## 1 Introduction  
Minimally invasive techniques have been developed in many aspects of dentistry including endodontics and the restoration of associated teeth, cavity preparations in operative dentistry, and the use of lasers for surgical procedures [1]. This study will focus on the use of a CO2 laser to provide minimally invasive cavity preparations with respect to the use of local anesthesia. Lasers have been used in dentistry in the United States for caries removal and cavity preparation since receiving FDA approval in 1997 [2]. Since this time, the erbium family of lasers, including Er:YAG and Er:YSGG, have demonstrated cutting efficiency without sacrificing vitality of pulpal tissues in many studies from 1988 to 1999 [3; 4; 5; 6; 7]. This is due to a combination of factors, including use of water spray, a pulsed mode of energy delivery, and an intermittent laser use. Ablation of enamel from erbium laser energy is caused by the rapid subsurface expansion of the interstitially trapped water within the mineral substrate causing a massive volume expansion and explosion of the surrounding material creating a photoacoustic effect and classic popping sound [2]. Multiple studies prior to 2004 have shown erbium lasers to make cavity preparations in enamel and dentin with minimal-to-no local anesthesia [8; 9; 10; 11; 12; 13; 14]. [PERSON] et al. (1996) reported that use of Er:YAG lasers on class V cavities resulted in a pain-free experience for 48/60 (80%) patients and had no adverse reactions [15]. Similarly, [PERSON] et al. (1998) found the Er:YAG laser to be 80% more comfortable than conventional mechanical treatment, required less need for anesthesia, and had high patient preferences with 82% of participants preferring the laser for future caries removal treatments. They concluded that Er:YAG laser therapy was a more comfortable alternative or adjunct to conventional mechanical cavity preparation with air-driven turbine handpieces [16]. Similar results have been reported for children, with 82.5% reporting no pain when using an Er:YAG laser for cavity preparations, and 92% saying they preferred a laser for future studies [17]. While Er:YAG lasers are traditionally more common in dental clinics, there is one 9300 nm CO\({}_{2}\) laser that is FDA-approved for caries removal and cavity preparation (Solea, Convergent Dental, Needham, MA, USA). The characteristics of this wavelength are the ability to ablate hydroxyapatite (HA) and vaporize water, which comprise about 97% of enamel content [18]. When one considers both reflection and absorption, the total energy transferred into HA is much greater at 9300 nm than at the Er:YAG lasers wavelength of 2940 nm (considering the peak absorption of HA occurs at 9600 nm). At this wavelength, the reflection coefficient is low while the absorption coefficient is high [18]. The ability to target HA allows this CO\({}_{2}\) laser to outperform erbium lasers in the cutting of enamel and dentin [18] and has been proposed as another \"candidate\" (joining Er:YAG) to provide \"painless preparations\" [19]. CO\({}_{2}\) lasers have also been shown to produce less pain and less risk to pulpal vitality than traditional handpiece therapy. As early as 1994, [PERSON] showed a 10,600 nm CO\({}_{2}\) laser produced little-to-no pulpal response (178 of 187 procedures) during enamel etching, dentin desensitization, increased fluoride uptake, external resorption, and pulp capping. Furthermore, only four procedures required anesthesia, showing a strong analgesic-like effect of the laser, and there was no post-operative sensitivity or loss of pulpal vitality [20]. Similarly, [PERSON] and [PERSON] (2002) detected no pulpal damage to teeth treated with laser irradiation using a 9600 nm CO\({}_{2}\) laser at energy levels that did not elevate pulp temperature [21]. Finally, in a 2005 in vitro study using a similar 9600 nm CO\({}_{2}\) laser, [PERSON] et al. determined the ability to efficiently cut enamel and dentin [22].