Micromorphology of Root Canal Walls After Laser Activated Irrigation

This study aims to investigate the effects of laser-activated irrigation on root canal dentin using different laser wavelengths. Sixty-six roots were prepared and split longitudinally. First, lasers with different power settings were tested on 34 samples, pre-etched with phosphoric acid, or remaining with a smear-layer to determine the test parameters. Selected parameters were then applied on thirty roots (9 groups) covered with smear layer: 1. Smear-layer removed; 2. Smear-layer untouched; 3. Conventional needle irrigation with NaOCl and EDTA; 4. ER:YAG laser; 5. 9.3 μm CO₂ laser; 6-9. Diode lasers. All lasers were applied in ultra-pure water as an irrigant. Root halves were examined by scanning electron microscope to analyze the intracanal dentin micromorphology on 9 consequent photos per specimen @ a magnification of 1000X. The results showed that conventional needle irrigation was effective in removing the smear-layer from coronal and middle root parts, while laser-activated irrigation had two main mechanisms: cleaning and opening of the dentinal tubules by removing the smear layer (Er:YAG laser) and melting of dentin (CO₂ and diode lasers) in all root parts. The study concluded that laseractivated irrigation with different wavelengths impacted the smear layer and root canal dentin differently through pure physical/mechanical effects.

Restoration of Severely Damaged Endodontically Treated Premolars: Influence of the Ferrule Effect on Marginal Integrity and Fracture Load of Resin Nano-ceramic CAD-CAM Endocrowns

OBJECTIVES

To explore the ferrule effect on Resin Nano-Ceramic (RNC) premolar endocrown marginal integrity and fracture resistance.

METHODS

Thirty-six root-canal-treated premolars were cut 2 mm above the cemento-enamel junction (CEJ). They were restored with standardized RNC computer-aided design/computer-aided manufacturing (CAD/CAM) restorations (Lava Ultimate, 3M Oral Care, St. Paul, MN, USA) and divided into three groups (n=12): endocrowns with a 3-mm endo-core (Group 1), endocrowns with a 3-mm endo-core and a 2-mm ferrule (Group 2), and conventional post-and-core crowns with a 2-mm ferrule (Group 3). All specimens were submitted to thermo-mechanical cycling loading (TMCL) (1.7 Hz, 49 N, 600 000 cycles, 1500 thermocycles). Margins were analyzed before and after the TMCL. In the second part of the experiment, the surviving specimens were submitted to unidirectional monotonic loading until fracture. Fragments were then analyzed using scanning electron microscopy (SEM) and the fracture mode was established.

RESULTS

Endocrowns of Groups 1 and 2 performed better than conventional crowns (Group 3) in terms of marginal continuity. Differences in fracture load values within all groups were not statistically significant. Most of the specimens fractured in a non-repairable way.

CONCLUSIONS

The present test failed to provide evidence of any kind of difference between endocrowns with and without a ferrule in terms of load-bearing capacity and marginal integrity after fatigue. Further studies are needed to confirm the role of the ferrule in adhesive restorations of endodontically treated teeth.

Caries Detection with Near-Infrared Transillumination Using Deep Learning

Dental caries is the most prevalent chronic condition worldwide. Early detection can significantly improve treatment outcomes and reduce the need for invasive procedures. Recently, near-infrared transillumination (TI) imaging has been shown to be effective for the detection of early stage lesions. In this work, we present a deep learning model for the automated detection and localization of dental lesions in TI images. Our method is based on a convolutional neural network (CNN) trained on a semantic segmentation task. We use various strategies to mitigate issues related to training data scarcity, class imbalance, and overfitting. With only 185 training samples, our model achieved an overall mean intersection-over-union (IOU) score of 72.7% on a 5-class segmentation task and specifically an IOU score of 49.5% and 49.0% for proximal and occlusal carious lesions, respectively. In addition, we constructed a simplified task, in which regions of interest were evaluated for the binary presence or absence of carious lesions. For this task, our model achieved an area under the receiver operating characteristic curve of 83.6% and 85.6% for occlusal and proximal lesions, respectively. Our work demonstrates that a deep learning approach for the analysis of dental images holds promise for increasing the speed and accuracy of caries detection, supporting the diagnoses of dental practitioners, and improving patient outcomes.

Correction to: Color stability of different composite resins after polishing

In the original publication of the article, the author's name "Prof. René Daher" was inadvertently missed in the author group. This has been updated in this erratum. Also, the original article has been corrected.

Intra-pulpal and subsurface temperature rise during tooth irradiation with 808 nm diode laser: an in vitro study

AIM

This in vitro study evaluated the pulpal and subsurface temperatures during proximal tooth surface irradiation with different settings of an 808 nm diode laser.

