Accuracy of self-perforating impression tray for maxillary dental implant

| Objectives: To analyze the accuracy of a pre-fabricated self-perforating tray for implant impression in an edentulous maxilla. Methods: Four implants (13, 16, 23, 26) were placed in an acrylic resin model of an edentulous maxilla. Implant impressions (n = 7) were taken using a customized open tray (Control Group) and a pre-fabricated selfperforating tray (Test Group). A metal bar was fabricated and screw-retained on implant 13 and the vestibular gap between the framework and implants was measured by stereomicroscopy on implants 16, 23, and 26. Data were analyzed by ANOVA repeated measures and Tukey tests with a significance level (α) of 0.05. Results: There was no statistical difference between self-perforating and customized open tray groups. Control group showed a gap of 73.31± 26.01 for I1; 149.16± 53.90 for I2; and 115.46± 73.34 for I3. Whereas Test Group showed a gap of 154.41± 74.64 for I1; 159.45± 87.64 for I2; and 109.28± 49.18 for I3. Conclusion: The pre-fabricated self-perforating and custom trays showed a similar accuracy for implant impression of edentulous maxilla. DESCRIPTORS | Impression Technique; Dental Implants; Dimensional Measurement Accuracy. RESUMO | Precisão de moldeira autoperfurante para impressão de implante dentário maxilar • Objetivos: Analisar a precisão de uma moldeira autoperfurante de impressão pré-fabricada para implantes na maxila edêntula. Métodos: Quatro implantes (13, 16, 23, 26) foram colocados em um modelo de resina acrílica de uma maxila edêntula. As impressões dos implantes (n = 7) foram tiradas com uma moldeira aberta customizada (Grupo Controle) e uma moldeira autoperfurante pré-fabricada (Grupo Teste). Uma barra de metal foi fabricada e aparafusada no implante 13, e o gap vestibular entre a estrutura e os implantes foi medido por estereomicroscopia nos implantes 16, 23 e 26. Os dados foram analisados por Anova de medidas repetidas e teste de Tukey, com um nível de significância (α) de 0,05. Resultados: Não houve diferença estatística entre os grupos de moldeiras, tanto autoperfurante quanto aberta customizada. O grupo controle apresentou gaps de 73,31 ± 26,01 para I1; 149,16 ± 53,90 no I2; e 115,46 ± 73,34 para o I3. Ao passo que o Grupo Teste apresentou gaps de 154,41 ± 74,64 no I1; 159,45 ± 87,64 no I2; e 109,28 ± 49,18 para o I3. Conclusão: A moldeira autoperfurante pré-fabricada e a moldeira customizada apresentaram precisão similar na impressão de implantes da maxila edêntula. DESCRITORES | Técnica de Impressão; Implantes Dentários; Precisão da Medição Dimensional. CORRESPONDING AUTHOR | • Lauren Oliveira Lima Bohner Department of Prosthodontics, School of Dentistry, University of São Paulo • Av. Prof. Lineu Prestes, 2227 São Paulo, SP, Brazil • 05508-000 E-mail: lauren@usp.br • Received Aug 11, 2017 • Accepted Dec 20, 2017 • DOI http://dx.doi.org/10.11606/issn.2357-8041.clrd.2018.135626 Accuracy of self-perforating impression tray for maxillary dental implant 2 ● Clin Lab Res Den 2017: 1-7 INTRODUCTION Passive fit of an implant-supported dental prosthesis is determinant to provide the long-term success of oral rehabilitation, since a misfit may lead to mechanical complications such as screw loosening, screw fracture or the induction of an internal load on the prosthesis, implants, and bone. Furthermore, biological events have been reported due to the increase in plaque accumulation, resulting in implant failure.1-5 The accuracy of an implant impression is one of the most important factors to determine the fit of restorations, provided that the implant position in the patient̀ s mouth is entirely reproduced in the cast model.6,7,8 Therefore, obtaining an adequate implant impression is an important step to avoid misfit of the implant-supported prosthesis.1,3,5,6,9,10 Currently, the pick-up technique offers the most accurate implant positioning reproduction when the impression is taken of 3 or more implants.11,12 The main disadvantage of the pick-up technique is the large tray holes and long guide screws, which make them difficult to use in mouths with opening restrictions and in the posterior areas.13,14 However, a tray design was developed to make it faster and easier to take impressions of dental implants. The self-perforating tray holds a thin plastic film on the occlusal surface, allowing it to be perforated by the transfers during tray positioning. This feature leads to a clean and precise impression, without excess material on abutments.15 Despite all its advantages, the accuracy of impressions obtained with the self-perforating tray is still controversial.15 Furthermore, there are no reports evaluating the use of this new technology for maxillary impressions. Several studies reported the influence of impression technique and implant position on the accuracy of dental casts.16-23 With this regard, gap measurements are commonly used