Fabricating a chairside CAD-CAM radiographic and surgical guide for dental implants: A dental technique.

The conventional method of diagnosing and treatment planning an implant-supported restoration involves making a diagnostic alginate impression and fabricating a radiographic and surgical guide. The procedure described uses an intraoral scanner and milling unit to fabricate a chairside computer-aided design and computer-aided manufacturing radiographic and surgical guide for use with a cone beam computed tomography system.

Fracture strength of various titanium-based, CAD-CAM and PFM implant crowns.

OBJECTIVE: CAD-CAM has dramatically advanced dental restorative procedures to include implant-supported crowns. The purpose of this study was to compare the fracture resistance following mechanical loading and thermocycling of various screw-retained and cement-retained ceramic and polymethylmethacrylate material combinations using the TiBase abutment compared to PFM implant-supported crowns. OVERVIEW: Twelve implant restorations were fabricated for each of eight groups. Three groups were screw-retained and five groups were cement-retained implant restorations. The ceramic and polymethylmethacrylate restorations were fabricated on the TiBase abutment while the PFM restorations were fabricated on an UCLA abutment. Data were analyzed with a one way Analysis of Variance and Tukey's post-hoc test to evaluate the effect of abutment and crown type on fracture load (alpha = 0.05). A significant difference was found in the maximum fracture load between groups (P < 0.001). CONCLUSIONS: The screw-retained implant restorations demonstrated higher fracture loads than their cement-retained counterparts. The TiBase abutment compared favorably to the UCLA abutment. CLINICAL SIGNIFICANCE: The TiBase abutment is a titanium insert which combines the esthetics of a ceramic abutment with the mechanical properties of a titanium abutment and should be considered a viable clinical alternative to the conventional implant-supported PFM crown based on theses in vitro results and in context of in vivo studies. The lithium disilicate hybrid abutment/crown implant-supported restoration utilizing the TiBase abutment may be an ideal clinical choice due to simplicity, single appointment CAD-CAM, and esthetics.

Effect of Molar Preparation Axial Height on Retention of Adhesively-luted CAD-CAM Ceramic Crowns.

PURPOSE: To evaluate the effect of axial wall height (AWH) on failure resistance of CAD-CAM adhesively-bonded, all-ceramic crowns on molar preparations with a conservative total occlusal convergence (TOC). MATERIALS AND METHODS: 60 newly extracted maxillary third molars were divided into 5 groups (n = 12) and prepared for all-ceramic crowns with occlusal cervical AWH of 0, 1, 2, 3, and 4 mm, all containing a conservative 10-degree TOC. Scanned preparations were fitted with lithium-disilicate glass-ceramic crowns using a self-adhesive resin-composite luting agent after intaglio surface preparation with hydrofluoric acid and silane. Specimens were stored at 37°C/98% humidity for 24 h and tested to failure at a 45-degree angle applied to the palatal cusp on a universal testing machine. Mean results were analyzed using ANOVA and Tukey's test (p = 0.05). RESULTS: Preparations containing 2, 3, and 4 mm AWH demonstrated similar and higher failure resistance than the 0- and 1-mm axial wall height groups. CONCLUSIONS: Under the conditions of this study, evidence is presented that under certain conditions CAD-CAM adhesive technology may compensate for less than optimal AWH. Based on both failure load results and failure mode analysis, adhesively-luted maxillary molar CAD-CAM crowns based on a preparation containing 10-degree TOC require at least 2 mm AWH for adequate resistance and retention. However, adoption of these findings is cautioned until both fatigue analysis and appropriate clinical evidence has been provided.

Fracture resistance of all-ceramic crowns based on different preparation designs for restoring endodontically treated molars.

