4.4 Fixed Prosthesis Try-In, Delivery, Complications and Repair
Key Takeaways
At try-in, adjust proximal contacts first, because a tight contact prevents seating and makes the marginal and occlusal checks misleading.
Caries of abutment teeth is the most frequent biological complication of fixed partial dentures, followed by the need for endodontic treatment and loss of retention.
Excess resin cement is removed after a brief tack cure, glass ionomer at its gel stage, and zinc phosphate after it has set.
Intraoral repair of chipped glass ceramic uses roughening, hydrofluoric acid etching, silane, adhesive and composite; exposed metal is air-abraded and primed before opaquer.
A loose crown with sound tooth structure and adequate preparation geometry can be re-cemented; recurrent caries or an over-tapered short preparation requires a new preparation and restoration.
A perfectly prepared tooth can still end up with a failed crown if delivery is rushed. The SDLE blueprint includes delivering and cementing final prostheses with occlusal harmony, and providing follow-up, adjustments and repairs. Expect questions on the order of try-in checks, cement clean-up, and diagnosing failures years later.
Try-In Sequence
| Step | What to check | How |
|---|---|---|
| 1. Remove provisional and clean | Temporary cement removed, tissues healthy | Hand instruments, pumice, rinse |
| 2. Proximal contacts | Floss passes with resistance similar to natural contacts | Floss, shimstock; adjust and polish |
| 3. Marginal fit | No open or overhanging margins | Explorer, magnification, bitewing radiograph for posterior units |
| 4. Internal fit and seating | Restoration seats fully without rocking | Silicone fit checker or disclosing paste |
| 5. Occlusion | Contacts in maximum intercuspation and excursions match the plan | Articulating paper, shimstock (8-12 micrometer foil) |
| 6. Esthetics and phonetics | Shade, contour, emergence, patient approval | Natural light, patient mirror |
Contacts come first because a tight contact keeps the crown from seating, which makes the margins look open and the occlusion look high. For metal-ceramic and layered restorations, try in at the bisque bake stage so that contour and shade can still be modified before glazing.
Cementation
- Select the cement for the material and retention (see the dental cements and luting section): conventional cements for retentive preparations with metal, metal-ceramic or high-strength zirconia; adhesive resin cement for glass ceramics, veneers and short or tapered preparations.
- Isolate, clean and condition the preparation and the intaglio surface as required.
- Seat with firm, steady pressure; have the patient bite on a cotton roll if appropriate.
- Remove excess cement at the right time:
- Resin cement: brief tack cure (2-5 seconds), remove gel-state excess, floss interproximally, then complete curing.
- Glass ionomer and RMGI: remove at the rubbery gel stage.
- Zinc phosphate: remove after the cement has set.
- Recheck occlusion and take a post-cementation radiograph for posterior bridges to confirm no residual subgingival cement.
Provisional Cementation and Adjustment Before Final Cementation
Long-span or full-arch restorations are sometimes cemented with a temporary cement for a trial period so that occlusion, phonetics and tissue response can be judged. Any porcelain adjusted at try-in should be re-glazed or polished with a graded diamond polishing system before cementation; a rough ceramic surface wears the opposing enamel and fractures more easily. Zirconia adjusted with diamonds should be polished (and, ideally, re-heat-treated if the manufacturer recommends it) to remove surface flaws.
Post-Cementation Sensitivity
Short-lived thermal sensitivity after cementation is common and usually comes from dentin desiccation or a high contact. Persistent or spontaneous pain suggests pulpitis and needs vitality testing and radiographs. Pain only on biting points to a premature contact, a cracked tooth, or residual cement in the sulcus.
Patient Instructions and Maintenance
- Teach cleaning under pontics with floss threaders, superfloss or interdental brushes; a water flosser may help.
- Recall at intervals set by caries and periodontal risk (commonly 3-6 months for high-risk patients); check margins, probing depths, mobility and occlusion.
- Bruxists receive a hard occlusal guard to protect ceramics.
Complications and Their Causes
| Complication | Typical cause | Management |
|---|---|---|
| Recurrent caries (most common biological failure of FPD abutments) | Plaque at margins, high caries risk | Remove the prosthesis, restore, re-make; fluoride and hygiene |
| Need for endodontic treatment | Preparation trauma, deep caries, pre-existing pulp disease | Root canal through the crown, then seal the access |
| Loss of retention | Over-taper, short walls, cement washout, caries | Re-cement only if tooth is sound and geometry adequate; otherwise re-prepare with grooves or crown lengthening |
| Periodontal disease | Overcontour, subgingival margins, poor hygiene | Periodontal therapy, recontour or replace |
| Porcelain chipping | Thin ceramic, unsupported porcelain, occlusal overload, veneered zirconia | Polish small chips; repair or remake larger fractures |
| Connector fracture | Undersized connectors, long spans | Remake with adequate connector size |
| Abutment or root fracture | Lack of ferrule, oversized post | Extraction or major revision |
Goodacre and colleagues' review of clinical complications found caries, the need for endodontic treatment and loss of retention to be the leading problems with FPDs; single crowns more often needed endodontic treatment or showed porcelain fracture.
Retrieving a Failed Crown
Conventional cements may allow removal with a crown remover, but forceful tapping can fracture porcelain or teeth. Bonded restorations and zirconia usually have to be sectioned with a fine diamond or carbide bur. Always warn the patient that the restoration may be destroyed during removal.
Intraoral Repair of Ceramic Fractures
| Substrate exposed | Surface treatment | Then |
|---|---|---|
| Feldspathic or glass ceramic | Roughen, 9-10% hydrofluoric acid gel (often about 1-2 minutes for feldspathic porcelain), rinse, dry | Silane, adhesive, composite |
| Zirconia | Air-abrasion with aluminum oxide | 10-MDP primer, adhesive, opaquer if needed, composite |
| Metal | Air-abrasion | Metal primer, opaquer to mask, composite |
Use rubber dam and protect soft tissue when hydrofluoric acid is used intraorally. Repairs are a compromise; large fractures in functional areas usually need a new restoration.
Exam Traps
- Adjusting occlusion before contacts are corrected is the classic sequencing error.
- A crown that keeps coming off with an over-tapered short preparation needs added retention, not stronger cement alone.
- Residual cement left around abutments causes inflammation; around implants it is a recognized cause of peri-implantitis.
At the try-in of a lithium disilicate crown on tooth 14, the crown does not seat fully and the buccal margin appears open by 0.3 mm. What should be checked first?
The shade under daylight, because value errors distort marginal readings
Occlusion in lateral excursions, because high cusps lift the crown margins
Proximal contacts, because a tight contact can stop the crown from seating
The cement choice, because a resin cement will reliably close a 0.3 mm marginal gap
Six years after a bridge from tooth 13 to tooth 15 was cemented, the patient presents with a mobile bridge and soft dark dentin under the 15 retainer. Which statement best describes the finding?
Recurrent caries at an abutment, the most common biological failure of bridges
Normal cement washout that is corrected by simply re-cementing the same bridge in place
Vertical root fracture, which always presents as softened dentin under crowns
Porcelain fatigue, the most common mechanical failure of metal-ceramic bridges
A patient has a small porcelain chip on the facial cusp of a metal-ceramic crown on tooth 24, with no metal exposed and no functional contact on the chipped area. Which repair protocol is appropriate?
Apply metal primer and opaquer, because chipped metal-ceramic always exposes the alloy
Etch the porcelain with 37% phosphoric acid only and bond composite directly
Air-abrade the porcelain and apply a 10-MDP zirconia primer before composite
Roughen, etch with hydrofluoric acid, apply silane and adhesive, then composite
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