Press-Fit Placement of a Rectangular Block Implant in the Resorbed Alveolar Ridge: Surgical and Biomechanical Considerations.

Rectangular Block Implant (RBIs) were manufactured, using computer-aided-design lathe turning, surface roughened with grit blasting and gamma irradiated. Implants were surgically placed into the resorbed edentulous mandibular ridges of both greyhound dogs (ex vivo and in vivo) and humans; the pooled total was 17 placements. The aim was to achieve mechanical stability and full implant submergence without damage to the mandibular canal and without bone fracture: fulfilment of all of these criteria was deemed to be a successful surgical outcome. Rectangular osteotomy sites were prepared with piezo surgical instrumentation. Sixteen implants were fully submerged and achieved good primary stability without bone fracture and without evidence of impingement of the mandibular canal. One implant placement was deemed a failure due to bone fracture: the event of a random successful outcome was rejected (p < 0.01 confidence, binomial analysis). Technique of placement yielded excellent mechanical retention: key biomechanical factors that emerged in this process included under preparation of the osteotomy site with the use of specifically designed trial-fit gauges, the viscoelastic property of the peri-implant bone, the flat faces and cornered edges of the block surfaces which enhance stress distribution and mechanical retention, respectively. It was concluded that the surgical protocol for the RBI placement in the resorbed alveolus is a predictable clinical procedure tailored to its specific, unique biomechanical profile.

Measuring tooth movement with treatment using the Dahl principle: An observational study.

STATEMENT OF PROBLEM: Research on the quantification of 3-dimensional tooth movements in patients undergoing treatment using the Dahl principle is lacking. PURPOSE: The purpose of this observational clinical study was to measure the magnitude, direction, duration, and rate of tooth movement occurring in patients to reestablish tooth contact and create restorative space. MATERIAL AND METHODS: A total of 104 paired preoperative and postoperative physical and virtual casts from 26 patients were obtained. Commencement and completion dates were recorded to calculate movement duration to reestablish occlusion. Dental casts were digitized, and the 3-dimensional digital casts obtained were superimposed via a surface matching and analysis software program by using the global registration function. Color maps were used to visualize direction, and the annotation feature quantified magnitude of tooth movement in millimeters when specific reference points were selected. Teeth within the arch were categorized as per their location to evaluate their impact on occlusal reestablishment. The average rate of movement was determined by time taken for extrusive and intrusive movements over the treatment duration. Post hoc Tukey tests were applied if a significant difference was present in the magnitude of movement between different tooth categories. RESULTS: All participants showed evidence of tooth movement during treatment. Duration of occlusal reestablishment ranged from 3.9 to 28.2 months, with more posterior tooth extrusive movements (56.9%) than anterior tooth intrusive (43.1%) movements occurring. A comparison of magnitude of extrusive or intrusive movement between categories (molar-anterior, premolar-anterior, and premolar-molar) showed that premolar and molar extrusive movements and anterior intrusive movements were significantly different (P<.001). The amount of buccal and lingual movement for molars and premolars was similar. Anterior teeth demonstrated more buccal than lingual movements. All teeth showed more mesial than distal movements. The extrusive and intrusive movement rate was 0.13 and 0.11 mm/mo, respectively. CONCLUSIONS: Tooth movement occurred in patients regardless of age and sex. The results of this study indicated that tooth movements have a 3-dimensional nature. Occlusal reestablishment mainly occurred via a combination of extrusive and intrusive movements. The study further highlighted the advantages of digital technology such as surface scanners and 3-dimensional software programs that can be used to quantify change in patients undergoing treatment.

The Biomechanical Profile of an Osseo-Integrated Rectangular Block Implant: A Pilot In Vivo Strain Analysis.

