A clinical comparison of the caries inhibitory potential of aluminum gallium arsenide LASER in conjunction with a remineralization paste in non-cavitated carious lesions

Abstract

Background:

Dental caries is a progressive disease with varying phases of demineralization and remineralization. If diagnosed before surface cavitation, the scope of reversing the carious lesion is increased.

Aim:

To evaluate caries preventive and caries inhibitory potential of Aluminum Gallium Arsenide (Al Ga As ) Laser irradiation in incipient noncavitated pit and fissure caries.

Methodology:

One hundred four patients between the age of 18–25 years exhibiting site 1 size 0, bilateral noncavitated carious lesions on mandibular molars were selected. The contralateral tooth type served as control. The quantitative baseline assessment of carious lesions of both the groups was by a Laser fluorescence method (DIAGNOdent). Group A (Test) cases were irradiated with Al Ga As laser of 3.5 W for 30 s followed by application of CPP-ACP F remineralizing paste. On the contralateral tooth type only remineralizing paste was applied and these cases were included In Group B (Control). The follow up was done by laser fluorescence (LF) and IOPA radiographs every 3 months for 12 months. Decrease or fall in laser fluorescence values from baseline values indicated remineralization.

Result:

Categorical variables were presented in number and percentage (%) and continuous variables were presented as mean ± SD. Normality of data was tested by Kolmogorov-Smirnov test. Qualitative variables were compared using Chi-Square test /Fisher’s exact test. Student’s unpaired “t” test was applied to test the difference between mean values of two groups. Student’s paired “t” test was applied to test the relative change between different time points. One-way ANOVA was applied to compare mean values between more than two groups followed by post hoc test “Tukeys HSD” for multiple comparisons. As per Lussi criteria, it was observed in Control group : 53 patients scored 4 and required operative intervention, 38 patients scored 3 which would necessitate repeating the remineralizing protocol, whereas Test group: 3 patients scored 4 and 5 patients scoring 3. Comparing the LF values, it was observed progression of caries denoted by increase in LF values in control was statistically significant with p value < 0.001 and SD of 7.04. Test group exhibited a fall in LF denoting caries reversal which was statistically significant with p value < 0.001 and SD of 5.80. The failure rate of Control was 51.5% and Test was 3%.

Conclusion:

Based on the clinical results it was concluded that Al Ga As lasers can clinically bring about caries inhibition and can be a valuable tool in caries prevention.

Keywords

LASER dental caries caries prevention caries inhibition LASER fluorescence

Introduction

Dental caries is a highly prevalent oral disease and till date continues to be an omnipresent global health care concern.^1–3 In India, it remains an unsurmountable oral health issue due to the diversity in ethnicity, food habits, socioeconomic strata, cultural beliefs and habits. The immensely diverse variables are further impacted by a serpentine oral health care policy with a on-ground meager dedicated workforce. Thus, dental caries continues to be a menace which is the prime cause of loss of teeth accompanied by the psychological trauma it entails.^1,3

Dental caries is a multifactorial oral affliction due to microbiome dysbiosis with amplification of cariogenic microflora.^4,5 Carious lesions are a result of microbial metabolism leading to ecological imbalance of biofilm with increased metabolic activity.⁶ The interplay of host factors like tooth morphology, saliva, genetics with factors like diet and causative microorganisms over a period of time may make the tooth susceptible to acidic challenges.^4–7

Since dental caries is a progressive disease with varying stages of demineralization and remineralization, the potential for reversing the carious lesion is increased if it is diagnosed prior to the development of surface cavities.⁵ Hence, remineralizing strategies over a period of time have prudently been limited to topical applications, ranging from incorporating fluorides in combination with remineralizing pastes like casein phospho peptide with amorphous calcium phosphate (CPP ACP).^8,9 These newer nanocomplexes have shown to have anticariogenic potential in lab, animal and human in situ experiments.⁸ The limitations of remineralizing studies is that most of the evidence based studies are in vitro and outcome is divergent when translated to complex dynamic oral milieu. The other impediments are remineralization to occur within the body of a subsurface lesion, calcium and phosphate ions must penetrate the intact surface layer of the enamel.^5,10

Thus, an efficacious preventive regime would be one, which not only has a synergistic caries preventive or caries inhibitory outcome but also increase the effectuality of these remineralizing pastes. One such therapeutic modality is inclusion of lasers in the caries preventive and caries inbition protocol.

