INLAY WAXES DETALED DISSCUSSION ALONG WITH ITS TYOES

detailed discussion about inlay wax

1. INLAY WAX PRESENTED BY- DR. SHREEYA JAISWAL POST GRADUATE TRAINEE FIRST YEAR DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS GUIDED BY – DR. RANA K. VARGHESE,PROFESSOR AND HOD DR.MALWIKA SISODIYA,READER DR. RAUNAK SINGH, READER DR. NAVEEN KUMAR GUPTA , READER. DR. CHANDRABHAN GENDLEY, SR. LECTURER DR. ANITA CHANDRAKAR, SR. LECTURER

2. CONTENTS INTRODUCTION CLASSIFICATION ANSI/ADA SPECIFICATION DIRECT WAX PATTERN INDIRECT WAX PATTERN COMPOSITION TRADE NAMES PROPERTIES FLOW THERMAL EXPANSION WARPAGE MANIPULATION USES CONCLUSION REFERENCE

3. INTRODUCTION: Wax patterns for inlays or cast posts can be produced either by a direct or indirect technique . The use of direct wax patterns is normally reserved only for the most simple designs of cast posts/cores on anterior teeth. These patterns can be removed from the prepared tooth or root with a minimum of distortion.

4. Inlay waxes may be softened over a flame or in water at 54˚–60˚ C (130˚–140˚ F) to enable their flow in the liquid state and adaptation to the prepared tooth or die. These waxes are designed to maintain uniform workability over a wide temperature range, thereby facilitating accurate adaptation under pressure. Additive layers and corrections may be applied to produce a homogeneous pattern. Inlay waxes can be carved easily without chipping or flaking.

5. Inlay casting waxes are currently classified as follows: Type 1 medium Type 2 soft The type 2 materials are designed for use in the indirect technique, being suitable for making patterns outside the mouth for the production of inlays, crowns and cast pontics . The type 1 materials are suitable for use in the direct technique (and may also be suitable for indirect use) for the production of inlays and crowns. CLASSIFICATION

6. The difference between the two types of wax is characterized by their flow behavior. Type 1 wax has limited flow characteristic as compared to Type 2, to minimize the possibility of distortion of the pattern during removal from the tooth cavity Both types of waxes are commonly produced in the form of cones and sticks.

7. ANSI/ADA SPECIFICATION Revised ANSI/ADA Specification No. 4 (IS01561) for dental inlay casting wax has been formulated for waxes used in direct and indirect waxing techniques Because the wax patterns are to be melted and vaporized from the investment mold, it is essential that no excessive residue remain in the mold because of incomplete wax burnout.

8. Excess residue may result in the incomplete casting of inlay margins. The specification therefore limits the nonvolatile residue of these waxes to a maximum of 0.10% at an ignition temperature of 700 The specification also requires the manufacturers to include instructions regarding the method of softening and the working temperature for the wax preparatory to forming a direct pattern. Both types should soften without becoming flaky, and when trimmed to a fine margin during the pattern-carving operation, they should not chip or flake.  

9. DIRECT WAX PATTERN For direct wax patterns the softened wax is forced into the tooth cavity and held under pressure until it cools. The wax should soften just above mouth temperature and should not be raised to a higher temperature than necessary, in order to reduce the magnitude of thermal contraction and internal stresses. In addition, the softening temperature must be tolerated without pain by the patient.

10. The thermal contraction occurring on removal of the direct pattern material from the mouth is of the order of 0.1–0.5%. This would seem sufficient to cause problems of fit with the final cast restoration although serious problems are rarely encountered in practice, possibly because of the relatively simple nature of the restorations produced by the direct technique. Dimensional changes caused by stress relief are minimized by investing the pattern as soon as possible.

11. The material should be hard at mouth temperature and when removed from the cavity should fracture rather than flow if the cavity has unwanted undercuts. This enables the undercuts to be located and removed. The wax should ideally have a good colour contrast with enamel and be easy to carve without flaking so that the exposed surfaces of wax can be easily contoured to shape and the margins readily observed.

12. Direct patterns for post cores are built up using a different approach. The post channel is usually prepared using a proprietary system and a pre-formed pattern for the post is installed into the canal. The core is then built up in wax by melting the wax on an instrument and carrying the molten wax into the tooth.

