Resin Restorations Research Articles

Fracture strength test of digitally produced ceramic-filled and unfilled dental resin restorations via 3d printing: An in vitro study.

Purpose of this study was to investigate the mechanical efficiency of 3D-printed permanent and provisional implant cemented fixed bridges produced via CAD/CAM technology using an interim and a permanent ceramic filled hybrid material. Two groups with twenty specimens each were designed and 3D-printed via digital light processing technology (DLP). A fracture strength test was performed. Statistical analysis was performed (p>0.05) for impression distance and force. For the fracture resistance and impression distance no significant difference (p = 0.643) were detected. The specimens of interim resin showed a mean value of 365.90 ± 86.67 N. Whereas specimens of permanent ceramic filled hybrid material showed a mean value of 363.45 ± 87.57 N. In this in vitro study 3D-printed ceramic filled hybrid material and interim resin based on methacrylic acid esters showed an acceptable resistance to bite forces with no differences in fracture mechanism. Key words:CAD-CAM, dental resin, 3D printing.

Effect of cigarettes smoke on bonded polymeric restorations: OCT study

BackgroundUp to date, the effect of cigarette smoke (CS) on the adhesive properties of the restorative materials bonded to tooth structure is still unclear. It is still questionable if it interferes with the durability and clinical success of these restorations. Few numbers of studies reported the assessment of microgaps of dental composite using cross-polarization optical coherence tomography (CP-OCT). The aim of this study was to evaluate the presence of interfacial microgaps between composite resin restoration and the tooth structure with or without exposure to CS under the CP-OCT. Materials and methodsIn this in-vitro study, a standardized round class-V cavities were prepared in twenty extracted, caries-free human molar teeth, and they were divided randomly into two groups (n = 10). Adhesive system (Gluma universal, Kulzer GmbH) was applied followed by filing the prepared cavities with flowable composite restoration (Charisma, Kulzer GmbH). Then, exposure to CS (40 cigarettes/day) was carried out for 14 days and the samples were stored in normal saline solution after each smoke exposure cycle. Next, all samples were immersed in ammoniac silver nitrate for 24 h, followed by immersion in a photo-developing solution for 8 h. Optical comparison was carried out by CP-OCT to assess microgaps percentage between smoke (SG) and non-smoke groups (NSG) at the axial walls (AW) and cavity floor (CF). ResultsIndependent T-test showed that there was a significant difference between the two groups (SG, NSG) in AW microgaps percentage (p = 0.008), while there was no difference in CF (p = 0.15) ConclusionIt can be inferred from the current finding that OCT can be used to predict the adaptability of the bonded restoration under the thermochemical influence. CS has a negative effect on the marginal integrity of the bonded polymeric restorations.

Semi-Automated Planimetric Quantification of Dental Plaque Using an Intraoral Fluorescence Camera.

Dental plaque accumulation is quantified using clinical indices or, otherwise, the planimetric plaque index (PPI),which measures the relative area of a tooth that is covered by plaque deposits. Compared to clinical indices, the PPI has a higher discriminatory power, but traditional planimetry is a time-consuming analysis, as the plaque-covered and clean tooth areas have to be determined manually for each image using image-processing software. Here, we present a method for the semi-automated planimetric quantification of dental plaque, which allows for the rapid processing of up to 1,000 images simultaneously. The method exploits the enhanced contrast between disclosed plaque, sound tooth surfaces, and soft tissues in fluorescence images acquired with an intraoral camera. Careful execution of the clinical procedures and accurate image acquisition are crucial steps for the successful semi-automated identification of the plaque-covered areas. The method is suitable for planimetry on sound facial and oral tooth surfaces, on most composite resin restorations, and on teeth with orthodontic brackets, but not on metallic restorations. Compared to traditional PPI recordings, semi-automated planimetry considerably reduces the amount of time spent on the analysis, as well as the subjective human input, thus increasing the reproducibility of planimetric measurements.

