Physical Properties, Film Thickness, and Bond Strengths of Resin-Modified Glass Ionomer Cements According to Their Delivery Method.

PURPOSE: To determine the effect of changing the dispensing or mixing method of resin-modified glass ionomer (RMGI) cements on their water sorption, solubility, film thickness, and shear bond strength. MATERIALS AND METHODS: Disc-shaped specimens of RMGI cements (RelyX: Luting [handmix], Luting Plus [clicker-handmix], Luting Plus [automix], GC: Fuji PLUS [capsule-automix], FujiCEM 2 [automix], [n = 10]) were prepared according to ISO standard 4049 for water sorption and solubility tests. Furthermore, the percentage of mass change, percentage of solubility, and percentage of water absorbed was also determined. Film thickness was measured according to ISO standard 9917-2; the mean of 5 measurements for each cement was calculated. Shear bond strength for each cement was determined according to ISO standard 29022 before and after thermocycling at 20,000 cycles, temperatures 5 to 55°C with a 15-second dwell time (n = 10/subgroup). Two- and one-way ANOVA were used to analyze data for statistical significance (p < 0.05). RESULTS: Water sorptions of the RMGI cements were in close range (214-250 µg/mm3 ) with no statistical differences between counterparts (p > 0.05). RelyX Luting Plus (clicker-handmix) displayed lower solubility than its handmix and automix counterparts (p < 0.05). Film thickness of RelyX cements was significantly different (p < 0.05). RelyX Luting Plus (automix) had the lowest film thickness (19 µm) compared to its handmix (48 µm) and clicker-handmix (117 µm) counterparts (p < 0.05). GC Fuji PLUS (capsule-automix, 22 µm) was significantly lower than the automix version (GC FujiCEM 2, 127 µm) (p < 0.05). Shear bond strength of RelyX Luting Plus (automix) was significantly lower than its handmix and clicker-handmix versions (p < 0.05). GC Fuji PLUS (capsule-automix) was significantly higher than GC FujiCEM 2 (automix) (p < 0.05). The binary interaction of the two independent variables (dispensing/mixing method and thermocycling) was significant for the shear bond strengths of the GC cements only (p < 0.05). CONCLUSIONS: Change in the dispensing/mixing method of RMGI cement from the same brand may have an effect on its physical properties, in addition to its film thickness and shear bond strength. Newer, easier, and faster cement delivery systems are not necessarily better. Clinical outcomes of these differences are yet to be confirmed.

Effect of composite type and placement technique on cuspal strain.

OBJECTIVE: To compare the cuspal strain in Class II restorations made with bulk-fill and conventional composite resins. MATERIALS AND METHODS: Fifty extracted maxillary premolars were mounted into phenolic rings and divided into five groups (n = 10). Specimens received standardized MOD preparations. A two-step self-etch adhesive was applied and the preparations were restored using a custom matrix as follows: Filtek Supreme Ultra in eight 2-mm increments (FSUI); Filtek Supreme Ultra in bulk (FSUB); SonicFill in bulk (SF); SureFil SDR flow in bulk, covered with a 2-mm occlusal layer of Filtek Supreme Ultra (SDR/FSU); Tetric EvoCeram Bulk Fill in bulk (TEBF). Strain gages bonded to the buccal and lingual cusps recorded cuspal strain during restorations. End strain values were determined and data were subjected to Kruskal-Wallis testing, followed by one-way ANOVA and Tukey´s post hoc test. RESULTS: Combined strain values and standard deviations (in µÉ›) were: FSUI: 723 ± 102.8, FSUB: 929.2 ± 571.9, SF: 519.1 ± 80.2, SDR-FSU: 497.4 ± 67.6 and TEBF: 604.5 ± 127.1. A significant difference was found between group FSUI and groups SF, SDR-FSU, and TEBF. Group FSUB showed significantly higher mean strain and greater standard deviation than all other groups due to cuspal fractures, and was thus excluded from the statistical analysis. CONCLUSIONS: The tested bulk-fill composite resins exerted less strain onto tooth structure than the incrementally placed conventional composite resin, although the magnitude of generated strain was product-dependent. Bulk-filling with conventional composite resins is contraindicated. CLINICAL SIGNIFICANCE: Bulk-fill composite resins exerted less strain onto adjacent tooth structure than a traditional composite, even when that composite is was placed incrementally. Bulk-filling with traditional composite resins is unpredictable and contraindicated.

Mechanical properties of resin-based cements with different dispensing and mixing methods.

