Enhancing oral function: A case report on mandibular overdenture utilization with custom-made subperiosteal implant.

Subperiosteal implants, previously set aside because of complications, are now emerging again as effective treatments for severe mandibular atrophy, aided by recent improvements in digital dentistry. Traditional dentures in such cases often face challenges with support and retention, necessitating complex regenerative procedures. This paper presents a case report of a 54-year-old male patient with significant mandibular atrophy who received a custom-made subperiosteal implant, showcasing promising results. The implant was precisely designed utilizing computed tomography (CT) scans, a 3D-printed model, the selective laser melting (SLM) technique, and constructed with biocompatible Ti6Al4V material. This innovative approach offered a practical solution, resulting in high patient satisfaction and no complications over a year of use.

Effect of shape and design of the internal connection of tissue-level and bone-level implants on detorque values and removal forces: An in vitro study.

STATEMENT OF PROBLEM: Optimal implant stability and preventing complications such as screw loosening are paramount concerns for implant-supported prostheses. However, studies examining the influence of various internal connection designs on detorque values and removal forces, critical aspects of implant success, are lacking. PURPOSE: The purpose of this in vitro study was to assess the impact of the shape and design of the internal connection in tissue-level and bone-level implants on the detorque value and the force required for abutment removal from the implant. MATERIAL AND METHODS: Forty dental implants were securely mounted in 10×6×20-mm acrylic resin blocks positioned perpendicular to the surface. The implants were divided into 4 groups (n=10): bone-level SM Torx, tissue-level PSI Torx, bone-level UF Hex, and tissue-level UF Hex implants. After exposure to a dynamic loading test at 31.2 N, 2 Hz and 106 cycles, measurements were made of both detorque values and removal forces. Statistical analyses, including 1-way ANOVA with a post hoc Tukey test and Kolmogorov-Smirnov test, were conducted to assess the results (α=.05). RESULTS: The differences in detorque values among the 4 groups were statistically similar (P=.087). In terms of removal force values, tissue-level PSI implants exhibited the highest values, while bone-level UF implants had the lowest values, with significant differences in the removal forces among the 4 groups (P<.001). Pairwise comparisons revealed significant differences among the groups (P<.001), except for the comparison between tissue-level PSI and bone-level SM implants (P=.108). CONCLUSIONS: While detorque values remain consistent across implant types, the shape and design of the internal connection of implants has a significant impact on the removal force required for abutment detachment from the implant.

The Effect of Abutment Angulation and Crown Material Compositions on Stress Distribution in 3-Unit Fixed Implant-Supported Prostheses: A Finite Element Analysis.

Objective: The aim of this study was to evaluate influence of abutment angulation and restoration material compositions on the stress pattern in dental implants and their surrounding bone. Materials and Methods: In this finite element study, the six different solid 3D models of "mandibular 3-unit fixed implant-supported prostheses" were analyzed. In all of these models, a straight abutment was used for anterior implants at the second premolar site, and in order to posterior implant at the second molar site, abutments with three different angles (straight, 15, and 20°) were used. Also, two different restoration material compositions (porcelain fused to base metal (PFBM) and porcelain fused to noble metal (PFNM)) were considered for fixed implant supported restorations. A 450 N static force was exerted in a straight manner along the longitudinal axis of the anterior implant in a tripod, and the stress distribution was measured based on the restoration materials and abutment angulations of the models in the 3 sites of cortical, cancellous bone, and fixtures. The simulation was performed with ABAQUS 6.13 Software. Results: In all models, stress values in surrounding cortical bone were more than in spongy bone. Maximum stress levels in an anterior abutment-implant complex were seen in models with angled implants. In models with parallel implants, the stress level of a molar straight abutment-implant complex was less than that of premolar straight ones. In an angled posterior abutment-implant complex, less stress level was detected compared to straight ones. In all PFNB models, stress values were slightly more and distributed in a wider area of premolar straight abutments. Conclusion: Increasing an abutment angle, increases stress in surrounding bone and straight implant-abutment combination. It seems that the crown material composition affects stress distribution of the implant-abutment combination but does not affect stress distribution of surrounding bone.

Comparing the color match of monolithic CAD-CAM dental ceramics with the VITA Classical shade guide.