Since 1960 when the first laser was developed by Maiman, lasers have been experimented with the aim to improve acid resistance and serve as an alternative to fluoride.¹¹ Synergistic action of fluorides along with irradiation of high powered lasers on sound and intact enamel surfaces was observed to provide immunity against caries initiation and progression.^11–13

High powered lasers have been discontinued for caries inhibition owing to their high cost, bulky equipment and lack of any evidence based therapeutic application.^11–13 Low powered laser has a large number of soft tissue oriented clinical applications. Today they are being explored as an alternative to high powered lasers in hard tissue applications.^11,14

Currently the research is ongoing to develop a versatile laser which is portable, highly efficient, cost effective and has a wide range of clinical applications. One such elaboration is aluminum gallium arsenide lasers (Al Ga As). It has a wide range of soft tissue centric clinical applications and it is hypothesized, that it can increase the acid resistance of tooth structure. The greater selectivity of these wavelengths lead to removal of carbonate ions from enamel crystal thus increasing uptake of fluoride ions.^15–22

The proposed study is intended to bring better understanding among clinicians regarding the current caries preventive and inhibitory modalities available. The study’s findings shall help formulate standard treatment guidelines, and suitable recommendations for caries prevention and inhibition and thus, help reduce the caries burden. It will save precious man-hours spent in restorative and endodontic work. Hence this study has been designed to explore the possibility and hypothesis of using aluminum arsenide laser as a caries preventive and inhibitory tool in caries prone population.

Methodology

Institutional Ethical Clearance was obtained. Patients of either sex between 18 and 25 years, reporting to OPD of Conservative Dentistry and Endodontics having initial pit and fissure caries bilaterally on first and/ second mandibular molar were included in the study and its respective contralateral tooth served as control. Out of the initial screening, 279 patients fulfilled the criteria for Site 1 Size 0 (Mount and Hume classification) bilateral non-cavitated carious lesion of mandibular first molar and/ or second molar.

Out of the screened patients, 134 patients were further shortlisted based on Ekstraand clinical and radiological scoring of 0,1,2 and R0 or R1 respectively and ICDAS scoring of 0 and 1. The final selection was completed by Lussi Criteria for laser fluorescence device (DIAGNOdent pen 2190 KaVo, Biberach, Germany) and patients scoring between 14 and 30 laser fluorescence (LF) values were selected.

Thus 104 patients satisfying the inclusion criteria of exhibiting site1 and size 0 carious lesion bilaterally on mandibular first and/or second molars and scoring 0,1,2 by Ekstrand Clinical scores and (0 or 1 by ICDAS scoring) and scoring R0 or R1 by Ekstand radiographic scoring and also scoring LASER Fluorescence values of 14–30 by Laser fluorescence device were included in the study. The selected teeth on one side served as the test and the similar lesion on the contralateral tooth type was the control. The group allocation was by randomly assigning to two groups: test group that is, Group A and the control group that is, Group B ( contralateral tooth type).

The selected teeth – (Group A) were irradiated with 3.5 W, 810 nm Aluminum Gallium Arsenide (AlGaAs) diode laser, (Whitestar™, Creation, Verona, Italy; Figure 1) followed by application of remineralization paste, Casein Phosphopeptide – Amorphous Calcium Phosphate Fluoride (CPP-ACPF) paste (GC Tooth Mousse Plus) The contralateral tooth type served as control – (Group B), in which after noting laser fluorescence method readings only remineralization paste was applied by the operator. The patient were given a tube of remineralizing paste. The patient was advised to apply a pea size application only to the control tooth at night and maintain a chart (Figure 1). The application on control tooth was advised for a month, the test tooth had no application of remineralization paste, other than what was applied by the operator. Patients were reassessed with a laser fluorescence device after a week then after a month. Thereafter, follow-up at 3 monthly intervals included serial scanning with the Laser fluorescence method and comparison with baseline reading. The readings determined if caries has been inhibited, arrested or progressed. The follow-up was carried out for a total period of 12 months (Figure 2).

Figure 1.

Clinical cases: procedure.

Figure 2.

Clinical cases: follow up.

The data was statistically analyzed by parametric tests that is, student unpaired t-test, paired “t” test and Chi² test of significance for nominal and categorical data. The Excel and SPSS Version 17.0 (SPSS Inc, Chicago) software packages were used for data entry and analysis. SPSS was initially developed as a Statistical package for the social sciences (SPSS). SPSS provides a number of facilities for data manipulation, allowing a variety of data transformations and restructurings to be simply performed. The tooth was considered as a single unit of scrutiny and thus each tooth was referred to as a case. Median survival time was compared using Kaplan Meier test. At the bivariate levels, the following independent variables were assessed: patient’s sex and age, treatment modality. Categorical variables were presented in number and percentage (%) and continuous variables were presented as mean ± SD. Normality of data was tested by Kolmogorov-Smirnov test.

