Abstract
Direct laser metal forming (DLMF) is a new technique which allows solids with complex geometry to be produced by annealing metal powder microparticles in a focused laser beam, according to a computer-generated three-dimensional (3D) model. For dental implants, the fabrication process involves the laser-induced fusion of titanium microparticles, in order to build, layer by layer, the desired object. Modern computed tomography (CT) acquisition and 3D image conversion, combined with the DLMF process, allows the fabrication of custom-made, root-analogue implants (RAI), perfect copies of the radicular units that need replacing. This report demonstrates the successful clinical use of a custom-made, root-analogue DLMF implant. CT images of the residual non-restorable root of a right maxillary premolar were acquired and modified with specific software into a 3D model. From this model, a custom-made, root-analogue, DLMF implant was fabricated. Immediately after tooth extraction, the root-analogue implant was placed in the extraction socket and restored with a single crown. At the 1-year follow-up examination, the custom-made implant showed almost perfect functional and aesthetic integration. The possibility of fabricating custom-made, root-analogue DLMF implants opens new interesting perspectives for immediate placement of dental implants.
Immediate implants are implants inserted immediately after surgical extraction of the teeth to be replaced . The idea underpinning immediate implant placement is to preserve the alveolar height and width, reducing the marginal bone resorption that typically follows extraction socket healing . The advantages of immediate implantation include shortening of the rehabilitation treatment time and the avoidance of a second surgical intervention . There are some disadvantages related to immediate implant placement in fresh alveolar sockets .
Primary stability represents a fundamental pre-requisite for osseointegration and in a fresh extraction socket it can be difficult to achieve . As adequate bone quantity and quality are essential prerequisites for achieving primary implant stability, the surgical requirements for immediate implantation include extraction with the least trauma possible and the careful preservation of the alveolar socket walls. Primary implant stability seems to be related to the implant macroscopic features (shape, length and diameter). Until now, primary implant stability in fresh post-extraction sockets has been achieved by placing implants exceeding the alveolar apex by 3–5 mm, or by inserting implants of greater diameter than the remnant alveolus .
One possible alternative to the traditional threaded, straight or tapered implant systems intended to replace a missing tooth is the fabrication of a customized, dental root-analogue implant (RAI) . Few studies describing the techniques of creating and placing custom-made RAI have been noted in the literature . In the last few years, considerable progress has been made in the development of rapid prototyping (RP) methods, including direct laser metal forming (DLMF) . DLMF is a timesaving procedure in which a high power laser beam is directed on a metal powder bed and programmed to fuse particles according to a computer assisted design (CAD) file, generating a thin metal layer. Apposition of subsequent layers gives shape to a desired 3D form with minimal post-processing requirements . With DLMF it is possible to fabricate dental implants of different size and shape, directly from CAD models .
Modern computed tomography (CT) acquisition and 3D image conversion, combined with the DLMF process, allows the fabrication of custom-made RAI, which are perfect copies of the radicular units to be replaced . Perfect implant fit could lead to excellent primary stability, however, it might be responsible for the intermediate term failure, because of the subsequent uniform pressure-induced resorption concerning the entire alveolar surface simultaneously affecting the thin buccal layer, which is prone to fracture and pressure-induced resorption .
The aim of the present study was to demonstrate how new DLMF technologies permit the fabrication of a custom-made, titanium RAI, which can be predictably inserted in a fresh extraction socket, with immediate restoration.
Case study
A 50-year-old healthy female patient with a fractured non-restorable second maxillary right premolar was selected for this study. The patient gave consent for implant therapy. This study was performed according to the principles outlined in the World Medical Association’s Declaration of Helsinki on experimentation involving human subjects, as revised in 2008.
Implant fabrication
CT datasets of the fractured tooth were acquired using a modern cone beam scanner (Verawiewepocs 3D R , Morita Corporation, Tokyo, Japan). CT datasets were transferred in the DICOM format to specific 3D reconstruction software (Mimics R , Materialise, Leuven, Belgium). With this software, it was possible to construct a 3D projection of the maxilla and the residual root, simulating a ‘virtual’ extraction of the root ( Fig. 1 ). The root was isolated as a stereolithographic (STL) file and transferred to proprietary reverse-engineering software (Leader-Novaxa R , Milan, Italy). The root was smoothed to obtain a regular surface. The STL file was returned to the 3D reconstruction software (Mimics R , Materialise, Leuven, Belgio), to test the congruence between the root and the alveolar socket. The file was transferred to Pro/Engineering CAD 3D software (PTC Group R , Needham, MA, USA) where a prosthetic conical abutment was designed, and a reduction of the diameter of the implant neck next to the thin vestibular cortical bone was made ( Fig. 2 ). With the aid of another 3D image reconstruction programme (Magics R , Materialise, Leuven, Belgium), copies of the final STL file (virtual root plus abutment) were prepared, with sequential percentage dimensional increments, in order to provide the surgeon with three different STL files representing different size increments (0%, 5%, 10%) of the same object (to avoid potential distortions or errors related to the 3D projection steps). All three STL copies were used to manufacture the implants using the DLMF technique (Leader-Novaxa R , Milan, Italy) . The implants were made of Ti–6Al–4V alloy powder, with a particle size of 25–45 μm as the basic material. Processing was carried out in an argon atmosphere using a powerful ytterbium (Yb) fibre laser system (Eos Laser Systems R , Munich, Germany) with the capacity to build a volume up to 250 mm × 250 mm × 215 mm using a wavelength of 1054 nm with a continuous power of 200 W, at a scanning rate of 7 m/s. The size of the laser spot was 0.1 mm. This procedure allowed the creation of three incremental custom-made titanium implants, perfect copies of the natural root, with integral abutments. To remove residual particles from the manufacturing process, the implants were sonicated for 5 min in distilled water at 25 °C, immersed in NaOH (20 g/l) and hydrogen peroxide (20 g/l) at 80 °C for 30 min, and then sonicated for 5 min in distilled water. Acid etching was carried out by immersion of the samples in a mixture of 50% oxalic acid and 50% maleic acid at 80 °C for 45 min, followed by washing for 5 min in distilled water in a sonic bath. The implants were packaged in custom-made disposable packaging fabricated with the aid of specific software (Pro/Engineering CAD 3D R , PTC, Needham, MA, USA).
