Effect of fabrication methods and number of supporting teeth on the surface accuracy and dimensional stability of implant surgical guides.

Statement of problem: Implant surgical guides manufactured using different fabrication methods have been commonly used for computer-guided implant placement. However, how fabrication methods and the number of supporting teeth influence accuracy and stability remains uncertain.

Purpose: The purpose of this in vitro study was to evaluate the influence of fabrication methods and number of supporting teeth on the surface accuracy and dimensional stability of implant surgical guides with 3 different 3-dimensional (3D) printers and 1 computer numeric controlled (CNC) milling machine.

Material and methods: Two tooth-supported maxillary implant surgical guides with different number of supporting teeth (S: short span with 4 supporting teeth, L: long span with complete arch supporting) were used to fabricate the specimens. Eighty surgical guides were fabricated from 3 different 3D printers and 1 milling machine as follows: group SLA-S (n=10) and SLA-L (n=10) were fabricated with a desktop stereolithography (SLA) 3D printer and photopolymerizing resin; group PolyJet-S (n=10) and PolyJet-L (n=10) were fabricated with a PolyJet 3D printer and photopolymerizing resins; group DLP-S (n=10) and DLP-L (n=10) were fabricated with a desktop digital light processing (DLP) 3D printer and photopolymerizing resin; and group MILL-S (n=10) and group MILL-L (n=10) were fabricated with a 5-axis milling machine and polymethyl methacrylate (PMMA) blanks. All surgical guides were digitized immediately after postprocessing and after 1, 2, and 3 months using a desktop scanner. The congruency between design files and digitized files was quantified with the root mean square (RMS) error with a metrology program (Geomagic Control X). Two-way ANOVA was used to analyze trueness, and the Levene test was used to assess precision (α=.05).

Results: The fabrication methods and number of supporting teeth significantly affected the surface trueness of the guide (P<.001). Milled guides had the lowest mean RMS value for surface trueness, 45 µm for guides with 4 supporting teeth and 59 µm for guides with complete arch supporting. Regarding precision, the Levene test revealed significant difference among fabrication methods (P<.05), while no significant difference was found in the same fabrication method group (P>.05). After 3 months of storage, RMS values increased significantly in the complete arch supporting group comparison of SLA, PolyJet, and DLP (P<.001, P<.001, and P=.015, respectively). RMS values remained similar in other groups.

Conclusions: The trueness and dimensional stability of the surface of the implant surgical guides were affected by fabrication methods and the number of supporting teeth. However, the precision was only affected by fabrication methods. Milled surgical guides showed higher accuracy and better dimensional stability after storage than those produced with 3D printers. Among the groups of 3D printing, guides with 4 supporting teeth showed higher trueness and a lower degree of deformation after storage.