Methodological approaches in graded dental ceramics.

BACKGROUND: Functionally graded materials (FGM) with indistinct boundaries potentially eliminate the damaging stresses occurring at the interfaces. FGM applications in dental ceramics have enhanced their fatigue resistance and interfacial toughness. OBJECTIVES: This scoping review aims to map graded designs in dental ceramics, distinguish their methodological approaches with their material characteristics and properties, and understand the factors affecting the outcomes of each of the graded approaches. METHODS: A systematic electronic search was performed with the databases MEDLINE (PubMed), Scopus, Cochrane Library, EBSCO, and Google Scholar along with a manual search. RESULTS: About 2675 articles were initially found from all the searches with no date restriction till July 2023. After rejecting duplicates and based on exclusion criteria, about 52 articles were included. SIGNIFICANCE: Methodological approaches in grading such as glass-infiltration and silica-infiltration have been investigated on pre-sintered zirconia. The type of infiltration and the method of infiltrate application significantly influenced the phase transformation of zirconia, its microstructure, surface hardness, fracture toughness, flexural strength, wear, and fatigue strength of graded dental zirconia. Interlayers were accommodated between metal-ceramic and veneer-core all-ceramic layers. Fractions of zirconia-porcelain and alumina-porcelain showed high bending strength and better stress distribution. The results of finite element analysis studies predicted that using 10-layered graded layers reduced the stresses at the crown-cement-dentin interface.

Artificial intelligence systems in dental shade-matching: A systematic review.

PURPOSE: Uses for artificial intelligence (AI) are being explored in contemporary dentistry, but artificial intelligence in dental shade-matching has not been systematically reviewed and evaluated. The purpose of this systematic review was to evaluate the accuracy of artificial intelligence in predicting dental shades in restorative dentistry. METHODS: A systematic electronic search was performed with the databases MEDLINE (PubMed), Scopus, Cochrane Library, and Google Scholar. A manual search was also conducted. All titles and abstracts were subject to the inclusion criteria of observational, interventional studies, and studies published in the English language. Narrative reviews, systematic reviews, case reports, case series, letters to the editor, commentaries, studies that were not AI-based, studies that were not related to dentistry, and studies that were related to other disciplines in dentistry, other than restorative dentistry (prosthodontics and endodontics) were excluded. Two investigators independently evaluated the quality assessment of the studies by applying the Joanna Briggs Institute Critical Appraisal Checklist for Quasi-Experimental Studies (non-randomized experimental studies). A third investigator was consulted to resolve the lack of consensus. RESULTS: Fifty-three articles were initially found from all the searches combined from articles published from 2008 till March 2023. A total of 15 articles met the inclusion criteria and were included in the systematic review. AI algorithms for shade-matching include fuzzy logic, a genetic algorithm with back-propagation neural network, back-propagation neural networks, convolutional neural networks, artificial neural networks, support vector machine algorithms, K-nearest neighbor with decision tree and random forest, deep learning for detection of dental prostheses based on object-detection applications, You Only Look Once-YOLO. Moment invariant was used for feature extraction.  XG (Xtreme Gradient) Boost was used in one study as a gradient-boosting machine learning algorithm. The highest accuracy in the prediction of dental shades was the decision tree regression model for leucite-based dental ceramics of 99.7% followed by the fuzzy decision of 99.62%, and support vector machine using cross-validation of 97%. CONCLUSIONS: Lighting conditions, shade-matching devices and color space models, and the type of AI algorithm influence the accuracy of the prediction of dental shades. Knowledge-based systems and neural networks have shown better accuracy in predicting dental shades.

Investigation of Spark Plasma Sintering on Microstructure-Properties of Zirconia Reinforced Fluormica Glass for Dental Restorations.

