Caries-affected dentin is useful because its low permeability compared with healthy dentin^7,8 protects the pulp from any remaining bacteria in the affected dentin. In response to the carious process, the odontoblasts precipitate calcium phosphate to form plugs in the dentin tubules, creating the odontoblastic reaction zone. When this effect is combined with isolation of bacteria from external sources of nutrients, caries progress has been shown to be arrested over periods of up to 10 years.⁹ Unfortunately, carbide or diamond burs, when used for cavity preparation, often remove reversibly affected dentin along with the odontoblastic reaction zone plugs, resulting in exposure of the more permeable healthy dentin.

Anusavice and Kincheloe¹⁰ demonstrated that cutting or removing carious dentin generally elicits little or no sensation, while cutting sound dentin often results in some level of pain. This has been the basis of extensive experimentation with, and clinical evaluation of, chemomechanical systems for caries removal.^11,12 However, chemomechanical removal of caries is quite time-consuming, and it results in low levels of clinician and patient acceptance.¹³

The polymer instrument will not cut sound dentin unless applied with great force.

	CAVITY PREPARATION

TOP ABSTRACT CAVITY PREPARATION SUBJECTS, MATERIALS AND METHODS RESTORATIVE PROCEDURES ANALYTIC PROCEDURES RESULTS DISCUSSION CONCLUSION REFERENCES

 
Fusayama¹⁴ proposed a pain-free method of cavity preparation based on selective penetration of enamel and use of a caries-detecting dye to prevent cutting sound dentin. This approach is coupled with adhesive dentistry materials and techniques. Adhesive cavity design has not been accepted generally because clinicians have been trained to extend cavity preparations beyond the carious tissue to allow for mechanical retention of the restorative material.

Hence, traditional cavity preparations involving the use of carbide or diamond burs and extending into sound dentin are coupled routinely with LA to prevent painful stimuli. This results in overcutting of enamel and dentin.^15,16 Minimally invasive dentistry depends on adhesive-style cavity design and would be greatly aided by an instrument whose cutting is limited to caries-affected dentin. In addition, cutting only within the affected dentin could minimize or eliminate the need for local anesthesia (LA) in most patients.

Recently, Yoshiyama and colleagues¹⁷ demonstrated that the Knoop hardness of caries-affected dentin is in the range of 10 to 40 kilograms/ square millimeter, and healthy dentin is in the range of 45 to 63 kg/mm². SS White Burs (Lakeland, N.J.) has developed a dental instrument (SmartPrep) for selective removal of carious dentin that is made of a medical-grade polymer with hardness less than that of healthy dentin. The instrument is based on the concepts and patents of Daniel Boston, D.M.D., Temple University School of Dentistry, Philadelphia.^18,19 This single-use, burlike instrument is designed to lose its cutting efficiency while in the caries-affected dentin. Thus, the polymer instrument is self-limiting and will not cut sound dentin unless applied with great force, and then it will only wear away, rather than cut, the healthy dentin.

Clinicians can monitor the cutting efficiency easily via the feel of the resistance of the dentin. Our study was designed to compare acceptance (within the same subject) of Class I cavity preparations done using a polymer instrument without LA with that of preparations done using a conventional carbide bur with LA. We evaluated whether patients preferred the polymer instrument over the carbide bur; whether use of the polymer instrument resulted in more pain or other sensations than did use of the carbide bur; and whether preference for the polymer instrument, if found, was mediated by its more benign side-effect profile.

	SUBJECTS, MATERIALS AND METHODS

TOP ABSTRACT CAVITY PREPARATION SUBJECTS, MATERIALS AND METHODS RESTORATIVE PROCEDURES ANALYTIC PROCEDURES RESULTS DISCUSSION CONCLUSION REFERENCES

 
We enrolled patients who had at least two Class I primary carious lesions to receive resin-based composite restorations. Two of us (K.A., T.S.) restored one lesion after using the polymer instrument to remove the carious dentin. The clinicians restored the other lesion after administering LA, followed by carbide bur instrumentation to remove the carious tissue. They completed both restorations using standardized methods of dentin bonding and polymerization of resin-based composite placed in increments.

