Сraig. Dental Materials

&WIVE, $ dur n Fluonds (0.15% whl lluortda on)

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Fig. 8-4 A 'ryplcal anti-tartar toothpaste w~thcontents noted on the label, mcludmg several pyrophosphates

in reducing calc~ilusformation and the control of periodontal problems is well documented, but they do have some side effects that prohibit their use in certain individuals. They create a slightly more alkaline environment as part of the active prevention mechanism, and this can lead to softtissue sensitivity reactions such as burning sensations, tissue sloughing, erythema, ulceration, or migratory glossitis. Because the pyrophosphates have a bitter taste, such pastes also have an increased concentration of flavoring agents and detergents, both of which can increase the

Fig. 8-5A high-fluoride content toothpaste (1.I%) currently under prescription drug regulation.

possibility of an adverse tissue response. The concentrations of fluoride in toothpastes range from 0.025% to 0.15%, with great variations among brands. The effectiveness of fluoridecontaining toothpastes in preventing caries is highly dependent on fluoride concentration. Prescription pastes are also available with concentrations around 0.5% for use in professionally managed programs for patients at high risk for caries (Fig. 8-5). Bleaching toothpastes based on low-level peroxide formulations are also available to whiten teeth for esthetic purposes. They are effective in whitening teeth when used daily.

MOUTHWASH

Another vehicle for delivering active agents with desirable effects to the surfaces of the teeth and gingiva is mouthwash. Mouthwash is a liquid solution that is applied as a rinse on a regular basis to enhance oral health, esthetics, and breath freshness (Fig. 8-6). Mouthwashes are most effective when applied in the morning or the evening following mechanical cleansing of the tooth surfaces with a brush and toothpaste. The usual purpose is to deliver an active ingredient to the clean surface of teeth or tissues in a manner that will produce the greatest treatment effect.

Fig. 8-6 A variety of typical commercial mouthwashes.

Mouthwashes are composed of three main ingredients. An active agent is selected for a specific health care benefit, such as anticaries activity, antimicrobial effect, fluoride delivery, or reduction of plaque adhesion. The active agent is then delivered in a solution of water and/or alcohol. Alcohol is used to dissolve some active ingredients, enhance flavor, and act as a preservative to prolong shelf life. Surfactants are also added to most mouthwashes to help remove debris from the teeth and dissolve other ingredients. Surfactants can be nonionic block copolymers, anionic chemicals like sodium lauryl sulfate, or cetyl pyridinium chloride, which is cationic with antibacterial properties. Flavoring agents added for breath freshening include eucalyptol, menthol, thymol, and methyl salicylate. In formulating a mouthwash, it is extremely critical to guard against the use of additives that diminish the main effect of the active ingredient.

Two factors that should be considered in evaluating a mouthwash are its acidity and the ethanol content of the final solution. In measuring 12 proprietary mouthwashes in the United Kingdom, most were acidic, ranging from a pH of 3.4 to 6.6, one was almost neutral (6.9), and one was basic (8.3). For the same mouthwashes, the ethanol content ranged from a high of 27% to 0%, with little correlation between acidity and

Fig. 8-7 Labels for the mouthwashes shown in Fig. 8-6, highlighting the alcohol content of each

material: Listerine (top), 21.6%;Scope (center), 15%; ACT (bottom), 0%.

ethanol content. In evaluating a similar group of rinses on the U.S. market, the ethanol content showed a similar range from 27% to 0% (Fig. 8-7). To compare with alcoholic beverages, beer contains about 4% and wine about 11% ethanol. Although these mouthwashes are not ingested as alcoholic beverages are, there are topical effects to be avoided by using solutions with such high ethanol content.

The two main active ingredients in mouthwashes with a positive treatment effect are chlorhexidine and fluoride. Chlorhexidine is a strong antibacterial agent that is used primarily in patients with soft-tissue or gum infections, such as gingivitis or pericoronitis (Fig. 8-8). Acceptable concentrations are between 0.1% and 0.2%. Chlorhexidine gluconate has been shown to reduce the aerosol associated with dental operations when it is used as a preoperative rinse. It is also effective in reducing soft-tissue inflammation associated with periodontal disease, but patient acceptance is compromised by a rather bitter taste and a tendency to stain tooth surfaces.

