulectomy at the initial stage so as to increase clinical crown size; however patient refused and postponed it to the end of treatment, together with a frenulectomy to prevent space relapse
ClinCheck 1: Requirements for the Technician
- Close spacing by crown retrusion, both in upper and lower
- Intrude both upper and lower incisors to solve deep bite and gummy smile by applying deep bite sequence with optimized extrusion or bevelled to gingival attachments on distal tooth
- Upper laterals extrude at the same moment as central incisors are intruding, producing a countermovement and levelling gingival architecture
- In order to correct upper spacing, 10 degrees extra palatal root torque added to upper incisors, as well as the lower ones, with ClinCheck PRO
Fig. 17.19 Intraoral views left, front, right, upper, lower.
Fig. 17.20 Smile and pretreatment panoramic X‐ray.
Fig. 17.21 Pretreatment Clinchecks.
Fig. 17.22 Refinement: intraoral views, left, front, and right
Stay updated, free dental videos. Join our Telegram channel
VIDEdental - Online dental courses
