Does a black light lens aid in composite removal?

OBJECTIVE: To evaluate the effectiveness of a black light lens as visual aid in composite restoration removal. Lost tooth structure, residual composite, and removal time were compared for operators with different levels of experience. METHODS: Occlusal preparations in 24 matched-pair extracted molars were etched, bonded, restored with composite, and thermocycled. The restored teeth were radiographed and two faculty and two student doctors removed the restorations with or without a black light lens while time was recorded. Digital scans of the cavity before and after restoration removal were used to calculate lost tooth structure and residual composite. RESULTS: Removal of restorations resulted in tooth structure loss and left residual composite. The use of the black light lens had no significant effect (two-way ANOVA; p value >0.05). However, operator experience significantly affected operating times and average depth of tooth structure loss (two-way ANOVA; p value <0.05). Student doctors assisted by the black light lost less tooth structure than experienced operators and improved their operating times (multiple comparisons; p value <0.05). CONCLUSIONS: The black light lens did not conserve tooth structure or avoid composite remnants compared to routine operation, nor affected the operating time. However, less-experienced operators did benefit from the black light in conserving tooth structure and time. CLINICAL SIGNIFICANCE: Replacement of defective composite restorations is a regular practice in restorative dentistry. When existing composite restorations are removed, loss of tooth structure is unavoidable. A black light lens might improve the ability of operators with less experience to conserve tooth structure even though it did not provide benefits for the experienced operators.

Millennial drinks: acidity, fluoride content, and enamel softening.

This in vitro study aimed to evaluate the acidity and fluoride content of beverages commonly consumed by millennials and the enamel-softening effect of these drinks on tooth enamel. The study included 13 beverages in 4 categories: energy (sports) drink, flavored sparkling water, kombucha, and other (an unsweetened iced tea, a vegetable-fruit juice blend, and a soft drink). The acidity was measured with a pH/ion meter, and the fluoride concentration was measured with a combined fluoride electrode coupled to the meter (n = 10 measurements per beverage). The Vickers hardness number of extracted molars was measured before and after a 30-minute immersion in 4 representative beverages via 2 immersion protocols (n = 10 per beverage per protocol): (1) immersion in the beverage only and (2) immersion alternating between the beverage and artificial saliva every other minute. The pH and fluoride concentrations of the beverages ranged from 2.652 to 4.242 and from 0.0033 to 0.6045 ppm, respectively. One-way analysis of variance (ANOVA) revealed that all differences between beverages in pH values were statistically significant, as were the majority of differences in fluoride concentrations (P < 0.001). The beverages and the 2 immersion methods significantly affected enamel softening (2-way ANOVA, P = 0.0001 to 0.033). The representative energy drink (pH 2.990; 0.0102 ppm fluoride) caused the greatest enamel softening followed by the representative kombucha (pH 2.820; 0.2036 ppm fluoride). The representative flavored sparkling water (pH 4.066; 0.0098 ppm fluoride) caused significantly less enamel softening than the energy drink and kombucha. A root beer (pH 4.185; 0.6045 ppm fluoride) had the least enamel softening effect. All tested beverages were acidic and had a pH below 4.5; only some contained fluoride. Flavored sparkling water, likely due to its higher pH, caused less enamel softening than the tested energy drink and kombucha. The fluoride content of kombucha and root beer lower their enamel-softening effects. It is imperative that consumers be aware of the erosive potential of beverages they consume.

Failure load of milled, 3D-printed, and conventional chairside-dispensed interim 3-unit fixed dental prostheses.

