Yada Chaiyabutr

Problem Although there is a high prevalence of noncarious cervical lesions (NCCLs), the etiology of these lesions remains contentious. Purpose To evaluate the combined effects of cyclic fatigue stress and biocorrosion activity on NCCLs. Materials and Methods Extracted premolar teeth were allocated into four groups (N = 10). Two groups were cyclically fatigue loaded (100 N; 72 cycles per minute; 9,200 cycles) and placed in either hydrochloric acid gel (pH = 0.1) or orange juice (pH = 4). The other two groups were stored in identical chemical solutions without fatigue load. The buccal–lingual width of each tooth was measured before and after testing. The depth of biocorrosion, normalized by the percentage change in buccolingual width, normalized by time (hour) was calculated. The data were analyzed using a two-way analysis of variance and Tukey's HSD multiple comparison test (α = 0.05). Results Mean (SD) of the depth of biocorrosion values were as follows: teeth receiving fatigue loading with hydrochloric acid gel exposure (1.003%/hour [0.063]) revealed a significantly higher depth of biocorrosion than the fatigue-loaded group with orange juice exposure (0.511%/hour [0.281]) (p < 0.01). For the groups without fatigue loading, those with hydrochloric acid gel (0.022%/hour [0.006]) had a significantly higher depth of biocorrosion than the group with orange juice (0.009%/hour [0.004]) (p < 0.01). The cyclically fatigue-loaded teeth with hydrochloric acid gel had a significantly greater depth of biocorrosion than either group without fatigue loading (p < 0.001). Conclusions Cyclic fatigue stress—acidic biocorrosion had a significant effect on the depth of the NCCLs. Clinical Significance In order to manage the destructive NCCLs lesions properly, it is essential to understand the etiology of these lesions. The present study indicated that the combined mechanisms of cyclic fatigue stress and biocorrosion could contribute to the formation of NCCLs.

Statement of Problem: Interest in posterior partial coverage restorations has increased because these restorations provide a more conservative treatment option than traditional cohesively based restorations; however, material selection has been a controversial topic in the current literature.Purpose: To evaluate the fracture resistance of posterior partial coverage restorations restored with different materials, examine their stress distribution, and calculate failure risks using three‐dimensional (3D) finite element analysis.Methods: Sixty extracted third molar teeth received 2‐mm occlusal reduction maintaining cusp steepness of 45 degrees relative to occlusal surface. Teeth were allocated into four groups (N = 15) and restored with different materials: feldspathic ceramic, leucite‐reinforced ceramic, lithium disilicate‐reinforced ceramic (EMX), or indirect resin‐based composite (COM). Restorations were luted with resin cement and submitted to compressive loads (Instron Corp, Norwood, MA, USA). The data were analyzed with one‐way analysis of variance, followed by Tukey's HSD tests. A 3D finite element model of posterior partial coverage restorations was developed and validated. The model was used to approximate the maximum principal stress in each of the materials under a 100‐N static vertical compression at the occlusal surface of the tooth. The risk of restoration failure was quantified and compared among the four different materials.Results: Group EMX had fracture resistance significantly higher than other testing groups. Group COM presented the most extensive fractures involving tooth and root structures. When compared with the other materials, group EMX exhibited higher stress concentration; however, the failure risk of the restoration was lower.Conclusions: Fracture resistance and failure risks of posterior partial coverage restorations are significantly influenced by material selection.Clinical Significance: Many restorative materials have been advocated for partial coverage restorations. It is essential to ensure that restorative materials have sufficient strength to support occlusal forces and, in case of fracture, the remaining tooth structure is not compromised or placed at risk. This study revealed that all‐ceramic materials had high incidences of fractures involving the materials themselves, whereas the predominant failure of resin‐based composite involved the tooth structure in a catastrophic manner.

The objective of this study was to evaluate the load-fatigue performance of posterior ceramic onlay restorations relative to two variables: preparation design (with or without buccal veneers); and the existing amount of tooth structure (non-worn tooth, worn tooth). Sixty extracted third molars were divided into five groups. One group received a mesial-occlusal-distal (MOD) gold onlay restoration (control). The other four experimental groups were prepared for ceramic onlay restorations. Two of the groups additionally received 2-mm occlusal reduction to simulate occlusal wear. All restored teeth were subjected to thermocycling prior to fatigue testing. A fatigue load of 150 N was applied on the occlusal surface at a frequency of 1.2 hz, at an angle of 135 degrees to the long axis of the tooth. Specimen failure was defined as the occurrence of crack propagation in the luting cement layer. This was monitored by the strain gauge on the specimen. All specimens restored on worn tooth had significantly lower fatigue failure cycle counts than those of non-worn tooth. The fracture mode analysis revealed that ceramic fracture tended to be demonstrated only in the group of worn tooth groups. The addition of a buccal veneer component had no significant effect on the load-fatigue performance of posterior ceramic onlay restorations, but the existing amount of tooth structure did have a significant effect on the load-fatigue performance of posterior ceramic onlay restorations. Catastrophic failures (ceramic fracture) occurred only in the group of worn tooth.

This study evaluated the effect of tooth-preparation cleansing protocols on the bond strength of a self-adhesive resin cement to dentin contaminated with two different types of hemostatic agents. The occlusal surface of extracted third molars was flattened to expose the dentin surface and prepared for a full crown. Acrylic temporary crowns were fabricated and placed using temporary cement. The specimens were stored at 100% relative humidity for seven days. Following removal of the temporary crowns, the specimens were surface debrided using aluminum oxide abrasion with a particle size of 27 μm at 40 psi. The specimens were randomly assigned to three groups, according to the hemostatic agents: Group I–an agent containing aluminum chloride was applied to the tooth surface; Group II–an agent containing ferric sulfate was applied to the tooth surface and Group III–uncontaminated (control). The contaminated specimens were then further subdivided into three subgroups (A–C; n=12): Group A–tooth surface cleansing with water spray; Group B–tooth surface cleansing with phosphoric acid etch and Group C–tooth surface cleansing with aluminum oxide abrasion with a particle size of 27 μm at 40 psi. Ceramic blocks were treated with a 9.5% hydrofluoric acid-etch and silanized prior to being cemented with self-adhesive resin luting agent (RelyX Unicem) to the prepared dentin. The shear bond strength was determined at a crosshead speed of 0.5 mm/minute. The data were analyzed with two-way ANOVA, followed by the Duncan multiple range test, to determine any significant differences between the testing groups. The microstructure morphology of the tooth surface was evaluated using SEM analysis. The results revealed that there was a significant difference between the bond strength of the control and the contaminated testing groups (pp<0.05).

The concept of tooth preparation for ceramic veneers remains controversial regarding whether the use of a palatal chamfer would affect the longevity of restorations. This study aimed to evaluate the load-fatigue testing of ceramic veneers using two different preparation designs-an incisal shoulder finish line with or without a palatal chamfer. A pressable ceramic veneer was bonded to the prepared maxillary central incisor using resin cement. The number of cycles until fatigue failure for each tooth-veneer specimen was recorded. Results revealed that using a palatal chamfer margin design significantly increased the fatigue failure cycle count.

Clinical Relevance: Tooth preparation cleaning protocol surface management with lower pressure aluminous particle abrasion provides a significant improvement in bond strength to dentin.