Progress in Dental Adhesive Materials.

There have been significant advances in adhesive dentistry in recent decades, with efforts being made to improve the mechanical and bonding properties of resin-based dental adhesive materials. Various attempts have been made to achieve versatility, introducing functional monomers and silanes into the materials' composition to enable the chemical reaction with tooth structure and restorative materials and a multimode use. The novel adhesive materials also tend to be simpler in terms of clinical use, requiring reduced number of steps, making them less technique sensitive. However, these materials must also be reliable and have a long-lasting bond with different substrates. In order to fulfill these arduous tasks, different chemical constituents and different techniques are continuously being developed and introduced into dental adhesive materials. This critical review aims to discuss the concepts behind novel monomers, bioactive molecules, and alternative techniques recently implemented in adhesive dentistry. Incorporating monomers that are more resistant to hydrolytic degradation and functional monomers that enhance the micromechanical retention and improve chemical interactions between adhesive resin materials and various substrates improved the performance of adhesive materials. The current trend is to blend bioactive molecules into adhesive materials to enhance the mechanical properties and prevent endogenous enzymatic degradation of the dental substrate, thus ensuring the longevity of resin-dentin bonds. Moreover, alternative etching materials and techniques have been developed to address the drawbacks of phosphoric acid dentin etching. Altogether, we are witnessing a dynamic era in adhesive dentistry, with advancements aiming to bring us closer to simple and reliable bonding. However, simplification and novelty should not be achieved at the expense of material properties.

Dental anomalies as a possible clue of 1p36 deletion syndrome due to germline mosaicism: a case report.

BACKGROUND: Monosomy 1p36 is the most common terminal deletion syndrome with an autosomal dominant pattern of inheritance. This syndrome is defined by an extremely wide spectrum of characteristics; however, developmental delay and intellectual disability of various degree are present in all patients and about the 90% of patients have a severe intellectual disability. Dental agenesis or other dental anomalies have not been described in previous reports. CASE PRESENTATION: We report the case of two little sisters born from healthy and non-consanguineous parents, presenting with dental anomalies and one of them with epilepsy, dilated cardiomyopathy with left-ventricular non-compaction, strabismus, history of poor growth, hypotonia and mild language delay. Patients were evaluated in several departments (genetic, child neuropsychiatric, cardiology, odontostomatology, ophthalmology, otorhinolaryngology) of Institute for Maternal and Child Health, IRCCS Burlo Garofolo, Trieste, Italy. They underwent investigations such as electrocardiogram, echocardiogram, dental orthopantomography X-Ray and Computed Tomography, electroencephalograms, abdomen ultrasound, blood tests, IQ tests, genetic analysis. They both have an Intelligence Quotient greater than 70 and a negative neurologic exam. Each sister carries the same 1p36 deletion of about 2.3 Mb. Genetic analysis of the parents' blood samples (Single Nucleotide Polymorphism- array, karyotype and Fluorescent In Situ Hybridization) did not reveal any deletion, translocation or inversion and confirmed the paternity. A third sib of the probands does not carry the 1p36 deletion or other quantitative alterations. CONCLUSION: This report describes a new trait linked to monosomy 1p36, namely a mild intellectual outcome associated with significant dental anomalies. Our finding suggests that 1p36 deletion syndrome may present with a mild cognitive impairment or even with a normal intellectual development: this is very important for the genetic counselling, especially in a prenatal setting. Moreover, we report the third study with recurrent 1p36 deletion syndrome in two siblings, likely due to germline mosaicism. Finally, we believe that the dental anomalies should be investigated in 1p36 deletion syndrome and that the spectrum of the condition could be broader than we assume.

Academy of Dental Materials guidance-Resin composites: Part II-Technique sensitivity (handling, polymerization, dimensional changes).

