The advantages of, and reasons for, using a dental explorer to probe suspected carious lesions are numerous. This article will expand on these and investigate the level of evidence supporting an opposing point of view.

THE ADVANTAGES OF EXPLORER USE Dentists are well-trained in using a sharp explorer as an aid in diagnosing carious lesions. In the United States, the formal training in explorer use starts in dental school, and the principles of the technique are well-documented in operative dentistry textbooks.^1–3 The skills developed in dental school are continually refined and re-evaluated during years of clinical practice. With each increased level of technical and diagnostic refinement, dentists are able to question and re-evaluate the usefulness, acceptability and benefit to patients and their practice of these procedures. Dentists’ continuing acceptance throughout their careers of the technique of probing suspected carious lesions with a sharp explorer is one measure of the confidence given it.

The procedure of probing teeth for suspected carious lesions is well-accepted by dentists, dental insurance companies and patients. Probing for caries is part of the standard of care when examining teeth during a dental examination. The accepted procedure for using a dental explorer as an aid in diagnosing carious lesions is noted in both "Principles and Practice of Operative Dentistry"¹ and in the "Proceedings of the Conference on the Clinical Testing of Cariostatic Agents."⁴ These references note, "[an] area is carious when the explorer ‘catches’ or resists removal after the insertion into a pit or fissure with moderate to firm pressure, and when this is accompanied by one or more of the following signs of caries:

– "a softness at the base of the area;

– "opacity adjacent to the pit or fissure;

– "softened enamel adjacent to the pit or fissure."

It is important to note that the simple "catch" of an explorer is not enough to diagnose a carious lesion. Any explorer can be forced into a hard healthy crevice and be retained if the geometry of the explorer tip is similar to that of the pit or fissure. The use of only a "catch" may be the entire basis for some finding fault with a sharp explorer to probe pits and fissures. For example, in her 1984 article, Kidd⁵ noted under the heading "Pits and Fissures," "The fissure that is sticky to a sharp probe may not be carious histologically." This implies that the other criteria necessary for diagnosing caries were not considered. A 1985 article by Mjör⁶ noted, "Any condition where the probe sticks or catches might be recorded as recurrent caries." No other criteria were noted to justify the diagnosis of caries. In his 1998 article, Mjör⁷ noted, "This diagnosis [secondary caries] is often made if the explorer tends to catch at the tooth-restoration interface." Again, he noted no other criteria as necessary for diagnosing a carious lesion.

In the introduction to their article, Ekstrand and colleagues⁸ repeatedly used the term "sticky fissure." They, too, mentioned no other criteria as necessary for diagnosing a carious lesion. One has to ask if any of the research articles that questioned the use of an explorer used the currently accepted criteria that are necessary to properly diagnose a carious lesion. Other criteria are necessary, as noted in the references by Radike⁴ and Charbeneau and Brandau.¹

Dental explorers are a time-honored part of a dentist’s armamentarium. Explorers are acquired easily and require no special maintenance other than sharpening. The use of explorers does not require additional training, extra time, special sterilization procedures or protective sleeves. Explorers easily demonstrate to patients defective restorations or hard tissues. The broad popularity of this instrument is supported by its many different available configurations.

Explorer use is time-efficient. The time it takes to use an explorer throughout the mouth to aid in caries diagnosis is minimal compared with that required to use other aids in caries diagnosis. Detecting softness at the base of a pit or fissure or eliciting a patient’s response requires one or two seconds. Detecting hard and smooth fissures is even faster. Some newer instrumentation costing thousands of dollars has calibration and tooth-cleaning requirements. Although claims have been made supporting quantitative laser fluorescence devices in caries detection, there still are questions concerning their effectiveness.^9,10

The explorer’s excellent sensitivity has been demonstrated in in vivo research. In a randomized controlled clinical study to investigate the benefits of early operative intervention into incipient carious lesions, an explorer was used independently by two dentists at each six-month recall appointment according to the aforementioned procedure^1,4 as an aid in diagnosing caries in the pits and fissures of posterior teeth.^11,12 After two years, all teeth diagnosed with a carious lesion in the control group had caries penetrating into dentin, for a false-positive rate of zero and a sensitivity of 1. The rate of caries in the control group, surprisingly, was less than expected. The false-negative rate for caries diagnosis in this study was unknown; however, the authors did not consider this to be a problem, as in the same study there was no difference between the volume of the cavity preparations into dentin treated at baseline in the early treatment group and that in the control group treated up to two years later. Also, no patient in this randomized controlled clinical trial experienced any preoperative or postoperative sensitivity associated with any tooth in the study. Consequently, these researchers noted no adverse effects owing to the unknown level of caries penetrating into dentin that went undiscovered because of the method of caries diagnosis, which included probing suspected pits and fissures with a dental explorer.

