Marginal microleakage of alternative restorative treatment and conventional glass ionomer restorations in extracted primary molars.

PURPOSE: The objective of this study was to compare the marginal leakage of cervical glass ionomer restorations made using alternative restorative treatment (ART) and conventional restoration techniques. METHODS: Twenty primary molars with Class V carious dentin on the buccal surfaces were prepared using ART, and a second set of 20 noncarious molars had Class V preparations made with a high-speed handpiece. The occlusal margin was located in enamel and the gingival margin in dentin/cementum. All teeth were restored with high-density glass ionomer cement (GIC; Fuji IXgp) according to manufacturers' instructions, thermally stressed for 300 cycles, and stained with methylene blue. Samples were sectioned and evaluated for microleakage. RESULTS: One-way analysis of variance revealed no statistically significant difference between leakage at margins of ART and conventional restorations. (P=.92) There was no significant difference between leakage at the enamel and dentin margins. CONCLUSIONS: Alternative restorative treatment with high-density glass ionomer cement provides enamel and dentin margins that show marginal leakage comparable to conventionally restored primary teeth. These results show the potential of ART in conjunction with high-density GIC in providing treatment for children and adolescents in situations where traditional cavity preparation and restoration is not possible.

An in vitro comparison of marginal microleakage of alternative restorative treatment and conventional glass ionomer restorations in extracted permanent molars.

PURPOSE: The objective of this study was to compare the marginal leakage of cervical restorations made using alternative restorative treatment (ART) and conventional glass ionomer restorations. METHODS: Sixteen permanent maxillary and mandibular first and second molars extracted for periodontal reasons with Class V carious dentin on the buccal surfaces were prepared using ART while a second set of 29 noncarious molars had Class V preparations made with a high-speed handpiece. The occlusal margin was located in the enamel, and the gingival margin was located in the dentin/cementum. All teeth were restored with glass ionomer cement (GIC). The teeth were thermally stressed for 300 cycles and stained with methylene blue. Samples were sectioned and evaluated for microleakage. RESULTS: One-way analysis of variance on ranks revealed no significant difference in leakage at both the dentin and enamel margins between the conventional and ART groups. The microleakage at the dentin margin, however, was significantly greater (P < .001) than at the enamel margins in the conventional group. CONCLUSION: Alternative restorative treatment with GIC provides enamel and dentin margins that show comparable marginal leakage to conventionally restored permanent teeth. For the conventional restorations, leakage at the dentin margins occurs to a significantly higher extent than at the enamel margins.

Effects of two adhesion boosters on the shear bond strength of new and rebonded orthodontic brackets.

The purpose of this study was to evaluate the effects of 2 adhesion boosters, Enhance LC (Reliance, Itasca, Ill) and All-Bond 2 (Bisco, Schaumburg, Ill), on the shear bond strength of new and rebonded (previously debonded) brackets. Sixty new and 60 sandblasted rebonded brackets were bonded to 120 extracted human premolars with composite resin and divided equally into 6 groups based on the 2 adhesion boosters used: (1) new brackets/no booster (2) rebonded brackets/no booster (3) new brackets/Enhance (4) rebonded brackets/Enhance (5) new brackets/All-Bond (6) rebonded brackets/All-Bond. Shear bond strength of each sample was tested with an Instron machine (Instron Corp, Canton, Mass). Results show that the new brackets/All-Bond group yielded the highest strength (20.8 +/- 7.5 MPa), followed by the new brackets/Enhance group (18.6 +/- 6.5 MPa), rebond brackets/All-Bond group (17.3 +/- 7.2 MPa), new brackets/no booster group (16.8 +/- 6.3 MPa), rebonded brackets/no booster group (14.2 +/- 7.2 MPa), and rebonded brackets/Enhance group (13.6 +/- 6.7 MPa). No statistically significant difference was found among the 3 groups utilizing new brackets. For groups of rebonded brackets/no booster and rebonded brackets/Enhance, bond strength was significantly lower than groups of 3 new brackets and rebonded brackets/All-Bond. Rebonded brackets/All-Bond group had comparable bond strength to all 3 new brackets groups. It was concluded that in the process of replacing a failed bracket, (1) when new brackets are used, neither All-Bond 2 or Enhance LC improves bond strength significantly, (2) without the use of any adhesion booster, sandblasted rebonded brackets yield significantly less bond strength than new brackets, (3) Enhance LC fails to increase bond strength of sandblasted rebonded brackets, (4) All-Bond 2 significantly increases bond strength of sandblasted rebonded brackets, (5) sandblasted rebonded brackets with All-Bond 2 yield comparable bond strength to new brackets.

