Efficacy and persistence of tooth bleaching using a diode laser with three different treatment regimens.

STATEMENT OF PROBLEM: Studies have measured the effectiveness of tooth bleaching, however there are very few studies that have measured the persistence in color change after a 6-month follow-up. PURPOSE: This study assessed the efficacy of the laser bleaching process using different regimens, and the persistence of color change over a 6-month period. METHOD AND MATERIALS: Sixty patients divided into three equal groups were subjected to bleaching using a diode laser with 34% hydrogen peroxide. Group 1: patients subjected to one session of laser bleaching. Group 2: patients subjected to two sessions of laser bleaching with a 1-week interval. Group 3: the same as Group 2 but followed by home bleaching once a month for 3 months. The color was assessed four times: before bleaching, directly after bleaching, 3 months after bleaching, and 6 months after bleaching. RESULTS: All teeth had a significant color change at 6 months, but all teeth had regressed from the maximum value. There was significantly less regression in color for Group 3, followed by Groups 2 and 1, respectively. CONCLUSION: The combined technique of in-office laser bleaching for two sessions with a 1-week interval, followed by home bleaching once a month for 3 months gave more persistence in color change. CLINICAL SIGNIFICANCE: In-office power bleaching using a laser assisted hydrogen peroxide system repeated after a week, combined with home bleaching once a month for 3 months, is an effective bleaching regimen with less color regression after 6 months compared to a regimen of in-office bleaching alone.

Variables related to materials and preparing for bond strength testing irrespective of the test protocol.

INTRODUCTION: Resin bonding can be compared to making a sandwich with the tooth on one side and the restoration on the other, a layer of bonding resin is applied to either side and a filled resin (composite) placed in between. This presentation considers factors that influence the restoration side of the sandwich and various ways that the assembled testpieces may be "aged" prior to testing. The materials to be bonded may be either ceramic, metal or composite formed by methods such as casting, pressing, sintering or machining. The fabrication method determines the susceptibility of the bonding surface to physical or chemical modification. The treatment of the surface prior to bonding can be physical (e.g. sandblasting) or chemical (e.g. metal primer); but is more likely to be a combination (e.g. silica deposition+silane). PREPARATION OF THE BONDING SURFACE: Successful bonding depends on establishing a surface with a high population of unreacted vinyl groups (-CC) that can then be cross-polymerized to the resin in the bonding composite. The physical approach has involved etching or sandblasting the surfaces; but the ability to form a microretentive surface in this way depends on a heterogeneous surface. Noble metals and modern high strength ceramics have a more homogeneous surface and are not easily etched. To overcome this problem a number of ways to deposit a silica layer on the bonding surface have been developed: the Silicoater that involves baking on a silica layer, the Rocatec technique (CoJet) that involves air blasting silica onto the surface in conjunction with an abrasive; and two more modern approaches: sol-gel evaporation and molecular vapor deposition (MVD). All these techniques require the subsequent application of a silane layer to provide the -CC moieties. The use of primers without an intervening silica layer has been tested and found to be successful with some specialized bonding systems that contain agents such as methacryloyloxydecyldihydrogen-phosphate (MDP) (PanaviaEX). AGING OF TESTPIECES PRIOR TO BONDING: The most common type of aging is storage in water at temperatures from ambient to 100 degrees Celsius. This generally decreases bond strengths; but not to catastrophic values. A more exacting pre-test regime is thermal cycling. In some studies this caused a slightly greater reduction in bond strength than storage in water; but in other tests it resulted in total failure. As some testpieces have spontaneously debonded during thermal cycling, it seems sensible to include TC in any screening test of new materials. Mechanical cycling (fatigue) prior to testing has a very significant effect and the bond strength that can withstand 1,000,000 cycles can be one sixth of the bond strength in a simple monotonic test (tensile, shear or compression). Whereas simple monotonic tests provide a blunt instrument for eliminating poorly performing techniques their use for discriminating between established techniques is open to discussion.

