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Applications

Smart fiber tips for dental laser applications

13/09/2016  |  Tags: dental laser manufacturer, ,
Abstract
During the early days of laser medicine, progress was triggered by the development of new laser types with new wavelengths or power regimes, but now applicators and application conditions have assumed this role. Specially designed distal fiber tips allow (a) to increase the quality of laser ablation, (b) to modify laser-induced tissue effects significantly, and (c) to conceive new indications that are otherwise not possible. In this paper, several newly developed and optimized applicators and fiber tips for various dental Er:YAG-laser applications are presented, including an optimized chisel-shaped tip for improved calculus removal in periodontal pockets, a fiber tip for ‘‘remote’’ calculus removal in tooth furcations, a contact tip for caries therapy, and two contact tips, one with increased hemostasis for oral surgery and the other one for cleaning and disinfection of implants. Most of these tips were designed and optimized using optical ray-tracing. Promising designs were realized and investigated by in vitro experiments to evaluate the ablation quality, ablation efficiency, thermal effects, and to determine the suitable laser parameters. After the successful in vitro tests the applicators and tips were used in clinical tests.
The results show that all of the developed fiber tips lead to an approval of the particular application. In conclusion, from our point of view the development of applicators and special fiber tips has more impact on the progress of laser dentistry than modifications of the laser itself.

Introduction
During the early days of laser medicine, progress was triggered by the development of new laser types with new wavelengths or power regimes. Nowadays, more and more new applicators and application conditions have already become and will be in future a mover of progression. In former times, applicators were typically either bare optical fibers or simple focusing handpieces connected to them or adapted to an articulated arm for laser light delivery. For the Nd:YAG and the diode laser bare fibers are still in use, and the contamination and subsequent  burning  of  the  fiber  end  are  essential conditions for efficient cutting [1] . To avoid the burning of the delivery fiber and to improve the cutting quality, nowadays some medical Nd:YAG or diode laser systems are provided with handpieces with exchangeable special fiber tips [2,3] . Also for Erbium lasers handpieces are available with exchangeable fiber tips. The geometric parameters of these  tips  are  mainly  adapted  to  the  application conditions, and alterations of the laser light emission are rather accidental than specifically designed. For example, we developed a handpiece for treatment of periodontitis with a chisel-shaped tip, which can be inserted into deep periodontal pockets. The rectangular output end face of this tip provides a better ablation quality compared to a thin cylindrical fiber tip [4–8] , but initially no special attention was paid to details of the laser light emission. In the following, we describe a new generation of fiber tips which were specifically designed to increase the quality of laser ablation, to modify laser-induced tissue effects significantly, or to conceive new indications that are otherwise not possible. The particular tips have been developed for various dental Er:YAG-laser applica- tions, including an optimized chisel-shaped tip for improved calculus removal in periodontal pockets, a fiber  tip  for  ‘‘remote’’  calculus  removal  in  tooth furcations, a contact tip for caries therapy, and two contact tips, one with increased hemostasis for oral surgery and the other one for cleaning and disinfection of implants.

