All-on-X Prosthetics: PMMA, Zirconia or Hybrid Resin — Which Material for the Definitive Prosthesis?

The choice of prosthetic material for an All-on-X rehabilitation determines durability, aesthetics, occlusal load transmitted to implants and maintenance ease. PMMA, monolithic zirconia, titanium-acrylic, reinforced hybrid resin: state of the art 2024.

Once the All-on-4 or All-on-6 rehabilitation is osseointegrated, the transition from the PMMA provisional prosthesis to the definitive one represents one of the most impactful decisions for the longevity of the result. The choice of prosthetic material determines long-term mechanical resistance, transmission of occlusal forces to implants and peri-implant bone, aesthetics and surface morphology, and maintenance and repairability. In 2024, four material families share the full-arch implant-supported prosthetics market, each with specific indications and limitations.

1. PMMA (Polymethyl Methacrylate): The Provisional and Economical Prosthesis

PMMA (acrylic resin) remains the reference material for All-on-X immediate loading provisional prostheses. Its advantages are numerous: rapid fabrication (milling or 3D printing in a few hours), moderate cost, simple repairability in case of fracture, easy occlusal adjustment. Its limitations for definitive prosthetics are documented: modest flexural strength (60–80 MPa), progressive wear of acrylic teeth under masticatory load (medium-term VDO loss), water absorption and discolouration over time, fracture rate of 15–22% at 1 year when used as a definitive prosthesis without reinforcement framework. Adding a milled titanium framework (CAD/CAM) or fibreglass braid increases flexural strength to 110–140 MPa — making framework-reinforced PMMA acceptable as a definitive prosthesis for budget-constrained cases.

2. Comparative Table of All-on-X Prosthetic Materials

3. Monolithic All-on-X Zirconia: Advantages and Pitfalls

Monolithic zirconia has established itself as the reference material for the definitive All-on-X prosthesis in advanced implantology centres. Its exceptional flexural strength (900–1,200 MPa depending on grade), total absence of corrosion and impeccable biocompatibility make it a logical choice for a prosthesis intended to serve 15 to 25 years. However, several pitfalls specific to zirconia in All-on-X prosthetics deserve the practitioner's attention. Antagonist wear: the high elastic modulus of zirconia (200 GPa vs 80 GPa for natural enamel) can cause abrasive wear of natural antagonist teeth in cases of excursive contacts — a 2024 study (Clin. Oral Investig.) documents antagonist wear 2.3 times greater against zirconia compared to composite resin. Chipping fracture: despite overall strength, marginal "chipping" fractures can occur if prosthetic thickness is insufficient (< 2 mm in functional zones). Irreparability: in the event of fracture or need for morphological correction, zirconia cannot be added to — the prosthesis must be completely re-fabricated.

4. Hybrid Resins and Nano-filled Composite Materials: The Middle Way

Hybrid resins (Vita Enamic, Shofu Block HC, Brilliant Crios) combine a polymer matrix and a submicron ceramic filler (60–85% by mass) to achieve a material with properties intermediate between composite and ceramic. Their elastic modulus (25–30 GPa) is close to that of natural dentin (18 GPa) — reducing stress transmission to implants compared to rigid zirconia. Their flexural strength (150–200 MPa) makes them suitable for definitive anterior prosthetics or for patients at risk of prosthetic fracture (severe bruxers, poor occlusal compliance). A systematic review published in the Journal of Prosthetic Dentistry (2024) on 1,340 All-on-X hybrid material prostheses at 3 years documents a major complication rate (complete fracture) of only 2.8% — lower than PMMA (8.4%) and comparable to zirconia (1.9%).

5. Provisional → Definitive Transition Protocol: Timing and Steps

• D0–D2: delivery of PMMA provisional prosthesis (immediate loading) — preliminary occlusal adjustment, peri-implant hygiene instructions
• 3–4 months: osseointegration check by RFA (Osstell) and panoramic radiological control — target ISQ ≥ 70 before transition to definitive
• 4–6 months: definitive impression or intraoral scan on MUA abutments — verification of gingival level and available prosthetic space (min. 15 mm for zirconia, 12 mm for PMMA)
• 5–7 months: fitting of PMMA or printed resin prosthetic mock-up — validation of aesthetics, phonetics and occlusion by the patient
• 6–8 months: delivery of definitive prosthesis — abutment screw tightening to prescribed torque (25–35 N·cm), screw access closure, maintenance instructions
• Maintenance: check at 3 months, 6 months, then annual — professional cleaning with interdental brushes and irrigator, annual RFA and radiological monitoring