STATEMENT OF PROBLEM: New techniques and materials for the laboratory fabrication of interim fixed dental prostheses have gained in popularity, yet how their failure strengths compare with conventional chairside materials is unclear. PURPOSE: The purpose of this in vitro study was to compare the strength of computer-aided design and computer-aided manufacturing (CAD-CAM) milled polymethylmethacrylate (PMMA) or 3-dimensionally (3D) printed bis-acryl interim fixed dental prostheses with a traditional chairside-dispensed autopolymerizing bis-acryl prosthesis while taking into account the effect of loading rate and storage time. MATERIAL AND METHODS: A dentiform mandibular second premolar and second molar with a first molar pontic were prepared and scanned. Three groups of 3-unit interim fixed dental prostheses were fabricated: milled PMMA, 3D-printed bis-acryl, and chairside-dispensed autopolymerizing bis-acryl. The interim prostheses were evaluated for fit with a silicone disclosing material and cemented onto 3D-printed resin dies. The specimens were stored in 100% humidity at 37 °C. After 1 or 30 days of storage, the cemented interim prostheses were loaded to failure in a universal testing machine at 1 or 10 mm/min (n=15/group). Failure loads were analyzed by 3-way analysis of variance and multiple comparisons (α=.05). RESULTS: Mean ±standard deviation failure loads ranged from 363 ±93 N (3D-printed bis-acryl, 30 days, 1 mm/min) to 729 ±113 N (milled PMMA, 24 hours, 1 mm/min). Loading rate did not significantly affect failure load of the interim prostheses (P=.306). After 30 days of storage in 100% humidity, the failure load of milled PMMA and 3D-printed bis-acryl interim prostheses decreased significantly, but the chairside autopolymerizing bis-acryl prostheses were not affected. After 30 days of storage, the failure loads of milled PMMA and chairside autopolymerizing bis-acryl were not significantly different. CONCLUSIONS: Regardless of loading rate, interim fixed dental prostheses from milled PMMA had the highest initial strength 1 day after storage. Thirty days of exposure to humidity, however, reduced the strength of the CAD-CAM-manufactured interim prostheses, whereas the traditional chairside prostheses retained their strength.

Strength and stiffness of interim materials and interim fixed dental prostheses when tested at different loading rates.

STATEMENT OF PROBLEM: How the loading rate might affect the mechanical properties of interim materials and interim fixed dental prostheses is unclear. PURPOSE: The purpose of this in vitro study was to compare the material stiffness, material strength, and structural strength of interim 3-unit fixed dental prostheses fabricated from 3 interim materials when stressed at different loading rates. MATERIAL AND METHODS: Bar-shaped specimens and anatomically correct interim 3-unit fixed dental prostheses with a modified-ridge lap pontic were fabricated from polyethyl methacrylate resin (Trim) and 2 bis-acrylic composite resins (TempSmart; Integrity) (n=10). Flexural modulus and strength of the bar specimens, representing material stiffness and strength, were determined with a 4-point bend test in a universal testing machine. The structural strength of the prosthesis was assessed from the failure load from a vertical force applied on the occlusal surface of the pontic. Three loading rates, 0.5, 5, or 10 mm/min, were evaluated. Results were statistically analyzed with 2-way analysis of variance and multiple comparisons (α=.05). RESULTS: Loading rate and material significantly affected flexural modulus, flexural strength, and structural strength (P<.05). Increasing loading rate significantly increased the flexural modulus of all materials (P<.05), but the effect of loading rate on the flexural strength of bis-acrylic composite resins was mostly insignificant. Polyethyl methacrylate specimens did not fracture when loaded at 0.5 or 5 mm/min, and the interim fixed dental prostheses made from polyethyl methacrylate did not fracture at the 0.5 mm/min loading rate. Dual-polymerizing bis-acrylic composite resin had significantly higher flexural modulus and strengths than autopolymerizing bis-acrylic composite resin. CONCLUSIONS: Polyethyl methacrylate resin had the lowest stiffness among the interim materials tested and did not fracture but excessively deformed at the low loading rate. Dual-polymerizing bis-acrylic composite resin consistently had higher stiffness and material strength and provided higher structural strength than the autopolymerizing bis-acrylic composite resin. Loading rate significantly affected the mechanical properties of polyethyl methacrylate resin (P<.05), but the effect was indistinct for the bis-acrylic materials.

