Grey levels and radiolucent lesion depth as cavity predictors for approximal dentin caries lesions in primary teeth

OBJECTIVES: This study investigated grey levels and radiolucent lesion depth as cavity predictors for approximal dentin caries lesions in primary teeth. METHODS: 51 children (4-10 years old), presenting with radiolucency in the outer half of the dentin on the approximal surfaces of deciduous molar teeth and approximal anatomic contact with the adjacent tooth (without restoration or cavitated caries lesion), participated in the study. Bitewing radiographs were made, and temporary tooth separation was performed and an impression taken to detect cavitation. Radiographs were scanned (300 dpi) and grey levels were measured in carious and sound dentin. Impressions were also scanned and the size of cavity opening was measured in square millimetres. RESULTS: Grey levels of carious dentin (115.27+/-33.52) were significantly lower compared with sound dentin (151.88+/-30.99). No significant differences were observed in the dentin degree of radiolucency between "cavitated" and "non-cavitated" carious dentin. Cavitated lesions showed deeper radiolucent lesions compared with non-cavitated ones (P=0.03). There was no association between the size of cavitation and radiolucent lesion depth. CONCLUSIONS: Grey levels did not indicate cavitation in the outer half of the approximal dentin lesions. However, extension of a radiolucent lesion deep into the outer half of the dentin was associated with cavitated lesions independently of the size of cavitation. A computer-aided image analysis may help clinicians in monitoring caries progression and evaluating the probability of occurrence of cavitated caries lesions.     

Digital enhancement of radiographs for assessment of interproximal dental caries

OBJECTIVES: Evaluation of a particular digital caries image-enhancing mode (filter) for its effect on the validity of measurements of caries lesion depth. METHODS: Standardized radiographs of 44 extracted teeth exhibiting interproximal caries lesions were obtained. Six radiographs were obtained of each tooth and digitized. Four radiographs were made using D-speed film with and without soft tissue scattering equivalent (STSE) at normal exposure time (0.32 s) and underexposed (0.16 s). Two were made using E-speed film with STSE normally (0.16 s) and underexposed (0.08 s). On each of the 264 radiographs, 4 independent examiners measured the central depth (CD) of 1 carious lesion per tooth both on the unchanged radiographic image and after use of the filter. Histometric CD assessments provided a gold standard for comparison with the radiographic measurements (validity). Repeated measures ANOVA was calculated for validity in relation to examiner, lesion type, filter, film type, exposure time and STSE. RESULTS: The lesion type was identified to statistically significantly influence the validity of CD measurements. Examiner in combination with defect type (P<0.001), filter (P = 0.017), exposure (P = 0.027) and film type (P = 0.044) had an additional albeit small effect. CONCLUSIONS: The lesion type significantly influenced the validity of CD measurements: enamel lesions were less underestimated than dentin lesions.     

Caries development in a young population managed by a restrictive attitude to radiography and operative intervention: II. A study at the surface level

OBJECTIVES: To longitudinally assess the distribution of fillings and carious lesions in permanent posterior tooth surfaces, caries states fillings were made, and survival time of proximal lesions in different states in a young population managed by minimal operative treatment and a restrictive attitude to radiography. METHODS: Bitewing radiographs from age 6-20 in 285 patients were analysed. Proximal and occlusal surfaces were coded for caries depth and fillings. Start and end dates for different caries states in proximal surfaces were assigned and survival times in these states calculated by means of survival statistics. RESULTS: The frequency of carious/filled occlusal surfaces in the population increased from 6 to 19% and that of proximal surfaces from 1 to 26%. At age 19, 86% of the occlusal and 7% of the proximal surfaces affected by caries were filled. An overwhelming majority of unfilled carious proximal surfaces had enamel lesions only. Of all fillings, 81% were placed in surfaces with dentine lesions. The occlusal and proximal surfaces of the first molar and the distal surface of the second premolar accounted for most lesions and fillings among the 19-year-olds. The average survival time of lesions in the enamel was 8.0 years and in the outer half of the dentine 3.4 years when right-censored data were taken into account. CONCLUSION: In a young population exposed to optimal levels of fluoride with a caries preventive programme, a restrictive attitude towards operative treatment can be combined with longer average intervals between radiographic examinations than those prescribed by current guidelines.     