OBJECTIVE: The objective of this work, commissioned by the Academy of Dental Materials, was to review and critically appraise test methods to characterize properties related to critical issues for dental resin composites, including technique sensitivity and handling, polymerization, and dimensional stability, in order to provide specific guidance to investigators planning studies of these properties. METHODS: The properties that relate to each of the main clinical issues identified were ranked in terms of their priority for testing, and the specific test methods within each property were ranked. An attempt was made to focus on the tests and methods likely to be the most useful, applicable, and supported by the literature, and where possible, those showing a correlation with clinical outcomes. Certain methods are only briefly mentioned to be all-inclusive. When a standard test method exists, whether from dentistry or another field, this test has been identified. Specific examples from the literature are included for each test method. RESULTS: The properties for evaluating resin composites were ranked in the priority of measurement as follows: (1) porosity, radiopacity, sensitivity to ambient light, degree of conversion, polymerization kinetics, depth of cure, polymerization shrinkage and rate, polymerization stress, and hygroscopic expansion; (2) stickiness, slump resistance, and viscosity; and (3) thermal expansion. SIGNIFICANCE: The following guidance is meant to aid the researcher in choosing the most appropriate test methods when planning studies designed to assess certain key properties and characteristics of dental resin composites, specifically technique sensitivity and handling during placement, polymerization, and dimensional stability.

Academy of Dental Materials guidance-Resin composites: Part I-Mechanical properties.

OBJECTIVE: The objective of this project, which was initiated from the Academy of Dental Materials, was to review and critically appraise methods to determine fracture, deformation and wear resistance of dental resin composites, in an attempt to provide guidance for investigators endeavoring to study these properties for these materials. METHODS: Test methods have been ranked in the priority of the specific property being tested, as well as of the specific test methods for evaluating that property. Focus was placed on the tests that are considered to be of the highest priority in terms of being the most useful, applicable, supported by the literature, and which show a correlation with clinical findings. Others are mentioned briefly for the purpose of being inclusive. When a standard test method exists, including those used in other fields, these have been identified in the beginning of each section. Also, some examples from the resin composite literature are included for each test method. RESULTS: The properties for evaluating resin composites were ranked in the priority of measurement as following: (1) Strength, Elastic Modulus, Fracture toughness, Fatigue, Indentation Hardness, Wear-abrasion (third body) and Wear-attrition (contact/two body), (2) Toughness, Edge strength (chipping) and (3) Wear determined by toothbrush. SIGNIFICANCE: The following guidance is meant to aid the researcher in choosing the proper method to assess key properties of dental resin composites with regard to their fracture, deformation and wear resistance.

Degree of Conversion of Self-etch Adhesives: In Situ Micro-Raman Analysis.

PURPOSE: Degree of conversion (DC) affects the physicochemical properties of dental adhesives. The aim of this study was to measure the DC within the hybrid layer of four one-step self-etch adhesives using Raman microspectroscopy. The hypothesis tested was that there was no difference among the tested adhesives. METHODS AND MATERIALS: The selected one-step self-etch adhesives (Clearfil S3 Bond Plus, I-BOND, G-BOND, and Adper Easy Bond) were applied on human dentin disks and polymerized in accordance with the manufacturers' instructions. Specimens were transversally cut to expose the bonded interfaces to the micro-Raman beam, and Raman spectra were collected along the dentin/adhesive interface. Measurements were performed at 1-µm intervals. The relative intensities of bands associated with the C=C bond (at 1640 cm-1) and an internal stable peak (1610 cm-1) were determined to calculate the degree of conversion within the hybrid layer. Data were statistically analyzed with Kolmogorov-Smirnov and Bartlett tests and Kruskal-Wallis and Mann-Whitney U-tests. RESULTS: The DC ranked as follows: G-BOND (93%±6%) ≥ Adper Easy Bond (92%±6%) ≥ I-BOND (89%±7%) > Clearfil S3 Bond Plus (80%±14%) (p<0.05). CONCLUSIONS: Based on the results of this study, all of the tested self-etch adhesives showed a clinically acceptable DC that was material dependent.

Silver-polysaccharide antimicrobial nanocomposite coating for methacrylic surfaces reduces Streptococcus mutans biofilm formation in vitro.

