Complexos polieletrólitos de quitosana e xantana carregados com ativos naturais e sintéticos: estudo físico/químico e microbiológico para aplicação de drug delivery / Polyelectrolyte complexes of chitosan and xanthan loaded with natural and synthetic actives: physicochemical and microbiological study for drug delivery application

A eficácia dos implantes osseointegrados é amplamente reconhecida na literatura científica. Contudo, infiltrações bacterianas na junção implante-pilar podem desencadear inflamação nos tecidos circundantes, contribuindo para a evolução de condições mais sérias, como a peri-implantite. O objetivo desse estudo foi produzir complexos polieletrólitos (PECs) de quitosana (Q) e xantana (X) em forma de membranas, carregá-las com ativos naturais e sintéticos antimicrobianos, caracterizálas estruturalmente e avaliá-las frente a degradação enzimática, cinética de liberação e ações antimicrobianas com finalidade de aplicação para drug delivery. Membranas de QX a 1% (m/v) foram produzidas em três proporções, totalizando doze grupos experimentais: QX (1:1); QX (1:2), QX (2:1), QX-P (com própolis) (1:1); QX-P (1:2); QX-P (2:1); QX-C (com canela) (1:1); QX-C (1:2); QX-C (2:1) e CLX (com clorexidina 0,2%) (1:1); CLX (1:2); CLX (2:1). Para os estudos de caracterização foram feitas análises da espessura em estado seco; análises morfológicas superficial e transversal em Microscopia Eletrônica de Varredura (MEV); análise estrutural de espectroscopia de infravermelho por transformada de Fourier (FTIR); análise de degradação por perda de massa sob ação da enzima lisozima; e análise da cinética de liberação dos ativos em saliva artificial. Para os testes microbiológicos, análises de verificação de halo de inibição e ação antibiofilme foram feitas contra cepas de Staphylococcus aureus (S. aureus) e Escherichia coli (E. coli). Os resultados demonstraram que a espessura das membranas variou conforme a proporção, sendo que o grupo QX (1:2) apresentou a maior média de 1,022 mm ± 0,2, seguida respectivamente do QX (1:1) com 0,641 mm ± 0,1 e QX (2:1) com 0,249 mm ± 0,1. Nas imagens de MEV é possível observar uma maior presença de fibras, rugosidade e porosidade nos grupos QX (1:2) e QX (1:1) respectivamente, e, no QX (2:1) uma superfície mais lisa, uniforme e fina. No FTIR foram confirmados os picos característicos dos materiais isoladamente, além de observar as ligações iônicas que ocorreram para formação dos PECs. Na análise de degradação, os grupos com ativos naturais adicionados tiveram melhores taxas de sobrevida do que os grupos QX. No teste de liberação, os grupos QX-P tiveram uma cinética mais lenta que os QX-C, cuja liberação acumulada de 100% foi feita em 24 h. Já nos testes do halo inibitório, somente os grupos CLX tiveram ação sobre as duas cepas, e os QX-P tiveram sobre S. aureus. Nas análises antibiofilme, os grupos CLX apresentaram as maiores taxas de redução metabólica nas duas cepas (± 79%); os grupos QX-P apresentaram taxas de redução similares em ambas as cepas, porém com percentual um pouco maior para E. coli (60- 80%) e os grupos QX-C tiveram grande discrepância entre as duas cepas: de 35 a 70% para S. aureus e 14 a 19% para E. coli. Pode-se concluir que, frente as análises feitas, o comportamento do material foi afetado diretamente pelos ativos adicionados a matriz polimérica. As proporções de Q ou X afetaram somente a espessura final. Quanto a aplicação proposta de drug delivery, os dispositivos apresentaram grande potencial, principalmente os grupos CLX e QX-P. (AU)

The effectiveness of osseointegrated implants is widely recognized in scientific literature. However, bacterial infiltrations at the implant-abutment interface may trigger inflammation in surrounding tissues, contributing to the development of more serious conditions, such as peri-implantitis. The aim of this study was to produce chitosan (Q) and xanthan (X) polyelectrolyte complexes (PECs) in the form of membranes, load and evaluate them for enzymatic degradation, release kinetics, and antimicrobial actions for drug delivery applications. QX membranes at 1% (w/v) were produced in three proportions, totaling twelve experimental groups: QX (1:1), QX (1:2), QX (2:1), QX-P (with propolis) (1:1), QX-P (1:2), QX-P (2:1), QX-C (with cinnamon) (1:1), QX-C (1:2), QX-C (2:1), and CLX (with 0.2% chlorhexidine) (1:1), CLX (1:2), CLX (2:1). Characterization studies included analyses of dry state thickness, surface and crosssectional morphology using Scanning Electron Microscopy (SEM), structural analysis by Fourier Transform Infrared (FTIR) spectroscopy, mass loss degradation analysis under lysozyme action, and active release kinetics analysis in artificial saliva. Microbiological tests included verification analyses of inhibition halos and antibiofilm action against strains of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Results showed that membrane thickness varied according to proportion, with group QX (1:2) presenting the highest average of 1.022 mm ± 0.2, followed by QX (1:1) with 0.641 mm ± 0.1, and QX (2:1) with 0.249 mm ± 0.1. SEM images showed greater presence of fibers, roughness, and porosity in groups QX (1:2) and QX (1:1) respectively, while QX (2:1) exhibited a smoother, more uniform, and thinner surface. FTIR confirmed characteristic peaks of the materials individually, besides showing ionic bonds formed for PECs. Degradation analysis revealed that groups with added natural actives had better survival rates than QX groups. In release tests, QX-P groups exhibited slower kinetics than QX-C, with 100% cumulative release achieved in 24 h. inhibitory halo tests, only CLX groups exhibited action against both strains, while QX-P acted against S. aureus. Antibiofilm analyses showed CLX groups with the highest metabolic reduction rates in both strains (± 79%); QX-P groups showed similar reduction rates in both strains, slightly higher for E. coli (60-80%), and QX-C groups had a significant discrepancy between strains: 35-70% for S. aureus and 14-19% for E. coli. In conclusion, material behavior was directly affected by added actives to the polymeric matrix. Proportions of Q or X only affected final thickness. Regarding proposed drug delivery applications, the devices showed great potential, especially CLX and QX-P groups.(AU)

Effect of electrochemically dealloying Ti6Al4V abutments on human gingival fibroblasts / 口腔疾病防治

