Intact Enamel Research Articles

A fogszabályozó bracketek ragasztásának módszerei, összehasonlításuk a bracketleválási ráta alapján

Fogszabályozó kezelés során sok esetben ív rögzítésére szolgáló bracketeket ragasztanak a fogzománcra. A keletkezőrendszernek ellen kell állnia az egész kezelési idő alatt az elmozdító erőknek (okklúzió, rágóerő, ív ereje), és amikor abracket eltávolításra kerül, lehetőleg sértetlen zománcfelületet kell hátrahagynia maga után. A bracket-ragasztás minőségéta választott technika határozza meg. Célunk a napjainkban használt különböző ragasztási technikák összehasonlítóelemzése a bracket-leválási ráta alapján a következő szempontok szerint: direkt-indirekt módszer, használt bracketragasztóanyagok és a fogzománc előkészítése. A szakirodalmi adatok, vizsgálatok felkutatására a PubMed és a GoogleScholar keresőmotorokat használtuk. Az összehasonlítás kiegészítéseként a Fogászati és Szájsebészeti Oktató Intézetbenfogszabályozó kezelésben résztvevő páciensekről gyűjtöttünk adatokat (direkt technika, kompozit alapú ragasztó,többlépéses zománc kondicionálás). A felhasznált bracketek megrendelési és utánrendelési számai alapján a leválásiráta 4,1%, ami a szakirodalom által elfogadott 10% alatti értéken belül helyezkedik el [24, 6].Összességében a direkt és indirekt bracket-ragasztást összehasonlítva a feldolgozott források alapján nem találtunkszignifikáns eltérést a kétféle módszer között. Ragasztóanyagok tekintetében a legnagyobb kötőerők a kompozit rezinekhasználatakor keletkeznek. A fogzománc hagyományos, többlépéses kondicionálása a legtöbb vizsgálat szerint kisebbleválási rátát eredményez, mint a self-etch rendszerek használata.

Development of a new approach to diagnosis of the early fluorosis forms by means of FTIR and Raman microspectroscopy

This study is aimed at investigating the features of mineralization of the enamel apatite at initial stages of fluorosis development. Samples of teeth with intact and fluorotic enamel in an early stage of the disease development (Thylstrup–Fejerskov Index = 1–3) were studied by Raman scattering and FTIR using Infrared Microspectroscopy beamline at Australian Synchrotron equipment. Based on the data obtained by optical microspectroscopy and calculation of the coefficient R [A-type/B-type], which represents the ratio of carbonation fraction of CO32−, replacing phosphate or hydroxyl radicals in the enamel apatite lattice, the features of mineralization of enamel apatite in the initial stages of development of the pathology caused by an increased content of fluorine in the oral cavity were established. Statistical analysis of the data showed significant differences in the mean values of R [A-type/B-type] ratio between the control and experimental groups for surface layers (p < 0.01). The data obtained are potentially significant as benchmarks in the development of a new approach to preventive diagnostics of the development of initial and clinically unregistered stages of human teeth fluorosis, as well as personalized control of the use of fluoride-containing caries-preventive agents.

Laser Conditioning: A Preferred Option Over Conventional Acid Etching for Orthodontic Bonding

Aim: To evaluate the demineralization resistance and the shear bond strength of enamel surfaces after erbium, chromium: yttrium–scandium–gallium-garnet (Er,Cr:YSGG) laser etching (2 W/15 Hz, 2 W/25 Hz) and to compare them with conventional acid etching for orthodontic bonding. Materials and Methods: A total of 60 extracted human premolars with intact enamel surface were used for this study. Demineralization Resistance was estimated using ion-coupled plasma atomic emission spectrometer (ICP-AES). Shear bond strength was evaluated using Universal Testing Machine—Instron. Results: Statistically significant difference ( P &lt; .001) was found in the concentration of dissolved calcium (Ca) and phosphorus (P), with the highest mean Ca and P in the acid-etched group, followed by 2 W/15 Hz laser-etched group and least with 2 W/25 Hz laser-etched group. Maximum bond strength was found in the acid-etched group (12.06 MPa), followed by the 2 W/25 Hz laser-etched group (9.01 MPa) and 2 W/15 Hz laser-etched group (8.39 MPa). The differences were statistically significant. Conclusions: Laser conditioning of enamel surface revealed significant demineralization resistance with a minimal dissolution of Ca and P ions in the demineralizing solution. Moreover, optimum bond strength was obtained similar to that of acid etching; hence, Er,Cr:YSGG laser conditioning of enamel surface is preferred over the conventional phosphoric acid etching for orthodontic bonding.