The anticaries effect of fluoride mouthwashes are also well documented. It would appear to result from a two-stage reaction. Initially, a layer of calcium fluoride-like material is deposited on the surfaces of exposed teeth. In time, this surface layer is absorbed and the underlying mineral structure is converted from hydroxyapatite to

Fig. 8-8 A standard solution of chlorhexidene antibacterial oral rinse (Peridex).

fluorapatite, which is harder and more resistant to demineralization. The fluoride uptake was found to be dependent on concentration, with 0.2% NaF having a greater uptake than 0.05%. Uptake was also time dependent, with longer exposure times producing a greater treatment effect.

Mouthwashes can also have an effect upon restorative materials.Those with a higher ethanol content can produce softening of the surfaces of resin materials, such as resin composites, compomers, and sealants. Although more significant in light-cured resin materials, the softening effect, as demonstrated by an increased water sorption rate, was also found in laboratory-processed composites. A residual staining effect was also found using one popular rinsing material that also contained eugenol. The staining effect of chlorhexidine is dependent on concentration, so it is imperative to find an effective mid-range

Fig. 8-9 Fluoride-containing cavity varnishes for professional application, supplied in a tube (Duraphat) or as a solution in unit doses (Fluor Protector).

concentration that will produce only minimal staining.

There is also a question about toxicity or biocompatibility in prescribing the routine use of mouthwashes, particularly those with a high ethanol content. Carcinogenic risks seem to go up with increased duration of exposure and frequency of use. The risk factor is similar to that resulting from increased ingestion of alcoholic beverages. Although there are mixed results among the various clinical studies, the association seems to be present only when the ethanol content of the rinse is high and the use is excessive.

FLUORIDE VARNISHES

Fluoride-containing varnishes provide an additional means of delivering fluoride topically to the surfaces of teeth in patients at risk for caries. Research has established their routine use in Europe for this purpose; however, the FDA has refused to approve them as anticariogenic agents. They are approved as cavity varnishes to be used under restorations and along the root surfaces of sensitive teeth with gingival recession. There are three products used routinely for topical application, usually after a prophylaxis. Two of these products contain 5% sodium fluoride (2.26% F- or 22,600 ppm) and one contains 1%difluorsilane(0.1%Por 1,000ppm) (Fig. 8-9). The fluoride is dissolved in an organic solvent

that evaporates when applied or sets when exposed to moisture, leaving a thin film of material covering all exposed tooth surfaces. The mechanism of action for a fluoride varnish is similar to that described for a fluoride mouthwash; calcium fluoride is deposited on the tooth surface and later converted through a remineralization reaction to fluorapatite.

The one advantage of the varnish mode of application is the extended time of exposure for the active fluoride ingredient against the tooth surface. Instead of seconds, as with a mouthwash, it may be hours before a varnish wears off. Clinical trials have documented the efficacy of varnish in treating young children at risk for caries, with reductions reported as high as 70%. Another potential use for this type of material is in the prevention of root caries in an older population, which has increasing risk as aging occurs. Semiannual application of fluoride varnishes seems to provide optimum efficacy. The only negative aspect of using cavity varnishes is a slightly bitter taste, which is transient, and tooth discoloration, which lasts less than 24 hours. More research is necessary to fully document the value of using these materials in specific clinical situations with moderate to high caries risk.

PIT AND FISSURE S E W .?+$..

Pits and fissures in the occlusal surfaces of permanent teeth are particularly susceptible to decay, and fluoride treatments have been least effective in preventing caries in these areas. The susceptibility of occlusal pits and fissures to caries is related to the physical size and morphology of the individual pit or fissure, which can provide shelter for organisms and obstruct oral hygiene procedures. Cross-sectional views of typical fissure morphology, varying from a wide V shape to a bottleneck shape, are shown in Fig. 8-10.

A technique termed occlusal sealing was introduced in 1965. This procedure involved the use of methyl-2-cyanoacrylate,which was mixed with poly(methy1 methacrylate) and inorganic powder and then placed in the pits and fissures. The cyanoacrylate polymerized on exposure to

moisture. Since that time, sealant systems have included the Bis-GMA resins (polymerized either by chemical means or by visible light), a polyurethane sealant containing inorganic fluoride compounds, and -glass ionomers. The use of sealant materials that exhibit a slow release of the fluoride ion has been advocated as a way to maintain a high surface concentration of fluoride

for a longer period of time than is possible with the usual topical gel treatments.

