[Research of implant accuracy using a digital registration method].

PURPOSE: The aim of this study was to introduce a new method to evaluate the clinical accuracy of implant position. The results were compared to traditional cone beam CT (CBCT) method. METHODS: A total of 36 implants from 24 patients with sufficient bone volume were enrolled into the study. CBCT method and digital registration method were compared to evaluate the accuracy of implant position. The measurement parameters were defined as deviations between ideal and postsurgical implant position at occlusal point(d1), apical point(d2) and axis(α). The deviations between two methods were analyzed with SPSS 19.0 software package. RESULTS: The deviations between ideal and postsurgical implant position using CBCT were (0.88±0.64) mm for occlusal point, (1.07±0.85) mm for apical point and (4.74±2.35)° for angle. In digital registration method, the deviations were (0.86±0.67) mm for occlusal point, (1.12±0.88) mm for apical point and (4.56±2.66)° for angle. No significant difference(P＞0.05) was found between the two methods. CONCLUSIONS: There was no significant difference between the two methods in evaluating the clinical accuracy of implant position. Digital registration method could be accepted in clinical application.

Dexamethasone-loaded zeolitic imidazolate frameworks nanocomposite hydrogel with antibacterial and anti-inflammatory effects for periodontitis treatment.

Periodontitis is a bacterial-induced, chronic inflammatory disease characterized by progressive destruction of tooth-supporting structures. Pathogenic bacteria residing in deep periodontal pockets after traditional manual debridement can still lead to local inflammatory microenvironment, which remains a challenging problem and an urgent need for better therapeutic strategies. Here, we integrated the advantages of metal-organic frameworks (MOFs) and hydrogels to prepare an injectable nanocomposite hydrogel by incorporating dexamethasone-loaded zeolitic imidazolate frameworks-8 (DZIF) nanoparticles into the photocrosslinking matrix of methacrylic polyphosphoester (PPEMA) and methacrylic gelatin (GelMA). The injectable hydrogel could be easily injected into deep periodontal pockets, achieving high local concentrations without leading to antibiotic resistance. The nanocomposite hydrogel had high antibacterial activity and constructs with stable microenvironments maintain cell viability, proliferation, spreading, as well as osteogenesis, and down-regulated inflammatory genes expression in vitro. When evaluated on an experimental periodontitis rat model, micro-computed tomography and histological analyses showed that the nanocomposite hydrogel effectively reduced periodontal inflammation and attenuated inflammation-induced bone loss in a rat model of periodontitis. These findings suggest that the nanocomposite hydrogel might be a promising therapeutic candidate for treating periodontal disease.

Influence of different base materials and thicknesses on the fracture resistance of endocrown: A three-dimensional finite element analysis.

INTRODUCTION: To analyze the stress distribution of the all-ceramic endocrown with different base materials and thicknesses using three-dimensional finite element analysis. METHODS: A endodontically treated maxillary premolar was scanned by micro-CT, a three-dimensional finite element model of the endocrown with fluid resin as the base material was divided into control (0 mm), 1 mm, 2 mm, and 3 mm groups according to base thickness. Three kinds of conventional base materials were used and divided into glass ion group (A), fluid resin group (B), and nanocomposite resin group (C), and a three-dimensional finite element model of the endocrown with 1.0 mm thickness of base was established. A static loading with axial and 45° direction was applied to each model, the stress distribution of each part of the endocrown was analyzed under different base materials and thicknesses. RESULTS: The different thickness of the base layer has an influence on the components of the restoration and the tooth. The stress in the control group was the largest. The stress was the lowest when the thickness of the base layer was 1 mm; The maximum of the equivalent stress, the first, second, and third principal stress in the endocrown, abutment, and alveolar bone, are basically the same with the different base materials. The stress on the base layer increases with the elastic modulus of base materials increases. CONCLUSIONS: The base layer played a force buffering effect on the dental body restored with endocrowns, and the effect was the best at 1 mm; The selection of base material has little influence on the whole, but in order to protect the weak tissues of the cavity bottom, the base material with lower elastic modulus can be used.

