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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. more...

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. more...

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.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).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.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. more...

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. more...

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. more...

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.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.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).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.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. more...

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. more...

How the loading rate might affect the mechanical properties of interim materials and interim fixed dental prostheses is unclear.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.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).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.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. more...

SUMMARY Objective: Cracks in amalgam-filled teeth may be related to amalgam expansion. This study measured cuspal flexure and used finite element analysis to assess associated stress levels in amalgam-filled teeth. Methods and Materials: External surfaces of 18 extracted molars were scanned in three dimensions. Nine molars were restored with mesio-occluso-distal amalgam fillings; the other teeth were left intact as controls. All teeth were stored in saline and scanned after two, four, and eight weeks. Cuspal flexure and restoration expansion were determined by calculating the difference between scanned surfaces. Stresses in a flexed tooth were calculated using finite element analysis. Results: Cusps of amalgam-filled teeth flexed outward approximately 3 μm, and restoration surfaces expanded 4 to 8 μm during storage. Cuspal flexure was significantly higher in the amalgam group (multivariate tests, p0.05). Expansion caused stress concentrations at the cavity line angles. These stress concentrations increased stresses due to mastication 44% to 178%. Conclusions: Amalgam expansion pushed cavity walls outward, which created stress concentrations at the cavity line angles. Expansion stresses can raise stresses in amalgam-filled teeth and contribute to incidentally observed cracks. more...

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. more...

Purpose To determine the effect of substrate on the depth-of-cure determination when using hardness profiles in a covered-slot technique and to introduce a new covered-slot method that uses tooth substrates. Materials and methods Three bulk-fill composites and one conventional composite were tested: Tetric EvoCeram Bulk Fill, Venus Bulk Fill, Filtek Bulk Fill Flowable, Filtek Supreme Ultra. The composites were light-cured in rectangular slots (2 mm deep, 2 mm wide) made in a plaster mold or an extracted tooth. The slots were covered with an orange glass plate during curing, leaving one end exposed for light-curing. After curing, the glass plate was removed and the sample was stored in the dark for 24 hours before Vickers hardness was measured as a function of depth at 0.5-mm intervals. Results were analyzed using two-way analysis of variance (ANOVA) and pairwise comparisons (significance level 0.05). Results The hardness of composites cured in covered-slot molds decreased with increasing depth (p < 0.001). Bulk-filled composites cured in plaster molds had a slightly lower depth-of-cure than those cured in natural tooth substrates. Differences between the tooth and plaster substrates were significant at all depths in the “packable” bulk-fill composite (Tetric EvoCeram Bulk Fill), and were significant at ≥2.5 and ≥3.5 mm in the flowable bulk-fill composites (Filtek Bulk Fill Flowable and Venus Bulk Fill) respectively. Conclusion Using natural tooth substrates in the covered-slot method increased the depth-of-cure of bulk-filled composites in comparison to opaque plaster molds. How to cite this article Church BW, Tantbirojn D, Do T, Wells MH, Versluis A. Depth-of-cure of Bulk-fill Composites Cured in Tooth or Opaque Substrate. Int J Experiment Dent Sci 2017;6(2):68-73. more...

Objectives Adding a new layer of material to cured resin-based composite (RBC) or resin-modified glass ionomer (RMGI) restorations is necessary in dental practice. This study investigated strengths of additions to the two materials. Material and methods Beam-shaped specimens were made from monolithic RBC or RMGI, or additions of RBC and RMGI onto RBC or RMGI half-bar substrates. For the additions, the substrates were left undisturbed or were ground with silicon carbide paper followed by the application of a self-etch adhesive. Sample size was 10. Flexural strengths were determined by a 4-point bending test in a universal testing machine. Results were statistically analyzed with one-way ANOVA followed by Student–Newman–Keuls post-hoc test (α=0.05). Results Flexural strength of the monolithic RBC (86.7±21.8 MPa) was significantly higher than RMGI (52.6±13.1 MPa). Addition of RBC to cured RBC significantly reduced flexural strength regardless of the substrate surface conditions (34.1±11.5–45.7±21.1 MPa). Addition of RMGI to cured RMGI did not significantly reduce flexural strength (36.2±8.4–52.7±25.2 MPa). Flexural strength of RBC added onto cured RMGI that was ground and bonded was the lowest (21.5±10.0 MPa). Most specimens from this group exhibited adhesive failure. Conclusions RBC/RBC additions reduced flexural strength whereas flexural strength of RMGI/RMGI additions was not significantly lower than its cohesive strength. RBC added onto RMGI in the sandwich restorative configuration had lowest failure strength. more...

