A randomised trial comparing the antibacterial effects of dentine primers against bacteria in natural root caries.

As people are living longer and retaining their teeth into old age, root caries is an increasingly significant problem. A minimally invasive treatment strategy, involving sealing the root caries lesion with an antibacterial resin sealant, could be highly beneficial. The aim of this study was to compare the antibacterial properties of the primers of two proprietary dentine bonding agents, Clearfil SE Bond (SE; Kuraray Medical, Japan) and Clearfil Protect Bond (PB; Kuraray Medical), which contains the antibacterial monomer methacryloyloxydodecylpyridinium bromide. Fifty-two root caries lesions were identified and randomly assigned to a primer. The lesion was cleaned, isolated, sampled with a sharp spoon excavator, a primer applied and a second sample taken. Samples were transported in fastidious anaerobe broth, vortex-dispersed and serial dilutions inoculated onto selective agars. Reduction in colony-forming units (CFU, %) after primer application was calculated for both primers for bacterial growth on each selective agar and compared to a hypothesised mean of 100% (one-sample t test, p < 0.05). No significant differences between primers were seen, indicating efficient bacterial elimination by both materials. Comparing percent reduction between SE and PB for each agar (Mann-Whitney test, p < 0.05), a significantly greater CFU reduction by PB was seen for streptococci but not other bacteria. More lesions exhibited bacterial growth and several lesions demonstrated marked bacterial growth after treatment with SE compared with PB. Therefore, PB appears to exhibit superior antimicrobial properties, particularly against streptococci. Both primers are highly antibacterial towards root caries bacteria and may therefore be suitable for minimally invasive treatment.

Smart materials in dentistry.

Most dental materials are designed to have a relatively 'neutral' existence in the mouth. It is considered that if they are 'passive' and do not react with the oral environment they will be more stable and have a greater durability. At the same time, it is hoped that our materials will be well accepted and will cause neither harm nor injury. This is an entirely negative approach to material tolerance and biocompatibility and hides the possibility that some positive gains can be achieved by using materials which behave in a more dynamic fashion in the environment in which they are placed. An example of materials which have potential for 'dynamic' behaviour exists with structures which are partly water-based or have phases or zones with significant water content and for which the water within the material can react to changes in the ambient conditions. Such materials may even be said to have the potential for 'smart' behaviour, i.e. they can react to changes in the environment to bring about advantageous changes in properties, either within the material itself or in the material-tooth complex. The controlled movement of water or aqueous media through the material may cause changes in dimensions, may be the carrier for various dissolved species, and may influence the potential for the formation of biofilms at the surface. Some of these issues may be closely interrelated. Clearly, materials which do not have the capacity for water transport or storage do not have the potential for this sort of behaviour. Some materials which are normally resistant to the healthy oral environment can undergo controlled degradation at low pH in order to release ions which may prove beneficial or protective. It is doubtful whether such behaviour should be classified as 'smart' because the material cannot readily return to its original condition when the stimulus is removed. Other materials, such as certain alloys, having no means of transporting water through their structure, can display smart behaviour by undergoing predictable changes in structure in response to applied mechanical or thermal stimuli. It has been difficult to harness such behaviour to the benefit of patients but progress in this area is slowly being made.

Rheological properties of veneer trial pastes relevant to clinical success.

