Effect of composite insertion technique on cuspal deflection using an in vitro simulation model.

OBJECTIVE: The objective of this study was to investigate, by simulation, the effect of conventional composite resin insertion techniques on cuspal deflection using bonded typodont artificial teeth. The deflection produced by a new low-shrinkage composite was also determined. MATERIALS AND METHODS: Sixty standardized MOD preparations on ivorine maxillary premolars were prepared: group A at 4 mm depth and group B at 6 mm depth. Each group was further subdivided according to composite insertion technique (n=6), as follows: 1) bulk insertion, 2) horizontal increments, 3) tangential increments, and 4) a modified tangential technique. Preparations were microetched, acid-cleaned, and bonded with adhesive resin to provide micromechanical attachment before restoration with a conventional composite (Spectrum TPH( 3 ), Dentsply). Two additional subgroups at 4 mm and 6 mm depth (n=6) were restored in bulk using low-shrinkage composite (Filtek LS, 3M/ESPE). All groups received the same total photo-polymerization time. Cuspal deflection was measured during the restorative procedure using two Linear Variable Differential Transformers attached to a data acquisition system. RESULTS: The average cuspal deflections for group A were 1) 40.17 ± 1.18 µm, 2) 25.80 ± 4.98 µm, 3) 28.27 ± 5.12 µm, and 4) 27.33 ± 2.42 µm. The deflections in group B were 1) 38.82 ± 3.64 µm, 2) 50.39 ± 9.17 µm, 3) 55.62 ± 8.16 µm, and 4) 49.61 ± 8.01 µm. Cuspal flexure for the low-shrinkage composite was 11.14 ± 1.67 µm (group A: 4 mm depth) and 16.53 ± 2.79 µm (group B: 6 mm depth). CONCLUSIONS: All insertion techniques using conventional composite caused cuspal deformation. In general, deeper preparations showed increased cuspal deflection-except in the case of bulk insertion, which was likely affected by decreased depth of cure. Cuspal movement using low-shrinkage composite was significantly reduced.

Comparative translucency of esthetic composite resin restorative materials.

OBJECTIVE: To evaluate the translucency of currently available composites classified by their respective manufacturers as "opaque," "dentin," "body" (or "universal") and "enamel" materials. MATERIALS AND METHODS: Four disk-shaped specimens were produced using a split-ring mould (13 mm in diameter and 2 mm in thickness) from each of 39 proprietary composite restorative materials. Enamel and dentin samples of equivalent thickness were obtained from extracted human teeth. Colour values for lightness (L*), red-green chromatic coordinate (a*) and blue-yellow chromatic coordinate (b*) were recorded against standard white and black backgrounds with a Minolta CR-300 chroma meter under the standard illuminant D65. Translucency parameter values were calculated and compared using analysis of variance and the Tukey test, with significance set at p < 0.05. RESULTS: A continuum of values for the translucency parameter was obtained, ranging from the most opaque (Filtek Supreme Plus A2D) to the most translucent (Ceram X Duo E2). In general, "opaque" and "dentin" composites yielded relatively low translucency values, "body" (or "universal") composites yielded intermediate values, and "enamel" composites yielded relatively high values. However, the boundaries between these categories were not distinct, and there was some overlap. The mean value of the translucency parameter for human enamel was within the range of values for "enamel" shade composites. The individual values for specimens of human dentin were more variable (i.e., greater standard deviation around the mean) than those for human enamel. The mean value obtained for dentin was intermediate between the ranges for composites with low and intermediate translucency. CONCLUSIONS: The various categories of composite from different manufacturers yielded a wide range of translucency, with minimal distinction between the extremes in adjacent categories. The measured translucency values provided more information than the respective category types. Knowledge of the relative translucency and opacity of different commercial materials can assist clinicians in the choice of composite for clinical use.

Flexural strength, elastic modulus, and pH profile of self-etch resin luting cements.

