Dental Waxes–A Review

 

Ahmed Hilal Sheriff1, Preetham Prasad Nittla2*

1Undergraduate Student, Saveetha Dental College, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, India

2Senior Lecturer, Department of Prosthodontics, Saveetha Dental College, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, India

*Corresponding Author E-mail: preetham.nittla@gmail.com

 

ABSTRACT:

The aim of this review is to describe and understand the different types of dental waxes used in complete dentures, removable partial dentures and fixed partial dentures and the importance of dental waxes in dentistry. Many procedures in dentistry require the use of waxes. Waxes used in dentistry are combinations of two or more natural waxes plus small amounts of additives, such as oils, natural resins, synthetic waxes, and coloring agents. There are different waxes used specifically for clinical and laboratory procedures. The ultimate goal of the combination of waxes and additives is to produce dental waxes that possess a set of given physical properties over a specified range of temperature. Therefore, the successful use of waxes must be with a full understanding of waxes’ characteristics.

 

KEYWORDS: Paraffin, Oils, Resins, Beeswax.

 

 

 

INTRODUCTION:

Dentistry has evolved by leaps and bounds over the last century. Numerous materials are used in dentistry for a wide number of clinical and laboratory procedures. Waxes are used in dentistry for many clinical and laboratory procedures. There are different forms of waxes that are available but the most important property is that waxes are thermoplastic in nature which are hard at room temperature but melt without decomposition to form fluids. Clinically, they can be used to fabricate direct wax patterns for cast restorations, alterations and adaptations of impression trays and wax bite registrations. In the laboratory scenario, their uses range from as simple as boxing an impression before pouring any gypsum product to provide indirect patterns for casting procedures. The dental waxes are used in many dental procedures such as wax patterns for inlays, crowns, pontics complete dentures and partial dentures. They are also very useful in recording bite impressions and edentulous areas of the oral cavity. This article provides information regarding the composition of dental waxes, classification, physical properties, mechanical properties, rheology of dental waxes and its application in dentistry. Hence this article provides an in depth review about the waxes used in dentistry.

 

Composition:

Dental waxes are composed of a combination of components which are natural and synthetic. Origin of natural waxes are from plants (carnauba wax), insects (beeswax), and minerals (paraffin wax). These natural waxes are rarely used in their pure form and are most commonly used in combination with other components which provide a wide range of properties to the dental wax. They are combined or mixed with synthetic waxes, gums, fats, oils, resins, and coloring agents. Each component is added to attain the physical properties desirable for the wax application. The desirable properties of the dental waxes can be determined by their use in dental procedures. The major use of waxes in dentistry is to make a patterns of appliances prior to casting as many dental restorations are made by lost-wax technique, in which a pattern is made in wax and invested. After setting, the wax is burnt out and the space is filled with molten metal or plastic acrylic. Chemically waxes are polymers comprising of hydrocarbon and their derivatives like ester and alcohol.

 

At present, the useful applications of waxes in dentistry are immense, in fabricating metallic or polymeric products. The waxes have a special combination of properties, viz. they are weak solids to be readily shaped and moulded, plastic, have a low melting point, can be easily carved, are combustible easily, entirely organic composition (for burnout) and non-toxic. [1] For dentists and technicians, wax is a critical component in the creation of many restorations and procedures. There are still not many restorative procedures that can be carried out without the help of dental waxes.[2] The specific uses of dental waxes are determined by the physical properties that are most desirable for a successful application. Traditionally, the physical properties, such as melting, thermal expansion, ductility etc, can be investigated using the normal methods.

 

The dental waxes being viscoelastic material, rheological behaviour clearly must depend on the mechanical properties of the various phases, their proportions, and particularly the operating temperature, which is in relation to their melting points.[3] Evidently, this allows properties to be manipulated to adapt the product to suit the task. [4,5] The working environment provides other demands. Whether temperate or tropical, air conditioned or not, extra-oral mechanical modulus will be ‘room temperature’-sensitive.