INTRODUCTION: The porcelain veneer is a relatively conservative means of improving the appearance of teeth. As these restorations are usually highly visible it is essential to gain the approval of the patient before final cementation takes place. As a result a variety of trial pastes are available that match the shades of the resins that are used ultimately to finally cement the veneer in place. Such restorations, by virtue of their small size and fragility, are difficult to handle and position. It is therefore important that the application of trial paste does not impede placement and retention upon the tooth surface at try in whilst the patient assesses its appearance. OBJECTIVE: To determine the rheological properties of three makes of trial pastes (Calibra - Dentsply Caulk, USA; Nexus - Kerr, USA; Rely X - 3M Espe, USA) and assess if temperature affected these. Design In vitro rheological measurement. METHOD: For each product the rheological properties of three shades were determined at both 25 degrees C and 35 degrees C three times. Measurements of both the Initial Yield Stress and Shear Rate Index were undertaken using a controlled stress rheometer (Carri-med, Dorking, UK) in flow mode with a cone-and-plate test configuration. RESULTS: One way analyses of variance of the initial yield and shear rate index for each shade of material at 25 and 35 degrees C demonstrated no significant effects of temperature with the exception of the initial yield of Nexus (P = 0.0024) where the yield stress of the white shade was significantly (P <0.01) higher at 35 degrees C than at 25 degrees C. In all cases the yield stress for Nexus was of the order of ten times higher than the other materials. All materials demonstrated pseudoplastic behaviour. CONCLUSIONS: The variation in yield stress displayed by the materials will affect the handling of veneers and offers a potentially useful choice parameter to the clinician as to which paste bests suits their requirements.

Quantitative determination of radio-opacity: equivalence of digital and film X-ray systems.

OBJECTIVES: To evaluate the equivalence of a digital X-ray system (DenOptix) to conventional X-ray film in terms of the measured radio-opacity of known filled-resin materials and the suitability of attenuation coefficient for radio-opacity determination. METHODS: Discs of five thicknesses (0.5-2.5mm) and step-wedges of each of three composite materials of nominal aluminum-equivalence of 50%, 200% and 450% were used. X-ray images of a set of discs (or step-wedge), an aluminum step-wedge, and a lead block were taken at 65 kV and 10 mA at a focus-film distance of 400 mm for 0.15s and 1.6s using an X-ray film or imaging plate. Radio-opacity was determined as equivalent aluminum thickness and attenuation coefficient. The logarithm of the individual optical density or gray scale value, corrected for background, was plotted against thickness, and the attenuation coefficient determined from the slope. The method of ISO 4049 was used for equivalent aluminum thickness. RESULTS: The equivalent aluminum thickness method is not suitable for materials of low radio-opacity, while the attenuation coefficient method could be used for all without difficulty. The digital system gave attenuation coefficients of greater precision than did film, but the use of automatic gain control (AGC) distorted the outcome unusably. CONCLUSION: Attenuation coefficient is a more precise and generally applicable approach to the determination of radio-opacity. The digital system was equivalent to film but with less noise. The use of AGC is inappropriate for such determinations.

Effects of temperature on the fluoride release and recharging ability of glass ionomers.

This study investigated the effects of environmental temperature on the fluoride release and recharging ability of glass ionomers. Five disk specimens (15 mm in diameter and 1 mm thick) were made of each of the following materials: a conventional luting glass ionomer, two high viscosity restorative glass ionomers and a restorative resin-modified glass ionomer. The fluoride release of each material was measured at 4 degrees C, 37 degrees C and 55 degrees C. An additional three groups, which were made of the same materials, were stored in distilled and deionized water for 30 days and recharged in 250 ppm fluoride solution at 4 degrees C, 37 degrees C and 55 degrees C for five minutes. The fluoride re-release was measured daily from two days prior to two days after the recharging process. At all temperatures, the luting glass ionomers showed the greatest fluoride release and recharging ability, followed by the resin-modified glass ionomer, then the high viscosity glass ionomers. For each material, the fluoride release increased with increasing temperature and all glass ionomers showed greater recharging ability at higher temperatures. An increase in environmental temperature increased both the fluoride release and recharging of the glass ionomers. This may be important in developing regimes for improving the delivery of topical fluoride products.

Recording surface detail on moist surfaces with elastomeric impression materials.

The objective was to assess the ability to accurately record detail on moist surfaces for three elastomeric impression materials derived from different polymers. One polyvinylsiloxane, one polyether and one hybrid material containing a copolymer of siloxane and polyether polymers were used. Impressions were recorded of moist gypsum casts having both a shallow (approximately 20 microm) and deep (approximately 180 microm) groove reproduced on their surface. The grooves in the casts and in the impressions were profiled using a non-contacting laser profilometer Comparisons were made between the groove depths in the casts and impressions (paired t-test). The results indicated that all of the tested materials accurately recorded dimensions in the x-y plane. However, there was evidence that the polyether and hybrid materials were more accurate than the polyvinylsiloxane in recording the true depths of the deep grooves (z plane) under moist conditions. It was concluded that the more hydrophilic nature of the polyether and hybrid materials enabled them to record more accurate impressions of moist surfaces, particularly in areas of difficult access as modelled by the deep grooves.

