Increased Handpiece Speeds without Air Coolant: Aerosols and Thermal Impact.

This study assessed the impact of increased speed of high-speed contra-angle handpieces (HSCAHs) on the aerosolization of a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) surrogate virus and any concomitant thermal impact on dental pulp. A bacteriophage phantom-head model was used for bioaerosol detection. Crown preparations were performed with an NSK Z95L Contra-Angle 1:5 (HSCAH-A) and a Bien Air Contra-Angle 1:5 Nova Micro Series (HSCAH-B) at speeds of 60,000, 100,000, and 200,000 revolutions per minute (rpm), with no air coolant. Bioaerosol dispersal was measured with Φ6-bacteriophage settle plates, air sampling, and particle counters. Heating of the internal walls of the pulp chambers during crown preparation was assessed with an infrared camera with HSCAH-A and HSCAH-B at 200,000 rpm (water flows ≈15 mL min-1 and ≈30 mL min-1) and an air-turbine control (≈23.5 mL min-1) and correlated with remaining tissue thickness measurements. Minimal bacteriophage was detected on settle or air samples with no notable differences observed between handpieces or speeds (P > 0.05). At all speeds, maximum settled aerosol and average air detection was 1.00 plaque-forming units (pfu) and 0.08 pfu/m3, respectively. Irrespective of water flow rate or handpiece, both maximum temperature (41.5°C) and temperature difference (5.5°C) thresholds for pulpal health were exceeded more frequently with reduced tissue thickness. Moderate and strong negative correlations were observed based on Pearson's correlation coefficient, between remaining dentine thickness and either differential (r = -0.588) or maximum temperature (r = -0.629) measurements, respectively. Overall, HSCAH-B generated more thermal energy and exceeded more temperature thresholds compared to HSCAH-A. HSCAHs without air coolant operating at speeds of 200,000 rpm did not increase bioaerosolization in the dental surgery. Thermal risk is variable, dependent on handpiece design and remaining dentine thickness.

Color Changes Associated with Sandblasting, Hydrofluoric Acid Etching, and Er:YAG Laser Irradiation of Milled Feldspathic Porcelain Laminate Veneers.

OBJECTIVES: To evaluate color changes in milled feldspathic porcelain laminate veneers following hydrofluoric acid etching (HFA), sandblasting (SB), or Er:YAG laser irradiation (LI). METHODS AND MATERIALS: Disc-shaped specimens (thickness=1 mm, diameter=8 mm) were milled from feldspathic porcelain blocks (n=40). Glazed specimens were randomly assigned to four subgroups (n=10 each) according to surface treatment: negative control, HFA, SB, and LI. A layer of translucent, light-cured resin cement (thickness=0.1 mm) was then applied following silanization. The color was characterized by the L*, a*, and b* uniform color space (CIE) using a reflection spectrophotometer. CIEDE2000 (ΔE00) was calculated to determine the color difference between each surface treatment and negative control groups. Data were statistically analyzed using analysis of variance (ANOVA), Kruskal-Wallis, and Dunn-Bonferroni post hoc tests. RESULTS: There were no significant differences in CIEL* and CIEb* coordinates between negative control and all surface treatment groups (p≥0.108). The SB group demonstrated significantly lower mean CIEa* (higher greenish hue) compared to other groups (p≤0.003). HFA exhibited significantly higher CIEa* (closer to red) when compared to LI (p=0.039). LI induced the smallest overall color change compared to negative control (ΔE00=1.43 [1.07]). However, the differences in ΔE00 values were not statistically significant (p=0.648). CONCLUSIONS: The tested surface treatments did not affect the lightness or the yellowness of the 1-mm-thick milled feldspathic porcelain veneers. However, sandblasting resulted in a significant increase in the greenish hue. The Er:YAG laser resulted in the closest ΔE00 (1.43) to the 50:50% perceptibility threshold (ΔE00=1.2).

Dental Mitigation Strategies to Reduce Aerosolization of SARS-CoV-2.

