Roger J. Smales

Identifying and Reducing Risks for Potential Fractures in Endodontically Treated Teeth

INTRODUCTION Although long-term functional survival rates can be high for initial endodontically treated permanent teeth, they are generally more susceptible to fracture than teeth with vital pulps. Tooth extraction is often the consequence of an unfavorable prognosis after coronal and root fractures, but their occurrence in endodontically treated teeth might be reduced by identifying the risks for fracture associated with various operative procedures. METHODS This article presents an overview of the risk factors for potential tooth fractures in endodontically treated teeth on the basis of literature retrieved from PubMed and selected journal searches. RESULTS Postendodontic tooth fractures might occur because of the loss of tooth structure and induced stresses caused by endodontic and restorative procedures such as access cavity preparation, instrumentation and irrigation of the root canal, obturation of the instrumented root canal, post-space preparation, post selection, and coronal restoration and from inappropriate selection of tooth abutments for prostheses. CONCLUSIONS Potential tooth fractures might be reduced by practitioners being aware during dental treatments of controllable and noncontrollable risks.

Micro-tensile bond strengths to sclerotic dentin using a self-etching and a total-etching technique

OBJECTIVES To evaluate the in vitro regional micro-tensile bond strengths of a self-etching/self-priming adhesive system to sclerotic dentin, in the absence or presence of phosphoric acid conditioning. METHODS Naturally-occurring, non-carious cervical lesions on extracted premolars were hand-cleaned with a slurry of pumice and chlorhexidine, then bonded without further cavity preparation. One group was bonded using Clearfil Liner Bond 2V (Kuraray Co. Ltd., Osaka, Japan). The other group was first conditioned with K-etchant; 40% phosphoric acid gel (Kuraray) prior to the application of the self-etching primer. Artificially prepared wedge-shaped cavities were also made in sound premolars and bonded with the two methods as controls. Resin composite build-ups were made using Clearfil Protect Liner F and AP-X resin composite (Kuraray). After storage in water for 24h, the teeth were sectioned into 0.7 x 0.7 mm composite-dentin beams along the occlusal and gingival walls, and at the apex of the lesions. The use of two conditioning methods, two substrate types, and three different locations yielded 10-14 beams for each of the 12 groups. After testing for the microTBS, representative beams that were stressed to failure were examined with SEM. Remaining fractured beams were demineralized and processed for TEM examination. Statistical analysis was performed using a three-way ANOVA and Student-Newman-Keuls tests. RESULTS Regardless of the conditioning methods, bond strengths to sound dentin were significantly higher than to sclerotic dentin (P< 0.05). With sclerotic dentin, there was no significant difference for the conditioning methods used, except that K-etchant significantly improved the bond strength at the gingival aspect of the lesions. Fractographic analysis revealed that the self-etching primer could not etch beyond the surface hypermineralized layer of sclerotic dentin. Interfacial failure occurred along the surface of the mineralized intermicrobial matrix and/or hypermineralized layer. With the use of phosphoric acid, a hybrid layer was only seen when the surface layers were thin. Incompletely removed sclerotic casts were evident in both groups. SIGNIFICANCE Removal of the surface layers of sclerotic dentin and/or conditioning with stronger acids may be beneficial to obtain stronger bonding to sclerotic dentin.

Partial denture failures: A long-term clinical survey

Abstract An assessment of 150 partial dentures which had been worn from 1966 onwards by 64 patients, revealed that 65 per cent had been replaced or could not be worn. Several dentures had been replaced four or more times. Posterior free-end saddle dentures were often not worn, and there was obvious evidence of oral tissue damage when partial dentures were worn. Failures were especially high with acrylic resin partials, and stress-breaker cobalt-chromium frame designs, whereas maxillary plate designs had the lowest failures. However, few partial dentures survived for more than 5–6 years. There is a need for more stringent selection of patients for partial dentures, to whom the biological consequences must be fully explained.

Gastroesophageal Reflux Disease and Tooth Erosion

The increasing prevalence of gastroesophageal reflux disease (GERD) in children and adults, and of “silent refluxers” in particular, increases the responsibility of dentists to be alert to this potentially severe condition when observing unexplained instances of tooth erosion. Although gastroesophageal reflux is a normal physiologic occurrence, excessive gastric and duodenal regurgitation combined with a decrease in normal protective mechanisms, including an adequate production of saliva, may result in many esophageal and extraesophageal adverse conditions. Sleep-related GERD is particularly insidious as the supine position enhances the proximal migration of gastric contents, and normal saliva production is much reduced. Gastric acid will displace saliva easily from tooth surfaces, and proteolytic pepsin will remove protective dental pellicle. Though increasing evidence of associations between GERD and tooth erosion has been shown in both animal and human studies, relatively few clinical studies have been carried out under controlled trial conditions. Suspicion of an endogenous source of acid being associated with observed tooth erosion requires medical referral and management of the patient as the primary method for its prevention and control.

Plaque growth on dental restorative materials

Assessments were made of plaque growth and retention on 6 restorative materials placed in denture teeth. Aspa retained the most plaque and also had the roughest surface. Isopast had the least plaque although its surface was slightly rougher than the amalgams. Leachable elements present in some of the materials did not result in any less plaque than on the other materials.

