A novel design solution to the fraenal notch of maxillary dentures.

This study investigates a novel design feature for the fraenal notch of maxillary dentures, using computational and experimental methods, and shows that its use could significantly increase the longevity of the prosthesis. A two-step process can be used to create the design feature with current denture base materials, but would be highly dependent on the individual skill of the dental technician. Therefore, an alternative form of manufacture, multi-material additive layer manufacture (or '3D printing'), has been proposed as a future method for the direct production of complete dentures with multi-material design features.

Defective dental restorations: to repair or not to repair? Part 1: direct composite restorations.

The presentation of patients with failing dental restorations that exhibit minor defects is a common clinical situation in everyday dental practice. The repair of such restorations, rather than replacement, is increasingly considered to be a viable alternative to the replacement of the defective restoration. This first of two papers considers indications and techniques for the repair of defective direct composite restorations. It is possible that some dental practitioners are unaware of the option of repair rather than replacement of composite restorations. This article provides an overview of contemporary knowledge and understanding of restoration repair in the clinical management of defective composite restorations.

Defective dental restorations: to repair or not to repair? Part 2: all-ceramics and porcelain fused to metal systems.

With the increasing use of ceramics in restorative dentistry, and trends to extend restoration longevity through the use of minimal interventive techniques, dental practitioners should be familiar with the factors that may influence the decision either to repair or replace fractured metal-ceramic and all-ceramic restorations and, also, the materials and techniques available to repair these restorations. This second of two papers addresses the possible modes of failure of ceramic restorations and outlines indications and techniques in this developing aspect of restoration repair in clinical practice.

A survey of undergraduate education in dental implantology in UK dental schools.

The aim of this study was to ascertain knowledge on current teaching of implant dentistry in the undergraduate curriculum of Dental Schools in the UK. Information on the teaching modalities, including year of introduction of implant dentistry into undergraduate curriculum, departments involved in teaching, format of teaching, use of adjunctive teaching aids, and types of implant systems used in undergraduate teaching was collected by means of a questionnaire, which was sent to all undergraduate dental schools in the UK. Based on a 100% response rate, the findings indicate that all dental schools in the UK reported that they included dental implantology in their undergraduate curriculum; however there were marked variations in the content and delivery of the teaching.

The effect of a range of disinfectants on the dimensional accuracy and stability of some impression materials.

Disinfection of dental impressions should be considered as a routine procedure in dental surgeries and dental laboratories. Disinfectants can have deleterious effects on some properties of impression materials. The aim of this study was to evaluate the dimensional accuracy and dimensional stability of a model dental stone, reproduced from five commonly used impression materials (Aquasil soft putty/Aquasil Ultra LV; Aquasil Monophase; Aquasil Ultra Heavy; Impregum F and Provil putty/Provil Light CD wash) retained by their adhesives in acrylic resin trays and exposed to three disinfectant solutions (Perform ID; Haz-Tabs and MD 520). Two hundred models were used to investigate the effect of the three disinfectants on the dimensional accuracy of the five impression materials. Five impressions were taken for each impression material for each disinfection treatment group. Measurements were carried out using a High Precision Reflex Microscope. All materials demonstrated a percentage change in dimensions when subjected to no disinfection when compared to the brass master die and all materials demonstrated a percentage change in dimension when subjected to the different disinfection procedures. The results of this study have demonstrated that for all of the materials investigated, the changes in dimensional stability were small in the order of microns. These changes may however be of clinical significance for procedures requiring a high degree of accuracy, for example fixed prosthodontics. The materials respond differently depending on the disinfectant used and it may therefore be appropriate that manufacturers recommend the use of particular disinfectants for their products in order to ensure optimum dimensional accuracy and stability.

An investigation of the shear bond strength of compomer restorative material to enamel and dentine.