OBJECTIVES: To evaluate endodontically treated molar fracture resistance restored with CAD/CAM lithium disilicate (LDS) crowns with different amalgam core preparation design. MATERIALS AND METHODS: Eighty-four recently extracted mandibular third molars were divided into seven groups (n = 12) and embedded in autopolymerizing resin. Coronal tooth structure was removed, pulp chamber exposed, and pulpal remnants removed. One group received LDS endocrowns, while three groups received amalgam cores with 2, 1, and 0 dentin axial wall heights (AWH). Three additional groups were likewise restored using an amalgam adhesive. Scanned preparations were restored with LDS crowns luted with a self-adhesive luting cement. After 24 hours, specimens were loaded to failure with results analyzed with Welch's Test/REGW Range Test at a 95% level of confidence (α = 0.05). RESULTS: The 1 mm-AWH amalgam core group had the highest failure load and was similar to the 2 mm-AWH amalgam, 2 mm-AWH bonded amalgam, and the 1 mm-AWH bonded amalgam core groups. The endocrowns had lower failure load than the 1 mm and 2 mm AWH amalgam groups but was similar to other groups. CONCLUSIONS: Adhesively luted LDS crowns with amalgam core preparations overall displayed similar failure load, as endocrown restorations. However, crowns based on amalgam cores demonstrated favorable failure modes. CLINICAL SIGNIFICANCE: The results of this in vitro test suggests that when suitable tooth structure and sufficient interact restorative space exists, endodontically treated molars restored with lithium disilicate complete crowns based on preparations with amalgam core foundations containing 1 mm and 2 mm of dentin axial wall height could serve as a suitable restorative option that may provide more recoverable failure modes than endocrown restorations.

Preparation Ferrule Design Effect on Endocrown Failure Resistance.

PURPOSE: To evaluate the effect of preparation ferrule inclusion with fracture resistance of mandibular molar endocrowns. MATERIALS AND METHODS: Recently extracted mandibular third molars were randomly divided into 3 groups (n = 12) with the coronal tooth structure removed perpendicular to the root long axis approximately 2 mm above the cemento-enamel junction with a slow-speed diamond saw. The pulp chamber was exposed using a diamond bur in a high-speed handpiece with pulpal remnants removed and canals instrumented using endodontic hand instruments. The chamber floor was restored using a resin core material with a two-step, self-etch adhesive and photopolymerized with a visible light-curing unit to create a 2 mm endocrown preparation pulp chamber extension. One and two millimeter ferrule height groups were prepared using a diamond bur in a high-speed handpiece following CAD/CAM guidelines. Completed preparation surface area was determined using a digital measuring microscope. Scanned preparations were restored with lithium disilicate restorations with a self-adhesive resin luting agent. All manufacturer recommendations were followed. Specimens were stored at 37°C/98% humidity and tested to failure after 24 hours at a 45° angle to the tooth long axis using a universal testing machine. Failure load was converted to MPa using the available bonding surface area with mean data analyzed using Kruskal-Wallis/Dunn (p = 0.05). RESULTS: Calculated failure stress found no difference in failure resistance among the three groups; however, failure load results identified that the endocrown preparations without ferrule had significantly lower fracture load resistance. Failure mode analysis identified that all preparations demonstrated a high number of catastrophic failures. CONCLUSIONS: Under the conditions of this study, ferrule-containing endocrown preparations demonstrated significantly greater failure loads than standard endocrown restorations; however, calculated failure stress based on available surface area for adhesive bonding found no difference between the groups. Lower instances of catastrophic failure were observed with the endocrown preparations containing 1 mm of preparation ferrule design; however, regardless of the presence of ferrule, this study found that all endocrown restorations suffered a high proportion of catastrophic failures but at loads greater than reported under normal masticatory function.

Effect of Premolar Axial Wall Height on Computer-Aided Design/Computer-Assisted Manufacture Crown Retention.

PURPOSE: To evaluate the effect of premolar axial wall height on the retention of adhesive, full-coverage, computer-aided design/computer-assisted manufacture (CAD/CAM) restorations. MATERIALS AND METHODS: A total of 48 premolar teeth randomized into four groups (n = 12 per group) received all-ceramic CAD/CAM restorations with axial wall heights (AWH) of 3, 2, 1, and 0 mm and 16-degree total occlusal convergence (TOC). Specimens were restored with lithium disilicate material and cemented with self-adhesive resin cement. Specimens were loaded to failure after 24 hours. RESULTS: The 3- and 2-mm AWH specimens demonstrated significantly greater failure load. Failure analysis suggests a 2-mm minimum AWH for premolars with a TOC of 16 degrees. CONCLUSION: Adhesive technology may compensate for compromised AWH.

Failure load effect of molar axial wall height with CAD/CAM ceramic crowns with moderate occlusal convergence.

