Charles F. Cox

Evaluation of wear: Enamel opposing three ceramic materials and a gold alloy

STATEMENT OF PROBLEM The wear of human enamel and of the restorative material is often a critical concern when selecting a restorative material for any given clinical restorative treatment. PURPOSE This in vitro wear investigation evaluated three ceramic restorative materials and one type III gold (the control) opposing enamel. MATERIAL AND METHODS The area of enamel lost at specified time intervals, the stylus area lost, and the combined stylus and enamel vertical height lost were evaluated. RESULTS Enamel wear opposing one type III gold was statistically similar to that of Dicor MGC, which was lower than that of Vita Mark II and IPS Empress, which were also statistically similar in value. CONCLUSIONS The total vertical height lost from the type III gold specimens and opposing enamel was statistically lower than that of Dicor MGC and IPS Empress (alpha < 0.05).

THE WALKING BLEACH PROCEDURE: AN IN VITRO STUDY TO MEASURE MICROLEAKAGE OF FIVE TEMPORARY SEALING AGENTS

The purpose of this study was to compare the in vitro sealing capacity of five materials, each used as a temporary sealing agent for the walking bleach technique. All teeth received traditional biomechanical root canal instrumentation, after which the walking bleach agent was placed in the pulp chamber space. The occlusal access was sealed with one of five temporary materials: two hydraulic filling materials, a photoactivated resin composite, a zinc oxide-eugenol cement, and a zinc oxide phosphate cement with/without the placement of a piece of rubber sheet that was placed as a barrier to isolate filling material from the bleaching agent. All teeth were stored in a 1% solution of Alcian blue with thermal cycling stress. After 1 wk, they were sectioned longitudinally, and ranked by graded scores of 0 to 3, according to the degree of the dye penetration. Significantly less dye microleakage was observed in the two hydraulic materials than in the photoactivated resin. Both zinc oxide-eugenol and zinc phosphate cements showed a considerable amount of microleakage. There were no significant differences between the groups with and without a rubber sheet. Our data demonstrate that hydraulic filling materials provide the most favorable cavosurface seal when they are firmly packed into the cavity space to prevent microleakage.

Effect of Canal Drying Methods on the Apical Seal

The purpose of this study was to observe the seal obtained in human root canals under different in vitro treatment conditions. Root canals of freshly extracted human maxillary incisors received traditional biomechanical preparation and irrigation with 10% NaClO, followed by a final rinse of distilled water. Teeth were divided into four groups. In group 1, each root canal was dried with one paper point. In group 2, each root canal was dried with four paper points. Group 3 was dried with four paper points, followed by a gentle burst of warm air. Group 4 was dried using four paper points, followed by an internal 200 degrees C heat probe. Twenty canals in each group were filled with a gutta-percha cone and a zinc oxide-eugenol sealer, whereas 20 were filled with a glass ionomer sealer. All teeth were immediately immersed in India ink for 1 or 4 wk. The teeth were cleared, and the dye penetration-leakage measured with an accuracy of +/- 0.01 mm. Optimum sealing conditions were observed when the canal was dried with paper points and a 200 degrees C probe. There were no significant differences between 1 and 4 wk immersion. Glass ionomer sealer appeared more susceptible to the wet condition of the root canal walls than zinc oxide-eugenol sealer. An additional 40 teeth were prepared in the same manner as the dye penetration tests to observe the drying conditions of the root canal walls, and the moisture inside the canals was measured to an accuracy of 0.0001 g. The highest degree of internal canal wall dryness was found in group 4.

Human pulp response after partial pulpotomy with two calcium hydroxide products

Twenty human permanent teeth were used to study the pulpal response of two calcium hydroxide products, Dycal and Pulpdent Multi-Cal, after partial pulpotomy. Teeth were extracted at 4 months, fixed, and prepared for histologic examination. All 10 teeth treated with Dycal showed complete soft tissue healing and bridge formation. No stained bacteria were seen throughout the serial sections. One tooth treated with Dycal showed acceptable histologic results, dentin deposition in the root canal. Six cases dressed with Pulpdent Multi-Cal showed acceptable histologic results, whereas four teeth showed severe inflammation or necrosis associated with bacterial penetration into the pulp tissue. Clinically, one tooth treated with Pulpdent Multi-Cal showed pulpal pain and was extracted at 90 days. Our data support the thesis that human permanent pulps will promote tissue healing and dentin bridge formation as long as bacterial microleakage is excluded.

Nd:YAG laser irradiation of the human dental pulp: implications as a predictor of pulp hemodynamics.

The aim of study this was to evaluate in vivo the pulpal blood flow rate, pulpal responsiveness, systemic blood pressure, and pulse rate during Nd:YAG laser irradiation of an isolated tooth.

How histology enriched endodontics as a specialty & nurtured pulp biology: Our endodontic continuum from 1528 into the 1900’s – Part I

