Surrounding Tooth Structure Research Articles

Release of contraction stress of dental resin composites by water sorption

Polymerization shrinkage of bonded resin composite restorations will result in the development of curing contraction stresses during setting and can cause debonding of the restoration or failure of the surrounding tooth structure. However, the hygroscopic expansion that occurs after exposure of the restorative to the wet oral environment can compensate for this shrinkage. ObjectivesThe purpose of this study was to determine the hygroscopic expansion of six commercial resin composites and relate it to their composition, mechanical properties, shrinkage, and contraction stress development. MethodsShort-term volumetric shrinkage and contraction stress of the different composites were measured by mercury dilatometry and a universal testing machine. The long-term contraction stress was measured by the deflection of a bilayer strip of metal and a resin composite, which were stored dry as well as wet to determine the effect of hygroscopic expansion. The curvature of the strip was measured by profilometry over a period of 3 months. ResultsThe curvature of the strip correlated well (r2 =0.74) with the initial contraction stress, showing that the contraction stress is an important factor in initial deformation. The water sorption in all specimens showed that the initial deformation, within 2–4 weeks after curing, was completely counteracted. A high correlation (r2 =0.90) between deflection and relative water sorption was found, where the relative water sorption is defined as the absolute water sorption corrected for the inorganic filler volume of the composite. SignificanceWithin a period of 2–4 weeks after curing most of the curing contraction stresses of resin composite restoratives will be released by hygroscopic expansion.

Visual and Instrumental Color Match Evaluation of Single Shade Composites before and after Bleaching Procedures: A Pilot Study

Background: One of the major challenges in restorative dentistry is to obtain an adequate color match between composite restorations and the surrounding tooth. This match depends on several chromatic variables related to the composite itself but also to the teeth. Bleaching procedures are not to be able to modify the shade of composite restorations to a lighter color as it does on natural teeth. Objective: The objective of this study is to evaluate the visual and instrumental color match of two single-shade resin-based composites in human-extracted teeth before and after bleaching treatment. Methods: Six extracted human posterior sound teeth were used. Round-shaped V-class cavities (2x2x4mm) were prepared buccally 2mm away from the CEJ. Two single-shade resin composites (OM-Omnichroma and VE-Venus Diamond One) were used for the restorations. Tooth color was measured using an intraoral spectrophotometer. Visual analysis was carried out by 16 calibrated observers, and the differences were graded from 0 (excellent match) to 4 (huge mismatch). Teeth were then bleached using 40% H 2O2 (Opalescence Boost PF, Ultradent), and visual and instrumental evaluations were performed after 24 hours. Results: Before bleaching, visual analysis showed a mean value of 0.16 for OM and 0.24 for VE. After bleaching, the color match showed a mean value of 0.14 for OM and 0.22 for VE. Regarding the instrumental analysis, each restoration matched the tooth VITA scale grade before bleaching and followed the natural tooth VITA scale grade after bleaching procedures. Conclusion: Within the limits of this pilot study, both composites seem to have excellent color-match properties with the surrounding tooth structure.

The effect of silver diamine fluoride on the microleakage of glass ionomer restoration in primary teeth at different time intervals

Silver diamine fluoride (SDF) has shown effectiveness in hardening tooth structure and killing bacteria. Therefore, it can be used to prevent and arrest dental caries. Riva Star (SDF) treatment alone will stop cavities but will not reverse the cavitation. The Silver Modified Atraumatic Procedure, often known as Smart, is the optimum technique for regaining the tooth's structure and function. Glass ionomer was introduced in (1972) as a new material that has become one of the most widely used materials in restorative dentistry. By releasing fluoride ions, this material has a therapeutic impact on the surrounding tooth structure. Microleakage is the ingress of bacteria, its byproducts, toxins, chemicals, oral fluids, and ions between the margins of the restoration and the cavity walls. Dental restoration lifetime is significantly influenced by microleakage at the toothrestoration contact. Material and method: In this study, we used 32 primary molars, class V cavities prepared on the buccal surface of all teeth. The teeth were divided into 2 groups: Group 1: 16 teeth treated with 38%SDF 8 of them restored directly with GIC filling and the other 8 restored after 14 days; Group 2: 16 teeth as control group left untreated with 38% SDF,8 teeth restored directly and 8 restored after 14 days. Samples were thermocycled, immersed in 2% methylene blue and then sectioned in a buccolingual direction. Dye penetration was measured with a digital camera connected to a stereo microscope. Result: results of this study showed a significant difference in microleakage between two-time intervals in which microleakage in GIC filling decreased at 14-day intervals than that of first-day interval in the experimental group, while in the control group, microleakage at 14 days intervals was higher than first-day interval, but it was not significant. Conclusion: Pretreatment of the primary teeth with SDF can decrease the microleakage of GIC restoration. If placed after 14 days, the microleakage would be lesser than that if the restoration was placed directly after SDF treatment. Therefore, it is recommended that SDF treatment be done, followed by a permanent restoration after 14 days, so the null hypothesis cannot be accepted. Keywords: Microleakage, Silver diamine fluoride, Glass ionomer filling, noninvasive dentistry