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. more...

Prefabricated zirconia crowns (ZRCs) require a passive fit and more reduction than stainless steel crowns (SSC). To determine the mean and maximum reduction depths in the mesial-buccal and occlusal areas for three ZRC brands and one SSC in posterior primary typodont molars and to compare reduction depths to existing literature to determine the preparation’s proximity to pulpal tissue. Four primary maxillary and mandibular typodont teeth (J and S) were prepared according to the manufacturers’ guidelines for three ZRCs and an SSC. The teeth were scanned before and after preparation with an optical scanner, and the mean and maximum depths of reduction for each tooth were calculated in triplicate with custom software and statistically compared among the types of crown. The results were compared to existing data on primary tooth enamel and dentin thickness. Maximum mesial-buccal and occlusal depth respectively of preparation for any ZRC for tooth J was 1.19 mm and 1.58 mm while for tooth S it was 1.06 and 2.07mm Both EZ Crowns and Kinder Krowns required an additional 0.5mm occlusal reduction beyond the manufacturer’s recommendation for tooth S. Ideal preparations of ZRCs require more reduction than SSCs. Both EZ Crowns and Kinder Krowns require more reduction than the manufacturer’s recommendation for a mandibular first primary molar. more...

SUMMARY Objectives: This study tested whether delayed photoactivation could reduce shrinkage stresses in dual-cure composites and how it affected the depth-of-cure and mechanical properties. Methods and Materials: Two dual-cure composites (ACTIVA and Bulk EZ) were subjected to two polymerization protocols: photoactivation at 45 seconds (immediate) or 165 seconds (2 minutes delayed) after extrusion. Typodont premolars with standardized preparations were restored with the composites, and cuspal flexure caused by polymerization shrinkage was determined with three-dimensional scanning of the external tooth surfaces before restoration (baseline) and at 10 minutes and one hour after photoactivation. Bond integrity (intact interface) was verified with dye penetration. Depth-of-cure was determined by measuring Vickers hardness through the depth at 1-mm increments. Elastic modulus and maximum stress were determined by four-point bending tests (n=10). Results were analyzed with two- or three-way analysis of variance and pairwise comparisons (Bonferroni; α=0.05). Results: Delayed photoactivation significantly reduced cuspal flexure for both composites at 10 minutes and one hour (p≤0.003). Interface was >99% intact in every group. Depth-of-cure, elastic modulus, and flexural strength were not significantly different between the immediate and delayed photoactivation (p>0.05). The hardness of ACTIVA reduced significantly with depth (p Conclusions: Delayed photoactivation of dual-cure restorative composites can reduce shrinkage stresses without negatively affecting the degree-of-cure or mechanical properties (elastic modulus and flexural strength). more...

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 (P0.05) 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 (P0.05) 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. more...

The purpose of this study was to investigate the relationship between hygroscopic expansion and polymerization shrinkage for compensation of polymerization shrinkage stresses in a restored tooth. One resin-modified glass-ionomer (RMGI) (Ketac Nano, 3M ESPE), 2 compomers (Dyract, Dentsply; Compoglass, Ivoclar), and a universal resin-based composite (Esthet•X HD, Dentsply) were tested. Volumetric change after polymerization (“total shrinkage”) and during 4 wk of water storage at 37°C was measured using an optical method ( n = 10). Post-gel shrinkage was measured during polymerization using a strain gauge method ( n = 10). Extracted human molars with large mesio-occluso-distal slot preparations were restored with the tested restorative materials. Tooth surfaces at baseline (preparation), after restoration, and during 4 wk of 37°C water storage were scanned with an optical scanner to determine cuspal flexure ( n = 8). Occlusal interface integrity was measured using dye penetration. Data were analyzed using analysis of variance and post hoc tests (significance level 0.05). All tested materials shrunk after polymerization. RMGI had the highest total shrinkage (4.65%) but lowest post-gel shrinkage (0.35%). Shrinkage values dropped significantly during storage in water but had not completely compensated polymerization shrinkage after 4 wk. All restored teeth initially exhibited inward (negative) cuspal flexure due to polymerization shrinkage. Cuspal flexure with the RMGI restoration was significantly less (–6.4 µm) than with the other materials (−12.1 to −14.1 µm). After 1 d, cuspal flexure reversed to +5.0 µm cuspal expansion with the RMGI and increased to +9.3 µm at 4 wk. After 4 wk, hygroscopic expansion compensated cuspal flexure in a compomer (Compoglass) and reduced flexure with Dyract and resin-based composite. Marginal integrity (93.7% intact restoration wall) was best for the Compoglass restorations and lowest (73.1%) for the RMGI restorations. Hygroscopic expansion was more effective in compensating shrinkage stress than would be assumed based on total shrinkage, because only post-gel shrinkage needed compensation. Effective expansion is therefore hygroscopic expansion minus post-gel shrinkage. more...