牙釉质表层区抗龋坏作用离体牙实验及扫描电镜观察

将实验牙去除牙釉质表层区，壳冠修复开窗，浸泡在含有蔗糖的致龋溶液中５７周，实验组与保留釉质表层对照组抗龋坏能力有显著差别。ＥＳＭ观察，正常釉质表层１０３０μｍ，有的部位轻薄或缺乏，尤以牙面沟凹，点隙区明显。龋坏的釉质表层边缘，呈风化石层样改变，裂缝方向与釉柱垂直，支持釉质龋表层带形成与釉质结构有关及存在着脱矿     

The influence of amalgam fillings on the detection of approximal caries by cone beam CT: in vitro study

Objectives:

The aim of this CBCT investigation on the detection of caries was to assess the influence of artefacts produced by the presence of amalgam fillings located in the vicinity.

Methods:

102 non-cavitated pre-molar and molar teeth were placed in blocks of silicone with approximal contacts consisting of 3 sound or carious teeth and 1 mesial–occlusal–distal amalgam-filled tooth in-between. Radiographs of all the teeth were recorded using the CBCT system (NewTom™ 3G; QR Srl, Verona, Italy; field of view, 9 inches). Data from the CBCT unit were reconstructed and sectioned in the mesiodistal tooth plane. Images were evaluated twice by two observers, using a five-step confidence scale. After the CBCT examination, the teeth were individually sectioned in the mesiodistal direction with a diamond saw. Using a light microscope at ×40 magnification, the true morphological status of all approximal surfaces was established.

Results:

Sensitivity of the CBCT for the detection of caries on surfaces located proximally and distally to an amalgam filing ranged from 0.27 to 0.30 for enamel and from 0.47 to 0.56 for dentin. Specificity values for enamel proximal and distal lesions were 0.48 and 0.53, respectively, for enamel and 0.33 to 0.38, respectively, for proximal and distal dentin cases. Intra-observer reliability was 0.84, and interobserver reliability was 0.49.

Conclusions:

Owing to its low specificity, scans from a CBCT examination should not be used to determine the presence of demineralization of the tooth surface when amalgam fillings are present in the region of interest.     

Effect of ambient light and monitor brightness and contrast settings on the detection of approximal caries in digital radiographs: an in vitro study

OBJECTIVES: The aim of this study was to investigate how brightness and contrast settings of the display monitor and ambient light level (illuminance) in the viewing room affect the clinician's ability to diagnose carious lesions in digital radiographs. METHODS: Standardized radiographs were taken of 100 extracted teeth. Seven observers evaluated the images for approximal carious lesions twice, once under 50 lux and once under 1000 lux room illumination. Monitor brightness and contrast were varied +/-50% and +/-6%, respectively, to mimic the normal limits of monitor adjustment by an inexperienced user and one optimal setting. This was done by adjusting radiograph brightness and contrast by +/-25%. Thus, five radiographs of each tooth were evaluated. Receiver operating characteristic (ROC) analyses were performed. Histological examinations of the teeth served as the criterion standard. A paired t-test was used to evaluate whether differences in the areas under the ROC curves were significant and kappa was used to evaluate intraobserver agreement. RESULTS: When a monitor with optimal brightness and contrast settings was used to detect approximal carious lesions, ambient light levels less than 50 lux were significantly better than levels above 1000 lux (dentin and enamel lesions, P < 0.01; dentin lesions, P < 0.02). Increasing the contrast setting of the monitor by 6% did not change these results; 50 lux was still significantly better than 1000 lux (enamel lesions, P < 0.01; dentin and enamel lesions, P < 0.02) for evaluating radiographs. Intraobserver agreement differed from fair to good. CONCLUSIONS: Reducing ambient light to less than 50 lux significantly increased the accuracy of diagnosing approximal carious lesions on a monitor with an optimal brightness setting and an optimal or slightly higher than optimal contrast setting.     

深龋腐质及龋损下方牙本质中有机酸含量测定

 目的 观察牙本质深龋中有机酸含量与龋损活动性的关系.方法 选择无症状牙本质深龋智齿共21颗,其中急性龋12颗,慢性龋9颗.用气相色谱法测定龋损腐质及下方牙本质中乳酸、乙酸与丙酸的含量.结果 所有龋损腐质及部分龋损下方牙本质中均检测出3种有机酸,其中以乳酸含量最高;急性龋腐质及下方的牙本质中乳酸含量明显高于慢性龋,但乙酸与丙酸含量二者间无显著差别;而在正常牙本质中则未检出3种有机酸.结论 牙本质深龋腐质及其下方牙本质中有机酸的含量与龋损活动性相关.     

