A prospective study assessing the effect of coronal tooth structure loss on the outcome of root canal retreatment.

AIM: To evaluate the outcome of secondary root canal treatment (retreatment) on posterior teeth in relation to the residual volume of coronal tooth structure, measured with an intraoral scanner, using periapical radiography and cone beam computed tomography (CBCT). METHODOLOGY: A total of 137 posterior teeth in 121 patients were assessed clinically and radiographically using periapical radiographs and CBCT scans at baseline and 1 year after root canal retreatment. The increase or decrease in the size of preoperative periapical radiolucencies and development of new radiolucencies were assessed by a consensus panel consisting of two pre-calibrated examiners. A clinical impression was obtained for each tooth after completion of root canal retreatment, before the placement of the temporary restoration and following cast restoration placement to produce two casts. All casts were scanned using an intraoral digital scanner and the three-dimensional volume of remaining tooth structure calculated. Teeth were also classified according to the number of remaining coronal walls before core build-up. χ2 test was used to determine the association between the outcome of root canal retreatments and the volume of remaining coronal tooth structure. RESULTS: At the 1-year recall, teeth retaining less than 30% of their original tooth structure volume had a significantly higher proportion of unfavourable outcomes (χ2 , P < 0.05, odds ratio [OR], 2.58; 95% CI, 1.026-6.487). CONCLUSIONS: The loss of tooth structure volume is an objective parameter that can be used to predict the probability of success of root canal retreatments. At 1-year follow-up, the percentage of unfavourable outcomes of root canal retreated teeth was significantly higher when less than 30% of the original tooth tissue structure was present at baseline.

Comparison of the possible protective effect of the salivary pellicle of individuals with and without erosion.

The acquired pellicle adheres to tooth surfaces and has been suggested to provide differing degrees of protection against acidic erosion. This study investigated whether pellicle formed on enamel blocks in patients suffering dietary dental erosion modified the effect of an in vitro simulated dietary challenge, in comparison with pellicle formed on enamel blocks in healthy subjects and to no-pellicle enamel samples. Sixty subjects recruited from dental erosion clinics were compared to healthy age-matched controls. Subjects wore a custom-made maxillary splint holding human enamel blocks for 1 h during which the acquired enamel pellicle was formed. Enamel blocks were removed from the splints and a simulated dietary erosive challenge of 10 min was performed. In addition the challenge was performed on 30 enamel samples without pellicle. Profilometry showed no statistical difference between samples from the erosion subjects with a mean step height of 1.74 µm (SD 0.88) and median roughness (Sa) of 0.39 µm (interquartile range, IQR 0.3-0.56) and the controls with 1.34 µm (SD 0.66) and 0.33 µm (IQR 0.27-0.38), respectively. The control samples without pellicle had Sa of 0.44 µm (IQR 0.36-0.69) and these differences were statistically significant compared to those from the healthy subjects (p = 0.002). Mean (SD) microhardness reduction with a 100-gram load for the erosion group was 113.5 (10) KHN, for healthy subjects was 93 (15.4) KHN and for the enamel samples without pellicle 139.6 (21.8) KHN and all groups were statistically different. The microhardness and roughness data suggested the pellicle influenced erosion under these study conditions.

Accuracy of CBCT for volumetric measurement of simulated periapical lesions.

AIM: To compare the accuracy of cone beam computed tomography (CBCT) and micro-computed tomography (µCT) when measuring the volume of bone cavities. METHODOLOGY: Ten irregular-shaped cavities of varying dimensions were created in bovine bone specimens using a rotary diamond bur. The samples were then scanned using the Accuitomo 3D CBCT scanner. The scanned information was converted to the Digital Imaging and Communication in Medicine (DICOM) format ready for analysis. Once formatted, 10 trained and calibrated examiners segmented the scans and measured the volumes of the lesions. Intra/interexaminer agreement was assessed by each examiner re-segmenting each scan after a 2-week interval. Micro-CT scans were analysed by a single examiner. To achieve a physical reading of the artificially created cavities, replicas were created using dimensionally stable silicone impression material. After measuring the mass of each impression sample, the volume was calculated by dividing the mass of each sample by the density of the set impression material. Further corroboration of these measurements was obtained by employing Archimedes' principle to measure the volume of each impression sample. Intraclass correlation was used to assess agreement. RESULTS: Both CBCT (mean volume: 175.9 mm3) and µCT (mean volume: 163.1 mm3) showed a high degree of agreement (intraclass correlation coefficient >0.9) when compared to both weighed and 'Archimedes' principle' measurements (mean volume: 177.7 and 182.6 mm3, respectively). CONCLUSION: Cone beam computed tomography is an accurate means of measuring volume of artificially created bone cavities in an ex vivo model. This may provide a valuable tool for monitoring the healing rate of apical periodontitis; further investigations are warranted.