Evaluation of the Color Adjustment Potential of Single-Shade Composite Resin in Primary Teeth

Restoring composite resins with the optimal shades for all primary teeth is a great challenge for pediatric dentists. A newly developed single-shade composite resin can exhibit a color similar to that of the surrounding tooth structure based on the structural color phenomenon. This study aims to evaluate the color adjustment potential (CAP) of a single-shade composite resin compared to conventional multi-shade composite resins in primary teeth. A single-shade composite resin and two conventional multi-shade composite resins were included in this study. Two types of specimens, a single specimen and a dual specimen, were evaluated. For single specimens, duplications of the primary second molar denture teeth were made using experimental composite resins. For dual specimens, cavities were prepared on the buccal surfaces of extracted primary second molars and restored with experimental composite resins. The L*, a*, and b* values were measured using a colorimeter for the extracted teeth and specimens. The mean ΔE<sub>ab</sub><sup>*</sup> values for single and dual specimens and CAP were calculated. Bonferroni post-hoc analysis was performed to confirm the statistical significance between the ΔE<sub>ab</sub><sup>*</sup> and CAP values of the experimental resins. Among the single specimens, the single-shade composite resin showed significantly higher ΔE<sub>Single</sub> compared to other composite resins (<i>p</i> < 0.0167). There was no significant difference between ΔE<sub>Dual</sub> for all experimental resins. The single-shade composite resin showed highest CAP compared to other multi-shade composite resins. A single-shade composite resin exhibited the most prominent color adaptability compared to other conventional multi-shade composite resins for primary second molars. A single-shade composite resin can simplify shade matching and provide esthetic outcomes for the restoration of primary second molars.

Effect of bleaching on the color match of single-shade resin composites.

To evaluate the color match of single-shade resin composites before and after bleaching procedures, through instrumental and visual analyses. Class V cavities were created on the buccal surfaces of 80 extracted human molars, restored with 4 single-shade composites (Omnichroma; Clearfil Majesty ES-2 Universal; Essentia Universal; Venus Diamond One). A spectrophotometer (VITA Easyshade V) was used to evaluate the tooth/resin color match before (T0), and 24 h (T1) and one week (T2) after dental bleaching (Opalescence Boost PF 40%). Color variations (ΔE00) were calculated and statistically analyzed (P < 0.05). Visual analysis was performed before and after tooth bleaching. Spectrophotometric evaluations revealed statistically significant differences between materials at T0, T1, and T2 (P < 0.05). Visual analysis reported excellent and very good grades (0 and 1, respectively), irrespective of the materials and timepoints. Data seem to indicate that single shade composites are able to shift their color when the surrounding tooth undergoes bleaching effects. Single-shade composites seem to achieve a good color match with the surrounding tooth structure, before and after professional bleaching.

