What is Beyond the Drill?

Abstract
The development of the dental drill was one of the most significant innovations in dentistry, occurring in the late 1800’s; 150 years later, it is still our “go-to” instrument for most procedures, whether for removal of decay, endodontic instrumentation or surgical extraction. We have witnessed these machines being powered in many different ways, as technology changes, and since the 1990’s, there has been an increased popularity of electric handpieces, however sufficient evidence to support its superiority over the more conventional air-turbine is lacking.

Minimally invasive approach to tooth preservation was the catalyst behind the development of such methods as ART (Atraumatic Restorative Treatment) and CMCR (Chemo-Mechanical Caries Removal). The power of light has been harnessed as a possible alternative to “drilling” teeth, through the use of hard tissue dental lasers. Erbium lasers have been used for hard tissue removal and have had FDA approval for cavity preparation since 1990’s (KaVo Er:YAG 1992, Fotona Er:YAG 1993, Biolase Millenium 1995). A recent addition to all-tissue laser family is the 9300nm CO2 laser, which claims to have solved the problem of “slow cutting” previously associated with the Erbium lasers. This article will attempt to look into the future of dentistry by examining its past.

History
The design of the first air driven turbine goes back further than most of us think. In the 15th century, none other than Leonardo da Vinci (1452-1519) sketched a design for a turbine, powered by compressed air (Fig. 1) which, like many of his inventions, was likely never built and the application of this devise is hard to guess. 1

The first fluid-driven dental motor was patented by George F. Green in 1868 and was called “pneumatic tooth burr and drill”. 2 In 1871, James Beall Morrison patented a foot pedal engine, which was acclaimed as “one of the greatest and most useful achievements” 3, however, the public opinion of the invention was somewhat at odds with that claim. Rather, it was called “an instrument of torture that reminds most ladies of their sewing machines”. 4 Straub and Wilkerson, in 1877, was the first to develop a cooling method for the cutting instrument, by directing a fine stream of water onto point of contact between the burr and tooth surface. In 1893, Doriot patented a system, based upon a continuous cord running over a series of pulleys, as the standard means of transmitting rotary energy from the electric motor to the handpiece. 5 The maximum speeds of these dental turbines was 700 rpm for foot driven and 1000 rpm for electrically driven engines. 6

In the early 1900’s, the relationship between rotation rates, vibration perception and unpleasantness of the dental experience became quite apparent. Evidence in favour of higher speeds in order to lower vibration perception was provided by Walsh and Symmons. 7 650Hz was found to be the upper frequency threshold of vibration perception, and maximum unpleasantness was perceived in the range of 100-200Hz; speeds of 3000-4000 rpm produced vibrations in the range of 110-150Hz. This study fueled the development of air turbine handpieces with high rotation rates, producing vibrations beyond the limits of perception. Simultaneously, higher rotation rates were shown to remove enamel faster, while staying in the same range of temperature rise, and allowing better control and with less effort for the dentist. Dental cutting using high rotary speeds became possible in 1948, when tungsten carbide burrs which could withstand such high speeds were introduced by SS White Co. The Page-Chayes handpiece from 1955 could be used to drive tungsten carbide burrs at speeds up to 100,000 rpm.

In 1957, the Borden Airotor (manufactured by the Ritter Co) became the first commercially viable high-speed air turbine handpiece capable of speeds up to 300,000rpm (Fig. 2). The energy was accomplished by supplying the compressed air carrying a stream of oil droplets for bearing lubrication, and integral water jet for cooling of the cutting burr. Since then, only minor modifications, such as smaller head size, reduced noise, improved cooling system, reduced need for lubrication have been made to this 1950’s era design. 8

Fig. 1
Sketch of compressed air turbine by Leonardo da Vinci. Redrawn from Gibbs-Smith and Rees. 13

Fig. 2
THE BORDEN AIROTOR
The only turbine with a top speed of over 300,000 r.p.m. 1958 advertisement for Borden Airotor.✝✝

