Estimated prevalence of erosive tooth wear in permanent teeth of children and adolescents: an epidemiological systematic review and meta-regression analysis

OBJECTIVES

The main purpose of this systematic review was to estimate the prevalence of dental erosion in permanent teeth of children and adolescents.

METHODS

An electronic search was performed up to and including March 2014. Eligibility criteria included population-based studies in permanent teeth of children and adolescents aged 8-19-year-old reporting the prevalence or data that allowed the calculation of prevalence rates of tooth erosion. Data collection assessed information regarding geographic location, type of index used for clinical examination, sample size, year of publication, age, examined teeth and tissue exposure. The estimated prevalence of erosive wear was determined, followed by a meta-regression analysis.

RESULTS

Twenty-two papers were included in the systematic review. The overall estimated prevalence of tooth erosion was 30.4% (95%IC 23.8-37.0). In the multivariate meta-regression model use of the Tooth Wear Index for clinical examination, studies with sample smaller than 1000 subjects and those conducted in the Middle East and Africa remained associated with higher dental erosion prevalence rates.

CONCLUSIONS

Our results demonstrated that the estimated prevalence of erosive wear in permanent teeth of children and adolescents is 30.4% with high heterogeneity between studies. Additionally, the correct choice of a clinical index for dental erosion detection and the geographic location play an important role for the large variability of erosive tooth wear in permanent teeth of children and adolescents.

CLINICAL SIGNIFICANCE

The prevalence of tooth erosion observed in permanent teeth of children and adolescents was considerable high. Our results demonstrated that prevalence rate of erosive wear was influenced by methodological and diagnosis factors. When tooth erosion is assessed, the clinical index should be considered.

[Is Dutch swimming pool water erosive?]

Etiological factors in the development of dental erosion are usually listed as dietary acids, for instance in soft drinks and fruit juices, and intrinsic acid exposure due to gastro-intestinal disease or frequent vomiting. Quite often the list of causes in reviews and textbooks also includes frequent swimming. This paper evaluates the evidence behind this erosion etiology. The main disinfection techniques using gas chlorination and sodium hypochlorite are described, and their relative risk for development of low pH water is discussed. In the Netherlands only the relatively safe sodium hypochlorite method is used, and the quality of the water in public swimming pools is monitored monthly by independent test laboratories. Data for 2001 from such a test laboratory show that the percentage of low-pH results is very low (0.14%). It is concluded that the risk of dental erosion from frequent swimming in acidic pool water is probably negligible in the Netherlands.

[Caries diagnosis: the lesions are central]

In this paper two new visual scoring systems are described, aimed at estimating both depth and activity of occlusal lesions. Their validity is acceptable for lesion depth estimation. However, the validity of the activity estimate is to be questioned. Both for approximal enamel and dentine lesions as for deep dentinal occlusal lesions, bite-wing radiographs are still useful for evaluation of new lesions and lesion progression. Many quantitative caries diagnostic methods are being developed, but to this date none of them has been shown to be reliably applicable in lesion monitoring. The evaluation of caries risk factors is primarily useful for selecting preventive treatment options. Other caries prediction-tests than those based on the present caries lesions are of little value. The main disadvantage of such prediction models is that they are usually limited to application in children, where caries is a disease that affects all ages.

Caries detection methods: can they aid decision making for invasive sealant treatment?

The decision to place sealants is a difficult one, and it has been suggested that in a low risk population it may be efficient to wait until caries is detected in the fissure. An invasive sealant technique with fissure preparation may then be indicated. The diagnostic method used in the indication of such a procedure should accurately detect both dentine caries and sound fissures: high sensitivity for dentine caries (at D3 threshold) with high specificity for enamel caries (at D1 threshold). The aims of this study were to assess the diagnostic performance of selected diagnostic methods at normal cut-offs for traditional dentine caries detection and at reduced cut-offs in relation to the desired performance mentioned above, and to assess whether fissure opening allows for accurate visual detection of dentinal caries. Data were obtained from 230 occlusal sites of 101 extracted human molar teeth. Diagnostic methods used on the entire sample were: visual inspection, electrical conductance measurements and laser fluorescence measurements. The sample was then divided into two groups. Group 1 was subjected to visual inspection after application of a dye. Group 2 was subjected to visual inspection after fissure opening only, and after subsequent dye application. Validation was performed by histological investigation. The results with cut-offs normally used in dentine caries detection were roughly in accordance with the literature, except for laser fluorescence. The sensitivity of visual inspection for dentinal caries (D3) was 17% before and 70% after fissure opening. Using reduced cut-offs, a 100% sensitivity (D3) was achieved with 2 methods, but this also resulted in 63 or 87% false positive diagnoses of sound surfaces. Visual inspection and electrical methods both showed a moderate to high sensitivity (D3) with a higher than 50% specificity (D1). It was concluded that visual inspection and electrical methods at reduced cut-offs may aid the indication of invasive sealant treatment. The visual detection of dentinal caries is substantially increased, but not perfect after fissure opening.