Direct diastema closure: a case report

The maxillary diastema is a common asthetic problem in patients. Assess and diagnose may be challenging due to the many factors that influences the alteration of tooth eruption process and tooth shape. Appropriate technique and material for effective treatment are based on time, physical, psychological, and economical limitations. Direct composite resins in diastema cases allow dentist and patient complete control of these limitations and formation of natural smile. In this case report multiple maxillary diastemas were closed with direct composite resin restorations in without any preparation.

Survival assessment of fractured porcelain-fused-to-metal crowns surface roughened by sandblasted and repaired by composite resin after in vitro thermal fatigue

Background/purposeIntraoral repair usually takes the convenience of the patient's daily life as the starting point, taking into account the bonding strength, operational feasibility, and safety. This study aimed to evaluate the survival of composite resin by simulating cavity fracture repair in porcelain-fused-to-metal (PFM) crowns and referring to the G.V. Black classification of caries as ceramic- and metal-site exposure. Materials and methodsMechanical sandblast experimental and a nonsandblast control groups comprised 120 samples, and interfacial locking was enhanced through acid etching, bonding, and light-curing composite resin restoration. Classes of VI buccal (B), III mesial (M), and IV mesiobuccal (MB) types, were investigated. Load tests were performed on two sets, with one set at room temperature for 24 h and the other via thermal cycling at 5 °C/50 °C 720 times. Loading was gradually applied to the samples until a maximum of 450 N was reached. ResultsResults showed that 24 h survival rates of B-, M − , and MB-repaired PFM crowns were 88%, 84%, and 88%, respectively. The repaired PFM survival rates for B, M, and MB were 52%, 44%, and 28%, respectively, after thermal cycling and loading tests. Multiple logistic regression and chi-square test (α = 0.05) showed that the regression results of factors affecting survival assessment were only significant between groups after thermal fatigue (P < 0.05). Survival rate of repairing metal-site in the MB model was significantly higher than that of ceramic-sites repairing in non-blasted samples. For the MB cavity model, sandblasting can significantly improve the survival rate of the repair of ceramic parts in the MB model (P < 0.05). ConclusionOur results suggest that sandblasting can be further considered, especially for MB cavity fractures when ceramic-site restorations are required.

Microleakage Study of a Bulk Fill over an Uncured Adhesive System

This study aimed to evaluate and compare the microleakage of composite resin restorations under a total-etch adhesive system applied with two different techniques, with and without cure. Cavities were made on the buccal surface of twenty-six intact teeth and subsequently restored with bulk-fill flow composite resin (SDR®® flow+) and conventional resin (Spectra™ ST HV). Two experimental groups were created, one where the total-etch adhesive (Prime &amp; Bond Active®) was cured and another where the adhesive was not cured before placing the flowable resin. Two control groups were also created, negative and positive. After the restorations were finished the, teeth were submerged in a solution of sodium pertechnetate (99mTcNaO4) for 3 h to evaluate the microleakage. The results showed more infiltration of radioisotopes characterized by the highest total count values of microleakage in group 1 (cured adhesive) and in the positive control. Group 2 (noncured adhesive) and the negative control showed lower values. We therefore considered that these groups were similar since their p-value was less than 0.05, with no statistically significant difference. Group 4 showed a statistically significant increase in relation to group 3 (p = 0.027). We concluded that the method of bulk-fill composite resins with noncured adhesive agents can have a positive effect on the longevity of bond strengths, with reduced microleakage.

Comparative Evaluation of Flexural Strength of Heat Polymerised Polymethyl Methacrylate Provisional Fixed Restorative Resin Reinforced with Different Percentages of Silanised Zirconium Oxide Nanoparticles: An In-vitro Study

