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Surface Quality of Direct Composite Resin Restorations Fabricated Using Different Resin Injection Guides
The International Journal of Prosthodontics
|January 16, 2026
Summary
Resin injection guides (RIGs) improve composite resin restoration quality. 3D-printed guides (FR, RG) offer superior microhardness and conversion degree compared to freehand or PVS methods, though surface roughness varies.
Area of Science:
- Dental Materials Science
- Biomaterials Engineering
- Restorative Dentistry
Background:
- Direct composite resin restorations are fundamental in modern dentistry.
- Achieving optimal surface properties and material integrity is crucial for restoration longevity.
- The oxygen inhibition layer can negatively affect the surface properties of composite resins.
Purpose of the Study:
- To investigate the influence of various resin injection guides (RIGs) on surface roughness (Ra), microhardness (MH), and conversion degree (CD) of direct composite restorations.
- To compare the performance of freehand filling against different types of RIGs.
- To determine which RIG design yields the best material properties for composite restorations.
Main Methods:
- Disc-shaped specimens were fabricated using five methods: freehand (FH), polyester strip (PS), polyvinyl siloxane guide (PVS), flexible resin guide with rigid shell (FR), and rigid resin guide (RG).
- Surface roughness (Ra) was assessed using a tribometer.
- Microhardness (MH) and conversion degree (CD) were measured using a microhardness tester and Fourier transform infrared spectroscopy, respectively.
- Statistical analysis was performed using ANOVA and post hoc tests.
Main Results:
- Significant differences in surface roughness were observed, with the order PS < FH < PVS < FR < RG.
- The polyester strip (PS), flexible resin (FR), and rigid resin (RG) guides showed comparable, high microhardness and conversion degree.
- These values were significantly higher than those achieved with freehand (FH) and polyvinyl siloxane (PVS) methods.
- The PVS group demonstrated higher microhardness and conversion degree than the freehand group.
Conclusions:
- Resin injection guides effectively prevent the oxygen inhibition layer, enhancing microhardness and conversion degree by up to 22% compared to freehand placement.
- While all RIGs increased surface roughness relative to the polyester strip, the PVS guide yielded the smoothest surfaces among the tested guides.
- 3D-printed guides (FR, RG) demonstrated superior microhardness and conversion degree compared to the PVS guide and freehand technique.
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