A Subgingival Crown-Root Fracture With 45% Bone Loss: Forced Eruption, Intrusion, and Interdisciplinary Sequencing
A 45-year-old man has completed non-surgical periodontal therapy 4 months ago. Probing depths are now 3-4 mm generally, with bleeding on probing at 12 sites. Tooth 21, endodontically treated 2 years ago, has a palatal crown-root fracture whose line lies 2.0 mm below the palatal gingival margin; the tooth is grade I mobile with a 5 mm palatal pocket and only 2 mm of attached gingiva. Radiographs show about 45% horizontal bone loss on 21, 11, and 22. The 21 root is 13 mm long and the fracture is 9 mm from the apex. Teeth 11 and 22 are extruded 2 mm relative to the occlusal plane, and there is 4 mm of space between 11 and 22. There is 2 mm of buccal recession on 21 and Miller class I recession on 12. The patient grinds at night, has a 2 mm overjet and a 5 mm overbite. The restorative plan is a full-coverage crown on 21 and ceramic veneers on 11 and 22.
1. How much extrusion of 21 do you need, what force will you use, and how will you control the gingival margin and bone during eruption?
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Calculate the target first. The fracture is 2.0 mm below the palatal margin. A crown margin must end up 2-3 mm coronal to the bone crest and you need at least 1.5-2 mm of sound axial tooth structure for a ferrule, ideally 3 mm. To place the fracture line 2-3 mm supragingivally, you need to move the tooth coronally by roughly 2 mm (to bring the fracture to the margin) plus 2-3 mm (to place it supragingivally), that is about 4-5 mm of extrusion. Note the consequence: 4-5 mm of extrusion on a 9 mm residual root leaves only 4-5 mm of root within bone, so the crown-root ratio is poor, the tooth must be splinted to its neighbours during the process, and the long-term prognosis should be discussed honestly with the patient before starting.
Force: 20-30 g of light continuous force is sufficient for forced eruption; heavier force does not accelerate it and increases the risk of ankylosis and root resorption. Deliver it with a light sectional NiTi wire (0.012-0.014) from a rigid anchorage segment on 11 and 22, or from a miniscrew, and reactivate every 2-3 weeks.
Gingival control is the key decision, and it depends on the objective. If the goal is to expose sound tooth structure while leaving the gingival margin where it is-which is what this patient needs, since a 2 mm attached gingiva band on 21 cannot afford to migrate-perform a circumferential supracrestal fiberotomy every 7-10 days during eruption. Severing the supracrestal fibers prevents the gingiva and junctional epithelium from following the tooth, so the tooth erupts through the attachment and the margin stays put. If instead the goal were implant site development, you would use rapid extrusion (2-3 mm per week) with no fiberotomy so that bone and gingiva travel with the tooth. Here use slow extrusion, roughly 1 mm per 1-2 weeks, with serial fiberotomies, over about 8-10 weeks.
Plan the occlusal consequence now: extruding 21 by 4-5 mm while the overbite is already 5 mm creates an interference. That is the reason to intrude or hold 11 and 22 rather than simply allowing them to follow. After extrusion, stabilise the tooth with a flexible splint for 4-8 weeks and take a radiograph to check for resorption and ankylosis before the crown preparation.
2. You plan miniscrew-assisted intrusion of 11 and 22. How does 45% bone loss change the biomechanics, what force do you use, and what risks are specific to this patient?
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The single biggest change is the position of the center of resistance. With 45% horizontal bone loss, the center of resistance shifts apically to roughly the junction of the middle and apical thirds of the remaining supported root. The perpendicular distance from the bracket to that point therefore increases, so for the same force the tipping moment increases. A simple labial force to an intrusion hook will produce uncontrolled labial crown tipping and lingual root movement, which risks fenestration through an already thin labial plate and worsens the 2 mm recession already present on 21. You must add a counter-moment: place the intrusive force through a power arm or lever arm positioned so its line of action passes close to the shifted center of resistance, or use a palatal miniscrew with a force vector passing closer to the long axis.
Force: with a reduced periodontal ligament area, use lighter forces than in an intact periodontium-about 10-15 g per incisor, so 30-45 g for the 11, 21, 22 unit-rather than the 60-100 g often quoted for four incisors with normal support. Reactivate every 4-6 weeks, not more often, and check mobility and probing depths at each visit.
Patient-specific risks. First, intrusion pushes plaque and calculus subgingivally, so oral hygiene and 4-6 week periodontal maintenance are not optional; without them you can convert a stable treated periodontitis case into an active one. Second, root resorption is more likely with light but prolonged forces in a reduced periodontium-take periapicals at 6 months. Third, and most important, do not intrude 21. It has a fractured, short, endodontically treated root with 45% bone loss, and intruding it adds resorption and ankylosis risk for a tooth whose long-term prognosis is already guarded. Restore it slightly out of the plane, or accept a minor occlusal discrepancy, and intrude only 11 and 22. Fourth, address the cause: 11 and 22 likely over-erupted because 21 lost occlusal contact after the fracture, so treat the occlusal cause and provide a night guard for the bruxism before and throughout.
Finally, recognise the limit of the plan. Intrusion of periodontally compromised incisors is feasible and often appropriate, but the endpoint is a tooth in the arch that is restorable and stable, not a perfect occlusal plane.
3. Set out the interdisciplinary sequence from now to final restoration, and state the retention plan.
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Phase 1, periodontal stabilisation: re-evaluate 4-6 weeks after therapy with a full periodontal chart. Do not start tooth movement while bleeding on probing remains above about 15-20% of sites or while pockets remain ≥5 mm. In this patient the 5 mm palatal pocket on 21 is largely the fracture, so it will resolve with the extrusion rather than with more scaling.
Phase 2, endodontic verification on 21: it is already treated, but confirm the seal and the absence of apical pathology before loading the tooth for 10 weeks. If the coronal seal is compromised, place a temporary restoration or an apical plug now, not after eruption.
Phase 3, habit and occlusal control: fit a maxillary night guard for the bruxism, and explain that it must be worn during eruption and after restoration. Start oral hygiene instruction aimed at the surgical site.
Phase 4, orthodontics: splint 11-22 with a flexible sectional wire, begin slow extrusion of 21 with fiberotomies, and start light intrusion of 11 and 22 with the miniscrew and lever arm. Reassess at each visit with probing depths, mobility, periapical radiographs at 6 months, and a check that 21's fracture line is emerging as planned. Expect 8-12 weeks for the extrusion.
Phase 5, stabilisation: hold the teeth for 4-8 weeks after the desired position is reached, confirm with a radiograph that the fracture line sits 2-3 mm supragingivally with a ferrule, and confirm periodontal stability. Only then prepare 21 for a full-coverage crown-preparation before stabilisation risks the crown margin migrating apically as the tooth settles.
Phase 6, restoration: provisional crown on 21, evaluate the gingival architecture for 3-6 months, then the definitive crown and the ceramic veneers on 11 and 22 in a single esthetic phase. The margin on 21 is placed at the newly established gingival level, not at the old one.
Retention: a bonded lingual retainer from 13 to 23 plus a vacuum-formed night guard that also serves as the retainer for the bruxism. Periodontal maintenance every 3 months for the first year, then every 4-6 months, with radiographs at 1 and 3 years to monitor bone and root resorption. Tell the patient explicitly that the prognosis of 21 depends as much on maintenance as on the treatment.