A single appointment CAD-CAM esthetic resin crown restoration was performed. Slight differences to the crown trimming for stainless steel crown included a larger occlusal reduction and a feather-edge subgingival margin. The custom-made crown was printed in a 3D printer after scanning the preparation and designing the crown in a CAD software. The total elapsed time for the procedure was 70 minutes. Advantages of this technique include a one single appointment custom-made esthetic crown resulting in a milder reduction of the tooth, exact fit of the crown, and good esthetics. The main disadvantage at present time is the poor wear and compressive resistance of the material.
custom-made crown, primary molars, CAD-CAM.
Se realizó una restauración con corona de resina estética CAD-CAM en una sola cita. Las ligeras diferencias con el recorte de la corona de acero inoxidable incluyeron una mayor reducción oclusal y un margen subgingival de borde de pluma. La corona hecha a medida se imprimió en una impresora 3D tras escanear la preparación y diseñar la corona en un software CAD. El tiempo total del procedimiento fue de 70 minutos. Las ventajas de esta técnica incluyen una corona estética hecha a medida en una sola cita, lo que resulta en una reducción más suave del diente, un ajuste exacto de la corona y una buena estética. La principal desventaja en la actualidad es la escasa resistencia al desgaste y a la compresión del material.
The restoration of extensive lesions and badly broken down primary molars, in pediatric dentistry follows different restorative approaches in where full coverage is preferred over multisurface restorations.1,2 Since the 1950’s, stainless steel crowns (SSCs) have been widely used by pediatric dentists worldwide to restore primary molars. SSCs offer several advantages: cost-effectiveness, longevity and margin adaptability. However, its main disadvantage is the non-esthetic silver-colored metallic appearance.3
Over the years, several alternative techniques for esthetic full-coverage restorations on primary molars have been attempted, some of these include policarbonate crowns, open-faced veneer SSCs placed on chair side, commercially pre-veneered crowns, and zirconia crowns.4 The effective use of these techniques has technical and functional implications. For instance, crowns are pre-made in a variety of sizes with the correct being chosen to fit the trimmed down tooth.
CAD-CAM (Computer Aided Design-Computer Aided Manufacturing) systems have been used in dentistry since the mid-1980’s and have become increasingly popular because of their application in multiple areas of dentistry: prosthodontics, crown and bridge, implantology, orthodontics, and pediatric dentistry.5 This technology results in esthetic restorations that are resistant and can be easily and accurately created.
Three-dimensional (3D) printing is a state-of-the-art technology that is becoming widely accepted in dentistry. The continuous improvement of intraoral scanning, CAD software, 3D printers, and biological and physical properties of materials (resins, plastics, metals and ceramics) allows for increased accuracy and speeds the adoption of this developing technology with great impact in different fields of dentistry.6
A 4-year old hispanic female, healthy with no remarkable medical history attended a private pediatric dentistry clinic in Mexico City, Mexico, for an oral examination. The child was diagnosed with early childhood caries (ECC), preventive care and treatment plans were performed. The latter included four resin-modified glass ionomer restorations on: primary maxillary right second molar, primary maxillary right first molar and primary maxillary right cuspid and a full-coverage restoration on the primary maxillary left first molar.
The female child’s mother asked an esthetic restoration on the primary maxillary left first molar and was provided the options of: a) prefabricated zirconia crowns or b) an in-office custom-made resin crown restoration. It was explained to him that option b) was a recently technique uses new materials with the advantage of a custom-made, less expensive crown that would fit the tooth preparation with great accuracy and could be placed in the same appointment, as opposed to option a) where a standard pre-made zirconia crown required more trimming of the tooth to fit the crown. Given the novelty of this technique, and the uncertainty regarding the compressive and wear resistance of the material, they were offered two replacement crowns to be used in case of failure. She accepted, signed the informed consent, and appointments were scheduled.
The primary maxillary left first molar was trimmed in a way similar to a SSC preparation, but with a more occlusal reduction (2 mm) and a feather-edged one-millimeter subgingival preparation in the proximal, buccal, and lingual surfaces. The reduction of the occlusal surface was done with a coarse football-shaped diamond bur (368.021 SS White, Lakewood NJ, USA) followed by a circumferential reduction with a flame-shaped diamond bur (862-012C SS White, Lakewood NJ, USA) with a subgingival margin carefully extended to a feather-edge 1 mm subgingival on all surfaces, and an adequate proximal reduction to attain the correct fitting of the crown and to allow for contact with the adjacent tooth; finally, line and point angles were slightly rounded.