RESIN SEALANTS

The most common sealants are based on Bis-GMA resin and are light cured, although some self-cured products are still available. The

full name for Bis-GMA is 2,2-bis[4(2-hydroxy-

3-methacryloyloxy-propy1oxy)-phenyllpropane. The chemistry of Bis-GMA sealants is the same as that described for composites in Chapters 7 and 9. The principal difference is that the Bis-GMA sealants must be much more fluid to penetrate into the pits, fissures, and etched areas produced on the enamel, which provide for retention of the sealant. Three parts of the viscous Bis-GMA are mixed with one part of diluent, such as methyl methacrylate or triethylene glycol dimethacrylate, to obtain a reasonably low-viscosity sealant. An alternative but similar oligomer base is urethane dimethacrylate; some materials are formulated from a combination of the two base resins. To provide stiffness to the material and improve wear resistance, filler particles of fumed silica or silanated inorganic glasses can be added to form low-viscosity composites.

Light-Cured Sealants Today, most sealants are light cured, activated by a diketone and an aliphatic amine. The complete reactions for composites are given in Chapter 7. Bis-GMA- light-cured sealant is supplied in a light-tight container and should be usable for a 12-month period. The sealant is applied to the pit and fissure area with an appropriate applicator and, when polymerization is desired, the end of the light source is held 1to 2 mm from the surface and the sealant is exposed to light for 20 seconds. Sealants are applied in such thin sections that depth of cure should be adequate with minimal exposure times, even for opaque materials. The advantage in using a light-cured sealant is that the working time can be completely controlled by the operator and integrated with patient behavior. This control is particularly valuable when sealant is applied to very young patients or when cooperation is a problem.

Self-cured Sealants The first generation of chemically-initiated Bis-GMA sealants was polymerized by an organic amine accelerator; commercial self-cured sealants are still available. The material is supplied as a two-component system: one component contains Bis-GMA resin

and benzoyl peroxide initiator, and the other contains Bis-GMA resin with 5% organic amine accelerator. The two components are dispensed as viscous drops onto a suitable mixing surface (e.g., dappen dish, paper pad), and, after adequate mixing, they are applied directly to the tooth surface. The polymerization is an addition reaction in response to the formation of radicals, although somewhat less cross-linked than those of the composite restorative materials. The reaction is exothermic, but the clinical effect is minimal because the material is placed in limited bulk. The rate of reaction for all materials is sensitive to temperature, and the material sets more quickly in the mouth (typically 3 to 5 minutes) than on the mixing surface. Because quantities are usually small, use caution to include all material in the mixing and use a gentle motion to minimize air incorporation. Air inclusions during mixing and insertion can be manifested clinically as surface voids, which can discolor and retain plaque. To ensure optimum penetration, apply the self-cured sealant quickly after mixing. Manipulation late in the setting reaction can disrupt the polymerization and induce bond failure.

Air Inhibition of Polymerization During polymerization there is a surface layer of air inhibition that varies in depth with different commercial products. Sufficient material must be applied to completely coat all pits and fissures with a layer thick enough to ensure complete polymerization after removal of the tacky surface layer. This chemically active surface layer of unpolymerized resin is considered a source of potential biotoxicity. One of the components in the raw resin reaction is Bisphenol A (BPA), which has recently been related to estrogenic activity because of the similarity of its chemical structure to estrogen. The measurement of BPA in saliva is time dependent and material specific. For some materials, it has been detected in small quantities immediately after sealant placement but not after 1 or 24 hours post-placement. To remove this layer as soon as possible after curing, use an abrasive slurry of pumice, applied on a cotton pellet or with a prophylaxis cup in a rotary

handpiece; this method is more effective than wiping or rinsing procedures. Premature contamination with moisture during insertion and the early application of biting forces can disrupt the setting and affect its strength and clinical durability.

