Oral Health and Behavior Patterns of Women with Eating Disorders-A Clinical Pilot Study.

BACKGROUND: Chronic stomach regurgitation associated with eating disorders (EDs) poses a high risk for tooth erosion. This study investigated oral health conditions, behavioral patterns, and tooth erosion in women with EDs. METHODS: 16 ED and 13 healthy women were enrolled; 14 ED and 10 healthy control subjects completed the study. Subjects completed demographic, medical, oral, and behavioral health history questionnaires. Dental caries status was recorded as Decayed, Missing and Filled Teeth (DMFT)index and the severity of tooth erosion as Basic Erosive Wear Examination (BEWE) scores. Saliva was collected for flow rate, pH, and buffering capacity analysis. RESULTS: The ED group had a lower stimulated saliva flow rate and higher DMFT index but no significant difference in BEWE scores compared to the controls (t-test, significance level 0.05). Five of the fourteen ED subjects exhibited extensive tooth erosion, which may have been exacerbated by their tooth-brushing behavior. CONCLUSIONS: Although some ED subjects showed extensive tooth erosion in this pilot study, the average BEWE score of the ED group was not significantly different from the controls. Extensive tooth erosion in ED may relate to the low stimulated salivary flow. A larger-scale clinical study is necessary to validate these results.

A Structural Analysis of 3D Printed Pediatric Space Maintainers.

Purpose: To design, fabricate, and evaluate in vitro 3D printed space maintainers (SMs) and compare their retentive capabilities to tradi- tional stainless-steel (SS) space maintainers. Methods: E-Guard was selected as the printing material based on flexural strength and elastic modulus. SMs with a claw design were printed, cemented to testing blocks, and vertically loaded to determine failure strength and flexure (n equals 10). The intaglio surfaces of SM bands, printed with plain, crosshatched, or horizontal ridges, were cemented to extracted primary teeth. The force needed to dislodge the bands was compared to cemented traditional SS bands (n equals 14). Results: Flexural strength (mean±standard deviation [SD]) of E-Guide, E-Dent, and E-Guard materials was 65±12, 90±13, 134±25 MPa, respectively. Elastic modulus (mean±SD) was 1.54±0.40, 2.49±0.14, 2.65±0.89 GPa, respectively. When subjected to vertical loading, the mean failure load of 3D printed SMs (E-Guard) was 124 N and the mean deflection at fracture was 1.73 mm. Retention strengths (mean±SD) of 3D printed bands were 32±13, 43±13, 43±16 N for the plain printed, cross- hatched, and horizontal ridges designs, respectively. The retention strength of traditional SS bands was 126±27 N. Conclusions: E-Guard had superior mechanical properties among tested printing resins. Strength and deflection under the vertical load of claw-design 3D printed space maintainers may be adequate as a viable alternative to traditional SMs. Retention of 3D printed SMs was significantly lower than for traditional SS bands. Textured intaglio surfaces did not significantly improve the retention of 3D printed bands.

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.

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.

File Breakage in Conventional Versus Contracted Endodontic Cavities.

OBJECTIVE: To compare rotations to failure and tip separation length of a nickel-titanium (Ni-Ti) rotary in- strument within a simulated mesio-buccal canal of a mandibular molar with a conventional or contracted endodontic cavity. METHODS: Two identical lithium disilicate #30 crowns were milled. A conventional or contracted endodontic cavity was prepared. A custom glass tube was fabricated with taper and length replicating a mesio-buccal canal, including buccal and lingual curvature, and placed at the mesio-buccal orifice of each crown, held in a silicone mold. Instrumentation was simulated using 30/.04 Ni-Ti rotary files following manufacturer recommended 1.8 Nm torque and 500 RPM (n=20 per access type). Instrumentation was video recorded to determine time (sec- onds) and rotations to failure. The length of broken tips was measured. The experimental data were compared using a t-test (significance level 0.05). Stresses in the instruments were examined using finite element analysis. RESULTS: Number of rotations to failure (mean±standard deviation) was 599±126 for conventional and 465±65 and for contracted access; tip separation lengths (mean±standard deviation) were 3.99±0.29 for conventional and 4.90±1.02 mm for contracted access. Number of rotations to failure and tip separation lengths were signifi- cantly different between the two access openings (p<0.001). Finite element analysis confirmed higher file curva- ture and accompanying higher stress levels with contracted access and the maximum stress further from the tip. CONCLUSION: Within the limitations of this study, the contracted access caused earlier failure of the Ni-Ti in- strument with longer tip separation lengths than the conventional access due to higher stresses towards the middle section of the instrument. (EEJ-2022-11-143).