Characterization of Enamel and Dentine about a White Spot Lesion: Mechanical Properties, Mineral Density, Microstructure and Molecular Composition.

The study focuses on in vitro tracing of some fundamental changes that emerge in teeth at the initial stage of caries development using multiple approaches. The research was conducted on a mostly sound maxillary molar tooth but with a clearly visible natural proximal white spot lesion (WSL). Values of mineral density, reduced Young’s modulus, indentation hardness and creep as well as the molecular composition and surface microstructure of the WSL and bordering dentine area were studied. The results obtained were compared to those of sound enamel and dentine on the same tooth. A decrease of mechanical properties and mineral density both for the WSL and bordering dentine was detected in comparison to the sound counterparts, as well as increase of creep for the enamel WSL. Differences in molecular composition and surface microstructure (including the indenter impressions) were found and described. WSL induces a serious change in the state of not only the visually affected enamel but also surrounding visually intact enamel and dentine in its vicinity. The results provide the basis for future studies of efficacy of minimal invasive treatments of caries.

Marginal staining of ultra-thin ceramic veneers

The pigmentation of the resin cement at the tooth/ceramic interface compromises the esthetic and longevity of ultra-thin ceramic veneers. Aim: The aim of this study was to evaluate marginal staining of ultra-thin ceramic veneers cemented to intact enamel (non-prepared) and prepared enamel. Methods: Thirty-two (32) permanent central incisors were selected and randomly divided into two groups: intact enamel (IE) and prepared enamel (PE). The ceramic veneers of PE group were bonded to the prepared enamel and the ceramic veneers of IE group were cemented directly onto the intact enamel, with no preparation. Both preparation and cementation were standardized and performed by a single operator. Each group was subdivided into two subgroups (n = 8) with different immersion media - coffee and water. After an immersion period of 10 days, stereomicroscope images were made at 20X magnification of the mesial, distal, cervical and incisal surface of each specimen. Three blinded, trained and calibrated examiners evaluated the images of the resin cement interface of each surface. The data were subjected to Kruskal‑Wallis and Mann‑Whitney statistical analysis. Immersion media and enamel preparation influenced the marginal staining of the tooth/ceramic interface. Results: When immersed in coffee, prepared interfaces presented greater marginal staining than unprepared interfaces. When immersed in water, there was no statistically significant difference between the groups. Conclusion: The cementation of ultra-thin ceramic veneers onto intact enamel is associated with less marginal staining and, consequently, improved esthetics.

Longevity of immediate rehabilitation with direct fiber reinforced composite fixed partial dentures after up to 9 years

ObjectivesThis retrospective, single-center, practice-based cohort study aimed to analyze the longevity of direct fiber reinforced composite fixed partial dentures (DFRC-FPD) and to analyze factors influencing their survival and success. MethodsWithin one private practice 100 DFRC-FPD were directly applied. The preparation of a proximal cavity was limited to abutment teeth with an existing filling (minimal-invasive approach). All intact enamel surfaces were preserved (micro-invasive approach). DFRC-FPD were reinforced by fiber-splints with semi polymer network matrices (Everstick C + B©). At the last follow-up DFRC-FPD were considered successful if they were still in function without any need of therapy. DFRC-FPD were considered as survived if they were repaired or replaced. Multi-level Cox proportional hazard models were used to evaluate the association between clinical factors and time. ResultsWithin a mean follow-up period (range) of 53 (2-109) months 7 bridges did not survive (cumulative survival rate: 93%) and further 24 bridges had received a restorative follow-up treatment (cumulative success rate: 69%). The annual failure rate was 1.6% for survival and 8.3% for success. The main failure type was fracture of the composite material (n = 30). In multivariate analysis no significant predictor could be found for success and survival. ConclusionsFor directly prepared fiber reinforced composite bridges high survival and moderate success times were observed after up to nine years. Based on the present results DFRC-FPD might be an immediate, short- to medium-term solution for replacing 1 to 2 missing teeth with no or minimal tooth preparation. Clinical significanceWithin the limitations of the present study DFRC-FPD offered an immediate, micro-/minimal-invasive, inexpensive short- and medium-term solution to replace missing teeth, even if no box-shaped proximal cavity was prepared.