Explorer use in the United States is consistent with a low decayed, missing and filled teeth (DMFT) index. The caries rate in the United States has been falling, as noted by Brown and colleagues.^13,14 There also is a decrease in DMFT throughout the world, according to data compiled by the World Health Organization.¹⁵ If the use of the explorer to probe suspected carious lesions has caused significant damage, then it becomes difficult to explain how this damage is significant in light of a falling DMFT. It also is interesting to note that the DMFT is falling similarly in industrialized countries that do and do not recommend the use of dental explorers to probe suspected carious lesions.¹⁵

REVIEW: STUDIES NOT IN FAVOR OF CARIES DETECTION VIA THE EXPLORER In 1973, Loesche and colleagues¹⁶ noted in 15 patients that Streptococcus mutans was isolated in large numbers from a dental explorer after it had been used in the examination of a carious tooth. This raised the possibility that the explorer can serve to inoculate other teeth in the same mouth with the bacteria that are associated with dental caries. Yet, this same article mentioned that this organism was present in humans on a worldwide basis, which would present the possibility that other teeth in the same person already were subjected to similar bacteria. Would the transfer of S. mutans–infected plaque make any difference if other teeth in the mouth already were coated with the organism?

In a larger study published in 1995 involving more than 861 patients, Hujoel and colleagues¹⁷ noted, "Examining a sound second molar with a contaminated dental explorer either does not affect the caries risk, or results in such a small increase in caries risk that it can only be reliably identified in studies where the exposure of sound teeth to contaminated dental explorers is randomized." One would think that if probing teeth leads to more caries, this problem soon would become obvious, since millions of teeth are probed every day.

Three commonly cited articles related to damage associated with the use of dental explorers to probe suspected carious lesions were written by van Dorp and colleagues,¹⁸ Ekstrand and colleagues⁸ and Yassin.¹⁹ The value of these studies may be addressed using guidelines from evidence-based dentistry.²⁰ The strongest evidence comes from systematic reviews and randomized clinical trials that use endpoints that are clear and meaningful to the clinical practitioner and the public. Case reports and expert opinion are the lowest level of evidence considered. It is notable that benchtop research is not even considered or mentioned.²⁰ Two of the above-mentioned studies commonly cited against explorer use in caries detection^18,19 are in vitro (benchtop) studies, and one of them¹⁸ did not even involve human teeth. All three studies used microscopic analysis of at least x25 magnification to show any damage to enamel, a level of magnification at which measurable damage is not meaningful to either clinical dentists or patients. No long-term clinical studies have demonstrated that such microscopic damage has caused any treatable condition. Microscopic damage to teeth can be attributed to probing with an explorer; however, there are no clinical studies that demonstrate that this microscopic damage is consequential in any way.

The randomized controlled study by Ekstrand and colleagues⁸ could have been more important if the probed teeth had been followed up for longer than one week to see if the microscopic damage was progressing, remineralizing or arresting. But, as in all of the aforementioned frequently cited studies, the microscopic analysis in this study was done on extracted teeth. Dentists do not treat teeth with damage that cannot be seen without extensive magnification. In addition, there is no evidence that teeth with microscopic damage need treatment.

Another concern related to the use of a sharp explorer to probe a suspected carious lesion is that, according to published studies,^5–8,21 it does not give useful diagnostic information concerning the presence of a carious lesion. The simple explanation is that in these studies, the criterion used to diagnose caries with an explorer was only a "stick" or a "catch." Yet, as noted above, a recent randomized controlled clinical trial in which an explorer was used as an aid to caries diagnosis (according to the criteria noted by Radike⁴ and Charbeneau and Brandau¹) and in which pits and fissures were probed independently by two dentists, all teeth diagnosed with caries did have carious lesions that extended into dentin when treated operatively with minimal intervention.

SUMMARY The caries rate is dropping worldwide, a fact that appears to have no relationship to whether dentists in the affected countries use an explorer to probe suspected carious lesions. Questions have been raised about this procedure on the basis of the purported inaccuracy of its contribution to caries diagnosis,^5–8,21 its possible spread of infective plaque from other teeth in the mouth¹⁶ or the damage it can cause to pits and fissures.^8,18,19 Long-term randomized clinical trials are necessary in these areas of question, trials that use endpoints that are clear and meaningful to clinical dentists. Until the time comes that facts emerge from acceptable long-term clinical trials, dentists should feel comfortable using the dental explorer to probe suspected carious lesions.