MATERIALS AND METHODS

The elevation of pulpal and subsurface temperature during irradiation was measured using thermocouples positioned in the centre of the pulp chamber (n=30) and in the centre of a prepared 1.5 mm deep coronal cavity (n=30). Each sample was irradiated 3 times within one-week interval using different exposure settings. A temperature increase of 3.5°C was regarded as critical value for pulpal heath. Results were analysed with one-way ANOVA and Duncan post hoc tests. Micromorphological investigation by digital microscopy was carried out for the irradiated and non-irradiated tooth surface. RESULTS Measurable temperature increase within the pulp chamber (delta PT) and the subsurface (delta ST) were observed with all laser settings tested. The highest recorded delta PT and delta ST were 3.1°C and 8.5°C, respectively. Delivery mode, beam diameter, and exposure time influenced the temperature rise. No alterations on the enamel surface were observed when inspected by the digital microscope after undergoing irradiation with the tested parameters. Cconclusion: From the thermal point of view, under the conditions of the present study the application of an 808 nm diode laser on the outer surface of the tooth at 1W in the continuous mode and at 5W in the pulsed mode for two cycles of 30 s each proved to be safe.

In Vitro Evaluation of Marginal Adaptation of Direct Class II Composite Restorations Made of Different “Low-Shrinkage” Systems

The present study evaluated the influence of various low-shrinkage restorative systems in class II direct composite restorations following simulated occlusal loading. Forty MOD class II cavities were prepared on freshly extracted human lower third molars with proximal margins located mesially 1.0 mm coronal to and distally 1 mm apical to the cementoenamel junction. The samples were randomly distributed into five experimental groups corresponding to the following restorative systems: a conventional resin composite (Tetric) as active control group, a low-shrinkage composite (Extra Low Shrinkage [ELS]) alone or combined with its corresponding flowable version (ELSflow) used as a 1- to 1.5-mm liner, a bulk-filling flowable composite (Surefil SDR) covered by a 1-mm layer of restorative composite (Ceram-X), and a restorative bulk-filling composite (SonicFill). All specimens were submitted to 1,000,000 cycles with a 100N eccentric load into saline. Tooth restoration margins were analyzed semiquantitatively by scanning electron microscopy before and after loading. The percentage of perfect adaptation to enamel varied from 94.15% (SonicFill) to 100% (ELS) before loading and from 69.22% (SonicFill) to 93.61% (ELS and ELSflow) after loading. Continuous adaptation to cervical dentin varied from 22.9% (Tetric) to 79.48% (SDR/Ceram-X) before loading and from 18.66% (Tetric) to 56.84% (SDR/Ceram-X) after loading. SDR/CeramX and SonicFill showed the best cervical dentin adaptation.

The effect of a fiber reinforced cavity configuration on load bearing capacity and failure mode of endodontically treated molars restored with CAD/CAM resin composite overlay restorations

OBJECTIVES

To evaluate the fracture strength and the mode of failure of endodontically treated molars restored with CAD/CAM overlays with fiber reinforced composite build-up of the pulp chamber.

METHODS

40 Devitalized molars were cut over the CEJ and divided into five groups (n=8). The pulp chamber area was filled with: group 0 (control), no resin build-up; group 1, hybrid composite build-up (G-aenial posterior, GC); group 2, as in group 1 but covered with 3 nets of bi-directional E-glass fibers (EverStickNET, Stick Tech Ltd.); group 3, a FRC resin (EverX posterior, GC); group 4, as in group 3 but covered by the bi-directional fibers. The crowns were restored with CAD-CAM composite restorations (Lava Ultimate, 3M ESPE). Maximum fracture loads were recorded in Newton and data were analyzed using Kruskal-Wallis test (p<0.05). Fragments were analyzed using SEM.

RESULTS

The mean static loads in Newton were: group 0: 2448 (546); group 1: 2817 (873); group 2: 2128 (952); group 3: 2429 (1091); group 4: 2577 (833). No significant differences were found between the groups (p>0.05). All specimens fractured in a catastrophic way, under the CEJ. The main crack evolved in the corono-apical direction. In groups 2 and 4 secondary fracture paths with apico-coronal direction were detected close to the bi-directional fibers' layer.

CONCLUSIONS

For the restoration of endodontically treated molars, the incorporation of FRCs did not influence the load-bearing capacity of the tooth-restoration complex. The SEM analysis showed a low ability of the bi-directional fibers net in deviating the fracture but this effect was not sufficient to lead more favorable fracture patterns, over the CEJ.

CLINICAL SIGNIFICANCE

The use of FRCs to reinforce the "core" of devitalized molars against vertical fractures under static loads seems useless when the thickness of the CAD/CAM composite overlay restoration is high.

Immediate endodontic access cavity sealing: fundamentals of a new restorative technique

Endodontic access cavity sealing is conventionally performed after endodontic irrigation, referred to as delayed endodontic sealing (DES). Evidence shows that endodontic irrigation with NaOCl decreases dentinal bond quality and could cause coronal leakage. Access cavity sealing before endodontic irrigation is a new restorative approach, referred to as immediate endodontic sealing (IES). The primary aim of this in vitro study was to investigate whether IES improved internal adaptation. The secondary aim was to investigate the influence of the viscosity of the composite used to seal the dentine, on the internal adaptation in both IES and DES groups. Third molars (n= 40) with fully developed apices were used. The teeth were prepared into standard Class II MO cavities, and divided in 4 groups according to the approach, and composite viscosity was used for sealing. Group 1: IES + low viscosity composite; group 2: IES + high viscosity composite; group 3: DES + low viscosity composite; and group 4: DES + high viscosity composite. Samples were then sectioned axially for observation using scanning electron microscopy. Outcome was evaluated by determining the internal adaptation of the samples, which was judged based on the percentage of a continuous margin at the tooth-composite interface. The results were analyzed using a two-way analysis of variance and Mann-Whitney test. IES groups exhibited significantly greater internal adaptation (p = 0.000) as compared with DES groups. Composite viscosity did not significantly affect internal adaptation in either IES or DES groups (p > 0.005).

