Cytotoxicity of dental cement on soft tissue associated with dental implants at different time intervals

Background

To investigate and compare the effect of four commercially used dental cement at 24 hours, 48 hours,72 hours (h) and 6 days on the cellular response of human gingival fibroblast (HGF).

Methods

3 cement pellet samples were made for each 4-test cement (n=12). The cement used for this study were zinc phosphate (ZP), zinc oxide non-eugenol (ZOE), RelyX U200 (RU200), and glass ionomer cement (GIC). The cytotoxicity of peri-implant tissues was investigated using one commercial cell line. All processing was done following International Organization for Standardization (ISO) methods 10993-5 and 10993-12 (MTT assay Test). Cell cultures without dental cement were considered as control. Standard laboratory procedures were followed to permit cell growth and confluence over 48 hrs after sub-cultivation. Before being subjected to analysis, the cells were kept in direct contact with the cement samples for the suggested time period. To validate the results the specimens were tested three times each. Cell death and inhibition of cell growth were measured quantitatively. Results were analyzed using 1-way ANOVA (a=0.05) followed by Tukey B post hoc test.

Results

The study showed the dental cement test material was cytotoxic. ZOE, ZP, GIC, and RU200 were cytotoxic in decreasing order, respectively, significantly reducing cell viability after exposure to HGF (p <0.001).

Conclusions

Within the limitations of this in-vitro cellular study, results indicated that HGF were vulnerable to the test the dental cement. The highest cytotoxicity was observed in ZOE, followed by ZP, GIC, and RU200.

The effect of thermomechanical aging on the retention of a conometric system in a chewing simulator

PURPOSE

To evaluate the retention force of a novel conometric system after thermomechanical aging. In addition, the conometric system's retention force was compared with that of the cemented implant-retained crowns.

MATERIALS AND METHODS

Two systems to retain implant crowns were tested in this study: a conometric system and a cement-retained system. Forty-eight zirconia crowns were fabricated using computer-aided design and computer-aided manufacturing technology. Twenty-four zirconia crowns were cemented onto conometric caps with resin-modified glass ionomer cement, which were then connected with abutments. These specimens were divided into three groups, and each group was subjected to the pull-out test. A-control group: 12 specimens directly subjected to pull-out test; A-aged group: 12 specimens subjected to thermomechanical aging followed by pull-out test; A-repeat group: After the pull-out, the specimens in the aging group (A-aged) were reconnected, and the pull-out test was repeated once more. The remaining 24 zirconia crowns were cemented on standard abutments with zinc phosphate cement, and two groups were formed. C-control group: 12 specimens directly subjected to the pull-out test; C-aged group: 12 specimens subjected to thermomechanical aging followed by pull-out. Scanning electron microscope (SEM) was used to evaluate the surfaces of caps and abutments. To analyze the data, repeated measures, one-way ANOVA, and Bonferroni tests were used (p < 0.05).

RESULTS

The mean retention force value of the A-control group was 148.22 ± 16.37 N. The highest mean retention force value was measured in the A-aged group (204.93 ± 51.67 N), and the lowest mean retention force value was seen in the A-repeated group (77.02 ± 21.48 N). Thermomechanical aging had a significant influence (p < 0.05) on both systems. No significant differences in retention force were found between the thermomechanical aged groups of both systems (p > 0.05). SEM analysis revealed that aging had an impact on the surface of the conometric system's caps and abutments.

CONCLUSIONS

The retention force of the conometric system increased significantly following thermomechanical aging. No crown separation occurred during the thermomechanical aging of the conometric system. There was no significant difference in the retention of the conometric and cemented systems after thermomechanical aging.

Effects of cyclic loading on loss of abutment screw torque of angled screw channel single implant crowns on narrow diameter implants

STATEMENT OF PROBLEM

Screw access channels that emerge on the facial aspect of anterior screw-retained implant crowns can compromise esthetics. Recently, angled screw channels (ASCs) have been developed that can alter screw access channel angulations to improve esthetics. While ASCs can be used on narrow-diameter implants, information is limited on the loss of abutment screw torque on narrow-diameter implants with ASCs.

PURPOSE

The purpose of this in vitro study was to compare the loss of abutment screw torque after thermocycling and the cyclic loading of ASCs from 3 different companies connected to narrow-diameter implants.

MATERIAL AND METHODS

A total of 40 narrow-diameter implants (NobelReplace Conical Connection 3.5×11.5 mm) were mounted individually in acrylic resin blocks and divided equally into 4 groups. The first group, NB-0 (Control), consisted of screw-retained zirconia crowns fabricated on ASCs at 0-degree angulation (n=10). The other 3 groups consisted of a total of 30 screw-retained zirconia crowns fabricated on ASCs at 20-degree angulation: NB-20 (Angulated Screw Channel Solutions), ATL-20 (Atlantis Custom Base Solution with angulated screw access), and DA-20 (Dynamic TiBase). Each crown was secured on the mounted implant with its corresponding titanium base insert and screw and then tightened to the manufacturer's recommended torque with a digital torque gauge. The initial reverse torque value (RTVI) was obtained and recorded at baseline. Subsequently, a new set of screws were tightened to recommended values, and each specimen underwent thermocycling and then cyclic loading at 0 to 100 N at 10 Hz for 1 million cycles to simulate 1year of functional loading. After cyclic loading, the final reverse torque values (RTVF) were recorded and compared with the RTVI to evaluate the percentage torque loss (PTLF). Statistical analysis was performed using the Kruskal-Wallis analysis, Rank base analysis of covariance (ANCOVA), and the Tukey HSD post hoc comparisons (α=.05).

RESULTS

Significant differences were found for the PTLF among all groups after cyclic loading (P<.001). The PTLF in ATL-20 (51.4%) was significantly higher than in NB-0 (22.2%) (P<.001) and NB-20 (29.2%) (P=.010). No significant difference was found in the PTLF among other groups (P>.05).

CONCLUSIONS

The abutment screw torque loss after cyclic loading of the ASCs on narrow diameter implants among the 4 groups did not perform comparably. The largest percentage torque loss was recorded for the ATL-20 group. The NB-20 group demonstrated the lowest percentage torque loss. DA-20 showed percentage torque loss less than ATL-20; however, its RTVF was the lowest.