Present
Electric motor handpieces have been available since the 1960’s, but have not gained enough popularity to replace the high-speed air turbine handpieces. Why? Modern high speed handpieces have speeds from 250,000-420,000 rpm, but with low torque. This means that when they are in contact with hard material, the speed will drop by as much as 40% due to the resistance or hardness of the material being cut. Electric motor handpieces rotate at around 200,000 rpm and have high torque, which translates into smooth movement through hard materials. Absence of air also reduced chances of air embolism during surgical procedures. 9 A recent study by Choi, et at 10 compared cutting efficiency of air turbine (KaVo OPTItorque LUX3 649B) vs. an electric motor (Ti-Max NL400 Brasseler) with respect to materials of various hardness. The results of the study are shown in Figure 3.

Figure 3
Interaction between handpieces and materials tested. Error bars signify standard deviations.

So, it stands to reason that, although electric motor-driven handpieces have improved performance when cutting through noble metal alloys and amalgams, their extra cost may not be worth the investment. This alone may be one of the main reasons that electric motors have not replaced the high speed handpieces.

What about the non-rotary cutting systems, including Air Abrasion systems, Ultrasonic devices, ART (Atraumatic Restorative Treatment) and hard tissue lasers? Air abrasion systems first appeared in 1945 and claimed to cut enamel and dentin using the action of abrasive particles of aluminum oxide using compressed air under high pressure of 80psi(550kPa). Airdent Unit by S.S. White Co. was one such device, though it was found to be suitable only for small incipient carious lesions. The advantages of this system included less generated heat, noise and vibration, whereas the disadvantages were the inability to remove existing restorations, finishing cavity surfaces and treatment of large carious lesions. Currently Air/Powder abrasive systems are mainly used in hygiene practice, such as Prophy-Jet for removal of tenacious stains from enamel and root surface. 8

Ultrasonic devices first appeared in 1955 and consisted of a handpiece with a tip vibrating at a frequency of 25kHz, to which a slurry of aluminum oxide was applied in order to cut hard tissues. This system was eventually discontinued as a possible method of cavity preparation due to poor visibility, lack of operator control and the possibility of damage to the pulp from excessive vibrations. 8 Today’s ultrasonics, such as Cavitron by Dentsply, only have applications in hygiene and endodontics for post removal and accessing of calcified canals.

The concept of ART (Atraumatic Restorative Treatment) developed to address dental anxiety and pain associated with the sound and vibrations of dental drills. A number of studies have been conducted to investigate success rates and patient acceptance of such novel approach to caries removal. The authors concluded that ART is less painful and better accepted by children, than conventional restoration technique. 11 ART uses only hand instruments to open and clean the cavity, preserves sounder tooth structure and rarely requires local anesthesia. 12 Systems like Caridex and Carisolv have been developed for chemo-mechanical caries removal (CMCR), whereby the mechanism of action is on the collagen fibers of the carious lesion. It has been suggested that oxidation of glycine residues in the collagen makes it more friable and easier to remove with hand instrumentation. Caridex received FDA approval in 1984 and consisted of two solutions which were mixed together and heated to body temperature, while pumped through a handpiece. The solution had to be replenished frequently, requiring large quantities and was only stable for one hour, which proved to be expensive. When this product came out, dentine bonding was not considered to be reliable and mechanical undercuts still had to be made by drilling. 13 In 1998, a product called Carisolv (Fig. 4) was marketed in Sweden by Mediteam and addressed the shortcomings of Caridex. Carisolv is available in the single mix or multi-mix gel form, does not require heating or delivery system. It contains sodium hypochlorite solution mixed with amino acids (lysine, leucine and glutamic acid) and carboxymethyl cellulose for gel-like consistency. The addition of urea to the product resulted in improved efficiency of caries removal, however, the product still performed better in primary teeth. 14 Special hand instruments sold together with Carisolv gel are used to remove the carious dentin layer by layer. Studies carried out to evaluate efficacy of caries removal by Carisolv, compared to other methods, concluded that the density of remaining dentin was 81.8% of sound dentine. 15 Airotor was still the most efficient method of caries removal, while Carisolv was the least painful and most time consuming. 16

Figure 4

Future
Although lasers in general have been around since the 1960’s, and hard tissue lasers have been approved for applications in teeth and bone since the 1990’s, their penetration into the dental practices remains only at around 5%. The introduction to this technology is not included in dental school curriculum, it involves a significant financial investment and a learning curve which leaves a lot of dentists frustrated.