The 1980 Oral Science Monograph by L.J. Baume of Geneva is an erudite review, which recognized notables who elevated the respect of histology of dentine & pulp to scientific maturity [1]. Before 1500, “dental surgery” was basically tooth extraction until 1528 when Johannes Stocker recommended treating tooth pain with pulp cautery & filling some canals with copper. Microscopic observation began in 1675 when Anton van Leeuwenhoek (1632-1723) described transparent pipes from pieces of his wife’s tooth using his homemade microscope & compared tooth enamel & cementum to tree bark. In 1824, Edward Hudson (1762-1857) of Philadelphia cauterized the tooth pulp & plugged the canal with gold foil. In 1840, Robert Owen (1804-1892) received recognition by many colleagues for introducing the histologic term DENTINE into our dental lexicon. Histologic knowledge of normal & pathologic tooth tissues rapidly advanced with microscopic technologies of sectioning & staining. In 1879, professor Adolph Witzel’s (1847-1906) histological study described pulp inflammation & neo-dentine formations following vital pulp capping of human teeth treated with arsenious acid—he is recognized as the father of histological endodontics [2]. Grossman’s 1940 textbook advanced ENDODONTICS as a US clinical specialty by promoting DIFFERENTIAL DIAGNOSIS in patients who were suffering from pulpal or periapical pathology, which led to PROGNOSIS & TREATMENT based on a blend of clinical observations with knowledge of pulp histology. Histological advancements of tooth tissue rapidly advanced the knowledge of normal & pathological healing, which fostered ENDODONTICS & RESTORATIVE clinical specialties in the early 1900’s. Dr. Wm. Cotton personally backed the PULP BIOLOGY GROUP as a research specialty during the 1975 London IADR meeting. Endodontic tooth treatment rapidly progressed by using new technologies to assist the diagnosis & treatment of tooth infections. Correspondence to: Charles F. Cox, DMD, PhD, Department of Operative Dentistry, School of Dental Medicine, Tsurumi University, 2-1-3, Tsurumi, Tsurumi-ku, Yokohama 230-8501, Japan, Tel: (810)-275-8361; Fax: (810)636-4201, E-mail: cfcox@phoenixdental.com

A timeline of biological assessments: Our nonspatial continuum

Much of our dental history is recognized through oral tradition, which has led to myths and misconceptions regarding the efficacy of early restorative agents. Dental biomaterial history has tended to report only certain aspects research in a few textbooks that are expensive and not readily available to the larger dental audience. Our purpose is to provide a detailed peer-reviewed document, which provides a chronological account of our in vitro and in vitro biological continuum. This document follows a published historical chronological timeline of biomaterial testing literature beginning with its little known inception in 1779. Many of the early dental restorative agents evolved due to their anodyne capacity to alleviate tooth pain and provide a modest bacteriostatic capacity. Those that were successful were modified as temporary cavity filling agents and evolved to more permanent fillings. Unfortunately, many of the early agents e.g. antimony, arsenic, asbestos, canthrides, formalin, mercury, mustard, phenol to name a few were toxic to the tooth and supporting periodontal tissues as well as failing to support lost tooth structure. The National Institute of Dental Research required biomaterial testing in the late 1940’s. Even today, the agency permits many pre-1950 agents via the grandfather clause for commercial inclusion and clinical use, while requiring all new post-1958 agents to pass both in-vitro and in vivo testing hurdles. We routinely place restorative agents that infiltrate in graded interphases to interdiffuse into vital enamel, dentine and even cementum by forming a unique biomimetic substrate that mimics the color and opacity of the human tooth. Our biological continuum is still evolving with technologies that will continue to change our clinical future. Our profession has been the global benefactor of dynamic change. Unfortunately, our biomaterials testing status quo is not acceptable as many toxic agents e.g. formalin still remain in our clinics.

Operative dentistry’s beginnings & its rapid but steady continuum

Generations before sugar was implicated with caries—vitamin-C deficiency (scurvy) had plagued humans for millennia. Early humans treated tooth pain with folkremedies & bloodletting by moonlight—when these cures failed, roadside itinerants with little training promoted extractions. King Philip II established the Parisian Barber-Surgeon Guild in 1210, requiring proper credentials to extract teeth. Edentulous US colonists of the 1800’s supported development of MECHANICAL DENTISTRY to fabricate dentures with artificial teeth. Cheap sugar inspired increased consumption, creating a rapid increase in worldwide caries. OPERATIVE DENTISTRY advanced in the Americas with a few clinicians attempting removal of cavity debris, decay, cleansing & restoration with agents to reestablish form & function. Dr. C.A. Harris of Ohio is acknowledged to have actively endorsed dentistry as a clinical profession. Dr. M.H. Webb’s 1883 OPERATIVE DENTISTRY textbook commanded international recognition by defining gold-foil cavity preparation & restoration, stressing attention to detail. By 1890, Dr. G.V. Black had outlined scientific guidelines for amalgam composition & defined OPERATIVE cavity resistance & retention form & restoration. By 1839, Drs. Harris & Hayden were recognized to have given OPERATIVE DENTISTRY its parturition at Baltimore Dental College. By 1870, America gained international respect with the founding of 9-accreditated dental schools. US clinicians organized active regional dental societies, developed vulcanite-dentures, scalers, rubber-dam, adjustable dental-chairs, steel burs, electric-handpieces, round-end burs, mouth-mirrors, matrix bands, local anesthesia & more. Circa 1967, Professor Takao Fusayama of Tokyo Medical Dental College introduced a caries stain that was 1st to differentiate non-vital from vital dentine & defined MINIMAL CAVITY INTERVENTION & restoration with polymers that hybridized vital enamel & dentine. This OPERATIVE continuum has endeavored to examine those dental materials & technologies, which have advanced our OPERATIVE standards. “Pay attention to the details—never be content with what you know—there is always more” Dr. Miles Markley (1903-2000). Correspondence to: Dr. Charles F. Cox, DMD, PhD, Department of Operative Dentistry, School of Dental Medicine, Tsurumi University, 2-1-3, Tsurumi, Tsurumi-ku, Yokohama 230-8501, Japan, Tel: 1 (810) 275-8361; Fax: 1 (810) 6364201, E-mail: cfcoxctwos@gmail.com