Introduction: The purpose of providing a provisional restoration includes immediate replacement of missing teeth, for protection of pulp and maintenance of periodontal health, to maintain occlusal stability, to preserve the position of the teeth and for masticatory efficiency. Provisional restorations fabricated from heat processed acrylic resin have been used successfully. Incorporation of inorganic nanoparticles into Polymethyl Methacrylates (PMMA) resin has been shown to improve its physical properties. Aim: To evaluate and compare the flexural strength of heat polymerised PMMA provisional restorative resin reinforced with different percentages of silanised zirconium oxide nanoparticles. Materials and Methods: This is an in-vitro study performed in the Department of Prosthodontics, VSPM’s Dental College and Research Centre, Nagpur, Maharashtra, India, from June 2018 to February 2020. A die was used to create sixty heatcured PMMA resin specimens, which were then divided into four groups: group A includes controls with conventional heat polymerised provisional restorative resin (PMMA) and groups B, C and D conventional heat polymerised provisional restorative resin reinforced with different percentages of silanised zirconium oxide nanoparticles (1 wt%, 2.5 wt%, 5 wt%, respectively), having fifteen specimens in each group. Three point bending tests were conducted on all samples using a universal testing machine. The flexural strength of each specimen was calculated. Mean value of flexural strength of each group was used for statistical analysis. One-way analysis of variance test was used to find out the mean value of flexural strength of each group. Results: The mean flexural strength for control group was 53.76±2.97 MPa. For group B (1% Zirconium oxide) it was 58.14±4.86 MPa, for group C (2.5% Zirconium oxide) was 63.29±4.22 and for group D (5% Zirconium oxide) it was 59.02±3.99 MPa. Statistical analysis showed that maximum strength was obtained by reinforcement with 2.5% silanised zirconium oxide nanoparticles. Conclusion: Polymethyl methacrylate reinforced with silanised 2.5% of zirconium oxide nanoparticles promises to be better material in terms of flexural strength.

28 - Shear Bond Strength of 3D Printed Resin for Indirect Restoration

28 - Shear Bond Strength of 3D Printed Resin for Indirect Restoration

Etiology of dental implant complication and failure—an overview

&lt;abstract&gt; &lt;p&gt;Dental implant treatment is turning into a widely accepted and popular treatment option for patients. With the growing era of dental implant therapy, complications and failures have also become common. Such intricacies are becoming a vexing issue for clinicians as well as patients. Implant failures can be due to mechanical or biological reasons. Failure of osseointegration of the implant falls under biological failures, whereas mechanical complications include fracture of the implant, framework or prosthetic components. Diligently observing the implant after placement is the first step in managing the declining circumstances. It is important to have a thorough understanding of how and why implants fail to achieve successful treatment outcomes in the long run. In dentistry, nanoparticles are used to make antibacterial chemicals that improve dental implants. They can be used in conjunction with acrylic resins for fabricating removable dentures during prosthetic treatments, composite resins for direct restoration during restorative treatments, endodontic irrigants and obturation materials during endodontic procedures, orthodontic adhesives and titanium coating during dental implant procedures. This article aimed to review the etiological factors that lead to implant failure and their solutions.&lt;/p&gt; &lt;/abstract&gt;

An In Vitro Comparative Evaluation of Fracture Strength of Composite Resin and Activa Kids Bioactive Restorative for Use in Strip Crowns

Background Advanced stages of early childhood caries requires complex measures such as strip crowns for the anterior teeth and stainless steel crowns for the posterior teeth. Composite resin is the traditional material of choice for use in strip crowns. ACTIVA KIDS Bio ACTIVE-RESTORATIVE is the first bioactive composite with pedo shade delivering all the chemical properties of glass-ionomer cement and physical properties of composite resins.Aim The aim of this study was to compare the fracture strengths of composite resin and ACTIVA KIDS BioActive Restorative Pulpdent USA when used with a strip crown for restoring primary anterior teeth.Methodology Twenty exfoliated non-carious human maxillary primary central and lateral incisors were selected for the study to receive strip crowns and the dimensions were standardized for all the samples. In Group I Composite resin Te-Encom Plus Ivoclar vivadent and in Group II ACTIVA Kids BioActive Restorative Pulpdent USA were used to fill the strip crowns respectively after etching and application of bonding agent. After light curing the samples strip crowns were then removed assessed for fracture strength under Universal testing machine. Fracture strength of both the groups was statistically analyzed and recorded using student ldquotrdquo test.Results The minimum to maximum force obtained was 235.08ndash682.71 N for Group 1 which when compared to Group II 167.57ndash449.29 N was higher. However fracture strength between both the groups p .062 showed no significant difference statistically. Deformation at break percentage has shown significant difference between both the groups p.004 which was higher for Group I 1.34 when compared to Group II 0.68.Conclusion The fracture strength of experimental group restored with ACTIVA Kids Bioactive Restorative was comparable with composite resin when used as a core material inside the strip crown for anterior restorations. ACTIVA Kids Bioactive Restorative can be a better material of choice compared to traditional composite resins because of its excellent chemical and physical properties. The data also showed the fracture strength of ACTIVA Kids Bioactive Restorative to be comparable to composite resins.