Statistical tests were applied as follows-

Qualitative variables were compared using Chi-Square test/Fisher’s exact test .

Student’s unpaired “t” test was applied to test the difference between mean values of two groups.

Student’s paired “t” test was applied to test the relative change between different time points.

One-way ANOVA was applied to compare mean values between more than two groups followed by post hoc test “Tukeys HSD” for multiple comparisons.

Results

The gender distribution in a sample size of 104 cases was 57 females and 47 males. The distribution was 55% females to 45% males. The age range was 18 –25 years. 29 patients were in age group of 21 years. 18 patients were in age group of 19 years. Maximum patients were in age range of 19–23 years. In the control group there is non-significant difference between male and female with p-value < 0.05 except at preop to postop 1 week, where male have higher change than female with p-value 0.05. There is significant difference in change from pre to post 1 week between male and female. In case of male patients, this change is more than female patients. At all other time points, there is non-significant difference. In the test group There is non-significant difference between male and female with p-value < 0.05 except at preop to postop 1 week and 1 week to 1 month change. In preop to postop 1 week male have higher change, whereas female have higher change than male at time 1 week to 1 month with p-value < 0.05. In this study the test and control values are measured from the same patients and hence related with each other. So, by applying paired t-test to see the pair-wise difference, values of test and control are compared. There is significant difference in control and test values at all the time points with p-value < 0.05. The value of laser fluorescence in test group decreasing significantly up to postop 6 months and after 6 months, it stabilizes and there is no significant change observed up to post op 12 months of the study. The value of laser fluorescence in the test group decreased significantly up to postop 6 months and after 6 months there is a significant difference in mean fluorescence of the control group with the test group at all time points and the difference increases with an increase in time after post-op, it stabilizes and there is no significant change observed up to post-op 12 months of the study. The longitudinal monitoring of caries in the control group revealed that there is a significant change with respect to time at all-time points with a p-value < 0.05. To observe the change with respect to time within the control group, a paired t-test was applied. Since the p-value in the last column is less than 0.05 at all pairs, so we can say that there is a significant change in laser fluorescence at each time point. The value of laser fluorescence first decreased significantly up to postoperative 1 month and after 1 month it rose significantly up to post-op 12 months of the study. In the test group it was observed the change with respect to time within Groups ANOVA was applied. It was observed there was statistically significant changes within groups There is significant change with respect to time up to 6 months with a p-value < 0.05. However, after 6 months there is non-significant change up to 12 months (Table 1, Graph 1). When the success-failure rate correlated with LUSSI criteria, for the control group it was observed that as per Lussi criteria, 53 patients scored 4 that is, requiring definitive operative intervention (Graph 2A & 2B).

Table 1.

Comparison of mean laser fluorescence values between test and control group.

LASER FLUORESCENCE (LF ) Values	Mean	N	Std. deviation	Mean difference	t-Value	p-Value
PRE-OP LASER FLUORESCENCE C	25.58	104	2.92	−1.18	7.15	<0.001
PRE-OP LASER FLUORESCENCE T	26.76	104	2.42
POST-OP 1 week C	24.15	104	2.47	5.95	19.02	<0.001
POST-OP 1 week T	18.20	104	2.93
POST-OP 1Mth C	23.32	98	2.34	8.63	30.36	<0.001
POST-OP 1Mth T	14.68	98	2.10
POST-OP 3Mth C	23.98	102	3.20	10.46	29.46	<0.001
POST-OP 3Mth T	13.52	102	2.57
POST-OP 6 Mth C	25.51	102	4.62	13.48	27.25	<0.001
POST-OP 6Mth T	12.03	102	3.40
POST-OP 9Mth C	27.72	101	5.97	15.65	25.51	<0.001
POST-OP 9Mth T	12.07	101	4.69
POST-OP 12 Mth C	29.73	101	7.04	17.30	23.89	<0.001
POST-OP 12Mth T	12.44	101	5.80

In this study the test and control values are measured from the same patients and hence related with each other. So, by applying paired t-test to see the pair-wise difference, values of test and control are compared. There is significant difference in control and test values at all the time points with p-value < 0.05. The value of laser fluorescence in test group decreasing significantly up to postop 6 months and after 6 month, it stabilizes and there is no significant change observed up to post op 12 months of the study. The value of laser fluorescence in test group decreasing significantly up to postop 6 months and after 6 month there is significant difference in mean fluorescence of control group with test group at all time points and the difference increases with increase in time after post-op, it stabilizes and there is no significant change observed up to post op 12 months of the study.