Limiting infection transmission is central to the safety of all in dentistry, particularly during the current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Aerosol-generating procedures (AGPs) are crucial to the practice of dentistry; it is imperative to understand the inherent risks of viral dispersion associated with AGPs and the efficacy of available mitigation strategies. In a dental surgery setting, crown preparation and root canal access procedures were performed with an air turbine or high-speed contra-angle handpiece (HSCAH), with mitigation via rubber dam or high-volume aspiration and a no-mitigation control. A phantom head was used with a 1.5-mL min-1 flow of artificial saliva infected with Φ6-bacteriophage (a surrogate virus for SARS-CoV-2) at ~108 plaque-forming units mL-1, reflecting the upper limits of reported salivary SARS-CoV-2 levels. Bioaerosol dispersal was measured using agar settle plates lawned with the Φ6-bacteriophage host, Pseudomonas syringae. Viral air concentrations were assessed using MicroBio MB2 air sampling and particle quantities using Kanomax 3889 GEOα counters. Compared to an air turbine, the HSCAH reduced settled bioaerosols by 99.72%, 100.00%, and 100.00% for no mitigation, aspiration, and rubber dam, respectively. Bacteriophage concentrations in the air were reduced by 99.98%, 100.00%, and 100.00% with the same mitigations. Use of the HSCAH with high-volume aspiration resulted in no detectable bacteriophage, both on nonsplatter settle plates and in air samples taken 6 to 10 min postprocedure. To our knowledge, this study is the first to report the aerosolization in a dental clinic of active virus as a marker for risk determination. While this model represents a worst-case scenario for possible SARS-CoV-2 dispersal, these data showed that the use of HSCAHs can vastly reduce the risk of viral aerosolization and therefore remove the need for clinic fallow time. Furthermore, our findings indicate that the use of particle analysis alone cannot provide sufficient insight to understand bioaerosol infection risk.

An Evaluation of the Efficacy of LED Light Curing Units in Primary and Secondary Dental Settings in the United Kingdom.

OBJECTIVE: This study aimed to evaluate the irradiance and the quality of LED light curing units (LCUs) in primary and secondary clinics in the UK and to assess the effect of damage, contamination, use of protective sleeves, and distance of light tips to target on the irradiance and performance of LCUs. METHODS: The irradiance levels (mW/cm2) of 26 LED LCUs from general dental practices and 207 LED LCUs from two dental hospitals were measured using a digital radiometer (Blue Phase II, Ivoclar, Vivadent, Amherst, NY). Ten LED light guide tips (Satelec Mini, Acteon, Merignac, France) were selected to evaluate the effect of chipping, contamination (tip debris), and use of protective sleeves and tips to sensor distance on irradiance (mW/cm2) using a MARC Resin Calibrator (Blue Light Analytics, Halifax, Canada). Homogeneity of the light output was evaluated using a laser beam profiler (SP620; Ophir-Spiricon, North Longan, UT, USA). Statistical analysis was conducted using a one-way analysis of variance (ANOVA) with post hoc Tukey test (α=0.05) and linear regression with stepwise correlation tests. RESULTS: Thirty-three percent of the LCUs delivered irradiance output less than 500 mW/cm2. The condition of the light curing tips was poor, with 16% contaminated with resin debris, 26% damaged, and 10% both contaminated and damaged. The irradiance output was significantly reduced in contaminated (62%) and chipped (50%) light curing tips and when using protective sleeves (24%) (p<0.05). Irradiance was also reduced when increasing the distance with 25% and 34% reduction at 7 mm and 10 mm, respectively (p<0.05). CONCLUSION: There remains a lack of awareness of the need for regular monitoring and maintenance of dental LCUs. Damaged and contaminated light curing tips, use of protective sleeves, and increasing the distance from the restoration significantly reduced the irradiance output and the performance of the LCUs.

Interprofessional education in dentistry.

A collaborative health workforce is required to respond to the increasing demands on healthcare resources. Various national and international bodies are promoting interprofessional education (IPE) as a method to provide this collaborative health workforce. IPE is therefore becoming increasingly prominent within healthcare training and will be an essential aspect of dental education. A literature search was completed to provide this narrative review which will introduce IPE, discuss the rationale for IPE within dentistry and the challenges faced. Based on current literature, it will provide practical advice on how to implement an effective IPE learning activity within dentistry.

Penetration of fluoride into natural plaque biofilms.