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.

Dual-cure dental composites: can light curing interfere with conversion?

Dual-cure composites used for dental restorations offer photo- and self-activation, promising unlimited curing depth. This study examined depth of cure with respect to light- and self-cure capabilities. Four dual-cure composites (BulkEZ; Activa; HyperFIL; Injectafil) were tested, with bulk fill (Tetric) and universal (TPH) light-cure composites as comparison. Composites were irradiated from one direction in molds. Additionally, dual-cure composites were left to self-cure without irradiation. Vickers hardness was measured up to 6 mm deep. Results were analyzed with two-way ANOVA and pairwise comparisons (α = 0.05). Hardness dropped significantly with depth in light- and dual-cured composites, except BulkEZ. Self-cured dual-cure composites achieved constant hardness throughout their depth. Only BulkEZ was unaffected by curing mode. Irradiation significantly decreased hardness in middle sections of Hyperfil and Injectafil compared with self-cured samples. Dual-cure composites cured substantially through 6 mm depths but curing behaviors differed. Whereas irradiation did not affect one dual-cure composite, in two other dual-cure composites low-density light levels interfered with the self-polymerization aspect.

Tooth Structure Removed in Primary Molar Prefabricated Crown Preparations of Typodont Teeth.

PURPOSE: Esthetic prefabricated pediatric crowns require more tooth reduction than stainless steel crowns due to their passive fit. The purpose of this study was to determine tooth reduction in primary molar preparations for various pediatric prefabricated crowns. METHODS: Fifty primary maxillary and fifty mandibular typodont molars were scanned with an optical scanner. The teeth were mounted in a typodont, and 10 experienced pediatric clinicians prepared them for five types of pediatric prefabricated crowns: (1) stainless steel (SS); (2) zirconia EZCrowns™ (EZ); (3) NuSmile ® ZR (NS); (4) Zirconia Kinder Krowns ® (KD); and (5) an experimental composite crown (PS). The prepared teeth were rescanned, and the pre- and postpreparation scans were precisely aligned. Mean and maximum reduction depths were calculated for occlusal and mesio- buccal surfaces. Differences in reduction among crown types were compared using one-way analysis of variance followed by the Student-Newman- Keuls post hoc test (α equals 0.05). RESULTS: Reduction depths were not significantly different among the esthetic crowns but were significantly higher than SS crowns. Maximum reduction exceeded two mm in some of the KD and NS crown preparations, with KD consistently showing the highest reduction. CONCLUSIONS: Preparations for esthetic prefabricated molar crowns were more extensive than SS crowns, especially at occlusal and mesiobuccal surfaces. Clinicians should carefully follow manufacturer preparation guidelines to avoid encroaching the mesiobucccal pulp horn.

Using a professional DSLR camera to measure total shrinkage of resin composites.

