Oral Function Improves Interfacial Integrity and Sealing Ability Between Conventional Glass Ionomer Cements and Dentin

The aim of this study was to investigate if load cycling affects interfacial integrity of glass ionomer cements bonded to sound- or caries-affected dentin. A conventional glass ionomer, Ketac Bond, and a resin-modified glass ionomer (Vitrebond Plus), were applied to dentin. Half of the specimens were load cycled. The interfaces were submitted to dye-assisted confocal microscopy evaluation. The unloaded specimens of sound and carious dentin were deficiently hybridized when Ketac Bond was used. Ketac Bond samples showed an absorption layer and an adhesive layer that were scarcely affected by fluorescein penetration (nanoleakage), in sound dentin. Nevertheless, a higher degree of micropermeability was found in carious dentin. In Ketac Bond specimens, load cycling improves the sealing capability and remineralization at the cement-dentin interface as porosity and nanoleakage was reduced. In contrast, samples treated with Vitrebond Plus exhibited a Rhodamine B-labeled absorption layer with scarce nanoleakage in both sound and carious unloaded dentin. The adhesive layer was affected by dye sorption throughout the porous cement-dentin interface. Samples treated with Vitrebond Plus had significant increases in nanoleakage and cement-dye sorption after load cycling. Within the limitations of an in vitro study, it is expected that conventional glass ionomers will provide major clinical efficacy when applied to carious-affected or sound dentin.

In-Vitro Comparison Of Micro-Leakage Between Nanocomposite And Microhybrid Composite In Class V Cavities Treated With The Self-Etch Technique

BACKGROUND

When a light cure composite resin is used to restore a class V lesion, certain stresses are generated at the tooth-restoration interface. If these stresses exceed the bond strength of the restorative material, microscopic gaps are formed which eventually cause micro-leakage at the tooth-restoration interface. The objective of the present study was to compare the micro-leakage values at the tooth-restoration interface using dye penetration method between a Nano filled and a Micro hybrid light cured composite resin in class V cavities using the self-etch technique.

METHODS

Sixty class V cavities were made coronal to the cemento-enamel junction in the extracted premolars. These were then randomly divided into two study groups. Group A: Self-etch; filled with P-60 (microhybrid) n=30. Group B: Self-etch; filled with Z-350 (nano-filled) n=30. Specimens were subjected to thermo-cycling at 5-55 °C±2 °C with a 30 seconds dwell time. After which they were stained with 2% methylene blue. Later, sectioned bucco-lingually and examined using a stereo microscope (magnification X4) at the occlusal, axial and gingival surfaces. Micro-leakage around the toothrestoration interface was assessed by using the degree of dye penetration in millimetres.

RESULTS

There was 100% micro leakage seen at both the occlusal and gingival surfaces when using the P-60 composite. With the Z-350 composite 84% occlusal and 88% of the gingival surfaces exhibited microleakage..

CONCLUSIONS

With respect to micro-leakage in class V cavities, Z-350 was found to be a superior restorative material compared to P-60 on the occlusal surface. Overall, there is no statistically significant difference in the micro-leakage exhibited by the two restorative materials in class V preparations subjected to self-etch protocol.

Detection of marginal leakage of Class V restorations in vitro by micro-computed tomography

This in vitro study evaluated the efficacy of micro-computed tomography (CT) in marginal leakage detection of Class V restorations. Standardized Class V preparations with cervical margins in dentin and occlusal margins in enamel were made in 20 extracted human molars and restored with dental bonding agents and resin composite. All teeth were then immersed in 50% ammoniacal silver nitrate solution for 12 hours, followed by a developing solution for eight hours. Each restoration was scanned by micro-CT, the depth of marginal silver leakage in the central scanning section was measured, and the three-dimensional images of the silver leakage around each restoration were reconstructed. Afterward, all restorations were cut through the center and examined for leakage depth using a microscope. The silver leakage depth of each restoration obtained by the micro-CT and the microscope were compared for equivalency. The silver leakage depth in cervical walls observed by micro-CT and microscope showed no significant difference; however, in certain cases the judgment of leakage depth in the occlusal wall in micro-CT image was affected by adjacent enamel structure, providing less leakage depth than was observed with the microscope (p<0.01). Micro-CT displayed the three-dimensional image of the leakage around the Class V restorations with clear borders only in the dentin region. It can be concluded that micro-CT can detect nondestructively the leakage around a resin composite restoration in two and three dimensions, with accuracy comparable to that of the conventional microscope method in the dentin region but with inferior accuracy in the enamel region.