Graph 1.

Comparison of control & test laser fluorescence values. The value of laser fluorescence in test group decreasing significantly up to postop 6 months and after 6 month, it stabilizes and there is no significant change observed up to post op 12 months of the study. The value of laser fluorescence in test group decreasing significantly up to postop 6 months and after 6 month There is significant difference in mean fluorescence of control group with test group at all time points and the difference increases with increase in time after post-op, it stabilizes and there is no significant change observed up to post op 12 months of the study.

Graph 2.

(A) Success failure score of control compared with Lussi criteria. For control group correlating with LUSSI criteria. As per Lussi criteria score 4 are which require definitive operative intervention. In control group 53 patients require operative intervention Score 3 indicates questionable prognosis thus in control group there 38 patients may need operative intervention. whereas in test group there are 3 failures. The deterioration in score is seen right from 3 months. (B) Success failure score of test compared with Lussi criteria. In test group 3 patients had score 4 and 5 had score 5. Thus, there are three definitive failures and five need to be kept under observation. Deterioration in score first is seen in 9 months.

Score 3 indicates questionable prognosis thus in the control group 38 patients may need operative intervention whereas in the test group, there are three failures. The deterioration in the score is seen right from 3 months for the control group. In the test group 3 patients had scored 4 and 5 had scored 5 as per the Lussi Criteria. Thus, there are three definitive failures and five need to be kept under observation. Deterioration in score first is seen in 9 months in the test experimental intervention group (Graph 3).

Graph 3.

Failures in control and test. The frequency of failure increase right from 3 months in control group and steeply rises in number to 53 at end of 12 months. Control group there is a margin rise to three failure and that is discerned at end of 9 months.

Discussion

The advances in research, its evolution in nature and extent, in the last decade, has completely revolutionized the way dental caries have been perceived, understood, prevented, and intercepted and the resultant innovative management strategies clinically integrated. Dental caries delineates the results, the sign and symptoms, of a circumscribed chemical deliquescence of the tooth surface caused by metabolic phenomenon taking place in the biofilm canopying the affected area. The confined ruination can originate in enamel and then progress to deeper hard tissues of the tooth. Thus, if we can detect the signs and symptoms at the very onset, we can halt the disease process.^4–7

Jain et al. in an epidemiological study found that currently there is a change in pattern and trend of dental caries. Thus there is an increase in the number of non cavitated lesions as compared to cavitated lesion and its more common at the age of 14 years and above.²³ The steep proportion of non-cavitated caries lesions in succedaneous molars can mainly be ascribed to the initiation of the caries process post eruptively within 6 years of tooth eruption.^23–26 Young adults aged 18–25 years are vital in cariology research, as this is the age group in which there is a metamorphosis from turbulent teens to adulthood. This age groups encompasses complex diversiform development physically, psychologically, socially and furthered impacted by peer pressure and new found financial independence.^23–26 Hence in this study the sample population was drawn from 18 to 25 years and specifically the first and second molars were included in the study. The sample population was more or less equi distributed amongst both the genders. In a sample size of 104 cases there were 57 females and 47 males. The distribution was 55% females to 45% males

Under physiological conditions when the pH of saliva is 7.4, the oral fluent are supersaturated for hydroxyapatite and fluoroapatite. When the pH in the oral fluids decreases, the tooth mineral apatite solubility dramatically increases. The solubility of apatite spirals by a factor of 10 with a drop of each single pH unit. At a critical pH the fluids become precisely saturated for hydroxyapatite. As fluorapatite is less soluble than hydroxyapatite, the plaque fluid remains supersaturated for fluorapatite when it is undersaturated with respect to hydroxyapatite. Under these conditions, a carious lesion is initiated. This dissolution of initial enamel crystals and/or dentin crystals is known as demineralization.⁵ The net loss of mineral loss of mineral from tooth surface results in the earliest clinical manifestation that is, white spot. The complete depth of enamel layer may be involved by caries but still the lesion may not be cavitated. This is because enamel is not homogenous throughout in its thickness and composition. At ultrastructural level enamel is formed of closely appositioned hydroxyl apatite crystals. Outer 50–100 µm of enamel layer is heavily impregnated with fluoride. Below this zone there is more concentration of carbonate ions and less of fluoride ion concentration. The greater concentration at the surface could be attributed to the fact that that during tooth development the unerupted enamel is bathed in tissue fluid rich in fluoride and thus gets deposited on surface enamel. The supersaturation at surface layer chokes out fluoride from permeating into subsurface layers. The incipient carious lesion and non cavitated lesions are thus characterized by intact surface layer due to more fluoride in the 50–100 µm of the tooth’s outer surface and subsurface dissolution due to decreased fluoride ion concentration.^5,10,27

