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.

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.

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.

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.

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.

Casein Phosphopeptide-Amorphous Calcium Phosphate Reduces Streptococcus mutans Biofilm Development on Glass Ionomer Cement and Disrupts Established Biofilms.

Glass ionomer cements (GIC) are dental restorative materials that are suitable for modification to help prevent dental plaque (biofilm) formation. The aim of this study was to determine the effects of incorporating casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) into a GIC on the colonisation and establishment of Streptococcus mutans biofilms and the effects of aqueous CPP-ACP on established S mutans biofilms. S. mutans biofilms were either established in flow cells before a single ten min exposure to 1% w/v CPP-ACP treatment or cultured in static wells or flow cells with either GIC or GIC containing 3% w/w CPP-ACP as the substratum. The biofilms were then visualised using confocal laser scanning microscopy after BacLight LIVE/DEAD staining. A significant decrease in biovolume and average thickness of S. mutans biofilms was observed in both static and flow cell assays when 3% CPP-ACP was incorporated into the GIC substratum. A single ten min treatment with aqueous 1% CPP-ACP resulted in a 58% decrease in biofilm biomass and thickness of established S. mutans biofilms grown in a flow cell. The treatment also significantly altered the structure of these biofilms compared with controls. The incorporation of 3% CPP-ACP into GIC significantly reduced S. mutans biofilm development indicating another potential anticariogenic mechanism of this material. Additionally aqueous CPP-ACP disrupted established S. mutans biofilms. The use of CPP-ACP containing GIC combined with regular CPP-ACP treatment may lower S. mutans challenge.

Push-out bond strength of CPP-ACP-modified calcium silicate-based cements.

This study evaluated the push-out bond strength of 0%, 0.5%, 1.0%, 2.0% and 3.0% (w/w) casein phosphopeptide-amorphous calcium phosphate (CPP-ACP)-modified calcium silicate-based cements (CSCs). The push-out bond strength of a trial MTA was also compared with two CSCs (Biodentine(™) and Angelus(®) MTA). Three hundred 1 mm thick horizontal root sections were prepared from 60 singlerooted human teeth. The canal space of each section was enlarged and filled with the cements. The sections were stored in a phosphate buffer solution. After incubation for 2 months, the push-out bond strength was measured and the data were analyzed using one way analysis of variance followed by Tukey's test. The addition of CPP-ACP to the test cements increased the push-out bond strength (p<0.05). The push-out bond strength of Biodentine(™) was higher than the other cements (p<0.05). There was no statistically significant difference between Angelus(®) MTA and the trial MTA with most of CPP-ACP concentrations.

Thin and thick layers of resin-based sealer cement bonded to root dentine compared: Adhesive behaviour.

This study aims to evaluate tensile and shear bond strengths of one epoxy (AH) and two methacrylate resin-based sealers (EZ and RS) in thin and thick layers bonded to root dentine. An alignment device was prepared for accurate positioning of 20 root dentine cylinders in a predefined gap of 0.1 or 1 mm. Sealer was placed in the interface. Bond strength tests were conducted. Mode of failures and representative surfaces were evaluated. Data were analysed using anova and post-hoc tests, with P < 0.05. The thick layer of sealer produced higher bond strength, except for the shear bond strength of EZ. Significant differences between thin and thick layers were found only in tensile bond strengths of AH and RS. Mixed type of failure was constantly found with all sealers. Bond strengths of thick layers of resin-based sealers to root dentine tended to be higher than with thin layers.

Bonding of resin composite precured or postcured to primary dentin.

PURPOSE: The purpose of this study was to examine in vitro the effect of cure mode on the shear bond strength (SBS), failure mode (FM), microleakage (ML), and resin tag penetration (RTP) of two resin composite (RC)/adhesive systems: (1) Clearfil Majesty Esthetic/Clearfil SE Bond (CME/SEB); and (2) TPH 3 Micro Matrix Restorative/Prime&Bond NT (TPH/P&B). METHODS: Paired RC samples (10 CME/SEB; 10 TPH/P&B) were precured or postcured with adhesive on primary molar dentinal substrates and tested for SBS (10 per group); debonded surfaces were examined. Cavities (Class V) in extracted primary molars were restored (20 CME/SEB; 20 TPH/P&B), following precuring or postcuring the adhesive, and examined for ML (eight per group) and RTP (two per group). RESULTS: Mean SBS (MPa) values differed: precured CME/SEB exceeded postcured CME/SEB (20.16±2.70 versus 10.97±4.39; P<.001), and postcured TPH/P&B exceeded precured TPH/P&B (14.17±3.73 versus 11.10±2.62; P=.007). The FM differed between systems: CME/SEB: precured (four adhesive-dentin; six mixed), postcured (10 adhesive-dentin); TPH/P&B: precured (10 adhesive-dentin), postcured (nine adhesive-dentin; one mixed). Only one specimen showed true ML (postcured TPH/P&B). The RTP was greater in postcured than precured specimens. CONCLUSION: Precured CME/SEB was deemed superior for restoration of primary teeth, despite extra time required clinically to precure the adhesive.