SUMMARY Objectives To evaluate the effect of the restorative protocol on cuspal strain, fracture resistance, residual stress, and mechanical properties of restorative materials in endodontically treated molars. Methods Forty-five molars received mesio-occlusal-distal (MOD) Class II preparations and endodontic treatment followed by direct restorations using three restorative protocols: composite resin (CR) only (Filtek Supreme, 3M-ESPE), resin modified glass ionomer cement in combination with CR (Vitremer, 3M-ESPE in pulp chamber and Filtek Supreme in MOD cavity), conventional glass ionomer cement in combination with composite resin (CGI-CR) (Ketac Fil, 3M-ESPE in pulp chamber and Filtek Supreme in MOD cavity). Cuspal strain was measured using strain gauges, and fracture resistance was tested with an occlusal load. Elastic modulus (EM) and Vickers hardness (VH) of the restorative materials were determined at different depths using dynamic microhardness indentation. Curing shrinkage was measured using the strain gauge technique. The restorative protocols were also simulated in finite element analysis (FEA). The shrinkage strain, cuspal strain, EM, VH, and fracture resistance data were statistically analyzed using split-plot analysis of variance and Tukey test (p=0.05). Residual shrinkage stresses were expressed in modified von Mises equivalent stresses. Results Shrinkage strain values (in volume %) were Ketac Fil (0.08±0.01) < Vitremer (0.18±0.01) < Filtek Supreme (0.54±0.03). Cuspal strain was higher and fracture resistance was lower when using CR only compared with the techniques that used glass ionomer. The EM and VH of the materials in the pulp chamber were significantly lower for glass ionomer. The FEA showed that using CR only resulted in higher residual stresses in enamel and root dentin close to the pulp chamber than the combinations with glass ionomers (RMGI-CR and CGI-CR). Conclusions The choice of restorative protocol significantly affected the biomechanical behavior of endodontically treated molars. Using glass ionomer to fill the pulp chamber is recommended when endodontically treated molars receive direct composite restorations because it reduces cuspal strain and increases fracture resistance. more...

Objectives A simple optical method for measuring polymerization shrinkage of dental composites is compared with an established dilatometer. Methods Five restorative composites were used to test the methods: Filtek Supreme Ultra (3M ESPE), Filtek LS (3M ESPE), Premise (Kerr), Gradia Direct (GC), and GC Kalore (GC). Uncured composites were attached to sandblasted silane-treated glass slides. The slides were placed sample side inside a mercury-filled dilatometer (ADAF). The mercury levels were recorded as the materials were light-cured through the glass-slides (40 s). Mercury levels, which correlated with volumetric shrinkage, were recorded for 60 min ( N = 6). For the optical method, uncured composite was placed on a smooth silicone platform. A pre-polymerization image was captured under a stereomicroscope, and the specimen was light-cured (40 s). Post-polymerization images were captured at 2, 10, 60, and 90 min ( N = 10). Composite outlines were traced to obtain projected surface areas (ImageJ) and volumetric shrinkage was calculated. Results were analyzed using two-way ANOVA ( α = 0.05) and Pearson Correlation tests. Shrinkage deformation for both methods was modeled using finite element analysis. Results Volumetric shrinkage at 60 min ranged between 1.24% and 2.24% for dilatometer and 1.35–2.68% for optical methods. Optical method shrinkage was consistently higher than the dilatometer ( P = .0001), but the ranking of the composites was the same (Pearson Correlation Coefficient 0.9997). Finite element analysis showed that lower shrinkage values of the dilatometer method could be attributed to bonding of its samples. Significance The optical method using a general-purpose stereomicroscope and public-domain software is a simple and accurate alternative to measure free shrinkage. more...

