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


Endodontics emerged as a clinical specialty in the early 1900's, which became strengthened through histological knowledge with pulp biology technologies
Who were some of the European notables that advanced discoveries from 1860 to 1900, which became recognized as the classical era of histological innovation? Who published the 1 st controlled histologic study that studied the histopathology of an endodontic agent on a human pulp? When was the term endodontia 1 st reported to describe the clinical procedure to treat an infected human tooth pulp. Who was the 1 st clinician to limit his clinical practice to endodontia? When did the concept of root canal therapy come into accepted treatment of tooth pain? When & where did the American Dental Association (ADA) & the American Association of Endodontics (AAE) become organized? When did endodontia-endodontics become a recognized specialty of the ADA? How have recent technological devices advanced the treatment phase of canal instrumentation & obturation? Who were some of those European colleagues who rapidly advanced the research frontiers of oral biology in the US in the 1940's? When did the PULP BIOLOGY GROUP OF THE IADR become recognized as the organization that defined the standards for the histological testing of vital pulps? As you read through this article, we hope you will learn the answers to these & other questions.
In the early 1800's of the US, Edward Hudson filled canals with various cements, however many failed due to their solubility & disintegration, which led to failure & eventual extraction. Having learned of Fauchard's success with plugging canals with gold foil, Hudson designed his own pluggers to fill the open canals with gold foil, for which he charged his patients a $10.00 plugging fee. Following his success, a few clinicians in the larger US cities soon practiced Hudson's gold foil plugging concepts-but there was no mention of treating the instrumented canal with any sort of therapeutic agent [10]. Into the mid 1800's-a few essential oils had become known to have an anodyne effect against pain, but there were no standardized root canal instruments. Consequently, a few clinicians fashioned their own broaches from jeweler's instruments & watch springs to create small barbs that enabled removal of pulp tissues.

The era of classical histological discoveries fostered clinical progress in the treatment of pulp inflammation
The CLASSICAL HISTOLOGICAL ERA is considered as spanning 76-years from 1830 to 1906. Without any sort of widely available research press during those decades, it is difficult to recognize the individual who named a particular structure or cell, since most ideasharing occurred through handwritten letters between colleagues e.g. Nasmyth  Baume (1848Baume ( -1907) throughout academies at Baltimore, Breslau, Berlin, Göttingen, Hamburg, Heidelberg, London, Louvian, Paris, Philadelphia, Stockholm, Vienna, Wurzburg, Zurich [11].
One of the most important leaders & mentors for young colleagues throughout the CLASSICAL HISTOLOGICAL ERA was Professor Johannes E.K. von Purkinje (1787-1869)-founder of the famous Breslau School of Microscopic Anatomy & Histology in Prague Czechoslovakia, which ushered in the era of light microscopy (LM) of tissues [12]. One of his personal contributions to the technical advancement of histological technology was the development of a microtome that operated on the principle of squeezing-rather than cutting, as well as collaborating with Lister on the development of a compound achromatic microscope in 1830. Two of Purkinje's famous students (M. Fränkel & J. Raschkow) of his academy were responsible for the very 1 st hand-drawn reproductions of the progressive stages of developing dental tissues with precise tissue detail. Purkinge's students proposed that dentine originated from pulp fibers, which became mineralized & left continuous canaliculi between them. Raschkow was 1 st to demonstrate that the central nerves projected as fine branching fibers to the periphery of the pulp in the vital pulp. In 1865, Waldeyer (1836-1921) formally introduced the term odontoblast into our dental lexicon. Fränkel & Raschkow's research demonstrated that dentine was formed by odontoblasts of mesenchymal origin, which formed immediately subjacent to the basement membrane, that formed the irregular enamel-dentine junction & became known as Raschkow's dentine deposition theory & was supported by T. Huxley [13,14].
London in 1848, Sir John Tomes (1815-1898)-a famous student of professor Thomas Bell (1792-1880)-had become a distinguished prolific researcher & clinician within his own lifetime, for which he received the honored title of Sir. Tomes is well known for using LM to: 1) describe the minute tubules that projected perpendicularly from the pulp-dentine interface to the EDJ, each with small fibrillar contents that projected from each tubule, leaving a granular layer of tomes in root dentine with occasional fibrils that seemed to connect with cells in