PURPOSE: To determine the flexural strength, modulus of elasticity, and 24-hour pH profile of three self-etching resin luting cements and to obtain comparative data for representative conventional resin and resin-modified glass ionomer luting cements. MATERIALS AND METHODS: Three self-etching resin luting cements [RelyX Unicem (3M ESPE), Maxcem (Kerr), Embrace Wetbond (Pulpdent)] were tested and compared with two conventional resin cements [RelyX ARC (3M ESPE), Linkmax (GC)] plus two resin-modified glass ionomer luting cements [Fuji Plus (GC), RelyX Luting Plus (3M ESPE)]. Flexural strength and modulus of elasticity were determined using bar-shaped specimens (2 x 2 x 25 mm(3)) at 24 hours, using an Instron universal testing machine. Setting pH was measured using a flat-surface pH electrode at 0, 2, 5, 15, and 30 minutes and 1, 2, 4, 6, and 24 hours after mixing. Testing was performed under both dual-cured and self-cured conditions for all dual-cure cements. Data analysis included ANOVA and Tukey's test (p < 0.05). RESULTS: The self-etching cements showed similar flexural strength to the conventional resin cements, except for Embrace Wetbond self-cured, which was considerably lower. Modulus of elasticity results were both higher and lower than for conventional resin cements. All photopolymerized conventional and self-etch dual-cure cements showed markedly higher flexural strength and modulus than when solely self-cured. The resin-modified glass ionomer cements were characterized by lower flexural strength and elastic modulus. Self-etching resin cements showed lower initial pH (2.0 to 2.4) than conventional resin cements (4.8 to 5.2) and a wide range of final pH values (3.9 to 7.3) at 24 hours. One self-etching cement (Unicem) revealed a unique pH profile characterized by a more rapid rise in pH to neutrality both when dual-cured (15 minutes) and when auto-cured (1 hour). CONCLUSIONS: The self-etching resin cements evaluated in this study displayed disparate properties and cannot be considered a homogeneous group. Flexural strength properties were most uniform and were similar to those of the conventional resin cements, whereas moduli of elasticity showed greater variation. Setting pH profiles differed, depending on the brand and mode of cure, even within the same category of luting cement. All cements with dual-cure capability, both conventional and self-etch, showed significantly superior properties when photopolymerized.

No reliable evidence that ozone gas stops or reverses tooth decay.

DATA SOURCES: The Cochrane Oral Health Group's Trials Register, Cochrane Central Register of Controlled Trials, Medline and Premedline, Embase, CINAHL (Cumulative Index to nursing and Allied Health Literature)l and the Allied and Complementary Medicine Database were searched. The journal Quintessence was searched by hand and KaVo Dental (Biberach, Germany) manufacturers of HealOzone apparatus were contacted for any additional published or unpublished trials. STUDY SELECTION: Inclusion was assessed independently by at least two reviewers. Trials were only included if they met the following criteria: randomisation in a controlled trial; single surface in vivo carious lesion accessible to ozone application; clear allocation concealment; ozone application to the lesions in the intervention group; no such application of ozone in the control group; and outcomes measured after at least 6 months. DATA EXTRACTION AND SYNTHESIS: Reviewers independently extracted information in duplicate. A paucity of comparable data did not allow meta-analytic pooling of the included studies. RESULTS: Three trials were included, with a combined total of 432 randomised lesions (137 participants). Forty-two conference papers, abstracts and posters were excluded (from an unknown number of studies). The risk of bias in all studies appeared high. The analyses of all three studies were conducted at the level of the lesion, which is not independent of the person. For this reason, pooling of data was not appropriate or attempted. Individual studies showed inconsistent effects of ozone on caries, across different measures of caries progression or regression. Few secondary outcomes were reported, but one trial reported an absence of adverse events. CONCLUSIONS: Given the high risk of bias in the available studies and lack of consistency between different outcome measures, there is no reliable evidence that application of ozone gas to the surface of decayed teeth stops or reverses the decay process. There is a fundamental need for more evidence of appropriate rigour and quality before the use of ozone can be accepted into mainstream primary dental care or can be considered a viable alternative to current methods for the management and treatment of dental caries.

Conservative operative management strategies.

Operative conservatism, including delayed operative intervention, is recommended to promote tooth longevity. Effective conservative operative strategies for the permanent dentition are the occlusal preventive resin and the proximal only restoration. Conservative strategies for the primary dentition have proves less successful. Conventional and conservative restorations are vulnerable to caries recurrence, material failure, and technical deficiencies. Successful conservatism demands discerning diagnostic decisions, effective disease management, and technical excellence. The diagnostic accuracy of radiographs and visual criteria is briefly reviewed for proximal and occlusal caries. Improved visual ranking criteria are supported for occlusal caries diagnosis. The use of dyes for occlusal diagnosis is not recommended.

Class I and Class II silver amalgam and resin composite posterior restorations: teaching approaches in Canadian faculties of dentistry.