The subsurface lesion in erosive tooth wear.

OBJECTIVES: This study compared the surface change on natural and polished enamel exposed to a joint mechanical and chemical wear regimen. METHODS: Human enamel samples were randomly assigned to natural (n = 30) or polished (n = 30) groups, subjected to erosion (n = 10, 0.3% citric acid, 5 min), abrasion (n = 10, 30 s), or a combination (n = 10). Wear in the form of step height was measured with a non-contact profilometer, and surface changes were inspected with SEM on selected sections. Data was normalised and underwent repeated measures MANOVA, accounting for substrate and erosive challenge as independent variables, with Bonferroni correction for significant post hoc interactions. RESULTS: After four cycles, polished samples had mean step heights of 3.08 (0.40) µm after erosion and 4.08 (0.37) µm after erosion/abrasion. For natural samples, these measurements were 1.52 (0.22) µm and 3.62 (0.39) µm, respectively. Natural surfaces displayed less wear than polished surfaces under erosion-only conditions (p<0.0001), but the difference disappeared with added abrasion. SEM revealed a shallow subsurface layer for polished surfaces and natural ones undergoing only erosion. However, natural surfaces exposed to both erosion and abrasion showed deeper subsurface changes up to 50 µm. CONCLUSION: Natural enamel, when exposed to erosion alone, showed less wear and minimal subsurface alterations. But with added abrasion, natural enamel surfaces saw increased wear and notable subsurface changes compared to polished ones. CLINICAL SIGNIFICANCE: The pronounced subsurface lesions observed on eroded/abraded natural enamel surfaces highlight how combined wear challenges may accelerate tooth tissue loss.

In vivo measurements of tooth wear over 12 months.

The aim of this study was to measure the progression of tooth wear in a cohort of 63 patients, 43 males and 20 females with a mean age of 39.1 years. Recruitment followed referral from general practice to Guy's Hospital for advice/management of tooth wear. Addition silicone impressions were taken at 6-month intervals for a total of 12 months; impressions were subsequently poured in type IV gypsum. Casts were scanned using a non-contacting laser profilometer and then superimposed using Geomagic® Qualify 11. Wear was measured in µm by tooth per time interval. A questionnaire highlighting dietary, parafunctional and gastric risk factors was obtained from each participant. Clustered multiple regression analysis was used to determine the relationship between tooth wear progression and risk factors. Maximum follow-up times were 6 months for 63 participants and 12 months for 30 participants. The measurement error was 15 µm. At the tooth level, 72.2% of 1,078 teeth wore <15 µm over a 6-month period. At the subject level, 77.7% of 63 participants showed median wear <15 µm over a 6-month period. There was a statistical trend towards tooth wear progression being associated with gastric risk factors (p < 0.05). The lower molars and the upper anterior teeth were the most commonly affected teeth; the lower molars and the upper central incisors were the most severely affected teeth. Tooth wear progression was slow in this cohort, suggesting that tooth wear may be cyclical and inactive in the majority of participants.

In vitro evaluation of the early erosive lesion in polished and natural human enamel.