From tooth extraction as a quick fix to alleviate a patient's pain -To endodontics as an accepted clinical treatment to remove a painful pulp & maintain a tooth in function
Treatment of tooth pain before the 1800's was basically that of extraction [3] except with the exception of a few enterprising individuals who wished to save the tooth by employing innovative clinical procedures. Some would open the pulp to allow drainage & then cauterize the pulp tissues by rapidly forcing a hot needle into the canal, which they would leave open to drain the inflammatory "mephitic exhalation of fluids" through the access site. A few critical thinking clinicians placed a dry fiber into the canal to prevent impaction of food debris into the access hole. If a gumboil swelling formed after a few days to weeks, some clinicians would place cotton to serve as a "wick" to draw-out the fluids of the connecting gum boil & wait for the boil to subside rather than extract the tooth. In 1776 Robert Wolfendale travelled to New York from England & practiced cauterization of the infected pulp with a hot wire without attempting to fill the canal. In some regions of the US in the 1700's, a clinician would saturate a orangewood peg in phenol & knock it into the canal by a sudden blow to obliterate the pulp tissue [4].
Studies by John Hunter (1728-1793) in London contributed significantly to the knowledge of dentine morphology & its slowrhythmic deposition throughout post-eruption. He fed an organic colored food (madder) to pigs & demonstrated that teeth were not composed of the same tissues as bone-noting that enamel, dentine & cementum were separate tissues with their own types of vascularization. Hunter observed that the deposition of tertiary dentine in aged vital teeth demonstrated well-defined mineralized madder-colored deposition-lines of dentine, which he characterized as reparative dentine, which theorized that prevented a pulp exposure by creating an internal seal on the pulp interface [5]. Another of Hunter's unique in vivo biological studies was his transplantation of a developing human tooth into the vital tissue of a rooster's highly vascularized chin-comb, which continued to develop with a well-formed root & then proceeded to eruption through the epithelium of the roosters comb [6].