A low-temperature-printed hierarchical porous sponge-like scaffold that promotes cell-material interaction and modulates paracrine activity of MSCs for vascularized bone regeneration.

Mesenchymal stem cells (MSCs) secrete paracrine trophic factors that are beneficial for tissue regeneration. In this study, a sponge-like scaffold with hierarchical and interconnected pores was developed using low-temperature deposition modeling (LDM) printing. Its effects on the cellular behavior, especially on the paracrine secretion patterns of MSCs, were comprehensively investigated. We found that compared with the scaffolds printed via the fused deposition modeling (FDM) technique, the LDM-printed sponges enhanced the adhesion, retention, survival, and ingrowth of MSCs and promoted cell-material interactions. Moreover, the paracrine functions of the cultured MSCs on the LDM-printed sponges were improved, with significant secretion of upregulated immunomodulatory, angiogenic, and osteogenic factors. MSCs on the LDM-printed sponges exert beneficial paracrine effects on multiple regenerative processes, including macrophage polarization, tube formation, and osteogenesis, verifying the enhanced immunomodulatory, angiogenic, and osteogenic potential. Further protein function assays indicated that focal adhesion kinase (FAK), downstream AKT, and yes-associated-protein (YAP) signaling might participate in the required mechanotransductive pathways, through which the hierarchical porous structures stimulated the paracrine effects of MSCs. In a rat distal femoral defect model, the MSC-laden LDM-printed sponges significantly promoted vascularized bone regeneration. The results of the present study demonstrate that the hierarchical porous biomimetic sponges prepared via LDM printing have potential applications in tissue engineering based on their cell-material interaction promotion and MSC paracrine function modulation effects. Furthermore, our findings suggest that the optimization of biomaterial properties to direct the paracrine signaling of MSCs would enhance tissue regeneration.

A multifunctional electrowritten bi-layered scaffold for guided bone regeneration.

The guided bone regeneration (GBR) concept has been extensively utilized to treat maxillofacial bone defects in clinical practice. However, the repair efficacy of currently available GBR membranes is often compromised by their limited bone regeneration potential and deficient antibacterial activity. In this study, inspired by the bi-layered structure design of the commonly used Bio-GideⓇmembrane, we designed and fabricated a new kind of multifunctional bi-layered "GBR scaffold" combining solution electrospinning writing (SEW) and solution electrospinning (SES) techniques using a single SEW printer. Copper-loaded mesoporous silica nanoparticles (Cu@MSNs) were incorporated into the poly(lactic-co-glycolic acid)/gelatin (PLGA/Gel, denoted as PG) fiber matrix to construct a composite PG-Cu@MSNs fibrous scaffold. The obtained GBR scaffold consisted of a loose and porous SEW layer to support and facilitate bone ingrowth, and a dense and compact SES layer to resist non-osteoblast interference. The resulting enhanced mechanical properties, coordinated degradation profile, and facile preparation procedure imparted the composite scaffold with good clinical feasibility. In vitro biological experiments indicate that the PG-Cu@MSNs composite scaffold exhibited favorable osteogenic and antibacterial properties. Furthermore, an in vivo rat periodontal defect model further confirmed the promising bone regeneration efficacy of the PG-Cu@MSNs scaffold. In conclusion, the developed electrowritten Cu@MSNs-incorporated bi-layered scaffold with hierarchical architecture and concurrent osteogenic and antibacterial functions may hold great potential for application in GBR.

An enzyme-responsive membrane for antibiotic drug release and local periodontal treatment.

Periodontitis is a chronic, destructive inflammatory disease that injures tooth- supporting tissues, eventually leading to tooth loss. Complete eradication of periodontal pathogenic microorganisms is fundamental to allow periodontal healing and commonly precedes periodontal tissue regeneration. To address this challenge, we report a strategy for developing an enzyme-mediated periodontal membrane for targeted antibiotic delivery into infectious periodontal pockets; the unique components of the membrane will also benefit periodontal alveolar bone repair. In this approach, a chitosan membrane containing polyphosphoester and minocycline hydrochloride (PPEM) was prepared. Physical, morphological, and ultrastructural analyses were carried out in order to assess cellular compatibility, drug release and antibacterial activity in vitro. Additionally, the functionality of the PPEM membrane was evaluated in vivo with a periodontal defect model in rats. The results confirm that the PPEM membrane exhibits good physical properties with excellent antibacterial activity and successfully promotes periodontal tissue repair, making it promising for periodontal treatment.

