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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...

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...

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...

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...

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...

Objectives . Chipping and bulk fracture are major contributors in clinical failures of composite restorations. Fracture toughness ( K Ic ) quantifies susceptibility for fracture, but experimental determination is complicated. It would be beneficial for the dental community if a relatively simple experiment, such as microhardness (HK), could be used to screen composites for fracture resistance. This study explores a possible correlation between K Ic and HK. Methods . Composite cylinders (4 mm diameter and ∼7 mm long) were cured for five combinations of light intensity ( I , mW/cm 2 ) and curing time ( T , s) to achieve a range of different total light energy densities ( I × T =100×10, 100×20, 300×20, 300×40, and 700×60 mW s/cm 2 ). A chevron-notch was cut in the median plane of the cylinders for the fracture toughness test, which was executed in a displacement control mode at 6 μm/s cross-head speed (sample size 4). Knoop hardness was determined at the median plane of the cylinders (sample size 6). The tests were performed 15 min and 24 h after curing. Results . Both the K Ic and HK increased with increased light energy density and storage time. Linear regression analysis indicated a strong correlation between HK and K Ic tested at the same time period ( R 2 =0.97 and 0.90 for 15 min and 24 h, respectively). The correlation became weaker between the different storage times ( R 2 =0.71), indicating a change in fracture toughness and/or microhardness mechanisms. Conclusion . Fracture toughness of a composite cannot be simply extrapolated from microhardness. more...

A new bond strength test method proposed by Lin et al. (Lin CP, Douglas WH, Fields RP. J Dent Res 1992;71(IADR Abstracts #74):524) is presented to overcome the shortcomings of traditional bond strength measurements, which are based on nominal stress concepts. This paper is a theoretical analysis based on a linear elastic fracture mechanics approach. The analytical relationship between the elastic energy release rate G Ic and the critical load is derived approximately as a function of specimen shape and material properties. more...