In vitro Evaluation of Laser vs. Handpiece for Tooth Preparation

Abstract

Background:

The erbium-doped yttrium aluminium garnet (Er:YAG) laser has been revealed to effectively ablate dental hard tissues, and its utilisation to caries eradication and cavity preparation is envisaged. Nevertheless, only a limited research has been performed on the Er:YAG laser's capacity to treat caries.

Aim and Objectives:

The efficiency of caries elimination with an Er:YAG laser in vitro was equated to that of traditional mechanical therapy in this study.

Methodology:

The investigation made use of teeth that had suffered from root caries. The Er:YAG laser was used to treat half of each tooth, while the other half was either removed with a conventional bur or left untouched as a control. Each therapy was evaluated in terms of how long it took to remove cavities, histological examinations of decalcified serial sections, scanning electron microscopy (SEM) analyses and the density of the dentin.

Result:

A longer treatment time was required for the Er:YAG laser to completely eradicate carious dentin because of its precise irradiation strategy. However, the Er:YAG laser was effective in removing diseased and softening carious dentin with little heat injury to neighbouring intact dentin, much as the bur treatment. It was also shown that the Er:YAG laser treatment had a lower amount of vibration than other methods. The SEM study of the lased dentin surface revealed characteristic micro-irregularities.

Conclusion:

The Er:YAG laser system appears to be a potential novel technical option for caries therapy, based on our findings.

INTRODUCTION

Lasers were initially used in dentistry to replace mechanical cutting and drilling for hard-tissue procedures like caries excavation and cavity preparation. Hibst in addition to Keller was the first to use the Er:YAG laser in dentistry for hard-tissue therapy. Numerous investigators have testified that the Er:YAG laser ablates dental hard tissues further effectually and proficiently than other hard lasers, with less thermal damage to the teeth, exclusively in a wet field along with water spray.[1,2,3,4,5] Because of the technological issues such as accessibility and laser irradiation operation, clinical usage of the Er:YAG laser for caries eradication is currently restricted. One of the most common indications for laser therapy appears to be root caries, which occurs frequently in ageing patients and patients having maintenance therapy following periodontal therapy. Its simple cavity structure, non-requirement for caries elimination in the undercut area, makes it suitable for laser therapy, along with lesions in the labial or buccal areas that may be simply treated.[6,7,8,9,10] “As well, because a root caries cavity does not require a huge quantity of enamel ablation, cavity preparation of a root caries lesion can be done quickly. Root caries therapy with the Er:YAG laser was accomplished in particular in vitro using a recently constructed Er:YAG laser equipment with a contact probe system, and the results were equated to traditional bur therapy. The properties of the laser-treated cavity moreover the efficiency of the pulsed Er:YAG laser for caries eradication were studied.”

METHODOLOGY

A total of 31 human anterior and premolar teeth with proximal root caries were included in the investigation. Our school's ethical norms allowed us to utilise human teeth. The Saudi dental clinics that donated the teeth were spread throughout the country. At each clinic, we contacted patients who had agreed to have their teeth removed for research and education due to periodontal disease (chronic periodontitis). “The teeth were kept in 4°C water up to the commencement of the experiment. A pulsed Er:YAG laser (Erwin®) made by HOYA Corporation in Tokyo, Japan and J. Morita Mfg. Corp. in Kyoto, Japan was chosen for the experiment. During each pulse, it had a length of 200 ps and pulse repetition rates of 1, 3.3, 5, and 10 per second each (pps). The output energy ranged from 30 to 350 mJ/pulse for a wavelength of 2.94 nm. An optical microscope was utilised to examine each tooth decay. Two places on the perimeter of each lesion were marked with black felt-tip markers along the central line that divides the lesion into two almost equal halves. Using the Er:YAG laser and a conventional burst to eliminate the remaining half of the lesion (or leave it untreated), we proceeded to treat half of the lesion. For laser and bur treatment of 31 teeth, a randomization procedure was used (LB group). Only six teeth were treated with lasers, with the other half of the lesion serving as a control (LC group).” Er:YAG laser was first used to eliminate all of the cavities in teeth. Plastic lens goggles were worn by the operator and his assistants as a kind of eye protection. There had been substantial training before doing the research on using a laser to remove caries. While wearing gloves, the dentist gripped the tooth in his palm. Dentists used an Er:YAG laser to irradiate each tooth with 180 mJ of energy per pulse and a repetition rate of 10 pulses per second while the teeth were immersed in water at 12.6 mL/min (3.7 L/min) (pps). A micromotor spinning at 10,000 rpm was utilised to treat the remaining half-lesions in the LB group following laser therapy with four different sizes of round steel burs (0.05, 0.10, 0.14 and 0.18). Coloured with acid red 52 in propylene glycol (Caries Detector®, Kuraray Corp., Osaka, Japan), the stained caries lesion was removed and water sprayed over the cavity floor to eliminate any traces of the caries detector solution. In order to avoid the dentin from discolouring anymore, we repeated the operation many times using the caries detector. Photographs of the lesion and macroscopy and stereomicroscope examinations of the treated cavity were obtained to record the treatment's progression. While administering the medication, the following measurements and observations were made: How long it takes to fill a tooth cavity. Using this method, the micromotor running time was divided by the laser irradiation period for each tooth. The cavity was examined after the histological processing has been completed. Six teeth from each of the two groups were examined histologically after treatment. The Knoop hardness of the cavity floor dentin of ten LB teeth was measured. Five unique sites in each treated cavity were subjected to a 50 g load for 15 s at a time to determine the Knoop hardness number (KHN). Dentin floor dentin KHN values were averaged from all five measurements. The Wilcoxon signed-rank test found that the KHNs of laser and bur treatments were substantially different. Afterwards, we used the same specimens that had been exposed to subsurface KHN examination to determine how much softened dentin was removed with each approach.