Stud vs Bar Attachments for Maxillary Four-Implant-Supported Overdentures: 3- to 9-year Results from a Retrospective Study.

PURPOSE: The aim of this study was to compare the clinical outcomes of four-implant-supported overdentures retained by stud or bar attachments for patients with an edentulous maxilla. MATERIALS AND METHODS: From January 2008 to December 2014, patients with maxillary edentulism were enrolled in this retrospective study. The insertion of four maxillary dental implants was followed by restoration with either stud-retained or bar-retained overdentures. The characteristics of the subjects and implants were recorded. Implant survival rates, marginal bone loss, peri-implant clinical parameters, and prosthetic maintenance efforts were evaluated at the last follow-up time. Furthermore, patients were asked to complete a satisfaction questionnaire using a modified Denture Satisfaction scale at their last follow-up visit. The data were statistically analyzed, and the level of significance was set at α = .05. RESULTS: A total of 132 implants were placed in 33 patients, of whom 18 were restored with four-implant-supported overdentures retained by stud attachments, and the other 15 with four-implant-supported overdentures retained by bar attachments. Thirty-one patients and 124 implants were available for the entire follow-up. During a mean follow-up period of 77 months (range: 36 to 111 months), five among 72 implants failed for three patients in the stud-retained group and two among 60 implants failed for two patients in the bar-retained group, resulting in estimated cumulative implant survival rates of 81.4% and 86.2% for the stud-retained group and the bar-retained group, respectively. Except for the modified Plaque Index (mPI, P = .035), no significant differences were indicated between the two attachment groups in terms of implant survival rate, marginal bone loss, or peri-implant clinical parameters. Peri-/inter-implant gingival hyperplasia occurred only with implants under bar attachments. Over the entire observation period, the incidence of prosthetic maintenance treatments was 2.12 per patient per study for the stud-retained group and 2.29 per patient per study for the bar-retained group. Patients in both groups reported a high degree of satisfaction. CONCLUSION: Within the limitations of this study, no significant differences were indicated between the clinical outcomes of maxillary four-implant-supported overdentures with either stud or bar attachments, although a higher modified Plaque Index was observed for the bar-retained group. Furthermore, prostheses with stud attachments were advantageous for their convenient cleaning and repair. Patients with compromised systemic and periodontal conditions should be treated with caution. Further clinical studies with larger sample sizes and stricter epidemiologic designs are still needed.

Factors that Influence Direction Deviation in Freehand Implant Placement.

PURPOSE: This retrospective study investigates the accuracy of freehand implant placement and whether the factors of presence of an adjacent tooth, implant quadrant, number of missing teeth, and location of the implant site influence direction and angulation deviations. MATERIALS AND METHODS: According to specific inclusion and exclusion criteria, a total of 112 implants from 75 partially edentulous patients were recruited for this retrospective study. The implants were inserted using a freehand approach by one experienced clinician (right-handed). The full thickness flap was elevated to expose the alveolar bone in the implant surgery, and the implant crown consisted of an all-ceramic restoration retained by cement. The planned implant position was preoperatively determined using implant planning software. The postoperative implant position was determined by analyzing the alignment after optically scanning the dentition using a specifically designed registration model in Geomagic Studio software. The deviations between the planned and postoperative implant positions were then calculated. The outcomes included direction and angulation deviations between the planned and postoperative implant positions. All data were analyzed by ANOVA, Bonferroni correction, regression analysis, and one-sample t-tests conducted using SPSS. RESULTS: The 3D deviations between planned and postoperative implant positions were 1.22 ± 0.63 mm at the entrance point, 1.91 ± 1.17 mm at the apical point, and 7.93 ± 5.56° in angulation. The presence of adjacent teeth influenced deviations in the mesiodistal (F = 4.338, p = 0.006) and buccolingual directions (F = 3.017, p = 0.033) at the entrance point and mesiodistal angulation (F = 7.979, p < 0.001). The quadrant influenced deviation in the buccolingual direction at the apical point (F = 6.093, p = 0.001) and buccolingual angulation (F = 6.457, p < 0.001). The number of missing teeth had no effect on deviations of direction and angulation of implants. The location of the implant site affected the deviation in the buccolingual direction at the entrance point (F = 3.096, p = 0.049) and the mesiodistal direction at the apical point (F = 3.724, p = 0.027). CONCLUSION: The 3D accuracy of freehand-placed implants could be acceptable in clinical situations. The results showed that the presence of an adjacent tooth and the quadrant and the location of the implant site influenced the direction and angulation deviations of the implant position; however, the factor of number of missing teeth did not.