Objective@#To investigate the effects of electrochemically dealloying of Ti6Al4V abutments on human gingival fibroblasts (HGFs) and to provide experimental evidence for surface modification of implant abutments.@*Methods@#The samples were divided into an NC group (negative control, no other treatment on a smooth surface), an NM-1 group (nanomesh-1, electrochemical dealloying treatment in 1 mol/L NaOH 1 h on 2 V voltage), and an NM-2 group (nanomesh-2, electrochemical dealloying treatment in 5 mol/L NaOH 1 h on 2 V voltage). The surface morphologies of the samples and the adhesion of HGFs on the sample surfaces were observed with scanning electron microscopy (SEM). The surface hydrophilicities of the samples were measured with a contact angle measuring instrument. The proliferation of HGFs on the different samples were evaluated with CCK-8, and the expression of adhesion-related genes, including collagen Ⅰ (COL1A1), collagen Ⅲ (COL3A1), fibronectin 1 (FN1), focal adhesion kinase (FAK), vinculin (VCL), integrin α2 (ITGA2), and integrin β1 (ITGB1), on the different samples was measured with qRT-PCR. The expression of vinculin on the surfaces of HGFs was observed via confocal laser scanning microscopy (CLSM) after immunofluorescent staining. Collagen fiber secretion and syntheses of HGFs from different samples were evaluated via Sirius red staining.@*Results@#SEM revealed the formation of ordered and uniform three-dimensional mesh structures on the surfaces of the NM-1 and NM-2 groups, with grid diameters of approximately 30 nm for the NM-1 group and approximately 150 nm for the NM-2 group. Compared with that of the NC group, the water contact angles of the NM-1 group and NM-2 groups were significantly lower (P<0.000 1). Cell proliferation in the NM-1 group was significantly greater than that in the NC group (P<0.01). Moreover, there was no significant difference in the water contact angles or cell proliferation between the NM-1 group and the NM-2 group. SEM revealed that HGFs were adhered well to the surfaces of all samples, while the HGFs in the NM-1 and NM-2 groups showed more extended areas, longer morphologies, and more developed pseudopodia than did those in the NC group after 24 h. qRT-PCR revealed that the expression levels of the adhesion-related genes COL1A1, COL3A1, FN1, FAK and VCL in the NM-1 group were significantly greater than those in the NC and NM-2 groups (P<0.01). The expression of vinculin protein in the NM-1 group was the highest, and the number of focal adhesions was greatest in the NM-1 group (P<0.01). The results of Sirius red staining showed that the NM-1 group had the highest secretion and syntheses of collagen fibers (P<0.000 1).@*Conclusion@#The three-dimensional nanomechanical structure of Ti6Al4V modified by electrochemical dealloying promoted the adhesion, proliferation, collagen fiber secretion and syntheses of HGFs, and electrochemical dealloying of Ti6Al4V with a grid diameter of approximately 30 nm obviously promoted HGF formation.

Evaluation the scanning accuracy of Blue-Light laboratory scanners in complete edentulous Maxilla with multiple implants with titanium scan bodies / Evaluación de la precisión de escaneado de los escáneres de laboratorio de luz azul en maxilares desdentados completos con implantes múltiples con cuerpos de escaneado de titanio

Abstract To evaluate the accuracy of complete arch scanning with multiple implant titanium scan bodies using laboratory scanners. A master model of an edentulous maxillary arch with 6 implants was fabricated. Titanium scan bodies were inserted into the model. Three laboratory scanners were used: D2000 (3Shape), Vinyl High Resolution (Smart Optics), and inEos X5 (Dentsply Sirona). The master model was consecutively scanned ten times using dental laboratory scanners (LS) without detaching and repositioning the scan bodies. Linear and angular accuracy between adjacent implants was measured using inspection software (Control X, Geomagic). The accuracy of the complete arch scans was calculated. Implant regions were defined as; parallel (R1: #24-26 and #16-14), angled (R2: #22-24 and #14-12), angled to occlusal plane (R3: #12-22), and cross-arch (R4: #16-26). The effect of LS and implant region on accuracy was compared using two-Way ANOVA (α=0.05). Significant greater linear distortion was noted in R4 (61.2±17.9µm) compared to R1 (23.4±15.5µm) and R2 (26±17.7µm) (p<0.01). Greater linear distortions were noted in R4 with D2000 (0.07±0.016 degrees) and Vinyl High Resolution (0.067±0.02 degrees) than inEos X5 (0.032±0.021 degrees) (p>0.05). Greater mean linear precisions were noted in R1 (9±8µm) and R3 (9.3±8.3µm) than R4 (12.6±10.3µm) (p<0.05). The highest linear precision was noted in D2000 (7.2±7.6µm) (p<0.05). The angular precision of D2000 (0.02±0.015 degrees) was the highest (p<0.01). The angular precisión of R4 (0.036±0.018 degrees) was the lowest (p<0.01). This study revealed that the trueness was affected by the implant region and the precision was affected by both LS and implant region.

Resumen Evaluar la precisión del escaneado de la arcada completa con cuerpos de escaneado de titanio de múltiples implantes utilizando escáneres de laboratorio. Se fabricó un modelo maestro de una arcada maxilar edéntula con 6 implantes. Se insertaron cuerpos de escaneo de titanio en el modelo. Se utilizaron tres escáneres de laboratorio: D2000 (3Shape), Vinyl High Resolution (Smart Optics) e inEos X5 (Dentsply Sirona). El modelo maestro se escaneó consecutivamente diez veces usando escáneres de laboratorio dental (LS) sin separar y reposicionar los cuerpos de escaneo. La precisión lineal y angular entre implantes adyacentes se midió utilizando un software de inspección (Control X, Geomagic). Se calculó la precisión de los escaneos completos del arco. Las regiones del implante se definieron como; paralelo (R1: #24-26 y #16-14), angulado (R2: #22-24 y #14-12), angulado al plano oclusal (R3: #12-22) y cruzado (R4: #16-26). El efecto de LS y la región del implante en la precisión se comparó mediante ANOVA de dos vías (α=0,05). Se observó una distorsión lineal significativamente mayor en R4 (61,2±17,9µm) en comparación con R1 (23,4±15,5µm) y R2 (26 ±17,7µm) (p<0,01). Se observaron mayores distorsiones lineales en R4 con D2000 (0,07±0,016 grados) y vinilo de alta resolución (0,067±0,02 grados) que en inEos X5 (0,032±0,021 grados) (p>0,05). Se observaron precisiones lineales medias mayores en R1 (9±8µm) y R3 (9,3±8,3µm) que en R4 (12,6±10,3µm) (p<0,05). La mayor precisión lineal se observó en D2000 (7,2±7,6 µm) (p<0,05). La precisión angular de D2000 (0,02±0,015 grados) fue la más alta (p<0,01). La precisión angular de R4 (0,036±0,018 grados) fue la más baja (p<0,01). Este estudio reveló que la veracidad se vio afectada por la región del implante y la precisión se vio afectada tanto por LS como por la región del implante.