OBJECTIVES: The aim of this study was to determine the in vitro microbiological performances of a lactose-modified chitosan (Chitlac) coating inside which silver nanoparticles were embedded (Chitlac-nAg) for BisGMA/TEGDMA methacrylic specimens. METHODS: Different concentrations of nAg inside Chitlac coating were tested (1 mM, 2 mM, 5 mM). Specimen surface was analyzed by means of field-emission scanning electron microscopy (FEISEM) and energy-dispersive X-ray spectroscopy (EDS). A 48 h monospecific Streptococcus mutans biofilm was developed over the specimen surfaces using a modified drip-flow bioreactor; adherent viable biomass was assessed by MTT test and biofilm was imaged by confocal laser-scanning microscopy (CLSM). RESULTS: The presence of finely dispersed nanoparticles inside the Chitlac coating was confirmed by FEISEM and EDS analysis. All nanoparticles were embedded in the Chitlac coating layer. Chitlac-nAg coatings were able to significantly decrease biofilm formation depending on the nAg concentration, reaching a -80% viable biomass decrease when the 5 mM nAg-Chitlac group was confronted to non-coated control specimens. CLSM analysis did not provide evidence of a contact-killing activity, however the antibacterial Chitlac-nAg coating was able to alter biofilm morphology preventing the development of mature biofilm structures. CONCLUSIONS: The microbiological model applied in this study helped in assessing the antibacterial properties of a coating designed for methacrylate surfaces. CLINICAL SIGNIFICANCE: A microbiological model based on a bioreactor-grown biofilm is useful for preliminary in vitro tests of dental materials. In translational terms, an antibacterial nanocomposite coating based on Chitlac-nAg and designed to be applied to methacrylic surfaces may be a promising way to obtain dental materials able to actively prevent secondary caries.

The effects of two 10% carbamide peroxide nightguard bleaching agents, with and without desensitizer, on enamel and sensitivity: an in vivo study.

OBJECTIVES: This study aimed to compare the effects of two 10% carbamide peroxide (CP) agents with or without desensitizers on tooth sensitivity, colour and enamel morphological changes. METHODS: Twenty subjects used a 10% carbamide peroxide gel with or without fluoride and potassium nitrate for 2 weeks. Sensitivity, spectrophotometric evaluation of colour and morphological analyses of replicas with scanning electron microscope (SEM) were performed before and after treatment. All data were analysed statistically. RESULTS: Both bleaching agents induced sensitivity; however, the 10% CP bleaching agent with fluoride and potassium nitrate produced significantly lower sensitivity (P < 0.05) than the bleaching product without desensitizing agents. In spectrophotometric evaluation, no difference in bleaching effectiveness was found between the tested bleaching gels, and the SEM analysis confirmed the absence of relevant alterations of the enamel surface in both groups. CONCLUSION: The use of 10% carbamide peroxide gel with fluoride and potassium nitrate reduced the incidence of sensitivity during the bleaching treatment compared to a bleaching agent that did not contain desensitizing agents. The bleaching effectiveness of the tested products was comparable.

The importance of size-exclusion characteristics of type I collagen in bonding to dentin matrices.

The mineral phase of dentin is located primarily within collagen fibrils. During development, bone or dentin collagen fibrils are formed first and then water within the fibril is replaced with apatite crystallites. Mineralized collagen contains very little water. During dentin bonding, acid-etching of mineralized dentin solubilizes the mineral crystallites and replaces them with water. During the infiltration phase of dentin bonding, adhesive comonomers are supposed to replace all of the collagen water with adhesive monomers that are then polymerized into copolymers. The authors of a recently published review suggested that dental monomers were too large to enter and displace water from collagen fibrils. If that were true, the endogenous proteases bound to dentin collagen could be responsible for unimpeded collagen degradation that is responsible for the poor durability of resin-dentin bonds. The current work studied the size-exclusion characteristics of dentin collagen, using a gel-filtration-like column chromatography technique, using dentin powder instead of Sephadex. The elution volumes of test molecules, including adhesive monomers, revealed that adhesive monomers smaller than ∼1000 Da can freely diffuse into collagen water, while molecules of 10,000 Da begin to be excluded, and bovine serum albumin (66,000 Da) was fully excluded. These results validate the concept that dental monomers can permeate between collagen molecules during infiltration by etch-and-rinse adhesives in water-saturated matrices.