Aim: To load-test the osseo-integrated rectangular block implant (RBI), measure the generated cortical peri-implant strains, and relate these findings to known human physiological parameters. Materials and methods: Two RBIs were placed into the posterior mandibular saddle in a mature greyhound dog and allowed to osseo-integrate. The half mandible (implants in situ) was mounted in a servohydraulic system. Four triple-stacked rosette gauges were placed cortically (mesial, distal, buccal, and lingual). A modified ISO-14801 protocol was used (1000 N, 300, 2 Hz, 1 h) and the generated principal strains (ep, eq) and their angular orientations (F), were calculated. Results: (1) Bucco-lingual "horizontal" dimension: dominant "horizontal" compressive stresses were on the lingual aspect and "horizontal" tensile stresses on the buccal aspect. The buccal cortex was elastically tensile-stretched, while the lingual cortex was elastically compressed. (2) Bucco-lingual "vertical" dimension: dominant vertical torsional stresses were oriented buccally and apically, with an overall buccally inclined torsional effect. This was also evidenced on the lingual aspect, where there remained high torsional rotation elements (high F and e2). (3) Mesio-distal "horizontal" dimension: dominant torsional stresses oriented as a distal-lingual "counter-clockwise" rotation. Conclusions: The applied off-axial loads generated a heterogeneous pattern of bucco-lingual and mesio-distal cortical strains, both vertically and horizontally. The short dimensioned osseo-integrated RBI design appeared to biomechanically withstand the applied loads and to maintain the strains generated to levels that were within physiological limits. More studies and statistical analyses are needed to confirm these findings.

Effect of Aging on the Load-to-Failure of Molar Implant-Supported Monolithic Zirconia Crowns: A Laboratory Study.

PURPOSE: To evaluate the effect of hydrothermal aging on the load to failure and number of cycles to failure of implant-supported monolithic zirconia molar crowns under cyclic loading. MATERIALS AND METHODS: Twenty identical implant-supported monolithic zirconia crowns with molar morphology were produced. Half of the crowns were aged according to ISO standard 13356 to simulate 5 years in vivo. The non-aged crowns served as a control group. All crowns were subjected to cyclic loading with increasing increments of load until failure. The load to failure, the number of cycles to failure, and the failure pattern were determined for each crown. RESULTS: The load to failure values were 3,630 N (SD: 547.8 N) and 3,640 N (SD: 389.3 N) for the non-aged and aged crowns, respectively. The non-aged crowns failed after 33,480.1 cycles (SD: 23,138.4 cycles), and the aged crowns failed after 28,456.1 cycles (SD: 10,158.7 cycles). There was no significant difference between the two groups for the load to failure or number of cycles to failure. The predominant form of failure was catastrophic crown fracture, which was observed for all the non-aged crowns and 9 of the aged crowns. CONCLUSION: Within the limitations of this study, aging of the implant-supported monolithic zirconia crowns with molar morphology did not affect the load to failure or the number of cycles to failure under cyclic loading. Since all the crowns failed at much higher loads than the expected physiologic loads, clinical application of implant-supported monolithic zirconia crowns to replace missing molars seems reasonable.

The biomechanical profile of an osseo-integrated rectangular block implant: A pilot in vivo experimental study.

OBJECTIVE: A novel implant design, the rectangular block implant (RBI), was investigated as a possible solution to the restoration of the posterior resorbed ridge. AIM: To maximally load test the osseo-integrated RBI in shear and tensile loads and relate these findings to known human masticatory loads as biomechanical proof of the study concept. MATERIALS AND METHODS: Twelve RBIs were design-manufactured and placed into posterior mandibular saddles in 3 mature greyhound dogs.-2 per left and right. After 12 weeks of healing, osseo-integration was confirmed using resonance frequency analysis (RFA) and wrench torque tests. Three bone blocks each with two RBIs were dissected and mounted in acrylic. Micro-computerized tomography (µ-CT) was performed to assess bone to implant contact (BIC), and load analysis was performed using a Universal Test System. Three force applications were conducted until failure: pull-out (tensile), buccal push from the lingual (shear) and distal push from the mesial (shear). The osteotomy sites were examined using light magnification and scanning electron microscopy (SEM). RESULTS: Pull-out, buccal and distal force failures occurred at differing levels. Post-detachment sites showed complex patterns of bone failure, including trabecular and cortical fracture, as well as shearing at varying distances from the BIC. Interfacial shear strength was calculated at 14.4 MPa. CONCLUSION: The osseo-integrated RBIs were able to withstand simulations of the demanding axially, bucco-lingually and mesio-distally oriented biomechanical challenges of the posterior saddle, under conditions of reduced bone volume. These values exceeded equivalent force components of maximal masticatory loads in humans.

Accuracy of digital impressions versus conventional impressions for 2 implants: an in vitro study evaluating the effect of implant angulation.