Micro-CT evaluation of cavities prepared with with different Er:YAG handpieces

AIM

The aim of the study was to compare several cavity shapes after application using different handpieces and tips of Er:YAG laser.

MATERIALS AND METHODS

Firstly, this in vitro investigation was performed on two upper molars. Their crowns were cut horizontally underneath the occlusal fissures in order to obtain a flat dentin surface. Afterwards, minimal cavities were prepared by using an Er:YAG laser device with a variety of handpieces and tips (Kavo KEY Laser Plus). All cavities were prepared using the following parameters: 250 mJ and 10 Hz during 30s, and were scanned using Micro-CT. Secondly, thirteen caries-free, human upper molars were prepared according to the same protocol. Five cavities were prepared on each tooth, using five different tips and the same laser settings as step one. The cavities' depths were measured with a digital micrometer. The width and morphology were controlled under scanning electron microscope (SEM).

RESULTS

Noticeable differences in the dimensions of the cavities were observed, even if the same laser parameters were used for all preparations. Two main shapes were registered: triangle and rectangle.

CONCLUSION

None of the cavities presented an adhesive configuration, rounded shape often found in hidden caries; they were straighter (rectangle) or focusing (triangle). For the moment, there is no ideal Er:YAG laser handpiece/tip in order to prepare conservative adhesive cavity.

Composite vs Ceramic Computer-aided Design/Computer-assisted Manufacturing Crowns in Endodontically Treated Teeth: Analysis of Marginal Adaptation

Objectives

To compare the marginal adaptation between ceramic and composite CEREC crowns in endodontically treated teeth restored with endocrowns or with a short or a long post.

Methodology

Forty-eight intact maxillary incisors were used. After endodontic treatment, the crowns were sectioned 2 mm coronally to the cemento-enamel junction, which provided a ferrule of 2 mm. The prepared teeth were divided randomly into six groups (n=8). Group 1 was restored with a large fiberglass post, composite core, and ceramic full-coverage computer-aided design/computer-assisted manufacturing (CAD-CAM) crown. Group 2 was restored with a short fiberglass post, composite core, and ceramic full-coverage CAD-CAM crown. Group 3 was restored with a large fiberglass post, composite core, and composite full-coverage CAD-CAM crown (LPCpr). Group 4 was restored with a short fiberglass post, composite core, and composite full-coverage CAD-CAM crown (SPCpr). Groups 5 and 6 were restored with ceramic and composite CEREC machined endocrowns, respectively (EndoCer and EndoCpr). The restored teeth were loaded thermomechanically in a computer-controlled chewing machine. Impressions of each restoration were made in a polyvinylsiloxane material before and after loading. Gold-coated epoxy replicas were prepared for scanning electron microscopy examination at 200× magnification.

Results

Loading had a statistically significant effect (p&lt;0.05) on the percentage of “continuous margin” in all groups. The LPCpr, SPCpr, and EndoCpr groups showed the highest percentage of continuous margin initially and after loading. The effect of the different post lengths on marginal adaptation was not significant (p&gt;0.05).

Conclusion

CAD-CAM crowns fabricated from millable composite resin blocks (Paradigm MZ100) offer a superior option to all-ceramic crowns (IPS Empress CAD).

Understanding MIH: definition, epidemiology, differential diagnosis and new treatment guidelines

Molar-Incisor Hypomineralisation (MIH) is a congenital disease which increases in prevalence. It affects permanent first molars and, often to a lesser degree, permanent incisors with variable severity. The aetiology is unknown, but different hypotheses have been advanced. Differential diagnosis is mandatory not to confound MIH with other diseases. Treatment consists in a minimally invasive approach by reinforcing and protecting the existing dental structure. In more severe cases, restorative treatment may be indicated.

In Vitro Performance of Class I and II Composite Restorations: A Literature review on Nondestructive Laboratory Trials—Part II

A literature review was conducted on adhesive Class I and II restorations and nondestructive in vitro tests using the PubMed/Medline database for the 1995-2010 period. The first part of this review has presented and critically appraised selected literature dealing with the quality and in vitro behavior of adhesive Class II restorations using photoelasticity, finite element analysis, and microleakage study protocols. This second part reviews additional parameters, which are deformation and fracture resistance to cyclic loading, shrinkage stress and tooth deformation following restoration placement, bond strength (microtensile, tensile, and shear tests), and marginal and internal adaptation. In addition, a “relevance score” has been proposed that aims to classify the different study protocols according, firstly, to the resulting quality, quantity, and consistency of the evidence and then, secondly, to their potential clinical relevance, as estimated by their ability to simulate oral and biomechanical strains. The highest clinical relevance was attributed to marginal and internal adaptation studies, following cyclic loading in a moist environement. However, a combination of in vitro protocols will have an even greater predictive potential and has to be considered as a crucial preclinical research approach with which to investigate the numerous restorative configurations that cannot be efficiently and rapidly tested in vivo.