An Insight Performance of Zirconia Implant Abutment: A Systematic Review and Meta?Analysis of Randomized Controlled Clinical Trial

To determine the clinical performance of zirconia abutment (ZA) by comparing with a titanium abutment (TA) and sub?mucosal?modified zirconia abutment. A systematic search was conducted to retrieve eligible randomised controlled trials (RCTs) from Medline, Cochrane Library, SCOPUS, Embase, Web of Science, and Google Scholar. A search was further divided in two parts. Part I comprises eligible RCTs between zirconia abutment and titanium abutment, and part II included RCTs of zirconia abutment with sub?mucosal modified, pink?veneered glass ceramic versus non?veneered zirconia abutment. Esthetic, biological, and abutment survival was a primary outcome, and technical complications were included as an additional outcome. Fifteen eligible RCTs (Part I: N = 9 and Part II: N = 6) were evaluated, and a total of 362 abutments in 364 subjects were analysed for outcome variables. A sub?group meta?analysis reported no significant difference for Esthetic outcome. However, the overall mean (p =0.03) was higher for zirconia group in those of thin gingival phenotype. Spectrophotometric evaluation of peri?implant mucosal Esthetic does not show any significant difference. Similarly, pink?veneered versus non?veneered group reported no significant difference for thin (<2 mm) and thick (>2 mm) mucosal attachment. Biological outcome does not show any significant difference for comparable groups in both parts. There is marginally lower abutment survival for internally connected zirconia abutment (ZA: 95.4% TA: 100%). Zirconia abutment exhibited excellent Esthetic compared to titanium abutment in those of thin gingival phenotype. Sub?mucosa veneering of zirconia abutment with pink glass c

Biomechanical Effects of Jumping Distance on Stress Distributions of Anterior Dental Implant with Socket-Shield Technique / 医用生物力学

Objective To study the biomechanical effect of jumping distance on dental implants with socket-shield technique (SST), so as to provide references for clinical standards of jump distance. Methods Based on clinical characteristics, four groups of three-dimensional (3D) SST implant system models with 0, 0. 5, 1 and 1. 5 mm jumping distance were established, and the corresponding material parameters were assigned. The peak stress and stress distributions on models were simulated under specific occlusal condition. Results When the jumpingdistance was non-zero, namely, the implant was not in contact with the retained root fragment, the stress of the implant and abutment increased with the increase of jumping distance, and the peak stress in root fragment and periodontal membrane decreased with the increase of jumping distance. When the jumping distance was zero, the peak stress of the implant, abutment, root fragment and periodontal membrane reached the maximum, far exceeding that of the other groups. Conclusions The jumping distance has a significant effect on the SST implant system. It is recommended to take a larger jumping distance in clinical practices. The edge of the root fragment should be rounded, and the size of the lower edge should not be too small.

A comparative study of the clinical application of anatomical healing abutments versus finished healing abutments for mandibular first molar implants / 口腔疾病防治

Objective @#To evaluate the effect of anatomical healing abutments for mandibular first molars on the morphological changes of gingival soft tissue after implant restoration, as well as on peri-implant gingival molding, food ingrowth and patient satisfaction, to provide a basis for clinical selection. @*Methods @# Twenty-six patients who received implant restoration for a single missing mandibular first molar between September 2020 and September 2021 at the Oral Implant Center of Changsha Stomatological Hospital were randomly divided into a control group (13 cases with 14 implants) and a trial group (13 cases with 14 implants), of which 12 were male and 14 were female; the trial group had anatomical healing abutments applied for 4 weeks and then underwent crown restoration, while the control group finished five time points (before the second stage surgery, 4 weeks after the second stage surgery, immediately after the crown restoration, 4 weeks after the crown restoration, and 12 weeks after the crown restoration). A 3Shape intraoral scanner was used to scan the jaw before and 4 weeks after the second stage surgery to quantify the soft tissue changes and compare the effect of the healing abutment on gingival molding between the two groups. The incidence of food impaction was recorded and compared between the two groups at 4 weeks and 12 weeks after crown restoration. Patient satisfaction was recorded and compared between the two groups immediately after crown restoration, 4 weeks after crown restoration and 12 weeks after crown restoration@*Results @# Four weeks after implant surgery, it was observed that the gingival proximal and distal gingival papillae increased on the coronal side in the test group compared to the control group, 0.50 (0.26, 0.72) mm in the near-medium test group and 0.27 (0.24, 0.38) mm in the control group, with a statistically significant difference (P = 0.029), and 0.48 (0.26, 0.62) mm in the far-medium test group and 0.23 (0.13, 0.39) mm in the control group, with a statistically significant difference (P = 0.004). There was no statistically significant difference (P>0.05) in the buccolingual to gingival margin apex to coronal molding or in the buccolingual to lingual soft tissue at 0, 1, or 2 mm of the root of the middle 1/3 apex of the buccal and lingual gingival margins between the two groups. Compared to the control group, there was no statistically significant difference in the incidence of food impaction observed 4 weeks and 12 weeks after crown restoration in the test group (P>0.05). The satisfaction scores were higher in the trial group than in the control group immediately, 4 weeks, and 12 weeks after crown restoration, and the difference between the groups was statistically significant (P < 0.05). @*Conclusion @# The anatomical healing abutment for the implant mandibular first molar was superior to the finished healing abutment in terms of soft tissue contouring with an increase in the coronal aspect of the proximal and distal gingival papillae, resulting in high patient satisfaction.