Nanoindentation studies of titanium single crystals.

Titanium single crystal planes of different atomic density have been reported to show different oxidation characteristics. The differences in oxide characteristics have further been demonstrated to lead to differences in osteoblast attachment. Investigations of the preferred crystallographic planes of titanium for osteoblast attachment can be used to optimize the surfaces of single crystal and polycrystalline titanium implants for anchoring various prostheses. Nanoindentation techniques were used to determine mechanical properties of two crystallographic planes of titanium of different atomic density. Modulus of elasticity of 128 +/- 10 GPa was obtained for polycrystalline titanium and 123 +/- 5 and 124 +/- 6 GPa for the basal plane and pyramidal planes, respectively. The variation of modulus with crystal orientation was not greater than the statistical variation in the data. Surface hardness values were 2.1 +/- 0.1 GPa for the polycrystalline sample and 1.6 +/- 0.1 and 1.9 +/- 0.1 GPa, respectively, for the basal and pyramidal planes. Curves of hardness as a function of depth (0-2000 nm) obtained from electrochemically polished surfaces showed a sharp increase at shallow depths and may reflect changes caused by oxidation of the titanium surfaces.

Shear bond strengths of two resin-modified glass ionomer cements to porcelain.

Shear bond strength of a composite resin adhesive (Concise) and two resin-modified glass ionomer cements (Fuji Ortho LC and Geristore) bonded to porcelain surface was tested. Orthodontic brackets were bonded to 120 porcelain disks (Finesse) etched with 9% HF. Samples were divided into six groups: (1) Concise, (2) Concise/silane, (3) Geristore, (4) Geristore/silane, (5) Fuji, (6) Fuji/silane. No statistical difference in mean shear bond strength was found between silanated Concise (15.8 MPa), Geristore (19.4 MPa), and Fuji (18.5 MPa) groups, which were significantly higher than nonsilanated groups. Porcelain fracture was observed in all silanated groups and nonsilanated Geristore group. We conclude that (1) silane increases bond strength to porcelain significantly for composite resin and resin-modified glass ionomer cement, (2) Concise, Geristore, and Fuji Ortho LC provide comparable shear bond strength to porcelain.

Shear bond strength of a resin-reinforced glass ionomer cement: an in vitro comparative study.

Shear bond strength of Concise (a composite resin adhesive) and Fuji Ortho LC (a light-cured resin-reinforced glass ionomer cement) bonded to extracted teeth was tested under different bonding conditions: (1) Concise/etched/dry (2) Fuji/etched/dry (3) Fuji/etched/wet (4) Fuji/unetched/dry (5) Fuji/unetched/wet. Concise/etched/dry and Fuji/etched/dry groups showed comparable mean shear bond strength (10.5 and 8.2 MPa, respectively); the other three groups had considerably lower values. The difference between Fuji/etched/dry and Fuji/etched/wet was not statistically significant. The site of bond failure was between bracket and adhesive in all etched groups and between adhesive and enamel in the unetched groups. We conclude that (1) enamel surface etching is required for Fuji Ortho LC to achieve optimum bond strength, (2) moisture does not affect bond strength of Fuji Ortho LC significantly.

Softening patterns of light cured glass ionomer cements.