In Vitro Performance of Class I and II Composite Restorations: A Literature Review on Nondestructive Laboratory Trials—Part I

Posterior adhesive restorations are a basic procedure in general dental practices, but their application remains poorly standardized as a result of the number of available options. An abundant number of study hypotheses corresponding to almost unlimited combinations of preparation techniques, adhesive procedures, restorative options, and materials have been described in the literature and submitted to various evaluation protocols. A literature review was thus conducted on adhesive Class I and II restorations and nondestructive in vitro tests using the PubMed/Medline database for the 1995-2010 period. The first part of this review discusses the selected literature related to photoelasticity, finite element analysis (FEM), and microleakage protocols. Based on the aforementioned evaluation methods, the following parameters proved influential: cavity dimensions and design, activation mode (light or chemical), type of curing light, layering technique, and composite structure or physical characteristics. Photoelasticity has various limitations and has been largely (and advantageously) replaced by the FEM technique. The results of microleakage studies proved to be highly inconsistent, and the further use of this technique should be strictly limited. Other study protocols for adhesive Class II restorations were also reviewed and will be addressed in part II of this article, together with a tentative relevance hierarchy of selected in vitro methods.

Cutting and coagulation during intraoral soft tissue surgery using Er: YAG laser

AIM

To find the optimal techniques and parameters that enables Er:YAG laser to be used successfully for small intraoral soft tissue interventions, in respect to its cutting and coagulation abilities.

CASE REPORT

In vitro pre-tests: 4 different Er:YAG laser units and one CO2 unit as the control were used for incision and coagulation on porcine lower jaws and optimal parameters were established for each type of intervention and each laser unit: energy, frequency, type, pulse duration and distance.

CASE SERIES

3 different types of intervention using Er:YAG units are presented: crown lengthening, gingivoplasty and maxillary labial frenectomy with parameters found in the in vitro pre-tests.

RESULTS

The results showed a great decrease of the EMG activity of masseter and anterior temporalis muscles. Moreover, the height and width of the chewing cycles in the frontal plane increased after therapy.

CONCLUSION

Er:YAG is able to provide good cutting and coagulation effects on soft tissues. Specific parameters have to be defined for each laser unit in order to obtain the desired effect. Reduced or absent water spray, defocused light beam, local anaesthesia and the most effective use of long pulses are methods to obtain optimal coagulation and bleeding control.

Marginal adaptation of direct class II composite restorations with different cavity liners

The aim of this study was to evaluate how cavity linings with different elastic modulus can influence the marginal adaptation (MA) of Class II composite restorations before and after thermo-mechanical loading.

MATERIALS AND METHODS

Forty Class II cavities with margins extending 1 mm below the cement-enamel junction were prepared in extracted human third molars. In each group except the control group, a lining material of 1-mm thickness was applied to the bottom of the cavity and polymerized before placing the resin composite Herculite XRV Ultra (group A: control; group B: Premise Flowable lining; group C: Herculite XRV Ultra lining; and group D: Optibond FL lining). MA was evaluated (with a scanning electron microscope) before and after loading (200,000 loading cycles). Statistical analysis was done using the Shapiro-Wilks test, the analysis of variance test, and Duncan post hoc test at p<0.05.

RESULTS

Before loading, the percentages of continuous margins in dentin were superior (p<0.05) for groups C and D (71.1% and 87.2%, respectively) compared to groups A and B (55.7% and 48.3%, respectively). After loading, group D (79.8%) was statistically superior in dentin compared to all of the other groups (43.6%, 35.9%, and 54.4%, respectively). In occlusal enamel, no significant difference was found between groups. The percentage of enamel fractures and the percentage of noncontinuous margins in proximal enamel were high, with no significant difference between liners. It can be concluded that for the materials used in this study, a 1-mm-thick lining with an extremely low elastic modulus (2-3 GPa) could redistribute shrinkage stress. The use of a flowable composite did not significantly improve MA.

Amelogenesis Imperfecta: A Conservative and Progressive Adhesive Treatment Concept

Objective

The aim of this study was to present a case report of a patient affected by amelogenesis imperfecta showing a possible minimal and conservative adhesive treatment approach.

Clinical Procedure

A treatment philosophy of amelogenesis imperfecta is illustrated by means of a case report of a 14-year-old boy who consulted us for a full mouth rehabilitation.

Discussion

This clinical report describes step by step how to manage a case of amelogenesis imperfecta from childhood over time.

Significance

This kind of minimally invasive, progressive approach allows the conservation of maximum tooth substance together with an acceptable esthetic outcome.

Caries diagnosis using light fluorescence devices: VistaProof and DIAGNOdent

The modern concept of minimally invasive dentistry encompasses early detection of incipient carious lesions and their treatment. Due to the low sensitivity of visual inspection and radiography in the detection of occlusal hidden carious lesions under a macroscopically sound surface, several devices have been developed to increase detection accuracy. DIAGNOdent is one of the tools used for that purpose and VistaProof is a new device recently introduced into the market. They both use light fluorescence to detect incipient carious lesions. DIAGNOdent is based on the fact that carious lesions show higher level of fluorescence than sound tissues when excited by light at specific wavelength. Vistaproof is based on the same principle, but it uses a different wavelength of excitation than DIAGNOdent and a video camera for the detection of fluorescence. The aim of this article was to compare these two devices and present their clinical use.