The aim of this study was to investigate the effect of one step adhesives on the shear bond strength of a compomer restorative material to both enamel and dentine. Human extracted teeth were used for the study. Ten samples were prepared for both enamel and dentine specimens for each of the five groups: Tooth, no etch, Prime and Bond NT (P+B NT); tooth, Non-Rinse Conditioner (NRC), P+B NT; tooth, NRC, Prime and Bond 2.1 (P+B 2.1); tooth, etch, P+B NT; tooth, etch, P+B 2.1. The specimens were subjected to bond testing. The shear bond strength was measured using an Inston 1193 testing machine using a cross head speed of 1 mm/minute. The specimens were tested to destruction. The results show that for the enamel specimens the highest bond strength was recorded for those specimens subjected to Etch, P+B 2.1 (22.1 MPa) and Etch P+B NT (20.0 MPa). The groups of specimens which did not undergo etching had very low bond strengths ranging from 11.4 MPa for NRC, P+B 2.1, 8.5 MPa for NRC P+B NT to 6.9 MPa for P+B NT. For the dentine specimens, for all of the groups, the shear bond strengths were low. Those groups subjected to etching produced the highest values of 7.9 MPa for NRC P+B 2.1 with the lowest value of 6.1 MPa for NRC P+B NT. These bond strengths were significantly lower than those achieved for bonding to enamel. Prime and Bond NT and Prime and Bond 2.1, used in conjunction with acid etching, produce satisfactory bond strengths of compomer restorative material to enamel. Bond strengths to dentine were low.

An in vitro investigation of the effect of some analgesics on human enamel.

The sale of over-the-counter pain relief medication has increased dramatically in recent years, and typically amounts to several hundred thousands of pounds per year in the UK. Many soluble analgesic preparations contain citric acid, and it has been suggested that these formulations may cause dental erosion. The aim of this study was to investigate the effect of some over-the-counter analgesics on tooth surface loss from human enamel. Six commonly available analgesics were chosen for this study and the effect of immersing unerupted human enamel was examined using non-contact optical profilometry. Two of the six analgesics investigated caused no detectable erosion (Boots soluble aspirin and Anadin Extra). Three caused statistically significant enamel erosion, but this was very slight and is thought to be clinically insignificant (Alka Seltzer, Panadol and Solpadeine). Only one analgesic caused possible potentially clinical significant enamel erosion. Further studies are needed to determine whether Aspro causes clinically significant enamel erosion.

An in vitro investigation of the effect of the addition of untreated and surface treated silica on the transverse and impact strength of poly(methyl methacrylate) acrylic resin.

Silica is a commonly used filler in dental materials and as a reinforcing agent in industry. The aim of this study was to further investigate the effect of the addition of untreated and a novel surface treated silica on the transverse bend and impact strength of acrylic resin denture base material. It was hypothesized that the silica/resin composite materials would have an improved flexural and impact strength than the conventional heat-cured acrylic resin. Three types of untreated and two of treated silica powder were used in this study. The range of percentages used were 1%, 0.5%, 0.2%, 0.1%. The treated particles were coated with hexamethyldisilazane or dimethyldichloridesilazane. Conventional heat cured acrylic resin was used as a control. The modulus of rupture for all groups of acrylic resin containing silica was significantly lower than for the control. The modulus of elasticity was not significantly greater than the control group. For the impact strength statistical analysis revealed a significant difference between the groups. There was a nonsignificant increase in the impact strength for specimens compared to the control. In conclusion the addition of silica to poly(methyl methacrylate) denture base materials did not produce a significant improvement in the transverse bend or impact strength compared to conventional heat-cured acrylic resin. The incorporation of untreated and surface treated silica cannot be recommended as a method of reinforcement.

An in vitro investigation of a comparison of bond strengths of composite to etched and air-abraded human enamel surfaces.