OBJECTIVE: The aim of this study was to determine the effects of commonly used food simulating solutions and sodium hydroxide on the softening of light cured glass ionomer cements. METHODS: Four types of light cured glass ionomers (classified on the basis of the liquid component) as follows: (1) materials that combine a polymerizable monomer and polyalkenoic acid (PMPA); (2) use of a polymerizable polyalkenoic acid (PPA); (3) acid monomer (AM) in place of the polyalkenoic acid; and (4) replacement of polyalkenoic acid with polymerizable monomer (PMPR). A traditional glass ionomer and a microfil composite were used as controls. Disc-shaped specimens aged for a week at 37 degrees C and 100% relative humidity were stored in water, ethanol, heptane and 0.1 M sodium hydroxide for a period of 28 days. Barcol hardness measurements were made before immersion as well as at intervals of 24 h, 3 days, 7 days and 28 days after immersion. RESULTS: In general the softening effect was lowest on the resin composite control. Hardness could not be measured for the traditional glass ionomer after 24 h due to breakage and dissolution of samples. The different solutions had varying effects on the different classes of light cured glass ionomers. The change in hardness after 28 days ranged from an increase of +6.7% for PMPA material in heptane to a complete disintegration of PPA amd PMPR in NaOH at 60 degrees C. SIGNIFICANCE: The softening effect of food simulating solutions is dependent on the formulation of light cured glass ionomers. In clinical use, the role of softening in wear will consequently vary.

Evaluating parameters of osseointegrated dental implants using finite element analysis--a two-dimensional comparative study examining the effects of implant diameter, implant shape, and load direction.

Finite element analysis (FEA) has been proven to be a precise and applicable method for evaluating dental implant systems. By means of FEA, a parasaggital model was digitized from a computed tomography (CT)-generated patient data set, and various single-tooth, osseointegrated, two-dimensional dental implant models were simulated. The specific aims of the study were to: (1) examine the effect of implant diameter variation (3.8 mm-6.5 mm) of both a press-fit, stepped cylindrical implant type and a press-fit, straight cylindrical implant type as osseointegrated in the posterior mandible; (2) compare the stress-dissipating characteristics of the stepped implant versus the straight implant design; and (3) analyze the significance of bite force direction (vertical, horizontal, and oblique 45 degrees) on both implant types. The results of the FEA suggested that (1) using the widest diameter implant is not necessarily the best choice when considering stress distribution to surrounding bone, but within certain morphological limits, for both implant types, an optimum dental implant exists for decreasing the stress magnitudes at the bone-implant interface; (2) stress is more evenly dissipated throughout the stepped cylindrical implant when compared to the straight implant type; and (3) it is important in FEA of dental implants to consider not only axial forces (vertical loading) and horizontal forces (moment-causing loads), but also to consider a combined load (oblique bite force), since these are more realistic bite directions and for a given force will cause the highest localized stress in cortical bone. The theoretical analysis performed implies that clinically, whenever possible, an optimum, not necessarily larger, dental implant should be used based on the specific morphological limitations of the mandible and that a stepped cylindrical design for press-fit situations is most desirable from the standpoint of stress distribution to surrounding bone.

Comparison of surface-treated and untreated orthodontic bands: evaluation of shear force and surface roughness.

In an attempt to increase retention of orthodontic bands, orthodontic companies market bands with surfaces prepared to increase roughness. A comparison of six groups of bands, including two with untreated surfaces, revealed a wide range of variation in shear forces. Three classes of retention may be differentiated on the basis of non-statistically significantly different mean shear forces in each category: high (Unitek, treated), moderate (Unitek, untreated; A Co., treated; GAC, treated), and low (A Co., untreated; Dentaurum, treated). Surface roughness, as evaluated through atomic force microscopy, correlated moderately with shear force (r = 0.61; p < 0.05). This method is examined and compared with the qualitative profiles of the orthodontic band surfaces provided by optical micrography.

