THE NETFIL MESH TOOL FOR REINFORCING HAND SCULPTED COMPOSITE

A crucial aspect of evaluating the mechanical reliability of composite veneers and bridges is not merely to measure the enhancement of modulus or nominal strength, but a deeper understanding of their stress states and their relation to the fracture toughness of the dental restoration or prosthesis. 

Owing to its geometry, a very thin section of a dental composite laminate veneer operates predominantly under a state of in-plane stress rather than in-plane strain.¹,² This distinction is fundamental because, under a state of in-plane stress, stresses are distributed primarily within the plane of the veneer, allowing greater strain accommodation within the composite material.¹,² This, in turn, reduces the likelihood of catastrophic fracture during bending, as predicted by classical fracture mechanics.¹,²

However, a slightly thicker section of the same composite laminate veneer operates predominantly under a state of in-plane strain rather than in-plane stress.¹,² Under a state of in-plane strain, stresses act across the thickness of the veneer (perpendicular to its surface), and deformation or bending through the thickness of the veneer is restricted.¹,² This leads to the development of additional, highly constrained internal stresses, which increase with the thickness of the composite veneer section.¹,² Consequently, only limited strain accommodation or flexion is possible in a thick cross-section of a composite veneer, increasing the likelihood of catastrophic fracture, as predicted by classical fracture mechanics.¹,²,³

It is well known that dental composite laminate veneers rarely possess uniform thickness. Rather, their geometry typically includes both thinner and thicker cross-sections, depending on tooth morphology and preparation design.⁴,⁵,⁶ As a result, different sections of the same dental composite veneer may experience different mechanical stress states.¹,⁴,⁵ Some sections of the veneer may be under a state of in-plane stress, while others may be closer to a state of in-plane strain.¹,² This geometric variability makes it difficult to determine how many different stress states may exist within the same veneer and suggests that the fracture mechanics governing crack initiation and propagation may vary across different cross-sections of a dental composite laminate veneer.¹,²,⁴,⁵

It is also well known that bonding between incremental layers of dental composite occurs primarily through chemical bonding, resulting from polymer chain interdiffusion and covalent bond formation across the oxygen-inhibited layer during the placement of subsequent increments.⁷,⁸

 Despite this chemical bonding, the interface between successive composite layers can exhibit a considerable degree of interlayer shear compliance.⁸,⁹ As a result, interlayer slip can occur under high strain-rate loading conditions.⁸,⁹ Therefore, material properties such as bending stiffness and fracture toughness of a composite veneer can be simultaneously influenced by the increased stiffness of thicker sections of the composite veneer, which are closer to a state of in-plane strain.¹,³,⁹

Therefore, the very presence of mixed stress states in a dental composite veneer or any other dental restoration may make it highly brittle or mechanically unpredictable.¹,²,⁵ Cyclic deformation during mastication may significantly increase cyclic strain and fatigue loading in a dental composite laminate veneer.¹⁰,¹¹,¹² Over time, cyclic bending promotes crack initiation and propagation, which may ultimately result in fracture of the dental composite veneer during clinical service.¹⁰,¹¹,¹² Such fracture failure may occur even when the elastic modulus and flexural strength of the dental composite resin veneer are optimal.¹⁰,¹¹,¹² This may simply be due to the presence of mixed stress states within the veneer.¹,²,¹⁰

1. Kotousov A, Lazzarin P, Berto F, Harding S. Effect of the thickness on elastic deformation and quasi-brittle fracture of plate components. Engineering Fracture Mechanics. 2010;77(11):1665–1681. https://doi.org/10.1016/j.engfracmech.2010.04.008

2. Folias ES. On the three-dimensional theory of cracked plates. Journal of Applied Mechanics. 1975;42(3):663–674. https://doi.org/10.1115/1.3423660

3. Tribst JPM, Tach Q, de Kok P, Dal Piva AMO, Kuijs RH, Kleverlaan CJ. Thickness and substrate effect on the mechanical behaviour of direct occlusal veneers. International Dental Journal. 2023;73(5):612–619. https://doi.org/10.1016/j.identj.2022.11.006