Kinetics of polymerization and contraction stress development in self-adhesive resin cements.

OBJECTIVES: The aim of the study was to evaluate the contraction stress, microhardness and polymerization kinetics of three self-adhesive cements vs. conventional dual-cure resin cement. METHODS: Cements tested were: RelyX Unicem (3M ESPE, St. Paul, MN, USA), MaxCem Elite (Kerr, Orange, CA, USA), Clearfil SA Cement (Kuraray, Tokyo, Japan) and Duolink (Bisco Inc., Schaumburg, IL, USA). Cements were irradiated with a LED-curing unit (bluephase, IvoclarVivadent) for 20 or 40 s and the contraction forces (N) generated during polymerization were continuously recorded for 6 h with a universal testing machine. Polymerization kinetics were monitored using micro-Raman spectroscopy and degree of conversion was calculated. Vickers microhardness was also recorded. All measurements were performed at 10 min and 6h. Data were statistically analyzed by three-way ANOVA with repeated measures and Tukey's post hoc test (α=0.05). RESULTS: Irrespective of exposure time, stress analysis ranked in the following order: Clearfil SA Cement

Carbodiimide cross-linking inactivates soluble and matrix-bound MMPs, in vitro.

Matrix metalloproteinases (MMPs) cause collagen degradation in hybrid layers created by dentin adhesives. This in vitro study evaluated the feasibility of using a cross-linking agent, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), to inactivate soluble rhMMP-9, as an example of dentin MMPs, and matrix-bound dentin proteases. The inhibitory effects of 5 EDC concentrations (0.01-0.3 M) and 5 incubation times (1-30 min) on soluble rhMMP-9 were screened with an MMP assay kit. The same EDC concentrations were used to evaluate their inhibitory effects on endogenous proteinases from completely demineralized dentin beams that were incubated in simulated body fluid for 30 days. Decreases in modulus of elasticity (E) and dry mass of the beams, and increases in hydroxyproline content of hydrolysates derived from the incubation medium were used as indirect measures of matrix collagen hydrolysis. All EDC concentrations and pre-treatment times inactivated MMP-9 by 98% to 100% (p < 0.05) compared with non-cross-linked controls. Dentin beams incubated in 0.3 M EDC showed only a 9% decrease in E (45% decrease in control), a 3.6% to 5% loss of dry mass (18% loss in control), and significantly less solubilized hydroxyproline when compared with the control without EDC cross-linking (p < 0.05). It is concluded that EDC application for 1 min may be a clinically relevant and effective means for inactivating soluble rhMMP-9 and matrix-bound dentin proteinases if further studies demonstrate that EDC is not toxic to pulpal tissues.

The inhibitory effects of quaternary ammonium methacrylates on soluble and matrix-bound MMPs.

Matrix metalloproteinases (MMPs) bound to dentin contribute to the progressive degradation of collagen fibrils in hybrid layers created by dentin adhesives. This study evaluated the MMP-inhibiting potential of quaternary ammonium methacrylates (QAMs), with soluble rhMMP-9 and a matrix-bound endogenous MMP model. Six different QAMs were initially screened by a rhMMP-9 colorimetric assay. For the matrix-bound endogenous MMPs, we aged demineralized dentin beams for 30 days in calcium- and zinc-containing media (CM; control), chlorhexidine, or QAMs in CM to determine the changes in dry mass loss and solubilization of collagen peptides against baseline levels. The inhibitory effects of QAMs on soluble rhMMP-9 varied between 34 and 100%. Beams incubated in CM showed a 29% decrease in dry mass (p < 0.05), whereas beams incubated with QAMs showed only 0.2%-6% loss of dry mass. Significantly more solubilized collagen was detected from beams incubated in CM (p < 0.05). It is concluded that QAMs exhibited dentin MMP inhibition comparable with that of chlorhexidine, but required higher concentrations.