Fiber-reinforced resin coating for endocrown preparations: a technical report

Coronal rehabilitation of endodontically treated posterior teeth is still a controversial issue. Although the use of classical crowns supported by radicular metal posts remains widespread in dentistry, their invasiveness has been largely criticized. New materials and therapeutic options based entirely on adhesion are available nowadays, from direct composite resins to indirect endocrowns. They allow for a more conservative, faster, and less expensive dental treatment. However, the absence of a metal or high-strength ceramic substructure as in full-crown restorations can expose this kind of restoration to a higher risk of irreversible fracture in case of crack propagation. The aim of this case report is to present a technique to reinforce the cavity of an endodontically treated tooth by incorporating a fiber-reinforced composite (FRC) layer into the resin coating of the tooth preparation, before the final impressions of the cavity. This technique allows the use of FRCs in combination with any kind of restorative material for an adhesive overlay/endocrown.

A combined chemo-mechanical approach for aesthetic management of superficial enamel defects

OBJECTIVE

The aim of this article is to describe an easy technique for managing small superficial defects in light to medium fluorosis.

METHOD AND MATERIALS

The proposed technique is based on a selective abrasion of the superficial enamel and a recreation of the superficial macro and micro morphology. The aesthetic appearance can be enhanced by power or home bleaching.

RESULTS

The presented technique can manage enamel defects which are confined in the most external enamel surface with satisfying aesthetic results.

CONCLUSIONS

This conservative approach may be considered an interesting alternative to more invasive prosthetic techniques based on composite reconstructions or ceramic veneers, minimising invasivity, chairside time and costs for patients.

Modulary effects of oxytocin and carbetocin on stress-induced changes in rat behavior in the open-field

Oxytocin (OXY) has been shown to attenuate some of the physiological and behavioral alterations appearing in stressed rats. Carbetocin (CBT), an oxytocin analog [deamino-1-monocarba-(2-O-methyltyrosine)-oxytocin], was designed to exert prolonged action. In the present study we investigated the impact of these peptides on the behavioral changes in rats exposed repeatedly to restraint stressors. Wistar male rats were exposed to restraint for 1 hour; saline or drugs were administered intraperitoneally immediately after stress termination. Recording of the exploratory activity in the open-field started 60 min later. To explore the possibility of persisting effects of stress and/or drugs, the procedure was repeated for three consecutive days. Restraint moderately suppressed locomotion and rearing, and increased grooming. OXY in 0.3 mg/kg dose showed a tendency to restore the suppressed exploratory activity. In contrast, 1 mg/kg dose potentiated the stress-induced behavioral deficit. Both OXY doses slightly increased grooming. CBT in the same two doses restored the stress-induced deficits in locomotion and rearing but did not influence grooming. The locomotor depression after 1 mg dose of OXY was found also in non-stressed rats in contrast to the increased activity after CBT. The data support the view that post-stress administered CBT exerts a significant effect on the stress-altered spontaneous behavior.

Proximal direct composite restorations and chairside CAD/CAM inlays: Marginal adaptation of a two-step self-etch adhesive with and without selective enamel conditioning

The aim of this study was to evaluate the marginal adaptation of CEREC ceramic inlays, CEREC composite inlays and direct composite restorations in unbeveled proximal slot cavities under artificial aging conditions. Two groups of each restoration type were prepared (n = 6), one group with a self-etch adhesive, the other group with H(3)PO(4) enamel etching before the self-etch adhesive application. Replicas were generated before and after long-term thermo-mechanical loading under dentinal fluid simulation and margins were evaluated at x200 magnification in the scanning electron miscroscope (SEM). Statistically, significant differences were found before and after loading with respect to the percentages of "continuous margins", the direct composite filling with H(3)PO(4) enamel etching giving the lowest percentages of "continuous margins" after loading (p < 0.05). The highest percentage of "continuous margin" was attained by composite inlays without H(3)PO(4) enamel etching. However, these results were not significantly different from ceramic inlays after stressing. Polymerization shrinkage is still one critical property of composite restorative materials. The marginal adaptation of indirect adhesive proximal slot restorations without enamel bevels both fabricated out of composite and ceramic is better than that of directly placed composite restorations.

Light curing time reduction: in vitro evaluation of new intensive light-emitting diode curing units

The aim of the present in vitro study was to establish the minimum necessary curing time to bond stainless steel brackets (Mini Diamond Twin) using new, intensive, light-emitting diode (LED) curing units. Seventy-five bovine primary incisors were divided into five equal groups. A standard light curing adhesive (Transbond XT) was used to bond the stainless steel brackets using different lamps and curing times. Two groups were bonded using an intensive LED curing lamp (Ortholux LED) for 5 and 10 seconds. Two more groups were bonded using another intensive LED curing device (Ultra-Lume LED 5) also for 5 and 10 seconds. Finally, a high-output halogen lamp (Optilux 501) was used for 40 seconds to bond the final group, which served as a positive control. All teeth were fixed in hard acrylic and stored for 24 hours in water at 37 degrees C. Shear bond strength (SBS) was measured using an Instron testing machine. Weibull distribution and analysis of variance were used to test for significant differences. The SBS values obtained were significantly different between groups (P < 0.001). When used for 10 seconds, the intensive LED curing units achieved sufficient SBS, comparable with the control. In contrast, 5 seconds resulted in significantly lower SBS. The adhesive remnant index (ARI) was not significantly affected.A curing time of 10 seconds was found to be sufficient to bond metallic brackets to incisors using intensive LED curing units. These new, comparatively inexpensive, curing lamps seem to be an advantageous alternative to conventional halogen lamps for bonding orthodontic brackets.