Fauchard's pulp removal & filling of the empty canal with gold foil becomes a clinically acceptable treatment
In 1746, Pierre Fauchard (1678-1761) described the opening of a painful tooth with a hand drill in order to remove the pulp with a barbed needle, after which he placed a piece of cotton saturated with an essential oil e.g. clove or cinnamon to plug the access hole. During that era, some clinicians realized that essential oils had an anodyne effect, however they had no concept about their antimicrobial effects. If the patient's pain persisted, Fauchard replaced the essential oil dressing until the pain subsided, after which he would fill the canal with tin, lead or gold foil to provide closure of the access site to oral debris [7]. Some clinicians throughout major cities of Europe practiced his clinical plugging procedure. In 1757 Etienne Bourdet (1722-1789)-a clinician in Paris limited his procedure to only plugging anterior teeth. In his famous text Chirurgien-dentiste "The Surgeon Dentist" Fauchard described a tooth as consisting of 4-dental tissues-with dentine as the largest tooth component being similar to bone [8]. His text made reference to the microscopic appearance of parallel fibers within the dentine, which may have been his intended description of odontoblastic processes as earlier described by Gabriel-Philippe de la Hire (1677-1719) who is also credited with the discovery of the enamel microstructure of Hunter-Schreger-bands [9]. cementum; 2) he described a protective barrier of secondary dentine as being more coarse & less tubular than primary/mantle dentine (1848); 3) the intimate & dynamic relationship of the pulp-dentine interface (1852-1863); 4) he identified peritubular dentine & the presence of fine nerve processes in certain of the dentine tubules (1863-1868); 5) he defined the concept of ontogeny recapitulating phylogeny [15].
Throughout the 76-years of dental & medical classical histological advancements, Rudolf A. von Kolliker (1817-1906) 1 st of Zurich & later Würzburg was acknowledged as a principal histologist of the classical LM era publishing 6-editions of his histology textbook between 1852 & 1903. As a testimonial to his in-depth understanding & ability to provide detailed hand-drawings, his 1 st edition of Human Microscopic anatomy was a comprehensive description of the progressive embryological stages of tooth development to eruption as well as adult tooth histology. He was 1 st to recognize that the secretory function of the odontoblasts was a continuous physiological process without any cell modification. He also postulated that through the aging process, certain primary odontoblast cells would die & pioneer cells would migrate to the pulp periphery & reorganize themselves as new replacement odontoblastoid cells to form along the pulp-predentine interface to replace the lost odontoblasts [16]. Dr. Harris obtained his DDS through membership of the American Society of Dental Surgery (ASDS)-an honorary DDS degree was also conferred to him in 1854 by Philadelphia Dental College. At the 1840 ASDS meeting his motion "resolved that a ASDS be formed" to become reality-serving as its first President & Secretary in 1844. The ASDS was split in 1856 due to the emotional dental amalgam controversy-Chapin became a prime organizer of the American Dental Convention (ADC) as the main alternative to the ASDS, serving as the ADC president in 1856-57. In 1859-a year before his death-the ADA was established during a meeting at Niagara-on-the-Lake in New York. Before 1861, most dentists belonged to the ADC or ADA, both of which promoted education & research in dentistry. During the US Civil war, all Southern US dentists withdrew their ADA memberships & established their own Southern Dental Association (SDA). After the Civil War, the southern dentists merged with the ADA in 1897 to form the National Dental Association (NDA), which was later renamed the ADA in 1922. In 1839, there were only about 300-trained dentists throughout the US-other operators were quacks or charlatans with little to no training. In 1898 the subscribers list to the ASDS journal was discovered & published by G.V. Black-being the core group of true professional American dentists to become the leaders of the new US dental profession [17]. GV was perhaps the first to assemble the scientific puzzle regarding the cause of human caries-having ready access to the literature. His personal LM research & clinical observations gave him a unique perspective on the existing science of caries of that day, which most others failed to consider. GV pieced together the complex puzzle of human caries from his reading of W.D. Miller's (1853Miller's ( -1907) & others papers, writing that tooth decay occurred when mouth fluids were habitually acid or alkaline & that initiation of caries was directly dependent upon lodging of food particles & plaque in tooth pits & fissures, followed by fermentation & acid production that began the demineralization process. GV wrote "what is called fermentation by an organized fermentable agent is but the first step in true fermentation." Until that time, fermentation was mainly a study of the digestive agent & its waste products (acids) [20].

G.V. Black's pyramid of knowledge: He grasped basic biological, histological & pathological concepts & integrated them into his daily clinical treatment procedures
It is difficult to decide, which of GV's contributions-biological, bacteriological or material sciences-were most important. Although he was born in humble surroundings, he was a self-taught student & remained so throughout his life. His personal research standards guide many of today's colleagues. GV presented more than 1,300 papers & lectures over his lifetime-all without governmental research support, computers, Google, face-book or twitter. GV is likely known to most of today's dental students & colleagues throughout today's world who have read his biological & clinical contributions, which still have relevance for today's dentists.