OBJECTIVES: To evaluate the significance of axial wall height (AWH) in molar fracture resistance involving CAD/CAM adhesively bonded, all-ceramic full coverage restorations on preparations with moderate total occlusal convergence (TOC) (16°). MATERIALS AND METHODS: 60 newly extracted maxillary third molars were divided into 5 groups (n = 12). Specimens were prepared for full-coverage, all ceramic restorations with occlusal cervical AWHs of 4, 3, 2, 1 as well as a flat preparation (0 mm AWH) with all preparations with AWH containing a moderate 16° TOC. Scanned preparations were fitted with a lithium disilicate restoration with a self-adhesive resin luting agent after intaglio surface preparation with hydrofluoric acid and silanation. Specimens were stored at 37°C/98% humidity for 24 hours and tested to failure at a 45° angle applied to the palatal cusp on a universal testing machine. Mean results were analyzed using ANOVA/Tukey's (P = .05). RESULTS: Preparations containing 2, 3, and 4 millimeters of AWH demonstrated similar and higher resistance to fracture than the 1 and zero millimeter AWH groups. CONCLUSIONS: Under the conditions of this study, results suggest that adhesive CAD/CAM technology may compensate for reduced axial wall height. However, more definitive results depend on fatigue testing. CLINICAL SIGNIFICANCE: These in vitro results suggest that adhesive CAD/CAM technology may compensate for less than optimal AWH.

Bicuspid Axial Wall Height Effect on CAD/CAM Crown Fracture Mode on Preparations Containing Advanced Total Occlusal Convergence.

PURPOSE: To evaluate bicuspid axial wall height effect on the fracture mode of adhesively luted, all-ceramic CAD/CAM crowns with a 20° total occlusal convergence (TOC). MATERIALS AND METHODS: Recently extracted premolars were randomly divided into 4 groups (n = 12) with all-ceramic crown preparations accomplished using a high-speed handpiece inserted into a milling device. Specimens were prepared containing occlusogingival axial wall heights of 3, 2, and 1 mm as well as a group containing a flat preparation surface with no axial wall height. All preparations contained a 20° TOC. Completed preparation surface area was determined, and preparation features confirmed using a digital measuring microscope. Scanned preparations (CEREC) were fitted with milled and crystallized lithium disilicate full coverage restorations and luted with a self-etching adhesive resin cement after hydrofluoric acid etching and silanation. All manufacturer recommendations were followed. Specimens were stored at 37°C/98% humidity for 24 hours. Specimens were tested to failure at a 45° angle to the long axis of the tooth root on a universal testing machine. Failure load was converted to MPa using the available bonding surface area with mean data analyzed using Kruskal-Wallis/Dunn's (p = 0.05) RESULTS: The 3 mm preparation height specimens were similar to the 2 mm specimens, and both demonstrated significantly stronger failure load than the 1 mm axial wall height and flat preparation specimens. The flat preparation and 1 mm axial wall height specimens all failed adhesively, while the 2 mm and 3 mm specimens failed largely due to tooth fracture. CONCLUSIONS: Further evidence is provided that CAD/CAM adhesive techniques may compensate for less than ideal preparation features. Under the conditions of this study, bicuspid preparations with a 20° TOC restored with adhesively luted, CAD/CAM e.max CAD crowns require at least 2 mm of axial wall height, but further planned fatigue studies are necessary before definitive recommendations can be made.

'From Defensive Paranoia to Openness to Outside Scrutiny': Prison Medical Officers in England and Wales, 1979-86.

This article examines how a branch of medicine based within the criminal justice system responded to a society which by the 1970s and 1980s was increasingly critical of the prison system and medical authority. The Prison Medical Service, responsible for the health care of prisoners in England and Wales, was criticised by prison campaigners and doctors alike for being unethical, isolated, secretive, and beholden to the interests of the Home Office rather than those of their patients. While prison doctors responded defensively to criticisms in the 1970s and 1980s, comparing their own standards of practice favourably with those found in the NHS, and arguing that doctors from outside would struggle to cope in the prison environment, by 1985 their attitudes had changed. Giving evidence to a House of Commons committee, prison doctors displayed a much greater willingness to discuss how the prison system made their work more difficult, and expressed a pronounced desire to engage openly with the rest of the profession to address these problems. The change of attitude partly reflects a desire by the Home Secretary William Whitelaw to make the Prison Service more open, and an acceptance of a need for greater accountability in medicine generally. Most important, however, was a greater interest in prison health care and appreciation of the difficulties of prison practice among the wider medical profession, encouraging prison doctors to speak out. This provides a case study of how a professional group could engage openly with criticisms of their work under favourable circumstances.

Selected physical properties of new resin-modified glass ionomer luting cements.

