Hoda Abdellatif BDS, MPH, DrPH; Sarah Gray DDS, MS; Steven Jefferies MS, DDS, PhD
Both polyether and vinyl polysiloxane are effective materials for taking implant impressions, but there is no clinical evidence that one works better than the other.
This review considered only in-vitro studies and provided limited evidence on the factors that determine the accuracy of implant impressions.
How do various materials and techniques affect the accuracy of implant impressions?
The authors searched three databases from their through June 2008, for English-language articles published in peer-reviewed journals. The authors also hand-searched eight independent journals published between January 1980 and May 2008. The authors included experimental studies that investigated the accuracy of implant impressions. The authors excluded clinical or technical reports that described a particular material or technique, and structurally incomplete publications such as abstracts and review articles. Outcomes assessed included impression accuracy using various impression materials and techniques, and with implants of varying depth and angulation.
The initial search yielded 41 articles, all of which were in-vitro studies. Of the 17 studies comparing the accuracy between the splint and nonsplint techniques, seven advocated the splint technique, three advocated the nonsplint technique, and seven reported no difference. Fourteen studies compared the accuracy of pick-up and transfer impression techniques. Five showed more accuracy with the pick-up technique, two with the transfer technique, and seven showed no difference. For impressions of four or more implants, more studies (five versus one) showed higher accuracy with the pick-up technique, while three studies showed no difference. Four studies investigated the snap-fit technique. Two found it more accurate than the pick-up technique, one found it more accurate than the transfer technique, and one found no difference between the snap-fit and pick-up techniques. Ten of 11 studies that compared the accuracy of polyether versus vinyl polysiloxane (VPS) impression materials showed no difference, while the remaining study favored VPS. Of the four studies that examined implant angulation, two showed increased accuracy with straight implants while the others showed no angulation effect.
Both polyether and vinyl polysiloxane were effective materials for taking implant impressions. For impressions involving four or more implants, several studies indicated that impressions may be more accurate with the pick-up technique than with the transfer technique.
Source of Funding:
Importance and Context:
An accurate dental impression is necessary to ensure the proper fit of a dental prosthesis, particularly over dental implants. A misfit prosthesis could cause a screw to loosen or fracture, result in occlusal inaccuracy and even implant failure. Numerous clinical factors can affect impression accuracy, including materials and techniques, coping design, and implant number and positioning. As the use of implants becomes more prevalent, practitioners need to find reliable methods for making accurate impressions to ensure the success of overlying prostheses.
Strengths and Weaknesses of the Systematic Review:
The authors used acceptable methods to search for, select and analyze the evidence. They limited inclusion and exclusion criteria to experimental in-vitro studies in English-language journals. They did not adequately evaluate the studies for bias or heterogeneity. The authors provided a list of studies and the characteristics of those studies, but their review methodology was limited. They also did not assess the validaty of the findings of the included studies. There was no formal quality assessment of the articles, and it lacked several standard steps in conducting and reporting systematic reviews. Because of heterogeneity, the authors did not perform statistical analyses. Thus, they based their conclusions on mean differences. To strengthen this review, the authors should have included studies published in non-English-language journals, limited the number of outcomes they assessed, and controlled for variables such as implant type.
Strengths and Weaknesses of the Evidence:
Studies evaluated were in-vitro experimental comparisons. Although designed to provide clinically relevant measures, their value is limited when compared to randomized controlled studies on human subjects. The lack of a clinical question made it difficult to evaluate the evidence. Because of both the poor quality and quantity of the evidence, the authors could not make reliable conclusions about implant impression techniques. Findings were inconsistent across all studies except the impression material studies. The authors cited one study as "not clinically relevant.” Results from more recent studies tended to be more consistent.
Implications for Dental Practice:
At this time, there is no clinical evidence to support the use of one impression material, or impression technique, over another for taking implant impressions.