Do composite resin polishing systems damage enamel?

Finishing and polishing of composite resin restorations may cause damage to the bordering enamel. Although many studies have investigated the effect of polish on restorative materials, few have quantified the effect on bordering enamel. The objective of this study was to compare enamel loss surrounding composite restorations after finishing and polishing sequences. The null hypothesis was that there would be no difference in enamel loss between different finishing and polishing sequences. Class V preparations on the buccal and lingual surfaces of 15 extracted human molars were restored with a composite resin and assigned to 1 of 2 finishing and polishing sequences, so that each tooth underwent both sequences (n = 15 per sequence). In sequence 1, a tungsten carbide finishing bur and aluminum oxide polishing discs were used; in sequence 2, a diamond finishing bur, aluminum oxide-impregnated finishing cup, and diamond-impregnated polishing cup were used. Tooth surfaces were scanned with an optical scanner after preparation, finishing, initial polishing, and final polishing. The finishing and polishing scans were aligned to the preparation scan using Cumulus software. The depth of enamel surface loss was calculated and statistically analyzed (α = 0.05; paired t test). Most enamel loss (mean [SD]) resulted from the finishing step with the tungsten carbide bur (51.8 [21.3] µm) or diamond bur (43.3 [12.6] µm). Each polishing step increased mean enamel loss by only a few microns. There was no statistically significant difference between the 2 finishing and polishing sequences. The majority of enamel damage during finishing and polishing of composite resin restorations resulted from the finishing burs. Little enamel was removed by either of the tested composite resin polishing systems.

Influence of ceramic veneer thickness and antagonist on impact stresses during dental trauma with and without a mouthguard assessed with finite element analysis.

BACKGROUND/AIM: Little is known about the effect of dental trauma and mouthguards (MG) on teeth with ceramic laminate veneers (CLV). The aim was to evaluate the influence of CLV thickness and the presence of a MG with and without antagonist tooth contact on impact stresses during dental trauma. MATERIALS AND METHODS: Twelve 2D-finite element models of a head with maxillary structures and upper incisors, six with and six without antagonist tooth, were created in three CLV conditions: sound incisor (no CLV), 0.3 mm CLV, and 1.0 mm CLV. These were evaluated with and without a 4.0-mm ethylene-vinyl acetate MG, with and without an antagonist tooth. An impact analysis was performed in which the head frontally hits a rigid surface at a speed of 1 m/s (3.6 km/h). The results were analyzed using Critical modified von Mises (MPa). The mean of the 10% highest modified von Mises stresses in each structure was collected. RESULTS: MG presence substantially reduced impact stresses in the CLV and tooth structures. The contact of the antagonist tooth promoted better stress distribution and reduced the stress levels in the traumatized tooth. Critical stress areas were found in the palatal enamel, incisal enamel, labial cervical area, and enamel under the CLV for all models without MG. In the models with MG, the stresses reduced significantly. Critical modified von Mises stress showed that sound or prepared enamel experienced more critical impact stresses than 0.3 or 1.0-mm thick CLV. CONCLUSIONS: The use of 4.0 mm EVA mouthguard reduced the impact stress levels in models with 0.3-mm CLV and 1.0-mm CLV, similar to a sound tooth. The contact of an antagonist tooth and the MG better distributed the stresses and reduced the impact stress in the traumatized tooth.

Evaluation of fluoride levels in commercially available tea in the United States.