BACKGROUND: Accurate implant impression is an essential requirement for the fabrication of implant prosthesis. This in vitro study evaluated the accuracy of digital impressions by intraoral scanner (IOS) systems in comparison to conventional impressions for recording the position of 2 parallel implants and 2 divergent implants. MATERIALS AND METHODS: In vitro 3-unit prosthesis master models with 2 tissue level implants were fabricated; one model had parallel implants, and the other model had one 15° tilted implant. The conventional open-tray impressions were obtained with non-splinted (NSP) and splinted (SP) impression copings. Trios 4 (TS), Medit i500 (MT), and True Definition (TD) were used to make digital impressions with scan bodies. A total of 10 impressions were obtained with every technique. The virtual test images of the conventional and digital impressions were converted to 2 virtual implant images. For each group, trueness, precision, inter-implant distance deviation, and angle deviation were measured. RESULTS: There was a general tendency for digital impressions to provide a more accurate outcome for trueness, precision, and angle deviation. The 2 conventional impressions showed similar accuracy, except for the angle deviation, where the NSP was significantly inferior than SP (p < 0.01) for the divergent implants model. The TD was generally the least accurate among all the IOS systems, especially for the inter-implant distance deviation (p < 0.05). CONCLUSIONS: Within the limitations of the laboratory set-up of the present study and the limited clinical resemblance, the digital impressions appeared to have sufficient accuracy for 2 implants and were least affected by the presence of angle between implants. The most inferior outcome was observed for the NSP technique.

Comprehensive characterisation of flexural mechanical properties and a new classification for porosity of 11 contemporary ion-leaching dental restorative materials.

The objectives of this study were to evaluate 4 aspects of ion-leaching restorative materials (ILMs): 4-point bending flexural strength (4 PB-FS) and relative mechanical properties; biaxial flexural strength (B-FS) in relation to 4 PB-FS; porosity; and surface morphology. Eleven ILMs were used for the 4-point bending test. Bar-shaped (n = 15) samples were fabricated, stored in distilled water for 7 days. Then 4 PB-FS and the other mechanical properties were determined. Five ILMs were selected for the B-FS test using disk specimens (n = 15). The correlation between 4 PB-FS and B-FS was addressed. After the 4 PB test, 5 randomised fragments from each material were used to make 0.5 mm-thick sections for light microscopy to investigate the degree of porosity using reflected and transmitted lights. Eight ILMs were selected for quantitative analysis of the fractional % pore volume (PV%) due to their relative pore prominence using ImageJ software. One-way ANOVA/Dunnett's T3 was used to test for significance. Resin-based ILMs (RB-ILMs) were ranked first (p < 0.05) for 4 PB-FS values (53.3-110.2 MPa) followed by resin-modified glass-ionomer cements (RMGICs; 30.9-44.3 MPa) and high-viscosity glass-ionomer cements (HVGICs; 12.9-19.6 MPa), respectively. 'Flexural modulus' (4 PB-E) and 'flexural toughness' (4 PB-T) of ILMs varied even though similar 4 PB-FS values were observed. There was a positive correlation (p < 0.001) between 4PB-FS and B-FS (R2 = 0.992) with B-FS>4 PB-FS. There was no correlation between PV% and 4 PB-FS. In summary, material type played a major role in 4 PB-FS outcomes, whereas PV% seemed to have a minor effect when evaluating each material group of ILMs. Brittleness/ductility of ILMs was observed when determining 4 PB-E and 4 PB-T relative to 4 PB-FS. When selecting materials for posterior load-bearing dental restorations in high-caries risk patients, RB-ILMs or RMGICs would be more appropriate due to their superior flexural properties compared with recently introduced HVGICs. The decision for each situation will also be dependent on further evidence of the ion-leaching capacity.

Influence of the application of a pre-sintered surface augmentation on zirconia and lithium disilicate bonding using an adhesive composite resin cement.