Microcomputed tomography evaluation of cement shrinkage under zirconia versus lithium disilicate veneers

Statement of problemComputer-aided design and computer-aided manufacturing (CAD-CAM) technology and the improved translucency of recently developed high-strength monolithic zirconia could make them clinically acceptable for veneers if bonding to zirconia was as predictable as to glass-ceramics. Few studies have compared how resin cements behave between glass-ceramic and zirconia veneers before and after polymerization. PurposeThe purpose of this in vitro study was to evaluate the volumetric polymerization shrinkage of resin cement, marginal discrepancy, and cement thickness before and after polymerization for glass-ceramic and zirconia veneers with light-polymerizing resin cement. Material and methodsTen lithium disilicate veneers and 10 zirconia veneers were fabricated with a CAD-CAM workflow on extracted human maxillary anterior teeth with intact enamel surfaces. Zirconia veneers were treated with airborne-particle abrasion, and lithium disilicate veneers were etched with 5% hydrofluoric acid. All specimens were treated with ceramic primer and cemented with a light-polymerized resin cement. All specimens were scanned before and after resin cement polymerization by microcomputed tomography. The data were processed by the Amira software program to compare polymerization volumetric shrinkage, cement thickness, and marginal discrepancy. The data were compared by using a t test and analysis of variance (α=.05). Two bonded veneers were loaded in a mastication simulator for 400 000 cycles to investigate the effect of cyclic fatigue loading. ResultsMean volumetric polymerization shrinkage was 4.2 ±0.8% for the lithium disilicate group and 6.4 ±3.5% for the zirconia group. No significant difference was found for volumetric shrinkage between materials (P=.132). The mean ±standard deviations of the marginal discrepancies before and after polymerization were 178 ±41 μm and 158 ±37 μm for lithium disilicate and 115 ±33 μm and 107 ±32 μm for zirconia. A smaller marginal discrepancy was found for both materials after polymerization (P=.011) and for zirconia compared with lithium disilicate (P=.004). The mean ±standard deviation cement thickness values before and after polymerization were 157 ±27 μm and 147 ±27 μm for lithium disilicate and 162 ±53 μm and 147 ±52 μm for zirconia. Smaller cement thickness was found after polymerization (P<.001), whereas no significant difference was found in cement thickness between materials (P=.144). No changes were noted in marginal discrepancy and cement thickness as a result of the fatigue loading. ConclusionsThe difference in the volumetric polymerization shrinkage of cement between lithium disilicate and zirconia veneers was not statistically significant. Polymerization shrinkage resulted in smaller marginal discrepancy and cement thickness for both veneer materials.

Effect of different debonding techniques on shear bond strength and enamel cracks in simulated clinical set-ups

ObjectiveThe aim of this study was to evaluate the relationship between debonding forces and enamel cracks length change between different debonding techniques. Methods80 extracted premolar teeth with intact buccal enamel were divided into five groups. In each group, enamel cracks were evaluated by stereomicroscope before and after debonding. All teeth were bonded with metal brackets by self-cure adhesive (3M, USA) and then debonded by bracket debonding plier, fixed on the UTM machine, through five methods based on location of plier on brackets: OGwing (occlusogingival), MDwing (mesiodistal), Oblique, OGbase (occlusogingival) and Cusp-base. ResultsBased on non-parametric distribution of data, there was no significant difference between groups in ARI and enamel cracks length change. The highest shear bond strength for debonding presented in OG base method (25.25 ± 8.4) and the difference was statistically significant (P-value = 0.029). There was no linear relationship between shear bond strength and cracks length change and also between ARI and cracks length change. ConclusionDespite the lower cracks length change in Cusp-base method than other groups, there wasn’t significant difference between debonding methods. Also the amount of debonding forces and ARI do not affect the changes of cracks length.