The objective of this study was to compare fluoride levels in commercially available black tea, green tea, and matcha tea. Tea samples were purchased from a local supermarket in the United States and prepared according to the manufacturer's directions to mimic consumer activity. The selected products included 3 black teas (Bigelow Earl Grey, Twinings of London Lady Grey, and Lipton), 2 green teas (Bigelow and Lipton), and 3 matcha teas (Mighty Leaf, Celestial Seasonings, and Matcha Love). For all products except Mighty Leaf and Matcha Love, 250 mL of deionized water (DIW) was heated to boiling. One tea bag was added and stirred for 2 minutes. For Mighty Leaf matcha, 300 mL of DIW was used, but the sample was otherwise prepared as previously described. Matcha Love was prepared by stirring 0.5 tsp of green tea powder for 2 minutes in 30 mL of DIW heated to boiling. A 10-mL aliquot was taken from each tea group and from DIW alone (control) and combined with 10 mL of total ionic strength adjustment buffer (TISAB II) before it was measured with a combination fluoride electrode and pH/ion meter. The sample size was 5 separately prepared and independently measured tea servings per group. Fluoride concentrations were calculated from a calibration curve constructed from appropriate fluoride standards and then statistically analyzed using analysis of variance followed by the Student-Newman-Keuls post hoc test (α = 0.05). The DIW control group had negligible fluoride content. All tested tea samples contained fluoride in amounts ranging from 0.521 to 6.082 mg/L. The mean concentration differed significantly among brands and types of tea. Matcha green tea powder had the highest concentration of fluoride. Most teas contain a higher fluoride concentration than optimally fluoridated water (0.7 mg/L). Dental healthcare professionals should consider this information when advising caries prevention regimens for patients and determining the potential for dental or skeletal fluorosis in at-risk patients.

Microscopic evaluation of luting techniques for a fiber-reinforced post system.

This study assessed application techniques for cementation of fiber-reinforced posts (FRPs). The treatment groups were defined by FRP luting application techniques and included 5 groups of 10 simulated teeth each: 1, application of the cement on the post using a syringe; 2, application of the cement in the canal using a syringe; 3, application of the cement in the canal and on the post using a syringe; 4, application of the cement in the canal using a syringe/Lentulo spiral instrument; and 5, application of the cement in the canal using a syringe/Lentulo spiral and on the post using a syringe. A dual-curing, automixing cement was utilized as the luting agent. For each group, the canals were endodontically prepared using tapered hand and rotary files and obturated, and then the FRPs were cemented in place. All specimens were encased in acrylic and sectioned at 2 locations, creating 4 viewing surfaces: coronal (C), middle coronal (MC), middle apical (MA), and apical (A). The surfaces were examined using a stereomicroscope and digitized computer software. The efficacy of each FRP application technique was determined in terms of percentages of cement void area by group and by surface. Group 1 exhibited a significantly (P < 0.05) greater overall percentage of cement void area than all other groups. Group 2 exhibited the smallest overall percentage of void area, although the difference was not always statistically significant. There were no statistically significant differences among the surfaces in cement void area (P > 0.05) when the areas of the different groups were combined. The most efficacious cementation method was the injection of cement into the canal space with a syringe, while the use of a Lentulo spiral instrument was found to be an unnecessary step.

Do denture processing techniques affect the mechanical properties of denture teeth?

STATEMENT OF PROBLEM: Denture tooth fracture may limit the longevity of dental prostheses. Whether the strength of the denture tooth material is affected by the denture processing technique is unclear. PURPOSE: The purpose of this in vitro study was to investigate whether the denture processing technique affects the mechanical properties of denture tooth materials. MATERIAL AND METHODS: Two denture processing techniques, injection and compression molding, were tested for 3 types of denture teeth: nanohybrid composite (NHC), interpenetrating network (IPN), and microfiller-reinforced polyacrylic (MRP). Denture teeth were processed by using an injection-molded resin or a compression-molded resin. Unprocessed denture teeth served as the control. After teeth were processed, they were sectioned into rectangular beams for 3-point bend testing (n=20 to 24). Elastic moduli were determined from load deflection and maximum stress from maximum bending load. The results were statistically analyzed by using 2-way ANOVA and multiple comparisons (α=.05). RESULTS: The processing technique and the type of denture tooth affected both the elastic modulus and the maximum stress. The injection-molded technique resulted in significantly higher (24% to 26%) elastic modulus for NHC and IPN (12% higher in MRP, but not statistically significant) and higher (12% to 17%) maximum stresses for IPN and MRP (3% lower in NHC, but not statistically significant). Compression-molded technique increased the elastic modulus of IPN and NHC by 10% to 17% (3% lower in MRP but not statistically significant), but maximum stresses were not statistically significantly different in any of the tested teeth. Regardless of processing, MRP teeth had the highest elastic modulus (8.0 to 9.2 GPa) but the lowest maximum stresses (97 to 124 MPa), whereas IPN teeth had the lowest elastic modulus (5.5 GPa) but high or highest maximum stress (171 to 192 MPa). CONCLUSIONS: The injection-molded technique significantly increased the elastic modulus of NHC and IPN teeth and significantly increased the maximum stress of IPN teeth. The compression-molded technique did not significantly affect mechanical properties of denture teeth.