STATEMENT OF PROBLEM: Matching the shade selected and the final color of a ceramic restoration is challenging, and studies on matching monolithic ceramics to the shade selected are lacking. PURPOSE: The purpose of this in vitro study was to compare the color match of monolithic lithium disilicate (LDS), zirconia-reinforced lithium silicate (ZLS), presintered zirconia-reinforced lithium silicate (PS-ZLS), polymer-infiltrated ceramic network (PICN), and multilayer zirconia with the 3 modes of the VITA Classical shade guide. MATERIAL AND METHODS: This study was performed on 50 rectangular plates (14×12×1 mm) of 5 types of ceramics with A2 shade (n=10). Zirconia specimens were evaluated in 3 locations: incisal, medial, and cervical thirds. The color coordinates of the specimens of all 7 groups were measured on #3 and #8 Ivoclar Natural Die Color material by using a reflective spectrophotometer. The color coordinates of A2 VITA shade were measured in 5 modes: without backing placed in specimen holder, shade tab on the backgrounds #3 and #8, and 1-mm-thick shade tab on the backgrounds #3 and #8. The color difference of each specimen with 3 modes of A2 shade (without backing and on similar backgrounds) was calculated by using the ΔE00 formula, and comparison among groups was performed by using 2-way ANOVA and Tamhane post hoc tests. The comparison of ΔE00 between the values obtained from backgrounds #3 and #8 was performed by using the independent t test (α=.05). RESULTS: In both backgrounds, statistically significant differences were found between the studied groups and VITA shade (P<.001). In most situations, the amount of color difference was lowest for the "shade tab on the backgrounds" mode. On background #3, the highest color difference was related to ZLS (6.48 ±0.23), and the lowest values were observed in the PICN group (1.02 ±0.31). On background #8, the highest color difference was related to ZLS compared with the "without backing" mode (8.62 ±0.27), and the lowest values were reported for ZLS compared with the "shade tab on the backgrounds" mode (1.27 ±0.44). The independent t test showed a statistically significant color difference on the 2 different backgrounds for all situations (P<.001). CONCLUSIONS: Color selection of monolithic ceramics with the VITA Classical shade guide is improved by placing the VITA tabs on a similar background. Background color has a significant effect on the final shade of the monolithic ceramics. Choosing the correct color for LDS, ZLS, and PS-ZLS requires more care than for PICN and zirconia.

Prevalence of Proximal Contact Loss between Implant-Supported Prostheses and Adjacent Natural Teeth: An Umbrella Review.

Contact loss between the implant prosthesis and adjacent natural teeth is a clinical complication whose overall prevalence is uncertain. Therefore, the main purpose of this umbrella study was to evaluate the extent of contact loss between implant prostheses and adjacent natural teeth. Electronic database of MEDLINE/PubMed, Cochrane, and Google Scholar was searched until August 2021 without considering language restrictions and according to Preferred Report Items for Systematic and Meta-Analysis guidelines (preferential reporting items for systematic review and meta-analysis). Inclusion criteria were systematic/meta-analysis review articles related to contact loss between implant prostheses and adjacent natural teeth. Inclusion criteria and risk of bias for the selected systematic/meta-analysis review studies were assessed by two or three qualified researchers, and the fourth researcher was used to resolve the ambiguities. From 43 eligible articles, five systematic/meta-analysis review studies were selected for this study. Important information such as the range of contact points, the prevalence, and the location of the contact loss was extracted. Three research studies had a low risk of bias and were considered clinical evidence. Analysis of low-risk studies showed that the superiority of open contact loss was excessive. Prevalence of proximal contact loss was more in mesial contact, especially in the mandibular arch. No significant differences were reported in sex or between the posterior and anterior regions.

Comparative Evaluation of the Effect of Core Type and Antirotational Post on Stress Distribution in an Endodontically Treated Maxillary First Molar: FEA.

Background: This study aims to analyze and compare the stress distribution in an endodontically treated maxillary first molar restored with various post and core systems and assess the benefit of the presence of an antirotational post and the effect of its length using finite element analysis. Materials and Methods: Five 3D models of maxillary first molar restored with variable designs of post and core were constructed using CT scanning and information obtained from textbook and FEM software. Variables were types of core, presence or absence of an antirotational post, and length of the antirotational post. A load of 480 (N) vertically and a load of 240 (N) with 45° to the occlusal plane were applied. Results were analyzed using 3D von Mises criteria. Results: The results showed that the most homogeneous stress distribution pattern along with dentin and the post-core system was observed in the model with one main post in the palatal canal and in the model with a two-piece core and one main post in the palatal canal and shorter antirotational post in the distal-buccal canal. However, models with one-piece core and antirotational post (either the same length or shorter than the main post) in the distal-buccal canal had the most stress concentration sites. Conclusion: In this study, it was found that the presence of an antirotational post, its length, and type of core affected the distribution of stress along the dentin and post-core system. This study indicated that if the antirotational post is considered in the post-core design, it is better to use a two-piece core type due to more homogeneous stress distribution along the dentin and post-core system.