Properties of Sealants Reports of the physical properties of sealants have been scarce because specimen preparation with such lowviscosity materials is difficult. The relationship between properties and clinical service is even more speculative than for most restorative materials. Typical properties obtained for an unfilled sealant and a filled sealant are given in Table 8-1. By adding about 40% by weight of finely divided filler particles, as in the composite systems, all properties except tensile strength show improvement. The specimens are usually tested for tensile failure by the diametral method, and the high deformation before fracture affects the reliability of the data. The modulus of elasticity shows the most dramatic improvement, and the increased rigidity makes the filled material less subject to deflection under occlusal stress. Filler is also added with the hope of improving wear resistance and making the material more visible on clinical inspection (Fig. 8-11).

Penetration studies on closed capillary tubes, which are somewhat analogous to pits and fissures, have indicated that a sealant will adapt more closely to the enamel surface if it possesses a high coefficient of penetration. Optimal penetration will occur when the sealant has a high surface tension, good wetting, and a low viscosity, thus permitting it to flow readily along the enamel surface. The surface wettability is demonstrated by the contact angle of a drop of liquid on the enamel surface. A drop that spreads readily has a low contact angle and is indicative of a highly wetted surface that is most conducive to a strong bond. Polymer tags that form in direct apposition to the surface irregularitiescreated by acid etching are responsible for the mechanical bond that retains the sealant to enamel. Functional durability of the sealant bond can be related to stresses induced by initial polymer

shrinkage, thermal cycling, deflection under occlusal forces, water sorption, and abrasion, with total failure manifested by the clinical loss of material.

Sealant materials have a variety of features that must be selected carefully by the health care provider. As previously stated, there are filled sealants that behave more like composite resins, and unfilled materials that are pure resins. Most current materials are light cured rather than selfcured because of the ease and speed of application. Tooth-colored or clear resins are available that are very natural looking on the tooth surface, but they are also available in opaque or tinted materials to make the recall examination process easier (Fig. 8-12). An increasing number of sealants are marketed as vehicles for the slow release of fluoride, which has been documented in vitro in water solutions for a number of products. The release is highest in the first 24 hours after placement and then tapers to a low maintenance level, which may or may not be sufficient to provide extended clinical protection against caries.

Clinical Studies Many clinical studies have been reported using the Bis-GMA systems. In earlier studies on effectiveness of treatment with sealant in newly erupting teeth, a lightcured sealant demonstrated a retention rate of

42% and an effectiveness of 35% in caries reduction after 5 years. In a similar study, a filled resin sealant showed a retention rate of j3% and a clinical effectiveness of 54% after 4 years. Results involving a quicker-setting unfilled resin sealant with very good penetration showed a retention rate of 80% and an effectiveness of 69% after 3 years. The longest published study on sealant effectiveness is a 15-year evaluation of a selfcured unfilled material, which showed 27.6% complete retention and 35.4% partial retention.

In pairwise comparisons, the treated first molars had 31.3 dfs and the untreated controls had 82.8 dfs. In a more current 4-year study comparing a fluoride-releasing sealant with one that did not have fluoride, retention rates were 91% for the fluoride material (77% complete and 14% partial) and 95%for the non-fluoride sealant (89% complete and 6% partial). Although the retention was somewhat lower in the fluoridecontaining sealant, the caries incidence for both groups was identical (10%). In a study conducted in private practice, the 2-year retention rates for two newer fluoride-containing resins were greater than 90%, and no caries was detected on the test teeth. In a continuing study with retreatment of all defective sealant surfaces at 6-month recalls, the teeth were maintained caries free for a 5-year period. The retreatment rate

Fig. 8-12 A maxillary molar tooth with opaque sealant that has been in place for five years.

was highest (18%) at 6 months, and then diminished as time progressed, but at each recall period at least two teeth (about 4%) required reapplication.

Almost all studies show a direct correlation between sealant retention and caries protection. Therefore it is important to develop materials that are retentive to enamel, resistant against occlusal wear, and easily applied with minimal opportunities for surface contamination. Current evidence indicates that sealants are most effective on occlusal surfaces where pits and fissures are well defined and retentive to food and in patients with a demonstrated risk for pit and fissure caries.

Manipulation of Sealants The handling characteristics of a sealant are dependent on the composition of the material and the nature of the surface to which it is applied. Optimal preparation of both aspects will lead to close adaptation of the sealant to the tooth enamel, a strong seal against the ingress of oral fluids and debris, and long-term material retention.