Activity-based Costing of Common Caries Treatments Among Paediatric Patients

Background: Activity-based costing (ABC) is a micro-costing method. Despite being an accurate tool for cost calculation, ABC system is rarely applied in the dental fraternity as it is complex to be conducted. Data gathered through ABC is beneficial in bridging the gap between policy makers who emphasise on cost saving and the practitioners who emphasise on quality of treatment. Aim: To conduct an ABC of common treatments for caries management among paediatric patients at Hospital Canselor Tuanku Muhriz (HCTM), Malaysia. Methods: ABC was conducted through a clinical pathway to lay out the routine activities of dental caries management among paediatric patients, and to gather information about the equipment, instruments and consumables used, personnel involved, and the time spent for each procedure. Then, these resources were assigned into different categories namely equipment more than RM 500.00, instruments less than RM 500.00, consumables and staff salary. Finally, cost drivers were determined by calculating the amount of resources used and the time spent. Results: Based on the clinical pathway conducted, there were 10 common treatments for caries management for paediatric patients. The common treatments involved were fissure sealant, glass ionomer cement (GIC) restoration for primary teeth, composite resin (CR) restoration for primary teeth, CR restoration for permanent teeth, strip crown restoration, stainless steel crown (SSC) restoration, pulpotomy, pulpectomy, extraction and scaling. The price range of treatment ranged from RM 60.00 to RM 450.00. Pulpotomy had the highest cost, whereas extraction of teeth had the lowest cost. Conclusion: Study on costing is important to reduce the gap between the demand in dental treatment and the limited resources available to perform the treatment. ABC is deemed to be appropriate to be used in this study as dental treatments are largely procedure-based and this costing method produces a a more precise and transparent data. The outcome of this data provides a tool for other hospitals to be used as a standardised approach for treating these patients and subsequently improve the quality of dental care given.

Impact of access cavities on root canal preparation, restorative protocol quality, and fracture resistance of teeth.

The survival of endodontically treated teeth depends on the remaining tooth structure. The aim of this study was to evaluate the impact of different access cavities on root canal preparation, restorative protocol, and fracture resistance of endodontically treated teeth. Fifty-six mandibular molars were divided into control (n=8) and experimental (n=16) groups according to access cavity: Traditional, Conservative, and Truss; and redistributed (n=8) according to instrumentation protocols: Reciproc Blue and R-motion. After, teeth were scanned in micro-CT and then filled and redistributed according to composite resin restoration (n=8): Filtek One BulkFill and Filtek Z350. A new micro-CT scan was performed to analyze the restorative material. Then, samples were submitted to fracture resistance testing and the failure pattern was determined. Data were analyzed using paired T-test, ANOVA, Tukey, and chi-square tests (α=0.05). In Truss, R-Motion promoted less transportation in different thirds of root canals. Higher percentages of voids (5.05%) and filling material (11.7%) were observed in Truss. Fracture resistance values were higher for the control group, followed by Truss, Conservative, and Traditional. The predominant failure pattern was type-II. In Truss, reciprocating instruments with smaller taper showed less canal transportation. Also, Truss provided higher values of fracture resistance, although it presented a higher percentage of voids and remaining filling material. Thus, in Truss, reciprocating files with smaller taper showed less canal transportation, and these cavities provided higher values of fracture resistance, although it presented a higher percentage of voids and remaining filling material.

Surface roughness and microhardness evaluation of composite resin restorations subjected to three different polishing systems immediately and after 24 h: An in vitro study.