PURPOSE: The purposes of the study were to measure the tensile bond strength of composite resin to human enamel specimens that had been either etched or air-abraded, and to compare the quality of the marginal seal, through the assessment of microleakage, of composite resin to human enamel specimens that had been either etched or air-abraded. MATERIALS AND METHODS: Thirty mandibular molar teeth were decoronated and sectioned mesio-distally to produce six groups, each containing ten specimens that were embedded in acrylic resin using a jig. In each of the four treatment groups, the specimen surfaces were treated by either abrasion with 27 or 50 microm alumina at 4 mm or 20 mm distance, and a composite resin was bonded to the treated surfaces in a standardized manner. In the two control groups the specimens were treated with 15 seconds exposure to 36% phosphoric acid gel and then similarly treated before being stored in sterile water for 1 week. All specimens were then subjected to tensile bond strength testing at either 1 or 5 mm/min crosshead speed. For the microleakage study, the degree of dye penetration was measured 32 times for each treatment group, using a neutral methylene blue dye at the interface between composite and either 27 or 50 microm air-abraded tooth structure or etched enamel surfaces. RESULTS: The mean bond strength values recorded for Group 1 (phosphoric acid etch, 5 mm/min crosshead speed) was 25.4 MPa; Group 2 (phosphoric acid etch, 1 mm/min), 22.2 MPa; Group 3 (27 microm alumina at 4 mm distance), 16.8 MPa; Group 4 (50 microm alumina at 4 mm distance), 16.9 MPa; Group 5 (27 microm alumina at 20 mm distance), 4.2 MPa; and for Group 6 (50 microm alumina at 20 mm distance) 3.4 MPa. An analysis of variance (ANOVA) demonstrated significant differences among the groups, and a multiple comparison test (Tukey) demonstrated that conventionally etched specimens had a greater bond strength than air-abraded specimen groups. No significant difference in dye penetration could be demonstrated among the groups (p= 0.58). CONCLUSIONS: Composite resin applied to enamel surfaces prepared using an acid etch procedure exhibited higher bond strengths than those prepared with air abrasion technology. The abrasion particle size did not affect the bond strength produced, but the latter was adversely affected by the distance of the air abrasion nozzle from the enamel surface. The crosshead speed of the bond testing apparatus had no effect on the bond strengths recorded. The marginal seal of composite to prepared enamel was unaffected by the method of enamel preparation.

An in-vitro investigation of the effect of a water additive and a new acidic primer on the tensile bond strength of composite resin to human enamel and dentine.

The aim of this study was to investigate the effect of a water additive on the bond strength of a composite restorative material to enamel and dentine which have undergone a range of surface treatments regimes. Human enamel and dentine specimens were prepared and divided into 3 surface treatment groups. Composite resin restorative material was bonded to the surface prepared enamel and dentine specimens. The tensile bond strength of the composite resin was measured using a Lloyd's testing machine. The tensile bond strength of composite resin to etched enamel surfaces using a standard etch technique was significantly greater than that to dentine (p < 0.05). For those specimens subjected to the addition of the water additive 'Alpron' the bond strength to the enamel was still significantly greater than to the dentine (p< 0.005). The addition of 'Alpron' to the water significantly improved the bond strength of composite to enamel and dentine when etched and placed with 'Prime&BondNT' (p < 0.05). There was no significant difference in bond strength of enamel and dentine specimens bonded using Xeno III (p> 0.05). However, the bond strength of dentine specimens bonded with Xeno III was significantly greater than other dentine specimens bonded with Prime&BondNT (p< 0.05). For those groups of specimens which included the water additive 'Alpron' in the regime, the tensile bond strength of the composite resin restorative material to enamel and dentine was greater than for those non water additive groups. The tensile bond strength of composite resin bonded to enamel surfaces prepared with 'Alpron' was significantly higher than that bonded to dentine surfaces.

Implant-supported facial prostheses provided by a maxillofacial unit in a U.K. regional hospital: longevity and patient opinions.

PURPOSE: The aim of this study was to acquire information on the types and longevity of implant-retained facial prostheses and the opinions of patients on several factors related to their prostheses. MATERIALS AND METHODS: A survey of 75 maxillofacial prosthetic patients currently under treatment and review at the Maxillofacial Unit, Morriston Regional Hospital was conducted through a 23-question postal questionnaire. These patients were selected as representative of a group of individuals receiving treatment or under review for the fabrication of maxillofacial prostheses. RESULTS: Of the prosthetic replacements, 83% were ear prostheses, 8% nose, 6% eye, and 2% combination prostheses. Of the 47 respondents, 8 (17%) reported that they were currently wearing their original prostheses. The remaining 39 (83%) respondents had all been provided with at least 1 replacement prosthesis. The mean lifetime of the prostheses was found to be 14 months (range: 4-36 months). The majority of replacement prostheses in this study were provided as a result of color fade or wear of the silicone material of the previous prosthesis. Individuals with no previous experience wearing a prosthesis had an unrealistic expectation of their prosthesis longevity, with a mean value of 17.8 months. In comparison, individuals with previous experience had reduced expectations, with a mean of 14.4 months. In terms of the patients' opinions of the overall quality of their prostheses, the results demonstrated that a large number of patients were satisfied. Thirty-five patients rated their prostheses as excellent and 9 as good. At 7-12 months, 4 patients rated their prostheses as excellent and 8 as good. At 13 months, 4 patients rated their prostheses as excellent and 5 as good. CONCLUSIONS: It is important that advice be given to patients on the expected average longevity of their prostheses, together with information on factors affecting the longevity (i.e., environmental staining, cosmetics, and cleaning regimes). In this study, 26% of the replacement prostheses were provided due to color fading of the original prosthesis. This highlights the need for continuing research in the development of materials used for the construction of facial prostheses with improved properties, and in particular, improved color stability.

