Is there more than one way to skin a newt? Convergent toxin resistance in snakes is not due to a common genetic mechanism.

This corrects the article DOI: 10.1038/hdy.2015.73.

Is there more than one way to skin a newt? Convergent toxin resistance in snakes is not due to a common genetic mechanism.

Convergent evolution of tetrodotoxin (TTX) resistance, at both the phenotypic and genetic levels, characterizes coevolutionary arms races between amphibians and their snake predators around the world, and reveals remarkable predictability in the process of adaptation. Here we examine the repeatability of the evolution of TTX resistance in an undescribed predator-prey relationship between TTX-bearing Eastern Newts (Notophthalmus viridescens) and Eastern Hog-nosed Snakes (Heterodon platirhinos). We found that that local newts contain levels of TTX dangerous enough to dissuade most predators, and that Eastern Hog-nosed Snakes within newt range are highly resistant to TTX. In fact, these populations of Eastern Hog-nosed Snakes are so resistant to TTX that the potential for current reciprocal selection might be limited. Unlike all other cases of TTX resistance in vertebrates, H. platirhinos lacks the adaptive amino acid substitutions in the skeletal muscle sodium channel that reduce TTX binding, suggesting that physiological resistance in Eastern Hog-nosed Snakes is conferred by an alternate genetic mechanism. Thus, phenotypic convergence in this case is not due to parallel molecular evolution, indicating that there may be more than one way for this adaptation to arise, even among closely related species.

Efficiency of preparative and process column distribution systems.

An analytical method for computing the residence time distribution of the liquid distribution system in chromatography columns is described. The impact of the distributor design on the separation efficiency is predicted as a function of media properties and packed bed dimensions. The efficiency loss due to the distributor when increasing column diameter during scale-up is quantified. It is shown that this loss can be compensated by modulating the local bed height via a moderate inclination of the bed support. It is concluded that the selection of an appropriate distributor design concept with optimised dimensions enables a scale-up of chromatographic separations without any significant loss of chromatographic efficiency due to the distribution system.

Fracture behavior of human mandibular incisors following endodontic treatment and porcelain veneer restoration.

PURPOSE: Because of existing controversy, the present study investigated the individual and combined effects of endodontic treatment and porcelain veneer restoration on the fracture behavior of human mandibular incisors. MATERIALS AND METHODS: Forty extracted intact human mandibular incisors were assigned to four groups of ten with a similar range of labiolingual widths at the cementoenamel junctions. Group A consisted of intact teeth; group B consisted of endodontically treated teeth; group C teeth were restored with labial porcelain veneers; and those of group D were endodontically treated and had labial porcelain veneers. All teeth were subjected to a slow continuous loading test at 30 degrees to the long axis of the teeth and 1 mm below the incisal edge on the labial side. RESULTS: Fracture forces were 415 +/- 220 N, 370 +/- 89 N, 420 +/- 128 N, and 448 +/- 156 N for groups A, B, C, and D, respectively. Root fracture was the most common mode of failure. There were no statistically significant differences between the groups in terms of fracture forces and modes of failure. CONCLUSION: Human mandibular incisors with endodontic treatment and/or porcelain veneer restorations were able to withstand the same magnitude of oblique loading as intact teeth. Endodontic treatment and/or porcelain veneer restoration did not affect the mode of failure of mandibular incisors.

An in vitro microleakage study of three restorative techniques for Class II restorations in posterior teeth.

Microleakage associated with a silver reinforced restorative glass ionomer cement used alone and also as a laminate restoration with a composite resin and dentine adhesive in extracted premolar and molar teeth was evaluated. The influence of artificial saliva, thermal and load cycling was also determined. The composite and dentine adhesive alone were used for comparative purposes. The results showed that the composite resin/dentine adhesive restorations showed substantial microleakage at both the cervical and occlusal margins of the Class II restorations, whereas the glass ionomer alone showed little or no leakage after storage in water for seven days at 37 degrees C. These results were confirmed when the restorations were thermo-cycled and load stressed. The addition of glass ionomer as a base to the composite forming the laminate restoration reduced the leakage substantially and in certain conditions the leakage was less than that observed with glass ionomer restoratives alone.

An in vitro microleakage study of a new multi-purpose dental adhesive system.

