Tooth Preparation Research Articles

Three-dimensional assessment of internal adaptation measurement of three cad/cam ceramic systems

This study aimed to evaluate the internal adaptation of three different computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic crowns. The internal adaptation of a polymer-infiltrated ceramic network material (Vita Enamic [VE]) was compared to two machinable glass-ceramics; Zirconia-reinforced lithium silicate (Vita Suprinity [VS]) and a lithium disilicate glass-ceramic (IPS e.max. CAD). Thirty human premolars of average size were prepared (n=10 each group) by computer numerical control to fulfill the criteria of all-ceramic crown design. Optical impressions were taken for each tooth preparation using the CAD/CAM scanner. Thirty crowns were fabricated using CAD/CAM system and divided into three groups (IPS e.max, VE, and VS). To assess the internal fit of tested crowns, the gap between the intaglio of each crown and the corresponding tooth surface was evaluated using a 3D digital scanner using the Triple-scan Protocol. One-way ANOVA followed by Tukey Post Hoc statistical tests were used to statistically analyze results of the internal fit. There was a statistically significant difference for all groups at the four axial walls (p = 0.000002). For total internal fit between groups, comparisons showed a statistically significant difference between all tested groups (p=0.000002). When each pair of groups was statistically compared with each other, all pair comparisons showed a statistically significant difference. IPS e.max CAD had the best internal fit, followed by Vita Enamic, then Vita Suprinity. For all ceramics tested, values of internal fit of all ceramics tested were within the clinically acceptable range.

Overview of Lithium Disilicate as a restorative material in dentistry

Lithium disilicate was first introduced to the dental field as an indirect restorative material in 1998. It was marketed under the name IPS Empress 2, and was intended for use with press technology. It was later replaced by modified versions including IPS e.max® Press and IPS e.max® CAD. Newer versions have since emerged,namely Amber Mill GC Initial and CEREC Tesseratwo.The latter has part crystal composition of lithium disilicate,embedded in a glassy zirconia matrix. The CAD versionis provided in a meta-silicate state, characterised by40% platelet-shaped lithium meta-silicate crystals and aglassy matrix that is bluish in colour. To obtain the desired lithium disilicate structure and tooth shades, a process ofcrystallization is required. This involves firing at 840 °C,for 25 minutes. The resulting glass-ceramic material has the benefit of providing maximum aesthetic translucency along with good fracture resistance of about 2MPa, and mechanical strength of 360MPa. Developments in the all-ceramic dental materials have led to improvements in their physical properties and aesthetic appeal, leading to a substantial increase in their clinical use. This paper present a review of lithium disilicate with particular reference to its chemical composition, aesthetic versatility, and durability for use in crowns, veneers, and implant retained restorations. It also covers the recommended techniques prescribed to ensure predictable bonding and cementation. An electronic literature search on the use of lithium disilicate in dentistry was carried out using EBSCOhost search engine. This included all papers relating to its use for conventional veneers, crowns and bridge work, for CAD/CAM restorations, dentine bonding procedures and luting agents. It covered all papers published in peer reviewed journals from 1988 to 2021. The review indicates that lithium disilicate can be a useful and versatile material in dentistry providing it is handled correctly and the recommended tooth and restoration surface preparations and bonding procedures are carried out. The latter involves tooth etching and silane treatment of the fitting surfaces of restorations prior to cementation to improve adhesion and fracture resistance.

A literature review on various luting cements used in dentistry

The success rate of the given fixed partial denture and the longevity of the fixed partial denture is depend on the tooth preparation and the usage of the luting cement under the fixed partial denture prosthesis. Luting cement plays an important role in maintaining or securing the fixed partial denture prosthesis in the cemented position. Luting cement should be bio compatible, it should be non-irritating to the underlying tooth structure and non-irritating to the pulp, it should maintain the adequate marginal seal. In recent days so many newer luting cements has been introduced in to the dentistry, that are claiming for good as well as better clinical performance from the existing cements in the terms of improved and better characteristic properties. The different cements which can be used as luting cements are glass ionomer cements, zinc phosphate, zinc poly carboxylate, zinc oxide eugenol, newer cements like resin modified glass ionomer cements, compomers and resin cements.