to evaluate the fit of implants; hence, most studies use the gap width to evaluate the marginal discrepancy.1,9,24,25 Thus, the aim of this study was to evaluate the accuracy of the self-perforating tray for taking an implant impression of the edentulous maxilla when compared with the conventional pick-up technique. The null hypothesis was that there would be no difference in accuracy between the two types of trays for maxillary implant impressions. MATERIAL AND METHODS Sample preparation An acrylic resin master model representing an edentulous maxilla was used in this study. Perforations were made in the region of the canine and first molar (13,16,23,26), in which 4 implants (Straumann, Basel, Switzerland) were fixed with utility wax (Epoxiglass, Diadema, Brazil), as shown in Figure 1. The implant on tooth 13 was kept as reference (IR) for screw tightening and the remaining implants were evaluated (Tooth 16= I1, 23= I2, and 26= I3). Figure 1 | Master model. Bohner L • Marques ADA • Keedi CB • Steagall W • Tortamano Neto P • Clin Lab Res Den 2017: 1-7 ● 3 A cobalt-chromium bar was fabricated using a wax pattern (S-U-Flexible Wax; Schuler-Dental) and cast in cobalt chromium alloy (Remanium 2000; Dentaurum J.P. Winkelstroeter KG). Posteriorly, the bar was screw-retained onto the implants. Toensure an optimal fit, the implants were firstly removed from the model to be individually fixed to the bar. After that, the whole set was fixed to the model using acrylic resin. Subsequently, the entire set was repositioned in the perforations and the implants were fixed to the master model with acrylic resin.15 Impression procedures Two types of impression trays were evaluated (n = 7): Customized open impression trays (G1 Control group) and pre-fabricated selfperforating impression trays (G2 Test group). For the conventional open tray group, individual trays with perforations at the site of the impression copings were fabricated with acrylic resin (Jet, Clássico, São Paulo, Brazil). One tray was used to each impression. Likewise, for the self-perforating group, as the film was perforated after use, a new tray was obtained (Miratray Implant, Hager and Werken GmbH) to each impression (Figure 2). Figure 2 | Self-perforating tray. Firstly, the impression copings (Square transfer, 4.5, Conexão, São Paulo, Brazil) were positioned on the implants and an adhesive (Universal Tray Adhesive, Zhermack, Rome, Italy) was applied to the trays. For both groups, impressions were taken with polyvinyl siloxane (Express, 3M ESPE, St. Paul, USA), manipulated according to the manufacturer’s instructions. After impressiontaking, implant analogs were positioned on the transfer components and dental stone (Type IV, Durone, Dentsply, Petrópolis, Brazil) was poured, after being mixed in accordance with the manufacturer̀ s instructions. Dental casts were stored at 37 °C for 2 weeks. Accuracy analysis For both groups, the metal bar was adapted to each cast model, to analyze the fit accuracy Accuracy of self-perforating impression tray for maxillary dental implant 4 ● Clin Lab Res Den 2017: 1-7 between the bar and the implants. The bar was tightened on implant IR with a torque of 30 Ncm, and the vertical distance between the implant and the bar was measured in implants I1, I2, and I3. The gap was evaluated with a stereomicroscope (40x magnification, Zeiss SV11, Carl Zeiss, Jena, Germany). Measurements were taken in the entire gap and the mean value was calculated and determined as the value of the gap (Figure 3). For each implant, measurements were performed 3 times by the same examiner at intervals of one week. The final gap was defined as the average value of these measurements. The effects of “Tray type” and “Position of implants” were assessed by ANOVA repeated measures and Tukey tests. The T-test was used to evaluate the effect of “Tray type” for each implant. Statistical analysis was performed with the software SPSS 20 (IBM Corp., Chicago, USA) at a level of significance p = 0.05. Figure 3 | Measurement area to determine the mean gap value. RESULTS All data presented variance normality and homogeneity, and were described as mean value ± standard deviation (Table 1, Figure 4). The tray type presented no statistically significant difference (p = 0.192), and no relationship was found between the tray and the implant position (p = 0.224). However, when analyzing the factor “Tray type” individually, implant I1 showed a lower gap value for G1 compared with G2 (p = 0.019). Table 1 | Mean± Standard Deviation (SD) and Confidence of Interval 95% (IC 95%) of the mean gap for customized (G1) and self-perforating (G2) trays according to the different implant locations (I1, I2, I3). I1 I2 I3 p Mean±SD IC 95% Mean±SD IC 95% Mean±SD IC95% G1 73.31±26.01* 49.26; 97.37 149.16±53.90 99.30; 199.02 115.46±73.34 41.63;183.30 >0.05 G2 154.41±74.64 85.37; 223.44 159.45±87.64 78.39; 240.51 109.28±49.18 61.28;155.26 >0.05