Alginoplast

The method used for intracochlear sound pressure measurement is described in detail in a previous publication^{16 (link)}. Here, sound pressure in SV (P_SV) and ST (P_ST) was recorded simultaneously with fiber-optic pressure transducers with a diameter of 310 µm (FOP-M260, FISO Technologies, Canada) connected to a two-channel signal conditioner (Veloce 50, FISO Technologies, Canada). Transducers were inserted 100–300 µm (visually estimated) into both scalae through fenestrations of approx. 0.4 mm diameter and sealed with a 3 mm piece of silicone tube (Sedat, France) permanently mounted to the optical fiber and dental impression material alginate (Alginoplast®, Heraeus Kulzer GmbH, Germany) (Fig. 1). Phases of the pressure transducers were calibrated in air against a 1/4” reference microphone (Type 4939, Brüel & Kjær, Denmark) and amplitudes against a probe microphone (ER-7C, Etymotic Research Inc., USA). The ICPD (ΔP) was calculated as the vector difference of P_SV and P_ST in the frequency domain.Figure 1

Temporal bone preparation for the incus stimulation. The tip of the T2 actuator was attached to the incus body and the FISO FOP-M260 transducers were inserted in scala vestibuli (SV) and scala tympani (ST) next to the round window membrane (RWM).

Digital impressions were performed either as partial- or complete-arch with IOS 1 (3M True Definition, 3M ESPE, St. Paul, MN, USA) and IOS 2 (TRIOS^® 3, 3Shape, Copenhagen, Denmark). Tooth surfaces were scanned with IOS 2 following IOS 1, as the latter requires coating with a spray applicator (3M Powder Sprayer; 3M, St. Paul, MN, USA). Bite registration (vestibular scan) was conducted in the maximum intercuspal position (MIP). Scans were aligned by the proprietary IOS software and exported as STL.
Conventional impressions were performed with a polyether impression material (Impregum^TM Penta^TM, 3M ESPE, Seefeld, Germany) for the implant site and an alginate material (Alginoplast, Kulzer GmbH, Hanau, Germany) for the opposing jaw. The bite was registered in MIP using a vinylpolysiloxane material (Take 1^® Advanced Bite Registration, Kerr, Brea, CA, USA) in an upright seated position. Gypsum-based casts were poured in dental type V stone and mounted in an articulator (Artex^®, Amann Girrbach, Pforzheim, Germany). After that, the casts were scanned in both enabled and disabled mode [LS (+), LS (−)] to avoid intersection using a laboratory scanner (Ceramill^® Map 600, Amann Girrbach, Pforzheim, Germany) and aligned in the proprietary software (Ceramill^® Mind, Amann Girrbach, Pforzheim, Germany). The scans were exported as PLY.

Conventional impressions were taken using an open-tray transfer coping and a polyether impression material (Impregum^TM Penta^TM, 3M ESPE, Seefeld, Germany). The seating of the transfer coping was always verified by an intraoral X-ray. Impressions of the opposing jaw were taken using an alginate-based material (Alginoplast^®, Kulzer GmbH, Hanau, Germany). Bite registration was accomplished using a vinylpolysiloxane material (Take 1^® Advanced Bite Registration, Kerr, Brea, CA, USA). An implant analog was fixed to the implant transfer coping. The implant model was poured in dental type V, and the alginate impression was created in a gypsum-based stone. Both were mounted in an articulator (Artex^®, Amann Girrbach, Pforzheim, Germany) and digitized in a laboratory scanner (Ceramill^® Map 600, Amann Girrbach, Pforzheim, Germany). Full-contour zirconia crowns with a screw-access hole were designed by an experienced dental technician using CAD software (Ceramill^® Mind 3.0, Amann Girrbach, Pforzheim, Germany) and milled in house (Ceramill^® zirconia, Amann Girrbach, Pforzheim, Germany). The crowns were finalized by glazing and luting on the ti-base (Variobase^®, Institut Straumann AG, Basel, Switzerland).

For this in-vitro study, dental impressions were made of the maxillary and mandibular of a young female patient (Alginoplast, Kulzer, Hanau, Germany), and master plaster models (pico rock 280, Picodent, Wipperfürth, Germany) were fabricated. The maxilla was fully dentate (14 teeth in total) and symmetrical and showed anatomical occlusal surfaces. The mandible had a gap caused by a missing tooth (35, premolar) and the front was slightly interlocked (13 teeth in total). The two master models were scanned with the Ceramill Map 400 (Amann Girrbach, Koblach, Austria), and the data were converted into the STL format and saved as master STL datasets. Dental models were generated based on master STL datasets using Meshmixer (V3.5, Autodesk, San Rafael, CA, USA) and saved as STL files. With the help of the SIMPLEX sliceware (Renfert, Hitzingen, Germany), the STL data of the dental models were converted into the g-code format. These provided specific printing instructions to the FFF printer.

Dental casts of the upper jaw were made for the 12 subjects (Alginoplast®, Kulzer GmbH, Hanau, Germany). On the resulting plaster model, an occlusal splint made of plastic was manufactured using the thermoplastic deep drawing procedure (Erkodur, Erkodent® Erich Kopp GmbH, Pfalzgrafenweiler, Germany). A barrier was then fitted in the posterior region to hold the cheek and tongue. This barrier resembled a shield, such as those used for the function regulator of Fränkel [39 ]. Using sprinkle and spray technology, clear plastic (Orthocryl®, Dentaurum GmbH & Co. KG, Ispringen, Germany) was applied to a wire retainer (Fino, DT & Shop GmbH, Bad Bocklet, Germany), which was connected to the occlusal splint, and polymerized. This resulted in a gap of a few millimeters between the deep-drawn occlusal splint and the shield-like construction (Fig. 1a).Fig. 1

a Occlusal splint with vestibular plastic shield-like construction and b, c fixed test specimens in premolar and molar region (arrows)