William N. Ha

A retrospective analysis of oral and maxillofacial pathology in an Australian paediatric population.

BACKGROUND The prevalence of oral and maxillofacial pathology has not previously been reported in the Australian paediatric population. This study aimed to audit a large pathology service to provide insight into the prevalence of oral and maxillofacial pathology. METHODS Written records of a major Australian oral pathology service were imported into an electronic database. Age, gender and histological diagnosis were assessed. Prevalence of histological diagnoses as a percentage of the major diagnostic categories and of the whole sample were calculated, as well as gender predilections and mean age of presentation of disease. RESULTS A total of 1305 oral pathology specimens, collected from paediatric patients aged 16 and under were included in the analysis. The most common pathology was dental pathology (24.4%), followed by odontogenic cysts (18.5%) and mucosal pathology (17.0%). The most frequently encountered lesion was the dentigerous cyst (9.4%), followed by fibrous hyperplasia (8.3%), radicular cyst (5.2%) and chronic periapical granuloma (5.2%). CONCLUSIONS In the paediatric population, dental pathology and specifically, the dentigerous cyst is the most common pathology type sent for histopathology, suggesting a high prevalence of pathology of dental origin occurring in Australian children.

Particle Size Changes in Unsealed Mineral Trioxide Aggregate Powder

INTRODUCTION Mineral trioxide aggregate (MTA) is commonly supplied in 1-g packages of powder that are used by some clinicians across several treatments against the manufacturers instructions. ProRoot MTA cannot be resealed after opening, whereas MTA Angelus has a resealable lid. This study assessed changes in particle size distribution once the packaging had been opened. METHODS Fresh ProRoot MTA and MTA Angelus powder were analyzed by using laser diffraction and scanning electron microscopy and compared with powder from packages that had been opened once and kept in storage for 2 years. The ProRoot packet was folded over, whereas the MTA Angelus jar had the lid twisted back to its original position. RESULTS After 2 years, ProRoot MTA powder showed a 6-fold increase in particle size (lower 10% from 1.13 to 4.37 μm, median particle size from 1.99 to 12.87 μm, and upper 10% from 4.30 to 34.67 μm), with an accompanying 50-fold change in particle surface area. MTA Angelus showed only a 2-fold increase in particle size (4.15 to 8.32 μm, 12.72 to 23.79 μm, and 42.66 to 47.91 μm, respectively) and a 2-fold change in particle size surface area. CONCLUSIONS MTA reacts with atmospheric moisture, causing an increase in particle size that may adversely affect the properties and shelf life of the material. Smaller particles have a greater predisposition to absorb moisture. Single-use systems are advised.

D90: The Strongest Contributor to Setting Time in Mineral Trioxide Aggregate and Portland Cement

INTRODUCTION The setting times of commercial mineral trioxide aggregate (MTA) and Portland cements vary. It was hypothesized that much of this variation was caused by differences in particle size distribution. METHODS Two gram samples from 11 MTA-type cements were analyzed by laser diffraction to determine their particle size distributions characterized by their percentile equivalent diameters (the 10th percentile, the median, and the 90th percentile [d90], respectively). Setting time data were received from manufacturers who performed indentation setting time tests as specified by the standards relevant to dentistry, ISO 6786 (9 respondents) or ISO 9917.1 (1 respondent), or not divulged to the authors (1 respondent). In a parallel experiment, 6 samples of different size graded Portland cements were produced using the same cement clinker. The measurement of setting time for Portland cement pastes was performed using American Society for Testing and Materials C 191. Cumulative heat release was measured using isothermal calorimetry to assess the reactions occurring during the setting of these pastes. In all experiments, linear correlations were assessed between setting times, heat release, and the 3 particle size parameters. RESULTS Particle size varied considerably among MTA cements. For MTA cements, d90 was the particle size characteristic showing the highest positive linear correlation with setting time (r = 0.538). For Portland cement, d90 gave an even higher linear correlation for the initial setting time (r = 0.804) and the final setting time (r = 0.873) and exhibited a strong negative linear correlation for cumulative heat release (r = 0.901). CONCLUSIONS Smaller particle sizes result in faster setting times, with d90 (the largest particles) being most closely correlated with the setting times of the samples.