13. INDIRECT WAX PATTERN The procedure for indirect patterns is similar to that described for direct patterns except that the softened wax is forced into a cavity on the gypsum die. Since this procedure is carried out at room temperature rather than mouth temperature, inlay waxes for indirect patterns may soften at a somewhat lower temperature than direct pattern waxes, although the softening temperature should not be so low that the wax will flow at room temperature.

14. The value of thermal contraction for the indirect technique is much lower as a result of the lower softening temperature. This may be considered a distinct advantage of the indirect technique. However, it should be appreciated that the die has been produced in an impression which was itself recorded at mouth temperature and then cooled to room temperature – thus undergoing a thermal contraction which may approach the value of a direct wax pattern material. Because the thermal expansion coefficient of wax is extremely high compared with the values for other dental materials, a wax pattern made in the mouth (direct method) will shrink appreciably as it is cooled to room temperature.

15. A pattern made using the indirect method may not shrink as much, although the amount depends on whether the pattern was allowed to reach room temperature before it was removed from the die.

16. COMPOSITION The principal waxes used to formulate inlay waxes are Paraffin, Microcrystalline wax, Ceresin Carnauba Candelilla Beeswax

17. For example, an inlay wax may contain Paraffin 60% Carnauba 25% Ceresin 10% Beeswax 5% Therefore, hydrocarbon waxes constitute the major portion of this formulation. Some inlay waxes are described as hard, regular (medium), or soft, which is a general indication of their flow.

18. The flow can be reduced by adding more carnauba wax or by selecting a higher melting point paraffin wax. An interesting example is that a hard inlay wax may contain a lower percentage of carnauba wax than a regular inlay wax, but the flow of the hard inlay wax is less than the regular wax because of the selection of a higher-melting-point paraffin in the formulation of the hard wax. Resins in small amounts, such as 1%, also affect the flow of inlay waxes.

19. Paraffin is derived from the high-boiling fractions of petroleum. It is composed mainly of a complex mixture of hydrocarbons of the methane series, together with a minor amount of amorphous or microcrystalline phases. PARAFFIN

20. Paraffin can be produced with a range of melting points. The presence of oils in the wax, however, lowers the melting temperature; paraffin waxes used in dentistry are refined waxes and have less than 0.5% oil. For example, paraffin used for Type I wax is required to have a higher melting point than does the paraffin used for Type II waxes. Paraffin wax is likely to flake when it is trimmed, and it does not present a smooth, glossy surface, which is a desirable requisite for an inlay wax. Consequently, other waxes and natural resins are added as modifying agents.

21. GUM DAMMAR Gum dammar, or dammar resin, is a natural resin added to paraffin to improve its smoothness in molding and to render it more resistant to cracking and flaking. Dammar resin also increases the toughness of the wax and enhances the smoothness and luster of the surface.

22. Carnauba wax occurs as a fine powder on the leaves of certain tropical palms. This wax is quite hard, and it has a relatively high melting point. It is combined with paraffin to decrease the flow at mouth temperature. Carnauba wax has an agreeable odor, and it contributes to the glossiness of the wax surface even more than does dammar resin. CARNAUBA WAX

23. Adding 10% of carnauba wax to paraffin wax with a melting range of 20 degree C increases the melting range to 46 degree C In modern inlay waxes, carnauba wax is often replaced in part with certain synthetic waxes that are compatible with paraffin wax.

24. For an impression compound, a synthetic wax is preferable to a natural wax, because it has greater uniformity. Because of the high melting point of the synthetic waxes, more paraffin can be incorporated and the general working qualities of the product are improved. Control of the properties of the inlay wax is accomplished by a combination of factors, including the amount of carnauba wax used, the melting range of the hydrocarbon wax, and the presence of resin.

25. CANDELILA WAX Candelilla wax can also be added to the paraffin to partially or entirely replace the carnauba wax. The candelilla wax provides the same general qualities as the carnauba wax, but its melting point is lower, and it is not as hard as carnauba wax.

26. CERESIN Ceresin is a term used to describe waxes from wax-bearing distillates from natural-mineral petroleum refining or lignite refining. Ceresin may replace part of the paraffin to modify the toughness and carving characteristics of the wax.

