I’ve use the same laser.
You didn’t mention settings, duration, pulse width.
The lowest power that does the job, there should be not charring, or tooth changes.
Do you check your power at the tip with a power meter?
Machines can vary by 20% over or under machine settings at tip.
When is training? Be careful.

In light of the hydrokinetics discussion, I thought this might fit in well in this thread.

Lasers in Surgery and Medicine
Volume 31, Issue 3, 2002. Pages: 186-193

Published Online: 10 Sep 2002

Copyright © 2002 Wiley-Liss, Inc.

Article
Mechanism of water augmentation during IR laser ablation of dental enamel
Daniel Fried, PhD 1 *, Nahal Ashouri, DDS 2, Thomas Breunig, PhD 1, Ramesh Shori, PhD 3
1Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California 94143
2Department of Growth and Development, University of California, San Francisco, San Francisco, California 94143
3Department of Electrical Engineering, University of California, Los Angeles, Los Angeles, California 90095

email: Daniel Fried (dfried@itsa.ucsf.edu)

*Correspondence to Daniel Fried, Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, 707 Parnassus Ave., San Francisco, CA 94143.

Funded by:
NIH/NIDCR; Grant Number: ROI-DE14554, R29-DE12091, T35-DE07103
DOE; Grant Number: DE-AC03-76SF00098

Keywords
erbium laser • CO2 laser • dental enamel • laser ablation • infrared spectromicroscopy

Abstract

Background and Objectives
The mechanism of water augmentation during IR laser ablation of dental hard tissues is controversial and poorly understood. The influence of an optically thick applied water layer on the laser ablation of enamel was investigated at wavelengths in which water is a primary absorber and the magnitude of absorption varies markedly.

Study Design/Materials and Methods
Q-switched and free running Er: YSGG (2.79 m) and Er:YAG (2.94 m), free running Ho:YAG and 9.6 m TEA CO2 laser systems were used to produce linear incisions in dental enamel with and without water. Synchrotron-radiation IR spectromicroscopy with the Advanced Light Source at Lawrence Berkeley National Laboratory was used to determine the chemical changes across the laser ablation profiles with a spatial resolution of 10-m.

Results
The addition of water increased the rate of ablation and produced a more desirable surface morphology during enamel ablation with all the erbium systems. Moreover, ablation was markedly more efficient for Q-switched (0.15 microsecond) versus free-running (150 microsecond) erbium laser pulses with the added water layer. Although the addition of a thick water layer reduced the rate of ablation during CO2 laser ablation, the addition of the water removed undesirable deposits of non-apatite mineral phases from the crater surface. IR spectromicroscopy indicates that the chemical composition of the crater walls deviates markedly from that of hydroxyapatite after Er:YAG and CO2 laser irradiation without added water. New mineral phases were resolved that have not been previously observed using conventional IR spectroscopy. There was extensive peripheral damage after irradiation with the Ho:YAG laser with and without added water without effective ablation of enamel.

Conclusions
We postulate that condensed mineral phases from the plume are deposited along the crater walls after repetitive laser pulses and such non-apatitic phases interfere with subsequent laser pulses during IR laser irradiation reducing the rate and efficiency of ablation. The ablative recoil associated with the displacement and vaporization of the applied water layer removes such loosely adherent phases maintaining efficient ablation during multiple pulse irradiation. Lasers Surg. Med. 31:186-193, 2002. © 2002 Wiley-Liss, Inc.

Ron –

Fried’s postulation outlined in bold in your message was derived from CO2 ablation at 9.6 um.  Below are his Figures 7a and 7b showing the difference in composition (by FTIR reflectance) with and without water for CO2.  

As shown in Figure 7a, crater surface composition is very different after dry CO2 ablation and Fig 7b shows that composition is maintained when water film was present.   The heavy black line is unaltered enamel.

Figure 8 is the corresponding FTIR measurements for Er:YAG and there are relatively minor differences in between dry and wet ablation such that absorbance does not get reduced a lot after a first pulse.  In the CO2 9.6um case, absorbance is drastically reduced after the first pulse and I can buy the argument that you would need to expose fresh enamel to keep ablation going.  Not the case for Er.  Besides 9.6 um is not well absorb in water so mechanism of water cleaning would be rinsing which would be interesting if that works.

There are two problems with his postulation, (1) how does pulverized/vaporized material deposit itself on the crater surface when there is such a big pressure gradient from the crater to the outside of the crater (2) the CO2 composition results are so different than Er (also the much lower absorbance of the CO2 wavelength in water)  results that it would be hard to extrapolate CO2 postulations to Er even if they are valid.

Thanks Ron.  see if this works.

The figure on the left is 7a and 7b.  The vertical dotted line is inverse of CO2 wavelength at 9.6 um.  Er wavelength is off the chart to the left at about 3500 cm-1.

Figure 8 is on the right comparing dry and wet ErYAG craters.  It would be interesting to see the changes if any near 3500 cm-1.

(Edited by lagunabb at 12:22 pm on Mar. 10, 2003)

(Edited by lagunabb at 12:24 pm on Mar. 10, 2003)

Hi Ron,

That’s an easy one:

3.0-3.5 watts at the fiber tip, 20 hz, 150-250 usec.  

Same technique as described above. Don’t linger or drag…..

Welcome to another Periolase user, Rick Williams from West Texas.:biggrin:

Bob

Ok, review time for me (I lent Todd my books)
Pulse Width is…
time of the pulse?
636usec vs. 250 usec
_   _    _
l  l_l  l_l  l_    length(time) peaks??

and the purpose of the increased pulse width-deeper penetration?

Thanks for yopur patience,

Wider pulse, same power, but less penetration, less thermal tissue relaxation,
Allows coagulation without any charring. Want tissue 60-100 degrees C for coagulation.
Do not want vaporization or ablation.

Ok im back!…nice stuff glenn as always….I will post a bunch this week so we can discuss….all the best to everyone!!