SUMMARY Objectives This study tested the hypothesis that photoactivation timing and resin cement affect mechanical properties and bond strength of fiberglass posts to root dentin at different depths. Methods Fiberglass posts (Exacto, Angelus) were luted with RelyX Unicem (3M ESPE), Panavia F 2.0 (Kuraray), or RelyX ARC (3M ESPE) using three photoactivation timings: light curing immediately, after three minutes, or after five minutes. Push-out bonding strength, PBS (n=10) was measured on each root region (coronal, middle, apical). The elastic modulus (E) and Vickers hardness (VHN) of the cement layer along the root canal were determined using dynamic indentation (n=5). A strain-gauge test was used to measure post-gel shrinkage of each cement (n=10). Residual shrinkage stress was assessed with finite element analysis. Data were analyzed with two-way analysis of variance in a split-plot arrangement and a Tukey test (α=0.05). Multiple linear regression analysis was used to determine the influence of study factors. Results The five-minute delay photoactivation timing significantly increased the PBS for all resin cements evaluated. The PBS decreased significantly from coronal to apical root canal regions. The mean values for E and VHN increased significantly with the delayed photoactivation for RelyX Unicem and decreased from coronal to apical root regions for all resin cements with the immediate-curing timing. Conclusions The PBS of fiber posts to root dentin, E, and VHN values were affected by the root canal region, photoactivation timing, and resin cement type. Shrinkage stress values decreased gradually with delayed photoactivation for all the cements. more...

Objective: To evaluate adhesive performance in terms of debonding forces of precoated metal and ceramic brackets 4 years after expiration. Materials and Methods: Buccal and lingual surfaces of embedded extracted maxillary premolars were etched with 34% Tooth Conditioner Gel (Dentsply Caulk, Milford, Del), rinsed, and dried. Transbond MIP (3M Unitek, Monrovia, Calif) was applied prior to placing adhesive precoated brackets (APC II Victory stainless steel and APC Plus Clarity ceramic brackets, 3M Unitek). The preexpiration brackets had 29–35 months before, and the postexpiration brackets were 45–52 months past, their expiration dates. Sample size was 17–21 per group. Debonding forces were determined by subjecting the bonded brackets to a shear force in a universal testing machine. Debonding forces were compared using two-way ANOVA. Debonded surfaces were examined under a stereomicroscope to determine failure modes, which were compared using the chi-square test. Results: No statistically significant difference was found in debonding forces (P = .8581) or failure modes (P = .4538) between expired and unexpired brackets. Metal brackets required statistically significantly higher debonding forces than did ceramic brackets (P = .0001). For both expired and unexpired brackets, failure modes were mostly cohesive in the adhesive layer for ceramic brackets, and mixed between adhesive and cohesive failure in the adhesive layer for metal brackets. Conclusions: Adhesive precoated brackets did not have any reduction in enamel-adhesion properties up to 4 years after their expiration date. Extended shelf life testing for precoated dental brackets may be worth considering. more...

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. more...