The effect of resin infiltration and oxidative pre-treatment on microshear bond strength of resin composite to hypomineralised enamel.

BACKGROUND: Reduced bond strengths of resin composites to hypomineralised enamel increase restorative failure. AIM: To investigate if the adhesion of resin composite to hypomineralised enamel can be improved by pre-treatments: resin infiltration, oxidative pre-treatment followed by a resin infiltration, or oxidative pre-treatment. DESIGN: Twenty-one enamel specimens in each of five Groups: 1) Normal enamel; 2) Hypomineralised enamel; 3) Hypomineralised enamel pre-treated with a resin infiltrant, (Icon(®)); 4) Hypomineralised enamel pre-treated with 5.25% sodium hypochlorite then treatment with resin infiltrant; 5) Hypomineralised enamel pre-treated with 5.25% sodium hypochlorite. A resin composite rod was bonded to each specimen using Clearfil™ SE bond as the adhesive (hereafter termed 'routine bonding'), then subjected to microshear bond strength (MSBS) testing. RESULTS: Overall, the mean MSBS between the five groups differed significantly (P = 0.001). Pre-treatment of hypomineralised enamel with 5.25% sodium hypochlorite with or without subsequent resin infiltration in Groups 4 and 5 prior to routine bonding resulted in increased mean MSBS compared to Groups 2 and 3, with mean MSBS values not differing significantly when compared to routine bonding to normal enamel. CONCLUSION: Increased bond strength of resin composite to hypomineralised enamel was obtained by pre-treatment of hypomineralised enamel specimens with 5.25% sodium hypochlorite with or without subsequent resin infiltration.

Evaluation of the interfacial work of fracture of glass-ionomer cements bonded to dentin.

OBJECTIVE: The aim of this study was to investigate the interfacial work of fracture of conventional (C-) and resin-modified (RM-) glass-ionomer cements (GICs) bonded to dentin. METHODS: One hundred and sixty five aries-free human molars were embedded in epoxy resin, sectioned and polished with 300- and 600- grit silicon carbide paper to remove enamel on the occlusal surface. Equilateral triangular-shaped plastic molds (4×4×4×5mm(4)) were clamped to the prepared dentin surfaces by a stainless steel test apparatus. Teflon tape was placed under one internal vertex of the mold to create a 0.1-mm notch at the material-dentin interface. Interfacial work of fracture (γwofint) in tensile fracture mode-I (opening) was determined for six C-GIC, three RM-GIC, and two GIC luting cements at a cross-head speed of 0.1mm/min and a crosshead distance (L) from the interface of 4.3mm. The debonded surfaces were evaluated for the predominant failure mode. SEM analysis of examples showing interfacial and notch areas was performed. RESULTS: ANOVA and Tukey's post hoc test demonstrated the highest mean γwofint value (90.16±16.6J/m(2)) of one RM-GIC was significantly different (p<0.05) from the other materials. 'High viscosity' GICs achieved lower results with the lowest recorded at 20.4±10.1J/m(2). There was a significant difference observed (p<0.05) between the mean γwofint of luting C-GIC and luting RM-GIC. Although differences were observed between different material mean γwofint, when comparing groups no significant differences (p=0.181) were observed. For all groups, mixed GIC-interface failure (41%) was the most commonly observed, followed by cohesive failure in GIC (25%) and adhesive failure (20%). SEM analysis revealed that specimens generally fractured from the notch initiation point into the GIC or along the dentin-GIC interface. CONCLUSION: Within the limits of this study, significant differences (p<0.05) were observed in the γwofint between different glass-ionomer materials. The null hypothesis that there is no difference in the γwofint among different glass-ionomer materials bonded to human dentin was rejected. RELEVANCE: In the current study, the interfacial work of fracture (γwofint) of glass-ionomer adhesive interfaces has been reported using a simple method that can be used to study the fracture mechanics of an adhesive interface without the need for complicated specimen preparation.

In vitro bone strain analysis of implant following occlusal overload.

OBJECTIVES: To enumerate peri-implant bone strain pattern under quantified occlusal load and verify the bone response through comparison with the critical strain thresholds defined by Frost's bone mechanostat theory. MATERIAL AND METHODS: Mandibular unilateral recipient sites in two greyhound dogs were established with posterior teeth extractions. After 6 weeks, four titanium implants were placed in each dog mandible. Following 12 weeks of healing, successfully osseointegrated implants were placed in supra-occlusal contact via screw-retained non-splinted metal crowns. Plaque control and a dental health enhancing diet were prescribed. A bite force detection device was used to quantify in vivo occlusal load as the dogs functioned with supra-occlusal contact. After 8 weeks, the dogs were sacrificed. In vitro peri-implant bone strain under quantified occlusal load was measured using bonded stacked rosette strain gauges. RESULTS: The average and peak in vivo occlusal load measured were 434 and 795 newton (N). When individually and simultaneously loaded in vitro (≤476 N), absolute bone strains up to 1133 and 753 microstrains (µÎµ) were measured at implant apices, respectively. Bone strain reaching 229 µÎµ was recorded at distant sites. For bone strain to reach the pathological overload threshold defined by Frost's bone mechanostat theory (3000 µÎµ), an occlusal load of 1344 N (greater than peak measured in vivo) is required based on the simple linear regression model. CONCLUSION: Under the in vivo and in vitro conditions investigated in this study, peri-implant bone was not found to be under pathological overload following supra-occlusal contact function. Strain dissipation to distant sites appeared to be an effective mechanism by which implant overload was avoided.