Three-dimensional finite element analysis of cement flow in abutment margin-crown platform switching / 北京大学学报(医学版)

OBJECTIVE@#To analyze the cement flow in the abutment margin-crown platform switching structure by using the three-dimensional finite element analysis, in order to prove that whether the abutment margin-crown platform switching structure can reduce the inflow depth of cement in the implantation adhesive retention.@*METHODS@#By using ANSYS 19.0 software, two models were created, including the one with regular margin and crown (Model one, the traditional group), and the other one with abutment margin-crown platform switching structure (Model two, the platform switching group). Both abutments of the two models were wrapped by gingiva, and the depth of the abutment margins was 1.5 mm submucosal. Two-way fluid structure coupling calculations were produced in two models by using ANSYS 19.0 software. In the two models, the same amount of cement were put between the inner side of the crowns and the abutments. The process of cementing the crown to the abutment was simulated when the crown was 0.6 mm above the abutment. The crown was falling at a constant speed in the whole process spending 0.1 s. Then we observed the cement flow outside the crowns at the time of 0.025 s, 0.05 s, 0.075 s, 0.1 s, and measured the depth of cement over the margins at the time of 0.1 s.@*RESULTS@#At the time of 0 s, 0.025 s, 0.05 s, the cements in the two models were all above the abutment margins. At the time of 0.075 s, in Model one, the gingiva was squeezed by the cement and became deformed, and then a gap was formed between the gingiva and the abutment into which the cement started to flow. In Model two, because of the narrow neck of the crown, the cement flowed out from the gingival as it was pressed by the upward counterforce from the gingival and the abutment margin. At the time of 0.1 s, in Model one, the cement continued to flow deep inside with the gravity force and pressure, and the depth of the cement over the margin was 1 mm. In Model two, the cement continued to flow out from the gingival at the time of 0.075 s, and the depth of the cement over the margin was 0 mm.@*CONCLUSION@#When the abutment was wrapped by the gingiva, the inflow depth of cement in the implantation adhesive retention can be reduced in the abutment margin-crown platform switching structure.

The assessment of periimplant soft tissue condition with morse taper abutment connection: a rapid review

Aim: This study aims to evaluate the clinical assessment results of periimplant soft tissue with morse taper (internal abutment connection). Methods: The study was conducted using a rapid review by searching the articles from PubMed NCBI and Cochrane by using keywords. All articles were selected by the year, duplication, title, abstract, full-text, and finally, all selected articles were processed for final review. Following clinical parameters were included; Periimplant Probing Pocket Depth (PPD), Plaque Score (PS), modified Plaque Index (mPI), Mucosal Thickness (MTh), Gingival Height (GH), periimplant mucosal zenith, Pink Esthetic Score (PES), Bleeding On Probing (BOP), Sulcus Bleeding Index (SBI), and modified Gingival Index (mGI). Results: 9 selected articles were obtained from the initial literature searching count of 70 articles. The overall samples included 326 morse taper implants. Based on the evaluation, 3 out of 4 articles reported pocket depth < 4 mm, no bleeding was reported in 2 out of 4 articles. 4 out of 4 articles reported low plaque accumulation, low soft tissue recession was reported in 3 out of 3 articles, and 4 out of 4 articles reported acceptable PES values. Conclusion: The evaluations indicate that the morse taper (internal abutment connection) has favorable assessment results based on various clinical parameters

Design and fabrication of anatomic healing abutment for mandibular first molar implant / 口腔疾病防治

Objective@# To explore the design and manufacture of anatomical healing abutment for mandibular first molar implant in order to provide more choices for clinical healing abutment@*Methods@# The buccal lingual diameter and mesial distal diameter of the tooth neck, as well as the slope data of the four axial surfaces of the natural isolated teeth, were obtained by scanning the isolated mandibular first molar with a shining scanner. After statistical analysis of the data, the anatomical healing abutment of the mandibular first molar was designed and constructed using computer aided design/computer aided manufacturing (CAD/CAM).@*Results@#The mean buccal and lingual diameters of the mesial and distal diameters of the isolated mandibular first molars were (8.54 ± 0.78) mm and (7.87 ± 0.86) mm, and the tooth neck slopes of each axial surface of the isolated mandibular first molars were 17.53 °(buccal), 14.41 °(lingal), 13.40 °(mesial) and 13.43 °(distal), respectively. Three anatomical healing abutments with different peripheral diameters and heights of 5 mm were obtained according to a certain proportion of reduction of the natural teeth of the mandibular first molars@*Conclusion@#The anatomical healing abutment of the mandibular first molar can be quickly obtained by Shining scanning and CAD/CAM technology.

Analysis of the Mechanical Behavior and Effect of Cyclic Fatigue on the Implant-Abutment Interface / Análisis del comportamiento mecánico y efecto de la fatiga cíclica en la interface implante-pilar

ABSTRACT: Purpose: The seal of the interface formed at the implant-abutment connection is essential for the long-term success of the implant-supported restoration. The aim of this study was to analyze the mechanical behavior and the effect of cyclic fatigue before and after in the marginal fit of implant-abutment according to the manufacturing technique of the abutment. Materials and methods: Machined titanium abutments (DENTIS), cast abutments with Nickel-Chromium alloy (VeraBond II), and manufacturing custom milled Zirconia abutments (Zirkonzahn) were evaluated. The implant-abutment assemblies were subjected to cyclic loads of 133 N at a frequency of 19.1 Hz for 200,000 cycles. The microgap was measured using Scanning Electronic Microscope and the distribution of compressive stress by the three-dimensional Finite Element (FE) method. Results: The microgap measurement values of the machined abutments were 1.62μm and 1.92μm, cast abutments were 14.14 μm, and 28.44 μm, and the milled abutments were 14.18μm and 20.15μm before and after cyclic fatigue, respectively. Only the cast abutments and the machined abutments showed a statistically significant difference before and after cyclic fatigue (p≤0.05). The FE analysis showed that the critical areas of compressive stress were located at the implant-abutment connection, increasing in the cast abutments and decreasing in the milled and the machined abutments. Conclusion: Cyclic fatigue exerts an effect on the dimensions of the microgap at the implant-abutment interface before and after loading; this microgap depends of the type of abutment material and the manufacturing technique.