From his humble beginnings of a log cabin in the maine wilderness Williams became an accomplished scientist & clinician to the 1 st president of the IADR
J. Leon Williams (1852-1932) was the major force who guided US dentistry into a science based clinical profession. The Maine dental society owned a microscope for LM, but as none of his colleagues cared about the device he borrowed it for several years. After saving $100, he purchased his own microscope & for the next 7-years he used his microscope for personal research on studying the development of human teeth. He arranged a research lab in his office with a window to the south to catch the daily sun for his microscopes mirror. At age-30 Dr. Gysi validated John Neill's (1819-1880) 1842 theory of dentine fluid dynamics in the dentine tubules by correctly defining the mechanism of human tooth sensitivity from his clinical observations of fluid movement along cavity walls during restorative procedures [22]. Stirred by Dr. Neill's 1842 thesis, Gysi published his thoughts on the fluid theory of dentine sensitivity in 1899, which was later confirmed by the scientific research of Dr. Martin Brännström (1922Brännström ( -2001 in 1968 [23,24]. Some colleagues believed dentine sensitivity was due to the presence of nerves in human dentinal tubules that responded to various stimuli, while others accepted that dentine sensitivity theory was due to the odontoblast process extending the length of the dentinal tubule complex, which registered the initial sensory stimuli & conveyed it to the sub-odontoblastic nerve plexus & the brain as pain. Alfred wrote in his daily clinical diary, that during gentle removal of the outer infected soft carious dentine-before local anesthesia & electric dental engines were commonplace-he would periodically stop to provide the patient momentary relief from the drilling. After returning to the cavity, he observed fluid on the cavity floor & during its removal with a small dry wick, some patients complained of a sharp painful reaction-gaining relief when he rapidly removed the moist wick. From his clinical observations, he realized that the rapid drying of fluid from the dentine cavity floor & walls supported Neill's 1842 theory of fluid dynamics in vital dentine. Dr. Gysi published his erudite article An attempt to explain the sensitiveness of dentine in the 1900 Brit Jour of Dent Res, which considered fluid flow in the dentinal tubule complex-69-years before Dr. Brännström's hydrodynamic theory of human dentine sensitivity [25]. While a professor at Zurich in 1894, Gysi constructed his own microphotographic camera, which used lamps for nightlong exposures to produce the 1 st published photomicrographs of the developing human enamel-dentine-pulp interface. In the US an active group of young LM histologists was led by Dr. Carl Heitzman-originally from Vienna-began a biological school of dental medicine in New York. One of his most notable students was C.F. Bödecker (1895-1965) who wrote the 1 st American text of dental anatomy & pathology based his LM histological studies that demonstrated dentinogenesis from the embryonic stages into aged tooth development. In 1879 & 1882, Bödecker was 1 st to accurately describe the pattern of sequential mineralization of human dentine [26]. In addition to defining histological demineralization, processing, celloidine embedding, sectioning & staining, he used oil-immersion to clarify his observation of the fine spindle-shaped fibers that were present between odontoblasts during their initial deposition of dentine-these fibers are now called von Korff fibers & have been demonstrated in the initial matrix deposition of new dentine bridge deposition by the newly formed pioneer odontoblastoid cells of mesenchymal origin [27].

The american era of dental research comes of age during the 1940's with the migration of oral biology colleagues from Vienna Austria
In 1926, Dr. William J. Gies submitted a detailed report to The Carnegie Foundation on the status & needs of teaching & research advancements of dental education in the US. His report recognized the need for improving the development of oral biology research within the dental institutions & to integrate their biological aspects into US dental school curricula [28]. This report was most timely, as US dentistry had finally moved beyond its previous recognized status as nothing other than a technical trade that made oral prosthesis. By 1943 some US schools that allied with major university medical schools had become recognized as an equal profession to that of medicine. that occurred in carious dentine, which had not been previously demonstrated by LM histology. His 0.5µm ultrathin sections showed 4-zones of degeneration based on the degree of microbial invasion. It was not only papers that he published, but he was also instrumental in writing several chapters in more than 10-books. Dr. Bernick was the 1 st to employ TEM to differentiate 4-zones of degeneration in the caries lesion. The outermost zone was called the superficial infected carious zone of non-vital dead dentine-seen as a soft crumbly mass with millions of coccid & rods shaped microörganisms. The 2 nd deeper zone is an incipient layer that is just beginning to show HAp demineralization, in which the peritubular wall is destroyed with disruption of any normal tubule morphology. The pioneer microörganisms are strep & LBA, however the collagen remains unaltered, which provides a substrate for possible remineralization into a future zone of dense sclerotic dentine. Sol showed by TEM, that the 3 rd deeper zone is filled with small transparent refractory nano-crystals & is considered as a self-healing zone of remineralization, in which the tooth produces on its own. The deepest 4 th zone is very thin, being situated quite far ahead of any actual demineralization of the peritubular dentine-where only a few pioneer microörganisms may be located [36,37].