BACKGROUND: Conventional sintering methods of dental ceramics have limitations of high temperature and slow cooling rates with requirements of additional heat treatment for crystallization. Spark plasma sintering (SPS) is an emerging technique that has the potential to process dental restorations with dense microstructures and tailor-made clinically relevant properties with optimized processing parameters. This study explored the potential of the SPS of zirconia-reinforced fluormica glass (FM) for dental restorative materials. METHODS: FM glass frit was obtained through the melt-quench technique (44.5 SiO2-16.7 Al2O3-9.5 K2O-14.5 MgO-8.5 B2O3-6.3 F (wt.%)). The glass frit was ball-milled with 20 wt.% of 3 mol% yttria-stabilized zirconia (FMZ) for enhanced fracture toughness. The mixtures were SPS sintered at a pressure of 50 MPa and a heating rate of 100 °C/min for 5 min with an increase in temperature from 650-750 °C-850 °C-950 °C. Phase analysis was carried out using XRD and microstructural characterization with SEM. Micro-hardness, nano-indentation, porosity, density, indentation fracture toughness, and genotoxicity were assessed. CONCLUSIONS: The increase in the SPS temperature of FMZ influenced its microstructure and resulted in reduced porosity, improved density, and optimal mechanical properties with the absence of genotoxicity on human gingival fibroblast cells.

Glazing as a bonding system for zirconia dental ceramics.

Studies have reported challenges of debonding of dental zirconia crowns to from luting cement and prepared teeth. The aim of the study was to explore the application of dental glazing systems for enhancing the bonding of zirconia dental ceramics to luting resin cement. Commercial glaze powder and liquid (Vita Akzent) and experimental mica-based glaze powders were used for the study. X-ray diffraction analysis of the glaze powders (XRD) and Fourier Transform InfraRed Spectroscopy (FTIR) was done on the glaze liquid. Sandblasted sintered dental zirconia (Katana, Noritake) were the control samples. Glazed zirconia samples were coated with commercial glaze and experimental glaze powders which were further etched with 5% hydrofluoric acid. Shear bond strengths of sandblasted and glazed zirconia samples to resin composites were evaluated. XRD of commercial and experimental glaze powders revealed a broad peak confirming the amorphous nature of glass and FTIR analysis of the glaze liquid revealed symmetrical stretching (CH2-CH3) of the alcohol group indicating a mixture of iso-butane and ethanol. Glazed and etched zirconia showed significantly higher shear bond strength to resin cement compared to sand-blasted zirconia. The study confirms the glassy nature of dental glaze powders and the presence of ethanol-based mixtures in the commercial glaze liquid. Glazing systems have the potential to be explored for enhancing the bonding of non-etchable zirconia ceramics to resin cement and tooth substrates.

Case-based Virtual Seminars on Masticatory Muscle Disorders during the COVID-19 Pandemic.

Due to the significant influence of COVID-19 pandemic on dental education in the recent past, interactive educational strategies were explored to engage students. Case-based seminars (CBS) were proposed on masticatory muscle disorders (MMDs) for post-graduate dental students through integration of pathophysiology with its etiology, diagnosis, and management. Effectiveness of CBS was done at Kirkpatrick's level 1 and level 2 hierarchy with a pre-test and a post-test. CBS enhanced learning outcomes of post-graduate students in understanding MMDs. Thus, this report could serve as a useful model for other dental schools in prosthodontic post-graduate curriculum.

Troubleshooting Ocular Prosthesis: A Case Series.

This case series reports on clinical challenges faced during the rehabilitation of custom ocular prosthesis. Each of these cases relate the challenges of making ocular impressions for an improved retention and support of ocular prosthesis and presents the significance of scleral contouring in overcoming cosmetic defects of the eye. In addition, evaluation of scleral wax pattern, methods of iris location and scleral characterization methods in ocular rehabilitation are further discussed.

A technique of designing a 3-dimensionally printed elastomeric impression mixing tip for reuse: A step toward eco-friendly dentistry.

Single-use plastics in dentistry are significant contributors to biomedical waste. Various plastic tubes and mixing cartridges with different plastic mixing tips are widely used for elastomeric impression materials. To minimize the dental plastic footprint, a technique is described for making reusable plastic mixing tips for elastomeric impression materials.