Clinical report and fractographic analysis of a fractured partial laminate veneer

Ceramic partial laminate veneers represent a conservative option for the correction of morphological abnormalities, diastemas, and fractured anterior teeth, with minimal or no tooth preparation. The present clinical report describes the use of a partial laminate veneer to correct the shape of a maxillary right central incisor to match the restoration of the more damaged adjacent tooth. The failure of the partial laminate veneer after only 18 months was analyzed using a systematic fractographic approach, identifying critical considerations that should be addressed when providing this type of restoration.

Comparison of occlusal contact errors of 6 chairside CAD/CAM crowns: a self-controlled clinical study.

The purpose of this self-controlled clinical study was to evaluate the trueness of occlusal contacts of chairside CAD/CAM crowns fabricated using different ceramic materials. Ten volunteers (8 females, 2 males, average aged 20-30) were recruited in this study registered in the Clinical Trials Registry (#NCT05346744). After tooth preparation on tooth 36 or 46, an optical scan unit (CEREC Omnicam, Sirona Dental Systems, Germany) was utilized to perform the intraoral scanning. For each volunteer, 6 crowns were fabricated via the chairside CAD/CAM process (CEREC, Sirona Dental Systems, Germany) using the following materials: InCoris TZI (ZIR), Celtra Duo (CD), e.max CAD (EMA), UP.CAD (UP), Enamic (ENA) and Hyramic (HY). The microhardness of the milled surfaces was measured through a Vickers hardness Tester (HVS-50Z, Trojan, China). Together with the amount of occlusal adjustment, the occlusal contact trueness at both milling and postprocessing stages were quantitatively analyzed by using a high-precision scanner (ATOS, GOM Technologies, USA) and a reverse engineering software (Geomagic Control, 3D Systems, Rock Hill, SC). The times of chairside occlusal adjustment were also recorded. Data were analyzed by one-way analysis of variance (ANOVA) and ANOVA with randomized block design followed by Bonferroni test (p = 0.05). Significant differences were found in surface microhardness of the materials tested (CD > EMA ~ UP > ENA > HY > ZIR, p < 0.05). Regarding the occlusal contact trueness at milling stage, ZIR showed the lowest (p < 0.05), while no significant difference was found among others (p > 0.05). At postprocessing stage, except for ENA, the occlusal contact trueness of ZIR was significantly lower than that of others (p < 0.05). As for occlusal adjustment amount, ZIR was lower than CD and ENA (p < 0.05). In addition, ENA, HY and ZIR required fewer times of occlusal adjustment than EMA, UP and CD. The type of chairside CAD/CAM ceramic materials affected the occlusal contact trueness throughout the process of manufacturing and the amount of clinical occlusal adjustment as well. Zirconia exhibited the worst occlusal contact trueness at both milling and postprocessing stages, while the amount of occlusal adjustment was the least, which recommended the least occlusal compensation. For better trueness, different negative occlusal offsets are suggested to be applied in the design process, so as to suit the material of the restoration.

Physicochemical, Mechanical, and Esthetic Properties of the Composite Resin Manipulated with Glove Powder and Adhesive as a Modeling Liquid.

Composite resins with low flowability are usually handled and manipulated before insertion into the tooth preparation with gloved hands and/or using an instrument covered with a little amount of adhesive to facilitate modeling. We investigated if the modeling techniques (combined or not) affected physicochemical and esthetic properties of a composite resin. Specimens were fabricated and divided into groups according to the handling/modeling technique: Gloved-hands (composite was hand-manipulated with powdered latex gloves); Adhesive (adhesive was used in between the composite layers); Gloved-hands + Adhesive; Control (no adhesive and no touch with gloved-hands). The highest values for flexural strength (MPa), modulus of elasticity (GPa), and fracture toughness (MPa.m0.5) were obtained for Adhesive and Gloved-hands + Adhesive (p < 0.05); the lowest values were obtained for Control and Gloved-hands (p < 0.05). The Control group had the highest sorption. The Gloved-hands (p < 0.05) group had the highest solubility. Adhesive and Gloved-hands + Adhesive had a similar solubility (p > 0.05). The Control group (p < 0.05) had the lowest solubility. There was no statistical interaction between translucency vs. handling/modeling techniques and color stability vs. handling/modeling techniques. Adhesive as a modeling liquid protected the composite against sorption and solubility (if powdered gloves were used) and improved its physical/mechanical properties. Translucency and color stability were not correlated with modeling techniques.

