## 4 Discussion
However, it is important to note that this resin is not intended for long-term use in the oral cavity, and this was an important factor to consider as per the manufacturer's instructions to optimise the mechanical properties of the guides, which are only used during the surgical placement of the implants. Nonetheless, their accuracy varied significantly, with the DentaClear resin demonstrating improved dimensional accuracy compared to the DentaGuide, which consistently produced undersized surgical guides. Both resins, as per the manufacturer's specifications, are composed of 7,7,9(or 7,9,9)-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecane-1,16-diylbismethacrylate and tetrahydrofuranyl methacrylate polymer resins, with Diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide as a photoinitiator. Despite their identical composition, the DentaClear produced translucent surgical guides, while the DentaGuide produced significantly more opaque ones (Figure 6). The difference in opacity, and consequent light penetration, polymerisation, and degree of conversion between these otherwise identical resins may account for the detected variation in accuracy. Whilst the maxillary surgical guide was larger in size than the mandibular one, it was evident that the size difference was insufficient to produce any significant errors. This study followed the manufacturer's instructions for using both resins in terms of washing and post-processing whilst testing alternative approaches. For the washing of the guides, the DentaClear guides were handwashed for 5 min, instead of 2.5 min, to allow for direct comparison against the DentaGuide guides, which were also washed for 5 min. The results of this study demonstrated no statistically significant difference between handwashing, ultrasonic washing, or a combination of both washing techniques. Thus, it is not likely that the washing method alone can significantly impact the dimensional accuracy of implant surgical guides. The findings of this study also identified that using nitrogen during the post-curing significantly impacted accuracy, with the guides post-cured with the presence of nitrogen gas in the UV curing unit demonstrating higher dimensional accuracy regardless of the resin type and post-processing washing technique used. Indeed, the manufacturer's instructions for both DentaClear and DentaGuide resins recommend using nitrogen for post-curing. It was evident from this study that post-curing the surgical guides with nitrogen showed statistically significant results in terms of dimensional accuracy for both precision and trueness. Similar results of improved mechanical properties when using nitrogen for post-curing were also reported by [PERSON] et al. [21], who investigated 3D-printed occlusal splints. Their study showed that splints post-cured with nitrogen had improved monomer conversion and hardness according to Vickers hardness score. Figure 6: Upper implant surgical guides in both resins: (**a**) DentaClear; (**b**) DentaGuide. (**c**) Lower surgical guide in DentaGuide resin. Whilst all samples, irrespective of resin type, location, or post-processing technique, demonstrated a discrepancy, that discrepancy remained <70 \(\upmu\)m. Previous studies investigating implant-supported complete dental prostheses or hybrid bridges concluded that a maximum acceptable threshold of fit between the prostheses platform and the dental implants ranges between 59-150 \(\upmu\)m. As such, the surgical guides assessed in this study remain within the clinically acceptable threshold for implant placement. It is critical that the surgical drill and the guide hole are a suitable match with minimal tolerance to ensure implant placement in the prosthetically planned location. The placement of a metal sleeve or manual adjustment of the drill hole results in the introduction of errors into the surgical guide. Henceforth, identifying and accounting for any manufacturing errors of surgical splints is important. The type of cleaning medium can also have an impact on the properties of the resultant print.