This study evaluated the optical method for measuring free total shrinkage using a Digital Single Lens Reflex (DSLR) camera. Eight composites were evaluated, conventional, bulk fill and low-shrinkage: Z100 (3M Oral Care), Gradia Direct Anterior (GC corporation), Spectra Smart (Dentsply), Filtek Z350 XT (3M Oral Care), Aura Bulk Fill (SDI), Vittra APS (FGM), Opus Bulk Fill APS (FGM), and Beautifil II LS (Shofu Inc.). The samples (6 mm diameter and 1.5 mm thick, n = 10) were placed on a polyvinylsiloxane impression material. An image of the uncured sample was captured using a DSLR camera with 105 mm macro lens and a ring flash. Samples were light cured with a 700 mW/cm2 LED light-cure unit for 40s. Post-polymerization images were captured at 2, 10 and 60 min. Projected circumferential areas of the specimens were drawn using the ImageJ software. Volumetric total shrinkage was calculated from the ratio of the areas obtained from pre- and post-curing. Results were analyzed using One-way ANOVA (α = 0.05) and Tukey test. Volumetric total shrinkage values were significantly different among the composite materials (p < .001). The volumetric shrinkage (%) mean and results of Tukey test at 60 min were: Z100: 3.45±0.30 (A); Gradia Direct Anterior: 3.00 ± 0.23 (B); Spectra Smart 2.89 ± 0.35 (B); Filtek Z350 XT: 2.65 ± 0.37 (BC); Aura Bulk Fill: 2.42 ± 0.25 (CD); Vittra APS: 2.14 ± 0.35 (DE); Opus Bulk Fill APS: 1.91 ± 0.24 (E); Beautifil II LS: 1.18 ± 0.16 (F). The optical method using a DSLR camera, was suitable for total shrinkage evaluation and will allow assessment of total shrinkage without the need for specialized equipment.

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.

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.

Using a professional DSLR camera to measure total shrinkage of resin composites

Abstract This study evaluated the optical method for measuring free total shrinkage using a Digital Single Lens Reflex (DSLR) camera. Eight composites were evaluated, conventional, bulk fill and low-shrinkage: Z100 (3M Oral Care), Gradia Direct Anterior (GC corporation), Spectra Smart (Dentsply), Filtek Z350 XT (3M Oral Care), Aura Bulk Fill (SDI), Vittra APS (FGM), Opus Bulk Fill APS (FGM), and Beautifil II LS (Shofu Inc.). The samples (6 mm diameter and 1.5 mm thick, n = 10) were placed on a polyvinylsiloxane impression material. An image of the uncured sample was captured using a DSLR camera with 105 mm macro lens and a ring flash. Samples were light cured with a 700 mW/cm2 LED light-cure unit for 40s. Post-polymerization images were captured at 2, 10 and 60 min. Projected circumferential areas of the specimens were drawn using the ImageJ software. Volumetric total shrinkage was calculated from the ratio of the areas obtained from pre- and post-curing. Results were analyzed using One-way ANOVA (α = 0.05) and Tukey test. Volumetric total shrinkage values were significantly different among the composite materials (p < .001). The volumetric shrinkage (%) mean and results of Tukey test at 60 min were: Z100: 3.45±0.30 (A); Gradia Direct Anterior: 3.00 ± 0.23 (B); Spectra Smart 2.89 ± 0.35 (B); Filtek Z350 XT: 2.65 ± 0.37 (BC); Aura Bulk Fill: 2.42 ± 0.25 (CD); Vittra APS: 2.14 ± 0.35 (DE); Opus Bulk Fill APS: 1.91 ± 0.24 (E); Beautifil II LS: 1.18 ± 0.16 (F). The optical method using a DSLR camera, was suitable for total shrinkage evaluation and will allow assessment of total shrinkage without the need for specialized equipment.

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.

An In Vitro Comparison of Indirect Versus Direct Restorations of Incisal Edge Fractures.