27. TRADE NAMES Inlay waxes are usually produced in deep blue, green, purple rods or sticks about 7.5 cm long and 0.64 cm in diameter. Some manufacturers supply the wax in the form of small pellets or cones or in small, metal ointment jars. Trade Names - Maves Dental Inlay Wax , GC Inlay Wax , Corning Inlay Wax by Keystone Industries , Ampro Dental Inlay wax etc.

28. PROPERTIES When softened, the wax should be uniform. In other words, it should be compounded with ingredients that blend with one another so that there are no grainy areas or hard spots when the wax is softened. 2. The color should be such that it contrasts with the die material or prepared tooth. It is necessary to carve the wax margins close to the die. Therefore a definite contrast in color facilitates proper finishing of the margins. 3. There should be no flakiness or similar surface roughening when the wax is bent and molded after softening. Such flakiness is likely to be present in paraffin wax; this is one of the reasons modifiers are added.

29. 4. After the wax pattern has solidified, it is necessary to carve the original tooth anatomy in the wax and to carve the wax at the margins so that the pattern confirms exactly to the surface of the die. The latter procedure sometimes requires that the wax be carved to a very thin layer. If the wax pulls away with the carving instrument or if it chips as it is carved, such precision cannot be attained. 5. After the mold has been formed, the wax is eliminated from the mold. Elimination is usually accomplished by heating the mold to ignite the wax.

30. If, after burning, the wax leaves a residue that might provide an impervious coating on the walls of the mold, the final cast inlay may be adversely affected. Consequently, the wax should burn out, forming carbon, which is later eliminated by oxidation to volatile gases. ANSI/ADA Specification No. 4 requires that the melted wax, when vaporized at 500˚ C (932˚ F), leave no solid residue in excess of 0.10% of the original weight of the specimen. 6. The wax pattern should be completely rigid and dimensionally stable at all times until it is eliminated.

31. 6.The wax pattern is subjected to flow unless it is handled carefully. It is also subjected to relaxation, a factor that must be taken into consideration in its manipulation Expansion and shrinkage of casting wax is very sensitive to temperature. Normally , soft wax shrinks more than hard wax. High-shrinking wax may cause significant pattern distortion when it solidifies. Excessive shrinkage and expansion due to temperature change must be avoided.

32. For this reason, organic filler is added sometimes to the wax formulation. Such fillers should be completely miscible with the components of the inlay wax during manufacture, and they should not leave an undesirable residue after burnout.

33. FLOW When forming a wax pattern directly in the mouth, the wax must be heated to a temperature at which it has sufficient flow under compression to reproduce the prepared cavity walls in great detail. The working temperature , suggested by the manufacturer, which should be satisfactory for making direct wax patterns, must not be so high as to cause damage to the vital tooth structure or be uncomfortable to the patient. Insufficient flow of the wax caused by insufficient heating results in the lack of cavity detail and introduces excess stress within the pattern. An overabundant amount of flow resulting from excessive heating makes compression of the wax difficult because of a lack of "body" in the material.

34. The values listed represent minimum or maximum values of percent flow that occur at various temperatures when Types 1 and 2 wax specimens are subjected to a 19.6 N load for 10 minutes. The temperature that the Type 2 wax must attain to register cavity detail is usually somewhat above 45 ℃ . As seen from these values, the flow of the medium wax is no more than 1% at body temperature. The flow of the Type 2 wax is about 9% at this temperature. Low flow at this temperature tends to minimize distortion of a well-carved pattern as it is withdrawn from an adequately tapered cavity in the tooth.

35. Each type of casting wax exhibits a characteristic flow curve as a function of temperature. Each wax also exhibits a sharp transition point (temperature) at which it loses its plasticity. Soft wax exhibits this transition point at a lower temperature, and hard wax exhibits it at a relatively higher temperature. Inlay waxes do not solidify with a space lattice, as does a metal.

36. Instead the structure is more likely to consist of crystalline and amorphous structural regions, displaying limited ordering of the molecules. The wax lacks rigidity and may flow under stress even at room temperature. The flow is measured by subjecting cylindrical specimens to a designated load at the stated temperature and measuring the percentage of reduction in length. The maximum flow permitted for Type I waxes at 37˚ C (98˚ F) is 1%. The low flow at this temperature permits carving and removal of the pattern from the prepared cavity at oral temperature without distortion.

