Occlusal Onlay Preparation With the Mr Bur Occlusal Onlay Kit

A minimally invasive pathway to functional, aesthetic posterior restorations

Indirect posterior onlays have become one of the most reliable, tissue-preserving solutions for restoring worn, eroded, fractured, or carious posterior teeth without jumping straight to a full crown. Instead of cutting axial walls and dropping margins subgingivally like a traditional full-coverage crown, modern onlay/overlay prep is defect-oriented, adhesive, supragingival, and enamel-focused. The result: dramatically less tooth reduction, lower pulpal risk, and high long-term survival when bonded with contemporary ceramics such as lithium disilicate.

The Mr Bur Occlusal Onlay Kit is built exactly for this style of adhesive, minimally invasive preparation. The core idea behind the kit is anatomical preparation, not “flatten everything.” The OccluShaper diamonds (370 for premolars, 371 for molars) are designed to create smooth concave and convex contours on the occlusal surface, essentially pre-forming the final internal anatomy of an onlay while preserving enamel and rounding internal line angles for ceramic survival. This matches what current literature considers best practice for bonded partial-coverage restorations: maintain enamel as the bonding substrate whenever possible, avoid sharp internal line angles, and reduce only as much as the material actually needs.

Below, we’ll walk through:

• When to consider an onlay instead of a full crown
  

• Biological and mechanical requirements of modern occlusal/onlay preparations
  

• Step-by-step preparation workflow using the burs
  

• How each bur in the kit supports adhesive onlay design principles backed by current research
  
  

When is an Occlusal Onlay Indicated?

1. Severe occlusal wear and loss of vertical dimension

Patients with bruxism, erosion/biocorrosion, or advanced attrition often present with “cupped-out” occlusal surfaces and a collapsed occlusal scheme. Occlusal onlays allow you to rebuild occlusal anatomy, vertical dimension, and guidance without full circumferential reduction. 

2. Fractured cusps and large failing restorations

Instead of converting a cracked cusp or a failing MOD into a full crown, an adhesive onlay can cover and reinforce compromised cusps with far less axial reduction than a conventional PFM or zirconia crown prep, cutting the loss of sound tooth structure by half or better. Reported comparisons show traditional full-crown prep on a molar can sacrifice ~68% of coronal tooth substance, while an occlusal onlay approach can stay closer to ~30%. Less dentin sacrifice also similar to llower pulpal insult and reduced biologic risk.

3. Caries or restorations limited mostly to the occlusal table

When cavitation or existing restorations are primarily occlusal (rather than subgingival), the clinician can stay supragingival, maintain enamel margins, and bond a ceramic onlay/overlay. Preservation of enamel at the finish line is strongly associated with higher fracture resistance and fatigue survival of lithium disilicate overlays.

Biological and Mechanical Principles of Modern Onlay Prep

Preserve enamel wherever possible

Adhesively bonded lithium disilicate full-coverage occlusal onlays show significantly higher failure loads and better fatigue behavior when most of the bonding surface remains in enamel, compared with dentin bonding.

Keep preparations non-retentive and rounded

Unlike classic onlay designs that rely on mechanical retention (boxes, grooves, sharp internal walls), today’s adhesive onlay is intentionally non-retentive and smooth. Sharp internal line angles create stress points and interfere with complete seating due to localized cement film thickness. Modern guidance is to keep all internal transitions rounded and flowing.

Respect ceramic thickness requirements — but don’t overreduce

Most posterior onlay designs target approximately 1.5–2.0 mm of occlusal clearance on functional cusps to give monolithic ceramic enough bulk under load.
However, newer fatigue data on bonded lithium disilicate shows that even thin (1.0 mm) and ultrathin (0.5 mm) full-veneer overlays bonded to enamel can survive forces beyond normal mastication, provided the prep is enamel-based and non-retentive.

Stay supragingival if you can

Supragingival or equigingival margins reduce biological complications, simplify bonding, and improve inspection/finishing. Adhesive overlays are happiest when you’re not chasing subgingival margins unless absolutely necessary.

Step-by-Step Occlusal Onlay Preparation Workflow

Step 1. Depth orientation and pre-contouring

Bur: 33F (laser-marked pre-preparation bur)

• Purpose: controlled occlusal depth cuts and pre-contouring of functional / nonfunctional cusps.
  

• Why it matters: Literature consistently recommends reducing the occlusal surface approximately 1.5–2.0 mm in load-bearing areas to guarantee material thickness, especially for traditional onlay-style cuspal coverage. Depth-marking prevents the two common failures:

  • (1) under-reduction that leads to thin ceramic and fracture, and

  • (2) over-reduction that sacrifices enamel unnecessarily.
    

• Because 33F is laser-marked, you’re visually guided to stay conservative on premolars vs molars instead of blindly flattening the occlusal table.
  
  

Step 2. Anatomic occlusal reduction and internal shaping

Burs: 370 (OccluShaper diamond for premolars) and 371 (OccluShaper diamond for molars)

• Purpose: sculpt smooth concave/convex internal surfaces following the existing cusp/fissure architecture rather than turning the occlusal table into a flat helipad.
  