Purpose: To compare fracture strength, failure mode, and chairside time of Class IV fractures restored with CEREC (Chairside Economic Restorations of Esthetic Ceramics) technology or direct composite. Methods: Forty-eight fractured anterior bovine teeth were randomly assigned to three experimental groups (indirect restoration) with margin designs including: A) butt joint, B) short chamfer (one mm), and C) long chamfer (two mm) and a control group (direct composite). Preparations were scanned; restorations were milled from zirconia-reinforced lithium-silicate blocks and cemented. Fracture load (N) and failure mode were analyzed. Techniques were timed from start of margin preparation through finishing. Results were analyzed using one-way analysis of variance or the Kruskal-Wallis test (significance level: P=0.05). Results: Fracture loads (mean±standard deviation) for groups A, B, and C and control group were 2,177±644 N, 2,183±507 N, 2,666±609 N, and 2,358±886 N, respectively (not significantly different; P=0.26). The direct composite was significantly different from all indirect groups (P<0.01) for failure mode. Chairside time was longer for direct restoration. Conclusions: Fracture strength is similar for directly and indirectly fabricated Class IV restorations, with margin design not affecting strength or failure mode. Practitioner's chairside time, but not total time, is reduced when using indirect methods.

Direct resin composite restoration of endodontically-treated permanent molars in adolescents: bite force and patient-specific finite element analysis.

Objective To evaluate the influence of three levels of dental structure loss on stress distribution and bite load in root canal-treated young molar teeth that were filled with bulk-fill resin composite, using finite element analysis (FEA) to predict clinical failure. Methodology Three first mandibular molars with extensive caries lesions were selected in teenager patients. The habitual occlusion bite force was measured using gnathodynamometer before and after endodontic/restoration procedures. The recorded bite forces were used as input for patient-specific FEA models, generated from cone-beam computed tomographic (CT) scans of the teeth before and after treatment. Loads were simulated using the contact loading of the antagonist molars selected based on the CT scans and clinical evaluation. Pre and post treatment bite forces (N) in the 3 patients were 30.1/136.6, 34.3/133.4, and 47.9/124.1. Results Bite force increased 260% (from 36.7±11.6 to 131.9±17.8 N) after endodontic and direct restoration. Before endodontic intervention, the stress concentration was located in coronal tooth structure; after rehabilitation, the stresses were located in root dentin, regardless of the level of tooth structure loss. The bite force used on molar teeth after pulp removal during endodontic treatment resulted in high stress concentrations in weakened tooth areas and at the furcation. Conclusion Extensive caries negatively affected the bite force. After pulp removal and endodontic treatment, stress and strain concentrations were higher in the weakened dental structure. Root canal treatment associated with direct resin composite restorative procedure could restore the stress-strain conditions in permanent young molar teeth.

Post-gel shrinkage, elastic modulus, and stress generated by orthodontic adhesives.

OBJECTIVES: To measure post-gel shrinkage, elastic modulus, and flexural strength of orthodontic adhesives and to predict shrinkage stress using finite element analysis (FEA). MATERIALS AND METHODS: The following 6 orthodontic adhesives were tested: Transbond XT (3M Unitek, Monrovia, Calif), Transbond Plus Color Change (3M Unitek), Greengloo (Ormco, Brea, Calif), Ortho Connect (GC America, Alsip, Ill), Trulock (RMO, Denver, Colo), GoTo (Reliance, Itasca, Ill). Post-gel shrinkage was measured using a biaxial strain gauge during light curing. Elastic modulus and flexural strength were measured with a 4-point bending test. Analysis of variance and Student-Newman-Keuls post hoc tests were used to compare the shrinkage, elastic modulus, and flexural strengths among the materials (α = .05). Shrinkage stresses caused by the post-gel shrinkage and elastic modulus values were calculated using a cross-sectional FEA of a metallic bracket bonded to an incisor. RESULTS: Properties were highly different among the adhesives (P ≤ .0001). Transbond XT (0.38 ± 0.09 percent volumetric contraction) and GoTo (0.42 ± 0.05 percent volumetric contraction) had the lowest post-gel shrinkage; Transbond Plus Color Change had the highest (0.84 ± 0.08 percent volumetric contraction). OrthoConnect (6.8 ± 0.6 gigapascals) had the lowest elastic modulus; GoTo (28.3 ± 3.1 gigapascals) had the highest. Trulock (64.1 ± 8.2 megapascals) had the lowest flexural strength; Greengloo (139.1 ± 20.7 megapascals) had the highest. FEA showed that the highest shrinkage stresses were generated with Transbond Plus Color Change and the lowest with OrthoConnect. CONCLUSIONS: Post-gel shrinkage of orthodontic adhesives was comparable with restorative composites, which are known to create shrinkage stresses in restored teeth. FEA indicated that this shrinkage creates stresses in the adhesive and in the enamel around the brackets.