OBJECTIVE: The purpose of this laboratory study is to evaluate the application of a pre-sintered surface augmentation to zirconia (Zir) and lithium disilicate (LDS) ceramics on the delamination strength of adhesive resin cement. The applied surface augmentation was the ruling of lines to the pre-sintered surface of the ceramics. METHODS: Ninety milled Zir and sixty pressed LDS specimens (3mm×0.5mm×25mm) were created and divided into five groups (n=30). Group 1: Zir no surface treatment (control Zir-NT); Group 2: Zir airborne particle abraded (Zir-APA) with 30µm CoJet; Group 3: Zir pre-sintered surface augmentation (Zir-SA); Group 4: LDS etched (control LDS-etched) and; Group 5: LDS with pre-sintered surface augmentation and etching (LDS-SA). A resin adhesive cement (3mm×1mm×8mm) was then applied and cured to the ceramic specimens. The delamination strength values of the resin cement from the ceramic were recorded. The delamination strength data were analysed statistically using one-way ANOVA and Turkey post hoc analysis. RESULTS: The mean delamination strength and standard deviation, when comparing only the Zir-SA to the resin cement were statistically different (p<0.001); Zir-SA 63.42±11.85, Zir-NT 26.82±12.07, and Zir-APA 48.11±17.85MPa. Comparison between LDS groups were not significantly different (p=0.193); LDS-etched 33.49±16.07 and LDS-SA 28.83±10.15MPa. The delaminated Weibull modulus was highest for surface augmentation Zir specimens (m=13.56) but decreasing to less than half for Zir-APA (m=6.27) and Zir-NT (m=5.68). The Weibull values for the LDS-SA and LDS-etched specimens was 5.63 and 3.38 respectively. SIGNIFICANCE: Incorporating the pre-sintered surface augmentation to zirconia improved the delamination strength and reliability of Zir to the resin cement but not for LDS.

Remineralising effects of fluoride varnishes containing calcium phosphate on artificial root caries lesions with adjunctive application of proanthocyanidin.

OBJECTIVES: To evaluate the remineralising effects of fluoride (F) varnishes containing bioavailable calcium-phosphate compound (Ca-P) based remineralisation systems and 5000 ppm F toothpaste (FTP) on root caries lesions (RCLs) and the potential effects of proanthocyanidin (PA) for the treatments of RCLs when used as an adjunct to F regimens. METHODS: Demineralised root dentine and a pH-cycling model were used to mimic RCLs and the oral environment. Remineralising effects of MI VarnishTM (MIV) containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and Clinpro™ White Varnish (CPWV) containing tri-calcium phosphate (TCP) along with FTP and PA were evaluated regarding the birefringence, elemental composition, mechanical properties and mineral density of remineralised dentine with DuraphatTM as a comparison. RESULTS: MIV, CPWV and DuraphatTM promoted the incorporation of F into RCLs and increased mineral density but did not change microhardness of root dentine significantly. Surface microhardness increased significantly when MIV or CPWV was used with 5000 ppm FTP. Application of PA with F regimens significantly increased subsurface mineral density. When PA was applied with MIV or CPWV along with FTP, the highest ion uptake and relative mineral gain (%ΔZ) was achieved, and significant increase of microhardness was up to 30 µm depth. Generally, MIV was associated with a higher mineral content gain than CPWV. SIGNIFICANCE: Treatment of carious root surfaces remains challenging due to the complex pathological processes and difficulty in restoring the highly organised structure of root dentine. Treatment strategies targeting both remineralisation and preservation of the dentinal organic matrix have the potential to improve the fluoride-mediated remineralisation approaches.

Recharge and increase in hardness of GIC with CPP-ACP/F.

OBJECTIVE: To assess the effect of CPP-ACP/F recharging on ion release and hardness of GIC Fuji-Triage (VII) and Fuji-Triage-EP (VII-EP) containing CPP-ACP/F. METHODS: CPP-ACP distribution in Fuji-Triage-EP was determined using immunofluorescence. Thirty blocks of Fuji-Triage and Fuji-Triage-EP with the same surface area were placed individually in 5mL of 50mM lactic acid (pH 5) for three days. Every 12h ten Fuji-Triage and ten Fuji-Triage-EP blocks were treated with 2mL of either MI Paste Plus (CPP-ACP/F) solution (1g paste+4mL water), Placebo MI paste solution (no CPP-ACP/F), or distilled water for 2min. After each 2min treatment the blocks were rinsed with distilled water and placed back into the acid. Calcium, inorganic phosphate and fluoride levels in the acid solution were measured using atomic absorption spectrophotometry, colorimetry and ion specific electrode respectively. Vickers surface hardness of the GIC was also determined. Data were analysed using a two-sample t-test and one-way ANOVA with a Bonferroni-Holm correction for multiple comparisons. RESULTS: CPP-ACP was distributed throughout Fuji-Triage-EP. Significantly (p<0.001) higher calcium, inorganic phosphate and fluoride ion release and greater surface hardness (acid resistance) was observed in both GIC's treated with the CPP-ACP/F paste. Fuji-Triage-EP released higher ion levels and exhibited greater surface hardness (acid resistance) than Fuji-Triage. SIGNIFICANCE: Topical application of CPP-ACP/F paste to GIC Fuji-Triage-EP recharged ion release and increased surface hardness (acid resistance) which may help improve properties and resistance to degradation as well as improve ion release for caries control.