Finishing and polishing of composite resin restorations can be considered two different procedures or two steps of a single procedure. During the finishing procedure, contours are corrected while margins and irregularities are smoothened. The polishing procedures result in the production of a smooth and lustrous finish. Consensus regarding the correct timing for initiating the steps of finishing and polishing after the curing of the composite resins is divided. Some authors support immediate finishing and polishing while other authors support delaying the finishing and polishing procedures. The aim of this study is to evaluate the surface roughness and microhardness of composite resin restoration subjected to finishing and three different polishing systems immediately and after 24 h. Eighty composite resin samples were prepared. A Teflon mold was made which was customized for this study having dimensions of 10-mm diameter and 2-mm depth. For the first group of specimens, Group I (n = 20) the composite resin surface was covered with Mylar Strips which acted as control. The other specimens (n = 60) were prepared without the use of a Mylar strip, followed by curing. For all the samples, curing was done with a light-emitting diode for 40 s each. Eighty light-cured samples were divided equally into 4 groups, each group containing 20 samples (n = 20). Out of the 20 samples, in the second, third, and fourth groups, (Kenda C. G. I., Shofu Super-snap X-Treme, and Eve Diacomp Plus Twist) 10 samples were finished and polished immediately after curing and the other 10 samples were finished and polished after 24 h of curing. The samples in Groups II, III, and IV were subjected to finishing by a 12-fluted tungsten carbide bur and were polished according to the respective manufacturer's instructions. The samples were then subjected to quantitative analysis of surface roughness by a noncontact three-dimensional optical profilometer (Bruker GT-Q; Ettlingen, Germany) and qualitative analysis of surface roughness by a scanning electron microscope (Zeiss EVO 18 Special Edition; Carl-Zeiss-Strasse; Oberkochen Germany) at ×10,000 magnification. The samples were also subjected to Vickers microhardness measurement using a microhardness tester (Leica VMHT 001; Walter UHL GmbH, Germany) under 100 g load over 10 s. A. For surface roughness: The samples cured under Mylar strips gave the least surface roughness values (0.25 ± 0.032). Immediate finishing and polishing procedures led to statistically less surface roughness than when finishing and polishing procedures were performed after a delay of 24 h for all polishing systems used B. For microhardness: The samples cured under Mylar strips gave the least microhardness values (57.1 ± 2.03). Delayed finishing and polishing increased microhardness values in all finishing and polishing systems used. Different polishing systems did not have any significant effect on the microhardness values in immediate and delayed finishing and polishing groups.

Exploration and preliminary clinical investigation of an adhesive approach for primary tooth restoration.

The current study aims to investigate a suitable adhesive for primary tooth enamel. Shear bond strength (SBS) of primary teeth and the length of resin protrusion were analyzed using one-way ANOVA with Bonferroni multiple comparison tests after etching with 35% H 3PO 4. SBS and marginal microleakage tests were conducted with Single Bond Universal (SBU)/Single Bond 2 (SB2) adhesives with or without pre-etching using a nonparametric Kruskal-Wallis test. Clinical investigations were performed to validate the adhesive for primary teeth restoration using Chi-square tests. Results showed that the SBS and length of resin protrusion increased significantly with the etching time. Teeth in the SBU with 35% H 3PO 4 pre-etching groups had higher bond strength and lower marginal microleakage than those in the SB2 groups. Mixed fractures were more common in the 35% H 3PO 4 etched 30 s + SB2/SBU groups. Clinical investigations showed significant differences between the two groups in cumulative retention rates at the 6-, 12- and 18-month follow-up evaluations, as well as in marginal adaptation, discoloration, and secondary caries at the 12- and 18-month follow-up assessments. Together, pre-etching primary teeth enamel for 30 s before SBU treatment improved clinical composite resin restoration, which can provide a suitable approach for restoration of primary teeth.

Influence of filler types on wear and surface hardness of composite resin restorations.