Despite the advances made in the field of adhesive dentistry, microleakage still remains an area of concern, as a secure seal to dentine and cementum still cannot be achieved with certainty. This project compared the effectiveness of a new adhesive, Scotchbond Multi-Purpose Dental Adhesive System (SBMP) with an established product, Gluma Bonding System (Gluma) in preventing microleakage and the influence of storage, thermal and load cycling on microleakage patterns. In uncycled specimens, Gluma Bonding System had significantly less leakage (P < 0.01) at both occlusal and cervical margins. Thermocycling of composite restorations utilizing SBMP resulted in a significant decrease (P < 0.05) at the occlusal margins but had no effects on cervical leakage. Mechanical loading had no influence on leakage patterns either cervically or occlusally. Three months' storage and combined treatment resulted in a significant decrease in leakage (P < 0.05) at the occlusal margins.

Resin-bonded prostheses.

This article reviews the uses, advantages, and disadvantages of the different types of resin-bonded prostheses. Resin-bonded prostheses can be used for tooth replacement as well as for occlusal, cosmetic, and orthodontic/periodontic therapy. Proper case selection is essential to their success. Although long-term clinical studies are not available for some of these types of prosthesis, they are generally promising and have become important elements in the provision of dental health care.

Relation between incisal overjet and traumatic injury: a case control study.

Most previous studies have shown the prevalence of traumatic dental injuries in anterior teeth to increase with increasing overjet. This study identified 36 Singapore schoolchildren, age 7-18 years, from a clinic population of 11,179, who had suffered dental trauma while playing contact or collision sports. A case control group of 36 children, matched for age, sex, race and sporting activities, but who had not suffered dental trauma, was selected from the same clinic population. Both groups were examined and the nature of injuries received, together with overjet measured to the nearest 0.5 mm were determined. The mean overjet for the trauma group was 3.42 +/- 1.45 mm and for the injured group 3.42 +/- 1.33 mm. These means were not statistically different (p = 1.00), neither did the distribution of overjet between the groups differ. These data were not in accord with the majority of studies correlating incisal overjet and dental trauma, and they suggested that overjet was not a positive correlate with traumatic dental injury in Singapore schoolchildren.

A survey of tooth injury experience and attitudes to prevention in a group of Singapore schoolboys.

A survey of 246 boys aged 12-17 years (mean 13.8 years) determined the sports played, dental injury experience, knowledge and usage of and attitudes towards mouthguard wearing. Most played basketball and soccer. Twenty-one suffered 1 injury episode, 7-2 and 10-3 or more tooth injuries. Twenty-six subluxations, 19 fractures and 1 avulsion were reported. The sports with the highest prevalence of dental injury were boxing and wrestling (33%), soccer (20%), and basketball (19%). While 144 (56%) of boys knew about mouthguards, none wore one. Only 64 (25%) would wear a mouthguard if given one. Most dental injuries were minor, but four high-risk sports (> 19% injury prevalence) would justify preventive measures, including education for injury prevention and encouragement of mouthguard use.

Concepts of adhesion--a review.

This paper reviews the current concepts of adhesion in restorative dentistry. Despite the numerous products available in the market, adhesion occurs in one or a combination of four ways. 1. Acid-etch and formation of resin tags. 2. Formation of strongly bonded surface precipitates, to which a resin can be chemically or mechanically bonded. 3. Chemical bonding to the inorganic components of tooth structure. 4. Chemical bonding to the organic components of tooth structure. With the success of the acid-etch technique for bonding to enamel, much of today's adhesive research has been directed towards bonding to dentine. None of the currently available dentine adhesives can achieve an ideal bond to dentine.

Salivary contamination and post-cured resin/resin lute bond.