OBJECTIVE: This study evaluated the capability of profilometry, microhardness, Optical Coherence Tomography (OCT) and Tandem Scanning Confocal Microscopy (TSM) in characterising the early erosive lesion in polished and natural human enamel in vitro. METHODS: Polished (n=60) and natural (n=60) human enamel surfaces, were immersed and agitated in 0.3% citric acid erosion at 0s, 10s, 30s, 60s, 120s, and 300s (n=10). Changes in the surface were measured with 3D-step height change (µm), surface roughness (µm), surface microhardness (KHN), and images were assessed qualitatively with OCT and TSM. RESULTS: Mean (SD) 3D-step height change (µm) was measurable for polished enamel at: 60s (0.24±0.1), 120s (1.16±0.71), 300s (2.01±0.47; p<0.05); a step height change was not detectable on acid challenged natural enamel surfaces. Mean (SD) surface roughness (µm) of polished enamel was detected at 10s (0.270±0.013; p<0.05) and all erosion periods; and in natural enamel detected after 120s (0.830±0.125) and 300s (0.800±0.140; p<0.005). Polished enamel Mean (SD) microhardness (KHN) statistically significantly decreased at all time points (p<0.001); this was unmeasurable for natural enamel. Qualitative image analysis of both surface types indicated erosive change at the surface level, with progression after increasing erosion time. SIGNIFICANCE: The early erosive lesion in polished enamel could be characterised quantitatively surface roughness and microhardness and qualitatively using OCT and TSM; whilst in natural enamel only surface roughness could be utilised. Further investigation of early erosion in natural enamel is required to develop new more clinically relevant models.

Precision of 655nm Confocal Laser Profilometry for 3D surface texture characterisation of natural human enamel undergoing dietary acid mediated erosive wear.

OBJECTIVES: To assess the precision of optical profilometry for characterising the 3D surface roughness of natural and polished human enamel in order to reliably quantify acid mediated surface roughness changes in human enamel. METHODS: Forty-two enamel samples were prepared from extracted human molars and either polished flat or left unmodified. To investigate precision, the variability of thirty repeated measurements of five areas of one polished and one natural enamel sample was assessed using 655nm Confocal Laser Profilometry. Remaining samples were subjected to forty-five minutes orange juice erosion and microstructural changes were analysed using Sa roughness change (µm) and qualitatively using surface/subsurface confocal microscopy. RESULTS: Enamel surface profilometry from the selected areas revealed maximal precision of 5nm for polished enamel and 23nm for natural enamel. After erosion, the polished enamel revealed a 48% increase in mean (SD) Sa roughness of 0.10 (0.07)µm (P<0.05), whereas in contrast the natural enamel revealed a 45% decrease in mean (SD) roughness of -0.32 (0.42)µm (P<0.05). These data were supported by qualitative confocal images of the surface/subsurface enamel. SIGNIFICANCE: This study demonstrates a method for precise surface texture measurement of natural human enamel. Measurement precision was superior for polished flat enamel in contrast to natural enamel however, natural enamel responds very differently to polished enamel when exposed to erosion challenges. Therefore, thus future studies characterising enamel surface changes following erosion on natural enamel may provide more clinically relevant responses in comparison to polished enamel.

Measurement uncertainty associated with chromatic confocal profilometry for 3D surface texture characterization of natural human enamel.

OBJECTIVE: To investigate the measurement performance of a chromatic confocal profilometer for quantification of surface texture of natural human enamel in vitro. METHODS: Contributions to the measurement uncertainty from all potential sources of measurement error using a chromatic confocal profilometer and surface metrology software were quantified using a series of surface metrology calibration artifacts and pre-worn enamel samples. The 3D surface texture analysis protocol was optimized across 0.04mm2 of natural and unpolished enamel undergoing dietary acid erosion (pH 3.2, titratable acidity 41.3mmolOH/L). RESULTS: Flatness deviations due to the x, y stage mechanical movement were the major contribution to the measurement uncertainty; with maximum Sz flatness errors of 0.49µm. Whereas measurement noise; non-linearity's in x, y, z and enamel sample dimensional instability contributed minimal errors. The measurement errors were propagated into an uncertainty budget following a Type B uncertainty evaluation in order to calculate the Standard Combined Uncertainty (uc), which was ±0.28µm. Statistically significant increases in the median (IQR) roughness (Sa) of the polished samples occurred after 15 (+0.17 (0.13)µm), 30 (+0.12 (0.09)µm) and 45 (+0.18 (0.15)µm) min of erosion (P<0.001 vs. baseline). In contrast, natural unpolished enamel samples revealed a statistically significant decrease in Sa roughness of -0.14 (0.34) µm only after 45min erosion (P<0.05s vs. baseline). SIGNIFICANCE: The main contribution to measurement uncertainty using chromatic confocal profilometry was from flatness deviations however by optimizing measurement protocols the profilometer successfully characterized surface texture changes in enamel from erosive wear in vitro.