 

REQUIREMENTS:

The properties of dental waxes used in various dental procedures have a certain requirements, i.e. the dental waxes must conform to the exact size and shape and contour of the appliance which is to be made, it should have enough flow when melted to reproduce the fine details, there should not be any dimensional changes taking place once it is formed, easily carved and smooth surface can be produced, definite contrast in color to facilitate proper finishing of the margins. These are the basic requirements of the dental waxes that are being used in various dental procedures.

 

CLASSIFICATION OF WAXES ACCORDING TO ORIGIN:

MINERALS:

Paraffin wax - Refined from crude oil, has relatively low melting point (50-70°C) and relatively brittle.

Ceresin wax - Refined from petroleum, has medium melting range (60°C).

 

PLANTS:

Carnauba-Obtained from palm trees, it is hard, tough, and has high melting point (80-85°C).

 

Candelilla -It is hard, tough, and has high melting point (80-85°C), used to increase the melting point and reduce flow at mouth temperature.

 

ANIMALS:

Stearin Obtained from beef fat, has low melting point.

Bees wax -Obtained from honey-comb, consist of partially crystalline natural polyester. It is brittle, has medium melting temperature (60-70°C).

 

SYNTHETIC WAXES:

They are used to modify some properties of natural waxes like polyethylene.

 

CLASSIFICATION OF DENTAL WAX ACCORDING TO ITS USE

Pattern:

Inlay, Casting: sheet, ready shapes, wax-up, Baseplate.

 

Processing: Boxing, Utility, Sticky.

 

Impression: Corrective, Bite wax.

 

Uses:

Inlay Pattern Wax:

Such restorations as inlays, crowns and bridge units are formed in a gold casting process that uses the lost wax pattern technique.

 

Boxing wax:

To form a wax box around the edentulous functional impression before casting model.

 

Base Plate wax:

Red or pink color is normally supplied in sheets 1-2 mm thick. three types of wax according to the climate: soft (I), medium (II) or hard (III)

 

Casting wax:

The pattern for the metallic framework of removable partial dentures is fabricated from the casting waxes.

 

Utility wax:

Used to stabilize a bridge pontic with crowns, when denture is constructing and soldering

 

Sticky wax:

Sticky when melted, adheres well to the surfaces on which it is applied.

 

Corrective impression wax:

Waxes with the lower softening points are used to register functional impressions.

 

Bite registration wax:

For bite registration.

 

Melting Range of Dental Waxes:

With complicated components, waxes have a melting range rather than a single, sharp melting point. Generally the mixture has a wider melting range than one component of mixture of dental wax.[6] It is of primary importance in designing a commercial wax product because this, and particularly the lower limit, controls the applicability of a given wax formulation in a particular function.[1] But it is difficult to obtain precise values for the top and bottom of the melting range merely by studying ordinary cooling curves, because of the strong chemical similarities of components. There are several methods for the determination of the melting point of waxes. The two commonly used are Ring and Ball Softening Point and Ubelohde Drop Melt Point. These two methods yield different results, with the Ring and Ball method generally yielding slightly lower value.[7]

 

Waxes which are mainly composed of hydrocarbons soften at low temperatures and over large temperature ranges.[8] The rate of temperature change during solidification and the presence of discontinuities in the cooling curves below solidification indicate the extent of crystallinity present in a wax. The more crystalline the wax, the greater is the internal stress in a wax when manipulated below these temperatures. For beeswax, the rate of temperature change during solidification is much greater than that of paraffin during solidification.[8] Like other materials, waxes expand when subjected to a rise in temperature and contract as the temperature is decreased. In general, dental waxes and their components have the largest coefficient of thermal expansion of any material used in restorative dentistry, particularly around the melting range.[9] Waxes are somewhat elastic in nature and tend to return to their original shape after deformation.

 

In a study conducted by Reiber, Th and Hupfauf, S. [10] they tested three bite registration waxes (Kerr No.8-wax, Beauty Pink Hardwax and Aluwax) for their thermic dimensional behaviour under several heating and cooling conditions. The recommendations for clinical application are as follows: They should not be heated more than required for achieving a sufficiently plastic quality for use and it should be stored in ice water to be resistant enough to deformation during the model mounting.