Inadvertent injection of sodium hypochlorite into the periradicular tissues during root canal treatment.

This paper describes a sodium hypochlorite (NaOCl) incident occurring during routine endodontic treatment of a patient who presented with chronic periapical periodontitis of a maxillary canine tooth and discusses the immediate and late treatment of this case.

Comparison of Shear Bond Strength, Fatigue Limit and Fatigue Life in resin-bonded metal to enamel bonds.

OBJECTIVE: To compare the Shear Bond Strength (SBS) of resin-bonded metal/enamel bonds with the Fatigue Limit and Fatigue Life of identical joints. METHODS: 285 discs of Ni/Cr-alloy (dia 5 mmx4 mm) were cast and treated by either (1) Sandblasting with aluminium oxide or (2) Sandblast+15 min electrolyticetch in HCl. The discs were bonded to etched enamel (37% HPO4/30 s) using 3 bonding systems. Ten discs of each group were subjected to a shear bond test (SBT) in a Universal Testing Machine5 (CHS=50 mm/min). Seventeen discs of each group were used to determine the Fatigue Limit using the Staircase method (5000 cycles, 4 kg increment). Further batches of 10 discs were subjected to cyclic loads of either 5, 10, or 20 kg to determine the number of cycles at failure (Fatigue Life). The SBS and Fatigue Limit results were compared by correlation analysis. The Fatigue-Life cycles were compared by Weibull analysis to determine the beta (reliability) and alpha (number of cycles) coefficients for the 3 loads. RESULTS: For all materials and treatments, the Fatigue-Limit results were much lower than the SBS and there was no correlation between the values (r=0.49, p=0.18). The Fatigue Limit for the samples using 5000 cycles ranged from 10.7 to 16.1 MPa. In the Fatigue-Life study, the stress at which the samples were reliably able to withstand more than 1 million cycles (beta>5) was 2.5 MPa. CONCLUSION: The Fatigue Limit of the bonds was much lower than the SBS and there was no correlation between the two values. In this study the Fatigue Limit was not a good predictor of the long term Fatigue-Life failure of the specimens.

Bonding of composite to water aged composite with surface treatments.

OBJECTIVE: The purpose of this study was to determine the shear bond strength of new composite to water aged composite with and without interfacial surface treatment. METHODS: Two hundred and eighty cylindrical samples were prepared for each of three resin composites (Spectrum, Dentsply; Durafill, Kulzer; Herculite, Kerr). Seventy samples of each material were bonded immediately and the remaining were stored in water. After 1, 4 and 12 weeks 70 samples were removed and the surface treated prior to bonding a second fresh increment. The treatments were: (1) no treatment, (2) abrasion with pumice, (3) a layer of Prime and Bond (Dentsply), (4) abrasion+Prime and Bond, (5) a layer of Optibond Solo Plus (Kerr), (6) abrasion+Optibond and (7) a layer of bis-GMA/TEGDMA. The specimens were loaded to failure in shear mode with a crosshead speed of 50 mm/min until fracture. The fracture surface of a number of specimens were examined in a scanning electron microscope. RESULTS: At all time intervals the treatment that resulted in the highest bond strengths (>20 MPa) was treatment with the dentine bonding agents (DBS) Prime and Bond or Optibond Solobond Plus. No treatment or abrasion alone resulted in very low bond strengths even after 1 week in water. When used in conjunction with DBS's abrasion did not increase the bond strength over the use of the DBS alone. The bis-GMA/TEGDMA was not as effective as the DBS's. SIGNIFICANCE: When bonding new composite to composite that has been underwater it is essential to treat the original composite surface. The results of this study indicated that the application of a dentine bonding agent significantly enhanced the bond. Abrasion alone did not produce an adequate bond.

Thermal conductivity through various restorative lining materials.