A survey of various endodontic procedures related to mineral trioxide aggregate usage by members of the Australian Society of Endodontology

This study aims to assess education on the use of mineral trioxide aggregate (MTA) and Biodentine among members of the Australian Society of Endodontology (ASE), a society of specialist endodontists (ED) and general dentists with an interest in endodontics (GD). The study also aims to compare the procedural preferences relating to perforation repair, apical barrier, root-end filling and regenerative endodontics. A structured online questionnaire was used, which sought details of the education in the use of MTA and the procedural steps involved in perforation repair, apical barrier, root-end filling and regenerative endodontics. Fishers exact test was performed to compare the GD with ED. Responses were received from 208 out of 499 ASE members. Some 40% of the total respondents were ED. Almost all ED (98.8%) and some GD (39.8%) used MTA for perforation repairs. Likewise, almost all ED (96.3%) and some GD (42.7%) used MTA for apical barrier procedures. Lack of experience was more of a barrier to its use for GD (48.7%) than its high cost (31.6%). Few members used Biodentine. Significant differences exist in how MTA is used between GD and ED. Experience in handling MTA is a larger barrier to its widespread use in endodontics than its cost.

Methodologies for measuring the setting times of mineral trioxide aggregate and Portland cement products used in dentistry

Abstract Objective The current standard used to measure setting time for Mineral Trioxide Aggregate (MTA) involves indentation testing with arbitrary weights. This study compared indentation testing against rheological measurements and assessed the influences of particle size and the inclusion of bismuth oxide on the setting time of experimental MTA and Portland cement (PC). Material and methods Two PCs (P1 and P2) of different particle sizes were produced using the same clinker. From these two PCs, two experimental MTAs (M1 and M2) were created with the addition of bismuth oxide. Particle size distributions were assessed using laser diffraction analysis. Indentation setting time tests were performed in accordance to the Gillmore needle test. Elastic modulus was assessed using a strain-controlled rheometer at 1 rad s−1 and an applied strain of 0.01%. Results P1, P2, M1 and M2 cements had median particle sizes of 6.1, 12.5, 6.5 and 13.0 μm, respectively. Using indentation testing, final setting times were ranked P1 < M1 < P2 < M2. The ranking of the final setting time corresponded with the rheological assessment of time required to reach 95% of the elastic modulus plateau. Conclusions The time to reach 95% elastic modulus plateau of 9.3 min corresponds to a time close to the point where the material can be overlaid with another restorative material to give a final restoration. The 95% plateau value for elastic modulus may be a more useful parameter for determining how the setting reaction of PC and MTA cements progress over time.

Deconvolution of the particle size distribution of ProRoot MTA and MTA Angelus

Abstract Objective Mineral trioxide aggregate (MTA) cements contain two types of particles, namely Portland cement (PC) (nominally 80% w/w) and bismuth oxide (BO) (20%). This study aims to determine the particle size distribution (PSD) of PC and BO found in MTA. Materials and methods The PSDs of ProRoot MTA (MTA-P) and MTA Angelus (MTA-A) powder were determined using laser diffraction, and compared to samples of PC (at three different particle sizes) and BO. The non-linear least squares method was used to deconvolute the PSDs into the constituents. MTA-P and MTA-A powders were also assessed with scanning electron microscopy. Results BO showed a near Gaussian distribution for particle size, with a mode distribution peak at 10.48 μm. PC samples milled to differing degrees of fineness had mode distribution peaks from 19.31 down to 4.88 μm. MTA-P had a complex PSD composed of both fine and large PC particles, with BO at an intermediate size, whereas MTA-A had only small BO particles and large PC particles. Conclusions The PSD of MTA cement products is bimodal or more complex, which has implications for understanding how particle size influences the overall properties of the material. Smaller particles may be reactive PC or unreactive radiopaque agent. Manufacturers should disclose particle size information for PC and radiopaque agents to prevent simplistic conclusions being drawn from statements of average particle size for MTA materials.

The influence of particle size and curing conditions on testing mineral trioxide aggregate cement

Abstract Objectives: To assess the effects on curing conditions (dry versus submerged curing) and particle size on the compressive strength (CS) and flexural strength (FS) of set MTA cement. Materials and methods: Two different Portland cements were created, P1 and P2, with P1 < P2 in particle size. These were then used to create two experimental MTA products, M1 and M2, with M1 < M2 in particle size. Particle size analysis was performed according to ISO 13320. The particle size at the 90th percentile (i.e. the larger particles) was P1: 15.2 μm, P2: 29.1 μm, M1: 16.5 μm, and M2: 37.1 μm. M2 was cured exposed to air, or submerged in fluids of pH 5.0, 7.2 (PBS), or 7.5 for 1 week. CS and FS of the set cement were determined using a modified ISO 9917-1 and ISO 4049 methods, respectively. P1, P2, M1 and M2 were cured in PBS at physiological pH (7.2) and likewise tested for CS and FS. Results: Curing under dry conditions gave a significantly lower CS than when cured in PBS. There was a trend for lower FS for dry versus wet curing. However, this did not reach statistical significance. Cements with smaller particle sizes showed greater CS and FS at 1 day than those with larger particle sizes. However, this advantage was lost over the following 1–3 weeks. Conclusions: Experiments that test the properties of MTA should cure the MTA under wet conditions and at physiological pH.