Influence of luting material filler content on post cementation.

Luting of fiber posts to intra-radicular dentin represents the worst-case scenario in terms of control of polymerization shrinkage. This study tested the hypothesis that filler content of resin cements does not influence luting of fiber posts to intra-radicular dentin, by assaying polymerization stress, push-out bond strength, and nanoleakage expression. The polymerization stress of experimental cements containing 10%, 30%, 50%, or 70% in filler content was investigated. Post spaces were prepared in endodontically treated teeth, and fiber posts were cemented with the experimental cements. A push-out test was performed, and interfacial nanoleakage expression was analyzed. Results showed that luting cements with higher filler content were related to increased polymerization stress (p < 0.05), decreased push-out bond strength (p < 0.05), and increased interfacial nanoleakage expression (p < 0.05). Conversely, lower-stress luting materials increased bonding of fiber posts to intra-radicular dentin. Further in vivo studies are needed to investigate the long-term clinical performance of these materials.

Influence of chlorhexidine on the degree of conversion and E-modulus of experimental adhesive blends.

OBJECTIVES: This study examined the effect of chlorhexidine (CHX) content on degree of conversion (DC) and E-modulus of experimental adhesive blends. The hypothesis tested was that increasing concentrations of CHX result in decreased DC and E-modulus in relation to adhesive hydrophilicity. METHODS: Experimental adhesive blends with increasing hydrophilicity R2 (70% bisGMA, 28.75% TEGDMA); R3 (70% BisGMA, 28.75% HEMA); R4 (40% BisGMA, 30% TCDM, 28.75% TEGDMA); R5 (40% BisGMA, 30% BisMP, 28.75% HEMA) and different CHX concentrations (1 and 5%) were analyzed. 5% CHX could not be dissolved in R2. A differential scanning calorimeter was used to measure the DC of resin blends. Photopolymerized disks of the experimental comonomer mixtures (n=10/gp) were used to measure the E-modulus of each specimen using a biaxial flexure test. Data were analyzed with two-way ANOVA (resin type and CHX concentration) and Tukey's post hoc test. RESULTS: The addition of 1% CHX did not significantly alter the DC of R2 and R3. Significant decrease in R3 DC values was observed when 5% CHX was added. CHX significantly increased the DC of R4 and R5. 1% CHX reduced the E-modulus of all resins (p<0.05) except for R2, in which the E-modulus was significantly increased (p<0.05). 5% CHX significantly reduced the E-modulus of resins R3 to R5 (p<0.05). SIGNIFICANCE: In conclusion, increasing concentrations of CHX dissolved in resin blends had little adverse effect on DC but decreased the E-modulus 27-48% compared to controls. Solvation of CHX in ethanol prior to incorporation of CHX into R2 may permit higher CHX concentrations without lower polymer stiffness.

Influence of air abrasion and etching on enamel and adaptation of a dental sealant.

AIM: Aim of this study was to evaluate the marginal microleakage of a dental sealant using different pre-treatment techniques of the enamel surface. METHODS: Thirty extracted human intact teeth were selected and divided into 3 groups (n = 10) (1: acid etching with 37% orthophosphoric acid - 3M ESPE, St. Paul, Minnesota, USA; 2: air abrasion; 3: air abrasion + acid etching). The sealant (Helioseal, Vivadent Ivoclar AG, Liechtenstein) was applied into occlusal pits and fissures and light cured for 40 sec. All samples were thermocycled for 500 cycles (5 degrees -55 degrees C). Teeth were then immersed into a 2% methylene blue solution for 24 hrs and sectioned in a mesio-distal direction. Forty-eight sections were obtained for each group. Each section was analysed and photographed with a stereomicroscope (50x) assessing dye penetration (0: no dye penetration; 1: dye penetration restricted to the outer half of the sealant; 2: dye penetration restricted to the inner half of the sealant; 3: dye penetration into the underlying fissure). STATISTICS: Data were statistically analysed (Mann-Whitney test). RESULTS: Specimens prepared after air abrasion combined with acid etching showed lower microleakage expression if compared with the other two groups (p<0.01). Conclusion A combination of mechanical air abrasion and chemical acid etching represents an effective pre-treatment of enamel surface that may significantly reduce the risk of microleakage.

