Forums › Erbium Lasers › General Erbium Discussion › Hydrokinetics Article
- This topic is empty.
-
AuthorPosts
-
Glenn van AsSpectatorIf I understand the function of the water is to cool the pulp, flush away debris, and keep the tooth hydrated.
Correct me if I am wrong but this is the function of the water.
The erbium stalls out pretty fast in narrow deep troughs where the water cant get to it.
Glenn
lagunabbSpectatorGlenn,
Take the two limiting cases (1) ablation rate is high enough to remove all heated material and (2) ablation rate below threshold rate where heat builds up. Your question refers to (2). The heat transfer is limited by heat capacity of the water and rate of transfer. For the simplified case where water is static, we could frame the cooling in terms of 2 general ideas:cooling rate = H(Tt-Tw)
max amount of cooling = Vw(Cw)(Tt-Tw)+Vph*Ephwhere H is overall heat transfer coefficient
Vw water volume
Cw water heat capacity
Eph water to vapor phase change enthalpy and Vph is water volume converted to vapor
Tt tooth temperature
Tw water temperatureHow effective would this cooling mechanism be?
It would be effective if the tooth temperature is high. It would really be effective if tooth temperature is 100C so you get Eph in the picture. It is not very effective if Tt is close to that of Tw. In fact, there is no cooling at all when Tt = Tw. How do you get to a state where Tt is close to ambient (ambient define as undisturbed tooth temperature)? You remove the stuff faster than heat can penetrate. That is the whole point of Neev’s work. In fact, there is experimental evidence that Tt is 2 F or so lower than ambient because of the dual effects of ablation rate greater than threshold AND water convertion to vapor by laser energy. Note however though that this neither supports nor refutes the proposed theories (including HK) of water augmented ablation. Just thinking out loud based on what I have reviewed thus far.
Robert Gregg DDSSpectatorHi Ray–
How’s Yossi doing? I’m still waiting for my phone call for a tour of Y-Beam! Lunch is still on me if it ever happens….;)
Del has been playing wth erbiums since 1990, and he and I did quite a bit in 1996 as consultants to a start-up company that did not bring their laser to market.
I know you are teasing, but Del and I love lasers. ALL laser devices, wavelengths and configurations. That’s why he and I get peturbed when they are misrepresented in their features and functions.:(
Yossi has it partly right about the char and the cooling. (His patent description is unbelievably detailed!!!):o
Here’s why: Water spray (See Laser Endo Tech/Biolase patent from circa 1990) prevents charring when using the pulsed Nd:YAG on hard tissue (i.e. Laser 35). So is that HK or simply oxygen exclusion and debris removal? If it’s HK, then the Fr Neodymium:YAG has an HK effect as well and Er, Cr, YSGG is nothing unusual from Erbium:YAG, let alone Nd:YAG for the “cooling” mechanism on hard tissue–contrary to the marketing claims (that they seem to be distancing themselves from lately).
When you came to visit, I didn’t demonstrate char prevention or removal with the Fr, Nd:YAG. Happy to show you that. I use that phenomenon of physics every time I laser etch dentin.
Take a look a this Laser Endo Technic (later renamed to Laser Medical Technologies, then Biolase) patent by Guy Levy et all from 1994 and you can see the evolution in their thinking about the function of water.
5,318,562
Levy , et al. June 7, 1994Levy; Guy (Tustin, CA); Tillotson; James H. (Rancho Mirage, CA); Gollihar; William A. (Moreno Valley, CA)
Assignee: Laser Endo Technic Corporation (San Clemente, CA)
Appl. No.: 848179
Filed: March 10, 1992“By providing a flow of cooling fluid through the handpiece, and particularly through the chamber which is adjacent the radiation delivery end of the handpiece, those surfaces or bodies which transmit, receive or reflect laser radiation can be effectively cooled, thereby allowing the handpiece to successfully conduct laser radiation having higher power levels. The cooling effect serves, in particular, to prevent damage or deterioration at surfaces from which radiation is reflected or through which radiation passes, and additionally promotes dimensional stability of optical components which act to focus the laser radiation, thereby stabilizing the optical performance of those components.”
It is up to Biolase to provide the scientific evidence to proove the new physics of HK. But you and I know they have no plans to spend $$ do this. New FDA claims, marketing and advertising is where they spend their money, not on hard science to proove their claims.