Micro-CT for measuring marginal leakage of Class II resin composite restorations in primary molars prepared in vivo

PURPOSE

To evaluate the reliability of marginal leakage assessment of self-etch adhesive Class II resin composite restorations in primary molars prepared in vivo using the micro-CT.

METHODS

Fourteen primary molars, divided over seven ART and seven traditional resin composite Class II restorations, were subjected to marginal leakage test using a 50% (w/v) silver nitrate solution for 4 hours by a micro-CT. Two evaluators selected the image with the deepest marginal dye penetration for each restoration from the occlusal and approximal surfaces on consensus. The deepest dye penetration depth and total length of the axial cavity wall from both the occlusal and from the approximl surface were measured manually using morphometric quantification software by three evaluators independently. ANOVA was applied to test for differences in marginal leakage scores between the three evaluators.

RESULTS

There was no marginal leakage found in five traditional and one ART restoration. The percentage of silver nitrate penetration depth from the cervical-approximal site ranged from 10.2-92.6%. There was only a statistically significant difference observed in measuring total axial wall length from the cervical-approximal site between the three evaluators (P = 0.02). This explanatory investigation showed that the micro-CT was a very useful device for developing a standardized method for measuring marginal leakage from samples obtained in vivo. In combination with 50% (w/v) silver nitrate and 4-hour immersion, marginal leakage along the restoration-tooth tissue interface was accurately and reliably measured. (Am J Dent 2008;21:393-397).

The sealing ability of GuttaFlow in oval-shaped canals: an ex vivo study using a polymicrobial leakage model

AIM

To compare systematically the sealing ability provided by four endodontic cements: AH Plus, Pulp Canal Sealer EWT, RoekoSeal and GuttaFlow.

METHODOLOGY

A sample of 100 human mandibular incisors with oval-shaped canals was selected from an initial sampling of two hundred teeth. The root canals in 80 teeth were prepared and filled by the same operator using the cold lateral compaction technique with one of the following four cements (n = 20): G1: AH Plus; G2: Pulp Canal Sealer EWT; G3: RoekoSeal and G4: GuttaFlow. Ten teeth with intact crowns served as negative controls and 10 teeth that were not root filled served as positive controls. All teeth were mounted in a two chamber apparatus and then exposed to human saliva. The number of days over a 9-weeks-period was recorded for the appearance of turbidity in the BHI broth. A Log-rank test was used to analyse the leakage data.

RESULTS

Overall, 30% of the samples of the AH Plus group (G1) and 35% of the Pulp Canal Sealer EWT group (G2) were fully contaminated after 9 weeks, whereas 15% of RoekoSeal (G3) and GuttaFlow (G4) groups were fully contaminated. There was a significant difference between (G1/G2) and (G3/G4) (P < 0.05). There was no significant difference between G1 and G2 or between G3 and G4 (P > 0.05).

CONCLUSION

The silicone-based sealers revealed the best results throughout the experimental period. Leakage patterns of AH plus and Pulp Canal Sealer were statistically similar.

An evaluation of the quality of root fillings in mandibular incisors and maxillary and mandibular canines using different methodologies

OBJECTIVES

To evaluate the quality of root fillings in mandibular incisors and maxillary and mandibular canines using different methodologies of evaluation, namely radiographs, the fluid transport test and the percentage of gutta-percha (PGP), and to determine if a correlation occurs between the results of the different methodologies used.

METHODS

One group of mandibular incisors with oval canals (n=20) and one group of maxillary and mandibular canines (n=20) were instrumented and obturated by cold lateral compaction using AH 26 as the sealer. The filled roots were bucco-lingually and mesio-distally radiographed. Using a scoring system, the quality of each root filling was radiographically evaluated, the higher the score the poorer the quality. Fluid transport along the root filling was then measured using a fluid transportation device. Each root was horizontally sectioned 4 and 6mm from the apex. Images of the cross-sections were taken, using a microscope and a digital camera. Images were scanned into a PC as TIFF images. Using a KS 100 Imaging system the canal area and the gutta-percha filled areas were measured. The percentage of gutta-percha filled areas was calculated.