RESUMEN: Propósito: El sellado de la interface de la conexión implante-pilar es esencial para el éxito a largo plazo de la restauración implantosoportada. El objetivo de este estudio fue analizar el comportamiento mecánico y el efecto de la fatiga cíclica antes y después en el sellado de la conexión implante-pilar de acuerdo a la ténica de fabricación del pilar. Materiales y Métodos: Pilares mecanizados de titanio (DENTIS), pilares calcinables colados con aleación Niquel-Cromo (VeraBond II) y pilares fresados de Zirconia (Zirkonzahn) fueron evaluados. Los implantes y pilares atornillados se sometieron a una carga de 133 N a una frecuencia de 19.1 Hz durante 200 000 ciclos. El microgap fue medido con el Microscopio Electrónico de Barrido y la distribución del esfuerzo de compresión por el método tridimensional de Elemento Finito (EF). Los valores del microgap de los pilares mecanizados fueron de 1.62μm y 1.92μm, en los pilares calcinables fue de 14.14μm y 20.15μm, y los pilares fresados fue de 14.18μm y 28.44 μm antes y después de la fatiga cíclica, respectivamente. Los pilares calcinables y lo mecanizados mostraron diferencia estadísticamente significativa antes y después de la fatiga cíclica (p≤0.05). El análisis por EF mostró que las áreas críticas del esfuerzo de compresión estaban localizadas en la conexión implante-pilar, aumentando en los pilares calcinables y disminuyendo en los pilares fresados y en los mecanizados. Conclusión: La fatiga cíclica ejerce un efecto sobre las dimensiones del microgap en la interface implante-pilar antes y después de la carga cíclica; este microgap depende del tipo de material y de la técnica de fabricación del pilar.

Evaluation of tensile strength after insertions andremovals of abutments on frictional Morse taper implants

ABSTRACT: This study aimed to evaluate possible changes in final retention after nine sequences of insertion and removal (SIR) of a frictional Morse taper implant/abutment system, evaluating the force required for dissociating this set between sequences, and verifying possible deformations in the implant heads. Ten implants, 13 mm long and 3.3 mm in diameter, were coupled to a universal mechanical testing machine. Ten anti-rotational abutments, 13 mm long and 3.5 mm in diameter, were connected to the implants parallel to the long axis, using an instrument called beat-connection, and subjected to tensile tests and SEM analysis. The results were analyzed using the Kruskal-Wallis test with Dunn's post-test, and the significance level was set at 5 %. There was no statistically significant difference in final retention among the nine SIRs evaluated. The force needed to uncouple the abutment from the implant increased as SIRs were performed on all ten implants, and an increase of 29.03 % was observed in the ninth SIR compared to the first SIR. After SEM analysis, no significant deformations, fractures, or cracks were observed in the implant heads.

RESUMEN: Este estudio tuvo como objetivo evaluar los posibles cambios en la retención final después de nueve secuencias de inserción y extracción (SIR) de un sistema de implante / pilar de cono de fricción Morse, evaluando la fuerza necesaria para disociar este conjunto entre secuencias y verificando posibles deformaciones en las cabezas de los implantes. Se acoplaron diez implantes, de 13 mm de largo y 3,3 mm de diámetro, a una máquina universal de ensayos mecánicos. Se conectaron a los implantes en paralelo al eje largo diez pilares antirrotacionales, de 13 mm de largo y 3,5 mm de diámetro, mediante un instrumento llamado beat-connection, y se sometieron a pruebas de tracción y análisis SEM. Los resultados se analizaron mediante la prueba de Kruskal-Wallis con la prueba posterior de Dunn, y el nivel de significancia se estableció en 5 %. No hubo diferencias estadísticamente significativas en la retención final entre los nueve SIR evaluados. La fuerza necesaria para desacoplar el pilar del implante aumentó a medida que se realizaban SIR en los diez implantes, y se observó un aumento del 29,03 % en el noveno SIR en comparación con el primer SIR. Después del análisis SEM, no se observaron deformaciones, fracturas o grietas significativas en las cabezas de los implantes.

Retention of cemented zirconia copings on TiBase abutments / Retenção de copings de zirconia cimentados sobre pilares tibase

ABSTRACT This study evaluated the influence of resin cements and glass ionomers on tensile strength and types of failure of zirconia copings cemented on titanium base abutments. Forty-two samples were prepared, which were formed by a Cone Morse implant, a titanium abutment with the fixing screw, and a zirconia structure made using a CAD/CAM system. The samples (n = 42) were randomly distributed according to the cementing agent: resin-modified glass ionomer cement (RelyX Luting 2), self-adhesive resin cement (RelyX U200), and self-curing resin cement (Multilink N). After cementation of the copings, half of the samples from each group (n = 7) were randomly selected and subjected to thermocycling (5000 cycles). A tensile load test was performed on a universal testing machine until failure occurred (1 mm). In addition, the type of failure was analyzed using the two-way analysis of variance test and Tukey's post-hoc test (α = 0.05). Lower tensile load was observed for the glass ionomer cement (p < 0.001) regardless of the evaluation period. After thermocycling, a significant reduction in tensile load values was verified for both evaluated cements (p = 0.047). For the resin cements, failures were predominantly of the screw fracture type (82.1%) already with the use of glass ionomer cement, and 28.5% of the failures were of an adhesive type between the zirconia coping and the cement. Resin cements have better stability under tensile load compared to resin glass ionomers when cementing zirconia copings on titanium base abutments.

RESUMO Este estudo avaliou influência dos cimentos resinosos e a base de ionômero de vidro na resistência à tração e os tipos de falhas de copings de zircônia cimentados sobre pilares TiBase. Foram confeccionadas 42 amostras, sendo estas formadas por implante cone morse, pilar de titânio (TiBase) com o parafuso de fixação e uma estrutura de zircônia (coping de Zr) confeccionado através do sistema CAD/CAM. As amostras (n =42) foram aleatoriamente distribuídas de acordo com o agente de cimentação: (cimento de ionômero de vidro modificado por resina [RelyXTMLuting2]; cimento resinoso autoadesivo [RelyXTM U200] e cimento resinoso autopolimerizavel (Multilink® N). Após cimentação dos copings, metade das amostras de cada grupo (n = 7) foram aleatoriamente selecionadas e submetidas a termociclagem (5000 ciclos). O Teste de resistência a tração foi realizado em uma máquina de ensaio universal, até que ocorresse a falha (1 mm/min). Adicionalmente, o tipo de falha foi analizado. Os dados foram analisados pelo teste ANOVA two-way e post teste de Tukey's (α = 0.05). Menor média de resistência a tração foi observada para o cimento de ionômero de vidro (p < 0,001) independente do período de avaliação. Após a termociclagem, foi verificada uma redução significativa nos valores de resistênca a tração, para os cimentos avaliados (p=0,047). Para os cimentos resinosos, as falhas foram predominantemente do tipo fratura do parafuso (82,1%) já com o uso do cimento de ionômero de vidro, 28,5% das falhas foram de tipo adesiva entre o coping de Zr e o cimento. Cimentos resinosos apresentam melhor estabilidade na resistência a tração em comparação a ionmeros de vidro resinosos na cimentação de copings de zircônia sobre pilares TiBase.