A reappraisal of the incremental packing technique for light cured composite resins.

The cuspal flexure caused by a direct placement composite resin was measured using a technique that did not interfere with cuspal movement. Twenty upper premolar teeth with mesial-occlusal-distal (MOD) cavity preparations were restored using a posterior composite resin. Ten teeth were restored using a bulk packing technique and 10 were restored using three 'U' shaped bucco-lingual increments. Total cuspal movement was measured 1 h following the initiation of curing. Bulk placement of the composite resin produced slightly more cuspal movement (12.5 microm) compared with the incremental placement of composite (11.3 microm). This difference was not statistically significant. The technique of incremental packing to reduce cuspal flexure is therefore questioned.

The development of a new index for measurement of incisal/occlusal tooth wear.

A number of indices have been developed for the measurement of tooth surface loss but they have not achieved universal acceptance. The aim of this study was to develop a new index suitable for the monitoring of incisal/occlusal tooth wear on serial study models. The new index recorded incisal/cuspal wear for individual teeth. Each tooth was scored on a six-point scale ranging from 0-5. Six assessors evaluated the index and it was applied to baseline and sequential models taken after 20 years. The study demonstrated the value of maintaining long-term dental records in the form of study models for monitoring progressive tooth wear.

The effect of a range of disinfectants on the dimensional accuracy of some impression materials.

In this study the dimensional accuracy of two model materials; dental stone and plaster of Paris, reproduced from three commonly used impression materials; alginate, polyether and addition-cured silicone, retained by their adhesives in acrylic resin trays and exposed to four disinfectant solutions was evaluated. Ninety casts were used to investigate the effect of the four disinfectants on the dimensional accuracy of alginate, polyether and addition-cured silicone impression material. For each impression material 30 impressions were taken, half were poured in dental stone and half in plaster of Paris. The disinfectants used were Dimenol, Perform-ID, MD-520, and Haz-tabs. Measurements were carried out using a High Precision Reflex Microscope. For the alginate impressions only those disinfected by 5-minute immersion in Haz-tabs solution and in full-strength MD 520 were not adversely affected by the disinfection treatment. All polyether impressions subjected to immersion disinfection exhibited a clinically acceptable expansion. Disinfected addition-cured silicone impressions produced very accurate stone casts. Those disinfected by spraying with fill-strength Dimenol produced casts that were very similar to those left as controls, but those treated by immersion disinfection exhibited negligible and clinically acceptable expansion. The results of the studied demonstrated that the various disinfection treatments had different effects on the impression materials. It is important that an appropriate disinfectant is used for each type of impression material.

Abfraction lesions: myth or reality?

UNLABELLED: Loss of tooth substance in the cervical region is usually attributed to toothbrush abrasion, erosion, or a combination of both factors. Recently the role of occlusal loading has become increasingly prominent. It is suggested that high occlusal loads cause large cervical stress concentrations, resulting in a disruption of the bonds between the hydroxyapatite crystals and the eventual loss of cervical enamel. This process has been called noncarious cervical tooth loss or abfraction. This article reviews the available evidence to support the thesis that occlusal loading can contribute to the process of abfraction. It also reviews the potential interactions between occlusal loading and erosion that may contribute to abfraction lesion formation. CLINICAL SIGNIFICANCE: It is important to recognize the potential role of occlusal loading in the loss of cervical tooth tissue so that management of the occlusion can be incorporated into a treatment plan for a patient with abfraction lesions.

The effect of the addition of poly (methyl methacrylate) fibres on the transverse strength of repaired heat-cured acrylic resin.