Machinability of Zirconia Toughened Mica Glass Ceramics for Dental Restorations / Usinabilidade de cerâmica de vidro de mica temperada com zircônia para restaurações dentárias

Objective: For a dental material to be machinable for CAD/CAM technology, it must offer convenient machining, under a given set of cutting conditions. Quantitative evaluation of machinability has been assessed in literature through various parameters such as tool wear, penetration rates, surface roughness, cutting force and power. A machinable ceramic will typically demonstrate a higher tool penetration rate with signs of reduced diamond tool wear and edge chipping. The purpose of this in vitro study was to evaluate the feasibility of machining an experimental ceramic, 20 wt.% zirconia reinforced mica glass ceramics (G20Z) for indirect dental restorations and compare the tool penetration rates of G20Z to commercially available dental ceramics, Presintered Zirconia (PSZ) and IPS emax CAD. Material and Methods: Precursors of base glass (SiO2 -Al2O3 -K2O -MgO-B2O3 -F) were melted at 15000C for 2 h in a platinum crucible and quenched in deionised water. The glass frit was ball milled with 20 wt. % YSZ (G20Z) and subject to two stage heat treatment in a muffle furnace. Specimens of G20Z (12 X 2 mm) were evaluated for their feasibility of machining under varying spindle speed, depth of cut, and feed rates. Influence of depth of cut, spindle speed and feed rate (vc=8000-16000 rpm, d=0.4-0.8 mm, f=0.1- 0.3 mm/tooth) on cutting forces, material response, surface roughness and tool wear were investigated. Tool penetration rates, tool wear and margin chipping were also evaluated and compared with Pre-sintered Zirconia (PSZ) and e.max CAD in a custom dental milling surveyor at 30,000 rpm with a load of 0.98 N under water lubrication for 6 min. Tool penetration rates were calculated as the ratio of length of cut and milling time with a measuring microscope and scanning electron microscope was used for tool wear and edge chipping. ANOVA and Tukey Kramer tests were used for statistically comparing the means of each group. Results: Spindle speed and feed rate play a significant role in influencing surface roughness, thrust force, cutting forces and tool wear. Penetration rates of G20Z (0.32 ±0.12 mm/min) was significantly greater than PSZ (0.26 ±0.06 mm/min) and IPS e.max CAD (0.21 ±0.05 mm/min). SEM observations reveal tool abrasion and edge chipping regardless of the ceramic type. Conclusion: High spindle speeds delivers low cutting forces with an average surface roughness of 1.61 µm, with abrasive wear of the tool insert and brittle fracture of zirconia mica glass ceramic composites. G20Z with its machinable nature demonstrates greater tool penetration rates than PSZ and IPS e.max CAD. Tool wear and edge chipping is seen in all the investigated ceramics. (AU)