Caries occurs at inaccessible stagnation sites where plaque removal is difficult. Here, the penetration through plaque of protective components, such as fluoride, is likely to be crucial in caries inhibition. We hypothesized that topically applied fluoride would readily penetrate such plaque deposits. In this study, plaque biofilms generated in vivo on natural enamel surfaces were exposed to NaF (1000 ppm F-) for 30 or 120 sec (equivalent to toothbrushing) or for 30 min. Biofilms were then sectioned throughout their depth, and the fluoride content of each section was determined with the use of a fluoride electrode. Exposure to NaF for 30 or 120 sec increased plaque fluoride concentrations near the saliva interface, while concentrations near the enamel surface remained low. Fluoride penetration increased with duration of NaF exposure. Removal of exogenous fluoride resulted in fluoride loss and redistribution. Penetration of fluoride into plaque biofilms during brief topical exposure is restricted, which may limit anti-caries efficacy.

Minimizing prion risk without compromising the microbial composition of biofilms grown in vivo in a human plaque model.

AIMS: To determine whether the stringency of sterilization procedures for biological components of in vivo dental plaque-generating devices based on enamel can be increased to minimize prion risk without compromising natural biofilm composition. METHODS AND RESULTS: The composition of in vitro biofilms, grown on hypochlorite-treated and untreated autoclaved enamel surfaces, was determined using culture-based methods and checkerboard DNA: DNA hybridization analysis. No differences were found between biofilms recovered from either substrate. SIGNIFICANCE: Several in situ models allow generation of plaque in the oral cavity, followed by recovery of intact biofilms for experimentation. Approaches allowing plaque formation on natural tooth surfaces are most valuable, but present a possible infection risk to volunteers wearing plaque-collecting devices, particularly with respect to prions. Hypochlorite treatment of biological material, as an adjunct to autoclaving, reduces infection risk without compromising biofilm composition and should be adopted in all future studies using plaque-generating devices incorporating enamel, where there is a potential prion threat, and further investigated in other biological hard tissues.

Improving student learning in root canal treatment using self-assessment.

AIM: This paper reports the first attempts to implement a new course in endodontology for undergraduate dental students based upon independent, reflective learning and self-assessment. METHODOLOGY: The responses were analysed of two successive cohorts of third-year students to laboratory courses in (i) the restoration of teeth with crowns and (ii) endodontology and root canal treatment. The major changes introduced to the endodontology course were a substantial reduction in the number of formal lectures, the introduction of a series of structured tutorials, time for private study and the use of self-assessment in practical classes. RESULTS: The evidence indicates that the new approach increased student confidence in practical skills, although the time available for operative practice was actually reduced; there was a perceived increase in problem-solving ability; and that students felt encouraged to pursue greater understanding. Reports from tutors suggested that students' self-assessments became more accurate as the courses proceeded. Seven experimental learning points were derived from the study. These included the importance of careful planning, well-designed assessment procedures and the creation of a climate of trust and openness. CONCLUSIONS: The task of developing fully the students' skills of accurate self-assessment remains a challenge.

Evaluation of X-ray beam angulation for successful twin canal identification in mandibular incisors.

This study was undertaken to determine the most effective horizontal beam angulation for the diagnosis of twin canals in mandibular incisors. Two hundred extracted mandibular incisor teeth, in groups of four, were aligned in the form of a lower dental arch and radiographed using a beam alignment device at 10 degrees intervals between 0 degree and 50 degrees from both right and left sides. Five observers with varying degrees of experience were asked to assess the number of canals in each of the four teeth from these radiographs. A further radiograph of each individual tooth was taken at 90 degrees through the mesio-distal plane to identify the number of twin canals present. A random sample of 10% of the radiographs were viewed for a second time 3 months later to assess intra-observer variation. The 20 degrees right and 30 degrees left horizontal beam angulations showed significantly more accurate diagnosis of twin canals than the ortho-radial view (0 degree) by all five observers. Analysis of the inter-observer results suggests that the experienced viewers were no better but more consistent at identifying twin canals in mandibular incisors.

A model for the teaching of clinical techniques in root canal treatment.

A practical model to aid the understanding and practice of endodontic techniques is described. The model uses extracted teeth mounted in light-cured acrylic resin and set in a preformed model tray. Before mounting, the root surfaces of teeth are dipped in wax to simulate the periodontal ligament space. This model allows endodontic techniques to be practised in the operative technique classroom in a way that simulates the clinical situation and enables radiographs of good diagnostic quality to be taken during treatment. Subsequently, teeth can be reset to allow restoration of the root-filled tooth.

An in vitro assessment of tooth preparation for porcelain veneer restorations.