Finite element analysis of the stress distribution of dental implant crowns with different all-ceramic materials and thicknesses / 口腔疾病防治

Objective@# To compare the stress distribution of different all-ceramic restoration materials and thicknesses in dental crown restorations using the finite element method and provide a reference for the selection and design of clinical crown restoration materials.@*Methods@#A finite element model of mandibular first molar implant crown restoration was created, and 6 crown thickness designs and 4 different crown restoration materials were evaluated, namely, resin-based ceramics (Lava Ultimate and Vita Enamic), lithium disilicate glass-ceramics (IPS e.max CAD), and zirconia ceramic (Cercon) designs. The mandibular first molars were loaded at 600 N, and the stress distribution was analyzed by using the finite element software ANSYS 10.0.@*Results@#The crown stress analysis showed that 156.05 MPa was the highest in 4 mm Cercon group and 18.85 MPa was the lowest in 1 mm Lava Ultimate group. The stress analysis of resin cement showed that 62.52 MPa was the highest in the 4 mm Lava Ultimate group and 16.74 MPa was the lowest in 1 mm IPS e.max CAD group. During the use of the finished platform, the stress concentration of the Lava Ultimate group in the crown prosthesis and resin cement was higher than that of the personalized platform with the same crown thickness.@*Conclusion@# With increasing crown thickness, the maximum principal stress concentration in crown restoration and resin cement increases. Personalized abutments are more conducive to reducing stress concentrations for resin-based ceramics.

Clinical application of integrated angulated screw channel abutment crown in implant-supported rehabilitation of aesthetic area / 华西口腔医学杂志

OBJECTIVES@#To evaluate the clinical effect of integrated angulated screw channel (ASC) abutment crown in implant-supported rehabilitation of the aesthetic area.@*METHODS@#Sixteen patients who received single implant-supported rehabilitation using integrated ASC abutment crown in the aesthetic area were included in the study. After one-year follow-up, the cumulative survival rate, aesthetic effectiveness, bone resorption around implants, and patient satisfaction were analyzed through periapical film, clinical examination, and the visual analog scale (VAS).@*RESULTS@#The implant cumulative survival rate of the integrated ASC abutment crown in the implant-supported rehabilitation of the aesthetic area was 100%. The average pink esthetic index scores reached 9.5, and the white esthetic index scores reached 9.4. The mean marginal bone loss of implants was (0.439±0.123) mm at the mesial side and (0.341±0.118) mm at the distal side. The average VAS satisfaction score was 8.9, which showed that all patients were satisfied with the final restorative effect.@*CONCLUSIONS@#Using integrated ASC abutment crown for implant restoration is an ideal implant restoration design in the aesthetic zone and can be applied clinically.

Effects of Different Implant Design Parameters on Mandibular Tooth Implantation / 医用生物力学

Objective To establish the implant-mandible model with different design parameters, observe stress distributions on the implant and surrounding bone, and analyze the influence of different design parameters on dental implant of the mandible. Methods Eight implant models were designed based on structural characteristic parameters (implant diameter, thread depth, height of abutment through gingiva, thread shape), and assembly of the mandibular model was performed respectively. The models were applied with static 150 N vertical and oblique 45° loads, so as to analyze peak von Mises stress of the implant and bone tissues and explore the structural parameter variables of implant most sensitive to peak von Mises stress. Results The peak stress of the mandible was larger under inclined load than that under vertical load. Implant diameter was the key factor affecting the peak von Mises stress of cortical bone, while thread depth was the key factor affecting the peak von Mises stress of cancellous bone. The peak von Mises stress was also affected by the height of abutment through gingiva, but the effect was not as significant as thread depth and implant diameter. Thread shape had little effect on the peak von Mises stress of the mandible. Conclusions Different implant design parameters can affect the peak stress of different tissues of the mandible, so it is necessary to carefully consider the selection of implant parameters for personalized implants. This study can provide theoretical guidance for structural parameter design of oral implants and provide references for accurate prediction of oral implants.

Challenges in Managing a Fractured Cement retained Crown Located at the Aesthetic Zone: A Case Report

ABSTRACT@#Implant prosthesis is a popular treatment modality but it is not complication free. This article discussed the management of a cemented, all-ceramic implant crown in the maxillary anterior region that had veneering ceramic fracture after three years in function. A screw-retained prosthesis was prescribed to avoid the show of the screw access channel on the incisal edge of the crown. This was achieved by changing the location of the screw hole using the angle screw channel that overcame the angulation issue.

Implant volume loss, misfit, screw loosening, and stress in custom titanium and zirconia abutments

Abstract The aim of this study was to verify the effect of the implant volume loss, vertical misfit between abutment and prosthetic platform, prosthetic screw loosening torque, and screw stress distribution in titanium and zirconia abutments. Ten CAD/CAM system custom abutments of each material were milled and attached to the titanium implants. The implant volume loss was evaluated by microtomography, the vertical misfit with optical microscopy, and digital torque wrench measured the prosthetic screw loosening. All experimental analyses were performed before and after mechanical cycle (1,000,000 cycles, 100 N/2 Hz). Virtual models of the structures were created for finite element analysis, and the stress on the screw obtained with von Mises procedure. Data were analyzed using an independent t-test, two-way ANOVA for repeated measures, and Tukey's HSD test (a=0.05). There was no significant difference in the implant volume loss for the two abutment materials (p=0.662). Titanium abutments provided higher loosening torque values after mechanical cycling (p<0.001). Lesser marginal misfit was obtained with titanium abutments before and after mechanical cycling (p<0.001). The stress distribution on the screw was similar between abutment materials. In conclusion, CAD/CAM custom titanium abutment reduced the marginal misfit and increased the torque maintenance of prosthetic screws when compared to CAD/CAM custom zirconia abutment.