37. In addition, both Type I and Type II waxes must have a minimal flow of 70% and a maximum flow of 90% at 45˚ C (113˚ F). At this temperature, the wax is inserted into the prepared cavity. If the wax does not have sufficient plasticity, it will not flow into all of the areas in the preparation and reproduce the required detail. Casting shrinkage decreased when the flow of the wax pattern increased. The flow of the wax pattern increased as the exothermic reaction increased. ( Ito, M., Yamagishi, T., Oshida , Y., & Munoz)

38. THERMAL COEFFICIENT OF EXPANSION THERMAL EXPANSION Knowing the amount of wax expansion or contraction allows one to judge the compensation necessary to produce an accurate casting. Data sufficient to show the thermal contraction of the wax from its working temperature to room temperature may be included in each package of inlay wax. The wax may expand as much as 0.7% with an increase in temperature of 20˚ C (36˚ F), or it may contract as much as 0.35% when it is cooled from 37˚ to 25˚ C (99˚ to 77˚ F).

39. The average linear coefficient of thermal expansion over such a temperature range is 350 × 10−6/˚ C. Once the wax pattern is carved, its removal from the tooth cavity and transfer to the laboratory bring about a reduction in temperature and subsequent thermal contraction. A decrease of 12 ℃ to 13℃ in temperature, from mouth temperature to a room temperature of about 24℃ , causes a 0.4% linear contraction of the wax, or about 0.04% change for each degree change in temperature.

40. Curve A represents the thermal expansion of an inlay wax that has been previously cooled under pressure. As shown, the expansion rate increases abruptly above approximately 35˚ C (95˚ F). The temperature at which the change in rate occurs is known as the glass transition temperature. Some constituents of the wax probably change crystalline form at this temperature, and the wax is more plastic at higher temperatures. Not all waxes exhibit glass transition temperatures. The transition point is characteristic of a high paraffin wax content.

41. If the wax is allowed to cool without being placed under pressure, the transition temperature is not so pronounced when it is reheated, nor is the change in the thermal expansion so great. Another possible explanation exists for the difference in behavior, on reheating, of a wax cooled under pressure and the same wax cooled without applied pressure. This explanation is related to the behavior of dissolved or occluded air or solvents. Certain waxes have a phenomenal capacity for gas and solvent retention, which may often remain undetected.

42. The gas trapped within the wax expands on reheating, causing a pronounced expansion as the wax becomes sufficiently plastic to flow.

43. WARPAGE OF WAX PATTERNS Inlay pattern wax has a high coefficient of expansion and tends to warp or distort when allowed to stand unrestrained. The distortion is increased generally as the temperature and time of storage are increased. This quality of wax patterns is related to the release of residual stress developed in the pattern during the process of formation. This characteristic of stress release and warpage is present in all dental waxes, but is particularly troublesome in inlay patterns because of the critical dimensional relations that must be maintained in inlay castings.

44. Because warpage of the pattern is related to the temperature during pattern formation and storage, the rules related to the pattern temperature must be understood. In general, the higher the temperature of the wax at the time the pattern was adapted and shaped, the less the tendency for distortion in the prepared pattern. This is reasonable, because the residual stress in the pattern causing the distortion is associated with the forces necessary to shape the wax originally. The incorporation of residual stress can be minimized by softening a wax uniformly by heating at 50℃ for at least 15 minutes before use, by using warmed carving instruments and a warmed die, and by adding wax to the die in small amounts.

45. Because the release of internal stress and subsequent warpage are associated with the storage temperature, it follows that greater warpage results at higher storage temperatures. Lower temperature does not completely prevent distortion, but generally the amount is reduced when the storage temperature is kept to a minimum. If inlay wax patterns must be allowed to stand uninvested for a time longer than 30 minutes, they should be kept in a refrigerator. The distortion begins within 1 minute after the initial set of the investment and reaches its maximum within 1 hour. The investment has unequal dimensional change throughout its mass during setting and this is an ever-present source of distortion.

46. Although some distortion may take place at this temperature, it will be less than at normal room temperature. Such a practice of storage for long periods is not recommended if freedom from warpage is desired. The best way to minimize the warpage of inlay wax patterns is to invest the pattern immediately after it is completely shaped. A refrigerated wax pattern should be allowed to warm to room temperature before it is invested. During spruing , distortion can be reduced by use of a solid wax sprue or a hollow metal sprue filled with sticky wax.