Wear and surface hardness of resin composites are of relevance from the clinical standpoint. With the incorporation of novel filler system, more studies need to be performed to investigate newly marketed resin composites. The objective of this study was to investigate the abrasive wear and surface hardness of dental restorative with different filler types. Nanohybrid filled Harmonize (HM) and Tetric N-Ceram (TNC), microhybrid filled Filtek Z250 (Z250), nanofilled Filtek Z350 (Z350) were included in the study. Twelve cylindrical resin composites specimens with 10 mm in diameter and 6 mm in thickness were prepared for abrasive wear test. Eight hundred cycles under 17 kg load were conducted for final wear by CW3-1 wear machine. The specimen was cleaned with an ultrasonic unit for 3 min followed with drying procedure. After measurement of weight loss and the density of specimens, the specimens were kept for measurement of surface hardness. Surface hardness was measured using a micro-hardness tester with a Vickers diamond indenter after polishing. Three specimens of each material were observed by scanning electron microscopy (SEM) after the abrasion to evaluate the morphology of the surface. Data were analyzed using one-way analysis of variance (ANOVA), followed by Tukey HSD test (α = .05). Z250 performed the least volume wear loss (41.1 ± 2.1 mm3), as well as the hardest value (102.7 ± 2.9 HV). There was no significant difference with the volume wear loss (p = 1.000) and surface hardness (p = 0.874) of HM and TNC. SEM images of nanohybrid filled HM and TNC represented smoother surface compared with other types of resin composites. Microhybrid Z250 showed the highest wear resistance and surface hardness, nanofilled and nanohybrid resin composites may still face the insufficient of wear and surface hardness quality.

Stress distribution of endodontically treated mandibular molars with varying amounts of tooth structure restored with direct composite resin with or without cuspal coverage: A 3D finite element analysis.

Decision-making regarding whether cuspal coverage is required or not for the restoration of root canal-treated posterior teeth is still a matter of challenge for the dentist. Four models of endodontically treated mandibular molars with mesio-occlusal (MO) cavity were designed and simulated with direct composite resin restorations. Group 1A - cavity width <½ the intercuspal distance restored without cuspal coverage, Group 1B - same as Group 1A but with cuspal coverage, Group 2A - MO cavity width >½ but <2/3rd the intercuspal distance restored without cuspal coverage, and Group 2B - same as Group 2A but with cuspal coverage. The models received occlusal load to simulate a mastication load. Static finite element analysis (FEA) was adopted for predicting the stress distribution generated in the restored tooth by the loading condition. FEA of the models have shown that the variations in stress values were significant in bulk-fill material compared to enamel and other structures. Comparing the maximum and minimum principal stress values in the overall region demonstrated that 2A was safer, whereas 2B was found to be the worst case. The results indicate that restoration of endodontically treated mandibular molar with loss of one marginal ridge with composite resin without cuspal coverage revealed minimal internal stress values and showed the best performance overall.

The Impact of Saliva and Oral Microbiome on Restorative Dental Materials

Saliva and the oral microbiome play critical roles in the performance and longevity of dental restorative materials. Saliva's buffering capacity, pH regulation, and remineralization impact the durability and stability of materials. Variations in saliva composition among individuals can influence wear resistance and surface degradation of these materials. This review explores the intricate relationship between saliva, the oral microbiome, and restorative dental materials, emphasizing their mutual influences and the implications for dental practice. The oral microbiome, consisting of diverse microorganisms, further complicates this interaction. Bacterial adhesion, biofilm formation, and microbial metabolism significantly affect the integrity of restorative materials. For example, the degradation of composite resins by oral bacteria and their acidic byproducts can compromise the mechanical properties of these materials. Clinical manifestations of these interactions include deterioration of composite resin restorations, biofilm formation, and corrosion of amalgam restorations. Recognizing these manifestations is crucial for dentists to implement timely interventions and personalized management strategies. Regular monitoring and timely intervention, coupled with advancements in biomaterials, are key to enhancing the durability and effectiveness of restorative dental treatments.

Do different adhesives influence the color stability and fluorescence of composite restorations after aging?