Enamel and dentin mineralization in familial hypophosphatemic rickets: a micro-CT study

Objectives:

The aim of the present study was to analyse the mineralization pattern of enamel and dentin in patients affected by X-linked hypophosphatemic rickets (XLHR) using micro-CT (µCT), and to associate enamel and dentin mineralization in primary and permanent teeth with tooth position, gender and the presence/absence of this disease.

Methods:

19 teeth were collected from 5 individuals from the same family, 1 non-affected by XLHR and 4 affected by XLHR. Gender, age, tooth position (anterior/posterior) and tooth type (deciduous/permanent) were recorded for each patient. Following collection, teeth were placed in 0.1% thymol solution until µCT scan. Projection images were reconstructed and analysed. A plot profile describing the greyscale distance relationship in µCT images was achieved through a line bisecting each tooth in a region with the presence of enamel and dentin. The enamel and dentin mineralization densities were measured and compared. Univariate ANOVA and post hoc Tukey tests were used for all comparisons.

Results:

Teeth of all affected patients presented dentin with a different mineralization pattern compared with the teeth of healthy patients with dentin defects observed next to the pulp chambers. Highly significant differences were found for gray values between anterior and posterior teeth (p < 0.05), affected and non-affected (p < 0.05), as well as when position and disease status were considered (p < 0.05).

Conclusions:

In conclusion, the mineralization patterns of dentin differed when comparing teeth from patients with and without FHR, mainly next to pulp chambers where areas with porosity and consequently lower mineral density and dentin defects were found.     

Diagnosis of occlusal caries lesions in deciduous molars by coherent light scattering pattern speckle

BackgroundThis study presents the correlation between laser speckle images and detection of incipient caries lesions from changs in the microstructure of the surface of tooth enamel.MethodsWe used 30 healthy deciduous molar teeth collected from the Biobank Human Teeth, Faculty of Dentistry, University of São Paulo who had carious lesions induced by the pH cycling method. The samples were evaluated for the diagnosis of caries by two methods ICDAS and speckle pattern of coherent light scattering after 5, 10 and 15 days and the results were statistically analyzed using α = 0.05 significance level.ResultsA significant difference was observed between the image of the speckle scattering of healthy and injured areas within the 3 study groups, but not when comparing the three groups, showing us that it is an innovative technique that needs further study, but can be used as a diagnostic method for the detection of early caries lesions.ConclusionIt can be concluded that the analysis of scattering speckle pattern is a diagnostic technique that provides information on the microstructure of the surface of tooth enamel which has sensitivity for detection of incipient caries lesions.     

Performance of film, desktop monitor and laptop displays in caries detection

OBJECTIVES: To compare film, desktop monitor and laptop displays of digitized film images for accuracy of caries detection. METHODS: Sixty-four extracted teeth were mounted in eight models and radiographed with E-speed bitewing film. Films were digitized and displayed on a desktop monitor and a laptop display. Six observers scored the presence or absence of enamel and dentinal caries for each proximal surface for film, desktop and laptop displays. Results were compared with the histology of ground sections. ROC curve areas for each display mode and observer were assessed for significant differences with ANOVA. RESULTS: Diagnostic accuracy for proximal surface caries detection was not significantly different for conventional film or desktop monitor and laptop displays for detection of enamel caries (P = 0.9112) or dentin caries (P = 0.2796). CONCLUSIONS: Current laptop active matrix liquid crystal displays provide diagnostic quality for caries detection comparable with conventional film and desktop monitor displays.     

Application of scanning microradiography and x-ray microtomography to studies of bones and teeth