SUMMARY Purpose When adding composite to a cured composite restoration, the intent is to achieve the same failure strength as the original restorative material. This study evaluated the failure strengths of added or repaired composite using various chemical and/or mechanical surface treatments. Methods Failure strengths were determined using a four-point bending test. Beam-shaped specimens were fabricated by adding new composite to cured composite (Filtek Supreme Ultra). The cured composites were either fresh or aged seven days (N=10-14). The composite surfaces were left unground or were ground before treatment with various combinations of roughening, acid etching, silane, and dental adhesives (conventional Adper SingleBond Plus or new multimode Scotchbond Universal) and/or tribochemistry (CoJet system). Monolithic composite specimens were the control. Failure strengths were statistically analyzed using one-way analysis of variance and the Fisher protected least significant difference (α=0.05). Results Failure strengths (mean ± standard deviation) when composite was added to unground freshly cured composites (111±25 MPa) and aged composites using a new multimode adhesive with (102±22 MPa) or without (98±22 MPa) tribochemical treatment were not significantly lower than the monolithic specimens (122±23 MPa). Grinding the surfaces of freshly cured composite significantly reduced failure strength, either with (81±30 MPa) or without (86±31 MPa) use of conventional adhesive. Failure strengths of aged composites were also significantly lower (51±21 MPa with SingleBond Plus), even after tribochemical treatment (71±29 MPa with SingleBond Plus; 73±35 MPa with Silane-Visiobond). Conclusions Using a new multimode adhesive when adding composite to freshly cured or aged composite substrates recovered the failure strength to that of the original monolithic composite. more...

a b s t r a c t Purpose: This study compared the fracture strengths and failure modes of ultrathin (0.3-mm) occlusal composite or hybrid ceramic veneers. Methods: Sixty extracted maxillary molars were sectioned to remove the entire coronal structure 4 mm occlusal to the cementoenamel junction (CEJ), leaving a flat area of exposed dentin and peripheral enamel. Standardized occlusal veneers with a central fossa thickness of 0.3 mm were milled from a computer-aided design (CAD)/computer-aided manufacturing (CAM) composite (Paradigm MZ100), a resin nanoceramic (Lava Ultimate), and a hybrid ceramic (Vita Enamic) (N = 20). Each occlusal veneer was cemented with a self-adhesive resin cement (RelyX Unicem) on the prepared teeth. The restored teeth were loaded vertically to determine the fracture strength. Strength values were statistically analyzed using one-way analysis of variance (ANOVA) and Scheffe's post hoc test (significance level 0.05). The mode of failure of each specimen was classified and the correlation between fracture strength and failure mode was analyzed using Spearman's rank-order test. Results: The fracture strengths (mean ± standard deviation) were 2416 ± 640, 1752 ± 676, and 1777 ± 697 N for Lava Ultimate, Paradigm MZ100, and Vita Enamic, respectively. Lava Ultimate had signif- icantly higher fracture strength than the other two materials (p < 0.05); the fracture strengths of Paradigm MZ100 and Vita Enamic were not significantly different. No correlation between fracture strengths and failure modes was found within each material. Most specimens (48 out of 60) fractured in the restoration without involving tooth structures. Conclusions: The fracture strength of ultrathin occlusal veneers made from the novel ceramic hybrid matched the strength of CAD/CAM composite. The highest strength was found with the resin nanoceramic material. more...

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.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).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.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. more...

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. more...

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. more...

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; P0.05) 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. more...

The relationship between post-gel shrinkage, total shrinkage, and cuspal flexure was examined. Cuspal flexure was measured on restored typodont teeth, which offered a standardized tooth shape for comparison of shrinkage stress effects among restorative composites.Six restorative composites were compared (Filtek LS, Venus Flowable, Tetric EvoCeram, Filtek Flowable, Esthet-X, and Filtek Supreme). Total shrinkage was determined from changes in projected surface area before and after polymerization (n=10). Post-gel shrinkage was determined with a biaxial strain gauge that measured strain development during polymerization (n=10). Cuspal flexure was determined using typodont maxillary second premolars with standard MOD slot preparation (n=10). Flexure was determined by comparing the three-dimensionally scanned cuspal surfaces before and after restoration. Restoration bonding to the typodont cavity was achieved by sandblasting and adhesive application. Bond integrity was verified by measuring dye penetration. Results were analyzed using ANOVA and Student-Newman-Keuls post hoc test (significance level 0.05). Pearson was used for correlations.Total and post-gel shrinkage were significant different for all composites (t-test; P0.001). Depending on the composite, only 9-41% of the total shrinkage was recorded as post-gel shrinkage. Bond integrity of restored typodont teeth was 96-99%. Cuspal flexure correlated strongly with post-gel shrinkage, but there was no correlation with total shrinkage.Cuspal flexure of restored typodont teeth showed the effect of shrinkage stress caused by polymerizing composite restorations, ensuring standardization while maintaining the effects of tooth/cavity geometry. Post-gel shrinkage gave a good indication to screen composites for the stress they may generate; total shrinkage had no direct correlation with stress. more...

