Flame to Furnace: Turning Up the Heat in Dentistry

Cured Rubber

Beginning in the mid-1800s, natural rubber, combined with sulphur and coloring agents, was the material “cured” in a special oven to create what was called a vulcanite-based denture. Porcelain teeth, rather than being held in place by pins and soldered to a denture’s cast metal base, were inserted into the upper or lower denture while it was cradled within the lower half of a metal dental flask. Strips of prepared rubber material were packed into the mold, and the upper half of the dental flask screwed down tight. The flask and its contents were steam-heated under pressure in a vulcanizer oven. Initially, the rubber became soft enough to fill the mold crevices and surround the porcelain teeth. With additional heating, the rubber continued to cure, becoming vulcanized. Ideally, the process made a denture with teeth securely fixed in a fully hardened but flexible plate and gums.

Rueggeberg cites the authors of an 1891 dentistry textbook as they described the potential perils for the dentist using a vulcanite oven — “The pressure nearly doubles with the addition of each 50° of heat, and allowing a vulcanizer to run up to 400° or 420° is shown to be a piece of unpardonable carelessness and proceeding fraught with the greatest danger to life and property.” And, although it provided a satisfactory alternative to its predecessor — the laboriously constructed gold swaged denture of the early 1800s — vulcanite as a denture material had its disadvantages for the patient. Being porous, when improperly cured it succumbed to the moist environment of the mouth, becoming discolored and foul-smelling over time. Despite the dangers of its curing and the shortcomings of its use, vulcanite remained the denture material of choice from the mid-1800s to the 1930s.

Shown here are several vulcanite ovens and related materials used by dentists making vulcanite dentures, including base rubber, artificial porcelain teeth, vulcanite dental flasks, and finished vulcanite dentures, as well as patents for vulcanite ovens (some showing their Bunsen burner heat sources), vulcanized rubber, and vulcanized dentures.

Glenner, R.A. 1997. How it evolved: The 19th Century Dentist’s Laboratory. J Hist Dent 45(1):23-25, March; Ring, M. E. 1984. The rubber denture murder case: The true story of the vulcanite litigations. Bull Hist Dent 32(1):3-18, April; Rueggeberg, F.A. 2002. From vulcanite to vinyl, a history of resins in restorative dentistry. J Pros Dent 87(4):364-379; Ladha, K. and Verma, M. 2011. 19th century denture base materials revisited. J Hist Dent 59(1):1-11; Williams, B. 2021. Denture-curing oven. Brit Dent J 231(1):11; Guyton, William R.A. (1938) Denture. US Patent 2,107,181. Filed April 4, 1935, and issued February 1, 1938; Gilbert, Edmund D. (1906) Vulcanizer. US Patent 825,901. Filed January 23, 1905, and issued July 17, 1906; Kelsey, Cyrus M. (1869) Improvement in Vulcanizing Rubber for Dental Plates and For Other Purposes. US Patent 93,623. Issued August 10, 1869.

Rubber, Teeth and Flask

Selection of dental vulcanite rubber colors

Sales ad, Hettinger Bros Mfg Co Illustrated catalogue of dental supplies, 1901 (D443.1)
University of the Pacific Permanent Collection, Donor: Robert Reid, DDS, P&S Class of 1951

Traun’s New Tough Pink Base denture rubber, Atlantic Rubber Mfg Corp
“Vulcanizes at 320° F. in 55 minutes” (written on product box)

University of the Pacific Permanent Collection, Donor: Unknown

Porcelain tooth samples

University of the Pacific Permanent Collection, Donor: Unknown

Porcelain teeth for rubber work, SS White Dental Mfg Co

Sales ad, James W Edwards’ Illustrated catalogue of dental instruments and materials, c. 1894
University of the Pacific Permanent Collection, Donor: Unknown

Dental flasks for vulcanite work

Sales ad, Hettinger Bros Mfg Co Illustrated catalogue of dental supplies, 1901 (D536.1)
University of the Pacific Permanent Collection, Donor: Robert Reid, DDS (P&S ’51)

Vulcanizers

Gilbert’s 1906 Vulcanizer patent
Figure 2 shows the basic vulcanizer components: boiler (1), supporting-jacket or oven (2), lid or cover (3), supporting-yoke (4), and collar (5) connected to the supporting-yoke. In this design, the boiler unit contained both the dental flasks and the water for generating steam.

Possible early-1800s vulcanizer supporting-jacket

University of the Pacific Permanent Collection, Donor: Family of Mr Bo Suter

Kelsey’s 1869 Improved Method of Vulcanizing Rubber patent
Figure 1 shows sand packed around the dental flask (C) (“containing the rubber gum and teeth prepared as by the old method”) inside a cylinder of sheet metal (A) with cover (B). The sand serves “to prevent the rubber from burning, and to retain, modify and equalize the heat.” No use of water or steam is mentioned in the patent. The large heating device using either gas or a “burning-fluid of some kind” sits below the cylinder and within the jacket (D), where it ideally generates temperatures from 320° to 380° F.

Seabury’s 1884 Dental Vulcanizer patent
Figure 1 shows multiple dental flasks (E) stacked in the “oven or heater” (D) with the “steam-generator” (B) situated below them. At the top of the oven, each flask is treated to dry heat sequentially, so that the artificial denture teeth become fixed in the surrounding softened rubber. The flask is then locked tight and removed from the oven. This process is repeated for up to a total of four flasks. Following this stage, the flasks are returned to the oven, being “placed into the lower part of the stove or heater until the same is filled. [T]he oven or heater is closed, and steam is applied until the process of vulcanization is completed” at a temperature of 300° to 330° F.