Biomimetic Effect of Nano-Hydroxyapatite in Demineralized Enamel before Orthodontic Bonding of Brackets and Attachments: Visual, Adhesion Strength, and Hardness in In Vitro Tests

Dietary habits with high consumption of acidic food can induce in orthodontic patients an increased risk of demineralization lesions around orthodontic brackets and bands. The purpose of the present laboratory study is to assess the in vitro visual efficacy of a biomimetic nano-hydroxyapatite remineralizing solution in a hypomineralized enamel surface and its effect on adhesion of fixed orthodontic appliances and on enamel microhardness. Intact teeth were demineralized, and subsequently the areas of demineralization were visually recorded using a 0–100 scale. Subsequently, a remineralizing solution (Biorepair® Repair Shock Treatment) was applied for ten minutes once a day/for one week per month for a total remineralizing treatment of 3 months. Visual effects were recorded. Moreover, bond strength was recorded and adhesive remnant index scores were measured for both orthodontic brackets and composite attachments both before demineralization and after demineralization and application of remineralizing solution. Also, Vickers microhardness was measured. All data were submitted to statistical analysis. The application of remineralizing solution induced a significant in vitro reduction of demineralized areas after the first week of application. No significant differences between untreated enamel surfaces and remineralized surfaces were detected after 2 months of remineralizing treatment. Bond strength values were significantly reduced for both brackets and attachments after remineralizing treatment. However, attachments showed higher adhesion values than brackets in both conditions tested. Remineralized enamel showed significantly higher microhardness values than demineralized enamel and lower values than intact enamel.

WEAR RESISTANCE OF DENTAL MATERIALS WHICH ARE USED FOR ANTERIOR TEETH RESTORATIONS

The aim of this study was to compare the wear resistance of such restorative materials as composite resin, feldspathic ceramic, leucite glass ceramic with intact enamel and to draw an analogy with some similar researches. Materials and methods: In this research 20 extracted human teeth (maxillary incisors) without fillings and carious cavities were used as samples. All samples were disinfected and stored in saline in order to prevent dehydration. Teeth roots were cut off for the measure of fixation on an organic glass plate using chemically polymerizable resin. If necessary, the teeth were also cut on their lateral sides in order to give them equal size. The samples were placed in a frame-holder, located on the lever of the machine MI-2, which determines abrasion resistance under slipping. Results: The research has revealed that the average wear resistance of natural teeth was 122,67±4.9 J/mm3 (Tab 1). The archived result overcomes dental composite resin twice more (62.8±1.21 J/mm3), feldspathic ceramic 6.5 times more (16.32±1.2 J/mm3) and leucite ceramic over the half (73.79±3.12 J/mm3). Conclusion: Thus, according to this performed research and the analysis of the relative literature sources it can be stated that dental composite resin and leucite ceramics may be proposed as the materials of choice for anterior restoration of teeth. They have shown the good wear resistance and tolerance to antagonizing natural teeth.

Effect of preheating and ultrasonic energy on penetration of low viscosity enamel resin infiltrant

Objectives: to determine the depth of resin infiltrated hybrid enamel after application of TTEMA/TEGDMA resin infiltration agent enriched with nano-hydroxy apatite applied on early carious enamel lesions.Materials and Methods: Sound maxillary centrals were coated with a nail varnish, leaving a window of 4 mm × 4 mm on buccal surface of sound and intact enamel. All specimens were subsequently immersed in a demineralizing solution to produce artificial enamel lesions then etched with a mixture of 2% chlorhexidine and 10% hydrochloric acid. After washing and drying the enamel was coated with a low viscosity TTEMA/TEGDMA resin infiltration agent followed by light polymerization. The effect of addition of 10% nano-hydroxy apatite, preheating at 45oC, and ultrasonic activation was tested in separate groups. Sectioned specimens were examined under a stereomicroscope equipped with a high-resolution digital camera for determining of the depth of penetration of the low viscosity resin in microns (α=0.05).Results: Data analysis revealed significant difference in depth of enamel hybrid layer between the tested groups (F=14.2, P<0.001). Average penetration depth was 185 ± 17 µm for TTEMA/TEGDMA resin infiltration agent. Addition of 10% nano-hydroxy apatite reduced penetration depth to 141± 19 µm. On the contrary, preheating and ultrasonic activation increased penetration depth to 211± 13 µm and 221 ± 12 µm respectively.Conclusions: Within the limitations of this study, the penetration depth of TTEMA/TEGDMA resin infiltration agent was significantly influenced by addition of nano-hydroxy apatite particles. Preheating and ultrasonic activation increased penetration depth significantly.