Does Tack Curing Luting Cements Affect the Final Cure?

PURPOSE: Short initial light curing or "tack curing" is used to create a semi-gel state in luting cements for easier excess material cleanup. The effect of tack curing on the final cure of luting cements was measured in terms of hardness. MATERIALS AND METHODS: Three cement types were tested: two dual-curing composite cements (RelyX Unicem 2; Maxcem Elite); three light-curing veneer cements (Choice 2; Variolink Esthetic LC; RelyX Veneer); and two self-curing resin-modified glass-ionomer (RMGI) luting cements (RelyX Luting Plus; Nexus RMGI). Cements were placed in 1.5 × 2 × 8 mm plaster slots covered with orange glass during curing and were cured from one end. Tack curing was performed for 2 to 5 s using an LED curing light, followed 2 min later by 10-40 s final light curing or self-curing, as per manufacturer instructions (n = 10). Control groups received only final light curing or self-curing. After 24 h storage (37°C, 100% humidity), Vickers hardness was measured in 0.5-mm depth increments. Results were analyzed using two-way ANOVA and pairwise comparisons (α = 0.05). RESULTS: The hardness of dual-curing and light-curing cements significantly decreased with increasing depth (p = 0.0001). Tack curing of dual-curing and light-curing cements tended to increase hardness at all depths, except near the surface for light-curing veneer cements. Self-curing cements showed no hardness reduction with depth and no effect from tack curing. CONCLUSION: Although a slight surface hardness reduction may occur in light-curing veneer cements, the overall effect on three luting cement types was insignificant or resulted in only a slight increase in depth-of-cure.

The effect of antagonist tooth contact on the biomechanical response of custom-fitted mouthguards.

BACKGROUND/AIM: Custom-fitted mouthguards are devices used to prevent dental injuries. The aim of this study was to verify the influence of the antagonist contact on the stresses and strains of the anterior teeth, shock absorption and displacement of EVA custom-fitted mouthguards during a horizontal impact. MATERIALS AND METHODS: Finite element models of human maxillary central incisors with and without a mouthguard for different occlusion conditions (with and without antagonist contact) were created based on tomography. A nonlinear dynamic impact analysis using the single-step Houbolt method was performed in which a rigid object hit the model at 1 m s-1 . Strain and stress were evaluated by means of Von Mises and Critical modified Von Mises criterion and shock absorption during impact were calculated as well as the mouthguard displacement. RESULTS: The model without mouthguard and without antagonist contact showed the highest stress and strain values at the enamel and dentin in the tooth crown on impact compared to the model without mouthguard and with antagonist contact. Mouthguard presence reduced the stress and strain values regardless of the occlusion condition. The mouthguard displacement decreased with the mandibular antagonist contact. CONCLUSIONS: Mouthguards are efficient at decreasing the stress and strain values on the tooth in front of an impact reaching more than 90% of shock absorption. A mouthguard with balanced occlusion and maximum number of contacts with mandibular anterior teeth should be considered because it reduces mouthguard displacement.

The importance of the cement spacer for proper crown seating Erratum.