47. If the pattern was stored, the margins should be readapted. Temperature of formation, time and condition of storage, and promptness of investing the pattern are major factors related to all techniques of pattern formation. A freshly made wax pattern tends to change its shape and size over a period of time. Upon cooling it contracts, and after it attains equilibrium, the pattern reaches a state of dimensional stability.

48. Waxes, like other thermoplastics, tend to return partially to their original shape after manipulation. The property responsible for this phenomenon is commonly known as elastic memory . A stick of inlay wax can be softened over a Bunsen burner, bent into a horseshoe shape, and chilled in this position. If it is then floated in room-temperature water for a number of hours, the horseshoe will open .

49. The elastic memory of waxes is further illustrated during the measurement of the thermal expansion of a wax held under pressure during cooling. The expansion increases above the glass transition temperature, more so than when it is cooled without pressure. Again, this result illustrates the nature of wax to attempt to return to its normal, stress-free state. When the wax was bent into a horseshoe, the inner molecules were under compression and the outer ones were under tension. Once the stresses were gradually relieved at room temperature, the wax tend to straighten.

50. A pattern made of hard wax is less sensitive to temperature conditions than one made of soft wax. The exothermic heat generated during the setting of investment affects the pattern selectively. A soft wax pattern may result in a slightly larger and relatively rougher casting than a hard wax pattern.

51. Manipulation of inlay wax HEATING OF INLAY WAX : An Open Flame A Water Bath An Air Bath Air baths are probably the best way for heating waxes uniformly and without extracting any of their components. Water baths should be avoided because they are capable of extracting soluble parts of the wax and thereby change its composition and subsequently its physical and mechanical characteristics

52. It can result in the inclusions of droplets of water, which would splatter on flaming, smear the wax surface during polishing and distort the pattern during thermal changes. The open flame is commonly used because with some experience, excellent results can be achieved. The major problem associated with flame heating is that: 1). It is difficult to soften the wax uniformly 2). Avoid extracting some of its ingredients

53. CAVITY PREPARATION OF INLAY.

54. METHODS OF WAX APPLICATION A) WAX DIPPING METHOD – Dipping the die into a bath of molten wax. After the die is removed, the wax is allowed to cool at room temperature. This process is repeated until a sufficient amount of wax is formed on the die .

55. B) WAX ADDITION METHOD – Melting and dropping wax on the die until complete building of the pattern. This includes adding small increments of molten wax to the die with a small spatula. This permits development of the final pattern with little or no carving of the wax. This procedure allows much of the non-uniform thermal contraction to be corrected by subsequent additions rather than to result in an entrapment of residual stresses.

56. USES To make pattern for metallic restorations To make pattern for inlays To make crowns and bridges

57. MANIPULATION OF INLAY WAX In the process of manipulating inlay wax, dry heat is generally preferred to the use of a water bath. The latter can result in the inclusion of droplets of water, which could splatter on flaming, smear the wax surface during polishing, and distort the pattern during thermal changes. When stick wax is softened over a flame, care should be taken not to overheat it. The wax should be twirled until it becomes shiny and then removed from the flame.

58. The process is repeated until the wax is warm throughout. It is then kneaded together and shaped to the prepared cavity. Type I wax has adequate plasticity in a temperature range safely tolerated by the pulp. Pressure should be applied by the clinician’s finger or by the patient biting on the wax. The wax should be cooled gradually at mouth temperature, not by cold water. Care should be exercised in removing the pattern. It should be hooked with an explorer point and carefully removed from the cavity.

59. A mesial-occlusal-distal (MOD) pattern can best be removed by luting a staple or loop of thread so that each prong is fastened above a corresponding proximal box portion. The pattern can then be removed with minimum distortion by passing dental floss through the staple and withdrawing it in a direction parallel to the axial walls. After removal, avoid touching the wax pattern with the fingers as much as possible to prevent any temperature changes.

60. Inlay waxes are also used widely in the dental laboratory to prepare casting patterns for metallic restorations, either crowns or bridges. The first layer of wax is applied to a die either by adapting a softened thin sheet of wax or using a hot dipping technique. The wax pattern is then developed using a wax-additive technique in which molten wax is applied to the die of the tooth to rebuild gradually the form of the tooth.