In scanning microradiography (SMR), a thin section is stepped across a 15-μm diameter X-ray beam and the transmitted intensity measured at each point. This technique has permitted more accurate measurements of the spatial variation of the mineral concentration in sections of dentin and enamel than conventional photographic microradiography. Moreover, because the section is not in close contact with an emulsion, SMR allows continuous study while the specimen is bathed in a reaction solution. The present studies have been particularly directed to gaining an understanding of the formation and repair of carious lesions in teeth: one particular puzzle is subsurface demineralization, in which the initial loss of mineral appears to take place some 20 to 50 μm below the tooth surface. SMR studies are reported here on the demineralization in dilute acids and the subsequent partial remineralization in supersaturated calcium phosphate solutions in model systems for dental caries. In order to develop a theoretical model for de- and remineralization of carious lesions, it is necessary to quantify transport processes within the tooth. To this end, we are developing a method of measuring effective diffusion coefficients of strongly X-ray-absorbing ions in water within permeable solids in which the diffusion coefficient varies with position. The method uses sequential concentration/distance profiles determined by SMR. As a test, diffusion coefficients of potassium iodide in water within a permeable glass frit have been measured. X-ray microtomography (XMT) can be carried out by adding an axis of rotation to the SMR apparatus. Using this method, linear absorption coefficients, and hence mineral concentrations, can be measured in 15 X 15 X 15-μm3 voxels. This has advantages over SMR in that superposition within the depth of the section and errors in determining its thickness are avoided. XMT studies of de- and remineralization similar to those described above for SMR, and also XMT studies of the variation in mineral concentration in the cortical bone of a rat femur along its length, are reported.     

Assessment of dental caries lesion activity status using quantitative parameters obtained from the quantitative light-induced fluorescence method and difference of microbial distribution in primary molars

BackgroundThis study aimed to assess differences in quantitative measures obtained from the quantitative light-induced fluorescence method and microbial composition of carious dentin and saliva according to the activity status of caries lesions in primary molars.MethodsA total of 34 teeth from 34 children were evaluated in this study. The activity status of carious lesions was classified using the International Caries Classification and Management System criteria (active or inactive). Images of the carious lesions were captured using a quantitative light-induced fluorescence device for quantitative analyses. Carious dentin and saliva were collected to detect and quantify selected bacterial species (S. mutans, S. sobrinus, Lactobacillus species, F. nucleatum, P. nigrescence, P. intermedia) and C. albicans by quantitative polymerase chain reaction. Mann–Whitney U tests were performed to evaluate differences in quantitative measures from quantitative light-induced fluorescence, the microbial composition of carious dentin, and saliva according to the activity status of carious lesions.ResultsRed fluorescence values (∆R, ∆Rmax) from the quantitative light-induced fluorescence method were significantly higher in active lesions (∆R, p = 0.009; ∆Rmax, p = 0.014). The quantitative mean levels of Lactobacillus species (p = 0.010) in carious dentin and S. sobrinus (p = 0.017) in saliva were significantly higher in the active-lesion group.ConclusionsQuantitative measures related to red fluorescence from the quantitative light-induced fluorescence method, levels of Lactobacillus species from carious dentin, and levels of S. sobrinus from saliva were associated with caries lesion activity.     

Diagnostic accuracy of cone beam computed tomography scans compared with intraoral image modalities for detection of caries lesions

OBJECTIVES: The aim was to compare the caries diagnostic accuracy of two cone beam CT systems (CBCT) with two intraoral receptors, one digital and one film. METHODS: 100 non-cavitated extracted human teeth were placed with approximal contacts: each row of teeth comprised 1 canine, 1 first and second premolar, and 1 first and second molar. Radiographs of each tooth were recorded using two intraoral modalities: Digora-fmx (Soredex) and film (Kodak Insight), and two CBCT systems: NewTom 3G (Quantitative Radiology) in three fields of view (FOVs): pixel size of 0.36 mm (FOV 12 inches), pixel size of 0.25 mm (FOV 9 inches), pixel size of 0.16 mm (FOV 6 inches); and 3DX Accuitomo (Morita), pixel size of 0.125 (FOV 4 cm). The volumetric data from the CBCT systems were reconstructed and sectioned (0.5 mm) in the mesiodistal tooth plane. Six observers scored approximal and occlusal surfaces for the detection of caries lesions. The teeth were clinically sectioned and microscopy served as the validation tool. Two-way ANOVA tested differences in sensitivity, specificity and overall true score (true positives plus true negatives) between the modalities. RESULTS: Microscopy of approximal surfaces found 63% sound, 31% enamel and 6% dentin lesions; of occlusal surfaces, 6% sound, 59% enamel, 19% dentin lesions and 16% had fillings. For approximal surfaces, NewTom 12 inch and 9 inch images had significantly lower sensitivities than Accuitomo (P < 0.02); and NewTom 9 inch and 6 inch had significantly lower specificities than film and Digora-fmx (P < 0.04). Accuitomo images were not significantly different from film or Digora-fmx images for any of the tested variables (P > 0.2). For occlusal surfaces, the Accuitomo presented a higher sensitivity than the other systems. Specificity and overall true score did not differ (P > 0.06) among the modalities. CONCLUSIONS: In conclusion, the NewTom 3G CBCT had a lower diagnostic accuracy for detection of caries lesions than intraoral modalities and the 3DX Accuitomo CBCT. The Accuitomo CBCT had a higher sensitivity than the intraoral systems for detection of lesions in dentin, but the overall true score was not higher.     