Comparative evaluation of the microhardness of 4 dental sealants.

AIM: Aim of this study was the evaluation of the microhardness of 4 dental sealants polymerised with two different curing units. METHODS: Twenty samples (5 x 5x 2 mm) were prepared with 4 different sealants; 10 samples for each group were polymerised with a plasma curing unit (Apollo 95 E DMD) and 10 with a halogen curing light (Heliolux DLX Vivadent ETS, Schaan, Liechtenstein). For each section 6 Vickers microhardness measurements were performed (VMHT 30A, Leica Wien, Austria), 3 on the surface exposed to the light and 3 on the opposite surface. After the baseline assessment all samples were stored in artificial saliva at 37 degrees C for 30, 60, 90, 180 and 360 days, and then analysed again with the microhardness indenter and observed under steromicroscope 10X (Leica DM2500 Wien, Austria). Data were then statistically analysed. RESULTS: The hybrid composite Tetric flow (group IV) showed the higher microhardness values compared to the other tested materials (group I, II, III); surfaces exposed to curing light showed higher microhardness values than opposite surfaces. Moreover, a significant microhardness reduction was observed after 30 days; values remained unmodified after 60, 90, 180 and 360 days. STATISTICS: Data were then statistically analysed with Anova test for repeated measures, with a global significance level of 0.05. CONCLUSION: Because of the good mechanical properties of dental sealants they represent the first choice materials in pits and fissures sealing.

Surface roughness of three resin restorative materials after finishing and polishing.

AIM: The surface roughness of 3 different resin restorative materials polymerized with a halogen and a plasma arc curing light, following finishing and polishing was evaluated in vitro. METHODS: Using a metal mold, 10 block specimens were prepared from each material. A Mylar strip was placed on both sides of the mold. Five specimens from each material were cured with the halogen lamp, while the other 5 were polymerized with the plasma arc lamp. In both groups the surface exposed to curing light was finished and polished with the Enhance system (Dentsply). The opposite surface was not treated and served as a control. Both surfaces of each specimen were analyzed with a laser profilometer: the roughness average (R(a)) was evaluated. The Vickers microhardness of the polished surfaces was also calculated. All data were statistically analyzed with the Mann-Whitney test. A regression test was carried out to evaluate the possible correlation between roughness and microhardness. RESULTS: The smoothest surfaces were obtained when composites were cured against a Mylar strip. Roughness was significantly increased in both groups in the treated surfaces. A significant correlation between roughness and microhardness could not be demonstrated. CONCLUSIONS: This study demonstrated that the surface polymerized against a Mylar strip was the smoothest surface produced, while the roughness of the Mylar-formed surface was significantly increased by finishing and polishing. Surface roughness following polishing is material-dependent.

Cyclosporin A specifically affects nuclear PLCbeta1 in immunodepressed heart transplant patients with gingival overgrowth.

One of the most commonly observed adverse effects of cyclosporin A (CsA) is the development of gingival overgrowth (GO). Fibroblasts are involved in GO, but the question why only a percentage of patients undergoing CsA treatment shows this side-effect remains unanswered. In a previous study, CsA has been demonstrated to induce over-expression of phospholipase C (PLC) beta(1) in fibroblasts of patients with clinical GO, in cells from both enlarged and clinically healthy gingival sites. In this work, we assessed the expression of PLCbeta isoforms to investigate whether the exaggerated fibroblast response to CsA related to increased PLCbeta(1) expression could also be detected in CsA-treated patients without clinical signs of GO. Our results support the hypothesis of a multi-factorial origin of gingival overgrowth, including specific changes within the gingival tissues orchestrating fibroblastic hyper-responsiveness as a consequence of a long-term in vivo exposure to cyclosporin A.