Relationship between mineral distributions in dentine lesions and subsequent remineralization in vitro

Though the mineral distribution of the dentine carious lesion varies largely from tooth to tooth and from patient to patient, there are two main distribution profiles that characterize natural carious lesions in dentine. These profiles include softened and subsurface lesion types. The mineral distribution relationship between the starting profile and the profile after remineralization is not known. In order to study the relational aspects, we have produced demineralized dentine samples in vitro with mineral profiles similar to those of typical natural carious lesions, and subsequently remineralized the samples in a remineralizing solution with various fluoride concentrations (0, 2 and 10 ppm F). The mineral distributions were obtained by using an improved microradiographic technique. In addition, the nature of deposited mineral was analyzed by diamond-coupled total internal reflectance spectroscopy. Definite relationship was observed between the original lesion mineral distribution and the mineral distributions following remineralization. The amount of mineral present in approximately the first 50 microm of the lesion influenced the overall mineral profile after remineralization, possibly through influencing ion transport. If the amount was high (> approximately 10 vol%), the deposited mineral was confined to the surface (0-50 microm). The original mineral at those depths acted like a nucleus of mineral regrowth when the amount of residual mineral was intermediate, and like a transport barrier when the surface layer was well mineralized. If a surface barrier was not present, mineral was deposited at deeper depths in the lesion. Fluoride effect on dentine remineralization was dependent on the original mineral content and its distribution in the lesion. Although a high concentration of fluoride was very effective in low-mineral lesions, it produced hyperremineralization on well-mineralized subsurface lesions so that it prevented effective remineralization especially in deeper lesions.

Developments in caries diagnosis and their relationship to treatment decisions and quality of care. ORCA Saturday Afternoon Symposium 1997

This symposium report evaluates the achievements made in caries diagnostic research since the previous symposium held in 1992. The symposium aimed at presenting the state of the art of caries diagnostic methods, on presenting the links between caries diagnosis and subsequent treatment decisions and their effect on the treatment outcomes, particularly the quality of dental care. The variation among dentists in diagnosing (small) caries lesions and in treatment decision making is considerable. This has been explained by the imperfection of caries decision making tests, but also by making incorrect treatment decisions due to incorrect or partial understanding of diagnostic test parameters. Meta-analyses into the performance of caries diagnostic tests revealed that the available quantitative methods are very promising. It was concluded that these methods had high correlations with lesion depth. They were considered suitable to monitor small changes in lesions. Many obstacles have been experienced in attempting to transfer the outcomes of diagnostic research into clinical practice and it was concluded that caries diagnosis researchers should co-operate with manufacturers to introducing valid new diagnostic tools to the market. Main research priorities for the coming 10 years are to conduct cost-effectiveness and cost-utility studies of caries diagnostic tools, to continue to review the performances of diagnostic tests, to transfer diagnostic knowledge and experience to the general practitioners particularly by constructing evidence-based clinical guide-lines, to study the relationship between diagnosis and treatment decision, and to assess the effect of diagnostic and treatment decisions on the outcome of care.

Electrical methods in occlusal caries diagnosis: An in vitro comparison with visual inspection and bite-wing radiography

The aim of this study was to compare in vitro diagnostic performance of three electrical methods for occlusal caries diagnosis with that of visual inspection and bite-wing radiography. One hundred and seven extracted molar and premolar teeth were subjected to the diagnostic methods by 2 operators and subsequently sectioned for histological validation. Electrical measurements were made at site level and at surface level using two different instruments. The diagnostic parameters calculated from the results were: sensitivity, specificity, diagnostic accuracy at a theoretical caries prevalence of 10% and area under the ROC curve. The electrical methods and bite-wing radiography showed higher sensitivity and lower specificity than visual inspection. Diagnostic accuracy was significantly lower for bite-wing radiography and one electrical method than for visual inspection. Overall diagnostic performance of two electrical methods was superior.