Material and methods
All the presented fiber tips were developed for dental laser applications using an Er:YAG laser (wavelength 2.94 m m, Key3-laser, KaVo Biberach) with delivery fiber and exchangeable handpieces. This laser system includes a feedback system, which detects residual caries or subgingival calculus by detection of fluorescence follow- ing excitation by red light [9] . Defining a threshold level for the detection signal, caries or calculus can be automatically removed without the need to visually inspect the treated area. Both the fiber tips for oral surgery and for disinfection of implants were designed by manually ray-tracing the principal ray and the marginal rays. The other fiber tips were designed and optimized using optical ray-tracing software  (Z EMAX ;  always  the  actual  version;  non- sequential mode). The output end face of the laser system’s delivery fiber was simulated by a circular homogenous light source with a beam divergence as measured for the actual laser system. Complicated fiber tip geometries were constructed in a CAD system (Solid works) and imported into Z EMAX . Typically the beam profile  and  total  energy  of  the  laser  beam  were calculated for several positions in front of and behind the fiber tip (using the Z EMAX element detector). If necessary the ray data were transferred to graphing software  (Sigma  Plot)  for  further  analysis  (beam divergence, Gaussian beam fitting, etc.). So we were able to investigate and optimize hundreds of different fiber tip designs. Only the most promising tips were fabricated and then investigated by several in vitro experiments. The ablation quality was evaluated by irradiation of slices of extracted human teeth with various laser parameters and subsequent microscopic analysis. The ablation efficiency was determined by measuring the mass loss of human teeth produced by a defined number of laser pulses. Fresh porcine oral mucosa was used for test cuts with the fiber tip for oral surgery. The tips were manually moved along the tissue surface in contact. From these cuts histological sections were prepared by a microtome. The histological sections were stained with hematoxylin–eosin and then microscopically analyzed to determine the cut shape and the thermal damage zone. For investigation of the fiber tip for implant disinfec- tion,  first  the  ablation  threshold  was  determined. Subsequently, implants were contaminated with saliva and then treated with various parameters (laser energy, laser repetition rate, movement of tip, number of treatment cycles). The treated implants and the un- treated control sample were pressed into blood agar. After cultivation the bacterial colonies were analyzed and photographed. After successful in vitro tests the applicators and tips were used in clinical tests.dental laser handpiece
Results
Fiber tip for treatment in periodontal pockets Optimized chisel-shaped tip Fig. 1 shows the outline of the initially developed chisel-shaped tip. Its geometry (length 22 mm, output end 0.5 mm 1.65 mm) allows its introduction into deep periodontal pockets for removal of subgingival calculus. The homogeneity of the output beam profile and therewith  the  ablation  quality  can  be  remarkably approved by variation of the inclination angle and length of the chisel. As can be seen in Fig. 2 , after optimization the ablation induced by Er:YAG laser takes place across the whole output area and not just within a part as observed before optimization. The output end face is large enough to allow the application of laser pulses with an energy of 200 mJ without damaging the chisel surface. The beam homogeneity at the output face is important not only for the ablation quality  but  also  for  the  feedback  system.  Before optimization the detection area of the feedback system was larger than the ablation area. So in unfavorable cases residual calculus was detected but not ablated. The perfect situation exactly matches the excitation, detec- tion, and ablation area. In a real situation, the detection area depends on the inclination angle between the tip and the tooth surface and the threshold of the feedback system. Fiber tip for remote treatment in furcations The removal of calculus in the tooth furcations requires a fiber tip, which allows the irradiation from the proximal tooth side. The significant specifications for such a tip are to provide side firing and a distant ablation effect. Fig. 3 shows the distal end of the designed and realized tip for remote treatment. The 45 1 chamfer for beam deflection is gold-plated. In order to avoid the focusing effect of a cylindrical fiber surface the output area is shaped as a plane. This conserves the low laser beam  divergence  and  thereby  the  required  distant ablation effect. As can be deduced from the simulated beam profiles at various distances from the output face ( Fig. 4 ), the maximum intensity is kept nearly constant over a distance up to 5 mm. Solely the steep flanks of the profile become smoother for larger distance. This allows ablation even in 5 mm distance, with a less but still acceptable efficiency compared to ablation in contact ( Fig. 5 ). Determination of the crater volume by laser scanning microscopy and successive calculation of the required pulse energy per volume leads to 9.1 J/mm 3 in contact, 24.7 J/mm 3 at 2.5 mm, and 39.7 J/mm 3 at 5 mm distance. For comparison in prior investigations with an excellent top head profile, we measured 7.2 J/mm 3 in dentin.

Fiber tip for oral surgery
One of the main advantages of the Er:YAG laser radiation is its strong absorption by water and its so- called  thermo-mechanical  ablation,  which  is  quite efficient and causes only minimal thermal damage. The resulting coagulation zone of typically 30 m m is so small that deeper cuts are followed by capillary bleeding. To prevent bleeding, which might be helpful in soft tissue surgery,  a  coagulation  depth  of  about  100 m mis necessary. Thus, a fiber tip for soft tissue cutting is desired which provides both good cutting quality and increased thermal effect for bloodless cutting. The fiber tip especially designed for this function has a conically shaped output region. The cone angle is chosen such that the part of the laser beam which strikes the The histological sections of the test cuts, made with this specially designed fiber tip, show a significantly increased  thermal  damage  zone  of  about  100 m m , which is enough for hemostasis of small blood vessels.
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