OBJECTIVES: Traditional teaching has advocated the placement of insulating materials under restorations to protect against 'thermal shock'. Often this involves placement of a thick zinc-oxide eugenol cement lining. The purpose of this in vitro study was to assess the heat transfer through four lining materials and dentine and to relate these findings to the temperature exposures that may be experienced in the oral environment. METHODS: Two 'traditional' linings, zinc oxide eugenol cement (ZNOE) and calcium hydroxide paste (CAOH), and two more contemporary materials, a resin modified glass polyalkenoate (RMGP) and dentine bonding system (DBS) were studied in addition to dentine itself. Seven samples of each material were tested by utilising a Lees' Disc apparatus. Incorporation of thermocouples allowed heat transfer through the sample to be recorded. Thermal conductivity (J/m/s/ degrees C) was calculated for individual samples and a mean value obtained for each material. One way ANOVA and post hoc Tukey's tests were applied to the data obtained. RESULTS: In ascending order of thermal conductivity, DBS

The measurement of degradation and wear of three glass ionomers following peroxide bleaching.

OBJECTIVES: To investigate, for three glass ionomer dental materials, the effects of a hydrogen peroxide solution on the elution of key elements, and the effects of a novel 6% hydrogen peroxide tooth whitening gel on subsequent wear rates with a toothpaste slurry. METHODS: Discs specimens of three glass ionomers (ChemFlex, Fuji II and Ketac-Fil) were prepared. One set of discs was exposed to either 6% hydrogen peroxide in phosphate buffer, phosphate buffer, water, a carbonated beverage or 38% orthophosphoric acid for 60 min. The ions eluted from the discs were determined by inductively coupled plasma-optical emmision spectroscopy. A second set of discs were conditioned with either a 6% hydrogen peroxide gel (30 min), water (30 min), a carbonated beverage (2 min) or 38% orthophosphoric acid gel (2 min) followed by a three-body abrasive wear treatment (2 min) with a toothpaste slurry. Changes in height of the samples were measured with a digital comparitor. The conditioning and abrasive cycles were repeated thirteen times. RESULTS: For the elution study, the solutions gave only minor release of sodium except orthophosphoric acid which showed increased elution levels of aluminium, silicon and sodium ions. For the wear study, the orthophosphoric acid gave the highest level of wear whilst for the other treatments there were no statistical significant differences in the level of wear (one-way ANOVA). CONCLUSIONS: A 6% hydrogen peroxide solution did not cause significant dissolution, and a novel 6% hydrogen peroxide tooth whitening gel did not significantly increase the three-body wear rate of any of the materials tested.

The recharge of esthetic dental restorative materials with fluoride in vitro-two years' results.

OBJECTIVES: A range of esthetic restorative dental materials are now available to dental clinicians. The aim of this study was to evaluate the relative fluoride recharge potential of a number of these materials in vitro over two years. METHODS: Disc samples (12 mm x 2 mm) of each of the materials were placed into artificial saliva at neutral pH. The materials tested were: two glass ionomers (Chemfil; Ketac-Fil), two resin-modified glass ionomers (Photac-Fil Aplicap; Vitremer), two compomers (Dyract; Compoglass) and two composites (Heliomolar; Concise). At 13 intervals over a two years period the discs were subjected to a 2 min fluoride recharge by exposure to sodium fluoride (500 ppm F). The pre- and post-recharge fluoride release values were determined using an ion sensitive electrode. RESULTS: At all time intervals the post-recharge fluoride release of the materials was significantly different (MANOVA p<0.0001). The mean values for post-recharge fluoride release after two years were: Chemfil 10.3, Ketac 3.0, Vitremer 9.0, Photac-Fil Aplicap 12.1, Compoglass 5.0, Dyract 3.6, Concise 0.3, Heliomolar 0.2 (units = microgF/cm(2)/h). SIGNIFICANCE: Esthetic fillings vary significantly in their capacity to absorb and re-release fluoride. The glass ionomer-based materials displayed a far greater potential for fluoride recharge than the composites, in which the recharge was virtually negligible. Whilst it cannot be assumed that fluoride release is directly proportional to cariostatic potential, these results suggest that, where possible, glass ionomer-based materials should be used in patients who have a high caries rate.