Surface-specific electrical occlusal caries diagnosis: reproducibility, correlation with histological lesion depth, and tooth type dependence

Electrical conductance measurements are being used experimentally for occlusal caries detection. Recently, it was suggested to cover the fissure system with a conducting medium, resulting in a surface-specific measurement. It was the aim of this study to determine in vitro the reproducibility of this modified technique for occlusal caries in posterior teeth, to determine for a large study sample the correlation between the electrical measurements and histological lesion depth, and to evaluate the difference between results for premolars and molars. For the reproducibility determination, surface-specific electrical resistance measurements were made using a sample of 68 posterior teeth. Eight operators performed measurements on all teeth, and repeated measurements on 24 teeth. The validity study included the previous sample and the collected samples from two more studies, resulting in a total sample of 325 posterior teeth. One operator had performed electrical resistance measurements on all teeth in the sample. Reproducibility was good: mean Pearson's correlation coefficient 0.89 (+/-0.05) for interexaminer correlation, and 0.86 (+/-0.12) for intra-examiner correlation, using log (resistance) as the result parameter. The correlation coefficient between log(resistance) and histological lesion depth for the large sample was -0.78 for all teeth, -0.64 for premolars, and -0.73 for molars. The regression line for molars was located below the regression line for premolars: at a hypothetical histology score of 2.5 (a dentine caries threshold) the estimated resistance threshold would be 507 kOmega for premolars, and 233 kOmega for molars. Converted to Electronic Caries Monitor (ECM) readings, the difference is about 1.4 on the ECM scale. It was concluded that the in vitro reproducibility of the described surface-specific method for electrical resistance measurement is very good, even for inexperienced operators. The correlation between measurements and histological lesion depth is moderate to good. The method is sensitive to electrode area differences, which will result in different clinical cut-offs for caries diagnosis in premolar and molar teeth.

Temperature dependence of the electrical resistance of sound and carious teeth

Temperature variations are expected to influence measurement error in electrical resistance of teeth. It was the aim of this study to determine the changes in electrical behavior of extracted human teeth due to temperature changes in the range of room temperature to intra-oral temperature. Nine extracted teeth were selected, and the occlusal or an approximal surface was chosen for measurement. Carious involvement of the surfaces ranged from sound to cavitated. Electrical impedance spectroscopy sweeps in a frequency range of about 100 kHz to 10 Hz were completed at selected temperatures between 22 degrees C and 40 degrees C. After fitting the data to equivalent circuits that yielded parameter values for components of the equivalent circuit, we calculated the dc bulk resistance (Rh). The temperature dependence of Rb of the surfaces with different carious involvement was very similar, and the mean drop of Rb from 20 to 35 degrees C was 45% (SD 2%). It was concluded that the electrical resistance of sound and carious tooth surfaces is inversely related to temperature.

Ultrasonic measurement of enamel thickness: a tool for monitoring dental erosion?

OBJECTIVES

Wear of dental hard tissues, e.g. dental erosion, is reported to be a growing problem. A non-destructive measurement of enamel layer thickness would provide the opportunity for both early diagnosis, and longitudinal measurement of progressive enamel loss. It was the aim of this study to investigate the potential of ultrasonic pulse-echo measurements for the enamel thickness measurement.

METHODS

Nine extracted human incisor teeth were selected and stored in physiological saline. Mesial and distal tooth parts were removed, resulting in a central tooth slice of about 2 mm thickness. Where possible three buccal, and one palatal measuring sites were selected and indicated by pencil marks on one of the section planes. Ultrasonic pulse-echo measurements were made at each site using a Panametrics 25DL thickness gauge (Panametrics, Waltham, MA, USA), using a perspex delay line transducer (15 MHz) and glycerine coupling medium. Ultrasonic measurements were validated by measuring the thickness of the enamel layer at the marked side of the tooth slices with a light stereomicroscope at 120 x magnification. Two observers performed independent measurements.