STATEMENT OF PROBLEM: Resin-based cements are frequently used in clinical practice. To reduce time and technique sensitivity, manufacturers have introduced the same brand of cement with different dispensing methods. The effect of this change on properties of the cement is unknown. PURPOSE: The purpose of this in vitro study was to evaluate the mechanical properties of resin-based cements with different dispensing systems. MATERIAL AND METHODS: Specimens of resin-based cements (n=14) PANAVIA SA Cement Plus Handmix, PANAVIA SA Cement Plus Automix, RelyX Unicem Handmix, RelyX Unicem 2 Automix, G-CEM Capsule Automix, G-CEM LinkAce Automix, Variolink II Handmix, and Variolink Esthetic Automix were prepared for each mechanical test. They were examined after thermocycling (n=7/subgroup) for 20000 cycles as to fracture toughness (FT) (ISO standard 6872; single-edge V-notched beam method), compressive strength (CS) (ISO 9917-1), and diametral tensile strength (DTS). The specimens were mounted and loaded at a crosshead rate of 1 mm/min (0.5 mm/min for FT) with a universal testing machine until failure occurred. The 2-and 1-way ANOVA followed by the Tukey HSD post hoc test were used to analyze data for statistical significance (α=05). RESULTS: Thermocycling had a significant effect in reducing the FT property of all resin-based cements except RelyX Unicem 2 and G-CEM LinkAce (P<.05). Variolink II and G-CEM LinkAce showed better FT properties than their automixed counterparts (P<.05). The overall CS of all automixed resin-based cements was better than that of their hand-mixed counterpart, except for Variolink II. PANAVIA SA Automixed and G-CEM LinkAce had higher DTS than their hand-mixed counterparts (P<.05). CONCLUSIONS: Changing the dispensing method alters the mechanical properties of resin-based cements. The clinical significance of these results is yet to be determined.

The erosive potential of additive artificial flavoring in bottled water.

Acidic beverage consumption is a well-recognized contributor to extrinsic dental erosion. Although the pH values of some commercially available bottled waters are below neutral pH, water is still considered to be a safe and healthy choice. Artificial flavoring liquids or powders, known as water enhancers (WEs), have been introduced to the market to modify the taste of water. The purposes of the present study were to measure the pH and titratable acidity of WEs and to perform gravimetric analysis of teeth immersed in solutions of WEs mixed with different brands of bottled water in order to determine the erosive potential in vitro. The pH and titratable acidity using 0.1M sodium hydroxide were calculated for 7 brands of WEs added to 3 brands of bottled water, which had different initial pH values. Extracted human molar teeth were submerged in each combination of solutions for gravimetric analysis. Distilled water was used as the positive control and citric acid as the negative control. Data were analyzed with 2-way analysis of variance and post hoc Tukey-Kramer testing (P = 0.05). The pH value (2.9-3.0) and titratable acidity (32.2-35.3 mmol/L hydroxide) of all of the experimental solutions were considered acidic, regardless of the WE brand. Average tooth structure loss after 1 month of immersion in the solutions was 4%, and surface changes were consistent with erosive dissolution. The results showed that adding a WE to water significantly increases the potential for dental erosion. The high content of citric acid in WEs is believed to be the cause. Patients should be advised to use WEs with caution.

Survey of dentists to determine contemporary use of endodontic posts.

STATEMENT OF PROBLEM: Although the scientific literature provides sound decision-making tools for the restoration of endodontically treated teeth, dentists have different opinions on the rationale for the use of endodontic posts (dowels) and selection of post systems. The decision to place a post is at times contrary to the literature. Updated information on the treatment of endodontically treated teeth among general dentists is lacking. PURPOSE: The purpose of this survey was to gain insight into the rationale for choice of endodontic posts and the different endodontic post systems currently used by dental practitioners. Post and core restorations distribute stress and replace missing tooth structure in endodontically treated teeth. Guidelines exist to help select post systems. With the advent of new materials, prefabricated posts have gained popularity among dentists. However, cast-metal post-and-core systems are still considered the gold standard. MATERIAL AND METHODS: Surveys were distributed to dentists attending continuing education meetings in the United States, Canada, Scotland, Ireland, and Greece. The questions addressed years of practice, specialty training, and brand, type, shape, and material of the endodontic post systems used. RESULTS: Descriptive statistical analysis was used to assess the percentage of respondents. Ninety-two percent of the participants were general practitioners with 25.94 ±13.35 years of experience. The majority agreed upon using endodontic posts when insufficient coronal tooth structure remains and for stress distribution. Passive, parallel posts were the most commonly reported type and shape. With regard to post material, fiber posts were the most frequently used (72.2%), followed by prefabricated alloys (38.6%), cast-metal posts (33.9%), prefabricated titanium posts (30.1%), and stainless-steel posts (21.7%). For cementation, resin-modified glass ionomer (40%) was most frequently used, followed by self-adhesive resin (29.6%). CONCLUSIONS: The majority of the practitioners used fiber posts. This may be because, in terms of fracture, they compare favorably with cast-metal post and core, although little evidence in the literature validates this claim.