The effect of noble metals on the mechanical properties of dispersed phase dental amalgam.

The effects of noble metals added as part of a Ag-Cu dispersant on the compressive strength and creep of dental amalgams was determined. The Ag-Cu eutectic used in high copper dispersant alloy L(0), was altered by adding 15 per cent by weight (wt%) of noble metal in place of Ag. In L(1) the noble metal was Pd. In L(2), Au and Pd were combined in equal proportions. In L(3), the noble metal content was Pd and Pt in equal proportions. A low copper lathe-cut amalgam, Aristalloy was used as the matrix. Amalgams S(0) and S(1) had the same composition as L(0) and L(1) except that the the low copper alloy matrix was Spheralloy, a low copper spherical amalgam. The compressive strength and creep were measured according to American Dental Association specification No. 1 and the results analysed by ANOVA. The addition of noble metals to the dispersant significantly lowered the 1-h compressive strength of amalgams. Compared to the control amalgam L(0), the 24-h compressive strength was increased for L(1) and L(2) but lowered for L(3). The ADA creep values were significantly lowered by addition of all combinations of noble metals. Reported microstructural changes such as an increase in unreacted particles, and a slowed setting reaction may account for the findings.

Enamel preparation for orthodontic bonding: a comparison between the use of a sandblaster and current techniques.

Four methods of enamel preparation before orthodontic bonding that are currently in use or proposed for use were investigated. The study consisted of two parts. Part one evaluated the roughness of the prepared enamel surfaces by using optical profilometry and scanning electron microscopy (SEM). Part two compared the debonding force for the prepared enamel surfaces by using a mechanical testing machine. The teeth were divided into four groups as follows: In group A, the surfaces were only sandblasted. In group B, the surfaces were sandblasted and acid etched. In group C, the surfaces were buffed with an 1172 fluted bur and acid etched. In group D, the surfaces were pumiced and acid etched. There was no statistical difference in surface roughness among the four groups at p < 0.05, nor was there any statistical difference in bond strength among the three groups that were acid etched. However, there was a significant difference in bond strength between these groups and the group that received only sandblasting (no acid etching). Thus, in this preliminary study, sandblasting does not appear to damage the enamel surface and can therefore be used as a substitute for polishing with pumice. It should be followed by acid etching to produce enamel surfaces with comparable bond strengths.

Comparison of Periotest values of integrated implants with and without healing abutments: a pilot study.

The role of the Periotest in the clinical evaluation of osseointegration has been well documented. Some clinicians have used the initial Periotest values at second-stage surgery as a baseline to measure changes in integration at the bone-implant interface over time. The purpose of this pilot study was to compare Periotest values made with and without healing abutments in place. A statistically significant difference was found between the Periotest values that were recorded with and without healing abutments, with the values without the healing abutments being more negative and suggestive of greater osseointegration.

Marginal leakage of combinations of glass-ionomer and composite resin restorations.

This study compared the microleakage of four different combinations of glass-ionomer and composite resin restorations. Forty class V cavities were prepared in permanent posterior teeth. The gingival margin of the cavities were placed in cementum and the occlusal wall in enamel. The cavities were restored as either 1) light-cured glass-ionomer cement (LC-GIC); 2) chemically cured glass-ionomer cement (CC-GIC); 3) composite resin (with dentin bonding agent); or 4) light-cured glass-ionomer and composite resin (sandwich). Marginal microleakage was assessed by methylene blue dye penetration after thermocycling between 5 degrees C and 60 degrees C for 300 cycles. Microleakage of LC-GIC restorations and the dentin-bonded composite resin restorations were significantly lower than the CC-GIC and the LC-GIC sandwich technique restorations. There was no significant difference in the microleakage between the LC-GIC and the dentin-bonded composite resin restorations. The degree of microleakage of the sandwich restorations was significantly lower than the CC-GIC restorations. Light-cured glass-ionomer and dentin bonded composite resin restorations exhibited a lower degree of leakage than the glass-ionomer/composite sandwich and chemically cured glass-ionomer restorations at the gingival margins of class V restorations.