Clinically, the non cavitated lesions appear as white spots, brown spots, or as dark shadow from dentin appearing on enamel surface. These lesions if diagnosed at the incipient stage, then timely preventive therapies can be instituted to repair and rebuild the lesions to restore form and functionality.⁵ Thus, to harness the remineralization potential of initial noncavitated lesion we have in our inclusion criteria selected site 1 size 0 lesions (Mount and Hume classification) which have scored V0, V1, or V2 in Ekstraand criteria for visual scoring for dental caries and 0, 1, or 2 in ICDAS index.^28–30 The Ekstraand criteria for radiographic scoring was within R0 or R1. The tooth which is most prone to dental caries is first mandibular molar, especially young permanent molars.^22–26 Hence in this study we have selected mandibular first and second molars. The test and the control are in the same person and test tooth is the contralateral tooth type of that of control. This makes the challenges of oral environment similar for both test and control teeth.

The potential and functional accuracy of caries detection and diagnosis methods is evaluated based on two important parameters: that is, reproducibility and validity.^5,31–33 Caries detection and diagnosis since centuries has pivoted on visual acuity and tactile methods. The detection was dependent on variation in color of occlusal pits and fissures and compromised enamel integrity. The visual and tactile method depends on the clinical acuity of the clinician and it is not reproducible even for the same clinician leave alone for other observers. The carious process is a disease continuum and to monitor it at a specific point will give an unfounded, inaccurate and unrealistic result. Since the remineralization process is to be harnessed to reverse the carious progression a method of caries detection and diagnosis is required which detects incipient or early reversible lesions. The validity of visual caries detection is also questionable especially in incipient lesions. The radiographic method can be used as a base line diagnostic tool, estimating the depth of lesion and for assessing and monitoring progression of the lesion over a period of time, and is more sensitive investigative or detection aid than clinical inspection. However, since caries detection on radiographs relies on mineral loss, the lesion may have burgeoned beyond ambit of remineralization before it is sighted. Moreover, radiography cannot distinguish between active and arrested lesions and diagnosis is dependent on the interpretation skill of the dentist.^28–31 Hence a diagnostic adjunct or tool is mandatory to provide acceptable concessions between sensitivity and speciﬁcity for a wide range of applications such as for individual caries control and management as well as for research purposes. Current caries diagnostic aids utilize and analyze the revision in laser ﬂuorescence, enamel reﬂectance, enamel electrical conductance or impedance, and ultrasound transmittal properties of enamel with respect to demineralization and remineralization during the continuum of a carious lesion over a period of time.^5,32–34

The reviewed methods have demonstrated that laser fluorescence (DIAGNOdent™; KAVO, Biberach, Germany) is a promising quantitative accurate and reproducible method for diagnosis of caries, particularly when used as an adjunct to visual inspection.^5,32–39 It not only detects early and hidden caries but also aids in longitudinal assessment and monitoring of caries activity. Lussi criteria gives the range of values of the laser fluorescence with its clinical implication and application.³⁵ Moriyama et al. in an in vitro study estimated the adequacy of fluorescence-based methods to detect demineralization and remineralization on smooth surfaces and he concluded that it was an effectual computation of smooth surfaces lesions.³⁴ Studies by Lussi and Hellwig,³⁵ Fung et al.,³⁶ Burin et al.,³⁷ Attrill and Ashley,³⁸ Novaes et al.³⁹ construed that laser fluorescence technique is a promising predictive diagnostic aid and is more sensitive than the traditional method of visual and radiographic examination and most studies have recommended it as adjunct in diagnosis of carious lesions.^35–38 The specificity of laser fluorescence method is 86%–90% and sensitivity between 87% and 92%.^{5,9–13,38,39} Visual method for detection of visible pit and fissure caries have a sensitivity of 60%–90% and specificity greater than 90%, but for subsurface lesion the sensitivity plummeted to 12%. In studies conducted by Sharma et al. it was observed that laser fluorescence is reliable and a valid tool to detect demineralization and remineralization and is a valuable tool in the longitudinal monitoring of dental caries.^40,41 Hence in this study laser fluorescence was selected as an assessment tool to study the effect of aluminum gallium arsenide laser on enamel surface.