Effect of Different pH Beverages on the Color Stability of Smart Monochromatic Composite

Omnichroma is a smart monochromatic material and is believed to attain the shade of the surrounding tooth structure in which it is placed. However, the color stability of this material is unknown. Therefore, this study was conducted to evaluate the effect of different pH beverages on the color stability of the Omnichroma composite and its comparison with micro-hybrid composite resin. Sixty extracted human maxillary premolars of different shades, viz. A2, A3, B2 and B3, were selected in equal numbers. A Class V cavity was prepared on the buccal and palatal sides of each tooth. After the cavity preparation, etching of the cavity was performed with 35% phosphoric acid followed by bonding. The prepared cavities were then filled with Omnichroma composite resin on the buccal side and Filtek Z250 composite on the palatal side. The baseline color measurements of all tooth samples were performed by a spectrophotometer. The teeth were then divided into three groups, the Pepsi group, coffee group and milk tea group. Five teeth from each shade, viz. A2, A3, B2 and B3, were immersed in 10-mL of Pepsi, coffee, and milk tea for 14 days. After the completion of the 14 days, the teeth were rinsed and kept in distilled water for 24 h. Finally, a spectrophotometer was used to calculate the color alteration value ΔE. Mean difference in ΔE values of the samples before and after immersion in different beverages was calculated and analysed by SPSS 25. One-way ANOVA test was applied to compare groups. Further stratification was performed using the Post-Hoc Tukeys test. Samples immersed in milk tea showed a statistically significant difference (p &lt; 0.05) in A2, A3, and B2 shades of the OM-milk tea group in comparison with the FT-milk tea group. In summary, the immersion of teeth in beverages with a different pH and colorants showed an apparent alteration in the color of both the smart monochromatic and micro-hybrid composites. Hence, the type of resin composite material should be selected wisely depending on the patient’s drinking and social habits.

Shade Matching of OMNICHROMA Analyzed by Four Digital and Visual Shade Selection Techniques: An In Vitro Study

Introduction: To evaluate the shade matching of teeth restored with OMNICHROMA using four different teeth shade-selection techniques. Methods: Thirty sound upper first premolar teeth were used. Shade was taken by the VITA Linearguide 3D-MASTER, the VITA Easyshade V, digital photography, and the TRIOS 3 intraoral scanner for the cervical area. Subsequently, a Class V cavity was prepared and filled with an OMNICHROMA filling, and another reading for the shade was taken. Results: Value of ΔE in all groups were significantly higher than the clinically acceptable value (ΔE: 3.7) (P < 0.001). One-way ANOVA measurements showed statistically significant differences among the groups (P < 0.001). Conclusion: OMNICHROMA composite showed some degree of mismatch with the surrounding tooth structure. This in vitro model could not simulate complex oral situation and more clinical studies are necessary.

Stress Distributions for Hybrid Composite Endodontic Post Designs with and without a Ferrule: FEA Study.

The aim of the current work was to analyze the influence of the ferrule effect for hybrid composite endodontic post designs consisting of carbon (C) and glass (G) fiber-reinforced polyetherimide (PEI), in upper canine teeth. Starting from theoretical designs of C-G/PEI hybrid composite posts with different Young’s moduli (Post A—57.7 GPa, Post B—31.6 GPa, Post C—graduated from 57.7 to 9.0 GPa in the coronal–apical direction) in endodontically treated anterior teeth, the influence of the ferrule effect was determined through finite element analysis (FEA). On the surface of the crown, a load of 50 N was applied at 45° to the longitudinal axis of the tooth. Maximum principal stresses were evaluated along the C-G/PEI post as well as at the interface between the surrounding tooth structure and the post. Maximum stress values were lower than those obtained for the corresponding models without a ferrule. The presence of a ferrule led to a marked decrease of stress and gradients especially for posts A and B. A less marked effect was globally found for Post C, except in a cervical margin section along a specific direction, where a significant decrease of the stress was probably due to local geometric features, compared to the model without a ferrule. The presence of a ferrule did not generally provide a marked benefit in the case of the graduated Post C, in comparison to other C-G/PEI posts. The outcomes suggest how such a hybrid composite post alone should be sufficient to optimize the stress distribution, dissipating stress from the coronal to the apical end.

In vivo spectral guided removal of composite from tooth surfaces with a CO2 laser.