I know Bill Gollihar reasonably well, and I know you spent some time talking with him recently. What did he tell you about HK??
Beautiful day outside!
Bob
(Edited by Robert Gregg DDS at 2:02 pm on Mar. 2, 2003)
lagunabbSpectatorHi Bob,
It’s been several months since I talked to Bill. Laser jocks still don’t know how ablation (not even considering the role of water) really works. Like I said to Glenn, they are finally trying to use simulations to understand ablation mechanisms. Look up the stuff being done at U. of Montreal by Danny Perez and Laurent Lewis. Until we can understand the simple case of laser ablating a uniform material, there will be no hope of complete understanding of tooth ablation. All I see is one dimensional experiments and guesses and debates of what is happening and not much else. We will still be here debating 10 years from now if we depend on for-profit companies to fund studies. Thank the lord for the physics folks that are looking at industrial applications and doing fundamental laser research. There are plenty of pseudo-scientific types in the medical laser field drawing all sorts of meaningless conclusions from useless experiments. Gosh, did I get too blunt again. Sorry.It was a beautiful day at the beach.
Glenn – forgot to answer your question about stalling out in deep trenches. Below the threshold ablation rate, Neev’s work indicate you start to get into all sorts of problems associated with heating so that would be consistent with his model.
(Edited by lagunabb at 8:22 am on Mar. 3, 2003)
Robert GreggParticipantHey Ray,
Not too blunt for me.
I appreciate the lead that Glenn took in causing dentists to think a little about science versus claims and hype. He took a lot of heat for that on Dental Town by a few “vocal” posters (not Rod), who said something like, “what does the mechanism matter, it works, so shut-up about it already!” Then in the next post say something like, “It works great because it is HK!! “It must be the HK, cuz no other laser works as good as this!” (Well, maybe it just might be that the pulse duration of 140 usec versus 300 usec might have a role……..???)
Neither Glenn, nor any of us, should have to apologize or back down for wanting to see the evidence that a proponent relys on to support a clinical or scientific claim.
Heck, for 12 years the periodontists and the AAP have been slamming and hammering us to show them the SCIENTIFIC evidence of using lasers in the perio pocket is better than SR/P alone. Not once have I felt those request were unreasonable–but it has taken time to do the research (by a for profit company).
QUOTEWe will still be here debating 10 years from now if we depend on for-profit companies to fund studies.Of course you didn’t mean EVERY for-profit laser company…….now did you? :biggrin:
It was a gorgeous day out! Here come da rain….
Bob
lagunabbSpectatorBob, I can understand the AAP position given the early experiments using relatively high powers as you had noted on Dental Town and the implication of potential damage because of low absorption of 1064 nm in hydroxyapetite and water.
Speaking of absorption, Hibst stated something in his paper that pigued my interest. He wrote that hydroxyapetite has higher absorption at the YSGG wavelengths compared to Er:YAG. I had assume they were about the same. Know any references on absorption spectrum of hydroxyapetite?
Glenn van AsSpectatorHi Ray and Bob……..you live and learn. Each day I come here I learn.
Granted some of my rants were beyond what most dentists care about but someone had to ask the question about where was the science behind HK.
Even someone as knowledgeable as Ray and Bob still ask the same questions.
ANyways, guys got tired of it. I worry thought that many companies are not as concerned about educating their users like Bob and Millenium are.
I dont own an Nd Yag but would be interested to read Bobs packet to educate myself to why the Nd Yag may be so good for perio. I know he has 7 pulse durations and that is good for decreasing pain during treatment.
I have said many times that I just want to learn more and each day I come here I do. My staff wonder if I lie awake at night dreaming up these uses for the laser but in fact its really not that. I learn so much from everyone here.
I hope that others who buy lasers may be like Ron , and Al (to pick on two guys) who didnt know that much in the beginning but became involved in learning , educating themselves and now know one heck of alot about lasers.
I commend those who come here repeatedly ( I watch to see who the active users are and what they are reading….thanks ROn for that) and I think that this forum is marvelous for education.
Thanks to all of you for putting up with my HK rants. I got put up to it from alot of my long talks with Tom Haney at Conbio about it.
Kudos to Biolase for taking the ads down and for their wonderful marketing ads (busty models aside)!!
Keep the threads coming.
Glenn
Robert Gregg DDSSpectatorHi Ray,
Yes, I do have a hydroxyapatite absorption spectral chart that compares YSGG to Er: YAG.