Preventive therapeutic strategies are directed toward enhancing the acid resistance of the enamel substrate. The caries progression may be regressed by the application of risk modifiers. Fluoride is an effectual therapeutic risk modifier and thus the cornerstone of caries preventive strategy. Risk modifiers work by impacting factors that promote the caries process, mitigating or negating their effects. The mineral alters the caries process by interfering with the progression of the carious lesion by enhancing remineralization, reducing demineralization, and inhibiting bacteria. Fluoride has played a pivotal role in the prevention of dental caries since the inception of water fluoridation in the mid 20th century. However, Ten Cate have inferred that to remineralize subsurface lesions 150 µm deep we require 5000 ppm of fluoride, misuse and excessive doses of fluoride can lead to toxic side effects and even be fatal.¹⁰ Repeated topical application can give rise to either acquired fluoride-resistant S. mutans which can be in turn be can be transient or permanent. Stable, or permanent, fluoride resistance persists for at least 50 generations of S mutans.⁴²

Hence an alternative remineralizing paste which could substantiate the effect of fluoride was sought. Evidence-based literature has shown that fluoride and CPP ACP are used as adjuncts in remineralization protocol with varying degrees of success. CPP ACP when combined with fluoride has a synergistic additive effect and it has been documented that CPP ACP will ensure a reservoir of fluoride ions in the plaque and thus facilitate the fluoride uptake into subsurface enamel lesion, CPP ACP thus provides and maintains the correct molar ration bioavailability of fluoride, calcium ions, phosphate ions which leads to acid resistance fluorapatite layer.^8,43–47 Jayarajan et al. conducted an invitro comparative analysis of the remineralizing potentiality of CPP ACP and CPP ACP F. The inclusion of NaF in CPP ACP F has been attributed to better remineralizing potentiality than CPP ACP alone.⁴⁸ Hence in this clinical study we have used casein phosphopeptide amorphous calcium phosphate with fluoride [CPP ACP F] as remineralizing paste both in test and control group.

The limitations of remineralizing studies is that most of the evidence-based studies are invitro and is divergent when juxtaposed on heterogenous, variegated dynamic oral domain. The other limitations are remineralization to occur within the body of a subsurface lesion, calcium and phosphate ions must penetrate the surface layer of the enamel. The highly mineralized and charged property of the surface zone poses a challenge for ion penetration. CPP ACP products if ingested in significant quantities will cause side effects. The potential risk increases with patients who have allergic diathesis especially IgE immunglobulinopathies. The effectiveness of CPP ACP in remineralizing subsurface lesion is questionable.²² Another limitation is that repeated application of remineralizing paste is needed to maintain and replenish a constant supply of the lost remineralizing ions. Thus, an efficacious remineralizing protocol would be one which brings about a change in enamel crystal and makes it more resistant to acidic challenges of oral cavity, one such modality is inclusion of LASER.^16–20,22

In the in vitro studies by Sharma et al. CPP ACP F has been compared with other surface treatment protocols like Enafix and Laser. It was observed that CPP ACP F in synergism with LASER improved the microhardness and reverted the calcium phosphate ratio in the demineralized sample to that of intact teeth. Though it was also reiterated that LASER alone increased the microhardness and reverted the calcium phosphate levels substantially^19,20

Since it was postulated by Stern in 1974 that LASER irradiation can bring about increase in acid resistance of the irradiated substrate like enamel, a sweeping range of hypothesized mechanisms of actions have emerged. Spectrum of doctrine ranged from reduced permeability of enamel to chemicals agents caused by melting of hydroxyapatite crystals to changed enamel crystal lattice orientation. The lasers which have been investigated in the past for caries inhibition are CO₂, Nd: YAG, Er: YAG, Er Cr: YSGG.^11–14 Hicks et al. conducted a scanning electron microscopy to assess the surface changes when surface treatment is done with argon alone or with fluoride. Both combinations had a caries inhibitory role.⁴⁹ Lasers like CO₂, Nd: YAG, Erbium: YAG have all said to have a caries inhibitory role. These lasers had disadvantage of high cost, being bulky and result obtained was debatable. Further, most of the studies evaluating the high-power lasers are in vitro studies.^11–14