Marginal integrity is important for the longevity of a restoration. An increase in the marginal discrepancy after cementation contributes adversely to the longevity of a restoration. In the past, the preferred method to overcome this discrepancy was to create internal space for the cement by using a number of coats of a die-spacing material. In the digital age, however, this method is no longer the only option. Currently, an amount of die spacer is engineered into the computer program and forms part of the milling process. The present study attempted to identify the optimal setting of the Spacer parameter that a) is necessary for the complete cementation of a Cerec milled all-ceramic crown, and b) does not compromise the strength of the crown postcementation.

Protocol for measurement of enamel loss from brushing with an anti-erosive toothpaste after an acidic episode.

Tooth erosion from an acidic insult may be exacerbated by toothbrushing. The purposes of this study were to develop an in vitro methodology to measure enamel loss after brushing immediately following an acidic episode and to investigate the effect of brushing with an anti-erosive toothpaste. The null hypotheses tested were that tooth erosion after brushing with the toothpaste would not be different from brushing with water and that a 1-hour delay before brushing would not reduce tooth erosion. Forty bovine enamel slabs were embedded, polished, and subjected to baseline profilometry. Specimens were bathed in hydrochloric acid for 10 minutes to simulate stomach acid exposure before post-acid profilometry. Toothbrushing was then simulated with a cross-brushing machine and followed by postbrushing profilometry. Group 1 was brushed with water; group 2 was brushed with a 50:50 toothpaste-water slurry; and groups 3 and 4 were immersed in artificial saliva for 1 hour before brushing with water or the toothpaste slurry, respectively. The depth of enamel loss was analyzed and compared using 1-way analysis of variance and post hoc testing (α = 0.05). Greater enamel loss was measured in groups brushed with toothpaste than in groups brushed with water. One-hour immersion in artificial saliva significantly reduced enamel loss when teeth were brushed with water (group 3; P < 0.05) but not with toothpaste (group 4). This study established a protocol for measuring enamel loss resulting from erosion followed by toothbrush abrasion. The results confirmed the abrasive action of toothpaste on acid-softened enamel.

Heat generated during light-curing of restorative composites: Effect of curing light, exotherm, and experiment substrate.

PURPOSE: To investigate temperature rise, separating heat caused by irradiation and exotherm for three composites polymerized with three curing lights. The effect of substrate on temperature measurements was also determined. METHODS: Composite samples (n= 5) (Filtek Supreme Ultra, Filtek LS, and EsthetX HD) were placed on a thermocouple tip inside three substrates (aluminum, Delrin, and tooth). The composites were photoactivated using three curing lights (Elipar 2500 QTH, SmartLite Max LED, DemiUltra LED) at 1 mm distance. Irradiance was 798, 980, and 1,135 mW/cm2, respectively. Exotherm was determined by subtracting post-cure from the polymerization temperature curves. ANOVA and Student-Newman-Keuls post-hoc tests were used to analyze differences among peak temperatures and exotherms (significance level 0.05). RESULTS: SmartLite LED curing light resulted in higher peak temperatures and exotherms compared to the DemiUltra LED and QTH for all tested composites (16.9-20.4°C vs 12.3-14.7°C vs 8.9-9.7°C). Thus, the LEDs produced higher temperature rises than the QTH, and the LED with lower irradiance caused higher temperature rise than the LED with higher irradiance. The silorane-based Filtek LS generated significantly higher exotherm than the methacrylate-based EsthetX HD and Filtek Supreme Ultra (6.2-7.6°C vs 3.6-4.5°C vs 2.7-3.6°C). Substrate affected temperatures significantly. Temperature profiles found in Delrin substrate were comparable to tooth substrate, while aluminum substrate reduced temperatures 10-20 degrees. CLINICAL SIGNIFICANCE: Curing of restorative composites raises the temperature under a restoration due to irradiation and exothermic reaction; how much the temperature increases depends on curing light design, type of composite, and surrounding substrate. The silorane-based Filtek LS generated significantly higher exotherm than the methacrylate-based EsthetX HD and Filtek Supreme Ultra.