Effect of modified tray design on accuracy of different impression techniques for parallel and divergent implants.

This study evaluated the effect of a modified tray design on the accuracy of implant impressions in comparison with the non-splinted and splinted impression techniques. Two titanium frameworks were produced to fit two parallel implants and two divergent implants with a 15o angle. According to the frameworks employed, two acrylic resin master models were fabricated. For each model, 10 impressions were taken with every technique. The maximum framework principal strain was calculated for every generated cast. For the parallel implant model, the strains of the non-splinted (118.4 µÎµ), splinted (89.0 µÎµ), and modified tray design impression (49.4 µÎµ) techniques were statistically similar (P = 0.16). For the divergent implant model, all the impression techniques showed a considerably higher strain than the parallel implant model. The splinted (287.0 µÎµ) and the modified (262.9 µÎµ) tray design impression techniques showed similar strains for the divergent implant model, which were significantly less than the strains for the non-splinted impression (518.0 µÎµ) technique (P < 0.05). Therefore, for two parallel implants, all the impression techniques exhibited similar accuracy. When angulation existed between the implants, the splinted and the modified tray design impression techniques were more accurate than the non-splinted impression technique.

Evaluation of F, Ca, and P release and microhardness of eleven ion-leaching restorative materials and the recharge efficacy using a new Ca/P containing fluoride varnish.

OBJECTIVES: The objectives of this study were to evaluate fluoride (F), calcium (Ca), and phosphate (P) release of ion-leaching restorative materials (ILMs), their recharge efficacy with a Ca/P-containing F varnish, and relative microhardness. METHODS: Thirteen groups of materials were investigated. Cylindrical-shaped specimens were fabricated. Deionised water or lactic-acid solution were used as the storage media. Solutions were changed after 1d, 4d, 7d, and 14d of ion release and at the same periods after recharge with MI Varnish (7 -h storage). F, Ca, and P measurements were accomplished using a fluoride-ion selective electrode, atomic absorption spectrometry, and colourimetric method by spectrophotometer, respectively. Relative Vickers hardness was proceeded with similar specimens used in the F assay (4 periods). SEM/EDS was additionally performed. Statistical analyses were calculated in each parameter (p < 0.05). RESULT: Hardness of several ILMs immediately increased after recharge. After 28d, Ketac Universal [a high-viscosity glass-ionomer cement (HVGIC)] showed the highest hardness similar to the resin composite control. Although 2 HVGICs (Zirconomer and Equia Forte Fil) ranked as first and second for F release/re-release, some HVGICs had inferior or comparable F capacity to RMGICs (Fuji VIII and Fuji II LC) and a resin-based (RB) ILM (Cention N). Cention N, Activa-Restorative (RB-ILM), and Zirconomer were the top-3 ranking for Ca release/re-release. Activa-Restorative showed the highest P release, whereas Cention N displayed the greatest recharge ability for P. CONCLUSIONS: Zirconomer showed a versatile performance for ion-release/re-release, especially for F. Cention N had excellent capacity in relation to Ca release and recharge ability of Ca/P. CLINICAL SIGNIFICANCE: With the F varnish recharge protocol, Zirconomer, Equia Forte, and Fuji VIII seems to have an ability to inhibit initial caries initiation. Cention N is a promising resin-based material that could be an alternative for high caries risk patients due to the high Ca release/recharge with acceptable F release.

Laboratory Evaluation of Novel Implant Metal-Acrylic Prosthesis Design: Influence of Monolithic Acrylic Veneer.