Currently the research is ongoing to develop a versatile laser which is portable, highly efficient, cost effective and has a wide range of clinical applications. Low powered laser has a large number of clinical applications mainly directed toward soft tissues. But today they are being explored as an substitute to high powered lasers in hard tissue applications.^{11,12,15–20}

Today, aluminum gallium arsenide laser is being investigated as an alternative to high powered lasers.^16–20 The hypothesized mechanism of action is that these wavelengths selectively target and remove carbonate ions from hydroxyapatite crystals which results in increasing acid resistance of enamel. Additionally, the altered mineral has greater uptake of topically applied fluoride and thus greater acid resistance and leads to remineralization of noncavitated lesions.¹⁶ Sant’anna De G R carried out a FT–Raman study to analyze the compositional changes in enamel induced by a combination of low-level lasers and photo-absorbing cream. It was found that low-level lasers like diode lasers modified the organic matrix content which led to caries inhibition.¹⁵ In a study by Sharma et al. a Fourier Transformation Infra-Red (FTIR) Spectroscopic analysis of enamel following different surface treatments was conducted. It was observed that Laser irradiation of 3.5 W followed by CPP ACP F application led to compositional change with disappearance of the weakest link in remineralization that is, carbonate group.²⁰ Thus, in the clinical study too we have selected aluminum gallium arsenide laser to increase the acid resistance and the remineralizing potentiality of incipient non cavitated lesions.

For any clinical application of laser, the optical interaction of laser with enamel and dentin must be comprehensively surmised. The laser interaction with dental hard tissues depends upon irradiation parameters such as wavelength, pulsed or continuous emission, pulse duration, repetition rate, beam spot size, and delivery method. All reviewed studies agreed upon the caries inhibitory role of lasers but none ascertained the parameters like optimal wattage to bring about the desired result.^10–15 Thus, in vitro studies were first conducted to determine an optimum wattage and exposure time which will bring about the desired results. In the in vitro study the authors correlated the effect of different wattages and time on demineralized enamel to bring about reversal to remineralization. It was observed that 30 s exposure time at 3.5 W brings the desired results with fall in laser fluorescence values.^17,18

Another challenge in this study was to determine the sequence of the protocol of laser and remineralizing paste application. Carounanidy has opined that laser activated fluoride method can enhance the remineralization potential of an acid challenged tooth.⁵⁰ Various studies have been done to evaluate the synergistic approach of laser with fluoride.^51–53 Although several studies have found that there is synergistic action when laser is used with remineralizing paste, on the other hand some studies have found equally good result with laser irradiation alone. Further the scientific world is divided on the synergistic role of lasers and fluoride in caries prevention.^49,53,54 In the present study, on the test group the fluoride application follows the laser treatment. There has been a fall in the laser fluorescence values in test group (Group A) which was irradiated by laser followed by fluoride application. This fall in values was seen throughout the follow up period. However, in control group, (Group B) in which only remineralizing paste was applied, the values initially fell and then again increased (Table 1, Graph 1). Thereby indicating that laser irradiation followed by remineralizing paste is more effective than remineralizing paste used alone. Comparison between control and test showed that there is statistically significant difference between test and control from day 1 to 12 months.

Ana et al. reviewed the effect of different lasers on caries inhibition and fluoride uptake.⁵⁵ The study group inferred that laser irradiation led to 30%–97.2% caries inhibition and better results were with laser and fluoride application. Ana et al.⁵⁵ deduced that under specific conditions laser irradiation can change crystallographic properties of apatite crystals and increasing the acid resistance of lased tooth as well as increased fluoride uptake.⁵⁵ De Melo found a caries inhibition rate of 29.2% when the teeth were irradiated with CO₂ laser.⁵⁶ The lasers which have been reviewed in the literature for caries prevention were Nd: YAG, Er : YAG; Er, Cr: YAG; and Argon.^49–55 Most of the studies reviewed were in vitro studies and the diode laser was not evaluated. Clinical studies at best have been pilot studies or short term.¹⁵ Thus, in this clinical study we have evaluated aluminum gallium arsenide laser therapy as a caries inhibitory tool. Comparing test and control, it can be inferred that the preoperative laser fluorescence values for all were in the same range to begin with. Laser fluorescence values over time have increased in control group thereby indicating demineralization but decreased in test group thereby indicating remineralization and thus it can be deduced that laser irradiation brings about changes in the crystallographic properties of enamel apatite and increases uptake of CPP ACP F paste much more than when the paste is used alone as in control. In the present study laser fluorescence values if it increased over 30 that is, score 4 during follow up, by Lussi’s criteria, indicated that it required intervention, was regarded as failure. Out 104 patients who had enrolled, the control had 53 cases which scored 4 and 37 which scored 3 by Lussi criteria. Whereas, the failure was three in test group and five patients had to be kept under observation as they had scored 3 (Graph 2A and 2B). It can also be inferred from the result that laser fluorescence values which are recorded at 7 days have a significant bearing on the success or failure of control and test. The comparison between preoperative variable 1 and the postoperative values for both test and control are statistically significant but for control it has negative impact indicating failure (Graph 1, 2A, 2B, and 3). Thus, our study is in confirmation with other reviewed in vitro studies and short-term pilot studies.