Accuracy of the evaluation of implant position using a completely digital registration method compared with a radiographic method.

STATEMENT OF PROBLEM: Conventional radiographic methods are widely used to evaluate the clinical accuracy of implant position. However, such methods require a second computerized tomography (CT) scan and manual registration between presurgical and postsurgical CT data. The alignment errors cannot be calculated. PURPOSE: The purpose of this clinical study was to introduce a completely digital registration method to evaluate the clinical accuracy of implant position. The digital registration method was then compared with the radiographic method in evaluating accuracy. Some of the alignment errors produced in the digital registration procedures were recorded. MATERIAL AND METHODS: A total of 32 implants from 19 patients with sufficient bone volume were enrolled in the study, and all implant surgeries were conducted by one experienced practitioner. Before the surgery, a cone beam computerized tomography (CBCT) scan was made for each patient along with a diagnostic impression to design the ideal implant position using the Simplant software. After the surgery, the postsurgical implant position was determined using an optical scan of the dentition cast and a series of custom registration models (the digital registration method). A simulated cylinder was designed using the Geomagic Studio software to represent the implant, and the deviation of the ideal and postsurgical implant position was calculated. The accuracy evaluated by the 2 methods was also compared. The parameters of the entrance point, apical point, and axis were recorded for each implant. A part of the alignment errors in the digital registration was calculated automatically and recorded. One sample t test and paired t test were conducted by using a statistical software program. RESULTS: The mean deviation between the ideal and postsurgical implant positions evaluated using the digital registration method was 0.84 ±0.57 mm for the entrance point, 1.03 ±0.78 mm for the apical point, and 4.52 ±2.37 degrees for the angulation. No significant difference was found between the accuracy evaluated by the digital registration method and the radiographic method (P>.05). In the digital registration procedure, the alignment error was 0.03 mm for the registration model and 0.29 mm for the dentition. Significant differences were found in the alignment procedure of the impression cylinder (P<.001) and dentition (P<.001). The average positive and negative errors were +0.09 and -0.19 mm for the simulated cylinder of the ideal implant and +0.08 and -0.15 mm for the simulated cylinder of the postsurgical implant. CONCLUSIONS: The precision of the digital registration method could be accepted in clinical applications. No significant difference was found between the digital registration method and the radiographic method in evaluating the clinical accuracy of the implant position. The digital registration method was able to control and minimize the alignment errors produced during data processing.

Bi-layered electrospun nanofibrous membrane with osteogenic and antibacterial properties for guided bone regeneration.