The chief clinical research coordinator questioned patients before, during and after the procedures to rate their sensations of pressure, vibration, heat, cold and pain, as well as their feelings of fear and anxiety. In addition, we determined patients’ preferences with regard to the procedure immediately after the procedure and at scheduled posttreatment (48 hours and one week) telephone contacts. Patients were surveyed at these postoperative times to determine if any hypersensitivity developed as a result of the procedures.

Inclusion criteria. Subjects were between the ages of 18 and 65 years, and they came to the Bluestone Center for Clinical Research, New York University (NYU) College of Dentistry, New York City, for treatment of two posterior carious lesions on premolar or molar teeth that were suitable for Class I restorations. We placed at least 50 percent of the restorations on mandibular teeth. All subjects had had at least one dental restoration placed with the use of LA. We based caries diagnoses on radiographs and the results of clinical examinations.

Patients were recruited and treated at the Bluestone Center. We obtained written consent from subjects to participate in the study, according to the approved protocol of the NYU Medical School Institutional Review Board.

Exclusion criteria. We excluded from participation in the study subjects who needed antibiotic prophylaxis, those who had periodontitis involving the teeth to be treated (as evidenced by probing depths greater than 4 millimeters, plaque and calculus, and/or bleeding on periodontal probing) and those who had radiographic evidence of a closed pulpal space.

	RESTORATIVE PROCEDURES

TOP ABSTRACT CAVITY PREPARATION SUBJECTS, MATERIALS AND METHODS RESTORATIVE PROCEDURES ANALYTIC PROCEDURES RESULTS DISCUSSION CONCLUSION REFERENCES

 
We randomly determined the order of polymer instrument or carbide bur treatment. We gave each subject the option of requesting LA (or additional LA) at any time during the procedure. Recent diagnostic radiographs were available for the dentist to review before each restorative procedure.

Before undergoing the restorative procedures, all subjects completed questionnaires that determined their experience with dental restorations and LA, their pain report bias (Situational Pain Questionnaire [SPQ])^20,21 and their fear and anxiety about dental procedures (Dental Anxiety Scale [DAS]).²²

The two clinicians placed all of the restorations. Before using the polymer instrument clinically, they performed at least 10 cavity preparations on extracted carious teeth, using the polymer instrument in a range of sizes (equivalent to round burs nos. 2, 4 and 6) at speeds approximating the lowest range of low-speed handpieces (500 to 800 revolutions per minute), as recommended by the manufacturer.

The clinicians were standardized with regard to placement of the dentin bonding agent (PQ1, Ultradent Products, South Jordon, Utah) and resin-based composite (Filtek Supreme, 3M ESPE, St. Paul, Minn.). They used high-speed handpieces and carbide burs to remove enamel in all patients.

At specific points in the restorative procedure (that is, baseline, enamel removal, caries removal, dentin bonding, restoration placement and finishing), as well as every 60 seconds during dentin removal, each subject rated his or her experience on 10-point rating scales. These scales assessed anxiety, fear, cold, heat, pain, pressure and vibration. All scales were anchored similarly (for example, they were formatted as "no pain" to "strong pain," "no heat" to "strong heat," "no vibration" to "strong vibration").

	ANALYTIC PROCEDURES

TOP ABSTRACT CAVITY PREPARATION SUBJECTS, MATERIALS AND METHODS RESTORATIVE PROCEDURES ANALYTIC PROCEDURES RESULTS DISCUSSION CONCLUSION REFERENCES

 
We evaluated the proportion of subjects who preferred treatment with the polymer instrument to treatment with the carbide bur using the z-approximation of the binomial test with a two-tailed type 1 error rate of .05. We analyzed the sensation and affect ratings by comparing the treatments at each assessment point on each scale via a two-way repeated-measures analysis of variance (ANOVA), with treatment and time factors. The main effects of treatment indicated an overall difference between treatments that was similar at different assessment points, while the main effects of time indicated a difference between one or more assessment points that was similar under the two treatment conditions.

