Review of nanomaterials in dentistry: interactions with the oral microenvironment, clinical applications, hazards, and benefits.

Interest in the use of engineered nanomaterials (ENMs) as either nanomedicines or dental materials/devices in clinical dentistry is growing. This review aims to detail the ultrafine structure, chemical composition, and reactivity of dental tissues in the context of interactions with ENMs, including the saliva, pellicle layer, and oral biofilm; then describes the applications of ENMs in dentistry in context with beneficial clinical outcomes versus potential risks. The flow rate and quality of saliva are likely to influence the behavior of ENMs in the oral cavity, but how the protein corona formed on the ENMs will alter bioavailability, or interact with the structure and proteins of the pellicle layer, as well as microbes in the biofilm, remains unclear. The tooth enamel is a dense crystalline structure that is likely to act as a barrier to ENM penetration, but underlying dentinal tubules are not. Consequently, ENMs may be used to strengthen dentine or regenerate pulp tissue. ENMs have dental applications as antibacterials for infection control, as nanofillers to improve the mechanical and bioactive properties of restoration materials, and as novel coatings on dental implants. Dentifrices and some related personal care products are already available for oral health applications. Overall, the clinical benefits generally outweigh the hazards of using ENMs in the oral cavity, and the latter should not prevent the responsible innovation of nanotechnology in dentistry. However, the clinical safety regulations for dental materials have not been specifically updated for ENMs, and some guidance on occupational health for practitioners is also needed. Knowledge gaps for future research include the formation of protein corona in the oral cavity, ENM diffusion through clinically relevant biofilms, and mechanistic investigations on how ENMs strengthen the tooth structure.

Hydroxyapatite, fluor-hydroxyapatite and fluorapatite produced via the sol-gel method: dissolution behaviour and biological properties after crystallisation.

Hydroxyapatite (HA), fluor-hydroxyapatite (FHA) with varying levels of fluoride ion substitution and fluorapatite (FA) were synthesised by the sol-gel method as possible implant coating or bone-grafting materials. Calcium nitrate and triethyl phosphite were used as precursors under an ethanol-water based solution. Different amounts of ammonium fluoride were incorporated for the preparation of the FHA and FA sol-gels. After heating and powdering the sol-gels, dissolution behaviour was assessed using ion chromatography to measure Ca(2+) and PO4 (3-) ion release. Biological behaviour was assessed using cellular proliferation with human osteosarcoma cells and alamarBlue™ assay. Statistical analysis was performed with a two way analysis of variance and post hoc testing with a Bonferroni correction. Increasing fluoride substitution into an apatite structure decreased the dissolution rate. Increasing the firing temperature of the HA, FHA and FA sol-gels up to 1,000 °C decreased the dissolution rate. There was significantly higher cellular proliferation on highly substituted FHA and FA than on HA or Titanium. The properties of an implant coating or bone grafting material can be tailored to meet specific requirements by altering the amount of fluoride that is incorporated into the original apatite structure. The dissolution behaviour can further be altered by the temperature at which the sol-gel is fired.

Hydroxyapatite, fluor-hydroxyapatite and fluorapatite produced via the sol-gel method: bonding to titanium and scanning electron microscopy.

OBJECTIVES: Hydroxyapatite (HA), fluor-hydroxyapatite (FHA) with varying levels of fluoride ion substitution and fluorapatite (FA) production has been characterised and optimised by the sol-gel method and the dissolution and biological properties of these materials were investigated. It was the objective of this study to investigate the potential bond strength and interaction of these materials with titanium. METHODS: HA, FHA and FA were synthesised by a sol-gel method. Calcium nitrate and triethyl phosphite were used as precursors under an ethanol-water based solution. Different amounts of ammonium fluoride (NH4F) were incorporated for the preparation of the FHA and FA sol-gels. Using a spin coating technique the sol-gels were coated onto commercially pure titanium disks and crystallised at various temperatures. Using scanning electron microscopy (SEM) and elemental analysis, the surface characteristics, coating thickness and interaction of the Ti substrate and coating were investigated. The bond strengths of the coating to the Ti were investigated using an Instron Universal Load Testing Machine. Statistical analysis was performed with a two-way analysis of variance and post hoc testing with a Bonferroni correction. RESULTS: (1) Coating speed inversely influenced the coating thickness. (2) Increasing fluoride ion substitution and heating temperature significantly increased bond strength and (3) increasing fluoride ion substitution increased the coating thickness. SIGNIFICANCE: FHA and FA synthesised using the sol-gel technique may offer a superior alternative to coating titanium implants with HA and plasma spraying. HA, FHA and FA materials synthesised by the sol-gel method may also have a use as bone grafting materials.