PURPOSE: To test a novel implant metal-acrylic prosthesis design in comparison to a conventional prosthesis design through simulation of cyclic masticatory loading. The novel design involved digital designing and fabrication of the framework and the matched veneering acrylic resin material. MATERIALS AND METHODS: Ten prostheses were fabricated for each group. All the prostheses exhibited a similar external design on two implants with a distal cantilever. The conventional group comprised a milled metal framework with mechanically retained acrylic denture teeth via vertical pins. The digital prosthesis group incorporated an inverted T-shape bar and a monolithic milled acrylic resin veneer. The resin veneer was subsequently adhesively attached on the bar. All prostheses were thermally aged and subjected to laboratory cyclic loading at the cantilever region. The load-to-failure and the number of cycles until failure were collected. Furthermore, failed specimens were analyzed to determine the mode of failure. RESULTS: The digital prostheses failed at significantly greater load-to-failure (1,570.0 N ± 116.0 N) and number of cycles (124,857 ± 21,608) than the conventional prostheses (load-to-failure = 1,015.0 N ± 47.4 N; number of cycles = 28,452 ± 6,559). The conventional prostheses failed by fracturing of the acrylic teeth and veneering material that led to exposure of the metal framework. Half of the digital prostheses failed by superficial chipping of the veneering material, while the other half failed by the deformation and fracture of screws. CONCLUSION: Within the limitations of this study, the digital prostheses with the novel design and monolithic veneering material showed significantly higher strength compared with the conventional prostheses. The mode of acrylic failure of the digital prostheses was more favorable.

Effects of silver diamine fluoride/potassium iodide on artificial root caries lesions with adjunctive application of proanthocyanidin.

Treatment of carious root surfaces remains challenging due to the complex pathological processes and difficulty in restoring the original structure of root dentine. Current treatments targeting the de-/re-mineralisation processes are not entirely satisfactory in terms of the protection of the dentinal organic matrix and the highly organised structure of dentine. In this in vitro study, a cross-linking agent - proanthocyanidin (PA) was used in conjunction with a fluoride-based treatment - silver diamine fluoride/potassium iodide (SDF/KI) to putatively stabilise the organic dentinal framework as well as strengthen the collagen-mineral phase interaction. The effectiveness of this strategy was evaluated 24 h after application in terms of the distribution of ion uptake and microstructure of dentine after treatment as well as analysis of the nano-mechanical properties using a dynamic behaviour model. Results showed that individual use of SDF/KI significantly improved the surface microhardness and integrated mineral density (Z) up to 60 µm depth and the recovery of creep behaviour of demineralised dentine in the surface area compared to that treated with deionised distilled water (DDW). The combined treatment of PA and SDF/KI achieved a more homogenous mineral distribution throughout the lesions than SDF/KI alone; a more significant incremental increase in surface microhardness and Z was observed. Specifically, a superior effect on the subsurface area occurred with PA + SDF/KI, with significant improvements in microhardness, elastic modulus and recovery of creep behaviour of the demineralised dentine. Application of SDF/KI induced small discrete crystal formation distributed over the dentine surface and PA contributed to the formation of slit-shaped orifices of the dentinal tubules that were partially occluded. STATEMENT OF SIGNIFICANCE: Demographic transitions and improved oral health behaviour have resulted in increased tooth retention in elderly people. As a consequence, the risk of root dentine caries is increasing due to the age-associated gingival recession and the related frequent exposure of cervical root dentine. Root caries is difficult to repair because of the complex aetiology and dentine structure. The recovery of dentine quality depends not only on reincorporation of minerals but also an intact dentinal organic matrix and the organic-inorganic interfacial structure, which contribute to the biomechanics of dentine. With the capability of dentine modification, cross-linking agents were applied with a fluoride regimen, which improved its treatment efficacy of root caries regarding the distribution of ion uptake and recovery of dentine biomechanics.

Accuracy of Different Implant Impression Techniques: Evaluation of New Tray Design Concept.

