Wear resistance of contemporary composite materials: evidence and clinical decisions

Composite wear is a loss of material under interacting mechanical and chemical conditions. It matters for contour, contacts and maintenance, but a wear measurement is not a restoration-survival estimate. Choose a restorative system for the tooth, preparation, opposing surface and patient, then follow its instructions for placement, bonding and polishing. Neither a “nano” label nor industrial polymerization guarantees the longest clinical service.

What wears, and how?

Two-body abrasion involves direct contact between surfaces; three-body abrasion includes an intervening abrasive medium. Repeated loading can contribute to fatigue damage and particle loss. Chemical exposure and water can alter the resin matrix or filler interface and interact with mechanical loading. In natural teeth, attrition, abrasion and erosive tooth wear describe related but distinct processes. Enamel dissolution should not be treated as identical to polymer degradation. The original biodegradation study by de Paula and colleagues tested restorative materials experimentally, rather than measuring patients’ annual wear. [de Paula]

Force, contact geometry, sliding, antagonist roughness, lubrication, exposure time and chemical conditions all matter. A high force in one test does not reproduce every aspect of bruxism. The worn restoration and its opposing tooth must be assessed separately: low material loss can coexist with appreciable antagonist wear. D’Arcangelo and colleagues’ ceramic–enamel comparison is laboratory evidence, not a clinical ranking of all composites. [D’Arcangelo]

Composition is a starting point, not a league table

Matrix chemistry, conversion, filler loading and distribution, filler–matrix coupling, porosity and surface treatment work together. Bis-GMA-, UDMA-, silorane- and organically modified ceramic systems cannot be ranked clinically from monomer names alone. Smaller particles may help some surface properties, but size and filler percentage do not by themselves establish wear resistance. Ferracane’s analysis and the Academy of Dental Materials guidance distinguish laboratory material properties from the clinical outcomes they are sometimes asked to predict. [Ferracane] [Ilie]

• Microhybrid, nanohybrid and nanofilled direct composites: these labels describe aspects of formulation, not universal annual wear rates. Select products indicated for the intended restoration, supported by relevant evidence and a feasible curing protocol.
• Bulk-fill composites: allowable increment depth and any required occlusal capping layer are product-specific. “Flowable” does not automatically mean every product needs the same cap, and “bulk-fill” does not authorize an arbitrary 4–5 mm increment under every light or shade.
• Fiber-reinforced composites: coverage and the intended core or surface application matter. For example, GC specifies everX Posterior as dentin replacement covered with light-cured restorative composite; it is not an exposed surface layer. Fracture reinforcement should not be presented as proof of lower occlusal wear. [everX Posterior]
• CAD/CAM resin composites and polymer-infiltrated ceramic networks: these are not interchangeable structures. VITA Enamic is a polymer-infiltrated ceramic network; Lava Ultimate is a resin-matrix material containing ceramic fillers. Processing, machinability and reparability need to be considered alongside bonding and clinical indication. [Ruse and Sadoun]

Low-shrinkage chemistry is also a different endpoint: Kruly and colleagues’ meta-analysis concerns clinical behavior of low-shrinkage versus methacrylate restorations, not a universal wear advantage for a matrix class. Johnsen and colleagues examined own-brand restorative materials; brand category alone is not a clinical wear specification. [Kruly] [Johnsen]

Read the test before comparing the number

Two-body and three-body simulators, toothbrush tests and thermomechanical aging impose different conditions. Report the product, antagonist, load, cycles, medium, aging, surface preparation and measurement method. Maximum vertical loss, average depth, volume loss, roughness and gloss are different endpoints. A surface can become smoother while losing material. Laboratory cycles must not be converted into clinical years without a validated relationship.

Barkmeier and colleagues explicitly compared localized and generalized simulated wear. Heintze and colleagues reviewed the relationship between laboratory mechanical parameters and clinical fractures and wear; laboratory results do not provide a general replacement for clinical follow-up. Nawafleh and colleagues’ fatigue review concerned lithium-disilicate crowns and fixed prostheses, with heterogeneous test setups, rather than composite annual wear. [Barkmeier] [Heintze] [Nawafleh]

Clinical evaluation combines symptoms, function, margins, fracture and caries assessment with serial records. FDI or USPHS ratings are clinical scores, not direct micrometre measurements. Serial scans or casts need reproducible acquisition, stable registration regions and a stated uncertainty before differences are interpreted as progression. Passos and colleagues compared measurement methods on experimentally eroded or abraded enamel and dentin; their findings cannot simply be transferred to clinical composite wear. [Passos]

What the retained evidence actually shows

Laboratory CAD/CAM wear

Zhi, Bortolotto and Krejci’s 2016 experiment tested five CAD/CAM materials, with 10 specimens per material, against human enamel cusps. It used 200,000 mechanical cycles at 49 N with thermal cycling and assessed maximum vertical substance loss. The tested feldspathic ceramic, VITA Mark II, resisted wear better than the tested resin-containing blocks. This was not a direct-versus-indirect clinical trial and did not establish annual clinical wear rates, patient survival, or a universal ranking of CAD/CAM materials. [Zhi]