Guided bone regeneration (GBR) membranes have the potential to prevent the invasion of epithelial and connective tissues as well as to maintain a stable space for facilitating the ingrowth of regenerative bone tissue. However, the bioactivity and regeneration potential of currently available membranes still need to be improved. In this study, a novel bi-layered membrane with both osteogenic and antibacterial functions was developed for GBR applications. The loose layer (LL) of the membrane was composed of conjugated electrospun poly (lactic-co-glycolic acid) (PLGA)/gelatin nanofibers incorporating dexamethasone-loaded mesoporous silica nanoparticles (DEX@MSNs), while the dense layer (DL) of the membrane consisted of traditionally electrospun PLGA nanofibers loaded with the broad-spectrum antibiotic doxycycline hyclate (DCH). Morphological results showed that the LL (DEX@MSNs/PLGA/Gel) membrane exhibited a porous and loosely packed structure, which was beneficial for cell adhesion and infiltration, while the DL (DCH/PLGA) membrane remained dense enough to act as a barrier. In vitro drug release tests indicated that both DEX and DCH followed a favorable sustained release profile. The cell viability evaluation suggested that the electrospun membranes possessed good cytocompatibility. Furthermore, in vitro osteogenesis analyses demonstrated that the DEX@MSNs/PLGA/Gel composite membrane possessed an enhanced osteoinductive capacity for rat bone marrow stem cells (BMSCs), which was verified by the increased alkaline phosphatase (ALP) activity, the enhanced calcium deposition, and the upregulated osteocalcin (OCN) expression. In vitro antimicrobial experiments revealed the effective antibacterial potency of the DCH/PLGA membrane. In conclusion, the prepared nanocarrier-incorporated bi-layered composite membrane with combined osteogenic and antibacterial properties may be a promising candidate for GBR application.

Antibacterial activity, cytotoxicity and mechanical behavior of nano-enhanced denture base resin with different kinds of inorganic antibacterial agents.

Silanized aluminum borate whiskers (ABWs) of 4 wt%, silanized zirconium dioxide nanoparticles (nano-ZrO2) of 2 wt% were mixed with polymethyl methacrylate (PMMA) powder to get ZrO2-ABWs/PMMA composites. Titanium dioxide (TiO2), silver-supported titanium dioxide (Ag/TiO2), silver-supported zirconium phosphate (Novaron) and tetrapod-like zinc oxide whiskers (T-ZnOw) antibacterial agents of 3 wt% were mixed with ZrO2-ABWs/PMMA composites respectively to fabricate standard specimens. Plaque biofilms on the specimens surface were investigated for colony-forming units (CFUs). In addition, cytotoxicity and mechanical behavior were evaluated. Results showed that the CFUs values of S. mutans and C. albican biofilms on the four antibacterial composites surface were all reduced (p<0.05) compared to the blank and control groups. The antibacterial composites did not have an adverse effect on fibroblast growth in this study (p>0.05) except TiO2 and Ag/TiO2 groups of undiluted extracts. The flexural strength and surface hardness of Novaron and T-ZnOw groups were increased (p<0.05) compared to the control group.

Multidimensional esthetic evaluation of patients with a cleft lip and palate wearing a maxillary partial removable dental prosthesis: A 5-year retrospective study.

STATEMENT OF PROBLEM: No published quantitative or qualitative studies are available of the 2-dimensional (2D) and 3D esthetic evaluation of patients with a cleft lip and palate (CLP) wearing a maxillary partial removable dental prosthesis (MPRDP). PURPOSE: The purpose of this retrospective clinical study was to qualitatively and quantitatively evaluate the facial esthetic improvements of patients with CLP wearing an MPRDP for 5 years by using 2D cephalometric and 3D photogrammetry methods. MATERIAL AND METHODS: Six patients, 2 men and 4 women, with CLP deformity were recruited and treated with an MPRDP by the same dentist over 5 years. Results of the clinical examination were recorded before and after wearing the MPRDP. Sella-nasion-A (SNA) point, the U1-SN, 0-meridian to SN, nasolabial angle, and maxillary incisor exposure were measured by 2D cephalometric analysis before and after wearing the MPRDP. 3D photographs were captured by 3dMD software. Geomagic Spark Studio software was also used to measure the patients' improved upper lip projection after the MPRDP was worn. The paired sample t test was used to compare the participants (α=.05). RESULTS: U1-SN (P<.05) and 0-meridian to SN (P<.01) had significant deviation statistically. After patients underwent clinical examination, SNA and nasiolabial angles were found to have improved, although no statistical significance was observed. CONCLUSIONS: A maxillary partial removable dental prosthesis (MPRDP) can advance the upper lip forward, restoring the subnasal and upper lip projection. Patients' nasiolabial angles with MPRDPs were decreased, which led to a more harmonious facial contour.