Failure strengths of denture teeth fabricated on injection molded or compression molded denture base resins.

STATEMENT OF PROBLEM: Denture tooth fracture or debonding remains a common problem in removable prosthodontics. PURPOSE: The purpose of this in vitro study was to explore factors determining failure strengths for combinations of different denture tooth designs (shape, materials) and injection or compression molded denture base resins. MATERIAL AND METHODS: Three central incisor denture tooth designs were tested: nanohybrid composite (NHC; Ivoclar Phonares II), interpenetrating network (IPN; Dentsply Portrait), and microfiller reinforced polyacrylic (MRP; VITA Physiodens). Denture teeth of each type were processed on an injection molded resin (IvoBase HI; Ivoclar Vivadent AG) or a compression molded resin (Lucitone 199; Dentsply Intl) (n=11 or 12). The denture teeth were loaded at 45 degrees on the incisal edge. The failure load was recorded and analyzed with 2-way ANOVA (α=.05), and the fracture mode was categorized from observed fracture surfaces as cohesive, adhesive, or mixed failure. RESULTS: The following failure loads (mean ±SD) were recorded: NHC/injection molded 280 ±52 N; IPN/injection molded 331 ±41 N; MRP/injection molded 247 ±23 N; NHC/compression molded 204 ±31 N; IPN/compression molded 184 ±17 N; MRP/compression molded 201 ±16 N. Injection molded resin yielded significantly higher failure strength for all denture teeth (P<.001), among which IPN had the highest strength. Failure was predominantly cohesive in the teeth, with the exception of mixed mode for the IPN/compression group. CONCLUSIONS: When good bonding was achieved, the strength of the structure (denture tooth/base resin combination) was determined by the strength of the denture teeth, which may be affected by the processing technique.

Custom-Fitted EVA Mouthguards: what is the ideal thickness? a dynamic finite element impact study.

BACKGROUND/AIM: The aim of this study was to evaluate the tooth stresses and strains, shock absorption, and displacement during impact of custom-fitted mouthguards with different thicknesses. METHODS: Six bar-shaped specimens of the EVA were made and subjected to tensile test for elastic modulus assessment. Two-dimensional plane-strain models of a human maxillary central incisor, periodontal ligament, bone support, soft tissue, and mouthguard (MTG) were created. The mouthguards were modeled in five different thicknesses (2, 3, 4, 5, and 6 mm). One model was created without mouthguard. A nonlinear dynamic impact analysis was performed in which a rigid object hit the model at 1 m s(-1). Strain and stress (von Mises and Critical modified von Mises) distributions were evaluated, and the displacement of the mouthguard with respect to the tooth was calculated. RESULTS: The mean [SD] for the EVA elastic modulus was 18.075 [0.457] MPa. The model without mouthguard showed the highest stress values at the enamel and dentin structures in the tooth crown during the impact. For the MTG models, the location of the stress concentrations changed to the root, regardless of the MTG thickness, but maximum stresses in the enamel and dentin were lower compared with the model without MTG. Increasing the mouthguard thickness did not notably decrease the stress-strain values. CONCLUSION: It was concluded that the use of a mouthguard promoted lower stresses and strains in teeth during an impact with a rigid object. There was no substantial difference in peak stresses and strains and in shock absorption among the different mouthguard thicknesses.

Evaluation of a dentoalveolar model for testing mouthguards: stress and strain analyses.