OBJECTIVES: This in vitro study aimed to examine the depth of preparation and incidence of dentine exposure resulting from the use of a 'freehand' technique to prepare maxillary central incisors for porcelain veneers. METHODS: Twenty-two maxillary central incisors were selected. Prior to preparation an index of the labial surface of each tooth was recorded and the tooth secured in a jig to permit accurate relocation. Two operators each prepared 11 teeth aiming to reduce the labial thickness evenly by 0.5 mm. Low viscosity silicone impression material was then placed on the index and the teeth relocated into the jig. Upon removal, this material was sectioned in the cervical, middle and incisal thirds of the tooth and its thickness measured using a toolmaker's microscope. The teeth were acid etched and also stained with a dentine dye to identify any area of dentine exposed during preparation. RESULTS: Significant differences (P < 0.001) in the depth of preparation at different sites, with least reduction in the mid-incisal region, were found. Greater reduction was found at the cervical and proximal margins with areas of dentine exposed at those sites in the majority of teeth. CONCLUSIONS: In view of the incidence and position of dentine exposure found in this study, the use of a dentine bonding system during the placement of porcelain veneers would appear essential when employing a 'freehand' preparation technique.

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

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

Comparison of the quality of obturation following endosonic versus hand instrumentation.

This study was undertaken to compare the quality of root canal obturation following preparation by endosonic or hand instrumentation. Forty single-canal, extracted lower premolar teeth were selected. One group of 20 teeth was prepared using a standard step-back technique, the other 20 teeth were prepared with an ultrasonic machine. The groups were subdivided, with two operators preparing 10 teeth of each group. The teeth were obturated by a third operator using cold laterally condensed gutta percha. The root apices were then immersed in methylene blue dye for 48 h and the teeth sectioned longitudinally. Image analysis recorded the amount of sealer and void within the obturated canal. The linear distance of dye penetration was measured to provide an indication of apical seal. Examination of the root canal shape resulting from the different preparation techniques used was also undertaken. No significant difference was noted in the percentage of sealer and void present in the root canals obturated after endosonic or hand instrumentation. There was a slightly greater although not significant increase in the degree of linear penetration of dye in canals prepared endosonically. The endosonic technique used in this study appeared to produce a canal preparation of slightly less continuous taper than that obtained with hand preparation.

Determination of volumes of fluid in the mouth by fluoride dilution.

A dilution technique, with fluoride as a marker, has been developed to measure the volume of saliva and other fluids in the mouth. Immediately after swallowing, a small amount of fluoride solution is placed in the mouth, mixed with the oral fluids, and expelled from the mouth. The fluoride concentration of the expelled oral fluid is measured and the volume of fluid in the mouth at the time of spitting calculated from the fluoride dilution. Mean values of 0.75 +/- (SD) 0.28 ml for males and 0.72 +/- (SD) 0.16 ml for females were recorded. The accuracy of the volume determination is about +/- 0.10 ml in vivo. This technique has provided a convenient and rapid means of determining saliva volumes. It could also be used to determine rates of secretion and may prove useful in the clinic for assessing a patient's salivary competence.

Predictability of radiographic diagnosis of variations in root canal anatomy in mandibular incisor and premolar teeth.

Four hundred and fifty-five extracted mandibular incisor and 340 extracted mandibular premolar teeth were radiographed to assess the incidence of twin canals as visualized on radiographs taken in the mesio-distal direction. The ability to detect the presence of these twin canals by viewing radiographs taken in the standard bucco-lingual direction was then assessed. Using the guideline that 'disappearance or narrowing infers division' when viewing these radiographs resulted in a failure to diagnose one-third of the twin canals.

Site-specific variations in the concentrations of substances in the mouth.

Estimates of the concentration of soluble substances in the oral fluids have generally been obtained by the analysis of whole saliva, either mixed in the mouth or obtained directly from the salivary duct. Such values may give little indication of concentrations at any particular site in the mouth. This is partly because substances do not always move easily about the mouth and also because there are large regional differences between the rates of oral clearance or retention of substances dissolved in saliva. Differential patterns therefore develop and are related, via the patterns of salivary flow, to the anatomy and physiology of the mouth. There are general features in these patterns common to all mouths and variations, which relate to characteristics of the individual, which may influence the rates of reactions occurring at different sites. The patterns may be associated with the site-specific patterns of dental disease, and they may have implications with regard to the best use of pharmaceutical agents. This paper describes some of the more recent data, problems and future possibilities in this hitherto unexplored area of oral physiology.