• Adhesive occlusal veneers and onlays work best with flowing, rounded internal geometry. Sharp internal angles concentrate stress in brittle ceramics and can trap resin cement, preventing full seating.
  

• The OccluShaper burs are specifically designed to generate those continuous concave fossae and convex cusp slopes in one motion, matching what minimally invasive overlay papers describe as “anatomical, non-retentive, enamel-based” preparation.
  
  

Step 3. Break interproximal contact conservatively (when indicated)

Bur: 555F (slim, needle-shaped diamond for proximal areas)

• Purpose: open or smooth interproximal access paths, remove caries or failing restorative margins, and create draw for an indirect restoration without dropping a deep box form.
  

• Classic onlay preps used vertical boxes and sharp interproximal line angles for mechanical retention. Adhesive overlay protocols now steer us away from those retentive boxes because they weaken remaining tooth structure and lower fracture resistance in thin ceramics.
  

• Mr Bur 555F is intentionally slim to “sneak” between teeth and finish margins supragingivally, in enamel, instead of dropping subgingival shoulders. Keeping margins clean and supragingival is associated with better periodontal response and easier bonding.
  
  

Step 4. Blend cusp coverage and marginal transitions

Bur: 37BF (tapered chamfer diamond for preparing transitions)

• Purpose: create a smooth chamfer/butt-joint style transition at the cusp line angles and functional cusp wrap if you’re covering a cusp.
  

• Why it matters: Contemporary overlay design reviews describe that posterior overlays often use conservative chamfer or butt-joint margins with 1.5–2.0 mm thickness at functional cusps. These designs preserve tooth structure and distribute compressive forces rather than shear.
  

• Mr Bur 37BF lets you generate a gentle chamfered transition zone from occlusal coverage onto the cusp incline instead of a harsh step or shoulder. This supports compressive loading of ceramic rather than lateral shear, a key factor in long-term survival of lithium disilicate overlays. 

Step 5. Fine finishing and smoothing of all internal surfaces

Burs: 370F (OccluShaper finishing diamond for premolars), 371F (OccluShaper finishing diamond for molars), and 38F (finisher matched to 555F)

• Purpose: polish and soften every internal line angle, remove micro-steps, and finalize margins with a uniform, enamel-based chamfer/butt-joint.
  
  

• Systematic reviews show that ceramic occlusal onlays benefit from smooth internal geometry and precise marginal adaptation. Well-finished, rounded internal anatomy reduces tensile peak stresses in brittle ceramics and improves seating accuracy, both of which correlate with higher fracture strength and fatigue resistance.
  
  

• 38F follows wherever 555F worked interproximally, refining those proximal margins without gouging or creating unsupported enamel tags.
  
  

How This Kit Maps to the Literature

OccluShaper 370 / 371 (and 370F / 371F finishers)

• Reproduce anatomical concave fossae and convex cusp inclines instead of flattening.
  

• Support non-retentive, enamel-preserving full-coverage occlusal for premolars and molars, which have shown excellent fatigue survival even at reduced ceramic thicknesses (0.5–1.0 mm) when adhesively bonded.
  

• Help you round internal line angles and keep preparations flowing, consistent with what fracture-strength and marginal-fit data recommend.
  
  

33F laser-marked depth/orientation bur

• Gives you visual reduction control in the 1.5–2.0 mm range typically recommended for cuspal coverage, while preventing unnecessary over-reduction of enamel. 

• Allows predictable clearance for lithium disilicate or similar ceramics, which require sufficient bulk to resist functional load.
  
  

555F + 38F (slim needle bur and its finisher)

• Conservative access to interproximal areas and margin refinement without dropping a traditional retention box.
  

• Aligns with adhesive/restorative philosophy: we no longer cut aggressive boxes to get “mechanical lock,” because that weakens tooth structure and reduces restoration fatigue resistance.
  

• Keeps margins supragingival and mostly in enamel — ideal for bonding and for periodontal health.
  
  

37BF (tapered chamfer bur for transitions)

• Forms smooth butt-joint / chamfer margins and controlled cusp wrap, which current overlay prep reviews (2024) describe as conservative, load-friendly, and long-lasting when kept around 1.5–2.0 mm in thickness.
  

• Supports compressive loading of the ceramic, avoiding lateral shear on thin cuspal veneers.
  

Clinical Takeaways for Cosmetic Restorative Dentistry

1. Anatomy > aggressive retention

Rounded, flowing, enamel-based preps outperform boxy, retentive, sharp-angle designs in terms of load distribution and restoration longevity.
The OccluShaper burs were created specifically to generate that anatomy predictably.

2. Thickness control is everything

You want enough ceramic to survive function (1.5–2.0 mm at heavy-load cusps is still a reliable target), but you do not want to grind away enamel unnecessarily. Depth-marked burs like 33F make this step objective and repeatable. 

3. Supragingival = simpler bonding + happier pulp

By staying supragingival and preserving enamel at the margin, you reduce biologic trauma, simplify cement cleanup, and keep the pulp calmer compared with a deep crown prep that removes ~60–70% of coronal structure. 

In other words: it’s not “just another crown prep kit.” It’s a dedicated occlusal onlay system aligned with what current literature describes as the high standard for conservative posterior rehabilitation.

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