Cytotoxicity of dental cement on soft tissue associated with dental implants at different time intervals

Background: To investigate and compare the effect of four commercially used dental cement at 24 hours, 48 hours,72 hours (h) and 6 days on the cellular response of human gingival fibroblast (HGF). Methods: 3 cement pellet samples were made for each 4-test cement (n=12). The cement used for this study were zinc phosphate (ZP), zinc oxide non-eugenol (ZOE), RelyX U200 (RU200), and glass ionomer cement (GIC). The cytotoxicity of peri-implant tissues was investigated using one commercial cell line. All processing was done following International Organization for Standardization (ISO) methods 10993-5 and 10993-12 (MTT assay Test). Cell cultures without dental cement were considered as control. Standard laboratory procedures were followed to permit cell growth and confluence over 48 hrs after sub-cultivation. Before being subjected to analysis, the cells were kept in direct contact with the cement samples for the suggested time period. To validate the results the specimens were tested three times each. Cell death and inhibition of cell growth were measured quantitatively. Results were analyzed using 1-way ANOVA (a=0.05) followed by Tukey B post hoc test. Results: The study showed the dental cement test material was cytotoxic. ZOE, ZP, GIC, and RU200 were cytotoxic in decreasing order, respectively, significantly reducing cell viability after exposure to HGF (p <0.001). Conclusions: Within the limitations of this in-vitro cellular study, results indicated that HGF were vulnerable to the test the dental cement. The highest cytotoxicity was observed in ZOE, followed by ZP, GIC, and RU200.

Occlusion as a predisposing factor for peri-implant disease: A review article

BACKGROUND

The restoration of dental implants presents a unique challenge due to the intrinsic biomechanical differences between osseointegrated implants and natural teeth, and their subsequent responses to occlusal loading. However, controversy exists regarding the role that occlusion plays in the physiology of the peri-implant complex.

PURPOSE

To provide an overview of the scientific literature regarding occlusion as it relates to implant dentistry and peri-implant disease.

MATERIALS AND METHODS

This article presents a narrative review on occlusal loading and its potential effects on the peri-implant complex, as well as some generally accepted guidelines for occlusion in implant dentistry.

RESULTS AND CONCLUSIONS

Although there is strong evidence linking occlusal factors to mechanical complications of dental implants, the same cannot be said regarding biological complications. There is no clear scientific evidence on the relationship between occlusal overload and peri-implant disease. However, occlusal overload may be an accelerating factor for peri-implant disease in the presence of inflammation. As the biomechanical properties of dental implants differ from that of the natural dentition, modifications to classic concepts of occlusion may be necessary when dental implants are involved. Thus, clinical recommendations are proposed which function to minimize unfavorable occlusal forces on implant restorations and reduce the associated biological and mechanical complications.

A prospective multicenter clinical study on the efficiency of detachable ball- and spring-retained implant prosthesis

PURPOSE

This prospective clinical study was conducted to evaluate the clinical usefulness of the freely detachable zirconia ball- and spring-retained implant prosthesis (BSRP) through a comparative analysis of screw- and cement-retained implant prosthesis (SCRP).

MATERIALS AND METHODS

A multi-center, randomized, prospective clinical study evaluating the clinical usefulness of the detachable zirconia ball- and spring-retained implant prostheses was conducted. Sixty-four implant prostheses in 64 patients were examined. Periodic observational studies were conducted at 0, 3, 6, and 12 months after delivery of the implant prosthesis. Factors such as implant success rate, marginal bone resorption, periodontal pocket depth, plaque and bleeding index, and prosthetic complications were evaluated, respectively.

RESULTS

During the 1-year observation period, all implants survived without functional problems and clinical mobility, showing a 100% implant success rate. Marginal bone resorption was significantly higher in the SCRP group than in the BSRP group only at the time of implant prosthesis delivery (P = .043). In all observation periods, periodontal pocket depth was slightly higher in the BSRP group than in the SCRP group, but there was no significant difference (P > .05). The modified plaque index (mPI) scores of both groups were moderate. Higher ratio of a score 2 in modified sulcus bleeding index (mBI) was observed in the BSRP group in the 6- and 12-months observation.

CONCLUSION

Within the limitations of this study, the newly developed zirconia ball- and spring-retained implant prosthesis could be considered as an applicable and predictable treatment method along with the existing screw- and cement-retained prosthesis.

Cytotoxicity of Dental Cements on Soft Tissue Associated with Dental Implants

Purpose

To investigate and compare the cellular host response of human gingival fibroblasts (HGF) on four currently used cements. Methods and Material. 5 cement pellet samples were made for each of the 4 test cements (n = 20). The cements used for this study were zinc phosphate, zinc oxide noneugenol (ZOE), RelyX U200, and glass ionomer cement (GIC). One commercially available cell line was used to investigate the cytotoxicity of peri-implant tissues. Direct contact cell culture testing was conducted following International Organization for Standardization (ISO) methods 10993-5 and 10993-12 (MTT assay test). Cell cultures without dental cement were considered as control. Cells were allowed to grow and confluence over 48 hours after subcultivation according to standard laboratory procedures. The cells were kept in direct contact with the cement samples for 24 hours before being subjected to analysis. All specimens were tested in triplicate to validate the results. Quantitative evaluation of cytotoxicity was done to measure cell death and inhibition of cell growth. Results were analyzed using 1-way ANOVA (a = 0.05) followed by Tukey B post hoc test.

Results

The results of the study showed that HGF was vulnerable to the dental cement test material. GIC, zinc phosphate, ZOE, and resin cement were cytotoxic in decreasing order, respectively, and significantly reduced the cell viability after exposure to HGF (p < 0.001).

Conclusions

Within the limitations of this in vitro cellular study, results indicated that the test dental cements were cytotoxic to HGF. The highest cytotoxicity was observed in GIC followed by zinc phosphate, ZOE, and resin cement.

Influence of an Implant Fixture including a Freely Removable Micro-Locking Implant Prosthesis on Peri-Implant Tissues and Implant Prostheses: A Prospective Clinical Study

This prospective study was undertaken to evaluate the clinical usefulness of a newly developed one-piece, screw-free, and micro-locking implant system, which was designed to overcome the shortcomings of the existing implant systems. Thirty-eight patients were recruited and randomly and equally assigned to an experimental group (micro-locking one-piece fixture, MLF; n = 19) or a control group (micro-locking abutment, MLA). Cumulative implant survival rates, marginal bone resorptions, probing depths, plaque indices, bleeding indices, and complications were obtained by using clinical and radiographic findings at 6 months and 12 months after prosthesis placement. Complications that occurred multiple times for single implants were counted. During the 12 month observation period, survival rates were 100% in both groups. No significant intergroup differences were observed for marginal bone resorption, probe depth, or bleeding index. However, mean plaque index was significantly lower in the MLF group at 12 months (p < 0.05). During the 12-month observation period, food impaction (26.3%) was the main complication in the MLF group and screw loosening (5.3%), prosthesis detachment (5.3%), and food impaction (5.3%) were observed in the MLA group. The results of this study suggest that the one-piece micro-locking implant system offers a predictable treatment method.

In vitro validation of Digital Image Analysis Sequence (DIAS) for the assessment of the marginal fit of cement-retained implant-supported experimental crowns

BACKGROUND

The replica technique with its modifications (negative replica) has been used for the assessment of marginal fit (MF). However, identification of the boundaries between prosthesis, cement, and abutment is challenging. The recently developed Digital Image Analysis Sequence (DIAS) addresses this limitation. Although DIAS is applicable, its reliability has not yet been proven. The purpose of this study was to verify the DIAS as an acceptable method for the quantitative assessment of MF at cemented crowns, by conducting statistical tests of agreement between different examiners.