Matzinger and colleagues’ 2019 laboratory study compared polishing, specimen wear and antagonist wear across seven chairside CAD/CAM materials. Material ranking depended on whether mean depth, maximum depth or volume was used. Its polished surfaces and wear simulation support careful finishing and endpoint-specific comparison, not a promise of fewer clinical remakes. [Matzinger]

Tsujimoto and colleagues’ 2017 experiment compared six CAD/CAM materials after water storage or 10,000 thermal cycles, followed by localized simulated wear. Aging effects varied by material and endpoint. Stawarczyk and colleagues’ mechanical and optical characterization is additional material-property evidence, not a clinical longevity trial. [Tsujimoto] [Stawarczyk]

Clinical restoration survival and maintenance

Loomans and colleagues’ 2018 prospective study treated 34 patients with severe tooth wear using 1,256 direct composite restorations. At a mean observation of 39.7 months, 69 failures were recorded: 61 restorations were repaired and eight replaced. Reported 3.5-year success and survival were 94.8% and 99.3%, respectively. Those distinct figures reflect the importance of repair in the outcome definition. This study supports the feasibility of a direct composite rehabilitation strategy in its setting; it does not compare direct nanofill against CAD/CAM blocks or provide category-wide micrometres per year. [Loomans]

Borgia and colleagues’ retrospective posterior-restoration study adds long-term clinical observation, but its design and population differ from the laboratory comparisons and the full-mouth rehabilitation cohort. Neither source justifies prescribing one material for every patient who reports grinding. [Borgia]

A practical workflow for a worn posterior restoration

Illustrative decision pathway, not a reported patient case. When a patient presents with worn restorations and possible parafunction, document the history, symptoms, remaining tooth structure, opposing surfaces, margins, caries and functional contacts. Determine whether repair, replacement or broader rehabilitation is needed. Wear facets or a history of grinding alone do not establish the cause of every defect or quantify loss of vertical dimension.

1. Establish a baseline. Record photographs, clinical scores and, where useful, digital scans. Document the intended follow-up method and measurement limitations before comparing later scans.
2. Select the restoration and material together. Consider available space, retention, bondable substrate, isolation, restoration thickness, antagonist and reparability. Direct composite and an indicated indirect onlay can both be options; this is not a controlled within-patient material comparison.
3. Use conservative preparation and reliable isolation. Preserve sound structure, obtain appropriate access and follow the chosen material’s preparation and adhesive instructions.
4. Respect the specific bonding system. Scan, design, mill and try in an indirect restoration as appropriate; verify contacts and fit before surface pretreatment. Do not apply a single generic silane-plus-adhesive sequence to every resin-containing block.
5. Place and cure direct composite to its instructions. For a product such as Filtek Supreme Ultra, use its current shade-, increment- and light-specific directions. An extra 20 seconds from each side is not a universal validated curing prescription. Check light output, access and tip position rather than relying on time alone.
6. Finish, adjust and repolish. Check contacts and occlusion clinically and use the material’s polishing system. Do not add heat treatment or firing unless the specific system permits it.
7. Plan maintenance. Reassess causes and progression, discuss appropriate protection where indicated, and document repairs separately from replacements. A protective appliance does not guarantee wear prevention or establish a material’s superiority. Irreversible occlusal equilibration is not a routine requirement inferred from grinding alone.

Lava Ultimate: retain the product-specific safeguards

The manufacturer’s 2015 instructions specify inlays, onlays and veneers and exclude crowns because of debonding risk. Onlays require an internal retentive design element; the term “overlay” alone does not establish that a preparation meets the indication. The instructions describe alumina abrasion at no more than 50 μm and 2 bar, alcohol cleaning and dry, oil-free air. They prohibit HF or phosphoric-acid etching of the restoration. For the RelyX Ultimate/Scotchbond Universal combination, the adhesive acts as primer; other cements require their recommended priming sequence. The block must not be fired. These instructions are product-specific and must be checked against the current local package directions before use. [Lava Ultimate instructions]

Research directions and the clinical bottom line

When evaluating proposed self-healing polymers, bioactive fillers, modified networks or computationally designed materials, ask which properties and outcomes were actually tested. A laboratory improvement in hardness, strength, conversion or gloss is not automatically a demonstrated reduction in patient wear, fracture, repair or replacement. Emerging chemistry needs biocompatibility, processing and clinical evaluation as well as wear testing.

The retained evidence does not support a universal annual wear-rate table for the broad categories used here. Compare like-for-like tests, retain the distinction between restorative and antagonist wear, and assess clinical survival separately. Product-specific technique, patient assessment and planned maintenance remain central to a useful treatment decision.

References and product documentation