The clinical evolution of root canal therapy from pulp removal & plugging with gold foil to the introduction of therapeutic agents to eliminate microörganisms
From the early 1800's to the 1860's root canal treatment was generally confined to the removal of the exposed pulp tissues with barbed instruments & then just left open to drain any fluids. By 1873 the research of A. Wetzel & others had begun to understand that the presence of bacteria in the dentine tubules as well along the crevices & walls of infected pulp canals were responsible for continuing infection & periapical inflammation. From these observations, Wetzel realized that following the removal of an infected pulp tissue, that it was important to provide a septic phase of therapeutic canal treatment to kill those bacteria that remained following tissue removal. He introduced the use of phenol (carbolic acid) as a therapeutic agent to treat the instrumented root canal surfaces. Witzel

Endodontics becomes a clinical reality & develops as a recognized ADA specialty
With advances in the knowledge of pulp histology by the 1900's some clinicians in the US-instead of just extracting a painful toothattempted to treat & maintain an infected tooth as a functioning part of the human dentition for the patient. By that time, root canal treatment in the US was being attempted by some clinicians & was referred to as pathodontia. By 1928 Dr. H.B. Johnson of Atlanta GA was acknowledged to be the 1 st clinician to limit his practice to endodontics-a term he defined by merging 2-words en from Greek meaning inside or within & odous from the Greek lexicon (ὀδόντα) referring to the tooth [39].

The use of natural plants & minerals, which led to the pharmacological rational that promoted the therapeutic phase of endodontic treatment
Aristotle (384-322BC) from nearby Thessaloniki Greece, credited Hippocrates (460-370BC)-from Kos in northern Greece-as the Father of Medicine who taught his student to move beyond the ancient consideration of unnatural or supernatural myths of disease by teaching that critically thinking people should employ independence of thought in all of their actions as well as teaching & practice in their treatment of infirmities & pain control of diseases [41].
Paracelsus (1493-1541) the Swiss physician studied medicine at Basel University at age of 16-years & gained his doctorate at Farrara University in 1516. He is considered the founder of toxicology who proposed the use of rational therapeutics & was one of the 1 st individuals to report that plants contained natural agents, which promoted therapeutic values. He regarded that superstitions were ridiculous tales that had no ability to promote healing of diseases [42].
In 1865, Dr. Claude Bernard (1813-1878) of France published his textbook An Introduction to the Study of Experimental Medicine [43]. He introduced experimental medicine & the study of disease in the living human body. He studied the role of the pancreas in the digestion process of fats & sugar on the blood & he also demonstrated the pharmacological action of many drugs on the human body & made it acceptable to visualize tissue reactions to drugs rather than by just accepting previous statements that had been based only on clinical observations without any sort of long-term studies with scientific evidence to validate the mechanisms of action.