In vitro comparison of conventional film and direct digital imaging in the detection of approximal caries

OBJECTIVES: To compare the diagnostic accuracy of conventional film, unenhanced direct digital and inversion grayscale direct digital imaging in the detection of approximal caries. METHODS: 150 approximal surfaces of extracted permanent molars and premolars were selected for the study on the basis of varying lesion depth. The teeth were radiographed using Ektaspeed Plus film; digital images were made with a Schick CMOS-APS sensor. 7 examiners evaluated 58 randomized images of each modality. Histological sectioning of the teeth was used to verify the presence and extent of decay. RESULTS: No significant difference was found between the diagnostic accuracies of the three imaging modalities (P=0.226). Analysis of the diagnostic accuracy of the three modalities on lesion depth showed no statistically significant interaction; however, the main effect of the lesion depth was significant (P<0.001, eta(2)=0.936). CONCLUSIONS: The overall diagnostic accuracy of the three modalities in the detection of approximal carious lesions was comparable. All three modalities performed poorly in the detection of enamel lesions.     

Dental caries risk assessment

The United Kingdom Defence Dental Agency assesses United Kingdom servicemen as being at low, moderate, or high risk of developing morbidity during the next year, based on the examining dental officer's assessment of their dental status. The most frequent reason for assessing a patient as being at high risk of experiencing a dental emergency is the presence of extensive caries; however, dental officers' perceptions of which caries render a patient at high risk vary considerably. An investigation was carried out with records for Royal Air Force recruits who had been assessed as needing restorative work at their initial dental inspections but for whom this treatment had not been provided for > or = 1 year. Intraoral radiographs taken at the initial dental inspection were examined, and the width of apparently sound dentine remaining between the edge of the carious lesion and the pulp was measured. The results indicate that, when there is > or = 2 mm of apparently sound dentine remaining, there is very little risk that the patient will experience symptoms during the next year. Personnel with a carious tooth with < 2 mm of sound dentine remaining should be classified as high risk.     

A study of volumetric visualization and quantitative evaluation of bone trabeculae in helical CT

OBJECTIVES: The aim of this study was to investigate the reliability of quantitative evaluation of bone trabeculae by helical CT. METHODS: Ten specimens of human cadaver mandibular condyles were examined using both micro-CT and helical CT, and volume rendered three-dimensional (3D) images were obtained from the CT data. Micro-CT was used as the reference standard. From the micro-CT data images, bone trabeculae in each condyle were extracted by image processing and their volumes were calculated automatically. From the helical CT data images, the cortical bone was manually removed and bone trabeculae in each condyle were extracted using opacity curve and colour mapping thresholds. The optimal cut-off CT value that resulted in a similar volume of bone trabeculae obtained from helical CT and micro-CT data was investigated. RESULTS: The optimal cut-off CT value to assess the volume of bone trabeculae accurately on 3D images obtained with helical CT data was found to be 200 Hounsfield units. CONCLUSIONS: This study suggests that quantitative evaluation of bone trabeculae using helical CT might be a valid and useful method.     

Effects of healthcare policy and education on reading accuracy of bitewing radiographs for interproximal caries

ObjectivesThe aim of this study is to assess the accuracy of bitewing radiograph interpretation of predoctoral students, residents and general dentists who work under different core curriculum of dental education and healthcare policy.MethodsA total of 118 examiners including predoctoral dental students, residents and general dentists from USA and Japan were tasked with evaluating a series of bitewing radiographs and diagnosing interproximal carious lesions. This study was approved by the Harvard Medical School Institutional Review Board (IRB). Participants graded interproximal aspects of those images and categorized the following criteria; “intact”, “enamel caries <1/2 width”, “enamel caries >1/2 width” or “caries into dentin”. The gold-standard was determined by the consensus of two HSDM full-time faculty.ResultsThere was significant difference in the sensitivity for all three caries levels between the two groups but there was no significant difference on specificity. The positive-predictive and negative-predictive values of the USA group for the enamel caries (<1/2 of enamel) were significantly higher than the Japanese group. The average of AUC (ROC) was significantly higher in the USA group (0.885 ± 0.04) than the Japanese group (0.785 ± 0.08, p<0.01).ConclusionTeaching and adopting BW radiographs for diagnosis of interproximal caries is integral for dental providers to accurately and efficiently use them in their practices. It is critical that all dental educators approach policymakers to explain the importance of BW radiographs and promote their efficacy for prevention and early diagnosis of interproximal caries.     