BACKGROUND/AIM: Custom-fitted mouthguards are devices used to decrease the likelihood of dental trauma. The aim of this study was to develop an experimental bovine dentoalveolar model with periodontal ligament to evaluate mouthguard shock absorption, and impact strain and stress behavior. METHODS: A pendulum impact device was developed to perform the impact tests with two different impact materials (steel ball and baseball). Five bovine jaws were selected with standard age and dimensions. Six-mm mouthguards were made for the impact tests. The jaws were fixed in a pendulum device and impacts were performed from 90, 60, and 45° angles, with and without mouthguard. Strain gauges were attached at the palatal surface of the impacted tooth. The strain and shock absorption of the mouthguards was calculated and data were analyzed with 3-way anova and Tukey's test (α = 0.05). Two-dimensional finite element models were created based on the cross-section of the bovine dentoalveolar model used in the experiment. A nonlinear dynamic impact analysis was performed to evaluate the strain and stress distributions. RESULTS: Without mouthguards, the increase in impact angulation significantly increased strains and stresses. Mouthguards reduced strain and stress values. CONCLUSIONS: Impact velocity, impact object (steel ball or baseball), and mouthguard presence affected the impact stresses and strains in a bovine dentoalveolar model. Experimental strain measurements and finite element models predicted similar behavior; therefore, both methodologies are suitable for evaluating the biomechanical performance of mouthguards.

We May Have Done Something Right: Composite Restorations at the College of Dentistry, University of Tennessee Health Science Center.

The success of composite restorations requires meticulous clinical technique in addition to reliable restorative materials and armamentarium. Early failure of restorations is undesirable and are usually replaced at no cost to patients. A metaanalysis study reported a mean annual failure rate of 1.46% for posterior composite restorations. At the University of Tennessee Health Science Center College of Dentistry (UTHSC CoD) predoctoral clinic the percentage of posterior composite restorations replaced within 12 months, retrieved from 2007-2014 electronic chart 'redo' records, was on average 0.58%. Several factors may have contributed to the quality of composite restorations placed by novice clinicians with modest experience. Student doctors are educated about composite placement in preclinical courses and then work under close supervision during their clinical training. This article describes restorative techniques for composites and the rationales taught at the UTHSC CoD Department of Restorative Dentistry. The objective is to share the information, which can be adopted or modified by general practitioners in daily practice.

Introduction to Clinical Practice in Dentistry: Transitioning from Pre-clinical to Clinical Student Doctors at The University of Tennessee Health Science Center College of Dentistry.

Matriculation from the pre-clinical setting to the clinical environment is a tremendous accomplishment and exemplifies the student's perseverance in learning the fundamental concepts necessary for success in the clinical application of dentistry. In an effort to maximize its educational philosophy for the teaching program, the University of Tennessee's College of Dentistry has implemented Introduction to Clinical Practice I and II within the dental curriculum. Introduction to Clinical Practice I and II are designed to help the dental students effectively and smoothly transition to the clinical setting from the classroom and pre-clinical setting. This article describes the university's efforts and continuous improvements within the pre-clinical dental curriculum for advancing students to the clinics. The purpose of this article is to provide helpful information to other dental educational institutions on how to assist their pre-clinical dental students in transitioning to clinical student-doctors.

Modifying the biomechanical response of mouthguards with hard inserts: A finite element study.

PURPOSE: To investigate the influence of a high elastic modulus material insert on the stress, shock absorption and displacement of mouthguards. METHODS: Finite element models of a human maxillary central incisor with and without mouthguard were created based on cross-sectional CT-tomography. The mouthguard models had four designs: without insert, and middle, external, or palatal hard insert. The hard inserts had a relatively high elastic modulus when compared to the elastic modulus of ethylene vinyl acetate (EVA): 15 GPa versus 18 MPa. A non-linear dynamic impact analysis was performed in which a heavy rigid object hit the model at 1 m/s. Strain and stress (von Mises and critical modified von Mises) distributions and shock absorption during impact were calculated as well as the mouthguard displacement. RESULTS: The model without mouthguard had the highest stress values at the enamel and dentin structures in the tooth crown during the impact. It was concluded that the use of a mouthguard promoted lower stress and strain values in the teeth during impact. Hard insertion in the middle and palatal side of the mouthguard improved biomechanical response by lowering stress and strain on the teeth and lowering mouthguard displacement.