Risk-Factors-with-Porcelain-Laminate-Veneers-During-Cementation.pptx

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1. Risk Factors with Porcelain Laminate Veneers During Cementation Porcelain laminate veneers (PLVs) are bonded ceramic restorations that restore facial, incisal, and part of the proximal surfaces of teeth requiring esthetic reconstruction. Their clinical success depends on many factors from planning to execution, with adhesive cementation being particularly significant. A precise cementation technique - including field isolation, adhesion materials selection, proper manipulation, veneer seating, polymerization, and cement excess elimination - is crucial for PLV success and longevity. Several steps performed before cementation, including treatment planning, preparation, impression, and material choice, can also affect cementation quality.

2. Ceramic Materials for Porcelain Laminate Veneers Feldspathic Veneers Created by layering glass-based powder and liquid materials, followed by firing. High glass phase (55-70%) provides excellent translucency for superior esthetics. Lower flexural strength (60-70 MPa) makes them more susceptible to fracture under stress, requiring good bonding and enamel support. Their minimal thickness (less than 0.5mm) allows for conservative preparations. Reinforced Glass-Based Ceramics Glass matrix infiltrated with crystals of leucite or lithium disilicate. Higher crystalline content improves strength while maintaining translucency due to the low refractive index of the crystals. Requires minimum thickness of 0.8mm. Can be fabricated via heat-pressing or CAD/CAM milling, resulting in less porosity than feldspathic ceramics. High-Translucent Zirconia Recently used for PLVs with modified microstructure for adequate translucency. Significantly higher flexural strength allows less critical try-in and cementation. Main disadvantage is less effective adhesion to resin cement with risk of debonding. Best used when mechanical strength is prioritized over optimal esthetics.

3. Tooth Substrate and Preparation Design Importance of Enamel PLV survival rates are higher when bonding to intact enamel rather than dentin. Guidelines emphasize preserving maximum tooth structure. Bonding to enamel is more reliable than to dentin, with weaker bonds to dentin leading to more debonding, especially under high occlusal loads. The absence of rigid enamel causes higher tooth flexure, increasing rates of veneer debonding or fracture. Preparation Depth Ideal depth ranges from 0.3mm at cervical third to 0.7mm at incisal third. Deeper preparations risk dentin exposure, particularly in cervical and proximal regions. Over-preparation leads to total facial enamel removal, significantly increasing tensile stresses due to increased flexure of the dentin core. Preparation Design Options Designs include those with or without incisal overlap. Most clinicians prefer covering the incisal edge (butt-joint design). Some extend with a chamfer finish line on the palatal/lingual surface. Research shows no definitive advantage between design types, with survival rates varying from 85.5% to 95.8% depending on the study.

4. Surface Treatment Prior to Bonding Temporary Cement Removal Cleanliness of tooth surface before final cementation affects final bonding quality. Various cleaning protocols can be used: prophy cup with pumice, explorer with air-water spray, chlorhexidine on cotton pellet, or cleaning burs. Regardless of technique, complete elimination of temporary cement is crucial to prevent compromised etching, hybridization, and veneer fit. Tooth Surface Etching When no dentin is exposed, 37% phosphoric acid can be applied to create a retentive surface. For exposed dentin, phosphoric acid may be too aggressive, potentially denaturing collagen fibers or causing sensitivity. Selective enamel etching with self-etch adhesives for dentin is recommended. Immediate dentin sealing after preparation can prevent bacterial invasion and hypersensitivity. Ceramic Surface Conditioning Glass-based ceramics are etched with hydrofluoric acid (HF) to create micromechanical retention, followed by silane application. HF concentration and application time are specific to each ceramic type. Silane coupling agents link organic resin to inorganic ceramic, forming chemical bonds through condensation polymerization.

5. Cementation and Curing Procedures 1 DBA Application Decision Whether to polymerize dentin bonding agent (DBA) before cementation remains debatable. Unpolymerized dentin-resin hybrid layer might collapse during veneer seating. However, pre-polymerized DBA thickness (0-500μm) may interfere with complete veneer seating, especially on concave structures like marginal chamfers where thickness reaches 200-300μm. 2 Cement Thickness Considerations Cement thickness influences shear bond strength of veneers. Thermal stress causes forces that induce cracks when cement layer is thick relative to ceramic. Ideal cement space is below 40.55±12μm. Final thickness relates to internal fit, fabrication procedure, material, preparation geometry, seating technique, and cement viscosity. 3 Color Matching Challenges Color reproduction involves interaction between veneer, cement, and underlying substrate. With ceramic thickness below 1.0mm, substrate shade significantly influences final appearance. Lighter and darker substrates show more color shifts with thin veneers. Resin cements in different colors and translucencies can help mask darker substrates.

6. Factors Affecting Polymerization of Resin Cement 0.8 Thickness Limit (mm) Maximum restoration thickness for purely light-cured cement. Beyond this thickness, dual-cured cement should be used (up to 2.0mm). 2X Curing Time Increase Required increase in photoactivation time with opaque ceramics and darker restoration shades. 800 Minimum Light Intensity Minimum light intensity (mW/cm²) required for proper polymerization. Lower intensity requires longer curing time. 40 Critical Cement Thickness Maximum ideal cement thickness in microns (μm). Thicker cement layers lead to decreased bond strength values during thermal cycling. Cement polymerization depends on ceramic type, thickness, shade, opacity, cement type, film thickness, light source, and curing protocols. Light-cured cements work best with thin, translucent veneers, while dual-cured options are needed for thicker or more opaque restorations.

7. Post-Cementation Risk Factors Cement Residue Removal Residual cement at margins impairs gingival health. Tack cure excess cement for 2-3 seconds from 1-2cm distance to achieve gel-like material easy to remove. Complete removal is crucial before final polymerization. 1 Structural Failures Fractures occur with insufficient preparation space for ceramic material. Probability of debonding is three times higher in patients with bruxism. Sharp line angles can generate internal microcracks that propagate with time-dependent stresses. 2 Occlusal Adjustment Unevenly distributed occlusal contacts and traumatic anterior guidance can lead to mechanical failures. Immediate occlusal adjustment is crucial. Mouthguard recommended for patients with parafunctional habits or involved in contact sports. 3 Surface Corrections Post-cementation corrections must be performed under cooling spray with fine diamond finishing burs, silicone points, and polishing discs and strips. 4

8. Conclusions and Best Practices 1 Proper Cementation Execution Meticulous attention to adhesive protocol is crucial for long-term success 2 Material Selection Choose ceramic based on substrate, volume, preparation, and expected stresses 3 Conservative Preparation Maintain maximum enamel for optimal bonding and reduced flexure 4 Complete Cleaning Ensure thorough substrate and ceramic surface cleaning before bonding 5 Controlled Polymerization Adapt curing to material, thickness, shade, translucency, and geometry The success of porcelain veneers hinges on attention to detail throughout the entire process. From case selection and treatment planning to tooth preparation, material choice, and cementation technique, each step influences the final outcome. Particularly critical is the adhesive cementation procedure, where suboptimal technique can lead to esthetic, mechanical, and biological complications.