 

Mechanical Properties of Dental Waxes:

The mechanical properties of waxes play a vital role in the dental procedures. Wax patterns must be adequately tough to resist breakage during assembly and must not alter if dimensional tolerances are to be maintained. Dental waxes have lower mechanical properties, and these properties are strongly dependent on temperature than any dental materials used in various dental procedures. The temperature is inversely proportional to the mechanical properties of the dental waxes, if the temperature increases the mechanical properties of the dental waxes decreases and vise-versa.[11]

 

The cooling curve of the dental wax has two parts, melting point and transition point. At temperature above the melting point, the wax is fully fluid. At a temperature below the transition temperature the wax is rigid and strong and cannot easily be moulded. At temperatures between the melting point and the transition temperature, the waxes are partially fluid and partially solid, i.e. it is viscoelastic.[9] Attempting to shape the wax at temperature below the melting point will not result in full and permanent deformation. Thus, to increase the flow and decrease any possible subsequent stress relief, all moulding of wax should, ideally, be carried out above the melting point.

 

Wax has a tendency to flow.[12] Flow of waxes is clearly important, not only as part of the moulding process but also an undesirable aspect after the pattern or impression has been made. Flow results from the slippage of wax molecules over each other. It is a measure of a wax’s ability to deform under light forces and is analogous to creep.[13]

 

A straight relationship was found between the flow of the wax and the casting shrinkage that could affect the precision fit of the final restoration.[14] The plastic deformation or percentage of flow is directly proportional to the temperature under forces, so the percentage of flow increases with increasing temperature and under forces.[12] The most important factor which determines the extent of flow for a given wax is temperature. At a temperature close to its melting range, a wax may flow under its own weight. In liquids, flow is measured by viscosity. In solids, flow is measured by the degree of plastic deformation over a fixed period of time.[15]

 

Usually, increased amount of flow is required while the adaptation is being carried out, while minimum flow is much appreciated when the procedure is complete. The magnitude of flow has an influence in the degree of setting expansion of dental waxes used in various procedures.[14] The amount of flow required from a wax depends on its use.[16,17] In the direct inlay technique waxes need to flow well to reproduce details of the cavity preparation.[18] However, when the wax is cooled to the oral temperature, flow should be minimized to reduce any distortion that might occur when the pattern is removed.

 

Ito et al [14] investigated the relationship between flow characteristics, bending strength, and softening temperature of paraffin and dental inlay waxes to casting shrinkage. They found that the casting shrinkage decreased as the flow of the wax pattern increased. It is of great importance to select the type of wax which has the most desirable properties for the margin and the occlusal portions. They also concluded that, to accurately fabricate castings, it is necessary to understand the physical properties of the chosen waxes.

 

Rheology of dental waxes:

The use of dental waxes in various dental procedures are due to their outstanding factors like: they are cheap, non-toxic, low melting, weak solids that can be shaped and moulded very easily. They are used for some of the highest precision work in dentistry, as well as cruder tasks. Even though there are many advantages of the dental waxes, they have the worst thermal expansion coefficients of all in dentistry.[13]

 

The dental waxes contain various components in the final product leading it to provide a melting range and not a fixed melting point. The mechanical behaviour is therefore temperature sensitive, depending on composition and number of phases.

 

Traditionally, the mechanical behaviour of dental waxes depends on the temperature, according to its composition and number of phases.[19] Supposedly, this allows properties to be manipulated to adapt the product to the task [4,5]. The working environment provides for other demands, especially the temperature condition in a dental clinic setting or a hospital setting. The rheological behaviours of waxes have a great influence in the accuracy of the finished products.