Racemization in enamel among different types of teeth from the same individual

We measured the quantity of D-aspartic acid (degree of racemization of aspartic acid) in the enamel of different types of teeth from the same individual. We studied the correlation between the degree of racemization and the time of formation of each particular tooth, as well as the applicability of the degree of racemization to estimation of chronological age. If the environmental condition of the teeth is the same, the degree of racemization is expected to be highest in teeth that completed formation in the earliest period of time. Different degrees of racemization in enamel were found among different types of teeth, even in the same individual. The degree of racemization in enamel was found to be higher in molars than in incisors, and showed a tendency that did not necessarily coincide with the time of formation. This seemed to be due to the fact that the environmental temperature was higher in the molar region located deeper in the oral cavity than the front region, and that enamel was more affected by breathing air than dentin because the D/L ratios in enamel were lower than those in dentin. Using enamel, a better estimation of chronological age was obtained from calculations based on the degree of racemization of each type of tooth than from all the different teeth together. However, these estimated ages were not better than those from dentin.     

The 3DX multi image micro-CT device in clinical dental practice

OBJECTIVES: To evaluate the usefulness of 3DX multi-image micro-CT device in clinical dental practice. METHODS: Images of 198 examinations performed with a 3DX device during a 6 month period in a private dental practice were evaluated retrospectively for the benefit of additional information compared with panoramic or intraoral radiographs. RESULTS: The main indication for the use of 3DX micro-CT was planning of dental implant placement in 49% of the examinations. Diagnosis or exclusion of dental infection or peri-implantitis represented 28% of the examinations and tooth, root or foreign body localization represented 13%. Temporomandibular joint (TMJ) imaging and cyst or tumour diagnosis represented 7.5% and 2.5% of the examinations, respectively. In implant planning and tooth, root or foreign body localization examinations, the required information was obtained in every case except three implant planning examinations, in which the exact measurements were hampered by artefacts caused by root fillings and retrograde fillings or metal posts. When compared with conventional radiography, additional radiographic information was obtained in 51% of the micro-CT examinations performed to confirm or exclude dental infection or peri-implantitis. Micro-CT also showed the bone structure of TMJs precisely. CONCLUSIONS: The 3DX micro-CT device visualizes bony anatomical structures precisely, which makes it a reliable tool for, for example, planning of implant treatment. The device is highly suitable for diagnosing dental infections. Dental restorations may cause disturbing artefacts and in 4.5% of the examinations the small imaging area resulted in re-examination.     

Composition and relaxation of the proton magnetization of human enamel and its contribution to the tooth NMR image

The spin-spin, T2, and spin-lattice, T1, relaxation times and the magnetization of protons were measured in human enamel. The proton free induction decay was analyzed into solid-like interstitial water, enamel apatite, and semiliquid-like water components. The solid-like interstitial water was evaluated to be approximately 5 wt% and the semiliquid-like water to be approximately 1 to 2%. Neither in wet nor in dry natural enamel does the solid water exchange upon deuteration nor can it be extracted in vacuum. The semiliquid natural water, which is in the closed pores of the structure in the two samples above also remains unexchanged upon an 8 hr deuteration and cannot be extracted in a vacuum. With the lineshape-relaxation correlation NMR the free induction decays from heads and tails of the enamel rods were resolved. The solid-like water with T2 of approximately 14 microseconds and the apatite with a T2 of approximately 61 microseconds have T2's too short to be observed in an NMR zeugmatogram. Therefore only the semiliquid water component having an apparent T*2 of about 240 microseconds would contribute to the NMR image of human enamel. Since the relative intensity of this proton magnetization component in tooth is quite small the NMR image of tooth would show primarily the dentin and liquids within the tooth and on its surface.