RESULTS

Considering the radiographic scores of the two different projections together the score was significantly higher for the mandibular incisors than for the canines (P=0.039). The radiographic score was significantly higher for the mesio-distal radiograph in comparison with the bucco-lingual radiograph (P=0.0001), for the canines as well as the incisors. Using only the bucco-lingual radiograph there was no significant difference between the mandibular incisors and the canines (P=0.992). The mandibular incisors displayed significantly more fluid transport than the canines (P=0.049). A significantly greater percentage of gutta-percha filled areas was found in the cross-sections of canines as compared to the cross-sections of mandibular incisors (P=0.000001). The correlation between the radiographic score of the mesio-distal radiograph and the PGP 4 and 6mm was significant (P=0.013). There was no significant correlation between the FT and the radiograph or the FT and the PGP.

CONCLUSIONS

The quality of the root fillings in oval canal-mandibular incisors may be compromised.

[Coronal leakage reconsidered]

The aim of the present study was to evaluate the impact of the quality of the coronal restoration and of the root filling on periapical health. In a sample of 937 root filled teeth which had not received restorative treatment in the previous year, the technical quality of the coronal restorations and of the root fillings was radiographically scored; in addition the technical quality of the coronal restorations was clinically scored as well. The data showed that the technical standard of both coronal restoration and root filling were essential to periapical health. The study also showed the relatively limited value of epidemiologic findings. Epidemiologic research is descriptive as well as analytical in approach. According to the present data, endodontic failure cannot be fully explained by radiographic analysis only. Nevertheless, epidemiologic data remain a valuable component to the source of knowledge regarding etiologic factors and proper treatment procedures in order to improve the results of endodontic practice.

Evaluation of adhesive defects using an ultrasonic pulse-reflection technique

The purpose of this study was to examine the application of an ultrasonic pulse-reflection technique for the evaluation of adhesive defects. First, the sonic velocities in the enamel and dentin of human molars and bovine incisors were measured with a pulsar receiver attached to an ultrasonic transducer. The identification of the dentino-enamel junction and pulp-dentin interface using the ultrasonic method based on intrinsic sonic velocities showed good agreement with the actual measured thicknesses. Next, a cemented restoration with artificial faults was prepared. Half of the Au-Ag-Pd alloy plate area was cemented to the dentin slab using luting resin cement. The adhesive interface was evaluated with a high-resolution ultrasonic imaging system. Clear internal faults were evident from the ultrasonic tomogram. The findings of this study suggest that the ultrasonic pulse-reflection technique may be useful for inspecting and imaging structural defects of adhesive interfaces.

The effect of immediate vs. delayed post space preparation on the apical seal of a root canal filling: a study in an increased-sensitivity pressure-driven system

A 5 mm remaining length of root canal filling, after post space preparation, is commonly assumed to maintain sealing ability similar to that of the intact filling. Post spaces were prepared either immediately using hot pluggers, or later, using drills. The sealing ability of the fillings, 5 mm remaining length, were compared with each other and with an intact root canal filling control, using radioactive tracer in a pressure-driven system. When no pressure was applied, no differences could be detected between either of the groups and the control. When a pressure of 120 mm Hg was applied to the same teeth, the control group clearly maintained a better seal than each of the experimental groups, which did not significantly differ from each other. These results suggest that (a) the pressure-driven system was more sensitive than the passive leakage assay that failed to detect differences even at 14 days; (b) a remaining root canal filling of 5 mm was inferior to the intact root canal filling; and (c) the immediate post space preparation with hot pluggers did not differ from a delayed preparation with drills.

An in vitro investigation of coronal leakage with three gutta-percha backfilling techniques

The aim of this study was to compare the backfilling capabilities of System B, Obtura II and Alphaseal. Forty-six lower premolar teeth were prepared chemomechanically and allocated to four experimental and two control groups. Ten were obturated using lateral condensation as a standard and 30 were obturated in the apical third using the System B. The latter 30 teeth were then backfilled using one of three techniques, System B, Obtura II or Alphaseal (n = 10 in each group). The remaining six teeth served as controls. Roots were radiographed from the proximal in order to evaluate voids and then placed in India ink for 65 h prior to being demineralized and rendered transparent, coronal leakage was quantified by linear measurement of ink penetration. No significant difference was found between the four groups with respect to the presence of voids radiographically (P < 0.05). The difference in leakage between the System B and Obtura II groups was not significant (P > 0.05). Both System B and Obtura II leaked significantly less than Alphaseal and lateral condensation (P < 0.001).