The combined approach to evaluation of mechanical behavior of tooth enamel in artificially induced caries lesions

Improved knowledge of caries initiation and progression on the base of modern mechanobiology could facilitate effective preventing and therapeutic strategies. Not all of previously developed experimental models of artificial caries comply with required standards. The aim of the study was to investigate microstructural and mechanical properties of 12 artificial caries lesions, induced on human intact premolars according to original protocol. The tooth specimens were subjected to imaging by X-ray CT system Nikon Metrology XT H 225, with further morphometric analysis of lesion geometry, depth, surface layer thickness and mineral density in the areas of interest. Mechanical characteristics (penetration depth, microhardness, elastic modulus) in enamel lesion, perifocal intact enamel and remote zones were obtained using Micro CombiTester system. Clinically all lesions fully corresponded to ICDAS – 2 code. According to µCT data, LDµCT of the lesions ranged from 346.4 to 531 µm, mineral density range from 2.03±0.15 g/cm3 in transparent zone to 1.05±0.08 g/cm3 in the surface zone of the lesion. Microhardness of demineralized enamel lesion more than 5 times reduced in comparison with perifocal and remote intact enamel. Nanoindentation and µCT data are corresponds to those presenting on the base of other classical protocols of artificial caries formation and close to the typical mechanical characteristics of enamel caries in vivo.

Quantitative evaluation of masking effect of resin infiltration on developmental defects of enamel.

Qualitative developmental defects of enamel (DDEs) are characterized by an intact hypermineralized surface enamel layer and a porous subsurface hypomineralized layer. This structure is similar to natural early caries lesions, which are effectively arrested by resin infiltration, a micro-invasive clinical procedure. An additional reported effect in early enamel caries is recovery of enamel translucency. Due to structural similarities, a similar mechanism is expected in qualitative DDEs. The objective of the present study was to observe quantitative color masking of qualitative DDEs when subjected to resin infiltration. A total of 70 selected enamel defects were subjected to resin infiltration in a nonrandomized study design. Each defect was subjected to photographic imaging using a digital camera both pre- and post-intervention. Each image was assessed using ImageJ digital software (National Institutes of Health) for CIE L*a*b coordinates. There were significant changes observed in L*a*b coordinates of all DDEs, when subjected to resin infiltration. The resin infiltration intervention was successful in masking the "white" opaque discolorations of developmentally affected enamel.

Compositional and micromorphological features of hypoplastic enamel in children’s permanent teeth

Enamel hypoplasia is the most common disease of hard tooth tissues of non-carious origin emerging before their eruption. It develops as a result of a delayed and perverse function of ameloblasts leading to the violation of the processes of formation and mineralization of tooth protein structures. The clinical manifestations of enamel hypoplasia are spots, defects in the form of pits, cup-shaped depressions, grooves on various surfaces of child’s teeth. The work is devoted to a comparative investigation of microstructural and compositional features of intact and hypoplastic enamel in children’s permanent teeth using analytical scanning electron microscopy with energy-dispersive X-ray spectroscopy. The hypoplastic enamel is enriched in organic substance and has an irregular structure without keyhole-shaped prismatic structure. Mineral deposition is indicated for hypoplastic enamel including hydroxyapatite with globular structure and calcite and halite, which might have been caused by the violation of extracellular local environment probably due to the enamel hypoplasia development.

Effect of Yd:YAG laser irradiation on the shear bond strength of orthodontic metal brackets.

ABSTRACTObjective: The purpose of this study was to evaluate the effect of the Yd:YAG laser irradiation on orthodontic bracket base surface. Shear bond strength (SBS) values and sites of the bonding failure interfaces were quantified. Methods: Brackets were divided into two groups: OP (One Piece - integral sandblast base) and OPL (One Piece - laser irradiation). The brackets were randomly bonded on an intact enamel surface of 40 bovine incisors. The SBS tests were carry out using a universal test machine. A stereomicroscopy was used to evaluate the adhesive remnant index (ARI), and surface characterization was performed by scanning electron microscopy (SEM). Student’s t-test was used to compare the SBS between the two groups (p< 0.05). Frequencies and chi-square analysis were applied to evaluate the ARI scores. Results: OPL group showed higher value (p< 0.001) of SBS than OP group (43.95 MPa and 34.81 MPa, respectively). ARI showed significant difference (p< 0.001) between OPL group (ARI 0 = 100%) and OP group (ARI 0 = 15%). SEM showed a higher affinity between the adhesive and the irradiated laser base surface. Conclusions: Yd:YAG laser irradiation on bracket base increased SBS values, showing that bonding failure occurs at the enamel/adhesive interface. Laser-etched bracket base may be used instead of conventional bases in cases where higher adhesion is required, reducing bracket-bonding failure.

Estimation and correlation of salivary calcium, phosphorous, alkaline phosphatase, pH, white spot lesions, and oral hygiene status among orthodontic patients.