A comparison of the aspirating abilities of re-usable and partly disposable dental cartridge syringes in vitro.

OBJECTIVES: To compare the ability of re-usable and partly disposable dental cartridge syringes to aspirate in vitro. METHODS: A laboratory investigation comparing two re-usable (Astra and Rotor) and one partly disposable (Ultra Safety-plus) dental cartridge syringes. Forces needed to move the cartridge plunger and forces required to produce aspiration of Bonney's Blue dye were measured using an Instron testing machine. RESULTS: There were significant differences in the forces needed to produce aspiration in the different systems (F = 194, p<0.001). The Astra system needed the least force to produce aspiration. The forces required to aspirate in the Rotor and Ultra Safety-plus systems did not differ. Each system aspirated effectively in vitro at the initial aspiration manoeuvre. The forces available for subsequent aspiration attempts varied with the speed of cartridge plunger movement. The volume of local anaesthetic cartridge used did not affect the force needed to produce aspiration in the Ultra Safety-plus syringe. The method of testing free-flow of solution through the needle affected the force generated at subsequent plunger movements. CONCLUSIONS: The re-usable and partly disposable syringes investigated aspirated effectively at the initial aspiration manoeuvre. The force available to produce aspiration at subsequent attempts varies with the speed of injection. The method of testing free-flow of solution through the needle in a loaded syringe affects the force available at the first aspiration manoeuvre.

Salivary contamination and bond strength of glass-ionomers to dentin.

This study evaluated the effect of salivary contamination on the shear bond strength of two highly viscous glass ionomer cements (Fuji IX GP Fast and Ketac-Molar Maxicap) to conditioned dentin and assessed the effect of cleaning the contaminated field prior to bonding. The buccal surfaces of 90 human molars and premolars were ground to expose dentin and the teeth were then set in resin. The specimens were divided into two groups for each material, then further subdivided into three groups of 15 teeth each: Group 1--uncontaminated (control), Group 2--dentin contaminated with saliva, Group 3--dentin contaminated, washed and air dried. The specimens were made by bonding the test material to dentin using a 4 mm diameter gelatin capsule. All specimens were protected with varnish and placed in distilled water at 37 degrees C for seven days prior to measuring bond strength in shear. Fractured surfaces were examined visually and by using SEM to assess mode of failure. There were no significant differences in mean shear bond strength among the three test groups for either material (ANOVA). However, shear bond strength of Fuji IX to dentin was significantly greater than Ketac-Molar (p=0.019) for all groups. Weibull analysis showed that contaminated (Group 2) specimens had a greater probability of failure at low stresses. Modes of failure were mostly cohesive for Fuji IX and adhesive/cohesive for Ketac-Molar. In conclusion, salivary contamination did not affect the mean shear bond strength of Fuji IX GP Fast and Ketac-Molar Maxicap to conditioned dentin; however, it increased the probability of failure at low stresses.

Endodontic complications after plastic restorations in general practice.