Clinical evaluation and marginal leakage of Amalgambond Plus: three-year results

Amalgambond Plus with a high-performance additive was evaluated for its ability to bond a resin composite or an amalgam alloy to deep dentin in primary teeth with nonretentive cavity preparations. The clinical performance of amalgam and resin composite mesio-occlusodistal restorations bonded with Amalgambond Plus was evaluated at 15 months and 2 and 3 years. There was no statistically significant difference in the retention, marginal adaptation, secondary caries, and post-operative sensitivity over the times of the evaluation or between amalgam and resin composite restorations. After 3 years, most of the teeth were extracted because it was their exfoliation time, and 29 restorations limited within buccal and lingual cusps were evaluated for marginal leakage. There were no significant differences in microleakage between amalgam and resin composite restorations lined with Amalgambond Plus. Amalgambond Plus has the potential for serving successfully as a cavity liner with either amalgam or resin composite restorations.

Adaptation and radiographic evaluation of four adhesive systems

OBJECTIVES

The purpose of this study was to compare microleakage, gap formation, thickness of the adhesive layer and its radiographic appearance associated with four adhesive restorative procedures for class I cavities.

METHODS

Adhesive systems with easy handling characteristics were selected for the restoration of class I cavities in extracted third molars. Bitewing radiographs were taken of each tooth and four observers were asked to assess the presence of the adhesive layer. Microleakage, gap width and the thickness of the adhesive layer of each restoration were measured upon sectioning of the teeth.

RESULTS

Microleakage in the experimental restorations was minimal. The thickness of the adhesive layers and gap formation varied among different adhesive systems. The adhesive system with self-etching primer produced the highest percentage gap-free restorations. Thick adhesive layers could be detected on the radiograph. ROC analysis of the results validates the diagnosis from the radiograph.

CONCLUSIONS

The four restorative systems performed well in the prevention of microleakage. The use of a resin modified glass-ionomer cement base did not prevent gap formation compared with the all-etch bonding systems used in this study. The presence of an adhesive layer contributed to the prevention of gap formation, independently of the bonding system used. Thick adhesive layers could be detected on the radiograph.

Microleakage evaluation of bonded amalgam restorations: confocal microscopy versus radioisotope

The purpose of this study was to compare the degree and pathway of microleakage in bonded amalgam restorations utilizing fluorescent dyes with scanning laser confocal microscopy and 45Ca radioisotope with autoradiographs. Mesial slot preparations with enamel cervical margins and distal preparations with dentin margins were prepared in extracted human molars. Four liners, Copalite (control) All-Bond 2/Resinomer, Amalcoden, and Panavia 21, were used. Teeth were restored with Dispersalloy or Tytin. After thermocycling, 7 days' storage, and staining, the degree of microleakage was measured on an ordinal scale. Dental adhesive liners minimized microleakage; the ranking was, from most to least effective, All-Bond 2, Panavia 21, and Amalcoden. The control exhibited the greatest microleakage. Microleakage occurred most frequently at the liner-tooth interface. No significant difference was observed between amalgams. The high correlation between the results of the fluorescent and radioisotope studies indicated that these two microleakage tests can be directly compared.

Late failure of root canal therapy: a diagnostic and treatment planning challenge. Case report

This report describes a case in which failure of conventional root canal therapy presented 17 years following initial treatment. The apical pathology was curetted, the tooth root resected and a root-end filling placed. The possible reasons for failure of the initial orthograde root canal therapy are discussed with the conclusion that the cause may not have been addressed fully by surgical intervention. The case highlights the challenge facing clinicians when assessing failed root fillings, not only in determining the exact cause of failure but deciding the appropriate treatment for the individual tooth and patient.