METHODS

One hundred fifty-one implant-supported experimental crowns were cemented. Equal negative replicas were produced from the assemblies. Each replica was sectioned in six parts, which were photographed under an optical microscope. From the 906 standardized digital photomicrographs (0.65 μm/pixel), 130 were randomly selected for analysis. DIAS included tracing the profile of the crown and the abutment and marking the margin definition points before cementation. Next, the traced and marked outlines were superimposed on each digital image, highlighting the components' boundaries and enabling MF measurements. One researcher ran the analysis twice and three others once, independently. Five groups of 130 measurements were formed. Intra- and interobserver reliability was evaluated with intraclass correlation coefficient (ICC). Agreement was estimated with the standard error of measurement (SEM), the smallest detectable change at the 95% confidence level (SDC_95%), and the Bland and Altman method of limits of agreement (LoA).

RESULTS

Measured MF ranged between 22.83 and 286.58 pixels. Both the intra- and interobserver reliability were excellent, ICC = 1 at 95% confidence level. The intra- and interobserver SEM and SDC_95% were less than 1 and 3 pixels, respectively. The Bland-Altman analysis presented graphically high level of agreement between the mean measurement of the first observer and each of the three other observers' measurements. Differences between observers were normally distributed. In all three cases, the mean difference was less than 1 pixel and within ± 3 pixels LoA laid at least 95% of differences. T tests of the differences did not reveal any fixed bias (P > .05, not significant).

CONCLUSION

The DIAS is an objective and reliable method able to detect and quantify MF at ranges observed in clinical practice.

Effect of screw access channel on the fracture rate of lithium disilicate cement-retained implant-supported posterior crowns

STATEMENT OF PROBLEM

Whether the presence of a screw access channel on the occlusal surface of a lithium disilicate cement-retained single tooth implant restoration reduces its fracture rate is unclear.

PURPOSE

The purpose of this randomized controlled clinical trial was to compare the fracture rate of lithium disilicate cement-retained posterior single tooth implant restorations with or without screw access channels. The study also evaluated whether the crown dimensions and location of the occlusal screw access channel would affect the fracture rate.

MATERIAL AND METHODS

A split-mouth study was conducted where 40 participants having 2 implants placed to restore single missing posterior teeth with crowns were enrolled. Implants were randomly allocated into a conventional crown group or a screw access group, receiving cement-retained restorations fabricated from lithium disilicate glass-ceramic with and without an occlusal screw access channel. Crown dimensions were recorded in millimeters from the designing software. Follow-up evaluations were made at 3, 6, and 12 months by observing visible cracks or fractures of the crowns. The Kolmogorov-Smirnov test of normality was used. Comparisons were carried out by using the Student and Welch t tests (α=.05).

RESULTS

After a 12-month follow-up period, no crowns fractured or revealed visible cracks, resulting in a 100% success rate. No statistically significant differences were found between the conventional crown group and screw access channel group in all crown dimensions (P>.05).

CONCLUSIONS

The presence of an occlusal screw access channel did not affect the short-term fracture rate of lithium disilicate cement-retained single implant-supported posterior crowns. The amount of axial cantilever, occlusal ceramic thickness, and location of the screw access channel on the occlusal surface of the restoration have no effect on its fracture rate.

Cleaning Efficacy of Poly-ether-ether-ketone Tips in Eliminating Cement Remnants Around Implants With Different Abutment Heights

The excess cement not removed after the cementation of fixed implant-supported restorations may cause loss of peri-implant attachment or adjacent bone. The aims of this study were to evaluate the amount of residual cement at different abutment-crown connection levels and to test the cleaning efficacy of poly-ether-ether-ketone (PEEK) ultrasonic tips after cementation. One implant was placed in an anterior central tooth position 5 mm below the gingival margin in an acrylic model, and 32 stone models were obtained with implant analogs. Abutment heights of 1-2 and 2.5-4 mm were used on the vestibular and lingual sides, respectively. Crowns were cemented and cleaned, and half of the samples were cleaned again using PEEK tips. The abutment-crown suprastructure was then disconnected, and cleaning efficacy was evaluated. Varying amounts of excess cement were found on all specimens except for the PEEK group with abutment-crown connections 1 mm below the gingival margin. An increase of undetected cement remnants was observed when the restoration margins were located deeper subgingivally. Various amounts of excess cement associated with margin location were detected on the abutment-restoration complex despite meticulous cleaning efforts. Ultrasonic PEEK tips were effective at cleaning the cement remnants around implants to a certain depth.

Self-healing biomaterials: The next generation is nano

The U.S. Agency for Healthcare Research and Quality estimates that there are over 1 million total hip and total knee replacements each year in the U.S. alone. Twenty five percent of those implants will experience aseptic loosening, and bone cement failure is an important part of this. Bone cements are based on poly(methyl methacrylate) (PMMA) systems that are strong but brittle polymers. PMMA-based materials are also essential to modern dental fillings, and likewise, the failure rates are high with lifetimes of 3-10 years. These brittle polymers are an obvious target for self-healing systems which could reduce revision surgeries and visits to dentist. Self-healing polymers have been described in the literature since 1996 and examples from Roman times are known, but their application in medicine has been challenging. This review looks at the development of self-healing biomaterials for these applications and the challenges that lie between development and the clinic. Many of the most promising formulations involve introducing nanoscale components which offer substantial potential benefits over their microscale counterparts especially in composite systems. There is substantial promise for translation, but issues with toxicity, robustness, and reproducibility of these materials in the complex environment of the body must be addressed. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Implantable Materials and Surgical Technologies > Nanomaterials and Implants.

Fabricating a screw-retained, complete arch, fixed implant prosthesis using selective metal laser sintering: A clinical report

In contemporary prosthodontic practice, implant-supported therapy has consistently resulted in high success rates, with satisfactory and predictable outcomes for completely edentulous patients. Of the several options, complete-arch, fixed screw-retained solutions are generally considered to be the preferred treatment solution. Screw retention offers advantages such as predictable retrievability and potentially easy prosthodontic maintenance, as well as excess cement not being a concern. However, implant mispositioning and malalignment may often necessitate the use of cement-retained prostheses. This clinical report describes a method of fabricating a complete-arch, implant screw-retained, double framework metal-ceramic prosthesis, despite the unfavorable implant positioning, by using selective direct metal laser sintering technology.

Virtual Implant Rehabilitation of the Severely Atrophic Maxilla: A Radiographic Study

BACKGROUND

Advanced maxillary atrophy is one of the most common clinical scenarios where implant placement could become difficult. Nevertheless, a volumetric evaluation using a suitable diagnostic software could facilitate the implant planning. The purpose of the present study is to suggest the potential application of the maxillary retro-canine area as the designated location for virtual tilted implants.