Resumo O objetivo neste estudo foi verificar o efeito da diminuição de volume do implante, desajuste vertical entre o pilar e plataforma protética, torque de afrouxamento do parafuso protético e distribuição da tensão no parafuso em pilares de titânio e zircônia. Dez pilares personalizados de cada material foram fresados e conectados aos implantes de titânio. A diminuição de volume do implante foi avaliada com microtomografia, o desajuste vertical com microscopia óptica e o torque de afrouxamento do parafuso protético com chave de torque digital. Todas as análises experimentais foram realizadas antes e após aplicação do ciclo mecânico (1.000.000 ciclos, 100 N/2 Hz). Modelos virtuais das estruturas foram criados para análise por elementos finitos e a tensão no parafuso obtida com valores de von Mises. Os dados foram analisados usando teste t independente, análise de varância dois fatores para medidas repetidas e teste de Tukey HSD (a=0,05). Não houve diferença significativa na diminuição de volume do implante para os dois materiais do pilar (p= 0,662). Os pilares de titânio proporcionaram maiores valores de torque de afrouxamento após o ciclo mecânico (p<0,001). O menor desajuste marginal foi obtido com os pilares de titânio antes e após o ciclo mecânico (p<0,001). A distribuição da tensão no parafuso foi similar entre os materiais. Em conclusão, os pilares personalizados de titânio reduziram o desajuste marginal e aumentaram a manutenção do torque dos parafusos protéticos quando comparados aos pilares de zircônia.

Influence of metal bar lever-arm on screws detorque for dental prosthesis implant supported / Influência do cantilever no destorque de parafusos de barras metálicas utilizadas em próteses do tipo protocolo de Brannemark

Introduction: The cantilever length of implant-supported fixed prosthesis metal structure has been considered an important factor to transfer occlusion forces to the dental implant. Objective: This study evaluated the influence of different extensions of cantilevers of Branemark protocol implant prosthesis when submitted to mechanical thermocycling by screw loosening evaluation. Material and method: The groups G10 (n = 5), G15 (n = 5) and G20 (n = 5) were formed according to the distance in millimeters between the force application site in the cantilever and the center of the last implant. All metal structures (n = 15) were submitted to a 120 N cyclic vertical load in a chewing simulation machine (MSM-Elquip, São Carlos-SP, Brazil) under controlled temperature and moisture conditions. Two hundred and fifty thousand mechanical cycles were performed with a frequency of 2 Hz that simulates a masticatory activity similar to 3 months. To compare the data obtained regarding the loosening of the metal structure screws, implant position and sites of load application, the analysis of variance with two factors and the Tukey test were performed. Result: Statistical analysis showed that the G10 group presented greater torque loss, statistically different from G15 (p = 0.001) and G20 (p = 0.002), and there was no significant difference between groups G15 and G20. Conclusion: It can be concluded from the results that all the screws presented torque loss after simulation of 3 month masticatory activity, suggesting the need for periodical evaluation to prevent failures in the treatment.

Introdução: O comprimento do cantilever da infraestrutura de prótese implanto-suportada tem sido considerado um importante fator de transferência de força de oclusão para o implante dentário. Objetivo: Esse trabalho avaliou a influência das diferentes extensões do cantilever da prótese sobre implantes tipo protocolo de Branemark submetidas à termociclagem mecânica pela avaliação dos afrouxamentos dos parafusos de fixação. Material e método: Os grupos G10 (n=5), G15 (n=5) e G20 (n=5) foram formados de acordo com a distância, em milímetros, entre o local de aplicação de força no cantilever e o centro do último implante. Todas as barras (n=15) foram submetidas a carga vertical cíclica de 120 N em uma máquina de simulação de mastigação (MSM-Elquip, São Carlos/SP, Brasil), em condições de temperatura e umidade controladas. Foram realizados 250 mil ciclos mecânicos com frequência de 2 Hz que simulou uma atividade mastigatória correspondente a 3 meses. Para comparar os dados obtidos quanto à soltura dos parafusos da barra, a posição dos implantes e os locais de aplicação de carga, foi realizada a análise de variância com dois fatores e o teste de Tukey. Resultado: A análise estatística mostrou que o grupo G10 apresentou maior perda de torque, diferente estatisticamente de G15 (p=0,001) e G20 (p=0,002) e que não houve diferença significante entre os grupos G15 e G20. Conclusão: Pode-se concluir que todos os parafusos apresentaram perda de torque após o ensaio simulando uma atividade mastigatória de 3 meses, sugerindo a necessidade de avaliação clínica periódica afim de prevenir fracasso no tratamento.

Adaptación de pilares rectos sobre implantes con conexión hexagonal interna y externa por microscopía electrónica de barrido / Adaptation of straight pillars on implants with internal and external hexagonal connection by scanning electronic mi-croscopy / Adaptação de pilares retos em implantes com conexão hexagonal interna e externa por microscopia eletrônica de varredura

En implantología oral, ha sido motivo de investigación y constante evolución la interfase implante-pilar, princi-palmente desde el punto de vista biomecánico y biológico. Objetivo: Valorar el espacio o "gap" en la interfase implante-pilar en implantes de conexión hexagonal interna y externa por medio de microscopía electrónica de barrido (MEB). Materiales y Métodos: Estudio in vitro en 24 implantes (Bionnovation®) divididos en dos gru-pos (n=12): conexión hexagonal interna y externa. Para el experimento, se atornillaron pilares rectos con 30N de torque. A su vez 6 implantes por grupo se sometieron a 500000 ciclos de carga dinámica; posteriormente, se evaluó por MEB el espacio de la interfase implante pilar en 3 puntos de todas las muestras, las medias de los resultados de cada espécimen se respaldaron en tablas de Excel y se analizaron en el programa BioEstat 5.3. Resultados: Mediante test T para muestras independientes, con una significancia del 95%, se encontró una diferencia muy significativa luego de la aplicación de la carga dinámica en los implantes de hexágono ex-terno (p= 0.0002). En los implantes de hexágono interno también existió diferencia estadística (p= 0.03). Entre los implantes de hexágono externo e interno existieron diferencias muy significativas en la precisión del ajuste en la interfase implante pilar antes y después de la aplicación de las cargas dinámicas (p= <0.0001 y p= 0.0003 respectivamente). Conclusiones: Las cargas dinámicas aumentaron significativamente la discrepan-cia en la conexión implante-pilar de los implantes de hexágono externo e interno (p= < 0.05); adicionalmente, la distancia del "gap" fue mayor para los implantes de hexágono externo en contraste con los implantes de Hexágono Interno antes y después de la carga dinámica, siendo muy significativo (p= < 0.0003).

