Biomimetic implant restoration made of human enamel and CAD/CAM block: a short report

Biomimetic implant restoration made of human enamel and CAD/CAM block: a short report

MENA Clinical Dentistry

1. January 2020

Federico Mandelli, Paolo Ghensi, Tonino Traini

This short report describes a clinical case in which an implant-supported crown was made using an extracted natural tooth as the outer shell. The same tooth had been previously relined for immediate loading without occlusal contacts. Using digital software, a composite resin mesostructure was fabricated in order to place the crown in the correct occlusal position, and the natural crown was ground using a computer-controlled milling machine to perfectly fit on the mesostructure. (Quintessence Int 2019;50:​–0; doi: 10.3290/j.qi.a42159)

Introduction

Ceramics are considered the gold-standard materials for final restorations either for natural teeth or implants. Nevertheless, due to the brittle behavior they have to be supported by a metal framework or high-strength polycrystalline ceramic cores.1,2 Most of the clinical studies present in the literature report that all ceramic materials (with some differences) are more abrasive than natural enamel, while the composite materials appear to be more abraded than natural enamel (like dentin).3,4 Since there is no established consensus about this topic, it can be stated that natural enamel is the gold standard reference material for prosthetic restorations. Following this concept, Magne and Schlichting5 reported the possibility to use the occlusal part of an extracted third molar as a material to create an overlay restoration. This was possible using advanced digital dentistry technologies. What was accomplished by Magne and Schlichting was far from a manufacturer-suggested workflow, because a natural tooth was milled by a milling unit that is built to mill blocks and that does not have a feedback system needed to mill an organic structure like a tooth. The aim of this case report is to extend to dental implants what can be accomplished with natural teeth: an extracted natural tooth was transformed into an implant-supported crown using a completely digital workflow. The used protocol should be considered experimental and anecdotal.

 

Short case presentation

A 61-year-old male presented with a deep caries lesion on the mandibular left second premolar (tooth 35 according to FDI notation) that could not be restored (Fig 1a) and a post-extraction implant was planned. An intraoral scan was performed before the extraction (Scan 1), then the tooth was extracted and an implant was placed into the fresh extraction socket (Ankylos 3.5 x 9.5 mm, Dentsply-Sirona). A standard, one-piece abutment was placed. Since the extracted tooth had the decay located mostly below the gingival margin, it was decided to use the tooth itself as provisional crown, after adaptation, as follows (Figs 1b to 1h). The caries lesion localized at the middle-third of the tooth was treated extraorally: carious dentin was removed, the deep dentin was conditioned with a standard adhesive protocol, and a composite resin (Evo Ceram, 3M Espe) was packed into the cavity; before curing, the natural crown was placed over the implant abutment, out of occlusion, and cured for 20 seconds. After a careful finishing and polishing procedure, the “natural tooth crown” was removed from the abutment analog and cemented onto the fixed abutment in the oral cavity.

After 3 months the patient asked to maintain the “natural tooth crown” as a final restoration. The patient was informed about the fact that the literature unsupported this treatment plan. The challenge was to place the tooth back in occlusion, while keeping the occlusal enamel intact. An intraoral scan was made (Scan 2) to record the tooth position. After removing the crown, a scan of the abutment, opposing arch, and occlusion was performed (Scan 3) and the crown was scanned extraorally to get a full three-dimensional (3D) model of its shape (Scan 4). In a digital environment, all the scans were aligned together and the occlusal gap created during immediate loading was evaluated (exoCad) (Figs 2a and 2b). In the CAD software, the relined crown (Scan 4) was moved coronally in order to overlap Scan 1. This movement created a gap between the apical part of the tooth and the abutment, which was filled by designing a sort of mesostructure as a restoration (Figs 2c and 2d). A polymethyl methacrylate (PMMA) crown of this project was milled to test the project. In the dental office, the provisional crown was removed and the PMMA crown was cemented to check if the virtual movement was correct and if a correct occlusion was obtained. The patient left the office with the PMMA crown, while his natural tooth was sent to the dental laboratory.

 

A composite material was selected to mill the mesostructure because its elastic modulus was closer to natural dentin compared to ceramics or zirconia. Using a customized mounter, the natural tooth was inserted into a milling unit that milled the female coupling with specifically developed milling strategies (Figs 2e and 2f). Composite resin was used to cement the inlay to the natural tooth (Fig 3a). The final restoration was delivered and the crown showed an acceptable occlusal contact (Figs 3b to 3e).

It was chosen to use part of an extracted tooth in order to obtain a final restoration that had natural enamel. Two challenges were faced: the first was the digital repositioning of a tooth in order to match the preoperative situation. The second, more challenging, was the ability to design a custom hole within the anatomy of a natural tooth and to mill it, getting a perfect match with a custom-designed mesostructure. The presented technique was developed empirically, with no evidence supporting it, and to date it is strongly operator-dependent; for this reason, it cannot yet be considered as a treatment option for daily practice. 

Acknowledgments

The authors thank Camaioni Odontotecnici dental laboratory, in particular CDT Valerio Zarroli for his support.

References

1. Weigl P, Sander A, Wu Y, Felber R, Lauer HC, Rosentritt M. In-vitro performance and fracture strength of thin monolithic zirconia crowns. J Adv Prosthodont 2018;10:79–84.

2. Stefanescu C, Ionita C, Nechita V, Drafta S, Oancea L, Petre A. Survival rates and complications for zirconia-based fixed dental prostheses in a period up to 10 years: a systematic review. Eur J Prosthodont Restor Dent 2018;26:54–61.

3. Sripetchdanond J, Leevailoj C. Wear of human enamel opposing monolithic zirconia, glass ceramic, and composite resin: an in vitro study. J Prosthet Dent 2014;112:1141–1150.

4. Lawson NC, Bansal R, Burgess JO. Wear, strength, modulus and hardness of CAD/CAM restorative materials. Dent Mater 2016;32:e275–e283.

5. Magne P, Schlichting LH. Biomimetic CAD/CAM restoration made of human enamel and dentin: case report at 4th year of clinical service. Int J Esthet Dent 2016;11:472–480.

Federico Mandelli
Federico Mandelli

Strada Padana Superiore, 15 – 20096 Pioltello, Milan, Italy.

Paolo Ghensi

CIBIO – Department of Cellular, Computational
and Integrative Biology, University of Trento, Trento, Italy.

Tonino Traini
Associate Professor

Chair of Dental Materials, Chair of Prosthetic and Laboratory Technologies, Department of Medical Oral and Biotechnological Sciences, School of Dentistry, University “G. d’Annunzio” of Chieti-Pescara, Chieti, Italy.