Shane N. White

Outcomes of root canal treatment and restoration, implant-supported single crowns, fixed partial dentures, and extraction without replacement: a systematic review

STATEMENT OF PROBLEM Dentists and patients are regularly confronted by a difficult treatment question: should a tooth be saved through root canal treatment and restoration (RCT), be extracted without any tooth replacement, be replaced with a fixed partial denture (FPD) or an implant-supported single crown (ISC)? PURPOSE The purpose of this systematic review was to compare the outcomes, benefits, and harms of endodontic care and restoration compared to extraction and placement of ISCs, FPDs, or extraction without tooth replacement. MATERIAL AND METHODS Searches performed in MEDLINE, Cochrane, and EMBASE databases were enriched by hand searches, citation mining, and expert recommendation. Evidence tables were developed following quality and inclusion criteria assessment. Pooled and weighted mean success and survival rates, with associated confidence intervals, were calculated for single implant crowns, fixed partial dentures, and initial nonsurgical root canal treatments. Data related to extraction without tooth replacement and psychosocial outcomes were evaluated by a narrative review due to literature limitations. RESULTS The 143 selected studies varied considerably in design, success definition, assessment methods, operator type, and sample size. Direct comparison of treatment types was extremely rare. Limited psychosocial data revealed the traumatic effect of loss of visible teeth. Economic data were largely absent. Success rates for ISCs were higher than for RCTs and FPDs, respectively; however, success criteria differed greatly among treatment types, rendering direct comparison of success rates futile. Long-term survival rates for ISCs and RCTs were similar and superior to those for FPDs. CONCLUSIONS Lack of comparative studies with similar outcomes criteria with comparable time intervals limited comparison of these treatments. ISC and RCT treatments resulted in superior long-term survival, compared to FPDs. Limited data suggested that extraction without replacement resulted in inferior psychosocial outcomes compared to alternatives. Long-term, prospective clinical trials with large sample sizes and clearly defined outcomes criteria are needed.

Mechanical properties of dental luting cements

STATEMENT OF PROBLEM Dental luting cements fail by microcrack formation and bacterial ingress or by gross failure and crown dislodgment. Both of these failure modes are related to mechanical properties and deformation. PURPOSE This study evaluated those mechanical properties of cements. METHODS AND MATERIAL. Elastic modulus for 8 representative cements (zinc phosphate, polycarboxylate, glass ionomer, encapsulated glass ionomer, resin-modified glass ionomer, resin composite, and adhesive resin composite) was measured by using a nondestructive technique and evaluated for cement type and storage time (1 hour, 1 day, 1 week, 1 month, 1 year) by 2-way ANOVA (P <.05). Compressive properties (proportional limit, resilience, and toughness), ultimate strengths (compressive, diametral tensile, and flexural), and flexural toughness were determined and evaluated by 2-way ANOVA for 2 crosshead testing rates (5 and 0.5 mm/min) and cement type (P <.05). RESULTS Cements varied with respect to elastic moduli, compressive proportional limit, compressive resilience, compressive strength, compressive toughness, diametral tensile strength, flexural strength, and flexural toughness. Storage time affected the elastic moduli of different materials in different ways. Elastic moduli of polycarboxylate and glass ionomer cements increased over time, whereas the other materials changed little after the first day. Crosshead rate only significantly affected compressive proportional limit and resilience. CONCLUSIONS Luting cements differed considerably with respect to mechanical properties.

Biological Organization of Hydroxyapatite Crystallites into a Fibrous Continuum Toughens and Controls Anisotropy in Human Enamel

Enamel forms the outer surface of teeth, which are of complex shape and are loaded in a multitude of ways during function. Enamel has previously been assumed to be formed from discrete rods and to be markedly aniostropic, but marked anisotropy might be expected to lead to frequent fracture. Since frequent fracture is not observed, we measured enamel organization using histology, imaging, and fracture mechanics modalities, and compared enamel with crystalline hydroxyapatite (Hap), its major component. Enamel was approximately three times tougher than geologic Hap, demonstrating the critical importance of biological manufacturing. Only modest levels of enamel anisotropy were discerned; rather, our measurements suggest that enamel is a composite ceramic with the crystallites oriented in a complex three-dimensional continuum. Geologic apatite crystals are much harder than enamel, suggesting that inclusion of biological contaminants, such as protein, influences the properties of enamel. Based on our findings, we propose a new structural model.

Nano-mechanical properties profiles across dentin–enamel junction of human incisor teeth

Abstract Understanding how load is transferred from enamel to dentin and how the two tissues function as a single mechanical unit during mastication requires studies of micromechanics in relation to microstructure of the dentin–enamel junction (DEJ) zone. In this investigation, nano-hardness and elastic modulus of human incisor teeth were studied across the DEJ. It was found that, over a length scale of about 20 μm, there were decreasing trends in both hardness and elastic modulus across the DEJ zone profiling from enamel to dentin. Images obtained using atomic force microscopy from polished surfaces of cross-sectioned dental samples showed an interpenetrated microstructure of enamel and dentin at the DEJ zone. This result suggests that the nano-mechanical property profiles across the DEJ were due to a continuous variation in the ratios of relative amount of enamel and dentin. These characteristics of the DEJ zone could be significant for describing the structural and mechanical coupling of the two tissues. By increasing the contact area across the interface between the two hard tissues the stresses are dissipated reducing interfacial stress concentrations at the DEJ, thereby promoting effective load transfer from the hard (brittle) enamel to soft (tough) dentin.