RESULTS

Limits of agreement for measurements by two observers (n = 42) were -0.09 and 0.09 mm. Measurements performed at 21 degrees C and 34 degrees C were not significantly different, as analysed by paired Student's t-test (p = 0.19). Pearson's correlation coefficient between ultrasonic and microscopic measurements was 0.90. Analysis of all measurements from both observers at both temperatures yielded a sound velocity in enamel of 6.5 x 10(3) m/s (standard error 0.1 x 10(3) m/s).

CONCLUSIONS

It was concluded that the ultrasonic measurement of the enamel thickness is feasible without enamel preparation.

Effects of alternating and direct electrical current application on the odontoblastic layer in human teeth: an in vitro study

AIM

The aim of this study was to investigate the influence of a low intensity alternating current on the odontoblasts and odontoblast layer and compare this with the effects of a direct current.

METHODOLOGY

Teeth extracted for orthodontic reasons were immersed in physiological saline stabilized with thymol crystals. Within 1 h of extraction, an alternating or direct current was applied on the crown in the direction of the apex of the tooth for 120-360 s. The current doses were 12, 30, 60, 600, 1800, 3600, 7200, 24,000 and 144,000 microC. The teeth were fixed in Bouin or Baker fluids, the pulps removed, dehydrated and immersed in paraffin, then sectioned, stained with haematoxylin and eosin, and studied under a light microscope.

RESULTS

Neither direct nor alternating current, similar to that applied in electrical caries diagnosis caused histological changes in the odontoblasts.

CONCLUSIONS

There was no difference between direct and low intensity alternating current in the response of the odontoblast.

Effect of exposure time on in vitro caries diagnosis using the Digora system

The aim of this study was to determine the in vitro diagnostic performance for approximal caries and occlusal dentine caries diagnosis of the Digora system for digital radiography in relation to the exposure time. Radiographs were made of 220 extracted human posterior teeth and cuspids at exposure time levels of 3%, 6%, 10%, 20%, and 78% of the exposure time needed for E-speed film (image sets I, II, III, IV, and V, respectively). The image sets were put in random order (III, I, IV, II, V) and assessed independently by 3 observers using a 5-point confidence scale. True caries status was determined histologically after sectioning of the teeth. Evaluated parameters were: interexaminer kappa, sensitivity, specificity, Dz3/4 (the distance of one operating point to the diagonal in the ROC domain) and area under the ROC curve. The Spearman correlation coefficients between the parameters and both exposure time and order of viewing of the sets were calculated. For approximal surfaces, the ranges of mean parameter values were: sensitivity 26-33%, specificity 93-95%, Dz3/4 0.63-0.84, area 0.61-0.69. For occlusal surfaces, the ranges were: sensitivity 52-60%, specificity 91-95%, Dz3/4 1.03-1.34, area 0.79-0.87. Out of 24 pairwise comparisons between sets V and I, 5 were significant. Out of 24 comparisons between set V and II, only 2 were significant. It was concluded that diagnostic performance is unlikely to be impaired for an exposure time as short as 6% of E-speed film exposure. When reducing the exposure time to 3% of E-speed film exposure, caries diagnosis may be impaired.

Wavelength-dependent fibre-optic transillumination of small approximal caries lesions: the use of a dye, and a comparison to bitewing radiography

