# Comparison of marginal gap in implant-supported hybrid nanoceramic crowns fabricated by additive vs. subtractive manufacturing

## TL;DR

This study compares the precision of 3D printed and milled hybrid nanoceramic crowns, finding that milling produces smaller gaps, which may improve long-term dental outcomes.

## Contribution

The study introduces a comparison of additive and subtractive manufacturing for a new class of hybrid nanoceramic crowns.

## Key findings

- Milled crowns had significantly smaller marginal gaps than 3D printed ones before and after aging.
- 3D printed crowns showed larger gaps (59.71 and 63.83 μm) compared to milled ones (34.08 and 37.76 μm).
- Milling technique provided superior marginal fit for hybrid nanoceramic crowns.

## Abstract

Achieving optimal marginal accuracy is a critical factor in the long-term success of implant-supported crowns. The purpose of this study was to evaluate and compare the marginal gap of implant-supported novel hybrid nanoceramic crowns, Nanoksa G-Plus and Nanoksa BioGuard, which are innovative due to their unique composition when manufactured using two distinct digital workflows—milling and 3D printing—to determine which technique provides superior precision for this new class of restorative materials.

Twenty implant fixtures were embedded into epoxy resin blocks. Stock straight titanium abutment was screwed to each fixture according to manufacturer recommendations. The samples were divided into 2 groups according to the technique of fabrication of Nanoksa hybrid nanoceramic crowns (n = 10/group). Group I subtractive technique using Nanoksa G Plus discs and group II additive technique using Nanoksa BioGuard. Stock abutments were scanned using a laboratory scanner, the crowns were fabricated and cemented with resin cement after pretreatment of all crowns according to manufacturer recommendation. Using a stereomicroscope (35X), the marginal gaps were assessed both prior to cementation and following thermomechanical accelerated aging. Mean values were calculated, and differences between groups were tested for statistical significance using paired t-test and Student t-test. A value of (P < 0.05) was considered statistically significant.

Significant differences were detected in the marginal gaps between the groups. Before cementation and following thermomechanical accelerated aging, 3D printing crowns showed a statistically significant larger marginal gap distance (59.71 and 63.83 μm, respectively) than the milled one (34.08 and 37.76 μm).

The milling technique demonstrated significantly lower discrepancy values compared to additive technique, indicating superior marginal fit for Nanoksa hybrid nanoceramic crowns. Clinically, these findings suggest that utilizing milling for these restorations may enhance long-term outcomes by reducing the risks associated with larger gaps.