Influence of Operator Experience on Clinically Achieved Convergence Angle of Tooth Preparations for Metal-Ceramic Crowns

Objective: To compare clinically achieved convergence angle values of teeth prepared by operators having different experience levels and relate them with recommended values.&#x0D; Study Design: Cross-sectional analytical study.&#x0D; Place and Duration of Study: Department of Prosthodontics, Islamic International Dental Hospital, Islamabad Pakistan, from Dec 2018 to May 2019.&#x0D; Methodology: A total of 100 crown dies of molars prepared by House Officers (Group-I) and Postgraduate Residents (Group-II) of the Prosthodontics department were collected retrospectively. Auto CAD 2007 software was used for the measurement of convergence angle. One sample t-test was applied to compare the mean convergence angle values with theoretical values. In addition, independent samples t-test was applied to compare convergence angle values among Clinician Groups with different experience levels.&#x0D; Results: Significant difference (p &lt;0.001) was found between the tooth preparations performed by both study Groups. Greater convergence angles were achieved by operators having lesser experience, i.e., Group-I (House Officers) in contrast to Group-II (Post-graduate Residents). The convergence angle achieved by both study groups was far greater than the recommended values (4-14 degrees).&#x0D; Conclusion: Significant discrepancy exists between the recommended guidelines and the clinically achieved convergence angle values recorded in this study. The recommended values were rarely achieved. Operator experience seems to be an important determinant for achieving better convergence angle values.

New approach to expedite the delivery of the final crowns for teeth requiring crown lengthening surgery: a pilot study

BackgroundThe healing period from crown lengthening procedures (CLPs) often delays the final crown delivery. This study aimed to explore the feasibility of a new approach expediting the delivery of the final crowns for teeth requiring CLPs.MethodsTeeth requiring CLPs and single-crown restorations between the canine and the second molar were included. After the initial tooth preparation, a CLP was performed. In the experimental group, the final tooth preparation and final impression were made during the CLP; the final crown was then delivered at the suture-removal appointment. In the control group, the final impression was made 8 weeks after the CLP. The level of gingival margin (GM), pocket depth (PD), and crestal bone levels (CBLs) were compared between the two groups before CLPs (T0), at delivery of the crowns (T1), and at 12 months in function (T2).ResultsTwenty-one lithium-disilicate crowns were delivered to 20 subjects and followed up. The mean interval between the CLPs and the delivery of crowns was 2.5 weeks for the experimental group and 12 weeks for the control group. No significant differences were observed between the two groups in the level of GM, PD, and CBLs at each time point. No significant treatment difference in crestal bone loss was observed between the two groups at T2 (Experimental = -0.11 mm, Control = -0.03 mm; p = 0.67).ConclusionMaking the final tooth preparation and the final impression at the CLP significantly reduced the time between the CLP and the delivery of the final crown and showed comparable clinical outcomes.

Marginal and Internal Misfit of Occlusal Veneers Made in Resin-matrix Ceramics.