AIM: To test the hypothesis that dentine and pulp protection by conditioning-and-sealing is no less effective than using a conventional calcium hydroxide lining. METHODOLOGY: A cohort of healthy adults requiring a new or replacement restoration in a posterior tooth was recruited in six general practices. All procedures received local Ethics Committee approval. Exclusion criteria included signs and symptoms of pulp necrosis or inflammation, and patients unable to commit to a long-term trial. Cavity preparations were randomized to receive a calcium hydroxide lining or conditioning-and-sealing with a smear-removing bonding system. Choice of bulk restorative material (composite resin or amalgam) was at the discretion of the dentist. The key outcome measure was evidence of pulpal breakdown identified at unscheduled (emergency) or scheduled recall examinations. Postoperative sensitivity was recorded on 100 mm VAS at 24 h, 4 days and 7 days. Pulp status was assessed at 6, 12, 24 and 36 month recall, and at any emergency recall appointment. The relationship between pre-treatment and treatment variables and pulp breakdown was assessed by logistic regression (P = 0.05). RESULTS: A total of 602 teeth were recruited, with comparable numbers of cavities lined (288, 47.8%) or conditioned and sealed (314, 52.2%). The majority (492, 81.7%) were replacement restorations, and amalgam was the most common bulk restorative material (377, 62.6%). A total of 390 (64.8%) restored teeth were reviewed at 6 months, 307 (51%) at 12 months, 363 (60.3%) at 24 months, and 279 (46.3%) at 36 months post-restoration. Sixteen cases of pulp breakdown were identified within 36 months of restoration placement, 11 presenting as emergencies and five detected at routine recall examination. Logistic regression showed that preoperative pain, cavity treatment by lining or conditioning-and-sealing and the use of rubber dam isolation had no association with pulp breakdown. Pulp breakdown was associated with deep or pulpally exposed cavities (P < 0.001, odds ratio 7.8) and with composite rather than amalgam restorations (P = 0.001, odds ratio 2.13). Re-coding to identify teeth with pulp exposures revealed that pulpal exposure was the key determinant of adverse pulp outcomes (P < 0.0001, odds ratio 28.4) and that composite resin restorations were again more likely to be associated with pulp breakdown than amalgam (P = 0.017, odds ratio 3.92). CONCLUSIONS: Considered within the context of routine primary dental care: Dentists can be confident that pulps will be equally well protected from post-restorative breakdown up to 36 months by calcium hydroxide lining and conditioning-and-sealing with adhesive resins. Residual dentine thickness appears to be a key determinant of pulp responses after restorative dental treatment. In deep and pulpally exposed cavities in posterior teeth, composites were associated with more pulpal breakdown than amalgams.

Viscoelasticity of dental tissue conditioners during the sol-gel transition.

Formation of tissue conditioners is a process of polymer chain entanglements. This study evaluated the influence of composition and structure on dynamic viscoelasticity of concentrated polymer solutions based on poly(ethyl methacrylate) (PEMA) used as tissue conditioners through the sol-gel transition. The hypothesis was that the ethanol content is the most influential factor in determining gelation speed. Rheological parameters were determined with the use of a controlled-stress rheometer. Analysis of variance by orthogonal array L(16)(4(5)) indicated that the strong polar bonding of ethanol (contribution ratio rho = 53.8%; confirming the hypothesis) and molecular weight of polymer powders (rho = 26.7%) had a greater influence on the gelation times of PEMA-based systems than did the molar volume of plasticizers (rho = 9.0%) and concentration of polymers (i.e., powder/liquid ratio) (rho = 4.5%). The results suggest that the gelation of tissue conditioners based on PEMA can be controlled over a wide range by varying the polymer molecular weight, and especially ethanol content.

An ex vivo investigation to compare orthodontic bonding using a 4-META-based adhesive or a composite adhesive to acid-etched and sandblasted enamel.

OBJECTIVE: This study investigates the shear-peel orthodontic bond strengths of brackets bonded with an unfilled acrylic resin containing 4-META (MCP Bond or a no-mix composite adhesive (Right On) to acid-etched or sandblasted enamel. DESIGN: Ex vivo. MATERIALS AND METHODS: Eighty human pre-molar teeth were separated into four equal groups, according to the adhesive used and method of enamel pre-treatment. Group I-Right On with enamel etched using phosphoric acid for 30 seconds. Group II-Right On with enamel sandblasted using 50- microm alumina particles at 80 psi for 3 seconds. Group III-MCP Bond with enamel etched using phosphoric acid for 30 seconds. Group IV-MCP Bond with enamel sandblasted using 50- microm alumina particles at 80 psi for 3 seconds. Subsequently, the specimens were stored in distilled water for 24 hours prior to bond strength testing using an Instron universal testing machine. Each debonded tooth was scored using the adhesive remnant index (ARI) to determine the site of bond failure. RESULTS: The mean bond strength (1 SD) were Group I: 10.7 (2.7) MPa, Group II: 5.3 (1.3) MPa, Group III: 15.9 (3.4) MPa, Group IV: 15.0 (2.2) MPa. Statistical analysis using one-way analysis of variance and Tukey test found no statistical difference between Group III and Group IV (P > 0.05), but the other groups were statistically different from each other (P < 0.05). The data were found to fit the Weibull distribution and Weibull analysis showed stress required for a 5 per cent probability of failure was: Group I: 5.77 MPa; Group II: 3.32 MPa; Group III: 10.31 MPa; Group IV: 10.58 MPa. Chi-square test showed a statistically significant difference existed between the ARI scores (P < 0.001), principally through less adhesive remnants being observed on the sandblasted specimens. CONCLUSION: The adhesive containing 4-META achieved significantly higher bond strengths than the composite adhesive, particularly in the case of sandblasted enamel.