Dental composites are used as restorative materials to replace tooth structure after the removal of caries, shaping, covering teeth for esthetic purposes and as adhesives. Dentists spend more time replacing existing restorations that fail than they do placing new restorations. Tooth colored restorations are difficult to differentiate from the surrounding tooth structure making them challenging to remove completely without incidental removal of healthy tooth structure. Previous studies have demonstrated that CO2 lasers in conjunction with spectral feedback can be used to selectively remove composite from tooth surfaces. In addition, we assembled a system feasible for clinical use that incorporates a spectral feedback system, scanning system, articulating arm and a clinical handpiece and subsequently evaluated the performance of that system on extracted teeth. The purpose of this study was to test this system in vivo to demonstrate its efficacy relative to dental clinicians. Eight test subjects with premolar teeth scheduled for extraction for orthodontic reasons had bilateral premolars prepared with small occlusal cavity preparations and filled with dental composite. The laser scanning system was used to remove the composite from one of the preparations and a dental handpiece was used to remove the composite from the other. Cross polarization optical coherence tomography was used to measure the volume of the preparation before and after composite placement and removal. There was no significant difference in the loss of enamel and residual composite between the laser and the handpiece. This study demonstrated that a computer controlled spectral guided CO2 laser scanning system can be used in vivo to selectively remove composite from tooth surfaces.

Effective Protocol for Daily High-quality Direct Posterior Composite Restorations: Layering and Finishing.

Currently, there is a trend towards simplification of materials and clinical procedures. Simplification and quality can go together if the dentist works with materials and techniques that are well proven in vitro and in vivo. The placement of a high-quality class-1/2 direct posterior composite restoration can be time efficient following a standardized layering protocol and using composite materials that adapt well to the tooth surface and are able to mimic the natural tooth. When these materials are applied in a controlled way, finishing and polishing can also be shortened. In this article, an effective layering and finishing/polishing protocol for medium-sized class-1/2 direct posterior composite restorations is presented. Following the histo-anatomic buildup of natural teeth, dentin must be concave, as opposed to convex enamel. An isochromatic, medium-opaque, highly filled flowable composite is used to replace dentin. Enamel is replaced with a medium-translucent small-particle hybrid composite. Enamel is modelled in an anatomical way, following a successive cusp-by-cusp buildup approach. Clinical experience shows that the combination of both materials used according to this so-called bi-laminar histo-anatomical layering approach results in restorations that blend in very well within the surrounding tooth structure. Following a simplified finishing and polishing protocol, the composite restorations will have a correct contour, seamless margins, and a smooth, glossy surface.

Automated ablation of dental composite using an IR pulsed laser coupled to a plume emission spectral feedback system.

Dental composites are used as restorative materials for filling cavities, shaping, and covering teeth for esthetic purposes, and as adhesives. Dentists spend more time replacing existing restorations that fail than they do placing new restorations. Tooth colored restorations are difficult to differentiate from the surrounding tooth structure making them challenging to remove without damaging healthy tooth structure. Previous studies have demonstrated that CO2 lasers in conjunction with spectral feedback can be used to selectively remove composite from tooth surfaces. The purpose of this study is to assemble a system that is feasible for clinical use incorporating a spectral feedback system, a scanning system, articulating arm and a clinical handpiece and then evaluate the performance of that system on extracted teeth. In addition, the selectivity of composite removal was analyzed using a high-speed optical coherence tomography system that is suitable for clinical use. The system was capable of rapidly removing composite from small preparations on tooth occlusal surfaces with a mean loss of enamel of less than 20-μm.

Three-dimensional finite element analysis of the stress distribution pattern in a mandibular first molar tooth restored with five different restorative materials.