An Umbrella Review of Systematic Reviews and Meta-Analyses Evaluating the Success Rate of Prosthetic Restorations on Endodontically Treated Teeth.

MATERIALS AND METHODS: The electronic search was conducted in the MEDLINE/PubMed, Cochrane, and Google Scholar databases until November 2020, regardless of language limitations. The inclusion criterion was as follows: S/M-R regarding prosthetic restorations in endodontically treated teeth. Three qualified researchers evaluated the inclusion criteria and bias risk. The fourth investigator was referred to when facing any doubtfulness. RESULTS: From 43 achieved S/M-R, 14 studies were selected for this inquiry. Primary extracted information included success rate, survival rate, and postendodontic failure rate. Five S/M-R had a moderate risk of bias, and nine S/M-R had a low risk of bias and were considered strong clinical evidence in this examination. According to the low-risk reports, the success rate of fiber posts was higher than that of metal posts; the rate of root fracture in metallic and fiber posts was alike; the failure rate for fiber posts was comparable to fixed partial dentures or single crowns; the construction of endocrowns was likely to perform better than intracanal posts, composite resin, or inlay/onlay restorations. CONCLUSION: It appears that with practice and experience, deciding which type of restoration to choose changes. In dental restorations associated with root canal therapy, the single crowns are likely to be a proper option. Nevertheless, due to the heterogeneity of the studies, more clinical assessments are required to achieve more specific findings in this field.

Effect of Two Whitening Toothpastes on Composite Resin Restorations Discolored by 0.2% Chlorhexidine Mouthwash.

Objectives: This study compared the effect of two whitening toothpastes on composite specimens discolored with 0.2% chlorhexidine (CHX). Materials and Methods: Twenty-four composite specimens were fabricated from Charisma Diamond composite resin. The initial color of specimens was measured according to the CIE L*a*b* color system using a spectrophotometer. The specimens were immersed in 0.2% CHX twice a day for 1 minute each time, for 2 weeks. The color of specimens was measured again, and the specimens were assigned to three groups (n=8). The control group specimens were immersed in distilled water. The two test group specimens were brushed twice daily for 21 days with Oral B toothbrush and Signal White Now and Crest 3D White whitening toothpastes each time for 30 seconds. The color of specimens was measured again. Data were analyzed by one-way ANOVA and t-test. Results: CHX increased the a, b, and L color parameters in all groups. There were no significant differences in ΔL (P=0.10), Δa (P=0.24), and Δb (P=0.07) among the study groups. The a, b, and L parameters decreased after brushing the specimens discolored with 0.2% CHX with the whitening toothpastes. There were significant differences in ΔL (P=0.03), Δa (P=0.02), and Δb (P=0.01) among the three study groups after using the whitening toothpastes. The highest ΔL, Δa, Δb, and ΔE values were recorded in Crest 3D White group, followed by Signal White Now group. Conclusion: Crest 3D White whitening toothpaste had higher efficacy to resume the original color of composite specimens discolored with 0.2% CHX.

Investigating the Effect of Nonrigid Connectors on the Success of Tooth-and-Implant-Supported Fixed Partial Prostheses in Maxillary Anterior Region: A Finite Element Analysis (FEA).

