The controlled and randomized clinical trial was performed at the Department of Dentistry of the Federal University of Rio Grande do Norte (UFRN), and was approved by the local Ethics and Research Committee (CEP-UFRN/protocol 3.673.666) and followed the recommendations of the Declaration of Helsinki 1975 (revised August 26, 2018). The present study considered the CONSORT guidelines (Consolidated Standards of Reporting Trials) [19] (Fig. 1).
Participants were selected at the Department of Dentistry at the Federal University of Rio Grande do Norte (UFRN), from August 2018 to July 2020, based on data from medical records of patients rehabilitated with prostheses on implants, configuring a systematic sampling type. A total of twenty-three participants, nine with three implants and fourteen with four implants (Neodent; Straumann), as well as twenty-one females and two males, previously rehabilitated with implant-supported fixed total fixed mandibular prosthesis, in need of replacement with a hybrid prosthesis and opposed to a conventional complete denture, were included in the sample. Cases of implant loss and peri-implant diseases were excluded from the study. All received a detailed description of the procedures and an informed consent form was obtained before participation.
With all framework already fabricated and passive, the samples of this study were randomized, considering the type of maxillomandibular record (conventional or digital). For this, we used black envelopes containing a piece of paper with the name: conventional record maxillary oclusal (CMR) or digital record maxillary oclusal (DMR), configuring a simple process. Randomization was performed manually, at the same time for all participants, by an independent evaluator (A.C.S.P.T.) to prosthetic procedures.
For participants allocated to the CMR group, the following procedures were performed. The transfer impression of the position of the implants was obtained using the open tray technique to obtain the working model. For this, square-type copings (Neodent; Institut Straumann AG) were screwed under the mini-abutments with a torque of 10 N·cm. These were joined with metal fragments (dental drills/points) and stabilized with self-curing acrylic resin (Pattern Resin LS; GC Corp). After the resin polymerization reaction, a plastic tray was prepared, then it was loaded with dense addition silicone (Express XT; 3M).
The copings were involved with low viscosity addition silicone (Express XT; 3M) and, in sequence, the tray loaded with the dense impression material was positioned in the mouth. After the reaction of pressure of the material, the copings were unscrewed and the tray/copings set was removed from the oral cavity. The analogues of the abutments were positioned in the mold obtained and the space corresponding to the ridge was filled with artificial gingiva (Zhermack; Moema), and the other anatomical structures with plaster type IV (Dentsply).20
The working model and framework were used to make an orientation plan (Wax Pink 7; Lysandra). This plane was screwed under the abutments and adjusted according to the aesthetic and functional parameters (Fig. 2A), followed by performing the record maxillary oclusal (Zinc-enol impression dental paste; Lysandra). Finally, the antagonist arch was molded with irreversible hydrocolloid (Jeltrate Plus; Dentsply) (Fig. 2B). Once the participants presented a complete upper denture, it was inserted into a stainless steel tray for teething and molded outside the oral cavity. The mold was poured (Plaster Stone Type III; Asfer) and after the plaster had crystallized, the casts (upper and lower) were mounted on a semi-adjustable articulator (4000-S; Bioart) (Fig. 2C), using the table of camper for assembly of the upper model and register for assembly of the lower model.
The teeth were assembled using acrylic resin teeth (Trilux; VIPI), followed by clinical testing of the teeth and selection of the gingiva color (STG; VIPI). The base of the prosthesis was polymerized by microwave, followed by reassembly of the lower model for occlusal adjustment, until the incisal pin of the articulator was in contact with the incisal table.
The participants allocated in the DMR group underwent the following steps. Initially, the participants allocated to the DMR group were submitted to the digital image acquisition stage, namely: intraoral scanning of the antagonist arch (STL1), intraoral scanning of the position of the implants with the scan bodies (STL2), intraoral scanning of the position of the implants with the device (STL3)21 and intraoral occlusion scanning (STL4). From these images, the planning of articulated 3D casts was carried out. STL2 and STL3 files were superimposed in the inspection software program (GOM Inspect; GOM GmbH), using 3-point alignment and best fit, generating a single STL file. This was articulated (two posterior points and one anterior) to the STL1 file, which generated the final articulated model (Fig. 3A). The model was printed (Cosmos; Yller) in a 3D printing unit (Form 3; Formlabs) and allowed to cure for 15 minutes, followed by washing in isopropyl alcohol. The analogues of the abutments (Neodent; Institut Straumann AG) were fixed in the corresponding spaces, using flow resin (Opallis; FGM), followed by light curing for 15 seconds, on each surface of the analogue.
Upon generation of the articulated model (Fig. 3B), the infrastructure was positioned on the analogues for the assembly of the teeth. Then, a clinical test of the teeth in wax was performed (Fig. 4A) and the color of the gingiva was selected (STG; VIPI). The base of the prosthesis was polymerized by microwave, followed by the positioning of the prosthesis in the articulated model for occlusal adjustment, until contact was achieved with the anterior pin of the printed articulator on the incisal table.
The prostheses of both groups (CMR and DMR) were installed by a single examiner blinded (A.F.P.C.) to the type of prosthesis (Fig. 4B). In this session, the participants were positioned at 90 degrees and immediately after screwing the prosthesis to the abutments (Neodent; Institut Straumann AG), the examiner highlighted the occlusal contact points with 12 µm carbon paper (AccFilm II; Parkell) attached to carbon trippers (Muller; Golgran). Then, using an occlusal photography mirror (Mirror for metallic photography; Indusbello) and a professional camera (EOS Rebel T7i; Canon), an occlusal photograph was obtained of the distribution of occlusal contact points.
After capturing the photographic images, all the prostheses were adjusted (Maxicut pm7110.080hp spherical tungsten drill; American Burrs) for a straight piece (Straight piece intra 500; Kavo), maintaining the contacts as “clinically excellent” (Table 1). The time for occlusal adjustment was timed, counting from the moment the patient started bitting the carbon paper until the occlusal contact points were distributed as previously reported.
The photographic images were randomized using Microsoft Excel program (Excel; Microsoft) and inserted into PowerPoint program (PowerPoint; Microsoft) to analyze the accuracy of the classification of the distribution quality and quantity of the occlusal contact points (Table 1), blinding the patient's name and type of prosthesis.
The time required, in the clinical and laboratory steps to obtain working casts and register CMR and DMR, was timed to determine the working time of each method. For the CMR method, the following steps were included: implant position transfer impression and mold pouring, antagonist arch impression (complete denture) and mold pouring, preparation and adjustment of the plane, relation records and assembly in an articulator. For the DMR method, the steps included were: intraoral scanning of the antagonist arch (complete denture), intraoral scanning with the scan bodies, intraoral scanning with the device, intraoral scanning of the occlusion, digital planning of the casts, insertion of the joint, impression, washing and post-cure.
Data were analyzed using the statistical software IBM SPSS (Statistics V22.0; IBM Corp). A descriptive analysis was performed to evaluate the distribution of occlusal contact points between the relation records methods. Assuming the non-normality of the data, the Wilcoxon test was used to evaluate the number of points of occlusal contact points, and the Mann-Whitney test, working time between the two methods of relation records and occlusal adjustment, assuming a significance of p<0.05.