PURPOSE: To evaluate implant impression accuracy with a new tray design concept in comparison to nonsplinted and splinted impression techniques for a 2-implant situation. MATERIALS AND METHODS: A reference bar titanium framework was fabricated to fit on 2 parallel implants. The framework was used to generate a resin master model with 2 implants that fit precisely against the framework. Three impression techniques were evaluated: (1) nonsplinted, (2) splinted, and (3) nonsplinted with modified tray impressions. All the trays were fabricated from light-cured acrylic resin material with openings that corresponded to the implant impression copings. Ten impressions were taken for each technique using poly(vinyl siloxane) impression material. The impressions were poured with type IV dental stone to generate the test casts. A rosette strain gauge was bonded to the middle of the framework. As the framework retaining screws were tightened on each test cast, the developed strains were recorded until the completion of the tightening to 35 Ncm. The generated strains of the rosette strain gauge were used to calculate the maximum principal strain. RESULTS: A statistically significant difference was observed among the different impression techniques. The modified tray design impression technique was associated with the least framework strains, which indicates greater accuracy compared with the other techniques. There was no significant difference between the splinted and the nonsplinted impression techniques. CONCLUSIONS: The new tray design concept appeared to produce more accurate implant impressions than the other techniques. Despite the statistical difference among the impression techniques, the clinical significance of this difference is yet to be determined.

Fracture toughness of glass ionomers measured with two different methods.

Glass Ionomer Cements (GICs) are brittle materials with low fracture toughness and strength. Therefore, understanding the fracture toughness is an important parameter to know, due to GICs being promoted for load-bearing restorations. Also, little is known about the effects of artificial saliva (AS) on fracture toughness of GICs. This project aimed to study the effects of storage and compare two different fracture toughness test methods, namely: Compact-Tension test and 4-point bending test. Samples were made from a Zinc-reinforced-GIC (ChemFil), High viscosity bulk-fill-GIC (HV) with and without LC-coating (EQUIA), Resin-Modified GIC (RM-GIC) (Riva-LC), HV-RMGIC (Riva-HV-LC) and flowable bulk-fill Giomer (Beautifil-Bulk Flowable) using a custom-made mould. Specimens were stored in either AS or distilled-water (DW) for 7 or 30 days. After storage, specimens were tested for fracture toughness. Results were analysed with Analysis of variance (ANOVA), Mann-Whitney and Weibull statistics. ANOVA showed a significant difference (P < 0.05) between methods, however the same trend among materials was observed in both methods. Some materials showed significantly higher values for samples stored in DW and others revealed the same trend but were not significant. Significantly higher (P < 0.05) mean fracture toughness values were observed for materials stored for 30 days. Since both fracture toughness test methods revealed the same fracture toughness strength order among materials, either test appears appropriate. GICs maturation led to a difference between 7 and 30-day results. The AS used had a high ionic strength compared to DW, which may have led to increased solubility of GICs and consequently to the reduced fracture toughness values. The results revealed that coating the GIC has a protective effect against storage media.

Influence of novel implant selective laser melting framework design on mechanical durability of acrylic veneer.

BACKGROUND: A novel implant framework design is proposed to improve the mechanical durability of acrylic veneer. PURPOSES: Comparing the mechanical durability of acrylic veneer on implant frameworks fabricated from selective laser melting (SLM) with novel design against conventional computer numeric controlled (CNC) milled frameworks. MATERIALS AND METHODS: Implant titanium frameworks with distal cantilever were fabricated by SLM (n = 10) and CNC milling (n = 10). The CNC frameworks had multiple vertical pins, while the SLM frameworks had 3D metal networks of horizontal beams connected by vertical struts. All the frameworks were veneered with acrylic teeth and resin material and were subjected to a static load-to-failure test at the cantilever region. The load-to-failure readings and the pattern of prosthesis damage were recorded for each prosthesis. RESULTS: The CNC and SLM prostheses failed at statistically similar loads. The acrylic veneer around the CNC frameworks tend to initially crack around the distal implant followed by acrylic chipping. Six SLM prostheses failed at the framework connector on the mesial implant by separation of the screw seat. After reloading these prostheses, they failed by acrylic veneer chipping. The SLM prostheses had significantly less incidence of acrylic flexure and severity of acrylic veneer chipping than CNC prostheses. CONCLUSIONS: The SLM framework with novel design is efficient in reinforcing acrylic veneering. However, the SLM frameworks appeared weak in thin sections, such as the screw seat.

Comparison of ART and conventional techniques on clinical performance of glass-ionomer cement restorations in load bearing areas of permanent and primary dentitions: A systematic review.