4. Li Z, Yang Z, Zuo L, Meng Y. A three-dimensional finite element study on anterior laminate veneers with different incisal preparations. Journal of Prosthetic Dentistry. 2014;112(2):325–333. https://doi.org/10.1016/j.prosdent.2013.09.023

5. Kintopp CCA, Diógenes AN, Lopes RT, et al. Stress distribution on teeth restored with veneers using various incisal preparation designs: A 3D finite element analysis study. Journal of Prosthetic Dentistry. 2024;131(6):1159.e1–1159.e10. https://doi.org/10.1016/j.prosdent.2024.03.005

6. Luo T, Xiang Q, Wu J, Shui Y, Yu H. Effect of injection guide design on the accuracy of direct composite veneers: An in vitro study. Journal of Esthetic and Restorative Dentistry. 2026;38(7):1376–1385. https://doi.org/10.1111/jerd.70135

7. Shawkat ES, Shortall AC, Addison O, Palin WM. Oxygen inhibition and incremental layer bond strengths of resin composites. Dental Materials. 2009;25(11):1338–1346. https://doi.org/10.1016/j.dental.2009.06.003

8. Bijelic-Donova J, Garoushi S, Lassila LVJ, Vallittu PK. Oxygen inhibition layer of composite resins: Effects of layer thickness and surface layer treatment on the interlayer bond strength. European Journal of Oral Sciences. 2015;123(1):53–60. https://doi.org/10.1111/eos.12167

9. Kovarik RE, Ergle JW. Fracture toughness of posterior composite resins fabricated by incremental layering. Journal of Prosthetic Dentistry. 1993;69(6):557–560. https://doi.org/10.1016/0022-3913(93)90280-2

10. Arola D. Fatigue testing of biomaterials and their interfaces. Dental Materials. 2017;33(4):367–381. https://doi.org/10.1016/j.dental.2017.01.012

11. Loughran GM, Versluis A, Douglas WH. Evaluation of sub-critical fatigue crack propagation in a restorative composite. Dental Materials. 2005;21(3):252–261. https://doi.org/10.1016/j.dental.2004.04.005

12. Shah MB, Ferracane JL, Kruzic JJ. Mechanistic aspects of fatigue crack growth behavior in resin based dental restorative composites. Dental Materials. 2009;25(7):909–916. https://doi.org/10.1016/j.dental.2009.01.097

Depending on clinical requirements, dental composite veneers invariably need to be made thicker and may transition towards a state of in-plane strain, with more constrained geometries that unfortunately allow fracture mechanics to play a significant role in determining their longevity.

In clinical practice, dental composite laminate veneers rarely possess a perfectly uniform cross-sectional thickness. This is because esthetic requirements, tooth morphology, and preparation design inevitably result in thicker cross-sections in certain areas. Designing a uniformly thick composite veneer that remains entirely under a state of in-plane stress is therefore not practically possible.

Under a state of in-plane strain, it is well known that crack-tip constraint increases and the local stress state becomes more triaxial. This significantly reduces the ability of thicker sections of composite to accommodate deformation without cracking. 

Under such constrained conditions, defects such as pores or voids, which act as severe stress concentrators, can readily initiate cracks. Nanoporosity within dental composites therefore becomes highly undesirable, particularly in the thicker cross-sections of a composite restoration or veneer that are under a state of in-plane strain. 

Consequently, minimizing nanoporosity and molecular scale defects such as free volume voids within dental composite pastes and liquids using our Netfil process, becomes an important modality and requirement for improving the surface profile, fracture toughness and durability of chairside hand-sculpted or 3D-printed dental composite laminate veneers.

The true performance of a dental composite restoration or veneer therefore depends not only on the fracture toughness of the composite material itself but also on the various fracture-toughening mechanisms and features comprehensively employed to make the veneer more resistant to fracture. 

In the oral environment, dental composite veneers are repeatedly exposed to high-strain-rate loading conditions generated by rapid and intermittent masticatory forces. Occlusal loading can occur over very short periods, and materials that lack adequate stiffness and fracture toughness may fail unpredictably in a brittle manner, despite possessing optimal ultimate strength values.