Considering that misfit is a significant predictor of the clinical success of indirect restorations, the objective of this study was to evaluate the marginal and internal misfit of two computer-aided design and manufacturing (CAD/CAM) RMC ceramic materials used as occlusal veneers (OVs) of different thicknesses. A CAD model of a mandibular first molar was obtained and OV preparations 0.5-, 1.0-, and 1.5-mm thick were modeled and milled in two different materials (n=10/group): resin nanoceramic (RNC) and polymer-infiltrated ceramic network (PICN). Using the same CAD model, tooth preparations were milled in fiber-reinforced epoxy resin (n=20/thickness). The marginal and internal misfit of the restorations was assessed by X-ray microtomography. The measurements of the marginal gap (MG) and absolute marginal discrepancy were performed in two locations on each slice, whereas internal gap (IG) measurements were performed at ten locations on each slice. The data obtained were analyzed using two-way analysis of variance and Tukey post-hoc tests (α=0.05). No significant effect was attributable to the material type or material-thickness interaction for the MG, absolute marginal discrepancy (AMD), or IG (p>0.05). However, the thickness significantly affected the IG of the restorations (p<0.05). CAD/CAM RNC and PICN systems presented similar MG and AMD for OVs 0.5-, 1.0-, and 1.5-mm thick. However, the IG varied between thicknesses.

THE EFFECT OF CONVERGENCE ANGLE OF TOOTH PREPARATION IN PATIENTS WITH GENERAL PERIODONTITIS ACCORDING FINITE ELEMENT ANALYSIS

Purpose of the research. To study the character of displacement and stress distribution after prosthetics of the lower central incisor with the metal-ceramic crown, depending on the convergence angle of preparation and the degree of resorption of alveolar septa using finite element analysis. Research methods. The computer models have been studied using the calculated software complex “Lira 9.6” to reproduce intact (before preparation) and treated teeth, taking into account subsequent imposition of a metal-ceramic crown. Calculations have been made for different convergence angles, from 20 to the maximum possible, for four types of loads (constant from own weight; vertical from food biting off; at an angle of 300 to vertical; at an angle of 450 to vertical) and for different degrees of preservation of alveolar septa: 100 %, 75 % and 50 %. Scientific novelty. It has been established that in the calculated model the increase of the convergence angle of tooth surfaces, as well as the decrease in alveolar septa height, cause the increase in displacements in the biomechanical system “crown – tooth – alveolar bone”, the maximum of which are localized in the neck area of the tooth on its lingual surface. The increase in the angle of preparation causes the increase in stresses in the same area, while the increase in the degree of resorption of alveolar septa results with the displacement of the maximum stress zone from the tooth neck to the apical part of the root. Conclusions. The obtained results indicate the need for tooth preparation with the minimum convergence angle of surfaces in patients with general periodontitis. It could prevent the risks of the progression of the pathological process in periodontal tissues due to the increase of stresses and displacements.

Guideline for chairside computer aided design and computer aided manufacturing all ceramic rehabilitation

With the rapid development of digital techniques and the lack of reference standards for chairside computer aided design and computer aided manufacturing (CAD/CAM) operation and application, it is imperative to draft guidelines for chairside CAD/CAM restoration techniques for all ceramics. Therefore, the Society of Prosthodontics, Chinese Stomatological Association recruited experts to compose a recommended application guideline based on the relevant literatures and clinical experiences, including the selection of indications, tooth preparation, optical impression making and other key steps. This guideline is aimed at providing a standardized operation procedure to improve the quality and long-term success rate of chairside CAD/CAM rehabilitation for all ceramics.

The practicability of different preparation of mandibular molar restored by modified endocrown with intracanal extension: Computational analysis using finite element models