METHODS

A sample of Cone Beam Computed Tomography (CBCT) images from the Department of Dentistry (IRCSS San Raffaele, Milan, Italy) was evaluated. After a 3D anatomical evaluation, tilted implants were virtually positioned in the retro-canine regions. All the implants were inserted using the same procedure at 30° and 45° degrees of tilting. The length, palatal angulation and diameter of the placed implant were identified.

RESULTS

A total of 220 tilted implants were placed. An average implant measurement of 13.51 mm in length and 3.42 mm in diameter were calculated. Additionally, an average buccal-palatal angulation of 6° was identified. Upon statistical analysis, the implant length was found to be significantly higher at 45° degrees of mesio-distal angulation than at 30° degrees (<0.0001).

CONCLUSIONS

A considerable number of patients show a significant degree of bone atrophy. The implant-supported treatment plan can rely on three-dimensional imaging of the residual bone as a guiding tool to establish the most effective implant position for each specific case. In this study, it was found that an implant could have a greater length if its mesio-distal angulation was more accentuated. In addition, owing to the volumetric evaluation, it was possible to virtually insert tilted implants in almost all of the cases of atrophy. This could lead clinicians to consider the retro-canine area as a viable place to insert a longer tilted implant.

Monolithic Zirconia FPD on Modified Titanium Bonding Bases in Limited Interocclusal Distance: A Case Report

A 62-year-old male patient sought treatment for missing maxillary teeth. A diagnostic cast demonstrated that the interocclusal distance was insufficient. A 5-unit screw-retained implant-supported fixed partial denture (FPD) was used to restore missing maxillary teeth. The restoration of multiple missing teeth using an implant-supported FPD is challenging when the interocclusal distance is limited due to lack of retention and inadequate esthetics. In this case, a hexagonal, screw-retained, and subgingivally located titanium-based zirconia implant-supported FPD with a conical abutment base was used for restoration to overcome the limited interocclusal distance. This implant-supported FPD, consisting of CAD/CAM-designed monolithic zirconia cemented to a titanium bonding base in the laboratory, is expected to facilitate predictable retention and adequate esthetics as well as provide ease of retrieval.

An in vitro investigation comparing methods of minimizing excess luting agent for cement-retained implant-supported fixed partial dentures

STATEMENT OF PROBLEM

The use of cement-retained implant-supported prostheses is a well-established treatment option. Techniques have been proposed to reduce the amount of residual excess cement (REC) around cement-retained single-implant restorations. However, studies evaluating the effectiveness of such techniques related to cement-retained implant-supported fixed partial dentures (CRISFPDs) are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the effectiveness of various cement application techniques for CRISFPDs.

MATERIAL AND METHODS

Two implant analogs were placed in the lateral incisor sites in a maxillary, 3D printed cast with 4 missing incisors. Twenty standardized, removable, printed soft-tissue replicas, 40 milled titanium custom abutments, and 20 milled zirconia CRISFPDs were fabricated. Two cement application techniques, the brush on technique (BOT), and the polyvinyl siloxane index (PI) technique were compared. Two cementation techniques, without bib (control) (n=10) and with a polytetrafluoroethylene (PTFE) bib (test) (n=10), were used. A premeasured amount of interim cement was used to cement the CRISFPDs. The CRISFPDs were retrieved after cementation, and standardized photographs of 4 quadrants of each abutment-CRISFPD assembly were made by using a software program that is used to calculate the ratio between the area covered with REC and the total specimen area. The extension of the REC on both the abutment and soft-tissue replica was measured at sites before and after cleaning the REC. A generalized linear mixed-model procedure was used for statistical analysis (α=.05).

RESULTS

For cement application, the polyvinyl siloxane (PVS) index technique had significantly less REC than the brush on technique (P<.05). The use of a PTFE bib led to significantly less REC than when no bib was used (P<.05).

CONCLUSIONS

The use of the PVS index technique along with a PTFE bib was effective in reducing REC for CRISFPDs.

Biological Responses to the Transitional Area of Dental Implants: Material- and Structure-Dependent Responses of Peri-Implant Tissue to Abutments

The stability of peri-implant tissue is essential for the long-term success of dental implants. Although various types of implant connections are used, little is known about the effects of the physical mechanisms of dental implants on the stability of peri-implant tissue. This review summarizes the relevant literature to establish guidelines regarding the effects of connection type between abutments and implants in soft and hard tissues. Soft tissue seals can affect soft tissue around implants. In external connections, micromobility between the abutment and the hex component of the implant, resulting from machining tolerance, can destroy the soft tissue seal, potentially leading to microbial invasion. Internal friction connection implants induce strain on the surrounding bone via implant wall expansion that translates into masticatory force. This strain is advantageous because it increases the amount and quality of peri-implant bone. The comparison of internal and external connections, the two most commonly used connection types, reveals that internal friction has a positive influence on both soft and hard tissues.

A Prosthetic Solution to Poorly Placed Implants in the Posterior Mandible

The objective of the present study is to find a solution for patients who have multiple implants that are poorly placed in the posterior mandible and require a solution to be rehabilitated, taking into account some diagnostic principles such as maintenance of the occlusal plane, maintenance of correct dental arch inclination, and adequate vertical dimension.

Effects of modifying implant screw access channels on the amount of extruded excess cement and retention of cement-retained implant-supported dental prostheses: A systematic review

STATEMENT OF PROBLEM

Cement-retained implant-supported prostheses eliminate screw loosening and enhance esthetics. However, retrievability and the possibility of removing extruded excess cement (EEC) have been problematic.

PURPOSE

The purpose of this systematic review was to analyze the effects of modifying the screw access channel (SAC) on the amount of EEC and the retention of cement-retained implant-supported prostheses.

MATERIAL AND METHODS

PubMed, Web of Science, Scopus, and Google Scholar databases were searched with appropriate key words. Related titles and abstracts published up to June 2017 were screened and selected on the basis of defined inclusion criteria. Full texts of all studies were read and subjected to quality assessments. After the initial search, 1521 articles were included in the study. Of these, 11 studies were subjected to critical appraisal, and 10 of them were reliable enough in methodology to be systemically reviewed.

RESULTS

All the studies were in vitro and described a total of 260 specimens. According to the interpreted results, closed SACs caused lower retention with a higher amount of EEC, whereas open SACs caused the reverse. Also, as the abutment height decreased, retention decreased.

CONCLUSIONS

Extending the crown's margin into the SAC, leaving the SAC open, and using internal vents in the SAC space are possible methods of modifying the SAC to gain higher retentive values. Also, the use of internal vents in the SAC system and open or partially filled SAC space reduce the amount of EEC.