A 10-question survey was mailed to the 10 Canadian faculties of dentistry to determine current approaches to teaching undergraduates about silver amalgam and resin composite for posterior restorations in adults and children. Responses were received from all 10 pedodontic programs and from 8 of the 10 operative and restorative programs. The use of silver amalgam and posterior composite for restorations of primary and permanent teeth is covered in the curricula of all dental schools, but the relative emphasis on the 2 materials varies. In the operative and restorative programs, curriculum time devoted to silver amalgam is either greater than or equal to that devoted to posterior composite. Five of the 8 schools reported greater educational emphasis on silver amalgam for the permanent dentition; however, course directors noted that the preference among patients seen in clinics is tending toward composite restorations. Curricula appear designed to educate students about the optimal use of both materials. Requirements for performance of restorations during training generally do not specify the type of material; these requirements range from 60 restorations to 250 surfaces. Five of the 8 schools conduct clinical competency tests with both materials. The responses from the pedodontic programs were more diverse. The proportion of curriculum time devoted to each type of material in these programs ranged from less than 25% to more than 75%. Five schools reported more emphasis on silver amalgam, 3 schools reported equal emphasis, and 2 schools reported more emphasis on posterior composite. No clinical requirements were specified in any of the undergraduate pedodontic programs. Within some of the faculties, there were differences between the operative and restorative program and the pedodontic program with respect to emphasis on different materials for the posterior dentition.

The effect of dentin adhesive and cure mode on film thickness and microtensile bond strength to dentin in indirect restorations.

This study evaluated the influence of dentin adhesive application technique (pre-curing vs non precuring) on microtensile bond strength (microTBS) to dentin and adhesive layer thickness in indirect resin restorations. Seven proprietary dentin adhesives were tested, including one-step and multistep products. Experimental groups included adhesive pre-cure (PC) with a halogen light source and no pre-cure (NPC) prior to resin cement insertion. Thirty caries-free molars received an MO inlay preparation. Inlays made with Tetric Ceram resin composite were cemented using a dual-cured resin luting agent. Prior to inlay cementation, each tooth was treated with one dentin bonding agent, using pre-cure (PC) or no pre-cure (NPC). After storage in distilled water at 37 degrees C for 24 hours, the teeth were sectioned along their long axis to produce serial sticks for microtensile bond strength testing at 0.5 mm/minute. The results were subjected to statistical analysis by one-way and two-way analysis of variance (ANOVA) and Tukey's multiple comparison test (p < or = 0.05). For the film thickness evaluation, 10 additional teeth were restored and sectioned mesiodistally. The thickness of the adhesive layer was evaluated by SEM at 1000x magnification at the pre-selected locations. The microTBS varied from 11.7 +/- 4.5 MPa to 43.4 +/- 9.8 MPa. The effect of pre-curing the adhesive was material specific. No adhesive layer was visualized for the adhesives used without the pre-curing step. The thickness of the adhesive layer for the pre-cured groups varied according to the different areas analyzed.

Flow, strength, stiffness and radiopacity of flowable resin composites.

OBJECTIVE: This study was undertaken to characterize 9 currently available proprietary flowable composites with respect to key properties of flow, flexural strength, stiffness (modulus of elasticity) and radiopacity. METHODS: Seven proprietary flowable composites (Aelite Flo, Filtek Flow, Heliomolar Flow, PermaFlo, Revolution Formula 2, Tetric Flow, Wave) and 2 flowable compomers (Compoglass Flow, Dyract Flow) were evaluated. A universal hybrid composite (Filtek Z250) and a restorative compomer (Dyract AP) were used as controls. Standard mechanical testing of 25 x 2 x 2 mm bar specimens was carried out at 24 hours and 1 month. Flow testing used a fixed volume of material under consistent loading, and radiopacity was measured simultaneously for all materials using disk specimens of 1 mm thickness. RESULTS: As expected, flowable composites showed higher flow and lower mechanical properties than the controls. Moduli of the composites were approximately 50% or less of the moduli of control materials, which indicates high flexibility. Flexural strengths approached that of the control composite. Flow properties varied widely. The material Tetric Flow had the highest radiopacity, above that of enamel and the control composite. Lowest radiopacity, below or equivalent to that of dentin, was shown by Wave and Revolution Formula 2. CONCLUSIONS: The flowable materials possessed a wide range of mechanical and physical properties. Their lower mechanical properties suggest that they should not be used in bulk in areas of high occlusal loading. Within intracoronal restorations, clinicians are advised to use materials with high radiopacity. A wide range of fluidity options is available. The clinical applications and performance of these materials require further study.

Mechanical and physical properties of contemporary dental luting agents.