Accuracy of endodontic microleakage results: autoradiographic vs. volumetric measurements

The correlation between autoradiographic and volumetric leakage measurements was evaluated. Seventy-two anterior teeth with a single canal were selected and divided into three groups of 24. Group 1 served as control (no obturation), group 2 was obturated with gutta-percha only, and group 3 was obturated with gutta-percha and endodontic sealer. Samples were placed in a vertical position in 48-well cell culture plates and immersed in 1 ml of [14C]urea for 14 days. One-mm-thick horizontal serial sections were cut with a diamond disk cooled with liquid-nitrogen gas. Linear penetration was recorded by five independent evaluators from autoradiographs. Volumetric results were based on counts per minute registered in a liquid scintillation spectrometer. Pearson's correlation coefficient test was used to determine the lineal correlation between both methods of evaluation. No acceptable correlation values were found in any of the three groups (group 1, r = 0.34; group 2, r = 0.23; group 3, r = 0.20). Our results indicate that there is no correlation between linear and volumetric measurements of leakage.

In vitro radiographic representation of the extent of voids within obturated root canals

The aim of this study was to determine whether radiographs provide an accurate representation of the degree of root canal obturation following a cold lateral condensation technique. A total of 40 extracted single-rooted lower premolar teeth were prepared using either a standardized step-back technique or an ultrasonic device by one of two operators. The four groups each of 10 teeth were obturated using lateral condensation by a third operator. To assess apical leakage the obturated teeth were coated with nail varnish to within 2 mm of the apex and immersed in methylene blue for 48 h. The teeth were then radiographed in bucco-lingual and mesio-distal planes prior to subsequent sectioning in a bucco-lingual plane. Sections and radiographs were analysed using an image analysis apparatus to determine the proportion of root canal occupied by gutta-percha, void and/or sealer. Mean percentages of void calculated from the bucco-lingual radiographs, mesiodistal radiographs and tooth sections were 4.14%, 5.98% and 4.98%, respectively. Statistical analysis showed no significant differences between the radiographic views and the tooth sections (P > 0.05). Both planes of radiograph accurately represented the proportion of void when compared with the tooth section.

The adaptation achieved by four root canal filling techniques as assessed by three methods

Four root canal filling techniques--lateral condensation, McSpadden compaction, ultrasonic activation (Enac), and thermoplastic injection (Ultrafil)--were assessed for adaptation of the filling material to the canal wall. The adaptation and leakage were examined quantitatively using an electrochemical method and a linear dye penetration method, and qualitatively by radiographic evaluation. Using the electrochemical method, differences among obturation techniques were relatively small, although a greater proportion of the teeth that had been filled by lateral condensation exhibited no leakage. Radiographically, the techniques appeared to exhibit similar adaptation in the apical 6 mm. The techniques of lateral condensation and ultrasonic activation showed superior control of length of the root canal filling.

The apical seal of root canal sealing cements using a radionuclide detection technique

The aim of this study was to evaluate the apical seal obtained with various root canal sealing cements using a new method based on the use of a radionuclide and an external detection technique. A total of 150 maxillary incisors and canines, which had been kept in saline solution, were used. The root canals were instrumented with a stepback technique and circumferential filing. Six experimental groups and two control groups were randomly formed. Each experimental group was obturated by a lateral condensation technique with gutta-percha points and a different sealing cement (two based on zinc oxide-eugenol cement, two based on resins and two on calcium hydroxide); the positive control used gutta-percha without sealing cement, while in the negative control the apex was covered with nail varnish, leaving the root canal empty. The apical leakage was measured using an external detection technique after submerging the root apices in a solution containing the radioisotope metastable 99Tc. No leakage was observed in the negative control group. There was a large difference between the leakage observed in the positive control group and the experimental groups. The best seal was obtained using Sealapex cement, which differed significantly from AH26, Tubli-Seal and Diaket; there was no significant difference between the latter. The poorest results were obtained with Endomethasone and CRCS; there was a significant difference between these and the previous three sealing cements.

Quantitative radioactive analysis of microleakage of four different retrograde fillings

Sealing properties of four different retrograde filling materials were investigated in vitro. Radioactive isotopes were applied in the root canal, and leakage into an extraradicular fluid was measured at regular intervals. The method permitted repeated observation of the specimens over prolonged periods of time. Forty single-rooted human teeth were biomechanically instrumented and obturated using calcium-hydroxide paste. Following obturation, an apicectomy was performed and retrograde cavities were filled with four different materials: group 1, non gamma 2 amalgam (Amalcap); group 2, glass ionomer cement (Ketac Silver); group 3, calcium-hydroxide-based root canal sealer (Sealapex); group 4, composite resin (Palfique Light-S). After removal of the calcium hydroxide, the teeth were immersed in a fluid. An isotope solution was then placed in the root canals. Samples were taken from the fluid at 0, 3, 7, 28, 56, 105, 210, 285 and 376 days to determine the radioactivity. It was found that Sealapex and Palfique Light-S showed significantly less leakage than amalgam and glass ionomer cement, which had the highest apical leakage.