OBJECTIVE: This study was designed to assess the effect of nonrigid connectors (NRCs) and their location in the success of tooth-and-implant-supported fixed prostheses in the maxillary anterior region by finite element analysis (FEA). MATERIALS AND METHODS: Three 3D FEA models were designed, presuming maxillary lateral incisor and canine to be extracted. Implant (replacing canine), abutment, bone (spongious and cortical), central incisor (containing dentin, root cement, gutta-percha, and casting post and core), periodontal ligament, and three three-unit cemented PFM prostheses (a rigid one and two nonrigid) were modeled. The NRC was once in the tooth side and once in the implant side. The prostheses were loaded twice: 250N to the incisal edges (0° to the long axis) and 200 N to the cingula (45° to the long axis). The von-Mises stress and vertical displacement were analyzed. RESULTS: Under both vertical and oblique loadings, the rigid model presented the highest stress. Under vertical loading, the NRC caused a significant decrease in the applied stress to the prosthesis, bone, implant, and tooth. Locating the NRC in the tooth side decreased the applied stress to the prosthesis and NRC. Under oblique loading, prosthesis and implant tolerated less stress in the presence of an NRC. Placing the NRC in the tooth side resulted in the least stress in all of the components except for porcelain and patrix. Vertical displacement of the tooth apex was approximately equal in all models. CONCLUSION: Using an NRC on the tooth side is the most efficient method in reducing the applied stress to prosthesis, implant, tooth, and bone. The amount of intrusion is not dependent on using an NRC or not.

Comparison of translucency and opalescence among different dental monolithic ceramics.

STATEMENT OF PROBLEM: Monolithic ceramic restorations designed by computer-aided design and computer-aided manufacturing are increasingly being used by clinicians. With the introduction of new materials, their optical characteristics also need to be investigated. PURPOSE: The purpose of this in vitro study was to compare the translucency and opalescence of lithium disilicate, zirconia-reinforced lithium silicate, presintered zirconia-reinforced lithium silicate, polymer-infiltrated ceramic-network material, and multilayer zirconia. MATERIAL AND METHODS: A total of 50 rectangular plates (14×12×1 mm) of 5 monolithic ceramics were prepared in this in vitro study (n=10). Each zirconia specimen was divided into 3 groups of incisal, middle, and gingival thirds. Each group was then evaluated separately. The color parameters of specimens were measured on 3 backgrounds, white, black, and #3 Ivoclar Natural Die Color material, by using a spectrophotometer. The translucency and opalescence of the specimens were determined by the relevant equations, and between-group comparisons were made. One-way ANOVA and Tamhane post hoc tests were used to compare groups (α=.05). RESULTS: The difference among the groups was significant in translucency (F=137.346, df=6, P<.001), contrast ratio (F=134.148, df=6, P<.001), and opalescence parameters (F=128.028, df=6, P<.001). The 3 zirconia groups (10.87 ±0.54 to 11.88 ±0.26) had a significantly lower translucency than the other groups, and the zirconia-reinforced lithium silicate group (18.14 ±0.74) showed the highest translucency. Zirconia-reinforced lithium silicate (12.36 ±0.42) had the highest opalescence, and the lowest opalescence was found for polymer-infiltrated ceramic-network (5.43 ±0.28) and the incisal third of zirconia (5.45 ±1.06). CONCLUSIONS: The zirconia-reinforced lithium silicate and presintered zirconia-reinforced lithium silicate specimens had the highest translucency and opalescence. The studied multilayer zirconia, which had different cubic phase values from incisal to gingival blank, showed similar translucency over the entire range, and differences among different regions were related to chromatic variables.

The effects of cement space thickness and material type on marginal discrepancy of restoration / Efeitos da espessura do cimento e do tipo de material na discrepância marginal da restauração

Objetivo: Estudos demostraram que a zircônia monolítica um dos materiais restauradores desenvolvidos recentemente, resolveu vários problemas de restauração de zircônia. Portanto, a precisão marginal e o ajuste interno são necessários para o sucesso clinico e para a qualidade da restauração, e o espaço do cimento pode influenciar o ajuste marginal. Assim, o presente estudo teve como objetivo investigar os efeitos da espessura do cimento e o tipo de restauração na discrepância marginal. Material e métodos: foram usadas para fabricação de coroa total. Dois tipos de materiais incluindo Zirconia monolítica (Zolid) e Sintron foram usadas para produzir a coroa total. As amostras de cada grupo foram digitalizadas em laboratório dentário por um scanner 3D, projetadas e acessadas usando CAD-CAM. As amostras foram divididas em quatro grupos de cinco com espaço de 30 e 50 mícrons de cimento. Para avaliar a discrepância marginal, as coroas foram colocadas em seus respectivos dentes sem o uso de qualquer intermediário e examinados em micro-CT. Os dados foram avaliados pelo software SPSS. Resultados: Descobriu-se que a discrepância marginal do Sintron é maior que a discrepância da zircônia monolítica. Na verdade, a zircônia monolítica com espaço de 50 µm de cimento exibiu uma menor discrepância marginal, e o espaço de cimento do Sintron não influenciou significantemente na discrepância marginal. Conclusão: Concluiu-se que os tipos de material e o espaço do cimento influencia na discrepância marginal da restauração construída pelo fluxo digital (AU)