Gingival displacement: Survey results of dentists' practice procedures.

STATEMENT OF PROBLEM: A high percentage of fixed prosthodontic restorations require a subgingival margin placement, which requires the practice of gingival displacement or a deflection procedure to replicate the margins in impression. PURPOSE: The purpose of this study was to learn the different gingival displacement techniques that are currently used by dentists in their practice and to compare the current concepts of gingival displacement with previously published articles. MATERIALS AND METHODS: A survey of questions pertaining to gingival deflection methods was distributed as part of continuing education (CE) course material to dentists attending CE meetings in 7 states in the U.S. and 1 Canadian province. Question topics included initial patient assessment procedures, gingival displacement methods, dentist's knowledge and assessment of systemic manifestations, and brand names of materials used. RESULTS: Ninety-four percent of the participants were general practitioners with 24.11 ± 12.5 years of experience. Ninety-two percent used gingival displacement cords, while 20.2% used a soft tissue laser and 32% used electrosurgery as an adjunct. Sixty percent of the dentists used displacement cords impregnated with a medicament. Of the preimpregnated cords, 29% were impregnated with epinephrine, 13% with aluminum chloride, and 18% with aluminum potassium sulfate. CONCLUSION: The study showed a steady decrease compared with results of previously published articles in the use of epinephrine as a gingival deflection medicament.

Teaching methodologies for improving dental students' implementation of ergonomic operator and patient positioning.

OBJECTIVES: Musculoskeletal disorders (MSDs) related to operator and patient positioning are prevalent among dentists. Knowledge of correct operator and patient positioning promotes safe working postures that can prevent the development of MSDs. The aim of this study was to assess the impact of inter-professional teaching on the application of those skills associated with correct operator and patient positioning in dental settings. METHODS: A randomized case-control study was conducted with 83 first-year dental students at the UNC-Chapel Hill Adams School of Dentistry in 2019. Forty-one (n = 41) of the students solicited for the project participated. All 83 students in the cohort participated in a didactic lecture on ergonomics and correct operator and patient positioning, along with a pre-clinical practice session with peer patients. During the clinical practice session, students in the case group received an additional 10 minutes of 1-on-1 instruction by a trained physical therapy student or dental faculty member. Two weeks later, the final cohort (n = 41) was assessed by 2 faculty members using a scored rubric on operator and patient positioning for restorative work on an anterior tooth, posterior mandibular tooth, and posterior maxillary tooth. RESULTS: There was a statistically significant difference between the 2 groups with respect to the composite ergonomic positioning score (P = 0.006), operator shoulder abduction position (P = 0.03), and lateral flexion of the spinal column (P = 0.02). CONCLUSIONS: Hands on instruction with physical therapists and trained dental faculty positively affects ergonomic compliance and provides students with tailored feedback that can be applied to clinical practice.

Development and Assessment of Discrimination Exercises for Faculty Calibration in Preclinical Operative Dentistry.

The aims of this study were to identify the level of interexaminer agreement among preclinical operative dentistry faculty members when grading Class II preparations performed by first-year dental students; to develop discrimination exercises for specific preparation components where interexaminer agreement was poor; and to evaluate if the discrimination exercises were able to improve inter- and intraexaminer agreement. In the preliminary phase of this study, 13 components of 32 Class II cavity preparations were assessed by eight course faculty members at one U.S. dental school. Analysis of average interexaminer agreement on these components revealed that six were below 60%. These were proximal contact clearance, retention groove placement, retention groove depth, preparation walls, preparation margins, and preparation toilet/debris. A 30-minute calibration session was subsequently developed to provide discrimination exercises utilizing 3-D models and digital images of various levels of student performance for five of the six components. Immediately following calibration, the course faculty assessed the same 32 preparations (Phase I) followed by a delayed assessment without calibration (Phase II) approximately six months later. The results showed that overall interexaminer reliability improved after calibration. Although there was a decline in interexaminer reliability after an interval of six months (Phase II), the degree of variation among examiners was lower than in the preliminary assessment. These findings support the use of discrimination exercises for preclinical operative dentistry course faculty to increase interexaminer agreement and thereby improve the consistency of faculty-student communication.