 

In the past only ‘flow’ was determined using different methods which is the basic rheological property. Flow limits are defined in terms of the percentage change in length of a cylindrical specimen. According to ADA [20], flow is measured by the arbitrary compressive loading of a cylindrical specimen of arbitrary size for an arbitrary period (10 min) at various temperatures, after which, flow is expressed as percentage of the initial length. Because of the fixed method and the arbitrary measuring conditions, we can only get a “critical flow property” of waxes.[16]

 

Another proposed method is the Needle Penetration Test. [13] A ‘needle’/ or a ‘probe’ of specified dimensions and mass was to be held vertically against the surface of the wax specimen and released. After ‘(5±0.1) s’ the needle was to be stopped, the vertical travel defining the penetrative ‘flow’. Unfortunately, this method is similarly flawed by arbitrariness and also the level of accuracy that could be attained is questionable. This needle penetration test can provide only a guideline indication of rheological properties. This needle penetration method can also be used to determine the hardness of a wax. Softer waxes in dentistry will tend to bend or deform more easily, whereas a harder wax will be stronger and there are less chances for wax patterns to undergo deformation. Harder waxes are more dimensionally stable than softer waxes generally.

 

In 1989, Darvell B. W. and Wong N.B. [21] showed a method to obtain the fundamental material property of viscosity by a modification of the Stokes’ Law. The basic principle is that at equilibrium an object falling under gravity has a terminal velocity determined by the viscous drag on the body. With the help of a “push” to the ball, it was possible to get detailed data on wax viscosity as a function of temperature and load. This method can only measure the “apparent” viscosity and consistent specimen annealing, which is only an approximation to the waxes’ property of viscosity. Meanwhile, the mechanical control to the load and recording of velocity also make deviation to the results.

 

The other methods used to determine the viscosity of a wax include: U-Tube, Brookfield, vibrating sphere, and stress/strain Rheometer. The U-Tube uses a kinematic technique to calculate the viscosity of the material, whereas the Brookfield, vibrating sphere, and Rheometer use a dynamic technique. The U-Tube is used for unfilled waxes and measures the flow of a specific amount of liquid wax over a certain interval. But it can only be applied to measure viscosities at particular temperatures per the manufacturer of the wax. The Brookfield viscometer is used for filled waxes and measures the viscous drag of the spindle. The vibrating sphere viscometer utilizes an oscillating sphere that maintains a certain amplitude, which is correlated to viscosity. It can be used for unfilled and filled waxes [22].

 

Strength Properties:

Each component of the wax has different strength properties in dental and commercial casting waxes that are of most important, since these dental waxes undergo forces that are developed during the setting of investments and to various temperature changes that are developed during the setting reactions.[15] Strength properties are particularly important when considerable expansion takes place in the investment, such as when the hygroscopic procedure is used with calcium sulphate-bonded investments or when silica sols are used with the phosphate bonded investments. The silicate-bonded investment shrinks during setting, also applying stress to the wax pattern.

 

Shell [23] reported the force necessary to restrict the longitudinal hygroscopic expansion of a calcium sulfate-bonded investment to be approximately 1,000 Gm./cm.2 and concluded that the hygroscopic expansion had adequate strength to move invested wax patterns. Shell also observed in his study that the normal setting expansion has a higher strength compared to the hygroscopic expansion.

 

 

In a study that was done by Lorey, Asgar, and Peyton [24] they used the water-added hygroscopic procedure and came to a conclusion that crowns and bridges could be cast as a single unit. they carried our the study by making the gingival portions of the wax pattersns with hard wax and the occlusal portions were made of softer wax. So when the expansion of the investment took place, the physical properties of the soft wax allowed this wax to be deformed easily compared to the hard wax, thus it resulted in adequate dimensional compensation in the various regions.

 

In a study done by RG. Craig, J. D. Eick0, and F. A. Peyton [6], The strength properties in compression of elastic modulus, proportional limit, and ultimate strength of some representative natural and dental waxes were determined at temperatures from 230 to 40'C. The strength properties of natural waxes at room temperature were in the decreasing order of carnauba, paraffin, and beeswax, and those of the dental inlay waxes were higher than a dental casting wax. The strength properties decreased with increasing temperatures although the order of the waxes at 40'C. was not always the same as at 230C.