Retrievability of implant-supported zirconia restorations cemented on zirconia abutments

STATEMENT OF PROBLEM

Retrievability of implant-supported restorations is important. Data are lacking for cemented zirconia crowns on zirconia abutments.

PURPOSE

The purpose of this in vitro study was to investigate the influence of different cements and marginal discrepancy on the retrievability of implant-supported zirconia crowns. Furthermore, the influence of thermocycling on retrievability was evaluated.

MATERIAL AND METHODS

Thirty tapered Camlog zirconia abutments (6-degree taper, 6×4.3 mm) were used. Thirty zirconia crowns with 3 different marginal cementation discrepancies (70, 130, 190 μm) were fabricated by using computer-aided design and computer-aided manufacturing (CAD-CAM) technology. Five cements for interim or semidefinitive cementation were used: eugenol-free zinc oxide (Freegenol) and acrylurethane (ImProv) and 3 different composite resin cements (X-Pand Implant, Dyna Implant, Telio CS Cem Implant). Specimens underwent either 3-day storage in sodium chloride or thermocycling (10 000 cycles). Crowns were removed by using a universal testing machine (UTM) and a clinical removal device. Data were analyzed using 1-way ANOVA and the Scheffé test (α=.05).

RESULTS

Thermocycling decreased the retention force significantly (P<.001). Marginal discrepancy (70 to 190 μm) was not significantly influential on retrievability (P>.05). Therefore, groups were pooled according to the factor of marginal discrepancy. The mean retention force using the UTM after 3-day storage and thermocycling was as follows: Freegenol, 235 ±42 N (thermocycling, 29 ±9 N); Improv, 110 ±50 N (thermocycling, 35 ±38 N); Telio CS, 104 ±17 N (thermocycling, 6 ±10 N); Dyna implant, 61 ±17 N (thermocycling, 1 ±1 N); and X-Pand, 50 ±16 N (thermocycling, 2 ±2 N).

CONCLUSIONS

Retention forces of the tested cements were significantly different and decreased considerably after thermocycling. Marginal cementation discrepancy between 70 and 190 μm did not influence retrievability.

Load-Bearing Capacity and Retention of Newly Developed Micro-Locking Implant Prosthetic System: An In Vitro Pilot Study

The aim of this study was to introduce the newly developed micro-locking implant prosthetic system and to evaluate the resulting its characteristics. To evaluate load-bearing capacity, 25 implants were divided into five groups: external-hexagon connection (EH), internal-octagon connection (IO), internal-hexagon connection (IH), one-body implant (OB), micro-locking implant system (ML). The maximum compressive load was measured using a universal testing machine (UTM) according to the ISO 14801. Retention was evaluated in two experiments: (1) a tensile test of the structure modifications of the components (attachment and implant) and (2) a tensile test after cyclic loading (total 5,000,000 cycles, 100 N, 2 Hz). The load-bearing capacity of the ML group was not significantly different from the other groups (p > 0.05). The number of balls in the attachment and the presence of a hexagonal receptacle did not show a significant correlation with retention (p > 0.05), but the shape of the retentive groove in the implant post had a statistically significant effect on retention (p < 0.05). On the other hand, the retention loss was observed during the initial 1,000,000 cycles, but an overall constant retention was maintained afterward. Various preclinical studies on this novel micro-locking implant prosthetic system should continue so that it can be applied in clinical practice.

Evaluation of Effectiveness of Cement Removal From Implant-Retained Crowns Using a Proposed "Circular Crisscross" Flossing Technique

Extruded cement during dental implant crown cementation may cause peri-implant diseases if not removed adequately. The purpose of this study was to evaluate the efficiency of removal of cement after cementation of implant crowns using an experimental circular crisscross flossing technique (CCFT) flossing technique, compared to the conventional "C"-shape flossing technique (CSFT). Twenty-four patients rendered 29 experimental and 29 control crowns. Prefabricated abutments were secured to the implant such that the margins were at least 1 mm subgingivally. The abutments were scanned using computer-aided design/computer-aided manufacturing technology and Emax crowns were fabricated in duplicates. Each crown was cemented individually and excess cement was removed using the CSFT and the CCFT techniques. After completion of cementation was completed, the screw access holes were accessed and the crown was unscrewed along with the abutment. The samples were disinfected using 70% ethanol for 10 minutes. Crowns were divided into 4 parts using a marker to facilitate measurement data collection. Vertical and horizontal measurements were made for extruded cement for each control and experimental groups by means of a digital microscope. One-hundred and seventeen measurements were made for each group. Mann-Whitney test was applied to verify statistical significance between the groups. The CCFT showed a highly statistically significant result (104.8 ± 13.66, P < .0001) for cement removal compared with the CSFT (291.8 ± 21.96, P < .0001). The vertical measurements of the extruded cement showed a median of 231.1 μm (IQR = 112.79-398.39) and 43.62 μm (IQR = 0-180.21) for the control and the experimental flossing techniques, respectively. The horizontal measurements of the extruded cement showed a median of 987.1 μm (IQR = 476.7-1,933.58) and 139.2 μm (IQR = 0-858.28) for the control and the experimental flossing techniques, respectively. The CCFT showed highly statistically significant less cement after implant crowns cementation when compared with the CSFT.

Fracture Resistance of Internal Conical and External Hexagon: Regular and Narrow Implant-Abutment Assemblies

PURPOSE

The aim of this study was to compare the maximum load on the elastic limit of internal conical (IC) implants with regular external hexagon (REH) and narrow external hexagon (NEH) implants.

MATERIALS AND METHODS

Thirty cylindrical implants were divided in 3 groups (n = 10): REH (3.75 mm); NEH (3.3 mm); IC (3.5 mm). The implants were evaluated by means of cantilever bending loads using a mechanical testing machine. A strain qualitative analysis and the corresponding angles were analyzed. Using single factor analysis of variance with Tukey Test and Friedman Test (P < 0.05) the statistical analysis for data were performed.

RESULTS

REH (294.37 N) and IC (294.37 N) groups presented statistically greater Fle than NEH (189.16 N). Regarding to the strain, there were no significant differences among groups. However, there were a greater number of fissures and more fractures present on NEH group.

CONCLUSION

The IC implant with smaller diameter did not result in reduction of elastic limit when compared with the REH implants. Nevertheless, the reduction of 0.45 mm of the hexagonal connection implant's diameter has significantly diminished the elastic limit.

Prosthetic maintenance of different mandibular implant overdentures: A systematic review

STATEMENT OF PROBLEM

Different factors can affect prosthetic maintenance requirements for mandibular implant overdentures (IODs). However, the literature shows a high level of disagreement concerning the effect of each factor on maintenance needs.

PURPOSE

The purpose of this systematic review was to address the focus question: "In the clinical studies published since 2004 of adult patients with totally edentulous mandibles treated by IODs with a variable number of implants and different designs, what were the maintenance types, frequencies, and complications?"