Introduction:Badly broken or structurally compromised posterior teeth are frequently associated with crown/root fracture. Numerous restorative materials have been used to fabricate indirect full-coverage restorations for such teeth. This study aims to evaluate and compare the effect of restorative materials on the stress distribution pattern in a mandibular first molar tooth, under varying loading conditions and to compare the stress distribution pattern in five commonly used indirect restorative materials.Materials and Methods:Five three-dimensional finite element models representing a mandibular first molar tooth restored with crowns of gold, porcelain fused to metal, composite (Artglass), alumina-based zirconia (In-Ceram Zirconia [ICZ]), and double-layered zirconia-based materials (zirconia core veneered with porcelain, Lava) were constructed, using a Finite Element Analysis Software (ANSYS version 10; ANSYS Inc., Canonsburg, PA, USA). Two loading conditions were applied, simulating maximum bite force of 600 N axially and normal masticatory bite force of 225 N axially and nonaxially.Results:Both all-ceramic crowns allowed the least amount of stress distribution to the surrounding tooth structure. In maximum bite force-simulation test, alumina-based all-ceramic crown displayed the highest von Mises stresses (123.745 MPa). In the masticatory bite force-simulation test, both all-ceramic crowns (122.503–133.13 MPa) displayed the highest von Mises stresses.Conclusions:ICZ crown displayed the highest peak von Mises stress values under maximum and masticatory bite forces. ICZ and Lava crowns also allowed the least amount of stress distribution to the surrounding tooth structure, which is indicative of a favorable response of the underlying tooth structure to the overlying full-coverage indirect restorative material. These results suggest that ICZ and Lava crowns can be recommended for clinical use in cases of badly damaged teeth.

THE EFFECT OF TWO DIFFERENT ADHESIVE SYSTEMS ON MICROLEAKAGE OF CLASS V COMPOSITE RESTORATION IN PRIMARY TEETH

INTRODUCTION: polymerization shrinkage of composite resins causes stresses that may exceed the strength of the bond with the surrounding tooth structure, leading to interfacial failure. The use of an adhesive system is always required. OBJECTIVE: The purpose of this in vitro study was to compare the effect of total-etch adhesive system with self-etch adhesive system on microleakage of universal nano-hybrid composite resin when used to restore class V cavities in primary teeth. MATERIALS AND METHODS: The sample consisted of 50 freshly extracted sound primary teeth. Standardized class V cavity preparations on the buccal surfaces were prepared and the sample was randomly divided into 2 equal groups: Group I: 25 teeth received total etch adhesive system. Group II: 25 teeth received self-etch adhesive system. The cavities were restored with a universal nano-hybrid restorative material. All specimens were thermocycled and immersed in 0.5% basic fuchsine dye at 37C˚ for 24 hours. Basic fuchsine penetration was assessed on a 4 point grading scale (0 to 4) using a stereomicroscope to evaluate the microleakage of the restorations. RESULTS: Comparing the percentage of microleakage scores of group I and group II at occlusal margin it was found that, the group I was significantly lower than group II (p=0.041). As for percentage of microleakage scores for the gingival margin between groups I and II it was found that there was no significant difference (p=0.741). Comparing the percentage of microleakage scores at both the gingival and occlusal margis of group I and II, no significant difference was revealed (p=0.105) (p=0.278) respectively. The sum of occlusal and gingival percentage of microleakage scores of group I compared to group II revealed no significant difference (p=0.325).. CONCLUSION: There is no significant difference in microleakage sum scores between total etch and self-etch adhesive system groups. At the occlusal margin, total-etch adhesive system was significantly better than the self-etch adhesive systems. KEYWORDS: microleakage, total etch adhesive, self- etch adhesive, primary teeth.

Dental Caries: A Review

Dental caries, a chronic disease is unique among human and is one of the most common important global oral health problems in the world today. It is the destruction of dental hard acellular tissue by acidic by-products from the bacterial fermentation of dietary carbohydrates especially sucrose. It progresses slowly in most of the people which results from an ecological imbalance in the equilibrium between tooth minerals and oral biofilms which is characterised by microbial activity, resulting in fluctuations in plaque pH due to bacterial acid production, buffering action from saliva and the surrounding tooth structure. The microbial community of caries is diverse and contains many facultatively and obligately-anaerobic bacteria. S. mutans is the most primary associated with it. Dental caries can affect the human in various ways i.e. presence of tooth pain, infection or dysfunction of the stomatognathic system can limit the necessary ingestion of energetic foods, affecting the growth in children and adults as well as their learning, communication skills and recreational activities. Moreover, oral and pharyngeal cancers and oral tissue lesions are also significant health concern. Cavernous sinus thrombosis and Ludwig angina can be life-threatening. Due to this, treatment is needed for dental diseases which cost is normally high and is not feasible for all community due to limited resources such as time, person and money. Therefore, prevention is more affordable. Personal hygiene cares and dietary modification should be recommended.