Direct resin composite restoration of endodontically-treated permanent molars in adolescents: bite force and patient-specific finite element analysis

Abstract Objective To evaluate the influence of three levels of dental structure loss on stress distribution and bite load in root canal-treated young molar teeth that were filled with bulk-fill resin composite, using finite element analysis (FEA) to predict clinical failure. Methodology Three first mandibular molars with extensive caries lesions were selected in teenager patients. The habitual occlusion bite force was measured using gnathodynamometer before and after endodontic/restoration procedures. The recorded bite forces were used as input for patient-specific FEA models, generated from cone-beam computed tomographic (CT) scans of the teeth before and after treatment. Loads were simulated using the contact loading of the antagonist molars selected based on the CT scans and clinical evaluation. Pre and post treatment bite forces (N) in the 3 patients were 30.1/136.6, 34.3/133.4, and 47.9/124.1. Results Bite force increased 260% (from 36.7±11.6 to 131.9±17.8 N) after endodontic and direct restoration. Before endodontic intervention, the stress concentration was located in coronal tooth structure; after rehabilitation, the stresses were located in root dentin, regardless of the level of tooth structure loss. The bite force used on molar teeth after pulp removal during endodontic treatment resulted in high stress concentrations in weakened tooth areas and at the furcation. Conclusion Extensive caries negatively affected the bite force. After pulp removal and endodontic treatment, stress and strain concentrations were higher in the weakened dental structure. Root canal treatment associated with direct resin composite restorative procedure could restore the stress-strain conditions in permanent young molar teeth.

Composite removal by means of erbium, chromium:yttrium-scandium-gallium-garnet laser compared with rotary instruments.

BACKGROUND: Complete removal of existing composite restorations without unnecessary removal of tooth structure is challenging. The authors compared the amount of tooth structure removed and composite remaining in Class III preparations when using an erbium laser or a rotary instrument. METHODS: Mesiolingual and distolingual preparations were prepared in 14 extracted anterior teeth, restored with shade-matched composite, finished, and polished. One restoration was removed with an erbium, chromium:yttrium-scandium-gallium-garnet laser and the other with a rotary instrument (handpiece and carbide burs). Gypsum models made from vinyl polysiloxane impressions of the preparation and removal stages were scanned. The 2 scans were precisely aligned to calculate the amount of tooth structure removed and residual composite, which were statistically compared (t test) between the bur and laser groups. RESULTS: Rotary instruments removed significantly more tooth structure than the laser in terms of mean depth (P = .0017) but not maximum depth (P = .0762). Although mean depth of tooth loss was smaller in the laser group, the area of tooth loss was significantly larger (P = .0004) because the rotary instrumentation left significantly more composite than the laser in terms of volume (P = .0104), mean depth (P = .0375), maximum depth (P = .0318), and area (P = .0056). CONCLUSIONS AND PRACTICAL IMPLICATIONS: The erbium, chromium:yttrium-scandium-gallium-garnet laser was more selective in removing existing composite restorations than a rotary instrument because it removed less tooth structure and left behind less composite. Unintentional loss of tooth structure and unnoticeable residual composite are inevitable when removing existing composites. Erbium lasers are alternative means of composite removal that may be more selective than a rotary instrument.

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.