The mere detection of caries lesions is insufficient for optimal treatment decision-making. Hence, the aim of this study was to investigate whether quantitative information about approximal lesion depth can be obtained from a technique based on the wavelength dependency of light propagation and additional use of a dye. Another aim was to compare the diagnostic performance of the optical technique and bitewing radiography. Measurements were performed on 33 extracted premolar teeth. Twelve proximal surfaces had white-spot, and 17 had discoloured small lesions. Four surfaces were sound. The teeth were transilluminated with a single glass fibre at the approximal surface before and after dye application. The occlusal surface was imaged with a CCD camera. Light in the blue and red part of the electromagnetic spectrum was selected using Schott glass filters. Average decadic optical thickness differences, delta bl-rd tau eff, were estimated and plotted as a function of normalised lesion depth, dhist, established from histological validation by two observers. The Spearman rank correlation was rs (delta bl-rd tau eff, dhist) = 0.87 (95% confidence interval, CI: 0.74-0.94). A marked increase in average decadic optical thickness in the blue part of the electromagnetic spectrum, delta dye tau eff, was observed for those lesion that, upon direct visual inspection of the approximal surface, clearly showed dye uptake. Bitewing radiographic depth ratings of two observers were plotted as a function of dhist. The correlations were rs (dRA,1, dhist) = 0.62 (95% CI: 0.34-0.80), rs (dRA,2, dhist) = 0.75 (95% CI: 0.54-0.87), and between the observers rs (dRA,1, dRA,2) = 0.44 (95% CI: 0.10-0.69). The p values of rs (delta bl-rd tau eff, dhist) -rs (dRA1,1, dhist) and rs (delta bl-rd tau eff, dhist) -rs (dRA,2, dhist) were p1 = 0.01 and p2 = 0.08, respectively. It was concluded that quantitative information about lesion depth can be obtained optically. The dye penetrates into only a limited number of caries lesions, in which cases dye uptake is detectable in transillumination geometry. Under laboratory circumstances the optical technique performs as well as bitewing radiography in the diagnosis of small approximal caries lesions.

Impedance spectroscopy of teeth with and without approximal caries lesions--an in vitro study

Caries diagnosis by the measurement of electrical resistance is hampered by polarization effects when dc or single-low-frequency ac currents are used. Electrical impedance spectroscopy, measuring impedance over a large range of frequencies, will provide more detailed information about the electrical characteristics of teeth. It was the aim of this study (a) to characterize the complex impedance behavior of whole extracted teeth, measured at the approximal surface, and (b) to identify parameters of the complex impedance behavior of the teeth which would be useful in distinguishing between degrees of carious involvement. Thirty-nine extracted premolar teeth with 59 unrestored and undamaged (excepting caries) approximal surfaces were selected. The tooth surfaces were divided into three groups according to their macroscopic appearance: sound (group S, n = 16), white- or brown-spot lesion present (group L, n = 33), or cavitated (group C, n = 10). The teeth were inserted into a jig which allowed for counter-electrode contact via a conducting gel. The working electrode consisted of a carbonated fiber material. Electrical impedance measurements were performed over a maximum range of about 1 MHz to 0.1 Hz. We analyzed electrical impedance data by fitting equivalent circuits. Fit was evaluated numerically and visually. The complex impedance spectra divided naturally into three groups which corresponded almost perfectly with the classifications of S,L, and C. The groups differed most in the dc resistance (Rdc), as calculated from the impedance parameters. Mean Rdc for groups S, L, and C were 68 M omega, 5.9 M omega, and 321 k omega, respectively. These means were significantly different from each other (log-transformed data, ANOVA, p < 0.001; Tukey multiple comparisons, p < 0.001). It is concluded that the in vitro performance of electrical impedance spectroscopy in differentiating among sound, non-cavitated carious, and cavitated approximal tooth surfaces is excellent.

The influence of simulated clinical handling on the flexural and compressive strength of posterior composite restorative materials

OBJECTIVES

The aim of this study was to investigate the influence of clinical handling on the flexural and compressive strengths of two commercially available posterior composites.

METHODS

Since the manufacturing of test specimens in a truly clinical situation presents many problems, an in vitro model was developed, consisting of a phantom-head set-up in a clinical operatory. Two composite materials, recommended for use in posterior teeth, were used: P50 APC (3M Dental Products) and Herculite XRV (Kerr, Dental Manufacturing). Beam specimens for 3-point bending tests of both materials and cylindrical specimens for compression test of P50 were made both under ideal laboratory circumstances and under simulated clinical circumstances.

RESULTS

The difference in mean flexural strength between laboratory prepared and the quasi-clinically prepared specimens was highly significant for both the specimens handled in a clinical manner was 15% of the flexural strength of the P50 specimens made under laboratory conditions, and the difference for Herculite XRV was 29%. No difference in compressive strength could be shown between the laboratory-fabricated and the quasi-clinically made specimens of P50.

SIGNIFICANCE

The relative flexural strength of composite materials in a clinical situation may differ significantly from that predicted from mechanical properties measured in vitro.