A previous study has shown that sandblasting and silane priming a post-cured inlay resin gave a secure bond to dual-cure luting resin. To determine the influence of salivary contamination 4 additional groups of 15 post-cured resin discs were mounted in acrylic cylinders, their faces sandblasted with 50 microns alumina and silane primed. Surface treatments with saliva (sa), air/water spray (a/w), phosphoric acid gel (pa), and silane (si) followed in the order listed: A) control, no further treatment; B) sa, a/w; C) sa, a/w, si; D) sa, a/w, pa a/w; E) sa, a/w, pa, a/w, si. A 3.9 mm diameter column of dual-cure resin lute was then bonded to the dry stored in water surfaces. Specimens were stored in water for 2 weeks after which the dual-cure resin columns were sheared off the post-cured resin discs. Shear bond strengths were A) 19.2 +/- 3.7, B) 17.4 +/- 3.9, C) 16.7 +/- 3.1, D) 15.6 +/- 3.5, E) 15.4 +/- 2.3 MPa. One-way ANOVA and Duncan's Multiple Range Procedure showed groups D and E to be significantly lower than the uncontaminated control group A (p < 0.05). There were 2 adhesive failures in group B and all others were cohesive within the post-cured resin discs. This implies that air/water alone after salivary contamination is an unreliable cleansing method. The low shear bond values for Groups D and E may have been related to inadequate clearance of the phosphoric acid gel. It was concluded that salivary contamination adversely affected the quality of the bonds studied and decontamination using phosphoric acid gel resulted in significantly reduced shear bond strengths.

Shear bond of resin cement to post-cured hybrid composites.

Various surface treatments affected the shear bond strength of a dual-cured resin cement to a post-cured composite. Disks of post-cured composite inlay 2.0 mm thick by 10.0 mm in diameter, were mounted in acrylic cylinders. Various surface treatments were tested including: 1) smooth material; 2) treated by sandblasting (air abrasion); 3) sandblasting and etching with hydrofluoric acid (HF); 4) sandblasting and silane priming; 5) sandblasting, HF etching and silane priming; 6) HF etching alone; 7) HF etching and silane priming; and 8) silane priming alone. Specimens of dual-cured cement, 4.0 mm in diameter, were light-cured onto the prepared surfaces. The samples were stored in water at 37 degrees C for 7d before shear bond testing. The highest mean shear bond strengths were achieved for specimens with the following surface treatments: 1) by a combination of sandblasting, HF etching and silane priming; 2) sandblasting and HF etching; and 3) sandblasting and silane priming. Most bond failures in these groups were cohesive within the post-cured composite inlay disks. The bond strengths of the specimen in other groups were significantly lower and bond failures were mainly adhesive at the interface between the disk of post-cured composite and dual-cured resin cement.

Mouthguards: an easy-to-fabricate element of practice preventive programmes.

Mouthguards reduce the prevalence of dental injuries in contact sports. All types are effective, but those which are closely adapted to the teeth are the best retained, most comfortable, and therefore best accepted by sports people. Closely fitting mouthguards can be directly adapted in the mouth or laboratory-made on a stone model of the dental arch. The mouth-formed types can be fitted without professional supervision, but the procedure is often more successful if undertaken or supervised by a dental professional. The mouth forming procedure is quick and involves little material cost compared to the laboratory-made type. These savings can be passed on to patients in the form of lower fees which should encourage the widespread acceptance of mouthguards as a cost-effective preventive measure. Professionally fitted laboratory-made mouthguards are particularly suitable for high risk activities such as boxing, where more specialised protection such as a bimaxillary guard is indicated.

Singapore dentists' knowledge, advocacy and utilisation of mouthguards.

A questionnaire was distributed to Singapore Registered Dental Practitioners, seeking demographic details, knowledge of mouthguards in preventing dental injury during contact sport, current attitudes to advice and provision to at-risk patients. 636 questionnaires were posted and 226 valid replies were received. Most dentists believed that mouthguards reduced the prevalence of dental injury in contact sports. Undergraduate education was the primary source of dentists' knowledge. Seventy-four per cent of respondents actively recommended mouthguards, but only 26 per cent made one or more in 1992. Only 3 dentists made more than 10. Twenty-eight per cent were comfortable with their knowledge in this area, and 76 per cent would be willing to assist a public awareness campaign.

Impact fracture characteristics of intact and crowned human central incisors.

Dynamic fracture energies and patterns of fracture in extracted human central incisors were determined for groups of intact controls, groups with Vita Dur N crowns, Vita Hi Ceram crowns, Dicor crowns and porcelain veneers. Teeth were struck on their middle labial surfaces by a pendulum impact device. The mean fracture energy for teeth with Dicor crowns was significantly lower than for all other groups (P < 0.05). Control tooth crowns fractured obliquely in an apical-direction. Vita Dur N and Dicor crowns shattered, the underlying tooth usually fracturing in the plane of the impact force. Vita Hi Ceram crowns chipped at the site of impact and some fractures were located in the roots. Gold crowns remained cemented and fracture occurred at the crown/root junction, or in the root. Porcelain veneers fractured at the site of impact but remained cemented. Dicor crowns were less fracture resistant than other restoration types tested. Porcelain veneers and full gold crowns stiffened teeth which led to more root fractures than the porcelain crowns.