Objective: Studies demonstrated that as one of then ewly developed restorative materials, monolithic zirconia resolved several issues of zirconia restoration. Therefore, marginal accuracy and internal fit are necessary for clinical success and quality of restorations, and cement space may influence the marginal fit. Thus, the present research aimed to investigate the effects of the cement thickness and kind of restoration on the marginal discrepancy. Material and methods: In this study, 20 maxillary left first molars, prepared by DRSK Co., were used to fabricate a full crown. Two types of material included monolithic zirconia (Zolid) and Sintron were used to make a full crown. Samples from each group were scanned by dental laboratory 3D scanner and designed and processed using CAD-CAM. The samples were divided into four groups of five with 30-and 50- µm cement spaces. In order to assess the vertical marginal discrepancy, the crowns were fittedon their respective teeth without using any mediator and examined by a micro-CT scanner. Data were analyzed by SPSS software. Results: It has been found that marginal discrepancy in Sintron is higher than the discrepancy of monolithic zirconia. In fact, monolithic zirconia with 50-micron cement space exhibited the least marginal discrepancy and the cement space in Sintron did not significantly influence the marginal discrepancy. Conclusion: It has been concluded that the material kinds and cement space influence the restoration marginal discrepancy constructed by digital workflow (AU)

Patient satisfaction with occlusal scheme of conventional complete dentures.

Occlusal scheme is a controversial topic that has been linked to patient satisfaction with conventional complete dentures (CCDs). This study aimed to compare the patient satisfaction with CCDs with four different occlusal schemes namely the lingualised occlusion (LO), buccalised occlusion (BO), fully bilateral balanced occlusion (FBBO) and partially group function occlusion (PGFO). In this clinical study, new CCDs were made for 121 patients; out of which, 97 patients (mean age of 57.87 ± 9.5 years) completed the 1-year follow-up. The CCD wearers were followed up at 1 month, 3 months and 1 year after CCD delivery. Data were collected via an interview and recorded in a checklist by a blinded examiner. The checklist included the demographic variables, the 19-item version of Oral Health Impact Profile for Edentulous Patients (OHIP-EDENT), and seven 100-mm line visual analogue scales (VASs) to assess the items related to patient satisfaction. The Kruskal-Wallis and Friedman tests followed by post hoc tests were used to compare the variables among the 4 groups and between the 3 follow-ups. P-value ≤ .05 was considered statistically significant for all tests. The patients with BO presented higher satisfaction scores for comfort, stability and retention at the 1-year follow-up compared with PGFO. Both PGFO and FBBO groups had higher physical pain scores compared with BO and LO. The psychological discomfort scores of FBBO group were significantly higher than those in LO group. Pairwise comparisons revealed no significant differences in the general patient satisfaction and total OHIP-EDENT scores between the 4 groups. For most items, within-group analysis showed significant improvement of the satisfaction scores and reduction of domain scores over time.

Effect of laser irradiation on push-out bond strength of dental fiber posts to composite resin core buildups: A systematic review and meta-analysis.

BACKGROUND: The bonding of fiber posts (FPs) to composite resin core buildups is a challenge due to limited penetration of resin to the polymeric matrix of FPs. This review article tries to answer this question: "What are the effects of laser surface treatment of FPs, compared to other surface roughening methods, on push-out bond strength (PBS) of FPs bonded to composite resin core buildups?" METHODS: Searches were run in seven electronic databases with a focus on proper key words. Related titles and abstracts, up to February 2019, were screened, selected, read and subjected to quality assessments. RESULTS: After the initial search, a total of 2635 articles were included in the study. Finally, 6 studies were reliable enough in methodology to be included. All the studies were in vitro with a total of 359 samples. Er:YAG (-0.05, 95% CI: -2.96 to 2.86; P = 0.97) and Er,Cr:YSGG (0.84, 95% CI: -0.12 to 1.81; P = 0.08) treated samples showed no significant overall mean differences in final PBS compared to the control groups. Moreover, pretreatment with Er,Cr:YSGG laser and sandblasting with 50 µm alumina showed an overall mean difference of -0.42 for PBS (95% CI: -1.23 to 0.39) with no significant differences. CONCLUSIONS: Laser irradiation of FPs seems to provide no significant increase in PBS values of FPs bonded to composite resin core buildups. Effects of surface treatment of FPs with laser irradiation and sandblasting with 50 µm alumina might be similar in increasing the final PBS, either.