To investigate intrapulpal temperature rise in a primary molar during light activation of a composite restoration to determine if clinically significant pulpal temperatures (greater than 5.5 degrees Celsius) were reached.Restorative composites (EsthetX HD, Filtek Supreme Ultra, Filtek Bulk Fill) were placed into a primary molar with occlusal preparation (1.5 mm depth; remaining pulpal floor thickness one mm). The pulp was extirpated through a root access to place a thermocouple against the pulpal roof. Temperature changes were recorded during composite restoration light polymerization with three curing lights (one quartz-tungsten-halogen, two LEDs). Sample size was 10. Samples received additional irradiation to assure complete polymerization, followed by a third irradiation for calculating the exothermic heat contribution (subtracting third irradiation temperatures from first irradiation temperatures). Cured restorations were removed after each test, and the tooth was reused. Results were analyzed with Kruskal-Wallis (α =0.05).Type of curing light and composite material affected the intrapulpal temperature rise, which was up to five degrees Celsius for one combination of LED-composite.Clinicians should be aware of the potential for clinically significant intrapulpal temperature rises when light-activating composite restorations in a primary molar with a moderately deep cavity. more...

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.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).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.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. more...

Objective: To measure enamel surface changes after ceramic bracket debonding and after cleanup. Materials and Methods: Forty extracted teeth were scanned in three dimensions using an optical scanner (baseline). Two ceramic bracket systems were placed (19 metal-reinforced polycrystalline ceramic brackets; 21 monocrystalline ceramic brackets). Seven days later, brackets were debonded and teeth scanned (post-debond). Adhesive remnants and bracket fragments were recorded. Tooth surfaces were cleaned using a finishing carbide bur and scanned again (post-cleanup). Post-debond and post-cleanup scans were aligned with the baseline, and surface changes were quantified. Results were statistically compared using t-tests and Mann-Whitney tests (α = .05). Results: The depth of enamel loss (mean ± standard deviation) post-debond was 21 ± 8 µm and 33 µm and post-cleanup was 28 ± 14 µm and 18 ± 8 µm (P = .0191); the post-debond remnant thickness was 188 ± 113 µm and 120 ± 37 µm (P = .2381) and post-cleanup was 16 ± 5 µm and 15 µm for polycrystalline and monocrystalline ceramic brackets, respectively. The monocrystalline ceramic brackets predominantly left all adhesive on the tooth; the polycrystalline ceramic brackets were more likely to leave bracket fragments attached. Conclusion: Both systems allowed successful removal of the brackets with minimal enamel loss. However, the polycrystalline ceramic brackets left more fragments on the tooth, which complicated cleanup efforts. more...

Purpose To determine the effect of material type and restoration thickness on the fracture strength of posterior occlusal veneers made from computer-milled composite (Paradigm MZ100) and composite-ceramic (Lava Ultimate) materials. Methods 60 maxillary molars were prepared and restored with CAD/CAM occlusal veneer restorations fabricated from either Paradigm MZ100 or Lava Ultimate blocks at minimal occlusal thicknesses of 0.3, 0.6, and 1.0mm. Restorations were adhesively bonded and subjected to vertical compressive loading. The maximum force at fracture and mode of failure were recorded. 2-Way ANOVA was used to identify any statistically significant relationships between fracture strength and material type or thickness. Spearman's rank correlation coefficient was used to analyze mode of failure with regard to fracture strength. Results The average maximum loads (N) at fracture for the Paradigm MZ100 groups were 1620±433, 1830±501, and 2027±704 for the material thicknesses of 0.3, 0.6, and 1.0mm, respectively. The Lava Ultimate groups fractured at slightly higher loads (N) of 2078±605, 2141±473, and 2115±462 at the respective 0.3, 0.6, and 1.0mm thickness. Statistical analyses revealed that, while no significant difference existed among the various restoration thicknesses in terms of fracture strength ( P >0.05), the material type was found to be influential ( P =0.04). The maximum load at fracture (N) for Lava Ultimate averaged over all thicknesses (2111±500) was significantly higher than that of the Paradigm MZ100 (1826±564). No correlation between mode of failure and fracture strength was found. Conclusions Under the conditions of this study, the maximal loads at fracture for these "non-ceramic" occlusal veneer restorations were found to be higher than human masticatory forces. Occlusal veneers made from the two materials tested are likely to survive occlusal forces regardless of restoration thickness, with those fabricated from the composite-ceramic hybrid material being more likely to survive heavier loads. more...