[Effect of amount of silane coupling agent on flexural strength of dental composite resins reinforced with aluminium borate whisker].

PURPOSE: To evaluate the effect of amount of silane coupling agent on flexural strength of dental composite resins reinforced with aluminium borate whisker (ABW). METHODS: ABW was surface-treated with 0%, 1%, 2%, 3% and 4% silan coupling agent (γ-MPS), and mixed with resin matrix to synthesize 5 groups of composite resins. After heat-cured at 120 degrees centigrade for 1 h, specimens were tested in three-point flexure to measure strength according to ISO-4049. One specimen was selected randomly from each group and observed under scanning electron microscope (SEM). The data was analyzed with SAS 9.2 software package. RESULTS: The flexural strength (117.93±11.9 Mpa) of the group treated with 2% silane coupling agent was the highest, and significantly different from that of the other 4 groups (α=0.01). CONCLUSIONS: The amount of silane coupling agent has impact on the flexural strength of dental composite resins reinforced with whiskers; The flexual strength will be reduced whenever the amount is higher or lower than the threshold. Supported by Research Fund of Science and Technology Committee of Shanghai Municipality (08DZ2271100).

Clinical marginal and internal fit of metal ceramic crowns fabricated with a selective laser melting technology.

STATEMENT OF PROBLEM: Selective laser melting (SLM) technology has been introduced to fabricate dental restorations. However, the fit of these restorations still needs further study. PURPOSE: The purpose of this in vivo investigation was to compare the marginal and internal fit of SLM metal ceramic crowns with 2 lost-wax cast metal ceramic crowns and to evaluate the influence of tooth type on the marginal and internal fit of these crowns. MATERIAL AND METHODS: A total of 330 metal ceramic crowns were evaluated. The metal copings were fabricated with SLM Co-Cr, cast Au-Pt, and cast Co-Cr alloy (n=110). The marginal and internal gaps of crowns were recorded by using a replica technique. The anterior and premolar replicas were sectioned 2 times, and molar replicas were sectioned 4 times. The marginal and internal gap width of each cross section was examined by stereomicroscope at ×30 magnification. Two-way analysis of variance was performed to identify the statistical difference among the groups. RESULTS: The marginal fit of the SLM Co-Cr group (75.6 ±32.6 µm) was not different from the cast Au-Pt group (76.8 ±32.1 µm) (P>.05) but was better than the cast Co-Cr group (91.0 ±36.3 µm) (P<.01). No significant difference was found among the SLM Co-Cr group (127.3 ±45.8 µm), cast Au-Pt group (129.9 ±61.1 µm). and cast Co-Cr group (142.5 ±63.7 µm) (P>.05). The mean occlusal gap width of the SLM Co-Cr group (309.8 ±106.6 µm) was significantly higher than that of the cast Au-Pt group (254.6 ±109.6 µm) and the cast Co-Cr group (249.6 ±110.4 µm) (P<.005). No significant difference was found in the marginal fit among the anterior group (84.4 ±35.1 µm), the premolar group (80.6 ±26.3 µm), and the molar group (82.7 ±38.0 µm) (P>.05). Also, no significant difference was found in the axial fit among the anterior group (138.3 ±52.5 µm), the premolar group (132.9 ±50.4 µm), and the molar group (134.4 ±52.5 µm) (P>.05). The anterior group (267.6 ±110.2 µm) did not differ from the premolar group (270.2 ±112.8 µm) and the molar group (268.6 ±110.5 µm) in occlusal fit (P>.05). CONCLUSIONS: The marginal fit of SLM Co-Cr metal ceramic crowns was similar to that of the cast Au-Pt metal ceramic crowns and was better than that of the cast Co-Cr metal ceramic crowns. The SLM Co-Cr metal ceramic crowns were not significantly different from the 2 cast metal ceramic crowns in axial fit but were less accurate in occlusal fit. Tooth type did not influence the marginal and internal fit of the metal ceramic crowns.

Clinical Marginal and Internal Fit of Crowns Fabricated Using Different CAD/CAM Technologies.