Relationship between enamel etch characteristics and resin-enamel bond strength.

OBJECTIVES: The aim of the study was to investigate the relationship between etch patterns produced on surface enamel by phosphoric acid and the corresponding bond strengths achieved. MATERIALS AND METHODS: Twenty-eight patients had the buccal surface of their teeth etched and replicated for examination under the scanning electron microscope, at the commencement of orthodontic treatment. Histometry was employed to assess the nature and quality of etch patterns using a four-point scale. Twenty of each tooth type (total of 240), were collected and A Company pre-adjusted orthodontic brackets, bonded using Transbond light-cured orthodontic adhesive according to the manufacturer's instructions and 24-hour bond strength testing was undertaken. The Adhesive Remnant Index (ARI) was recorded for the tooth and bracket surface for all specimens. RESULTS: The type of etch was not significantly affected by the side (left or right) of the mouth assessed (p = 0.532). Overall, there was no significant difference between etch types for upper and lower teeth (p = 0.218); however, there were significant differences between specific teeth in the upper and lower arch. The greatest amount of Type A etch (well-defined etched enamel prisms) was found on the lower incisors, yet in all cases this 'ideal' etch was found to occupy less than 5% of the etched buccal surface enamel. The greatest area of etched enamel surface was occupied by Type C (etched but enamel prisms not evident). The mean bond strength values varied significantly between different tooth types, with the lowest bond strength found on the upper first molar(6.5MPa) and the highest on the lower first molar (13.1 MPa). CONCLUSIONS: An ideal etch pattern is not essential in order to produce a strong bond.

Dynamic viscoelasticity of soft liners and masticatory function.

Soft denture liners are used for edentulous patients to cushion functional forces. We hypothesized that the application of soft liners having viscoelastic properties would lead to the most marked improvement in masticatory function. The shear storage modulus (G'), shear loss modulus (G''), and loss tangent (tan delta) were determined for 6 materials by means of a dynamic viscoelastometer. Masticatory function of ten subjects was evaluated by measurements of maximum bite forces and chewing times and frequencies for 2 food samples, and by the use of visual analogue scales. The acrylic materials exhibited viscoelastic behavior, while the silicones exhibited elastic behavior. The improvement in masticatory function compared with hard resin was found to be in the order: acrylic permanent materials > silicone > acrylic temporary materials. The results suggest that the use of materials with higher tan delta and G' provides the most optimum masticatory function for patients requiring the provision of soft liners on their dentures.

Treatment of dentin with polyacrylic acid--a retrospective observational study of the effect upon the durability of glass ionomer restorations.