With the increasing numbers of dental offices in major urban centres, alongside a reduction in the prevalence of dental decay, thanks to fluoridation of municipal water supply, the patient experience is becoming the driving force in the evolution of dental technology. The elimination of anxiety triggers, such as the “4S” rule (sight, sound, sensation and smell) is now an important consideration. 17 The sight is seeing the drills and local anesthetic syringes, the sound is high-pitched whirring of the drills, sensation is the vibration of the dental turbine, particularly the slow speed one. The smell is the only sensation we were able to almost eliminate by using high volume suction and water spray to control overheating.

Lastly, and perhaps the most notable change to the direction of the dental field and easing of patient experience, came about with the introduction of laser technology in the 1990’s. Hard tissue dental laser systems, like the Er:YAG 2940nm and Er,Cr:YSGG 2780nm, can remove hard tissues, such as enamel and dentin, with minimal thermal side-effects similar to a high-speed dental turbine with water spray. 18 Lasers have been shown to produce 400 times less vibration than a high speed burr preparation 19, and achieves an improved patient experience, as evidenced by a number of pediatric studies.

The removal of dental hard tissue is accomplished by a process of Thermo-Mechanical Photon-Induced Water-Mediated Ablation. The resultant micro-explosive force of photons on water droplets is responsible for the mechanism of removal of hard dental tissues (Figs. 5 & 6). In the last 10 years, numerous studies have been published showing reduced pain perception and improved patient acceptance of laser cavity preparations, with both the Er:YAG 20,21 and the Er,Cr:YSGG pulsed laser systems. 22,23 A recent Canadian clinical study included 400 cavities prepared in over 300 patients has shown an overall 85% pain-free experience during laser cavity preparation using Er,Cr:YSGG laser system (I-Plus, Biolase, Irvine, Ca, USA)24. The latest addition to the hard tissue lasers is the new Solea 9300nm CO2 laser by Convergent. It promises improved speed of ablation of dental hard tissues with same minimally invasive and atraumatic experience as the Erbium lasers, however, further in vitro and in vivo studies are required to substantiate manufacturer’s claims. Some clinical case reports are becoming available which show a promising future for this laser system as well.

Figure 5

Figure 6

Conclusion
Modern dentistry was revolutionized in the 1950’s, with the introduction of the Borden Airotor drill, and for the next 40 years, evolution of this technology seemed to be focused on increasing the speed, controlling temperature through water spray, improved visibility with fiber-optic light, and a reduction in the need for oiling and maintenance. In other words, improvements in the industry were mainly focused upon improving the dentist’s experience. Nowadays, with patients having easy access to information through the internet and social media, this new generation of well-informed dental patients has shifted the focus of the industry to improving their experience. They are learning what is available, perhaps at other clinics, or continents, for that matter, and are asking for it. This growing demand for dentists to offer minimally invasive approaches has had a profound effect upon the industry, and in turn the tools at its disposal. We are not ready to say goodbye to the drill, but other technologies are evolving to reduce our reliance on it, most notably lasers. What we need to do as dental professional is keep an open mind and critically examine what further investments of time, equipment and money needs to be incorporated into our practices which would benefit our patients the most. OH

Oral Health welcomes this original article.

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About the Author
Dr. Marina Polonsky DDS, MSc is a gold medal University of Toronto ’99 graduate, she maintains private general practice in Ottawa, Ontario with focus on multi-disciplinary treatment utilizing lasers of different wavelengths. She holds a Mastership from World Clinical Laser Institute (WCLI), Master of Science in Lasers in Dentistry from RWTH University in Aachen, Germany. She is the founder of the Canadian Dental Laser Institute (CDLI), the only study club affiliated with the Academy of Laser Dentistry. She serves on the Executive Committee for Oral Health and is the editor of the Laser Dentistry issue.