Detection of dental decay and its extent using a.c. impedance spectroscopy

Dental caries (decay), the most prevalent of diseases, represents a health problem of immense proportions. It principally affects posterior (back) teeth on occlusal (biting) and approximal (adjacent contacting) surfaces. Caries starts as a subsurface demineralization of enamel, may progress to the underlying dentine and, eventually, to cavitation of the surface. Accurate diagnosis before cavitation would permit targeted preventive treatment, thereby significantly improving dental health and reducing the need for expensive drilling and filling. Inaccessibility of caries initiation sites and recent changes in lesion morphology contribute to the relatively poor accuracy of conventional diagnostic methods. Among alternative techniques, measurements of electrical resistance have shown the most promise. Here we describe a new experimental technique that demonstrates an outstanding 100% correlation between a.c. impedance measurements of whole teeth and the actual extent of approximal caries in vitro. Only relatively minor modifications should be required to transfer the technique to in vivo applications.

[Quality control of intra-oral radiographs]

This paper deals with the different stages in the process of making intra-oral radiographs and the factors which influence their quality: the X-ray equipment, operator technique, and processing and film variables. Common errors at each stage are discussed and suggestions for quality assurance measures are given.

Mechanical longevity estimation model for post-and-core restorations

OBJECTIVES

The aim of this study was to integrate existing knowledge of in vitro strength of post-and-cores and masticatory loading to arrive at longevity estimates for post-and-core restorations when subjected to clinically relevant loads.

METHODS

A biomechanical model was developed to predict the in vivo longevity. This method was applied to direct post-and-core restorations with amalgam or composite cores. Both experimental laboratory strength values and theoretical clinical strength values were used in the model. The restorations made in the laboratory were assumed to be of a higher quality than clinically made restorations, due to factors such as ease of manipulation, absence of saliva, etc. Both a high and low level of average masticatory loading were considered. The model was used to estimate the probability of mechanical failure before 5 X 10(6) load cycles (5 to 15 years) for all combinations of load range and manufacturing quality.

RESULTS

The calculated failure probability was effectively zero for most combinations except for a clinical quality core subjected to loads in the high range. There the probability of mechanical failure before 5 X 10(6) cycles was estimated to be 2 X 10(-5) for amalgam and 5 X 10(-5) for composite cores. These results agree with the overall observed clinical failure rate of about 1% per year for post-and-core restorations.

SIGNIFICANCE

The mechanical properties of the post-and-core restorations were adequate for clinically relevant loading conditions.

Validity of electrical conductance measurements in evaluating the marginal integrity of sealant restorations

The use of sealants and sealant restorations has increased considerably over the past 10 years, and with it increased the problem of detecting secondary caries and marginal (micro)leakage. It was the purpose of this study to investigate the validity of electrical conductance measurements (ECMs) in diagnosing marginal leakage into dentine of sealants and sealant restorations. Ninety extracted premolar teeth were divided into three groups. Initial ECMs, denoted 'baseline ECMs', were conducted in all three groups by placing the probe tip of an Electronic Caries Monitor in the occlusal fissure which was filled with a dentifrice. The ECMs were divided by the area, yielding ECM/mm2 values. In group A 30 teeth were treated to receive 'nonleaking sealants'. In the 30 teeth of group B a narrow groove was cut at the occlusal surface reaching the dentine and restored by the application of a sealant without etching of the adjacent enamel to create a high probability of marginal leakage. The samples in group C received the same treatment as those in group B, but in this group the enamel was etched to reduce the probability of marginal leakage. The ECMs subsequently conducted were denoted 'sealed/restored ECMs'. Teeth in groups B and C were thermocycled 700 times (4-67 degrees C) to provoke leakage, after which ECMs were conducted (denoted 'ECMs after thermocycling'). The teeth were immersed in fuchsin for 24 h and cut along the fissure system to validate marginal leakage. The electrical conductance decreased significantly from baseline to the sealed/restored stage in all groups (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Electrical conductance and electrode area on sound smooth enamel in extracted teeth