Comparison of color stability and fracture resistance of two temporary fiber-reinforced fixed partial denture materials.

BACKGROUND: Temporary crown and bridge materials have to fulfill a couple of important functions within the timeframe between tooth preparations until luting of the definitive restoration. The aim of the current study was to evaluate the color stability and fracture resistance of two fiber-reinforced provisional fixed partial denture (FPD) materials. MATERIALS AND METHODS: In this in vitro study Using a plexiglass mold, 96 bar-shaped specimens (4 mm × 2 mm × 20 mm) were fabricated and divided into four groups (n = 24): nonreinforced composite (NRC) resin, glass fiber-reinforced composite resin (RC), nonreinforced polymethylmethacrylate (PMMA), and glass fiber-reinforced PMMA. Values of CIEL*a*b* were recorded for all the samples. Then, the samples were immersed in coffee, chlorhexidine mouthrinse, and distilled water. After 1 day and 1 and 4 weeks, CIEL*a*b* values were recorded again and color differences (ΔE) were calculated. All the specimens immersed in distilled water were then subjected to force to measure their fracture resistance. Data were analyzed with one-way ANOVA, honestly significant difference Tukey tests, and paired t-test (α = 0.05). RESULTS: The NRC group, immersed in coffee for 1 month, exhibited the highest ΔE (17.1 ± 0.69) and the lowest ΔE belonged to the RC group immersed in water for 1 day. The RC group, immersed in water, exhibited the highest fracture resistance. CONCLUSION: Coffee is considered as one of the most important factors affecting color changes in provisional FPDs, either in composite resins or in PMMAs. Fracture resistance of both composite resin and PMMA FPDs revealed no significant differences between the groups; however, there were significant differences between the nonreinforced and fiber-reinforced FPDs in both groups.

Effect of ceramic cooling protocols and zirconia coloring on fracture load of zirconia-based restorations.

BACKGROUND: Residual thermal stresses in dental porcelains can cause clinical failure. Porcelain cooling protocols may affect the amount of residual stresses within porcelain and also porcelain-zirconia bond strength. The objective of this study was to assess the effect of cooling protocols on the fracture load of porcelain veneered zirconia restorations. MATERIALS AND METHODS: Forty zirconia bars (31 mm × 6.5 mm × 1.35 mm ± 0.1 mm) were fabricated by computer-aided design and computer-aided manufacturing technology. Half of the specimens were immersed in the coloring agent for 2 min before sintering (yellow group). Thus, the specimens were divided into two groups of white (W) and yellow (Y) samples (n = 20). Heat-pressed ceramic was applied to all bars. After pressing, half of the samples in each group were immediately removed from the oven (fast cooling) while the other specimens remained in the partially open door (30%) oven until the temperature reached to 500°C. Samples were thermocycled for 5000 cycles and subjected to modified four-point flexural strength test by a universal testing machine at a crosshead speed of 0.5 mm/min. Two-way ANOVA, One-way ANOVA followed by post hoc Tukey honest significant difference tests were used for data analysis (α = 0.05). RESULTS: Fractures were cohesive in all samples (within the porcelain adjacent to the interface). Two-way ANOVA showed that the effect of cooling protocol on the fracture load of samples was statistically significant (P < 0.001). In addition, the fracture load of W and Y groups was significantly different (P < 0.001). The white slow group showed the highest fracture load (179.88 ± 23.43 N). CONCLUSION: Slow cooling protocol should be preferably applied for zirconia restorations. Coloring agent used in this study had a significant negative effect on fracture load.

Effect of Denture Tooth Material on Load Transmission Under Denture Bases.