Clinical evaluation of antibiotic prophylaxis before endodontic treatment of necrotic teeth.

AIM: The efficacy of antibiotic prophylaxis before endodontic treatment of necrotic teeth in the prevention of post-treatment flare-up pain and swelling was evaluated. METHODS: A total of 47 teeth with diagnosis of pulpal necrosis were selected in 39 patients, independently from the pre-operative symptomatology (painful or asymptomatic). Teeth were randomly divided into 2 groups. The first group (n=23) was given an antibiotic prophylaxis with 2 g amoxicillin 1 h before every appointment; the second group (n=24) did not receive any treatment (control group). The endodontic therapy was performed by shaping canals using the crown-down technique with hand devices, 5% sodium hypochlorite irrigations and 2 intermediate medications with Ca(OH)(2). Obturation was performed using randomly the vertical obturation technique or the no-stop wave technique. At the end of each appointment a questionnaire was given to each patient. The patient had to indicate if pain (absent, light, mild, severe) or swelling were present at 4, 8, 12, 24 h after every appointment. Data were statistically analysed with the Mann-Whitney, Wilcoxon and chi2 test. RESULTS: Only a case of flare-up pain and swelling was found in a patient of the study group. The statistical analysis showed that there were no significant differences between the 2 groups. CONCLUSIONS: An accurate endodontic treatment of necrotic canals is sufficient to guarantee an adequate control of post-treatment pain, with no need of antibiotic prophylaxis.

Reaction exothermia of 2 relining resins for temporary crowns.

AIM: The aim of the study was to evaluate the reaction exothermia of 2 relining resins for temporary crowns. The resins used were Duralay, a methacrylate-based resin, and Protemp II, a bisacrylic resin. METHODS: The coronal parts of an adult molar and of an impacted one were used. Abutments were obtained from the crowns, while the radicular part was sectioned in order to insert a thermocouple into the pulpal chamber. During the experiment the tooth with the polymerising resin was put into an oral cavity simulator to keep a constant temperature. The thermal increase during polymerisation of the 2 resins was recorded for 6 minutes at 5 seconds intervals and with 1 and 2.5 mm dentin thickness (n = 10). Data were statistically analysed by variance analysis with Scheffe test. RESULTS: The intrapulpal thermal increase was significantly higher in relation to the type of resin (Duralay p < 0.0001), thickness (1 mm p < 0.0001) and type of dentin (young dentin p < 00001). CONCLUSIONS: In order to protect the pulp, during the direct relining of a temporary crown, it is recommendable to choose the best combination among resin, type of dentin and its residual thickness, besides adequate cooling techniques.

[Evaluation of colour differences in fiber post all-ceramic prosthetic restoration by spectrophotometry]. / Analisi spettrofotometrica del colore di corone integrali in ceramica in denti ricostruiti con perni in fibra.

AIM: The aim of this study was to evaluate the influence of fiber post on all-ceramic prosthetic restorations, using the spectrophotometer Miniscan XE. Data were recorded according to the CIEL*a*b* system and the color difference (DE) was calculated. METHODS: Carbon fiber Composipost (RTD) and quartz fiber Lightpost (RTD) posts were used. Square specimens (12x12 mm) were prepared using 9 #1 posts, covered with Z100 (3M) composite layers of different thickness (2, 3 and 4 mm) and color A3; 12x12 mm ceramic specimens (Finesse All Ceramic - 3M) of 2 and 3 mm thickness and color A3, were prepared using both opaque dentin and not. RESULTS: With 2 and 3 mm thick ceramic layers, there was no color difference between carbon fiber specimens and quartz fiber specimens. Using the opaque dentin did not determine difference between groups. CONCLUSION: In this study, according to results, a 3 mm thick ceramic layer always produced a DE<1, independently from the endodontic post. However, 2 mm thick ceramic layers were able to cover every kind of endodontic posts, even if with a DE=+/-1.6, and therefore are clinically acceptable.