Electrical conductance measurements are being used experimentally to diagnose caries. Current equipment, e.g. the electronic caries monitor (ECM), uses a probe to scan occlusal fissures. For full-mouth examination this method is rather time-consuming. A method with which only one measurement is needed for an entire (occlusal) surface would be preferable. However, the enlargement of the area being measured will influence the conductance. It was the purpose of this study to investigate the relationship between the electrical conductance of human teeth and the enamel electrode area, and to compare the range of results of surface measurements with those of the scanning method. Twenty-five sound extracted teeth were selected for the study. The reference electrode of the ECM was connected to the roots. The buccal surface was blotted dry, and a coloured dentifrice was syringed in increments onto the surface. After each increment the surface was photographed together with a metric reference, a conductance measurement was performed by holding the ECM probe tip in the dentifrice, and the ECM reading was recorded. For each tooth between 5 and 10 increments were applied and measured. The photographs were digitised and the electrode areas were calculated. A least squares curve fitting procedure yielded a linear relationship between conductance and electrode area (0.88 < or = R2 < or = 1.0, mean R2 = 0.97). For most teeth the threshold for dentinal caries as used for scanning ECM measurements (ECM reading = 6.00) was reached only when the electrode area exceeded 12 mm2. For 6 teeth this conductance was already reached between 5 and 12 mm2.(ABSTRACT TRUNCATED AT 250 WORDS)

[Diagnosis of primary caries. Current techniques and their consequences for treatment]

The decline in caries prevalence in The Netherlands has incited dentists to focus their attention to the detection of small carious lesions rather than large cavities. The diagnosis of primary caries is, however, still predominantly being accomplished by the traditional diagnostic methods, used in the high caries prevalence era. Today's appearance and behaviour of caries lesions have led to the situation that incipient enamel lesions, dentinal caries and cavities are frequently missed during routine recall examinations. There is increasing concern with the occurrence of large caries lesions underneath visually intact enamel. These problems have induced diagnostic research aimed at developing and evaluating new caries diagnostic methods and some of them are already used in general practice. Visual inspection and bitewing radiography, however, still constitute the most important methods in the diagnosis of primary caries. The results from these examinations are used to classify an individual's caries risk, to monitor the progression of existing caries lesions, and to aid preventive or restorative treatment decision making.

Failure behaviour of fatigue-tested post and cores

Evaluation of the long-term behaviour of restorations in clinical trials can be time-consuming. A partial alternative to the clinical trial can be found in mechanical fatigue testing. The aim of this study was to evaluate the failure behaviour of post and core restored teeth when subjected to cyclic mechanical loading and to compare it with quasistatic failure. Eighty seven premolar teeth were restored with a titanium alloy post and an amalgam or composite core. Five to 21 days after restoration, the specimens were subjected to cyclic loading (frequency 5 Hz), at an angle of 45 degrees to the long axis of the tooth. The load levels were 50, 60, 65 and 70% of mean quasistatic failure loads. The specimens were divided into three groups according to their survival time: short (S) (< 10(4) cycles), intermediate (I) (10(4) < or = life < 10(5) cycles) and long (L) (> or = 10(5) cycles). For both core materials failure behaviour changed after approximately 10(5) cycles, and the change was most marked for the composite group. Catastrophic fatigue failure consisted of core fracture in the amalgam group (three times) and of post fracture in the composite L group (four times). Three post fractures occurred at a site theoretically predisposed to fatigue failure. It was concluded that fatigue failure characteristics of post and core restorations may be very different from those of quasistatic failure. Therefore, in addition to quasistatic tests, fatigue tests are necessary, covering at least 10(5) load cycles.

[The restoration of endodontically treated teeth. A literature study of the mechanical behavior of post-core restorations]

Rapid developments in dental health and science have resulted in an increasing number of teeth receiving post and core restoration. The dentist can choose from a wide range of restoration-modalities. Success or failure of these restorations largely depends on their ability to meet functional demands. This article presents a review of the literature on the mechanical behaviour of post-core restorations, as it is determined by functional forces, shape of the tooth and restoration and properties of the materials the construction encorporates. Some attention is drawn to the importance of failure characteristics in view of re-restoration possibilities. As a conclusion some guide-lines for the use of post and core restorations in the general dental practice are formulated.