Comparative efficiency of plasma and halogen light sources on composite micro-hardness in different curing conditions

OBJECTIVES

Recent developments have led to the introduction of high power curing lights, which are claimed to greatly reduce the total curing time. This study evaluated the effectiveness of a plasma-curing device (Apollo 95 E) and a halogen device (Heliolux DLX), in different curing conditions.

METHOD

Vicker's micro-hardness values were performed on 1 and 2 mm thick composite discs cured in a natural tooth mold by direct irradiation or indirect irradiation through composite material (2 or 4 mm) and dental tissues (1 mm enamel or 2 mm enamel-dentin). Measures were, respectively, performed after a 1, 3, 6 s (SC, step curing mode) or 18 s (3xSC) exposure to the plasma light, and a 5, 10, 20 or 40 s exposure to the halogen light.

RESULTS

With the PAC light used, a 3 s irradiation in the direct curing condition was necessary to reach hardness values similar to those obtained after a 40 s exposure to the halogen light. Using the indirect curing condition, hardness values reached after an 18 s exposure (3xSC mode) with the plasma light were either equivalent or inferior to those obtained with 40 s halogen irradiation.

SIGNIFICANCE

Direct polymerization with the plasma light used requires longer exposure times than those initially proposed by the manufacturer. The effectiveness of plasma generated light was lowered by composite or natural tissues, and therefore requires an important increase in the irradiation time when applied to indirect polymerization. The practical advantage of this polymerization method is less than expected, when compared to traditional halogen curing.

Marginal and internal adaptation of stratified compomer-composite Class II restorations

Different approaches have been proposed to improve the adaptation of Class II restorations, including applying low-elasticity modulus base liners. This in vitro fatigue test (or study) evaluated the influence of the compomer base-lining configuration on restoration adaptation. Direct Class II MOD box-shaped composite restorations with or without base and lining (n=3x8) were placed on intact human third molars with proximal margins 1 mm above or under the CEJ. The compomer (Dyract) was applied as a 1 mm-thick lining or as a base, closing proximo-gingival margins. Marginal adaptation was assessed before and after each phase of mechanical loading (250,000 cycles at 50N, 250,000 cycles at 75N and 500,000 cycles at 100N); internal adaptation was evaluated after test completion. Gold-sputtered resin replicas were observed in the SEM and restoration quality evaluated in percentages of continuity (C) at the margins and within the internal interface after sample section. Mechanical loading did not influence adaptation to enamel, while it adversely affected restoration adaptation to dentin for the full composite and compomer-base restorations (C varied, respectively, from 95.2 to 75.3% and from 98.0 to 10.6%). The internal adaptation quality showed the same general trend, however, with reduced scores of continuity. In this experimental condition, application of a low elasticity modulus layer under the restorative material proved advantageous but the compomer should not contact the gingival margins.

Long-term cytotoxicity of resin-based dental restorative materials

Highly filled composites, Ormocers (organically modified ceramics) and 'smart' materials have been developed to overcome the polymerization shrinkage problems of conventional composite materials. The purpose of the current study was to investigate the effect of longer-term (up to 8 weeks) ageing of these resin-based dental restorative materials and determine the effect of post-curing on cytotoxicity. Twelve discs of each material (Colombus/IDR, Definite/Degussa, Ariston pHc/Vivadent) were either light-cured (Lc) or light-cured and post-cured (Pc). For cytotoxicity testing, the discs were placed in contact with cell culture medium (DMEM) and incubated at 37 degrees C. Extracts from composite materials were collected after 24 h and weekly over a time period of 8 weeks. Cytotoxicity of the eluates to cultured fibroblasts (Balb/c3T3) were measured by the succinic dehydrogenase (SDH) activity (MTT assay) and the results expressed in percentage of negative controls (Teflon discs). The results showed that ageing significantly influenced the cytotoxicity of the materials. Except for Ariston pHc, materials were less cytotoxic after 8 weeks of ageing than they were in early intervals and post-curing was not generally useful in reducing cytotoxicity. The Ariston pHc was initially moderately toxic, but then become highly cytotoxic for 5 weeks before returning to initial levels. The current study demonstrated the importance of assessing the cytotoxicity of resin composite materials at multiple times.