OBJECTIVES: To review the clinical performance of GIC restorations using calculated annual failure rates (AFRs) and qualitative descriptions based on conventional and ART techniques from two aspects: occlusal and approximal cavities in permanent or deciduous posterior teeth. SOURCES: Search strategies were undertaken of the PubMed database from January 1983 to March 2018. Additional articles were collected by hand searching. STUDY SELECTION: The following basic search terms, "(glass ionomer cement) and (clinical performance or survival or ART or atraumatic restorative or high viscosity)" with inclusion and exclusion criteria according to PRISMA flow diagram were used. DATA: A total of 904 articles were initially identified. Finally, 67 articles were included for quantitative and qualitative analysis after applying the inclusion and exclusion criteria. Assessment of risk of bias was performed for all included studies using ROBINS-I. CONCLUSIONS: For single-surface occlusal or multi-surface GIC restorations, the conventional technique showed better survival than ART technique regardless of dentition type (primary or permanent). When comparing the same treatment technique, AFRs of approximal or multi-surface GIC restorations were greater than those of single-surface (occlusal) restorations, irrespective of dentition type. RMGIC-conventional technique seems to be promising for restoring approximal cavities of primary teeth compared to other restorative materials. CLINICAL SIGNIFICANCE: The GIC-ART technique is an alternative option for single-surface (occlusal) restorations in permanent and primary teeth. However, the application of the GIC-ART technique for load-bearing approximal restorations should be carefully considered before employing this option, especially in primary teeth.

Effect of different lateral occlusion schemes on peri-implant strain: A laboratory study.

PURPOSE: This study aims to investigate the effects of four different lateral occlusion schemes and different excursions on peri-implant strains of a maxillary canine implant. MATERIALS AND METHODS: Four metal crowns with different occlusion schemes were attached to an implant in the maxillary canine region of a resin model. The included schemes were canine-guided (CG) occlusion, group function (GF) occlusion, long centric (LC) occlusion, and implant-protected (IP) occlusion. Each crown was loaded in three sites that correspond to maximal intercuspation (MI), 1 mm excursion, and 2 mm excursion. A load of 140 N was applied on each site and was repeated 10 times. The peri-implant strain was recorded by a rosette strain gauge that was attached on the resin model buccal to the implant. For each loading condition, the maximum shear strain value was calculated. RESULTS: The different schemes and excursive positions had impact on the peri-implant strains. At MI and 1 mm positions, the GF had the least strains, followed by IP, CG, and LC. At 2 mm, the least strains were associated with GF, followed by CG, LC, and IP. However, regardless of the occlusion scheme, as the excursion increases, a linear increase of peri-implant strains was detected. CONCLUSION: The peri-implant strain is susceptible to occlusal factors. The eccentric location appears to be more influential on peri-implant strains than the occlusion scheme. Therefore, adopting an occlusion scheme that can reduce the occurrence of occlusal contacts laterally may be beneficial in reducing peri-implant strains.

Behavior of mineral trioxide aggregate apical plugs and root fillings under cyclic loading.

AIM: The aim of the present study was to develop a methodology for constant monitoring of the resistance to fluid flow during functional loading and to then compare the efficacy of 4-mm mineral trioxide aggregate (MTA) apical plugs and full-length MTA root fillings. METHODS: The root canals of 24 single-rooted teeth were instrumented and assigned into two groups: group 1 (filled with a 4-mm MTA apical plug and gutta percha) and group 2 (filled with MTA to cementoenamel junction level). All teeth were subjected to stepwise cyclic loading with a constant simulated interstitial pressure of 25 cm H2 O applied apically. A Flodec machine (De Marco Engineering, Geneva, Switzerland) constantly monitored the rate and direction of fluid flow. Student's t-test, Kruskal-Wallis test, Fisher's exact test, and Newcombe-Wilson test were used for statistical analysis, with P < 0.05. RESULTS: Crown fractures occurred in 21 teeth with no change in the rate of fluid flow. Three teeth (filled with full-length MTA) showed sudden change in the rate of fluid flow through the root canal after cyclic loading. CONCLUSIONS: The methodology reliably monitored fluid flow during cyclic loading. There was no difference between a 4-mm MTA apical plug and full-length MTA root filling after cyclic loading using a dynamic fluid-flow monitoring technique.