Objective To determine whether recommended short curing times of three high-power light emitting diode (LED) curing lights are sufficient to polymerize sealant materials. Methods Opaque-unfilled sealant (Delton LC Opaque), opaque-filled sealant (UltraSeal XT plus), and clear-filled sealant (FluroShield) were light cured in a covered slot-mold using the manufacturers' shortest recommended curing times with three high-power LED lights (3-s VALO, 5-s Fusion, 10-s Smartlite). A 40-s cure with a quartz-tungsten halogen (QTH) light was used as control. Vickers hardness was measured 24 h after curing at the sealant surface and through the depth (0.5 mm increments) (N = 10). Results were analyzed with two-way anova (pair-wise multiple comparisons, significance level 0.05). Results The high-power LEDs did not cure the sealants as deep as the QTH. Delton LC Opaque showed the least depth of cure as hardness values beyond a depth of 0.5 mm were not measurable regardless of the curing light. Even for UltraSeal XT plus, when surface hardness was about the same with all lights, hardness decreased more rapidly with depth for the LEDs. FluroShield showed the slowest decline in hardness through the depth for all lights. Conclusions Manufacturers' recommendations for shortest possible curing time with high-power LEDs were not sufficient for adequate polymerization of the tested sealants. more...

SUMMARY Objectives To evaluate the effect of composite resins (one conventional and two low-shrink composites) and filling techniques on cuspal strains (CS), microtensile bond strength (μTBS), composite ultimate tensile strength (UTS), and mechanical properties of the composites at various depths in molars with large Class II restorations. Materials and Methods One hundred seventeen human molars received standardized Class II mesio-oclusal-distal cavity preparations and restorations with three composites (Filtek LS [3M-ESPE]; Aelite LS [BISCO]; and Filtek Supreme [3M-ESPE]) using three filling techniques (bulk, eight increments, and 16 increments). CS was measured using strain gauges, after which the same restored teeth were used to assess μTBS and UTS. The elastic modulus (E) and Vickers hardness (VH) at different depths were determined from microhardness indentations. The CS, μTBS, UTS, E, and VH data were statistically analyzed using split-plot analysis of variance and Tukey test (p=0.05). Results The CS was higher when using 16 increments. The ‘low-shrink' composites caused lower CS. The μTBS and UTS were similar for eight- and 16-increment techniques and higher when compared to the bulk filling in all composites. E and VH were constant through the depth when applied in eight or 16 increments. Conclusions Type of composite and filling technique affected the CS, μTBS, UTS, and mechanical properties of large Class II restorations. The eight-increments filling technique resulted in generally less CS with the same μTBS and UTS than was obtained with 16 increments, without affecting E and VH through the depth of the composites. more...

Soft drinks containing caffeine have been associated with more aggressive forms of dental decay. Cariogenicity of caffeinated soft drinks may be attributed to the effect of caffeine on salivary flow. This study assessed whether caffeinated soft drinks produced short-term oral dryness in healthy adults.The authors collected saliva on two separate days from 35 participants before and one hour after drinking a soft drink. On one of the days the soft drink was caffeinated and on the other day it was not. Saliva collection involved 15 minutes unstimulated whole saliva, 5 minutes paraffin-stimulated whole saliva, and 10 seconds labial minor salivary gland output.Unstimulated and stimulated flow rates slightly increased and minor gland output slightly decreased one hour after the soft drink consumption regardless of caffeine content. These changes were not statistically significant (two-period two-treatment crossover trial using two-stage Grizzle model,Caffeinated soft drink consumption had no significant effect on salivary flow rate after one hour by any of the three measures employed in this study. Caffeine's contribution to the cariogenicity of soft drinks is likely by centrally-mediated effects on consumption patterns. more...