 

Application in Dentistry:

At present, the versatile applications of waxes in dentistry are inescapable, whether metallic or polymeric, because of their special combination of properties: cheap, weak solids to be readily shaped and moulded, plastic, low melting point, easily carved, combustible, entirely organic composition (for burnout) and non-toxic. For dentists and technicians, wax is a critical component in the creation of many restorations and procedures.[25]

 

Pattern waxes are used to form general predetermined size and contour of an artificial dental restoration. Pattern waxes include Inlay wax, Casting wax, Base plate wax.

 

Inlay wax is used to produce patterns for metal castings using the lost wax technique. Eg: Inlays, Onlays, crowns & pontics [26,27]. These waxes are supplied in different forms sticks, pellets and tins. They are also supplied in two colours i.e. blue and green. Important properties include low thermal conductivity and high coefficient of thermal expansion 300-700ppm/*c. there are two types of inlay wax, type 1 and type 2. Type 1 wax is directly used in the mouth and softened and placed into the prepared tooth in the direct waxing technique. It has lower melting range and has softening temp slightly higher than the mouth temperature. Type 2 wax, this is the most widely used where the wax is melted into the die outside the mouth in the indirect technique.

 

Casting Wax are used for thin sections removable and fixed partial denture patients. [28,29,30] They are highly ductile. They are available in the form of sheets of thickness 0.4mm.

 

Base plate wax is used to establish the vertical dimension, plane of occlusion [31], and the construction of complete denture patterns in the technique for complete denture restoration.[32] It is available in the form of sheets of red/pink colour.

 

Processing wax are used primarily as auxillary aids in the construction of restorations and appliances, both clinically and in the laboratory. They perform numerous tasks that simplify many dental procedures in such operations as denture construction and soldering.

 

Boxing waxes are used to form a wax box around an impression to pour casts.it is also used to fabricate replacement pontics for provisional fixed partial dentures.it is available in the form of long thin strips in red, green and white colour. The height is adjusted until a boxing wax strip extends approximately 13mm above the highest point on the impression.

 

Beading wax is used to customize the tray by beading around the impression. It is available in the form of ropes 3-4mm thickness. It is adapted approximately 4mm wide and 3-4mm below the borders of impression.

 

Utility wax is used on the periphery of the impression trays to customize and aid in comfort and to provide a better fit of the impression trays into the vestibule and control the movement of the impression material.

 

Sticky wax is a mixture manufacture intentionally to be quite rigid and brittle at room temperature. It is available in sticks. It is sticky when melted and applied in molten state and set rapidly to form a strong bond between the waxes parts assembled.

 

Impression waxes is limited to be used in the no undercut edentulous regions of the mouth and are generally used in combinations with other impression materials.

 

Recent Advances:

Dental waxes have many functions and are used for various procedures in the laboratory for high precision work. One such most important procedure done in the laboratory is the production of wax patterns for inlays, onlays, crowns and fixed partial dentures. conventionally the wax patterns are prepared manually and then casted, but there are newer advancements in the preparation of wax patterns using CAD CAM machines. The wax pattern is produced using the milling technique based on a virtual model created from the digital data that are obtained from the oral cavity. Similarly, rapid prototyping technique known as the 3D-printing [33], is being used now a days to design and print a wax pattern for a restoration. Later the wax pattern is cast in the same conventional manner. The advantages of these technologies include high precision of the patterns fabricated and also aids in reduced laboratory time and turn over of the restorations fabricated [34].

 

CONCLUSION:

Waxes in dentistry have applications in a large number of clinical and laboratory procedures. The alteration of its properties by modifying the compositions make it versatile and useful for most applications. The more recent advancements such as CAD CAM and 3D printing of patterns have led to increased accuracy which has decreased human errors drastically.

 

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Received on 23.08.2018           Modified on 19.11.2018

Accepted on 21.01.2019         © RJPT All right reserved

Research J. Pharm. and Tech. 2019; 12(11):5589-5594.

DOI: 10.5958/0974-360X.2019.00968.5