Evaluation of clinical methods for assessing restorations

I n recent years, there has been a large increase in the number of publications on clinical studies of restorative materials. Unfortunately, few of these publications have evaluated the reliability or sensitivity of the assessment methods used in such studies. Those studies that have made some evaluations suggest that the use of subjective, descriptive assessment methods in clinical research has significant limitations.1-8 In the present study, several clinical assessment methods were compared to evaluate their ability to discriminate between varying degrees of deterioration of restorations. MATERIAL AND METHODS Clinical assessments were made of selected characteristics of Concise (3M Co., St. Paul, Minn.), a BIS-GMA composite resin, and New True Dentalloy (S. S. White Dental Products International, Philadelphia, Pa.), a fine lathe-cut amalgam alloy. Fifty amalgam restorations (Class I) and 50 composite resin restorations (Classes III, IV, and V), aged up to 8 years, were examined by four methods. Method A was direct clinical observation of the restorations, using the subjective, descriptive criteria shown in Table I. The method was similar to that described by Ryge and others.‘-‘* In the present study, category 3 for the composite resins and category 2 for the amalgams corresponded approximately to category “Charlie” (replace for prevention) of the U.S. Public Health Service-Ryge system. Method B involved applying the same subjective criteria to 35 mm Ektachrome (Eastman Kodak Co., Rochester, N.Y.) color transparencies (magnification 1: 1) taken at the time of the examination.13 As nearly as possible, all photographs were taken at right angles to the occlusal, labial, and lingual restored tooth surfaces. The transparencies were examined without image enlargement using an x-ray viewer.

Oral manifestations of gastroesophageal reflux disease

Numerous case‐control and other studies involving confirmation of gastroesophageal reflux disease (GERD) by esophageal pH‐metry and the assessment of dental erosions have shown significant associations between the two conditions in both adults and children. By contrast, when asked to vote on whether GERD may cause dental erosions, only 42% of physicians strongly agreed that such an association existed in adults, and just 12.5% strongly agreed for children, respectively in two global consensus reports. Part of this divergence between the perceptions of physicians and the findings of research publications may reflect a general lack of oral health education during medical training, and cursory oral examinations being made under less‐than‐ideal conditions. Adequate salivary secretions are essential for the protection of the teeth and the oropharyngeal and esophageal mucosa. The quantity and quality of the saliva require monitoring as many drugs, including several of the proton pump inhibitors (PPIs), can cause hyposalivation. In addition, PPIs do not always result in adequate acid suppression. Therefore, collaboration between physicians and dentists is strongly advocated to prevent or ameliorate possible adverse oral effects from both endogenous and exogenous acids, and to promote adequate saliva production in patients with GERD.

Corrosion behaviour and surface analysis of a Co–Cr and two Ni–Cr dental alloys before and after simulated porcelain firing

This study evaluated the corrosion behaviour and surface properties of a commercial cobalt-chromium (Co-Cr) alloy and two nickel-chromium (Ni-Cr) alloys [beryllium (Be)-free and Be-containing] before and after a simulated porcelain-firing process. Before porcelain firing, the microstructure, surface composition and hardness, electrochemical corrosion properties, and metal-ion release of as-cast alloy specimens were examined. After firing, similar alloy specimens were examined for the same properties. In both as-cast and fired conditions, the Co-Cr alloy (Wirobond C) showed significantly more resistance to corrosion than the two Ni-Cr alloys. After firing, the corrosion rate of the Be-free Ni-Cr alloy (Stellite N9) increased significantly, which corresponded to a reduction in the levels of Cr, molybdenum (Mo), and Ni in the surface oxides and to a reduction in the thickness of the surface oxide film. The corrosion properties of the Co-Cr alloy and the Be-containing Ni-Cr alloy (ChangPing) were not significantly affected by the firing process. Porcelain firing also changed the microstructure and microhardness values of the alloys, and there were increases in the release of Co and Ni ions, especially for Ni from the Be-free Ni-Cr alloy. Thus, the corrosion rate of the Be-free Ni-Cr alloy increased significantly after porcelain firing, whereas the firing process had little effect on the corrosion susceptibility of the Co-Cr alloy and the Be-containing Ni-Cr alloy.

Comparative evaluation of micro-implant and headgear anchorage used with a pre-adjusted appliance system

The aim of this study was to compare and evaluate the anchorage effectiveness of using either micro-implants or extraoral headgear with the McLaughlin-Bennett-Trevisi (MBT) system. Thirty young Chinese adults (14 males and 16 females) aged 18-22 years with anterior bimaxillary protrusion were divided randomly into two equal groups, treated with the MBT system anchored by either micro-implants or headgear. Nine measurements obtained before and after treatment from lateral cephalometric radiographs were assessed for the two groups, using the Mann-Whitney U test with alpha = 0.05 for statistical significance. The maxillary incisors in the micro-implant group were significantly more retracted and intruded, while the lower incisors were more lingually inclined, than in the headgear group. The occlusal and mandibular planes were rotated more counterclockwise in the micro-implant group than in the headgear group (P < 0.05). Compared with headgear anchorage, micro-implant anchorage may counteract clockwise rotation of the occlusal and mandibular planes and result in different final positions for the maxillary and mandibular incisors.

Clinical evaluation of four anterior composite resins over five years

Four hundred and thirty nine chemical-cured composite resin restorations were placed in the anterior teeth of 86 patients treated in a private dental practice. Four anterior resins were used, and placement was performed with acid etching and appropriate enamel bonding resins. Assessments were made of the handling characteristics, condition of the gingiva, surface staining, marginal staining, color deterioration, and of the longevity of the four materials. Clinical deterioration rates and failures of the different types of composites were evaluated over periods of up to five years. Although all the assessed clinical factors deteriorated with time, there were very few unsatisfactory rating scores. Most of the composite restorations performed well over the study. Eight per cent of the restorations failed during the study. Class IV preparations showed the highest restoration failure rates.