The effect of different implant impression splinting techniques and time on the dimensional accuracy: An in vitro study

Background: Splinting of impression copings is generally recommended for complex implant-supported restorations. It can also be used in the digital workflow when a control model is needed to improve the fit of the prosthesis. However, there is a lack of knowledge on how dimensional accuracy is affected by different splinting techniques and time factors. Objectives: To evaluate the time factor on the dimensional stability of different implant impression splinting techniques used in the conventional and digital workflow. Materials and methods: Ten pairs of implant analogs were fixed to a stainless steel bar. Modified impression copings were connected to the analogs and eight splinting strategies evaluated (n=10): (1) type I impression plaster (PLA), (2) autopolymerizing acrylic resin, cut and rejoin technique (PTR), (3) light-cured acrylic resin, cut and rejoin technique (ILC), (4) light-cured acrylic resin, no cutting and rejoining (ILN), (5) VPS bite registration material (SBR), (6) bis-acryl bite registration material (LXB), (7) bis-acryl composite resin (PTP), (8) 3D printed splint (3DP). In each group, the position of modified impression copings was scanned with a laboratory scanner at different time points: (1) unsplinted impression copings (baseline), (2) 2 h after splinting, (3) 24 h after splinting. Modified impression coping design allowed using metrology software to measure and compare distance, vertical, angle and rotational deviations between impression copings. Results: All types of splints showed dimensional deviations. After 2 h of splinting, the lowest distance deviation was recorded in PTR (15.4 +/- 6.15 mu m), vertical deviation - in ILC (19.2 +/- 27.37 mu m), angle deviation - in ILC (0.08 +/- 0.1.), rotation - in LXB (0.2 +/- 0.24.) groups. Comparing results 2 and 24 h after connection of impression copings, statistically significant deviations in the distance were recorded in groups PLA (-5.6 +/- 5.95 mu m), PTR (5.5 +/- 7.01 mu m), ILN (19.2 +/- 14.26 mu m), PTP (23.8 +/- 12.55 mu m). Conclusions: The best dimensional accuracy was observed in the ILC group, followed by PTR and 3DP groups. Clinical significance: Proper selection of splinting technique and polymerization time can increase the accuracy of conventional or digital impressions. Splinting techniques with rigid materials, proper polymerization and compensating for material shrinkage seem to produce the best results.