Background and objectivePost-core-crown (PCC) and endocrown are two common restorative methods for severely damaged molars, but exhibit disadvantages. This study aimed to explore the practicability of modified endocrown with a 2 mm intracanal extension (MED) to restore defective teeth using finite element analysis (FEA). MethodsFive groups of numerical models of mandibular molars restored by three MEDs, a PCC, and a routine endocrown after root canal treatment were devised by FEA software. We constructed 4 mm, 3 mm, and 2 mm thickness of MED restorations to restore mandibular molars that were prepared to 1 mm, 2 mm, and 3 mm from the cemento-enamel junction (CEJ). Furthermore, PCC and routine endocrown were used to compare the stress distribution with MED. Lithium disilicate glass-ceramics (EMAX) and resin nanoceramics (LU) were considered restorative materials, and a vertical load of 600 N and an oblique load of 200 N were applied to the restorations. ResultsIn three MEDs by LU, 2 mm thickness of restoration generated the highest stress on prepared teeth, while the thickness of EMAX did not significantly influence the stress value. MED by LU generated higher stress around the CEJ, and reduced the stress on the middle and lower root compared to MEDs by EMAX, PCC by EMAX, and PCC by LU. MED by EMAX caused lower stress around the CEJ, and generated higher stress in the chamber walls after extended root canals compared with MED by LU, endocrowns by LU, and endocrowns by EMAX. There was an evident stress concentration at the last but one layer, which was a thin area of the tooth root in all restorative models. ConclusionsThe use of modified endocrown may be considered an effective restorative method to restore defective mandibular molar, but suitable restorative material must be selected based on the tooth preparation method and deficiencies in the tooth structure.

A case of precise prosthesis under the direction of target restoration space analysis after multidisciplinary combination therapy.

Quantitative grinding of abutment teeth is needed in crown and bridge restoration. Accurate quantitative preparation of teeth is one of the goals of minimally invasive restoration. In this paper, a case of congenital loss of upper and lower incisors was reported. Guided by the target restoration space (TRS), a personalized digital guide plate for tooth preparation was built to assist precise tooth preparation after the multidisciplinary combination therapy of orthodontic and periodontal teeth. Finally, the fixed bridge was prepared to meet the integrity, beauty, and function of the maxillary for the patient. In this case, the results suggest that the digital guide plate built under the guidance of TRS can be used to improve the accuracy of dental preparation.

Esthetic rehabilitation with direct composite veneering: Two case reports

Introduction: One of the most common treatment modalities in routine dental practice is restoring patients aesthetic appearance. Discolorations of the anterior teeth are common and have a variety of causes. Composite veneering has grown in popularity in recent years, thanks to the concept of minimal tooth preparation and improved aesthetic properties of composite resins. Composite resin has been envisioned as an alternative treatment to ceramic laminates due to its low cost, reduced treatment time, and improved aesthetics. Direct veneers are created by directly applying a composite material to the prepared tooth surface.Case Report: This article presents two case reports of direct composite veneering of anterior teeth using direct composite veneering with a six-month follow-up that resulted in a satisfactory outcome.Conclusion: Both the aesthetic and functional outcomes were satisfactory. As a result, direct composite veneers can be considered as a cost-effective and time-saving alternative to ceramic veneers.

Comparative Evaluation of the Effect of Degree of Convergence and Surface Area on the Retentive Force of Titanium Crowns Cemented with Various Adhesive Luting Agents on Extracted Human Teeth – A Laboratory Study

Introduction: The retention of base metal crowns and noble metal crowns cemented with various luting agents is well documented. However, little emphasis was given to the degree of convergence and surface area of tooth preparation. Aim and Objective: A study was planned to analyze the effect of the degree of convergence and surface area of the tooth preparation on the retention of titanium crowns with various adhesive luting agents. Materials and Methods: Forty-five caries-free extracted human premolars were obtained. They were divided into three groups according to the degree of convergence and further subdivided based on the type of luting agents used. The teeth were prepared with an angle of convergence of 5°, 10°, and 15° with a flat occlusal surface using K9 crown finishing installation, complete. Light body copper band impressions were made to determine the surface area. Titanium crowns thus obtained were sandblasted, ultrasonically cleaned, and cemented using Panavia F, Calibra, and Glass Ionomer Cement. Results: Results showed that Panavia F was the best luting agent exhibiting maximum retentive force to dislodge the crown in a vertical direction using the universal tensile testing machine at a cross-head speed of 1 mm/min. Conclusion: The force required to dislodge the titanium crown from the prepared tooth was maximum for Panavia F on 5°, 10°, and 15° angle of convergence at 65.23 kgf, 48.52 kgf, and 40.14 kgf. Retentive force values drastically reduced as the degree of convergence increased. There was a reduction in the surface area due to an increase in the taper.