Hydroxyapatite, fluor-hydroxyapatite and fluorapatite produced via the sol-gel method. Optimisation, characterisation and rheology.

OBJECTIVES: Currently, most titanium implant coatings are made using hydroxyapatite and a plasma spraying technique. There are however limitations associated with plasma spraying processes including poor adherence, high porosity and cost. An alternative method utilising the sol-gel technique offers many potential advantages but is currently lacking research data for this application. It was the objective of this study to characterise and optimise the production of Hydroxyapatite (HA), fluorhydroxyapatite (FHA) and fluorapatite (FA) using a sol-gel technique and assess the rheological properties of these materials. METHODS: HA, FHA and FA were synthesised by a sol-gel method. Calcium nitrate and triethylphosphite were used as precursors under an ethanol-water based solution. Different amounts of ammonium fluoride (NH4F) were incorporated for the preparation of the sol-gel derived FHA and FA. Optimisation of the chemistry and subsequent characterisation of the sol-gel derived materials was carried out using X-ray Diffraction (XRD) and Differential Thermal Analysis (DTA). Rheology of the sol-gels was investigated using a viscometer and contact angle measurement. RESULTS: A protocol was established that allowed synthesis of HA, FHA and FA that were at least 99% phase pure. The more fluoride incorporated into the apatite structure; the lower the crystallisation temperature, the smaller the unit cell size (changes in the a-axis), the higher the viscosity and contact angle of the sol-gel derived apatite. SIGNIFICANCE: A technique has been developed for the production of HA, FHA and FA by the sol-gel technique. Increasing fluoride substitution in the apatite structure alters the potential coating properties.

Orthodontics using an occlusal splint: a clinical report.

Careful management of the occlusion is necessary for successful prosthodontic treatment. A reorganized occlusal approach requires a more accurate registration of the desired jaw position, and where it is difficult to achieve this, an occlusal splint is indicated. This clinical report documents a 60-year-old man with a Prosthodontic Diagnostic Index Class IV dentition, who prior to a full-mouth reconstruction, underwent occlusal splint therapy with a Michigan-type splint that incorporated z-springs to allow concurrent orthodontic tooth movement of two anterior teeth to positions that would allow favorable restorations by correcting occlusal and esthetic form.

Taurodontism--a review.

UNLABELLED: Taurodontism is the morpho-anatomical change in the shape of a tooth, which involves enlargement of the body of the tooth and shortening of the roots. It has been reported in permanent and deciduous teeth, in premolars and molars and associated with certain syndromes, particularly in those involving an ectodermal defect. It has clinical implications which are relevant to both the general dental practitioner and the orthodontist. CLINICAL RELEVANCE: This review compiles the available literature concerning taurodont teeth and highlights the management issues raised by the anomaly.

The effect of engaging the screw access channel of an implant abutment with a cement-retained restoration.

PURPOSE: Factors affecting the retention of fixed prostheses to natural abutments are well understood. In contrast, little is known concerning the factors influencing the retention of fixed prostheses cemented to implant abutments. The purpose of this study was to investigate the effect that extending a casting into the screw access channel of an implant abutment has on the retention when cemented using Temp Bond. MATERIALS AND METHODS: Replace Select Straight abutments received set modifications (buccal wall removal at 15 degrees , 22 degrees , and 30 degrees ) using a milling machine; controls were unmodified. Two castings were fabricated for each of the modified abutments, one with and one without an extension into the screw access channel. Following cementation with Temp Bond under standardized conditions, the castings were removed from the abutments using an Instron machine, and the peak removal force was recorded. RESULTS: Extending the casting into the screw access channel significantly (p < 0.001) increased the peak load of removal. Significant differences (p < 0.05) were found between no modification and 30 degrees modification, 15 degrees and 30 degrees modification, and 22 degrees and 30 degrees modification in the groups when the casting extended into the abutment. In the group where the casting did not extend into the abutment, all groups were significantly different (p < 0.001) with the exception of 22 degrees and 30 degrees modification. CONCLUSIONS: The increased load required to remove a casting that extends into the screw access channel of an implant abutment may compensate for loss in retention, which occurs through unfavorable modification of the abutment.

An analysis of the effect of a vent hole on excess cement expressed at the crown-abutment margin for cement-retained implant crowns.