Rising to the challenge.

R. S. Austin, K. Ranshi, E. Jones, R. Watt, P. Briggs discuss training our future dental leaders and managers to make a positive difference against a background of ever-increasing complexity in NHS organisations.

Confocal laser scanning microscopy and area-scale analysis used to quantify enamel surface textural changes from citric acid demineralization and salivary remineralization in vitro.

OBJECTIVES: This paper investigates the application of confocal laser scanning microscopy to determine the effect of acid-mediated erosive enamel wear on the micro-texture of polished human enamel in vitro. METHODS: Twenty polished enamel samples were prepared and subjected to a citric acid erosion and pooled human saliva remineralization model. Enamel surface microhardness was measured using a Knoop hardness tester, which confirmed that an early enamel erosion lesion was formed which was then subsequently completely remineralized. A confocal laser scanning microscope was used to capture high-resolution images of the enamel surfaces undergoing demineralization and remineralization. Area-scale analysis was used to identify the optimal feature size following which the surface texture was determined using the 3D (areal) texture parameter Sa. RESULTS: The Sa successfully characterized the enamel erosion and remineralization for the polished enamel samples (P<0.001). SIGNIFICANCE: Areal surface texture characterization of the surface events occurring during enamel demineralization and remineralization requires optical imaging instrumentation with lateral resolution <2.5 µm, applied in combination with appropriate filtering in order to remove unwanted waviness and roughness. These techniques will facilitate the development of novel methods for measuring early enamel erosion lesions in natural enamel surfaces in vivo.

The influence of varnish and high fluoride on erosion and abrasion in a laboratory investigation.

BACKGROUND: The aim of this study was to investigate the potential of concentrated fluoride varnishes to reduce enamel loss from repeated cycles of citric acid erosion and toothbrush abrasion in vitro. METHODS: Polished human enamel samples were exposed to fluoride varnishes: Bifluorid10® (NaF&CaF2- 45,200 ppmF), Duraphat® (NaF 22,600 ppmF), Fluor-Protector® (difluorsilane 1000 ppmF) and a control coating of copal ether varnish (0 ppmF) group and a deionized water group. For each group of 16 samples, nine cycles of erosion and nine cycles of erosion-abrasion [1 cycle=erosion (0.3% citric acid, pH 3.2, 5 min)+artificial saliva (1 h, pH 7.0)+abrasion (120 linear strokes in artificial saliva from Oral B medium soft brushes 300 g loading]. The change in the enamel surface was evaluated using optical profilometry. RESULTS: Duraphat® and Bifluorid10® applications had a median (IQR) step height of 4.21 um (1.59) and 5.01 um (1.02). This was statistically significantly less than Fluor-Protector® 6.83 um (1.25), copal ether 7.22 um (1.97) and water 7.39 um (1.96) (p<0.001). For erosion-abrasion, both Duraphat® and Bifluorid® had statistically lower step heights than the other products (p<0.01). CONCLUSIONS: The action of fluoride in a range of single-application topical varnishes was effective in reducing enamel wear from erosion and erosion-abrasion in this laboratory study.

In vitro effect of air-abrasion operating parameters on dynamic cutting characteristics of alumina and bio-active glass powders.