An interaction between time and treatment indicates differences between sensory conditions at some, but not all, assessment periods. This last type of effect is of most interest, because it indicates differential effects of the two caries removal methods, which may be expected to differ only (or mostly) during surgical assessment periods.

We can interpret data most clearly when treatment conditions (such as pain) can be shown to be equivalent at baseline, at postoperative assessments or at both and different during active treatment times. Because some subjects had only one intraoperative assessment (in cases of short procedures), we considered this one intraoperative assessment when running the analyses for these subjects. For subjects who had more than one intraoperative assessment, we used the mean response over as many intraoperative assessments as they had.

We further evaluated omnibus F tests, which indicated time effects, via planned comparisons of baseline levels to levels at other assessment points.

	RESULTS

TOP ABSTRACT CAVITY PREPARATION SUBJECTS, MATERIALS AND METHODS RESTORATIVE PROCEDURES ANALYTIC PROCEDURES RESULTS DISCUSSION CONCLUSION REFERENCES

 
The study group was composed of eight women and 12 men. The women ranged in age from 25 to 37 years, and the men ranged in age from 26 to 41 years. Subjects had a mean of 5.5 dental restorations. About one-half of them had received some restorations without LA, and they reported that this caused them some discomfort. In general, the group acknowledged that they expected to experience a reasonable degree of inconvenience as a result of having LA injections.

The clinicians placed the Class I restorations in 14 different posterior teeth. Most teeth had bilateral lesions, although several had unilateral maxillary or mandibular preparations. The median excavation depth was 3 mm, with a range from 2 to 6 mm. The use of carbide burs and polymer instruments was evenly balanced between the first and second tooth restored. The figure shows scanning electron micrographs of a polymer instrument before and after use.

View larger version (106K): [in this window] [in a new window]   Figure. Scanning electron micrographs of the polymer instrument before use (left) and after use (right). Inset: Light microscopic photograph of the unused instrument. Mag: Magnification. kV: Kilovolts. WD: Working distance in millimeters. µm: Micrometers.

Immediately after the restorative procedure, 14 (70 percent) of 20 patients (P = .11) reported that they preferred the polymer instrument without LA, as evidenced by their stated desire to undergo that procedure on another occasion. One additional subject reported a preference for the polymer instrument for future restorations (75 percent, P < .05) at the 48-hour and one-week follow-up assessments.

Subjects who most disliked the side effects of LA tended to prefer the polymer instrument, while those expressing less satisfaction (or greater discomfort) during treatment with the polymer instrument tended to prefer the carbide bur (Table). For example, a subject who preferred the procedure without LA was more likely to rate the "discomfort" or "numbness" caused by the injection as more important than was a subject who preferred the procedure with LA. (Because ratings of the importance of each side effect were closely related to each other, subjects’ responses to any one of the questions were sufficient to explain the association between all of the side effects in determining treatment preference.)

One subject requested rescue LA during treatment with the polymer instrument, but no one requested additional LA when treated with the carbide bur. This incidence is too small to evaluate statistically.

Ratings of specific sensations and feelings during the restorative procedure also distinguished the two treatments. First, ratings of fear were reliably higher at the baseline assessment that preceded treatment with the polymer instrument (mean = 0.40, standard error [SE] = 0.11) than they were for the carbide bur treatment (mean = 0.03, SE = 0.05) (P < .005), reflecting subjects’ realistic assessment of the potential for discomfort without LA. Ratings of vibration also were higher at the baseline assessment, although it is not clear what these ratings represented in the absence of any rotary instrumentation. Baseline ratings of pain, pressure, heat, cold and fear were similar for the two treatment conditions.