Objetivo: Para que um material odontológico seja usinável para a tecnologia CAD / CAM, ele deve oferecer uma usinagem conveniente, sob um determinado conjunto de condições de corte. A avaliação quantitativa da usinabilidade tem sido avaliada na literatura por meio de vários parâmetros, como desgaste da ferramenta, taxas de penetração, rugosidade da superfície, força de corte e potência. Uma cerâmica usinável normalmente demonstrará uma maior taxa de penetração da ferramenta com sinais de desgaste reduzido da ferramenta de diamante e lascamento da borda. O objetivo deste estudo in vitro foi avaliar a viabilidade da usinagem de uma cerâmica experimental, 20% em peso de cerâmica de vidro de mica reforçada com zircônia (G20Z) para restaurações dentárias indiretas e comparar as taxas de penetração da ferramenta de G20Z com as cerâmicas dentais comercialmente disponíveis, Zircônia Presinterizada (PSZ) e IPS emax CAD. Material e Métodos: Precursores de vidro base (SiO2-Al2O3-K2O -MgO-B2O3 -F) foram fundidos a 15000C por 2 h em um cadinho de platina e temperados em água deionizada. A frita de vidro foi moída com 20% em peso de YSZ (G20Z) e submetida a tratamento térmico em duas fases em mufla. Amostras de G20Z (12 x 2 mm) foram avaliadas quanto à sua viabilidade de usinagem sob variação de velocidade do fuso, profundidade de corte e taxas de avanço. A influência da profundidade de corte, velocidade do fuso e taxa de avanço (vc = 8000-16000 rpm, d = 0,4-0,8 mm, f = 0,1- 0,3 mm / dente) nas forças de corte, resposta do material, rugosidade da superfície e desgaste da ferramenta foram investigadas. As taxas de penetração da ferramenta, o desgaste da ferramenta e o lascamento da margem também foram avaliados e comparados com Zircônia pré-sinterizada (PSZ) e e.max CAD em um topógrafo de fresamento dentário personalizado a 30.000 rpm com uma carga de 0,98 N de lubrificação subaquática por 6 min. As taxas de penetração da ferramenta foram calculadas como a razão entre o comprimento de corte e o tempo de fresamento com um microscópio de medição e um microscópio eletrônico de varredura foi usado para o desgaste da ferramenta e lascamento da borda. Os testes ANOVA e Tukey Kramer foram usados para comparar estatisticamente as médias de cada grupo. Resultados: a velocidade do fuso e a taxa de avanço desempenham um papel significativo em influenciar a rugosidade da superfície, força de impulso, forças de corte e desgaste da ferramenta. As taxas de penetração de G20Z (0,32 ± 0,12 mm / min) foram significativamente maiores do que PSZ (0,26 ± 0,06 mm / min) e IPS e.max CAD (0,21 ± 0,05 mm / min). As observações do SEM revelam a abrasão da ferramenta e o lascamento da borda, independentemente do tipo de cerâmica. Conclusão: As altas velocidades do fuso proporcionam baixas forças de corte com uma rugosidade superficial média de 1,61 µm, com desgaste abrasivo do inserto da ferramenta e fratura frágil de compósitos de cerâmica de vidro de zircônia. G20Z com sua natureza usinável demonstra maiores taxas de penetração da ferramenta do que PSZ e IPS e.max CAD. O desgaste da ferramenta e o lascamento da borda são vistos em todas as cerâmicas investigadas. (AU)

Current status of gerodontology curriculum in India and other parts of the world: A narrative review.

BACKGROUND: The current rise in the world's geriatric population has placed additional demands on dental professionals, as the management of geriatric patients requires distinct competencies. AIM: To review and perform a content analysis of the gerodontology undergraduate curriculum worldwide. DATA SOURCES: A search was carried out in PubMed, Web of Science, ERIC and EMBASE databases for the period-July 2008 till May 2019, using MeSH terms. A search for websites of Indian universities was also done, and undergraduate curricula were screened. STUDY ELIGIBILITY CRITERIA: The study included articles related to the undergraduate curriculum, which contained training in geriatric dentistry. Articles in foreign languages and those related to dental hygienists were excluded. RESULTS: A total of 218 articles were obtained, of which 19 met the inclusion criteria. A total of 301 colleges taught gerodontology. Amongst them, 50 colleges had a gerodontology department. Clinical training and outreach experience were provided in 175 and 73 colleges, respectively. There are no reports on the status of gerodontology in Asian countries (excluding Japan). In India, gerodontology is not taught as a separate subject. However, few gerodontology-related topics are covered in clinical subjects. CONCLUSIONS: There seems to be a wide variation in the content of gerodontology curriculum taught worldwide. Other than the European and American regions, gerodontology is yet to develop in other parts of the world. In India, a robust training programme is required to address the lack of dental care providers for the geriatric population using guidelines established by ECG and ADEA.

A reproducible 3-point contact device for tripoding a definitive cast.

A technique for tripoding a definitive cast by using a reproducible 3-point contact device is proposed and compared with the conventional technique.

Zirconia toughened mica glass ceramics for dental restorations: Wear, thermal, optical and cytocompatibility properties.