STATEMENT OF PROBLEM: New luting agents, particularly with adhesive capability, are being introduced in an attempt to improve clinical success. Independent studies of basic comparative data are necessary to characterize these materials in relation to mechanical and physical properties. PURPOSE: The purpose of this study was to compare the flexural strength, modulus of elasticity, and radiopacity and pH of representatives of 5 types (categories) of luting agents. MATERIAL AND METHODS: The luting agents included a zinc phosphate, a conventional and a resin-modified glass ionomer, 2 dual-polymerizing resins ("photopolymerized" after mixing and "unphotopolymerized" conditions), and an auto-polymerizing resin. The specimens were prepared and the testing was conducted by 1 person to maximize standardization. Flexural strength (MPa) and modulus of elasticity (GPa) were determined on bar-shaped specimens (2 x 2 x 20 mm) at 24 hours and 3 months (n = 8). Radiopacity (mm Al) was measured by exposing 1 mm thick specimens along with an aluminum step wedge (n = 4). pH was measured using a pH electrode immediately after mixing; at 1, 5, 15, 30 minutes; and at 1, 2, 4, 6, and 24 hours (n = 4). The data were subjected to statistical analyses with analysis of variance and Duncan's multiple range test (P<.05). RESULTS: The resin luting agents (64 to 97 MPa) showed higher flexural strength than all other materials tested (7 to 27 MPa), with the "photopolymerized" (83 to 97 MPa) conditions higher than "unphotopolymerized" (64 to 81 MPa) (P<.0005). Zinc phosphate was the most radiopaque (6.4 mm Al) (P<.0001) and provided the highest rigidity (9.2 GPa) (P<.05). The autopolymerization resin cement was the most radiolucent (1.1 mm Al) (P<.0001). Zinc phosphate and conventional glass ionomer cements were the most acidic immediately after mixing (pH 1.5 to 2.2) but were the least acidic after 24 hours (pH 6.4 to 6.8) (P<.0001). CONCLUSIONS: Within the limitations of this study the data showed a wide variation of material properties. The dual-polymerization resin luting agents tested showed the best combination of mechanical and physical properties combined with the highest setting pH. Photopolymerization of these resin-based materials was necessary to maximize strength and rigidity.

Effect of mode of polymerization of bonding agent on shear bond strength of autocured resin composite luting cements.

PURPOSE: There have been anecdotal reports of low bond strength with autocured resin composite materials, particularly when light-cured bonding agents that combine primer and adhesive in a 1-bottle preparation are used. The objective of this study was to determine if the mode of polymerization of the bonding agent influences the strength of the attachment of autocured resin composite luting cements to dentin. METHODS: The shear bond strength of 2 resin luting cements, Calibra and RelyX ARC, polymerized by autocuring, in combination with 4 different bonding agents, Scotchbond Multipurpose Plus, Prime & Bond NT, IntegraBond and Single Bond, polymerized to bovine dentin by light-curing, autocuring or dual-curing, was determined. The pH of each bonding agent and its components was measured. Two-way analysis of variance was used to test the effect of cement and adhesive on shear bond strength. For each bonding agent, the adhesive variable combined the factors product brand and mode of polymerization. With significant interaction among the above variables, the least square means of the 16 combinations of resin cement and adhesive were compared. RESULTS: There was no consistent relationship between shear bond strength and mode of polymerization of the bonding agent. Significant differences in bond strength were specific to the proprietary brand of bonding agent. The pH of the bonding agent depends on the manufacturer's formulation, and low pH may contribute to low bond strength. CONCLUSIONS: The low in vitro bond strength occurring with some combinations of bonding agent and resin cement could be clinically significant.

Minimally Invasive Dentistry--concepts and techniques in cariology.

The concept 'Minimally Invasive Dentistry' can be defined as maximal preservation of healthy dental structures. Within cariology, this concept includes the use of all available information and techniques ranging from accurate diagnosis of caries, caries risk assessment and prevention, to technical procedures in repairing restorations. Dentists are currently spending more than half their time replacing old restorations. The main reasons for restoration failures are secondary caries and fractures, factors that are generally not addressed in the technical process of replacing a restoration. Prevailing concepts on minimally invasive dentistry seem to be 'product or technique-motivated', challenging one technique or product with another, rather than focusing on a general concept. New knowledge of caries progression rates has also led to substantial modification of restorative intervention thresholds and further handling of the disease. New diagnostic tools for caries lesion detection, caries risk assessment and focused preventive treatments have decreased the need for early restorative interventions. In parallel to this, new techniques for cutting teeth and removing decay have evolved. This paper focuses on describing minimally invasive dentistry in cariology from a conceptual perspective, relating to clinical caries diagnosis, restorative intervention thresholds and operative procedures, with special reference to survival of tunnel and slot restorations and to repair vs. replacement of defective restorations.