[Radioactive isotope evaluation of apical seal of two types of thermoplasticized gutta-percha at high and low temperature]

The aim of this study was to evaluate the apical seal obtained using root canal filling techniques based on low and high temperature thermoplasticized gutta-percha, comparing them with the lateral condensation technique. The roots of thirty permanent upper canines and incisors were used, they were instrumented and obturated using each of the above techniques. The apical leakage was measured using a radioactive isotope and an external detection technique. No significant difference was found in the apical seal obtained by the three techniques.

An evaluation of four methods of root canal preparation using 14C urea

One-hundred twenty single-rooted teeth were used in vitro in order to compare the four following methods of endodontic preparation: manual, Giromatic, MM 3000 Sonic Air with, and sonic air without the contact shaping technique. Each endodontic preparation was filled according to the McSpadden technique. Teeth were immersed in 14C urea. Radioactivity was evaluated qualitatively by autoradiography and quantitatively by scintigraphy. Data were statistically analyzed with a nonparametric test. The results show that the highest degree of leakage occurs with the manual method and that for the three other methods, maximum leakage takes place near the apices.

[Observation of marginal leakage with 35SO4 =. 2. Marginal leakage of complete crowns]

The purpose of this study was to observe marginal leakage of complete crowns cemented with zinc phosphate cement and adhesive cement as determined by RI. After repeating load the samples were placed in gelatine solution with 35SO4 = labeled compound. 1. Most of complete crowns cemented with zinc phosphate cement showed remarkable marginal leakage as long as the entire length of the interface. 2. Complete crowns cemented with adhesive cement showed very little marginal leakage, a maximum depth of 0.53 mm from crown margins. 3. The repeating load test manifested proper position of crown margin, that is, the crown margin should be placed at least 1 mm far from the dowel core margin using adhesive cement. 4. The marginal distance of gaps was presumed from autoradiograms by using the regressive formula calculated from the relationship between the distance of gaps and the film density in Part 1.

[Observation of marginal leakage with 35SO4 =. 1. Method of testing for marginal leakage]

The purpose of this study was to develop a new observation method of marginal leakage of complete crowns with 35SO4 = labeled compound. The new point of this method was to use 15% gelatine solution, which was very effective to get clear autoradiograms. Once the labeled tracer penetrated marginal gaps, it didn't move away but stayed there. Complete crowns actually cemented to abutment teeth were treated using the new method, so that we could observe marginal condition more clearly than with the conventional method using various dyes or usual simple radioisotope. In this study, we found close relationship between film density of autoradiograms and marginal distance of gaps.

Clinical, radiographic, SEM evaluation and assessment of microleakage of Class II composite restorations

The influence of incremental or bulk filling techniques, and reapplication of unfilled resin (impregnation) to the margins with an enamel bonding agent, on marginal adaptation was evaluated in Class II composite restorations by clinical, radiographic, scanning electron microscope (SEM) and dye penetration techniques. Cavities were prepared in 80 extracted permanent posterior teeth. All cavity walls were treated with polyacrylic acid for 10 seconds. The enamel was etched for 1 minute, rinsed, dried, and lined with Scotchbond. Forty cavities were filled by increments of P30 and 40 cavities in bulk. The margins of the restorations of 20 teeth in each group were re-etched for 30 seconds and Concise Enamel Bond reapplied. The clinical scores were excellent for all restorations. Radiographic examination showed twice as many bubbles in the incrementally filled restoration than in the group filled in bulk. In 53 teeth, a radiolucent area between the dentin and the restorative material was found. After sectioning, this area was found to correspond to a hard material. The SEM revealed excellent margins in the groups of teeth that were impregnated with an unfilled resin, whereas 13 teeth without impregnation showed defective margins. The dye penetration, as a test for marginal leakage, was minimal at the occlusal surface of all teeth. At the cervical surface, 10.5% of the impregnated teeth showed severe dye penetration compared to 18% of the nonimpregnated teeth. No correlation was found between dye penetration at the cervical surface and the thickness of the residual enamel in this area.(ABSTRACT TRUNCATED AT 250 WORDS)