I’ll post it when I get back to my laptop.
I’m at the ALD right now on the hotel computer (it’s testing and proficiency day for everyone–and I ain’t an examiner this year!).
Glenn–only a few guys are tired of what you have been saying–the ones who are uncomfortable with being asked to provide some science to their advocacy. It’s a very REASONABLE thing you have been asking for. You are MUCH more gentile than Marshall would have been!!
See you soon Ron. Bring your rain wear, it’s gonna storm tonight and tomorrow.
Bob
AnonymousGuestIn 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: 186-193Published 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 90095email: 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-AC03-76SF00098Keywords
erbium laser • CO2 laser • dental enamel • laser ablation • infrared spectromicroscopyAbstract
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.
Accepted: 7 May 2002
lagunabbSpectatorRon –
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)
lagunabbSpectatorHi all,
Just reviewed some results from an university industrial affliates program, this time from simulations. Simulations (boundary shock layer model) suggest that the volume ablated (dry ablation of semiconductor material) is proportional to the number of pulses with the radiation flux below the plasma formation threshold which seems consistent with theory. This result is as expected, I think.
Now the question is why Fried et al’s results (“Mechanism of Water Augmentation” Lasers in Surgery and Medicine v31, 2002) show that ablated volume for the water film case is 135X that of the dry case, both after 5 pulses and same fluence. I would have expected based on theory and simulations that the wet ablation case would result only in 5X the volume ablated assuming that the water’s role is maintain a clean and unheated surface for the next 4 pulses. The measurements by Fried were done at 20-30 J/cm2 which is supposedly just below the plasma formation threshold.
AnonymousGuestRay,
Any chance of seeing the whole paper? I think that for most of us who don’t subscribe, all we can get is an abstract.
lagunabbSpectatorRon,
Sending you pdf pages of the paper now. Let me know if they don’t make it. Best.
AnonymousGuestInteresting abstract-
Pulsed erbium laser ablation of hard dental tissue: the effects of atomized water spray versus water surface film
Freiberg, Robert J., IMC Associates; Cozean, Colette D., ENO Vision, LLC
Publication: Proc. SPIE Vol. 4610, p. 74-84, Lasers in Dentistry VIII, Peter Rechmann; Daniel Fried; Thomas Hennig; Eds.
Publication Date: 6/2002
Abstract:
It has been established that the ability of erbium lasers to ablate hard dental tissue is due primarily to the laser- initiated subsurface expansion of the interstitial water trapped within the enamel and that by maintaining a thin film of water on the surface of the tooth, the efficiency of the laser ablation is enhanced. It has recently been suggested that a more aggressive ablative mechanism, designated as a hydrokinetic effect, occurs when atomized water droplets, introduced between the erbium laser and the surface of the tooth, are accelerated in the laser’s field and impact the tooth’s surface. It is the objective of this study to determine if the proposed hydrokinetic effect exists and to establish its contribution to the dental hard tissue ablation process. Two commercially available dental laser systems were employed in the hard tissue ablation studies. One system employed a water irrigation system in which the water was applied directly to the tooth, forming a thin film of water on the tooth’s surface. The other system employed pressurized air and water to create an atomized mist of water droplets between the laser hand piece and the tooth. The ablative properties of the two lasers were studied upon hard inorganic materials, which were void of any water content, as well as dental enamel, which contained interstitial water within its crystalline structure. In each case the erbium laser beam was moved across the surface of the target material at a constant velocity. When exposing material void of any water content, no ablation of the surfaces was observed with either laser system. In contrast, when the irrigated dental enamel was exposed to the laser radiation, a linear groove was formed in the enamel surface. The volume of ablated dental tissue associated with each irrigation method was measured and plotted as a function of the energy within the laser pulse. Both dental laser systems exhibited similar enamel ablation rates and comparable ablated surface characteristics. The results of the study suggest that, although the manner in which the water irrigation was introduced differed, the mechanism by which the enamel was removed appeared basically the same for both dental laser systems, namely rapid subsurface expansion of the interstitially trapped water. It is the conclusion of this study that if the proposed hydrokinetic effect exists, it is not effective on hard materials, which are void of water, and it does not contribute in any significant degree in the ablation of dental enamel.
ASISpectatorHi Ron,
Thanks for posting the abstract.
Andrew
-
AuthorPosts