Evaluation of a 10 percent carbamide peroxide gel vital bleaching agent.

A clinical study determined the whitening effect of a 10 percent carbamide peroxide gel on the teeth of 10 subjects. Histological evaluation of the effect of this agent on human tooth pulps and hamster cheek pouch tissues was also undertaken. The gel provided a modest, but unpredictable, whitening of discoloured teeth. A localised mild to moderate inflammatory response was found in some of the pulps of teeth that had been bleached. No soft-tissue changes were observed in the hamster cheek pouches.

Effect of peroxide bleaches on resin-enamel bonds.

Human third molar teeth were divided into three groups: untreated control; enamel treated with 35% hydrogen peroxide for 2 hours; and enamel treated with 10% carbamide peroxide gel for 14 days. All teeth were ground to present a flat enamel surface, to which cylinders of light-cured composite resin were bonded. Shear bond strengths were determined for each specimen. The mean shear bond strengths of resin-enamel bonds after pretreatment with both 35% hydrogen peroxide and 10% carbamide peroxide were significantly lower than those for untreated controls. External bleaching with these materials prior to resin bonding procedures may reduce the quality of resin-enamel bonds.

Lay and professional knowledge of methods for emergency management of avulsed teeth.

Proper treatment during the first 30 minutes offers the best prognosis for traumatically avulsed teeth. This study sought to determine both lay people's and dental professionals' knowledge of and attitude to emergency procedures. A 12-question survey was administered to 5 groups: (a) parents of learner swimmers and (b) coaches of college sports teams (lay); (c) State Dental Nurses, (d) dentists and (e) dental nurse/receptionists (professional). Respondents totalled 184 (a 32, b 86, c 24, d 18, e 24) i.e. 118 lay and 66 professional. Data revealed that group b had the greatest personal experience of avulsed teeth and groups c and e the least. Public hospital accident and emergency services (A & E) were perceived by all groups as most available. 18% of lay groups could not cite an emergency service. Lay people thought first of A & E for management whereas profession groups preferred the victim's own dentist. Most professional people would replant avulsed permanent teeth and about 1/3 would replant deciduous teeth: 1/2 lay people would replant permanent teeth and 1/8 deciduous teeth. Where treatment was not straightforward lay people would seek advice before acting. Half of the lay groups would transport an avulsed tooth dry. All the professionals had had advice on management of avulsed teeth but only 1/4 of the lay groups. This study highlighted the need for educational campaigns aimed at members of the lay public likely to be involved in the emergency management of traumatically avulsed teeth.

Effectiveness of sterilisation and disinfection procedures for dental amalgam carriers.

The potential for cross infection through dental amalgam carriers was investigated in 37 Dunedin dental practices and in the University of Otago School of Dentistry. Eighteen practitioners had autoclavable carriers, but only 2 autoclaved them at least daily. The School of Dentistry disinfected plastic carriers and autoclaved metal carriers. Microbiological examination, by culturing from the most commonly contaminated carrier site, showed that the School of Dentistry method for disinfection of plastic carriers was unreliable. Autoclaving was confirmed as the preferred method of sterilisation, but many existing carriers are not suited to this technique.

Influence of cavosurface configuration and composite resin type on impact fracture resistance of Class IV restorations.

The fracture behaviours of intact maxillary central incisor teeth, and teeth restored by five different composite resins utilising uninstrumented fractured etched margins and bevelled etched margins, were determined by a pendulum impact method. It was established that: 1. Intact teeth fractured in a predictable manner when struck by a pendulum hammer at predetermined points on the labial surfaces close to incisal angles. 2. The impact resistance of teeth with bevelled margin restorations was significantly greater than that of teeth restored using the uninstrumented fractured margins. 3. Differences in impact resistance between intact teeth and teeth restored with bevelled margins were not significant. 4. There was no significant difference in fracture energy between any of the composite resin materials in either the uninstrumented joint or bevelled joint modes. 5. For all restorations placed on uninstrumented margins, the fracture paths were at or near the adhesive interface; no restorations failed cohesively. 6. Fracture paths in the bevelled joint mode were variable, with fracture occurring either entirely in enamel, or entirely in composite resin, or at the interface.