Introduction:The initial carious lesions are the so-called “white spot” lesions (WSLs), which implies that there is a subsurface area with most of the mineral loss beneath a relatively intact enamel surface. It is common in patients who are taking orthodontic treatment. Salivary reservoir of calcium and phosphorous counteracts the demineralization and encourages re-mineralization providing protection against caries challenge. This study was aimed to estimate and correlate the oral hygiene status, WSLs and salivary calcium, phosphorus, alkaline phosphatase (ALP), and pH in patients undergoing fixed orthodontic therapy.Materials and Methods:All clinical and biochemical parameters were recorded in 27 patients before starting orthodontic treatment and at 6 months of orthodontic treatment. The salivary calcium, phosphorous, ALP, and pH were determined by Arsenazo III method, Molybdate – UV and the International Federation of Clinical Chemistry method, respectively. International caries detection and assessment system index for WSL, orthodontic plaque index, bleeding on probing, and gingival index were recorded. Shapiro–Wilk's test and Wilcoxon test were applied to the data collected for statistical analysis.Results:There was a statistically significant increase with ALP levels, orthodontic plaque index score, gingival index score, and bleeding on probing index score. A statistically significant reduction was seen with respect to levels of calcium and pH.Conclusion:Maxillary canines and lateral incisors were the most affected teeth with WSLs (78.84%). There is a need for more stringent prevention programs and oral hygiene practices prior to initiation of orthodontic treatment and also during orthodontic treatment.

Enamel protection after stripping procedures: An in vivo study

Interproximal enamel reduction (IPR) is a clinical procedure that has been in use since the advent of non-extraction orthodontic techniques. However, such a procedure affects the surface condition of the enamel and may predispose patients to cavities and hypersensitivity. The use of a remineralizing agent is recommended to prevent these side effects. The objective of our study was to evaluate the evolution of stripped proximal dental surfaces after exposure to the oral environment for 4 months with and without fluoride protection. Our sample consisted of 14 premolars (PM) from 6 patients of the Dentofacial Orthopaedics Department of the Consultation and Dental Treatment Centre of Rabat (CDTC) who required orthodontic treatment with PM extraction and had given their informed consent. The teeth were divided into 5 groups: group 1: intact enamel; group 2: intact enamel+fluoride varnish+4-month oral exposure; group 3: IPR (manual and mechanized)+extraction; group 4: IPR (manual and mechanized) without varnish+4-month oral exposure; group 5: IPR (manual and mechanized)+fluoride varnish+4-month oral exposure. Proximal surfaces were subjected to qualitative analysis by scanning electron microscopy and quantitative analysis by Dispersive Energy Spectroscopy (DES) to quantify the percentage of mineral elements. Exposure of stripped dental surfaces to the oral environment for 4 months with or without fluoride protection showed the persistence of surface irregularities caused by stripping. We noted an improvement in the percentage of mineral elements for both groups with and without fluoride protection. However, the percentages of calcium (Ca) and phosphorus (P) were close to that of intact enamel in the fluoride varnish group. Protecting stripped surfaces with fluoride varnish could help preserve the integrity of the enamel surface by restoring some of the mineral elements lost during stripping.

Analysis of edge morphology of partial veneers made by different processing techniques and materials

To compare the edge morphology of partial veneers made of different materials by slurry molding, heat-pressed and computer aided design/computer aided manufacturing (CAD/CAM) techniques. Thirty premolars with smooth surface and intact enamel were selected and randomly divided into five groups, 6 specimens for each group. Group A were made from feldspathic porcelain (Noritake®) by slurry molding, while Group B were made from lithium disilicate glass ceramic (IPS E.max® Press) by heat-pressed. Group C/D/E were respectively made from feldspar porcelain block (VITA Mark II®), zirconia-reinforced glass ceramic (VITA Suprinity®) and hybrid ceramic with a ceramic-polymer network (VITA Enamic®) by CAD/CAM techniques. All the partial veneers luted with light-cured composite resin. Then the partial veneers were trimmed and polished to achieve the smooth finishing margin, clinical polishing sets were used according to the product descriptions. Scanning electron microscope (SEM) was used to observe the edge morphology of prostheses and the exposure of resin cements. The smooth surface and knife-like edge of the partial veneers could be obtained after bonding, trimming and polishing. The edges of Group A were slightly rough and the width of the exposed adhesive was (106.00±9.17) μm. In Group B, the edges were smoother than Group A, and the exposed wide adhesive strip was visible, which was (138.33±20.59) μm. In Group E, the edges were smooth too, and the width of exposed adhesive strip was (186.00±5.66) μm. The edges of Group C and Group D were rough and uneven, and the adhesive was rarely exposed, they were (50.67±7.51) μm and (65.67±17.90) μm. There were all significant differences between two groups, except Group C and Group D. After trimming and polishing in accordance with clinical procedures, the expected knife-like edge can be obtained in all groups. The width of the exposed resin adhesive of each group is different, the order: Mark II/Suprinity < Noritake < E.max Press < Enamic. The edge morphology of partial veneers in different processing technic and materials are different.