A comparison of resin-modified glass-ionomer and resin composite polymerisation shrinkage stress in a wet environment.

OBJECTIVE: The aim of this study was to investigate the polymerisation shrinkage stress under water of four resin-modified glass-ionomers and three resin composite materials. METHODS: Transparent acrylic rods (5mm diameter×30mm) were prepared and secured into drill chucks connected to a universal testing machine. A plastics cup was placed around the lower rod and a distance of 1.00mm was established between the prepared surfaces which provided a C-factor of 2.5. For composite only, an adhesive layer (Scotchbond Universal Adhesive) was placed on the rod ends and cured to achieve a bond with the rod end. Materials were placed between the rods and a strain gauge extensometer was installed. Materials were light cured for 40s and the plastics cup was filled with ambient temperature water. To determine polymerisation shrinkage stress (σpol) three specimens of each material were tested for a 6-h period to determine mean maximum σpol (MPa), σpol rate (MPa/s) and final σpol (MPa). ANOVA and post hoc Tukey tests were used to determine significant differences between means. RESULTS: The highest mean maximum σpol of (5.4±0.5) MPa was recorded for RMGIC and (4.8±1.0) MPa for composite. The lowest mean final σpol of (0.8±0.4) MPa was recorded for RMGIC. For mean maximum σpol,σpol rate and final σpol there were significant differences between materials within groups, although no significant difference (p>0.05) was observed when comparing the RMGIC group to the composite group. CONCLUSION: When comparing mean σpol, maximum σpol, and σpol rates between individual RMGIC and composite materials significant differences (p<0.05) were observed. However when comparing the group RMGIC to composite no significant differences (p>0.05) were observed. The null hypothesis that there is no difference in the short term σpol of RMGIC materials when compared to composite materials is only partly rejected. RELEVANCE: Limited information is available on the comparison of RMGIC and resin composite σpol levels. This study provides information on the short term levels in a wet environment and will assist in understanding the initial σpol rates RMGIC place in cavities.

A comparison of the micro-shear bond strength and failure mode of non-enclosed and mold-enclosed luting cements bonded to metal.

The objective of the study was to compare 1) the mean micro-shear bond strength and 2) failure mode of cements to metals in nonenclosed and mold-enclosed specimens. Specimens were prepared in mold-enclosed and non-enclosed formats from two RMGIC's and a self-adhesive resin-cement. 3-way ANOVA analysis and Tukey post hoc tests were used to compare mean µSBS results (α=0.05). Failure mode was analysed with Pearson's chi-square test (α=0.05). µSBS was significantly affected by the factors substrate and method (p<0.001) but not by material (p=0.077). There was an interaction between substrate, method and material F (2,144)=3.57, p=0.031, and method and material (2,144)=5.86, p=0.004. All mold-enclosed specimens for the three cements bonded to titanium and non-precious metal exhibited higher (p<0.001) mean µSBS than the non-enclosed specimens. Within this study, mold-enclosed specimens exhibited significantly higher (p<0.001) mean µSBS and adhesive failure compared to non-enclosed specimens.

Characterisation of developmentally hypomineralised human enamel.

OBJECTIVES: To investigate and clarify physical and chemical properties of enamel affected by molar incisor hypomineralisation (MIH). METHODS: A series of in vitro studies were performed on extracted molars affected by MIH and sound teeth for controls. Tooth sections underwent Vickers microhardness testing before lapping and subsequent transverse microradiographic analysis and examination under polarised light microscopy. Carbonate content was determined by CO2 release from acid digestion. Unprepared and fractured surfaces were examined under scanning electron microscopy. RESULTS: MIH-affected molars demonstrated a severe degree of hypomineralisation with an average mineral content of only 58.8%vol% mineral. Vickers microhardness was significantly reduced in MIH compared with controls (1.8±1.1 v 4.4±1.0 GPa, p<0.05) and polarised light microscopy revealed the bulk of MIH lesions had a porosity of ≤5% but also substantial areas of ≥10% and smaller areas exceeding 25% porosity. A surface layer was frequently observed on both intact and broken-down lesions and cervical regions of MIH teeth were typically spared. Carbonate content of MIH enamel was higher than control samples (6.6±2.1 v 4.4±1.1 wt%, p<0.05). Scanning electron microscopy showed that both the enamel rod and surface ultrastructure were defective. Clinical characteristics did not consistently correlate with all properties. CONCLUSIONS: The properties of MIH-affected enamel significantly differ from those of normal enamel and were highly variable, however some common characteristics were observed. Implications for aetiology and clinical management are discussed.