Mineral Trioxide Aggregate-A Review of Properties and Testing Methodologies

Mineral trioxide aggregate (MTA) restoratives and MTA sealers are commonly used in endodontics. Commonly referenced standards for testing of MTA are ISO 6876, 9917-1 and 10993. A PubMed search was performed relating to the relevant tests within each ISO and “mineral trioxide aggregate”. MTA restoratives are typically tested with a mixture of tests from multiple standards. As the setting of MTA is dependent upon hydration, the results of various MTA restoratives and sealers are dependent upon the curing methodology. This includes physical properties after mixing, physical properties after setting and biocompatibility. The tests of flow, film thickness, working time and setting time can be superseded by rheology as it details how MTA hydrates. Physical property tests should replicate physiological conditions, i.e., 37 °C and submerged in physiological solution. Biocompatibility tests should involve immediate placement of samples immediately after mixing rather than being cured prior to placement as this does not replicate clinical usage. Biocompatibility tests should seek to replicate physiological conditions with MTA tested immediately after mixing.

Dental material choices for pulp therapy in paediatric dentistry

Objective: The purpose of this study was to assess the restorative choices for pulpal therapy by members of the Australian and New Zealand Society of Paediatric Dentistry (ANZSPD). Methods: Members of the ANZSPD were sent an online survey asking about the procedures that they performed and their choice of dental materials. Results: The respondents were 31 general dentists (GD) and 55 specialist paediatric dentists (PD). Materials used for indirect pulp capping included calcium hydroxide [Ca(OH)2] cement (CHC), glass ionomer cement or resin-modified glass ionomer cement (GIC/RMGIC), Ca(OH)2 paste (CHP) and mineral trioxide aggregate (MTA). Materials for direct pulp capping included MTA, CHP and CHC. Materials and techniques used for pulpotomy included MTA, ferric sulphate, formocresol and diathermy, CHP and CHC. GD and PD were similar in their choice of materials. However, there was no preferred product for pulp therapy. Most GD learnt how to use MTA from CPD lectures, while some PD learnt how to use MTA from their postgraduate training as well as CPD lectures. Many GD and PD did not have hands-on training from their education on how to use MTA (GD: 80%, PD: 43%). Most would like to attend hands-on MTA courses (GD: 86%, PD: 65%). Conclusion: There was no clear preferred product for the various types of pulp therapy in paediatric dentistry. Education appears to be the major barrier to the use of MTA rather than the cost of MTA.

Rheological characterization as an alternative method to indentation for determining the setting time of restorative and endodontic cements

This study explored an alternative approach using rheology to assess setting time. The following cements were tested: ProRoot® MTA (Dentsply, Tulsa, OK, USA), Biodentine® (Septodont, Saint Maur des Fosses, France), Fuji VII®, FujiVII® EP, and Fuji IX® (from GC Corporation, Tokyo, Japan), RealSeal SE™ Sealer (SybronEndo, Amersfoort, The Netherlands), AH 26® and AH Plus (both from Dentsply DeTrey, Konstanz, Germany). Freshly mixed cements were placed into a strain-controlled rheometer (1 rad·s−1 with an applied strain of 0.01%). From measurements of elastic modulus over time, the time taken to reach 90% of the plateau elastic modulus (designated as the setting time) was determined for each cement. In increasing order, the setting times were as follows: Fuji VII EP 3.3 min, Fuji VII 3.6 min, Fuji IX 3.7 min, ProRoot MTA 5.1 min, Biodentine 15.9 min, RealSeal 22.2 min, AH Plus 5933 min, and AH 26 5067 min. However, ProRoot MTA did not yield reliable results. The time to reach the 90% plateau elastic modulus correlates well with the setting time of glass ionomer cements and Biodentine. Using this approach gives much longer setting times for endodontic sealers than previously recognized.