Microhardness of resin composites polymerized by plasma arc or conventional visible light curing

This study evaluated the effectiveness of the plasma arc curing (PAC) unit for composite curing. To compare its effectiveness with conventional quartz tungsten halogen (QTH) light curing units, the microhardness of two composites (Z100 and Tetric Ceram) that had been light cured by the PAC or QTH units, were compared according to the depth from the composite surface. In addition, linear polymerization shrinkage was compared using a custom-made linometer between composites which were light cured by PAC or QTH units. Measuring polymerization shrinkage for two resin composites (Z100 and Tetric Ceram) was performed after polymerization with either QTH or PAC units. In the case of curing with the PAC unit, the composite was light cured with Apollo 95E for two (Group 1), three (Group 2), six (Group 3) or 2 x 6 (Group 4) seconds. For light curing with the QTH unit, the composite was light cured for 60 seconds with Optilux 500 (Group 5). The linear polymerization shrinkage of composites was determined in the linometer. Two resin composites were used to measure microhardness. Two-mm thick samples were light cured for three seconds (Group 1), six seconds (Group 2) or 12 (2 x 6) seconds (Group 3) with Apollo 95E or they were conventionally light cured with Optilux 500 for 30 seconds (Group 4) or 60 seconds (Group 5). For 3 mm thick samples, the composites were light cured for six seconds (Group 1), 12 (2 x 6) seconds (Group 2) or 18 (3 x 6) seconds (Group 3) with Apollo 95E or they were conventionally light cured with Optilux 500 for 30 seconds (Group 4) or 60 seconds (Group 5). Twenty samples were assigned to each group. The microhardness of the upper and lower surfaces was measured with a Vickers hardness-measuring instrument under load. The difference in microhardness between the upper and lower surfaces in each group was analyzed by paired t-test. For the upper or lower surfaces, one-way ANOVA with Tukey was used. For Tetric Ceram, the amount of polymerization shrinkage was lower when cured with the Apollo 95E for two or three seconds than when cured for six and 12 (2 x 6) seconds, or for 60 seconds with Optilux 500 (p<0.05). For Z100, the amount of linear polymerization shrinkage was lower when cured with the Apollo 95E for two, three and six seconds than for 12 (2 x 6) seconds with Apollo 95E or for 60 seconds with the Optilux 500 (p<0.05). The results of the microhardness test indicated that there was no statistically significant difference in microhardness between groups for the upper surface. However, for the lower surface, when the composites were light cured with Apollo 95E for three seconds as recommended by the manufacturer, microhardness of the lower surface was usually lower than that of the upper surface and did not cure sufficiently. Conclusively, when compared with conventional QTH unit, the PAC unit, Apollo 95E did not properly cure the lower composite surface when the layer thickness exceeded 2 mm. In addition, three seconds of curing time, which the manufacturer recommended, was insufficient for optimal curing of composites.

Amalgam substitutes: a critical analysis

PURPOSE

Quality standards for restorations recently have been defined in Switzerland. Amalgam substitutes must meet restoration Grade 2 requirements (i.e., pulp and dental hard substance must be preserved, and both form and function of the tooth have to be reconstituted). The pertinent operative technique has to be simple and amalgam-like. A minimum service life of 8 years is required. This in vitro study investigated the clinical potential of several amalgam substitutes, taking into account the operative requirements, the defined restorative guidelines, and the required service life.

MATERIALS AND METHODS

Potential amalgam substitutes evaluated in this study included compomers (Compoglass, Dyract, Dyract AP, Elan, F 2000) and resin-based composites (Alert, Ariston, Definite, Nulite, Solitaire, Surefil). The composites Adaptic and Tetric Cream, using a simplified placement technique, were tested as negative and positive controls, respectively. Marginal adaptation and wear properties were measured in vitro in mixed Class II cavities. Relative radiopacity was measured in terms of millimeters of equivalent aluminum.

RESULTS

All compomers showed a radiopacity of 2.5 mm or more aluminum. Only Dyract AP and Elan were more wear resistant than amalgam. After stressing, the percentage of continuous margin was at best 31% overall and 17% in dentin only. Among resin-based composites, the minimum requirements of radiopacity were fulfilled only by Alert, Surefil, and Tetric. Only Definite, Surefil, Solitaire, and Tetric exhibited wear resistance greater than amalgam. After stressing, the best marginal qualities were 41% continuous margin overall, and 8% in dentin only.

New perspectives on dentin adhesion--differing methods of bonding

The advent of adhesive dentistry has had a dramatic effect on the practice of aesthetic dentistry, significantly expanding the range of treatment alternatives that clinicians can provide for their patients. Although adhesion is generally associated with the total bonding technique, adhesive systems can be applied in several different manners that include selective, separate, and secure bonding. It is the goal of this article to present the different bonding procedures, to explain the rationales behind each, and to formulate their indications.

Hardness of celluloid strip-finished or polished composite surfaces with time

STATEMENT OF PROBLEM

An in-vitro study revealed that a celluloid strip-finished composite surface discolored more than the polished composite surface. Thus, the celluloid strip-finished composite surface may not cure enough compared with the polished composite surface.

PURPOSE

This study tested the hypothesis that the celluloid strip-finished composite surface did not cure enough compared with the polished composite surface.

METHODS AND MATERIAL

The composite was placed in a 1.5-mm thick aluminum mold and the upper surface was covered with a celluloid strip. Composite was light cured for 60 seconds, then a layer of approximately 200 microm thick was ground away from the lower surface and polished. The hardness of the upper composite surface that was polymerized under a celluloid strip and the polished lower surface were measured with Vickers hardness measuring instrument 15 minutes, 6 hours, and 6 days after light curing. The hardnesses of polished and celluloid strip-finished surfaces were compared using a paired t test. One-way ANOVA and Tukey was used for tests for the significant differences in hardnesses between 15 minutes, 6 hours, and 6 days after light curing for a given surface.