The aim of the present study was to investigate the effect of addition of an experimental poly (methyl methacrylate) (PMMA) fibre in linear form, 0.75 mm in diameter on the transverse strength of repaired heat-cured poly (methyl methacrylate) denture base material. Specimens of heat-cured PMMA were repaired with an autopolymerizing acrylic resin and an autopolymerizing acrylic resin together with the addition of untreated and surface-treated PMMA fibres in different arrangements. The transverse bend test was carried out using a LIoyd's Instrument Material Testing Machine. From the results, it can be concluded that the box incorporated into the repair joint produced a significant decrease in the moduli of elasticity and rupture which may be due to stress concentration effects. The addition of one layer of untreated PMMA fibres significantly decreased the modulus of rupture. The addition of two layers of untreated fibres produced a slight but statistically non-significant increase in the modulus of rupture. The addition of surface-treated (with butadiene styrene latex emulsion) fibres into the repair complex gave no improvement compared with the addition of untreated fibres in terms of transverse strength. There was an insignificant decrease in the modulus of rupture compared with the untreated fibres.

The effect of the addition of different fibres on the transverse and impact strength of acrylic resin denture base material.

The aim of the present study was to investigate the effect of the addition of different types of fibres on the transverse and impact strength of acrylic resin denture base material. The addition of glass fibres (strand) and polyethylene fibres produced a non significant increase in the modulus of elasticity, compared with the control of conventional heat-cured acrylic resin. The addition of glass fibres (woven and strand), polyethylene and carbon fibres to acrylic resin produced a non significant increase in the modulus of rupture. The addition of carbon, glass (strand) and polyethylene fibres produced a significant increase in the impact strength. Within the limitations of this study the addition of silk fibres did not produce an improvement in the mechanical properties.

Abfraction lesion formation in maxillary incisors, canines and premolars: a finite element study.

Abfraction lesions are angular, wedge-shaped defects found at the cervical region of teeth and are caused by mechanical overloading initiated by cuspal flexure. Clinically, these lesions are more prevalent on the labial aspect of maxillary incisors. The aim of this study was to provide a biomechanical explanation for this clinical variation. Two-dimensional plane strain finite element models of an maxillary incisor, canine and first premolar were developed and the cervical stress profiles were examined along a horizontal plane 1.1 mm above the amelo-cemental junction. The local X (horizontal) stress on the labial/buccal side was 176.4 MPa for the incisor, 57.8 MPa for the premolar, and 3.4 MPa for the canine. Similarly, the maximum labial/buccal principal stress was 181.4 MPa for the incisor, 25.2 MPa for the premolar, and 66.8 MPa for the canine. The labial/buccal stress profile in the cervical region of an maxillary incisor was always greater than that found in an maxillary canine or premolar tooth. These findings provide a biomechanical explanation for the clinical variation seen in the prevalence of cervical abfraction lesions.

Accuracy of adaptation of thermoformed poly(methyl methacrylate).

Thermoformed poly(methyl methacrylate) (PMMA) sheet is used to produce a number of different dental appliances such as stents, occlusal splints and baseplates for occlusal rims. The purpose of the present study was to measure the accuracy of adaptation of Perspex PMMA sheet and to determine the effect of annealing on the accuracy of the thermoformed specimens. The results of the study showed that PMMA can produce specimens that are accurately adapted to the cast. Immersion in water resulted in an increase in the space between the cast and the specimen for both thermoformed and thermoformed and annealed acrylic resin. Annealing of the thermoformed specimens had significantly less increase in space between the cast and the specimens when immersed in water over a period of 3 months.

The selection of anterior teeth appropriate for the age and sex of the individual. How variable are dental staff in their choice?

As part of the development of a guide to aid the undergraduate in the selection of artificial teeth, the aim of this study was to investigate the variability in choice of dental staff to select teeth appropriate to the age and sex of the individual with the aid of a series of three-dimensional guides. Four three-dimensional guides were produced for use in the study. Fifty dentists were asked to complete a questionnaire designed to assess the variability in selection of anterior teeth appropriate for the age and sex of an individual. From this study it can be concluded that there was little consistency in the selection of the shade, mould and arrangement of anterior teeth appropriate for the age and sex of the individual by qualified dental staff. The development and implementation of an aesthetic proforma to guide dental staff, dental undergraduates and patients through the process of choosing tooth mould, shade and arrangement based on age and sex may be helpful.