This paper reports on the results of a material specific, retrospective observational study. It sought to determine the consequence of pretreatment of cavity margins with the conventional glass polyalkenoate Chemfil II prior to restoration with Tooth Cleanser on restoration durability. All restorations were placed and varnished by senior dental students under the supervision of a staff member. Manufacturer recommendations were followed. Data on each restoration was collected and entered into a relational computer database. Data included details of cavity morphology and the use or non-use of Tooth Cleanser. Six years following the study start a manual search of all records was carried out to determine, for those patients continuing to attend the Dental Hospital, the number of failed and surviving restorations. This yielded a dataset of 149 restorations, of which 41 had been placed with the aid of Tooth Cleanser and 108 without. The number of failed restorations was 20 and 62, respectively. Survival analysis by the Kaplan-Meier method revealed median survival times of 2,094 days, when Tooth Cleanser was used and 1,748 days when not. Although 80% survival times of 1111.0 (SE = 6.3) (With Tooth Cleanser) and 285.0 (SE = 3.8) (Without Tooth Cleanser) days were observed, together with a Hazard Ratio of 1.49 (95% Confidence Intervals 0.92 & 2.31), a Logrank test revealed no statistically significant difference between the survival curves (p = 0.12). It was concluded that although there was a trend for the application of Tooth Cleanser to improve the chances of obtaining a dependable restoration, this effect was not statistically significant.

The bonding of composite resin to moist enamel.

OBJECTIVE: To determine the effect on the bond strength of modern dentine bonding agents to etched enamel of surface contamination with water. DESIGN: Fifteen bond strength measurements were made for bonds prepared to both moist and dry etched enamel for each of three test and one control materials. RESULTS: For two materials (Scotchbond 1 and Prime and Bond 2.1) the bond strength was not affected by the presence of water on the etched enamel surface. A mean bond strength in excess of 25 MPa was achieved for both materials under all conditions. One material (Optibond Solo) showed a 30% increase in bond strength when bonds were formed under wet condition (21.10 MPa compared with 15.35 MPa). The bond strength of the control material, a conventional unfilled bonding resin, decreased markedly with aqueous contamination (9.14 MPa compared with 26.75 MPa). CONCLUSION: Etched enamel should be rehydrated routinely prior to bonding composite resin to its surface using a water displacing dentine bonding system.

Suitability of a shear punch test for dental restorative materials.

OBJECTIVE: The aim of the study was to evaluate the suitability of a shear punch test for determining the mechanical properties of dental restorative materials. The method was evaluated by measuring and comparing the shear punch strength of seven different restorative materials, that is amalgam, composite resin, compomer, composite containing pre-reacted glass ionomer filler, resin modified glass ionomer, glass ionomer and polycarboxylate cement. METHOD: The effects of specimen restraining conditions, specimen thickness and test speed on the shear punch strength were evaluated using polycarboxylate cement and two different equipment set-ups. Using the preferred testing regime as determined in the preliminary experiments, the shear punch strength of seven different materials were measured and compared. Twenty disc specimens, 0.5mm thick and 10mm diameter, were prepared for each material, restrained within the test equipment and tested at a speed of 1.0mm/min. RESULTS: The shear punch strength increased as the torque used for restraining a specimen was increased. There was no difference in shear punch strength for specimens of different thickness. The greatest shear punch strength was obtained at the test speed of 1.0mm/min. The shear punch strength values decreased in the order composite>composite containing pre-reacted glass ionomer filler>amalgam>compomer>resin-modified glass ionomer>glass ionomer>polycarboxylate. A difference in the shear punch strength for seven different kinds of restorative materials clearly emerged. Specimen fracture occurred by circumferential cracking for the shear-punch test. However, for some glass ionomer and amalgam specimens radial cracking was also observed. SIGNIFICANCE: This study suggests that the simple test described is suitable for standardization purposes.

Effect of mixing methods on the compressive strength of glass ionomer cements.

OBJECTIVE: The purpose of the study was to evaluate the effect of the mixing method on the compressive strength and porosity of dental glass ionomer cements. METHOD: Five glass ionomer cements were chosen for use in the study. Two were hand mixed and three were encapsulated. The latter were mixed either by shaking or rotating. Following mixing by rotation some samples were centrifuged before use. The 24h compressive strength was determined for each cement/mixing regime combination and fracture surfaces were examined using SEM. RESULTS: The mixing method had a significant effect on compressive strength (P<0.05). For the luting/lining cement, hand mixing produced a significantly greater compressive strength (P<0.05). For the restorative cement, there were only small differences between specimens mixed by different methods and hand mixing gave a significantly lower compressive strength than mixing by rotation followed by centrifuging (P<0.05). Porosity was incorporated in all samples and low values of compressive strength were associated with larger pores. SIGNIFICANCE: The strength of glass ionomer cements is affected by incorporated porosity and this is dependent on the method of mixing. For some cements hand mixing is favoured in order to reduce porosity and increase strength but this is not generally applicable to all cements.