DENTINAL HYPERSENSITIVITY DURING TOOTH PREPARATION AMONG PATIENTS VISITING DENTAL OPD IN A TERTIARY CARE HOSPITAL

Background: Dentinal hypersensitivity during tooth preparation is a problem in dentistry. This study aimed to compare dentinal hypersensitivity before and after tooth preparation between gender and different age groups. Methods: This observational study was carried out in Shree Birendra Hospital, Chhauni, Kathmandu from May to December 2021. A total of 80 patients visiting dental OPD for fixed partial denture participated in this study through convenience sampling. Each abutment tooth received tactile and thermal stimuli and the measurement of sensitivity was carried out using 10cm visual analog scale before and after tooth preparation. The results were analyzed using Mann-Whitney U test and Wilcoxon signed rank tests with SPSS version 16. Results: The mean of dentinal hypersensitivity scores were higher among females in comparison to male (1.03±0.59 before tooth preparation; 7.14±1.61 after tooth preparation). The differences in the sensitivity between gender was statistically significant (z: -3.00, p: 0.003 before tooth preparation and z: -3.76, p:0.000 after tooth preparation). The sensitivity was higher in participants below 40 years (0.86±0.51 before tooth preparation; 6.84±1.39 after tooth preparation). However, the differences in sensitivity between participants below and above 40 years were statistically insignificant. The sensitivity score when compared before and after tooth preparation in the participants was statistically highly significant (p&lt;0.001). Conclusions: The dentinal hypersensitivity is more in women both before and after tooth preparation which if well explored helps to form basis for modification of tooth preparation procedure in target patient.

Clinical research on restorations using CAD/CAM-fabricated monolithic zirconia endocrowns and post and core crowns after up to 5 years.

To assess the clinical status of monolithic zirconia CAD/CAM endocrowns and crowns on post and core buildups in endodontically treated molars after 5 years of clinical service. A total of 670 patients who received restorations for excessive defects at Ansteel Group Hospital from 2012 to 2015 were selected and randomly divided into two groups: 334 patients in the endocrown group and 336 in the post and core crown group. All the treatments were performed using a digital CAD/CAM system. The prostheses restorations at 1, 3, and 5 years after treatment were evaluated using the USPHS (United States Public Health Service) criteria and satisfaction questionnaire. In addition, the time cost of tooth preparation was recorded by the clinicians. Most of the patients in both groups reported grade A at the after-treatment follow-ups. Gingival health, food impaction, marginal accuracy, and general satisfaction at 3 and 5 years after treatment in the endocrown group rated higher (P < 0.05) than in the post and core crown group. There was no statistical difference in other indicators between the two groups at all observational after-treatment timepoints (P > 0.05). The time cost of tooth preparation in the post and core crown group was significantly higher than that in the endocrown group. A CAD/CAM scanning system combined with a monolithic zirconia endocrown restoration was rated very positively by the participants. Endocrown restorations are a significantly superior choice compared with post and core crowns in clinical application. (Int J Comput Dent 2022;25(3):287-294; doi: 10.3290/j.ijcd.b2599661).

The accuracy comparison of 3D-printed post and core using castable resin and castable wax resin.

The purpose of this research was to compare the accuracy of three-dimensionally (3D) printed post and core fabricated with two different materials: reinforced wax and castable resin. MATERIALSAND METHODS: Fifteen extracted single root central incisors were selected. Root canal treatment and tooth preparation for crown were performed on all teeth. Eleven millimeters post space was created with standardized prefabricated fiber post drill. Polyvinylsiloxane impression material was used for root canal impressions. Each impression was then 3D scanned using an extraoral scanner and cast posts and cores were designed using 3Shape software. The digitally designed post and cores were 3D printed with two different materials: castable wax resin and castable resin. The castable resin patterns were scanned before and after complete polymerization. The wax patterns were also scanned. Digital volumetric measurement using Geomagic® Control X™ software was performed to determine accuracy. The printed post and core had reduced volume (16.09± 3.839 mm3 ) compared to the digital design (17.828± 3.904, p < 0.05). Before complete polymerization, the accuracy of 3D printed resin pattern (16.464± 3.017) was found to be superior to post and core printed with wax (16.193± 3.018, p < 0.05). However, no volume difference was found between completely polymerized resin (16.09± 3.839) and wax (16.044± 3.834, p = 1). 3D printed post and core showed significant volume shrinkage from the digital files used to create them. However, different materials had no effect on the accuracy of 3D printed post and core.