STATEMENT OF PROBLEM: Two resin-modified glass ionomer (RMGI)-based luting agents have been recently marketed without independent reports of their physical properties. PURPOSE: The purpose of this in vitro study was to evaluate selected physical properties of 2 newly marketed RMGI luting agents and compare the findings with traditional materials. MATERIAL AND METHODS: Specimens (N=12) of Nexus RMGI, UltraCem, GC Fuji Cem 2, and RelyX Luting Plus were fabricated using standardized molds for flexural strength and fracture toughness according to manufacturer recommendations and stored in physiologic phosphate-buffered saline solution at 37°C until testing. Specimens were tested at 1 and 24 hours, 1 week, and 1 month. Mean values for flexural strength, flexural modulus, flexural toughness, and fracture toughness were determined. Additionally, film thickness (N=12) for each material was determined following Amerian National Standards Association/American Dental Association (ANSI/ADA) specifications. Mean results were analyzed with Kruskal-Wallis and Mann-Whitney U tests (α=.05). RESULTS: All luting agents exhibited a similar film thickness that met ANSI/ADA requirements for aqueous-based luting agents. Nexus RMGI surprisingly demonstrated significantly greater flexural strength and fracture toughness at 1 hour, which decreased significantly at 24 hours, making it similar to the other materials evaluated. All materials had similar flexural strength values at 7 days. CONCLUSIONS: Physical property performance was material dependent. Nexus RMGI demonstrated greater early physical properties that were significantly less at 24 hours. UltraCem, GC Fuji Cem 2, and RelyX Luting Plus demonstrated the increasing physical property development that is normally associated with polyalkenoate-based systems.

'If experts differ, what are we to do in the matter?' The Medico-legal Investigation of Gunshot Wounds in a 1927 Scottish Murder Trial.

This article uses a notorious criminal trial, that of John Donald Merrett for the murder of his mother, as a case study to explore forensic medicine's treatment of gunshot wounding in pre-war Scotland. This topic, which has hitherto received little attention from historians, provides insight into two issues facing the discipline at this time. First, the competing attempts by prosecution and defence expert witnesses to recreate the wound in a laboratory setting, in order to determine the distance from which the shot had been fired, exposed the uncertainties surrounding the application of a well-known laboratory technique for which no fully agreed-upon protocol existed. Secondly, the case allows the examination of the working relationship of a medical expert and a gunsmith, in which disciplinary boundaries became indistinct and the wound a shared site of analysis, in a period before the separate profession of forensic science became institutionally grounded in Scotland.

The comparative efficacy of 0.12% chlorhexidine and amoxicillin to reduce the incidence and magnitude of bacteremia during third molar extractions: a prospective, blind, randomized clinical trial.

OBJECTIVE: The purpose of this study was to directly compare the incidence and magnitude of bacteremia of a 0.12% chlorhexidine pre-procedure rinse to the AHA and the ADA/AAOS recommended 2 g amoxicillin antibiotic prophylaxis during third molar extractions. STUDY DESIGN: This study was a randomized, blind, placebo-controlled prospective clinical trial involving subjects assigned to a placebo, rinse, or antibiotic group. The incidence and magnitude of bacteremia were analyzed via χ(2) and Kruskal-Wallis/Friedman tests, respectively. RESULTS: There was no statistically significant difference in the incidence and magnitude of bacteremia between the three groups. However, the placebo group apparently resulted in the largest range and highest mean magnitude of bacteremia, followed by the rinse then the antibiotic group. CONCLUSIONS: The results of this novel study may reasonably conclude an oral rinse or systemic antibiotic antimicrobial intervention does not statistically reduce the incidence and magnitude of bacteremia compared to no antimicrobial intervention.

Application of the functionally generated path technique to restore mandibular molars in bilateral group function occlusion.

The functionally generated path (FGP) is a static representation of the opposing cusps' dynamic eccentric movements from a centric position to achieve optimal articulation and occlusal harmony. When understood and appreciated, use of the FGP technique is a straightforward and practical method to achieve harmonious occlusal anatomy of restorations with the anterior determinant/anterior guidance, the posterior determinant/condylar guidance, existing occlusal and cuspal anatomy, and the neuromuscular system. Although the FGP technique is normally used in the fabrication of maxillary posterior indirect restorations, it is described and applied here in the fabrication of mandibular posterior restorations that maintained the patient's bilateral group function occlusion while eliminating the nonworking side and protrusive interferences. This novel procedure involved the use of a stone crib to intraorally construct a stone core that captured the FGP recording while simultaneously indexing to the contralateral and ipsilateral mandibular dentition. This technique lends additional stability to the stone core to minimize error during the mounting process.