Minimally invasive dentistry advocates the maintenance of all repairable tooth structures during operative caries management in combination with remineralization strategies. This study evaluated the effect of air-abrasion operating parameters on its cutting efficiency/pattern using bio-active glass (BAG) powder and alumina powder as a control in order to develop its use as a minimally invasive operative technique. The cutting efficiency/pattern assessment on an enamel analogue, Macor, was preceded by studying the powder flow rate (PFR) of two different commercial intraoral air-abrasion units with differing powder-air admix systems. The parameters tested included air pressure, powder flow rate, nozzle-substrate distance, nozzle angle, shrouding the air stream with a curtain of water, and the chemistry of abrasive powder. The abraded troughs were scanned and analyzed using confocal white light profilometry and MountainsMap surface analysis software. Data were analyzed statistically using one-way and repeated-measures analysis of variance tests (p=0.05). The air-abrasion unit using a vibration mechanism to admix the abrasive powder with the air stream exhibited a constant PFR regardless of the set air pressure. Significant differences in cutting efficiency were observed according to the tested parameters (p<0.05). Alumina powder removed significantly more material than did BAG powder. Using low air pressure and suitable consideration of the effect of air-abrasion parameters on cutting efficiency/patterns can improve the ultraconservative cutting characteristics of BAG air-abrasion, thereby allowing an introduction of this technology for the controlled cleaning/removal of enamel, where it is indicated clinically.

A method to evaluate profilometric tooth wear measurements.

OBJECTIVES: To test the accuracy of measurements of tooth wear using a non-contacting laser profilometer (NCLP) and surface matching software. METHODS: The accuracy and repeatability of the NCLP and software in measuring length was assessed by repeatedly scanning a calibrated 25 mm engineering steel gage block. Volumetric measurements were assessed after scanning commercially pure titanium frustums of varying volume. The accuracy and repeatability of the systems in measuring step height and volume after surface matching were assessed using a custom built model with cemented engineering slip gages and cemented onlays of super-plastically formed titanium. The overall effect on the uncertainty of measurement of repeated superimpositions of the same cast, repeated impressions of the same patient and using step-over distances smaller than the laser spot size were also quantified. RESULTS: The accuracy and repeatability were 1.3 µm and 1.6 µm in measuring length. The system was accurate for volumetric measurement with coefficients of variation <5%. Measurements using the model with cemented engineering slip gages and cemented super-plastically formed titanium onlays varied slightly (23.07 µm and 1.6 mm(3)). Scanning and superimposing the same model introduced mean error of 2.7 µm (SD=0.7). Scanning and superimposing separate casts from repeated impressions of a patient introduced mean error of 14.8 µm (SD=2.8). Decreasing step-over distances reduced measurement error (p<0.05). SIGNIFICANCE: The methodologies described here served to assess sources of error in tribology studies using surface mapping and surface matching technologies. The results optimized data interpretation. Study supported by Guy's and St. Thomas' Charity and the Royal College of Surgeons of England.

A qualitative and quantitative investigation into the effect of fluoride formulations on enamel erosion and erosion-abrasion in vitro.

OBJECTIVES: To investigate the effect of a single application of highly concentrated SnF(2) and NaF solutions and a NaF/CaF(2) varnish on human enamel subjected to hydrochloric acid erosion and tooth brush abrasion. METHODS: Forty enamel samples were prepared from human third molars and NaF (9500ppm, pH 8.0), SnF(2) (9500ppm, pH 2.6) solutions; Bifluorid10(®) varnish (42,500ppm, NaF 5%, CaF(2) 5%) and deionized water (control) was applied to the enamel. Following this three, six and nine cycles of erosion [1 cycle=erosion (0.01M HCl, pH 2.2, 2min)+artificial saliva (1h, pH 7.0)] and erosion-abrasion [1 cycle=erosion (0.01M HCl, pH 2.2, 2min)+artificial saliva (1h, pH 7.0)+abrasion (120 linear strokes in artificial saliva from Tepe medium soft brushes 200g loading)] were carried out. The fluoride treated enamel was analysed using Knoop microhardness, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). RESULTS: For erosion alone, there was significantly less microhardness reduction in the Bifluorid10(®) group after three and six cycles of erosion (P<0.05), however no other groups showed statistically different hardness (P>0.05). The EDS analysis showed that only the Bifluorid10(®) group had any detectable fluorine following erosion and erosion-abrasion (0.1wt.% and 0.2wt.% fluorine respectively). The surface fluorine was found to have been removed after erosion and erosion-abrasion for all other surface treatments. Although precipitates were observed after application of the surface treatments, following erosion-abrasion, no visible surface effects from any fluoride preparation remained. CONCLUSIONS: Enamel surface precipitates from application NaF, SnF(2) solutions appear to not be able to provide protection against gastric erosion and tooth brush abrasion. The NaF/CaF(2) varnish provided limited protection against erosion but the role for such varnishes in gastric erosion and tooth brush abrasion remains uncertain.