Once the tooth reduction was completed, a first gingival retraction cord (ROEKO Stay-put No 0, COLTENE/Whaledent AG, Altstätten, CH) was placed subgingivally all around the tooth, followed by a second retraction cord (ROEKO Stay-put No 1) placed in the same way. The second retraction cord was removed, and the tooth was rinsed with water spray. Leaving the first retraction cord in place (figure 1), we proceeded to scan the tooth with a intraoral scanner (CS 3600, Carestream Dental LLC, Atlanta, GA,USA); designed the crown with a chairside computer-aided design software (exocad GmbH, Darmstadt, Ger); and printed it with two more replicas in a 3D printer (Kulzer cara Print 4.0, KULZER, Mitsui Chemicals Group, Hanau, Ger) with a printable biocompatible resin material (dima Print denture resin, KULZER).
Once the crowns were printed (figure 2), were placed into an ultrasonic cleaner (BiosSonic UC125, COLTENE) in a container with isopropyl alcohol, for three minutes, followed by another three minutes washing in a container with water. The last step was the trimming and polishing of the crowns, preceded by a post-cured procedure in a composite curing oven (HiLite power 3D, Kulzer) for five minutes. One of the three crowns was chosen and cemented with a dual cure self-adhesive cement (RelyX™ U200, 3M™ ESPE, St. Paul, MN, USA). The entire procedure took 70 minutes, from the anesthetic infiltration to the crown cementation.
The patient returned to the office one week later with the fractured custom-made crown and bruxism was identified as the cause. One of the previously made replacement crowns was recemented, using a composite resin (Filtek™ Z350 XT, 3M™ ESPE) instead of the self-adhesive cement (figure 3), and the mother was given two other pre-printed replacement crowns.
Follow-up visit six months later showed a good clinical appearance of the crown with no fractures, good fit, no plaque retention and good gingival health (figure 4).
Figure 1. Crown preparation with retraction cord.
Figure 2. Printed crowns.
Figure 3. Recementation of the crown with composite resin.
Figure 4. Six months follow-up visit.
The most common esthetic full-coverage restorations available for primary molars are standard pre-made crowns (zirconia, pre-veneered, fiberglass) where we need to trim the tooth according to the size of the crown and margins can’t be altered because of their inability to crimp and contour, requiring passive crown fit.7 Zirconia crowns, which are preferred by many practitioners, require more tooth reduction when compared to alternative SSC’s.8 Custom-made crown restorations for primary molars result in an impractical and expensive treatment. They required impressions of the trimmed and antagonist teeth, bite registration, manufacturing of the crown in a dental lab with at least two appointments, and the use of a temporary crown placed for several days.
Dentistry is evolving, the development of CAD-CAM technologies provides the necessary resources to perform custom-made restorations for extensive caries lesions, developmental defects or trauma lesions of primary molars, in a single visit with several advantages including: exact fit of the restoration with great margin adaptability, less tooth reduction and the ability to perform several restorations at a time.
CAD-CAM dentistry uses substractive processes (milling) and additive processes (3D printing) to create dental restorations including crowns, inlays, onlays, veneers, dentures, and orthodontic appliances with different materials like ceramics, plastics, resins and metals.8
For the case presented here, the CAD-design crown was printed in a 3D printer, a procedure requiring relatively more affordable equipment, when compared to the CAD-CAM milling process. 3D printing is a rapidly developing technology that has gained widespread acceptance in dentistry since it offers process engineering advantages compared to conventional (lost-wax technique) and substractive computer numeric controlled methods.6
When preparing the tooth, a 2 mm occlusal reduction was created to ensure sufficient thickness of the crown and counteract the poor flexural strength of the printable resin material that was used (> 50 mPa).9 The lack of resistance of this material along with the bruxism of the patient was the main reason why cementing the crown with the self-adhesive cement failed. When it came to cementing, it was decided to use a composite resin to improve the physical properties of the restoration, given its bigger amount of inorganic filler.10 An alternative to this type of cementing could be a pre-heated composite.11
In the near future, continued improvement of the physical properties of esthetic materials, including printable resins, will make this technique a good option for the restoration of extensive lesions in primary molars.
JLRA: Led the writing and performed the clinical procedure.
EV: Assisted in the writing and designed and print the crowns.
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Leonardo Rubio Arguello.
Sierravista 284-1, Col. Lindavista, Alcaldía Gustavo A. Madero, C.P. 07300, México City, México.
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