MATERIAL AND METHODS

A search of MEDLINE and PubMed databases was performed targeting papers in English on prosthetic maintenance of mandibular IODs published between 2004 and June 2015, aiming at recognizing the needs for adjustment, repair, and renewal. The recorded data were divided into 6 categories, and a percentage value was attributed to each.

RESULTS

From a total of 130 articles, 33 studies met the specified inclusion criteria for the review (14 randomized controlled trials, 8 prospective clinical trials, 3 retrospective studies, and 4 systematic reviews). These articles provided evidence that a mean complication rate was impossible to determine because of the multiplicity of contributing factors. No clear identification of the causes of mechanical complications was found, nor was there any clear evidence of superiority of one implant and/or attachment design over another.

CONCLUSIONS

Prosthetic complications with IODs are unavoidable. However, they can be reduced to an expected level if a close follow-up protocol is implemented aiming at anticipating risks of unexpected complications. Further clinical studies are needed to achieve a constructive meta-analysis that accounts for different parameters such as opposite arch, attachment functional variety, connection method, and prosthesis quality.

A Current Perspective on Screw-Retained Single-Implant Restorations: A Review of Pertinent Literature

OBJECTIVE

There is a trend toward increased use of screw-retained single-implant restorations. A comprehensive literature review was undertaken to examine the data related to screw- and cement-retention and to objectively evaluate the innovations in implant dentistry that have led to this resurgence.

OVERVIEW

When comparing the two options, survival and complication rates are similar, bone and soft-tissue levels are comparable, and zirconia offers esthetic advantages for both selections. Zirconia abutments with bonded titanium inserts provide esthetic alternatives to titanium abutments for both choices. Bone- and soft-tissue responses are similar, but residual cement of cement-retained restorations is associated with significant soft- and hard-tissue complications. The potential weakness of ceramic discontinuity of screw-access openings can be lessened by the incorporation of stronger ceramic materials such as zirconia and lithium disilicate. The overriding remaining indication for cement-retained restorations is to compensate for angled implants.

CONCLUSIONS

Screw-retained single-implant crowns should be reconsidered for many clinical situations for the following reasons: Predictable retention and retrievability No potential for the biologic consequences associated with residual cement As with cement-retained restorations, the choice between metal ceramics or all ceramics Only one margin, at the implant/abutment interface A single abutment/crown ceramic margin that can extend gingivally to the implant interface Nearly imperceptible blend of a composite resin in ceramic abutment access openings One component instead of two, which may simplify the restorative process CLINICAL SIGNIFICANCE: Innovations in implant and ceramic technology now give screw-retained prostheses the potential for esthetic, functional, and biologic outcomes that are comparable to those for cement-retained prostheses, while providing the advantages of predictable retrievability and avoidance of residual cement. Angled implants, however, remain a major indication for cement-retained single-implant prostheses. (J Esthet Restor Dent 29:161-171, 2017).

Occlusal Pressure Redistribution with Single Implant Restorations

PURPOSE

To describe the occlusal pressure redistribution in dental arches following placement of single posterior implant-supported restorations in occlusion with natural dentitions.

MATERIALS AND METHODS

Fifteen patients who presented for successfully osseointegrated single posterior implant restorations participated in the study. Cement-retained, all-ceramic implant crowns were fabricated and delivered after adjustment for interproximal contacts, fit, and uniform occlusal contacts. Occlusal pressure distribution was recorded with a digital sensor that reported contact point forces as a percentage of total pressure applied to the sensor. Measurements were taken before and after restoration for comparison. The distribution of relative occlusal stress was analyzed for statistical significance by location.

RESULTS

The results indicated that placement of posterior implant-supported restorations increased the bite pressure in the sextants containing the restorations by an average of 4.18% (p = 0.019) of the maximum value registered (maximum bite pressure). The contralateral occlusal load was found to decrease by 2.9% (p = 0.047) of the maximum value registered; however, there was no significant difference among or between the tooth positions.

CONCLUSION

Single posterior implant-supported restorations significantly increased the percentage (%) of total occlusal pressure in the containing sextant and decreased percentage of total occlusal pressure in the contralateral sextant. When analyzing restorations by exact position, more posterior implant restorations decreased the occlusal pressure applied in anterior dentitions.

Hidden Overdenture Bar in Fixed Implant-retained Hybrid Prosthesis: Report of a Novel Technique

INTRODUCTION

Every patient needs a comprehensive treatment planning. Dentists must consider the advantages and disadvantages of the available implant prosthetic options and match them to patient's expectations. Hybrid denture prosthesis is one, i.e., fabricated and retained by screw threaded into implant abutments, most of the time on four implants. Sometimes due to failure of an implant, the prosthesis needs to be replaced with a newer casting to accommodate the existing implants. Clinical consideration: This article presents a novel technique, wherein the existing framework of the fixed prosthesis can be used to convert the fixed prosthesis to removable prosthesis on the existing implants, without recasting.

CLINICAL SIGNIFICANCE

The implant is economical and easily convertible from a fixed-fixed to a fixed-removable prosthesis. Hence, there is reduced morbidity, reduced cost, and an increased psychological comfort for the patient.

In Vitro Evaluation of Planktonic Growth on Experimental Cement-Retained Titanium Surfaces

Background

The purpose of this study was to compare the effects of selected cements, or their combination with titanium, on the growth of two periodontopathic bacteria: Prevotella intermedia (Pi) and Fusobacterium nucleatum (Fn).

Material/Methods

This study was comprised of several experimental groups: 1) Dental luting cements (glass ionomer cement, methacrylate-based resin cement, zinc-oxide eugenol cement, eugenol-free zinc oxide cement; 2) titanium discs; and 3) titanium combination cement discs. The disks were submerged in bacterial suspensions of either Fn or Pi. Planktonic bacterial growth within the test media was measured by determining the optical density of the cultures (OD₆₀₀). Mean and standard deviations were calculated for planktonic growth from three separate experiments.

Results

Intergroup comparison of all experimental groups revealed increased growth of Pi associated with cement-titanium specimens in comparison with cement specimens. Regarding the comparison of all groups for Fn, there was an increased amount of bacterial growth in cement-titanium specimens although the increase was not statistically significant.

Conclusions

The combination of cement with titanium may exacerbate the bacterial growth capacity of Pi and Fn in contrast to their sole effect.