Endodontic filling materials

The principal function of root filling materials is to prevent invasion of bacteria and infection of the root canal system after completed endodontic treatment. This is accomplished by the formation of a tight, permanent seal with the surrounding tooth structure, leaving no space for invasion of or colonization by bacteria. The materials can also have a direct antibacterial effect and kill the microbes when in contact with them. Materials applied onto larger areas of connective tissue, i.e. for retrograde root fillings or perforation repair, should also allow or stimulate complete repair or regeneration. Ideally, the selection of materials for various applications in endodontics should be based on clinical, scientifically valid data. However, most current endodontic practices and choice of materials are based on a convoluted history where data of varying relevance and validity is mixed with experts’ stated opinions and manufacturers’ advertising. In this review, the chemical, physical, and biological properties of different root filling materials are discussed together with their handling characteristics and recommended use in the clinic. Emphasis is placed on evidence generated from clinical practice and research.

Performance of Dental Students Versus Prosthodontics Residents on a 3D Immersive Haptic Simulator

This study evaluated the performance of dental students versus prosthodontics residents on a simulated caries removal exercise using a newly designed, 3D immersive haptic simulator. The intent of this study was to provide an initial assessment of the simulator's construct validity, which in the context of this experiment was defined as its ability to detect a statistically significant performance difference between novice dental students (n=12) and experienced prosthodontics residents (n=14). Both groups received equivalent calibration training on the simulator and repeated the same caries removal exercise three times. Novice and experienced subjects' average performance differed significantly on the caries removal exercise with respect to the percentage of carious lesion removed and volume of surrounding sound tooth structure removed (p<0.05). Experienced subjects removed a greater portion of the carious lesion, but also a greater volume of the surrounding tooth structure. Efficiency, defined as percentage of carious lesion removed over drilling time, improved significantly over the course of the experiment for both novice and experienced subjects (p<0.001). Within the limitations of this study, experienced subjects removed a greater portion of carious lesion on a 3D immersive haptic simulator. These results are a first step in establishing the validity of this device.

Physical and Mechanical Properties of Visible Light Cure Composites Based on Novel Organically Modified Ceramic Resins

Replacement of damaged tooth is necessary for proper functioning and better aesthetics. Polymeric composites based on organic resins are the most popular materials used for restoration of damaged tooth though they have many problems like polymerization shrinkage. The post gel polymerization shrinkage causes significant stresses in the surrounding tooth structure and composite tooth bonding leading to premature restoration failure. Other problems such as uncured organic monomers leaching from the dental composites into the surrounding gum tissue have been reported to cause cytotoxic effects, pulpal necrosis, requiring tooth extraction. The present paper describes the studies on visible light cure composites based on organically modified ceramic resins. Effect of different inorganic materials incorporated during resin synthesis on mechanical properties of photo cured composite was evaluated in terms of diametral tensile strength (DTS), compressive strength (CS) and surface hardness (VHN). The better properties of photocured composites based on the novel organically modified ceramic resin which are hybrid inorganic organic resins may be due to the effective bonding between the organic and inorganic parts within the resin.

Color Stability of Ten Resin‐Based Restorative Materials

Despite significant developments to improve the optical properties of composites, color stability remains a challenge with changes still observed immediately after polymerization and after some time of storage. This study aimed to evaluate the color change of ten commercially available resin composite systems immediately after polymerization, at 24 hours, and at 1 month of water storage. Five discs of two thicknesses (1 mm/3 mm) in two shades (A3/Bleach) were made from ten commercially available brands of resin composite. Color measurements were recorded with a colorimeter and expressed in terms of the CIE L*a*b* scale. Color change was calculated between baseline and immediate polymerization (ΔE*(1) ), between immediate polymerization and 24 hours (ΔE*(2) ), and between 24 hours and 1 month (ΔE*(3) ). Values ΔE* ≥ 3.3 were considered clinically unacceptable as color shifts over this threshold value may be noticeable. The results were analyzed using a three-way analysis of variance (ANOVA) and Student-Newman-Keuls's tests. A significance level of 0.05 was used for all tests. Color change was evidenced for all brands, shades, and thickness. The greatest color change was observed immediately after initial polymerization with ΔE* values ranging from 2.4 to 12.0. Color change after 24 hours and 1 month were significantly less than those observed after polymerization. Immediately after polymerization, only Tetric EvoCeram (Ivoclar-Vivadent, Amherst, NY, USA) showed changes below 3.3. At 24 hours, 20 out of the 40 groups including all materials in both shades and thicknesses showed changes above 3.3. At 1 month, color changes for all brands remained under 3.3. Overall, clinically relevant color changes (ΔE* ≥ 3.3) took place immediately after polymerization of current light-activated composites. These changes were predominantly attributed to shifts in the L* and b* parameters towards the dark and blue region, respectively. Color shifts continued at 24 hours with changes in the L* and b* parameters towards the light and yellow region, respectively. After 1 month, only minor changes under the 3.3 threshold took place. Ensuring an accurate color match of resin composite restorations to the surrounding tooth structure is a critical aspect of any esthetic restorative procedure. A better understanding of the changes taking place during the different stages of maturation and storage of composites may be of significant benefit to clinicians as this may help minimize shade mismatch issues.