Pain ratings. Under both treatment conditions, the absolute level of pain reported was less than 1 on a scale of 0 to 10, suggesting adequate levels of pain control. Over time, we noted basically parallel changes under the two treatment conditions, suggesting that subjects experienced higher levels of pain when clinicians removed enamel and dentin.

ANOVA showed a main effect of treatment (F_1,19 = 5.9, P = .025) and a main effect of time (F_5,95 = 8.6, P < .001). When assessments were averaged over all periods, subjects reported reliably more pain during treatment with the polymer instrument (mean rating = 0.3, SE = 0.07) than during treatment with the carbide bur (mean rating = 0.15, SE = 0.03). Subjects reported experiencing more pain during removal of enamel and dentin than at other assessment times, to a similar extent under both treatment conditions (mean ratings were 0.57 [SE = 0.13] and 0.40 [SE = 0.12] during enamel and dentin removal, respectively, compared with a mean of 0.2 [SE = 0.07] at baseline). We obtained similar results when using the mean intraoperative assessment instead of the first-period assessment (that is, the enamel removal assessment). Thus, it seems that subjects reported slightly, but reliably, more pain during the operative periods under both treatment conditions.

Pressure ratings. Ratings of pressure varied according to time (F_5,95 = 9.1, P = . 001), such that subjects reported reliably more pressure during enamel and dentin removal (mean = 0.45 and 0.32, respectively; SE = 0.10 and 0.09, respectively) than during preoperative (mean = 0.25, SE = 0.07) or postoperative assessments (mean = 0.02, SE = 0.02). The results of our analysis showed higher levels of pressure reported under the polymer instrument condition (F_1,19 = 9.0, P = .01).

Vibration, heat and cold ratings. Ratings of vibrations also varied according to time (F_5,95 = 14.2, P = .001). We noted higher ratings during removal of enamel and dentin (mean = 0.47 and 0.65, respectively; SE = 0.11 and 0.12, respectively) than at the baseline assessment (mean = 0.12, SE = 0.05). A treatment trend (F_1,19 = 3.4, P = .08) suggested somewhat higher ratings of heat with the polymer instrument. Our analysis also showed an effect of time on cold sensation ratings (F_5,95 = 3.4, P = .01) that indicated elevations only during the enamel removal period. These findings were similar in both treatment conditions and may reflect perceptions related to water used to lubricate the high-speed instrument.

The results of this study show that, in addition to ratings of pain, subjects reported experiencing some innocuous sensations (that is, pressure, heat) at higher levels under the polymer instrument condition than under the carbide bur condition. This is consistent with our expectations for patients receiving cavity preparations without anesthesia. The intensity of innocuous sensation ratings was elevated during operative phases of treatment, to a similar extent within the two treatment conditions.

Fear ratings. Ratings of fear also varied as a function of time and treatment. Although subjects reported quite low absolute levels, indicating that they experienced relatively little fear under either treatment condition, our analysis showed an interaction between time and treatment (F_5,95 = 3.2, P = .03). In contrast to treatment with the carbide bur (in which fear ratings remained nearly zero during all phases of treatment), treatment with the polymer instrument resulted in reports of reliably more fear at the preoperative baseline assessment and during enamel removal and other intraoperative periods (ratings rose to mean [SE] levels of 0.4 [0.11], 0.4 [0.13] and 0.3 [0.10] at baseline, enamel removal and other intraoperative assessments, respectively).

Similar to the pain ratings, these reliably elevated fear ratings did not rise to clinically meaningful levels. Ratings were similar under the two treatment conditions during the last assessment periods (that is, restoration placement and finishing). Thus, subjects appeared to have been more frightened before and during operative periods when they were treated with the polymer instrument. Unlike ratings of fear, however, ratings of anxiety remained at reliably higher levels for both treatment conditions at preoperative, enamel removal and other intraoperative assessments than at bonding or later assessments, which did not differ from one another.