PURPOSE: The labial margins of anterior implant-retained crowns are often positioned subgingivally for a superior esthetic appearance. One of the consequences of subgingival margins is the increased risk of leaving excess cement behind following cementation. This can lead to potential problems, including peri-implant inflammation, soft tissue swelling, soreness, bleeding or suppuration on probing, and bone loss. The purpose of this laboratory study was to investigate the effect of placement, location, and diameter of a vent hole on the amount of cement being expressed at the margin of an anterior implant abutment-retained crown. MATERIALS AND METHODS: Three implant crown copings were fabricated to fit on the same custom abutment. Three vent diameters (0.75, 1.25, and 1.65 mm) and three locations on the palatal surface of the coping (cervico-palatally, mid-palatally, inciso-palatally) were chosen for vent hole placement. For each test, the coping was cemented onto the abutment under standardized conditions. A preweighed thin coating of cement was applied to the fit surface of the coping. The amount of cement expressed at the margin and vent hole was measured by weight and calculated as a proportion of the amount of cement placed in the coping before seating. The procedure was completed 15 times for each variable. The results were statistically analyzed using univariate ANOVA with post hoc Bonferroni-adjusted independent samples t-tests. RESULTS: The presence of a vent hole influenced the proportion of cement expressed at the coping margin (p < 0.05). The location of a vent hole influenced the proportion of cement expressed at the coping margin (p < 0.05), with the exception of the mid-palatal and inciso-palatal positioning where there was no significant difference (p= 0.61) between groups. The diameter of the vent hole did not significantly influence the proportion of cement expressed at the coping margin (p= 0.096). CONCLUSIONS: When using anterior cement-retained implant crowns, the use of a 0.75-mm mid-palatal or inciso-palatal vent hole to minimize the amount of cement expressed at the margin during cementation should be considered.

Part-time versus full-time retainer wear following fixed appliance therapy: a randomized prospective controlled trial.

AIM: To compare part-time and full-time Essix-type retainer wear regimens following fixed appliance treatment, with respect to dental alignment and occlusal changes. METHODS: In this prospective study, 60 patients were randomly allocated to either full-time or part-time Essix retainer wear following fixed appliance therapy. Study casts were taken before treatment, at debonding, and 6 months following debonding. Little's irregularity index, the intercanine width, intermolar width, overjet, and overbite were measured blindly on both the maxillary and mandibular casts. RESULTS: Both groups showed pretreatment equivalence for start age, duration of fixed appliance treatment, Little's index, intercanine width, intermolar width, overjet, and overbite. The number of patients completing the trial was 29 (1 dropout) in the part-time group and 28 in the full-time group (2 dropouts). There was a significant reduction in both the maxillary and mandibular Little's index and mandibular intermolar width in both groups during active treatment. There was a significant reduction in overjet and overbite in only the part-time retention group during fixed appliance treatment. Between debonding and 6 months after debonding, there was no significant change in any of the intra- or intergroup study cast measurements. CONCLUSIONS: Night-time-only Essix retainer wear may be an acceptable retention regimen following the use of fixed appliances.

Resin-retained bridges as predictable and successful restorations.

Resin-retained bridges have been used clinically since the 1970s and offer a more conservative approach to the restoration of edentulous spaces than conventional bridgework. They are easy to place, cheap to fabricate, and have been shown to be cost-effective. Despite this, they are not frequently used in general dental practice and have an exaggerated reputation for premature failure. Since their initial introduction, they have undergone a number of changes to their method of retention and the materials used in their construction. This has resulted in a predictable, aesthetic restoration which, second only to restoration with dental implants, is often the treatment of choice when teeth adjacent to an edentulous space are minimally or not restored.

The importance of dentin collagen fibrils on the marginal sealing of adhesive restorations.

This study evaluated the importance of the union between dentin collagen and three different adhesive materials. Sixty Class V restorations were prepared on the buccal and lingual surfaces of 30 recently extracted human premolars, with the cervical margins in dentin and the occlusal margins in enamel. These restorations were distributed to three groups of 20 cavities each based on the employed adhesive system used: Group A: Single Bond; Group B: Prime&Bond NT; Group C: One Coat Bond. Each group was subdivided according to dentin treatment: (1) manufacturers' adhesive protocol and (2) removal of the collagens fibers (total etch + sodium hypochlorite 5% for two minutes) + adhesive protocol. After the restorations were completed, the teeth were stored in saline solution (24 hours/37 degrees C), subjected to thermal cycling, washing and scoring according to dye penetration. Dye penetration was evaluated, with the numbers ranging from 0 (no infiltration) to 3 (greatest infiltration). When the dentin microleakage scores were compared in subgroups A1XA2, B1XB2 and C1XC2, the Mann-Whitney Test revealed significant differences between groups B and C (p < 5%). The better results were shown in subgroups B2 (p = 0.0345) and C2 (p = 0.0029). The results showed that the collagen fibrils were not necessary for adhesion, and their removal positively influenced the marginal sealing of Prime&Bond NT and One Coat Bond.

Smile aesthetics.