Background Acid regurgitation resulting from gastroesophageal reflux disease (GERD) causes dissolution of tooth structure. The authors conducted a longitudinal clinical study to measure tooth surface loss associated with GERD. Methods The authors made replicas of dental impressions obtained from 12 participants with GERD and six control participants at baseline and six months. Using an optical scanner, they digitized the tooth surfaces of these replicas. They then analyzed the volume of tooth surface loss and characterized it as noncontact erosion or erosion/attrition. Results Mean (standard deviation) volume loss per tooth in participants with GERD (0.18 [0.12] cubic millimeter) was significantly higher than that in control participants (0.06 [0.03] mm 3 ; t test; P Conclusions Tooth surface loss in participants with GERD was significantly greater than that in control participants. The pattern of surface loss was characteristic of erosion in noncontact areas and around contact areas. Clinical Implications Anterior and posterior teeth of participants with GERD were affected by erosive tooth wear. In addition, the amount of erosive tooth wear on occlusal surfaces was twice as high when there was evidence of attrition. more...

The authors conducted a study to test the hypothesis that light-curing regimens affect depth of cure of clear versus opaque sealants.The authors light-cured samples of one clear and two opaque sealants at 20 seconds, 0 millimeters; 40 seconds, 0 mm; and 40 seconds, 2.2 mm (n = 5 each). They assessed the depth of cure with Knoop hardness at 0.5-mm increments five minutes and one hour after curing. The authors used analysis of variance.Curing regimens and sealant types affected the depth of cure. The clear sealant maintained a greater hardness than did the opaque sealants through a depth of 3 mm (P.001). A 20-second duration reduced the depth of cure for all sealants (P.001). The distance from the light source did not affect the cure depth of the clear sealant (P = .34), but it reduced the cure depth of the opaque sealants (P.05). Sealant hardness increased significantly one hour after light curing (P.001).A clear sealant cured deeper than did opaque sealants. Curing duration is crucial to achieve an adequate depth of cure. A 20-second duration may not suffice. Light source distance affected the depth of cure for the opaque sealants, but not for the clear sealant with sufficient curing duration.The authors advocate a curing duration of longer than 20 seconds to ensure thorough polymerization at the interface between the sealant and tooth. Insufficient curing could contribute to failure of the sealants, especially the opaque sealants, under clinical conditions that restrict the light tip position. more...

SUMMARY Objective: The aim of this study was to investigate the effect of delayed photo-activation on elastic modulus, Knoop hardness, and post-gel shrinkage of dual cure resin cements and how this affects residual shrinkage stresses in posterior teeth restored with ceramic inlays. Methods and Materials: Four self-adhesive (RelyX Unicem, 3M ESPE; GCem, GC; MonoCem, Shofu; and seT, SDI) and two conventional (RelyX ARC, 3M ESPE; and AllCem, FGM) dual cure resin cements for cementing posterior ceramic inlays were tested. Strain gauge and indentation tests were used to measure the post-gel shrinkage (Shr), elastic modulus (E), and Knoop hardness (KHN) when photo-activated immediately and 3 and 5 minutes after placement (n=10). Shr, E, and KHN results were analyzed using two-way analysis of variance followed by Tukey honestly significant difference post hoc tests (α=0.05). The experimentally determined properties were applied in a finite element analysis of a leucite ceramic inlay (Empress CAD, Ivoclar Vivadent) cemented in a premolar. Modified von Mises stresses were evaluated at the occlusal margins and cavity floor. Results: Shr, E, and KHN varied significantly among the resin cements (p Conclusions: KHN and E values varied among the different resin cements. Residual shrinkage stress levels decreased with increasing photo-activation delay with all resin cements. more...

Endodontic treatment procedures induce changes in tooth structure and may shift stress distributions in treated roots that make them more prone to fracture. This chapter discusses mechanical properties and changes in dentin characteristics and shape of the root canal caused by root canal therapy. Moisture, irrigants, medicaments, obturation materials, temperature rise, and canal taper may induce these changes. more...

Adding a post affects the biomechanical response of root canal-treated teeth. This chapter discusses the biomechanical performance of anterior and posterior root canal-treated teeth restored with fiber-reinforced resin posts and the effects of post systems, post lengths, luting procedures, ferrule design, and coronal restorations. The chapter includes discussion of anatomic glass fiber posts for severely weakened endodontically treated teeth and adhesive endocrown restorations. more...