PURPOSE: The aims of this in vivo investigation were to compare the marginal and internal fit of single-unit crowns fabricated using a selective laser melting (SLM) procedure with two CAD/CAM grinding procedures, and to evaluate the influence of tooth type on the parameters measured. MATERIALS AND METHODS: A total of 270 crowns were evaluated, including 90 SLM metal-ceramic crowns (group B), 90 zirconium-oxide-based ceramic crowns (group L), and 90 lithium disilicate ceramic crowns (group C). The marginal and internal gaps of the crowns were recorded using a replica technique with a silicone indicator paste stabilized with a light-body silicone. The gap replica specimen were sectioned buccolingually and mesiodistally and then examined using a stereomicroscope at 30× magnification. Ten reference points were measured on each anterior and premolar specimen, and 20 reference points were measured on each molar specimen. Two-way ANOVA was performed to identify the significant differences between the groups. RESULTS: The mean marginal fit of group B was significantly better than those of group C and group L (p < 0.005), but a significant difference was not found between group C and group L (p > 0.05). The mean axial gap of group B was significantly smaller than those of group C and group L (p < 0.01), while group C was not different from group L (p > 0.05). The mean occlusal gap of group B was significantly higher than those of group C and group L (p < 0.05), and no difference was found between group C and group L (p > 0.05). The marginal and internal gaps of crowns varying according to tooth type were not significantly different (p > 0.05). CONCLUSION: The SLM system demonstrated better marginal and internal fit compared to the two CAD/CAM grinding systems examined. Tooth type did not significantly influence the marginal or internal fit.

A comparison of the fracture resistance of three machinable ceramics after thermal and mechanical fatigue.

STATEMENT OF PROBLEM: Mechanical and thermal fatigue may affect ceramic restorations in the oral environment. PURPOSE: The purpose of this study was to determine the influence of thermal and mechanical cycling on the fracture load and fracture patterns of 3 machinable ceramics. MATERIAL AND METHODS: Seventy-two human third molar teeth were prepared for bonding ceramic specimens of Sirona CEREC Blocs, IPS e.maxCAD, or inCoris ZI meso blocks. The 24 specimens of each ceramic were divided into 4 groups (n=6), which underwent no preloading (control), thermocycling (5°C-55°C, 2000 cycles), mechanical cycling (10(5) cycles, 100 N), and thermocycling (5°C-55°C, 2000 cycles) plus mechanical cycling (10(5) cycles, 100 N). The specimens were subsequently loaded to failure, and both stereomicroscopy and scanning electron microscopy were used to investigate the fracture patterns. The data were analyzed with 2-way ANOVA and the Fisher exact probability test (α=.05). RESULTS: Mechanical and thermal cycling had a significant influence on the critical load to failure of the 3 ceramics. No significant difference was found between mechanical cycling for 10(5) times and thermocycling for 2000 times within the same ceramic. The specimens of inCoris ZI experienced significantly higher fracture loads for all the groups. The fracture patterns of the 3 machinable ceramics showed that failure mainly occurred at the cement-dentin interface. CONCLUSIONS: The effects of combined thermal and mechanical cycling on the fracture load of ceramics were more significant than any individual mode of cyclic fatigue. Overall, the inCoris ZI resisted thermal and mechanical fatigue better than the Sirona CEREC and IPS e.maxCAD.

Hybrid effects of zirconia nanoparticles with aluminum borate whiskers on mechanical properties of denture base resin PMMA.

The aim of this study was to investigate the hybrid effects of ZrO2 nanoparticles (nano-ZrO2) and aluminum borate whiskers (ABWs) on flexural strength and surface hardness of denture base resin, polymethyl methacrylate (PMMA). Both nano-ZrO2 and ABWs were modified by silane coupling agent (Z6030) before being mixed with PMMA. Various amounts of silanized nano-ZrO2 and ABWs were mixed with PMMA to prepare ZrO2-ABW/PMMA composites. Flexural strength and surface hardness were evaluated using three- point bending test and Vickers hardness test respectively. Fractured surfaces were also observed by scanning electron microscopy (SEM). The mechanical behaviors of silanized ZrO2-ABW/PMMA composites were significantly improved. Flexural strength reached a maximum value of 108.01 ± 5.54 MPa when 2 wt% of nano-ZrO2 was mixed with ABWs at a ZrO2/ABW ratio of 1:2, amounting to an increase of 52% when compared with pure PMMA. Surface hardness achieved a maximum value of 22.50 ± 0.86 MPa when 3 wt% of nano-ZrO2 was mixed with ABWs at the same ZrO2/ABW ratio, which was an increase of 27% when compared with pure PMMA.