UNLABELLED: The aim of this article is to outline some of the factors practitioners should take into consideration when planning optimal smile aesthetics. The components of the smile that will be discussed include the smile arc, incisor/gingival display, smile width, gingival aesthetics, tooth proportionality/symmetry, contacts/connectors/embrasures and the dental midlines. CLINICAL RELEVANCE: A systematic evaluation of the components of the smile when planning treatment will help to improve smile aesthetics and produce greater patient and dentist satisfaction.

The effects of abutment wall height, platform size, and screw access channel filling method on resistance to dislodgement of cement-retained, implant-supported restorations.

PURPOSE: Factors affecting the retention of fixed prostheses to natural abutments are well understood. In contrast, little is known concerning factors influencing the retention of fixed prostheses cemented to implant abutments. The purpose of this study was to investigate the effect that varying implant abutment wall height, platform size, and screw access channel filling method has on the retention of castings cemented to implant abutments using TempBond. MATERIALS AND METHODS: Four 15 degrees preangled abutments (Nobel Biocare Replace Select Esthetic) of each platform size--narrow (NP), regular (RP), and wide (WP)--were used. In each group of abutments the screw access axial wall was either unadjusted, one-third removed, two-thirds removed, or completely removed. The screw access channels were either fully or partially filled with Memosil, a vinyl polysiloxane impression material. For each abutment a casting was constructed that incorporated an attachment to allow removal. Castings were cemented to abutments with TempBond. The tensile force required to separate the cemented castings from the abutments was measured using an Instron Universal load-testing machine. RESULTS: The mean peak removal force for comparable abutments was significantly different ( p < 0.05): (1) where the screw access channel was completely filled with Memosil compared with those partially filled with Memosil; (2) with platform sizes--WP > RP > NP; (3) with alteration of axial wall height--1/3 removed > unadjusted = 2/3 removed > total wall removal. CONCLUSIONS: The retention of castings cemented to implant abutments with TempBond is influenced by the wall height, platform size, and the filling modality of the screw access channel.

The effect of disinfection on irreversible hydrocolloid and type III gypsum casts.

Under standardised conditions, 80 impressions were made of a ruled stainless steel die (ISO Specification 1563) using irreversible hydrocolloid (alginate). The alginates were subsequently treated with 3 commercially available disinfectants, Perform-ID, ImpressiVand Dimenol and poured with type III gypsum. The alginates were evaluated for surface detail reproduction and the gypsum for surface detail reproduction and hardness. Disinfection with Perform ID significantly affected the surface detail reproduction of alginate while Dimenol and ImpressiV did not. Perform ID and Dimenol both significantly affect the hardness of poured type III gypsum casts while ImpressiV did not.

Reproduction ofarticulator settings and movements with an ultrasonic jaw movement recorder.

The KaVo ARCUS digma is an ultrasonic mandibular movement recorder, which provides articulator setting information for Kavo articulators. The first part of this study examined the ability of the device to record condylar control values pre-set on Kavo's own articulators. Using a mechanical pantograph, the second part of the study tested the ability of the device to record, and then allow reproduction on a Kavo articulator, the movements of a Denar D5A articulator. The device was accurate in recording Sagittal Condylar Inclination, but less so for Progressive Side Shift. Immediate Side Shift was persistently under-recorded. Pantographic tracings demonstrated similar paths of articulator movements so long as Immediate Side Shift was not set.

Influence of surface treatments on the shear bond strength of Panavia 21 to a Type III gold alloy.

Cylinders of Type III gold alloy were sandblasted with either: 50 micron Aluminium Oxide particles (Group 1); CoJet Sand (Group 2); the CoJet System - CoJet Sand followed by application of silane primer (Group 3). Shear testing was undertaken following apposition of Panavia 21 resin. Mean shear bond strengths (+/- standard deviation) were Group 1, 32.9 (+/-18.2) MPa; Group 2, 26.5 (+/-10.8) MPa and Group 3, 45.6 (+/- 25.8) MPa. There was no statistically difference between Group 1 and 2; and between group 1 and 3. However, there was a significant; difference between Group 2 and 3 p < 0.05). While the CoJet System achieved the highest mean shear bond strength it conveyed no statistical advantage over the traditional method of sandblasting with aluminium oxide.

Treatment approaches for developmentally absent second premolars.

UNLABELLED: This paper sets out to discuss the treatment options available for the management of patients with agenesis of second premolars. These include: retention of the deciduous molar, extraction followed by space closure, extraction and utilization of the space for the correction of malocclusion and extraction followed by restoration of the edentulous space. CLINICAL RELEVANCE: Congenital absence of second premolars is a common clinical problem faced by practitioners. Dentists should be aware of the treatment options when managing such cases.