THE EXPLORER, REMINERALIZATION AND FALSE DIAGNOSES The caries process is a known continuum beginning with demineralization beneath dental plaque and progressing through various stages that include a so-called "white spot" and eventual cavitation. Since the 1966 report by Backer Dirks² documenting that white-spot lesions could be reversed completely and "disappear" clinically, many scientists have investigated the physicochemical dynamics of the caries process. Among the conclusions from these numerous studies is the fact that even though the white-spot lesion reflects the loss of mineral through the outer one-half of the enamel thickness, the lesion may be remineralized as long as the surface layer remains in place. Once the surface layer is broken, plaque acids diffuse into the lesion and the extent of the lesion progresses much more rapidly. Thus, an intact surface layer is considered essential to the reversal of the caries process, and penetration of this surface with an explorer converts a subsurface lesion into a frank cavity.^3,4

This realization, coupled with the observation that the use of the dental explorer in the historical manner resulted in an unacceptably high proportion of false-positive diagnoses on occlusal surfaces,^1,3 led a number of clinical scientists to re-examine the value of the use of the dental explorer as a probe for caries detection. The results of these studies indicated that this use of the dental explorer was of limited value for the detection of occlusal caries. For example, Lussi⁵ investigated the ability of faculty dentists and dental practitioners to diagnose fissure caries and determined that only 42 percent of the fissures were diagnosed correctly. In terms of reproducibility, a good level of which is expected to have a value approaching 0.75, faculty dentists had values of 0.21 using the explorer and 0.25 using only a visual examination. For dental practitioners, the values for the examinations were 0.24 and 0.23 with and without the aid of an explorer, respectively. Lussi also observed sensitivity and specificity values of 62 and 84 percent, respectively, indicating that practicing dentists were more likely to fail to treat carious fissures than to restore sound fissures.

Generally similar results of an unacceptably high number of false-negative diagnoses of fissure caries using the dental explorer have been reported by a substantial number of investigators.^3,4,6–18 As noted by Anusavice,¹⁹ many clinical decisions to place occlusal restorations are based on the inappropriate use of the dental explorer to determine the softness or tackiness of the fissure or the amount of resistance to the removal of the explorer from the fissure. Thus, Anusavice concluded that there is strong evidence to support the elimination of the use of the dental explorer in the historical manner.

The tip of the explorer should be moved gently across the surface of any noncavitated area to determine the presence or absence of surface roughness.

However, as noted by Kidd and colleagues,²⁰ the dental explorer continues to be an indispensable component of the caries diagnostic armamentarium. With the recognition that the caries process is a continuum and the caries process, if detected before cavitation, can be reversed or arrested with various professional and home-use fluoride measures, it is apparent that the mission of the clinical caries examination has changed from simply the identification of well-advanced lesions requiring restoration. Instead, the mission of the examination now includes the identification of lesions or demineralized areas at the precavitation stage that may be reversed or arrested if the thin surface layer covering the demineralized area remains intact. Thus, the use of the dental explorer in the traditional manner must be avoided, because it will fracture the surface layer and eliminate the possibility of reversing the caries process.

THE USES OF THE EXPLORER, PRESENT AND FUTURE The primary uses of the explorer are to remove dental plaque from the examination area and to determine the roughness of the surface of noncavitated lesions (white spots). Since dental plaque is essential for the development of dental caries, its presence is a clear indication that the area beneath the plaque needs to be examined carefully. The plaque biofilm may be removed gently with a scraping action of the explorer’s shaft or by the use of the explorer’s tip in fissures to expose the underlying enamel surface.

In addition, the tip of the explorer should be moved gently across the surface of any noncavitated area (white spot, brown spot) to determine the presence or absence of surface roughness as an indication of whether the underlying demineralized area reflects an active lesion. In the absence of imaging technologies, which still are evolving, the use of the explorer in this manner coupled with the visual examination appear in several studies to be the most effective means for the diagnosis of clinical caries and the identification of the most appropriate approach for caries management.^4,9,21–27 These studies have demonstrated clearly that the use of the dental explorer in this manner does not diminish the clinician’s ability to detect accurately more advanced lesions requiring restoration on both occlusal and smooth surfaces. Moreover, this procedure permits the detection of precavitation-stage lesions and the determination of whether these areas are active. This latter assessment of the precavitated lesion or demineralized area permits the clinician to identify the appropriate professional and home-use treatments to reverse or arrest the process and to monitor the success of the treatments at subsequent examinations. Thus, while the dental explorer continues to be a critical component of the clinician’s diagnostic armamentarium, its use as a probe in the historical manner for a tactile examination of the tooth surface is contraindicated.

CONCLUSION There is an increasing body of scientific data indicating that noncavitated incipient lesions may be remineralized if the surface layer covering the demineralized area or lesion (the white spot) remains intact. Because the use of the probe generally has disrupted this surface layer and prevented the possibility of reversing the noncavitated area through remineralization, the use of the probe to determine the softness or tackiness of the noncavitated lesion is contraindicated.