61. For fabricating indirect patterns, the die should be lubricated, preferably with a lubricant containing a wetting agent. Any excess must be avoided, because it would prevent intimate adaptation to the die. The melted wax may be added in layers with a spatula or a waxing instrument, or it may be painted on with a brush. The prepared cavity is overfilled, and the wax is then carved to the proper contour. When the margins are being carved, extreme care should be taken to avoid abrading any surface of the stone die.

62. A silk or other fine cloth may be used for a final polishing of the pattern, rubbing toward the margins. Theoretically, applying pressure is undesirable. However, many clinicians prefer to apply finger pressure as the wax cools to help fill the cavity and to prevent distortion during cooling. The fingers also accelerate cooling. Again, although temperature changes should be avoided, some technicians prefer to repeatedly remelt tiny portions around the margins while carving and examine them under a low-power microscope.

63. Regardless of the method chosen, the most practical method for avoiding any possible delayed distortion is to invest the pattern immediately after removal from the mouth or the die, as noted previously. Once the investment hardens, there will be no more distortion of the pattern. Softer waxes, having higher flow, produce larger castings than do harder waxes, because softer waxes expand more as the investment warms during setting. They also offer less resistance to the expanding investment during setting. As economy concerns continue to increase, faster waxing procedures are emphasized. Some dental laboratories virtually operate an assembly line process.

64. To meet this demand, laboratories sometimes use “dipping” waxes that are kept molten for constant usage. Although standard types of inlay waxes may be used, the trend has included newer types of waxes that are more “rubbery,” tending toward a more amorphous rather than crystalline nature. The properties of these dipping waxes have not been characterized, nor do they fall into any present specification. As these waxes become more popular and better understood, their standardization will eventually follow.

65. Waxes oxidize on heating, and on prolonged heating some evaporate. There will also be a darkening and a precipitation of gummy deposits. Therefore care should be exercised to use the lowest temperature possible.

66. CONCLUSION Dental restorations, such as inlays, may be produced by a direct wax pattern technique in which the inlay wax is adapted and shaped in the prepared cavity in the mouth or indirect wax pattern technique. Waxes used in the production of patterns by either the direct or indirect technique must have very precisely controlled properties in order that well fitting restorations or appliances may be constructed. The required properties are produced by using a blend of several types of wax including paraffin wax, carnauba, candelilla and beeswax with small quantities of other resins.

67. Inlay waxes may be softened over a flame or in water at 54˚–60˚ c (130˚–140˚ F) Inlay casting waxes are classified as Type 1 medium and Type 2 soft. Type 1 is used for Direct technique and Type 2 is used for Indirect technique. On the basis of their flow characteristics they are classifies as hard, medium( regular) and soft. Inlay wax is used for fabricating gold inlays , crowns and bridges etc.

68. Applied Dental Materials Ninth Edition by John F. McCabe and Angus W.G. Walls Restorative Dental Materials11th Edition by Robert G. Craig and John M. Powers. Philips Science Of Dental materials 11 th Edition by Anusavice . Textbook Of Operative Dentistry , 4 th Edition By Vimal K Sikri REFERENCE

69. Stanford, J. W., Weigel, K. V., & Paffenbarger , G. C. (1961). Second revision of American Dental Association Specification No. 4 for Dental Inlay Casting Wax. The Journal of the American Dental Association, 62(1), 45–53. doi:10.14219/jada.archive.1961.0005  Mumford, G., & Phillips, R. W. (1958). Dimensional Change in Wax Patterns During Setting of Gypsum Investments. Journal of Dental Research, 37(2), 351–358. Ito, M., Yamagishi, T., Oshida , Y., & Munoz, C. A. (1996). Effect of selected physical properties of waxes on investments and casting shrinkage. The Journal of Prosthetic Dentistry, 75(2), 211–216. doi:10.1016/s0022-3913(96)90101-8 

70. Taylor, N. O., Paffenbarger , G. C., & Sweeney, W. T. (1931). A Specification for Inlay Casting Wax**A report to the Research Commission of the American Dental Association.Cooperative research by the National Bureau of Standards and the American Dental Association.Publication approved by the director of the Bureau of Standards of the U. S. Department of Commerce.Read before the Section on Partial Denture Prosthesis at the Seventy-Second Annual Session of the American Dental Association, Denver, Colo., July 23, 1930. The Journal of the American Dental Association (1922), 18(1), 40–52.