Research Papers

Evaluation of Effectiveness of Er,Cr:YSGG Laser For Root Canal Disinfection: Theoretical Simulation of Temperature Elevations in Root Dentin

[+] Author and Article Information
L. Zhu1

Department of Mechanical Engineering, University of Maryland, Baltimore County, Baltimore, MD 21250zliang@umbc.edu

M. Tolba

Department of Endodonics, Prosthodontics and Operative Dentistry, and Department of Health Promotion and Policy, University of Maryland, Baltimore, Baltimore, MD 21201

D. Arola

Department of Mechanical Engineering, and Department of Endodonics, Prosthodontics and Operative Dentistry, University of Maryland, Baltimore County, Baltimore, MD 21250

M. Salloum

Department of Mechanical Engineering, University of Maryland, Baltimore County, Baltimore, MD 21250

F. Meza

Department of Endodonics, Prosthodontics and Operative Dentistry, University of Maryland, Baltimore, Baltimore, MD 21201


Corresponding author.

J Biomech Eng 131(7), 071004 (Jun 12, 2009) (8 pages) doi:10.1115/1.3147801 History: Received December 15, 2008; Revised April 16, 2009; Published June 12, 2009

Erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) lasers are currently being investigated for disinfecting the root canal system. Prior to using laser therapy, it is important to understand the temperature distribution and to assess thermal damage to the surrounding tissue. In this study, a theoretical simulation using the Pennes bioheat equation is conducted to evaluate how heat spreads from the canal surface using an Er,Cr:YSGG laser. Results of the investigation show that some of the proposed treatment protocols for killing bacteria in the deep dentin are ineffective, even for long heating durations. Based on the simulation, an alternative treatment protocol is identified that has improved effectiveness and is less likely to introduce collateral damage to the surrounding tissue. The alternative protocol uses 350 mW laser power with repeating laser tip movement to achieve bacterial disinfection in the deep dentin (800μm lateral from the canal surface), while avoiding thermal damage to the surrounding tissue (T<47°C). The alternative treatment protocol has the potential to not only achieve bacterial disinfection of deep dentin but also shorten the treatment time, thereby minimizing potential patient discomfort during laser procedures.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Schematic diagram of the axisymmetrical geometry of the tooth root and surrounding tissue. Laser tip is moved up and down in the canal and the heating time at each cylindrical segment is 1 s (6).

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Figure 2

Heat flux imposed to each cylindrical canal surface induced by the pulsed laser

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Figure 3

Temperature contours of the root dentin and surrounding tissue during laser treatment using 175 mW, and the simulation time is 10 s. The white solid line represents the root-tissue interface. The closest location along the interface to the root canal wall is marked by “A.”

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Figure 4

Radial temperature distribution along the white dashed lines shown in Fig. 3 during laser treatment using a laser power of 175 mW. Note that the temperature distribution represents that at various time instants.

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Figure 5

Temperatures at various locations including the canal surface (0 mm) and in the deep dentin (200 μm, 400 μm, 600 μm, and 800 μm lateral from the canal surface) at t=6 s. The effect of the laser power is represented by different bars. The primary y axis on the left gives the actual temperature values, while the secondary y axis on the right illustrates the temperature elevations from the baseline of 37°C.

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Figure 6

Temperature profile along the root-tissue interface at t=6 s using the 350 mW laser. The white dashed line represents the dentin location with a radial offset of 800 μm from the root canal surface.

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Figure 7

Schematic diagram of the proposed treatment protocol. Different line segments represent different cylindrical surface segments of the root canal. Laser tip stays in each surface segment for 2 s, and the total time for each cycle is 16 s.

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Figure 8

Simulated temperature contours in the dentin and surrounding tissue using the proposed treatment protocol

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Figure 9

Heat accumulation in the dentin during the first and second heating cycle (32 s) is illustrated by the average temperature of the entire dentin at various time instants

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Figure 10

Temperature profiles along the canal surface in the axial direction from the crown side. Initially the temperature distribution along the canal surface is represented by the heavy solid line. After the laser tip is moved to the next segment, the temperature distribution is replaced by the next solid line. Notice the shift of maximum temperature on the canal surface due to the fact that the laser tip is moved from one segment to another.

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Figure 11

Temperature distribution in the deep dentin (800 μm lateral from the canal surface, along the white dashed line in Fig. 8 at various time instants. Moving the laser tip up and down results in the shift of the maximum temperature. (a) The first heating cycle (0–16 s) and (b) the second heating cycle (16–32 s)

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Figure 12

Heat penetration from the canal surface to the soft tissue region is shown by the increasing temperature along the root-tissue interface with time. Temperatures are plotted along the root-tissue interface (the solid white line in Fig. 3) from the apex to the crown. The maximum temperature is lower than the critical temperature of 47°C when the heating time is shorter than 26 s.



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