At the 48-hour assessment, subjects reported that they had experienced four serious adverse events related to the dental treatment; one of these remained evident at the one-week follow-up assessment. All of these events were reported for teeth that were treated with the carbide bur, and they were thought to be related to soft-tissue injury resulting from the LA injection. One patient reported (at 48 hours only) tooth sensitivity associated with the soft-tissue tenderness.

	DISCUSSION

TOP ABSTRACT CAVITY PREPARATION SUBJECTS, MATERIALS AND METHODS RESTORATIVE PROCEDURES ANALYTIC PROCEDURES RESULTS DISCUSSION CONCLUSION REFERENCES

 
Conservative dentistry. Although the removal of infected dentin and sparing of dentin capable of remineralization has been a goal of conservative restorative dentistry, a rapid and controlled method of selective removal has proven elusive. Clinicians have used caries removal techniques such as chemomechanical treatment and hand excavation, but these techniques are not in general use. A rotary instrument that can be used with a low-speed handpiece—with cutting limited to the infected layer and the initial layer of affected dentin—has conceptual appeal.

Limited dentin cutting. Cutting that is limited to the superficial layer of affected dentin will not remove the odontoblast reaction zone of mineralized tubule plugs and can be completed without the use of LA. The results of this study support this contention. Immediately after the restorative procedures, 14 subjects reported that they preferred the polymer instrument procedure to the procedure that used a carbide bur and LA. This clinically significant finding became statistically significant (P < .05) at the 48-hour and one-week assessments. The increase in preference may have been the result (as the statistical analysis shows) of one subject’s re-evaluation of the secondary inconveniences of LA, which included soft-tissue trauma.

LA confounding. The design of this study limits its interpretation because LA confounded subjects’ responses to treatment with the carbide bur; likewise, the absence of LA confounded subjects’ responses to the polymer instrument. Thus, one could interpret these data to indicate that subjects preferred the absence of LA to its presence, regardless of the caries removal method. It also is possible that the polymer instrument, in combination with LA, would have been preferred even more.

Cutting that is limited to the superficial layer of affected dentin can be completed without the use of local anesthesia.

We need to point out, however, that somewhat higher levels of pain, fear and vibration were associated with use of the polymer instrument, as would be expected in the absence of LA. Still, subjects preferred this procedure (as noted below, bias toward the side effects of LA does not appear to have been present). Clearly, further studies are needed to replicate these findings, as well as to isolate the main effect and potentially interacting effects of the instrument and anesthesia.

To generalize these findings, we must rule out potential sources of bias. Participation bias might arise if the subjects who volunteered were inexperienced with regard to dental restorative procedures or had a bias against the use of LA. Data presented below support neither of these possibilities. First, all subjects who were asked to participate in the study agreed to do so, indicating no recruitment bias. Second, inclusion criteria required that patients had received at least one dental restoration before the study. In fact, these subjects had a median of 5.5 dental restorations; six subjects reported having 10 or more restorations and only two subjects reported having one restoration.

Attitudes regarding LA. With regard to attitudes about LA, 11 (55 percent) of 20 subjects reported that all of their restorations had been placed with LA and eight subjects (40 percent) reported that at least one restoration had been placed without LA (one subject requested rescue LA and was dropped from the study). All but one subject reported having experienced discomfort during that unanesthetized procedure, and four rated that discomfort at least 5 (out of 10). Two subjects (10 percent) reported that they had, on more than one occasion, declined LA for a restorative procedure. Although both subjects reported that they had expected the drilling procedure to cause pain, they cited injection pain as the reason for declining LA, and one of the two also cited postoperative numbness.