Enamel Surface Preparation The penetration of any of the sealants to the bottom of the pit is important. The wettability of the enamel by the sealant is improved by etching, and some advocate pretreatment with silanes in a volatile solvent. The problem of filling the fissure is real; air is often trapped in the bottom of the fissure, or the accumulation of debris at the base of the fissure prevents it from being completely filled, as shown in Fig. 8-13. Control of the viscosity of the sealant is important to obtain optimum results. The viscosity determines the penetration of resin into the etched areas of enamel to provide adequate retention of the sealant. Penetration of sealant, forming tags, to a depth of 25 to 50 pm is shown in Fig. 8-14.

Etch the pit and fissure surface for a specified time (15 to 30 seconds is adequate for enamel with a normal mineral and fluoride content) with a solution or a gel of 35% to 40% phosphoric acid. Flush the acid thoroughly with water, and dry the area with warm air. Inadequate rinsing permits

Fig. 8-13Section showing a fissure incompletely filled with sealant as a result of air, A, and debris, B,

(From Gwinnett AJ: J Am Soc Prevent Dent 3:21, 1973.)

phosphate salts to remain on the surface as a contaminant, interfering with bond formation. Avoid rubbing the etched surface during etching and drying because the roughness developed can easily be destroyed. Isolation of the site is imperative throughout the procedure to achieve optimum tag formation and clinical success. If salivary contamination occurs during the treatment, rinse and dry the surface and repeat the acid etching. On clinical inspection, acid-etched enamel should appear white and dull with an obviously rough texture. If this appearance is not uniform, perform an additional 30 seconds of etching. The etched area should extend be-

Fig. 8-14 Penetration of sealant into etched enamel; these tags are responsible for the bonding to enamel.

(From Gwinnett N :J Am Soc Prevent Dent 3:21, 1973.)

yond the anticipated area for sealant application to secure optimum bonding along the margin and reduce the potential for early leakage. Clinical studies have shown that the use of a lightcured bonding agent (see Chapter 10) against the freshly etched enamel before placing the sealant will improve retention, especially when there appears to be minor moisture or salivary contamination.

Sealant Application Depending on its viscosity and setting time, the sealant may best be applied with a thin brush, a ball applicator, or a syringe. Take care to avoid the buildup of excess material that could interfere with developing occlusion, but apply sufficient material to completely cover all exposed pits and provide a smooth transition along the inclines of the enamel cusps. Over-working of even the lightcured sealants on the tooth surface during application can introduce air voids that appear later as surface defects.

Wipe away the air-inhibited surface layer immediately after curing and inspect the coating carefully for voids or areas of incomplete coverage. Cover defects at this time by repeating the entire reapplication procedure, including the

acid etch, and applying fresh sealant only to those areas with insufficient coverage. After the sealant is applied and fully cured, check and adjust the occlusion, if necessary, to eliminate functional preinaturities that can result in hypersensitivity.

Glass Ionomer Sealants Because of their demonstrated ability to release fluoride and provide some caries protection on tooth surfaces at risk, glass ionomers have been suggested and tested for their ability to function as a fissure sealant. Glass ionomers are generally more viscous, and it is difficult to gain penetration to the depth of a fissure. Their lack of penetration also makes it difficult to obtain mechanical retention to the enamel surface to the same degree as Bis-GMA resins. They are also more brittle and less resistant to occlusal wear. Clinical studies using various formulations of glass ionomers have shown significantly lower retention rates, but greater fluoride deposition in the enamel surfaces.

In areas where high-risk children cannot afford dental care, a conservative holding technique has been advocated to seal remaining caries in a fluoride-rich environment and establish some degree of remineralization. Atraumatic restorative treatments involve opening a lesion, removing soft surface decay, and filling or sealing the surface with high-filled glass ionomer with a fast setting time. Future studies in this area may produce a new generation of sealant materials noted for their fluoride deposition rather than their mechanical obturation.

FLOWABLE COMPOSITES

Low-viscosity,high-flow composites marketed as flowable composites are advocated for a wide variety of applications, such as preventive resin restorations, cavity liners, restoration repairs, and cervical restorations. These applications are not well supported with data, but their clinical use is widespread. The properties of flowable composites are described in Chapter 9.