RESULTS

Microhardness of the celluloid strip-finished composite surface was 380.6 N/mm(2) at 15 minutes, 442.5 N/mm(2) at 6 hours, and 519.2 N/mm(2) at 6 days after light curing. Microhardnesses of the polished composite surface was 476.6 N/mm(2) at 15 minutes, 511.7 N/mm(2) at 6 hours, and 535.0 N/mm(2) at 6 days after light curing. The hardness of the celluloid strip-opposed composite surface was significantly lower than that of the polished surface 15 minutes and 6 hours after light curing (P <. 001). There was no difference in hardness between the celluloid strip-opposed surface and the polished surface on the sixth day.

CONCLUSION

The hardness of the celluloid strip-opposed composite surface was lower than that of the polished surface at 15 minutes and at 6 hours after light curing. However, there was no difference in microhardness in 6 days.

Resin composites in the post-amalgam age

Resin-based composites are now being used as either amalgam substitutes or amalgam alternatives for the direct placement of box-shaped, stress-bearing restorations in posterior teeth. The expected longevity of these restorations is 8 years. With amalgam substitutes, preservation of enamel and dentin and restoration of tooth form and function must be warranted for the full length of the envisaged service life. In addition, with amalgam alternatives, the restoration must be, and must remain, imperceptible at a normal talking distance. The limiting factor with amalgam substitutes is the elevated risk of secondary caries, which is a result of the marginal openings that are unavoidably associated with the nature of the operative technique. Restorations in permanent teeth using amalgam substitutes most likely fail in some critical aspect of the Swiss Dental Society quality guidelines. With amalgam alternatives, the high cost and the demanding operative technique remain the main criticisms. However, amalgam alternatives, if they are placed using a sophisticated operative technique resulting in perfectly adapted restorations, meet the high expectations outlined in the Swiss Dental Society quality guidelines and fit the clinical concept of the post-amalgam age.

Consistency in the amount of linear polymerization shrinkage in syringe-type composites

OBJECTIVES

The purpose of this study was to investigate whether the composite resin in a syringe showed a consistent shrinkage through its content. Additionally, the amount of linear shrinkage was compared between materials.

METHODS

Five brands of syringe-type and one brand of carpule-type composite resins were used in this study. To each brand, two to three syringes were assigned. In the carpule-type composite, 15 carpules were used. The linear polymerization shrinkage was measured using a custom-made linometer. In this linometer, the amount of displacement of an aluminum disk, which was caused by the linear shrinkage of composite resin, was recorded by a computer every second for 90 s.

RESULTS

The syringe-type composites showed similar consistencies in the amount of linear shrinkage except one. The linear shrinkage of the carpule-type Tetric Ceram showed more consistency compared with syringe-type composites. The amount of linear polymerization shrinkage varied between materials.

SIGNIFICANCE

This investigation demonstrates that the use of carpule-type composites is recommended instead of syringe-types, because of the consistency in its linear shrinkage. The custom-made linometer provides an effective way to study polymerization shrinkage.

The ultrastructure of a compomer adhesive interface in enamel and dentin, and its marginal adaptation under dentinal fluid as compared to that of a composite

OBJECTIVES

To visualise the ultrastructure of the interface of SCA compomer adhesive and of Optibond composite adhesive in enamel and dentin, and to relate the findings to the marginal adaptation of these two products in mixed class V restorations.

METHODS

The ultrastructure was investigated using a scanning electron microscope (SEM) with and without prior argon ion etching, an environmental SEM, a field emission SEM, a confocal laser scanning microscope, and a transmission electron microscope. The marginal adaptation was quantified in mixed class V restorations by using the replica technique and a SEM under simulated dentinal fluid before and after simultaneous mechanical and thermal loading.

RESULTS

The ultrastructure of the compomer adhesive interface differed from those of the composite. However, no significant difference was discerned as regards the percentage of "continuous margin" in the enamel marginal area before loading, and in the dentin area before and after loading (p < 0.05; unpaired t-test). Only after loading, the percentage of "continuous margin" in enamel was significantly (p < 0.05; unpaired t-test) better than that of the compomer.

SIGNIFICANCE

The results indicated that the ultrastructure of the adhesive interface allowed no clear conclusions to be drawn as to the quality of marginal adaptation.

Resin composite polishing--filling the gaps

OBJECTIVE

The search for the ideal polishing agent for resin composite materials is still ongoing. A new polishing brush with abrasive bristles for polishing resin-based restorations was tested to determine if it polishes restorations, including those with concave surfaces, macrostructured occlusal surfaces, and textured surfaces, without destroying their delicate texture or microstructure.

METHOD AND MATERIALS

The polishing effectiveness and the ultimate destructive potential of these brushes were assessed quantitatively and subjectively in vitro. In addition, the durability of the brushes after repeated use and autoclaving was also evaluated.

RESULTS

The brushes were nondestructive to resin-based restorative, enamel, dentin, and the restoration interface. They produced a shiny surface on resin-based restorative materials without destroying the surface texture. The abrasive brushes were autoclavable and demonstrated satisfactory durability, despite multiple heat sterilization cycles.

CONCLUSION

These brushes can be considered to be key products to polish concave surfaces, anatomically shaped occlusal surfaces, and textured surfaces without damaging the surface characteristics.