Therapeutic principles for the treatment of vital & nonvital teeth
The 1950 Endodontia textbook by Edgar A. Coolidge is an early classic academic clinical text with chapters that cover tooth pain, clinical treatment of hypersensitive dentine, treatment of infected & pulpless teeth, the maintenance of pulp vitality & removal of pulps in preparation for filling-the clinical information remains absolutely relevant for students & clinicians even today. The Coolidge's text is a must read for any endodontic graduates who wish to learn something of the notables who encouraged the emergence of endodontics as a dental specialty & contributed through the early 1900's as well as those clinicians who practice conservative pulp treatment. His comprehensive Endodontia text clarified clinical procedures for caries removal, temporary caries control with indirect placement of anodyne agents to alleviate patient pain as well as provide germicidal control of microörganisms using sulfonamides & antibiotics. Those early decades of the 1900's clarified diagnosis & root canal instrumentation, which served to usher in the therapeutic age of endodontics [44]. Dr. Coolidge, the Emeritus Professor at Chicago College of Dentistry at Loyola University text identified a number of clinical steps, by which each clinician should follow before attempting final filling of the instrumented canal. For those teeth with vital pulps: 1) establish an aseptic field. 2) control the patient's pain. 3) gain workable canal access. 4) remove all necrotic pulp tissue. 5) use a culture test to prove sterility. 6) fill to the pulp stump. 7) maintain periapical tissues. For nonvital pulpless teeth: 1) control the infection. 2) gain workable access. 3) thoroughly clean the canal. 4) disinfect the dentine. 5) control periapical sterility. 6) provide an apical seal. 7) prevent reinfection. 8) restore & maintain the periapical [bacteriometic] seal [49].
Dr. Coolidge wrote that an effective germicide needed to be strong enough to destroy the microörganisms without damaging the vital pulp stump or subjacent periapical tissues, or causing patient pain or discoloration of the tooth dentine [50]. Several of the early germicides were acids, metallic salts, zinc chloride, silver nitrate, formalin, alcohol & phenol were recognized canal germicides that coagulated albumen or were self-limiting due to limited penetration. Research by Feirer & Leonard demonstrated that it was important that therapeutic agents of low-surface tension would allow penetration into the irregular crevices & accessory canals otherwise their intended purpose would be limited or totally non-effective [51].
In his 1891 article, Dr. O. Walkoff of Leipzig recommended the use of camphorated monochlorophenol (CMCP)-an agent whose chemistry acted by the manner in which several hydrogen atoms of the CMCP are replaced by chlorine, which renders it effective. The final agent is more germicidal than phenol in that it penetrates into the accessory canals & irregular instrumentation irregularities & does not coagulate albumin or cauterize vital tissues. However, to be effective in root canal treatment, the CMCP needs to be placed as a moistened paper point & sealed into the canal for the time between appointments. Consequently, CMCP never became popular with most clinicians due to its multiple patient visits, which required additional filing of the canal walls & definition of the canal apex-periapical interface [52].
In 1917, Dakin & Dunham reported on the efficacy of a mixture of calcium hypochlorite & calcium chloride & buffered with the addition of boric acid to balance the solution to a 0.5% strength that kept it useful for 1-week without decomposition. The benefit of this agent was its rapidity of killing microorganisms with a solvent action on necrotic tissue & little to any injury to the vital tissues [53][54][55]. During the years after WW-I, other modifications of chlorine e.g. Chloramine-T & Dichloramine were developed, but they were found to be less effective than the Dakin solution.
This Part I document has attempted to highlight the efforts of those many notable histological researchers from previous centuries & to identify some of those enterprising clinicians who contributed to the inception of a healing specialty, which provides relief from pain & inflammation that provides an alternative to tooth extraction. It is our aim that Part II will provide a more comprehensive review of colleagues, technologies & pulp biology research (Table 1), which has advanced our endodontic specialty in the last century.

Acknowledgements
Each author owes an especial note of gratitude to those faculty, colleagues, family & friends who have supported each of us throughout our formative research & academic years & have given their personal time & individual kindness, in which they continued to encourage us throughout our careers.

Dr. John Neill 1819-1880
The 1 st to report on the nature of fluid in the dentine tubules to the cause of dentine sensitivity of human teeth [22].
Dr. Meyerus Frankel circa 1820-1870 A famous student of Purkinje at Breaslau who drew & first described the stages of human tooth development from his microscopic slides [13].