Mechanical and thermal properties of denture PMMA reinforced with silanized aluminum borate whiskers.

The aim of this study was to investigate the mechanical and thermal properties of denture polymethyl methacrylate (PMMA) reinforced with aluminum borate whiskers (ABWs). To improve bonding between ABWs and PMMA matrix, the surface of ABWs was modified with a silane coupling agent. Varied contents of silanized ABWs -ranging between 1 and 20 wt%- were mixed into the PMMA resin matrix to prepare ABW/PMMA composites, which were subjected to three-point bending test, Vickers hardness test, and thermal analysis. Silanized ABWs improved the flexural strength, surface hardness, and thermal stability of PMMA. Optimal amount of ABWs in the PMMA matrix was 5 wt%, which provided the ABW/PMMA with maximum reinforcement.

[Effect of nano ZrO2 on flexural strength and surface hardness of polymethylmethacrylate].

PURPOSE: To study the effect of polymethylmethacrylate(PMMA's) mechanical properties reinforced by nano ZrO(2) particles with different filling amounts. METHODS: The nano ZrO(2) particles were surface-treated by silane coupling agent(Z-6030) in 1.5wt% ratio, the untreated particles were regarded as the control group. The modified nano ZrO(2) particles were mixed with the PMMA powders in proportion of 0.5%,1%,1.5%,2%,2.5%,3% and 3.5%, respectively.Then the nano ZrO(2) /PMMA composites were synthesized. The specimens were examined by Vickers hardness test and three-point bending test, the surface of fracture was observed by SEM.All data were analyzed with ANOVA test by SAS 6.12 software package. RESULTS: Fourier transform infrared(FTIR) spectroscopy showed that the silane coupling agent linked to the nano ZrO(2) particles' surface after treating,the Vickers hardness was highest when the adding amount of nano ZrO(2) particles was 1.5% and 2%(P<0.05).The flexural strength of nano ZrO(2)/PMMA composites in the proportion of 1.5% was the highest(P<0.05). SEM indicated that the ductile fracture existed on the surface of fracture. CONCLUSIONS: The silane coupling agent can enhance the bonding strength of nano ZrO(2) particles and the PMMA matrix, the PMMA's mechanical properties could be improved by adding the nano ZrO(2) particle in an appropriate proportion. 1.5% and 2% of nano ZrO(2) particles render the nanocomposite the maximal Vickers hardness, while 1.5% ZrO(2) nanoparticles render the nanocomposite the maximal flexural strength.

The effects of adhesive type and thickness on stress distribution in molars restored with all-ceramic crowns.

PURPOSE: This study investigated the effects of luting cement type and thickness on the stress distribution within all-ceramic crowns using finite element analysis. MATERIALS AND METHODS: An all-ceramic crown restoration of the mandibular right first molar was prepared according to standard dental processes and scanned using micro-computed tomography. Eight 3D FE models were then developed that accounted for two adhesive systems, each with cement thickness of 60 µm, 90 µm, 120 µm, and 150 µm. The models were subjected to four loading conditions, and stresses in the veneer and core layers were evaluated. RESULTS: The stress distribution and maximum stresses in the veneer, core, and cement are presented in corresponding loading conditions. The cement with higher elastic modulus resulted in lower tensile stresses in the veneer and core layers, and the shear strength of the cement was critical to the intactness of the all-ceramic crown. CONCLUSION: The cement thickness acts as a cushion between the crown and dentin substrate. Although there is an optimal thickness (approximately 90 µm) that can reduce the stress level in ceramic crowns, cement thickness is not very important to stresses in the core or veneer in most cases when compared to the influence of loading conditions or cement moduli.