Stress distribution in implant-supported prostheses using different connection systems and cantilever lengths: digital photoelasticity

Photoelastic analysis was used to evaluate the biomechanical behaviour of implant-supported, double-screwed crowns with different connection systems and cantilever lengths. Three models were made in PL-2 photoelastic resin and divided into six groups, on the basis of the implant connection system (external hexagon [EH] or Morse taper [MT]), type of abutment (Mini Pilar [Neodent, Curitiba, Paraná, Brazil] or "UCLA") and number of crowns in the cantilever (one or two). The implant-prosthesis unit was placed in a circular polariscope. Occlusal surfaces of the crowns were subjected to 100-N loads in the axial and oblique (45°) directions in a universal testing machine (EMIC). Generated stresses were recorded and analysed qualitatively in a graphics program (Adobe Photoshop). Under axial loading, all of the groups had similar numbers of fringes, which were increased when the crowns were subjected to oblique loading. The highest number of fringes was found during oblique loading in the EH + Mini Pilar group. In conclusion, although the type of implant connection system did not have a direct influence on the stress distribution for axial loading, the cantilever length did have a direct influence on stress distribution. Models with two crowns in the cantilever showed more stress, with a greater concentration of force on the cervical part of the implant.

In Vitro Fit and Cementation Resistance of Provisional Crowns for Single Implant-Supported Restorations

Abstract: This study aimed to verify marginal fit and the effect of cement film thickness standardization on retention of provisional crowns made with prefabricated acrylic cylinders on abutments, using two temporary luting agents subjected or not to mechanical cycling. Provisional crowns were made from bis-acryl (Luxatemp Fluorescence) or methyl methacrylate (Duralay) resins on acrylic cylinders and marginal fit and cement film thickness were evaluated. For retention evaluation, crowns were cemented with two temporary luting agents: non-eugenol zinc oxide (Tempbond NE) or calcium hydroxide-based (Hydcal) cements and subjected to tensile strength in a universal testing machine. After cleaning, debonded crowns were cemented again, subjected to mechanical cycling and retention was reassessed. The results of marginal fit and cement film thickness were analyzed by Student's t-test while retention of cements before and after mechanical cycling was analyzed using a mixed linear model. Methyl methacrylate crowns presented greater marginal misfit (p=0.001) and occlusal cement film thickness (p=0.003) than the bis-acryl ones. No difference was observed at axial cement film thickness (p=0.606). Resins (p=0.281) did not affect crown retention, but luting agents (p=0.029) and mechanical cycling (p=0.027) showed significant effects. The only significant interaction was mechanical cycling*luting agents, which means that luting agents were differently affected by mechanical cycling (p=0.002). In conclusion, the results showed that bis-acryl resin associated to calcium-hydroxide luting agent provided the best retention and lower cement thickness.

Does Abutment Collar Length Affect Abutment Screw Loosening After Cyclic Loading?

A significant vertical space that is corrected with vertical ridge augmentation may necessitate selection of longer abutments, which would lead to an increased vertical cantilever. This study investigated the influence of different abutment collar heights on single-unit dental implant screw-loosening after cyclic loading. Fifteen implant-abutment assemblies each consisted of an internal hexagonal implant were randomly assigned to 3 groups: Group1, consisting of 5 abutments with 1.5 mm gingival height (GH); Group2, 5 abutments with 3.5 mm GH; and Group3, 5 abutments with 5.5 mm GH. Each specimen was mounted in transparent auto-polymerizing acrylic resin block, and the abutment screw was tightened to 35 Ncm with an electric torque wrench. After 5 minutes, initial torque loss (ITL) was recorded for all specimens. Metal crowns were fabricated with 45° occlusal surface and were placed on the abutments. A cyclic load of 75 N and frequency of 1 Hz were applied perpendicular to the long axis of each specimen. After 500 000 cycles, secondary torque loss (STL) was recorded. One-way ANOVA analysis was used to evaluate the effects of abutment collar height before and after cyclic loading. One-way ANOVA showed that ITL among the groups was not significantly different (P = .52), while STL was significantly different among the groups (P = .008). Post-hoc Tukey HSD tests showed that STL values were significantly different between the abutments with 1.5 mm GH (Group1) and with 5.5 mm GH (Group3) (P = .007). A paired comparison t-test showed that cyclic loading significantly influenced the STL in comparison with the ITL in each group. Within the limitations of this study, it can be concluded that increase in height of the abutment collar could adversely affect the torque loss of the abutment screw.

Scientific Interests of 21st Century Clinical Oral Implant Research: Topical Trend Analysis

BACKGROUND

Discrimination between ongoing and solved research questions may help to distinguish established dogmas from evidence-based implant dentistry.

PURPOSE

The purpose of this study was to investigate topics of interest in the field of oral implant science and evolving thematic trends in clinical studies during the last decade.

MATERIALS AND METHODS

Electronic and manual searches of English literature were performed to identify clinical studies on oral implants. Out of 15,695 publications screened, 2,875 clinical investigations were included.

RESULTS

Among the most prevalent topics were immediate loading (14.3%), bone substitutes (11.6%), lateral sinus grafting (10.7%), implant overdentures (10.5%), single-tooth implant crowns (8.8%), cross-arch implant bridges (8.0%), immediate implant placement (7.5%), implant surfaces (7.0%), simultaneous implant placement and augmentation (6.4%) as well as guided bone regeneration (5.3%). Significant increase of scientific interest was seen in immediate loading (+6.3%, p < .001), platform switching (+2.9%, p < 0.001), lateral sinus grafting (+2.3%, p = .024), flapless implant surgery (+2.2%, p < 0.001), and guided implant surgery (+1.9%, p = .011), while research on implant overdentures (-6.6%, p = .033) and tooth-to-implant connection (-2.5%, p = .010) was on the decline.

CONCLUSIONS

Literature coverage, since the beginning of the 21st century, has seen greater focus on surgical topics compared to prosthodontic issues (p = .005) while only few topics experienced decrease of interest indicating scientific consensus.

Effect of cement washout on loosening of abutment screws and vice versa in screw- and cement- retained implant-supported dental prosthesis

PURPOSE

The purpose of this study was to examine the abutment screw stability of screw- and cement-retained implant-supported dental prosthesis (SCP) after simulated cement washout as well as the stability of SCP cements after complete loosening of abutment screws.

MATERIALS AND METHODS

Thirty-six titanium CAD/CAM-made implant prostheses were fabricated on two implants placed in the resin models. Each prosthesis is a two-unit SCP: one screw-retained and the other cemented. After evaluating the passive fit of each prosthesis, all implant prostheses were randomly divided into 3 groups: screwed and cemented SCP (Control), screwed and noncemented SCP (Group 1), unscrewed and cemented SCP (Group 2). Each prosthesis in Control and Group 1 was screwed and/or cemented, and the preloading reverse torque value (RTV) was evaluated. SCP in Group 2 was screwed and cemented, and then unscrewed (RTV=0) after the cement was set. After cyclic loading was applied, the postloading RTV was measured. RTV loss and decementation ratios were calculated for statistical analysis.

RESULTS

There was no significant difference in RTV loss ratio between Control and Group 1 (P=.16). No decemented prosthesis was found among Control and Group 2.

CONCLUSION

Within the limits of this in vitro study, the stabilities of SCP abutment screws and cement were not significantly changed after simulated cement washout or screw loosening.

