Evaluation of Transfer Impressions for Osseointegrated Implants at Various Angulations

Evaluation of Transfer Impressions for Osseointegrated Implants at Various Angulations
Implant Dentistry: Volume 13(4) 2004 pp 358-366
Assuncao, Wirley Gon??alves DDS, MS, PhD*; Filho, Humberto Gennari DDS, MS, PhDÇƒÜ; Zaniquelli, Osvaldo DDS, MS, PhD
Lippincott Williams & Wilkins
Abstract
The accuracy of impressions that transfer the relationship of the implant to the metal framework of the prosthesis continues to be a problem. This study was designed to evaluate the accuracy of the transfer process under variable conditions with regard to implant analog angulations, impression materials, and techniques. Replicas (n = 60) of a metal matrix (control) containing four implants at 90¨?, 80¨?, 75¨?, and 65¨? in relation to the horizontal surface were obtained by using three impression techniques: T1-indirect technique with conical copings in closed trays; T2-direct technique with square copings in open trays; and T3-square copings splinted with autopolymerizing acrylic resin; and four elastomers: P-polysulfide; I-polyether; A-addition silicone; and Z-condensation silicone. The values of the implant analog angulations were assessed by a profilometer to the nearest 0.017¨?, then submitted to analysis of variance for comparisons at significance of 5% (P < .05). For implant analog at 90¨?, the material A associated with T2 and material Z with T3 behaved differently (P < .05) from all groups. At 80¨?, all materials behaved differently (P < .01) with T1. At 75¨?, when T1 was associated, materials P and A showed similar behavior, as well as materials I and Z; however, P and A were different from I and Z (P < .01). When T3 was associated, all experimental groups behaved differently among them (P < .01). At 65¨?, the materials P and Z behaved differently (P < .01) from the control group with T1, T2, and T3; the materials I and A behaved differently from the control group (P < .01) when T1 and T2, respectively, were associated. The more perpendicular the implant analog angulation is in relation to the horizontal surface, the more accurate the impression. The best materials were material I and A and the most satisfactory technique was technique 3.
One of the major concerns in implant-retained prostheses is with regard to the accuracy of impressions. This plays an essential role in prosthesis-implant adaptation. An accurate working cast for prosthesis components that have optimal adaptation depends on the impression material as well as the transfer techniques. Furthermore, problems related to investing, casting, alloy properties, and clinician skill should not be neglected.
According to Waskewicz et al.1 and Lorenzoni et al.,2 the original implant position and orientation must be reproduced in the working cast so that best prosthesis fit may be achieved without interfering in the path of prosthesis placement.
Indeed, the impression of implant-retained prosthetic components accounts for providing the transfer of the implant positions from the oral cavity to the working cast.3 However, not only are there a great variety of prosthetic components (conical and square), but also many impression techniques designed for each type of component, demanding an investigation into the quality of these procedures so that the most desirable technique may be indicated or perhaps even a new approach may be developed.
As far as impression materials and techniques are concerned, the splinting of square copings for a transfer impression to ensure desirable results regardless of the kind of impression materials has been recorded in the literature.4-6 However, some authors7-9 found no statistically significant difference for transfer impressions using splinted or isolated copings. The splinting material and technique used may also be different, including light-cure composite,10 direct splinting in the impression tray with autopolymerizing acrylic resin,11 and roughening of square copings by coating adhesive in the tray.12 Besides, different implant angulations in relation to the alveolar ridge may also influence the accuracy of the impression. The magnitude of this effect is still unclear.
The purpose of this study was to evaluate the effect of various implant angulations on the accuracy of implant impression transfers. The parameters studied included different impression transfer techniques and materials.
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