This study aimed to evaluate the influence of dental adhesive color on the chromatic stability and fluorescence intensity of composite resin restorations of different thicknesses. Ninety bovine enamel samples were obtained and restored with resin composite varying thicknesses of restorative material and enamel (1.0 mm enamel and 1.0 mm composite; 1.5 mm enamel and 0.5 mm composite; 0.5 mm enamel and 1.5 mm composite). The restorations were made of composite resin (Opallis E-bleach H) using different types of dental adhesives: Ambar, Ambar APS, and Single Bond Universal (n=10). The samples were subjected to color measurement tests in a spectrophotometer using CIEDE2000 and fluorescence intensity measurements before and after aging in a red wine coloring solution. Data were subjected to analysis of variance (ANOVA) and Tukey's test (α = 0.05). There were no statistically significant changes in color stability or fluorescence intensity for restorations made of different materials or thicknesses (p>0.05). Single Bond Universal showed greater color stability at 0.5 mm thickness (ΔE00 = 4.4 ± 1.6) compared to other thicknesses of the same material (p=0.003), as well as a greater difference in fluorescence intensity after aging at 1.5 mm thickness (-414.9 ± 103.8) compared to other materials (p=0.0002). Overall, it was concluded that the different adhesive systems did not influence the color stability and fluorescence of restorations of different thicknesses.

Marginal integrity of composite resin restoration in class I cavities prepared by hydro-abrasion

Aim To evaluate and compare the marginal integrity of composite resin restorations made by two different preparation techniques: conventional drill and hydro-abrasion. Materials and methods Forty extracted human premolars with simple occlusal caries were used. The teeth were fixed with sticky wax to the base of plastic cylinder. The cylinder was filled with self-curing acrylic resin so that only root was embedded within the self-curing acrylic resin. The teeth were randomly divided into two main groups (n = 20) according to the preparation technique. Group I: class I cavity preparation was done by the conventional drill method using a #245 Carbide bur and contra angle high-speed hand piece with water coolant. Cavity design was restricted to remove caries with no undercuts, and no beveling. Group II: class I cavity preparation was done by Aquacut Quattro air hydro-abrasion unit which uses a gamma irradiated aluminum oxide particle as abrasives (29 μm), cutting fluid and a hand piece of 0.6 mm diameter tip. The preparation in both groups was restored by the same composite resin (Grandio) and adhesive systems (Futurabond U) following the manufacturer's instructions. All specimens were thermocycled. Impressions for each tooth was made using a polyvinyl Siloxane material. The impressions were then poured with epoxy resin. These replicas were examined under scanning electron microscope. Scanning electron microscope photographs of tested samples were used for the gap evaluation. Results It was found that, group I recorded higher mean value of marginal gap length (157.57 ± 35.15 μm) than group II that recorded (69.55 ± 20.02 μm). Also, group I recorded higher mean value of marginal gap length ratio (10.72 ± 2.47) than group II that recorded (7.44 ± 2.69). Conclusion Conventional drilling technique was faster than the hydro-abrasion technique for cavity preparation. Hydro-abrasion technique showed more marginal adaptation than conventional drilling technique.

Nature-mimicking layering with composite resins through a bio-inspired analysis: 25 years of the polychromatic technique.

For decades, the dental community has discussed which materials would be the ideal substitutes for lost tooth structure. Initially, the biomimetic approach advocated that feldspathic ceramics would be the material of choice for enamel. However, given the complexity of obtaining excellent dental technicians and the financial cost, are composite resins a suitable replacement? The optical properties with opalescence and fluorescence effects, as well as this material's high fracture toughness, indicate it as a long-lasting restorative material. However, because this material depends on the operator's expertise, knowledge of layering techniques and the selection of each material for the different layers is required. Thus, knowledge of the polychromatic technique through a bioinspired approach is necessary to obtain results of life-like restorations. This article aims to review the polychromatic layering technique (PLT), considering the optical and mechanical properties of dentin and enamel and correlating these properties with current composite resins to guide clinicians in selecting the most suitable restoratives for their clinical challenges. The polychromatic layering technique is revisited, cross-referencing the properties of dentin and enamel with current composite resin restoratives and their biomimetic properties. The effectiveness and predictability of the PLT are corroborated in clinical cases of varying degrees of difficulty requiring different layering strategies. After the bio-inspired analysis, using nature as a model to be understood and followed, it is possible to note how the polychromatic technique remains current and viable in mimicking nature, providing esthetic and natural results in the layering of composite resins. Composite resins effectively replicate the optical and mechanical characteristics of natural dentin and enamel through the bioinspired approach presented by the polychromatic layering technique.