Sequelae of LA. In addition, the group had a benign assessment of the sequelae of dental LA. The median group ratings of "bothersome," "numbness," "drooling," "difficulty speaking" and "difficulty eating" varied between 2 and 3 (out of 10). Several subjects, however, expressed stronger opinions about anesthetic injections. For example, 25 to 30 percent of subjects rated "discomfort," "numbness" or "eating problems" as 5 or greater. In general, the group acknowledged a reasonable and expected degree of inconvenience accompanying anesthetic injections.

Subjects’ attitudes about restorations placed with LA generally were positive. Nine (45 percent) of 20 subjects reported having no fear of the cavity preparation if the procedure included LA. Only three (15 percent) of 20 subjects reported having no fear of the procedure if LA was not used. Thus, most subjects in the group believed that LA works to limit pain during cavity preparation, and generally were afraid that cavity preparation without LA would be painful. Thus, these data fail to support the idea that this group of subjects did not appreciate the value of LA.

Clinician training. The clinicians who performed the restorative procedures received training in the proper use of the polymer instrument, and this aided in caries removal. This training included working at a very low rotational speed (approximately 800 rpm) and working from the center of the lesion outward in a concentric pattern. The time needed to complete the restorative procedures was similar for the polymer and carbide bur conditions (although more time was needed to remove dentin with the polymer instrument, this was offset by the time needed to administer the LA).

The number of polymer instruments used and the time needed for dentin removal varied by operator and extent of the lesion; the study results showed a decided learning curve. The clinicians used caries-detecting dye to verify caries removal. Because of their inexperience, they used more new polymer instruments for the first patients. As the clinicians became more confident that the polymer instruments would remove carious dentin in a predictable manner (leaving affected dentin, which routinely stained pink or light pink), the time needed to prepare the dentin was reduced and the number of disposable instruments used dropped to one or two per preparation. A growing body of research suggests that leaving this amount of dye-stained dentin (pink or light pink) avoids overpreparation of the dentin.^4,23–26

A recent study suggested that several classes of dentin-bonding agents, including self-etching varieties, adhere more poorly to dentin prepared with a polymer instrument than to dentin prepared with a carbide bur (N.R.F.A. Silva and colleagues, unpublished data, 2004). These results parallel those of other studies of bonding to affected dentin prepared with alternative means.^17,27–30 However, reduced bond strength does not appear to play a role in the initial clinical outcomes resulting from use of the polymer instrument, as indicated by the lack of postoperative hypersensitivity reported by subjects in this study (confirmed at the 48-hour and one-week assessments).

One of the goals of conservative dentistry is to develop a method of removing caries-infected dentin while preserving caries-affected dentin. The polymer instrument appears to offer a straightforward and efficient means of achieving this goal and conserving healthy tooth structure. An instrument that is capable of removing diseased dentin only without causing pain helps move dental science into the 21st century.

	CONCLUSION

TOP ABSTRACT CAVITY PREPARATION SUBJECTS, MATERIALS AND METHODS RESTORATIVE PROCEDURES ANALYTIC PROCEDURES RESULTS DISCUSSION CONCLUSION REFERENCES

 
Fifteen (75 percent) of 20 subjects (P < .05) preferred the polymer instrument (without LA) to the carbide bur (with LA) for future dental treatment, on the basis of their positive experiences with the Class I restorative procedures performed in this study. Subjects expressing the highest levels of discomfort—or the least satisfaction—during removal of dentin with the polymer instrument endorsed the carbide bur for future dental treatment. Subjects who recommended the polymer instrument tended to be those who rated the disagreeable sequelae of LA as important.

Subjects generally rated themselves as being more fearful and perceived slightly more pain, pressure, heat and vibration when the polymer instrument was used than when the carbide bur was used. Ratings of cold and anxiety were not different between treatment conditions. If a subject reported having a good experience with the polymer instrument, he or she endorsed it for future use. Subjects whose experience was not satisfactory recommended use of the carbide bur with LA. On the basis of these study results, we believe that clinicians should consider incorporating the polymer instrument into their dental practices.

Dr. Thompson serves as a scientific consultant to SS White Burs.