RESULTS

Table 1 shows how long it takes to eradicate caries. The average bur operating time was 51.6 31.7 seconds, whereas the average laser irradiation time was 137.0 95.2 seconds (mean SD, n = 25). Because the laser treatment took a longer time to complete the cavity floor, the laser irradiation time was much longer than the bur operation time (P = 0.0001). With a standard deviation of more than 2 s, the laser/bur time ratio (n = 25) was shown to be very variable. According to histological staining for bacterial development, laser therapy at the same spot as bur application essentially eradicated the damaged dentin layer carrying Gram-positive or Gram-negative bacteria. Scanning electron microscopy study of the cross-section of a laser-treated hollow floor revealed various micro-irregularities in contrast to the flat surface following bur treatment, as shown by the results. Table 2 displays the findings of the tests to determine the hardness of the dentin in the cavity floor. KHN 50.4 for laser treatment and 51.7 + 18.1 for bur therapy showed the average results. Laser-treated and bur-treated cavity floors showed no significant variations in KHN.

Table 1.

Comparison of the time required for caries removal between the Er:YAG laser and bur therapies

Time(s)
Sample no.	Lasera	Burb	Laser/bur ratio
1	135	89	1.91
2	157	87	1.80
3	173	118	1.47
4	257	49	5.24
5	86	62	1.39
6	297	131	2.27
7	124	93	1.33
8	418	85	4.92
9	39	24	1.63
10	63	37	1.65
11	160	69	2.32
12	17	18	0.94
13	55	22	2.50
14	142	34	3.74
15	79	22	3.59
16	108	25	4.32
17	296	47	6.30
18	57	25	2.29
19	54	19	2.84
20	86	40	2.15
21	113	41	2.63
22	94	38	2.47
23	63	26	2.42
24	199	47	4.21
25	147	39	3.77
Mean±SD	137.0±95.2	51.6±31.7	2.80±1.37

Significance: P<0.0001. ^a Irradiation conditions: 145 mJ/pulse (51.3 J/cm₂ /pulse), 10 pps, under water spray. ^b Round steel burs mounted on a micromotor at 10,000 rpm

Table 2.

Comparison of KHN of the treated cavity floor dentin between the Er:YAG laser and bur therapies

KHNa(kg/mm2)
Sample no.	Laserb	Burc
1	65.4d	63.4
2	47.9	47.2
3	51.2d	52.9
4	52.6	49.9d
5	58.5	53.8d
6	57.6	50.5d
7	53.1d	63.1
8	39.9d	49.4
9	41.6d	45.5
10	37.8	37.3d
Mean±SD	50.4±8.5	51.7±8.1

Significance: NS. ^a Application of a 50 g load for 15 s. ^b Irradiation conditions: 145 mJ/pulse (51.3 J/cm²/pulse), 10 pps, under water spray. ^c Round steel burs mounted on a micromotor at 10,000 rpm. ^d The lower of the two KHN values for each sample

DISCUSSION

Despite changes in wavelength, pulse duration, and intensity, studies have demonstrated that the morphological properties of the dentin surface irradiated with laser, in addition to its benefits as a strategy for averting dental caries, are equivalent. Clinically, we found that laser preparation of hard tissue is tolerable in our study when water cooling is correctly applied. The adherence to irradiated tissues can be improved by morphological features of the surfaces prepared using lasers, such as analogous micromorphology, open dentinal tubules, selective removal of intertubular dentin and preservation of peritubular dentin, as well as the absence of thermal damage. Irradiation-induced microcracks, however, may make adhesion difficult on these surfaces.[1,2,3,4,5] When compared to traditional bur therapy, the Er:YAG laser required nearly three times the amount of time to remove cavities. We cannot be sure, but it is possible that the meticulous irradiation and unified energy setting used in this research went beyond what was therapeutically required due to the Er:YAG laser's first-ever examination of the extent to which caries might be eradicated. According to Keller and Hibst (1993b), the Er:YAG laser took almost twice as long as a high-speed bur to produce an enamel or dentin cavity. There are more and more reports demonstrating the Er:YAG laser's efficacy in treating hard tissues. The benefits and drawbacks of Er:YAG laser therapy in clinical settings, however, are largely unknown. More study into the structural modifications of laser-lasered dentin and enamel, their adhesion qualities to adhesive restorative materials and optimal irradiation settings and procedures are required before an effective Er:YAG laser treatment plan can be devised. Six, nine, and ten treating dental cavities using an Er:YAG laser system, which utilises light energy ablation rather than conventional mechanical cutting, may become a viable option for some time in the future.

CONCLUSION

Although laser expertise has a bright upcoming in dentistry, supplementary research is desired to determine the optimal irradiation settings for cavity preparation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.