THE EFFECT OF TWO DIFFERENT ANTIOXIDANTS ON THE SHEAR BOND STRENGTH OF RESIN BONDED GLASS CERAMICS TO BLEACHED ENAMEL

Aim of the work: The aim of this study was to evaluate the effect of antioxidant agents and delayed bonding on the shear bond strength (SBS) of glass ceramic veneers bonded to the bleached enamel.Materials & Methods: A total number of sixty extracted maxillary central incisors with intact labial enamel were collected and randomly divided to six groups of ten teeth each. Ten teeth were remain without bleaching and the remaining fifty teeth were bleached using 35% hydrogen peroxide, (SDI Polaoffice tooth whitening system ). Sixty lithium disilicate glass ceramic discs of 4mm diameter and 5mm height were fabricated from IPS e.max Press and divided to six groups of ten discs each. Group I glass ceramic discs bonded to the unbleached enamel surface. Group II glass ceramic discs immediately bonded the bleached enamel after bleaching procedure without antioxidant. Group III glass ceramic discs immediately bonded to the bleached enamel after 10% ascorbic acid antioxidant application to the bleached enamel. Group IV glass ceramic discs immediately bonded to the bleached enamel after 20% ascorbic acid antioxidant application to the bleached enamel. Group V glass ceramic discs immediately bonded to the bleached enamel after 2% green tea antioxidant application to the bleached enamel. Group VI glass ceramic discs bonded to the bleached enamel after 2 weeks waiting period. The tested specimens, were tested for shear bond strength using a universal testing machine at a crosshead speed of 0.5mm/min until failure. The failure load was then recorded and statistically analyzed.Results: Analysis of the mean SBS between all groups it was found that the highest mean SBS for the control group CG of 30.22 ±0.92 MPa followed by group VI, with a mean of 26.90 ±1.27 MPa and group V with a mean of 26.0 ±1.80 MPa then group III, with a mean of 25.0 ±1.60 MPa and group IV with a mean of18.99±1.69 MPa the lowest mean fracture loads of 13.25± 0.36 MPa was for group II. Conclusions : Within the limitations of this study, it was concluded that antioxidant agents neutralize the effect of bleaching agents and considered a viable alternative to delayed waiting period.

An Evaluation of Er:YAG Laser in an Intact Enamel Treatment on Bonding to the Resin Cement Compared to Four Traditional Techniques

Evaluation of the bond strength of the resin cement after enamel conditioning with erbium-doped yttrium aluminum garnet laser compared to other four different techniques. The study consisted of 50 enamel specimens excluded from the smooth surfaces of newly extracted human 3rd molars. The specimens were randomly divided into five groups in terms of the enamel treatment technique. Each group (n = 10) was conditioned differently by bevel and acid etching group (I), acid etching technique group (II), double acid etching technique group (III), air abrasion followed by acid etching group (IV), and Er:YAG laser followed by acid etching group (V). After enamel treatment, a resin cylinder was installed using split Teflon matrix on each enamel specimen. Then the specimens were exposed to a shear strength device, and shear force was applied. The results were recorded with Newton. The required data were collected and statistically analyzed. A one-way ANOVA test was conducted to compare the five study groups using SPSS version 21 (p < 0.05). All groups showed high shear bond strength values ranging from 19.26 MPa (for group III) to 27.05 MPa (for group V). The enamel treatment with Er:YAG laser followed by acid etching gave the best results with significant differences compared to the other groups. Within the limitations of the present study, it can be concluded that the combination between the Er:YAG laser and the acid etching enhances the bond strength of resin cement with the enamel. The use of Er:YAG laser followed by acid etching can be a successful technique for enamel conditioning and the results showed their superiority over the other groups.