Well-worn vulcanizer supporting-jacket, wrench & pot lifter (A19.3)
with gas heating apparatus enclosed within the base
This unit may have belonged to dental student Franklin Hammond Locke (see large whitish FHL initials), a 1902 P&S graduate.

University of the Pacific Permanent Collection, Donor: Unknown

Carll’s 1886 Vulcanizer patent
Figure 1 shows the Bunsen burner (D) supplying heat to the boiler (E) to initially produce wet steam for softening the rubber, allowing it to flow effectively into all parts of the denture molds (L). Later on, as the pressure and temperature increase, dry steam for completing the vulcanization process is delivered to the oven (A) via a “spiral superheating pipe” (a). “By means of my improvement the vulcanization or molding is accomplished with dry steam, the vulcanizer is made automatic in regulation of the pressure, and also in the timing of the work, and the continuously-blowing safety valve [f] renders the oven free from the danger of explosion.”

Vulcanizer boiler with cover, cross-bar yoke, & pressure regulator (A19.2)

University of the Pacific Permanent Collection, Donor: Unknown

Gilbert’s 1898 Vulcanizer patent
This design offers a unique clamping mechanism intended to improve the cover seal’s tightness during vulcanization, and to ease its breaking after vulcanization. The yoke or clamp bar (F) is specially equipped with securely locking parts such that “the operator is insured against accident that might otherwise be caused by the operating-lever being lifted by a thoughtless or ignorant person.”

Vulcanizer & gas-burner, SS White Dental Mfg Co, Pat. 1898 & 1906
suitable for heating with gasoline, alcohol or kerosene
The gas burner, as the heat source, would have been affixed to the underside of the vulcanizer supporting-jacket.

Sales ad, Jas W Edwards Co General catalog of dental furniture, instruments, and supplies, 1915 (D268.2)
University of the Pacific Permanent Collection, Donor: Mr William Sinott

“Supertherm” vulcanite curing unit (A547.4), SS White Dental Mfg Co, c. 1925

University of the Pacific Permanent Collection, Donor: Moylen D Peterson, DDS

Cogswell and Puckett’s 1909 Vulcanizing Apparatus patent
Figures 1 and 4 show a large self-regulating device that frees the “average dentist [who] has not the time or inclination to sit and watch a vulcanizer, so as to keep the heat perfectly regulated for the required time” of about 1.5 hours needed to bring it “up to the required temperature… and then hold it at that temperature without variation…” At a certain point in the vulcanization process, the gas (1) supplying the burner (16) automatically shuts off, and the clam-shell oven (A,B) automatically closes, thereby maintaining the appropriate curing temperature around the suspended vulcanizer (V) containing the dental flask.

Cured Rubber

Nelson Goodyear’s 1851 Improvement in the Manufacture of India-Rubber patent
In the first two paragraphs of his patent, Goodyear proclaims his invention of, “1. The combining of india-rubber and sulphur, either with our without shellac, for making a hard and inflexible substance hitherto unknown, substantially as herein set fourth. 2) The combining of india-rubber, sulphur, and magnesia or lime or a carbon or a sulphate of magnesia or of lime, either with or without shellac, for making a hard and inflexible substance hitherto unknown, substantially as herein set forth.”

John A Cummings, DDS’s 1864 Improvement in Artificial Gums & Palate patent
In this patent Cummings mentions the use of rubber and describes himself as having “invented certain new and useful improvements in the manner of forming artificial palates and gums used for inserting artificial teeth.” Goodyear acquired Dr. Cummings’s patent to solidify the company’s control over the manufacture of vulcanite dentures by dentists.

Vulcanite full dentures with porcelain teeth & hinged gold wire springs

University of the Pacific Permanent Collection, Donor: Family of Mr Bo Suter

Vulcanite upper denture with three different rubber colors (A527.25)

University of the Pacific Permanent Collection, Donor: James F Tackney, DDS, P&S Class of 1943

Vulcanite upper denture with metal base (A417.4)

University of the Pacific Permanent Collection, Donor: William V. Stenberg, DDS, UOP Class of 1982

Vulcanite upper denture with metal frame
These dentures show metal pegs exposed on the damaged side. The pegs were used to help retain the vulcanite material adhering to the metal framework (E. Giachetti, personal communication, April 27, 2022).

University of the Pacific Permanent Collection, Donor: Unknown

Vulcanite upper denture

University of the Pacific Permanent Collection, Donor: Unknown

Vulcanite upper denture with vulcanite gums & cast metal base

University of the Pacific Permanent Collection, Donor: Unknown

Vulcanite lower denture

University of the Pacific Permanent Collection, Donor: Unknown

Vulcanite upper denture with porcelain teeth (A452.6)
The palatal portion is gold colored, and the anterior “gum” portion is molted with dark and light pink to simulate “natural” gum in appearance (H. Stuart, personal communication, April 18, 1991).

University of the Pacific Permanent Collection, Donor: Unknown

Vulcanite lower denture with cast metal base

University of the Pacific Permanent Collection, Donor: Unknown

Vulcanite lower denture

University of the Pacific Permanent Collection, Donor: Unknown

Lower denture with vulcanite base (A452.1), early 1900s
The teeth and gums are porcelain, with sections of several teeth fitted into the denture as units rather than as single teeth – a special, expensive process. Excessive amounts of vulcanite were placed laterally to “fill out” the face. Acrylic was used later to make “gum” repairs near the incisors (H. Stuart, personal communication, April 18, 1991).

University of the Pacific Permanent Collection, Donor: Unknown