BACKGROUND: In an effort to design novel zirconia reinforced mica glass ceramics for dental restorations, clinically relevant properties such as wear, coefficient of thermal expansion, optical transmittance, and cytocompatibility with human gingival fibroblast cell lines were investigated in the present study. MATERIALS & METHODS: Microstructure analysis of two body wear of heat treated mica glass ceramic ceramics (47.2 SiO2-16.7 Al2O3-9.5 K2O-14.5 MgO-8.5 B2O3-6.3F wt.%) reinforced with 20wt.% YSZ, were evaluated against a steatite antagonist in a chewing simulator following Willytec Munich method. In addition, Coefficient of thermal expansion (CTE), total transmittance, scattering coefficient and cytocompatibility on human gingival fibroblast cell lines were performed and compared to the commercially available dental ceramic systems. RESULTS: The experimental mica glass ceramic demonstrate micro-ploughing, pull out and debris formation along the cutting surface, indicating abrasive wear mechanism. Thermal expansion of mica glass ceramic composite was recorded as 5×10-6/°C, which is lower than the thermal expansion of commercially available core and veneering ceramics. Further, significant differences of transmittance and scattering coefficient of mica glass ceramics with 20wt.% YSZ with commercial dental ceramics was found and extensive fibroblast cell spreading with filopodial extension, cell-to-cell bridges and proliferation with human gingival fibroblast cell lines. CONCLUSION: With acceptable cytocompatibility with human gingival fibroblast cells and better wear properties with respect to commercial IPS emax Press, the mica glass ceramic composites (47.2 SiO2-16.7Al2O3-9.5 K2O-14.5 MgO-8.5 B2O3-6.3F wt.%) with 20wt.% YSZ have the potential for dental restorative applications as machinable veneering ceramics.

Are Multiple Choice Questions for Post Graduate Dental Entrance Examinations Spot On?-Item Analysis of MCQs in Prosthodontics in India.

BACKGROUND: Construction of appropriate test items is a challenge in preparing quality multiple choice questions. Item analysis provides valuable feedback data on validity of multiple choice questions. The present study was conducted to evaluate the difficulty index, discrimination index and distracter efficiency of the items present in the multiple choice questions of post graduate dental entrance examinations. METHODS: A list consisting of 20 MCQs was taken from the entrance exam books of MCQs on an introductory topic and administered to 104 undergraduate students. RESULTS: In the present study 15% of the MCQs related to impression making procedure were difficult with difficulty index (p) less than 30%, 15% were poor discriminators and 55% had at least one non-functional distracter. CONCLUSION: Item analysis of MCQs in post graduate entrance examinations demonstrated low difficulty index, discrimination index and distracter efficiency. Hence, we propose a strong need for faculty training in test constructors and their post validation.

Zirconia toughened mica glass ceramics for dental restorations.

OBJECTIVE: The objective of the present study is to understand the role of yttria stabilized zirconia (YSZ) in achieving the desired spectrum of clinically relevant mechanical properties (hardness, elastic modulus, fracture toughness and brittleness index) and chemical solubility of mica glass ceramics. METHODS: The glass-zirconia mixtures with varying amounts of YSZ (0, 5, 10, 15 and 20wt.%) were ball milled, compacted and sintered to obtain pellets of glass ceramic-YSZ composites. Phase analysis was carried out using X-ray diffraction and microstructural characterization with SEM revealed the crystal morphology of the composites. Mechanical properties such as Vickers hardness, elastic modulus, indentation fracture toughness and chemical solubility were assessed. RESULTS: Phase analysis of sintered pellets of glass ceramic-YSZ composites revealed the characteristic peaks of fluorophlogopite (FPP) and tetragonal zirconia. Microstructural investigation showed plate and lath-like interlocking mica crystals with embedded zirconia. Vickers hardness of 9.2GPa, elastic modulus of 125GPa, indentation toughness of 3.6MPa·m1/2, and chemical solubility of 30µg/cm2 (well below the permissible limit) were recorded with mica glass ceramics containing 20wt.% YSZ. SIGNIFICANCE: An increase in hardness and toughness of the glass ceramic-YSZ composites with no compromise on their brittleness index and chemical solubility has been observed. Such spectrum of properties can be utilised for developing a machinable ceramic for low stress bearing inlays, onlays and veneers.