Survival analysis gives a clear forecast of the population surviving at the end of each time interval. In our study, we found that the patients only on the paste led to failures right from 1 months onward (Graph 3). When laser and fluoride are combined, it is possible to reduce laser energy density and fluoride levels required ⁵⁶; If this laser modality is available and is economically viable and the results can be extrapolated and routinely applied in clinical practice it may pave the way for a promising future for lasers in caries prevention.⁵⁷

Each study has its limitations and no study is flawless, nor should it be expected, as is envisaged in this study. The real concern, however, is whether any flaws are likely to influence outcomes and to what extent, rather than simply disregarding the conclusions. The definitive mode and is more sensitive a tool than clinical inspection. But since caries detection on radiographs depends on mineral loss, the lesion may have progressed beyond scope of remineralization before it is detected to determine the clinical footprint of a novel therapeutic intervention is through its endpoint such as reversal of carious lesion or survival of the tooth after laser caries inhibition. However, this standard may be impractical for the evaluation of new therapies, because long periods are required for these clinical endpoints to be achieved and trials with large numbers of patients are needed for their evaluation. This is a major impediment in clinical research. The issue of loss to follow-up has seriously compromised the reliability of many clinical studies, as a high proportion of subjects are unaccounted for. Therefore, high quality clinical trials using clinically meaningful endpoints are rare. A surrogate endpoint can accelerate the trial process and is described as a biomarker that is predetermined for replacement of a clinical endpoint. A surrogate endpoint is expected to foresee clinical benefit or lack of it or any risk accrued based on scientific evidence be it physiological, pathological, ameliorative, epidemiologic.⁵⁸ On the other hand, Clinical endpoints, are discrete, direct measurements that reflect how a patient will respond to treatment. Clinical endpoints are the most reliable traits used in the assessment of the risks and benefits of an therapeutic intervention in randomized clinical trials. In this study we have used clinical end point over a long follow up period of 12 months.⁵⁸ Since dental caries is a dynamic disease a surrogate endpoint should be determined to evaluate the validity of this novel technique.

Another limitation is that enamel chemistry studies should be also included to support the promising results. The synergism of the aluminum gallium and remineralizing paste needs to be studied at a molecular level.

Aluminum gallium arsenide lasers haven’t been evaluated as a clinical caries inhibitory tool in the past, further invivo studies are far and few between. Hence more such clinical studies need to be conducted. However, based on the results of this study, it can be inferred that aluminum gallium arsenide lasers seems a viable adjunct in the caries prevention protocol.

Thus, this novel concept of combining aluminum gallium arsenide lasers with remineralizing paste seems as a promising preventive and inhibitory modality for non-cavitated initial caries provided that they are diagnosed early. For early detection, laser fluorescence device is found to be reliable and accurate tool.

Conclusion

Based on the clinical results and corroborated by invitro study findings it can be concluded:

The optimal wattage which could bring about the caries inhibitory potentiality of aluminum gallium arsenide lasers clinically was 3.5 W.

The optimal time which could bring about the caries inhibitory potentiality of aluminum gallium arsenide lasers clinically was 30 s.

The aluminum gallium arsenide lasers increased the uptake of remineralizing paste in irradiated teeth.

Thus, lasers followed by remineralizing paste seems to be the appropriate sequence to be followed.

Remineralizing paste alone did not have sufficient long-term caries inhibitory potentiality.

Laser fluorescence device DIAGNOdent can be used as an viable caries detection and monitoring device.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Col Sonali Sharma

Mithra N Hegde

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