Finite element analysis of quasistatic and fatigue failure of post and cores

Finite element (FE) analysis of the mechanical behaviour of materials and structures facilitates the investigation of their internal stress distributions. However, the validity of the model is not always ascertained. In this study a three-dimensional (3D) FE model was developed, representing a laboratory set-up of direct post and core restored upper premolars. These restorations, using either composite or amalgam for core material, have been the subject of study in previous quasistatic and fatigue strength tests. The aim of this study was to validate the FE model for prefailure and failure modelling, by comparing the computational results with the laboratory observations and failure results. Two failure criteria were selected for investigation: Modified Von Mises and Drücker-Prager equivalent stress. Four model variations were carried out, representing different conditions at the core-tooth interface. Prefailure modelling was found to be adequate. The calculated failure results could only partly be fitted to the quasistatic tests. The best fit was effected with a model using partial bonding of the core, for the composite core. Fatigue failure was reproduced somewhat better by a model using no bonding at all, again to a higher degree for the composite core. Calculations of post stress using a model simulating increased core mobility supported an observation made previously (M. C. D. N. J. M. Huysmans et al., in press; Int. Endodont. J. XX, XXX-XXX), implying that a composite core raises the demands made on the post. The conclusion is made that validation of FE calculations is essential. A 3D model as presented here shows a satisfactory fit to fatigue data but not to quasistatic results.(ABSTRACT TRUNCATED AT 250 WORDS)

The Weibull distribution applied to post and core failure

In this study, data on initial failure loads of direct post and core-restored premolar teeth were analyzed using the Weibull distribution. Restorations consisted of a prefabricated titanium alloy post, and an amalgam, composite or glass cermet core buildup in human upper premolar teeth. The specimens were subjected to compressive forces until failure at angles of 10, 45 and 90 degrees to their long axis. The two- and three-parameter Weibull distributions were compared for applicability to the failure load data. For estimation of the parameters of the two-parameter distribution: sigma 0 (reference stress) and m (Weibull modulus), linear regression was used. In this distribution, it is assumed that the third parameter, sigma u (cut-off stress), equals 0. The Maximum Likelihood (MLH) method was used to estimate all three parameters. It was found that the choice of distribution has a strong influence on the estimated values and that the three-parameter distribution is best fitted for the failure loads in this study. Comparisons were made between the failure probability curves as found by MLH estimation for the different core materials and loading angles. The results indicated that the influence of loading angle on the failure mechanism was stronger than that of core material.

Failure characteristics of endodontically treated premolars restored with a post and direct restorative material

Ninety-one extracted maxillary premolar teeth were restored with a prefabricated post and amalgam, composite resin or glass-cermet core. Each group was again divided into three groups of 9-13 teeth to be subjected to an increasing load in one of three standardized directions (10, 45 and 90 degrees to the long axis of the tooth). Failure load and characteristics of failure were recorded. The glass-cermet-restored teeth had a lower strength than the other groups for every load direction (Student's t-test: P less than 0.01). Amalgam and composite resin groups showed a significant difference only for the 10 degrees loading condition (Student's t-test: P less than 0.02). Teeth restored with amalgam cores displayed a higher mean failure load, in combination with a 46% occurrence of root fracture.

Fatigue behavior of direct post-and-core-restored premolars

Evaluation of long-term mechanical behavior of new types of restorations in clinical trials is time-consuming. A partial alternative can be found in experimental fatigue-testing, which simulates accelerated mechanical deterioration. The aim of this study was to determine the feasibility of using fatigue-testing of a complex dental restoration and to evaluate the mechanical fatigue behavior of premolar teeth restored with a titanium alloy post and an amalgam or composite core. Eighty-seven human upper premolar teeth were decoronated, embedded, and restored with a prefabricated post of 1 mm diameter. The teeth were randomly assigned to one of two groups corresponding with a core build-up of amalgam or chemically-cured core composite, respectively. Five to 21 days after restoration, the specimens were subjected to cyclic loading (frequency, 5 Hz), at an angle of 45 degrees to the long axis of the tooth. The boundary technique was used for determination of the mean fatigue strengths of the restorations at 10(4), 10(5), and 10(6) cycles, simulating up to 1-3 years of clinical functioning. Mean fatigue strength was expressed in percentage of initial strength: For 10(4), 10(5), and 10(6) cycles, the results were 66%, 58%, and 52%, respectively, for the amalgam and 62%, 62%, and 53% for the composite group. It is concluded that fatigue-testing of more complex systems is possible, if a suitable testing method is selected. The restorations showed a comparable strength reduction after 10(6) cycles of about 50% of their initial strength. The composite core build-up showed a behavior less predictable than that of the amalgam, which might be attributed to handling parameters.