Evidence for bacterial causation of adverse pulpal responses in resin-based dental restorations.

The widespread use of resin and resin-monomers for bonding of dental restorations to dentin has occurred because of a fundamental shift in the view that injury to the pulp is induced by restorative procedures. While, for many years, the toxic effects of restorative materials were thought to be of crucial importance in the development of adverse pulpal responses, the key role of bacterial leakage at the restoration-tooth interface is now well-recognized. Consequently, if optimal conditions for the preservation of pulpal health are to be ensured, dental restorations should provide an impervious seal against the surrounding tooth structure. However, polymerization shrinkage and contraction stresses induced during setting, as well as a variety of technical difficulties encountered during the clinical operation, often produce less than perfect results. Therefore, modern restorative procedures involving resin and resin-bonded restoratives must still rely on the ability of the pulp to cope with the injurious elements to which it may be exposed during and after the procedure. This review examines factors that may govern the pulp's response to restorative procedures that involve adhesive technologies. An assessment is made of the risks involved as far as the continued vital function of the pulp is concerned. It is concluded that an intact, although thin, wall of primary dentin often enables the pulp to overcome both toxic material effects and the influences of bacterial leakage. In contrast, the pulp may not do equally well following capping of open exposures with resin composites. A dearth of controlled clinical studies in this area of dentistry calls for confirmation that pulpal health prevails over the long term following the use of total-etch and resin-bonding techniques.

Acid-Assisted Consolidation of Silver Alloys for Direct Fillings.

Silver-rich metal powders cold-welded by consolidation have been investigated as possible direct dental filling material. The surface of the silver powder must undergo an acid treatment to remove existing contaminants and prevent formation of new surface contaminants during consolidation. This study was designed to investigate the effect of the acid treatment on the strength of the consolidated alloy, its reactivity with the surrounding tooth structure, and its reactions with certain cavity liners.This study investigated the effects of pH and concentration of fluoboric acid on the flexural strength of silver powder consolidated into rectangular beams in a partial 4 × 4 design. The study also assessed, by visible and scanning electron microscopy, what effect the acid-treated powders had on dentin that had been pre-coated with different cavity liners. Mean flexural strengths for beams consolidated using dental hand instruments were in the range (77.0 ± 9.28) MPa to (166.1 ± 17.6) MPa, where the quoted uncertainties are standard uncertainties (i.e., one standard deviation estimates). ANOVA indicated that fluoboric acid pH was highly significant (p < 0.0001) with lower pH values resulting in higher flexural strength. Concentration alone was not a significant factor for flexural strengths, but there was a significant interaction between concentration and pH (p < 0.0001). Microscopy revealed that the acid-treated silver powder demineralized approximately 2 μm of dentin when used with no liner. The use of copal or polyamide varnishes eliminated most of this demineralization, but the use of a dentin adhesive liner resulted in some dislodgment and breakdown of the adhesive film by the acid.The results of this study indicate that this silver powder when treated with dilute fluoboric acid at a pH of approximately 1.0 can result in a filling material with strength equivalent to currently used conventional amalgam. The demineralization of tooth structure appears to be minimal and can be eliminated with the use of cavity liners.