The effect of three types of rasps on the occlusal surface of equine cheek teeth: a scanning electron microscopic study.

This study compared how two hand rasps and an electric bur alter the surface of horse cheek teeth and found that all methods damaged vital dentin, with distinct patterns of surface roughness, enamel/cement chipping, and smear layer formation. The authors urge caution in clinical practice and call for research to identify the safest, most effective rasping technique.

Study background and research question

• Routine “floating” (rasping) of equine cheek teeth aims to correct sharp points and malocclusions, but may inadvertently injure living dental tissues.
• The study asked: How do three commonly used instruments—a hand rasp with a solid carbide blade, a hand rasp with a tungsten chip blade, and an electrically driven solid carbide axial bur—affect the microscopic structure of the occlusal surface?
• The focus was on surface damage (enamel, dentin, peripheral cement), dentinal tubule status (including odontoblast processes), smear layer formation, and the size of particles generated.

Methods at a glance

• Subjects: Two horses with normal teeth examined immediately postmortem; a third horse with evidence of previous excessive dental treatment contributed additional specimens.
• Interventions:
  • Hand rasp with solid carbide blade.
  • Hand rasp with tungsten chip blade.
  • Electrically driven solid carbide axial bur.
• Controls: Six untreated cheek teeth per horse served as controls.
• Processing: Following standard, clinically “satisfactory” rasping, teeth were extracted; clinical crowns were removed and prepared for scanning electron microscopy (SEM).
• Debris analysis: Crown particles generated by each technique were collected and examined to compare particle size and characteristics.

Key SEM findings by instrument

• Common to all techniques:
  • Amputation of odontoblast processes within dentinal tubules, indicating direct injury to vital dentin components.
• Hand rasp, solid carbide blade:
  • Created deep gouges and grooves in dentin, leaving a roughened, uneven surface.
  • Chipped enamel and peripheral cementum at the occlusal margins.
  • No smear layer was formed, leaving tubules more open and the surface more irregular.
• Hand rasp, tungsten chip blade:
  • Produced a smoother finish than the solid carbide hand blade.
  • Generated a partial smear layer that partially covered or smeared over dentinal tubules.
• Electrically driven solid carbide axial bur:
  • Created a very smooth surface with a complete smear layer covering dentin.
  • Removed all dental tissues to a uniform plane but also caused enamel damage.
• Debris characteristics:
  • Hand rasping produced larger crown particles compared with the finer particulate from the electric bur.

What is the smear layer and why it matters

• Definition: The smear layer is a thin film of micro-debris that forms on cut dentin, partially or completely occluding dentinal tubules.
• Potential benefits:
  • Short-term sealing of tubules, which may reduce fluid flow and immediate dentin sensitivity.
  • Smoother surfaces may reduce plaque and feed debris retention in the short term.
• Potential downsides:
  • It can be unstable and may be rapidly worn away under occlusal loading, potentially re-exposing tubules.
  • It can entrap bacteria if contamination occurs, although clinical significance in equine occlusal surfaces is uncertain.
• Relevance here: The absence of a smear layer (solid carbide hand rasp) leaves open tubules and rough dentin, likely increasing sensitivity risk, whereas a complete smear layer (electric bur) could offer transient desensitization but came with enamel damage.

Interpretation and clinical relevance

• All tested techniques injured vital dentin by severing odontoblast processes, underscoring that even “satisfactory” rasping can be biologically traumatic.
• Surface integrity:
  • Solid carbide hand rasp caused the most macroscopic surface disruption (gouging, chipping) and left tubules unsealed.
  • Tungsten chip hand rasp produced an intermediate, smoother finish with partial tubule coverage.
  • Electric bur produced the smoothest surface and complete smear layer but still damaged enamel, a concern for long-term occlusal durability.
• Tissue-specific risks:
  • Dentin: Open tubules and severed odontoblast processes raise the risk of pain, hypersensitivity, and pulpal irritation—especially in hypsodont equine teeth with high occlusal wear and active dentin deposition.
  • Enamel/cementum: Chipping or damage compromises the protective occlusal surface, may accelerate wear, and can create sites for plaque retention or mechanical failure.
• Particle size suggests different cutting mechanics:
  • Hand rasps tend to fracture larger chips, reflecting a more tearing/planing action.
  • High-speed burs produce finer debris, consistent with more uniform abrasion but also greater heat/friction potential unless adequately cooled.
• Clinical takeaway: The balance between creating a smooth, potentially less sensitive surface and avoiding enamel/dentin injury is delicate; meticulous technique and conservative reduction are critical regardless of instrument choice.

Limitations to keep in mind

• Small sample size and ex vivo setting limit generalizability to live horses with perfused, moist tissues.
• Operator technique, pressure, duration, and cooling/irrigation parameters were not fully detailed and could markedly influence outcomes.
• Short-term, structural endpoints only; no assessment of pain, healing, bacterial colonization, or long-term wear.
• Instrument condition (sharpness, grit) and device settings for the electric bur may alter results but were not exhaustively standardized or reported.
• Horses with prior excessive treatment were included only for qualitative comparison, not controlled analysis.

Practical guidance for equine dentistry

• Adopt a minimally invasive philosophy:
  • Remove the least amount of tooth necessary to correct clinically meaningful pathology.
  • Avoid deep cuts and localized pressure, especially over suspected pulp horns.
• Instrument selection and maintenance:
  • Consider tungsten chip rasps when hand floating for a smoother finish and partial smear layer relative to solid carbide hand blades.
  • If using electric burs, use light, intermittent strokes with adequate cooling to limit enamel damage and thermal insult.
  • Keep instruments sharp and well-maintained to reduce tearing and gouging.
• Surface finishing:
  • Aim for smooth, even occlusal planes without unnecessary flattening of normal occlusal relief.
  • Consider brief final passes that reduce surface roughness while avoiding additional tissue removal.
• Pain mitigation and aftercare:
  • Be vigilant for signs of post-procedure sensitivity; consider analgesia when extensive reduction is unavoidable.
  • Avoid excessive treatment in a single session; stage procedures if substantial correction is required.
• Case selection:
  • Reserve aggressive reduction for clear indications (malocclusions causing soft-tissue trauma, wave mouth with functional compromise), not for routine “cosmetic” smoothing.

Future research priorities

• Prospective, randomized in vivo studies that correlate SEM findings with clinical pain scores, feeding behavior, and performance.
• Quantification of heat generation and the protective effect of irrigation/cooling during electric burring.
• Assessment of different bur designs, speeds, and abrasives, and of varying rasp tooth geometries.
• Longitudinal studies on enamel/dentin wear, secondary dentin response, and pulp vitality after different techniques.
• Evaluation of adjuncts (e.g., desensitizing agents, polishing protocols) to mitigate sensitivity without increasing tissue loss.