In oral implantology, the implant-pillar interface has been a subject of research and constant evolution, mainly from the biomechanical and biological point of view. Objective: To assess the gap in the implant-abutment interface in internal and external hexagonal connection implants by means of scanning electron microscopy (SEM). Materials and Methods: In vitro study in 24 implants (Bionnovation®) divided into two groups (n = 12): internal and external hexagonal connection. For the experiment, straight pillars with 30N of torque were screwed. In turn, 6 implants per group underwent 500,000 cycles of dynamic loading; Subsequently, the space of the pillar implant interface at 3 points of all samples was evaluated by MEB, the means of the results of each specimen were supported in Excel tables and analyzed in the BioEstat 5.3 program. Results: Using a T test for independent samples, with a significance of 95%, a very significant difference was found after the application of the dynamic load in the external hexagon implants (p = 0.0002). In the internal hexagon implants there was also a statistical difference (p = 0.03). Between the external and internal hexagon implants there were very significant differences in the accuracy of the adjustment in the abutment implant interface before and after the application of the dynamic loads (p = <0.0001 and p = 0.0003 respectively). Conclusions: Dynamic loads significantly increased the discrepancy in the implant-abutment connection of the external and internal hexa-gon implants (p = <0.05); additionally, the gap distance was greater for external hexagon implants in contrast to Internal Hexagon implants before and after dynamic loading, being very significant (p = <0.0003).

Na implantologia oral, a interface implante-pilar tem sido objeto de pesquisa e evolução constante, principal-mente do ponto de vista biomecânico e biológico. Objetivo: Avaliar o espaço ou "gap" na interface implan-te-pilar em implantes de conexão hexagonal interna e externa por meio de microscopia eletrônica de varre-dura (MEV). Materiais e Métodos: Estudo in vitro em 24 implantes (Bionnovation®) divididos em dois grupos (n = 12): conexão hexagonal interna e externa. Para o experimento, pilares retos com 30N de torque foram parafusados. Por sua vez, 6 implantes por grupo passaram por 500.000 ciclos de carregamento dinâmico; posteriormente, o espaço da interface do implante de pilar em 3 pontos de todas as amostras foi avaliado pelo MEV, as médias dos resultados de cada amostra foram suportadas em tabelas Excel e analisadas no programa BioEstat 5.3. Resultados: Usando um teste T para amostras independentes, com significância de 95%, foi encontrada uma diferença muito significativa após a aplicação da carga dinâmica nos implantes hexagonais externos (p = 0,0002). Nos implantes hexagonais internos também houve diferença estatística (p = 0,03). Entre os implantes hexágono externo e interno, houve diferenças muito significativas na precisão do ajuste na interface do implante de pilar antes e após a aplicação das cargas dinâmicas (p = <0,0001 ep = 0,0003, respectivamente). Conclusões: As cargas dinâmicas aumentaram significativamente a discrepância na conexão implante-pilar dos implantes hexágono externo e interno (p = <0,05); além disso, a distância do gap foi maior para os implantes hexagonais externos, em contraste com os implantes de hexágono interno antes e após o carregamento dinâmico, sendo muito significativa (p = <0,0003).

Influência do intermediário protético sobre a estética e a satisfação de pacientes reabilitados com próteses unitárias provisórias sobre implantes: um ensaio clínico / Influence of the prosthetic intermediary on the aesthetics and satisfaction of patients rehabilitated with temporary single prostheses on implants: a clinical trial

Objetivos: Avaliar a influência do tipo de intermediário protético e do condicionamento tecidual sobre a estética de coroas unitárias provisórias sobre implantes instalados na região do sorriso. Material e Métodos: Trinta implantes foram alocados sequencialmente: 15 foram reabilitados provisoriamente sobre um intermediário protético pré-fabricado em titânio (GT) e 15 sobre um intermediário protético preparável provisório (GP). Em ambos os grupos foi realizado condicionamento tecidual (CT) pela técnica não-cirúrgica de pressão gradual e a estética periimplantar foi avaliada antes e após esse processo, por meio do Pink Esthetic Score (PES). O PES também foi aplicado no dente homólogo à reabilitação. A satisfação estética foi analisada pela escala visual analógica (EVA) após o procedimento de CT. Dados clínicos da mucosa gengival também foram coletados. Resultados: 22 pacientes, totalizando 24 implantes, concluíram o estudo, sendo 14 implantes do GT e 10 do GP. A estética periimplantar antes e após o CT, bem como a satisfação dos pacientes foi semelhante entre os grupos, p>0,05. Diferenças significativas foram encontradas para os valores de PES antes e após o CT, e para a comparação com o dente homólogo em ambos os grupos, p<0,05. O processo de condicionamento tecidual não foi influenciado pelo tempo de implantação, tempo de carga e fenótipo periimplantar, p>0,05. Conclusão: O intermediário protético não influenciou nem no processo de condicionamento tecidual e nem na satisfação dos pacientes. A etapa de condicionamento tecidual foi capaz de melhorar os resultados estéticos periimplantares, entretanto, a estética gengival dos dentes naturais homólogos apresenta resultados significativamente superior (AU).

Objective: To evaluate the influence of prosthetic abutment and tissue conditioning on the esthetics of single implants' temporary crowns. Materials and Methods: Thirty implants were allocated sequentially: fifteen implants were provisionally rehabilitated with a titanium prefabricated prosthetic abutment (GT) and 15 with a provisional preparable prosthetic abutment (GP). In both groups, tissue conditioning (TC) was performed by the non-surgical gradual pressure technique and peri-implant aesthetics were assessed before and after this process, using the Pink Esthetic Score (PES). PES was also applied on homologous tooth. Aesthetic satisfaction was assessed using the visual analog scale (EVA) after the conditioning process. Clinical data on the gingival mucosa were also collected. Results: 22 patients (24 implants) completed this study, 14 implants from GT and 10 from GP. Peri-implant aesthetics before and after TC, as well as patient satisfaction was similar between groups, p> 0.05. Significant differences were found for PES values before and after TC, and for comparison with the homologous tooth in both groups, p <0.05. The TC process seems not be influenced by the implantation time, loading time and peri-implant biotype, p> 0.05. Conclusion: The prosthetic abutment seems not influence neither the TC process nor patient satisfaction. The TC step is able to improve the peri-implant aesthetic results, however, the gingival aesthetics of the natural teeth is still significantly greater (AU).