The effect of matrix phase morphology on the structure of Ag-Cu-Pd dispersed phase dental amalgam.

The effect of an Ag-Cu-Pd dispersant alloy on the structure of amalgams fabricated with two different particle types of low-copper amalgam matrices was investigated. In amalgams L and L (0), a low-copper lathe-cut amalgam Aristalloy was used as the matrix. In amalgams S and S(0), the matrix used was Spheralloy, a low-copper spherical amalgam. X-ray diffraction was used to analyse the relative content of the phases in the amalgams. The presence of Pd in the dispersant of amalgams L and S resulted in a decrease in the amount of eta' (Cu6Sn5) and an increase in the amount of unreacted particles when compared to the controls L(0) and S(0). Amalgams fabricated with a spherical alloy matrix (S and S(0)) showed a greater effect than amalgams fabricated with a lathe-cut matrix alloy (L and L(0)).

An investigation of the Impac custom abutment for root form dental implants.

PURPOSE: This study measured the tensile force required to separate a custom implant abutment fixture that had been cast onto a machined component using the Impac custom abutment system (Vident, Baldwin Park, CA). The characteristics of the interface between the cast and machined components were also investigated by scanning electron microscopy x-ray and energy-dispersive (JEOL T330A, Peabody, MA) analysis (Kevex Delta Level I, San Carlos, CA). MATERIALS AND METHODS: A polycarbonate custom abutment component, attached to a gold alloy component of the abutment, was invested in a phosphate-bonded investment and cast in a type III gold alloy (Argenco, Argen Precious Metals, San Diego, CA). Eight samples were cast after a burn-out of 900 degrees F and 13 samples were cast after a burn-out at 1300 degrees F. The abutment components were pulled in tension in a universal Testing Machine (Instron 4204, Canton, MA) until failure. The interface of as-cast and failed samples were examined by electron microscopy. RESULTS: Samples burned out at 1300 degrees F failed at a mean force of 2477 +/- 295 N (545 +/- 65 lb), and samples burned out at 900 degrees F failed at a mean force of 2182 +/- 91 N (484 +/- 20 lb). Electron microscopy of the interface between the cast and machined components showed retentive tags provided in the design of the machined components. There was also a zone of diffusion between components shown by a zone of void formation within the casting. Failure occurred at the interface of the cast and machined components for all samples. CONCLUSION: The cast component was retained by a combination of mechanical and chemical mechanisms.

Fracture toughness of high alumina core dental ceramics: the effect of water and artificial saliva.

The fracture toughnesses of two high alumina core ceramics were determined by using the single edge notched specimen method. Measurements were made in air, water, and artificial saliva. Fracture toughnesses of 1.89 and 1.75 MPa.m1/2 were obtained for Cerestore and Vitadur N samples, respectively, tested in air. Values obtained from Vitadur N samples that were tested in deionized water were significantly lower than those that were measured in air. Values for samples of both ceramics that were tested in artificial saliva were not significantly different from those that were tested in air. The fracture mode was a combination of intergranular and transgranular for Cerestore and predominantly transgranular for Vitadur N.

Softening patterns of post-cure heat-treated dental composites.

The softening of post-cure, heat-treated dental composites in various solutions was evaluated by Knoop hardness measurements. The samples were heated at 120 degrees C for 7 min immediately after curing and immersed in various solutions, water, ethanol, heptane and 0.1 N NaOH. Significant increases in hardness were observed for heated samples when compared to unheated samples. The various solutions softened both heated and unheated composites but heated samples were softened to a lesser degree. Plots of hardness of heated and unheated samples were nearly parallel, indicating that mechanisms such as penetration of the resin matrix, degradation of the silane coupling agent and fillers may be involved in the softening of both heated and unheated composites. Post-cure heat treatment improved the resistance to softening of dental composites.