Survival of In-Ceram crowns in a private practice: A prospective clinical trial

STATEMENT OF PROBLEM Prior reports on some all-ceramic crown systems have indicated high failure rates through fracture. PURPOSE This study prospectively evaluated the survival of infiltrated alumina crowns (In-Ceram) in a private practice. MATERIAL AND METHODS All the In-Ceram crowns placed in a prosthodontic practice since its introduction in 1990 were serially included. Patients were recalled at 6 monthly intervals. Those who did not attend in the previous 6 months were contacted by telephone and a series of answers to standardized questions recorded. The few patients who were lost to follow-up or who died were removed from the study from the time of last contact. RESULTS A total of 408 crowns in 107 patients were followed for periods from 1 to 86 months. As the 3-year data combined a meaningful period of service with a large sample size, these data were focused on. The 3-year survival rate was 96% for a sample size of 223. Three-year data indicated that core fracture and porcelain fracture occurred at rates of approximately 0.6% and 0.3% per year, respectively. Otherwise sound restorations were removed at a rate of approximately 0.3% per year for esthetic, endodontic, or prosthetic reasons. Anterior crowns tended to have a slightly higher 3-year survival rate (98%) than premolars or molars (94%). CONCLUSION Clinical failure rate of In-Ceram crowns was low. Crowns were lost because of core fracture, porcelain fracture, and removal without failure. Failure tended to be more common for molar and premolar crowns than for anterior crowns.

Microleakage of new crown and fixed partial denture luting agents

This study measured the in vitro microleakage of conventional and new FPD luting agents. Standardized preparations were made on 42 freshly extracted premolars. Facial and lingual chamfer margins were placed in enamel, mesial and distal in dentin and cementum, and castings were made in Rexillium III alloy and were then cemented with a standardized technique. Six groups of seven samples were tested, (1) polycarboxylate, (2) zinc phosphate, (3) glass ionomer, (4) Den-Mat Thin Film cement, (5) Panavia Ex, and (6) Den-Mat Thin Film cement with Tenure. The ranking of groups for stain ingress was from the greatest (1) to the least (6). A one-way analysis of variance and Tukey-Student range analysis revealed significantly similar groups, p less than 0.05:(1,2,3,4) (5,6).

Effect of cantilever length on stress transfer by implant-supported prostheses

Cantilever lengths for fixed implant supported prostheses have been based largely on empirical judgment. This study determined the effects of cantilever length on load transfer to the mandible. A photoelastic model of a moderately resorbed edentulous human mandible with five 13 mm Bränemark implants was constructed. Simulated occlusal loads at varying cantilever lengths were applied to the occlusal surface of a routinely fabricated fixed prosthesis. The highest stresses were located at the ridge crest on the distal surface of the distal implant for all cantilever lengths. Apical stresses at this implant developed in reciprocation to the effect of the distal tipping force on the cantilever. Curves describing the effect of cantilever length on maximal stress are presented. Little load transfer to adjacent implants was found. Disproportionate increases in maximum stress with increasing cantilever length occurred. Minor variations in implant angulation had a distinct effect on stress magnitude.

Customization of milled zirconia copings for all-ceramic crowns: A clinical report

Generically milled zirconia copings for all-ceramic crowns may not provide optimal thickness and form for the coping or the porcelain veneer. This article describes the customization of milled zirconia copings to provide even and controlled porcelain thickness with the aim of decreasing cohesive porcelain fracture and other failures. A full-contour waxing and cut back in conjunction with a dual-scan technique was used to ensure adequate coping thickness, adequate, even porcelain thickness, and butt joints at the porcelain-to-coping junctions.

Prevalence of Periapical Radiolucency and Root Canal Treatment: A Systematic Review of Cross-sectional Studies

INTRODUCTION Cross-sectional studies describe the health status of a population and measure the prevalence of disease or treatment. Neither the prevalence of periapical radiolucency, a surrogate for disease, nor the prevalence of root canal treatment have been subjected to a systematic review, which is the highest level of clinical evidence. The purpose of this study was to conduct a systematic review and meta-analysis of the prevalence of periapical radiolucency and nonsurgical root canal treatment. METHODS Inclusion/exclusion criteria were used for defined searches in MEDLINE and EMBASE. Title lists were scanned and abstracts were read to determine utility. Articles meeting the inclusion/exclusion criteria were analyzed for heterogeneity. Weighted mean percentages were calculated for the prevalence of overall periapical radiolucency, root canal treatment, and apical radiolucency in both treated and untreated teeth. RESULTS Defined searching produced 11,491 titles. Thirty-three articles were included. Most patient samples represented modern populations from countries with high or very high human development indices. Meta-analysis was performed on 300,861 teeth. Of these, 5% had periapical radiolucencies, and 10% were endodontically treated. Of the 28,881 endodontically treated teeth, 36% had periapical radiolucencies; however, cross-sectional studies cannot distinguish between healing and failing cases. Of the 271,980 untreated teeth, 2% had periapical radiolucencies. The technical quality of root canal treatment was decried by most authors of the included studies. CONCLUSIONS The prevalence of periapical radiolucency was very high, broadly equivalent to 1 radiolucency per patient. The prevalence of teeth with root canal treatment was very high, broadly equivalent to 2 treatments per patient. Billions of teeth are retained through root canal treatment.

In vivo microleakage of luting cements for cast crowns

Standardized tooth preparations were completed on previously intact human molars in vivo, and castings were made with a precious metal ceramic alloy by conventional techniques. The castings were randomly assigned to the following luting agents: zinc phosphate, composite resin-glass ionomer hybrid, and a composite resin-glass ionomer hybrid with a dentinal bonding agent and were cemented in a standardized manner to periodontally compromised molars. After 6 months the teeth were carefully extracted, stained, embedded, and sectioned, and the in vivo microleakage was measured. ANOVA disclosed significant differences between groups, and a multiple comparisons test revealed that the zinc phosphate group leaked significantly more than other cement groups.