In this context, our Netfil Mesh Composite Stencil Tool perfectly complements our Netfil nanoporosity-reducing process and offers a novel, convenient and fibre-free strategy to reinforce and toughen highly esthetic dental composites without interfering with their esthetic qualities, such as shade and color.

Though 3D-printed restorations are gaining popularity, hand-sculpted chairside composite veneers still offer some unique advantages that are not yet available with 3D-printed veneers. A dentist or dental technician can use multiple shades or translucencies of composite to create a more esthetic composite veneer that matches adjacent natural teeth even more closely.

Simply by introducing our Netfil Mesh Tool keys uniformly into every composite layer, an effective stress-coupling and fracture-toughening mechanism can be built into the dental composite veneer. Our Netfil Mesh Tool serves as a composite paste texturing stencil, helping skilled dentists and dental technicians introduce uniform Netfil macro-keys onto individual composite layers.

Once the dentist or dental technician finally cures the composite build-up, the resulting composite veneer becomes a macro-mechanically unified and reinforced structure, with improved apparent bending stiffness and fracture toughness.

The size and scale of our Netfil Mesh macro-keys are crucial for enabling the efficient transfer or redistribution of stresses and for facilitating composite fracture-toughening mechanisms. On the other hand, introducing mechanical keys that are too small or fall below a certain size threshold can lead to stress amplification during functional loading and subsequent fracture of the composite veneer.

The goal is to introduce the maximum possible number of Netfil Mesh Tool stencil texture keys into each and every layer of composite paste without distorting the overall shape of the composite build-up.

Our Netfil Mesh composite paste stencil tool has zero memory and offers unsurpassed flexibility and convenience, allowing dentists and dental technicians to texture the composite paste layer by layer.

It is worth noting that 3D-printing a composite veneer using our macro-textured Glimmer Film would produce only flat, textured layers rather than layers that follow the natural surface contours of the dental composite veneer.

When meticulously employed, our Netfil Mesh Tool concept reduces both stress concentrations and shear compliance in the composite laminate veneer. Its macro-mechanical keys also serve as an inbuilt fracture-toughening mechanism, making the dental composite veneer less susceptible to fracture.

The optical properties and esthetic characteristics of the composite remain unaffected by our process.

Composite reinforcing or toughening mechanisms may become counterproductive if they are not implemented properly. We see that even nature takes its time in creating tooth material that is fracture-tough and capable of lasting a lifetime. It is well known that tooth material is hierarchical in nature and is not isotropic like dental composites. 

Nature follows a carefully orchestrated sequence in forming tooth material, ensuring that layer tolerances and thicknesses are respected. Although there is some room for variation, the deviations are not excessively large or significant enough to result in substantial stress concentrations or stress build-up within the tooth material. The very same principles followed by nature are also applicable to the design of a Netfil bioinspired composite veneer.

 Composite paste should be carefully applied so that each textured composite layer introduced is a well-defined layer of its own. The meticulous attention to detail involved in this process goes a long way towards designing a highly stress-free Netfil bioinspired composite veneer.

Our NETFIL Mesh Stencil Tool may be used in conjunction with our NETFIL-processed chairside resin; however, this is not an absolute requirement. Our strategy can be employed with any condensable composite paste available on the market to design a Netfil bioinspired veneer. 

By significantly reducing intrinsic nanoporosity through our NETFIL process, we improve the flexural modulus (E) of the resin composite and also reduce its surface roughness parameter, Ra (arithmetic average roughness).

At this point, it is important to mention that simply removing nanoporosity from the resin composite can substantially improve the bending stiffness of a composite veneer. This is because the theoretical bending stiffness (EI) is equal to E × I, where E represents the elastic modulus of the composite resin and I represents the second moment of area. A higher theoretical bending stiffness, combined with the absence of pores, makes the composite veneer less susceptible to crack initiation and unstable crack growth. The suppression of internal flaw populations therefore delays the onset of fracture-driven failure.