Effect of laser radiation and sodium fluoride on the reactivity of prepared teeth

BACKGROUND: The use of esthetic restorations (metalceramic and metal-free) provides for the preparation of teeth within the enamel and surface or middle layers of the dentin, which entails an increase in the reactivity of teeth. One of the promising directions for increasing the resistance of the prepared teeth in the orthopedic treatment of patients using esthetic dental restorations is the combined and consistent use of fluorides and low-intensity laser radiation.&#x0D; AIM: To examine the effect of low-intensity laser radiation and sodium fluoride on the reactivity of dissected vital teeth.&#x0D; MATERIAL AND METHODS: A 2% aqueous solution of sodium fluoride was administered by electrophoresis with a portable device Desensitron-II. For laser exposure, a dental laser device Optodan was used in the first (anti-inflammatory) mode of operation. The research material was the results of orthopedic treatment of 120 patients aged 2039 years (57 men and 63 women). To assess the initial state of teeth reactivity and the effect of the therapeutic measures, the sensitivity of the teeth to temperature (thermoreactivity of the teeth), mechanical (sliding tangent test), and electrical (electrodontometry) influences was investigated.&#x0D; RESULTS: In the third group, the studied indicators before fixation demonstrated the maximum improvement in indicators relative to the data obtained in other groups.&#x0D; CONCLUSIONS: The combined sequential effect of low-intensity laser radiation and sodium fluoride reduces the reactivity of the prepared teeth while significantly improving the indicators of electrical excitability of the pulp and increasing the pain threshold in relation to temperature and mechanical stimuli.

Fracture Load and Fracture Patterns of Monolithic Three-Unit Anterior Fixed Dental Prostheses after In Vitro Artificial Aging-A Comparison between Color-Gradient and Strength-Gradient Multilayer Zirconia Materials with Varying Yttria Content.

(1) Background: Due to advantages such as avoidance of chipping, pulp-friendly tooth preparation and cost reduction, zirconia is increasingly being used monolithically without veneering. Nevertheless, to enable good aesthetics, various multilayer systems have been developed. The aim of this study was to investigate the impact of different zirconia multilayer strategies and yttria levels on fracture load, fracture pattern, stress distribution and surface roughness. (2) Methods: Monolithic three-unit anterior FDPs were made from three different color-gradient zirconia multilayer materials with different yttria levels corresponding to varying strength and degrees of translucency grades (Katana HTML, STML, UTML, Kuraray) and one strength-gradient zirconia multilayer material (Katana YML, Kuraray) and artificially aged in a chewing simulator (1.2 × 106 load cycles, 50 N, 2 × 3000 thermocycles, 5–55 °C). Analyses of fracture load, fracture pattern, fracture surfaces, stress distribution and roughness were performed after the fracture load test. Shapiro–Wilk, Kruskal–Wallis, Mann–Whitney U-tests and one-way ANOVA were used (p < 0.05). (3) Results: Fracture loads of the high strength color-gradient material HTML and the strength-gradient material YML were comparable after 5 years of aging (p = 0.645). Increasing yttria levels resulted in a decrease in fracture resistance of 42–57% (p < 0.05). Surface roughness of different zirconia generations is comparable after polishing and aging. (4) Conclusions: Color-gradient multilayer zirconia materials and new strength-gradient zirconia materials with similar yttria levels in the basal layers show comparable mechanical properties and are suitable for anterior FDPs.