Degree of conversion of composites measured by DTA and FTIR.

OBJECTIVE: Differential thermal analysis (DTA) using a split fiber optic light source has been reported to be a convenient method of measuring the degree of conversion (DC) of light-activated composites. The purpose of this study was to compare the results by DTA and Fourier transformation infrared spectroscopy (FTIR), and evaluate the usefulness of the DTA method. METHODS: Experimental 2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane-based composites containing SiO2 filler and various amounts of triethyleneglycol dimethacrylate (TEGDMA) were prepared, and the DC of each composite was determined by DTA or FTIR with 60s irradiation. The DC of three proprietary composites containing hybrid filler or prepolymerized resin filler were also measured by both methods with 20 or 60s irradiation. The results were analyzed by ANOVA and Fisher's protected least significant difference test. RESULTS: By both DTA and FTIR, the DC of experimental composites increased as the proportion of TEGDMA increased, although DTA showed 3-10% greater values (p<0.05) than FTIR. For proprietary composites that contain hybrid filler, the values by DTA were not significantly different from those by FTIR at 20s exposure. Longer irradiation time resulted in greater DC (p<0.05) for both methods, and DTA showed 5-7% greater values than FTIR. However, the DC of the composite containing prepolymerized resin filler was 30% less by FTIR than by DTA, possibly due to the influence of unpolymerized species in the filler. SIGNIFICANCE: The DC values determined by DTA and FTIR showed good agreement for most materials including model composites. In addition, DTA may be more useful than FTIR to measure the DC of composites containing prepolymerized resin filler.

Bond strength to surface enamel for different tooth types.

OBJECTIVES: Fixed appliance therapy in orthodontics relies on the effective bonding of brackets to surface enamel. Bracket de-bonding during treatment is both inconvenient and costly to both dentist and patient. Factors which control the efficacy of the bond are not fully understood. For example, there has never been a study to determine the efficacy of bonding to different teeth in the dentition. The aim of this study was to investigate the possible differences in bond strength to acid etched enamel on the different teeth of the dentition. METHODS: Two hundred and forty extracted sound human teeth were collected from white Caucasian subjects between the age of 10 and 22 years. Approximately 20 teeth of each tooth type were bonded using a standard acid etch technique with 'A company' stainless steel brackets using a light cured composite (Transbond, 3M Unitek). Shear bond strength (24 h) was measured using an Instron testing machine. RESULTS: Tooth type was found to have a significant effect on bond strength (p<0.001). The greatest mean bond strength was found on the lower first molar teeth, and the lowest on the upper first molar teeth. In the upper arch, bond strength was greater on anterior teeth than posterior teeth (p<0.001). In the lower arch bond strength was weaker on anterior teeth than posterior teeth (p<0.001). SIGNIFICANCE: The results have profound implications for bond strength testing of dental composites to enamel as well as to the expectations of bond reliability in orthodontic therapy. The findings suggest that, in order to achieve meaningful comparisons, enamel bond strength measurements should be made using the same tooth type, or that appropriate stratification of groups of test teeth should be used. These findings may also explain, in part, variability in enamel bonding efficacy despite the best efforts of the dental practitioner.

Quantitative measurements of edge-to-face aromatic interactions by using chemical double-mutant cycles.

Synthetic H-bonded zipper complexes have been used to quantify the magnitude of an edge-to-face aromatic interaction between a benzoyl group and an aniline ring. Four chemical double-mutant cycles were constructed by using a matrix of nine closely related complexes in which the aromatic rings were sequentially substituted for alkyl substituents. The stability constants and three-dimensional structures of the complexes were determined by using 1H NMR titrations in deuterochloroform at room temperature. The value of the interaction energy is similar in all cases, the average is -1.4 +/- 0.5 kJ mol(-1). The scope and limitations of the double-mutant approach are explored, and the consequences of conformational equilibria are discussed.