OBJECTIVES: Pressure transmission under denture bases can vary depending on the denture tooth material. The aim of the present study was to evaluate pressure transmission under denture bases using denture teeth of different materials in direct and indirect tooth contacts. MATERIALS AND METHODS: In this in-vitro study, the pressure transmission generated by five types of denture teeth, including ceramic, nanocomposite, composite-acrylic resin, cross-linked acrylic resin, and polymethyl methacrylate (PMMA), under direct and indirect pressures was evaluated (n=10). The maximum pressure (MPa) was measured using a strain gauge. Data were statistically analyzed with one-way analysis of variance (ANOVA; α=0.05). RESULTS: The denture tooth material had a significant effect on pressure transmission under denture bases (P<0.001). Under direct load, ceramic and PMMA teeth exhibited the maximum and minimum pressures, respectively, contrary to indirect load (P<0.001). CONCLUSIONS: Pressure transmission under denture bases significantly varies with the use of different denture tooth materials. Acrylic teeth could be the most favorable choice to reduce the pressure beneath denture bases. Nanocomposite and acrylic resin-composite teeth may be used as alternatives.

Effect of time interval between core preparation and post cementation on pushout bond strength of glass fiber-reinforced posts.

INTRODUCTION: The aim of this study was to investigate the effect of timing of coronal preparation on the pushout bond strength of fiber postluted with resin cement in the root canal. MATERIALS AND METHODS: In this experimental study, 48 mandibular human premolars were selected in a 3-week range. After root canal treatment and postspace preparation, a post #2(Angelus, Brazil) was cemented into the canal by a resin-based cement (Bifix SE, VOCO, Germany). Cylindrical resin composite cores were built on the posts. Then, the specimens were divided into 4 groups of 12 specimens each: one control group without core preparation and 3 experimental groups with core preparation that was done 15 min, 1 h, and 24 h after postcementation. One day after postcementation, each root was sectioned into 3 segments. Each slice was connected to universal testing machine. The load was applied at the speed of 0.5 mm/min till failure happened. The collected data were analyzed (SPSS/PC 20.0; SPSS Inc., Chicago, IL, USA) using two-way ANOVA and post hoc Tukey test at P < 0.05 level of significance. RESULTS: Mean shear bond strength differences among interventional groups were not statistically significant (P > 0.05). Nevertheless, there were significant differences among root regions (P < 0.001). CONCLUSION: It was concluded that core preparation and its timing does not affect adversely retention of fiber post and bond strength is higher in the cervical segment.

Effect of cantilever length on stress distribution around implants in mandibular overdentures supported by two and three implants.

OBJECTIVE: There is no definitive study comparing stress distribution around two versus three implants in implant-retained overdentures with different cantilever length. The purpose of this finite element study was to evaluate stress pattern around the implants of the 2 or 3 implant- supported mandibular overdenture with different cantilevered length. MATERIALS AND METHODS: The models used in this study were 2 and 3 implant-supported overdenture with bar and clip attachment system on an edentulous mandibular arch. Each model was modified according to cantilever length (0 mm, 7 mm, and 13 mm); thus, 6 models were obtained. The vertical load of 15 and 30 pounds were applied unilaterally to the first molar and 15 pounds to the first premolar, and the stress in bone was analyzed. RESULTS: With increasing cantilever length, no similar stress pattern changes were observed in different areas, but in most instances, an increase in cantilever length did not increase the stress around the implant adjacent to cantilever. CONCLUSIONS: Within the limitations of this study, it can be concluded that increasing of cantilever length in mandibular overdentures retained by 2-3 implants did not cause distinct increasing in stress, especially around the implant adjacent to cantilever, it may be helpful to use cantilever in cases of mandibular overdenture supported by splinted implants with insufficient retention and stability. Based on the findings of this study, optimal cantilever length in mandibular overdenture cannot be determined.

Finite Element Analysis of the Influence of Implant Inclination on Stress Distribution in Mandibular Overdentures.

The purpose of this finite element study was to evaluate the influence of implant inclination on the stress pattern in the bone surrounding the implants that support mandibular overdentures. The models used in this study were 3-implant-supported mandibular overdentures with a bar-and-clip attachment system. Each model was modified according to the distal implant inclination (0 and 20°). A unilateral vertical load was applied unilaterally to the first molar and first premolar of the overdenture, and the stress distribution in the bone was analyzed. Implant inclination decreased the stress distribution pattern in bone surrounding the implants when the load was applied on the molar site, but when applied at the premolar site, similar stress value changes were not found. Within the limitation of this study, it seems that the inclination of splinted implants in mandibular overdentures does not have any adverse effect on stress distribution pattern values around the implant.

A technique for relining bar-retained overdentures.

This article describes a technique for relining a mandibular bar-retained overdenture that allows recording the soft tissue beneath the bar and makes it possible to replace or modify the retentive bar attachment simultaneously with the reline procedure.