Using a guide template with a handpiece sleeve to locate the abutment screw position of a cement-retained implant restoration

The existing techniques for drilling a screw access hole in cement-retained restorations are limited by inaccurate drill guidance and ineffective cooling of the drilling area. An approach for fabricating a guide template to provide screw retrievability using computer-aided design and computer-aided manufacturing (CAD/CAM) is described. A handpiece sleeve was made by 3-dimensional printing and incorporating it into a vacuum-formed template. The handpiece sleeve not only guides the head of the handpiece accurately but also enables the cooling water to reach the area of drilling directly.

Effect of implant angulation and impression technique on impressions of NobelActive implants

STATEMENT OF PROBLEM

How the configuration of the NobelActive internal conical connection affects implant impressions is uncertain.

PURPOSE

The purpose of this study was to measure the effect in vitro of closed and open tray impression techniques for NobelActive implants placed at various angulations.

MATERIAL AND METHODS

Six NobelActive implants were placed in a master maxillary cast as follows: 0 degrees of angulation to a line drawn perpendicular to the occlusal plane in the first molar area, 15 degrees of angulation to a line drawn perpendicular to the occlusal plane in the first premolar area, and 30 degrees of angulation to a line drawn perpendicular to the occlusal plane in the lateral incisor area. Twelve open tray and 12 closed tray impressions were made. Occlusal, lateral, and frontal view photographs of the resulting casts were used to measure the linear and angular displacement of implant analogs. Statistical analysis was performed with a factorial analysis of variance (ANOVA), followed by the Tukey HSD test (α=.05).

RESULTS

No significant difference was found in the impressions made of NobelActive implants with the open or closed tray technique (linear displacement: F=0.93, P=.34; angular displacement: F=2.09, P=.15). In addition, implant angulation (0, 15, or 30 degrees) had no effect on the linear or angular displacement of impressions (linear displacement: F=2.72, P=.07; angular displacement: F=0.86, P=.43). Finally, no significant interaction was found between impression technique and implant angulation on NobelActive implants (F=0.25, P=.77; F=1.60, P=.20).

CONCLUSIONS

Within the limitations of this study, impression technique (open vs closed tray) and implant angulation (0, 15, and 30 degrees) had no significant effect on in vitro impressions of NobelActive implants.

Retentiveness of various luting agents used with implant-supported prosthesis: an in vitro study

Desired retrievability of cemented implant-supported fixed prosthesis makes the retentive strength of cementing agents an important consideration. The aim of the study was to evaluate the retentiveness of purposely designed implant cement and compare its retentiveness with dental cements that are commonly used with implant systems. Ten implant analogs were embedded in auto-polymerizing acrylic resin blocks and titanium abutments were attached to them. Fifty standardized copings were waxed directly on the abutment and casted. The cements used were: (1) resin-bonded zinc oxide eugenol cement, (2) purposely designed implant cement, (3) zinc phosphate cement, (4) zinc polycarboxylate cement, and (5) glass ionomer cement. After cementation, each sample was subjected to a pull-out test using universal testing machine and loads required to remove the crowns were recorded. The mean values and standard deviations of cement failure loads were analyzed using ANOVA and Bonferroni test. The mean values (± SD) of loads at failure (n = 10) for various cements were as follows (N): resin-bonded zinc oxide eugenol cement 394.62 (± 9.76), Premier implant cement 333.86 (± 18.91), zinc phosphate cement 629.30 (± 20.65), zinc polycarboxylate cement 810.08 (± 11.52), and glass ionomer cement 750.17 (± 13.78). The results do not suggest that one cement type is better than another, but they do provide a ranking order of the cements regarding their ability to retain the prosthesis and facilitate easy retrievability.

In vitro evaluation of a modified 4-META/MMA-TBB resin for filling access holes of screw-retained implant prostheses

This study evaluates a modified 4-META/MMA-TBB resin (M4M) as a candidate material for filling screw-retained implant access hole. Its characteristics were compared with a conventional composite resin (CR) with or without a bonding agent (BA) or a ceramic primer (CP). Ceramic blocks were divided into five groups, including (A) CR, (B) CR with BA, (C) CR with CP and BA, (D) M4M, and (E) M4M with CP. Shear bond strengths were measured after 5000 times of thermocycling. Groups A, B, and D were excluded from further tests as they showed no adhesion. A cylindrical cavity (2.5 mm diameter, 3 mm depth) simulating access hole was prepared in a ceramic block and glazed to evaluate micro-leakage and wear test of groups C and E. The results were statistically analyzed with Mann-Whitney test (p  <  0.05). Shear bond strength of groups C (7.6 ± 2.2 MPa) and E (8.6 ± 1.0 MPa) was not significantly different. In micro-leakage analysis, average wear depth and wear volume, group E (7.5 ± 3.3%, 59.3 ± 12.9 μm, 0.16 ± 0.04 mm(3) ) showed significantly lower values than those of group C (45.6 ± 24.4%, 76.0 ± 16.4 μm, 0.28 ± 0.03 mm(3) ). It is suggested that the combination of CP and M4M can be one of feasible systems to fill the ceramic access holes of the implant upper structure.

Cementing an Implant Crown: A Novel Measurement System Using Computational Fluid Dynamics Approach

BACKGROUND

Cementing restorations to implants is a widely used clinical procedure. Little is known about the dynamics of this process. Using a systems approach and advanced computing software modeling this can be investigated virtually. These models require validation against real-life models.

PURPOSE

The study aims to consider the system effect of a crown, abutment, and cement flow under different conditions and comparing real physical models to virtual computer simulations.

MATERIALS AND METHODS

A physical model of implant abutments and crowns provided three groups according to abutment screw access modification (n = 9): open (OA), closed (CA), and internal vented (IVA) abutment groups. Crowns were cemented using standardized amounts and site application. Proportion of cement retained within the crown-abutment system was recorded and compared. Differences among groups were identified using analysis of variance (ANOVA) with Tukey's post hoc test (α ≤ 0.05). Three-dimensional multiphysics numerical stimulation software (STAR-CCM+, CD-adapco) with computational fluid dynamics (CFD) approach was applied to a virtual model system of a scanned abutment and crown system. Three-dimensional real-time model simulations of cement and air displacement were produced, evaluating cement application site, speed of crown seating, and abutment modifications.

RESULTS

Statistically significant differences in cement retained within the system (p < 0.01) were found among the IVA > OA > OCA abutment groups. The CFD virtual simulations followed this trend. Site application and speed of seating also affected cement extrusion and cement marginal infill. Fast crown seating and occlusal cement site application produced air incorporation at the margins.

CONCLUSIONS

The CFD approach provides a convenient way to evaluate crown-cement-implant abutment systems with respect to cement flow. Preliminary evaluation indicates that the results achieved follow those of a physical actual cement-retained crown-implant abutment study.