Prosthetic rehabilitation of a geriatric patient with squamous cell carcinoma of the buccal mucosa: A report of clinical challenges.

OBJECTIVE: This article aims to highlight the rehabilitation of a geriatric patient with an orofacial cheek defect by an extraoral silicone prosthesis. METHODOLOGY: Structured extra- and intra-oral examination of tissues coupled with a justified choice of impression materials, techniques, and prosthetic rehabilitation with a high-temperature vulcanizing silicone was done. RESULTS: The presence of compressible tissues, static appearance of the prosthesis during patient's facial movements, variability in complexion of the skin around the defect, and manipulating heat-vulcanized silicone were the challenges faced during clinical procedures. Rehabilitation of orofacial defects is a challenge to the maxillofacial prosthodontist due to limited material properties, soft-tissue mobility, compromised retention of prostheses, and poor patient acceptance. The fabrication of a facial prosthesis is as much an art as it is science. Prosthetic form, coloration, and texture of the prosthesis must be indiscernible from the surrounding tissues. Prosthetic reconstruction helps in restoring functional disability and aids in raising the morale of the patient. Prosthetic options of rehabilitation include interim and definitive conventional adhesive-retained or implant-retained prostheses. Initially, vulcanite rubber and acrylic resins were used for reconstruction. CONCLUSION: We report clinical challenges during extraoral rehabilitation of orofacial tissues with a silicone cheek prosthesis such as impression making and shade matching during restoration in a geriatric patient. The use of silicone maxillofacial elastomers allowed intrinsic, extrinsic coloring and ease of construction.

A novel speech prosthesis for mandibular guidance therapy in hemimandibulectomy patient: A clinical report.

Treating diverse maxillofacial patients poses a challenge to the maxillofacial prosthodontist. Rehabilitation of hemimandibulectomy patients must aim at restoring mastication and other functions such as intelligible speech, swallowing, and esthetics. Prosthetic methods such as palatal ramp and mandibular guiding flange reposition the deviated mandible. Such prosthesis can also be used to restore speech in case of patients with debilitating speech following surgical resection. This clinical report gives detail of a hemimandibulectomy patient provided with an interim removable dental speech prosthesis with composite resin flange for mandibular guidance therapy.

Bridging the gap in 1(st) year dental material curriculum: A 3 year randomized cross over trial.

BACKGROUND: Case-oriented small group discussions (COSGDs) can help students to correlate and integrate the basic science of dental materials into clinical application. We used COSGDs along with didactic lectures in dental material curriculum and hypothesized that case-oriented group discussions would be more effective than traditional lecture alone in terms of performance of students, student perception on the above two teaching methodologies and the feasibility in classes of 2010, 2011 and 2012. METHODS: A total of 170 students were taught using both COSGD and didactic lecture in a randomized controlled crossover trial design. Their performance was assessed through multiple-choice questions (MCQs) as part of the formative assessment, and their perception was assessed through Likert scale questionnaire. RESULTS: The mean difference in the scores between case-oriented group discussions with lecture and didactic lecture showed significant difference only in few topics. Around 94-96% of students perceived COSGD with didactic lecture help them understand theory better; 76-92% of students feel more comfortable asking questions in a group discussion; 89-98% of students feel such discussions motivate them and 91-100% of students agree that discussions make the subject interesting in the respective years of 2010, 2011 and 2012. CONCLUSION: Effectiveness of COSGD in terms of scores through MCQs is comparable to traditional lecture. However, most of the students perceive COSGD help them understand the theory better; co-relate clinically; more motivating and interesting than a traditional lecture. Feasibility in institution needs more time and resources to conduct COSGD within the dental material curriculum.

Management of velopharyngeal disorders. A case series.

Patients with acquired defects or congenital malformations of the palate exhibit disturbances in speech, including hypernasality, nasal emission, and decreased intelligibility of speech. Maxillofacial prosthetic treatment can reestablish the palatopharyngeal integrity to provide the potential for acceptable speech. This article describes a case series of patients with palatopharyngeal disorders and their treatment approaches.