The geometric relationship between root length and root surface area determined from digital tooth models.

Area of Science:

• Dental Anatomy
• Biomechanical Engineering
• Periodontology

Background:

• External apical root resorption (EARR) can compromise tooth stability.
• Assessing the clinical impact of root length (RL) reduction requires understanding its effect on root surface area (RSA).

Purpose of the Study:

• To investigate the correlation between root length (RL) and root surface area (RSA) in permanent maxillary and mandibular teeth.
• To quantify the impact of simulated root length reduction on total root surface area (tRSA).

Main Methods:

• Generated 3D models of human teeth from a Japanese adult male population.
• Utilized a Python algorithm to simulate root shortening in 1 mm increments.
• Calculated total root surface area (tRSA) by summing circumferential (cRSA) and cross-sectional (CSA) areas.

Main Results:

• Maxillary and mandibular first molars had the largest tRSAs.
• Initial 3 mm of root shortening caused <7% tRSA reduction in most teeth.
• Beyond 3 mm, tRSA reduction averaged 19.4% (maxillary) and 27.77% (mandibular).
• CSA proportion increased with greater RL reduction, significantly contributing to tRSA.

Conclusions:

• RSA and CSA are critical for assessing clinical impact of RL loss, not just RL alone.
• Up to 20% (approx. 3 mm) RL loss retains over 90% of tRSA.
• Teeth with higher CSA, like molars, better maintain periodontal support despite significant RL loss.