The effect of increasing sodium fluoride concentrations on erosion and attrition of enamel and dentine in vitro.

OBJECTIVES: To investigate the effect of an aqueous sodium fluoride solution of increasing concentration on erosion and attrition of enamel and dentine in vitro. METHODS: Enamel and dentine sections from caries-free human third molars were polished flat and taped (exposing a 3 mm x 3 mm area) before being randomly allocated to 1 of 5 groups per substrate (n=10/gp): G1 (distilled water control); G2 (225 ppm NaF); G3 (1450 ppm NaF); G4 (5000 ppm NaF); G5 (19,000 ppm NaF). All specimens were subjected to 5, 10 and 15 cycles of experimental wear [1 cycle=artificial saliva (2h, pH 7.0)+erosion (0.3% citric acid, pH 3.2, 5 min)+fluoride/control (5 min)+attrition (60 linear strokes in artificial saliva from enamel antagonists loaded to 300 g)]. Following tape removal, step height (SH) in mum was measured using optical profilometry. RESULTS: When the number of cycles increased the amount of tooth surface loss increased significantly in enamel and dentine after attrition and erosion and for dentine after attrition. Attrition and erosion resulted in greater surface loss than attrition alone after 15 cycles of experimental wear of enamel. 5000 ppm and 19,000 ppm sodium fluoride solutions had a protective effect on erosive and attritional enamel tooth wear in vitro, however no other groups showed significant differences. CONCLUSIONS: The more intensive the fluoride regime the more protection was afforded to enamel from attrition and erosion. However, in this study no such protective effect was demonstrated for dentine.

Intraoperative monitoring and postoperative imaging of hepatic cryosurgery.

Because intraoperative sonography displays segmental anatomy, allows discovery of more lesions than previously suspected from preoperative imaging, surgical inspection, or palpation, and permits more certain diagnosis of problematic masses, it facilitates surgical decision-making when liver resection or cryoablation is anticipated. Intraoperative sonography provides a guidance modality to accurately place cryosurgery probes in liver masses. More precise treatment of metastatic and primary tumors of the liver is possible with cryoablation because intraoperative sonography provides a means of monitoring the growth of the enlarging freeze zone to insure adequate surgical margins. Postoperative detection of acute complications after cryosurgery is best done with computed tomography. Normally cryosurgery defects shrink with time and lose the peripheral contrast opacification seen after surgery. Gas collections, seen as a result of tissue necrosis, must be discriminated from infection. Tumor recurrence can be detected well with computed tomography or magnetic resonance imaging following hepatic cryosurgery.

Histochemical and biochemical studies of the hepatopancreas peroxidase of the freshwater crayfish, Cambarus robustus.

Crayfish are among the few invertebrate species reported to possess endogenous peroxidase activity. The enzyme is found within the hepatopancreas, the principal digestive and absorptive organ of the crustacean body. Cambarus robustus, a species found in abundance in the streams of western New York, was used in this study. Homogenates of 18 hepatopancreases were assayed for peroxidase activity using guaiacol as the substrate. Although present in all organs, peroxidase activity displayed a greater than 50-fold difference between the two extremes (0.05-;2.72 units/mg protein). Histochemical examination using diaminobenzidine revealed peroxidase activity within a line of cells extending along the distal two-thirds of the lengths of all hepatopancreatic tubules. The cells function to synthesize the enzyme, sequester it within vacuoles of increasing size, and eventually secrete it into the tubule lumen. Since the tubule is constantly renewed by distal mitotic activity and concomitant proximal exfoliation, this histochemical technique permits not only the examination of the ontogeny of this peroxidase-positive cell line, but also offers additional insight into the mechanism of hepatopancreatic tubule renewal.